Ore Genesis. in Copper Bearing Carbonatites; A

ORE GENESIS. IN COPPER BEARING CARBONATITES;

A GEOCHEMICAL, FLUID INCLUSION AND MINERALOGICAL STUDY

RICHARD T. H. ALDOUS, B.Sc., M.I.M.M.

A Thesis submitted for the Degree

Philosophiae Doctor

Mining Geology Division, Department of Geology, Imperial College of Science and Technology, University of London. 1980 ABSTRACT

Trace amounts of copper are not uncommon in documented carbonatites. Unusually high concentrations of copper are rare, but when present occur mostly in deeply eroded complexes. Copper sulphide occurrences and parageneses in carbonatites are classified into three groups. Detailed studies of the carbonatite copper deposit at Palabora suggest mineralization occurred autometasomatically in a continuum between carbgnatite met and residual fluids at temperatures between 600'C and 200 C and low f0.7. The lack of primary aqueous inclusions in Palabora apatites is unusual for a carbonatite, they do however contain crystallographically orientated copper sulphide inclusions. These are thought to have grown epitaxially and indicate the presence of copper in the apatite forming media. Their distribution varies with rock type. Rare earths show that the apatites are different generations in a system developing higher total rare earths and light RE/heavy RE enrichment. Melt inclusions in phoscorite olivines indicate that the earliest carbonatite magma at Palabora was unusually enriched in copper. It is concluded that copper was an integral part of the Palabora magmatism and not introduced from an extraneous source. Primary inclusions in pyroxene from a copper rich pyroxenite diatreme at Palabora are crystalline silicate melts, with a residual portion of aqueous Cu and K rich Cl /CO brine. Secondary aqueous inclusions contain large daughters of chalcopyrite which indicate an initial fluid concentration of 3000ppm Cu. Copper bearing carbonate rich aqueous fluids, which developed from the crystallization of the pyroxenite melt, were probably precursors of copper deposition in the pyroxenite diatreme. A copper bearing sulphide, apatite, pyroch1ore, phlogopite, magnetite (SAPPM) assemblage from the Sokli carbonatite in Finland of hydrothermal metasomatic origin is defined and described. Geochemical and petrographic studies of the assemblage suggest a hydrothermal metasomatic origin. Fluid inclusions in apatite from the assemblage are alkali (Na:K = approx. 2:1) bicarbonate/chloride brines deduced to be the parent fluids of the assemblage. Comparison of homogenization temperatures with temperature estimates from other geothermometers implies a formation pressure of 4 kilobars for these deposits. The nature and origin of phoscorites is reviewed in the light of melt inclusions and alteration chemistry from studies at Palabora, Sokli and Bukusu (Uganda). The theoretical aspects of copper accumulation and deposition in carbonatites are discussed. ACKNOWLEDGEMENTS

I would like to express my sincere thanks to Dr. A.H. Rankin for his supervision, help and guidance throughout the course of this work. Other members of staff from the Royal School of Mines also provided valuable advice, instruction or assistance, including:- Prof. R. Davis, Dr. S. Parry, Dr. C. Halls, Dr. R. Parker, P. Suddaby, N. Wilkinson, R. Curtis, B. Foster, E. Morris and P. Watkins. I am grateful to Palabora Mining Company and Rautaruukki Oy for making samples available and for their generous hospitality. I should particularly like to thank H. Vartiainen for his help. Thanks are also due to the following who provided samples for the study:- Dr. J. Baldock, S. Eriksson, Dr. A. Woolley, the Department of Geology, Leeds University, The Ugandan Geological Survey and Goldfields of South Africa. I thank the Natural Environment Research Council - who financed this work, Blue Circle Industries who printed the black and white plates and Mrs. D. Babbage for typing the final copy. My deepest thanks go to my wife, who not only typed the draft, but also translated numerous Russian papers. My Wife, Children and Parents provided an enormous amount of material and non-material support without which this work would not have been possible.

ii Table of Contents Page

INTRODUCTION 1 CHAPTER 1. A REVIEW OF THE OCCURRENCE AND BEHAVIOUR OF COPPER IN THE FORMATION OF CARBONATITES 7 1.1. THE OCCURRENCE OF COPPER AND SULPHUR IN CARBONATITES 7 1.1.1. The Sulphide Mineralogy of Carbonatites 9 A. Iron Sulphides, Pyrrhotite and Pyrite 10 B. Copper Sulphides 11 C. Pentlandite and Millerite 12 D. Molybdenite 15 E. Lead and Zinc Sulphides 15 F. Polymetallic Sulphides, Sulphosalts and Native Elements 16 1.1.2. Carbonatite Complexes with Pronounced Copper Enrichment 17 A. Copper Mineralization at Palabora 19 B. Bukusu, Uganda 19 C. Sokli, Finland 20 D. Glenover, South Africa 21 E. Kovdor, Kola Peninsula 21 F. Vuori Yarvi 22 G. Beloziminsk 22 1.1.3. A Classification of Copper Bearing Sulphide Parageneses 23 1.2. THE ORIGIN OF COPPER AND SULPHUR IN CARBONATITES 26 1.2.1. The Origin of the Copper 26 1.2.2. The Origin of the Sulphur 30 1.2.3. The Behaviour of Copper and Sulphur in Silicate Melts and Carbonatites 30

iii Page 1.3. CONTROLS AND P.T.V.X. OF ORE FORMING CARBONATITE FLUIDS 35 1.3.1. Fluid Inclusions 36 1.3.2. Experimental Work 39 1.3.3. Geochemistry 40 1.3.4. Sulphur Isotopes, T and f02 41 1.3.5. Structural Control 45 1.4. SUMMARY AND CONCLUSIONS 46

CHAPTER 2. THE CARBONATITE COPPER DEPOSIT AT PALABORA, SOUTH AFRICA 48

2.1. INTRODUCTION AND BACKGROUND GEOLOGY 48 2.1.1. Introduction 48 2.1.2. The General Geology 48 2.1.3. The Loolekop Pipe 51 2.1.4. The Mineralization at Loolekop 54 2.1.5. The Aim of the Present Work 57 2.2. ORE MICROSCOPY 58 2.2.1. Previous Work 58 2.2.2. The Present Work 60 2.2.3. The Relationship between Sulphides and Palabora Carbonatites 61 2.2.4. Sulphide Behaviour in Transgressive Carbonatite Dykes 72 2.2.5. Implications of Sulphide Carbonate Relationships 73 2.2.6. The Sulphide Paragenesis 75 2.2.7. The Oxide Minerals 82 2.2.8. The Ore Paragenetic Sequence 85 2.3. GEOCHEMISTRY OF THE SULPHIDE ASSEMBLAGE 87 2.3.1. Present Work 87 2.3.2. Deductions from Published Figures 89 2.4. THE ENVIRONMENT OF FORMATION OF PALABORA SULPHIDES 91

2.4.1. Temperature and Depth 91

2.4.2. Mineral Equilibria 91

iv Page 2.4.3. Magnetite-Ilmenite Pairs 93 2.4.4. Conditions of fS2 and f02 97 2.5. SUMMARY AND CONCLUSIONS 98 2.5.1. Summary 98

CHAPTER 3. INCLUSIONS AND RARE EARTH ELEMENTS IN PALABORA APATITES 100 3.1. INTRODUCTION ,100 3.2. APATITE DISTRIBUTION 100 3.3. TYPES OF INCLUSION IN THE APATITE 102 3.3.1. Aqueous Inclusions 102 3.3.2. a) Irregular Shaped Non Aligned Solid and b) Multisolid Inclusions 103 3.3.3. Elongate Inclusions Aligned Parallel to the C-Axis of the Apatite 103 3.3.4. Explanation and Deductions from Crystallographically Controlled Types 112 3.4. RARE EARTHS IN PALABORA APATITES 114 3.4.1. Previous Work 114 3.4.2. The Present Work 116 3.4.3. Results 116 3.5. SUMMARY AND CONCLUSIONS 123

CHAPTER 4. MELT INCLUSIONS IN OLIVINE AT PALABORA 126 4.1. INTRODUCTION 126 4.2. THE INCLUSIONS 126 4.3. PREVIOUS REPORTS OF MELT INCLUSIONS IN CARBONATITES 128 4.4. COMPOSITION OF THE INCLUSIONS 131 4.5. HEATING STUDIES • 133 4.6. SIMILAR INCLUSIONS FROM OTHER COMPLEXES (THIS WORK) 136 Page

4.7. CONCLUSIONS 136 CHAPTER 5. COPPER RICH AQUEOUS ALKALI CARBONATE INCLUSIONS IN PYROXENES FROM THE GUIDE COPPER MINE, PALABORA 140 5.1. INTRODUCTION 140 5.1.1. The Sulphide Assemblage 142 5.2. INCLUSIONS TYPES 146 5.2.1. Type 1: Solid Inclusions 146 5.2.2. Type 2: Secondary Aqueous Inclusions • 146 5.2.3. Type 3: Aqueous Multisolid Inclusions 146 5.2.4. Inclusions in Orthoclase 150 5.2.5. Similar Inclusions from the main Pyroxenite at Palabora 150 5.3. IDENTIFICATION OF DAUGHTER AND TRAPPED PHASES 151 5.4. HEATING STUDIES 153 5.5. INCLUSION COMPOSITION AND IMPLICATIONS 157 5.6. CONCLUSIONS 161 CHAPTER 6. HYDROTHERMAL ORE DEPOSITION AT THE SOKLI CARBONATITES, FINLAND 164 6.1. INTRODUCTION 164 6.2. THE GEOLOGY OF SOKLI 166 6.2.1. General Geology and Previous Work 166 . 6.2.2. The Present Work 167 6.3. SULPHIDES AT SOKLI 183 6.4. APATITE AS AN ACCESSORY MINERAL AT SOKLI 188 6.5. THE SULPHIDE APATITE PHLOGOPITE (YROC ORE MAGNETITE ASSEMBLAGE(S) 191 6.5.1. Mode of Occurrence 191 6.5.2. Petrography of the SAPPM Assemblage 192

• vi

Page 6.5.3. Similar Assemblages in Other Complexes 200 6.6. PYROCHLORE 201 6.6.1. The Occurrence of Pyrochlore 201 6.6.2. Pyrochlore Chemistry 203 6.6.3. Discussion of Results and Comparison with other Complexes 210 6.7. TEMPERATURE OF FORMATION OF THE SAPPM ASSEMBLAGE '212 6.7.1. The Sulphides 212 6.7.2. Ilmenite/Magnetite Pairs from the SAPPM Assemblage 213 6.7.3. Geobarometry using the Sphalerite- Pyrrhotite-Pyrite Equilibrium 215 6.7.4. Proposed Temperature of Formation 215 6.8. A GEOCHEMICAL EVALUATION OF THE SAPPM ASSEMBLAGE 218

6.8.1. Objectives 218 6.8.2. Methods of Sample Selection and Analysis 219

6.8.3. The Results 220 6.8.4. Correlation Matrices for Boreholes 274 and 275 227 6.8.5. Conclusions reached from the Analytical Study 228 6.9. SUMMARY AND CONCLUSIONS 229

CHAPTER 7. INCLUSIONS IN APATITE FROM THE SAPPM ASSEMBLAGE, SOKLI 231 7.1. INTRODUCTION 231 7.2. THE INCLUSION-TYPES IN SOKLI APATITES 232 7.2.1. Aqueous/Vapour Inclusions - Type 1 232 • 7.2.2. Monophase Aqueous Inclusions - Type 2 237 7.2.3. Monophase Gas Inclusions - Type 3 237 7.2.4. Monophase Sacharoidal/Opaque Inclusions - Type 4 238 vii Page 7.2.5. Multisolid Inclusions with Aqueous and Vapour Phases - Type 5 238 7.2.6. Mineral Inclusions in Apatite - Type 6 239 7.2.7. Elongate Solid Inclusions Aligned Parallel to the C-Axis -Type 8 239 7.2.8. Spherical Inclusions of Calcite - Type 7 239 7.3. DAUGHTER AND CAPTURED MINERALS 245 7.3.1. Identification of Daughters in Aqueous Inclusions 245 7.3.2. Identification of the Contents of Multisolid Inclusions 256 7.3.3. Counting of Daughter Minerals. 257 7.4. FLUID INCLUSION CHEMISTRY 259 7.4.1. Na:K Ratios of the Fluids 259 7.4.2. Crushing Studies 261 7.4.3. Cryometry 266 7.5. HEATING STUDIES AND PRESSURE DEDUCTIONS 271

7.6. INCLUSIONS IN OTHER MINERALS AT SOKLI 278 7.7. DISCUSSION OF INCLUSIONS AT SOKLI 279 7.8. SUMMARY, PROPOSED GENETIC MODEL AND CONCLUSIONS 281 7.8.1. Summary 281 7.8.2. Genetic Setting of Sokli Mineralization 282 7.8.3. Conclusions 283

CHAPTER 8. THE GENESIS OF PHOSCORITES AND THEIR RARE METAL MINERALIZATION 284

8.1. INTRODUCTION 284 8.2. PREVIOUS VIEWS ON THE GENESIS OF PHOSCORITES 285 8.2.1. Crystallization from a Melt 287 8.2.2. Hydrothermal/Metasomatic Origins 287 8.2.3. The Palabora Phoscorites 291

viii Page 8.3. CONCLUSIONS 299

CHAPTER 9. SUMMARY AND CONCLUSIONS 301 9.1. SUMMARY OF PREVIOUS CONCLUSIONS 301 9.2. CONCLUDING SYNTHESIS 303 9.2.1. Copper in Aqueous Fluids 303 9.2.2. Copper in less Aqueous Carbonatite Magmas 304 9.2.3. Depth of Erosion 305 9.3. PRACTICAL APPLICATION 306 9.4. SUGGESTIONS FOR FURTHER WORK 306

APPENDIX 1. An Aid to the Identification of Micro- scopic Opaque Phases in Transparent Minerals using Reflected Light 308 APPENDIX 2. Scanning Electron Microscopy of Daughter Minerals 312 APPENDIX 3. Quantitative Electron Probe Micro Analysis (EPMA) 319 APPENDIX 4. Fluid Inclusion Preparation and Heating/ Freezing Equipment 322 APPENDIX 5. Analytical Methods 326

5A. Atomic Absorption 326

5B. X-Ray Fluorescence 329

5C. Analytical Results for AA and XRF 331

5D. Neutron Activation 336

ix LIST OF FIGURES Page FIG. 1 Some Complexes with Anomalous Copper Mineralization 18 FIG. 2 Frolov's (1971) Depth of Erosion Scheme 24 FIG. 3 The System CaCO3-Ca(OH)2-CaS (from Helz & Wyllie 1979) 34 FIG. 4 Examples of Oxygen Isotopes in Carbonatites 42 FIG. 5 Palabora Igneous Complex 49 FIG. 6 The Palabora Carbonatites 52 FIG. 7 Sectibn Through Loolekop Orebody (after P.M.C. Staff 1976) 53 FIG. 8 Summaries of Events at Palabora 55 FIG. 9 Distribution of Cu, Fe, Ti and P on 122m Level, Loolekop Orebody 56 FIG. 10 Histogram of Dolomite Iron Contents 68 FIG. 11 A. Schematic Paragenetic Sequences 86 B. Overall Mineralization at Loolekop 86 FIG. 12 Probing of Magnetite Ilmenite Pairs 95 FIG. 13 Typical Palabora Apatites 101 FIG. 14 A. Secondary Aqueous Inclusions 104 B. Non Aligned Solid Inclusions 104 FIG. 15 Distribution of Aligned Inclusions in Different Rocks 108 FIG. 16 A. Aligned Inclusions in Apatite (Palabora) 110 B. Mixed Opaque/Transparent Types 110 FIG. 17 Rare Earths in Palabora Apatites 118 FIG. 18 Rare Earths in Palabora Whole Rocks 119 FIG. 19 Apatite REE Normalized to Internal 121 Standards FIG. 20 Rare Earths in Some Minerals From Palabora Carbonatites 122 FIG. 21 Strontium Values of Palabora Apatites 123a. FIG. 22 Melt Inclusions in Palabora Olivines 127 FIG. 23 Typical Melt Inclusion in Olivine from Palabora 134 FIG. 24 The Geology of the Guide Copper Mine 141 FIG. 25 Inclusions in Pyroxenes from Guide Mine 147 FIG. 26 Primary Inclusions in Pyroxenes from Guide Copper Mine 149 FIG. 27 Heating Studies from Type 3 Inclusions in Pyroxene 154 FIG. 28 Instances of High Temperature Immiscibility in Guide Inclusions 156 FIG. 29 The Geology of the Sokli Carbonatite Complex - Finland 165 FIG. 30 Key to Sokli Borehole Logs 170 FIG. 31 Reactions between Phoscorite & Carbona- tites (as seen in sectioned core) 177 FIG. 32 Sokli Borehole Sections 274 & 275 182 FIG. 33 Apatite Textural Types 190 FIG. 34 Pyrochlore Types 190 FIG. 35 Probe Analysis of Sokli Pyrochlores 206 FIG. 36 Probe Analysis of Sokli Pyrochlores contd 207 FIG. 37 Probe Analysis of Sokli Pyrochlores contd 208 FIG. 38 Plot of Analyses from Zoned Pyrochlore Crystal (393/12, No.1) 209 FIG. 39 Sulphur Isotopes at Sokli 214 FIG. 40 Analysis of Magnetite Ilmenite Pairs from the SAPPM Assemblage 216 FIG. 41 Temperature & f02 of Magnetite-Ilmenite Pairs 217 FIG. 42 Sokli Geochemistry - Scatter Plots 221 FIG. 43 Classification of Inclusions in Apatite 233 FIG. 44 Sr0 from Calcites in and around SAPPM Apatites 244

xi FIG. 45A Minerals in Aqueous Inclusions 246 FIG. 45B Minerals in Aqueous Inclusions - contd 247 FIG. 46 The Crushing Method 262 FIG. 47 Wt% NaHCO3 by Crushing in Acid 263 FIG. 48 The Solubility of Alkali Metal Carbonatites (after Kirk-Othmer 1969) 265 FIG. 49 P CO2-T Diagram of the System Na2CO3- NaHCO3-H20 (after Eugster & Milton - 1957) 265 FIG. 50 Typical Freezing Runs on Inclusions in Apatite 268 FIG. 51 Freezing Studies on Inclusions in Sokli Apatites 269 FIG. 52 Depression of Freezing Point for some Relevant Salts 270 FIG. 53 Homogenization Temperatures for Inclusions in Apatites from Sokli Carbonatite Complex 274 FIG. 54 Isochores for Diferent Aqueous Systems giving Th of 160'C 275 FIG. 55 Comparison of Olivines and Humite Minerals from Palabora and Sokli 295 FIG. 56 Observations of Opaques in Transparent Minerals 311 FIG. 57 Host Mineral Interference during EPMA of Daughter Minerals 317 FIG. 58 Schematic Representation of an Energy Dispersive Spectrometer 320 FIG. 59 Procedure used by Spectra Processing Programme ZAF/4 320 FIG. 60 Calibration Curves for Leitz Model 1350 Heating Stage 323

xii LIST OF TABLES Page TABLE 1 The Principal Features of Carbonatite Deposits (Smirnov, 1977) 5 TABLE 2 Copper Abundance in Various Rocks 8 TABLE 3 Some Complexes with Carbonatites anomalously Enriched in Copper (cf.Gold, Table 2) 17 TABLE 4 Comparison of Inclusion and Carbonatite Analysis ' 37 TABLE 6 Paragenetic Sequence of the Ore Minerals at Palabora (after Forster, 1958) 59 TABLE 7 Ore Mineral Assemblage at Palabora 60 TABLE 8 Intrasulphide Relationships in Palabora Ore 76 TABLE 9 Probe Analyses of Unknown Zr Ti Oxide and Baddeleyite 85 TABLE 10A Ratios of Minor Metals in Sulphide Assemblage from Transgressive Carbonatite 88 TABLE 10B Concentrated Samples of Sulphide 88 TABLE 11 Palabora Electrolytic Refinery Analyses 90 TABLE 12 Theoretical Metal Values in Sulphide Assemblage (ppm) 91 TABLE 13 Probing of Magnetite Ilmenite Pairs contd 96 TABLE 14 Comparison of Phlogopite from Inclusions with those in Phoscorite Rock 132 TABLE 15 EPMA Analysis of Phlogopites in Early Glimmerite BH 393/17 178 TABLE 16 Solubility of Nb20 and Ta205 in Carbonatite Type Solutions 211 TABLE 17 Sokli Geochemistry: Correlation Matrix for all Samples (Excepting Late Ankeritic Dykes) Sub Group 11 222 TABLE 18 Mean Element Values for Sokli Groups (Base 0) (excluding Group 11) 225 TABLE 19A Trace Element Values of Sulphide Assemblage (ppm) 226 TABLE 19B Correlation Matrices for Boreholes 275 and 274 227 TABLE 20 Some Inclusion and Daughter Mineral Statistics 258 TABLE 21 Results of Apatite Leachate Analysis 261 TABLE 22 Heating and Freezing Results 273 TABLE 23 Inclusion Phase Composition Vol % from Kovdor (after Khitarov et al.1978) 277 TABLE 24 A Short Description of Various Camaforite Deposits '286 TABLE 25 Electron Microprobe Analyses from Palabora Phoscorite Olivines Comparison with Phoscorite Olivines from other Complexes 292 TABLE 26 Table of Duplicates and Blanks 328 TABLE 27 Initial Standard Preparation 330 TABLE 28A Sokli Geochemistry - Results of Whole Rock Analysis by A.A. and X.R.F. 333 TABLE 28B Sokli Geochemistry - Results of Whole Rock Analysis by A.A. and X.R.F. contd 334 TABLE 29 Analyses of Palabora Samples 335 TABLE 30 The Isotopes and their Characteristic Photon Energies used for REE Analysis 337 TABLE 31 Rare Earth Analyses Palabora 339 TABLE 32 The Isotopes and their Photon Energies used for PGM Analysis 341

xiv LIST OF • PLATES

Page PLATE 1 Sulphides in Carbonatites 13 PLATE 2 Copper Sulphides in the Open Pit at Palabora 50 PLATE 3 Sulphide/Carbonate Relationships at Palabora I 62 PLATE 4 A. Magnetite and Chalcopyrite in Transgressive Carbonatite Dyke 65 B. Chalcopyrite Plate in Calcite 65 PLATE 5 Sulphide/Carbonate Relationships at Palabora II 69 PLATE 6 A. Contorted Bornite Bands in Chalcopyrite 71 B. Secondary Inclusions in Carbonate 71 PLATE 7 A. Sulphides in Phoscorite 78 B. Bornite and X-Bornite 78 PLATE 8 A. Low Ti Magnetite Rims on Sulphides 80 B. Parkerite with Wittichenite Rims 80

PLATE 9 Inclusions in Palabora Apatites 105

PLATE 10 A. Extracted Sulphide Inclusions from Apatite 111 B. Multisolid Inclusions in Apatite 111

PLATE 11 Inclusions in Palabora Olivine • 129

PLATE 12 Inclusions in Phoscorite Olivines Transmitted and Reflected Light 135

PLATE 13 Inclusions in the Guide Mine Pyroxenes 143

PLATE 14 Sulphide Daughter Minerals from Inclusions in Pyroxene 145

PLATE 15 A. Carbonatites in Core from Sokli 169 B. Sovites Cutting Glimmerites at Siilinjarvi 169 LIST OF PLATES Page

PLATE 16 Reaction Between Carbonatites and Silicate Rocks at Sokli 180 PLATE 17 Some Sulphide Occurrences at Sokli 185 PLATE 18 SAPPM Assemblage I 193 PLATE 19 Dual Mode Reflected/Transmitted Light Photomicrographs of SAPPM Assemblage 195 PLATE 20 SAPPM Assemblage II 196 PLATE 21 Aqueous Bearing Inclusions in Sokli Apatite 235 PLATE 22 Some Solid Inclusions in Apatite, Phlogopite and Pyrochlore 240 PLATE 23 Daughter Minerals in Aqueous Inclusions from Sokli Apatites 248 PLATE 24 SEM Photographs of Opened Inclusions I 250 PLATE 25 SEM Photographs of Opened Inclusions II 252 PLATE 26 SEM of a Multisolid Inclusion 254 PLATE 27 Phoscorites 296 PLATE 28 Sequence of Opening a Preselected Inclusion and Extracting Daughters for SEM Work 314

xvi INTRODUCTION

Carbonatites have attracted a great deal of interest during the last half century. They have fascinated and perplexed many petrologists and given rise to a vast array of theories concerning their genesis and relationship to kimberlites and silica poor alkali igneous rocks. Coupled with the purely scientific reasons for studying carbonatites, the realization that they may contain economic concentrations of a variety of elements and minerals has greatly increased interest in these enigmatic rocks. The rare elements Nb, Ta, Th and U and rare earths are of particular interest, but carbonatite complexes also provide phosphates, barite, vermiculite, fluorite, nepheline, Zr, Ti, Fe, CaCO3 and Cu. (Deans, 1966; Heinrich, 1966; Borodin et al., 1973; Frolov, 1975.) The petrological fascination for carbonatites has largely distracted western geologists from serious study of the ore forming processes at work in carbonatite systems. Numerous Soviet scientists have, by contrast, worked extensively in this field. In part this is a reflection of the different approach to the integration of mineral exploration and research which is taken behind the iron curtain. The situation in the West is well exemplified by some mining companies which find an isolated new carbonatite and drill it, analyzing the core for Cu, Pb, Zn, Ni and Nb. If this yields no significant results the'core is tipped by the drill site. Not only is this valuable material lost to scientists wishing to formulate a comprehensive understanding of mineralization and genesis in carbonatites, but the little information gleaned by logging and analysis often lies buried in private company reports. The U.S.S.R. has a large number of carbonatite complexes. This, together with what must be a more comprehensive approach to information pools pertaining to mineralization in carbonatites, has produced considerable progress in the field. Such progress has improved knowledge

1. of both the theoretical and practical aspects of ore deposition and evaluation in carbonatites, as well as of the theories of petrogenesis. Western scientists have of course made an enormous contribution to the field of carbonatite origin and occurrence. All too often individual mineralized deposits are well described, but work on the ore genesis is rarely extensive. Applied techniques are hardly ever used to enhance knowledge on mineralization processes in carbonatites by the West. It is hoped that this work on mineralization in copper bearing carbonatites will not only be a useful contribution, but will help to redress the balance in favour of the West.

Aims and Objectives The aim of this study is to investigate the causes and processes which are responsible for the concentration and enrichment of copper in carbonatites and related rocks. Peripheral to this, the research yields information on physico-chemical processes active in late stage formation of carbonatite complexes; processes which might also be responsible for the deposition of other valuable commodities which characterize some complexes. The result of this work was expected to be a better understanding of the role of aqueous rich carbonatite fluids in mineralization. A greater understanding of ore genesis in any rock type helps to delimit areas most likely to contain economic concentrations of metal. It was hoped that the present work might in this way provide a useful aid in the exploi- tation of the resources in carbonatites. It would be especially useful if some theoretical constraints could be placed on the economic potential of particular carbonatites with respect to copper. The Approach The overall occurrence of copper in carbonatites has been evaluated from the occurrences of copper mentioned in the literature and current models of the petrogenesis of

2. carbonatites. This has been supplemented by studying small suites of samples from numerous complexes with reported copper sulphides. Samples were studied from Bukusu, Uganda (material from Leeds University and the Geological Survey of Uganda); Glenover, South Africa (material from Goldfields of South Africa Ltd.); Great Beaver House, Canada (material from the Ontario Department of Mines), and Kortajarvi, Finland (material from the British Museum of Natural History). Initially the focus of the practical research was the copper Mineralization in the Palabora carbonatites of South Africa. The geology of the complex was well established, but a clear understanding of the ore genesis was lacking. A week's visit was arranged to this economic deposit, to collect samples, in September 1976. Studies of ore petrography and fluid inclusions were commenced with a view to elucidating some clues to the physico-chemical environment of deposition of the ore. It soon became clear, however, that fluid inclusions typical of apatite and other minerals in many carbonatite complexes were not present at Palabora. Whilst Palabora had apparently been subject to some hydrothermal activity, the fluid inclusion information on the composition of such fluids was absent. At this stage a few samples of core were sought from the Sokli carbonatite complex in Finland, following the report of high copper values by Vartiainen and Woolley (1976). On studying a few pieces of core made available by Rautaruukki Oy (a Finnish mining company working at Sokli), the association of the copper sulphides with fluid inclusion bearing apatites was immediately apparent. Sokli thus provided an opportunity to study the fluids responsible for the transport and deposition of copper in a carbonatite system. A visit to Sokli was made in August 1977 to sample more extensively. The research benefitted immensely from the study of two deposits, though the time spent on individual projects was necessarily reduced. The differences in the complexes

3. and the style of mineralization are remarkable and the range of processes active in carbonatites is made more clear. At Sokli the approach has been to establish that the fluid inclusions in the apatites were the parent fluids of the mineralization. Geochemical and petrographic programmes established this pedigree, allowing a detailed study of the fluid inclusions to be conducted with impunity. At Palabora melt inclusions in the earlier rocks were discovered, together with primary sulphide inclusions in apatites. Petrography and geochemistry relate these to, the mineralization process. The approach has thus been one of integrating normal petrographic, mineralogical and geochemical information with fluid inclusion analysis and interpretation. This has proved a penetrative approach to the problems of transport and deposition of copper (and to a lesser extent, niobium, Ta, Th, rare earth elements, etc.) in the late stages of carbonatite activity. Theories of Carbonatite Genesis and Emplacement The basis of any ore genetic study must of course be a: thorough understanding of the petrogenesis of the host and related rocks. Nowhere is this more important than in an ore genetic study of carbonatites. This is not only because the rocks are unusual and complex in their variety and form. Wide differences of opinion have existed concerning their origin and nature since they were first declared magmatic rocks by Hogbom at the turn of the century (Heinrich, 1966). It is not the intention to review the history of thought concerning carbonatite genesis, since excellent reviews of past and current theories are available (Verwoerd, 1964 and 1967; Heinrich, 1966; Smirnov, 1976 and 1977; Le Bas, 1977; Allen, 1978). Petro- genetic theories of particular authors are drawn on in the text and elucidated where necessary. Table 1, though essentially the view of the Soviet school, is a useful summary by Smirnov (1977) of carbonatite structure and ore

4. THE PRINCIPAL FEATURES OF CARBONATITE DEPOSITS (Smirnov, 1977)

1. They occur only in rigid, consolidated sectors of the crust and are associated with deep-seated faults, most commonly passing along the margins of platforms, on the junction between platforms and their folded surroundings, and also in typical rift zones. Their age is usually Cainozoic, Mesozoic or Palaeozoic and not older than late Proterozoic.

2. Carbonatites arise during final phases of development of ultrammfic-e1kelin magmatic complexes, including a series of early silicate rocks (ultramafics), alkaline ultramafica, ijolite-melteigite and nelilite rocks and nepheline and alkaline syenites. This entire assemblage of petro- .graphic varieties of rocks or part of it is usually involved in the composition of single massifa of the central type with an extremely complex concentrically zoned internal structure. Carbonatitee form either 'cores' of such massifs, or appear along their periphery in the form of annular dykes or lenses.

3. Massifs of ultramafic-al.kaline rocks and associated carbonatites are confined to a special type of tectonic structure, arising in sectors of intersection or merging of deep-seated faults. These are extremely long-continuing, repeatedly opening vertical pipe-like channels, extending to a depth of tens of kilometres. Such pipes may be arranged linearly, along deep-seated faults, or may be grouped in local 'rows'. Most of the massifs are cylindrical or conical, pipe-like bodies seemingly nested one in another, consisting of various silicate rocks and carbonatites. A characteristic feature of all carbonatite deposits in this association is their great vertical extent in the absence of marked changes in the nature of mineralization over a depth of at least 1 - 1.5km.

4. The pipe-like structures may reach the surface of the crust and appear in the form of both ancient and present day (active) volcanoes, erupting ultramafic-alkaline and even carbonatite laves (the Oldoyno-Lengai and Kerimasi volcanoes in Kenya), or may be 'blind' and surround massifs, the apical parts of which were formed at a definite depth. For the massifs from the various regions of the U.S.S.R., this depth is estimated at 1.5 - 3km. In some regions (the Maimecha-Kotui province and others) such massifs cut volcanic flows, which consist of erupted equivalents of ultramafic-alkaline rocks (ankaratritss and nphalinites.

5. In comparing the massifs, revealed by erosion at a different level, it is possible to establish a definite vertical zonation, which concerns the fact that weakly eroded masaifa are formed mainly of nepheline syenites, and the carbonatites are located directly among them, frequently extending into the surrounding fenitea. In deeper- sections the role of nepheline syenites in the structure of the maesife.markedly diminishes, the amount of ultramafic-a k ine rocks increases, and carbonatites occur mainly among meltteigite-ijolitea or ultramafic rocks.

6. In some massifs, extremely specific forsterite-apatite-magnetite-calcite rocks appear (Borodin et al. 1973) for which special names have been provided (foskorites, cama.phorites and an 'iron ore complex'). These rocks are distinguished from carbonatites by a small amount of calcite (less than 25%) and a large amount of magnetite and apatite. These are in fact iron or.phosphorus ores. Frequently they also contain rare metal minerals (tantalum-niobium and zirconium) which may have been extracted from the ores as a by-product during their treatment for iron or phosphorus. The ratios between these rocks and carbonatites proper are complex, and they may be regarded as definite carbonatite facies.

7. Carbonatites are essentially carbonate endogenic rocks, which arose during the course of the lengthy process of formation, in the temperature range from 630 to 19000. Throughout this process they regularly change in composition and during various stages of development they are associated, with different mineralization. Allowing for this, all investigators recognise definite types of carbarmt1tee corresponding to different phases of evolution of the carbonatite process. The early carbonatites (phases I and II) are calcitic and the ;ate types (phases III and IV) are dolomite-calcitic, dolomitic, dolomite-ankeritic and sideritic. Phase II of the early carbonatites is associated with iron-ore, tantalum-niobium, niobium, zirconium and phosphorus mineralization. Late carbonatites are associated with rare-earth, fluorite, and polymetallic mineralization. Early carbonatites were formed in the temperature range from 630° to 420°C and late types, from 420° to 190°0.

Table 1

5. deposition. Although a review of the petrogenesis of carbonatites (particularly with respect to their existence with, and/or evolution from, related silicate rocks) is considered beyond the scope of this work, it is fitting to mention one important divergence of opinion concerning the nature of carbonatite magmas and hydrothermal fluids. This is particularly relevant to the present work, since it concerns the nature of the material from which the carbonatites and ore crystallize. Broadly, two hypotheses exist. One considers carbonatites to be formed by crystallization of a magmatic carbonate melt. The other is that carbonatites are post magmatic hydrothermal deposits in, and replacements of, earlier silicate rocks. (See Gittins, 1966). Interest- ingly, the division is largely one of western geologists favouring the melt, whilst Soviet geologists favour the hydrothermal fluids. Because this division is one of schools of thought, each school tends to observe and describe carbonatites in the light of its own hypothesis; even experimental work is designed by each school to test its own theories. This polarization of views is further exag- gerated by a language and literature circulation barrier. The truth of the matter is that both processes are probably operative. For a long time individual authors have described both magmatic carbonatites in complexes with some carbonate metasomatism and hydrothermal/metasomatic complexes containing occasional transgressive dykes with flow structure typical of melts. Magmatic carbonatite lavas from Oldoinyo Lengai (Dawson,. 1962) and carbonate rich aqueous inclusions (Rankin, 1973) have provided evidence that both processes are at least active to some degree. Further, the alkaline rich nature of both systems suggests that a complete continuum could and does exist. From the point of view of ore genesis, it is important to keep both extremes of the above schools of thought in mind and, at the same time, to consider the possibility of a continuum. The argument for each is discussed as the evidence is presented. 6. CHAPTER 1: A REVIEW OF THE OCCURRENCE AND BEHAVIOUR OF COPPER IN THE FORMATION OF CARBONATITES

The purpose of this chapter is to provide a basis for the investigation of copper in the carbonatites (mentioned in the Introduction) chosen for study. The literature concerning reported occurrences of copper and other sulphides in these rocks is reviewed. This information is supplemented by reports on the examination of small suites of copper bearing rocks from a number of complexes (this work). The possible origin of the copper is also reviewed in the light of current knowledge on processes which might be active in carbonatite genesis. Finally, a review is presented of the more salient aspects of previous fluid inclusion, experimental and geochemical work which provides a direct insight into the origins and P.V.T.X. conditions leading to the formation of copper sulphides in carbonatites. 1.1 THE OCCURRENCE OF COPPER AND SULPHUR IN CARBONATITES Carbonatites have long been regarded as rocks impoverished with respect to copper. The mean value of copper in carbonatites suggested by Gold in 1963 was 2.5ppm. This is considerably lower than the value in many other rocks (see Table 2). The discovery of copper at Palabora, South Africa only partially dispelled this view, because with a grade in the carbonatites of 6900ppm copper, the complex was clearly an anomaly. Nevertheless, geologists investigating carbonatites became aware of the possibility of finding copper ore in carbonatites.

Table 2: Copper Abundance in Various Rocks

Rock Type Mean Copper Source in ppm. Carbonatites (mean) 2.5 Gold, 1963 Basalts 200 Zlobin et al. 1973 Granites 20 Jacobsen, 1975 Ultramafic rocks 20 It Palabora carbonatites 6900 Hanekom et al. 1965 Kaiserstuhl carbonatites (10-35ppm) Van Wambeke et al. 1964 E.Rift carbonatites 4.6-20ppm Gerasimovskii, 1973 W.Rift carbonatites (34 -58ppm)

A significant later discovery was the presence of copper at Bukusu, Uganda (Baldock, 1969). Here, drilling revealed copper sulphides largely related to the late stage activity of the complex, as at Palabora. Although the tonnage and grade were not economic, Palabora was no longer an isolated occurrence. The further observation that both Palabora and Bukusu were complexes in which a large proportion of ultrabasic rocks were present lead Deans (1966) to suggest that copper mineralization related to the ultrabasic type carbonatite complexes may be an intrinsic phase of the late stage carbonatitic development. He further implied that the carbonatites are not merely hosts to extraneous mineralization. Gerasimovskii and Belyayev (1963) working on alkali rocks of the Kola Peninsula (many of which contain carbonatites) pointed out that both miascitic (Na20 + K20/A12031) are marked by high copper contents, 0.1-4.Sppm being average, but rising to 570ppm. The high copper content in the syenites is ascribed to post magmatic processes redistributing copper and forming copper sulphides. They note that high copper concentrations are characteristic of alkaline ultramafic rocks. Heinrich (1966) reports that the green colour in flames of the lava lake of the volcano Nyiragongo (Congo)

8. results from the presence of copper in the highly undersaturated alkaline magma. Heinrich (op.cit.) points out that Gold's values. (1963) with respect to the major elements are heavily weighted by one or two localities. Levels of copper in carbonatites from other authors would also suggest that 2.5ppm Cu is not a representative mean (see Table 2). Van Wambeke et al. (1964) give ranges from 10-35ppm for the Kaiserstuhl carbonatite. Gerasimovskii (1973) analysed carbonatites of the African Rifts and also produced values somewhat higher than those obtained by Gold,. More interestingly, the carbonatites from the Eastern Rift had a different range (4.6-20ppm Cu) from those of the Western Rift (34-58ppm Cu). 1.1.1 The Sulphide Mineralogy of Carbonatites Levels of copper above a background of 2 or 3ppm in carbonatites are mostly explained by the presence of sulphides. The strong association of these two elements means that their behaviour and occurrence should be considered together. In doing this the small amounts of other base and precious metals associated with sulphides and copper are also noted. Sulphides in carbonatites can occur in a variety of forms and textures (this work). The sulphides may be small rare cubes of pyrite scattered in the carbonatite (see Plate 1.D.), or thin veinlets filling cracks and micro fractures in the carbonatite fabric. The textures and quantity vary from small blebs and specks in massive carbonatites (these may be parallel to any banding in the rock) to coarse grained crystals in vuggy ankeritic and sideritic dykes and veins. As Smirnov points out (Table 1) the polymetallic mineralization is most commonly associated with the later dolomitic and ankeritic carbonatites. Sulphides in the earlier carbonatites are usually less enriched in base metals, being predominantly the iron sulphides pyrrhotite and pyrite. Recrystallization, plastic flow and metasomatism of early formed sulphides in carbonatites, together with shearing and deformation, may make the relationships 9. with the carbonates in such early rocks difficult to interpret (see Chapter 2, this work). It is rarely easy to show that the sulphides are either conclusively comagmatic/autometasomatic, or a post consolidation hydrothermal/metasomatic introduction. 1.1.1.A Iron Sulphides, Pyrrhotite and Pyrite These are by far the most common sulphides and their continual appearance emphasizes the high sulphur content of carbonatites. Pyrrhotite is probably the most widely dis- persed and occurs in many carbonatites; Sokli, Finland;" Great Beaver House, Canada; Kortajarvi, Finland (this work); Iron Hill (Larsen, 1942); Magnet Cove (Erickson and Blade, 1963); Fen (Brogger, 1921); Alno (von Eckermann, 1948A); Palabora (Forster, 1958); Bukusu (Baldock, 1967); Vuori Yarvi, Kovdor and Sayansky (Kapustin, 1971); Callander Bay (Currie, 1976). Kapustin (1965) also records pyrrhotite as disseminations in ijolites and melanocratic fenites from Vuori Yarvi and the Eastern Sayan massifs. In the Vuori Yarvi, Kovdor and Sayansky complexes Kapustin (1971) recognised different generations of pyrrhotite deposition. These have characteristic Ni contents, dropping off with each generation. Percentage Ni in Pyrrhotite Generation Vuori Yarvi Kovdor Sayansky 1 .20-.28 .24-.20. .34 2 .22-.20 .19-.15 .17 3 .08-.14 4 .00-.04 - In the latest ahkeritic-dolomitic dykes, pyrrhotite commonly gives way to pyrite or marcasite (Sokli - this work; Mbeya - Fick and Van der Heyde, 1959). Pyrite is more typical in such late veins and is not so characteristic of earlier carbonatites, though it does occasionally occur in the latter. Pyrite is widely dis- persed in the carbonatites of Scandinavia (Brogger, 1921; von Eckermann,1948A), the U.S.A. and Canada (Larsen, 1942;

10. Olson et al., 1954; Heinrich, 1966; Currie, 1976), the Kola Peninsula (Kapustin, 1965; Kukharenko, 1965), South America (Melcher, 1966) and Africa (Verwoerd, 1967). 1.1.1.B. Copper Sulphides Copper sulphides are reported from a remarkable number of complexes. They are most commonly represented by chalcopyrite. Apart from Palabora, chalcopyrite is reported from five or six complexes in Canada (Currie, 1976); Sokli and Kortajarvi, Finland (this work); Glenover, South Africa (Verwoerd, 1967); Bukusu and Butriku, Uganda (Bloomfield', 1973); Iron Hill, Colorado (Nash, 1972); Elk Creek, Nebraska (Brookins et al. 1975); Sulphide Queen, Mountain Pass, California (Olsen et al. 1954); Kaiserstuhl, Germany (Van Wambeke et al. 1964); Kovdor, Kola Peninsula (Rimskaya- Korsakova, 1964); Vuori Yarvi, Kola (Kapustin, 1965); the carbonatite zone of the Ukranian Shield (Kapustin,et a1.1978) and Strangeways, Australia (Moore, 1973). In most of the recorded instances, the chalcopyrite is associated with pyrrhotite, apparently in a way well, represented by the suites of rocks studied from Great Beaver House, Sokli, Kortajarvi and Bukusu (this work). In these suites chalcopyrite is subordinate to pyrrhotite and appears to be closely related to it in terms of paragenesis. Typically the chalcopyrite occurs as irregular shapes on the edge of blebs of pyrrhotite and in a given sample, the percentage of chalcopyrite is approximately the same in each bleb, suggesting that the chalcopyrite has exsolved from the pyrrhotite (see Plate 1). Excluded from the structure completely, it has moved to the edge of the bleb. The chalcopyrite may also contain exsolved stars of sphalerite and small blebs of galena. At Palabora, and also Bukusu and Glenover, the chalcopyrite occurs more commonly on its own, or with other copper sulphides. This reflects increased levels of copper in the system against normal levels of sulphur and iron. At Glenover there is no pyrrhotite and at Palabora it is very subordinate. The

11. Bukusu complex has an early phase of pyrrhotite mineralisation free of copper and later phases associated with metasomatism which only contain chalcopyrite (Baldock 1967). Generally as the level of copper increases, it also combines to produce a greater spectrum of copper sulphides. Bornite is found at Palabora and Glenover (this work) and in carbonatites of the Ukranian Shield (Kapustin et al. 1978). Tetrahedrite (Cu12Sb4S13) has been found at Palabora (Hanekom et al.1965) and also at Vuori Yarvi and Salanlatva (Kapustin, 1965). In the latter instances it, occurs as small tetrahedral crystals in association with galena, ankerite, barite and strontianite. Kapustin (op. cit.) also found the rare sulpho-antimonide, bornonite (Pb Cu Sb S3) in the ankeritic veins of Vuori Yarvi. Cubanite is common at Palabora, but is not reported from other carbonatites. Covelite has been found at Palabora (Forster, 1958) where it may be part of the primary assemblage (see Chapter 2, this work). At Vuori Yarvi and Kovdor (Kapustin, 1965) and at Palabora it is a replacement (in association with bornite) of chalcopyrite. 1.1.1.C. Pentlandite and Millerite Pentlandite is not common in carbonatites, but it does occur at Palabora (Forster, 1958), Glenover, South Africa (this work) and Vuori Yarvi and Kovdor (Kapustin, 1965). At Palabora and Glenover it is mostly found as residual crystals partially replaced by chalcopyrite (this work, see Plate.l.F.), though it may also be found with pyrrhotite at Palabora and also Vuori Yarvi and Kovdor (Kapustin, 1965). ' Millerite is recorded at Palabora (Forster, 1958). See also this work (Chapter 2) where it is suggested that much of it is a secondary replacement. Kapustin (op.cit.) records millerite at Vuori Yarvi where it forms sheafs of needle like crystals (up to 5mm long) in vugs of ankeritic veins. These veins also have corroded crystals of pyrrhotite, which in turn have relicts of primary pentlandite.

12. PLATE 1: Sulphides in Carbonatites

A. Sulphide banding in sovite core from Sokli (top) and Bukusu (below). The sulphide is pyrrhotite in each case.

B. The sulphides in vuggy dolomitic and ankeritic veins at Sokli. This was the final stage of carbonatitic activity.

C. Undulating bands of pyrrhotite in sovite from Sokli. This is probably caused by plastic flow of the carbonate under later`. tectonic stress.

D. Rare pyrite (py) cubes in sovite from Mrima carbonatite complex. Typical of the limited sulphide occurrences of many carbonatites. Plane polarized reflected light. Bar = 500 microns.

E. Chalcopyrite (cp) exsolved on the edge of blebs of pyrrhotite (po) in an apatite/phlogopite/magnetite assemblage from Great Beaver House carbonatite, Canada. Plane polarized reflected light. Bar = 500 microns.

F. Chalcopyrite (cp) after early forme.d pentlandite (pn) in sovites from Glenover, South Africa. Plane polarized reflected light. Bar = 500 microns.

13. PLATE 1

B 1.1.1.D. Molybdenite This has been found in a limited number of complexes. Magnet Cove, (Heinrich, 1966) is one in which molybdenite occurs in late stage dykes. Certain areas here were drilled for molybdenum in the 1950s, but the grade was not sufficiently high. Currie (1976) reports the common occurrence of molybdenite in the fenite aureole of Callander Bay, Ontario, and suggests that fenites of other complexes be investigated for molybdenum mineralization. Small quantities are also recorded from Mrima Hill (Coetzee and Edwards, 1959), Ravalli and Fremont Counties (Heinrich and Levinson, 1961), complexes of the Kola Peninsula and Siberia (Kapustin, 1971, Kukharenko et al. 1965) and St. Honorē, Canada (Currie, 1976). 1.1.1.E. Lead and Zinc Sulphides Sphalerite is common in association with chalcopyrite as previously mentioned, but it is most typical in the late stage ankeritic veins. It is noted in many African carbonatites: Spitskop, South Africa (Verwoerd, 1967), Nkumbwa Hill, Zambia (Phillips, 1955), Mrima Hill, Kenya (Coetzee and Edwards, 1959), Mbeya, Tanganyika (James and McKie, 1958). In the U.S.A. at Ravalli and Fremont Counties (Heinrich, 1966); also Siberia (Gaidukova et al.1962), the Kola Peninsula (Kapustin, 1965) and Alno, Scandinavia (von Eckermann, 1958). It is especially common in Salanlatva and Vuori Yarvi (Kapustin, 1971) and in one of the Siberian complexes (Frolov,197lB) and at the Kaiserstuhl (Van Wambeke et al. 1964). Galena is not so commonly mentioned from the African carbonatites, (though it does occur at Palabora, Forster, 1958), or Siberian complexes (except for Frolov, 1971B). This may be because it is in very small amounts and has not been noticed. Heinrich (1966) thinks it is more widespread than sphalerite. It occurs in greater concentrations in the Siberian carbonatite lead zinc deposit mentioned by Frolov (1971B) and is also found with zinc at Salanlatva,

15. Vuori Yarvi and Kovdor (Kapustin, 1971). Kapustin (op.cit.) notes a close link between galena, orange barite and siderite and reports barite veins enriched with galena from Vuori Yarvi and Namo Vara. He also reports boulangerite. (Pb5Sb4S11), jamesonite (Pb4FeSb6S14) and bornonite (PbCuSbS3) at Vuori Yarvi. 1.1.1.F. Polymetallic Sulphides, Sulphosalts and Native Elements A variety of other sulphides have been recorded from Palabora, particularly where the ore has been subject td more scrutiny (see Chapter 3, this work). It is interesting to note the presence at Palabōra of bismuth phases witicherite and parkerite (discovered this work). Kapustin (1971) in his studies of Vuori Yarvi gives lists of elements detected by spectral analysis of the various phases. Consistently the sulphide minerals contain Bi, Sb, Ag and As and some also contain Ga and Cd. These elements are typical of the hydrothermal vein type deposits. This, together with their presence in the late stage vuggy veins/ dykes of carbonatite complexes, might be considered as evidence for a hydrothermal origin. At Palabora P.G.M. (platinum group metals), Au and Ag occur as native elements (Chapter 2, this work). These native metals have not been noted elsewhere but this may be due to the ores being subject to less scrutiny. Nevertheless none of these have been observed in samples from other complexes in this study and analysis for Au in the Sokli sulphides showed only 4ppb, compared with 0.1-1.4ppm from Palabora (see Chapters 3 and 6). Interestingly, Stricker (1978) has proposed that the Kirkland - Larder Lake gold deposit may be a stratiform volcanic carbonatite precipitate. He analysed 27 carbonatites for Au and suggested that carbo- 'natites might represent targets for Au exploration. It seems likely that Au is associated with sulphides in carbonatites (this work).

16. 1.1.2. Carbonatite Complexes with pronounced Copper Enrichment A comparison of complexes which are enriched in copper with more than average quantities of chalcopyrite shows a wide range of ages and locations. Figure 1 and Table 3 have been produced to compare the broad features of some of the better documented occurrences. A brief description of each complex, together with the style of mineralization, follows.

Table 3: Some Complexes with Carbonatites anomalously enriched in Copper (cf. Gold, Table 2)

Palabora Bukusu Sokli Glenover Kovdor Vuori Belozi- Yarvi minsk

Carbonatite (middle) last middle middle? (middle) middle last stage(s) last last last mineralized

Sulphide * cp bn cp po cp cp bn po cp po cp cp sl paragenesis (pn) (po) (pn) (pn) (pn) gl mo

High 7. ultra 4 none ,/ basic rocks N/ J N/ low

Phoscorites .1 none ,/ ,/ none present J J

Nepheline ✓ J rocks J I

Depth of x deep medium medium? deep? medium medium medium erosion deep deep

Nb none low ,/ none 4 4 4 REE Minerals ) - - - - some - 4 & fluorite ) Age (million 2060 25 350 1000 370 380- middle years) (approx) 400 proterozoic

* Principle sulphides only are mentioned (in order of abundance) cp = chalcopyrite pn = pentlandite mo = molybdenite bn = bornite sl = sphalerite po = pyrrhotite gl = galena x See Frolov (1971A), Heinrich (1966), and Fig. 2 (this work)

17. Some Complexes with Anomalous Copper Mineralization

N PALABORA - S. Africa N BUKUSU - Uganda 0 oa

after Hanekom 19651 N SOKLI - Finland T [ after Batdock 19691 N GLENOVER S. Africa

[ after Vartiainen&Woolley 1976 and oers. corn 19771 after Verwoerd 19671 KOVOOR - U.S.S.R. Kola N VUORI YARVI- U.S.S.R. Kola

( after Borodin et. al. 19731 KEY [ after Rimskaya-Korsakova Pyroclastics 19641 Carbonatites N BELOZIMINSK - Siberia T Phoscorites Syenites Melteigite,ijolite,urtite etc. Pyroxenite &dunite 5 kms

FI G.1

[ after Frolov in Smirnov 19771

18. 1.1.2.A. The Copper Mineralization at Palabora (see Fig.l) The'carbonatites here form a central plug in a body of pyroxenite. The plug (Loolekop pipe) contains phoscorites, a banded sovite and a later transgressive sovite. The latter is host to the bulk of the copper mineralization - mainly chalcopyrite-bornite, with cubanite and some pyrrhotite/pentlandite. Smaller quantities of copper sulphides in the earlier banded sovite and phoscorites have been ascribed to 1)an earlier phase of hydrothermal mineralization• (Hanekom, 1965) 2)an outer halo of the one major copper mineralizing event (Heinrich, 1970) and 3)copper mineralization cogenetic with these earlier rocks (this work, Chapters 3 and 4). The carbonatites are notably impoverished in niobium and rare earth minerals. This complex is the subject of Chapters 2, 3, 4 and 5. 1.1.2.B. Bukusu, Uganda The carbonatites are rounded and elongate zones, forming a discontinuous rise in alkaline (ijolite, melteigite and nepheline syenite) and ultrabasic rocks (pyroxenite and micapyroxenite). Carbonatites (probably early) cutting the ultrabasic rocks have screens of phoscorite associated with them and characteristically have pyrrhotite (little or no chalcopyrite) associated with them (Baldock, 1967). Metasomatic replacement of the areas in the alkaline rocks forms other carbonatites which in places have notable quantities of chalcopyrite. In these instances the chalcopyrite is intimately intergrown with titanomagne- tite (Baldock, 1967), with pyrrhotite and pyrite also present. These centres have been subject to later stage shearing and veining with chalcopyrite and pyrite (Bloomfield, 1973). Analysis of material (this work) collected by Baldock, stored at Leeds University, shows that fluids which deposited sulphides in the phoscorites also deposited apatite and phlogopite. The apatite has aqueous fluid 19. inclusions with sulphide daughter minerals. A similar occurrence at Sokli is documented in detail in Chapters 6 and 7. As at Sokli, the chalcopyrite pyrrhotite association at Bukusu suggests the formation of a solid solution iron-copper-sulphide which later unmixes chalcopyrite. The chalcopyrite in the metasomatised areas, by contrast, mostly occurs on its own as scattered specks in the carbonate and intergrown with magnetite. 1.1.2.C. Sokli The multistage carbonatite complex at Sokli has no' associated silicate rocks as exposed at the present level of erosion. There are, however, various stages of carbonatite activity (Makela and Vartiainen, 1978), including residual areas of phoscorites which have been altered and replaced by later sovites and rauhaugites. Various stages of sulphide deposition have been proposed by Makela and Vartianen (op.cit.). Quantities of pyrrhotite are present, especially in the phoscorites, and these have chalcopyrite apparently exsolved from solid solution as at Bukusu. In further likeness to the Bukusu pyrrhotite-chalcopyrite occurrence in the phoscorites, these sulphides at Sokli are commonly associated with apatite and phlogopite, and again the apatites have aqueous fluid inclusions (this work, Chapters 6 and 7). There are no large areas of extensive mineralization where chalcopyrite is dominant as at Bukusu, but the phoscorite may locally become almost entirely replaced by the pyrrhotite/chalcopyrite sulphide assemblage where shearing and partial remobilization of the chalcopyrite does produce areas of quite high copper values. A final series of vuggy ankeritic and sideritic dykes has a distinctive assemblage of pyrite and pyrrhotite, chalcopyrite being less common in these. This complex is covered in more detail in Chapters 6 and 7.

20. 1.1.2.D. Glenover (see Fig.1) This complex consists of biotite pyroxenites with con- centric calcitic and dolomitic carbonatite dykes and a small central agglomerate. Chalcopyrite was reported by Verwoerd (1967) in some of the material he studied. The complex is worked for apatite by Goldfields of South Africa, who kindly provided some material for this study. The copper mineralization is found in the dolomitic carbonatites (beforesites), and though it is not very common, it is striking for its similarity with Palabora; the sulphide assemblage consisting of chalcopyrite and bornite with partially replaced residual crystals of pentlandite (see Plate 1). Verwoerd also reports sightings of sphalerite and galena on outcrops. 1.1.2.E. Kovdor Kola Peninsula (see Fig.1) The Kovdor complex has a central area of ultrabasic rocks (olivinites and pyroxenites) with numerous later veins of the ijolite, melteigite series and areas of nephi- linised pyroxenites (Rimskaya-Korsakova, 1964). Phosco- rites cut this on the western rim and these are in turn cut by carbonatites, which also occur outside the western rim of intrusive silicate rocks. Sulphides of chalcopyrite and pyrrhotite are reported to be intimately associated with the phoscorite in which magnetite deposition has been sufficient to form economic iron ore deposits. Chalcopyrite, pyrrhotite and pyrite are reported in greater amounts in the sovitic veins and dykes which followed the formation of the phoscorite and are also present in dolomitic veins which follow the sovites. Late stage ankeritic and sideritic carbonatites complete the series containing barite, celestite, sulphides of lead and zinc and fluorocarbonates of rare earths. Rimskaya-Korsakova (op.cit.) ascribes the origin of the phoscorites and carbonatites to the changing chemistry

21. of metasomatic solutions ascending into continually re- worked fracture zones. The sulphides of the various stages are, in her view, clearly metasomatic phenomena. 1.1.2.F. Vuori Yarvi Kola Peninsula (see Fig.l) This complex is a plug of pyroxenites and nepheline pyroxenites with a rim of nepheline pyroxenites and ijolite- melteigites. It has been intruded (or replaced) by phoscorites and later carbonatites. The genesis of the carbonatites and phoscorites is apparently very similar to Kovdor, with the late stage ankeritic and sideritic carbonatites being well represented (Borodin et al.1973, Kapustin,1971). Pyrrhotite exists in all stages of carbonatite and has chalcopyrite associated with it; pentlandite is also found in the sulphide paragenesis here (Kapustin, 1965). Late stage dykes contain a variety of base metal sulphides. 1.1.2.G. Beloziminsk+ Siberia (see Fig.l) Pyroxenites and nepheline pyroxenite rocks, nepheline and alkaline syenites are intruded by a large area of carbonatites (about 10 square miles). The Russians (Frolov and Epstein, 1962; Smirnov, 1977) in characteristic fashion have delineated four stages of carbonatites, following the well recognised general trend of carbonatite emplacement, from calcitic carbonatites to those richer in dolomite and then ankerite and siderite (see Table 1). This is a less deeply eroded complex than many of the others mentioned here (on the basis of Frolov's depth classification, 1971) and, interestingly, there are no phoscorites present. Further, in fitting with the concept of rare earth mineralization being concentrated in the

+ The Russian literature seems particularly covert concerning the names and scale of deposits in Siberia. This deposit, detailed by Smirnov in 1977, is unnamed, but it corresponds to the shape and structure of the Beloziminsk complex drawn by Frolov (1971A) in his scheme of levels of erosion (he also provides a scale).

22. middle to upper reaches of the complexes (Frolov op.cit.), the large late ankerite/dolomite bodies at Beloziminsk constitute considerable rare earth deposits. Smirnov (1977) mentions that "copper, lead, zinc, molybdenum, fluorite, iron, phosphorus, barite, strontium and thorium may also be of practical interest". (The base metal mineralization is found associated with the REE - Rare Earth Elements - mineralization in the last stage of dolomitic/ankeritic carbonatite activity.) 1.1.3. A Classification of Copper Bearing Sulphide Parageneses From the above descriptions, it is apparent that many complexes containing copper sulphides are of the type in which ultrabasic rocks predominate. Most of them also contain phoscorites. The presence of a high percentage of ultrabasic ricks is thought by some authors to be indicative of a deeper level of erosion (Borodin, 1957; de Kun, 1961; Heinrich, 1966; Verwoerd, 1967; Frolov, 1971). Frolov (op.cit.) ascribes different styles of mineralization to various depths of erosion through a carbonatite column (see Fig.2). In this scheme Palabora is regarded as abyssal facies (about 8 kms. below the original surface). The more typical polymetallic mineralization (in late stage dolomitic and ankeritic dykes and veins) is confined to the upper reaches of his archetypal complex. Palabora thus falls into a class of its own on the basis of depth of erosion. There is evidence that some copper mineralization at Palabora is associated with dolomitization, but its extent is probably limited (see Chapter 2). On the basis of the preceding comparisons and discussions, it is possible to classify the occurrences of copper sulphides into three classes:- a) deep-seated complexes; sulphides, predominantly copper bearing The basis of this class is Palabora, not only because of the depth of erosion and enormous quantities of copper, but also because of the distinctive sulphide paragenesis. 23.

FROLOV'S [1971] DEPTH OF EROSION SCHEME Volcanic type of ma.41 Deep type of massif

Aru.tural parois Stands in the marginal seam. fio.bngI MASSIF/ Ie ffectwes along the of the plat forms and In the 01 nuuif. Mass11. In itans•nruamal and Sactinn and Rock.. fording massifs Economic minnrsli7Jtion periphery of the piatlom. Lercl feathering fractures •unosrd'ng more of terminal depths fades of elution folding Phunulitcs, ncphclinites, Dmburgites, augitttt's. li Tone ratervr nml Monazite, .tn•n[matit , barite, apatite, Nepa Lolekek l meymechpese cerbunatltes, tuffs, tuff-brtcctas crater !acme carhma[n, hematite te ii i"' •• and agglomerates Insnpndrearsly y'• FI.n,Jlm Otdonro eroded votcgnarc Meta Kaliango ,ompleres Maier, •• . D1 Subvolednic Ratite, cJrt.matt'/, apatite, monazite, subvolcanic tacit.) Torino La.harn• lacks and Mkertty, siderite. calcite, dolomite carbona- panutc, bj.tnf ete, annchte, sul- ...V.". Ratl Fan., Klwma fades of (lice; phunulttes, nrpheltnheo. 1ytnitcs, picnic fides of Pb. in. Cu and NA), fluorite, songr, M.. tsr O.ongumbo .` Kontofeto pu.rphyritic purphyrlicb. alnites, meymeeMtes, f jullixc hem.il tc, 71rcon, pvru.chlore, colum- Chrmas Ka atride I ntrugiurs bite, hatchettulte Cape T.eny Yatma dl..•tl~r, Conealed massif. !Crony rot exposed by Chuktukoa Khamne i/f••'•••o wellen Iobaa-Voyekaya mrr'U•.•lI.., T %%%% % 7777T7 7>•77 7~"7 j r/ ITITTIJiT/ '7'7'1'777 Kaltleld, '//!`/ jCotnoount TKos' r ~%, /~,ī// (Fauw of A V O1 / /~ / dkedrie rlmleek• / I y p.ibyssal • / /•t ol aduM~(Kala yenlnewa►/ / j/ . / // Yoin i •tarse ln[rupelu~ns)"/ ~ //~ tg ! /*. facit'e •OnOratwome Twee Rerler . rna / Pyruchlure, culumbite, hatchenolute. umee Cek Posormyy Calcite, calcite-el ilomute and ankeri(e carbons- Chiba Tundwu LuesI. f .u.. Po goy pat 'cite, hastnāsite, vnkylute. sul- 41141 (till, ijulutes. mardfeIgites, Jacupsraogrtc., Shallow 1 lib ha, V' fides re Pb. 7_n, Cu, Ma, apatite, syrnutrs, nt•{arheime pyruaervhn, turjaltes, and (hyp.by.sal Salaatambl IIIgIU perovsktte, phhgupitechalco• magnetite, )lemegu less pyrtnenlla and pernicettes facie.) N[wnbne Moms. o1 (5,,.,, ~, kl'shetapunsk baddeleyute, borons, pyrtte Bra M..r Arbarauakh ~':•, htesoabysaal TT~~ .0 -7,777,7 7~T7 7777 7. 1777 / iJ i', iōreī Lai • :% facie' T `"T 7T '77 l 111111~1 `~Q'1.' :~ 1 i 1111/tl, *n`'• Z: 11. Fen fbrdethare BeloMminek — San Medium 8e.0 Spitrkop ~—' ~āa..y. (mesoabyssal ~a.rr Caomoremk laue.) O=maya Varaka Sm.., Abyssal .und llumtes, pertduiItes, pyrusenutra, nepheline ultra- pyru.enites. and less frequently, Ijuliles. 8aldeley'te. ph1uganRe, apatite. ~ abyssal melteigutes, Jacupirangutea, and dulumtte-cal- perovektte, Irranornagneute ~( wyte I faele.) f r.a/ /jar la/ / facies cute carbkmaliIca Kovdar 2 nalma sk/ •~/ /// ,>j /

Sebliai at -Uah Fara ~ lsho hdoyek Deep(aloe• e1 Citgin nn ()Ifs., ... leshaya abyssal facie.) Afnkanda V afaka Oz.1

CEO/ ®t 123F Da r2:11 .i~ 1 EDEJ ®a fōds ®i EMI M I b Shave, slw.nslos end cion of osflfs of ultr.b•slc-elkaliM rocks and cartemm tites . blegran of vert'ul tonsils, of ealposttim, structure and distribution of economic deposits In massifs of ullraNNc alkalies rocks end orbQo•tIicf.

1- pvrocl•stics 1 -fyenites I it formations of volcanic centers • rocks of IM j.cglrenglt.rltslglse-Ijoli te- 2 - cor►m.elms - J•cu•i easel tes, mal total tes, 'Jot l tes, a - phenol ltes, nghel uni les) and ether effusive rocks molts series •- stocks ur l 'tes b- Iu1f•bfecc1■s end &biloma S . sltrebaslln (pyramblla., Mel , doltes) ▪ - veins - pyro.orlted, perldotitss, *mites g - t.rbo.ct1t&s 6 - t lobes.. • - stocks 7 • sedl.enlary deposits of tis platform cover b - veins S • ancient rocks of the platform basement 3 - nepheline end •Reline eyeni Ns 9 - frect,res Fig. 2 The sulphides are predominantly copper species. Glenover, though having very low levels of copper mineralization, could belong to this class on the basis of the sulphide assemblage and depth of erosion. b) the pyrrhotite-dominant sulphide assemblage This is probably the most typical of classes. The chalcopyrite occurs in association with pyrrhotite, to which it is subordinate. The sulphides are formed with different stages of carbonatite activity and in most cases are associated with apatite, phlogopite and occasionally pyrochlore. Examples include Sokli (see Chapter 6), Kovdor, Vuori Yarvi, the early mineralized phoscorites and carbonatites at Bukusu and also Great Beaver House. Bagdasarov (1971) suggested that the occurrences of this type at Kovdor and Vuori Yarvi might give way to more extensive mineralization at depth, possibly in the same way as at Palabora. Drilling at Kovdor revealed some increase in copper values with depth (Bagdasarov op.cit.) but it is conjectural that this might give way to the Palabora class a) type of mineralization at depth in this or any other complex. c) late stage ankerite/dolomite association This class is typically reported in the late stages of many complexes. The amount of base metal mineralization, however, varies from one locality to another. The paragenesis is characterized by the presence of sphalerite, galena, rare earth minerals, thorium, barite, fluorite and other typical low temperature minerals. The copper is usually as chalcopyrite and may be associated with pyrite, pyrrhotite and the other metal sulphides. The paragenesis appears to be present in greater amounts in the upper reaches of carbonatite columns (Frolov, 1971A). It is possible that a fourth class might be formed from examples where copper sulphides are in silicate rocks associated with carbonatites. Copper sulphides in the pyroxenite at Guide Mine, Palabora (see Chapter 5) are of

25. this type. Copper sulphides and native copper are also reported from the pyroxenites and fenites of the Cargill Complex, Canada (Erdosh pers.comm., 1977). The occurrence of molybdenite in the fenites of Callander Bay (Currie,1976) also suggest that fenitizing fluids can also be sulphide mineralizing fluids. In this context, it should be noted that copper sulphides are found in the fractured fenite aureoles surrounding deep seated nephelinitic complexes (Currie, 1976). The relationship of copper sulphides with magnetite, should also be noted. In classes a) and b) the sulphides are invariably preceded and succeeded by magnetite deposition. The magnetite is commonly cut and replaced by sulphides, but the whole may then be surrounded by later magnetite (this work, Chapters 2 and 6). At Bukusu and Kovdor (as mentioned in the above accounts) the sulphides and magnetite are intergrown. Such relationships may reflect alterations in the f02 and fS2 conditions as cooling and deposition occur. This is further discussed in the next section. 1.2. THE ORIGIN OF COPPER AND SULPHUR IN CARBONATITES 1.2.1. The Origin of the Copper There have been few ideas put forward to account for the heavy enrichment in copper in one complex while others remain impoverished. The possible origins of the copper are threefold:- i the copper is primary in the parent magma ii)the primary magma was contaminated by copper rich rocks at depth (deep crust) iii)the copper was introduced from an extraneous source by a post consolidation influx of water Point iii) can be fairly conclusively dismissed for a number of reasons, primarily because of the enormous vertical extent of mineralization in carbonatites. It has been shown by drilling at Palabora (and in other complexes) that the mineralization, lithology and structure of the carbonatite pipe may be exactly the same for at least one

26. or two kilometres (P.M.C.Staff, 1976). In some Siberian complexes (Frolov, 1971) pyrochlore mineralized carbonatites have a vertical extent of not less than 3-3.5kms. The rare earth and barite mineralization in the latter deposits, by contrast, is confined to only a few hundred metres. The implication at Palabora is that the copper bearing pipe was probably in excess of two or more kilometres in vertical extent. It seems unreasonable that extraneous ground water influxes would deposit copper sulphides so evenly in only one carbonatite lithology and over such a vast extent. Further, solutions of extraneous origin would be siliceous, not carbonate rich. There are no deposits of quartz associated with the Palabora ores. At Bukusu carbonate bearing solutions apparently metasomatized silicate rocks and deposited copper. Information on fenitizing processes mostly suggests that there is a massive exodus of solutions from carbonatite complexes, rather than an influx. On the basis of the above points, hypothesis iii) for the origin of the copper can be rejected. In this work (Chapter 4) it has been further shown that copper was an integral part of the carbonatite process at Palabora. Distinguishing between hypotheses i) and ii) is more difficult. The strontium isotope data at Palabora are compatible with limited crustal assimilation (Eriksson, 1978), but the sulphur isotopes indicate a mantle origin for 'the sulphur (von .Gehlen, 1967; Hoefs et al.1968; Mitchell and Krouse, 1975). The copper could thus conceivably have been introduced by limited crustal assimilation, as suggested by hypothesis ii). It has been suggested (Le Bas pers.comm.1976) that Palabora may have been contaminated by copper rich Bushveld material at depth. However, unless there had been an inordinately large segregation of copper sulphides in some other rocks in the deep crust, which the Palabora magma could have assimilated, it seems unlikely that any 'limited' contamination would provide the magma with substantially more copper and nickel than would be reasonably expected in a primary ultrabasic magma of mantle origin. The copper at Palabora is probably 27. of mantle origin, being introduced into the crust with the primary magma. To follow the origin of the copper further than this is difficult and any conclusions concerning the origins must be tentative. Processes active in what now appears to be a complex heterogeneous mantle are only slowly being understood. Nevertheless, the anomaly of Palabora may reflect a local anomaly in the ancient mantle. The nature of the mantle is an area of constant speculation, especially when considering the origin of kimberlites and carbonatites. Some recent observation of extensive metasomatism in the mantle beneath Southern Africa may be relevant to the present problem. Harte and Gurney (1978) and Gurney (1978) propose from investigation of kimberlite nodules that metasomatic processes in the mantle beneath Southern Africa are responsible for the introduction of Ti, K, S, Fe, Cu, Sr, Ba, Nb and REE into a broad spectrum of mantle rock types. The suite of elements mentioned bears a striking resemblance to the elements enriched in some carbonatites. Further evidence of metasomatic processes in the upper mantle is provided by Wass et al.(1978) who studied xenoliths in basaltic rocks from Australia. In these, veining and metasomatism introduced apatite, carbonate, sulphides (chalcopyrite, pyrrhotite, pentlandite and pyrite), mica, magnetite and ilmenite. Again a striking parallel with carbonatites, which is further emphasized by the REE trends in the apatite, which show light RE enrichment trends typical of carbonatites. No mention of the origin of carbonatites is made by any of the above authors, but Wass et al. (op.cit.) conclude that "mantle fluids can exist that affect metasomatism" as a product of high pressure differentiation of "a highly undersaturated hydrous alkali rich magma containing significant P, CO2 and REE". This kind of metasomatism in the mantle, together with the growing evidence of primary volatile rich H2O and CO2 fluids which appear to be progressively evolving from the

28. mantle, (Roedder, 1965; Bailey, 1974, 1978; Wyllie, 1978; Wendlandt and Harrison, 1978) are of tremendous interest to carbonatite geologists. The divisions are not solved however. Melting of a 'carbonatized' mantle could produce the carbonated ultrabasic magma of King and Sutherland (1960, Part III), or the metasomatizing fluids could follow the upward course of ultrabasic magma plugs, altering and metasomatizing the latter to produce carbonatites in a manner suggested by Borodin (1957, 1958) and Kukharenko et al. (1964). Many theories can no doubt be developed from these new observations, and as suggested by Borley (pers.comm. 1979) such observations put the problem of the ultimate origin of carbonatites and kimberlites one step deeper in the mantle and one step further from our grasp. Without attempting a synthesis or review of carbonatite origins (which is beyond the scope of this work) it can be seen that mantle heterogeneity is now well accepted. There is thus potential for variations in both copper and sulphur or volatiles (Bailey, 1978) which might affect the behaviour and transport of copper;.these could be responsible for occurrences of carbonatites unusually enriched in copper. Such speculation must, however, be put into perspec- tive. The quantity of basic magma that must have been available at Palabora to drive a 15sq.km. section pipe right through the crust should be able to provide the necessary copper in late fractions without having an anomalously high initial copper content. The fractionation process at work within the primary magma and the relationship of these to the generation of the carbonatites are fundamental to the problem, irrespective of the origin of the copper. A theoretical consideration of the behaviour of copper and sulphur in carbonatite evolution is presented in subsection 3.

29. 1.2.2. The Origin of the Sulphur The sulphur in most carbonatites can be shown to be of probable mantle origin using sulphur isotopes. The deep seated high temperature carbonatites such as Palabora have values close to the meteoritic mean (von Gehlen, 1967; Hoefs et al.1968; Mitchell and Krouse, 1975). The values are close to those of kimberlites (Tsai et al.1977) and the accepted mantle 634S. With reference to mantle variations though, Grinenko et al. (1970) observed variations in sulphur isotopes from one province to another. Sulphur isotopes must, however, be viewed with caution because both Grinenko (op.cit.) and Mitchell and Krouse (op. cit.) observe differences in the fractionation of the sulphur isotopes with changing conditions in individual complexes. 1.2.3. The Behaviour of Copper and Sulphur in Silicate Melts and Carbonatites Copper is a chalcophile element and, although it belongs to elements of the first transition group, it has properties unlike many of the other transition elements. A comprehensive investigation of the behaviour of these elements in mafic magmas by Curtis (1964) emphasizes this striking anomaly. Concepts explored here rest upon the petrogenetic idea that many carbonatites develop as late stage products (by crystal fractionation or immiscibility) of carbonated basic or ultrabasic silicate magmas generated in the mantle (see Verwoerd, 1964; Heinrich, 1966; Le Bas, 1977). The development of copper concentrations in the final product of such a magma is dependent upon four factors:- 1 the presence of Cu in the initial magma 2)the fractionation of the Cu into the later portions of this magma 3)the partition of most of the copper into residual carbonatites 4)continued fractionation within the carbonatites and final deposition

30. The presence of copper in the initial magma has been discussed, but it must be noted that alkali ultrabasic rocks associated with carbonatites invariably have low levels of Ni and also Cr (Erickson and Blade, 1963; Baldock 1967; Sorensen, 1974; Vasiljev, 1978 and this work, Chapter 8). These elements substitute easily into the lattice of olivine and pyroxenes, and their depletion is usually regarded as being indicative of fractional crystallization (Wager et al.1957; Curtis, 1964). Certainly the processes which depleted the magma at Palabora in Ni, Cr and Co did not deplete it in Cu, and by analogy with Skaergaard, (Wager et al., op.cit.) crystal settling may have been the cause. Indeed, Eriksson (1978) believes the pyroxenes of the Palabora complex are of cumulate origin. Chemical trends followed in the silicate magmas of alkali ultrabasic complexes may be critical for the retention of copper in the residual magmas. In the layered igneous complexes the concentration of sulphur in the melt controls the precipitation of sulphides. In the Skaergaard layered igneous complex, copper built up in the melt and precipitated out as sulphide fairly late in the development of the complex. The copper and sulphur in the magma were about 200ppm and 100ppm respectively when the sulphide precipitated (Wager et al.op.cit.). They suggested that the higher levels of nickel in the sulphides of the Bushveld and Insizwa were caused by the higher sulphur content of the magma, which caused the sulphides to precipitate early, before much of the Ni had been drawn off by settling pyroxenes. This process is fairly universal in silicate magmas and- Greenland and Lovering (1966) concluded that in tholeitic systems Ni and Co become greatly depleted in the residual magmas, whilst copper rises rapidly with differentiation to a maximum and is then removed. This is again presumably by separation of an immiscible sulphide phase as described by Skinner and Peck, 1969. Thus in alkali magmas, a high initial sulphur content could well cause the early formation of immiscible

31. sulphides which would deplete the magma of copper at an early stage. This would probably happen deep in the crust and the settled sulphides would not be accessible. In this way inhomogeneities in the mantle with respect to sulphur may also be important. Furthermore, it has been shown that other elements affect the sulphide capacity of a melt (Cs). Cs = Wt% sulphide dissolved in melt x 022 fS22 (Haughton et al. 1974). MacLean (1969) quotes Nockolds as deducing from bond energies that in melts S would re place 0 in Fe++O and concludes that the activity of Fe0 is very important in the solubility of sulphide. The Fe0 may be affected varying Si02 content of the liquid, by oxidizing Fe to Fe+++, or by precipitating Fe0 rich phases (for example wurstite, magnetite, fayalite). Sul- phide liquids can therefore be generated in two ways:- 1) enrichment of sulphide in melt by crystallization of other phases or 2) intersection of crystallizing silicate liquid with the immiscibility gap (i.e. decreasing f02) MacLean, 1969 (op.cit.) Shima and Naldrett (1975) point out that the sulphide capacity not only increases with temperature, but also with increasing FeO, Mg0 and Ca0 content. Extrapolation of this kind of information into the parents of carbonatites is difficult, not only because the nature of the parental magmas themselves is in question, but also because carbonated magmas are more oxidized. This, together with the presence of excess alkalis and volatiles,. will no doubt cause some departures from the theoretical melting silicate mantle which is assumed to produce normal basic magmas. However, these are the kind of controls that will affect the concentration of copper. Discussion of the later events in the hypothetical build up of copper and sulphur in carbonatites themselves is even more tenuous. Immiscibility is now a favoured mechanism for the separation of carbonate melts from silicate melts (Koster

32. van Groos and Wyllie, 1973; Rankin and Le Bas, 1974A; Le Bas, 1977; Wendlandt and Harrison, 1978; Hamilton et al. 1979). The partition of copper between the two melts presents another problem. There is no experimental work on this, but it seems reasonable to expect the copper to partition fairly strongly into the carbonatite for two reasons. Firstly because, as Helz and Wyllie (1979) have suggested, sulphur is probably more soluble in carbonatite than in silicate melts (copper may follow this). Secondly, since H20, CO2 and volatiles are partitioned into the carbonatite melt, the copper will probably follow, in view of its tendency to complex with the halides in aqueous rich conditions (Crerar and Barnes, 1976). The gradual fractionation of copper into the late stages will depend upon the precipitation of sulphides and the development of (and partition of copper into) volatile 'vapour' phases producing metasomatism. Helz and Wyllie (1979) have shown that sulphur in carbonatite magmas represented by the system CaCO3 - Ca(OH)2 - CaS at 1Kb forms a simple eutectic at 652°C with 46.1% CaCO3, 51.9% Ca(OH)2 and 2% CaS. (see Fig.3). They deduced that two crystallization sequences were possible for liquids precipitating calcite, depending on whether the liquid is on the low CaS side or the high CaS side of the line connecting CaCO3 to the eutectic liquid (see Fig.3.B). Low CaS liquids precipitate no sulphides until the eutectic temperature is reached, leading to sulphide enrichment. The higher CaS liquids precipitate some sulphides above the eutectic temperature, but the sulphide content of the melt is not greatly depleted as the eutectic temperature is approached. It is further explained that theoretically, a strong similarity exists in the processes controlling sulphur solubility in carbonate and in silicate melts. Indeed, carbonatites may be better sulphide solvents than silicate melts. They do, however, point out that varying the fCO2 would change fS2 dramatically (and hence the solubility of the sulphide) without changing the composition of the

33. THE SYSTEM CaCO3 -Ca (OH)., -CaS (from Helz &Wyllie 1979) Pressure I Kilobar

C. 4.8S CaS D 2.6% CaS a. als L

Caco .GS•L 'Os E ea10I9a • CaCO, • GS Catohtt •C.CO, • CaS Galle 00 • COON WO% IS • w CoCOs *GS • GS *CaS • CaS G OO u—co. • I--ions ' WEIGHT PER CENT-4. a. Experunental results for the micas CaCO,-CatOHyCaS at I kbar. A. Binary system CaIOHI -CaS. a C add D. Phase kids intersected by three Imm parallel to CatOHI,-CaCO, .

Pressure : 1 Kbar CoS CaS CoS }

10 + + + 4- ~yĪ + + 4- + 4- to 9.1% CaS

CaS

4.8% US S 145• E - 2.6% CaS 652•E Ca CO3

SOS' f 1 \ 1 510• 40 to Ca(OH)2 IWEI CaCO3 Weight per cent I, b. Low-temperature portion of the liquides surface for the system CaCO1-CalOH1=-CaS at I kbar. based on results from Fig. I. and published results for Ca(O112-CaCOS IWYLLIE and Turns. 1960; WYLLIE and RAYNOR. 19651. The points a. b and c are located in Figs. ID. C and B.

uoUto 50(005 -0 / /

`sCa / It -I / .,, % PIMA TIT/ / • % waN/TITt 01/44:0 -4 / t N // I 1 Fig. 3 ^ ō -8 / ; t` N /• O / \c°' `S E 3 > t, s 1 -8 .• %

0 CaCO3 % -10 I -22 -20 -18 -10 -14 -12 -10

lag 102

C. Calculated phase relationships at 650°C and I kbar. The point labelled E5 indicates the inferred fs,- fo, for the ternary eutectic melt in the experimental runs. Heavy dashed lines show how the calcite field expands as fps, it raised. 34 melt (see Fig.3.C.). Helz and Wyllie (op.cit.) conclude that natural carbonatite magmas at the same fS2, f02 and fCO2 as their experimental system would probably have a higher sulphide solubility because (by analogy with silicate melts) they would contain additional components forming sulphide complexes in the melt. Fluid inclusion evidence suggests that fCO2 in carbonatites may be quite variable (see Chapter 7, this work). Thus, although the experimental work of Helz and Wyllie (op.cit) shows the potential for sulphide solubility and late stage enrichment, there are too many unknown factors in nature for this preliminary investigation to be of any practical value. Nevertheless, the observation that carbonatite melts are similar in principal to silicate melts does enable comparisons to be made. For example; the precipitation of magnetite in the Bushveld intrusion sufficiently lowered the oxygen fugasity to cause the precipitation of sulphides (Buchanan, 1978, pers.comm.). It has been noticed in this work that magnetite commonly precedes sulphides in the paragenetic sequence in carbonatites. This would certainly reduce the f02 of the system and possibly directly cause the precipitation of the sulphides. The final deposition of sulphides may, of course, be from a carbonatite magma or aqueous hydrothermal fluids. Helz and Wyllie (op.cit.) imply that sulphides can be precipitated from classical carbonatite magmas by decreasing temperature, whilst hydrothermal transport and deposition is also in large part temperature controlled. The influence of PTVX conditions on the final deposition of sulphides is discussed in the following section and in later chapters. 1.3. CONTROLS AND PTVX OF ORE FORMING CARBONATITE FLUIDS The section reviews some of the methods and approaches used in studying carbonatites, which have particular relevance to ore formation. Little of the work was geared to ore genesis,.but many observations are directly relevant. This section also serves as a background to some of the

35. techniques which have been used in this work. 1.3.1. Fluid Inclusions Numerous fluid inclusion studies have been conducted on carbonatite complexes. Evidence of carbonate melts (Romanchev, 1972), highly mobile alkali carbonate brines (Rankin, 1975), CO2 rich aqueous fluids (von Eckermann, 1948A and B; Roedder, 1973), low density vapour phases (Valyashko and Kogarko, 1965) and silicate/carbonate immiscible melts (Rankin and Le Bas, 1974A) have all been found. This testifies to the diversity and range of formative processes involved in carbonatite formation, both within individual complexes and from one complex to another. Inclu- sions thus provide support for both magmatic and hydrothermal/metasomatic theories of carbonatite origin, as well as their development by immiscible CO2 rich fluids and melts from the earlier silicate rocks which form most complexes. They also provide information on the range of temperature of formation of carbonatites (see Table 1 and Table 23). Although magmatic carbonatite melts may be mineralizers, the potential of highly saline brines to transport and deposit metal is well known to economic geologists. The observations by Rankin and Le Bas (1974B) of nahcolite in aqueous inclusions from carbonatites confirmed the importance of alkalis in carbonatite fluids (as suggested by von Eckermann, 1948) and related these to the.alkali carbonate lavas of Oldoinyo Lengai (Dawson, 1962). The presence of pyrrhotite in such aqueous inclusions (Rankin, 1975, 1977) further suggested that these brines were capable of transporting significant amounts of sulphur and iron. Nesbitt and Kelly (1977), using scanning electron microscopy (S.E.M.) for studying daughter minerals in inclusions in monticellite, were able to deduce the composition of an early carbonatite melt at the Magnet Cove complex (Arkansas). It is pertinent to the present work that traces of Cu, Fe, and S were detected as impurities in some of the daughter minerals. The composition of the melt 36. deduced is shown in Table 4. No alkali daughters were detected and alkalis are conspicuously absent from the melt composition. Even if the aqueous portion which represented 11% of their inclusions were saturated with NaC1, this would only give 1.50% Na20 in the melt. Apatites at Magnet Cove (Nesbitt and Kelly, op.cit.), by contrast, contained CO2 and aqueous rich inclusions similar to other localities where such inclusions are usually alkali rich (Girault, 1966; Rankin, 1975; Althaus and Walther, 1977, and others). TABLE 4: Comparison of Inclusion and Carbonatite Analysis 1 2 3 4 Melt Average Oldoinyo Alkali Brine Inclusions Carbonatite Lengai Inclusions % % % % SiO2 15.7 10.3 - 1 CO2 16.7 28.5 32.4 1 Fe0 + Fe203 4.4 7.1 0.32 1-2 MgO 1.0 5.8 .4 - Ca0 49.7 36.1 12.8 low 1-2 ? P205 1.1 2.1 1.1 - ? Na20 - .4 29.7 10 K20 - 1.4 6.6 5 Cl - - 8.3 4 H2O 11.4 1.4 2.6 75 Others - 6.9 6.7 - 1 = Composition of melt in monticellite inclusions, Magnet Cove - Nesbitt and Kelly, 1977. 2 = Average composition of carbonatites compiled by Heinrich, 1966. 3 = Composition of lavas from Oldoinyo Lengai, Dawson,1962. 4 = Rough estimate of alkali brine inclusions from Sokli (this work, Chapter 6).

37. The inclusions in apatite were not investigated by Nesbitt and Kelly because of severe necking down. Secondary aqueous inclusions in calcite, however, provided them with an impressive array of daughter minerals, including alkali chlorides and sulphates, as well as carbonates, REE minerals and Fe-Cu sulphates. The range of inclusion types and compositions at Magnet Cove is typical of carbonatites and reflects the complexity of processes at work. Interpretation of these different fluid phases is extremely difficult. Fractiona- tion by crystallization (Heinrich, 1966) and immiscibility have both been invoked to explain the transition from carbonated silicate melts to carbonatite melts (with few alkalis present) and further to aqueous alkali rich fluids and low density vapour phases. Immiscibility between silicate and carbonate melts has been seen in inclusions (Romanchev, 1972; Rankin and Le Bas, 1974) and is also supported by experimental work (Koster van Groos and Wyllie, 1966, 1968, 1973 and Hamilton et al.1979) and petrological investigation (Le Bas, 1977; Donaldson and Dawson, 1978). The occurrence of two different types of fluid inclusion in the same crystal is not uncommon and this is interpreted as evidence of two immiscible phases co-existing in the same growth medium (Roedder and Coombs, 1967). Nesbitt and Kelly (1977) found similar inclusions in apatites from Magnet Cove. Inclusions packed with daughters (carbonatite melts ?) are commonly seen co-existing with aqueous rich brine inclusions in carbonatite apatites (Valyashko and Kogarko, 1965; Rankin, 1973; Khitarov et al. 1978). Haapala (1978) found this at Sokli and suggested that they represented a carbonatite melt and co-existing aqueous fluid. The experimental work of Koster van Groos and Wyllie (1973) not only found immiscibility between carbonate and silicate melts, but also found a third low density aqueous phase. This aqueous phase was enriched in Na20 and Si02.

38. Fluid inclusions can thus provide information on PTVX of carbonatites and ore forming media. It is, however, essential to relate any ore with the correct set of inclusions; especially when many types of inclusion are found in the same rock. For this reason an integrated approach using petrography, mineralogy, geochemistry and field relationships is required to make the most effective use of fluid inclusions. 1.3.2. Experimental Work A considerable amount of work has been done to investigate the petrogenesis of carbonatites, especially classical carbonate melts; from the early work of Miller (1952) on lowering the melting point of calcite to the more complex work of immiscibility from silicate magmas discussed above (see Wyllie, 1966, 1978; Koster van Groos and Wyllie, 1966, 1968, 1973; Koster van Groos, 1975 and others). Although. this has provided a good understanding of the possibilities in carbonatite systems, little of the work is directly relevant to the genesis of copper ore bodies. The Soviet school with its almost dogmatic view on the extreme metasomatic origin of much carbonatite material, has produced experimental work on aqueous alkali carbonate brines (Dernov-Pegarov and Malinin, 1976; Aleksandrov et al. 1971, 1972; Samoylov, 1974; Kotov et al. 1978). Work by Dernov-Pegarov and Malinin (op.cit) on the solubility of calcite in alkali carbonate solutions shows that, contrary to the immiscibility data, a gradual transition from hydrothermal solutions to melts may also be possible. If such fluids were indeed responsible for much carbonatite formation, they may also be responsible for mineralization.. The experimental work of Aleksandrov et al.(l971 and 1972) based upon these concepts, investigates the ability of alkali carbonates and chlorides to transport and deposit niobium and tantalum, which form ore deposits in some carbonatites. They conclude that there may be some difference in the alkalis; potassium tending to mobilize Nb and Ta, whilst Na (and Ca) tend to form more insoluble salts. 39. Work on the distribution of REE between carbonatite melts, silicate melts and CO2 vapour phases (Wendlandt and Harrison, 1978) showed the latter vapour phase to be strongly enriched in rare earths. This may be relevant to the formation of REE deposits (for example, Mountain Pass and Kangankunde). Unfortunately, there is no work on the solubility of sulphur and copper in such alkali carbonate brines. Never- theless, much of the work on the solubility of Cu and Fe in other alkali chloride systems (such as porphyry coppers) is probably relevant. Work by Crerar and Barnes (1976) showed that ore forming quantities of copper and iron could be carried in alkali chloride brines by forming CuCl+ and FeC1+. It is conceivable that similar chloride transport may also be important in less aqueous carbonatite melts. 1.3.3. Geochemistry Numerous works on individual carbonatite complexes have had a predominantly geochemical approach to the problem of petrogenesis and evolution. One of the most important works is that by Erickson and Blade (1963) who analysed most rocks and minerals of the Magnet Cove complex for a large number of elements, including copper. They found very small amounts of copper in all minerals at different stages of crystallization, but suggested that most of it was captured during the early stages of crystallization, particularly by pyrite. At Bukusu, however, Baldock (1967), analysing whole rocks, showed a progressive increase in copper (and zinc) to the later stages. Barber (1974), working on carbonatites from Kenya, does not mention copper, but does note that No is concentrated in the late stages. This type of approach also provides indirect information on the processes active in the complexes. The anomalously low levels (for urtrabasic rocks) of Ni, Co and Cr are reported in the early rocks of Bukusu by Baldock (op. cit.) who also reports similar low values for Magnet Cove

40. and Palabora. The concentration of incompatible elements Nb, Zr, Th,- Sr, Ba and particularly rare earth elements in the carbonatites is universally reported (Heinrich, 1966). The rare earth elements in particular are very characteristic in their behaviour, becoming both increasingly concentrated and developing higher Re : Ce/RE : Y ratios as the carbonatite stages develop (see Chapter 3, this work). The geochemistry of stable isotopes is also useful in understanding carbonatites. Their mantle origin is confirmed by 87Sr/86Sr (Heinrich, 1966), carbon and oxygen, isotopes (Deines and Gold, 1973 and Taylor et al. 1967), the Pb-U-Th isotope system (Lancelot and Allēgre, 1974) and sulphur isotopes (see 1.2.2. above). The order of formation may also be shown (carbon isotopes - Kukharenko and Dontsova, 1964; carbon and oxygen - Van Wambeke, 1964 and Suwa et al. 1975). Suwa et al.(op.cit.) showed the influence of atmos- pheric oxygen in some complexes. This oxygen was introduced from circulating fluids. Significantly, this was not the case at Palabora (see Fig.4.a.). Dontsova et al. (1978), questioning the designation 'carbonatite' given to some carbonate rocks of igneous association, showed that those likely to contain rare metal ore typical of 'true' carbonatites had characteristic 6180 values (see Fig.4.b.). Only the sulphur isotopes will be dealt with in detail, because of their direct relevance. 1.3.4. Sulphur Isotopes, T and f02 Von Gehlen (1967) and Hoefs et al. (1968) showed that sulphides at Palabora exhibited little variation in isotopic composition, the mean 634S being close (+1-2%.) to the meteoritic mean 6345 (0%.). But Grinenko et al. (1970) noted that individual Russian carbonatite complexes possess their own distinct average isotopic composition and that during the closing stages of magmatism, the sulphides became enriched in 32S. Mitchell and Krouse (1971 and 1975) also found this and were able to classify carbonatites (1975) in terms of

41. EXAMPLES OF OXYGEN ISOTOPES IN CARBONATITES

Palabora Older Sovite 0 Younger Sovites

Sp its koo • Calcites in dolomite sov,te 0 Ankentes in beforsite and apatite-rich beforsite l x Late stoge calcite and dolomite

Premier Mile a 'Carbonaliti dyke 0 Pale Piebald- Black K mberlite -2 0 x X • •

Oka Box ,Providencia(Rye. 1966) 0

-8 i-

L I I I I J 4 6 8 10 12 14 16 18 20 Si°o(%o)- A . The oxygen and carton isotopic ratios of carbonates in Precambrian Palaboru uarhon.itite, Spctslup carbonatitc and Premier Mine carbunatttc, South :Africa. (from Suwa etal.1975)

Intrusion l j 6 9 11 15 16 11 Z4

Odikhincha • • I • eo ma Kovdor I• I• • ® t4 I • Sokli • I • B. 6140 for: Cargill • East Sayan • 1) Rare-metal carbonatites and SIP ®0l carbonatite-like rocks, 2) barren • carbonatite-like rocks, 3) ankerite- Oka J• dolomite carbonatites, 4) sur- Novaya rounding marbles, 5) altered . !i4 • Poltava • . • marbles, calctphyres, and skarns. Vishev Hills ••I I♦ b 0 (after Dontsovaetal.1978) Siilinjicvl ~ i 41 Southeastern t O x0 0 0 m 0 ~7 Tuva p OC Ō .0 j 6 g 11 1.5 i0 11 6110. e/00 rel. to SMOW • 1 0I ®J 04 s 5

Fig 4

,2 T, f02 and pH during the formation of sulphur bearing assemblages. They suspected that isotopic fractionation in carbonatites is a function of T, f02 and pH, as is the case in hydrothermal systems (Ohmoto, 1972). However, lacking the necessary thermochemical data for S reactions in carbonatites, they extrapolated aqueous thermodynamic data, developing a qualitative guide to the expected S species distribution in carbonatites as a function of f02, pH and T. According to Mitchell and Krouse the falling temperatures in carbonatite magmas result in an increase of relative f02 and or pH which produces increased proportions of oxidised S species. Because of this, isotopic fractionation occurs, causing a redistribution of isotopes between reduced and oxidised S forms: i.e. sulphides crystallizing from carbonatite fluids at lower temperature are enriched in 32S relative to the isotope composition of the total S in the fluids, 634Se . With decreasing temperature the negative deviation of 634S from 634S increases. Thus only in carbonatites of the highest temperatures, in which the sulphur species in the magma were reduced, do the sulphides reflect the isotope distribution of the source. Thus the values mentioned above for Palabora, where there are no oxidised species of sulphur are the same as the accepted mantle 634S value of +1% (Schneider, 1970). In the light of this and the carbon and oxygen isotope data which Deines and Gold (1973) and Taylor et al. (1967) have shown to be compatible with a mantle origin, it seems likely that most sulphur in these systems is also mantle derived. The deviation from this mantle origin in the lower temperature carbonatites is adequately explained by Mitchell and Krouse, but an extraneous meteoric source cannot be ruled out. In the light of this, Makela and Vartiainen (1978) used sulphur isotopes to test their reconstruction of events at the Sokli carbonatite in Finland, five stages of which all have sulphides. Their spread of data for each stage is considerable, as with other investigations, and it seems

43. possible that there is some masking effect due to successive deposition of sulphide bearing fluids and the considerable metasomatism that has affected this complex. They do however successfully show a separation of at least two, and possibly three, events with temperatures in the region 0 of 300-600 C (using Mitchell and Krouse's work as a geothermometer). Concerning Mitchell and Krouse's concept, it is significant that the fluid inclusions associated with the sulphide assemblage at Sokli contain daughters of sulphides, but no oxidised forms of sulphur were noted (see Chapter 7). There may, however, be some fundamental flaws in the basis of Mitchell and Krouse's argument. The presence of thucolite at Palabora (de Vaal pers. comm.1976) might be expected from Mitchell and Krouse's interpretation; i.e. the f02 must be low in this high temperature carbonatite, but it is not necessarily true that the f02 always rises as temperature decreases. Hydrocarbons present in low temperature fluid inclusions from the Kaiserstuhl carbonatite (Althaus and Walther, 1977) and also at Sokli (present study - see Chapter 7) where they are associated with sulphides and hydrocarbons in the rock, suggest that a straightforward increase in oxidized forms may not always be the case. Indeed, in agpaitic rocks, Kogarko (1975) points out that the volatility of methane increases markedly with fall in temperature, while volati- lities of oxidised forms of carbon and sulphur decrease appreciably. Such effects would certainly have an upsetting effect on the isotopic distribution of sulphur relative to temperature as proposed by Mitchell and Krouse. They emphasized that their interpolation between the reducing conditions at Palabora and the obvious higher f02 where barite is deposited in low temperature carbonatites, was purely to generate a qualitative understanding of the chemistry of S isotope fractionation in carbonatite processes. The use of this isotope fractionation as a geothermometer does not seem justified, though its ability to reflect

44. differences in the environment of formation of sulphides at different stages may be useful. Temperature will certainly play a part in the deposition of any ore in carbonatites. Temperature conditions can be evaluated more effectively from fluid inclusions, mineral equilibria and experimental systems. Discussion of this will be developed in the present work. 1.3.5. Structural Control Structural analysis of carbonatites was introduced early on by von Eckermann (1948A and 1948B) who was able to show different depths of foci for various events by projec- ting the inclination of the cone sheet dykes to a central axis. Numerous other authors have also done this (summarized in Heinrich, 1966) and Carson (1959) was able to calculate depths of foci and a pressure of 60,000 pounds/ square inch at the Tundulu complex in Nyasaland. The presence of structures indicative of violent volcanic events such as agglomerates, cone sheets, etc., bears witness to the pressures commonly present in carbonatite formation. The effects of pressures and violent reaction in the more eroded complexes are usually less well defined, but any faults or fractured areas will control late stage aqueous rich melts and hydrothermal fluids and hence the deposition of ore. At Palabora the last copper rich carbonatite event is focused on a criss-cross fracture pattern (see Chapter 3). In complexes mined for niobium it is common to see the ore shoots cutting through earlier lithological boundaries, following brecciated zones, fractures and faults (e.g. Lake Nipissing, Ontario - Rowe, 1958; Oka, Quebec - Gold et al. 1967; Fen - Bjorlykke and Svinndal, 1960, and some complexes in Northern Siberia - Frolov, 1975). Frolov produced a monograph (1975) on carbonatite structure and mineralization in which he discusses the structural control of ore deposition in terms of fractures and faults. He presents details of stress and strain analysis, mineral orientation and banding in numerous Soviet

45. complexes. He also elucidates his previously proposed (1971, 1974) theories of vertical structure and zonation concepts, with special attention to ore deposition (see Fig.2.). 1.4. SUMMARY AND CONCLUSIONS Copper is probably a little more common in carbonatites than Gold's (1963) mean value of 2.5ppm implies. When found, it is usually in the last stages of carbonatite activity, where it occurs as sulphides. Carbonatites with unusual copper enrichment are usually deeply eroded, but polymetallic mineralization including copper may also be found in the less deeply eroded complexes. The characteristic copper bearing sulphide assemblages may be defined as follows:- 1 predominantly copper bearing assemblages 2 the pyrrhotite dominant assemblages 3 polymetallic sulphide assemblages these may be in part depth and temperature related. Copper and sulphur in carbonatites are probably of mantle origin and copper rich carbonatite complexes may originate from areas in the mantle anomalously enriched in copper, or some other elements which control the transport and concentration of copper. A theoretical investigation of the behaviour of copper in carbonatite complexes shows that copper could become concentrated in late fractions in a manner similar to other magmatic systems. The initial magma need not be unusually enriched in copper. Fluid inclusion and experimental studies provide an insight into the potential range of PTVX conditions prevai- ling in carbonatites. They show silicate melts, carbonate melts, carbonate aqueous phases and low density CO2 rich fluids, all of which may play a part in transporting and depositing economic mineralization. Geochemical studies of carbonatites show how copper and incompatible elements may become concentrated in the residual fractions of carbonatites. Fluid inclusions, isotopes, mineral equilibria and experimental systems

46. provide estimations of the temperature of these systems. Finally, the structure of carbonatites may be important in controlling mineralizing fluids.

47. CHAPTER 2: THE CARBONATITE COPPER DEPOSIT AT PALABORA, SOUTH AFRICA

2.1. INTRODUCTION AND BACKGROUND GEOLOGY 2.1.1. Introduction The Palabora carbonatite complex in the north eastern Transvaal (see Fig.5) is host to one of the largest copper deposits in the world. Originally estimated at 315 million tons of ore at 0.6970 Cu, (down to a depth of 3000 feet; no bottom having yet been found to the deposit) it is mined by open pit methods (see Plate 2A). The mining operation and infrastructure (run by the Palabora Mining Company, P.M.C., a joint venture of Rio Tinto Zinc and Newmont Mining) are the pride of the South African mining industry (Cartwright 1972). In 1977 it produced 120,000 tons of copper. The scale of the mineralization in a rock type thought to be impoverished in copper is an enigma which provided the stimulus for the present investigation. The geology of the deposit is well described (Hanekom et al.1965; P.M.C. Staff, 1976), but little work has been done on ore genesis. This work is an attempt to remedy this situation. The previous chapter has reviewed the theoretical considera- tions of copper in carbonatites, while this and the following three chapters develop the practical side of the argument. 2.1.2. The General Geology The details of geology, together with various early mining operations and the discovery of the copper deposit, have been extensively covered by previous authors (Hall, 1912; Du Toit, 1931; Shand, 1931; Gevers, 1948; Russell et al.1954; Bouwer, 1957; Lombard et al.1964; Hanekom et al. 1965; Heinrich, 1970; P.M.C. Staff, 1976). The complex is essentially a massive kidney shaped plug of pyroxenites intruded into Archaean gneisses (see Fig.5). A corona of variable width composed of feldspathic pyroxenite was formed by interaction with the gneisses. A later alkaline phase of activity introduced scores of plug like bodies of syenite (Frick, 1975) at various centres on the 48.

PALABORA IGNEOUS COMPLEX LOCALITY

• _ / / N

70- ■ // / / / / 1`` i 1 / /_, ,/ .~

.imm;:-:

~hw ,.r rate o 1 F / ., '//V. / Ī,'n7 / t \r

SOUTH _, ✓ AFRICA \ / i / / / /rr ; '1 / i r / / 7

C,Pt rvµ i / ,/ / (,) \ 1 \ / / /

'/ ,~/ / / / J `

r' DOLERITE DYKE

TRANSGRESSIVE CARBONATITE / `_f `- / / ' I Ci ~/ / Y 7 BANDED CARBONATITE .A ;1",'/ / / _ PHOSCORITE j / / // j / / / / /; ,A , /- A ~• SERPENTINE PEGMATOID / / 'r ii/ // j 771 ,1, 1 PYROXENE PEGMATOID // .,~~/ / //7/ ~ ,,10 / I C. 7 ; . . MICACEOUS PYROXENITE 7 /, . '? / MICA ROCK ' FELDSPATHIC PYROXENITE FENITE & SYENITE Fig.5 I 2kms ~ GRANITE GNEISS After Ilanekorn et al., 1965 PLATE 2

A. An economic deposit of copper in carbonatites; the open pit at Loolekop, Palabora. The hill in the distance is one of the many syenite plugs surrounding the complex.

B. Discontinuous sheets of copper sulphides in the transgressive carbonatite Palabora. The subject is 2 metres across. 50. periphery of the ultramafic pipe and away from it. A period of metasomatism is then thought to have developed ultrabasic pegmatoids at three localities in the pyroxenite (Hanekom et al. 1965). Of these three centres, one to the north, one to the south and one in the centre, only the latter was exploited by the carbonatite facies rocks. The carbonatite centre is called Loolekop and the carbonatites there are host to the copper ore. The complex has been dated at 2060 m.years (Holmes and Cahen, 1957). It is cut by a swarm of north-east striking, parallel, vertical , dolerite dykes dated from palaeomagnetic studies at 1880 ± 25 m.years (J.C. Briden reported in P.M.C., 1976). 2.1.3. The Loolekop Pipe The Loolekop pipe is a composite vertical structure with an elliptical interbanded configuration. The carbonatite and forsterite rocks were emplaced into what is locally a mica rich pyroxenite in the following order:- 1) phoscorite (forsterite-apatite-magnetite rock) 2)banded carbonatite (apatite-magnetite-dolomitic sovite) 3)transgressive carbonatite (apatite-magnetite- dolomitic sovite) The relationships are illustrated in Figs.5, 6 and 7. The interleaved relationships between the phoscorite, host rocks and banded carbonatite is further reflected in the vertical banding in the phoscorite and banded carbonatite due to the alignment of magnetite concentrations. Other minerals (olivine, chondrodite, apatite and phlogopite) are also aligned in bands. The contacts between the .phoscorite and the host micaceous pyroxenite and the banded carbonatite are sharp in some places, but gradational in others. The transgressive carbonatite was introduced into a criss-cross fracture structure in the centre. Divergent dykes of this cut through all the earlier rock types. It has been suggested that reactivation of these shear directions fractured the transgressive carbonatite, allowing mineralizing fluids to pervade the structure (Hanekom et al. 1965). A summary of Hanekom's view is compared with that elucidated by this work in Fig. 8. 51. THE PALABORA CARBONATITES

/ +'

+ Ca. .••

Fig.6 '3

3 \ 4. I+ +1 DOLE RITE I I I , I I TRANSGRESSIVE CARBONATITE • I 4, 63 ( 1 BANDED CARBONATITE , +

I PHOSCORITE * vc, / •+ • I I MICACEOUS PYROXENITE . ••'T'.::-:' : ; I I PYROXENE PEGMATOID .29 $;,"..// „4. I 1 MICA ROCK • .

I I FELDSPATHIC PYROXENITE

0 250 m. 1•:.• :.1 FENITE -C

23 SAMPLE No's.(Prefixed by -0 35 .00 ow. Modified after PM.C. pers.com1976 P in text.) .26 23. and PM.C. Staff 1976 -x37 .24 .27 SECTION THROUGH LOOLEKOP OREBODY (after P.M.C. Staff 1976 )

ION ♦ 111 31. III

LECEND

} Idmll EDNE Naomi!. Nrlwllle lukl Wheadl

Inlubl1 r-2-- I

FIGURE 7

NI N 1 IN --- 116 IN 161 2.1.4. The Mineralization at Loolekop The Loolekop pipe is host to a variety of valuable commodities. The P.M.C. pit produces baddeleyite (Zr02), uranium bearing thorianite, low Ti magnetite and apatite, as well as the copper sulphides. The presence of these other minerals makes the low grade ore more profitable to mine. The baddeleyite and apatite are most abundant in the phoscorite and banded carbonatite, where the magnetite is too high in Ti to be saleable. The central transgressive carbonatite contains low Ti magnetite, the bulk of the copper mineralization and also the thorianite. The details of this and the division of the reserves for separate mining and processing are shown in Fig.9 and by P.M.C. Staff (1976). Only the copper sulphides will be considered in more detail here. The sulphide mineralization is thought to have been formed in two stages, according to Hanekom et al.1965. An early phase associated with the banded carbonatites and phoscorites (pre-transgressive carbonatite) and a later, richer phase associated with the central transgressive carbonatite. Bornite is the dominant sulphide in the earlier ore, whilst chalcopyrite is dominant in the central area. The former is contained in the earlier rocks, which may be barren of sulphides in places. When sulphides are present they may be aligned together with magnetite, apatite and silicates. There is no obvious fracture control, as in the central area. In the central area the bulk of the sulphides occur in near vertical discontinuous veinlets, usually less than lcm wide in the transgressive carbonatite (see Plate 2.B). Commonly these are in zones up to 10 metres wide, but with very little strike continuity. Between such zones small sulphide blebs tend to lie haphazardly, though they are usually associated with fine fractures. Hanekom et al. (1965) used these facts as evidence for two phases of mineralization; one preceding the transgressive carbonatite and one following.

54.

SUMMARIES OF EVENTS AT PALABORA

HANEKOM' S SOMALI 1965 PROPOSED EVENTS

Emplacement of pyroenite and As Hanekom, with the addition that numumhation of gneiss to form textures suggest a cuzzdate origin feldspathic pyyoaenite. for much of the pyroxenite.

Emplacement of syenite plugs follows. (Erikason 1978)

•

Three fracture systems develop, is Raaekom. alteration and recrystallisation form pegmatite sons and dunites.

Hydrothermal introduction of phlogo- As Hanekom, apatite / phlogopite is

pits, apatite, nicrooline rocks at probably a precursor to the following

three centres and all over complex in carbonatite stage.

fractures. This continues after

formation of phoscorites. Fenitization.

Metasomatic alteration of invite plug at Olivine cumulate material with inter-

Loolekop to give phoecorite. Addition of stitial carbonate fills central plug

Fe, Ti, Zr and P205. Fluids change to at Loolekop. Metasomatic addition of produce alteration of phoecorite to re, Ti, Zr and P205. Handed carbonatite banded carbonatite. with some copper intrudes and replaces

central part of phoacoritee.

Slight fracturing of banded carbonatite filled by first stage of copper nin- eralization.

Intense fracturing followed by emplace- Intense fracturing followed by intrusion meat of transgressive carbonatite. of carbonatite, now futher enriched with

copper. Solidified carbonatite is auto-

netasomatical7y mineralized with copper

rich residual fluids.

Rejuvenation of shear directions allows Shearing continues with concomitant

2nd phase of mineralisation. brecciation, plastic flow and recrystal-

Overall steaming and valeriite de- ization; the centre is futher mineralized

position. by escaping copper charged volatiles.

As this process continues and cools

valleriite is deposited. The whole complex is cut by later dolerite dykes. Fig. 8

55. DISTRIBUTION OF Cu, Fe, Ti,& P on 122m LEVEL , LOOLEKOP OREBODY

• Heinrich (1970) reports that "more recent work, however, has indicated that there was but a single phase of mineralization and that the deposit is mineralogically zoned, with chalcopyrite predominating over bornite in the central part of the deposit 'core ore', chiefly in the younger carbonatite". There is, however, no indication of the work done to prove this, and personal communication with Heinrich (1976) reveals that this idea was presented mainly as the result of a visit to Palabora and on specimens collected and examined by him. He added that his conclur sions supported conclusions reached by the mine staff. The mine staff, however, in their later largely unoriginal paper (P.M.C. Staff, 1976) seem to follow Hanekom et al. Both Hanekom et al. (op.cit.) and Heinrich (op.cit.) favour a hydrothermal origin for the mineralization, whilst Bouwer (1957), who did some early work on the deposit, commented, "the mineralogical association and observed textural relations are not conclusive enough to establish whether the mineralization is magmatic, pyro-metasomatic or hydrothermal in origin". 2.1.5. The Aim of the Present Work The present work is an attempt to resolve some of the problems of the nature of the mineralization at Palabora and poses such questions as:- 1) Is the mineralization an intimate part of the carbonatitic process? 2) If so, was it introduced hydrothermally, or in a carbonatite magma? 3) What were the PTVX conditions of the parental fluid? 4) What is the relationship between this fluid and the rest of the complex? To answer these questions it has been necessary to become familiar with the previous work and also the deposit itself. The visit to Palabora in 1976 was for one week only, during which time samples were collected (see Fig.5) and the mineralization and rock types at Loolekop were studied. Unfortunately, requests to Palabora Mining Company to be

57. allowed to work for longer periods in the open pit were declined. Nevertheless, a large amount of descriptive work on the deposit already exists. It was felt that the above questions should be tackled using a new approach. The most striking thing about seeing the ore after the above mentioned descriptions is that the veinlets of sulphide are not only discontinuous, but they are not associated with any alteration or obvious deposition of carbonate, quartz or other minerals (see Plate 2B). Any similarity with other hydrothermal systems is thus limited. In places the carbonate is obviously recrystallized and extensive later shearing is filled with valleriite (see Plate 3 E). A special attempt was made to sample veinlets and dykes of the transgressive carbonatite where they cut earlier rocks. Large polished sections of dykelets and adjacent rocks allow the distribution of sulphides to be investigated. There is no obvious alteration next to these transgressive carbonatite dykes. A detailed textural study of the ore samples has been undertaken, especially concerning their relationship to the host rocks. This, combined with inclusion studies, probe work and geochemistry, gives a new insight to the deposit. In this chapter the microscopy and geochemistry of the ore is discussed. The inclusions are dealt with in the following three chapters. 2.2. ORE MICROSCOPY 2.2.1. Previous Work The opaque minerals have been consistently studied since the economic potential of the carbonatites was real- ized in 1954. Russell et al. (1954) summarized work dene by the South African government investigating the complex for radioactive material. Bouwer was also involved in this work and continued to produce a Ph.D. on the carbonatite at Palabora (1957). He defines the ore minerals observed in early boreholes, but the accent of the work is on the thorianite. Forster (1958) produced a slightly longer list of

58.

minerals and defined a paragenetic sequence (see Table 6). Resumes of this early work are given by Lombard et al. (1964) with some additions by Hanekom et al. (1965). P.M.C. employ a full-time mineralogist who is engaged in the mineralogical problems of grinding and flotation. The only published information on this however is a small section in P.M.C. Staff (1976) describing the problem of valleriite coating of other minerals, which interferes with sulphide flotation. Individual minerals at Palabora have attracted some attention. Hiemstra (1955) reported the occurrence, and properties of baddeleyite and Springer (1968) probed mackinawite and valleriite. TABLE 6: PARAGENETIC SEQUENCE OF THE ORE MINERALS AT PALABORA (after Forster, 1958)

Order of appearance Type of mineralization Temperature

3 Secondary "descendant" ore miner- Low alization (bravoite, chalcocite, covellite, millerite (?), linnaeite (?), bornite(?), pyrite(?), valleriite(?), hematite, iron hydroxides and magnetite).

2 Primary "ascendant" sulphides. ± 400°C. (Chalcopyrite, pentlandite, pentlandite-like mineral, at least two precious metals, zincblende, bornite, galena and magnetite).

Cataclasis in situ

1 "Ascendant" oxide ore. ("Uranoan Wel4 above thorianite", baddeleyite, unknown 400 C. lath-like oxide mineral, magnetite with exsolution products of ilmenite and spinel).

59. 2.2.2. The Present Work The present work brings together previous work and also provides new information on the ore minerals and their relationships. Particular attention has been paid to microscopic clues, textures and relationships between sulphides and gangue material which might provide answers to the questions posed in the introduction (2.1.5). This approach has not been used before. A suite of 75 polished specimens was used. Thirty five of these were polished thin sections, enabling more detailed observation of gangue/ore relationships. Numerous larger samples were cut and lapped for investigation under bino- cular microscopes. A list of all the opaque minerals observed in the study is given in Table 7. Dual mode reflected light /transmitted light microscopes were used for the work. Many of the minerals have been probed for qualitative and quantitative analyses (the equipment used is described in Appendices 2 and 3).

TABLE 7: ORE MINERAL ASSEMBLAGE AT PALABORA

OXIDES SULPHIDES NATIVE METALS Magnetite VC Chalcopyrite VC Copper VR Ilmenite VC Bornite VC Silver VR Baddeleyite VC Cubanite C Gold VR Thorianite VC Chalcocite C PGM VR Haematite R Pyrrhotite M 'Rhodium silver 'Unidentified Pentlandite M alloy VR Zr-Ti oxide VR Millerite M Thucolite VR Bravoite R Linnaeite R Violarite VR Covellite M +Tetrahedrite VR Sphalerite C Galena C 'Parkerite VR VC = very common 'Wittichenite VR C = common +Pyrite _ M M = moderately Marcasite VR common Valleriite VC R = rare Mackinawite M • VR = very rare

x = unreported minerals discovered in this + study = not observed in this study 60. 2.2.3. The Relationship between Sulphides and Palabora Carbonatites The relationship between the sulphides and carbonatites on the gross scale has already been discussed (2.1.4). The microscopic relationships are now reported. (This work is original) The sulphides usually replace and dissect all the other major minerals in the carbonatites; namely, calcite, dolomite, olivine (serpentinized), chondrodite, magnetite, thorianite and apatite. The carbonates are the most • extensively replaced, the other minerals mostly having only fractures infilled with sulphides. A variety of sulphide-carbonate relationships have been observed. These are:- i) Replacement a) stringers and mild replacement following cracks, fractures and early minerals. b) pervasive replacement ii) Isolated sulphides not replacing carbonate a)irregular blebs in carbonate b) extremely small sulphide plates in calcite crystals iii) Breccia infills of cataclastic textures iv) Sulphide associated with dolomite deposition v) Sulphide deposited in pressure shadows vi) Secondary inclusions in carbonate around sulphides i) Replacement Most of the sulphide at Palabora is seen replacing carbonate (see Plate 3A and B). The replacement is invariably around weaknesses in the fabric; grain boundaries, cleavages, cracks and fractures (see Plate 3A). The carbonate immediately surrounding clots and bands of earlier minerals (apatite, chondrodite, phlogopite, olivine, magnetite) is often heavily replaced, whilst the carbonate further from them may be barren. These minerals would be points of rigidity in the fabric during any plastic flow or cataclasis. It is interesting to compare this to the

61. PLATE 3: Sulphide/Carbonate Relationships at Palabora I

A. Sample P50B. Transgressive carbonatite at Palabora showing discontinuous sulphide streaks (S), mostly chalcopyrite, associated with apatite (op) and magnetite (mt).

B. Sample P40. Magnetite (mt) and sulphides (S) replacing transgressive carbonate. Plane polarized reflected light. Bar = 250 microns.

C. Sample P2A. Isolated sulphide blebs in banded carbonatite not extensively replacing carbonate. Transmitted plane polarized light. Bar = lmm.

D. Sample P62(b). Chalcopyrite infilling and replacing brecciated transgressive carbonatite. Plane polarized transmitted light. Bar = 500 microns.

E. Sample P13. Valleriite shear infilling from transgressive carbonatite. The black coating is valleriite, while the cut surface shows the internal brecciated structure of carbonate (white) infilled with valleriite (grey).

F. Polished section of P13 (photograph E) showing chalcopyrite (cp) in the breccia, the whole being replaced by valleriite (v). Plane polarized reflected light. Bar = lmm.

62.

PLATE 3

5cros I I 1 I 1-

A B observation of Howd and Barnes (1975) who found in experiments concerning the replacement of marble by sulphides that quartz grains were loci for sulphide deposition. Their experiments were designed to simulate hydrothermal ore bearing fluids reacting with carbonate and depositing sulphides at 450°C. They also found that sulphides replaced carbonate grains along cleavages and intergranular boundaries. In some areas the sulphides pervasively replace large areas of the carbonate fabric in many small, apparently unconnected patches. Blebs and grains may appear all over a slide. The individual areas of sulphide may be very small (a few tens of microns across) and are completely isolated from other grains. They are free of obvious surrounding cracks; none can be resolved even at the highest magnification. Nevertheless, the carbonate is still replaced from these isolated centres, with microscopic fingers and satellite grains reaching into the surrounding carbonate. This kind of pervasive replacement at isolated centres in a fabric is common in the porphyry coppers (Sillitoe, 1977 pers.comm). In these cases however, there is invariably a concommitant alteration of the silicate minerals, indicative of an overall influx of aqueous fluid. At Palabora this relationship is common in the dykes of transgressive carbonatite. The sulphides here, as in much of the Palabora ore, are closely related to the magnetite deposition which immediately preceded it. (The magnetite is discussed in subsection 2.2.5.) The isolated points in the carbonate matrix containing both magnetite and sulphides (see Plate 4A) may be indicative of deposition from residual fluids after the crystallization of the carbonate and other minerals. The absence of any pervasive alteration is notable, but this does not exclude the possibility. Fluids soaking through the whole rock could be largely inert to the carbonate. ii) Isolated sulphides not replacing Carbonate These sulphide occurrences are quite rare. There are two types. 64. PLATE 4

•

A. Isolated magnetite grains (white) surrounded by chalcopyrite specks (yellow) in transgressive carbonatite dyke. Plane polarized reflected light. Frame length = 4mm.

B. Section through a plate of chalcopyrite (10 microns length) isolated in calcite crystal; there are no apparent cracks leading to it. Oil immersion plane polarized reflected light. 65. a)Isolated grains and irregular blebs, mostly in the banded carbonatite, where they may be elongated and associated with bands or schlieren of other minerals. They are not obviously associated with macroscopic fractures and are mentioned by Hanekom (1965) who suggests that they were an early stage of mineralization. They are considered to be a primary product of the early magma in this work, certainly a phase of mineralization before the main mineralizing event (see Plate 3C). b) Microscopic plates as inclusions in calcite. These plates are well formed flat discs with parallel sides (showing rectangles when cut) which may be round or rounded hexagonal shapes in plan (see Plate 4B). Magnetite and ilmenite are also found like this. The plates are completely enclosed in the calcite crystals and there are no' observable cracks leading to them. They are so unlike any other occurrences of sulphides (and oxides) that it is concluded that they may have been trapped during growth or formed epitaxially. It is possible that they are the same as those mentioned by Reznitskii and Vorobyov (1978) who ascribed an exsolution origin to them. This is regarded as unlikely at Palabora because they are isolated individual crystals. An exsolution origin would be expected to produce numerous inclusions in each calcite crystal, rather than just one. iii) Infills of cataclastic textures In many samples from the central part of the transgressive carbonatite, brecciation of the original fabric has taken place. On a larger scale, the whole Loolekop centre was sheared, both before and after the transgressive carbonatite. Sulphides vigorously exploit the fractures and brecciated areas. There appear to be two categories; shears and fractures, mylonite heavily impregnated with valleriite and some chalcopyrite (Plate 3E and F), and brecciated and partly recrystallized zones with only minor valleriite (Plate 3D). They may both have belonged to the same period of activity, both being filled with chalcopyrite,

66. but with only the more linear well defined shears providing weaknesses, which were later exploited by valleriite depositing solutions. In the brecciated areas where the valleriite is insignificant the sulphides cut through and replace a fabric which has been brecciated and recrystallized. Coarse residual areas of carbonate are set in a fine grained recrystallized matrix. Mineralizing fluids certainly pass through the breccia and may even have caused the brecciation. The picture is however complicated by evidence of deformation in the sulphides. Folding and bending of bornite chalcopyrite intergrowths (which are usually straight) indicate some post depositional deformation (see Plate 6A). The valleriite rich shears are different in their greater continuity of dip and strike. The shears may be infilled with a carbonate-chalcopyrite valleriite impregnated mass up to 10cros.wide (see Plate 3E). In polished section the chalcopyrite replaces the carbonate of what may have been a brecciated shear related to the previously mentioned breccia inf ills (see Plate 3D). Later valleriite replaces this extensively, presumably finding easy access along these shears, which may have further moved after the deposition of the chalcopyrite. Evidence of even later movement is provided by the slickensides, which are common on the valleriite. iv) Sulphide associated with dolomite deposition Some sulphide, particularly in the transgressive carbonatite, has crystals of clean undeformed dolomite associated with it. This contrasts strongly with the surrounding calcite and dolomite which is commonly inundated by clouds of microscopic inclusions (see Plate 5B and D). At first it appears that the calcite is preferentially replaced, while the dolomite of the matrix, being more resistant to attack,is surrounded by sulphide. Whilst this is true, there is evidence that sōme dolomite was introduced with the sulphides or immediately prior to them. This is especially apparent in areas where calcite dolomite exsolution

67. is common and there are no large dolomite crystals in the matrix. The sulphides, however, still have large clear (inclusion free) dolomites associated with them. These are obviously not residuals of the original matrix. These clear dolomites are only found in immediate contact with the sulphides. They grow from the matrix carbonate in an irregular fashion; there is no clear boundary. The sulphides may partially replace them, though well defined crystal faces may jut into the sulphide. Weak zoning may be present in some such crystals. The difference between the dolomites of the matrix and the clear dolomite introduced with the sulphides is further reflected in their respective iron contents (see Fig.10). In rare instances, minute amounts of fluorite were associated with the sulphides in a similar manner. Fig.10 Histogram of Dolomite Iron Contents

Num- 5 Dolomite intro- ber 4 duced with of 3 Sulphide anal- 2 yses 1 0 600

Num- 5 Matrix Dolomite ber 4 of 3 anal- 2 yses 1 0 600 700 800 900 1000 1100 1200 1300 ppm Fe

v) Sulphides deposited in pressure shadows In some samples, recrystallization of carbonatite may have remobilized sulphides. Evidence of this is provided by the occurrence of sulphides in the pressure shadows of olivine, apatite and small blocks of carbonate which have not been recrystallized, as in Plate 5E. It is difficult

68. PLATE 5: Sulphide/Carbonate Relationships at Palabora II

A. Sample P28. Transgressive carbonatite vein (white) cuts phoscorite (black - p). Sulphides are confined to the carbonatite.

B. Sample P15. Clear dolomite (D) free of inclusions associated with the sulphides (S). Transmitted plane polarized light. Bar = 500 microns.

C. Sample P41. Unusual lace like replacement of carbonate by magnetite (mt). Reflected plane polarized light. Bar = 250 microns.

D. Sample P46. Contact (C) between transgressive carbonatite (T) and banded carbonatite (B). Copper sulphides run parallel to contact and are here confined to transgressive carbonatite. Note dolomite (D) associated with sulphides (5). The opaque in banded carbonatite is magnetite (mt). Transmitted plane polarized light. Bar = lcm.

E. Sample P15. Partly recrystallized carbonate (fine grained) with residual coarse carbonate grains (X). Sulphides (black) in pressure shadow (Y) of carbonate residual and also surrounding broken up apatite (ap). Transmitted plane polarized light. Bar = 0.5cm.

69. PLATE 5

D PLATE 6

A. Contorted bornite bands (brown) in chalcopyrite (yellow); evidence of sulphide deformation. For noLmal undeformed bornite/chalcopyrite relationship see Plate8A. Plane polarized reflected light. Frame length = 2mm.

B. Dual reflected light and transmitted light photomicrograph of clouds of secondary inclusions (c) joining a break in a remobilized sulphide vein (S) as the vein crosses a carbonate area in phoscorite. The sulphides are bornite (orange) and chalcocite (grey-blue). Frame length = 5mm. 71 _ conclusively to show remobilization of the primary sulphides as such textures may have been primary; the sulphides being deposited in a fabric under stress. vi) Secondary inclusions in carbonate surrounding sulphides Most of the sulphide occurrences may be surrounded by cloudy 'haloes' of extremely small inclusions in the carbonate. Rarely they can be resolved using the highest power objectives and oil immersion; when a liquid inclusion with a vapour bubble is seen. Only the constant brownian motion of the vapour bubble makes this identification possible. There may be other types of inclusion (some appear to be solid) associated with these, but the light microscope cannot resolve the inclusions clearly, let alone the contents. The inclusions are secondary (i.e. introduced after the formation of the mineral; see Roedder, 1967) and at least in part aqueous. Their small size precludes serious inclusion study, but their presence associated with the sulphides may indicate a hydrothermal origin for the sulphides. Because they are secondary, it is difficult positively to relate them to primary sulphide deposition; they could be related to later deposition of valleriite or secondary magnetite which coats many of the sulphides. They may also be representative of fluids which in some places have remobilized sulphides. An instance of remobilized sulphides associated with similar inclusions was found in one phoscorite sample (see Plate 6B). Here a break in a veinlet of •secondary (remobilized) bornite-chalcocite as it crosses some carbonate between two olivine crystals is filled with similar secondary inclusions. 2.2.4. Sulphide Behaviour in Transgressive Carbonatite Dykes The textures portrayed so far are of sulphides which have mostly replaced carbonates. The observations would be broadly consistent with mineralization introduced after the consolidation of the carbonatite; copper rich aqueous hydrothermal fluids pervading the fractured core of the 72. Loolekop centre. The picture is however complicated by the very close association of sulphides with the transgressive carbonatite, especially where it cuts through older rocks, reaching away from the central core. A study of such dykes, their contents, margins and effect on the older rocks reveals that the sulphides are carried in reasonable quantities to the extremities of the Loolekop centre and further, yet they remain intimately associated with the dykes. There is little tendency for sulphides to develop in older rocks adjacent to the dykes (see Plate 5A and D). Sulphide may be deposited on the immediate contact, but it is more commonly found in the dykelets as streaks and lenses running parallel to the dyke walls. The smaller ones may have a central streak of sulphides, as Verwoerd (1967) also observed, but he failed to comment on its significance. Textural information on the whole rock of these transgressive dykes is consistent with an influx of magmatic carbonatite, without a large volatile component. There is no wall rock alteration or carbonatization of the silicate rocks. The magma stoped off xenoliths and xenocrysts,of the earlier rocks and carried them, together with apatite phenocrysts, along the dykes. In some cases the apatites have their axes elongated in the same direction, typical of flow banding. 2.2.5. Implications of Sulphide Carbonate Relationships The study of the relationship between carbonate and sulphides shows two important points. Firstly, the bulk of the sulphides is intimately associated with the transgressive carbonatite. Secondly, the bulk of the sulphides always replaces carbonate and all the other minerals, in a manner indicative of pervasive hydrothermal replacement. These two points seem contradictory, especially since the transgressive carbonatite seems to have been a carbonatite magma without a large volatile component. The two apparently contradictory observations can however be united in an hypothesis of autometasomatic mineralization. The sulphides are introduced as part of the 73. magma, but the carbonates crystallize first, leaving a small volatile residual fluid. This mineralizes the carbonate, replacing it and producing typical hydrothermal replacement textures, lacking the typical vein continuity which would be expected from a normal hydrothermal introduction. In the central areas the volume of residual fluid would be much greater, especially considering the vast vertical extent of the mineralized Loolekop pipe (see Fig.7). At temperatures of -4000C as suggested by Forster (1958) the carbonate would still be plastic. The combination of autobrecciation, plastic flow and small quantities of residual, mineral rich, fluids could well produce the type of textures observed in the central area of the carbonatite. The same process on a smaller scale in the transgressive dykes and veinlets would account for the close association of sulphides with the carbonatite dykes and the isolated patches of 'pervasive' mineralization. The two carbonatites at Jacupiranga are very similar in many respects to the carbonatites at Palabora (Melcher, 1966). The compositions are very much alike and, as at Palabora, the second carbonatite at Jacupiranga is virtually the same as the first with a slight increase in MgO (see Hanekom et al.). Melcher (op.cit) explains discontinuous veinlets of sulphide and apatite at Jacupiranga in a similar way to that proposed above. He proposes crystallization of carbonates, leaving a "rest fluid enriched in P,F,Fe and S" which formed small veinlets of apatite, magnetite and sulphides in the carbonatite, parallel but occasionally dis- cordant to the flow structure. He adds, "the whole process must have been one of rapid cooling, since no settling (of silicates) occurs". A similar situation may well have occurred at Palabora, except that the phosphorus was withdrawn from the system as early crystals•of apatite. The outer zone sulphides in the banded carbonatites are also considered to be of a similar magmatic origin which pre-dated both transgressive carbonatite and the later mineralization. Two phases of mineralization are thus favoured, but a zonal distributionof a one phase

74. process, as suggested by Heinrich (1970) is not consistent with the observations of this study. 2.2.6. The Sulphide Paragenesis This has been largely studied by previous investigators, as mentioned in section 2.2.1. and only a brief account is presented here, with emphasis on new observations and deductions. A summary of the textural relationships between the major sulphides seen in this work is presented in Table 8. i) Chalcopyrite This makes up the bulk of the mineralization in the transgressive carbonatite and is equal, or just subordinate to bornite in the banded carbonatite and phoscorite. Chalcopyrite is found on its own or in intimate intergrowths with bornite, the relative amounts of each varying immensely. In chalcopyrite the bornite may consist of one or two veinlets or flame shapes a few microns wide, or it may develop a complex myrmekitic texture. Crystalographically controlled gratings are also common. Whilst some of these textures may be due to unmixing, as suggested by Hanekom et al. (1965); it is clear from this study that some is also formed in association with veins of secondary (post sulphide) magnetite which cut the chalcopyrite (see Plate 7A). Phases which commonly exsolve from chalcopyrite are; a)sphalerite in star shapes as described by Ramdohr, 1969 b) occasional blebs of galena c)pyrrhotite and pentlandite may be exsolved, but the textures are not conclusive (see pentlandite and pyrrhotite) ii) Bornite As well as occurring as intergrowths with chalcopyrite, bornite may form on'its own in large areas and also intergrown with chalcocite. This study has revealed for the first time complex intermediate phases part way between bornite and chalcopyrite. Bornite tongues are observed in chalcopyrite with rims of progressively lighter colour (see Plate 7B). Semi quantitative probe working reveals a

75. TARLP Q lNTRASIILPHTDE RELATIONdSHIPS IN PALABORA ORE

C halcoPyrite Bornite Cubanite cp bn Cb

Bornite ('on) Exsolution intergrowths & replacement: 1-bornite rims on bornite in cp.

Cubanite (cb) Exsolution laths Not observed and granular inclusions in cb.

Chalcocita (cc) Replacement of cp by Myrmeketic Not observed cc. Rare myrmekitic intergrowths (2) intergrowths & replace- between cc & cp/bn. ment.

Pyrrhotite (po) Grains of po in cp. Grains of po Coarse cp intergrowths in cp/bn intergrow- with po. mixtures. the

Pentlandite (pn) Pn grains in cp. Pn grains Not observed Replaced by cp with replaced & reaction rim of surrounded millerite & bn. by bn. • Sphalerite(al) Isolated areas & Large bodies Not observed exsolved stars in cp. in bn with mutual boundaries

Galena (g1) Mutual boundaries No observed Not observed with cp.

Pyrite (py) Cubes in cp (rare) Not observed Not observed

Mackinawite (mk) Exsolution in cp. Not observed Not observed Valleriite Replaces cp. Replaces bn Replaces cb Coexists with cp.

TABLE 8

76. gradual decrease in Cu from bornite, through the progressively lighter phases to chalcopyrite. It is very probable that stable bornites exist which have compositions considerably different from stoichiometric Cu5FeS4. Ramdohr (1969) considers that some bornites may contain an excess of CuFeS2 and others an excess of Cu2S. Thus values of the analysis could lie between Cu3FeS3 and Cu9FeS6. Brett and Yund (1964) point out that most bornites remain homogeneous when heated, but that a few exsolve chalcopyrite. These are of a slightly lighter colour, have somewhat smaller cell edges and contain more sulphur than normal bornites. Later Yund and Kullerud (1966) proposed that there was a separate phase, x-bornite with 0.4% more sulphur than bornite. They suggest that this phase can only form below 75°C. The observations of this at Palabora were associated with small blebs of covellite and this may be indicative of low temperature alteration of the original ore material. iii)Chalcocite and Djurleite Chalcocite occurs as myrmekitic intergrowths with bornite. Russell et al.(1954) identified this by XRD as the hexagonal form. Tatsuo Tatsumi (1967) reports some occurrences of djurleite. Chalcocite is only rarely associated with chalcopyrite. iv) Cubanite The cubanite occurs in the central area, especially in the transgressive carbonatite. It occurs'as exsolution laths in chalcopyrite. The Minor Phases i) Pyrrhotite This mineral was first reported by Bouwer (1957) and is one of the less common sulphides. It occurs as irregular granules in chalcopyrite, though without any clear signs of replacement. It also occurs in streaks and bands very similar to some of the occurrences in other carbonatites (see Chapter 1). In these situations there may be little or no chalcopyrite associated with it. It is also found with granular residuals of pentlandite. 77. PLATE 7

A. Sulphide in phoscorite; chalcopyrite (dark yellow) cut by veinlets of secondary low Ti magnetite (grey- brown), with bornite rims (brown) and associated areas of light yellow millerite. The latter may represent Ni introduced from serpentinized olivines. Plane polarized reflected light. Frame length = 2mm.

B. Bornite (dark orange-brown) with copper poor x-bornite rims (lighter orange-brown) in chalcopyrite (yellows). Plane polarized reflected light. Frame length = 2.5.mm. 78. ii) Pentlandite Pentlandite is a common accessory and is found as irregular grains in chalcopyrite or pyrrhotite and more rarely in bornite. The boundaries between the pentlandite and chalcopyrite are sometimes clean mutual boundaries, but more often the chalcopyrite cuts into the cleavages of the pentlandite (see Plate 8A). The corroded irregular outlines of pentlandite may then be mantled by bravoite and millerite. iii) Millerite Millerite is associated with the replacement of pentlandite as described. It is however, more commonly found closely related to the secondary generation of magnetite veinlets and bornite development in the chalcopyrite where it occurs in minute flames and patches, often surrounded by bornite (see Plate 7A). iv) Galena Galena is a member of the primary sulphide paragenesis, where it occurs on the rims of chalcopyrite with mutual boundaries. Also from the reaction of lead farmed by the radiogenic breakdown of uranium and thorium around the uranoan thorianite. v) Sphalerite Sphalerite occurs as exsolution stars in chalcopyrite and cubanite. Occasionally it forms large areas which are also probably exsolved. These areas may take the form of many star shapes joined together, their points interlocking. It is possible that growth in this manner may be responsible for the occurrence of the minute inclusions of chalcopyrite in the larger blocks of sphalerite. Large blocks also occur in bornite with inclusions of bornite and chalcopyrite. Bravoite and linnaeite were also seen as inclusions in sphalerite. vi) Covellite Covellite is found replacing sulphides and magnetite. It is rarely seen as tear drop shaped inclusions in chalcopyrite, suggesting that it might belong to the primary sulphide assemblage. The bulk of it is clearly a late stage alteration. 79. PLATE 8

A. Low Titanium magnetite rims (m) on chalcopyrite/ bornite intergrowths (grating texture - chalcopyrite medium yellow; bornite, orange-brown) and pentlandite (light yellow). The dark brown is carbonate. Plane polarized reflected light. Frame length = 2.5mm.

B. Parkerite islands (Ni3Bi2S2 - white) with Witti- chenite rims (3Cu2S.Bi2S3 grey) set in bornite (orange-brown) chalcopyrite (yellow) intergrowths. Plane polarized reflected light. Frame length = 500 microns.

80. vii) Parkerite Ni3Bi2S2 and Wittichenite 3Cu2S.Bi2S3 These minerals were observed in this study and are the first bismuth minerals recorded at Palabora. They occur as small rounded blebs of parkerite surrounded by a rim of wittichenite in massive bornite. They appear to represent early nickel bismuth phases replaced by later bornite. In one instance three closely spaced blebs of parkerite (each with a reaction rim of wittichenite) had their twinning lamellae orientated in the same direction, indicating that a larger crystal of parkerite had been attacked and divided up into residual islands (see Plate 8B). These were identified using probe and reflectance properties. viii) Pyrite Pyrite is seen as idiomorphic grains in chalcopyrite, it may be an alteration product. ix) Mackinawite Mackinawite occurs as rims on the cubanite laths and as a replacement of chalcopyrite,, The formula determined by Springer (1968) is (Fe 0.914NlO.1O2Co0.O02Cu0.O05)S Me1.023S x) Valleriite This is a major phase at Palabora. It replaces all minerals and is commonly associated with the secondary magnetite. It occurs in thick slabs associated with chalcopyrite up to 20cm. thick on late shear zones which clearly postdate the bulk of the mineralization. The replacement of other sulphides as well as magnetite, carbonates and silicates is extensive, even away from the shear zones, especially along grain boundaries, fracture partings and cleavage planes. It accounts for significant losses in flotation (P.M.C. Staff, 1976). Native Metals Numerous native metals have been recorded at Palabora. Gold, silver and platinum group metals are reported in the refinery sludge and these seem to bē related in part to native metals. In this study one or two specks of Au were seen and one occurrence of a silver rhodium alloy. Native copper has also been noted (P.de Vaal pers.comm., 1976). 81. 2.2.6. The Oxide Minerals Once again, only the salient points of the oxide minerals are presented, together with new observations. i) Magnetite Magnetite replaces all of the minerals at Palabora; the bulk of it however was deposited before the sulphides. Its distribution in the open pit is reflected by the iron contents in Fig.9. The same figure also shows that Ti, which is with the magnetite as ilmenite, is much higher in the phoscorite and banded carbonatite than in the transgressive. The magnetite with higher Ti values in the phoscorite was probably deposited first, with the low Ti magnetite of the transgressive carbonatite as a later stage. In this study a variety of textures has been observed:- a)coarse grained masses with inclusions of apatite, calcite, spinel, chondrodite, olivine, phlogopite and baddeleyite b) lace like intergrowths with calcite c)rims and veinlets deposited after the sulphides d)microscopic plates as inclusions in calcite e)magnetite specks in serpentinized olivine a) Coarse grained masses of magnetite; This makes up the bulk of the magnetite. Coarse grained masses may reach up to 30 or more centimetres across, though they are usually between 0.5cm and 4 or 5cm. The magnetite is transversed by irregular fractures which carry calcite and copper sulphides. Early stages of replacement of magnetite by chalcopyrite and valleriite along these fractures can be observed. In the high titanium areas, titanium bearing minerals are found exsolved in the magnetite (ilmenite, ulvospinel, hogbohmite and pseudobrookite - Lombard et al. 1964). Ilmenite is the most common and occurs as both lamellae arranged parallel to the crystallographic planes and as larger blebs on the rims of magnetite grains. The other titaniferous phases occur as small rounded and irregular

82. shaped inclusions. b)Lace like intergrowths with calcite; This previously unreported relationship occurs in a number of samples, but only from the transgressive carbonatite. The relationship between the calcite and magnetite is reminiscent of eutectic graphic intergrowths. The texture, shown in Plate SC, could be indicative of a close paragenetic relationship between magnetite and calcite. The texture may, however, be an unusual type of replacement. Typical of the transgressive carbonatite, there are no , exsolved Ti phases. A grain of magnetite may develop this texture on one side, whilst having a euhedral form on the other. c) Rims and veinlets deposited after the sulphides; (this work) This secondary deposition of magnetite occurs in all rock types, but is usually well developed in the phoscorite. The magnetite forms microscopic veinlets in the sulphides (see Plate 7A) and also forms crusted rims on them. Some- times these rims may have two or three layers (see Plate 8A). The magnetite which replaces chalcopyrite is always free from exsolved Ti minerals and probing shows it to be impoverished in Ti (<0.5%Ti) even in high Ti areas of the mine. There appears to be a relationship between this 'secondary' magnetite and some bornite development in chalcopyrite, as well as millerite and mackinawite (see Plate 8A). The cracks along which this secondary iron activity or oxidation developed may have allowed Ni to enter the microsystem (causing the development of millerite). Solution from the serpentinization of the phoscorite may be responsible for this, Ni and Fe being released from the olivine lattice. d)Microscopic plates in calcite; These are the same as those of chalcopyrite previously described. e)Magnetite specks in serpentinized olivine; This is typical of the serpentinization process.

83. ii)Thorianite Uranium bearing thorianite is found as idiomorphic and xenomorphic grains from a few microns across up to Imm. The occurrence of this is well described by Bouwer (1957), Forster (1958) and Hanekom et al.(1965). Little work has been done on it in this study. It should be mentioned that, like the copper sulphides, it is present in highest quantities in the transgressive carbonatite (see Bouwer, 1957). iii)Baddeleyite Baddeleyite is found in the phoscorite and banded carbonatite. Its occurrence had been described by Hiemstra (1955). In this study some baddeleyite crystals from the phoscorite were seen to have an overgrowth on them or a rim. The mineral has not been conclusively identified. It is isotropic in reflected light, with low reflectance and a grey colour. It appears to be somewhat speckled, perhaps indicating slight variation in composition. Probing revealed that it is a complex titanium-zirconium oxide. Its composition (see Table 9) does not correspond to any known Ti, Zr minerals defined by Vlasov (1966). It is probably of the zirconolite type, as its amorphous habit and different coloured irregular zones, as well as its cubic structure, are apparently similar. The large proportion of Ba0 present is peculiar. None 9f the Zr-Ti oxides mentioned by Vlasov (1966) or Borodin et al. (1973) have more than 1% BaO, and the only time such equally low values of TiO2 and Zr02 are recorded is in niobozirconolite, where Nb205 makes up a large portion of the mineral (up to 25%). There is no detectable Nb205 in the Palabora mineral.

84. TABLE 9: PROBE ANALYSES OF UNKNOWN Zr Ti OXIDE AND BADDELEYITE

Point 1 Point 2 Baddeleyite (Zr02) Fe0 5.76 6.17 2.8 Ca0 4.87 5.95 .8 1.65 TiO2 22.46 23.09 Zr02 24.51 23.49 95.1 Mg0 .56 .75 .65 Mn0 4.33 5.73 .24 Ba0 8.90 6.87 - TOTAL: 71.39x 72.05x 101.24 x No other detectable elements present. The mineral may be hydrated and may also contain F, like zirconolite. Some of the Zr Ti minerals have been only poorly studied. Vlasov (op.cit.) mentions that the structure of zirconolite has not been studied and that numerous other Zr Ti oxides have unreliable formulas and unknown chemical variations; such as oliveiraite, Zr3Ti20102H2O (?) and uhligite, Ca3(TiAlZr)9020(?). Calzirtite and zirkelite have characteristically higher Zr02 contents than the Palabora mineral. iv) Thucolite The presence of this rare radioactive hydrocarbon (Ellsworth, 1928) has been reported at Palabora by de Vaal (pers.comm., 1976). Its presence, together with that of native copper, is indicative of reducing conditions. 2.2.7. The Ore Paragenetic Sequence The ore paragenesis is essentially one of oxides followed by sulphides. The sequence occurs twice. The phoscorite and banded carbonatite were mineralized with magnetite and sulphides before the introduction of the transgressive carbonatite. The magnetite and sulphide deposition within the transgressive carbonatite is thus later than that in the banded carbonatite and phoscorite. Each phase may have had its own late stage valleriite phase.

85. FIG. 11 SCHEMATIC PARAGENETIC SEUUENCES

A. MAJOR SULPHIDES Cbalcopyrite ------Bomite

Cuban:1te

. ?yrrhotite

Pentl.a.D:11 te

Cbalcooite

SpMler1te

Pyrite

Mlller1te Valler11te . ------.

-----_... 2OO·C ---~r Fig.11 A·

B. OVERALL AT LOOLEKOP , . a,drotbel'llBl. 'Transgressive I AUtometa.solllLtia t.te stage introduction c:arbolBtite c:arbonatite lII1neraJ.i:zation . Shear.1ng ot apatite le I brecciatioJl

I • • I I A.patite i

I 'I I .: I I I Hagnetite ---.-... i I Ti content ot

Copper Vallerlite Sulphides ~I I ~ I I Thorianit..

I I :- ---- I ---~~----~----_L_ Deoreasinc plaatic nov ot car:bo::ra:te=-~---__:_I----r- --- - Fig.11 B

86. (The valleriite in the phoscorite has a different composition to that of the transgressive carbonatite - Springer, 1968). The sulphide paragenesis deduced from the ore textures is summarized in Fig.11A; a summary of the overall sequence at Loolekop is shown in Fig.11B.

2.3. GEOCHEMISTRY OF THE SULPHIDE ASSEMBLAGE There are no published data on the minor element concentrations of the Palabora sulphide assemblage. The scale of the mining operation does, however, allow trace and precious metals to be recovered in significant amounts. Analyses of some representative ore material together with published figures on copper anode and anode slime composition at Palabora, makes it possible to estimate the overall minor element composition of the sulphide ore. 2.3.1. Present Work Representative samples from the Loolekop pit- were analysed for Cu, Pb, Zn, Ni, Nb and Zr by atomic absorption and XRF (see Appendix 5). Similar work was done at Sokli and is reported and compared in Chapter 6. The rock samples analysed indicated the extreme impoverishment in Nb at Palabora; <35ppm in all samples, compared with Gold's (1963) figure for Nb in carbonatites of 1951ppm. Those with the higher levels of sulphides have been used to deduce ratios of Cu to other elements; Ni, Pb, Zn, Co and silver (see Table 10A). An indication of the actual levels of the copper sulphides was obtained by analysing four sulphide concentrates (see Table 10B); the ratios of elements in these are incorporated in Table 10A.

I 87. TABLE 10A: RATIOS OF MINOR METALS IN SULPHIDE ASSEMBLAGE FROM TRANSGRESSIVE CARBONATITE (Samples 7, 10, 12, 13, 14, 15, 14B, 19, 50, 50B) (Analysis by atomic absorbtion, see Appendix 5) mean standard range number of (ppm) deviation samples Cu/Ni 222 64.4 337-126 10 Cu/Pb 851 499 1511-216 10 Cu/Zn 418 255 191-939 9 Ni/Co 1.34 0.50. 0.73-2.32 9 Cu/Ag 24000 21000 5050-48285 3

TABLE 10B: CONCENTRATED SAMPLES OF SULPHIDE (Analysed by atomic absorbtion) Cu% Pb Zn Ni Co Ag Fe Ca Mg PPm PPm PPm PPm PPm 14 Predomi- nantly cp 31.5 500 330 1300 560 16 30.0 .46 1.8 50B Predomi- nantly cp 33.8 260 570 1200 700 7 19.0 1.4 0.18 19 Chalco- pyrite/ Bornite 20.2 200 1420 600 540 .40 16.5 7.2 11.2 38 Bornite Chalco- cite 65.0 90 65 300 20 .165 7.0 2.8 1.23

Analysis for Au amd PGM (Platinum Group Metals) was also attempted on sulphide concentrates (see Appendix 5), but the technique was not powerful enough to resolve the PGM. It was hoped that Pt:Pd ratios might reveal more information on the hydrothermal/magmatic nature of the sulphide ores and also the degree of differentiation that has occurred, as discussed by Cousins and Vermaak (1976) and Naldrett and Cabri (1976). Cousins and Vermaak (op.cit.) quote a value for Pd/Pd+Pt at Palabora of 0.65, but do not

88. indicate where the value came from. The PGM could not be resolved using neutron activation, a very powerful analytical technique (see Appendix 5). Cousins and Vermaak (op. cit.) probably analysed anode slime from the refining process. -This slime contains most of the trace element impurities from the blister copper. Gold was also analysed and resolved using neutron activation, (see Appendix 5) but the values in the Palabora material were variable (see Table 12). This is attributed to native gold particles. The values were one or two orders of magnitude higher than the evenly low Sokli sulphide samples (see Chapter 6). 2.3.2. Deductions from Published Figures Published figures on the copper anode and electrolytic slime for Palabora are available (Knoerr, 1971). The anodes are made from blister copper produced from the oxidation of copper matte. The latter is produced in the smelter from the oxidation of sulphides in the presence of silica-sand, which forms a slag for removal. The sand will introduce some minor elements and some volatile elements will be lost or depleted in the furnace; e.g. Zn, Pb, S. Nevertheless, the figures are useful as a guide, particularly those of the noble metals (see Table 11). The tonnage of copper produced ratioed against these elements gives a good approximation of the overall grades and can be compared with the limited analytical programme for this work (see Table 12). The overall sulphide mineralogy was taken as 60% chalcopyrite, 25% bornite, 10% cubanite, 1% chalcocite and 4% valleriite (figures from grade control - Knoerr, 1971).

89. TABLE 11: PALABORA ELECTROLYTIC REFINERY ANALYSES (after Knoerr, 1971) Composition of Anodes Composition of Anode Slime (approx. 1200gm/tonne of deposited copper) Cu 99.39% Cu 21 % Ni 0.45% Ni 7.02 Bi 8ppm Se 2.45 Se 28ppm Au 0.488 Pb 25ppm Ag 16.9 % As 4ppm Te 2.12 Sb 1ppm Au 3.63ppm Pt 488 ppm Ag 72.55ppm Pd 629 ppm Ru 7.3 ppm Rh 6.36 ppm Os 4:0.1 ppm Ir 4:0.1 ppm

The chemistry of the assemblage is fairly typical of a chalcophile ore assemblage, with small quantities of Zn and Pb which are characteristically associated with chalcopyrite. It might be expected that in a system which has undergone extreme fractionation, lower Ni and PGM values would be found. The latter elements fit easily into olivine structures and would be removed (Razin, 1971; Eckstrand, 1975; Stumpfl and Tarkian, 1976). The above authors mention that serpentinization of olivine may also release Ni and PGM to cause mineralization. This could be the case at Palabora, but the very low levels of Ni in the olivine suggest that it is unlikely (see Chapter 8). The ratios of elements and overall levels are quite different from the Sokli sulphides. The latter is probably a good representative of a normal carbonatite sulphide assemblage (see Chapter 6). The Palabora ores thus stand out for their unusual chemistry (note also the very low Nb) as well as their high copper.

90. TABLE 12: THEORETICAL METAL VALUES IN SULPHIDE ASSEMBLAGEx (PPm) From Electrolytic Refining From Sulphide Analysis Values (Table 9) (this work, Table 8) Ni 1805 - 1807 AA Au 1.46 0.1-1.4 NAA Ag 29.10 16.17 AA PGM 0.437 - NAA Se 11.00 N.D. - Te 8.24 N.D. - Pb (10.0) lost 471 AA Zn - during 960 AA Co - smelting? 1349 AA

DEDUCED OVERALL PIT GRADE, USING .56% COPPER

Cu 5600 ppm S 4456 Ni 25.2 Co 18.8 Zn 13.4 Pb 6.58 Ag 0.23 Au 0.020 PGM .0006 x Sulphide assemblage taken as 60% chalcopyrite, 25% bornite, 10% cubanite, 1% chalcocite, 4% valleriite (see text)

2.4. THE ENVIRONMENT OF FORMATION OF PALABORA SULPHIDES 2.4.1. Temperature and Depth The pressure and/or depth of formation of the Palabora ores cannot be deduced from a knowledge of regional geology. Its deepseated level of erosion has, however, been inferred from the structure of the complex (see Chapter 1) and it may be in the region of 5-10km. (Frolov, 1975). The temperatures of formation can be estimated from mineral equilibria, but with only limited knowledge of depth, such temperatures must be viewed with caution. 2.4.2. Mineral Equilibria Verwoerd (1967) used the calcite-dolomite exsolution in the banded carbonatite at Palabora and the subsolidus equilibrium diagram of Goldsmith and Heard (1961) to deduce

91. a minimum temperature of 675°C for its formation. This exsolution is common in many carbonatites (Jacupiranga - Melcher, 1966; Sangu - Coetzee, 1963; Mbeya - James and McKie, 1958;Siilinjarvi, Finland - Puustinen, 1975). Kononova and Tarashchina (1970) regard the exsolution as characteristic of early carbonatites. This offered potential as a useful geothermometer in carbonatites, especially using probe analysis. More recently, however, work by Gittins, (1978) has shown that the temperatures deduced from individual lamellae are variable within one crystal and that the temperature deduced is dependent on the time when the Mg diffusion became negligible. He concludes, "In view of all the factors which affect the result, it is doubtful whether the method is worth pursuing." Sphalerite geothermometry, based upon the mol.percent of FeS in ZnS (Kullerud, 1953) likewise had its heyday and has since been debunked (Stanton, 1972). The use of co- existing sphalerite, pyrrhotite and pyrite has, however, been suggested as a geobarometer (Hutcheon, 1978). Whilst Hutcheon managed to show its application in some metamorphic rocks, an attempted application on.Sokli and Palabora material proved inconclusive (see Chapter 6). The temperatures of ore deposition at Palabora postulated by Forster (1958) are based upon sulphide equilibria and exsolution temperatures. Unfortunately, many of the sulphide relationships are not conclusive of exsolution. Those which may be used are:- Pyrrhotite-pentlandite, the textures of which suggest exsolution, imply temperatures of 425-450° (Hewitt, 1938; Newhouse, 1927). Pyrrhotite-chalcopyrite show some evidence of solid solution and Hanekom et al.(1965) propose that this was formed at 600°C at Palabora. The textural relationships between these two seen in this study are however, not conclusive of exsolution. Chalaopyrite-cubanitI form a solid solution above 250-300°C according to Ramdohr (1969). The lath like intergrowths at Palabora are typical of exsolution.

92. Bornite-chalcocite form solid solutions from 175-225°C, (Edwards, 1947) but graphic textures resulting from replacement can frequently be recognized. Valleriite-chalcopyrite occur together in the late stages at galabora. Edwards (1947) reports that, if heated above 225 C, valleriite in chalcopyrite is converted to pyrrhotite. This is consistent with a later low temperature phase of valleriite deposition. The temperatures ascribed to these sulphide relationships must be viewed with caution because of the unknown depth of formation and also the environment of deposition. Both vary from the experimental work. The temperature 'of -400°C for the main sulphide parageneses mentioned by Forster (1958) is probably a little low. A temperature of 500-550°C is favoured for the bulk of the sulphide mineralization. This is a temperature above the complete solid solution of the above mentioned sulphide pairs and below the temperature of the banded carbonatite, of which 675°C must be a minimum temperature (Gittins, 1978). The temperature decreases during the late valleriite deposition to around 200°C. The carbonatites at Palabora might be equated with the Russian system Stage I and Stage II carbonatites. Petro- logical investigations by Pozharitskaya and Samoylov (1972) showed that the principal cause of most of the changes in the mineralogy from Stage I to Stage II in some Soviet complexes, is a decrease in temperature of the carbonatite fluid without substantial change in its total composition. Certainly there is little change in the overall carbonatite composition between the banded carbonatite (Stage I) and the transgressive carbonatite (Stage II?). The only differences are the presence of greater quantities of copper sulphide and thorianite and less titanium in the magnetite. 2.4.3. Magnetite-Ilmenite Pairs Two samples each of phoscorite and banded carbonatite with ilmenite-magnetite oxidation exsolution were analysed by electron microscope (see Appendix 3 and Chapter 6 on Sokli magnetite-ilmenite pairs) to determine temperature and oxygen fugasity (f02) using the curves of Buddington 93. and Lindsley (1964). Prinz (1972) used this system on numerous other African carbonatites. There are some problems associated with the interpretation of magnetite-ilmenite pairs; the nature of the exsolution process, which must involve some oxidation, and also the deviation from the experimental curves caused by large quantities of other elements (see Buddington and Lindsley - op.cit.; Anderson, 1968). As with other carbonatites (Prinz, 1972), Palabora magnetites have an extensive range of exsolution-oxidation textures, from large grains on the edge of magnetite masses, to the fine crystallographically controlled exsolutions of ilmenite, spinel and other phases (see 2.2.7). Only the coarser textures can be probed effectively without interference from other phases. As described by Rollinson (1979) the coarse textures probably represent a higher temperature process, whilst the small scale textures represent a low temperature. The probe results were recalculated using rogramme ILMAG by Rucklidge. Iron was allocated to Fe2+ and Fe3+ on the basis of mineral stoichiometry; the mole fractions of ulvospinel and R203 were calculated using the method of Carmichael (1967). The experimental work of Buddington and Lindsley (1964) allows the equilibration temperatures and oxygen fugasity of co-existing ilmenite and magnetite to be determined from their chemical composition. The results are displayed in,Fig.12 and Table 13. Those samples from the phoscorite and one of the samples from the banded carbonatite fall on the QFM buffer curve (heavy dashed line). The other sample falls in a block on its own. The samples on the QFM trend indicate that considerable change in the composition of the oxide occurred in response to changes in f02. The controlling buffer actually followed is not known. It is, however, essential to.riote that these samples have MgO levels in the ilmenite of 14-15%, which is higher than the 10% recommended by

94. PROBING OF MAGNETITE ILNENITE PAIRS Sample P47a Banded carbonatite Iln - A - Mt Ila - B - Mt Iln - C - Mt Ila - D- Mt Si02 0.00 .29 .31 .32 .43 .49 0.00 .31 TiO2 55.06 .51 54.38 .85 55.37 .85 56.41 .63 A1203 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Fed 34.53 92.25 34.55 92.30 30.95 93.06 32.14 93.19 Moo 2.93 - .0.00 2.86 0.00 3.81 0.00 3.84 0.00 MgO 8.39 .46 8.38 .46 9.83 .35 9.78 .38 SUM 100.91 93.51 100.48 93.93 100.39 94.75 102.17 94.51 RECALCULATED ANALYSIS MAGNETITE - ULVOSPINEL BASIS Fe2203 67.68 67.21 67.33 68.07 Fe 31.28 31.75 32.41 31.86 TOTAL 100.22 100.59 101.42 101.26 %USP /23T - 3.65 4.26 2.97 RECALCULLTED ANAL/SES ILMENITE - HEMATITE BLSIS Fe203 3.26 3.45 2.25 3.02 Feu 31.59 31.44 28.93 29.41 TOTAL 101.23 100.82 100.61 102.47 %ROMB 97.12 96.94 98.03 97.37 .

Ila - E - Mt Ila - 7 - Mt Ila - G - Mt Si02 0.00 .29 • .25 .29 .23 0.00. TiO2 55.71 1.09 53.98 .68 52.88 .42 41203 0.00 0.00 0.00 0.00 0.00 0.00 FeO 32.32 93.20 33.61 91.94 34.12 92.86 U' nO 4.19 0.00 3.98 0.00 4.13 0.00 MgO 10.10 .52 9.47 .36 9.14 .38 SUM 102.32 95.10 101.29 93.27 100.50 93.66 RECALCULATED ANALYSIS - MAGNETITE - ULVOSPINEL BASIS Fe2203 67.69 67.09 68.66 Fe 0 32.22 31.50 31.01 TOTAL 101.81 99.92 100.46 %USP 4.17 3.07 1.21 RENCAICULJTED ANALYSIS - ILMENITS . HEMATITE BASIS 752203 4.96 6.31 7.51 Fe0 27.85 27.93 27.35 TOTAL 102.81 101.91 101.24 MOMS 95.73 94.50 93.39

RESULTS PLOTTED ON CURVES OF BUDDINGTON & LINDSLEY 1964 Samples P1,P9,P27. (Bee over) Sample P47a (see above) MgO in ilaenite > 10% MgO in Limonite < 10%

520

30 500 600 700 600 300 400 500 600 700 800 Temperature, °C Temperature, °C

• = Phoecorite pairs • = Banded carbooatite pairs

FT1 17 9S PROBING OF MAGNETITE ILMENITE PAIRS (coat.)

Sample P9 Phoacorite

Ilm -A- Mt I]m -8- Mt Ilm -0- Mt Ila -D- Mt SA02 .20 .24 0.00 .23 .20 .29 0.00 .21 T102 57.10 1.64 58.36 .69 58.89 3.02 58.05 1.73 A1203 0.00 0.00 0.G0 0.00 0.00 .22 0.00 .26 Fe0 28.03 92.48 27.75 92.51 25.52 90.32 25.46 90.73 MnO 3.13 0.00 1.84 0.00 1.38 0.00 1.53 0.00 MgO 12.41 .65 14.04 .95 15.49 1.25 14.75 1.25 SUM 100.87 95.01 101.99 94.38 101.48 95.10 99.79 94.18 AFY;AICULATEO AxLLTSI3. - M&Gt1ETITE-ULVOSPINEI. BASIS Fe,0, 66.68 68.38 63.84 65.98 Fe0 32.40 30.90 32.81 31.29 TOTAL 101.62 101.16 101.43 100.72 'USP 5.54 2.82 9.58 5.70 RECALCULATED ANALISIS - ILNENtT$-FIEMATITE BASIS Fe22 0 1.92 2.40 1.48 1.22 FeO 3 26.30 25.59 24.19 24.36 TOTAL 101.06 102.23 101.63 99.91 %BOMB 98435 97.98 98.76 98.96 Sample P1 Phoecorite I]-- Mt rim -1.- Mt I1m -0- Mt SIO2 .22 .29 .24 0.00 0.00 .25 T10 57.87 .83 57.43 1.19 58.28 1.62 AL,0 0.00 0.00 0.00 0.00 0.00 0.00 3 F 27.66 93.07 27.47 91.73 21.70 89.88 MnO 1.80 0.00 1.66 0.00 1.39 0.00 MgO 14.15 .81 13.51 1.05 17.23 1.45 SUM 101.70 95.00 100.31 93.97 98.60 93.20 RECALCULATED AN/LISTS MAGNETITE ULVUSPINEL BASIS Fs2203 68.32 67.68 65.82 Fe0 31.52 30.76 30.58 TOTAL 101.77 100.68 99.72 %USP 3.43 3.39 5.59 RECALCULATED ANLI.ISIS ILMELaTE-EIBMITITS BASIS Fe 0 2.67 1.44 1.57 Fea 25.26 26.17 20.29 TOTAL 101.96 100.45 98.76 1.ROMB 97.76 98.76 98.67 Sample P21 Banded Carboaatite

Ila -A- Mt Ila -B- Mt Ilm -Cm Mt Ila -D.. Mt Si02 0.00 0.00 0.00 0.00 .25 .35 .23 0.00 T102 56.57 1.23 56.34 .93 57.62 1.29 56.49 1.23 11203 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Fe0 32.09• 92.95 30.37 91.65 26.02 91.28 27.40 92.50 Mn0 2.01 0.00 1.94 0.00 1.76 0.00 1.81 0.00 Mg0 10.70 .85 10.93 .68 14.23 .80 13.05 .40 SUM 101.37 95.03 99.58 93.26 99.88 93.72 98.98 94.13 RECALCULATED ANALISIS - MAGNETITE-ULVOSPINEL BASIS Fe,03 68.27 67.48 66.27 67.34 F 31.45 30.86 31.58 31.83 TOTAL 101.80 99.95 100.29 100.80 %USP 3.47 2.68 5.02 3.52 RECALCULATED Ax&&Ll3Z3 - ILMENITS-HIMATITE BASIS Fe 20 2.58 1.28 1.17 1.58 Pea 3 29.76 29.22 24.97 25.98 TOTAL 101.63 99.71 100.00 99.14 %ROME 97.76 98.87 99.00 98.63 I1m -b- Mt Tam -7- Mt S102 0.00 .29 .49 .27 T102 56.90 1.23 56.33 1.47 Al 0 3 0.00 0.00 0.00 0.00 FeC 27.53 91.92 26.92 92.05 Mn0 1.68 0.00 1.71 0.00 Mg0 13.52 1.01 13.46 .36 SUM 99.63 94.45 98.91 94.65 RECALCULATED ANALISIS - MLGZlEYIT8-ULV0SPINEL BASIS Fe 0 67.20 66.82 7.3 3 31.38 31.86 TOTAL 101.11 101.27 PSP 4.58 5.18 RECALCULATED ANALTSIS - ILMSNITE.8EX&fUITE BASIS Fe 03 2.40 1.56 Feb 25.37 25.52 TOTAL 99.87 99.06 .ROMB 97.93 98.65

TABLE 13

96. Buddington and Lindsley (op.cit.) as the probable outside limit of the curve's application. The sample which falls off the QFM has less than 10% MgO. Although the results do not give a definitive temperature of formation, they do show that temperatures must have been in excess of 500°C during formation of the magnetite. Furthermore, the oxygen fugasity at an unspecified later time in their cooling history is remarkably low. This could correspond to the conditions during which sulphides were deposited. The evidence is however not conclusive. The work was not continued or enlarged upon because of the non specific nature of the results. Rollinson (1979) and Bowles (1976) have shown that accurate ilmenite/magnetite geothermometry is only useful for volcanic rocks; slowly cooled igneous rocks continue to equilibrate below their solidus and show a range of temperatures. 2.4.4. Conditions of fS2 and f02 The theoretic deductions of Mitchell and Krouse (1975) concerning sulphur isotope geochemistry have been discussed (1.3.4.). Although their deductions go beyond the confines of experimental data, and the temperature of 700°C they ascribe to the Palabora sulphides may be too high, their deductions are nevertheless useful. They show that Palabora sulphides were probably deposited in a high sulphur fugasity, low oxygen fugasity environment (log fS2 between 0 and-5 and log f02 about -15). The magnetite-ilmenite work corro- borates the low f02 estimate. Low f02 (10-17.1) was also deduced for the Oka carbonatite using a solid electrolite oxygen fugasity sensor (Friel and Ulmer, 1974). Mitchell and Krouse's pH deductions are extrapolated from thermodynamic data given by Ohmoto (1972) on the isotopic composition of sulphur with changing mole fractions of sulphur ionic species in a hydrothermal fluid. They deduce a low pH but emphasize that this is to be used as a guide only to high temperature sulphur isotope distribution.

97. The concept of pH becomes complex at high temperature, because the ionization constant of water (at 600-700°C a super critical fluid) changes as temperature rises and is also very dependent on pressure (Krauskopf, 1967).

2.5. SUMMARY AND CONCLUSIONS 2.5.1. Summary Copper mineralization at Palabora is associated with the final phase of carbonatite activity. A microscope investigation of the relationship between t1e sulphides and the carbonate reveals that the carbonates have been largely replaced by sulphides, in a manner suggesting hydrothermal replacement. However, although there is apparently an early phase of limited sulphide deposition in the banded carbonatite and phoscorite, the bulk of the sulphide is associated with the transgressive carbonatite. This is well exemplified by the transgressive dykes which carry sulphides well away from the transgressive centre. The textural relationship of the magnetite and sulphide with the carbonatite is one of late stage replacement. A scheme is presented in which a copper rich magma is intruded into the fractured locus at Loolekop. On cooling this leaves residual fluids rich in copper, Fe and S. Magnetite is deposited first, followed by sulphides as the system cools and fractures. Late stage residual fluids from the extensive carbonatite column escape up through these later shears depositing valleriite. The sulphides are mainly chalcopyrite and bornite; early formed pentlandite may have preceded the deposition of the copper sulphides. The sulphide textures are indicative of exsolution during cooling, combined with reaction with residual late stage fluids. The magnetite precedes the sulphides and it is conceivable that its formation reduced the oxygen fugasity of the residual system, causing the precipitation of sulphides. The Palabora carbonatites have an unusual amount of copper, but furthermore the whole sulphide assemblage is

98. different to that of other complexes. There are also differences in the geochemistry of the sulphides. A most noticeable anomaly in the geochemistry of the Palabora carbonatite is the complete absence of Nb. The temperature of the ore forming process is estimated to have started at 550-600°C, falling off to 200°C when the valleriite was deposited. The oxygen fugasity•of the system was probably extremely low when the sulphides were deposited. Magmatic introduction, autometasomatism and later hydrothermal activity are all responsible for transport and deposition of copper sulphides. The copper rich melt crystallized apatite and, as the carbonates crystallized, magnetite and finally chalcopyrite were deposited. The latter is deposited from a predominantly volatile rich fluid which replaces the carbonate and magnetite, sometimes depositing Fe poor dolomite. Continued movement during this process would fracture the early minerals and cause rupturing of the core. The residual fluids escaping from below would tend to have a cataclastic effect on the partially consolidated, yet still hot (and therefore plastic) carbonate. The final 'steaming' of the deposit and cooling of these fluids deposited valleriite, the central shears being reactivated during this period. It is suggested that the Palabora copper deposits were formed in a natural continuum between a cooling flowing magma and its residual low density fluids. Heinrich (1966) notes that carbonatites probably more so than any other rocks exemplify the observation of Von Cotta (1858). "Kein Gesteine verharrt volkommen in dem Zustande seiner ersten Entstehung" (No rock solidifies completely in its position of first emplacement). Add to this the possibility of residual volatiles and plastic flow of the solid carbonate and the true complex picture of the sulphide deposition and carbonatite formation at Palabora is better understood.

99. CHAPTER 3: INCLUSIONS AND RARE EARTH ELEMENTS IN PALABORA APATITES 3.1. INTRODUCTION Apatites in many carbonatite complexes contain characteristic primary fluid inclusions (see Chapter 1). These inclusions are absent,-ar too small for use, at Palabora. The discovery of copper sulphide inclusions in many of the apatites however, demanded investigation; such inclusions . could reveal some clues to the progressive evolution and deposition of Palabora's copper. Apatites are found in most of the rock types at Palabora. Some rock types have apatites containing myriads of sulphide inclusions, while apatites from other rock types have none. Different generations of apatite are thus implied and these generations have been confirmed using REEs (rare earth elements). This REE programme also served to test Palabora's REE distribution and its conformity to other carbonatite complexes with respect to REE. 3.2. APATITE DISTRIBUTION. Apatite at Palabora is the fluor-hydroxy apatite typical of carbonatites (Prinz, 1973) and is found all over the complex, as described by Hanekom et al.(1965). Apatite is particularly abundant in the pyroxenite (Phoscor exploit the apatite rich pyroxenite in the north of the complex at grades of 11-14% P205). Most apatite is interstitial to the pyroxene grains (see Fig.13) though occasionally it is included in the pyroxenes. Veins of apatite/phlogopite have been extensively introduced into the pyroxenite (Hanekom et al. op.cit.) and the pyroxene-apatite rock is

recrystallized in places. -. Apatite in the phoscorites at Loolekop is mostly interstitial to the olivine (see Fig.13), though once again it may rarely be found enclosed in the olivine as small crystals. The banded carbonatite has coarse intergrowths of apatite and magnetite and also large (5 or more cm.long) prismatic crystals of apatite, sometimes forming radiating 100. TYPICAL PALABORA APATITES

l~/, Vj '5~ Fractured apatite prillJlUl in baDded Section- through parallsl allgned apatite. &%Xl traugresain carbomt1te. . iD. tranagreaain carbonatita vein.

~ I Carbomte/lIIILptite atr1x ( /. ( / ,\1, l &k\ ' ""'" ~: \ ,\/°l

xl!". :

I.rge radiating apatite prisu 111 Apatite le oUvina nDOCl"TstsVlltha) banded carbomtite banded le tralUtgrtlaaiTe ea.rbonatitaa

\ ' f \~ \ \ I . \ I ° ( \ \ , ! I

I I

J.pat1te le _ptit. surrouMing ollTinea (partiall,. serpent1D1:ed) ill Pboscorite

FIG.13

101. masses up to 25cm. across. Most of the apatite is however as xenocrysts or phenocrysts which have been strained and broken in the carbonate matrix. The xenocrysts may be attached to fragments of olivine, chondrodite and phlogopite, suggesting derivation from earlier phoscorite. The apatites are mostly rounded prisms. Phenocrysts (or xenocrysts) of apatite are similarly present in the transgressive carbonatite. They may be smaller than those of the banded carbonatite (1-2mm.long), though still as rounded elongate prisms. In the narrow , dykes of transgressive carbonatite they are commonly orientated parallel to dyke contacts, giving the impression of flow. 3.3. TYPES OF INCLUSION IN THE APATITE The types of solid inclusion seen in the apatites at Palabora are: 1) Minute (<5 microns) aqueous inclusions (secondary), these are also common in other minerals - see Fig.14A 2) Irregular shaped non aligned solid inclusions (primary) - see Fig.14B 3) Elongate rods and plates parallel to the C-axis (primary) - see Figs. 15 & 16 The inclusions have been studied using transmitted light, reflected light and SEM (scanning electron microscopy). 3.3.1. Aqueous Inclusions Although primary aqueous inclusions (captured during growth) were not observed in the apatite, secondary inclusions (introduced as fractures after growth) are common in rows and planes, usually running sub parallel to the imper- fect basal cleavage. The individual inclusions are invariably very small (<5 microns, though an unusually large one is shown in Plate 9E) and show evidence of extensive necking down (see Fig.14A and Roedder, 1967 for necking down and primary and secondary inclusions). The presence of large cubic daughter minerals (halite?) in some of them suggests that the fluids trapped were of sufficient salinity to be potential carriers of base metals. The presence of a

102. small triangular opaque daughter suggestive of chalcopyrite (see Plate 9E) confirms this possibility. Much of the sulphide mineralization is surrounded by crystals of calcite, dolomite and apatite, which are clouded by myriads of ultramicroscopic (.c1 micron) inclusions, some of which can be seen to be vapour/liquid. These inclusions may belong to any of the mineralizing or post mineralization events suggested by the ore microscopy (see Chapter 2). The small size of these fluid inclusions associated with the mineralization precludes any serious study, especially of homogenization and freezing. It can be demonstrated that some of these fluid inclusions are possibly representative of late stage fluids which remobilized some of the earlier-formed copper minerals. 3.3.2a) Irregular Shaped Non Aligned Solid and b) Multisolid Inclusions The origin of these inclusions is not clear, the monomineralic types (see Fig.14B(a)) are presumed to have either been early crystalline phases trapped-during the growth of the apatite, or grown epitaxially on the apatite. They include specks of magnetite, chalcopyrite, baddeleyite, rounded (elongate and spherical) calcites and two or more unidentified phases. The rounded/spherical calcite inclusions may contain very small aqueous inclusions. By analogy with Sokli (see Chapter 7) this may be indicative of replacement of earlier carbonate by apatite. The presence of this phenomenon in the phoscorites in particular may be indicative of replacement of an early interstitial carbonate matrix. A more detailed discussion of this type of inclusion is presented in Chapter 7. The multisolid types are mostly irregularly shaped carbonate inclusions with specks of chalcopyrite (see Fig. 14B,6) and occasionally phlogopite and magnetite. 3.3.3. Elongate Inclusions Aligned Parallel to the C-axis of the Apatite These inclusions are elongate rods and plates of various cross section (round, hexagonal, rectangular - see Fig.15) 103. Vapour babble (Y)

Birefringent daughter b)

down 10 ,um Necking

14A. SECONDARY AQUEOUS INCLUSIONS

C) Apatite crystal from transgressive carbooatite showing planes of secondary fluid inclusions nub parallel to basal cleavage

500 um c-axis

d) Secondary fluid inclusions may realign themselves with tha C axis of apatite

2,nm

14B. NON ALIGNED SOLID INCLUSIONS FLgnetite

5 um

Unkaovn mineral R.I..c apatite weakly birefringent

Calcite sphere with magnetite and unknown mineral (X) trapped in apatite.

104. PLATE 9: Inclusions in Palabora Apatites

A. Apatite crystal (op) in transgressive carbonatite (P47B) showing planes of secondary inclusions (2) and primary inclusions (P) aligned parallel to the C-axis. Transmitted light with crossed polars. Bar = 500 microns.

B. Birefringent inclusion aligned parallel to the apatite C-axis. Opaque speck is a sulphide (S). Transmitted light crossed polars. Bar = 75 microns.

C. Solid opaque inclusion aligned parallel to the C-axis in apatite. Note colourless tip (t). Transmitted plane polarized light. Bar = 100 microns.

D. Same inclusion as C viewed in reflected light (see Appendix 1). The reflected colours are yellow - chalcopyrite (cp) and orange-brown - bornite (bn). Bar = 20 microns.

E. Exceptionally large secondary aqueous (aq)/vapour (v) inclusion with triangular opaque daughter (o). Transmitted plane polarized light. Bar = 50 microns.

F. Colourless elongate silicate (amphibole?) inclusions extracted from apatite by HC1 digestion. Viewed using SEM. Bar = 10 microns.

G. Sulphide inclusion extracted from apatite by HC1 digestion. Atomic number contrast shows difference between chalcopyrite (cp) and bornite (bn). Bornite has more copper than chalcopyrite. This was confirmed by the x-ray spectra produced from the inclusion. SEM photomicrograph. Bar = 100 microns.

105. and are usually elongate parallel to the c-axis and rarely to 0001 (see Plate 9A,B and C). The size ranges from to 50011 in length with a length to breadth ratio of between 200:1 and 5:1 (see Fig.15). The ends of the inclusions may be rounded or pointed; the angles in the latter case 'corresponding to the interfacial angles of the apatite pyramid. The form appears to be strongly controlled by the apatite crystal structure. These inclusions may be divided into three broad types:- 1) Entirely opaque inclusions 2) Entirely transparent 3) Part opaque and part transparent The distribution of types 1) and 2) is shown in Fig.15 (counting was done on apatite concentrates mounted in Araldite and polished. The crystals were not whole, the grains being between 250FL and lmm. across; 200 crystals from each sample were counted). The inclusion distribution shown in the histograms is typical of what was observed in most slides studied. The colourless types are more common in the pyroxenite where there are virtually no opaques. The opaques are most common in the phoscorite, practically all crystals containing them; a high proportion of crystals here contain thousands of inclusions. The opaques are present in apatites from the transgressive carbonatites, but they are less common than in those from the phoscorite. i) Opaque Inclusion Types: The opaque types come in a variety of shapes (see Fig. 16) but most tend to be flat or rounded in section. They sometimes have a small indentation on one side (see Fig. 16 and Plate 9D), the shape of which may be controlled by apatite structure. Occasionally the inclusions may be hexagonal, when found on the plane 0001. In many cases they have a colourless, non-birefringent area at one end. It is not clear what this is; a liquid or solid, or even space caused by differential shrinkage (see 't' in Plate 9C). In some rare instances it is a notably birefringent solid.

107. Distribution of Aligned inclusions in Different Rocks

Phaaoorite Phosoorite / Bamed c:1 tita Tranagressive BaDled carbonat1te TRANSPARENT INCLUSIONS

I 23b 2b lS SOb OPAQUE 90 INCLUSIONS eo-

70 ~ ot Apatites with 60 i%JClus1ona ~O

JJJ

20 .

23b 41 1 32 a3 2b 1S SOb Apatite 8& Phoecorite ?hoscor1te / Bandecl c: I tite Tl'anagreas1"le lId.ea rock BaDied. alUte carbonat1te

K!~?~J :-; or C%"'/stal. rragments with inclusions m % ot !'ragmanta with>lOOO inclusions CATAGORIES OF ALIGNED INCLUSIONS In Plan b.. To 0001 In Section /I To 0001 1. OPAQUE /.

2. TRANSPARENT o o 0 ~

3: MIXED TYPES I I ( ? ) (DOt !een) (much less common)

FIGURE 1S

108. The opaque inclusions may show reflections in reflected light; provided they are orientated in the right direction in the polished crystal relative to the incident beam of the reflecting light microscope (see Appendix 1). Such reflections show that the opaque inclusions are mostly yellow copper sulphides. Usually about 90% of the inclusion is yellowy/brown, (bornite) the remainder being bright yellow (chalcopyrite) and the relationships suggest unmixing from a solid solution (see Fig.16 and Plates 9C, 9D and 10A). If bornite:chalcopyrite = 9:1, then the original solid, solution would be 60.4%Cu, 13.1%Fe and 26.5%S. The true reflected light colours of the opaques are not seen because of interference from the host apatite and for other reasons discussed in Appendix 1. The identification was verified by dissolving the apatite in dilute HC1, the inclusions falling onto a glass plate. This was then washed, taking care not to move the residue. When washed and dried it was possible to carbon coat the inclusions and obtain a semi quantitative analysis using a scanning electron microscope with an energy dispersive analytical facility (see Appendices 2 and 3). The SEM confirmed copper, iron and sulphur in both the yellow and orange/brown phases (see Plates 9G and 10A). Rarely, inclusions with grey reflections were observed, and these are assumed to be magnetite. None were found under the SEM. ii) Transparent Inclusions; These may be flattened, taking the same shapes as the opaque inclusions, or they may be hexagonal in section, being perfect replicas of the apatite structure. Some are isotropic and others anisotropic with inclined extinction. Some have an RI (refractive index) approximately the same as the apatite. These inclusions were extracted as for the opaque inclusions, using an HC1 digestion. The residual material (inclusions; see Plate 9F and G) was rolled into a ball of cow gum rubber glue and mounted in an x-ray camera. X-ray diffraction showed this to contain thorianite, chalcopyrite(?) and quartz(?). The SEM revealed thorium in some

109. ALIGNED INCLUSIONS IN APATITE (PALABORA)

A. Opaque types (A. observed in refloated light) C - axis Apatite crystals showing orientation of aligned inclusions

Most inclusions in this size I range I

\Cp / En Bn } Cp Bn Cp En 1

l Cp

Cp White/yellow reflections

Hegmotits (?) Cp grey in reflected light)

Cp CHAIGOPTRITE En Mt MAGNETITE(?)

B. Mixed opaque / transparent types (as observed in dual mode reflected /transmitted light ) Na J,~ B Bn < e \ Cp/ ) T

Cp En (p En ~Mt NB NB l B Bn / ( Bn

CP Mt Cp Bn Bn Bn En NB

APATITE GRAIN FROM BANDED CARBONATITP

Opaques types only Large birefringent solid (calcite?)

Mixed typee(see expanded area)

B = Colourless birefringent mineral NB = Colourless non-birefringent mineral.

FIG 16

110 PLATE 10

A. Copper sulphide inclusions extracted from Palabora apatite by HC1 digestion. The large inclusion in the centre shows the typical chalcopyrite (white) and bornite (yellow) relationship. Plane polarized reflected light. Frame length is 350 microns.

B. Multisolid inclusion in apatite with irregular chalcopyrite (white) in a regular lath like colourless phase. Plane polarized light (oil iluuersion). Frame length = 100 microns. of the isotropic rods with high RI (thorianite), whilst other isotropic rods had Ca, Mg, Si, Fe (Na) and were highly flexible (did not break when bent). Others noticeably anisotropic also had Ca, Mg, Si and Fe with minor Na and may be amphiboles. There may be other types, but any carbonates would.be easily dissolved in the acid digestion of the apatite and would not be seen. .iii) Mixed Types; These are less common than the all opaque, or all transparent types. They are combinations of the two (see Fig.16) and some are particularly long and narrow with a variety of colourless, birefringent and non birefringent phases, as well as opaques. Very rarely, combinations of colourless phases with magnetite and bornite/chalcopyrite are seen (see Plate 10B). 3.3.4. Explanation and Deductions from Crystallographically Controlled Types These inclusions are thought to have grown epitaxially with the apatites. Other possibilities are that they are an exsolution from the apatite, or have been introduced into the apatite by diffusion, replacing some other phase such as the hildenstockite of Vasilyeva (1978). These possibilities are discounted; firstly because the inclusions are not evenly distributed in the crystals, and secondly because there are more sulphide inclusions in the phoscorite, where the copper mineralization in the rock is less. Orientated inclusions of minerals in apatite have occasionally been observed in other environments. .Amli (1975) found larger but similarly orientated inclusions of xenotime, quartz, monazite, rutile, pyrite and goethite in apatite from a granite pegmatite in Norway. He was able to show that the apatite was depleted in rare earths next to the xenotime inclusions, but he was not able to present an entirely satisfactory explanation for the inclusions. Vasilyeva (1978) discusses epitaxial inclusions of tetra calcium phosphate (hildenstockite - Ca4P209) which have structures very similar to apatite. She suggests that 112. these are very common in high Ca content rocks, such as carbonatites. This could well be responsible for some of the colourless inclusions in the apatite at Palabora, the mineral is soluble in HC1. Genkin et al.(1961) observed a "tubular inclusion similar to some gaseous inclusions" and drop like sulphide inclusions in apatite from the magmatic copper nickel sulphide Norilsk deposit; some of the tubular inclusions had hexagonal sections. They suggest that the apatite grew in a sulphide liquid that had not begun to crystallize. This is considered unlikely in the light of the present work. The inclusions of sulphide and other minerals at Palabora are considered to be primary and most likely of epitaxial origin. The apatites are thought to have been present in the carbonatites as phenocrysts and in some cases xenocrysts. The presence of copper sulphides growing with the apatites in a carbonatite melt is good evidence for the presence of at least some copper and sulphur in the fluid from which the apatite was crystallizing. It is not clear why the sulphides are much more common in the phoscorite than the carbonatite, especially since there is less copper sulphide present in the actual rock. In the course of investigating other carbonatite deposits, similar elongate sulphide and colourless inclusions, have been seen in apatites from Bukusu, Sokli, Kortajarvi (Finland) and Great Beaver House. The occurrences are however extremely rare and they apparently represent the type of sulphide present in the rock; usually pyrrhotite. The presence of primary aqueous hydrothermal inclusions in some of these apatites from other deposits with crystallographically controlled solid inclusions further suggests an epitaxial origin for these enigmatic inclusions rather than the trapping of an immiscible sulphide melt as suggested by Genkin et al.(1961). Such a sulphide melt could certainly not co-exist with a carbonatite at the low temperature suggested for carbonatite formation at Palabora and other complexes. The apparent exsolution of bornite and chalcopyrite in the solid inclusions would suggest that the inclusions were formed at temperatures in excess of 475°C (Schwarz, 1931).

113. 3.4. RARE EARTHS IN PALABORA APATITES To follow up the work on inclusions in the apatites and to supplement the understanding of apatite genesis, a programme of rare earth analysis was undertaken. The inclusion populations are obviously different; it was hoped that the rare earths might reflect differences in formation conditions of each group. With unusual copper and niobium values and no RE minerals, Palabora is obviously chemically unusual. The RE study would also indicate whether Palabora is like other carbonatites in its rare earth distribution, or whether there are any unusual trends. A study of the whole rocks at Palabora is hampered ' considerably by the difficulty in obtaining a representative average sample of the coarse grained rock types, particularly the phoscorite. The varying amount of apatite severely affects the levels of REE in the rock. Since apatite is the major carrier of REE in most of the rock types, the rare earth distribution in the apatites is clearly important. 3.4.1. Previous Work There have been no previous attempts to study REE distribution patterns at Palabora. Rare earths have been extensively used to investigate petrogenesis in other carbonatite complexes. Many of the studies have been concerned with whole rock abundances of the rare earths. Heinrich (1966), Gerasimovskii et al.(1972), Loubet et al.(1972), Philpotts et al.(1972) and others have reported whole rock data for carbonatites which indicate a significant enrichment in light REE relative to heavy REE on chondrite normalized curves. Light REE enrichment is more severe in carbonatites than most crustal rocks. Heinrich (1966) noted that there is'an increase in total REE content with decreasing relative age of carbonatite phases within a given complex. In early carbonatite phases the REEs are concentrated in rhombohedral carbonates, apatite, perovskite and pyrochlore, while in the later carbonatite phases, the REE becomes concentrated in independent REE minerals (e.g. bast- nasite, synchesite, monazite). Kapustin (1966) and also

114. Balashov and Pozharitskaya (1968) have discussed the existence of several stages of carbonatite activity; each stage characterized by a distinct REE assemblage. This is, however, not present in all carbonatite complexes as pointed out by Mitchell and Brunfelt (1975) using Fen as an example. More integrated studies have recently been undertaken in which whole rock values and individual minerals have been studied together. Eby (1975) in this way produced REE data from Oka which, to him, are suggestive of REEs being selectively partitioned into a volatile rich phase which formed the calcites and apatites. The conclusion being that a silicate liquid co-existed with a volatile rich immiscible phase, the latter of which produced the carbonatites. Mitchell and Brunfelt (1975) also present a petrogenetic scheme based upon a REE study of the rock types at Fen, in which a carbonated nephelinite magma undergoes liquid immiscibility, differentiation and volatile transport. Although the REE trends in carbonatites are well documented, the reasons for such trends are not always clear. The interpretation of REE distribution must be based upon knowledge of the behaviour of REE in different environments. The split between Soviet and Western schools is well exemplified by the work directed to this end. In the Soviet hydrothermal school Aleksandrov et al.(1965) demonstrated a low solubility of light REEs in alkali carbonate solutions at both low (200-300°C) and high temperature, with the heavier REEs being more soluble at temperatures less than 300°C than above. Balashov and Pozharitskaya (1968) in a study of carbonatites in western Siberia correlated decrease in temperature of homogenization of fluid inclusions with changes in REE and supported Aleksandrov's (op.cit.) findings. In the Western magmatist school, recent experimental work by Wendlandt and Harrison (1978) shows in the system K20-Al203-Si02-0O2 at 1200°C immiscible silicate and carbonate melts co-existing with a CO2 rich vapour. The rare earth partitioning between the melts shows that the carbonate melt is more enriched in REE (and especially light REE) 115. than the silicate melt, whilst the CO2 vapour phase is enriched in light REE relative to both melts. This kind of work makes possible more confident interpretations of REE distributions. Apparently following the mantle metasomatism origins discussed in this work (Chapter 1), Wendlandt and Harrison suggest "Mantle metasomatism by a CO2 rich vapour enriched in light REEs may explain the enhanced REE content and light REE enrichment of carbonatites, potassium rich silicate magmas and kimberlites". 3.4.2. The Present Work Thirty two samples were analysed for La, Ce, Nd, Sm, Eu, Gd, Tb, Yb and Lu by instrumental neutron activation (see Appendix 5). Sixteen apatite concentrates from different rock types; 3 calcites, 1 baddeleyite, 1 chondrodite and 11 whole rocks, were analysed. The individual minerals were separated using conventional heavy liquid and magnetic techniques. These were then hand picked to purity. The samples were checked by XRD and those samples in which peaks of calcite or dolomite were visible were discarded. The results are presented as chondrite normalized curves (chondrite values after Haskin et al.1968, see Figs. 17, 18 and 20). Gadolinium results are only presented for the apatites since interference from other elements causes problems when analysing for this element. Long decay times and recounting of activity produced reasonable results for Gd in the apatites, but the procedure was considered unnecessary for the representative whole rocks. The details of this are presented in Appendix 5. 3.4.3. Results - The rare earth patterns at Palabora (see Figs.17, 18 and 20) have the high levels of rare earths and strong light rare earth enrichment typical of carbonatites (Heinrich, 1966). As with apatite at Oka, (Eby, 1975) the Palabora apatites have a weak negative Eu anomaly. This is a function of the ease of entrance of larger Eu2+ into the various crystal structures. Eby (op.cit.) suggests on the

116. basis of some unpublished work, that Oka apatites tend to reject Eu2+. Loubet et al.(1972) suggest that a Eu anomaly may indicate the change of Eu3+ to Eu2+ under reducing conditions, with Eu2+ being less acceptable in the lattice. As mentioned in the previous chapter, the presence of thucolite, native copper and sulphides, together with a low f02 indicated by the magnetite/ilmenite pairs, implies that the conditions during the formation of the Palabora carbonatites may have been reducing. There are other possible explanations however, such as the preferential absorbtion of Eu at some earlier stage in the magmatic evolution, leaving the system weakly depleted in Eu. This is not directly relevant and will not be considered further. The rare earths for the apatites, however, do fall into three groups on the basis of the total rare earth abundance and light rare earth enrichment. a) The phoscorite with - the lowest total REE of all rocks - the least light element enrichment b) The pyroxenites with - total REE variable, but mostly lower than the carbonatites - light element enrichment slightly greater than phoscorite - pronounced ytterbium depletion or luticium enrichment, see kick at bottom of curves c) The carbonatites with - high total REE - greatest light RE enrichment These groups can be seen to be different on the chondrite normalized curves (Fig.17), but if the original values are normalized against some internal standard, the differences are more pronounced. For example, in Fig.19, the original RE abundances have been normalized (divided) by the values for a Palabora pyroxenite (P53). The resultant lines reflect more clearly differences, both in the overall abundance of RE, and the light rare earth enrichment. It can be seen that the mean phoscorite values fall below the

117. RARE EARTHS IN PALABORA APATITES

10'

P15 P 0.~ Transgressive Banded carbonatite carbonatite

P 32 ~a to3 In phoscorite 2b d ~■ ` lose to pyroxeni c o % t m

•ti N 10a mean transgressive' whole rock •

io 10

La Ce Nd 5.11 Tb Yb Lu La Ce Nd Sm Eu Gd Tb Yt Lu

Phoscorite

La Ce Nd Sm Eo Gd Tb Yb Lu

— ----- Mean normalized curve• for transgressive carbonatite apatites Fig17

118. RARE EARTHS IN PALABORA WHOLE ROCKS

Transgressive • 1o' - — 10 Banded Carbonatite Carbonatite

P14 •50

— 101 •

10 — 10

La Ce Nd Sm Eu Tb Yb Lu La Ce Nd Sm Eu Yb Lu

Mean transgressive carbonatite (shown for comparison)

— 10'

Phoscorites Pyroxenites

— 101

10 10

1 La Ce Nd Sm Eu. Tb Yb Lu 1La Ce Nd Sm Eu Tb Yb Lu FIG.18

119. horizontal pyroxenite line and slope downwards on the light rare earth side relative to the pyroxenite. The mean transgressive carbonatite points similarly normalized are above the pyroxenite line (indicating higher overall levels of REE) and they slope upwards on the light RE side indicating the degree of light rare earth enrichment. Ideally, norma- lizing against RE patterns within the system should produce fairly straight lines and, whilst this is so for the phoscorites, the carbonatite points undulate more, possibly suggesting some other process which might be operating., For example, a Eu anomaly in one sample would show up as a strong peak or trough if normalized against samples without such Eu abnormalities. It is possible to use best fit (least squares) lines to display the comparative total RE levels and light RE enrichment for numerous samples. This has been done, norma- lizing the samples to the mean phoscorite (Fig.19B) which has the lowest overall RE levels and the least, light RE enrichment. It can be seen that the pyroxenites have higher and more variable values, with a tendency to be slightly enriched in the light RE (relative to the phoscorite). The carbonatites, both banded and transgressive, have strong light rare earth enrichment, greater than the pyroxenites and the phoscorites. This is well displayed in Fig.19B. Analysis of three carbonate samples, mostly calcite with a small amount of dolomite, (<5%) indicates that the apatite is an order .of magnitude more enriched in the light rare earths (see Fig.20). Apatite is the largest carrier of REE and its abundance overrides the contribution from other less common REE bearing minerals. The carbonatites with areas of 10% apatite will have half of the total REE supplied by the apatite. In the phoscorites and pyroxenites, the apatite levels are very variable and, with low carbonate concentrations, the whole rock values of REE largely reflect the percentage of apatite present (see Fig.18; phoscorite sample P1 has much less apatite than P48). Hanekom et al.(1965) favoured a metasomatic/hydrothermal origin for much of the apatite in the phoscorite and pyroxenite. This is not at variance with the observation 120.

F I g.19 APATITE R_EE_ NORMALIZED TO INTERNAL STANDARDS it 4.0 Best fit lines only 2.0 I

`` i ► I ► PYROXENITE P23a

► •r J '

APATITE PYROXENITE P31 MEAN TRANSGRESSIVE CARBONATITE s 1,; O

f~F 6 PYROXENITE P 53 - MICA APATITE ROCK P23b •° CC PYROXENITE P53

best fit line • '(HEAN PHŌSCŌRIfiE- " - ° MEAN PHOSCORITE 1.0 0.5

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho A. Apatite values normalized to Pyroxenite Apatite P 53 B.Apatite values normalized to mean Phoscorite Average apatite from transgressive carbonatite

Calcite • Baddeleyite --•••-- Chondrodite ---- Apatite ---

La-Ra Ce Pr N d Sm Eu Yb Lu of this study. At the Sokli complex (this work, Chapter 7) apatite is also introduced hydrothermally, not only into phoscorites, but also into the carbonatites where it super- imposes itself on early carbonate fabrics. It is apparent from this and the high levels of REE present in apatites, that the whole rock interpretations of rare earths in iso- lation are potentially misleading and may lead to erroneous conclusions. A short programme of EPMA (electron probe microanalysis) of some of the apatite grain mounts used for counting the sulphide inclusions shows a correlation between Sr and the REE - represented by La (see Fig.21). The range of strontium values for fine samples is plotted. The mean values of Ca, P, Sr, Na and the totals are shown below. Variation in the totals from one generation to another is also noticeable. This reflects the variations in Ca and P and concomitant variations of non-detectable OH- and F. The correlation between Sr and the REE is in part because of their similarity in ionic radius which is similar to calcium. The levels of Sr must, however, increase in the system, more being available for substitution in the apatite. 3.5. SUMMARY AND CONCLUSIONS Both rare earth and inclusion populations in the apatite at Palabora indicate the presence of different generations of apatite; whether the apatites are all magmatic or hydrothermal is a matter of conjecture. The lack of primary aqueous fluid inclusions is unusual, but not proof of a non-hydrothermal origin for the apatite. Hanekom et al.(1965) favouri a hydrothermal/metasomatic origin for the phoscorite, and thus presumably the apatite and also the bulk of the apatite/phlogopite introduced into the pyroxenite. The observations of this study are not at variance with this. Calcite balls in the phoscorite apatite may, by analogy with the calcite balls at Sokli, (see Chapter 7) be indicative of a hydrothermal/metasomatic replacement of carbonate. The carbonatites (formed after the phoscorites and pyroxenites) have apatites which are apparently early

123.

Sr VALUES OF PALABORA APATITES

Strontium v REL Creoresented 2 La)

Sample Sample Sample Sample Sample P1 P32 P53 P50 P15 Phosc, Banded Pyroxeni.te Transgressive et-bite 1.8' Sr ppm.

1.5

1.2

0 1000 2000 3000 La ppm. (from MS )

iiean and Standard Deviation of Aoatite Najors and :Minors r 1 I P1 P32 P53 P50 P15 N= 8 6 6 9 8 Na x nd nd nd .25 .18 d (.06) (.11) P x 41.43 38.94 38.41 40.28 40.13 (.35) (.37) (.60) (.57) (.72) Ca x 55.92 53.19 52.91 54.46 54.82 d (.51) (.65) (.99) (1.18) (0.91) Sr x 1.43 1.45 1.51 1.75 1.71 ð (.14) (.07) (.05) (.53) (.06) Total x 93.32 93.80 93.15 96.99 96.98 d (.80) (.31) (1:58) (1.71) (1.56)

N = number of points analysed or= standard deviation x = mean -.

FIG. 21

123 A phenocrysts (some may be xenocrysts from the phoscorite). A hydrothermal origin for these is more difficult to evoke; a magmatic origin seems more probable. The nature of the inclusion types, though not evenly distributed, implies that the formative medium would be the same for each type. The differences in rare earth patterns may, however, reflect some substantial difference in the formative medium, rather than just a decrease in temperature or a residual build up of rare earths. The data on this point are not conclusive. The elongate solid inclusions are considered to have formed by epitaxial growth with the apatite. The presence of thorianite and particularly copper sulphides implies that their elements were present in the system in sufficient amounts to develop minerals during the formation of the apatite. Why conditions were more favourable for the formation of sulphides in the phoscorite apatites than in the others is not clear. It is particularly puzzling because the phoscorite is less mineralized with copper sulphides than the later carbonatites. The primary nature of the inclusions does testify to the presence of copper in the system at an early stage. This adds weight to the thesis proposed in Chapter 2 that the copper is an integral part of the magmatism at Palabora and is not a late stage extraneous influx. Deductions on the origin of the complex from the REE data are not justified. Many complexes are studied using REE and the results are interpreted in the light of current theories of carbonatite genesis. The rare earth data is implied to fit such theories. Experimental work shows both hydrothermal and magmatic mechanisms for concentrating REE and light REE. Two points are however pertinent. The trends of increasing REE and Sr in the apatites at Palabora are in agreement with general trends in other carbonatites. Thus, although there are no rare earth minerals at Palabora, the Palabora complex is not significantly unusual in its REE geochemistry. •

124. Secondly, Wendlandt and Harrison's work (1978) indicates that H2O and especially CO2 rich vapour phases, are highly enriched in REE and light REE when co-existing with carbonate and silicate immiscible melts. Such vapour phases are also transporters of P205. The dangers of interpretation of whole rock REE determinations where such fluids have imperceptibly metasomatized the rocks cannot be over- emphasized.

125.

CHAPTER 4: MELT INCLUSIONS IN OLIVINE AT PALABORA

4.1. INTRODUCTION Fluid inclusions are apparently too small for study, or absent from the carbonatites at Palabora, but investigation of the olivines from the phoscorite (see Chapter 2) revealed the presence of primary and pseudosecondary multisolid inclusions of a type suggestive of a trapped melt. This chapter reports on the investigation of these inclusions, including the discovery that they contain copper' sulphides, and discusses their significance. 4.2. THE INCLUSIONS The olivine of the Palabora phoscorites is partially serpentinized. However, residual islands of forsteritic olivine remain. The inclusions are seen in these areas, and were studied using thin sections, polished thin sections, polished plates and grains immersed in oil (trytolyl phosphate). The inclusions are both irregular and rounded and are between 10 and 100 microns in diameter. The contents seen in transmitted light are various crystalline solids. Consistently present are carbonates (calcite and dolomite), a brown pleochroic mica and two or more opaques (see Fig.22 and Plates 11 and 12). The crystalline phases, particularly magnetite and phlogopite, are usually well formed individual crystals, but occasionally the mica and carbonate may be less well defined and consist of intergrowths of many small crystals. Rarely there may be no mica phase developed at all. In reflected light using oil immersion the opaques reveal reflections characteristic of sulphides and magnetite (see Appendix 1). The inclusions are not infrequently surrounded by irregular blebs and specks, as seen in many aqueous inclusions, which may have developed by necking down. The inclusion contents are remarkably consistent and this, together with their apparent primary and pseudosecondary

126. MELT INCLUSIONS IN PALABORA OLIVINES

A) As seen ill transmitted light

phlogopite I18gnetite

magnetite gopite

•

B) Aa seen ill dual reflected/transmitted light

yellow retlectiona

Fig. 22

127 habits, suggests that they are true inclusions of an original liquid; i.e. a melt, apparently of carbonatitic composition. It is interesting to note that the olivine residuals in the carbonatites also have the same inclusions. This provides some evidence that the olivines in the carbonatites were derived from the phoscorite as their corroded form suggests. 4.3. PREVIOUS REPORTS OF MELT INCLUSIONS IN CARBONATITES Previous reports of melt inclusions in minerals are numerous and in carbonatite complexes they are commonly mentioned in the silicate rocks. Panina and Shatskiy (1973) observed similar types of inclusion in pyroxene and nepheline of the Yessay complex (N.Siberia). These were probably silicate inclusions, but an opaque phase was also present. Some'of their inclusions were glassy and some were crystallized. Valyashko and Kogarko (1965) report heterogeneous, granular, solid material with or without gas and liquid, and occurring as tubular cavities within apatite. Rankin (1973) also observed crystallized and glassy carbonate and silicate melt inclusions in apatites from ijolites. Dawson et al.(1970) record inclusions in olivine from a mica dunite nodule from the carbonatitic pyroclastics of Lashaine volcano in N.Tanzania. The description of the nodule does not rule out a phoscorite origin (carbonate and magnetite are present in small amounts). The inclusions up to 20011 are larger than those at Palabora. They are of calcite, mica and black spinel, but the relative amounts vary, and monominerallic types occur. Calcite is the most common of these. Some cavities are reported as being empty but having possibly been filled with a vapour phase which has leaked. Interestingly, there is a zone of black altered olivine around the inclusions which may be a reaction with some volatiles from the trapped material.. It is pointed out that the contents of the inclusions comprise an assemblage with carbonatitic affinities. The conclusion concerning the inclusions is that they "result from the crystallization of volatile rich and alkali rich materials entrapped within the host mineral, the corollary being that 128. PLATE 11: Inclusions in Palabora Olivine

A. Plane of secondary or pseudosecondary melt inclusions in olivine fragment. Plane polarized transmitted light. Bar = 50 microns.

B. Typical inclusion showing opaque - magnetite (mt), phlogopite (p) and carbonate (c). Plane pōlarized transmitted light. Bar = 20 microns.

C. A large inclusion polished into for probing. Calcite (c), phlogopite (p) and magnetite (mt) were identified. Plane polarized transmitted light. Bar = 25 microns.

D. Inclusion with satellite inclusions. This is a typical fluid inclusion phenomenon. Phlogopite marked p. Plane polarized transmitted light. Bar = 20 microns.

E. Two inclusions. One has phlogopite (p) protruding into the olivine host. Plane polarized transmitted light. Bar = 100 microns.

F. Two adjacent inclusions. Plane polarized transmitted light. Bar = 100 microns.

129. PLATE 11

A B ilivp 7 •

41101. P

• C D

•

E F the melt from which the host crystallized must have been enriched in these substances". Inclusions thought to be representative of carbonatite melts have been found in apatite (Romanchev, 1972; Rankin and Le Bas, 1974A), monticellite (Nesbitt and Kelly, 1977) and also forsterite, (Khitarov et al.1978) though the detail of the contents of the latter is not mentioned. 4.4. COMPOSITION OF THE INCLUSIONS The inclusions were polished into and observed in reflected light. The opaque phases, magnetite and sulphides (chalcopyrite and rarely pentlandite?) could be identified optically. The larger polished inclusions could also be probed. Ten to fifteen inclusions were analysed, using the Imperial College microscan V with an EDS attachment (see Appendix 3). In the large inclusions the minerals could mostly be probed without any obvious interference effect from the underlying olivine or surrounding minerals. The carbonate portion of the inclusions was found to be made up of both calcite and dolomite, each with 1-2%Fe. Some inclusions have all calcite exposed on the polished surface, but most are all dolomite. Occasionally part dolomite and part calcite was recorded. It is conceivable that the mixed case is more common, but because the polished surface is only one plane through the inclusion, it is not possible to assess the relative abundances. The dolomite was apparently more common than the calcite, perhaps by as much as 2:1 (this estimate has been used in later calculations). The calcite and dolomite were always normal stoichiometric types; no mixtures were recorded. Though in some cases the carbonate could be seen to have specks in it and these areas gave traces of Cu, S, Fe and P on analysis. The ubiquitous mica in the inclusions is an unusual aluminium poor phlogopite (see Table 14). Aluminium poor phlogopites are common in many carbonatites and kimberlites,

131.

the A13+ being replaced by Fe3+. This produces anomalous red reversed pleochroism (Steinfink, 1962; Puustinen, 1973) and has been termed tetra-ferri-phlogopite by Rimskaya- Korsakova and Sokolova (1964). The phlogopites in these inclusions are consistently extremely impoverished in Al and, as Table 14 shows, this contrasts with the phlogopites interstitial to the olivine in the phoscorite proper. Aluminium poor phlogopites are only rarely less than 5%A1203, though Gittins et al.(1975) do report one with 0.2%A1203 from the Cargill complex, Canada. TABLE 14: COMPARISON OF PHLOGOPITE FROM INCLUSIONS WITH THOSE IN PHOSCORITE ROCK Phlogopite in Inclusions (N=9) Phlogopite in Phoscorite Rock (N=4) mean §t.dev. mean st.dev. Na20 < .20 - <.20 - Mg0 24.69 1.58 25.18 .23 SiO2 38.76 .48 40.62 .95 1(20 9.65 .77 10.57 .38 Fe0 17.92 1.54 3.38 .15 A1203 .40 .73 10.67 .47 TiO2 <.1 - .24 .05 91.63 .95 90.66 .32

The magnetite in the inclusions is also different from that in the rock. The small plates in the inclusions have low Ti values (< 1%Ti02), whereas those in the rock have between 2 and 3% TiO2 as well as exsolved ilmenite. The sulphides in the inclusions are only rarely exposed on the surface because of their small size, however, they are present in most inclusions, as revealed by oil immersion high power lenses using reflected light (see Appendix 1). When they are exposed by polishing, their small size makes an interference-free analysis impossible (x-rays are excited from surrounding minerals). Nevertheless, it is possible to detect copper-iron-sulphur phases and occasionally nickel-iron-sulphur. Reflected light suggests these phases are chalcopyrite and pentlandite. 132. From analysis of minerals and an estimation of the relative volumes of the respective phases, it is possible to estimate the mean composition of the whole inclusion. The dimensions of the phases present in 10 inclusions were estimated using olivine grains in oil; this allows the contents to be viewed from different directions. The ranges of wt% (minerals) and the overall calculated compositions are shown in Fig.23. It is difficult to deduce the size of the sulphides, and more importantly, it is not possible to quantify the relationship of Cu:Ni sulphides. The nickel sulphides were less common in the inclusions probed. 4.5. HEATING STUDIES Heating the inclusions in the normal way using polished plates in a Leitz 1350 heating stage did not produce conclusive results, partly because of problems in calibrating the instrument (Rankin, 1973) but mainly because the melting point of the inclusions could not be observed due to darkening of the olivine surrounding them above -750°C (temperatures may be -50°C - Rankin, 1973). The olivine gradually becomes darker, going from brown to opaque black if held at high temperature for a few minutes. The inclusions should ideally be heated slowly to allow equilibrium conditions to be reached at each temperature. The studies were also hampered by leakage of the contents. Nevertheless, some important observations were made:- a)The inclusions can be maintained at a temperature of 700°C for several hours without any change occurring. (Seven hours was the longest run). b) In short runs to higher temperatures, the carbonate was seen to melt, and a vapour bubble appeared in one inclusion at 900°C. c)Incipient melting of the phlogopite was observed, the edges becoming rounded as it was digested by the melt; in one this started at 750°C. d)Magnetite is less ready to dissolve than the other phases. It was not seen to dissolve, but at high temperatures only a few minutes of observation time are available before the olivine blackens. 133. TYPICAL MELT INCLUSION IN OLIVINE FROM PALABORA

Estimated total composition:-

Tetraferri-phlogopite 30-45 wt% Mg0 13-9-19.8 wt% S102 11.6-17-4 K20 2-9 - 4-3 Magnetite (low TO Ca0 17-5-23.3 3-5wt% Mn0 01 Fe0 8-2 - 13-0 CO2 20-9-27-9 OH-IF - 3-4 Sulphide -02 -1 wt% Cu 700-3000 ppm Carbonate 40 -60 wt % Ni up to 1000 ppm?

Unidentified specs CALCITE DOLOMITE S 700-3000 ppm. in carbonate. 3 P, Fe & S detected Average value Cu in other carbonatites = 2.5ppm. (from Gold.D.P 1963) 10jum I Fig. 23 PLATE 12

A. B.

An inclusion in olivine seen in transmitted light (A) and reflected light CB). In A the opaque is black, whilst' in B chalcopytite (white) and magnetite (yellow) can be distinguished. (Under the microscope these reflections were:- chalcopyrite (yellow) and magnetite (grey). The colours reproduced here are not true.

c .

•

Inclusion in olivine from Sokli phoscorites. The con tents are similar to those at Palabora. Opaque phase (black), tetra-ferri-phlogopite (brown) and birefringent carbonate (c). Note areas extending from inclusion, suggesting olivine deposition from the inclusion contents.

135. e) The olivine host next to inclusions melted into the inclusion at 1000°C, suggesting that some olivine was deposited on the inside of the inclusions from the melt when it originally cooled. 4.6. SIMILAR INCLUSIONS FROM OTHER COMPLEXES (THIS WORK) This study has revealed similar inclusions in phoscorite olivines from the Sokli complex and also the Bukusu complex. Those at Sokli are remarkably similar (see Plate 12C), whilst those at Bukusu are more complex, the phiogopite being less common and a sodic amphibole found instead. This probably represents increased levels of Na over K in the melt. Apatite is also present in the inclusions at Bukusu and the olivine is full of symplektitic magnetite, making interpretation of the inclusions more complex than at Palabora or Sokli (see Bell et al.1975). There are no sulphides in the inclusions at Bukusu, but once again, the rare phlogopite when present is Al poor and the magnetite is low in Ti; both these by contrast to the minerals in the whole rock. 4.7. CONCLUSIONS These inclusions are thought to represent high temperature melts (greater than 800-900°C) trapped by the growing olivine. It is,probable that they represent the earliest formed carbonatite melt at Palabora. (It is, however, conceivable that the olivine crystallized from a silicate melt which co-existed with a small amount of immiscible carbonate.) The heating observations suggest that the melt was capable of dissolving at least some olivine. Experimental work by Wendlandt and Harrison (1978) in the system K2O-A1203-Si02-0O2 shows that at 1200°C the quantity of silicate in two immiscible liquids (carbonate/silicate) is dependent on pressure. The silicate melt at 20kb can dissolve 28wt% carbonate, but this falls to 18wt% at 5kb. The co-existing carbonate melt contains less than 5wt% silicate and changes less with P than the carbonate in the

136. silicate melt. It may thus be possible to produce immiscible carbonate drops in the silicate melt as it cools, the pressure df intrusion having subsided after emplacement. Wyllie (1966) and Franz and Wyllie(1967) point out that forsterite could precipitate from carbonatite magmas, but at lower temperatures it would be unstable, reacting with the CaCO3 rich melt to form monticellite. However, the quantities are likely to be small. Nesbitt and Kelly (1977) found forsterite preserved in apatite grains at Magnet Cove, but the carbonatite rocks only contain monticellite, apparently a product of the breakdown of early forsterite. At higher temperatures it would thus be possible to precipitate small amounts of olivine from a carbonate magma, but the olivine would probably settle quickly. The resultant cumulates could be streaked into position to form the banded phoscorites as seen in many complexes associated with the early carbonatites. The close association of the olivine bearing phoscorites with the carbonatites and the presence of interstitial carbonate in the phoscorite does suggest that the olivine was intimately related to the carbonatites and crystallized from magmas of carbonatite composition. It is important to note, however, that the overall composition of the inclusions and the melt they represent, is quite different from that of the phoscorite. In particular there is little or no evidence of F, P, Zr, Ti and Al in the inclusions, yet these are all represented in the phoscorite. These elements may have been introduced later into the crystallized rock by hydrothermal/metasomatic activity. The euhedral form of many olivine crystals and their relationships suggests that the olivine crystallized early and may have been a cumulate from an early carbonatite magma. The origin of the phoscorites in the light of these inclusions and other mineralogical and chemical data is further discussed in Chapter 9. The presence of copper sulphides in these inclusions is of considerable relevance to the genesis of the copper 137. ore deposit at Palabora. If, as is suggested here, these inclusions represent an early carbonate melt at Palabora, then the composition of the melt as shown in Fig.23 is anomalously enriched in copper. So, the earliest carbonatite which developed at Palabora, possibly by immiscibility, was already highly charged with copper. This effectively shows that copper mineralization is an integral part of the carbonatitic process at Palabora and that it has not been introduced into the system from an extraneous source by late stage circulating hydrothermal fluids. The composition of the 'melt' is also of interest. It is similar to that of the transgressive carbonatite, but a little more Mg rich. Some unknown quantity of olivine should be added to the figures to produce true melt compositions to account for olivine deposited on the inside of the inclusions which dissolves when the inclusions are heated. The melt is noticeably potassic. Na was not detected in any of the minerals; the K:Na ratio is at least 10:1 (from detection limits). It should be pointed out that the fenitization at Palabora is largely potassic with an aluminium contribution (Hanekom et al.1965). This however, raises the question of water: the melt inclusions are apparently quite dry. There may be small pockets of aqueous fluid between the minerals in places, but there has been no clear observation of this. Some of the satellite ultramicroscopic inclusions that surround many melt inclusions may also be aqueous. Apart from this, the phlogopite is the only mineral which contains water, and this would only contribute 2 or 3% H2O to the total melt. The explanation for this may lie in the absence of Zr, P, F, Ti and Al in the inclusions. It has been seen in some experimental immiscible systems simulating carbonatite genesis that 3 phases may be present (Koster van Groos and Wyllie, 1973). These are a, silicate rich liquid, a carbonate liquid and a vapour phase with appreciable H2O and CO2. The latter phase at Palabora could be responsible for introducing the above mentioned elements.

138. The copper in the system would appear to be closely related to the carbonate melt, at least at the time of the olivine formation. The levels of copper are, however, an order of magnitude lower than the values in the transgressive carbonatite (which may reach 1 or 2% in places). The copper must have somehow become concentrated in the residual fraction of this early carbonatite magma. The formation of the banded carbonatites, only weakly mineralized with copper, may have been active in concentrating copper in the residual fraction later to become the transgressive carbonatite.

139. CHAPTER 5: COPPER RICH AQUEOUS ALKALI CARBONATE INCLUSIONS IN PYROXENES FROM THE GUIDE COPPER MINE, PALABORA

5.1. INTRODUCTION The Guide copper mine is an obsolete mine which exploited copper mineralization in the Kitcheners Kop syenite/feldspathic pyroxenite plug; a small diatreme of Palabora, situated about 5Km north west of the Loolekop centre (see Fig.24). The mine workings are inaccessible and the surrounding exposure is extremely poor. The situation was much the same when Shand described the deposit in 1934. Hanekom et al.(1965) mention some trenches dug over the area and present a map (see Fig.24). Kitcheners Kop (kop = hillock) is actually the syenite which sits between the horns of the pyroxenite body. The samples for this study were kindly provided by S.Eriksson who has been investigating the petrogenesis of the Palabora complex (Eriksson, 1978). The samples are from the old mine dumps. Shand (1931) describes the feldspathic pyroxenite as a coarse grained rock of large diopside crystals with interstitial K-feldspar and copper sulphides; bornite and chalcopyrite. He could find no signs of alteration and therefore assumed that the sulphides were primary. Indeed, the texture has a convincing cumulate texture as suggested for all the pyroxenite at Palabora by Eriksson (op.cit.); the sulphides being essentially intercumulate with the feldspar (see Plate 13A). Hanekom et al. (op.cit.) records accessory biotite, which may form nodules, and also sphene, apatite and vermiculite in the rock. He also notes that the pyroxene phenocrysts contain inclusions of sphene, grains of apatite, calcite, biotite and opaque ore. Eriksson (pers.comm.1978) has shown by EPMA that the diopside pyroxenes are zoned and more sodic than the diop- sides of the main Palabora pyroxenite. She prefers a cumulate origin for the rock, with the sulphides being immiscible and forming as an intercumulus liquid. Abundant aqueous inclusions are present in the pyroxenes. This is of considerable importance, especially since 140. THE GEOLOGY OF THE GUIDE COPPER MINE N

•

c•

•e•• •w . . •• • •• • . • • . ■

50m

Guide Mine v 4 0

• KEY

X Jr* Oolerite * X X• • ti Qtz-fetdspar vein. Diabase I vv I v vv Syenite Pyroxenite

1 Trench 0 Old working Shaft

0$ Borehole Modified after Hanekom et al. 1965 FIG. 24 141. they contain opaque daughter minerals which on later investigation proved to be copper sulphides. 5.1.1. The Sulphide Assemblage Although other authors (op.cit.) have mentioned that the sulphides at Guide are interstitial to the pyroxene phenocrysts, careful observation reveals that their primary intercumulate origin is by no means conclusive. The sulphides in the samples studied are predominantly bornite with subordinate patches of chalcopyrite. The two sulphides show mutual boundaries with each other; there is no sign of replacement. Chalcopyrite may be found as exsolution flames in the bornite, but this is not ubiquitous. Specks of galena are occasionally seen associated with the copper sulphides. The sulphides appear to be of one generation. The sulphides, when present, are essentially interstitial to the pyroxene, but their relationship with the feldspars is in part at least, one of replacement. Some samples have sulphides with diamond shaped feldspar residuals, suggesting replacement along cleavages (see Fig.14A). Sulphides may have preferentially replaced the feldspar, leaving the pyroxene phenocrysts as islands in what appears to have been an intercumulus sulphide liquid. The sulphides may occupy cracks in fractured pyroxenes. There are no signs of embayed or irregular replacement of pyroxene by sulphides. Whilst such replacements and fracture filling could be possible with a remobilized intercumulus sulphide liquid being pressed into certain areas, a hydrothermal origin or partial remobilization cannot be ruled out on the basis of the mineralography. The distinct lack of alteration is, however, a strong case against such hydrothermal action, unless the rock minerals were practically inert to the aqueous fluids concerned.

142. PLATE 13: Inclusions in the Guide Mine Pyroxenes

A. Diopside pyroxene crystals (py) with interstitial orthoclase feldspar (f) and sulphides (opaque - S). Plane polarized transmitted light. Bar = 3mm.

B. Typical inclusion inyroxene with aqueous solution (aq) vapour bubble (v), a strongly birefringent solid with RI as H2O in one direction (b), possibly kalicine; an unidentified non-birefringent phase (n); an opaque giving reflections indicative of chalcopyrite (cp) and a deposit on the inclusion walls (d. The area marked X appears to be a very weakly birefringent solid. This may be due to the deposit on the walls, the central cavity being aqueous filled. Plane polarized transmitted light. Bar = 50 microns.

C. Zoned pyroxene as shown in Fig.25. The white area on the right has elongate tubular inclusions, whilst grey area on left is a green zone with fewer large irregular inclusions, one of which is arrowed. Plane polarized transmitted light. Bar = 100 microns.

D. Same inclusion as C, showing aqueous (aq) phase, vapour (vp), birefringent (b) and non-birefringent (nb) solids and a triangular opaque, probably chalcopyrite (cp). Plane polarized transmitted light.

E. Two inclusions in Guide pyroxenes showing more solid contents, both birefringent and non-birefringent. Note aqueous/vapour phases and triangular opaque (o). Transmitted plane polarized light. Bar = 10 microns.

F. Two inclusions with a larger portion of aqueous (aq liquid, one birefringent phase (b) and an opaque (o). Transmitted plane polarized light. Bar = 30 microns.

G. Opened inclusion under SEM. Chalcopyrite daughter is arrowed and a close-up of it is shown in inset (cp). Bar = 1 micron.

H. Opened inclusion with well formed crystal (k) which only gives potassium x-rays and is probably KHCO3. A small crystal of apatite (op) is also present. Pyroxene fragments (px) have come from the pyroxene host. SEM photomicrograph. Bar = 2 microns.

143.

PLATE 13

A B

E F

PLATE 14

A. Sulphides, chalcopyrite (light yellow) and bornite (dark yellow) interstitial to pyroxenes (p) but replacing feldspar (f - diamond shapes). Plane polarized reflected light. Frame length = 3mm.

4 R

B. An inclusion in pyroxene from Guide in transmitted light (left), note opaque (black) and vapour bubble (v). The same inclusion in reflected light is shown on the right. The opaque is now yellow/white and is identified as chalcopyrite. The opaque is 10 microns across.

Alt

C. Similar to B above, but the opaque (o) is shown in reflected light to be part chalcopyrite (yellow/white) and part bornite (yellow). The opaque is 15 microns across. 145. 5.2. INCLUSION TYPES The inclusions in the diopside were studied using polished thin sections, doubly polished plates and as grains in oil (see Appendix 4). Some inclusions were opened and daughter minerals identified where possible using SEM (see Appendix 2). The inclusion population can be divided into 3 types, as shown in Fig.25. The main characteristics observed using the above mentioned techniques are briefly summarized below. 5.2.1. Type 1: Solid Inclusions (Fig.25A) Solid inclusions of sphene, apatite, calcite, orthoclase, biotite and chalcopyrite are found as well formed crystals and also as irregular specks. The solid inclusions are obviously primary and are interpreted as being captured solids. Acicular apatite crystals are common and their habit is suggestive of crystallization from a melt (Wyllie et al.1962). 5.2.2. Type 2: Secondary Aqueous Inclusions (Fig.25A) These inclusions are found in planes typical of secondary inclusions (Roedder, 1967). They are aqueous with a small vapour bubble and two or more daughter minerals; usually one triangular opaque and one irregular colourless birefringent solid. Some are all aqueous with no vapour bubble or daughter minerals. Many pyroxenes have planes of secondary inclusions, which reach to the edge of the pyroxene crystals, but the surrounding feldspar is unaf- fected. 5.2.3. Type 3: Aqueous Multisolid Inclusions (Fig.25A) This type of inclusion is the most common in the Guide pyroxenes. They have an aqueous fraction with a vapour bubble, but are characterized by numerous daughter minerals of colourless birefringent and non-birefringent solids. A triangular shaped opaque is invariably present which gives yellow reflections characteristic of chalcopyrite in reflected light (see Appendix 1 and Plate 14B and C). There is commonly a deposit on the inclusion walls of non-birefringent material which appears to have been deposited from the trapped microsystem (see Plate 13B). 146. INCLUSIONS IN PYROXENES FROM GUIDE MINE A. INCLUSION TYPES

1 Captured IOl1da ot eal.cite, sphena, apatite, pyraxeae, ~z, taldspar am CulFe sulphides. 4l1li 0/ ' 0 /00 2 PlaM. ot lecotldary aqueoua 1nclua1oUB am aqueous/vapour ~ ~ ~-=:>c;:6"" 1nclaa1oUB w1 th ODe or IIIOre Cl solid daughter phasea. Cbalco Prrite 1a comoan in :za%l7 ;llanea. G:!> ~~~~-. ~QO::::::::>~ , 3a Pr1mt.ry aqueous/vapour 1Ml- usiona w1 th three or l.a. daughter m1ner&ls. Cbalco- CciLJurle... depollit~B @ ~f?B~ • pyrite 1nvariably pneent on inclusion T t and oa. or two colourlesa ....u.. . :z:::=::r (0 ) '2) pba:ses. Depont on boat ~Coa" .. B am ( e 9 . ) \/ILll. il common. ~. ) SZ :I "

3b !tllU aal1d 1ncluaioUB (IIIOre B~ Z.. 0" -=::~ than 3 daughter III1nerale) W \11th a.queoua/TapOUl' fraction. Chalcopyrite common. (B~ HB~0 o 13 ~

3C Pr1mllr1' 1nclus1oUB aaeac1at- ed vi ;~ t.h or obviously i.ncorp- 0 orat:1.ll3 aollda ot typ. 1. 0

V 4 ~N- -::~~ ~a.ct

B =Bintr1ngent, NB =Non Bintrlngent, WB =Weak a, &'1. =Aqueous 1'J.u:1d, 0 =Opaqua, v =Vapour.

B. MINERALS IN TYPE 3 INCLUSIONS

SHAPE OP'rICJ.L CIIAJU.CTSRISTICS S.s .M./PROB& IDENTInCATIOH DAUGHTE.R/CAPTURED C Birefringent. RI 8&me It only KHCO) (1) Daughter c:?:...... 0 as aq in ona direction aJ LlJ R Isotropic KCl (some Ha) Sylvita Daughter and deposit collm)n 1n open from solution inc!usioUB C Stroll« bintlngence Ca Calcite Captured (&daughters?) 0, I C Biretr1ll8'ent, bigh Ca,n,S!. Sphene Captured <:> reli.t f =03 ~ C WB or :m K,Al,Sl. Orthoc:J.ase Daughter & captured. ~ '1 Not ident1t1ed P Ca Apatite Daughter & captured.

C Deposit on walls. WB or' '1 '1 Daughter deposit ~·O) NB.

VC Opaque, yallov in Cu, Fe, S. Cbalcopyrt te Daughters ( a:x1 A reflected llght captured 1) • R Opaque, grey in re- Fe Hagnsti te '1 ? ~ • tlected llght. Fe, Ni, Cr,1n Oxide 1 ? approrlmtely • equal amounts Fig.2S

1 I. 'j The inclusions are mostly between 5 and 50 microns across, but may reach up to 100 microns or more. The shape is usually irregular, but some smaller inclusions are tubular and aligned parallel to the c-axis of the pyroxenes, in this case they may be only a few microns wide. This is good evidence for their primary origin, especially when these small tubular inclusions are associated exclusively with a central light coloured core to the zoned pyroxenes; larger irregular shaped inclusions of similar contents being associated with the outer dark green pyroxene rim (see Fig.26 and Plate 13C and D). In some cases there has been considerable necking down, but this is not extensive. Of this type of inclusion three categories have been defined: 3a)Those with 3 or less daughter minerals 3b)Those with more than 3 daughter minerals 3c)Those which are associated with, or have obviously incorporated, the trapped solids of Type 1 The division between categories 3a) and 3b) is largely arbitrary, but serves to illustrate a real difference between inclusions packed with solid material and those with considerably less solid material (see Fig.25A). Those of category 3a) have few daughter minerals and are similar to the secondary Type 2 inclusions, but a deposit is invariably present on the walls and they appear to be primary. They are not as common as category 3b). Category 3b) inclusions (arbitrarily those Type 3 inclusions with more than 3 daughter minerals) are mostly packed with solids, the majority of which are either weakly birefringent, or non-birefringent. One or two strongly birefringent solids are also present. Chalcopyrite is rarely absent. In many inclusions a colourless weakly birefringent monomineralic mineral is found occupying up to one quarter of the inclusion and in intimate contact with the pyroxene. The total aqueous vapour portion of these inclusions is variable, but commonly occupies less than of the inclusion, the remainder being solid packed crystals. A deposit on the inclusion walls is common. 148. PRIMARY INCLUSIONS IN PYROXENES FROM GUIDE COPPER MINE

ZONED MC/SENS CRISTAL SHOWING POINTS ANAL/SED & SCHEMLTICALLI,THE t3RPHOLOGY OF INCLUSIONS. •

1. 19

Green zones

1.60 13.8 1.50 13.6 1.40 13.4

1.30 13.2 1.20 13.0

1.10 12.8 % Ne20 1.00

.90 12.1. .80 12.2

.70 12.0

.60 11.8 .50 11.6

.40 .4

.30 11.2 .20 11.0 NON ALIGNED INCLUSIONS w~ ALIGNED INCLUSIONS

Fig. 26

149 Category 3c) inclusions (those Type 3 inclusions associated with, or obviously incorporating, the trapped solids of Type 1) are frequently found. Small aqueous inclusions associated with extremely large trapped solids are easy to recognize, whilst those with smaller trapped solids are more difficult. It is conceivable that some of the 'daughters' in those inclusions packed with solids are in fact trapped Type 1 inclusions which have been incorporated in the inclusion. SEM work reveals large irregular crystals of calcite and sphene well buried in the walls of some inclusions. 5.2.4. Inclusions in Orthoclase The feldspar has a lot of material trapped in it, much of which seems to be crystallographically controlled plates of mica. Secondary aqueous inclusions are common, but are usually extremely small. Some are associated with opaque specks of copper sulphides. Inclusions which might be classed as primary are extremely rare. One or two have been observed.• These were aqueous with a vapour bubble and with two or more crystalline phases. A small opaque triangular solid is present in most of those seen and also a large weakly birefringent colourless daughter, oblong in shape. Irregular rounded greenish coloured minerals with RI greater than feldspar were inconsistently present. These are thought to be pyroxene trapped by the feldspar. Some inclusions contain 2 or 3 of these, whilst others have none. Some inclusions in the feldspar have a deposit on the walls. 5.2.5. Similar Inclusions from the main Pyroxenite at Palabora Numerous samples were studied from all over the Palabora pyroxenite and it was found that nowhere are the inclusions so well developed as at Guide. Inclusions similar to those at Guide, but much smaller, were seen in some cases. An aqueous/vapour fraction was present, but the inclusions were mostly too small and rare to allow serious study. Bire- fringent and non-birefringent daughters can be seen in some

150. inclusions from Sample P59, as well as small opaque daughters which could be Cu sulphides. 5.3. IDENTIFICATION OF DAUGHTER AND TRAPPED PHASES The optical characteristics of the daughter and/or trapped minerals were recorded where possible, Some inclusions were then broken open and investigated using SEM/EPMA (see Appendix 2). Inclusions with many more solids were polished into and analysed using EPMA (see Appendix 3). The identified phases resulting from this combined approach are summarized in Fig.25B. The most interesting observation is the presence of daughter minerals of copper sulphides, which in reflected light yield yellow reflections typical of chalcopyrite and occasionally orangy-brown reflections thought to be bornite. In one case (see Plate 14C) a daughter of bornite had exsolved a small portion of chalcopyrite, the differences in reflection colours being easily apparent, despite viewing them through pyroxene (see Appendix 1). SEM confirmed the presence of minerals of copper, iron and sulphur in the inclusions (see Plate 13G). The weak birefringence, together with the poorly formed, colourless nature of some of the phases makes conclusive optical identification impossible. However, the SEM and EPMA work indicates that orthoclase-feldspars, sphene and apatite, calcite and even one instance of quartz are present. The daughter mineral which tends towards an oblong shape is common and has an RI less than pyroxene; it is probably orthoclase feldspar. The much higher relief of sphene and its high birefringence allow it to be identified as a common trapped solid (Type 1), but when in an aqueous medium it is not easy conclusively to separate this from calcite, despite the lower RI of the latter. Both occur as trapped solids and may not be true daughters in the aqueous inclusions. In some cases a highly birefringent mineral can be identified which has an RI the same as the aqueous medium in one direction. On rotating the inclusion in polarized light the mineral disappears. This is consistent with the 151. characteristics of the alkali bicarbonates (Rankin and Le Bas, 1974B). One daughter mineral seen using SEM gave an x-ray spectrum of predominantly potassium (see Plate 13H). The only other peaks present were subordinate and consistent with the diopside host upon which the mineral was resting. There was no aluminium present in the spectrum, excluding the possibility of the mineral being orthoclase. It is concluded that the mineral is probably kalicine (KHCO3), being non-detectable by EPMA. The optical the HCO3 characteristics of this are consistent with the disappearance in some orientations of a highly birefringent mineral in an aqueous medium. The presence of primary calcite in the environment during pyroxene growth indicates that HCO3 ions could be feasible in residual aqueous solutions. Sylvite was.also noted as small cubes during SEM work and this would equate with the occasional cubic colourless mineral seen in some inclusions. Potassium and chlorine were detected on many of the other minerals seen during SEM work; this is thought to be a precipitate from the evaporation of the aqueous solution on opening the inclusions. Some Na was associated with these deposits, but no NaCl cubes were seen. Investigation of the walls of many inclusions using the SEM microprobe revealed no deviation from the normal diopside composition. The deposit on the walls of many inclusions is therefore thought to be essentially pyroxene of similar composition to the host. Attempts were made to crush the inclusions in acidified glycerine between two glass slides (see Fig.46) with a view to observing the reaction, if any, of the acid with the daughter minerals under the microscope. Carbonates could be readily identified in this way. On placing the crushed pyroxene grains into the acidified glycerine, there was considerable reaction, even before crushing from fractures and cracks, suggesting some carbonate material is present in these. Apatite and calcite trapped phases will also produce some CO2. Although it was possible to break individual inclusions and observe CO2being produced from the 152. contents, it was not possible to identify the individual daughters responsible (most of them do not react). When crushed in ordinary glycerine, the vapour bubble does not expand, indicating that there is no gas (e.g.0O2) under pressure. 5.4. HEATING STUDIES Heating studies were only conducted on primary Type 3 inclusions in the pyroxene which could be resolved when in the heating stage (see Appendix 4). Those chosen did not contain any extremely large phases which were obviously trapped. The results are not conclusive since it is very diff i- cult to observe phase changes. The sequence of changes on heating is displayed in Fig.27. The vapour bubble usually homogenizes between 200 and 250°C, before the bulk of the solids starts to dissolve. When the solids start to dissolve, the resultant liquid becomes progressively darker, and in the heating stage appears translucent or even opaque. A second vapour bubble develops in some (see Fig.27, column 2, 325°) and this may not disappear until approximately 700°. The inclusions eventually homogenize at around 1000°C or a little higher. The dark 'melt' may clear a little and then start to digest the pyroxene host. Temperatures given in Fig.27 are only a guide because the heating stage is subject to considerable errors at high temperatures (Rankin, 1973). Further, the inclusions were heated stepwise up to 1000°C at 50°-100° intervals and held at the predetermined temperature for between 10 minutes and 2 hours. These times are probably insufficient for complete equilibration of the contents at any given temperature. Most inclusions studied were held at 1100° (-1000) for periods up to two hours, then rapidly quenched in air to room temperature over a period of 5-10 minutes. The contents of the inclusions appeared to form a speckled isotropic glass. In one instance, however, this was seen to devitrify 5 minutes after reaching room temperature, producing what appeared to be an aqueous liquid (Fig.27, column 1) which occupied minute cracks in the 153. HEATING STUDIES FROM TYPE 3 INCLUSIONS. IN PYROXENE

NB 25 u 10u 20u 250'

Vapour bubble goes Vapour bubble goes

350' B VM 400'

New vapour bubble forms 600'

BOO'

980'

Melt digests host pyroxene Homogenization Homogenization 1150'

Homogenization incomplete Melt digests host pyroxene Melt digests host morons_ Homogenization

AIR QUE1CH AIR QUER AIR QUENCH AIR QUE:CH * 20°

Some crystals form and aq/v reappears. • minutes later KEY

NB - Non Birefringent WB - Weakly • Fig.27 B - Birefringent ✓ - Vapour sq - Aqueous solution (grades into I malt' ) Glass devitrifies,aqueous O - Opaque phase remains filling fracturse. NOTE - Temperatures of phase changes are only approximate; many hours are required to reach equilibration in such high temperature systems.

154. devitrified glass, producing a semi-opaque granular effect on the rim of the inclusion. Another inclusion on cooling formed a more crystalline product with a distinct aqueous fraction and vapour bubble (see Fig.27, column 4). In some instances inclusions heated to 1300°C developed two liquids with a well pronounced meniscus between them indicating immiscibility (see Fig.28). In two of the recorded instances shown in Fig.28 one of the liquids had bubbles in it (possibly globules of the other liquid) which dissolved or homogenized on heating. On cooling this same liquid deposited pyroxene(?) in optical continuity with the host (see Fig.28, column 1). When cooled to room temperature, the residual portion of the liquid which deposited pyroxene crystallized to a birefringent mineral or mineral mass. The other dominant liquid produced a non-birefringent glass(?). Such observations confirm that the inclusions represented melts, but interpretation of the phase relations at this stage is necessarily speculative. The fact that one of the immiscible liquids crystallizes to a birefringent mineral suggests that it may not be a silicate melt. Car- bonate melts tend to crystallize to carbonate minerals, carbonate glasses being unstable (Rankin, 1973). It is tentatively suggested that such an immiscible melt may have been present at the Guide diatreme. Significantly, there were no observations of immiscible sulphide melts in the inclusions studied. Immiscible sulphide melts have been observed in silicate melt inclusions in olivine from basalts (Clocchiatti et al.1978). If the sulphides at Guide had indeed separated from the silicate melt, then one might expect to see some indication of sulphide immiscibility in these sulphide bearing inclusions when heated. This was not seen. It has not been possible to clearly monitor the behaviour of the sulphides during heating runs. They do not dissolve at lower temperatures (less than 600°C) and at higher temperatures the darkening of the melt mostly inhibits observation of such small opaques. 155. INSTANCES OF HIGH TEMPERATURE IMMISCIBILITY IN GUIDE INCLUSIONS - 20·C opaques NB ®---' ~ 20'C c- ___ ,,, ...... C,.B_~ .qV ~-L- ~ aq C~ ~ ~ B 200·C 240'CC NB [ lNB ) aq C- -0 ag ~ 3S0'C (; 350·C , NB --C . - g C l aq ~ ~

COOLt20·C , NB L ~ - ~ . ~----,'.-. '~~-'"aq ® .' 'd~~~-;'5)J ~ ... ~ ..•..- .... -.. -.. .. ~ ... -... ~-'"':'- .... - .. ~ .

SOo-C SO~C~C -- - ~ . ;--'\.--NB ~.' B [~.~~ '- - =- :;;.- - ~ ; ->:.<-t.;" . :.?) .~.,.. Z---"":,Celt ? '7 - -~.' - ' .

700·C 900·C

, # •• ;..-

~~~~.,;q;; (52-1".~ ;.~~. I .':--...:,~ .. :., .1"": . r I • c- .::• ..!'. .- , - " .,;;...--'- ...... ',t;" -.".. ,'.. " . --...( - , ,- ."",..- melt ? . - .. '- / 1300·C 1300·C ObUb!e!? ! . Cl 0) -): b t. V? C:~i~ 0 ~LiqUid) liquid \:,meruscus Liquid 132~Cf:Ies go ( ~O ) COOLT[ COOL TO 900·C lOOO·c 0 Q f (J 0 :) Pyro:cene deposited 0 CJo. . . continuous with host ~~T[ COOL TO 1300'C _ 2 ~ 20·C .. .. 0 -) (" c-·=~. . . ) :::, U~( ". , ---.~

COOLTr i\: f\"i-- ~ -:.; •~ - . 'j.,/ 'A ~ aq = Aqueous pha se 20·C B ~'"~ • --,' '. ~ Cl V = Vapour I~~~' _-, ~t\ ~ 1: .'~ &. B Birefringent mineral ," \: r I... • = ;~c'.~ NB/' , .... NB = Non Birefringent solid '~/ ,~ ...... \, ~ \. . ~'.\),.-~.-; .l.:' ~

Fi g. 28 156. Leakage is common in many runs, indicated usually by a sudden escape of contents or appearance of a larger vapour bubble. Planes of new minute secondary inclusions may develop away from the leaked inclusions. It is possible that partial leakage occurs in other inclusions, possibly even in those runs presented here, where the leakage is gradual and does not give rise to a sudden change in the nature of the contents. 5.5. INCLUSION COMPOSITION AND IMPLICATIONS The primary inclusions in the Guide pyroxenes are thought to be portions of the parent melt from which the pyroxene was crystallizing. The exact composition of the melt cannot easily be deduced; however, some inferences of the likely composition can be made from the above described observations. It is probable that much of the weakly birefringent and non-birefringent material in the inclusions is feldspar. Much orthoclase feldspar was seen in the polished inclusions which were analysed by EPMA. This is not soluble at low temperatures, but gradually melts at higher temperatures to produce a melt capable of digesting the pyroxene. Relating this to the well defined cumulate textures in the rock it is possible to construct a picture of the crystallization process. The growing pyroxene crystals trap portions of the parent melt. Pyroxene left dissolved in the melt will be deposited on the inclusion walls as the inclusion cools. This may be the deposit seen in many inclusions. Gradually feldspars form in the inclusion, as they do in the intercumulus liquid of the rock. From the inclusion evidence this apparently leaves a substantial aqueous fraction with KC1(NaC1) and KHCO3(?) dissolved in it. The aqueous fraction would appear to be highly enriched in copper sulphides, judging by the presence of the chalcopyrite daughter minerals. Some of the secondary Type 2 inclusions may represent these residual aqueous fluids from the crystallization of the intercumulus liquid. The presence of 157. chalcopyrite in these has been noted. The chalcopyrite daughter minerals in these secondary inclusions are comparatively large and imply a high level of copper in the solutions. They are usually disphenoidal- tetrahedrons (triangles in transmitted light). In a typical tubular inclusion 5 microns by 25 microns the chalcopyrite daughter is a disphenoidal-tetrahedron of side 2 microns. This is equivalent to 3500ppm copper in the original solution. Such high levels of copper are probably the highest levels recorded for copper in aqueous fluid , inclusions. Eastoe (1978) records a fluid of 1900ppm Cu from inclusions in the Panguna porphyry copper deposit. An attempt was made to analyse the inclusions by crushing and leaching the cleaned pyroxenes. The leachates were analysed for Na and K by flame photometry. Blanks were run at every stage in the cleaning, crushing and centrifuging procedure. The K and Na values for the leachate were an order of magnitude higher than the blanks (see Chapter 7, Section 4 for details of method).

Sample P22 Ratio Na K Na:K Cleaned pyroxenes washed in DDWx .15 .22 Cleaned pyroxenes soaked overnight in DDW .30 .48 Washing and grinding empty pestle & mortar .25 .19 Pyroxenes (GCM 16) crushed and leached 6.00 5.75 1.06 Pyroxenes (GCM 17) crushed and leached 4.83 4.59 .95 Pyroxenes (GCM 16) recrushed and leached 1.85 1.10 1.68 Feldspars (GCM 16) crushed and leached 4.13 67.5 .07 x Distilled and Deionized Water However, the results must be viewed with caution. The freshly crushed and leached pyroxenes (with inclusions) give Na:K near to 1, but when the crushings are ground and crushed again, the levels of Na go up. This could be due

158. to the leaching of Na+ ions from the broken surfaces of the Na rich diopside. The K feldspar crushed and leached as a control produced very high potassium values although it contained few inclusions; K is possibly leached from the fresh surfaces of the feldspar. Such results invalidate the meaning of the Na:K ratio in the pyroxene; the values are unlikely to be representative of the fluid inclusions. For this reason, the deduction that the fluids are highly potassic is based largely upon the observations of the opened inclusions under the SEM. Not only are some of the daughter minerals potassic salts, but other minerals and even the walls of the inclusions give traces of K, Na and Cl. K is always much more abundant than Na in all the SEM work done. These observations are in stark contrast to the observations of aqueous inclusions in apatites from the Sokli carbonatite where the Na is always dominant, both in the daughter minerals, and in the deposit left from the evaporated solution (seen by SEM). These samples of apatite when crushed and leached show Na:K is about 2:1 (see Chapter 7). Analysis of inclusions from East African carbonatites (Rankin, 1973) show Na:K to be between 2.4 and 3.9. The only recorded examples contrary to this are two samples from a Soviet carbonatite (Evzikova and Moskalyuk, 1964). In this work leachates from inclusions in calcite and dolomite from late stage carbonatites gave K greater than Na, but it is not stated whether the inclusions are primary or secondary. A fluid inclusion analysis where Kis larger than Na is rare for fluid inclusions of any type (Roedder, 1972A), but such results might be expected from fluids associated with the late stage phases of K fenitization (e.g. Vartiainen and Woolley, 1976; Deans et al.1972). Fenitization is an indication of the type of fluids associated with alkali ultrabasic carbonatite complexes and may be variable with respect to Na and K. At Fen and Sokli there is both Na and K fenitization, whilst at Alno and Palabora it is predominantly potassic. Many observations of fenites have led 159. Woolley (pers.comm.1978) to believe that fenitization is mostly a sodic phenomenon, with a tendency to become potassic in its waning stages. There are however, complexes where K fenitization is more dominant and this has led Woolley (1973) to pose the question; "Are there magmas of differing Na:K ratios?" Dawson (1966) has also suggested this. Eriksson (1978) suggests from mineral chemistry studies that the cumulates of Palabora developed from a magma, low in Na and high in K, with kimberlitic affinities. The observations of possible melt inclusions with a high K:Na ratio and the aqueous inclusions at the neighbouring Guide copper mine with K greater than Na, together with the predominantly potassic nature of the fenitization at Palabora, are all in agreement with a derivation from a highly potassic magma. It is conjectural that the highly potassic nature of the Palabora system is in some way related to the anomalous values of copper. The differing behaviour of Na and K in geochemical systems (Shcherbina, 1963) can have profound effects on the migration of other elements. For example, K and Na have different effects on the solubility of the rare earth elements in carbonatitic systems (Sin'kova and Turanskaya, 1968) and also the transport and deposition of Nb and Ta (Aleksandrov et al.1971 and 1972). Dernov-Pegarov and Malinin (1976) observed differences in the solubility of Na and K carbonates which are relevant to some aspects of carbonatite formation. It is interesting to note whilst on this point, that the sodic and potassic fenites at Sokli (Vartiainen and Woolley, 1976) had different effects on the copper content of the host rocks. "There is no apparent trend of copper addition or subtraction amongst the potassic fenites, but with sodic fenitization the rather variable values of the country rocks are reduced to evenly low values of 30ppm or less." (Vartiainen and Woolley, op.cit.) Little can be drawn from such reports, excepting the suggestion that experimental work on the behaviour of copper

160. with solutions of Na and K chlorides and carbonates might reveal some interesting results; results that may throw some light on the anomalous enrichment of copper in some carbonatite complexes. Copper is known (from experimental work simulating the porphyry coppers) to be transported as chloride complexes (Crerar and Barnes, 1976). The fluid inclusion evidence suggests Na is the dominant alkali. The carbonatite system may however be substantially different. Study of the behaviour of Cu in alkali-chloride, carbonate, bicarbonate systems is considered worthwhile, but is beyond the scope of this work.

5.6. CONCLUSIONS Samples from the Guide Mine are copper bearing feldspathic pyroxenites. Quantities of chalcopyrite and bornite are found with orthoclase feldspar interstitial to pyroxene phenocrysts of apparent cumulate origin. Examination of the sulphide/silicate relationships in reflected light suggests that sulphides may have replaced intercumulus orthoclase rather than crystallizing from an immiscible melt. Fluid inclusions in the pyroxene support this concept. Primary inclusions in the pyroxenes are aqueous rich, copper bearing, highly potassic silicate melts. (Minor immiscible carbonate (?) droplets may also have been present.) They are thought to be the parent melt from which the pyroxene was crystallizing. Some inclusions have less solid material and more aqueous fluid. They have high levels of copper, judging from the large daughter minerals of copper iron sulphides. Many secondary aqueous inclusions have a copper iron sulphide daughter. From this complex range of inclusion types, it is possible to propose a scheme of mineralization at the Guide diatreme. Pyroxenes crystallizing from the copper bearing melt at Guide left a residual feldspar melt rich in copper and water. The intercumulate feldspar grew from this, yielding an aqueous, copper bearing, highly potassic chloride/bicarbonate brine. 161. This copper rich brine finally deposited sulphides whilst replacing feldspar. Some copper iron sulphides may have been deposited with the feldspar, but the textural relationships indicate replacement origin. The differences in the inclusion types are well explained by this hypothesis of development. The crystallization of the melt inclusions has also followed the same pattern, yielding a residual aqueous portion on cooling. This copper rich aqueous fraction is apparently the same as in some secondary inclusions. A lack of detailed knowledge of the geology, particularly the distribution of sulphides, and of the inclusion types at Guide, puts limitations on a thorough understanding of the process. The unusual alkali ratios (K.greater than Na) of the inclusions, together with the carbonate content and the levels of copper are, however, relevant to the problems of the origin of copper rich carbonatites at Palabora. There are, of course, some differences between the Guide rocks and those of the main complex. The main pyroxenite plug at Palabora is surrounded by a rim of feldspathic pyroxenite interpreted as a product of reaction with country rocks (Hanekom et al.1965). The diatreme at Guide is entirely feldspathic pyroxenite and may also be a product of country rock contamination of a pyroxenite magma. The pyroxenes of the main complex do not show zoning and are less sodic than the Guide pyroxenes (Eriksson pers.comm. 1978). In particular, there are no signs of interstitial sulphides in any of the pyroxenites other than Guide. These may exist at depth or could have formed at a higher level in the system which has since been eroded. There are nevertheless many similarities between Guide and the main body; the rocks are clearly related to the same primary magma. They both developed a residuum rich in copper. The copper would therefore seem to have been an integral part of the early pyroxenitic magma. The presence of calcite and KHCO3(?) in the inclusions at Guide is an indication of the carbonatitic affinity of 162. the pyroxenite at Guide. Hamilton et al.(1979) have pointed out that experimental immiscibility between CaCO3 rich carbonatites (as at Palabora) and silicate melts may not be so easily produced as immiscibility in alkali carbonate systems. The melt inclusion in the phoscorite suggests that the Palabora carbonatite melts were predominantly alkaline earth carbonates (see Chapter 4). Nevertheless, the observations of immiscible melts at high temperatures in the Guide inclusions tantalizingly suggest that immiscibility may play a part in the origin of Palabora carbonatites. The fluid inclusions at Guide thus provide evidence for (1) the presence of copper in the primary pyroxenite system, a better understanding of mineralization; (2) the highly potassic chemistry of the mineralizing fluids at Guide and, (3) a suggestion that the copper rich carbonatites at Palabora may have arisen from the pyroxenites by liquid immiscibility.

163. CHAPTER 6: HYDROTHERMAL ORE DEPOSITION AT THE SOKLI CARBONATITE, FINLAND

6.1. INTRODUCTION The absence of primary fluid inclusions at Palabora directly related to the ore forming events disallowed study of the actual ore forming fluids. Knowledge of the nature of these fluids was highly desirable for a full understanding of the process. For this reason other copper bearing carbonatites were investigated to find a deposit for study, in which fluid inclusions were apparently related to the mineralizing process. Material from Bukusu, Great Beaver House and Sokli had such fluid inclusions, but only at the latter was sufficient material available for a thorough study. The Finnish steel company, Rautaruukki Oy generously permitted a visit to the complex in N.Finland (see locality, Fig.29) and provided access to considerable quantities of drill core.' The deposit is currently being investigated as a potential apatite deposit, but U, Th, Nb, Ta, Mn and Cu may also be of interest. A visit was made to Sokli in August, 1977. Little was gleaned from the surface outcrop which is virtually non- existent due to weathering and glacial drift. Nevertheless, an extensive drilling operation provided ample material for the study. Six boreholes between 100 and 300 metres long were logged and sampled in detail. A number of other boreholes were also examined and sampled on a less intensive scale. The aim of the present study is not to unravel the complex geology of the Sokli complex (this has largely been done by Rautaruukki Oy), but rather to understand the relationship of the sulphides to the various rock types and other minerals. Although there are sulphides associated with most of the rock types at Sokli, many of the areas with higher levels of copper (and niobium) are associated with apatites rich in fluid inclusions.

164. LOCALITY OF SOKLI AND OTHER KOLA THE GEOLOGY OF ALKALI IGNEOUS COMPLEXES THE SOKLI CARBONATITE COMPLEX - FINLAND

•

• Silvi to & si li cosdvite Phoscorite .& silicosovite Metasomatic soy i to Metasomatic phoscorite ' Metasomatized dolomitic, • brecciated fenite fragments [1 Fenite Boreholes used in this study Basement gneiss & amphibolite • • •2 kms •

Fig. 29 MODIFIED AFTER PERS . COM. RAUTARUUKI OY 1977 AND VARTIAINEN & WOOLLEY 1976. ( See text) Before studying the inclusions, it has been essential to establish that the fluid inclusions are portions of the parent fluids of the mineralization. It has therefore been necessary to study the host apatite and its paragenetic relationship to other minerals, particularly the sulphides and pyrochlore. In this chapter these relationships are described and discussed. The following chapter deals with the fluid inclusions. 6.2. THE GEOLOGY OF SOKLI 6.2.1. General Geology and Previous Work The Sokli carbonatite complex was discovered by Rautaruukki Oy using Landsat Image interpretation followed by airborne geophysics (Paarma, 1970 and pers.comm.1977). It lies on the same fracture system as the Kovdor carbonatite, 50kms away over the Russian border (Paarma and Talvitie, 1976). The complex is intruded into a basement of gneissose granites, pegmatites, syenites, amphibolites, hornblende schists and ultramafic rocks of Archaean and earlier Precambrian age. The carbonatites are Caledonian in age, dates ranging from 334-392 m/years (Vartiainen and Woolley, 1974). The complex consists almost entirely of carbonatites which form an oval plug of some 20sq.km. The predominantly sodic fenites which extend up to 3km. from the carbonatite contacts have been extensively investigated by Vartiainen and Woolley (1976). The rocks of the complex are phoscorites, silicosovites, sovites and rauhaugites, with minor xenoliths of country rock and a late stage alkaline lampro- phyric dyke swarm (Vartiainen et al.1978). There are no precarbonatite ultrabasic or alkaline silicate rocks of the type usually found in carbonatite complexes. A central core of magmatic carbonate 2.5km. in diameter is surrounded by an area of metacarbonatite and fenites. Two types of phoscorite have been defined by Rautaruukki (magmatic and metasomatic; pers.comm.H. Vartiainen, 1977) shown in Fig.29. The geological history of the complex is complicated and so far not published in detail. Makela and Vartiainen (1978) have assigned five stages to the development of the 166. complex. This follows the Russian school (Pozharitskaya, 1962; Ginsberg, 1962; Ginsberg and Epstein, 1968; Pozharitskaya and Samoylov, 1972). The stages quoted by Makela and Vartiainen (op.cit.) are:- Stage 1: "Phoscorites which are the first segregations from the carbonatite magma. Medium to coarse grained magnetite, olivine-serpentine, green phlogopite, apatite, calcite and/or dolomite. The phoscorites occur as fragments in later carbonatites in the central and northern parts of the massif. Serpen- tinization of the olivine is the only alteration product in these rocks. Stage 2: Sovites and phlogopite sovites. They are massive and granitoid in texture and occur as stocks of variable size. Stage 3: Heterogeneous phoscorites originally belonging to Stage 1. They have been altered by the metasomatic front preceding the carbonatite intrusion of Stage 4. Green phlogopite is altered to red, olivine to clinohumite and amphiboles have begun to develop. Stage 4: The second effective carbonatite intrusion is connected with moderate to strong tectonisation. Foliated sovites and silicosovites contain red tetra-ferri-phlogopites. Stage 5: Minute late dolomitic and calcitic dykes characterized by pyrite and occasional hematite." The geological map (Fig.29), modified after pers.comm. Rautaruukki, 1977, is a partly diagrammatic representation of the subglacial geology, based upon over 300 boreholes, aerial photography (Paarma et al.1977) and geophysical work. A more detailed appraisal of the geology by Rautaruukki is in press (Vartiainen and Paarma, 1979). 6.2.2. The Present Work The positions of the boreholes made available by Rautaruukki Oy and referred to in this study are shown in Fig.29. The boreholes were chosen by Rautaruukki as representative of areas with well developed copper and pyrochlore mineralization. The boreholes were logged and sampled in detail, see Log Summaries 1-5. (Pages 170-175) My findings from study of the boreholes in these local areas is in broad agreement with the several stages of

167. magmatic and hydrothermal/metasomatic activity referred to by Makela and Vartiainen (op.cit.). Early rocks, phoscorites and mica rocks, have been progressively cut through, replaced and inundated by various stages of sovite and rauhaugite activity; both magmatic and metasomatic/hydrothermal. Large areas of unaltered coarse grained phoscorite (similar to that at Palabora) are seen in some boreholes (see BH390, log summary 1). In others however, the degree of intrusion, alteration and metasomatism has been so severe that extremely complex banded heterogeneous structures of rapidly, changing mineralogy are found (see BH 274 and 275, log summaries 3, 4 and 5). In surface trenches such banding in the complex is usually vertical, suggestive of flow in a vertical direction. However, intrusion of highly mobile fluids along vertical weaknesses, particularly in the mica rocks, may account for much of the banding. Replacement of early vertically foliated glimmerites by later carbonatites is well displayed in a section cut in another carbonatite in Finland, the Siilinjarvi complex (see Plate 15B).

Borehole 390 - Log . Summary 1: In this borehole a true phoscorite is developed as at Palabora, consisting of coarse grained serpentinized olivine and magnetite with subordinate carbonate, apatite and phlogopite. This has been heavily impregnated by later carbonatites, resulting in the breakup and partial digestion of the phoscorite, and the deposition of sulphides, phlogopite and apatite (see Fig.30A, B and C and Plate 16A and B). Fine grained phlogopite rocks, with interstitial subordinate calcite, magnetite and sulphides are banded and apparently flow around residual xenoliths of coarse grained monominerallic mica rocks and phoscorite. These rocks are probably the result of reaction between carbonatites and coarse mica rock, early phoscorites, or olivine-magnetite rocks. The fine grained mica rocks grade into silicosovites, sovites, silicorauhaugites and rauhaugites. The rauhaugitic or sovitic nature of these phlogopite rich carbonate rocks is evidence that they are a result of reaction between either sovites or rauhaugites and silicate rocks. 168. PLATE 15

A. Core from Sokli borehole 393, from 162m to 183m. Note variation from white carbonatites into fine grained carbonated mica rocks and coarse grained sulphide apatite mica rocks.

B. Sovites cutting through glinmerites (all mica rocks) at the Siilinjarvi complex, Finland. Note banded structure. 169. KEY TO SOKLI BOREHOLE LOGS.

Ultrabasic dykes (alkaline lamprophyres — Vartiainen et al. l978)

Late stage ankeritic/dolomitic dykes and vuggy veins.

S .A .P .P .M. assemblage (see text)

Rauhaugites.

Sovites.

Fine grained carbonated mica rocks and mica silico—sovites

Early coarse grained sovite with green phlogopite.

Residual areas of phoscorite and coarse mica rock (gli^rerite)

Fault cp/p0 Pyrrhotite/chalcopyrite

25 Sample numbers

Fig. 30

170 SOKLI BOREHOLE 390 Drilled at— 60° SUMMIT OF BOREHOLE LOGGING AND SAMPLING Depth in Sample metres Pos. OC 2 S .A.P . P ..•t. WHITE RaUHAUGITE NO CORE RECOVERED 27 Coarse apatite/phlog- 16 opite vein.

10 PH0SC0RITE 210 WHITE SOVITE

WHITE SOVITE Medium grained with •8 Sulphide bands •1 mica bands SILICO SOVITE 2 Grades into sovite with 20 2G 22 silicosovite bands.

- 9 PH0SC0RITE _11 Cut by sovite Monominerallic mica rock 3 residuals partly assim- 30 ilated into sovite 2 ULTRABASIC DIKE 12 Sovite with silicosovite bands. . Foliated sulphide bands 13 SAPPM. 4 Sulphide bands and 142 blebs 40 14b Partially assimilated 29 mica rock residuals Rauhaugite vein mica flakes cause 15 ,fixed rauhaugiteiThoscorit banding in sovite Vu ankeritic/doloticankeritic/dolomitic 50 25 ULTRABASIC DYKE WHITE RAUHAUGITE 30vi Medium - coarse grained white dolomitic rock with PH0SC0RITE magnetite & phlogopite Coarse olivine magnetite 5 rock inundated by sovite. Sulphides also deposited. ~17 Sulphide veinlets -/ 2 ° 8,t xed rauhaugite/phoscorite WHITE SOVITE °1 Rauhaugite veins PHOSCORITE 1290 Inundated by rauhaugite Sulphide banding becomes sulphide rich. 12 27 70 7 21 22 WPM vein,sulphides on 23 contact. 233 FAULT ZONE 24 80 2 Mica rock xenoliths carbonatized and grading WHITS SOVITE into banded silicosovite Sovite dykes 7 25 S.A.P.P.M. 10

o - 2 Banded apatite phlogopite --7: sulphide streaks. WHITE SOVITE

Grades into eilicoeovite 26u with patches of sovite and sulphides 100

LOG SUMMARY 1 171 SOKLI BOREHOLE 393 Drilled at-605 Depth in SUiL A tY ui 30REHOL. LOGGING AND SA1•iPLING metres Sami>le Sample 0 100 Nos. 200 . y L.08. JEATHEAED L.AUST w Ultrabasic dyke & Core Loss T -13 S.A.P.P.M. IN SOVITS III N, Ultrabasic dyke r , ,; w * V Ultrabasic dyke 1O" Y 210 - 0 0 11 > WHITE SOVITE Sovite with mica and / / x r magnetite i PHOSCORITE Coarse grained magnetite, mica, No core serpentine, dunite, calcite 1 .'/4 recovered __ _ rock, some pyrochlore. 20 120 220 X14 /0 \Sulphiiee. •HITS SOVITE with silico-sovite bands. ~.t 'white aovite cuts through mica S silicosovite & becomes contami- Ankerite/dolomite dyke hated forming bands of micace- _ ous sovite. The whole is cut — " a-2 through & in places pervasively 230 30 130 .~- = 3 inundated by SAPPM assemblage. S.A.P.P.M. veinlets

- -5 4C 110 210 —6 ANKERITE/DOLOOSTE DIKE J Fault Vuggy with coarse grained oyrrhotite. 15 ANIERITh/DOLOMITE DYKE SOVITE/SILICOSOVITE BANDS inundated by S.1.2 .P .11. —, WHITE SOVITE 50 150 ' Invades fine grained mica - Coarser grained apatite/magnetite 250 — - rock S,A.P.P.M.assembla _.- and ge WEATi0RED 7 CRUST

catch core loss SOVITE/SILICOSOVITE BANDS Fine grained carbonated mica rock, cut through and carbonated 60 160 f by later sovite. 260 Extensive development of S.A.P.P.M. /~ —8 16 Younger sovite vein 70 170 ^ Areas of clean white Sovite 270 9 17 =-410

280 80 180 AiiI ERITE/D0L014ITE DIKE Younger sovite vein 10 SOVITE/SILICOSOVITE BANDS ";:::-1":411 -19 Ankerite/dolomite dyke

.312 90 190 290 _ I

2 O Rauhaugite dyke,with sulphides

-21 100 20 300 LOG SUMMARY 2 172

SOKLI BOREHOLE 274 Drilled at-50° SUMMARY ur LOGGING AND SAMIPLING Depth in Depth in metres metres 0 100 / Sample Sample Noe. Nos. rH0SC0RITE/SILIC0S0VITE With sovite and s.A.P.P.M. / CORE i•ISSING Tremolite extensive.

/ ''- GMicro-foldedd -^_^ - 22 aniacz 10 110 - 2 3 WHITE SOVITE GREENISH SOVITE Coarse grained with green A .:- Fault phlogopite. Coarse grained with t---., _phlogo_pite. - - - -+ ------Sulphide phoecorite - - SOVITE/SILICOSOVITE ~ 2 / 3 with bands of fine grained - =24. }Elm: RAUHAUGīTE 20 — `4. mica rack.Much diseeminated 120 ma netite. g WHITE SOVITE , 5 Fault As above ;~ b 2cm sulphide vein 9 -25 30 130 --1O PHOSCORITE SILIC0S0VITE S.A.P.P.M. BAND nixed rock; fine grained / phlogopite rock, coarse intergrowths of phlogopite magnetite do olivine with j SAPPM. 13 Sovite bands and veinlets 2b 40 '14 - _ - - _ - _ also present. 140 FIi.E GRAILEll WHITE SGVIT::

/ -15 Filch S.A.P.P.i•1.

Coarse inter groutha of mica 50 -10 magnetite cut by sovitea and silicoaovites ~~

Fine grained magnetite 17. Sovite sovite grades into dark ti = _ magnetite mica rock with 60 --I Carbonated mica olivine, tremolite & SAPPM. i rock & phoecorite

18 Inundation by rathaugite 70 '41,19A --- - Inundation by sovite .17/ 19B WHITE SOVITE BO - iedium - fine grained with / -19c mica/magnetite bands and residuals. Some S.A.P.P.M1. /

'' Sulphide bands

90 -20

V21AJ PHOSCORITS/SILICOSOVITI; With bands of sovite %may Vuggy ankerite/ dolomite vein. ==218 100 LOG SUMMARY 3

173 r SOKLI BOREHOLE 275 Drilled at - 60° SUI.11•1ARY OF LOGGING & ai.iPLING Depth in Sample Depth in Sample btt metres Nos. / COARSE GREENISH SOVITE Grades — _ _ _ _- ______/ Xenolith of FINE WHITE SOVITE f. Coarse pU.og rock - 10 NO CORE RECOVERED 113 COARSE GREENISH SOVITE - Coarse grained sovite with scattered specs of magnetite and phlogopite. /

20 / 120 Fault with rauhaugite dyke tIICA RAUHAUGITE / Fine grained mica rock x--63 extensivly carbonated } DOLOMITEJANKERITE DYhn / • calk ,,Xenolith of 30 Y/ k Core missing 130 coarse mica rock 'ICA SOVITE n BANDED SOVITE/SILICOSOVITE ~ 6 Grades Fine•grained mica rock cut WHITE SOVITE and carbonated by sovite. Magnetite, sulphides and 7 COARSE GREENISH SOVITE - £'' tremolite well developed Coarse mica rockS.A.P 40 --/- P.M. āxtensive. 14 ,-/ xenoliths ? -68Core boxed? RAUHAUGITE Fault {.:,,, loss. Clean white rauhaugite with Rauhaugite dyke -r 9 S.A.P .P .M. bands +mica rock xenol. xenoliths of U.B. dyke X70 `j Q coarse mica rock m Many rauhaugite 50 J n. veinlets 150 C I O BANDED SOVITE/SILICOSOVITE 4--,4. ,D Banding strongly Sovite and silicosovite . 60 ` ,".:- 0 developed. 160 replacing and assimilating fine grained mica rock. Coarse mica roc}: hūch S.A.P.P.M. and tremolite m xenoliths /~ m Fine grained mica rock jj becomes more carbonated

70 17 Coarsening of Carbonate decreases 17 phlogopite i_ - aa / S"White sovite . /,e4.- X22 S .A.P .P.nt. X23 4 7, 80 18 - :O ominerallic mica rock, fine grained, Sulphides 2843 71 replace rock extensivly in places. J - . X49 52 5J 5 -72 n S.A.P.P.M. in -57 fine grained '-73 carbonated mica rock. 90 19 i, Carbonate / restricted to f.60 7einlets4 v -75 ==61 O76 COARSE GREENISH SOVITE, some magnetite 3c phlogopite ~'7 -77 100 2 LOG SUMMARY 4

174 OETAI L OF SOKLI BOREHOLE 275 30 - 80 metres Depth in Sample Depth 1n metres Nos. metres )0 ~~T------______~ 55~--r---~~~~------,Rauhaugite Tremolite \mITE SOVIrE WITH meA BAI ' Bands of mica from assimil CORE mSSING ation of fine grained mica rock. S.A.P.F .M. as streaks and eyes 1n 8Ovite.

alNDED SOVITE/SILICOSOVITE S..l.,p.P .M. 'Jith S.A.P.,p .H. magnetite && 50 Dark fine grained Glimmerite mica rock. residuals tremolite. Fine grained mica rock barxis 51 carbonated and replaced by ---Grades------Sonte veinlets later sovites. SILICOSOVITE/t'IICA ROCK 35 Extremely complex barxiing & replacement. l~stly fine grained mica rock, only partially carb- S.A.P.P.H. onated. Rauhaugite vein : ' A~ti te and tremolite Glimmerite __-+-~- Intrusive contact r~sidual8 and llto banding. 54 x9;Mli the.

Rauhaugite dykes 40 10 Grades------ 12 SOVITE/SILICOSOVITE 57 Sovite influence becomes progressivly greater', Sonte vein FINE GRAINED meA ROCK much banding. ;·agnetite ani gliJllmerlte I3a.nded fine grained mica xeru>llths rock partially replaced Rp.uhaugi te by carbonate. • W'HI TE RAUlU.U Cl TE j·agnetitel !lIica xenolithe 70 Phlogopi te becomes WIll TE OVI TE coarser.

ULTRA BASIC DYKE

FINE GRAINlill MICA ReeK

JiS above 'Ji th much S .A.,p.,p.N ani treIllOlite. .;-:r:;~.: -- S .A.P .P .11. ------

--'~ . -/ 50 75 58 ;.[HITJ:::SOVITE

l ~asive sulphide BANDED HICA ROCK/SOVITE "'; .A.? P .H. ~ . Partially carbonated fine U. B. Dyke grained mica rock. ~uch S.A.P.P.H.

!'Jedium to coarse grained 20 magnetite-Mica-sulphide 44 22 rock,broken up and part TrelllOlite 23 i ally replaced by sovite.

80~ __~ ______~ 55 ~--~~~------______~ LOG SUMMARY 5 17 5 In the sovites, sulphides, apatite, phlogopite, pyrochlore and occasionally magnetite give the rock a banded appearance. This could in some instances be a segregation effect caused by flow in the carbonatite, but microscopic investigation suggests that it is largely due to post- consolidation hydrothermal introduction, or autometasomatism as suggested for Palabora, (this work) and Jacupiranga (Melcher, 1966); the fluids exploiting weaknesses in the carbonate fabric, perhaps caused by plastic flow in the later stages of cooling. In sample 390/4 (sample locations shown on log summaries) sulphides follow a band which is severely kinked (see Fig.31D). A sulphide-apatite-phlogopite-pyrochlore assemblage runs parallel to this but does not follow the kinking. Such relationships indicate that the kinked band of sulphides was subjected to some plastic flow, which did not affect the later sulphide-apatite- phiogopite-pyrochlore band. The latter may have been introduced later, following the general weakness in the rock. A second phase of sovites intrudes the earlier ones as small dykes of clean white fine grained sovites with trace amounts of apatite, phlogopite, sulphides and magnetite. A phase of rauhaugites, which followed the sovites, produced some reaction with the early rocks similar to the sovites described above. Late stage vuggy ankeritic/dolomitic dykes with much pyrite and pyrrhotite are found in places. Borehole 393 - see Log Summary 2: The early rock type here is a coarse grained monominerallic phlogopite rock, the true phoscorite as in BH 390 is not well developed. The phlogopites have cores of speckled green (normal pleochroism) surrounded by a rim of red aluminium-deficient phlogopite with reversed pleochroism. In the tetra-ferri-phlogopite of Rimskaya-Korsakova and Sokolova (1964), Fe3+ replaces Al3+ (see Table 15, over page). This phlogopite rock is attacked by later carbonatites as in BH 390 and a continuum exists between these pure phlogopite rocks, through partially carbonated, fine grained (recrystallized?) mica-rock and into phlogopite rich 176. REACTIONS BETWEEN PHOSCORITE & CARBONATITES ( as seen in sectioned core )

A. SAMPLE 390/ 21. RAUHAUGITE REACTION WITH PHOSCORITE

. j • r j . .

( •i •. .6

Magnetite

Rauhau~gite &aphides I Bleached (light green) 3erpentiniaed Sulphides and mica Apati /mica serpentine olivine in cracks. pockets mica rim

SAMPLE 390/19 OLIVINE RESIDUALS IN MICA ROCK

C. SAMPLE 390/12A REACTION ON SOVITE PHOSCORITE CONTACT.

Sovite—> • 11 0 ii. • :'. - 40. s -

Olivine Magnetite Sulphide Residual olivine Apatite

D. SAMPLE 390/4 BANDING IN SOVITE

Fig.31 177.

silicosovites. The flakes of phlogopite in the silicosovite also have a central core of greenish normal phlogopite and tetra-ferri-phlogopite rims. This process of carbonatization is also associated with bands of sulphide, apatite, phlogopite, pyrochlore and magnetite (SAPPM) which are apparently derived in this borehole from the sovites. This assemblage is very common and may form veins, isolated pockets and schleren in the sovites and silicosovites. It may also be more evenly distributed through the rocks, but even then on a micro-, scopic scale there is still a tendency for it to occur in bands and pockets. The assemblage contains considerable amounts of clinohumite in some places, though in others it is not present. The assemblage is clearly closely related to the carbonatites, but its near consistent segregation from the carbonate (it commonly has little carbonate in it) is difficult to account for. In some areas it appears to be later than the calcite, cutting through and perhaps replacing earlier calcite; yet in some dykes cutting the earlier weakly carbonated mica-rock, it forms bands and schleren intimately associated with the carbonatite (see Plate 16G and H). The phlogopite of this assemblage is always the tetra-ferri-phlogopite.

TABLE 15: EPMA ANALYSIS OF PHLOGOPITES IN EARLY GLIMMERITE BH 393/17 Older Green Cores (N = 10) Tetra-ferri-phlogopite Rims (N = 4) standard standard mean deviation mean deviation Na20 <.1 - < .1 - MgO 22.95 (1.70) 24.45 (0.41) A1203 11.44<.(2.72)— N.B. 5.22 (1.33) Si02 38.97 (1.31) 40.12 (0.37) K20 10.16 (0.17) 9.55 (0.55) Ca0 <.1 - <.1 - Ti02 1.93 (1.52) < .05 - Fe0 6.40E(1.53)--- N.B. 10.83 (2.04) Cr204 0.09 (0.13) < .05 - TOTAL 91.33 (0.62) 90.32 (1.06) 178. In other places (sample 7, BH 393 - see Plate 16D) veins and dykes of coarsely crystalline material develop. Coarse crystals of phlogopite and magnetite are found up to four or five centimetres across, with interstitial calcite and sulphides. This assemblage has introduced a substantial amount of apatite into the surrounding sovites and silicosovites. The sulphides are pyrrhotite with a small quantity of chalcopyrite (2-5%) and appear to grow in plates and spikules cutting through the coarse magnetite phlogopite fabric. Recrystallization of the silicosovites may take, place; for example, in BH 393/10 (see Plate 16E) veins of coarse recrystallized silicosovite contain magnetite, phlogopite and sulphides and vast numbers of pyrochlore crystals developed in the silicosovite adjacent to these veins. There is very little apatite associated with this. Rauhaugites are not as well developed as in BH 390, but there are one or two dykes with blebs of sulphide. The late stage vuggy dolomitic/ankeritic dykes follow with a sulphide assemblage of pyrrhotite and pyrite with rare chalcopyrite and sphalerite in places. Boreholes 274 and 275 - Log Summaries 3 and 4 These two boreholes were drilled close together. The same processes are operative in these as in the other boreholes; early phoscorite and phlogopite rocks having been broken up by later carbonatites. The process is more intense, as can be seen from the complexity in the borehole summaries. Extensive deposition of carbonates, apatite, sulphide, phlogopite, pyrochlore, magnetite, clinohumite, pyrobitumens and tremolite obscures the essential rock types. A simp- lified picture of the geology is shown in Fig.32. The analyses shown for these boreholes were supplied by Rautaruukki Oy. An early coarse grained greenish sovite in the boreholes is probably equivalent to the Stage II carbonatites of Makela and Vartiainen (1978). The "banded mica rocks" approach phoscorite composition in places, but the concept of phoscorites is difficult to assess here. The influx of material has produced large amounts of magnetite and clinohumite. The designation of phoscorite is probably 179. PLATE 16: Reaction between Carbonatites and Silicate Rocks at Sokli

A. Sample 390/21. Rauhaugitic carbonatite reaction with serpentinized olivine ).(ol The partly serpentinized olivine is bleached to a light green serpentine (K), while phlogopite (p) is produced on the rim. Sul- phides (S), pyrrhotite/chalcopyrite are deposited on the contact. Note thin vein of carbonatite also phlogopitizes olivine. Plane polarized transmitted light. Bar = lcm.

B. Sample 390/19. Carbonatite cuts through coarse phlogopite rock (p) with some coarse magnetite (mt), assimilating these into itself.

C. Sample 275/21. Coarse phlogopite xenolith surrounded by fine grained phlogopite, magnetite carbonate rock (z). Both are cut by a later dolomite vein with sulphides. Plane polarized transmitted light. Bar = lcm.

D. Sample 393/7. Sovite with sulphide (S), pyrrhotite/ chalcopyrite cutting through fine grained mica rock not shown) produces reaction of coarse phlogopite (p) and apatite bearing SAPPM assemblage (Sx) - see text and Plate 18.

E. Sample 393/10. Recrystallization vein of fine grained phlogopite, magnetite, calcite rock (P) with introduction of sulphides (S).

F. Thin section of recrystallization in E showing development of coarse phlogopite (Ph) and calcite (c). Plane polarized transmitted light. Bar = 5mm.

G. Sample 393/2. SAPPM assemblage (Sx) in sovite (white) vein cutting through fine grained carbonated mica rock (M). See H below.

H. Sample 393/2. SAPPM assemblage, sulphides and magnetite are opaque (black - o),hlogopite (Ph) is coarse grained, whilst apatite )(ap and pyrochlore (y) are fine grained. Transmitted plane polarized light. Bar = 5mm. (See also Plate 18).

180.

PLATE 16

5cros

A B

SOKLI BOREHOLE SECTIONS 274 & 275

Moraine 0~ S. ar 40 Off' carb~onat.ites .---4,'-'e / y °• ~cy'- — 4 p.

X. ti'3 y' n 1 1• cll. lyb 25 metres 4i O . -a). 12. ../ ~~I Q. Ob b• N•'''- O' ti n a°1 ~^ ~~\ . ,6'~ ~~~' ~y ot Ih ch. 1~ ~ ^ 17 o ' ,I• ^i• b+ -0 ~5 ~L o 9 ro bIlll 1111 1 0' ~q 4 9 C• 9'? i o• y~ NY ~' ( n0' O • b•~ 1 * O ti 5 ~ h tib 1b• O lh ''4~ 0 Op. tiny~ O 42

150 'LO h I Q. ~. 1•~ \ VP -hn 1~ p. cflb

1~ p.~ Oti V• 10 !9

1•4, y,0 1 ,~Oh b9 • tiy 1~ ti cl p n o• 10 N1'' y 0• y y 0 qw 01 ', 1• O • 9' 'Y• 1 . \ Ni 0 O1 1 ly 19 1, '7 J o • 4• 1~ \ ~~ , h`~ \\p 9' •CO CARB3NATIV.S ob \ BLrmr9 PIIC.i ROCKS Coarse grained glimneritea,fine pb mica rocks,partially carbonated ' • '1• with ma gnetite,tremolite and • \ \ sp. S.d.P.P.N. Assemblage b ph p MON ULTRA BASIC DYKE 4> ~\ p ~ For detailed geology see borehole summaries 3, 4.& 5. (This work) pi h^ N to Element values and borehole inclinations b10 V 00 000 from Rautaxeuld Oy (Pers. con. 1977) lip 7.• ,'

O• • lq~lo ,r~ 0• rh $5 11 p b~ l fyr • N h~ o 0. p.o° b~ 5) ~. z \.." Fig. 32 a• •5.• bl' 1• 182. not strictly accurate. These rocks are certainly quite different from the olivine magnetite apatite rocks seen at Palabora and in the other boreholes studied at Sokli. They have been designated metasomatic carbonatites by Rautaruukki. In fact, both magmatic and hydrothermal components are probably present. The origin of phoscorites is discussed in Chapter 9. The conclusion drawn here is that hydrothermal/metasomatic deposition of much sulphide, apatite, phlogopite and pyrochlore occurred at Sokli, perhaps associated with and largely preceding the introduction of the later fine grained sovites and rauhaugites. This hydrothermal activity is probably equivalent to the Stage 3 of Makela and Vartiainen (1978). The extent of extensive hydrothermal activity on the scale seen in BH 274 and 275 is not known, nor is it clear whether it is structurally controlled. Rautaruukki have geophysical evidence of what may be a large fracture structure cutting the centre of the complex from SW to NE (pers.comm. Vartiainen, 1977). This cannot be proved from the limited borehole data available. 6.3. SULPHIDES AT SOKLI Sulphides occur in variable amounts in most of the rock types observed in the boreholes. Pyrrhotite is the most abundant with subordinate chalcopyrite and traces of sphalerite, galena and pyrite. Six major associations have been recognized on the basis of detailed borehole logging and microscopy:- 1) Sulphides filling cracks and shears in phoscorite and early mica rocks. ii)Sulphides in carbonatites with no associated minerals iii)A sulphide, apatite, phlogopite, pyrochlore (magnetite) assemblage. (SAPPM) iv)Remobilized and recrystallized sulphides. v)Coarse crystal intergrowths in late stage vuggy dykes and veins. vi)Late stage alteration and weathering. Each association is briefly considered:-

183. i)Sulphides filling cracks and shears in phoscorite and early mica rock; The sulphides fill shears and cracks, cutting across olivine, magnetite and coarse interlocking phlogopite crystals (see Plate 17D). The sulphide appears to have been introduced into the rock rather than being a primary constituent, if so the sulphide assemblage is not paragenetically associated with any other minerals. ii)Sulphides in carbonatites with no associated minerals; These sulphides are usually irregular shaped blebs and streaks and are found sparsely scattered in most of the carbonatites. Where there is banding in the rock, the sulphides are found as discontinuous streaks running parallel to the bands, giving the impression of being a primary constituent of a flowing magma (see Plate 17A). Under the microscope however, as at Palabora, the sulphides are found both in cracks and replacing the carbonate; suggesting post carbonate consolidation deposition. As at Palabora, this may be autometasomatic. In some instances sulphides are obviously post carbonate, being associated with recrystallization of adjacent carbonate which is clouded with minute fluid inclusions. One of the most enigmatic developments of those sulphides, not attended by other minerals in the carbonatites, is the interlocking growths of irregular bladed sulphides (pyrrhotite dominated). These may represent a true deposition from the carbonatite melt (see Plate 17B). iii)Sulphides associated with the SAPPM assemblage; Most of the sulphides in the altered mixed rock phoscorites at Sokli are thought to be associated with this assemblage. Because of this, and the association of apatite with fluid inclusions, this class is the focus of much work I have done at Sokli. A detailed textural and mineralogical account of the whole assemblage is given in section 6.5. iv)Remobilized and recrystallized sulphides; These make up a very small percentage of the total sulphides. They consist mainly of veinlets and microscopic

184. PLATE 17: Some Sulphide Occurrences at Sokli

A. Sample 390/20. Rauhaugite (R) cuts through early coarser phlogopite sovite(S). Sulphides (su) are deposited parallel to contact. Bar = lcm.

B. Sample 393/20(b). Thin section of above sulphide/ carbonate relationship. Sulphides are pyrrhotite with subordinate chalcopyrite. Plane polarized transmitted light. Bar = 5mm.

C. Sample 393/11. Isolated 'nests' of sulphide, apatite, phlogopite and magnetite. Surface of drill core. Bar = lcm.

D. Sample 390/5. Sulphides (S) associated with and replacing magnetite (mt) in olivine (01) phoscorite.

E. Sample 275/74. Sulphide bands in monominerallic phlogopite rock.

F. Sample 393/21. Sovite vein cuts through fine grained carbonate/mica rock (P). Sulphides (S) are deposited on the contact.

G. Thin section of contact in F. Note how sulphide blebs are developed away from immediate contact. Plane polarized transmitted light. Bar = lcm.

185. PLATE 17

T5-c m D veinlets of chalcopyrite, sphalerite and galena. They cut through earlier sulphides and magnetite and also are deposited on the edges of such grains. It is not clear at what stage this occurred. Such remobilization, especially of chalcopyrite in sheared zones of BH 275, accounts for some of the higher values of copper which aroused my interest in these boreholes and led to this study. v)Sulphides in the vuggy dolomitic/ankeritic dykes; These dykes are the youngest carbonate rocks in the complex and thus post date the above mentioned sulphide, classes. They have a distinctive sulphide paragenesis which consists of coarse crystals of pyrrhotite and pyrite. Chalcopyrite is present but in smaller amounts, as is sphalerite and galena (see Plate 1B, Chapter 1). vi) Alteration and oxidation; All of the above sulphides show alteration when near the surface or next to faults. In some places the pyrrhotite is locally altered, and small cubes of pyrite develop in it. Iron oxides, chalcocite, bornite and digenite are also present in small amounts. With the exception 'of the latter two categories (v and vi), the fairly constant ratio of chalcopyrite to pyrrhotite in the sulphide assemblage is quite remarkable (range 1-10%). The chalcopyrite has clearly exsolved from what was presumably a pyrrhotite chalcopyrite solid solution (see Plate 19A and B). The chalcopyrite is typically found on the periphery of the pyrrhotite grains and blebs, since the structures are incompatible,exsolved lamellae cannot occur. (Pyrrhotite is. monoclinic and has a pseudohexagonal NiAs structure with hexagonal close packing, whilst chalcopyrite is tetragonal with cubic close packing). Sphalerite, and less commonly, galena, are found associated with the exsolved chalcopyrite; the sphalerite in many cases as star shaped exsolution points in the chalcopyrite. Rare instances of small cubanite laths in the pyrrhotite have been seen and small blebs of bornite and chalcocite on the edge of some grains of pyrrhotite may be

187. due to weak later alteration by copper enriched fluids. This is on a very limited scale. The constant presence of copper in the sulphide assemblage is significant, especially if, as I think, the sulphides are associated with different generations of magmatic activity. The implication is that the copper and sulphur are both an intimate part of the magmatism at Sokli. These elements must then build up from trace quantities in the early rock types to more substantial amounts in the later carbonatites and carbothermal fluids. 6.4. APATITE AS AN ACCESSORY MINERAL AT SOKLI The presence of fluid inclusions in the Sokli apatite and its association with much of the sulphide necessitated a thorough study of the apatites. It is difficult to ascribe an indisputably primary magmatic or deuteric metasomatic origin to most of the occurrences. The problem it appears is universal and workers on other complexes have assigned apatites to both magmatic (Valyashko and Kogarko, 1965; Romanchev, 1972) and metasomatic/hydrothermal fluids (Althaus and Walther, 1977; Rankin, 1977; Khitarov et al. 1978). Experimental studies show that it is possible to grow apatite from carbonatite melts (Wyllie, Cox and Biggar, 1962; Wyllie and Biggar, 1966) and also from hydrothermal fluids (Argiolas, 1978). Cases of a definite melt origin for apatite are known, particularly when found in dykes of obvious primary magmatic origin, enclosed in other minerals or with high temperature melt inclusions (Romanchev, 1972). The hydrothermal/metasomatic origin is less easy to establish. Apatite may replace other minerals and still display well developed crystal forms (see this work, Chapter 7) which could be inadvertently interpreted as phenocrysts. Further, the presence of aqueous fluid inclusions is not conclusive proof of a hydrothermal origin. Roedder (1978) reviewed the possibilities for minerals growing from a melt, but with co-existing exsolved low density aqueous bubbles adhering to the growing surface and being trapped in preference to the melt. Bagdasarov (1971) defines three types of apatite formations in carbonatite complexes:- 188. 1)Metasomatites of the pre-carbonatite stage (associated with silicate rocks) 2)Apatite rocks of the carbonatite stage, formed on the early carbonatite front. Typically apatite zones on the contacts between carbonatites and silicate rocks. 3)Apatite of the carbonate-free facies of carbonatites, camaphorites or phoscorites. In the boreholes studied for this work a variety of textural types has been noted (see Fig.33); there appear to be three categories:- i)Massive coarse grained types intimately related to coarse olivine and phlogopite rocks (types A and B in Fig.33) ii)Those associated with the SAPPM assemblage (types C and D in Fig.33) iii)Isolated phenocrystoid disseminations (types E and F in Fig.33) These are by no means definitive of origin and two or three textural types may less commonly be found in one paragenesis. It is therefore necessary to work in terms of associated mineralogy, defining paragenetic associations. The SAPPM assemblage accounts for the bulk of the apatite in the boreholes studied (as well as the bulk of the sulphides). Category i) above is probably the earliest apatite. It has a distinctive texture and is further characterized by the lack of associated pyrochlore; the rare sulphide specks sometimes seen may not be co-genetic. Category ii), the SAPPM assemblage, will be described in detail later. It appears to be closely related to the carbonatite events which invade, recrystallize and assimilate the earlier phoscorites and monominerallic mica rocks. It forms rims on the contacts between the latter rock and carbonatites and also forms bands and schleren in some of the carbonates. Bagdasarov (1971) mentions apatite rocks which are co-eval with carbonatites of the second stage and which locally contain notable amounts of rare metals. He also describes stringers of pyrochlore bearing phlogopite- magnetite-apatite rock from carbonatites of the Sayan 189.

Fig.33 APATITE TEXTURAL TYPES Fig.34 PYROCHLORE TYPES • DESCRIPTION ASSOCIATION DESCRIPTION ASSOCIATION A oi; ! Massive anhedral coarse grain- Hostly interstitial to Even sized anhedral grains. With massive interlocking • • ed interlocking apatite. eerpentinized olivine. No Even colour in reflected apatite and apatite/mica rock Ap Cracked and infilled with pyrochlore and little or light, no zoning. later carbonate. no phlogopite and sulphides.

Euhedral crystals, zoned Isolated in carbonatites. Massive coarse interlocking Intergroun with phlogopite. B CC centre with clear non zoned coarse grained. No pyrochlore. overgrowth.One example had carbonate malt inclusions, see Ch. 7.6.

Elongate rounded to irregular Typical of S.A.P.P.M. C Well formed zoned crystals, Isolated in aovites and also shaped grains replacing aseemblage.Calcite next to no irregular overgrowths. in S.L.P.P.M. assemblage. calcite. Calcite spheres in the assemblage is filled the apatite. with secondary inclusions.

0 With inclusions of calcite Typical of S.A.P.P.M. Irregular interlocking grains, With S.A.P.P.M. assemblage. sulphides, phlogopite, apatite assemblage. no interstitial calcite. Probably a Hither development and magnetite. Both euhedral of type C , where all the and anhedral types,the latter calcite has been replaced. with amoeboid like growth.

Long prismatic crystals with Scattered in sovites and E Pyrochlorea with areas of Found in some areas of rounded ends. Some have central rauhaugitea. uneven reflectivity (some S.A.P.?.;1. assemblage. corse. patches are lighter than others

S..L.P.P.Ii. F ,._.c v Rounded and slightly elongate Scattered in sovites and F Intergrowths of pyrochlore In assemblage 7 Ap crystals. rauhaugites. May be trapped with:baddelsyite and apatite. inside calcite or dolomite Baddeleyite blades usually u / 1 protruding from pyrochlores. 1 • grains.

ir- 1 ' •

Massive fine grained apatite. In sovite as clots, not Small rounded to anhedral Found adjacent to calcite Interlocking crystals with common. Hay be a fragment of grains interstitial to veins veins..Ilo associatod no interstitial calcite or a monomineralic apatite rock, Ehlogopito in all mica rocks apatite. othor minerals. moved from original site. and silico-sovite.

Ap = Apatite Cl = Serpontinizod olivine cc = Calcite 11 = Mica S = Sulphide ? = Pyrochlore B = Baddeleyite — Bar =1 mm complex. They have 60-70% apatite, 10-15% phlogopite and 10-15% pyrochlore. These are apparently analagous to the SAPPM assemblage at Sokli. The third category of apatites, which occurs as phenocrysts and isolated clots (see Fig.33G) is found in all of the carbonatites, though in many it is only a minor accessory. A more detailed study of the apatites at Sokli, using trace element abundances (REE, Sr, U, Th, etc.) could provide a useful insight into the formative processes, , particularly metasomatic processes and their relationships to the various rock types. This was considered not only to be beyond the scope of this work, but also a digression from the original aim of obtaining information from fluid inclusions related to mineralization. It is sufficient to note that a considerable proportion of the apatite seen at Sokli is either directly or indirectly related to processes which also deposited (or remobilized) copper, iron, sulphur and niobium. Further, this apatite contains inclusions trapped at the same time, which are representative of these processes. 6.5. THE SULPHIDE APATITE PHLOGOPITE PYROCHLORE MAGNETITE ASSEMBLAGE(S) (SAPPM) 6.5.1. Mode of Occurrence The sulphide, apatite, phlogopite, pyrochlore, magnetite (SAPPM) assemblage is a loose term, because the mineralogy may vary from one area to another. The mode of occurrence is also variable. It may be found as veins obviously cutting through earlier rocks, or as a metasomatic edge or rim to certain carbonatites; late sovites and the early rauhaugites. It may also occur in the carbonatites and silica-carbonatites as bands, pockets, schleren (see Plate 16G and 18D) and even as loose nests of minerals in the carbonatite matrix (see Plate 17C). The association with late sovites and early rauhaugites which follow is most apparent where the phoscorites and glimmerites have been invaded and replaced by carbonate. Veinlets and haloes of

191. the SAPPM assemblage extend from the carbonatites into the other rocks. The fine grained phlogopite rich rocks with subordinate carbonate (less than 10%) which have apparently been formed by recrystallization, carbonatization and remobilization of the early silicate rocks as a result of the carbonatites, may have the SAPPM minerals extensively developed throughout the rock. 6.5.2. Petrography of the SAPPM Assemblage The minerals found in the assemblage are sulphides (pyrrhotite and chalcopyrite), apatite and tetra-ferri- • phlogopite, with variable amounts of pyrochiore, magnetite, ilmenite and clinohumMite. Calcite, dolomite, pyrobitumens/hydrocarbons, tremolite and baddeleyite may also be present. The mineral content may be extremely variable, but the bulk is usually between 50 and 70% of the assemblage and occurs as rounded anhedral grains, usually 0.5- lmm across. Sometimes a massive interlocking aggregate of apatite is developed. Phlogopite and sulphide make up to 10-20% each. pyrochlore and magnetite are usually between 0 and 10%, but may rarely reach up to 30% or more. The minerals are usually fresh and clean, showing relationships indicative of a broadly co-genetic deposition. Each mineral may enclose small specks and inclusions of the others. The apatite typically has plates of phlogopite, irregular and platy grains of sulphides, magnetite and occasional well formed crystals of pyrochiore (see Plate 18C and 20C). The apatite will also be intergrown with other minerals. Inclusions of larger crystals of apatite in the other minerals of the assemblage are more common than large crystals of the other minerals in apatite. This suggests a slightly early crystallization of the bulk of the apatite, perhaps with epitaxial growth of small quantities of the later minerals. The phlogopite is usually clean tetra-ferri-phlogopite which commonly shows zoning. It may be as aggregates of small flakes a few hundred microns across, or larger crystals 2-3mm across. Rarely green phlogopite cores are present, as mentioned for the monominerallic mica rocks. 192. PLATE 18: SAPPM Assemblage I

A. SAPPM assemblage (Sx) next to sovite (c). The calcite near the SAPPM is clouded (i) with secondary inclusions, as is the calcite interstitial to the SAPPM minerals. See also B below. Transmitted plane polarized light. Bar = lcm.

B. Sample 393/12. SAPPM assemblage with clouded inclusion filled calcite (c) interstitial to the apatite (ap), phlogopite (ph) and opaques (black). Transmitted plane polarized light. Bar = 1mm.

C. Sample 275/P. SAPPM assemblage without any calcite. A lot of pyrochlore (pc) is developed here. Bar = lmm.

D. Samples 275/2. Banded SAPPM assemblage in carbonate. Bar = lcm.

E. SAPPM apatite (ap) with interstitial clouded inclusion filled calcite (i). The apatite has fluid inclusion cavities (f), clear calcite (CO and inclusion filled calcite spheres (C2) trappedlin the apatite. Transmitted plane polarized light. Bar = 250 microns.

F. Apatite (ap) partially surrounding inclusion filled calcite (c) in SAPPM assemblage. Transmitted plane polarized light. Bar = 100 microns.

193. PLATE 18

. ap PLATE 19

A. Dual mode reflected/transmitted light photomicrograph of SAPPM assemblage. Phlogopite (fox brown), apatite (A), pyrrhotite (P) and chalcopyrite (cp) in carbonate host. Note how cp forms a rounded bleb on the edge of a large block of pyrrhotite. Frame length = lcm.(approx.)

B. Detail of SAPPM assemblage showing boundary between chalcopyrite (cp) and pyrrhotite (P). Phlogopite (light brown) and pyrochlore (pc) are intergrown with apatite (A) containing typical aqueous fluid inclusions (arrowed). Dual reflected/transmitted light. Frame length = 2.5unu. 195. PLATE 20: SAPPM Assemblage II

A. Sample 390/30. Coarse grained SAPPM (Sx) vein cuts through sovite depositing sulphides (S) on contact. Only contact region is shown here.

B. Sample 393/28. Carbon or hydrocarbon fibrous masses, found occasionally in sovite and SAPPM assemblage; fluoresces green in ultraviolet light and has extremely low reflectivity. Plane polarized transmitted light. Bar = 500 microns.

C. Sample 275/77. Pyrochlore (Pc) in SAPPM assemblage showing well formed crystals which have grown trapping other phases of the assemblage. Plane polarized reflected light. Bar = 500 microns.

D. Sample 393/2. Pyrochlore (Pc) intergrown with baddeleyite (b) and phlogopite (Ph). Pyrrhotite (S) shows the comparative reflectivity. Plane polarized reflected light. Bar = 500 microns.

E. Amphibole (tremolite - t) fibres growing through apatite in SAPPM assemblage. Transmitted plane polarized light. Bar = 300 microns.

F. Sample 393/9(b). Pyrochlore crystal in sovite with melt inclusions (see Plate 22J). Note zoning in central area and irregular non-zoned overgrowths towards rims. Plane polarized transmitted light. Bar = 500 microns.

196.

PLATE 20 5 cms

Pc Pr-

•

• l•

.0.11•111• •

•I

' 4

F Such grains are interpreted as being foreign to the system, probably scavenged from earlier rocks and may show bending, indicative of strain. Inclusions of apatite, sulphides and pyrochlore are very common. The sulphides are mostly pyrrhotite, with chalcopyrite making up between 1 and 5%; sphālerite and galena are usually less than 0.5%. Rarely bornite, cubanite, pyrite and chalcocite were seen, but only in minute amounts. Although the percentage of chalcopyrite varies from one borehole to another, and even within boreholes, the percentage in any one 10cm.sample is remarkably consistent. The chalcopyrite is usually found as individual blebs on the edge of the sulphide masses. The boundaries are mutual and not suggestive of replacement (see Plate 19A and B). The consistent pyrrhotite to chalcopyrite ratios and these textures suggest an exsolution, where chalcopyrite has been exsolved to the edge of the sulphide mass. This is typical of the chalcopyrite-pyrrhotite relationship seen in other carbonatites (Bukusu, Great Beaver House, Kortajaarvi). There may however have been some deposition of chalcopyrite alone after the bulk of the earlier pyrrhotite/chalcopyrite. This occurs as minute specks, and veinlets in cracks in surrounding gangue and on the rims of other minerals. It may be a late stage remobilization and is insignificant in terms of quantity. The bulk of the sulphide surrounds apatite and phlogopite, but small euhedral crystals of sulphide are found in the apatite and phlogopite as mentioned. Large areas of sulphide up to 1 or more centimetres across may be present. Early pyrochlore grains are mostly surrounded by irregular pyrochlore rims, the latter commonly having specks and blebs of sulphide. Pyrochlore, like the sulphides, may be found isolated in carbonatites, but in most samples it is exclusively associated with the SAPPM assemblage. The grains may be euhedral zoned crystals or irregular masses commonly replacing other minerals, or surrounding well zoned pyrochlore 198. cores. Usually intergrown with the apatite and phlogopite (see Plates 18C and 20C and D), the pyrochlore may also have inclusions of these minerals. It is not uncommon to find pyrochlore with intergrowths of baddeleyite (see Plate 20D). The general occurrences of pyrochlore, together with pyrochlore chemistry, are discussed in the following section. Magnetite and ilmenite are found both as exsolutions and as separate grains. When present, these oxides appear to be intimately related to the bulk of the apatite, phlogopite and pyrochlore, sometimes occurring as inclusions in these. Sulphides are deposited both before and after magnetite and ilmenite. Honey coloured clinohumite also develops in the assemblage in some cases. Irregular grains of it may occupy up to 15% of the assemblage, intergrown with the other minerals. It is particularly common in the phoscorite rocks and may in part be a replacement of olivine (e.g. samples 275/4, 275/27). It has inclusions of calcite, sulphides and pyrochlore, as well as aqueous fluid inclusions (see Chapter 7). Pyrobitumens are sometimes found as blebs or irregular masses of radiating fibres (see Plate 20B). Tremolite is also found, especially in boreholes 274 and 275, but this may be mostly due to a later influx of metasomatizing fluids, as it is found growing throughout adjacent rock fabrics; long fibres growing straight through one mineral into another (see Plate 20E). The relationship between the SAPPM assemblage and the other rocks is problematical. The impression from examining the core was that a highly penetrative fluid, perhaps evolving from the sovites and rauhaugites, may have deposited the SAPPM assemblage. Whilst clear cut veins of SAPPM cutting older rocks would conform to this concept, some of the relationships are extremely difficult to explain; in particular the segregations of SAPPM assemblage in the carbonatites as shown in Plate 16G and H. Here the SAPPM is found as streaked or discontinuous 'clots' in a sovite vein, but there is no obvious development of the SAPPM in the adjacent carbonated mica rock. Such occurrences could 199. be due to carbonatite following earlier SAPPM veins and carrying portions of them along. Under the microscope, however, the SAPPM assemblage shows no sign of being replaced by carbonates, although there is some indication of it replacing carbonate. Carbonate in the SAPPM, when it is found, is usually interstitial to the other minerals (see Plate 18B). By contrast to the other minerals of the SAPPM it is cloudy with secondary aqueous inclusions. The carbonate along the edge of the SAPPM assemblage may also have a similar cloudi- ness (see Plate 18A). The evidence for the SAPPM assemblage being a replacement of the carbonate matrix was supported by this and particularly by certain calcite inclusions in the apatite. The apatite typically contains spheroidal calcite inclusions, some of which are filled with secondary aqueous inclusions; i.e. the carbonate is similar to the carbonate surrounding the apatites. The details of this and other inclusions are presented in Chapter 7. These inclusions provide evidence that the apatite grew by replacing calcite. In some cases the apatite is found with amoeboid-like arms, partially engulfing some of the carbonate matrix (see Plate 18F). Despite this mode of replacement, the apatite maintains a tendency to form well shaped crystals. Although rounded, elongate crystals do form, when they can grow without coming into contact with other apatites. These observations tend to support the concept that the SAPPM is introduced into the rock by metasomatic/hydrothermal activity, apparently closely related to certain sovites and rauhaugites. The apatite and the sulphides are both clearly a part of the paragenesis; the implication being that the fluids in the apatites are the parental fluids of the whole assemblage. 6.5.3. Similar Assemblages in Other Complexes. Similar evidence of apatite bearing assemblages intimately related to, but replacing and cutting through carbonatites, has been reported from other complexes. Verwoerd (1967) recognized apatite stringers in a sovite at Kalkfield, 200. South Africa. Under the microscope the apatite appears to replace the sovite and is associated with biotite, magnetite, chlorite and sphalerite. Kapustin (1971) found in the fenites at Kovdor veins of pyrrhotite-biotite-apatite, up to two metres in width. Significant to the present observations at Sokli, these veins at Kovdor are arranged on a continuation of carbonatite veins. As at Sokli, there is an obvious association with the carbonatites. As mentioned, Bagdasarov (1971) describes pyrochlore bearing phlogopite- magnetite-apatite rocks from carbonatites of the Sayan , complex. At Bukusu an assemblage similar to that at Sokli appears to have invaded the early olivine bearing rocks (this work). Pyrochlore is not well developed, but sulphides (mostly pyrrhotite with subordinate chalcopyrite),_ apatite, phlogopite and magnetite all seem to have been introduced, replacing earlier minerals. Once again, as at Sokli, the Bukusu apatites contain primary aqueous inclusions. 6.6. PYROCHLORE 6.6.1. The Occurrence of Pyrochlore Pyrochlore is an important accessory mineral at Sokli. As in other complexes, it is closely related to the apatite (Van de Veen, 1963; Borodin et al.1973). This close association, particularly in the SAPPM assemblage, implies that any deductions concerning the conditions of formation of the apatite, sulphides and SAPPM assemblages will also apply to the pyrochlore and vice versa. For this reason a short programme of description and probe analysis of the pyrochlores was carried out. The pyrochlore at Sokli varies from dark brown, through various shades of light brown and orange to colourless. It is found in euhedral well zoned octahedrons and as highly irregular grains and aggregate masses (see Fig.34 - on the same page as Fig.33). The pyrochlore may have inclusions of other minerals in it, as well as fluid inclusions. Most of the pyrochlores have a light coloured irregular rim,

201. which more commonly has inclusions of other minerals, mostly calcite and apatite, which have been partially replaced. Though the pyrochlore occurs in different parageneses, no habit can be universally ascribed to any one association and commonly a whole range of habits is found in one rock. In particular, the emphasis has been on the pyrochlore from the SAPPM assemblage, both its characteristics and how it varies from other associations. Four associations have been recognized:- 1)Pyrochlore from the SAPPM Assemblage e.g. 393/2,, 392/12 (Fig.34C,D,E,F) This varies from dark brown (mostly in the centre of grains) to light honey colours on the rims. Apatite partially surrounds early well zoned crystals; the smaller of such crystals are found as inclusions in the apatite. Later deposited pyrochlore is much lighter in colour, less well zoned and grows interstitially between the apatites and phlogopites. Baddeleyite intergrowths are common in some examples, though not universal. The later pyrochlore grows irregularly on the rims of early grains, replacing earlier minerals in amoeboid fashion. The crystals may have a blotchy appearance in reflected light. The growth zones may also be clear in this mode. 2)Metasomatically Introduced Pyrochlore in Glimmerites and Carbonated Mica Rocks with no Associated Apatite e.g. 393/10, 275/70E (Fig.34G) This paragenesis has no associated apatite. The pyrochlore is usually in small crystals 2-500 microns across. The grains may surround or partially surround phlogopite crystals. The crystals are characteristically light brown in transmitted light and an even colour in reflected light, zoning, when present, is weak. These pyrochlores are usually found next to small veins of carbonate as they cut through the mica rich rocks. In the examples seen, the crystals have not grown more than a few centimetres from the vein. This association is free of associated phosphorus, and is apparently much less extensive than the SAPPM association. 202. 3)Colourless Pyrochlore associated with coarse interlocking Apatite e.g. 275/P and 275/44 (Fig.34A) This is probably another manifestation of the SAPPM assemblage. The grains of pyrochlore and apatite are sub- hedral and equigranular. Phlogopite and sulphides are also present, but the different colour and the greater percentage of pyrochlore in this assemblage suggests that it may be of a different, possibly earlier, generation (see Fig.34A). The chemistry, particularly the Nb:Ta ratio, does not support this latter concept (see subsection 6.6.2.). 4)Pyrochlore Grains in Sovite e.g. 275/77B and 393/96 (Fig.34B and C) These varied from very well zoned octahedra to less well zoned irregular anhedral grains. The grains are not common, and only 3 or 4 may be found in a slide. Large areas of carbonatite are barren of sulphides and pyrochlore and the sampling of such areas was not extensive. Never- theless, different generations of pyrochlore do exist in the rocks. Sample 393/96 has a well zoned crystal which has primary carbonate rich inclusions running parallel to the zoning, which might be indicative of a carbonatite melt (see Plate 22J - Chapter 7). The pyrochlores in this association are chemically distinct from the others. 6.6.2. Pyrochlore Chemistry Whilst the above associations were clear in some cases, it was not always easy to tell the difference between the SAPPM assemblage and what might be an early apatite pyrochlore stage of mineralization. -It was also not clear what the relationship was between the different associations described. For this reason, a short programme of probing was undertaken. In many other studies of pyrochlores in carbonatites the Nb:Ta ratio has been used to differentiate between early stages which have higher levels of Ta (Nb:Ta = 2-10) and later stages which have less Ta with Nb:Ta of 15-60 (Smirnov, 1977; Aleksandrov et al.1972; Borodin et al.1973). The probing was expected to yield some differences in Nb:Ta

203. ratio which might throw some light on the genesis and relationship between the various types. The samples were analysed using the energy dispersive system described in Appendix 3. Whilst this provides a rapid analysis, the system is pushed to the limit on minerals of such complex chemistry as these pyrochlores. The poorer resolution of the peaks can usually be resolved by the complex fitting and stripping routines used in processing the spectra (described in Appendix 3). However, many of the peaks in pyrochlore are close together and some minor elements may not be detected in regions where there is much peak overlap. Furthermore, the system was not initially calibrated for Nb, Ta, U and Th. The machine was calibrated for niobium and tantalum for this study, but U and Th, present in small amounts, were only recorded as counts per second above background. As U and Th are only very minor constituents, the absorption effects produced by them are not taken into account in the correction procedures. The levels of U and Th are unlikely to have a noticeable effect. Any variation caused by this is insignificant compared to that produced by the highly variable quantities of non- detectable elements in the pyrochlores. Both 0H and F substitute strongly into the X position and this results in poor totals. The analyses (tabulated in Figs.35, 36 and 37) are however considered to be quantitative of the major elements measured. The machine was operated under very stable conditions and continually checked for drift. The huge variations in most of the elements detected is easily resolvable and is certainly not affected by any slight loss of precision caused by the presence of U and Th. The pyrochlores have quite distinct chemical characteristics. The trend of decreasing Ta, U (and to a lesser extent, Th) as the crystals grew is matched by a concomitant increase in Nb, Ca and Na. This trend is found in most of the pyrochlores probed, but the severity of change varied from one habit type to another and also from one paragenesis to another. 204. The SAPPM assemblage characterized by both well zoned types and irregular types shows very variable chemistry. The large well zoned euhedral crystals which may have a central core of a slightly darker hue show a range of chemistry as illustrated by 393/12, crystal 1, Figs.35 and 38. Here twelve points were probed in a line from the middle to the rim of the crystal. The central irregular shaped portion has a high Ta and U content. The points nearer the edge of the crystal show a lower Ta and U and higher Na and Ca. The very edge which is light coloured and has irregular inclusions shows the extreme of this trend with a decrease in Th as well. It is obvious from the optical zoning, as well as the few points probed, that the composition varies considerably over short distances., but the overall trend is clearly apparent (see Fig.38). The Nb:Ta values of the central zone are between 5 and 10, whilst the outer zone has a Nb:Ta ratio of between 25 and 500. Smaller, less regular and less well zoned crystals, e.g. 393/12, crystal 2 (see Fig.35) are of similar composition at their centre, to the outer areas of the large crystal 1. The highly irregular types exemplified by 393/12 (crystal 3) have extremely low Ta, Th and U, typical of the very edge of crystals 1 and 2. The pyrochlore with no associated apatite, as exemplified by sample 393/10, crystals 1,2,3 and 4 (Fig.36) have less variation than those of the SAPPM assemblage. The Ta values are not so high in the centres and they do not drop off so much, except for a rim on the very edge (393/10, crystal 4 point. 3). The pyrochlores from 275/P (Fig.37) with coarse interlocking apatite also show little variation and the Ta levels are fairly constant with a mean Nb:Ta ratio of 12.16 (standard deviation = 2.84,N=9). This is probably a true SAPPM assemblage but of a different generation. Pyrochlores from the sovites are represented by 275/77B (Fig.37) and 393/9 (Fig.36). Those from 275/77B have middles of the highest Ta levels recorded in this study and with very much higher barium and low sodium. The pyrochlores tend to have a blotchy appearance and a rim of 205.

Sample 393/12 Scan of Pointe across Crystal from S.A.P.P.M. Assemblage, Crystal 1. (large and well zoned)

Pt.O Pt.1 Pt.2 Pt.3 Pt.4 Pt.5 Pt.6 Pt.7 Pt.8 Pt.9 Elmt. % Oxide % Oxide % Oxide % Oxide % Oxide % Oxide % Oxide % Oxide $ Oxide % Oxide Na 2.91 3.12 2.32 1.92 1.38 1.71 5.45 7.31 6.33 6.32 Ca 11.73 11.19 9.07 11.06 11.88 13.40 16.94 12.19 12.47 12.18 K .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 Fe 1.67 1.14 1.97 2.00 2.00 2.03 .41 .00 .72 .00 Nb 53.65 55.68 51.28 51.33 49.36 54.00 67.06 65.56 64.79 64.88 Ta 6.66 5.87 8.36 7.50 9.27 4.86 1.16 .51 .80 .00 Mn .00 .00 .00 .00 .00 .00 .00 .00 .00 .00 Mg .00 .27 .00 .00 .00 .00 .00 .00 .00 .00 Ba 1.27 2.00 3.08 2.22 3.18 4.45 1.44 1.71 1.67 1.58 Ti 4.28 4.10 4.77 3.13 4.80 5.97 4.33 4.29 5.01 4.90 Sr .92 .54 1.23 1.23 1.71 2.07 .90 .00 .57 .39 TOTAL: 83.06 83.90 82.07 80.40 83.57 88.48 97.67 91.58 92.37 90.25 Uranium and Thorium as Counts per Second above Background Th 5.40 4.32 5.00 4.94 5.20 6.06 1.30 5.00 4.96 4.92 U 7.20 8.08 8.50 6.46 6.84 4.54 1.06 3.40 2.90 2.54 Nb:Ta 8.07 9.49 6.13 6.84 5.32 11.12 57.91 128.05 80.77 7500

Pt.10 Pt.11 CRISTAL PLANS OF ANALiSEII POINTS SAMPLE 393/12 Elmt. % Oxide $ Oxide C ryetal 1 Crystal 2 Crystal 3 Na 4.04 6.22 Optically well zoned with Zoning optically Irregular amoeboid Ca 13.80 18.66 irregular shaped centre. weak. ehape.No zones. K .00 .00 0 1 2 3 4 5 6 7 8 9 10 11 1 2 3 1 2 3 Fe 1.49 .00 Nb 59.65 67.44 Ta 2.41 .87 Mu .00 .00 Mg .00 .00 Ba 2.04 1.28 Ti 5.82 4.60 Sr 1.28 .93 TOTAL: 90.54 100.00 , 500Mm 25Oum 500um Th & U cte/sec cte/eeo Th 5.28 0.48 U 2.62 0.0 Nb:Ta 24.74 77.43

Sample 393/12 Crystal 2. Sample 393/12 Crystal 3. Pt.1 Pt.2 Pt.3 Pt.1 Pt.2 Pt.3 Elmt. % Oxide $ Oxide S Oxide Elmt. 5 Oxide 5 Oxide % Oxide Na 2.58 4.24 5.66 Na 6.69 6.56 6.86 Ca 11.79 11.79 15.65 Ca 18.06 18.27 17.14 K .00 .00 .00 K .00 .00 .00 Fe 1.56 1.84 .69 Fe .00 .00 .00 Nb 58.30 57.16 66.51 Nb 67.41 66.03 66.91 Ta 2.57 3.82 .85 Ta .00 .56 .53 Mn .00 .00 .00 Mn .00 .00 .00 Mg .00 .00 .00 Mg .00 .00 .00 Ba 1.98 3.08 2.01 Ba .00 .69 .77 Ti 2.96 4.15 4.06 Ti 4.06 4.77 3.97 Sr .91 1.66 1.14 Sr .60 .66 .59 TOTAL: 82.64 87.74 96.57 TOM: 96.82 97.54 96.77 Th & U Gte/eec above background Th & II cte/sec above background Th 5.00 5.00 0.48 Th .00 .00 .20 u 3.00 2.60 .00 U .00 .00 .00 Nb:Ta 22.66 14.97 78.24 Nb:Ta >600 117.08 126.47 Sample 393/2 Crystal 1. CRISTAL PLANS 393/2 Sample 393/2 Crystal 2. Pt.1 Pt.2 Pt.3 Pt.1 Pt.2 Pt.3 Elmt. % Oxide 5 Oxide S Oxide Crystal 1 Elmt. S Oxide S Oxide S Oxide Na 4.52 5.56 3.44 250,um Na 6.44 7.86 6.26 Ca 14.51 13.99 13.73 Ca 18.62 12.27 18.31 K .00 .00 .00 K .00 .00 .00 Fe 1.26 1.44 1.16 Fe .00 2.14 .00 Nb 62.41 60.49 59.55 Nb 64.71 58.80 64.37 Ta 1.91 2.84 3.00 Ta .46 3.99 .00 Mn .00 .00 .00 .00 .00 .00 Mg .00 .00 .00 Mg .UO .00 .00 Ba .70 1.30 1.39 Crystal 2 Ba .00 .98 .00 Ti 5.86 5.87 6.73 LSOQum, Ti 6.54 6.04 6.18 Sr .75 1.08 1.09 Sr .62 1.37 .49 TOTAL: 91.91 92.57 90.07 TOTAL: 97.39 93.41 95.61 Th & U cte/sec above background Th &_ U cta/eec above background Th 3.80 3.1 3.40 Th 2.20 3.96 2.92 U 1.40 0.90 1.74 U 0.90 6 Nb:Ta 32.64 21.27 19.91 Nb:Ta 11.0 5 14.74 ;48 Fig. 35

206

probe Ana]1vsi a of Bokli Pyrochloree continued. Sample 393 9 Points across well zoned crystal with carbonate inclusions (mdta?).Gryatal 1.

Pt.1 Pt.2 Pt.3 Pt.4 Pt.5 Pt.6 Pt.7 Pt.8 Elmt. % Oxide % Oxide % Oxide % Oxide % Oxide % Oxide % Oxide % Oxide CRISTAL PLAN Na 6.27 8.15 6.47 6.52 6.25 5.80 6.85 6.20 Ca 16.04 16.41 16.54 15.90 16.27 16.31 16.08 17.31 K .00 .00 .00 .00 .00 .00 .00 .00 Fe .55 .67 .62 .68 .49 .50 .00 .00 Nb 62.91 62.97 62.43 63.59 64.15 64.63 64.45 63.15 .85 .00 1 Ta 1.75 1.44 1.68 1.62 1.29 .65 2 Mn .00 .00 .00 .00 .00 .00 .00 .00 Mg .00 .00 .00 .00 .00 .00 .00 .00 3 Ea .00 .00 .00 .00 .00 ..00 .00 .00 4 2.66 2.57 5 Ti 2.19 2.66 2.55 2.38 2.43 5.41 6 Sr .41 .36 .00 .00 .33 .00 ..00 .35 TOTAL: 90.29 90.70 91.48 90.52 90.60 92.42 7 90.11 90.68 8 U & Th as counts per second above background Th 6.30 5.88 5.28 5.00 5.98 4.95 5.00 5.14 U 3.04 2.96 2.90 2.36 3.79 3.18 2.92 3.40 1mm Nb:Ta 35.96 43.60 37.14 39.20 49.81 76.31 99.76 >600

Sample 393/9 Crystal 2 Sample 393/10 Crystal 1 No associate apatite Pt.1 Pt.2 Pt.3 CRISTAL PLAN. Pt.1 Pt.2 Pt.3 CRYSTAL PLAN Blest. % Oxide % Oxide % Oxide S Oxide % Oxide S Oxide Na 6.36 6.16 4.94 4.94 5.58 1.96 Ca 16.24 15.81 15.66 13.87 14.00 8.31 .00 .00 .00 .00 .00 .00 K Fe .67 .59 .54 1.99 2.75 3.35 Nb 63.74 62.35 61.07 64.37 63.95 57.68 1.81 2.25 Ta 1.47 1.73 1.56 3.37 •Mn .00 .00 .00 .00 .00 .00 Mg .00 .00 ..00 .00 .00 .00 . Na .00 .00 .73 1.36 1.21 6.71 Ti '2.28 2.22 5.54 5.81 5.06 5.34 Sr .00 .00 .45 .00 .00 .00 TOTAL: 90.77 88.85 90.46 95.70 96.22 89.91 Th & U cts/seo above background Th & U cts/sec above background Th 4.66 6.58 6.4 - 1mm 2.20 2.50 2.88 204um U 2.76 3.18 4.00 1.00 1.20 1.12 Nb:Ta 43.30 36.04 39.27 35.55 28.38 17.13 Sample 393/10 Crystal 2 Sample 393/10 crystal 3 Pt.1 Pt.2 Pt.3 CRISTAL PLAN, . Pt.l Pt.2 CRYSTAL PLAN Lint. % Oxide S Oxide S Oxide S Oxide S Oxide Na 2.61 5.38 5.31 5.30 3.62 Ca 7.75 13.61 13.65 11.68 11.55 K .00 .00 .00 .00 .00 Fe 2.98 2.57 2.50 1.32 2.02 Nb 42.45 62.96 60.35 57.52 57.68 Ta 4.21 2.93 2.21 5.41 4.20 Ma .00 .00 .00 .00 .00 Mg .00 .00 .00 .00 .34 Ba 4.45 .87 1.10 1.23 1.91 Ti 10.60* 5.01 5.43 3.36 3.92 Sr 1.04 1.60 .44 I 1.37 1.95 TOTAL: 76.09 94.92 91.33 87.19 86.84 cta/seo above background Th & U cte/sec above background I 20 Qum Th 3.80 2.36 2.60 200ium 1 2.40 4.80 U 2.4o 1.46 1.20 I 1.06 3.20 Nb:Ta 10.08 21.49 27.26 10.62 13.74 Sample 393/10 Crystal 4. Pt.1 Pt.2 Pt.3 CRISTAL PLAN Elmt. % Oxide S Oxide S Oxide DETECTION LIMITS Na 2.91 4.83 6.43 Ca 10.44 11.59 16.92 K .00 .00 .00 K .06 S Fe 1.67 .45 .00 Nb 57.54 55.56 66.41 Fe .12 5 Ta 3.70 3.90 .90 Mn .00 .00 .00 Ta .11 5 Mg .00 .00 .00 Ea 3.37 1.15 1.62 Ma .11 5 Ti 3.14 3.55 3.93 Sr 1.04 .56 .67 Mg .07 S TOTAL: 83.79 81.59 96.88 Ba .27 S Th & U cts/sec above background Th 4.32 4.60 .44 Ti .13 S U 2.76 3.06 .60 100u m Nb:Ta 45.55 14.24 73.95 Sr .13 S

Fig. 36 207 '

Probe analysis of Sbk1i Pyrochlores continued Sample275/77B t Crystal 1 Crystal 2 Pt. 1 Pt.2 Pt.3 Pt.1 Pt.2 Pt.3 Pt.4 Elmt. % Oxide % Oxide % Oxide CRYSTAL PLAN % Oxide % Oxide % Oxide % Oxide Na .92 1.12 2.03 .38 .00 .93 5.00 Ca 11.63 11.43 13.34 3.86 3.79 11.25 15.71 K .00 .23 .00 .00 .00 .00 .00 Fe .58 1.63 .75 1.99 2.08 1.70 .53 Nb 65.03 62.91 64.65 50.87 49.29 57.29 60.63 Ta 3.45 5.55 2.09 10.31 11.20 4.69 1.87 Nu .00 .00 .00 .00 .00 .00 .00 Hg .00 .00 .00 .00 .00 .00 .40 Ba 5.44 2.06 1.42 10.85 10.74 5.61 .92 Ti 3.36 3.43 3.78 3.96 3.52 4.00 4.48 Sr .97 1.30 .74 2.52 3.37 1.63 .50 TOTAL 91.37 89.65 88.81 84.73 83.98 87.11 90.02 Th & U ata/seo above background Th 2.00 2.66 3.00 200,um 2.66 2.66 3.44 3.70 U 2.34 2.44 2.60 2.28 2.66 2.20 1.90 Nb:Ta 18.85 11.34 30.93 4.94 4.60 12.21 32.46 Sample 275/776 Crystal 3 Pt.1 Pt.2 Pt.3 Pt.4 Stmt. % Oxide % Oxide % Oxide % Oxide Na .37 .00 5.53 .59 CRYSTAL PLAN CRYSTAL PLAN Ca 4.10 4.03 14.91 9.02 K .27 .00 .00 .00 Fe 2.11 2.55 .37 1.76 1 2 3 4 1 2 3 4 Nb 48.55 48.11 58.87 56.32 Ta 12.11 12.10 3.17 5.18 Na .00 .00 ;00 .00 Hg .30 -.00 .00 .00 Ba 9.92 9.38 -.93 6.96 Ti 3.78 3.75 4.07 3.54 Sr 4.33 3.74 .84 1.96 TOTAL 85.84 83.67 88.69 85.32 Th & U ate/sec above background 200,u m 200,u m Th 2.14 2.66 2.60 3.16 U 2.00 2.00 1.80 2.46 NbsTa 4.01 3.98 18.55 10.89 Sample 275/P Crystal 1 Crystal 2 Pt.1 Pt.2 Pt.3 Pt.1 Pt.2 Pt.3 Elmt. % Oxide % Oxide % Oxide % Oxide % Oxide % Oxide Na .97 1.51 .00 CRYSTAL PLAN .00 .80 .89 CRYSTAL PLAN Ca 11.67 12.39 12.59 10.58 12.05 11.92 K .00 .00 .00 1 2 3 .25 .00 .00 1 2 3 Fe 1.56 2.61 1.47 1.66 1.43 1.38 Nb 60.20 52.96 60.70 57.34 58.52 57.69 Ta 3.67 6.84 5.01 5.87 5.51 5.70 Mn .00 .00 .00 .00 .00 .00 Mg .00 .00 .00 .00 .00 .00 Ba 1.80 3.11 1.23 1.37 1.09 1.33 Ti 6.08 5.89 5.64 4.99 5.15 5.64 Sr 1.52 2.70 1.65 2.00 2.12 2.29 TOTAL: 87.47 88.00 88.31 84.07 86.67 86.85 Th & U cta/sec above background 200,um 20 Qum Th 3.60 4.80 5.36 6.84 5.90 5.80 U 3.40 2.00 3.40 4.00 3.90 3.80 Nb:Ta 16.40 7.74 12.10 9.77 10.63 10.11 Sample 275/P Crystal 3 -.Pt.1 Pt.2 Pt.3 Elmt. % Wilde % Oxide % Oxide Na .00 .00 .00 CRYSTAL PLAN Ca 12.45 13.09 7.17 K .00 .00 .00 3 2 3 Fe 1.87 1.41 5.02 Nb 59.15 61.16 58.57 Ta 4.19 3.73 4.70 Mn .00 .00 .00 Mg .00 .00 .00 Ba 1.74 1.69 4.95 Ti 5.45 5.57 6.15 Sr 1.97 1.82 2.38 TOTAL: 86.84 88.42 88.93 Th & U cte/sec above background Th 5.26 5.70 4.88 U 3.32 3.10 3.10 NbiTa 14.12 16.41 12.47 200,um

F i g. 37 ~n0 PLOT OFANALYSES FROM ZONED PYROCHLORE CRYSTAL(393/12,NQ1)

Points analysed (see fig 35 for full results ) I 0 1 2 3 \4 5 6 7 8 9 10 o 0 0 0 ; 0 0 0 o ) 0 0.' ,, 0

crystal core zo,n ens ,' rim

%Nbz05

9 Tap, 9

8 8

7 7 cnts/sec O/0 6 6 Taps Th 5 Na2 0—..J" \ 4 4

3 .` ► • ..,. 2 S\ N V' '1 2

0 0 1 2 3 4 5 6 7 8 9 10 11 points analyzed Fig. 38 209. lighter coloured material of a composition similar to those from the other parageneses; i.e. lower Ta. Those from 393/12, including the well zoned crystal with the melt inclusions of carbonate, have more uniform compositions. The Ta is slightly higher in the centre and steps down near the edge, the irregular lighter coloured border in these having no detectable Ta. These pyrochlores by further comparison with those from sovite 275/77B have barium contents below detection limits. They thus represent a type quite distinct from those of the SAPPM assemblages and also from the other sample of pyrochlore in sovite from borehole 275. 6.6.3. Discussion of Results and Comparison with other Complexes It is apparent that there is a variety of types of pyrochlore at Sokli which have characteristic habits, chemistry and paragenetic associations. These may only be some of the types present in the whole complex. A number of pyrochlore types are commonly found in an individual complex. The present discussion is mostly confined to the SAPPM assemblage and the information that can be drawn from the pyrochlore to contribute to an understanding of its genesis. The decrease in the levels of U and Ta towards the rims of many of the pyrochlores must reflect changing conditions during the formation of the crystals. In the earliest stages Ta and U were obviously readily available for incorporation into the structures. Decreasing temperature may have been responsible for the reduction in the availability of these elements. Solubility experiments on Nb205 and Ta205 in solutions of alkali carbonates, bicarbonates, hypo-phosphates and chlorites by Aleksandrov et al. (1972) showed that as the temperature falls below 450°C (at 1600kg/cm2), the Nb:Ta ratio in the solutions increases (see Table 16). They suggested on the basis of this that a high Ta content is only possible during high temperature niobium mineralization (450°C or higher) associated with solutions that have relatively low Nb:Ta ratios. 210. TABLE 16: SOLUBILITY OF Nb205 AND Ta205 IN CARBONATITE TYPE SOLUTIONS (after Aleksandrov et al.)

Initial Solution Concen- Temp. °C. tration (C) 400 450 500 (gms/litre) 0.5K2CO3+0.25MKHCO3 C Nb .080 .106 .131 +1.25MKC1; pH 9.8 C Ta .002 .004 .005 C Nb:C Ta 40 26 26

0.75M KHCO3+0.25MKF C Nb .027 .040 .070 +1.75M KC1; pH 8.0 C Ta .001 .005 .607 C Nb:C Ta 27 8 10

0.75M KHCO3+0.5M K2HP0 C Nb .090 .134 .204 +.75M KC1; pH 8.60 C Ta .001 .006 .011 C Nb:C Ta 90 22 19

Falling temperature may account for the chemistry of the pyrochlore in the SAPPM assemblage. The early crystals growing at high temperature, as temperature falls the rock becomes progressively more crystalline and the later pyrochlore is thus forced to grow both interstitial to, and by replacing other minerals. The later pyrochlore in this case will have lower and lower Ta values as the ability of the solutions to carry Ta decreases. The close association of pyrochlore with apatite and sulphides allows this information concerning the nature of the fluids to be extrapolated to the formation of the whole assemblage. It is conceivable that decreasing temperature brought about the precipitation of sulphides of iron and copper, the bulk of which tends to be slightly later than the pyrochlore. The close association of apatite and pyrochlore is emphasized in the Arbarasta massif (Zhabin, 1967) where pyrochlore-apatite veins are found in the fenite zones:- "The peculiarity of the veins lies in their extraordinarily simple mineral composition, they are composed of only pyrochlore and apatite. The quantitative interrelation between them varies, but usually pyrochlore shows a slight predominance." 211. Borodin et al.(1973) show figures of an apatite-pyrochlore aggregate from such a vein, with larger less common crystals of what they call hatchetolite (a Ta and U rich pyrochlore) joined together by a sinuous framework of pyrochlore of a more light coloured variety. They refer to the hatchetolite as generation one and the light coloured pyrochlore as generation two. They conclude that the finding of such apatite pyrochlore veins shows that on the formation of ultrabasic alkali carbonatite complexes, the conditions can arise i,n which essentially apatite fractions can be separated which have much higher niobium contents than the carbonatites. This deduction is well supported by the SAPPM at Sokli. 6.7. TEMPERATURE OF FORMATION OF THE SAPPM ASSEMBLAGE 6.7.1. The Sulphides The predominance of pyrrhotite over pyrite in the sulphide assemblage at Sokli suggests, by analogy with other ore deposits (Mitchell and Krouse, 1975) and from Fe-S-0 mineral equilibria, (Holland, 1959) that these sulphides have a high temperature of formation, between 500 and 700°C. This is supported by the apparent exsolution of chalcopyrite. To incorporate 5% chalcopyrite in a hot copper rich iron sulphide the temperature is likely to have been in excess of 600°C (Hewitt and Schwartz, 1937). Makela and Vartiainen (1978) used sulphur isotopes after the manner described by Mitchell and Krouse (op.cit.) - see Chapter 2, this work - as a qualitative check on the system of events, or carbonatite stages, which they describe at Sokli. They claim that all five major stages have sulphides associated with them. Whilst this is essentially true, the evidence from the present study suggests that the sulphides were rarely intimate parts of each stage of development, but over-prints of metasomatism. As discussed in Chapter 2, Mitchell and Krouse's analysis of S isotope chemistry in carbonatites is probably not a reliable method of gauging temperature; nevertheless, Makela and Vartiainen (op.cit.) present their isotope data and interpret this in 212. terms of temperature of the stages of development at Sokli (see Fig.39). An analysis of this data shows that their sulphur isotope data for the first four stages could in fact belong to two populations. Certainly, it is not possible to tell the difference between stages I and 2, or between stages 2 and 3 on the basis of these few samples. The Stage 5 sulphides are however mineralogically distinct and the sulphur isotopes are clearly different (Stage 5 corresponds to the late vuggy dykes with pyrite and pyrrhotite). The SAPPM assemblage (or assemblages) defined in this study is intimately linked to Makela and Vartiainen's Stages 3 and 4 (they regard Stage 3 as the phoscorites metasomatized by the front preceding Stage 4, the sovites and sillco- sovites). It is suggested here that, whilst there may have been one early stage of sulphide mineralization, much of the sulphide deposition/remobilization at Sokli could be related to the intrusion of later sovites and rauhaugites concomitant with the formation of the SAPPM assemblage. The qualitative estimate of temperature provided by the S isotopes is not at variance with that which is suggested by the association of exsolved pyrrhotite and chalcopyrite. However, these temperatures are at variance with the fluid inclusions of the associated apatite (see Chapter 7 where the temperature of homogenization is 160°- 180°C). For this reason some other methods of determining temperature and pressure were investigated. 6.7.2. Ilmenite/Magnetite Pairs from the SAPPM Assemblage As at Palabora, (see Chapter 2) the results of this work at Sokli are inconclusive (see Figs. 40 and 41). They indicate a minimum temperature of between 400 and 500°C, a low f02 for the exsolution-oxidation process. Although not providing an actual temperature of formation, the implication is that the assemblage was formed at a temperature in excess of 150-180°C suggested by aqueous fluid inclusions. The limitations of using this method are the same as those pointed out for the Palabora application.

213. SULPHUR ISOTOPES AT SOKLI

THE CARBONATITE STAGES AT SOKLI PLOTTED AGAINST TEMPERATURE FROM SULPHUR ISOTOPES USING DEDUCTIONS FROM MITCHELL AND KROUSE.1975. RELATIVE TIME -~ 700°

STAGE IT STAGE BT STAGE I --

500°- STAGE I[

STAGER'. 300° - (From iākela & Vartiainen 1978)

HISTOGRAM PLOT OF DATA USED BY -• A & VARTIAINEN (ABOVE)

Note that only three populations are recognizable.

4 N 3 mm II 2 III T I 1 I II IQ MID 1 Y 8 Y -1 -2 -3b Soo4 S T i n Aa A A E A S y A

Fig. 39

214. 6.7.3. Geobarometry using the Sphalerite-Pyrrhotite-Pyrite Equilibrium The temperature postulated from the above-mentioned geothermometer is much higher than the homogenization temperature of the fluid inclusions. A pressure correction of 4k.bars is needed to bring the fluid inclusion homogenization temperatures up to 400 or 500°C (see Chapter 7). An independent geobarometer would provide an insight into this problem. Hutcheon (1978) suggested the use of the mol% of FeS in sphalerite, in equilibrium with pyrrhotite and pyrite, A few instances of pyrite exist in the SAPPM assemblage which, from their intergrowths, appear to be in equilibrium with pyrrhotite and sphalerite. These sphalerites were probed, but the composition was found to be extremely variable (mol% FeS in sphalerite from 17.1 to 25.3%). This range was too wide to be meaningful and the study was discontinued. The reasons for such variations could'be numerous. The sphalerite at Sokli is largely exsolved from chalcopyrite and the small grains studied which were next to pyrite in pyrrhotite may have exsolved from the pyrrhotite/ chalcopyrite solid solution at a much lower temperature than the temperature of formation. The sphalerite had some cadmium in it. This may also upset the solubility relationship of FeS in ZnS (Stanton, 1972), though according to Kullerud (1953) the amounts usually found in sphalerite are unlikely to make much difference to the now debunked geothermometer. There is always the problem of re-equilibration in sulphides. These readily readjust to changes in T and P and as such, although Hutcheon had reasonable success plotting values of FeS in sphalerite from a metamorphic environment, it seems probable that this barometer will also be found to have limited application. 6.7.4. Proposed Temperature of Formation It must be concluded that the temperature of formation of the assemblage is about 500 or 600°C and that the temperature of homogenization of fluid inclusions associated

215.

ANALISIS OF MAGNETITE ILt,'6NITS PAIRS FROM THS S.A.P .P A ASSEZSFŪAG8

Sample Ho. 3938A area 1 ?air A Pair B Pair C Pair_ D % Pt.l Pt.2 ?t.3 Pt.4 Pt.5 Pt.6 Pt.7 Pt.8 Probe plan area 1. Ilm. Mt. Ilm. Mt. Ilm. ht. Ilm. Mt. SiO.00 .30 .00 .00 .00 .21 .20 .00 TioZ2 55.76 .93 55.93 .73 53.34 1.30 52 1.88 A1,0 .00 .00 .00 .00 .00 .00 .00 Fef7 3 25.69 91.62 26.11)3 89.04 31.37 89.13 31.34 90.64 Mr0 6.30 .00 6.38 .48 5.46 .36 5.38 .51 Mg0 11.44 1.34 11.19 1.38 9.73 1.16 10.01 1.11 SUM 99.19 94.19 99.68 91.63 99.90 92.16 99.28 94.14 Recalculated Analyaia - Magnetite - ULVOSPINEL BASIS Fe203 67.80 I 67.10 1 65.65 66.42 Fe0 30.54 28.59 29.98 30.80 TOTAL 100.91 98.28 98.67 100.72 % USP 3.77 2.13 4.58 5.35 Recalculated Analyaia - limonite - HEMATITE BASIS Fe203 2.57 I 2.54 6.97 Fe0 23.37 23.89 25.09 ( 24.02 TOTAL 99.45 99.93 100.59 100.08 %ROMB 97.74 97.77 93.86 92.82

Sample No. 393/8a area 2 Pair E Pair F Pair C Pair H Probe plan area 2. Pt.9 Pt.10 Pt.11 Pt.12 Pt.13 Pt.14 Pt.15 Pt.16 SiO2 .00 .00 .20 .00 .00 .26 .00 .25 TiO2 54 733 1.13 55.12 .58 51.27 1.45 54.42 2.70 o .00 .00 .00 .00 .00 .00 f4F 3 31.10 89.98 31.90 91.30 36.29 90.08 32.09 89.83 t-fa0 5.31 .46 5.51 .00 5.51 .44 5.02 .61 Mg0 8.87 .97 9.16 .88 6.40 .66 8.49 1.03 SUM 100.01 92.54 101.89 92.76 99.47 92.89 100.02 94.42 Recalculated Anelysia Magnetite - ULVCSPIiEL BASIS Fe203 66.70 67.95 65.47 64.25 Fe0 29.89 30.08 31.10 31.94 TOTAL 99.15 99.49 99.38 100.79 % USP 3.27 1.68 5.19 8.61 Recalculated Analysis - Iimenite - HEMATITE BASIS Fe203 3.41 4.44 1 7.96 3.74 FeO 28.03 27.90 29.12 28.72 TOTAL 100.35 102.33 100.26 100.39 %ROME 96.97 96.14 92.78 96.67

Sample No. 393/8a area 3 Sap urler 333/2 area 1 Pair I S Pt.l7P-.18 Probe plan area 3 Pt.l9 Pt.20 Probe plan 393/2 area 1 Ilm Mt Iln Mt SiO2 .00 .25 .29 .00 Ti 2 52.04 .92 51.42 1.96 220 .00 .00 .00 .00 Fe0 3 33.64 89.72 37.42 90.29 Mao 5.31 .00 5.05 .00 MgO 7.45 .74 5.06 .45 SUM 98.44 91.63 99.44 92.84 Recal.Mt. ULVOSP1NEL Fe 03 65.70 64.93 Fe3 30.53 31.79 TOTAL 98.14 99.27 % USP 3.67 5.68 Recal.Ilm. HEMATITE Fe203 6.11 5.80 Fe0 28.14 32.20 TOTAL 99.05 100.01 %RONB 94.45 94.69

Ilaecite Magnetite Gangue

The proportion of Fe*' to Fein the magnetite and ilmenite has been calculated according to the scheme of Carmichael (1967)uith the aid of programme IILMAGt - by J.C.Rucklidge. Scale bar= 250,um

Fig . 40

216. TEMPERATURE & f02 OF MAGNETITE — ILMENITE PAIRS

S.L.P.P.M. Assemblage Sokli 5 Calculated ulvospinel in magnetite and rhombohedral phase in ilmenite from probe analysis plotted on curves•from Buddington and Lindsley (1964)

v~1-N ' JyQh JSQ~

N r•O 0

ō 20 t

l .r Samples from 393/8a 4 Sample from 393/2 .16 C - I A-Jpair identification .40/

25— / /F. / / Ici /E /

- /A 1/

kTLange - . 30 I t 300 400 500 600 700 800 900 1000

Temperature, °C

Fig. 41

217. with the assemblage is not a true measure of the formation temperature. A large pressure correction may be the reason for this discrepancy (see Chapter 7). 6.8. A GEOCHEMICAL EVALUATION OF THE SAPPM ASSEMBLAGE 6.8.1. Objectives The association of sulphides, apatite, phlogopite and pyrochlore as described in the previous sections suggests that the assemblage may have been introduced into earlier rocks of differing composition by some metasomatic process. Since the apatite in the assemblage contains primary fluid inclusions which may be relevant to such a process, more information concerning the metasomatic origin of the assemblage was sought. It was considered that chemical analysis ' of a number of rock types which contained the assemblage in differing quantities might reveal constituent correlations between the elements characteristic of the assemblage; in particular, Cu, S, Nb and P. Good positive correlations between these elements would suggest that they had indeed been introduced into the earlier rock types by fluids with consistent ratios of the elements, whilst poor correlations would tend to favour other processes, such as crystal settling for the apatite and pyrochlore, with later introduction or remobilization of the sulphides and possibly the apatite, pyrochlore and phlogopite. Further to this, any correlation observed might provide useful element pathfinders for economic quantities of the assemblage. Niobium particularly, is not an easy element to analyse for and, since it clearly reaches ore grade concentrations in places at Sokli, other elements associated with it could well prove to be cheaper and more effective elements to analyse for in exploration geochemical programmes. Further impetus for the work was provided when some values of Nb and P provided by Rautaruukki from boreholes 274 and 275 (see Fig. 32)-were found to show good correlation, particularly in the areas where the sulphide levels were high enough to consider analysing for copper as well. 218. It became clear that the Nb and P showed a fairly consistent correlation in the highly mixed rock phoscorites, sovites and rauhaugites, whilst there appeared to be some earlier sovites which had levels of phosphorus without the equivalent values of niobium (see scatter plots, Fig.42A and B). The good correlation between P and Nb has been recorded from other carbonatites (Van de Veen, 1963), so any further observations at Sokli may be applicable to other complexes. A geochemical attempt to quantify the petrographically observed relationships was thus undertaken. 6.8.2. Methods of Sample Selection and Analysis From the material collected at Sokli 62 samples were selected. These were split borehole core (diameter 4.5cm); sample lengths were mostly between 10 and 15 cm. Larger samples would have been preferable, but they were not available, because sample lengths of more than 20cm. often consist of more than one rock type. The samples were divided into subgroups on the basis of the fundamental rock types so:- (For sample numbers and group allocation, see Appendix 5) Subgroup N 1 Phoscorite 2 2 Phoscorite - associated carbonate sovitic 8 3 Early(?) greenish sovite 6 4 Sovite with sulphide streaks 12 5 Mostly SAPPM assemblage - associated rock sovitic 10 6 Rauhaugite with sulphide streaks 5 7 MostlySAPPM assemblage - associated with rauhaugite 3 8 Sovitic magnetite rich mixed rocks 5 9 Silicosovite 4 10 Silicorauhaugite(?) 1 11 Dolomite/ankerite bearing late stage dykes 2 12 Phoscorite - associated carbonate dolomitic 4

Subgroups 2,4,5,8 and 9 were treated as the sovitic group, whilst groups 6,7,10 and 12 were treated as the dolomitic group (note groups 1,3,11 excluded). After logging the original core and studying thin sections, it seemed probable that the SAPPM (sulphide, apatite, pyrochlore, phlogopite assemblage) was indirectly associated with both

219. the sovitic and the dolomitic rocks. It was thus considered probable that metasomatism may have been caused by volatiles from both the sovitic and rauhaugitic events. The samples were crushed, milled and analysed using XRF and atomic absorption. For the details of method, see Appendix 5. Data for 18 elements were obtained and processed, using a computer programme package compiled by Parker (1979). This produced correlation matrices for all or any of the selected groups. An interactive graphics routine produced scatter diagrams which allowed a visual check of the more significant and relevant correlation values. These plots were recorded on microfilm and some are presented here (see Fig.42). The data were processed twice. In the first instance (data base 0) all of the values below detection limits were excluded; in the second (data base 1) these were ascribed a value of one ppm and included in the calculations. The poor resolution of the XRF method used for lower values of Th, Zr and Nb meant that a number of samples were excluded in the first processing. These samples with Th below detection limit had clearly related low values of Nb, copper and phosphorus. For this reason much of the work was done using data base 1. 6.8.3. The Results The correlation matrix of all the subgroups (except the late dolomitic/ankeritic dykes - group 11) is presented in Table 17. Matrices for the sovitic and dolomitic (rauhaugite) groups are also presented. There are many good positive and negative correlations which are significant at the 99.9% confidence limit in each of the matrices. Many of the values are to be expected from the mineral chemistry. For example, good positive correlations between Mg and Si, K and Si and Na and K were expected because all of the elements are chiefly represented in phlogopite. The consistent ratio of these elements in phlogopite in conjunction with variations in the modal % of phlogopite produces a good positive correlation. Correlation between strontium and calcium (see Fig.42F) is due to the similar ionic radius

220. SOKLI GEOCHEMISTRY - SCATTER PLOTS Nb v P20 Boreholes 275&274 Nb v P205 Boreholes 275&274 areas of high CU & Fe 4 B R : 0.6775 N = 20 R = 0.5699 N = 54 rn ( Low Cu &Fe19. High Cu&Feo

0 0

'O a .O~ O a O a a 'o a a 0 a a 0 O" 0 a O 0 a v 019 0 O ° (•1 a O C, ° v 0.80 1.60 2.40 3.20 0.80 1.60 2.40 ' 3.20 P205 WTPC P20.5 WTPC

Nb v P205 For all samples anlysed in this study D Nb v P205 dolomitic groups only Cto Poor overall correlation R : 0.4743 N S 76 O R = 0.7324 N = 14

GRP1 0 GRP{ 0 0► 0 GRP2 0 GRP2 0 GRPS A GRP11 • GRP4 + GRP12 + O GRP6 X N • GRPS a GRP10 + z GRP13 X GRP12 Z . a x Cm C 0 f x a 0 'o X • R 0 • 0 z • + • a

a • • a + a O S0 0 4.00 8.00 12.00 16.00 cb . 00 2.00 4.00 6.00 8.00 P205 WTPC P205 WTPC

Zn v Fe for sovitic samples analysed in this study Sr v Ca for sovitic samples analysed in this study a R 2 0.8143 N = 37 F• R = 0.8805 N 38 m a A ! GRP2 0 m • GRP? O GRPS 0 GRPS 0 GRP4 A GRP4 • O GRPB + 0 GRPS + O • • GRPS X • GRPS X • •

• •

+ O O v co a Q • 0 + a a O + 0 O 4. ° JO. • 0 + a + + X •Y X X °° •° 0 X • a •8 `ll 2b.00 4b.00 610.00 80.00 im0 .00 10.00 20.00 30.00 40.00 FE WTPC CA WTPC

Fig.42 221.

SOX= GE0CllEF18TRY: CORRELATION MATRIX FOR ALL SAI•?LES (Zxcepting Late Ankeritic Dyke:) Sub Group 11

Si S Fe Mn Mg Ca Na X P Nb Co Ni Cu Zn Zr Pb Sr Th Si 1.0000 Fe Nn Mg 1.0000 Ca -.3282 -.4, Na 1.0000 K .4725 %-.438') .4897 1.0000 P Nb Co Ni 1.0000 Cu .4447„ 1.0000 Zn 1.0000 Zr .3152 1.0000 Pb 060 Sr - 3937 .85 -.4525 .3533 .3072 1.0000 Th .5819 .5692 L3602 11.0000

Only significant correlations shown (greater than 97% confidence). Number of samples = 60 Data base 1 (i.e.valuea of Zr, Th dr Key to percentage confidence limits Nb below detection limite are taken 99.9,E aa 1 ppm.) L. 99.0% • 97.0% Blank box = no significant correlation

CORRELATION MATRIX FOR SOVITE GROUPS (Data Beae 1) N = 38 Si ,'S Fs Mn Mg Ca Na K P Nb Co Cu Zn Zr Pb Sr Si 1.0000 1.0000 Fe 1.0000 Mn 6722 1.0000 Mg .8419 .3876 1.0000 Ca -.694 .3606 -.8088 -.5545 -.6971 1.0000 Ne .5930 1,•.3873 1.0000 K .8401 .7034 -_.44241 .5507 1.0000 P .3789 1.0000 Nb 1.03445 , .4050 .3548 1.0000 Co p..4237 -.3600 1.0000 Cu :497 .3642 .3815 1.0000 Zn .8142 .8661.3656 -.7257 1.0000 Zr 57771 .4467 1.0000 Pb 4335 .4554 L.4758 .3622 5,51_21576 1.0000 Sr -.6446 ~.3483 ,..6915 .4600 6a64 .8805 I-,4210 .3325 -.62 1.0000 Th .6157 .49'7r-

column-10 MATRIX FOR DOLOMITIC GROUPS (Data Base 1) N = 12 Si S Fe Mn Mg Ca Na IC P Nb Co Cu ' Zn Zr Pb Sr Si 1.0000 S 1.0000 Fe .5883 1.0000 Mn L..6201 1.0000 Mg .6605 1.0000 Ca -.7174 1.0000 Na 1.0000 K 1.0000 P .6332 .6066 1.0000 Nb 1-.5970 .6490 1.0000 Co j-.594_.5914 1.0000 Cu -.5819 .7140 .8255 1.0000 Zn 6086 1.0000 Zr 6703 7 2 Pb 55 1.0000 ~470 _ 7026 .I8343 .6283 1.0000 Sr t_ 6120 .7239 .17211 Th 1.0000 .5895 .9121 .6918 .8801 .7773

Correlation significance:- 99.9% 99.0% 95.0% Blank box = no significant correlation Table 17 222. of the two elements and the ability of strontium to replace calcium in both carbonates and apatite. Negative correlations between calcium and iron, silica and sulphur are due to decreasing amounts of calcite and dolomite as levels of sulphides and phlogopite increase. It is the relationship between elements of the SAPPM assemblage however, which are most important. The positive correlation between niobium and phosphorus is seen in the matrices, as it was in the boreholes 274 and 275. The correlation coefficient .4250 is, however, not as high; probably due to small quantities of earlier apatite unrelated to mineralization, as seen in the boreholes 274 and 275. Nevertheless, it is significant at the 99.9% confidence limit. Correlations between copper and niobium and niobium and sulphur (.4015) are low, but with 60 samples, they are considered statistically significant at the 97% confidence limit. The overall relationship between phlogopite and the sulphide assemblage is reflected in the K/Cu (.3463) and K/Co (.3749) - Co has a higher correlation with sulphur than Cu - the reason for this is not clear, but it may reflect the variations of chalcopyrite:pyrrhotite. There is no correlation between phosphorus and sulphur and yet there is between sulphur/copper, cobalt with niobium and between niobium and phosphorus. Thus, while there is an indirect relationship in this way, the direct correlation between ' the sulphides and.the phosphorus is not clear. It is considered possible that the early apatite unrelated to mineralization in conjunction with a probably slight remobilization of sulphides has blurred this relationship. The trace elements also add some weight to the relationship between the constituent minerals of the SAPPM paragenesis. Zirconium and, to a lesser extent, thorium show significant relationships with sulphur, phosphorus and niobium. The sovitic and dolomitic groups show similar trends, implying that the same essential process is at work in both types. However, the small number of samples,

223. particularly in the dolomitic groups, makes evaluation of the differences between dolomitic and sovitic populations statistically unreasonable. The mean values of the various groups (see Table 18) show the remarkable similarity between the sovitic and dolomitic (rauhaugitic) groups. The levels of copper are, however, higher in the dolomitic types, but this is not statistically reliable with respect to the dolomitic groups. Although this may be a spurious effect brought about by sampling dolomitic groups with higher modal percentage of sulphide minerals, the mean values of the copper:sulphur ratios for the two groups also imply_ slightly more copper in the dolomitic types. From the ratio of copper to sulphur in each sample, the percentage of chalcopyrite in the sulphide assemblage can be calculated. For the purpose of this calculation the sulphide assemblage consists of pyrrhotite Fe0_95S and chalcopyrite CuFeS2 (the contribution from any other minerals is insignificant). The sulphide assemblage has a mean of 5.31% chalcopyrite (standard deviation 15.13, N = 62). From polished thin section work it was estimated that chalcopyrite made up between 5 and 6% of the sulphide assemblage. The ankerite bearing late stage dykes have much less copper and the calculated chalcopyrite percentage from analysis is 0.29% of the sulphides in these late dykes. This supports the sulphur isotope differences of Makela and Vartiainen (1978) where the sulphides of the last stage had values very different from the earlier sulphides (see section 6.7.1.). To allow comparison of the sulphide assemblage with Palabora, five samples of concentrated sulphides were analysed by atomic absorption (see Appendix 5,) PGM and gold were also sought, using neutron activation. Table 19 sum- marises this information and provides a comparison with Palabora. The differences are clearly enormous. Copper is obviously much higher in the Palabora assemblage (66 times). The same factor is not applicable to all elements. Zn, Ni, Co and Ag are all similar, but the Au and Pb are much higher at Palabora. The ratios are also 224. TABLE 18: MEAN ELEMENT VALUES FOR SOKLI GROUPS (BASE 0) (excluding Group 11)

All Samples Sovitic Groups Dolomitic Groups N=38 N=12 mean d N mean o' N mean d N SiO 9.00 57 8.06 7.72 36 10.31 10.62 11 S 2 6.91 7.11 60 7.04 7.20 38 9.08 7.98 12 Fe 18.9 15.03 59 20.21 15.26 37 21.30 16.23 12 Mn .32 .24 60 .28 .17 38 .34 .16 12 Mg 5.21 4.06 60 4.15 2.44 38 9.08 5.65 12 Ca 18.79 12.70 60 19.54 12.95 38 13.21 9.36 '12 Na .17 .14 60 .18 .16 38 .12 .82 12 K 1.03 1.47 60 .97 1.21 38 1.38 1.98 12 P 0 2.61 2.91 59 2.75 3.09 37 2.94. 3.17 12 Ng .33 .40 55 .35 .45 37 .36 .36 11

ppm Co 186 181 60 206 196 38 199 191 12 Ni 121 236 60 129 246 38 142 303 12 Cu 1207 2026 60 821 860 38 2284 3003 12 Zn 261 261 60 269 248 38 236 241 12 Zr 1124 1591 42 987 1646 31 1285 1155 8 Pb 45 17 55 42 17 36 44 18 12 Sr 3434 2702 59 3298 2678 37 2526 1998 12 Th 1078 1643 21 797 845 - 13 738 359 6 Si:Cu 147 129 151 (Si:Cu ratio in ankeritic dykes = 554) N.B. Figures below detection limits not included in means.

225. different, even Ni:Co ratios showing considerable differences. Some of these differences may be due to the different sulphide mineralogy at Sokli, their structures perhaps not being so amenable to the incorporation of other elements as those of the more variable assemblage at Palabora. This will not, however, account for such radical differences and it seems apparent that the sulphide mineralization is derived from a system chemically distinct from that at Palabora. TABLE 19A: TRACE ELEMENT VALUES OF SULPHIDE ASSEMBLAGE (ppm)

SOKLI PALABORA Factor Mean Standard (see difference Range N between ppm Deviation Chapter 2) Sokli & Palabora mean ppm

Cu 6066 (2274) (3380-9400) 5 400000 x66 Zn 155 (109) (56-310) 5 961 x6 Ni 196 (102) (70-250) 5 1807 x9 Co 732 (246) (450-1100) 5 1348 x1.8 Pb <0.5 - - 5 472 x900 Ag 26 (13.8) (24-42) 5 16.5 x.6 Au .004 (0) (0) 2 1.43 x358 PGM

Cu:Ni 41.69 (31.37) (14.102) 5 222 Cu:Zn 52.42 (24.83) (30-95) 5 418 Cu:Co 9.04 (3.98) (3.8-11.7) 5 579 Cu:Pb >12000 (>4548) (>6760-18800) 5 851 Ni:Co .25 (.07) (.15-.33) 5 1.34

Sulphur values from mean sulphide minerals (percentages)

If mean sulphur value at SOKLI = 537,000 PALABORA = 32,0000 (see Chapter 2)

S:Cu = 88.5 0.8 S:Zn = 3465 333 S:Ni = 2740 177 S:Co = 734 237 Electron microscope detection on Sokli pyrrhotite shows levels of Co between 1.1 and 1.4% (5 samples).

226. 6.8.4. Correlation Matrices for Boreholes 274 and 275 The element values for this borehole were provided by Rautaruukki Oy (see Fig.32). Correlation matrices produced with these values show the strong correlation between P and Nb (see Fig.42). The scale of sampling is much larger for these samples. The borehole was sampled in five metre sections and each sample thus shows a variety of rock types. A new correlation emerges between Fe and Nb (see Table 19B). This is present not only in banded micaceous rocks (the high pyrochlore and magnetite areas) but also in the low mag-, netite and niobium carbonatites, (see Table 19B and Fig.32). TABLE 19B: CORRELATION MATRICES FOR BOREHOLES 275 AND 274

Correlation Matrix Number of Samples used in Correlation Calculations BH 274/275 All Samples mean Fe Cu Mn P Nb Fe Cu Mn P Nb Fe (10.8) 1.000 62 Cu (.234) 1.000 21 Mn (.279) .6460 1.000 24 24 P (1.69) 1.000 62 Nb (.265) .7087 .6449 .5889 1.000 54 23 54 62

BH 274/275 Mixed Rock Phoscorites mean Fe Cu Mn P Nb Fe Cu Mn P Nb Fe (17.8) 1.000 20 Cu (.234) 1.000 20 Mn (.364) 1.000 11 P (1.95) 1.000 20 Nb (.461) .5937 .6775 1.000 20 20 20

BH 274/275 Carbonatites (low Nb and P, no Cu) mean Fe Mn P Nb Fe Mn P Nb Fe (7.47) 1.000 42 Mn (.207) 1.000 13 P (1.58) 1.000 42 Nb (.150) .4821 .4763 1.000 34 34 34

This iron is present in magnetite (which may have been introduced into the banded mica rocks before the SAPPM) and also in phlogopite, which makes up large proportions of the banded rocks (see Fig.32). The magnetite and sulphides deposited with the SAPPM assemblage provide insignificant Fe on this scale. The textural studies of the SAPPM assemblage

227. suggest that in some instances the micaceous rocks may have caused the precipitation of the assemblage. The correlation between Fe and P/Nb on this scale may be related to this. The complexity of the boreholes 274 and 275 is possibly related to large scale metasomatism. The magnetite may have been formed as part of this process, along with humite group minerals, phlogopite and apatite together with the SAPPM assemblage and extensive tremolite deposition. The SAPPM assemblage is present in boreholes 274 and 275, but its relationship with the other rocks is more complex than in, the other boreholes studied. There may have been an earlier (pre-SAPPM) stage of apatite, pyrochlore, magnetite mineralization. An early stage of pyrochlore mineralization is indicated by the low Nb:Ta ratios in the centre of some of the pyrochlores of the SAPPM assemblages (see section 6.6). The correlations observed in this large scale sampling are outside the context of the SAPPM assemblage and the work done in this study, where only rocks affected by SAPPM were analysed to test the hypothesis that the SAPPM assemblage is of hydrothermal/metasomatic origin. It is considered that these early silicate rocks have controlled the deposition of incompatible elements, perhaps carried from the carbonatites by volatiles. 6.8.5. Conclusions reached from the Analytical Study. The significant correlations between the elements of the SAPPM assemblage support the theory that the elements of the SAPPM assemblage were behaving in a similar coherent manner independent of the host rocks; i.e. some process apparently independent of the main rock types is probably responsible for the deposition of the SAPPM assemblage. A process of hydrothermal/metasomatic introduction is considered feasible. Elements which might be useful in exploration programmes for SAPPM minerals include phosphorus, copper, cobalt and thorium. Copper and cobalt can be analysed cheaply and thorium might provide radioactive anomalies. Orientation work would be required to establish these relationships in 228. any particular terrain or complex. From the limited number of samples studied, it is not possible to differentiate between SAPPM associated with rauhaugites and that associated with sovites. Many more analyses are required to make a statistical analysis of the relationship between tl-e groups and the subgroups.

6.9. SUMMARY AND CONCLUSIONS A copper bearing assemblage of sulphides, apatite, phlogopite, pyrochlore and magnetite is identified at Soli. Borehole logging, hand specimen and microscope work indicate that this assemblage is related to sovites and rauhaugites and is introduced into older phoscorites, carbonated phlogopite rocks and carbonatites, in many cases apparently replacing carbonate. Although sulphides of other associations exist in the complex, a large proportion of the sulphides belong to this assemblage. Petrographic/minerographic work reveals that the apatites, which contain aqueous fluid inclusions, were deposited together with the sulphides and the pyrochlore of the SAPPM assemblage. The fluid inclusions in the apatite can therefore be studied in the knowledge that they are closely related to the fluids responsible for the transport and deposition of niobium and copper. On the basis of chalcopyrite/pyrrhotite relationships and magnetite/ilmenite pairs, a temperature of 500-600°C is proposed for the formation of the assemblage. Probing of the pyrochlores shows that many types have cores with high Ta values, but that this drops off towards the rims. Experimental work by Aleksandrov et al.(1971,1972) suggests that such a process is temperature related; Ta only being transported in alkali carbonate aqueous systems in significant quantities above 450°C. The geochemical programme indicates that the SAPPM minerals could have been introduced into earlier rocks by solutions which deposited quantities of the elements in consistent proportions. The hydrothermal/metasomatic hypothesis

229. for the origin of the assemblage, proposed from the obser- vational data, is supported by geochemistry. The geochemistry also implies that soil geochemistry for Co, Cu and P might prove effective in finding economic quantities of Nb and Th.

230. CHAPTER 7: INCLUSIONS IN APATITE FROM THE SAPPM ASSEMBLAGE, SOKLI 7.1. INTRODUCTION The evidence presented in Chapter 6 suggests that much of the apatite at Sokli was co-genetic with both pyrochlore and iron and copper sulphide deposition. Primary fluid inclusions in the apatite provide a direct means of studying the physico-chemical conditions of ore transport and deposition in the Sokli carbonatites. As discussed in Chapter 1, previous studies of fluid inclusions in carbonatites have mostly been concerned with the temperature of formation and the genesis of the host carbonatites. A pilot study of inclusions at Sokli by Haapala (1978, Abstract) follows this trend and is geared towards understanding the petrogenesis of the complex. Haapala recognizes three major types of inclusion at Sokli:- 1)Multiphase; 70% daughter minerals (unidentified), 30% aqueous and vapour. Homogenization (Th) not attained. Decrepitation at about 400 C. 2)Aqueous; Aqueous solution with gas bubble, two opaque specks and colourless isotropic daughter, assumed to be a carbonate or halite (Th = 200°C). 3)Rarer inclusions with CO2 and also inclusions intermediate between 1 and 2. Haapala concludes that the solid inclusions may represent a carbonatite melt; the aqueous inclusions representing a co-existing aqueous phase. He comments however, that "the evidence is not unambiguous". The present work has been conducted concurrently with Haapala's work, but with a view to understanding ore genesis (particularly of the SAPPM assemblage) and its relationship to the carbonatite process. A more integrated study, including the petrographic and paragenetic relationships of the apatite, together with fluid inclusion work, was considered essential for a thorough understanding of the physico- chemical nature of the media responsible for sulphide transport and deposition in the SAPPM assemblage. Emphasis has

231. therefore been on elucidating the chemistry of the parent fluids, as well as the physical conditions operative during mineralization. Although the Sokli carbonatites do not represent an economic deposit of copper, this work provides a useful adjunct to the studies at Palabora, where fluid inclusions are not well represented in the final mineralizing events. Rarely phlogopite and pyrochlore have inclusions, mostly of the same type as those in the apatites. As mentioned in Chapter 6, the calcite and dolomite also contain a similar fluid inclusion assemblage, but these inclusions are usually severely necked and appear to be secondary. The inclusions in apatite have been studied using polished thin sections, doubly polished plates and apatite grains which have been immersed (after crushing and concentrating using heavy Liquids) in a suitable immersion oil (Rankin and Aldous, L979). Inclusions in the apatite have been investigated using transmitted and reflected light microscopy (see Appendix 1) and scanning electron microscopy (SEM)/electron probe micro-analysis (EPMA), (see Appendix 2). 7.2. THE INCLUSION TYPES IN SOKLI APATITES The various types of inclusion are depicted in Figs.43A (those of fluid origin) and 43B (solids). The types described by Haapala (op.cit.) are found in the first category. Of these the aqueous/vapour inclusions are by far the most common. These have been designated as Type 1 in this study and are the focus of much of the present work. 7.2.1. Aqueous/Vapour Inclusions - Type 1 (see Fig.43A) Spheroidal and tubular cavities are the most common shape for these inclusions (see Plate 21C and D), though both highly irregular and negative crystal shapes (see Plate 25B) are not rare. They are typical, in form and distribution, of the aqueous inclusions in apatites from carbonatites reported by other investigators (see Chapter 1). The inclusions may be isolated, in many cases only one per crystal of apatite, though groups of 2-10 or more are not 232. CLASSIFICATION OF INCUSIONS IN APATITE

A. FLUID AND GASEOUS BEARING INCLUSIONS mE 1 Aqueous am w.pour 1Dal.u8iona with or without daughter m1Mrals.

o (~ ~ c____ -"l _____j o 10 AI , 10 Al"

TIPE J KalJlPbase gas iMlua10na mE 4 Opa.&:tue black to greeaim brovn inclusions soma with saccharoid41 texture. Hydrocarbon &for pyrochlor-.. ;;~· ".~"- Qv.. ,: ~~ ""; -,'. . '~. ~-;: lOuO ,

mE S ltutisol1d inclua10na with &qUeous &at ...-pour phases. -the LIIINJ1t of aolid "ftl'iell. o C1')"~ne contents not vell de tined v

. .... NB - • 0 o

J.q =Aqueous solution. V =Vapour B =B:1.retr1ngent. NB =Non birei'l"ingent o =Opaque

8. SOLID INCLUSIONS mE 6 Captured solid il'lcluaiona. ~ trn:1denti.f'ied pba.se O/GNB colourless NB. , 200 J1 , Opaque solids (pyrrbotite) R.I. > than apatite Pyrocblore

mE 7 Roumed ealcite inclusions

calcit.

100 At

mE 8 Elongate inoluaions aligned parallel to apatite C-ex:1s.

c Sulph1dea > MagnSt1te

Phlogopite c , , v NB 25.u

Fig. 43 233. uncommon. In some instances (e.g. 275/10, see Plate 21A) single crystals may be packed with inclusions. In these cases, a central zone of each crystal is filled with inclusions whilst the outer zone is barren. This is good evidence of their primary origin (Roedder, 1967). The inclusions range in size from less than 1 micron up to 100 microns with most falling between 5 and 30 microns. Although the number density of inclusions varies immensely. from one slide to another, the degree of filling (an indication of the likely homogenization temperature),is remarkably constant. The degree of filling is defined as the ratio of liquid to vapour in a two-phase vapour and liquid inclusion (see Rankin, 1978). The degree of filling of the Sokli aqueous inclusions is about .95 as deduced from photographs of spherical inclusions. Assuming that it is a pure NaC1 brine, this should give an homogenization temperature (Th) between 130° and 140°C, depending on the brine concentration (Rankin, 1978 op.cit.). The mean measured Th is 161°C (see Table 22). The difference between the calculated and measured Th is either due to slight aberration in apparent bubble size or variation in chemistry (components other than NaC1 are important in this). As mentioned by Haapala (op.cit.), these inclusions may contain solid phases, which may be daughter minerals. Most common are one or two opaque specks (see Plate 21J), a dark (possibly opaque) acicular crystal (see Plate 21C) and one or more birefringent and non-birefringent colourless phases (Plate 21D). These are described in more detail in the next section. Necking down (Roedder, 1967) of the primary inclusions has obviously occurred in some crystals, especially where a number of inclusions are clustered together (Plate 21B and H and 24C). Considerable variation in the vapour bubble size and daughter mineral content are indicative of necking together with 'necked off' tubes between inclusions and daughter minerals half buried in the host walls (Plate 21G). For aspects of the study where necking produces ambiguous results, material of this type has been excluded.

234. PLATE 21: Aqueous Bearing Inclusions in Sokli Apatites

A. Sample 275/10. Zoned apatite crystal with central core containing many aqueous inclusions (dark spots). Apatite grain mounted in tritolyl phosphate viewed in plane polarized transmitted light. Bar = 200 microns.

B. High density of aqueous inclusions in SAPPM apatite. Transmitted plane polarized light. Bar = 100 microns.

C. Tubular inclusion with aqueous phase (aq), vapour (v), birefringent nahcolite (na) and amphibole? (a). The inclusion is aligned parallel to the c-axis of the apatite. Plane polarized transmitted light. Bar = 25 microns.

D. Spherical inclusion with aqueous liquid (aq), vapour (v), nahcolite (na) and amphibole?•(a). A large rounded solid inclusion of clear calcite (c) is also visible. Transmitted plane polarized light. Bar = 50 microns.

E. Aqueous inclusion which developed opaque(?) acicular crystals (amphibole - a) on heating and cooling (see text). Transmitted plane polarized light. Bar = 20 microns.

F. Sample 275/17. Multisolid inclusion with birefrin- ent minerals (b), a hexagonal non-birefringent phase mica - m) a vapour phase (v), a triangular opaque o) and other non-birefringent minerals (nb). Inclusion X (out of focus) is a normal aqueous/vapour inclusion. Plane polarized transmitted light. Bar = 10 microns.

G. Aqueous inclusion with large phlogopite (p) crystal buried in inclusion wall. This may be a captured solid. The small cube is probably halite. Transmitted plane polarized light. Bar = 10 microns.

H. An unusually high concentration of inclusions in one apatite. Under these circumstances necking down is probably severe. Transmitted plane polarized light. Bar = 50 microns.

I & J. Apatite crystal in tritolyl phosphate. The inclusion is photographed at different focus settings. The vapour bubble (v) is visible in I, whilst a sulphide daughter(s) is seen adhering to the wall in J. Note overgrowths of siderite (sd) on apatite. Transmitted plane polarized light. Bar = 100 microns.

235.

PLATE 21 A B.

• •

C D

n.. c

E F

(_a H

I Or" • jak 4.0 Most of the inclusions seen in phlogopite and clinohumite of the SAPPM assemblage, as well as the surrounding calcite and dolomite (where they are probably secondary) are of the Type 1 category (Fig.43). The co-genetic relationships between phlogopite, clinohumite and the apatite of the SAPPM assemblage has already been shown from textural work (Chapter 6). The presence of identical fluid inclusions is further evidence of this and also of the fact that the aqueous fluids are probably the common parent of the whole assemblage. Rarely a rim of liquid CO2 may be seen around the vapour bubble in these Type 1 inclusions. In this study only two such inclusions were seen. The liquid CO2 rims disappear very rapidly when being observed under the microscope; the heat from the focused substage lighting being sufficient to raise the temperature of the inclusions above the critical point of CO2 liquid (+31.1°C; Rankin, 1978). 7.2.2. Monophase Aqueous Inclusions - Type 2 (see Fig.43A) These are the same as Type 1 with respect to shape, size and daughter mineral content, but they are much less common. The lack of vapour bubbles is their only distinguishing feature. In some examples, these bubble-free inclusions may be a product of necking, but in some samples a crystal may contain four or five inclusions of this type and no others. In such instances an origin by necking is more difficult to evoke. It is possible that a necked-off portion containing a vapour bubble could be excluded from the crystal in rare instances, but other signs of necking would probably be present. Vapour bubbles could not be encouraged to nucleate in these inclusions even with cooling to -50°C, and yet their similarities with Type 1 suggest that they are related to the same system. 7.2.3. Monophase Gas Inclusions - Type 3 (see Fig.43A) These are rare and, as with Type 2, may be caused by necking. It is possible that some of these are empty voids caused by leakage of the inclusion contents during sample

237. preparation (Rankin, 1975, 1977). There appears to be no large expansion of contents on crushing in oil, though observation of this is difficult in what are usually small inclusions. 7.2.4. Monophase Saccharoidal/Opaque Inclusions - Type 4 (see Fig.43) These vary from brown translucent where a speckled or sacharoidal texture is apparent in them, to virtually opaque green black. (see Plate 22B,D and F). Though opaque, they give no reflections. Hydrocarbons in apatite have been observed from other complexes (Althaus and Walther, 1977) and the SAPPM assemblage as well as some of the carbonatites at Sokli, commonly have pyrobitumens. It is possible that some, especially the opaque greenish ones, are hydrocarbons. However, one granular partially opaque sphere was crushed out of the apatite, mounted on a beryllium holder and probed. The spectrum was of a pyrochlore. The non-granular varieties may be translucent green and are probably not pyrochlore. Hydrocarbons are considered possible, but this has not been confirmed. 7.2.5. Multisolid Inclusions with Aqueous and Vapour Phases - Type 5 (see Fig.43A) These are not as common as any of the above mentioned inclusions. When present, they are mostly associated with Type 1 aqueous/vapour inclusions and the two may be found in the same crystal. Rarely they may occur alone. The amount of solid in them varies from the one or two crystals seen in Type 1 inclusions to inclusions packed with solids (see Plate 21F). The solids are both colourless birefringent and non-birefringent; opaques are also seen. Occas- ionally the contents are ill-defined and may appear as a solid speckled mass with a vapour bubble (see Fig.43A). Such types may be indicative of a melt, as suggested by Haapala (op.cit.). The contents of these inclusions will be described in greater detail in the section on daughter minerals (7.3.).

238. 7.2.6. Mineral Inclusions in Apatite - Type 6 (see Fig.43B) Many of the solid inclusions in the apatite are an enigma, but the mineral inclusions of this type are thought to have been trapped as solids during the growth of the apatite (see Plate 22A). The minerals include phlogopite, pyrochlore, pyrrhotite and magnetite of the SAPPM assemblage and serve to emphasize the close paragenetic relationship of the apatite with these minerals. 7.2.7. Elongate Solid Inclusions Aligned Parallel to the C-axis - Type 8 (see Fig.43B) These inclusions of colourless non-birefringent minerals and opaques are similar to those described in detail at Palabora (see Chapter 3). They are, however, much less common at Sokli, the opaque sulphide inclusions of this type being rare. Some are shown in Plate 22G and H. 7.2.8. Spherical Inclusions of Calcite - Type 7 (see Fig. 43B) Spherical inclusions of calcite are characteristic of apatites from carbonatites. They have been seen at Palabora, Bukusu and other complexes studied for this work and have been reported by other authors (Girault, 1966; Rankin, 1975, 1977). Girault (op.cit.) recorded numerous such inclusions of rounded calcites in the apatite and tremolite from the carbonatites at Oka. He showed that they had a strontium composition (0.7%Sr) lower than that of the calcite which surrounded the apatites (1.1%Sr). "Ces differences morphologiques et chimiques suggērent un mode particulier de formation et de mise en place. La seule explication qui ne paraisse contradite par aucun fait d'observation est celle suivante laquelle les cristaux d'apatite et de tremolite ont englobe au cours de leur croissance, des monocristaux spheroidaux preexistant de calcite." Girault (op.cit.) He further quotes the experiments of Wyllie and Tuttle (1960) on the system CaO-CO2-H20 and their observations of

239. PLATE 22: Some Solid Inclusions in Apatite, Phlogopite and Pyrochlore

A. Calcite (c), pyrochlore (pc) and pyrrhotite (S) in zoned apatite crystal. Transmitted plane polarized light. Bar = lmm. B. Dark inclusion with crack. Original inclusion contents may have leaked. Transmitted plane polarized light. Bar = 250 microns.

C Calcite spheroid in apatite. Note (i) one of the many fluid inclusions in the calcite. A vapour bubble, visible under the microscope, is not seen here because of constant movement due to brownian motion. Transmitted light polars partially crossed. Bar = 10 microns.

D. Virtually opaque granular 'saccharoidal'sphere in apatite. May be pyrochlore (see text). Plane polarized transmitted light. Bar = 50 microns.

E. Large calcite inclusion is apatite crystal (ap). Transmitted light crossed polars. Bar = 400 microns.

F. Greenish/opaque hydrocarbon(?) (h) in inclusion with birefringent mineral (b). Plane polarized transmitted light. Bar = 50 microns.

G.& H. Solid sulphide inclusion (S) in Sokli apatite, aligned parallel to the c-axis. Transmitted light. Bar = 100 microns in both cases.

I. SEM view of surface of siderite overgrowth on some apatite (see Plate 21, I & J). Bar = 5 microns.

J. Primary 'melt' inclusions in zoned pyrochlore. Transmitted plane polarized light. Bar = 100 microns.

240.

PLATE 22 A B

••‘- D

H•

• • r

• • • • • • / • , . • ~+ •~• % •i• the following distinctive phases; CaO, Ca(OH)2, CaCO3, a liquid and a vapour. La plupart des cristaux de calcite obtenus au cours de leur experiences affectent une forme arrondie, sans contours polyedriques, lorsqu'ils ont pris naissance a l'ētat d'equilibre, en presence d'une phase liquide; en l'absence de cette derniēre, ils forment de petits rhomboedres nets." Rankin (1977) records similar inclusions from Tororo, Uganda, and further notes, "occasionally a small portion of aqueous fluid is actually trapped, together with these calcite crystals and complex inclusions of gas, liquid and captured calcite result." He concludes, " these calcites co-existed with the aqueous fluid (now preserved as aqueous inclusions ) during the growth of the apatites." At Sokli it has been possible to distinguish between two types of calcite inclusion:- a)Clear spheroidal calcites (see Plates 18E and 21C) b) Rounded spheroidal and irregular calcites with minute aqueous inclusions (see Plates 18E and 22C) The second type of inclusion itself contains large numbers of aqueous inclusions and, in this respect, is very similar to those calcites which are found interstitial to the apatites and surrounding the SAPPM assemblage. Such inclusions especially, are suggestive of replacement of the matrix calcite by apatite. In most cases, unlike the clear calcite balls, those with aqueous inclusions are in the same optical orientation as the surrounding calcite which is also filled with inclusions. The process of embayment of calcite by apatite, apparently growing with good crystal form, but with a tendency to encircle areas of calcite in an amoeba like fashion, can be seen half completed (see Plate 18F). This, in conjunction with the presence of small aqueous inclusions (presumably secondary) in the trapped calcite as well as the matrix calcite, is regarded as good evidence for replacement. Many of these have been observed with rims of aqueous/vapour phases (see Fig.43B, Type 7), implying the presence of aqueous fluids as the calcites were trapped by the apatite.

242. The clear inclusions however, do not align themselves with surrounding calcites. Commonly in any one apatite crystal there may be a number of clear inclusions, with different orientations. Some apatites may contain both clear calcite spheroids and the type filled with inclusions. Girault's observation of different Sr values in the calcite spheres at Oka prompted an investigation of those at Sokli. The calcite spheres were analysed by EPMA (see Appendix 3) and the results carefully checked for any sign of phosphorus (which would indicate interference from the host apatite). Only those results free of phosphorus were considered to be representative of the calcite spheres. The Sr0 values of the various calcites are shown in Fig.44. It became apparent that the division of the spheres into two types; those with inclusions and those without, was also reflected in the Sr values. Those spheres without inclusions tend to have values considerably higher than those with inclusions (see Fig.44). The calcite matrix was also seen to have similar variable values, the calcite free of inclusions having higher values than that containing inclusions (see Fig.44D). There are some calcite spheres which have variable values, but the association of higher Sr values with the clear, inclusion free spheres and matrix is still quite apparent. The results of this programme of probing would not support the findings of Girault at Oka that the Sr values were lower in the matrix calcite than in the calcite spheres. The above values found at Sokli are not at variance: with the apatite replacing calcite as suggested from the petrography. The reason for the Sr differences in the calcite are not clear. It is tentatively suggested that the secondary inclusions are associated with a recrystallization of early calcite. The process may have removed Sr from the calcite. The growth of apatite is apparently associated with this; both clear inclusion-free calcite and recrystallized inclusion-filled calcite being encircled by the metasomatically formed apatite.

243.

SrO FROM CALCITES IN AND AROUND SAPPM. APATITES

A. Two different types of calcite sphere.

'°— Calcite matrix with . I I :~ • ; secondary inclusions Clear calcite /i Sr0 = .45% sphere •• Sr0 = .99% Calcite sphere with ••': secondary inclusions •, ••. . • Sr0= .45% " • f. • • • • •; • .a • • 200u

B. Clear calcite sphere & . C. Variation in calcite sphere clear calcite matrix. with secondary inclusions.

1.2% .96% / y .81% .79% .23% .89% 1.1% .86% 200 u

D. Clear calcite island surrounded by calcite filled with secondary inclusions. Encircled calcite spheres are equivalent in Sr0 values and appearance to these calcite types. •

•

\ •

. • . • ~\ • . • 1 ♦ f • • ••

.36% 1 mm.

Fig. 44 244. Under the light microscope, the inclusions in the matrix calcite are mostly extremely small and show signs of considerable necking. One sample of calcite examined under SEM showed that the small cavities have holes in the walls (see Plate 24E). The depth of such holes is not known, but discontinuous tubes (a product of severe necking) are probably present. Such tubes were observed in some apatites by Rankin (1973).

7.3. DAUGHTER AND CAPTURED MINERALS 7.3.1. Identification of Daughters in Aqueous Inclusions Identification of the mineral phases present in the inclusions can give an indication of the inclusion chemistry. It is however necessary to establish the difference between daughter minerals (minerals which have crystallized from the inclusion contents) and captured phases (minerals trapped as crystals when the inclusion formed). A list of minerals seen and identified, where possible is shown in Figs.45A and B. A colourless birefringent mineral common in many inclusions was suspected to be an alkali bicarbonate (see Plates 22C and D and 23A). It characteristically disappears when viewed in one direction of polarized light, the RI being approximately the same as water in this orientation. Nah- colite (NaHCO3) has been described in similar inclusions from African carbonatites (Rankin and Le Bas, 1974B). In this study it has been possible to confirm that the mineral is indeed nahcolite by breaking open the inclusions and viewing the daughter minerals using SEM (see Appendix 2 and Plates 24,25 and 26). Not only does the mineral have a characteristic shape and twinning (see Plate 26A, cf.Rankin and Le Bas op.cit.), but an x-ray spectrum devoid of elements except for Na implies that the other elements are non- detectable (lighter than Na). The mineral deliquesces if left in air for a few days, forming acicular outgrowths of hydrated salts (see Plate 24D). The mineral reacts with acidified glycerine, giving off CO2. CO2 is probably given off under the electron beam of the SEM as a small hole is

245. MINERALS IN AQUEOUS INCLUSIONS A. USING LIGHT MICROSCOPE AND S. E. M.

S.X.H. IDEl-l'TIFICA. TIO N ~u omcu. AND PHISI~ P50PERTIES R/\l SHAPE lancy ELEl-jElrfS COM}~S ~ ~ Dl!.~:~ [.l!;lJ FOru·m.A

VC Opaques - j"8llav in reflected light. No W'ell orystalllne Fe, S. Pyrite 1eS2 e Cubic or irregular shapes the latter Some are cemented being aggregate tvina. Some • tree to to hoat 1oI8l.la. (more S • •• move did not do 80 1na IIII.ptic field • than Fe)

- vc Colcarles. 1tl'onsl7 b1re£r4-ngent phase. Ye. Deliqueecent 0V'e1 ll& Nahcolite NaHCO, ' R.I. varies atrcnglT ld.th orientation, & tev da78, long 1n ODe direction 1 t 1. the same &8 the ac1c:ula.r crystal!! aqueous solution ,in &J1Other 1 t 1s higher. develop. Focused. Both irregular am ve1l tormed shapes electron beam OD are seen I tv.lm1ing DOt uncollllllOl1e leave, & pit. .--- 0 .t 2ndo%')"'8tal ot a1m:Uar qpe 1s rare. Not seen Kalic1ne 7 meo, I VC Very thin ac1c:ula.r crystals, colourless No C178't&ls too thiI Mg,Fe,S1, Amph1bole? 7 (some t1mes seelll opaque Wen thin) tor good X-ray U, Ca,A, COllllDOnly curved and bent against the generation. Na,X Ha, Cl. 1nal.uaion ....us. Thay some t1mee appear Cl probably llOt ~) &tter heating iDClus1ons. Weakly bire- part ot ad.neral. trinpnt,,1nc.l1ned extinction length See text. I~ --- slav. Cl. Colourless isotropic cubes Large cubes rare, Nee 1 Hallte NaCl R - but deposit on DJ other m:1nera.la & 1Dclua1on walla 1. very collllDOn. 0 R Rarel:r & s8Comc\.be is aeen - • I,Cl SylT1te KCl ~ C Thin colourles8 pJ.a.tes, lIBy be pleochro1 No Basal cleavage K,Fe,S1,Mg l'et~ colourless to light brovn vhen thicker. Visible. Otten A1 very terri- Usuall:r very thin aM mst are· probably grove tram the small.) pblogop1te 0 missed optically. 1nclua1on wall•• _D0

C Colourless strongly b1re£lo1ngent RI • Yes CatmOt be poeiUve.ly related CuboDate . greater than aqueous solution. to a.rq thing seen under S.!}ol CJ CouJ.c1 be a N& carboDate or ~ted Na carbonate. \ ) '---'

C Colourless b1re£r1ngent high R.I. very Yes C&JlD)t be po~t1ve.ly related CuboDate 0 I!IUch greater than aqueous solution. to &JVth,1ng seen Wlder S.E.M ..---.. VR Very thin sheet,opaque 1:1 ona direction .- ~&mlOt ~ reated to &nTth1~ transparent bro'Wtl in the other. seen ~er S.E.H. ~ Yellav renections ncl1 ms.gnetic. L..--J

Bar scale on each is J microns VC Very common C Common R Rare Fig 4SA 246. VR Vary Rare MINERALS IN AQUEOUS INCLUSIONS-CONT.

B. MINERALS NOT SEEN OPTICALLY (S. E. M. ONLY)

F R SHAPE E ClWtACTERIS'l'ICS ~lENTS DE'l.'mTED IDEHTInC!.TION CO~l1-!EN'l'S Q

A.ngular irregular &bape C Cr)"stals, preaumabl7 opaque. re,Cr.Ni in app~ Spinal 7 Could. be an ax1de. O·0. imtal.7 equal I:JDCWlts

I I , C Elongated bla.ded Cr)"8tal. Ha 1s the oDl.7 Hydrat.d NlCO, This my be the same ... hole 18 produced by a element detec:ted. or liCO, as soma ot the bladed tiMl1' tocused electron Cr)"8tals seen optically. ;f beam. '---'

C Balls ot rad1atinc am S1, 'e, Ca(7) and ... sillcate This could be a a:Uicate interlocld.n3 bladed lesser amawrts ot vh1ch baa precipitated Cl7stalS. Two or IIIOre Hg. (Cl my also trolll the solution on ., -1' be tOUDi in the same be pr8Hnt.) opening. since none are 1%lIcJ.uaion. Hen in umpened 1ncl.- $--- uaiona.

0 VR No dist.1nctive shape Ca, Na & I 7 Probably a double salt carbaDate or bicarbonate I I ., D VR No dist:1nctive shape Mr, Mu, Na.& le I I

I 0 VR No diat1nctive shape Fe, Cl. Iron chloride 7 '---'

Haagonal priam. Ha, I, Cl, , Cazmot be a double salt chloride, because they R are cubic. It could be a chloride/carbo Data & double ealt. Rctmded irregular shape Ea onl7, though my V1theritel Be.riUl:l bic&rbomte 1s R aomatimas buriedFtJ,7 in partl.7 coated by NlCl BaC°3 unstable. () inclusion walls. &lid BDl deposits.

'---I

Scale bar on each ia 3 m1cro%l8. C = COIllll1011 R = Rare VR = Verr rare

Fig. 45 B 247. PLATE 23

A. Aqueous inclusion in apatite with two Nahcolite (NaHCO3) daughter minerals, showing different relief; In one direction the RI is the same as water, in the other it is higher. Transmitted plane polarized light. Frame length = 400 microns.

B. Aqueous inclusion with sulphide (pyrite) giving yellow reflections. (The sulphide was extracted and probed - see Plate 28E). Plane polarized reflected light. Frame length = 200 microns. 248. visible after focusing on a spot. The nahcolite dissolves at temperatures between 70 and 130°C and reappears when cooling the inclusions and is thus a true daughter. The dark acicular crystals (see Fig.45A) thought to be an amphibole, have only once been seen to dissolve on heating the inclusion above the homogenization temperature, by about 100°C. Others will not respond to this. In certain instances, however, inclusions free of such acicular crystals would, after heating, produce acicular crystals on cooling to room temperature (see Plate 21E). In these , instances, the inclusion fluid must have been supersaturated with respect to this mineral. The mineral shows a preference to grow lengthwise. Some of the needles grow up against the inclusion walls; continued growth forces the mineral to bend. Eventually, rather than grow in girth, a new crystal may develop elsewhere in the inclusion. These observations indicate that the acicular crystals (amphiboles?) are true daughter minerals. The hedgehog like balls of an unidentified bladed silicate mineral (see Fig.43B(C) and Plate 25A and B) may also be related to supersaturation, only precipitating out on opening of the inclusion. They were not seen by transmitted light observation of the inclusions. • Metastability was also observed with the nahcolite. Inclusions containing poorly formed crystals of nahcolite could be gently warmed and cooled to encourage development of well formed crystals of characteristic shape (Rankin and Le Bas, 1974B). However, once dissolved the crystals would not always return, even with cooling to -50°C. The sulphide minerals (opaque in transmitted light, yellow in reflected light - see Plate 23B and Appendix 1) were not seen to dissolve on heating. The ubiquitous presence and uniform size in relation to the size of the inclusion is evidence that they are daughter minerals. The well known poor solubility of sulphides in aqueous systems (Barnes and Czamanske, 1967) is probably responsible for the difficulty in dissolving the sulphides during short heating runs.

249. PLATE 24: SEM Photographs of Opened Inclusions I

A. Barite (ba) buried in the inclusion wall. Bar = 2 microns.

B. Inclusion cavity with acicular (amphibole?) crystal protruding. Bar = 1 micron.

C. Three inclusions, closely spaced. Bar = 5 microns.

D. Opened inclusion contains a nahcolite daughter (no) with overgrowths of a hydrate which developed by deliquescence over 3 days after opening. The cube (p) is pyrite, whilst the acicular crystal (a) is too small to obtain x-ray spectra from, but is probably an amphibole (see text). Bar = 2 microns.

E. Inclusion in calcite with holes (arrowed) in inclusion wall. These may lead to other inclusions and they may be indicative of necking down. Bar = 1 micron.

F. Inclusion cavity with mica(m), a large platy phase giving only Fe x-rays (F) may be magnetite. The elongate mineral (a) gave x-ray peaks indicative of Ca, Mg, Fe, Si and small amounts of K. It may be an amphibole. Bar = 2 microns.

250. PLATE 24

• PLATE 25: SEM Photographs of Opened Inclusions II

A. Opened inclusion with balls of interlocking bladed crystals. Elements consistently detected are Ca, Fe and Si, though certain parts have Na, K and Cl, probably as a result of alkali halides deposited from solution. Note platy outgrowths on inclusion walls. Bar = 10 microns.

B. As above, larger balls of the same silicate material. Note negative crystal shape of inclusion cavity. Bar = 10 microns.

C. Large inclusion in apatite (op) crystal, selectively broken into (see Appendix 2). Both top and bottom of inclusion are visible. The lid of the cavity on the left has been rotated through 180°. See Plate 26 for detail. Bar = 25 microns.

252.

PLATE 25

C PLATE 26: SEM of a Multisolid Inclusion

A. Bottom half of inclusion (see Plate 25C). The large crystals are all Na rich, giving only Na x-rays. They also volatilize under a finely focused electron beam, leaving a small pit. The crystal (NaHCO ) is twinned in a manner characteristic of nahcolitd (Rankin, 1973). The other crystals containing Na may be carbonates, hydrated carbonates or nahcolite. The crystal marked KC1 gave KC1 x-rays and is certainly sylvite. Ph is phlogopite. Bar = 10 microns.

B. The top of the inclusion has a hexagonal salt which gave K, Cl and Na when probed. Na is probably another nahcolite crystal, judging from the twinned form, better displayed in Plate 25C. Bar = 10 microns.

254. PLATE 26 The halides are particularly interesting. Only rarely have cubic crystals (halides) been seen and these in inclusions anomalously filled with daughters. Under the SEM however, small cubes of KC1 and NaC1 are seen. Furthermore, Na, K and Cl are also detected on other minerals and even on the walls of the inclusions. These deposits were presumably left after evaporation of the salt rich solutions. With the presence of large NaHCO3 daughter crystals, it is reasonable to assume that these residual salt deposits also contained undetected HCO3 The mica seems to be an aluminium poor tetra-ferri- phlogopite, much of which was probably captured as the inclusions formed, especially since it is also found trapped in the apatite without any aqueous fluid. SEM shows the mica to be commonly buried in the host walls (see Plate 21G and 24F). Barium carbonate is also found buried in the host walls and is likewise thought to be a captured phase (see Plate 24A). The characteristics of other phases seen are described in Figs.45A and B. Of all the minerals seen and not identified, the Fe, Cr, Ni bearing mineral (seen under SEM) in many inclusions is worth noting. The Fe, Cr and Ni are present in approximately equal amounts judging from the x-ray spectrum produced. The elements Cr and Ni are particularly impoverished in carbonatite rocks (Heinrich, 1966; Baldock, 1967). According to the analysis of Sokli rocks reported by Vartiainen and Woolley (1976), Sokli is no exception to this pattern (for Cr, 6 nil values and 1 sample of 13ppm - detection limits were not given). It is striking that the mineral should manifest itself in this apparently aqueous system. An adequate explanation of this has not been found. 7.3.2. Identification of the Contents of Multisolid Inclusions (Fig.43A, Type 5) These multisolid inclusions appear to have contents similar to the daughters in Type 1 and 2 inclusions. The colourless minerals are, however, much more numerous and 256. optical identification is impossible. Furthermore, the inclusions are less common than the Type 1 and 2 varieties and are usually small (less than 10 microns). For these reasons, it was extremely difficult to intersect them for SEM work. Only one unusually large multisolid inclusion was intersected (see Plates 26A and B) and the minerals found in it were mostly sodium bicarbonate and carbonate(?) with KC1, NaC1, an acicular silicate mineral and a mica crystal. A particular effort was made to locate any calcite or, dolomite, but none was found. Since both halves of the opened crystal were viewed and there appeared to be no spillage, it is concluded that this inclusion did not represent an alkaline earth carbonate melt. If this inclusion is typical of the smaller multisolid inclusions, then it is unlikely that there was a co-existing alkaline-earth carbonate melt, as suggested by Haapala (op.cit.). Without more exhaustive studies of these inclusions, it must be concluded that - the multisolid inclusions represent a necked down portion of other-aqueous inclusions or a highly concentrated version of the Type 1 aqueous inclusions. The latter perhaps resulting from a limited influx of fluid much more concentrated in the dissolved salts than Type 1. 7.3.3. Counting of Daughter Minerals Some samples from borehole 393 were counted in an attempt to quantify the variability of daughter phases in the Type 1 aqueous inclusions. The percentage occurrence of each optically identifiable mineral is depicted in Table 20. Two hundred inclusions were investigated for each sample. The small opaque sulphides are the most common, followed by the nahcolite and then the acicular mineral (amphibole); sample 390/23 has the highest percentage of both nahcolite and the acicular mineral. This sample is from an apatite assemblage associated with a rauhaugitic area (see Borehole summary 1). The other samples from the sovites have lower percentages. Representative samples from 275 and 393 were counted for comparison (see Table 20).

257. TABLE 20: SOME INCLUSION AND DAUGHTER MINERAL STATISTICS

"INCLUSION DISTRIBUTION DAUGHTER MINERALS

7. of apatite crystals h I t with number of

la i c •inclusions/crystal t i

J . t e 1 3 No. of inclusions/crystal 1 c ing Sample —I a No. (..) .c m fr 0 1-5 6-10 11-20 20-40 40 x °• °

z 1 Z Bire

390/2 67 17 4 5 3.5 3.5 43 16 10 2 - - 135 - 390/6 87 11 .1 0 1 0 58 2 1 4 - - 183 - 390/23 40 23 7 8 3 19 26 50 42 5 17 1.5 151 -8.37 390/24C 46 32 13 4 2 3 40 3 8 32 26 160 -10.1 390/27 92 6 2 0 0 0 75 - - 5 25 159

275/10 49 13 4 6 4 24 57 45 38 1 5 179 -9.3 275/44 91 7 1.5 0 0.5 0 Inclusions too small 154 -11.2 275/39 86 12 1.5 0.5 0 0 " " " 172 -11.6

393/24 56 25 8 11 4 6 , 66 37 28 6 - - 165 -5.2

x7. 68 16 5 4 2 6 52 21 18 8 - - 163° -9.3 °

258.

The relationship between nahcolite and amphibole rods is striking. The correlation between the two, shown in Table 20, is seen from plotting the percentages in each sample. However, the relationship is not clear in individual inclusions; i.e. whilst the majority have nahcolite and amphibole(?) together, a great many have one or the other alone, or with some other phase. e.g. for BH390/23 Nahcolite and amphibole = 28% of inclusions Amphibole without nahcolite) = 14% ti Nahcolite (without amphibole) = 22% n Whilst this relationship, shown in Table 20, is interesting, it may reflect a change in any one of innumerable factors of chemistry or particle characteristics (metastability,etc). In conclusion, the counting work does quantify the differences and range of typical daughter types which can be clearly resolved using a normal petrographic microscope. However, the results are so subject to inaccuracies caused by inclusion availability, size and metastability, that further work was not considered worthwhile, especially considering the vast time expenditure. 7.4. FLUID INCLUSION CHEMISTRY 7.4.1. Na:K Ratios of the Fluids The identification of daughter minerals, which have precipitated from the fluids, provides some indication of fluid chemistry. At Sokli, the observation of nahcolite, together with chlorides of sodium and potassium (Na>K) under the SEM suggests that the fluids were richer in Na than K (i.e. K:Na less than 1). To test this the leachates of crushed inclusion rich samples were analysed by flame photometry for Na and K. Numerous techniques for the extraction and partial chemical analysis of fluid inclusions from minerals have been tried (Roedder, 1972A, 1972B; Rankin, 1973; Poty et al. 1974). The procedures generally involve first cleaning the sample by boiling in nitric acid and deionized water, followed by electrodialysis or ion exchange procedures to remove all surface contamination. The sample is then crushed; usually in a ball mill or copper tube and leached with water 259. or acids. The leachate is separated from the crushed residue (by centrifuging, filtering or electro-dialysis through semi- permeable membranes) and analysed using atomic absorption spectrometry. The potential for contamination is enormous and reliable results can only be obtained by the most careful adherence to cleanliness. The method used for this study was comparatively simple, working on the principal of the less steps in the procedure, the less chance of contamination. All utensils were cleaned by boiling in 2% Decon 90 (a surface decontaminant) followed by 10% nitric acid and then soaking in distilled and deionized water - DDW. The apatites were cleaned by boiling in DDW (apatite is acid soluble). The cleaning was continued until apatite left overnight just covered by water did not contaminate the water above the background levels of blanks. The samples were then crushed in a small agate pestle and :mortar with a few drops of DDW and washed into teflon centri- fuge tubes. The pestle and mortar were cleaned each time in Decon 90, acid and distilled water as above. The effective- ness of the cleaning method was tested by blanks, the pestle and mortar being rubbed together for 5 minutes with a small quantity of DDW. The samples were centrifuged, the supernatent liquid being removed by means of sterilized medical syringes (also cleaned as above) and recentrifuged. The solutions were then analysed by flame photometry for Na and K. The results of the analyses are shown in Table 21. The results show that Na and K were released from the samples on crushing. 20m1. of water were used to wash the leachates, so the levels of Na and K represent at least 2 orders of magnitude above the blanks. There is apparently twice as much Na as K in the Leachates. Though this could conceivably reflect a preva- lence of sodium released from the apatite lattice, calcite rich in secondary inclusions also gave a similar ratio of Na:K (275/10). This suggests that the inclusion chemistry may be dominating the leachates. Nevertheless, a sample from Palabora (P55), apparently free of large inclusions, also gave similar values of Na and K (see Table 21). Thus, although the results are similar to results obtained by

260_ Rankin (1973) for apatite samples from East African carbonatites, and they also support the deductions made from SEM work of daughter minerals, they must be viewed with some caution (see also discussion of Na:K ratios at Guide Mine - Chapter 5).

TABLE 21: RESULTS OF APATITE LEACHATE ANALYSIS Sample Na (ppm) K (ppm) K:Na Blank DDW .05 .00 Blank Pestle & Mortar .12 .09 Blank Apatite Cleaning .12 .19 275/39 Apatite 1.45 1.10 ~.76 275/10 Apatite 2.00 0.98 .49 275/23 Apatite 2.45 1.29 .53 275/23 Repeat 2.41 1.33 .55 390/2 Apatite 1.53 0.88 .57 390/24 Apatite 2.67 0.64 .25 275/10 Carbonate 6.28 3.61 .58 P55 Palabora Apatite 2.66 1.39 .52

The SEM work at Sokli, in contrast to that for the Guide inclusions where K was the dominant alkali, suggest that Na is greater than K in the solutions which deposited the SAPPM assemblage. The figure put on the ratio of the elements by the analyses of leachates supports a Na dominant system, but may be subject to inaccuracies, as described above.

7.4.2. Crushing Studies Opening inclusions in a suitable immersion medium provides information on the nature of the contents; presence of gases under pressure, reaction with acid, etc. Many crushing stages have been developed for this (Roedder, 1970), but crushing between glass slides as used in this study is equally effective (see Fig.46A). A) Crushing in Tritolyl Phosphate: Inclusions rich in dissolved gases show expansion of the vapour bubble when opened by crushing in oil (Roedder, 1970). Apatite crystals from Sokli with large aqueous inclusions were crushed in oil between glass slides. The vapour bubble showed little or no expansion when the process

261. THE CRUSHING METHOD

Cover elip between elides prevents complete powdering of crystal.

B. SEZDE2EE ON OPENING A CARBONATE RICH I}CLUSION IN ACIDIFIED GLYCERIDE

1 Typical epherical aqueoue inclusions as seen under

the microscope. The inclusion diameter ie measured

on an eye-piece graticule.

2 The apatite is fractured by rocking the upper glass

elide. The apatite tends to break along its weak

basal cleavage. When the inclusion is opened the

contents react with the acidified glycerine to

produce CO2.

3 When the reaction is complete, the CO2 bubble produced

in at its maximum size. Its diameter is measured

against the eye-piece graticule.

4 The CO2 rapidly dissolves in the acidified glycerine.

Fig.46 262 Wt% NaHCO3 BY CRUSHING IN ACID CO2 is produced 3 Size of bubble produced is 2 measured N 1

x1 x2 x3 diameter of gas produced asa factor increase of inclusion size 20

Theoretical yield of CO2(at S.T.P.) from spherical inclusions. (Degree of filling is .96)

Wt% Na CO Salt in 3 Solution NaHCO3 10

, x1 x2 x3 Fiq.47 263 was observed under the microscope. Only two inclusions in the whole study were seen with the minutest rim of liquid CO2 around the vapour bubble. It is concluded from these observations that, unlike many inclusions from carbonatites, (Roedder, 1978) those at Sokli are not characterized by the presence at room temperature of CO2 in the vapour phase. B) Crushing in acidified glycerol: Opening the inclusions in a similar manner, but in acidified glycerine rather than oil, produces a vigorous reaction (see Fig. 46B). The aqueous content (and some,of the daughters, when present)react with the acid to produce CO2. Numerous inclusions were opened in this way, and occasionally it was possible to estimate the amount of CO2 produced. First the inclusion diameter was measured against an eye piece graticule grid. The size of the CO2 bubble produced was also measured when the inclusion was opened (see Fig.47). The presence of nahcolite in some inclusions suggests ions in solution. If that the CO2 was produced from HCO3 this is so, a crude estimate of the weight percent NaHCO3 can be deduced. A theoretical graph of this is presented in Fig.47, together with some measurements of CO2 bubbles produced from inclusions in 390/2. Although the method is far from accurate, the CO2 produced is approximately equivalent to between 2 and 5 weight percent NaHCO3 in most inclusions. This indicates that in most of the inclusions there is not a large quantity of potassium carbonate or bicarbonate in solution. These salts are more soluble than nahcolite (see Fig.48) and would not be seen as daughter minerals. The presence of nahcolite in some inclusions but not in others implies different concentrations of NaHCO3 in different inclusions. While this is possible, it is also possible that slight variation in what is obviously a low CO2 partial pressure (deduced from crushing in oil) could make nahcolite unstable. The more soluble soda and trona might then be produced (see Fig.49). Variations in salt content and/or CO2 partial pressure may thus explain the variable presence of nahcolite daughter minerals. 264. THE SOLUBILITY OF P CO2-T DIAGRAM OF THE SYSTEM ALKALI METAL CARBONATES Na2CO3-NaHCO3-H20. (after Kirk-Othmer 1969) (after Eugster & Milton —1957 ) 140 I I 1 1 I I I I 1 I I

5000 120 J w Nahcolite+Solution 2

100 1000 €

500 400 ti0 Air C. a 0 300 c U z Ē 'C 60 100 re,

tu 0 Trona+Solution ra

e r mp 40 d

Te U ō 1 Y 20 10 1zo ō _ CQ~ Soda+Solution T 01. 5

Ice v► Thermonalrits+Solution

—20 1 o"

A —40 , I I 1 I I 1 I i I I 1 1 1 1 1 0 10 20 30 40 50 60 70 10 20 30 40 50 60 Salt in 1120 solution. wt % —> Temperature in degrees centigrade

Fig.48 Fig. 4 9 There are many errors in the crushing method of esti- mating CO2 quantities. One major cause is the solubility of the CO2 in the glycerine, resulting in disappearance of the CO2 bubble. Although this is much slower than the reaction which produces the CO2, some CO2 is obviously dissolved before the bubble reaches maximum size. The values in Fig. 47 are thus a little low, but this is probably insignificant compared to the error in actually measuring the bubble. The initial inclusion size can be measured quite accurately when spherical inclusions are chosen. However, the speed of, solubility of the bubble means that the bubble is at maximum size for only a fraction of a second. This, combined with movement of the CO2 bubble produced, makes accurate measure- ment extremely difficult. A grid graticule proved to be superior to a bar scale for these reasons. In conclusion, the crushing method has obvious value as a qualitative test for carbonate or bicarbonate in solution, but its quantitative efficiency is limited. It could be improved by using a liquid in which CO2 is not soluble. 7.4.3. Cryometry Although the exact chemistry of the inclusion contents is elusive, the observations outlined so far provide a qualitative assessment of the chemistry. An attempt was made, by studying phase changes on cooling and reheating the inclusions, to place further constraints dn the composition. The inclusions were cooled to freezing (-40 to -50°C) in a Th 600 microscope stage. Most of the data was obtained by a method developed for this study, using unpolished apatite grains mounted in tritolyl-phosphate (Rankin and Aldous, 1979). See Appendix 3 for a description of apparatus and methods. .On freezing, the inclusions usually formed a metastable glass. First melting was observed as the inclusions were warmed at between -23°C and -25°C. At higher temperatures one or more ice crystals were visible, together with numerous crystals of an unidentified substance. The last melting of ice for seven rock samples studied is -9.73 (d'= 2.22), see Figs.50 and 51. The unidentified phase did not melt/dissolve until +2.84 (0- = 1.49, N (rock samples) = 5).

266. Characteristically, it formed pointed pyramid crystals which mostly grew from the inclusion walls (see Fig.50). The unidentified phase is probably a NaHCO3/NaCO3 hydrate. Occasionally nahcolite would be formed on cooling and, if nahcolite was already present, then the crystal would grow on cooling. In Fig.50 an example is shown where a well defined twin crystal grew from an irregular shaped crystal. This twinning is characteristic of nahcolite (Rankin and Le Bas, 1974B). In other inclusions, ice was not observable because of the presence of large amounts of the unknown, phase thought to be a hydrate. Rarely a small colourless non-birefringent(?) phase would be formed which would not dissolve even with heating. This is thought to be related to the metastability already mentioned with respect to the appearance of new daughters on heating. Although the phase changes are fairly complex, the ice melting point (i.e. the depression of freezing point caused by dissolved substances) is significant. The sodic carbonates and sodium and potassium bicarbonates cannot account for a depression of freezing point greater than -4°C at saturation (see Figs.48 and 52). Some other salt. with a greater solubility (not present as a daughter mineral) and more powerful depression of freezing point properties must also be present at Sokli to account for a depression of freezing point of 10° or more.. This is unlikely to be a more soluble alkali carbonate or bicarbonate (K2CO3 in particular is more soluble) since greater levels of CO2 would have been produced in the crushing studies. The observations of NaC1 (and limited KC1) deposits on minerals in opened inclusions provide a probable answer. Depression of freezing point by 10° is feasible for NaCl well below its saturation point (see Fig.52). Attempts to estimate the amount of NaC1 from the figures obtained from Sokli material are hampered by the interference effects from other salts. It is likely that the extra depression of freezing point below the 2 degrees expected from a saturated solution of NaHCO3 is accounted for by NaCl (and some KC1). The exact amount of chlorides 267. TYPICAL FREEZING RUNS ON INCLUSIONS IN APATITE

clusion No 3 Room T Room T 20 C 20 C v aq aq 'u' / O

-20 C

• v aq o

Irregular nahcollte grows a well formed rim.

-46C -48C

v glass nh;f s'D

-24.5 C -24.7 C J) y mai;. ^.~. r, 1 "~I ~ 7

Ist melting • Ist melting -18.0 C i -17.6 C

C:\_ / • _ ■ '

-12 C f ' 1 -12 C ,17 'fil ~~ I ,-, `~,

Ice crystals can be made to grow by cooling and warming S 3or 4 C. y -10 C w ---4/77"--.fr -9.4 C 1` j'-:'•/ \.,(r .. .T aq i~"aq , V nidentified Ice goes (i.e. freezing point) hydrate Ice goes -S C O aq

Pyramid shaped weakly birefringent hydrate visible +2.S C +1.0 C ~ aq/7ih.1 aq C) O

Unidentified hydrate goes Unidentified hydrate goes.

Room T Room T .3 20 C 20C aq O O aq ~%•

v = vapour • = Nahcollte Fig 50

268 FREEZING STUDIES ON INCLUSIONS IN SOKLI APATITES

freezing point of saturated solutions of :- KHCO3, NaHCO3 -0- 275/10 -°- • I -0- -s- I 1 -p- f V Y + 275144 -a -0- -s- -d-

275/51 f -s- -0-

275/39 + ~ +

390/ 23 .~ ++ -4.- -0-

390 / 24 -4- . -s-

'0° -15° -10° -5° 0'C +' + Last melting of ice Fig. 51 + Last melting of unknown hydrate DEPRESSION OF FREEZING POINT Fig. 52 -16° C FOR SOME RELEVANT SALTS NaCl F -14° R

E -12° Z --- - -c of ice melting at Sokli------I -10° N G -8° P K2CO3 0 -6° I N T -4' .turation NaHCO From figures in Kirk Othmer 1969 -2° KHCO3 saturation

0° 0 2 4 6 8 10 12 14 16 18 20 22 24% Weight % in solution cannot be deduced because of the mutual interference effects with the bicarbonates, but it must be in the region of 10-12 wt%, judging from Fig.52. In terms of depression of freezing point it is probably best to refer to the combination of salts in NaC1 equivalents as in most inclusion studies; i.e. the depression of freezing point observed in the Sokli inclusions is equivalent to 15 wt% NaC1 (see Fig.52). The quantity of alkali chlorides present in the system is obviously important with respect to metal transport. Although the presence of bicarbonate and carbonate in the system is spectacularly displayed, both by reactions with acid and the presence of daughter minerals, a more deductive approach has been required to show the presence of equal quantities of alkali chlorides. Alkali chloride salts are commonly responsible for the transport of copper in the porphyry copper deposits (Crerar and Barnes, 1976) and may well be active in this way at Sokli. 7.5. HEATING STUDIES AND PRESSURE DEDUCTIONS Heating the aqueous inclusions to evaluate the homogenization temperature was done using a Leitz 1350 microscope heating stage (see Appendix 4). The homogenization temperature of the inclusion contents represents the minimum temperature of formation of the inclusion (Roedder, 1967). Twelve samples were investigated, the number of inclusions (N) heated for each sample was dependent on the availability of inclusions. N varied from 2-27 (see Table 22). It became apparent that the homogenization temperature for the samples was fairly consistent. The mean of the twelve samples was 161.08°C with a standard deviation of 12.6. The degree of filling of inclusions (directly related to homogenization of the vapour/aqueous inclusions at a given salt content - see Rankin, 1978) in thin sections of other Sokli samples indicates that the homogenization temperature of inclusions in other apatites not heated is of the s ine order. Fluid inclusions from most of the samples belong to one population with respect to their homogenization temperatures. Histograms of some samples are shown in Fig.53. Some samples however (e.g. 390/2) have a range down to 70° 271. and a portion of the whole population is Type 2; i.e. no vapour bubble. Attempts to induce a vapour bubble in Type 2 inclusions by freezing have been fruitless. Haapala (1978 - Abstract) does not give details, but reports; "filling temperatures of around 200°C are indicated" for the Sokli material. The discrepancy of 40°C between the two studies cannot be explained (for method, apparatus and calibration used in this study, see Appendix 4). In some of the aqueous inclusions with nahcolite, the dissolution temperature of the nahcolite was noted. It varied (N=5) between 42° and 71°C. If the system was free of other salts, this would indicate a NaHCO3 concentration of between 12 and 15% (see Fig.48). The effect of other salts in solution is difficult to assess, but would probably lower this value (i.e. decrease the solubility of NaHCO3). Multisolid inclusions were not suitable for heating in this study, the rare ones observed in doubly polished plates being too small for observation while in the heating stage. Haapala (op.cit.) attempted to heat some of these, but reports no observation of homogenization. Decrepitation occurred at 550-620°C before all the solids had dissolved. The temperatures of homogenization (Th) of the aqueous Type 1 inclusions are remarkably low, even for carbonatites (see Tables 1 and 23 and also Rankin, 1975). Whilst temperatures of homogenization are only the minimum possible temperatures of formation and pressure corrections must be applied, the temperature is still low. The other geothermometers in the SAPPM assemblage imply temperatures of 500°C or more (see Chapter 6). To apply pressure corrections to homogenization temperatures it is necessary to plot isodensity lines (isochores) of the fluid system under consideration. The pressure required to bring the observed temperature at which such a fluid system is homogeneous up to the temperature suggested by other geothermometers may be read off such isochore plots. This is the pressure correction.

272. TABLE 22: HEATING AND FREEZING RESULTS

Homogenization ' Freezing (last Temperature 0C. melting points) 0C. ICE HYDRATE Sample Sample Description Tc o' mode N X of N 7

275/4 Apatite veinlets in 169 14 165 14 sovite 275/10 Magnetite sovite 179 18 177 27 -9.3 .24 4 +4.53 275/39 Contact sovite/ 173 9 170 16 -11.6 1.07 3 +3.25 phoscorite 275/44 Silicosovite 154 31 175 18 -11.2 .77 3 +3.13 275/51.3 Apatite rich 156 10 155 19 -12.3 .99 4 +3.24 phoscorite

393/9 Apatite veinlets in 150 15 - 3 sovite 393/21 Apatite veinlets in 165 22 165 12 -5.25 2 sovite

390/2 SAPPM in sovite 136 35 155 25 390/6 183 10 175 4 390/23 SAPPM in rauhaugite 151 20 155 14 -8.37 .66 3 +.03 390/27 " sovite 160 - 160 2 390/24C Apatite/dolomite in 160 12 160 6 -10.1 .05 2 phoscorite

OVERALL MEAN = 161 (12.6) -9.73 (2.22) +2.84 (and standard deviation)

* large spread of data (see Fig.53) Note: N - the number of inclusions measured is controlled by the availability of suitable inclusions.

273. HOMOGENIZATION TEMPERATURES FOR INCLUSIONS IN APATITES FROM SOKLI CARBONATITE COMPLEX

275/4 Apatite veinlets in sovite

275/39 Apatite and sulphides on shear

275/44 Silico-sovite with apatite sulphides and pyrochlore

275/10 Magnetite sdvite with apatite and sulphides 100 150 200

275/ 51 Apatite, sulp hide - phoscorite 100 150 200

390/2 Z_ Apatite mica vein in sdvite id° 150 200

390/23 Apatite mica sulphide vein in rauhaugite 160 150 200 Fig. 53

274 ISOCHORES FOR DIFFERENT AQUEOUS SYSTEMS GIVING Th OF 160' C

Projected from data by: Fisher 1976 (pure water) Polyakov 1965 (8 wt% NaHCO3 ) Rankin 1978 (10wt%NaC,) ( After data by Potter 1977)

& 15wt% 11 II U II II II

6.0

5.0

/ C-a 0

0 CL 4-rv

0 nn.0

2' 0 a.

1-0

Appr x Th curve for H2O

0 100 200 300 4.00 500 600 Trapping Temperature (°C )

Fig. 54

275 Isochores for homogenization temperatures of 160° (as for Sokli) prepared from data available in the literature are shown in Fig.54. Estimates of the amount of NaHCO3 present from crushing studies suggest that 5-10 wt% bicarbonate is probably present in the Sokli inclusions. The 8 wt% isochore (plotted on Fig.54 from data by Polyakov, 1965) indicates that isochores in the wt% NaHCO3 range deduced at Sokli (5-10 wt%) vary little from those of pure water. The isochores for 10 and 15 wt% NaC1 (shown on Fig. 54) are, however, quite different from the pure water , isochore (from data by Rankin, 1978, after Potter, 1977). The pressure correction for the system will only be severely affected by the NaC1 content. Taking 15 wt% of NaCl as equivalent to the total salt content of the Sokli system as suggested above (and assuming no severe curves in the projected isochores above 2k.bars) the correction required to bring the system up to the temperatures suggested by the other geothermometers (500-600°C) is around 4k.bars. At normal lithostatic pressures this would be equivalent to 14-15km.depth. Whilst this is possible, it is perhaps a little excessive. Once again, the effects of the combination of salts in the solution cannot be evaluated from combinations of one salt systems, but some reduction in the pressure correction is probable. A recent study of inclusions in the Kovdor carbonatite complex (Khitarov et al.1978), the sister of Sokli a mere 40km. away in Russia, found much higher homogenization temperatures than those at Sokli (see Table 23). A similar pressure correction at Kovdor would make the temperatures even higher. (Presumably both the complexes are at approximately a similar level of erosion). Interestingly, this would put the homogenization of the aqueous rich inclusions in apatite (marked with an asterisk in Table 23) near that of the homogenization temperature of the multisolid inclusions. The two types could well be analagous to the Type 1 and Type 5 inclusions of this study, the temperatures of the aqueous phases being subject to greater pressure correction than the multisolid varieties. 276. TABLE 23: INCLUSION PHASE COMPOSITION VOL % FROM KOVDOR (after Khitarov et al.1978)

Mineral Solid Phases Liquid Gas T (°C)

STAGE I

Nepheline S=5-70, C=0-80, X=20 5-20 0-85 930-850 Apatite X = 0-20 55-80 20-40 575-350

STAGE II

Forsterite C=10-90, X=0-95 0-15 5-15 890-640 Apatite X = 85-95 0-10 3-5 890, 790-690 Apatite X = 0-20 60-85 5-30 480-290

STAGE III

Apatite X = 90 5 5 760 Apatite 80-90 10-20 365-245 * Dolomite X = 80 5 15 >(610-640)

STAGE IV

Zircon (S+X) = 95 5 0 740-720, 625 Fe dolomite X = 80 10 10 ).(610-635)

(S = silicates; C = carbonates; X = unidentified)

Unfortunately Khitarov et al. (op.cit.) do not give the relative amounts of the two types, but significantly they do add; "The predominance of gas-liquid inclusions in apatite, as well as their homogenization to the liquid phase, suggest that the crystallization of the bulk of this. mineral took place from aqueous solution(s) which were similar in their properties to normal hydrothermal solutions." Their crystallized and crystal rich fluid inclusions homogenize • into highly concentrated liquids (melts) which, on cooling, quench to a glass or form microcrystalline phases. The possibility of carbonate melts co-existing immiscibly with

277. the aqueous solutions is not out of the question, but as Haapala (1978) admits, at Sokli the evidence for this is not unambiguous. The pressures suggested for correction though large, may be partly related to the pressure of intrusion rather than just normal lithostatic or hydrostatic pressure. In this way the depth suggested by the pressure at normal lithostatic gradients may not be so high. 7.6. INCLUSIONS IN OTHER MINERALS AT SOKLI Rarely inclusions were seen in phlogopite, clinohumite, amphiboles and pyrochlore. Inclusions of the Type 1 in apatites were seen in phlogopite and rarely in clinohumite and amphibole. This emphasizes a common origin from an aqueous parent fluid. A hydrothermal origin for the phlogopite is particularly significant. This is thought to be comparatively unusual (Baronnet, 1978), but it may be quite common in carbonatite bearing alkali igneous complexes. Baronnet (op.cit.) discusses the solubility of phlogopite in basic aqueous solutions. He shows that it is soluble in K2CO3 solutions, but not in Na2CO3 solutions. There is no mechanism proposed to account for this. The exact solubilities of phlogopite in more complex solutions with chloride and bicarbonate ions present is not known, but in the light of Baronnet's work, a hydrothermal parent for the phlogopite and thus apatite seems eminently feasible. Pyrochlore has many solid mineral inclusions but no aqueous inclusions were observed. One pyrochlore, from a carbonatite, chemically distinct from the SAPPM pyrochlores (see Chapter 6.6.2) was seen to have primary 'melt' inclusions in well defined zones (see Plate 22J). The inclusions are birefringent and apparently completely solid, with no vapour bubble visible. There was, however, some variation in the texture of the contents suggesting different minerals. The pyrochlore probably crystallized from a carbonatite melt. No further study of these was considered because of their rarity and obvious differences from the SAPPM pyrochlores.

278. Inclusions in olivine from the phoscorites are similar to those described at Palabora (see Chapter 4), containing tetra-ferri-phlogopite, magnetite and carbonate. The curved interleaved nature of the inclusion contents with the olivine (see Plate 12B) suggests, in the light of the observations at Palabora, that these represent carbonatite melts. The inclusions are not as common as at Palabora, being only rarely seen in what is mostly highly serpentinized olivine. 7.7. DISCUSSION OF INCLUSIONS AT SOKLI Koster van Groos and Wyllie (1973) investigated the' system NaA1Si308 - CaAl2Si208 - Na2CO3 - H2O between 650° and 950°C at lkb. with 10% H20. They found that three fluid phases could exist:- 1) Silicate rich liquid, peralkaline and undersaturated with Si02. This had a low Ca0 content. 2) A carbonate rich liquid containing appreciable amounts of Na CO and strongly enriched in CaO compared to the gilicate rich liquid. 3) A vapour phase composed of H,0 and CO strongly enriched in Na2O and to a legser extefit SiO2. Immiscibility between carbonate and silicate melts is now well established as a process at work in carbonatite formation (Rankin and Le Bas, 1974A; Hamilton et al.1979). It is conjectural that it may have given rise to the Sokli carbonatites; the silicate rock being left far below. It is the third fluid phase that Koster van Groos and Wyllie report in their experiments which is considered of possible similarity to the parent fluid of the SAPPM assemblage. Their results would support the emergence by immiscibility (or boiling off) of a supercritical low density fluid from a carbonatite magma. The Na20 and CO2 which they observed in their vapour phase could be equivalent to those elements combined (with water) as nahcolite in the Sokli inclusions at room temperature. The presence of Si02 in the system is shown by phlogopite and amphibole. Such an aqueous rich 'vapour'_ phase would certainly draw off a large proportion of incompatible elements,

279. redistributing them in surrounding rocks, finally spending itself on rocks peripheral to the complex forming the well developed alteration (fenites). In some instances, in other complexes the fenites may become mineralized with incompatible elements such as Nb and REE (Currie, 1973). Vartiainen and Woolley (1976) notice an increase in Nb and Ba in the fenites of Sokli. Interestingly, barium minerals (witherite?) were found in the aqueous inclusions from the apatite, but none were seen in the carbonatites. The aqueous fluids in the inclusions would seem to be ideal carriers of niobium, tantalum and copper from experimental work. Aleksandrov et al.(1972) showed Nb and Ta would be-transported by such fluids; the presence of C032 , F , PO4 and K particularly facilitating their transport. The work of Crerar and Barnes (1976) showed the transport of Cu and Fe was possible as chloride complexes. If these fluids react with calcium carbonate, lowering the activity of P042 and F by forming apatite, this alone may be sufficient to precipitate niobium. Aleksandrov et al.(op. cit.) however, noted that a decrease in temperature would also cause precipitation of niobium. Copper sulphides would also be deposited with decreasing temperature and also possibly by the changing chemistry of the aqueous system as a result of reaction with the wall rocks. EPMA analysis of the pyrochlores of the SAPPM assemblage (Chapter 6.6) imply deposition from a cooling regime. The development of the aqueous rich SAPPM parent fluid from the carbonatites at Sokli is supported by the close association of SAPPM with certain carbonatite veins and dykes. However, the argument for immiscibility, rather than crystallization leaving a residual fluid, is not conclusively supported. The multisolid inclusions may be indicative of immiscibility, but on the limited information available from these rare inclusions, the argument is only tentatively supported in this work. The emphasis here is placed upon the capability of the carbonatite system to develop a hydrothermal phase of

280. activity which is capable of transporting and depositing Nb, Ta and Cu. The inclusions provide considerable information on the chemistry of the fluids and the environment of ore deposition. 7.8. SUMMARY, PROPOSED GENETIC MODEL AND CONCLUSIONS 7.8.1. Summary The borehole logging, petrography and geochemistry provide the basis for the definition of the SAPPM assemblage at Sokli. These also show that the inclusion bearing apatites are an integral part of the assemblage (see Chapter 6). This is an excellent' background for the study of the aqueous fluid inclusions as probable parents of the whole assemblage, including copper sulphides and niobium/tantalum mineralization. Solid inclusions in the apatite are of minerals characteristic of the SAPPM assemblage, reaffirming the close genetic relationship between the constituent minerals. Spherical calcite inclusions provide evidence that the assemblage is largely a replacement of earlier calcite. Rare multisolid inclusions may be portions of a melt which co-existed with the aqueous fluid represented in most of the inclusions. The aqueous fluids are alkali bicarbonate/chloride brines with Na:K around 2:1. They were trapped in the inclusions at temperatures of around 500°C and pressures of 3-4.Ok.bars. Similar aqueous fluids are present in other minerals of the assemblage. The whole assemblage is therefore deduced to have been deposited from these fluids which, in their original state would have been richer in elements now comprising the mineral assemblage (viz. P205, F, Si02, etc.). The fluids would probably be supercritical. On the basis of experimental work by Koster van Groos and Wyllie, (1973) and Wendlandt and Harrison (1978) who find vapour phases co-existing with their immiscible carbonate/silicate systems, it is suggested that the SAPPM parent fluids may have co-existed with carbonatite melts in a similar way. There are many similarities between the

281. fluids in the aqueous inclusions and the 'vapour' phase of Koster van Groos and Wyllie's work (op.cit.). The suggestion by Haapala (1978) that the multisolid inclusions at Sokli may represent an immiscible carbonate melt would add weight to this concept. The multisolid inclusions, however, remain somewhat enigmatic and it has not been possible in this study conclusively to remove the ambiguities referred to by Haapala. That the aqueous fluid is closely related to the carbonatite activity and developed by some sort of fractionation from them is, however, without doubt. The mineralizing potential of these fluids is shown by the nature of the assemblage produced in the rocks, which, though not economic with respect to copper, has values considerably higher than the norm for copper in carbonatites. The fluids are clearly copper mineralizing fluids and are of the type likely to be found in other carbonatites. 7.8.2. Genetic Setting of Sokli Mineralization The data obtained from the boreholes examined in this study may be pieced together with information from fluid inclusions, geochemistry and petrographic work. This is combined with the sequences mentioned by Makela and Vartiainen (1978) to create a scheme of events which provide the setting for the mineralizing events at Sokli. The major events at Sokli were:- 1) Early Silicate Rocks; a)olivine rocks developing from early carbonatite magma (phoscorites). b) coarse grained phlogopite rocks. Probably developed by replacement of original crustal material or earlier silicate rocks by metasomatism (see Vartiainen and Woolley, 1976 for details on phlogopite fenites). 2Y Sovites and Phlogopite Sovites; Massive granitoid textured rocks (Makela and Vartiainen, 1978). Some sulphide and pyrochlore deposited with these carbonatites. 3) Sovites and Rauhaugites with SAPPM Sovites and rauhaugites cut through and assimilate early phlogopite and phoscorite rocks, producing silicosovites and fine grained carbonated mica rocks. These carbonatites are associated with and preceded by the SAPPM forming supercritical aqueous

282. fluids. During this extended stage the sovites precede the rauhaugites, though both are associated with SAPPM minerals. The bulk of the copper sulphide and niobium mineralization is deposited by these hydrothermal fluids. 4) Final Stage Medium to Coarse Grained Carbonatite Veins; These have vuggy cavities and are ankeritic and dolomitic veins with pyrrhotite, pyrite and barite. 7.8.3. Conclusions In conclusion, this work has shown that alkali bicarbonate/chloride brines of the type probably typical of , aqueous fluids in carbonatite systems are capable of transporting and depositing copper. Samples from Great Beaver House and Bukusu, together with information from complexes such as Kovdor, suggest that this type of fluid and the assemblage it produces is not unique. These deposits, however, are not so far economic copper ore. There are a number of possible reasons for this. The aqueous system may be incapable of carrying more copper. Large quantities of aqueous fluid might dilute and disperse final concentrations of copper. Lastly the igneous system may be impoverished in copper, either as a result of deep seated differentiation processes, or because of an impoverished mantle (see Chapter 1). The indications are that although the SAPPM type assemblages may be copper bearing, their economic significance lies with their niobium and tantalum minerals. The SAPPM assemblage is certainly not identified at Palabora where phlogopite-apatite rocks are barren of both copper and niobium. The fluid inclusion work has provided an insight into the type of aqueous fluids present in mineralizing carbonatite systems, but the extension of this to the Palabora deposit is tenuous. The lack of fluid inclusions and SAPPM type assemblages, together with the unusual nature of the sulphide mineralization, make the anomaly of Palabora all the more pronounced.

283. CHAPTER 8: THE GENESIS OF PHOSCORITES AND THEIR RARE METAL MINERALIZATION

8.1. INTRODUCTION This chapter examines the theories on the genesis of phoscorites in the light of the present work. Phoscorites at Palabora, Bukusu and Sokli have been investigated, particularly from the fluid inclusion standpoint. This makes possible some more conclusive statements on their origin and also on the rare metal mineralization with which they are commonly enriched. Phoscorites are typically coarse grained apatite- magnetite-forsterite rocks, with minor calcite and phlogopite. The forsterite is always serpentinized to some extent. Phoscorites may also contain variable amounts of other minerals; notably baddeleyite, zirconolite, calzirtite, pyrochlore, pyrrhotite and ilmenite.:. Compositional banding is common and may be so severe and on such a large scale that substantial volumes of rock may be lacking in any one of the major minerals. Occasionally monominerallic rocks may be found. The rocks are mostly associated with the early carbonatites and it is for this reason that Smirnov (1977, see Table 1, this work) designates them as carbonatite facies rocks. Phoscorite was first named at Palabora after 'Phoscor', the Phosphate Development Corporation, which mined the rock for apatite (Russell et al.1954). Similar rocks had, however, also been noted in the Kola Peninsula, at Kovdor (Koshitz, 1934 and Zlatkind, 1948). A more detailed study of Kovdor was made later by Rimskaya-Korsakova (1964). These Soviet examples were referred to as apatite-olivine- magnetite rock, apatite-magnetite rocks, calcite-olivine- magnetite rocks, or simply as 'ore complex' (at Kovdor they form an economic iron ore deposit). The variety of names reflects the tremendous heterogeneity of these rocks and this causes problems of classification. Borodin et al.(1973) tried to surmount this problem by defining a new term; 'camaforite'. This is an acronym 284. or abbreviated form of calcite, apatite, magnetite, forsterite and represents a "native genetic series of rocks" in which the above minerals are predominant. The authors, however, point out that the adoption of this term for one rock or another does not necessarily signify the presence of all four minerals (see Table 24). Yegorov (1975) points out that the term camaforite has to encompass two geologically distinct rock types in carbonatite complexes, in terms of both petrography and age. Firstly, the precarbonatite rocks of forsterite-magnetjte- apatite and calcite (true phoscorites as at Palabora) and secondly the post carbonatite apatite-magnetite rocks as at Nemegos and Yessay. He shows that the latter are super- ficially similar to the magnetite/ilmenite-apatite eruptive rocks associated with the diorite-anorthosite formations called nelsonites. His opinion, supported here, is that the term phoscorite for the early banded forsterite-magnetite- apatite rocks is well established and does not need changing, especially for a term which links two separate autonomous rock series. The term phoscorite has been used in this present work to refer to the first category of precarbonatite/early carbonatite rocks, as mentioned by Yegorov (op. cit.). The definition of these rocks in the field is not only made difficult by the large scale heterogeneity, but also by the fact that they may be subject to severe alteration (as at Sokli, see Chapter 6). These rocks are commonly host to economic deposits of iron ore, apatite and rare elements such as Zr, Nb, Ta, U and Th. The severe nature of these mineralizing processes in some complexes has led authors to favour a metasomatic origin for phoscorites, whilst in cōmplexes where such effects are less well pronounced, magmatic origins have been proposed. 8.2. PREVIOUS VIEWS ON THE GENESIIS OF PHOSCORITES Just as the definition of these rocks is complex, so too are ideas on their genesis. Theories on the origin of 285. A SHORT DESCRIPTION OF VARIOUS CAMAFORITE DEPOSITS (modified after Dorodin et al. 1973) Mineralogical-petrographic Features of Camoforitee Name of Massif Main Rock Types Morphology and Structural Predominant Petrographic Typomorphic Accessory in chronological Position of Cametorite Types Minerals . order Bodies

KOVDOR Olivinitea, neph- A system of veinlike bodies Forsterite-magnetite, Baddeleyite, pyrrhotite, Kola Peninsula eline-pyroxenitea in a linear tectonic zone. apatite-forsterite-magne- spinel; hatchettolite, U.S.S.R. & molilite rocks, Zone length 1.3km, width Lite, calcite-apatite- Nb-zirconolite, ilmsnite camaphoritee & 0.5 - 0 8km. forsterite-angnetits carbonatitee

VUORI YARVL Pyrorenites, mph- 1 net of echelon like veins Foreterite-magnetite, Pyrochlore, hatchetto- Kola Peninsula aline-pyroxenites, confined toga ayatem of stee- apatite-forsterits-magne- lite-baddeleyite, Nb- U.S.S.R. camaforites, and ply dipping conical fractures Lite, calcite-apatite- zirconolite, pyrrhotite carbonatites with a vein width of several foraterite-magnetite • metres & length up to 500m: individual blocks are enclosed in carbonatites. Block size up to 4.0-50 x 150m.

ARBABASTAX Pyroxenites, neph- Heart shaped veined bodies Forster/to-magnetite, Baddeleyite, pyrochlore, S. Yakutsk eline-pyroxenites, confined to a system of con- apatite-choodrodite- zirconolite pyrochlore U.S.S.R. alkaline & naphel- ical fractures & atocklike magnetite, apatite- ins syenitee, cam- core. Size of area of cams- forsterite-magnetite aforites and forite developed is 0.3km. carbonatitee

BSSAI Olivinitee, jacu- Dyke like circular body Apatite-magnetite with Baddeleyite, pyrochlore, Maimecha-Kotui pirangite-melts£- between dolomite core & forsterite, calcite, etc. U.S.S.R. gite, camaforites, outer zone of calcitic phlogopite (N. -Siberia) sovitee, rauhau- carbonatites. gitea BARCHI1.SKY Pyroxenitea, came- Vein like body measuring 1,00 Magnetite-apatites N. Kazakhstan forites x 5-6m amidst pyroxenites U.S.S.R.

PALABORA Pyroxeaites, !yen- Circular zone between a core Apatite-olivine-magne- Baddeleyite, thorianite, Transvaal ites, camaforites, of calcitic carbonatitee & tits with phlogopite chalcopyrite, etc. South Africa carbonatitee micatized pyroxenites, zone (vermiculite) approx. 120m. DOROWA Olivinites, ijo- Dykes & veins up to 5m in Apatite-magnetite with Baddelayite S. Rhodesia litee, foyaitee, size cutting through rani- olivine, essentially Africa camaforites, tea; irregular lens shaped magnatitic, essentially • carbonatites bodies from 150-200m long apatitic in the carbonatitee BUKUSU Dunites, pyroxe- Circular zone around a Phlogopite-magnetite- Uganda rites, ijolite- carbonatite core in ijolite apatite Africa melteigitee, foya- and other rocks. ites, camaforitea, carbonatites NalECAS Ijolites, nephe- Dyke like bodies in alkaline Apatite-magnetite n Pyrochlore Canadian Shield line syanitee, rocks; measuring up to 60 x Canada caoeforites, BOOm. . carbonatites

JUt1UTA Pyroxenitea, Circular dykes around car- The same S. Brazil nepheline syen- bonatite stocks, measuring ites, camaforites up to 50m. carbonatites ARAXA Alkaline rocks, Geological study weak. Apatite-magnetite • S. Brazil camaforites, with calcite, carbonatites barite, etc. SOKLI Camaforitea, Irregular corroded rem- Foraterite-magnetite- Pyrochlore, baddeleyite, Kola Peninsula silica-carbons- Hants in the carbonatites. apatite (with phlogo- pyrrhotite, chalcopyrite Finland titee, sovitee, Blocks up to 100 or more pits), foraterite- raniaugitee metres aoroea. magnetite, calcite- apatite-magnetite- forsterite-alinobumite

# Magnetite-Apatite rocks of nelsonitic type , not true phoecorites according to Iegorov 1975. Table 24

Translated from the Ruaaian by C.J.H. Aldona.

286 phoscorites have alternated from completely magmatic to entirely pneumatolitic or hydrothermal. A review of these theories is given here, since much of the material is not available in English. This also provides the background for discussion of the observations made in this study. 8.2.1. Crystallization from a Melt The Kovdor complex has been subject to much detailed investigation. The geology is described in this work, Chapter 1. According to Volotovskaya (1958A & B) the 'phoscorites' were formed in several stages; a shattered zone was first filled with a primary ultrabasic magma producing fine grained forsteritic olivine and apatite as it solidified. This was followed by periodic deposition of 'ore' in veins and lens like bodies with certain areas becoming enriched in calcite. She concludes: "the formation of magnetite ores of varying types is obviously related to the crystallization of the remaining ore material which separated from the silicate parts of the magma Judging from the high apatite, calcite and (in places) phlogopite content, the formation of the deposits occurred near areas with an enormous quantity of volatiles, among which CO2, H2O, P205 and F play the main role" Volotovskaya, 1958. Russell et al. (1954) favoured a magmatic origin for the phoscorites at Palabora in which the phoscorites followed by the carbonatites formed two consecutive intrusions from one centre or focus of carbonatite activity. 8.2.2. Hydrothermal/Metasomatic Origins The above mentioned earlier views on origin involved an important magmatic contribution. By 1965 however, views were changing in favour of a more metasomatic origin (Hanekom et al.1965 and Kukharenko et al.1965). Hanekom et al.(op.cit.) proposed a hydrothermal/metasomatic origin for the phoscorites at Palabora. Quoting some experiments by Bowen and Tuttle (1949) showing that in the system Mg0 - Si02 - H2O "silica was abstracted from the charges by water vapour, even when no free Si02 was present", these authors propose a scheme for silica abstraction at Palabora. Similarities are pointed out with Bowen and Tuttle's conclusions; if water vapour undersaturated in Si02

287. should stream through a crack formed in a mass of pyroxenite, the rocks adjacent to that crack would be converted to a type consisting mainly of olivine. Complete replacement would result in what would appear to be a dyke of olivine rock in pyroxenite. Hanekom et al. (op.cit.) develop this to explain the phoscorites; a dunite plug formed from the above process is altered pneumatolytically through the addition of iron, titanium, zirconium and possibly P205 to farm the phoscorite. A gradual change in the composition of these fluids, to fluids more enriched in Ca0 and CO2s produced the gradational change from phoscorites to the banded carbonatites (Hanekom et al.1965). At the same time, Kukharenko and Orlova (1965), developing the metasomatic ideas of Kukharenko and Dontsova (1964) distinguished in the phoscorites of Kovdor and other Kola Peninsula carbonatites three main rock types:- 1) phlogopite-apatite-forsterite (with some magnetite impurities) 2) phlogopite-apatite-magnetite (with varying calcite contents) 3) phlogopite-magnetite-calcite rocks (with apatite) appearing as transitional gradations between the earlier two types and the carbonatites. The first type is caused by the replacement of ijolite- melteigites and hyperbasites, apparently in a manner similar to that proposed by Hanekom et al.(1965). The alteration of these Soviet rocks to phlogopite and extreme apatite varieties is similar to the alteration of phoscorites observed in this work at Sokli (Chapter 6). It may be significant that Sokli is also in the Kola Peninsula. The Kola Peninsula alkaline igneous province may have a characteristically large volatile/hydrothermal component, compared to other provinces. The sources of the elements for the pneumatolitic formation of these rocks according to Kukharenko and Orlova (op.cit.) are; 1) the zones of melititization of the hyperbasites on their contacts with alkaline intrusions, and 2) the internal areas of the massifs, in the process of phlogopitization of dunites and pyroxenites from the action of solutions arising from the alkaline intrusions. Temperature

288. of formation of the phoscorites is given as between 450 and 600° on the basis of ilmenite/magnetite exsolutions and decrepitation of fluid inclusions. A more detailed hypothesis for the genesis of phoscorites and the other apatite-magnetite and apatite types (which would together be equivalent to Borodin et al.'s camaforites) is presented by Glagolev (1962). In his view, all the rock types are produced during one metasomatic process, the apatitization of pyroxenites, ijolites and other rocks; the varieties in rock type being due to con- jugate zoning. Preceded by a zone of monomineralic phlogopite metasomatites, forsterite-phlogopite-magnetite-apatite rocks develop with central magnetite-apatite and apatite zones. He suggests that carbonatites are later, but often confined to the same structure. The concept is similar to that of Hanekom et al.(1965) where the composition of the fluids changes from P rich to Ca0 and CO2 rich fluids which produce carbonatites. Baldock (1967) comments on the remarkable similarity between the phoscorites at Bukusu (Uganda) and those of Palabora. He favours a metasomatic replacement of earlier silicate rocks. The close relationship of carbonatites interbanded with sheets of phoscorite suggested to Baldock that the metasomatic formation of the phoscorites was in some places at least directly related to the carbonatites. In one area he observed magnetite iron ores associated with the effects of in situ carbonatization of pre-existing syenites and nepheline syenites and suggested that similar processes may have played a part in the formation of certain magnetite perovskite deposits and also phoscorites at Bukusu. "Relationships between the phoscorite and the inter- calated carbonatites are confusing; the contact is in places gradational, as at Palabora where phoscorite grades into the older banded carbonatite by replacement (Russell et al.1954). But a rather sharp contact between the pegmatitic phoscorite and dolomitic carbonatite, which in some specimens shows clear evidence of flow movement, is more usual. No such

289. flow structure can be detected in the phoscorite which is, indeed, so coarse grained that intrusive emplacement and consolidation from a melt is thought improbable." (Baldock, 1967) Borodin et al. (1973) favour a metasomatic/hydrothermal origin for all of the rocks of their camaforite series. The elements in the solutions may be divided into three groups on the basis of their origin:- 205, Zr02 1) Juvenile P205, CO2' CaO, Nb205, Ta borrowed from host rocks in situ 2) SiO2 and A1203 3) MgO, partial Ti02, Zr0 , Fe0 and Fe1 0.1 derived from ultrabasic rocks In thg process of ngtidi movement of solutions. These are redeposited in camaforites and surrounding metasomatic rocks. Essentially these authors suggest that solutions rising through a conduit like centre in magmatic alkaline rocks produce a series of vertical metasomatic zones. MgO, FeO, etc. are removed and deposited to form camaforites and a series of zones which rise through the complex as the process proceeds. They point out that phoscorites commonly have an aureole consisting of a phlogopite zone and a forsterite zone around them. Although favouring a metasomatic origin for most camaforites, Borodin et al.(op.cit.) do mention that like carbonatites, in one and the same complex, camaforites can be found both in the form of intrusive (magmatic?) bodies (dykes and veins of apatite magnetite rock) and also in the form of metasomatic bodies. On the former they quote Philpotts (1967) on the immiscible separation of magnetite apatite melts from silicate magmas which form nelsonites and draw an analogy between this and the above mentioned dykes and veins.• The conclusions of Borodin et al.(op.cit.) are thus confused, because their camaforites incorporate both phoscorites and these apatite-magnetite types, which in the opinion of Yegorov (1975) are not related. They do point out that camaforites are highly prospective rocks for rare metals. 290. 8.2.3. The Palabora Phoscorites Detailed descriptions of this rock are provided by Russell et al. 1954 and Hanekom et al. 1965. Briefly, the rock consists of coarse grained partly serpentinized olivine, magnetite, apatite and phlogopite with subordinate carbonates (calcite and dolomite) averaging about 6% (P.M.C.Staff,1976). It also contains smaller amounts of baddeleyite, thorianite and Cu sulphides. The olivine occurs as large euhedral or rounded crystals from a few millimetres up to 5cm. or more across and also as large aggregate blocks to which the term dunite would be applicable. The apatite, carbonate and magnetite are noticeably interstitial to the olivine, but do cut through it and replace it in places. Magnetite may also form coarse chunks, but it is always interstitial to the olivine. It usually makes up between 25 and 50% by weight of the rock and is noticeably titaniferous (3-5% Ti02; P.M.C. Staff, 1976). The apatite, ranging from 12-20% in the rock, is also interstitial to the olivine (rarely a small apatite crystal may be surrounded by olivine) and is surrounded by magnetite. In this work it has been revealed that the phoscorite apatites have a distinctive REE and Sr chemistry different from the carbonatites and pyroxenites (see Chapter 3). The olivine has been analysed using the electron microprobe (see Table 25) and it is, shown that, as in other phoscorites (Borodin et al.1973 and Vartiainen et al.1978) the Ni and Cr content of these forsteritic olivines is characteristically very low. The levels in the Palabora olivines were below detection limit (see Table 25). The low levels of Ni and Cr for rocks which have their ultimate origin in the mantle suggests that considerable fractionation must have taken place before their formation. (Crystal settling of mafic minerals removes Ni and Cr from the residual magmas - see Chapter 1). The inclusions noted in the phoscorite olivines at Palabora (described in Chapter 4) have some relevance to the genetic problems of these enigmatic rocks. As has been shown in the introductory review, the current views are 291. TABLE 25: ELECTRON MICROPROBE ANALYSES FROM PALABORA PHOSCORITE OLIVINES

Detection Pb(1) Pb(2) Pb(3) Limit Mean SiO2 40.09 40.42 40.86 .07 40.46 Ti0 n.d. n.d. n.d. .03 Al2a n.d. n.d. n.d. .02 Fe0 3 11.69 11.94 11.78 .09 11.80 Mn0 .30 0.27 0.23 .04 .27 MgO 47.61 47.30 47.55 .11 47.49 Ca0 n.d. 0.06 0.05 .03 .04 Na 0 n.d. n.d. n.d. .06 K 8 n.d. n.d. n.d. .02 Ni2O n.d. n.d. n.d. .05 Cr0 n.d. n.d. n.d. .03 TOTAL 99.69 99.99 100.47 100.06 n.d. = not detected

COMPARISON WITH PHOSCORITE OLIVINES FROM OTHER COMPLEXES

1 2 3 4 Palabora N=3 Kovdor N=3 Bukusu N=1 Sokli N=1 SiO2 40.46 41.26 39.49 40.5 Ti02 - - - - A126 - - - - Feb 3 11.80 5.81 19.53 12.5 Mn0 .27 .67 .74 .83 Mg0 47.49 51.78 40.74 46.80 Ca0 .04 - .18 .05 0 Ka8 - - - - NiO - .0032 - < .05 Cr0 - .004 - - TOTAL 100.06 99.53 100.69 100.70

1 Palabora means from above 2 Kovdor - results from Borodin et al. 1973 3 Bukusu - this work 4 Sokli - Vartiainen et al. 1978

292. predominantly in favour of a metasomatic origin for these rocks. For this reason, although they are apparently primary melts, the inclusions must be viewed with some caution. Since it is believed from this work that the inclusions are true melts a reappraisal of the genesis of these rocks is called for. Such a reappraisal might indicate that. the phoscorite olivines were crystallizing from a carbonatite melt and were then precipitated, forming a cumulate of olivine rich material with a carbonatite intercumulus liquid. Such a cumulate being streamed into the vertically banded condition it now displays by later carbonatite activity, or simply being intruded as a crystal mush lubricated by the still liquid carbonatite magma. Olivines are commonly present in early carbonatites. Melcher (1966) reports olivines in carbonatites at Jacupiranga which may be derived from the carbonatites. Wyllie (1966) points out that forsterite may be produced from carbonatite magmas, though only in small quantities. Nevertheless, if olivines were produced, the work of Wyllie and Biggar (1966) on the highly fluid nature of synthetic carbonatite melts would suggest that they would sink extremely rapidly. Cumulate olivines from carbonatites would thus not seem to be impossible. Another alternative (a$ mentioned in Chapter 4) is that the olivine crystallized from a basic melt containing droplets of carbonatitic fluid. This is considered less likely, although Roedder (1978) has shown that low density immiscible phases may adhere to the surfaces of crystals and become trapped in preference to the high density phase. It would, however, be difficult to produce pseudosecondary inclusions in this way. The most important point to arise from the study of the inclusions in the olivine is their distinct compositional variance from the whole rock as it now exists. The inclusions have low Ti magnetite, no phosphorus, very low Al, etc. (see Chapter 4). It must be concluded that for these elements to be present in the whole rock, they must have been introduced after the formation of the olivine. 293. An interesting adjunct to this observation is the presence of Ti rich chondrodite along cracks in the olivine and on the rims of the olivine, where they are in contact with the high Ti magnetite. The olivine appears to have been altered, being replaced by a mineral richer in Ti, F and OH (see Fig.55 and Plate 27C). The corollary for this is the fact that the difference between the inclusion contents and the whole rock was brought about by a later introduction of material of different composition. A pneumatolitic hydrothermal introduction of apatite and Ti rich magnetite would not contradict the observed facts. Signi- ficantly the baddeleyite, which apparently paragenetically precedes the apatite and magnetite mineralization, may be altered to a titanium bearing zirconolite phase; see this work, Chapter 2. The alteration of the large olivine crystals to humite group minerals in optical continuity with the olivine is not only found in the Palabora phoscorites. The same occurs in both the other phoscorites studied in this work; namely those of Bukusu and Sokli. At Bukusu Baldock (1967) uses the optical continuity of chondrodite with the olivine as a factor indicative .of a metasomatic origin for the whole rock, though he does state that the magnetite was deposited after the olivine. Investigation of a few samples of Bukusu phoscorite (kindly made available by Leeds University and also the Ugandan Geological Survey) shows the paragenetic sequence to be olivine, apatite, sulphides and magnetite. The inclusions in Bukusu olivine (see Plate 27E and H) as mentioned in Chapter 4 have Ti poor magnetite, while the magnetite in the rock is rich in Ti. The similarity with Palabora is striking. The genesis of the Bukusu phoscorite is, however, further clarified by the presence of aqueous inclusions in the apatite (see Plate 27F and G) with very minor chalcopyrite. The close apatite-pyrrhotite association (see Chapter 6) in the Bukusu phoscorites is well defined as at Sokli. The apatite is intergrown with the sulphide, but the textures 294.

Figure 55: Comparison of Olivines and Humite Minerals from Palabora and Sokli

Palabora

Olivine Chondrodite Mg0 47.49 47.78 47.85 Al 0 .02 .02 .02 Sial 46.46 36.35 35.53 TiO2 .03 .81 .85 Mn0 .03 .22 .16 Fe0 11.80 9.58 9.43 TOTAL 99.82 94.74 94.83

50 Mg0 --1.0 3z0~ 40 - .8

30 .6 Mg0 (%Mn0 SiO2 (& TiO2 Fe0 20 - .4

• Fe0 10 i .2 Mn0 __ - 0 0.0

Sokli

Olivine Clinohumite Mg0 40.5 52.3 Al 0 Si82 3 40.5 39.1 TiO - .90 Mn02 .83 .98 Fe0 12.5 4.8 TOTAL 100.70 98.1

295. PLATE 27: Phoscorites

A. Phoscorite from Palabora with irregular sovite veinlet. mt = magnetite; ol = serpentinized olivine.

B. Massive serpentinized olivine (ol) and magnetite (mt) from Palaborafphoscorite. Magnetite appears to cut through and replace serpentine.

C. Sample P6 (Palabora). Chondrodite (ch) next to magnetite veinlets replacing olivine (ol). Plane polarized transmitted light. Bar = 10 microns.

D. Sulphide bearing phoscorite from Sokli. Sulphide and magnetite replace olivine (ol).

E. Inclusions in phoscorite olivine from Bukusu. Mt = magnetite; c = carbonate; p = phlogopite. This is a more complex assembly than Sokli and Palabora inclusions. Plane polarized transmitted light. Bar = 50 microns.

F. Apatite from Bukusu phoscorite with both aqueous inclusions (aq) and aligned sulphide inclusions (S). Plane polarized transmitted light. Bar = 50 microns.

G. Aqueous inclusion (aq) in apatite from Bukusu phoscorite with cube of pyrite (p), gives yellow reflections in reflected light. Plane polarized transmitted light. Bar = 100 microns.

H. Magnetite symplectic intergrowths or exsolutions in Bukusu phoscorite olivine further complicate the inclusion population. Plane polarized transmitted light. Bar = 50 microns.

296.

PLATE 27

5cros

•

• S mt c It)* 4.44 P v 1.

Ilk 41110.1,

G H also indicate the deposition of sulphide after apatite. The aqueous inclusions contain daughters of sulphides (cubes - of pyrite? - giving yellow reflections in reflected light - see Plate 27G) as well as colourless birefringent phases. Homogenization of seven inclusions in Sample BK 7 (a typical phoscorite) gave a mean homogenization temperature of 315°C with a standard deviation of 15.6°C. There are no aqueous inclusions in the olivine. The similarity between this and the Sokli phoscorites is also notable; early olivine and olivine-magnetite rocks being invaded by apatite depositing solutions. The early olivines, partially serpentinized, as in the other examples, contain inclusions very similar to those at Palabora. They have not been probed, but the optical similarities are striking, especially the reversed pleochroism typical of the Al poor micas. The alteration of the olivine to titanium enriched humite minerals is also the same. At Sokli (see Chapter 6) clinohumite is found in the SAPPM assemblage cutting olivine phoscorites. This assemblage contained aqueous inclusions of the same type as those in the apatite. The inference is that the solution depositing apatite rich in F and H2O can form clinohumite, possibly in some cases by alteration of forsterite. Recently reported fluid inclusion work on -the Kovdor carbonatites by Khitarov et al. (1978) includes heating work on inclusions in forsterites (see Table 23 in this work, Chapter 6). The inclusions are designated as mostly filled with solids, both unidentified phases and carbonates. They homogenise to 'melts' at between 640° and 890°C. Apatites from this stage have two types of inclusion; high temperature melt inclusions (similar in composition and homogenization temperature to the olivines) and lower temperature (290-480°C) aqueous inclusions. It is not clear whether the inclusions in the apatite are of the same generation or not (they may belong to a different paragenesis). Although the inclusions are not well described, they probably represent an early melt (with some carbonate content) from which the olivine may have grown. 298. Borodin et al. (1973) report decrepitation temperatures for inclusions in phoscorite minerals; olivine (450-500°C), magnetite (350-550°C) and apatite (400-540°C). The decrepi- tometer method can be an unreliable measure of homogenization temperature, (Rankin, 1978) especially when comparing different minerals. The inclusions types are not described. In all the above mentioned phoscorites studied in this work there seems to be evidence of; 1)olivines intimately associated with an aqueous poor carbonatitic melt with low Al and Ti 2)the later introduction of apatite and magnetite' (high in Ti) with phlogopite (not impoverished in Al) 3)disturbance of phoscorites by later carbonatites, which both cut through and replace the phoscorites. 8.3. CONCLUSIONS The origin of phoscorites is considered from this work to be part of a multistage process, involving both magmatic and pneumatolitic/hydrothermal stages. The evidence from numerous complexes of euhedral olivines with carbonate melt inclusions suggests that phoscorite olivines are closely related to the early stages of some carbonatite magmas. A process of crystal settling from a carbonatite magma may explain such concentrations of olivine. Petrographic and fluid inclusion evidence shows that later hydrothermal/ pneumatolitic activity introduces apatite, magnetite and sometimes sulphides (which replace the calcite interstitial to the olivines). The chemistry of these fluids is substantially different to the melts from which the olivine formed (containing Ti, Zr, P, Al, F and H20). Later carbonatites may cut through these olivine rich rocks (phoscorites) to produce the banded appearance, as at Palabora and Bukusu, or the irregular blocks as at Sokli. Such later activity may be magmatic or hydrothermal/metasomatic and may be responsible for the glimmerite alteration zones between carbonatite/phoscorites and earlier silicate rocks of the complex. Phlogopitization of early silicate rocks is not only present around phoscorite bodies (as in Borodin et al.'s zoning system); Gittins et al.(1975) show

299. such phlogopitization of pyroxenites at Cargill is due to carbonatites and point out that it is in effect a type of fenitization. The phoscorites may themselves become altered (phlogo- pitized and carbonatized) as described in the Sokli chapter (6) ānd also at Kovdor (Borodin et al.1973). Serpentini- zation of the olivines will also occur during these later stages. The rare metal concentration in some phoscorites is not as constant as Borodin et al.(op.cit.) imply. Whilst in many examples (as at Sokli) pyrochlore with U and Ta is commonly present, the situation at Palabora and Bukusu is different. Palabora is impoverished in Nb and the Th and Cu are confined mainly to the latest carbonatite activity. The phoscorites at Bukusu are also low in Nb (Baldock,1967). Zirconium minerals do however seem to be universally present. It is unclear where the volatiles carrying F, P, Zr, Ti, REE and Al came from, but it is certain that they were not strongly represented in the system from which the olivine crystallized. It is tempting to suggest (in line with current thought on carbonatite systems) immiscibility of a super critical volatile phase carrying the above elements and advancing before the carbonatites (summarized in Chapter 2). From the above deductions concerning the origin of phoscorites, it is apparent that the presence of Nb, Th and U is dependent upon the presence of these minerals in the fluids which deposit the apatite and magnetite. The rare metal concentrations in these fluids obviously varies from one complex to another.

300. CHAPTER 9: SUMMARY AND CONCLUSIONS

9.1. SUMMARY OF PREVIOUS CONCLUSIONS Copper is not uncommon in trace amounts in carbonatites. Significant accumulations are however, rare. Nevertheless, the mean value for Cu in carbonatites of 2.5ppm given by Gold (1963) is probably an order of magnitude too low. Copper occurs in association with sulphur in carbonatites, mostly as chalcopyrite. Three types of copper bearing sulphide assemblage are recognized:- 1) Copper dominant assemblages 2) Pyrrhotite dominant assemblages 3) Pyrrhotite/pyrite dominant assemblages with sphalerite and galena. It is possible that these are related to the depth of formation. The copper is considered to be of primary mantle origin. Anomalous concentrations in some complexes are considered to be a result of either; i) unusual levels of copper in the mantle source region, or unusual levels of some other element involved in its transport and concentration and/or ii) unusual differentiation of (sulphur depressed?) ultrabasic magmas producing high residual concentrations of copper which are transferred to the carbonatites. A study of the Palabora copper deposits suggests that the copper mineralization is intimately related to that last magmatic carbonatite activity; the copper being deposited from a residual aqueous liquid as the carbonatite crystallized. In effect, the carbonatite is autometasomatized by its own residual fluids. Continued plastic flow and degassing fractures the carbonatites and partially redis- tributes the copper. An intrusion temperature of 600°C is considered probable for the copper bearing transgressive carbonatite, cooling to 450-500°C during the initial major ore deposition. Final degassing of the carbonatite column down to 250°C resulted in the deposition of valleriite along shears and cracks.

301. Apatites at Palabora do not show the fluid inclusions typical of carbonatites, but they do have unusual copper sulphide inclusions indicative of the presence of copper in the medium from which they crystallized. Such inclusions are most common in the phoscorite apatites. The apatites at Palabora have REE abundances typical of carbonatites. The apatites show a progressive increase in total REE and light RE enrichment from phoscorites and pyroxenites through to the carbonatites. Sr abundances follow this trend. REEs are predominantly held in the , apatites and, if apatites are introduced into the rocks by hydrothermal activity, this produces a highly anomalous picture of REE in the whole rock. Whole rock interpretations of REE should be carefully related to petrography and individual mineral analysis to avoid ambiguous conclusions in carbonatite complexes. Melt inclusions in phoscorite olivines contain copper sulphides equivalent to between 200 and 1000ppm Cu. This shows conclusively that the copper at Palabora was present in the earliest carbonatite magmas. The copper was thus an intimate part of the magmatism there and not introduced by later aqueous fluids from an extraneous source. The melt represented in the inclusions is a potassium rich, low aqueous alkaline earth carbonate - a classical carbonatite magma. Aqueous inclusions in pyroxene from the Guide copper mine present a complementary picture of an aqueous rich alkali carbonate/chloride system rich in copper, co-existing with a silicate melt which produced both diopside crystals and a (possible immiscible) sulphide phase. The aqueous alkali brine is highly potassic and carries about 3000ppm Cu. This demonstrates the potential of the aqueous fluids, associated with some carbonatite complexes, for carrying large quantities of copper. The, highly potassic nature of the Palabora system, suggested by these inclusions, is unusual and may be related to the anomalous minor element chemistry of this complex.

362. A copper bearing sulphide, apatite, pyrochlore, phlogopite, magnetite (SAPPM) assemblage has been defined at the Sokli carbonatite in Finland. Petrographic, geochemical and fluid inclusion studies indicate that it is a hydrothermal assemblage introduced into earlier carbonatites and phoscorites. The assemblage was deposited from aqueous hydrothermal fluids rich in Na+, C1+, CO3 - and/or HCO3 with smaller amounts of K. The solution was capable of transporting and depositing silicates, (phlogopite), pyrochlore, sulphides and apatite; it must therefore have contained F, Si, Mg, Fe, P, Nb, Ta, Cu and S. These fluids are thought to have developed by immiscibility from carbonatites, which they are closely related to. Phoscorites are concluded to be products of both magmatic and metasomatic events. Melt inclusions in conjunction with mineral analysis show that; 1)phoscorite olivines are very low in Ni and Cr 2)the olivines probably crystallized from an early carbonatite magma 3)olivine was subjected to later Ti rich aqueous fluids which caused the magnetite and apatite mineralization and partial alteration of olivine to humite minerals. 9.2. CONCLUDING SYNTHESIS A variety of processes have long been known to be active in carbonatite formation and development. The present work has shown that in an investigation of the behaviour of copper in carbonatites, all the major processes play a part. Copper can be carried in potentially mineralizing amounts in both classical carbonatite magmas and also in the aqueous alkali carbonate rich brines. The latter may produce carbonatites by metasomatism as well as by primary crystallization and vuggy vein infilling, the supernatent liquor being excluded, escaping to form fenites and other alterations characteristic of carbonatite bearing complexes. 9.2.1. Copper in Aqueous Fluids The fluid inclusions at Sokli, and the Guide Copper Mine, Palabora provide excellent evidence that alkali

303. chloride/carbonate brines are both active in carbonatite systems, and also that they are capable of carrying copper. The solubility of copper in these fluids is probably affected by the chlorides. As reviewed by Crerar and Barnes (1976), all earlier experimental studies of the solubility of chalcopyrite and pyrite failed to show base metal concentrations in excess of l0ppm metal in pure water and 100ppm in near neutral brines. They conducted experiments on the solubility of copper and iron from the assemblage pyrite-chalcopyrite-bornite in, saline solutions up to 100 bars. They found that "at 350°C with total sulphur <0.1, under the near neutral to weakly acidic conditions probably characteristic of porphyry copper ore forming fluids, approximately 1000ppm Fe and Cu dissolve in 1.0 molar NaC1 as the species CuCl, Fe+ and FeC1+. Under similar conditions at 250°C the solubility falls to roughly 100ppm Fe and l0ppm Cu." Thermodynamic data generated from the experiments indicate that; ".... concentrations exceeding 1000ppm of both Fe and Cu can be dissolved and transported by mildly acid NaC1 solutions at temperatures of 350°C and above; cooling such solutions to 250° precipitates roughly 99% and 90% of dissolved Cu and Fe respectively." Although their work was designed to simulate the porphyry environment, the relevance of the alkali chloride to the solubility of copper is clear. That such a mechanism is operative in the bicarbonate rich alkali chloride solutions of some carbonatites is conjectural, but does not seem unreasonable. The importance of decreasing temperature in depositing the sulphides should be emphasized. 9.2.2. Copper in less Aqueous Carbonatite Magmas The main mineralizing stage at Palabora is apparently an essentially magmatic carbonatite phenomenon. The presence of copper in the earliest stages of the carbonatite activity at Palabora indicates that copper sulphides may exist in carbonatite magmas. The presence of such large amounts of

_ 304. copper at Palabora may be related to the lack of great quantities of aqueous phase activity associated with, or following the intrusion of the copper bearing residual magma. Such aqueous fluids, if present, would surely sweep away, perhaps dispersing and diluting any potential copper ore deposit. In the absence of quantities of potent aqueous fluids, the temperature decrease in the system is also probably responsible for depositing the sulphides. 9.2.3. Depth of Erosion The upper reaches of carbonatite complexes have characteristic late stage polymetallic mineralization. This would seem logically to be a temperature controlled phenomenon (temperature being influenced by waning latent heat of the system, and also by the shallower level of emplacement). In a similar manner, there may be a temperature/ pressure barrier below which copper sulphides in aqueous poor magmatic systems will precipitate. Palabora is a deep seated, comparatively high temperature complex and it is conceivable that this critical level is not reached by erosion in other potentially copper rich complexes. Nevertheless, a simple dilution procedure exemplified by taking the mineralized carbonatite plug at Palabora (lsq. km. at .6770 Cu) and stretching this to fill the Sokli carbonatite area (20sq.km.) would still yield an overall value of 300ppm. This is a figure far above even an opti- mistic mean for all carbonatites and Sokli has one of the largest surface areas of carbonatite in the world. Such figures, of course, disregard the vertical extent of mineralization or dilution, but they do suggest that Palabora is more than just a coincidental funnelling or concentration at one focus, in the absence of quantities of aqueous fluid. Without similarly enriched complexes to compare with Palabora, the characteristics common to complexes enriched in copper are impossible to prove. An unusual source region must therefore be considered a prime factor in the occurrence of the Palabora type

305. carbonatite ore deposits. A source region highly enriched in copper or some other elements which control the behaviour of copper would seem probable. It is perhaps significant that the unusual copper deposits of Messina (Jacobsen and McCarthy, 1976) also occur in the same part of the crust. Here the copper is deposited from highly alkaline (in this case sodic) fluids, deficient in silica. The loose association of these deposits with carbonatites, some of which are nearby, may not be coincidental. (Jacobsen, pers.comm. 1977). 9.3. PRACTICAL APPLICATION The work undertaken will have some application in the investigation of carbonatite complexes for ore deposits. Copper sulphide inclusions in the apatite, as seen at Palabora, could provide evidence of potential copper sulphide mineralization in a carbonatite complex, particularly where the carbonatite was weathered and poorly exposed. Mineral exploration of carbonatites could be improved by the knowledge that copper and niobium may be associated with phosphorus, cobalt, thorium and uranium. Knowledge of the common association of such parageneses and their mode of formation will aid the investigation of potential deposits. Soil geochemistry and scintillometer surveys could also effectively be used in their discovery. 9.4. SUGGESTIONS FOR FUTURE WORK Solid inclusions in apatites from Palabora could be further investigated to determine the nature of their relationship to the apatite. Transmission electron microscopy could be usefully employed to investigate the structure of the apatite adjacent to the inclusions and thus establish whether they are trapped solids or exsolved. phases. Further work on the identification of colourless solid inclusions in these apatites is being undertaken in Poland using electron diffraction techniques. It may be possible to observe homogenization of the melt inclusions in olivine by introducing an inert or

306. reducing atmosphere to the microscope heating stage. This may prevent the olivine discolouring at high temperatures. Investigation of melt inclusions for sulphides may also have application in other types of ore deposit, where knowledge of early melts would be useful to an understanding of the system.

307. APPENDIX 1

An Aid to the Identification of Microscopic Opaque Phases in Transparent Minerals using Reflected Light The identification of minute opaque phases trapped in minerals, either as daughter minerals or captured phases in fluid inclusions (see Chapters 4 and 7), or as orientated exsolution or epitaxial growth phases in apatite, has been an important part of this work. In some studies such minerals are referred to as opaques, further identification being deemed impossible or unnecessary. In other works identif i- cation is deduced from outline shape and, in the case of fluid inclusions, magnetic susceptibility, but these features are rarely conclusive in themselves. Well formed crystals may be orientated in a manner giving a deceptively uncharac- teristic outline. Strongly magnetic daughter minerals (pyrrhotite and magnetite) may not respond to magnetic fields because they are cemented to the walls of fluid inclusions (this can be shown by SEM). Opaque inclusions in minerals or melt inclusions may be polished into if they are not associated with any aqueous or gaseous phase. Identification using routine reflected light and probe techniques is then possible. SEM techniques may also be used for identifying daughter opaques in fluid inclusions (see Appendix 2). These methods are, however, tedious and not without problems. Furthermore, having identified one opaque in this way, it then becomes necessary to establish that the rest of the population is the same - or different. Many opaque inclusions can, however, be readily observed using reflected light, when the inclusion is not exposed at the surface. The better information on shape obtained in this way, together with any reflection colours, may narrow down the field of possibilities considerably. Invariably the combination is definitive. Roedder et al.(1963) noted that reflected light could be used to see sulphide reflections from very large opaque (pyrite) grains when near the

308. surface. They concluded however, that in very few inclusions is the grain size sufficiently large to permit recognition of the colour and habit in reflected light. METHOD: Small opaque solids are best observed using a high power oil immersion objective (x60 or greater). It is the oil immersion which is the crucial factor in observing smaller inclusions. The.high magnification gives the best observation of the inclusion colours, while the oil reduces the reflections from the polished surface of the host. Closing the field aperture diaphragm around the inclusion further cuts out unwanted light from the host (internal reflections, etc.). Opaques with flat surfaces, such as commonly develop in fluid inclusions, may show colours close to their true colours (as observed in normal polished sections). To obtain these reflections the flat surface of the mineral must, of course, be approximately normal to the incident beam of light. (In practice the incident beam is probably diffused a little by the host, thus lighting the opaque surface from a variety of angles; the exact horizontal position is therefore not critical). Although a small number of the opaques may need to be investigated before one with the correct orientation is found, the ability to focus on and obtain reflections from inclusions up'to 100-200 microns below the surface provides information from many more inclusions than would be seen on the plane of a polished surface. In practice, a surprising number of opaque inclusions and daughter minerals do give reflections, even if only from a small facet (see Plates 12, 14 and 23). The method of observation is best conducted on polished plates, or polished thin sections. However, it can also be used successfully on individual grains. (Considerable care is needed when using grains to insure that there is no contact with the lens). One advantage with individual grains in oil is that the grains may be manipulated to give optimum reflection conditions for any one opaque. A dual mode

309. microscope with reflected and transmitted light is essential, both to find the opaques, and to investigate spurious reflections. Spurious reflections are produced by dislocations, other inclusions and even from the top of vapour bubbles in fluid inclusions. A dual mode microscope enables one to check on the origin of these reflections. After a little practice, it is mostly easy to distinguish between true reflections from an opaque surface and reflections from other sources. Those from the opaques have a clearer and stronger quality and are less diffuse. A reflected light observation of minute minerals in crystals, fluid inclusions and even melt inclusions often gives a better understanding of shape as a three dimensional surface can be viewed in reflected light. An apparently irregularly shaped mineral in transmitted light may be seen to have a well defined crystal form in reflected light, or even to consist of two different minerals with well defined shapes. Reflected light may give reflections from a well formed facet on an apparently amorphous mineral. The colours of the reflections are not always the exact colour of the mineral, as they are influenced by any body colour the host mineral may have (this is usually negligible). The colour may vary slightly with depth below surface and the orientation relative to the incident beam. Thus all the subtleties of reflected light microscopy cannot be applied. Nevertheless, in the first instance it is possible to tell whether the reflections are strong or weak and whether yellow, orange, white or grey, which, together with shape and some knowledge of the environment, is often sufficient to identify it as an oxide or a sulphide. It has been found possible to tell the difference between sulphides, e.g. bornite, chalcopyrite and pyrite.

310. FIG. 56: Observations of Opaques in Transparent Minerals

\\\ 4w HOST MINERAL 11 \\ \\\ \\ \\ REFLECTING OPAQUES

Conclusion: The method is by no means a panacea for identifying opaque inclusions, but it is an extremely useful addition to other techniques already being used and has the advantage of being easy to apply. It is particularly useful in assessing the distribution of types in a population, having established the identity of various opaque phases by other methods.

311. APPENDIX 2

Scanning Electron Microscopy of Daughter Minerals The scanning electron microscopy (SEM) method for studying and identifying daughter minerals has been well established (Metzger et al.1977; Grant, 1979). This appendix describes the hardware, spectra interpretation and preparation techniques distinctive to the present studies. Hardware: A variety of electron microscopes and qualitative-energy dispersive analytical facilities (Gasparrini, 1976) have been used. At first work was done using a Cambridge Instru- ments Stereoscan HA (SEM) with an Ortec solid state Li drifted silicon detector, the amplified signals being processed through an Econ II (1000 channel) multichannel analyser (MCA) and the resultant spectrum was displayed on an oscilloscope screen. Later the above mentioned analytical equipment was attached to a new Jeol J.S.M.35 SEM which gave much better image resolution. The bulk of the work was however done using the Jeol SEM with an Elsint E.D.S. system with automatic peak identification, stripping and spectra comparison facilities. This system had the capability of producing quantitative analysis by peak processing using a minicomputer system similar to that described in Appendix 3.' However, such quantitative results are not obtainable from daughter minerals for reasons mentioned below. Specimen preparation: In previous SEM studies of daughter minerals, it has been impossible to open preselected inclusions and to expose their contents for SEM work (e.g. Nesbitt and Kelly, 1977). In this study, however, a technique was developed whereby the larger inclusions with daughter minerals visible under •the optical microscope could be selected as individuals and opened. The starting material was the mineral concentrate (100- 1000 microns), portions of which were studied under tritolyl 312. phosphate (Rankin and Aldous, 1979). Individual grains with inclusions of interest were removed from the oil on a needle. Each grain was washed in alcohol and then transferred to a clean glass slide on which a small strip of 'double sided' sellotape was mounted. The selected grain was pushed into the gummy surface of the sellotape and orientated under the microscope so that the inclusion could be seen (the sellotape transmits light very well). Crushing was affected using a glass slide which was gently rocked on the crystal until the latter fractured. This process was continued until the inclusion was opened. With apatite a poor basal cleavage could sometimes be exploited; successive sections of an elongated crystal being broken along this cleavage, until the required inclusion was intersected. Careful observation of this process was possible under a normal petrographic microscope using a x10 objective (see Plate 28). The sellotape mounting ensures that the fragments are held firmly, but it also allows them to be carefully manipulated under the microscope (using a mounted needle) to expose the cavities for SEM. This process was extremely valuable in co-ordinating optical and SEM characteristics of the more important daughter minerals. For apatite it could be repeated with about 50% success rate in larger inclusions. The pyroxenes from Guide were more difficult, but results were still possible. In the crystals with many inclusions it was sufficient to break the crystal on the sellotape and separate the resulting fragments. Many inclusions for SEM observation were produced in this way. Having exposed the inclusions, the glass slide was then coated with carbon (from 2 or 3 different directions). This was monitored on an aluminium stub, electrical conductivity being provided by a track of 'aquadag' carbon from the coated surface to the aluminium stub. The whole was then offered up to the mounting block in the SEM. Occasionally gold coatings were used. This produces better resolution of the smaller phases, aiding identification of habit. Unfortunately, gold produces K-alpha x-rays of 313. PLATE 28: Sequence of Opening a Preselected Inclusion and Extracting Daughters for SEM Work

A. After selecting the crystal with the required inclusions it is washed in alcohol and mounted on double sided sellotape on a glass slide. The fibres are the sellotape. The crystal is then covered with another glass slide. Transmitted plane polarized light. Bar = 200 microns.

B. Under higher magnification the inclusions can be seen. There are two inclusions and the opaque daughters in each are marked A and B. Vapour bubbles are marked V. Plane polarized transmitted light. Bar = 100 microns.

C. The apatite is gently crushed until the inclusions are fractured open. The opaque from inclusion A is shown. Plane polarized transmitted light. Bar = 50 microns.

D. Daughter mineral A at highest power. Transmitted plane polarized light. Bar = 10 microns.

E. Using SEM, the morphology of the mineral A is revealed and x-rays produced indicate the presence of iron and sulphur with sulphur predominating over iron. The daughter is pyrite. Bar = 1 micron.

F. Daughter mineral B (see B above) is also pyrite, but has a less well defined habit (SEM). Bar = 1 micron.

314. PLATE 28

D similar energy to sulphur and thus the detection of sulphur is impeded. Carbon coating was used for analytical work. Identification of phases: In many cases the daughter minerals are lost from the opened cavities, but persistent investigation of many cavities provides the opportunity to find some in situ. The morphology and relationship to the inclusion walls were first studied. Deliquescent characteristics can also be observed. A finely focused electron beam is positioned on the. daughter mineral and a characteristic x-ray spectrum is produced. The resulting analysis is only 'semi-quantitative' for a number of reasons, some of which are discussed by Metzger et a1.1977. The errors result from the interference from surrounding minerals, (especially the host mineral) the unknown orientation of the faces/surfaces of material being analysed and difficulties in comparing the spectra of unknowns and standards. The interference from the host mineral is particularly irksome and is perhaps the most severe limitation. The electron beam at an operating voltage of 25kV excites x-rays to a depth of 3-5 microns (Anderson,1966). On small daughter minerals one micron or less across, more x-rays may come from the host mineral than the daughter. The depth of penetration can be reduced to 1 or 2 microns by reducing the operating voltage to 15 or even 10kV. This reduces the problem. There is also an effect of secondary excitation of x-rays from the surrounding host mineral by x-rays generated in the daughter mineral (see Fig.57). In some instances the host mineral may be partially shielding the daughter mineral, this can stop the radiation completely or preferentially absorb the lower energies (equivalent to the lighter elements) giving an erroneous resultant spectrum. The effect of these problems can be evaluated by comparing spectra (taken under similar operating conditions) of the host mineral and the daughter in question (see Fig.57). Moving the beam to different points on the daughter and also

316. HOST MINERAL INTERFERENCE DURING E.P.M.A. OF DAUGHTER MINERALS A. EXCITATION OF HOST MINERAL electron beam

HOST Detector INERAL N

B. PARTIAL SHIELDING OF X-RAYS BY HOST

Detector electron beam

N. \•a N

C SPECTRA INDICATING HOST INTEREERENCE

Caw`

C1l'A Pk" C14 Xray spectrum of KCl on apatite

pk, Caw` apatite spectrum

Pka

317 FIG 57 adjusting the position of the sample and again comparing spectra often shows a decrease or increase in all the elements of one phase but not of the other. Deposition of minerals originally in solution on to the surface of daughter minerals can be tackled in the same manner; the surface deposition being thicker in some areas. Again the two phases can be distinguished because the elements characteristic of one phase decrease or increase together on moving the beam from one point to another. Elements common to both phases can sometimes be established in this way. The other major problem in final identification is the inability of the system to detect elements lighter than sodium. The daughter minerals are commonly carbonates, bicarbonates and oxides; hydrated forms may also be present. The assessment of this must depend on morphology, apparent percentages of detectable elements and optical qualities, if known. Despite all these problems, it is possible to identify a large number of minerals and to make informed estimates of the composition of unidentified phases.

318. APPENDIX 3

Quantitative Electron Probe Micro Analysis (EPMA) Results were obtained using a Cambridge Instruments Microscan V equipped with KEVEX Li drifted Si detector and a Link Systems energy dispersive analytical facility (see Fig.58). Polished sample surfaces were used, carbon coated to a thickness giving blue interference colours on an adjacent brass surface. An operating voltage of 15kV was used with counting times of between 30 and 300 seconds.. The spectra produced were filtered and compared to standard profiles for each element which are stored in the minicomputer (a Data General, Nova II). Machine drift and current variation differences between the stored standard spectra and the sample spectrum were automatically adjusted for by intermittent counting of a pure cobalt reference standard. Apparent concentrations produced by the fitting and stripping routines were then subjected to atomic number absorption and fluorescence correction calculations (ZAFs). Standard factors and constants for this were *stored in the machine (see Fig.59). The final result, a quantitative analysis of the selected spot, together with apparent concentrations, detection limits and the number of ions (on the basis of a preselected number of oxygens) were printed on paper and also recorded on cassette. Large amounts of data collected in this way could be transferred to the Imperial College main frame computer from the cassette. Editing and oxide re- calculation programmes could then be used as required. The rapid analytical procedure enabled suspect analysis to be discarded, analysis of the same spot being repeated. Problems: The problems of EPMA include the inability to detect elements lighter than Na and differences in oxidation state (Fe44/Fem is a particular problem). Fluorinated and water bearing minerals thus produce low totals.

319. FIGURE 58 SCHEMATIC REPRESENTATION OF AN ENERGY DISPERSIVE SPECTROMETER (modified after Gasparrini 1976 )

DETECTOR CHAI=. HARWEELL PROCESSOR (Cooled by liquid nitrogen) F.T.E;TRON MAM I Pileup rejector

Si (Lii PRE ••0 Amplifier Field Effect Transistor

Bias supply

I•I

VIDEO DATA TELETilE._ DISPLAY

MEP

FIGURE 59 PROCEDURE USED BY SPECTRA PROCESSING PROGRAMME ZAF-4 (a Link Systems programme) SPECTRUM OF Uh'XIOWN :

I Digital Filter ` establishes backgrcnind

DIGITAL FILTrR

LEAST SQUARES FIT TO STANDARD PROFILES FILTERED PROFILES STORED Oie DISC

OUTPUT : APPARENT COItE1 TRATICIdS

STANDARD FACTORS ZAF CALCULATIONS STORED OIE DISC

OUTPUT : CORRECTED CONCENTRATIONS

320 The EDS system has many advantages and disadvantages which have been reviewed by Gasparrini (1976). In particular the poorer resolution of peaks can be a problem, though this has been largely overcome by the sophisticated fitting and stripping software. Comparatively few elements have their peaks so close together that the software is unable to separate them. Nevertheless, minerals with a large number of elements may still be difficult to assess because of the interference effects of minor peaks.

321. APPENDIX 4

Fluid Inclusion Preparation and Heating/Freezing Equipment Heating Studies: A Leitz model 1350 heating stage mounted on a Leitz Ortholux petrographic microscope was used for heating and observing the inclusions. The stage can be heated up to 1350°C. It is heated electrically with rheostat control; temperature measurements being made with a Pt-Rh-Pt thermocouple. The thermocouple is in contact with a sapphire , plate on which the sample rests in the sample chamber of the stage. Temperatures were recorded on a chart recorder which was calibrated using solids of known melting point (Grant, 1979) - see Fig. 60. Repeated measurements indicated an uncertainty (one standard deviation) of approximately ±0.02mv on the calibration curve; i.e. approximately -2.0°C over the range below 500°C. Grant (op.cit.) showed that the thermal gradients within the Leitz heating stage are quite severe, particularly at higher temperature. Difference in apparent melting of standard melting point substances at different heights above the thermocouple are shown in Fig.60. The standards were mounted on different thicknesses of quartz plates. It is concluded that any variance in measured temperature from the true temperature' is more likely to be due to thermal gradients within the sample material, and observa- tional uncertainties due to poor optical quality of much of the sample material, rather than machine drift and calibration errors. It is estimated that the figures for the low temperature work at Sokli are accurate to within two or three degrees, thermal gradients being much lower at these temperatures. Homogenization observation reproducibility is poorer probably than that in some of the small inclusions, perhaps -5°C. At higher temperatures, thermal gradients are severe and the temperatures given for the changes observed in the melt inclusions above 600°C are only a guide and may be as

322. CALIBRATION CURVES FOR LEITZ MODEL 1350 HEATING STAGE

1 .8mm BELOW 500°C SHOWING VARIATIONS ``l DUE TO HIGHT OF INCLUSION ABOVE Sample plate thickness BASE(THERMAL GRADIENTS) 1 .0mm

:ase 4a `3 0 MO

2 4-1 Z O.

2 Ō a) a 0 0 0 H a) .4 '1 H

Temperature (°C) 0 0 0 0 0 0 0 0 N C,) C L!) L

Fig 60

323 much as 100° out at 1000°C. The problems with the melt inclusions not reaching equilibrium in short periods of time make greater accuracy worthless. Meaningful conclusions can only be drawn by obtaining homogenization results from numerous inclusions in a sample. The quality of the data is also dependent on the optical quality of the specimen and the size of the inclusions present. Sample Preparation: A. Polished Plate: Conventional doubly polished wafers of rock were used for some of the low temperature and all of the higher temperature work. Depending on the material, the wafers were cut and polished to different thicknesses, usually between 300 and 500 microns. The dark body colour of pyroxenes obscures observation of the inclusions if the wafers are too thick. Apatites from some samples are highly friable and break up on the laps if cut too thinly. Sawn slices of rock were mounted in a casting resin ground down on both sides mounted in a holder so that one side could be polished and reversed for polishing the other side. B. Grains in Oil: Some heating (for the lower temperature Sokli inclusions) and freezing work was done using unpolished crystals mounted in tritolyl phosphate. This enabled apatite to be concentrated by heavy liquids and then picked through to find fluid inclusions. In some of the material fluid inclusions were rare and the chances of getting some in a polished plate of rock were slight. The method of picking out grains containing inclusions permitted data collection from samples containing very few inclusions. The same data could not have been obtained using even considerable numbers of polished wafers. Oil immersion improves the poor optics produced by irregular grain surfaces. The technique for freezing in the oil has been described by Rankin and Aldous (1979). The heating technique

324. is essentially the same; a drop of the oil is placed on the grain which is mounted on the sapphire plate in the stage. The oil can be heated up to about 250°C before boiling occurs. Homogenization temperatures were observed at around 180°C at Sokli and comparisons with polished plates in oil produced the same results. The method is not however recommended for general use in heating, since subsequent investigation of the liquid's properties suggests that highly toxic gases are produced from the oil when heated.

325. APPENDIX 5

Analytical Methods This appendix has been divided into sections on the basis of the different techniques used for rock and mineral analysis:- 5A) Atomic absorption (AA) 5B) X-ray fluorescence (XRF) 5C) Analytical results for AA and XRF SD) Neutron activation 5A. Atomic Absorption The analysis of certain elements from the carbonatites of Sokli and Palabora proved a difficult problem, because no one method could provide analysis for all elements. Niobium in particular could not be analysed easily by atomic absorption, colourimetry, plasma-emission or wet chemistry. Sul- phur and phosphorus also involved tedious methods. Thus a programme of AA and XRF was used. Elements analysed by AA were Ca, Mg, Na, K, Cu, Pb, Zn, Ni, Co, Fe, Mn and for a few separated sulphide samples silver was also analysed. The samples were crushed and milled using agate tema mills, taking all the usual precautions of cleanliness to avoid contamination. The samples were milled to approximately -125 mesh and stored in clean glass containers. An hydrofluoric, nitric and perchloric acid digestion was chosen as the most suitable attack for the rock samples to be analysed by AA. The preparation of the samples was carried out in the following manner:- 1.Boiling of PTFE beakers for 15 minutes in a 2% solution of Decon 90, a phosphate free surface active agent with deionized water (DIW). 2.Rinsing the teflon beakers with DIW and drying them in an oven. 3.Weighing out of the samples (-125 mesh; 0.25 gm.) and placing the weighed amount in the dry teflon beakers. 4. Addition of 10 ml. of 40% Analar HF. 5.Addition of 6 ml. of 1:1 HNO3:HC104. 6.Heating for 30 to 40 minutes until the samples were fuming. 326. 7.Fuming for 20 minutes. 8.Addition of 2 ml. of HF once the sample had ceased fuming. 9.Resuming of mild heating until the samples had evaporated to dryness. 10.Addition of 2 ml.HC104. 11.Fuming of the samples for 20 minutes. 12.Evaporation to dryness at low heat. 13.Addition of 5 ml. of 6 molar HC1. 14.Brief leaching period. 15.Dilution with DIW and samples washed into 25 ml. flasks and made up to volume with DIW. These solutions were then analysed using a Perkin Elmer 2403 AA spectrometer, diluting where necessary. One hundred and seventeen samples were analysed, including blanks and duplicates. The analyses were done in two batches of approximately 60 each. Blanks were run with each of the two batches and duplicates were run within each batch and between batches. The elements Co, Pb, Zn, Ag and to a lesser extent Ni and Cu, are subject to interference from calcium. "Specpure" CaCO3 standards were run to discern the interference factors for calcium for each element. The results were corrected for Ca, but in most cases the effect was negligible. The detection limits for the elements in solution are:- Cu .01 ppm Ag .01 ppm Zn .01 ' Pb .5 ' Ni .1 " Fe 10 " Mn .1 " Mg .5 " Na .01 " Ca .5 " K .01 " Reproducibility was tested by doing numerous duplicates and repeating some during each batch of samples. The results of these are shown in Table 26. The reproducibility was good (see Table 26) for most elements though Fe was slightly variable. However, the large variations in iron content of the samples make the effect negligible. The deviation for Na and K was upset in one sample in Batch 1 275/45, in which both Na and K were

327. TABLE 26: TABLE OF DUPLICATES AND BLANKS

Ca Mg Na K Cu •Pb Zn Ni Co Fe Mn Batch 1 can ppm) N=4 3650 310 12.25 5.05 80.25 1.25 0.30 0.80 0.92 122 7.35 SAMPLE P50 % variance 1.36 3.23 6.12 0.99 6.54 16.67 5.61 0 8.12 3.46 2.71 a' as % of mean 1.37 2.28 3.53 0.99 4.07 6.93 3.60 0 4.68 1.57 .10 Batch 1 Mean (ppm) N=6 3317 298 22.83 27.33 6.01 .833 1.19 0.50 .966 527 33.2 % variance 5.52 4.03 18.26 17.08 10.14 8.04 7.56 0 3.52 16.5 8.43 8.09 5.63 5.66 4.89 0 4.88 10.09 5.34 SAMPLE 275/45 a' as % of mean 3.22 1.25 9.26 Batch 2 Sample -275/45 3500 320 25.00 29.00 6.6 1.0 1.32 0.6 0.8 670 35 Repeat 3300 310 27.00 24.00 6.2 6.8 1.35 0.7 0.9 620 37 Batch 1 Sample 275/44 1100 700 28.00 160 42 0.7 5.4 0.5 2.5 2700 31 Repeat 1120 700 31.0 160 45 0.6 5.6 0.5 2.4 2700 31 SAMPLE 275/44 Batch 2 Sample 275/44 1150 710 28.0 133 46 0.6 5.9 0.6 2.5 2400 34 Repeat 1120 710 31.0 129 47 0.7 5.8 0.5 2.5 2500 34 Blanks Batch 1 3.0 ND ND ND 0.09 ND 0.02 ND ND ND ND BLANKS Batch 2 ND ND ND ND 0.04 ND 0.03 ND ND ND ND Batch 2 ND ND ND ND 0.02 ND 0.04 ND ND ND ND

o'= standard deviation % variance = greatest variation from mean as a % of the mean higher than the others by 17%. This may be due to inhomo- geneity in the sample. The levels of copper and zinc in the blanks are negligible. The results obtained are recorded in part C of this appendix, together with the XRF data. 5B. X-Ray Fluorescence X-ray fluorescence is one of the few reliable methods for niobium analysis available at Imperial College. It was used for the Sokli and Palabora whole rocks to obtain analysis for Nb, Si02, P205, Zr, S, Sr and Th. The highly variable chemistry of the rocks however, made correction for absorption extremely difficult. The.Norrish and Hutton (1969) method of whole rock analysis by making glass beads was used, but the large levels of phosphorus and sulphur, in conjunction with the carbonate, rendered the method inac- curate. The procedure finally adopted involved diluting the finely milled sample with cellulose fibre and creating synthetic standards to match the unusual chemistry of the rocks. The cellulose fibre reduces the absorption differences, enabling a direct comparison between sample and synthetic standards. 1) Preparation of the Standards; Initially a single sample was made with the composition shown in Table 27. The sulphur and silica were supplied from S.U.1. an international standard (Webber, 1965; Sine et al.1969). The deficit in the other elements required in the standard was made up with synthetic compounds (see Table 27). This initial standard was then diluted with calcium carbonate in the ratios 2:1 calcite:initial standard and then 1:2 of the same. This produced three types of standard with decreasing levels of the elements corresponding to the Sokli SAPPM assemblage and a concomitant increase in CaCO3. This followed the general trend of the samples to be analysed. Three discs were made from each of the three different standards produced in the manner described above.

329.

TABLE 27: INITIAL STANDARD PREPARATION

wt% of elements required wt% compound used 24.460 SiO 70.8901 S.U.1 Rock x 2 8.5777% S 9.000 S 0.4223% S 2.3565 Zr(SO4).4H20 0.600 Zr 9.000 P205 8.6330 KH2PO4

0.600 Nb 0.8584 Nb205 • 0.600 Sr 0.5930 1.3355 Sr(NO3)2 (Remaining 0.007 Sr from S.U.1) Remainder 15.9265 CaCO3 100.0000 x S.U.1 is an international standard for full analysis of all elements, see Sine et al. 1969.

Dilution and Preparation of Discs XRF discs were produced by diluting the finely ground samples with fine chromatographic methyl cellulose fibre; 24 parts fibre to 1 part sample. The mixture was then thoroughly shaken for 5 minutes and pressed into discs at a pressure of 10 tons/sq.inch for 20 seconds. Care was taken not to tap and bang the mould and mixture before pressing since this produced irregularities in the results. These were assumed to be due to some differential settling of the particles of fibre and sample. All utensils were carefully cleaned between each sample. Once the procedure was established it was scrupulously adhered to for each preparation. Reproducibility The reproducibility of the preparation was tested by making five discs using sample 275/44. The fluorescence from each disc was recorded as counts per second on the peaks for sulphur and phosphorus. The results were:-

330.

Phosphorus c/sec Sulphur c/sec 499 561 493 579 499 572 458 520 469 572 mean 483 (o=17) 561 (o=21) Standard deviation (o) as % of mean 3.50% 3.74% deviation of worst sample as % of mean 5.17% 7.30%, This error was comparable with that for AA and was acceptable.

Corrections and Results The counts per second of standards and samples were recorded for each element. The samples were run in batches of three with a standard to correct for instrumental drift. The results for the standards (prepared in triplicate) were corrected for dead time and instrumental drift and calibration lines were constructed (see Fig.61). At the higher concentrations the lines for some elements show a tendency to curve (see Sr, Fig.61) indicating that the absorption is beginning to exceed the equalizing effects of the dilution with cellulose. The samples analysed rarely fall into this range and at lower concentrations the lines are straight within the limits of the error. The counting results of the samples were corrected for dead time and instrumental drift, the analysis being read from the calibration lines. The analytical results are presented in section C. 5C. Analytical Results for AA and XRF The results for the Sokli samples are recorded in Tables 28A and B. The subgroup allocation of each sample as used in Chapter 6 is indicated above the analysis. The sample number is shown below the subgroup number. The results for Palabora samples are recorded in Table 29.

331. FIGURE 61 X RAY FLUORESCENCE CALIBRATION LINES FOR STANDARDS

S 900 -

800 -

700

600

Cls 500

400

300

200 -

100 - 0 3 i6 9% %S

500 Nb

400 2000 -

300 Counts Counts per sec. per. sec. 200 1000 -

100

0 0 2 4 6% %Nb

Zr 3000 (corrected for Sr. kp-see text)

200

1000

0 0 2 4 •6 % 0 •2 4 •6%

Table 28A

SOKLI GLOCHEHISTRY---RLSULTS OF NIIOLE F:OCK ANALYSIS BY A.A. AND X.P.F. SUB•GROUP 1 1 2 3 2 2 2 2 2 2 3 3 127554 127560 38821 111 127521 127543 138706 139005 139009 139018 127565 127556 POiCE11T SI02 39.29 1.01 1.11 1.03 7.91 14.84 3.31 13.13 15.84 5.52 15.92 S 3.77 2.1d .33 2.21 1.20 13.61 1..50 4.13 1.15 6.64 4.72 5 ... 4.12 FE 9.10 2.16 4..03 34.00 42.00 33.0C 55.03 41.00 18.5C 23.0C 28.12 8.4^ MN u 8 1.6 . .E.2 .1'; .36 .33 .71 53 .26 .59 .49 .2C MG 13.50 1.03 5.73 1..3 4.81 6.00 4.5G 7.t0 7.70 5.40 7.3.. 1.86 CA 3.60 14.63 3.94 35.10 4..33 8.44 5.20 1.90 13.30 3.10 1..2 32.02 NA .23 .14 .45 .13 .13 .55 .04 .12 .18 .04 .29 .12 K 5.10 .21 .44 .05 .19 .74 .23 1...G .3b .34 .F.. .50 P205 1.14 .03 29 2..3 1.3. 5.17 .07 .17 5.17 1.1, 4.32 1.33 Nd .25 .06 .C6 .32 .40 .58 .03 .74 1.53 .07 .28 C K /NA 25.65 1.50 1.0„ .38 1.35 6.85 5.75 11.07 2.30 6.5C 2.3.. 4.17 _ CA /ING .27 14.60 .6d 25.00 .83 1..0 1.16 .25 1.69 .62 .1 9 17. 71 S/C U 43.40 111.11 52.03 1.2.46 62.54 34.48 90.90 83.33 54.12 43.84 46.(r. 48.47 P.F.H. CO 106 80 7u 9J -00 390 90 56 150 100 140 160. NI 100 60 23 50 70 60 20 20 40 3 0 5C 90 GU 06u 14. .20 2u 2239 4250 470 142 1080 1..30 582 a5C ZN 123 33 034 56 538 358 770 72u 177 75C 342 30 ZF 4.60 0 223 J 234) 1510 63 40 2.60 200 172G 0 PE 65 7, 4. 52 43 41 40 0 60 71' 68 5F SF 70 '363 441 555u 013 1292 690 300 2430 .40 32.o 5970 TH 260 0 0 0 0 540 0 600 1130 0 0 0 L;2

SUB-GROUP 3 3 3 5 . 4 4 4 4 4 4 4 127576 139629 139318 2882 127532 127545 127577 138710 139006 139128 1393... 139305 PE1

SUE-GROUP 4 4 5 5 5 5 5 5 5 5 o 6 119314 139321 12757. 138703 138701 139427 139302 13'1303 139309 139312 12751, 127508 PERCLNT S102 .61 0 13.41 1.67 4.86 16.97 14.95 3.11 10.65 0 .51 5 5.74 4.6+. 20.33 7.29 1.54 17.00 12.33 11.61 6.42 2.25 0-2 4.51 FL 8.40 4.4J 40.30 23.7u 25.01 1, 31.41 15.90 1...5U 1.10 .27 7.50 MN .15 .16 .13 .31 .4) .67 .11 .18 .14 .J3 .77 .42 HG 1.18 1.4C 5.7J 3.11 4.50 6.00 4.10 2.50 3.60 .15 11.-u 15.7) CA 33.0C 38.00 1.33 23.JJ 21.30 11.03 11.50 26.06 22.33 35.13 23.0: 31.uC NA .11 .11 .11 .12 .91 .15 .22 .21 .23 .1F .10 .4 3 K .19 .17 .24 .40 .56 1.83 1.46 .41 2.10 .26 .f6 .C4 P205 .38 .42 4 12.87 4.36 5.82 7.33 11.24 6.18 3.34 .12 .o4 NE .08 .41 6 .25 .21 .33 .07 1.2E .27 1.53 .52 .C1 0_ K /NA 1.73 1 .55 2.55 3.33 0.22 12.53 8.45 1.95 9.13 1.03 .E•.. 1.33 CA /.10 30.56 27.1. .36 7.67 ..67 1.33 2.83 10.40 6.11 41.19 2.02 1.37 S,CU 54.15 57.35 446.15 197.03 123.24 83.74 80.06 53.44 64.23 75.1C 95.33 217.87 P.P.M. L. 150 120 583 100 30 220 300 220 190 13C 64 14G NI 1500 ou 161 9J .J QO 160 153 53 6C .0 59 CU 1360 983 455 370 125 2030 1540 1930 1000 40C 65 7 07 7U 40 3G 134 13. 305 91 320 85 111 17 18 52 ZR 6 C 566 -60 510 1.CG 1310 230 3363 1.0 C PR 44 .8 49 26 27 55 53 50 a7 52 34. 24. S.- 6730 9u0C 13J 3251 251 3 1720 1530 3700 3731 7.00 432C 6430 TH 0 0 336 341 0 13 1140 3000 1386 400 C 3 7]7 Table 28 B

SOKLI GEOCHCHISTRY---RLSULTS OF HHULE KOCK ANALYSIS BY A.A. ANO X.F.F. C1NTINUEi7. SUA-GROUP 6 6 6 7 7 7 a A 8 8 0 9 139017 139022 2c'1 127541 12754+ 139023 127531 138705 138707 138711 139131 127537

SI02 .42 1.09 5.64 7.09 15.37 6.42 20.06 11.75 3.53 4.43 21.43 35.18 S 1.44 20.24. 1.12 16.40 5.72 6.72 .78 15.57 25.56 4.10 '.21 .7L Fc 4.00 36.00 40.33 29.00 2..07 11.60 28.01 30.00 27.03 47.30 33.Cc 12.22 HN .42 .17 .53 .17 .34 .19 .50 .32 .04 .02 .27 .'6 MG 11.90 5.31 4.03 3.31 7.13 6.90 9.10 4.50 4.10 3.50 5.66 10.30 CA 22.03 8.01. t•.03 11.20 12.21 21.0u 5.33 9.7u' 15.50 7.,C .33 9.50 NA .10 .04 .10 .19 .31 .16 .1d .58 .29 .55 .15 .93 K .11 .15 .68 .72 1.23 1.26 3.60 2.00 1.18 .35 3.11 4.5C P205 .55 .08 2.25 7.12 5.22 8.38 .25 3.70 2.86 1.38 1.13 1.43 N6 .03 .3.3 .04 .75 .41 .43 .04 .54 1.50 .06 1.15 .i9 K /NA 1.10 '.53 6.8J 3.79 4.16 12.60 20.00 3.45 5.90 7.03 23.67 5.01 CA /NG 1.85 1.60 2.5J 3.73 1.72 2.90 .59 2.16 3.78 2.14 .01 .95 5/CU 40.30 776.9 202.22 14.77 12.23 64.00 27.84 133.80 116.18 130.10 82.24 22.77 P.F.M. CC 60 353 733 721 250 13C 99 194 42) 7C 261 53 NI 53 140 36 104 51 60 313 110 230 3C 30 390 CU 360 260 90 9900 4700 1350 280 1500 2201 41C 1121 325 Zh 44 56 1..33 136 580 66 548 275 93 17C +0C 146 ZR 0 J 313 510 2740 300 620 560 8644 .2 184 450 PB 45 20 35 69 50 49 44 39 17 2C ub 40 SF 5370 1434 2100 1654 201J 3251 963 1360 2180 1110 C 155C TH 0 C 0 594 793 500 0 0 147 0 1040 0

SUR-GROUP 9 9 9 10 2 4 4 11 11 12 12 12 139003 139311 139317 127534 939414 639101 839114 139030 139315 139015 139124 139125 PERCENT 5102 7.73 1.23 21.43 12.46 13.17 .59 .33 3.30 3.99 30.03 5.74 29.2) S .93 .52 1.67 1.1+ 5.71 .53 2.06 +.90 16.50 2.6C 16.60 23.30 FL 7.04 5.30 13.00 16.50 16.39 1.90 4.01 9.00 16.80 12.86 63.130 19.00 'IN .26 .14 .25 .53 .21 .34 .22 .S4 .55 .iC .00 .29 MG 4.80 2.1S 'a.5. 7.50 ..53 6.913 2.21 10.00 6.50 21.00 1.P6 17.00 CA 28.00 34.31 14.03 10.1,0 16.33 24.33 37.03 18.40 12.01 2.10 E.6 4.80 NA .18 .1.3 .24 .19 22 .10 .17 .19 .07 .13 .12 .16 K .76 1.30 4.8 j 2 .u0 .62 .11 .12 .07 .02 1.85 .74 1.73 P205 2.85 .78 .16 7.16 6.64 .69 .15 .07 .32 .02 2.c2 3.4) NR .10 .20 .0.i .6) .85 .34 •92 .36 1 .12 1.12 .29 K /NA 4.22 7.69 20.0) 10.53 2.82 1.10 .71 .37 .29 18.50 6.3? 17.33

CA /91. 5.83 15.60 1.47 2.23 1.48 3.48 16.82 1.88 1.85 .10 2.67 .37 S/CU 93.03 12.38 109.5o 57.00 40.74 115.22 54.21 231.13 657.14 355.56 24.13 74.19 F.F.M. CO 7C 133 400 61 173 50 100 80 63 LO 312 100 NT 80 50 780 30 70 50 54 70 30 . 110C 30 40 CU 100 420 140 233 1433 4u 350 212 196 360 6966 3130 Zh 141 88 161 242 223 49 38 463 630 578 106 323 ZF 650 321 110 1140 2750 20 0 0 0 314 70c 3 1.40 Pa 18 53 49 64 92 1 0 0 45 26 73 24) SF 600 7943 1.0.. 390u 1.593 5514 6440 39 9533 370 1,33 TN 0 0 0 510 1.750 3 0 7596 3 C 1440 r '75

SUh-GROUP 5 12 439001 396180 PERCENT 5102 12.67 5.41 S .48 1.95 FL 2.50 55.00 MN .04 .61 MG 4.86 4.73 CA 24.10 1.11 NA .43 .33 K 2.10 .11 D2n5 21.24 .24 NE 4.6C .13 K /NA ...88 1.67 CA /.16 5.30 .23 5/CU 103.70 39.64 P.F.M. 5y NINĪ 50 20 CU 27 2516 ZN 61 78C ZR 1530 130 PR 114 S; 5 673 lie IN 3411 0

334 TA3L 29: ANALYSES OF 9:LEE0 a 3:1PI S

5 5 ppm ppm ppm ppm ppm '. ppm ppm ppm ppm pom Ppm ppm 05 Ni Co Fe : 'o Zr 3r Na Ag Ca ::g SiO2 S P2 Cu Pb Zn : n ā P1 2.6 10.1 18.67 0.21 5.03 .330 <50 370 33 200 42.0 2200 <35 300 220 .01 .09 ND 6 3.3 20.2 22.57 6.25 1.23 5.5 <50 238 340 2CC 10.5 1500 <35 1100 570 .04 .025 4 7 29 6.0 3.37 0.12 6.64 1.3 60 68 60 60 7.6 1200 <35 110 7510 .11 1.2 2 10 30 4.1 0.33 4.19 0.23 3.35<50 129 160 220 39.0 2000 <35 120 1360o .16 .10 ,LID

12 34 3.0 0.15 1.06 0.78 1.864'50 43 100 90 16.0 1000 <35 <60 7360 .17 .11 .D 13 30 3.6 0.93 9.24 1.49 5.2% <50 15 200 65 5.0 940 <35 70 271Q .07 .03 2 14 28 3.0 0.52 9.91 0.63 6.a 00 96 300 165 - <35 <60 4740 .08 .03 :v 15 33 3.3 <.07 0.93 0.30 1.26 <50 35 100 80 16.0 700 <35 <60 651 .15 .08 ND 19 6.9 13.9 22.36 0.51 10.24 .72 <50 1C0 220 140 19 970 <35 1000 1020 .13 .15 3 20 29 1.9 0.39 0.45 3.19 .85 <50 70 80 60 12.2 800 <35 60 5350 .1C .06 1 21 14.5 2.6 2.53 0.08 14.1 .0O25 <50 200 210 130 41 1500 <35 800 780 .057 .025 1 23a 11.6 3.5 52.0 0.C5 7.67 .0O24 <50 40 20 1C 2.5 560 <35 140 1160 .41 7.3 `'D 23b 3.5 10 61.0 0.06 12.43 .CCC8 <50 75 100 30 5.6 650 <35 110 1070 .11 6.0 ND

45/47 33 4.0 1.96 0.09 8.67 .0365 <50 40 8C 60 4 780 <35 800 5000 .11 .055 :D P43 17 3.8 10.48 0.33 22.5 .3160 <50 121 210 130 15.0 1100 <35 500 2500 .06 .07 1M P50 36 3 .11 .34 1.15 .31 <50 25 60 60 1.2 720 <35 600 3C90 .12 .05 ND P53 20 7.8 52.7 .07 11.09..6090 <50 52 70 60 3.3 920 <35 130 1130 .29 .34 ND P55 16 9.3 37.6 .05 9.28 .0010 <50 55 80 55 3.5 570 <35 80 1250 .15 2.9 ND 956 19 3.6 39.79 .C6 3.59 400 450 64 190 SC 3.3 610 <35 150 1120 .26 .66 ND 957 19 10 55.01 .05 0.10 .0008 <50 30 80 30 1.53 420 <35 150 350 .12 .049 +D

SULPHIDE 00:C2NTRATES

P14 .46 1.3 31.5 500 330 1300 560 30 50 .04 .038 16 919 7.2 11.2 20.2 2CC 1420 600 540 16.5 500 .044 .072 40 938 2.3 1.2 65.0 90 65 300 20 7.0 21C .022 .031 165 P503 1.4 .13 33.3 260 570 1200 700 19.3 40 .13 .034 7 5D. Neutron Activation Neutron activation was used in this study for REE and P.G.M. analysis. The work was carried out at the London University reactor, Silwood Park, Ascot, and was supervised by Dr. S. Parry. 5D.1. Rare Earth Elements: The analysis of REEs was undertaken using Instrumental Neutron Activation Analysis (INAA) as used by Henderson et al.(1976) (cc group). Known weights (300-500mg.)•of the samples were placed in small polythene ampoules. Three ampoules containing elemental standards (from evaporation of standard solutions) were packed with eight samples into polythene tubes 20cm. long; a standard ampoule in the middle and one at each end. The samples were activated in a thermal neutron flux of about 1.0 x 1012 n cm-2 sec-1 for approximately 15 hours. The high levels of REE in the apatite samples and the absence of any readily available natural standards with similar values precluded the use of natural standards. Suitable decay times were adopted to allow the activity of sodium to decline, allowing the best possible observation of the relevant isotope peaks above the background activity. The shorter lived isotopes were counted after 3-4 days using a wide dynamic range Ge(Li) detector on a gamma ray spectrometer. The longer lived isotopes with lower energies were counted 10-12 days after activation, using a high resolution Germanium detector. The detectors were coupled via amplifiers to a Link systems multi channel analyser and video display system (similar to that described for EPMA work) incorporating a Nova II minicomputer which produced a printout of preselected channels and the integrals of the photopeaks of interest. Each sample was counted for two hours. After corrections due to interference from other isotopes (see Table 30), corrections were made for variations in neutron flux. This is made possible by having the standards at each end of the irradiated sample tube. The sample peak integrals are

336.

TABLE 30: THE ISOTOPES AND THEIR CHARACTERISTIC PHOTON ENERGIES USED FOR REE ANALYSIS

Isotope Energy (KeV) Half Life

815.5 40.27 hrs. La140 La 486.8 40.27 hrs. Counted after La 1595.4 40.27 hrs 3 days 7170 Lu 208.4 155 days 175 Yb 396.1 101 hrs. Ge(Li) detector Sm 69.7 47.1 hrs.

Yb169 63.5 30.6 days Sm 69.7 47.1 hrs. 166 80.6 30 years Ho170 Tm 84.4 129 days Counted 0 Tb 87.0 73 days after 147 Nd 91.4 11.1 days 14 days 153 Gd 69.6 236 days 153 Sm152 103.2 47.1 hrs. Eu (Ge detector) 141 121.8 12.2 years 145.4 32:5 days Ce153 Gd 97.5 236 days 175 Yb 113.8 101 hrs.

Other peaks counted for interference corrections:-

Lu x-ray at 56.1 KeV Th (Pa)233 94.8 Ta239 100.1 Np 106.1

The following correction factors were applied to the photopeak integrals before correction for flux variation at half life - see text.

Isotope Energy (KeV) Correcting

None La144 Ce (145.4) 9.257. of the 113.8KeV peak of Yb175 (negligible) Nd (91.4) None 153 Sm (69.7) None (103.2) 827. of 106.1KeV peak of Np239 8.47. of 94.8KeV peak of Pa233 152 Eu (121.1) None l53 153 Gd (69.6) Long decay required since same as Sm (97.5) 151.57. of 94.8KeV peak of Th (Pa233) 610 (87.0) 25.8% 11 ,,~~ Tb166 Ho (80.6) None 170 Tm (84.4) 177. of the 10O.1KeV peak of Ta152 169 Yb (63.1) 34.237. of 56.1KeV peak of x-ray of Lu (standards only) Lu175 (208.4) None Yb (113.8) 2597. of 208.4KeV peak of Lu177 337. adjusted to the variation in activity of the standards (which reflects any variation in the thermal neutron flux over the length of the tube). Corrections for decay during counting were also made. The peak integrals can then be compared to those of the standards and the value of each element computed. All corrections and calculations were done using a programmable hand calculator. The elemental standards were prepared from "speck pure" reagents. Dilute solutions .were pipetted into the polythene containers and evaporated to dryness. The results of the analyses are shown in Fig.31. Many of the samples have been analysed in duplicate and the deviation from the mean of each pair has been calculated as a percentage of the mean. The mean values of such percentage deviations are given below (an indication of precision) together with the mean detection limits, based on a statistical analysis of the background for each element.

Mean value of Mean % deviation Detection Element all duplicates from mean of each limit (ppm) pair (ppm)

La 1523 2.89 40 Ce 3782 5.37 65 Nd 1888 7.56 20 Sm 336 6.94 17 Eu 68 8.39 18 Gd 223 14.86 46 Tb 23 12.97 5 Ho - - 6 Tm - - 5 Yb 4.8 14.81 2.1 Lu 0.97 11.0 .45

It is clear that the precision based upon % deviation from the mean of each pair, is much better on the elements with higher values. The poorer precision on the heavier elements and lower abundance elements is however acceptable. The difference between 1ppm and 3ppm would produce a deviation of 50% from the mean of the two samples, but the difference is insignificant on the chondrite normalized loga- rithmic plots (see Chapter 4).

338.

T.,31.= 31: gm: EARTH kNILY63S ona

R. :_,:t EA.HT:L3 1 i AP.L_IT33 Tf..i:30.::6SIV SUVIT 5G7IT.i P::USC0:1T3 aci:2) P2(b) E22. 91 P13 La 2456 (2522) 2250 260C (2620) 1261 567 (572) 625 745 Ge 6990 (6328) 5066 6637 (6422) 3365 1691 (1604) 1633 1942 ::d 4010 (3656) 2927 3243 (3150) 1349 359 (964) 344 1017 8= 697 (650) 555 550 (540) 390 216 (1 0) 189 214 3u 35.1 (77.0) 79.2 1L0 (96.6) 65.0 42 (35.5) 33.S 42 Cd 334 (356) 299 297 (266) 238 120 (108) 144 311 Tb 31.7 (36.2) 30.4 30.0 (32.9) 25.3 13.9 (20.2) 16.9 21.2 Yb 5.32 (5.20) 5.25 4.36 (6.39) 6.57 2.17 (3.44) 4.06 1.99 Lu 4.41 (<.45) <.45 (.42 (<.45) <.95 4.33 (<.36) 0.57 <3.4

:aCA//PATIT3 ?.CCI': PYRG:MIT P2 b) Ea R22.(2.) Ella La 1365 (1332) 2028 (1932) 2343 12•45 Ce 3494 (3277) 5119 (4999) 6117 3283 al 1711 (1671) 2129 (1931) 2775 1E05 339 (292) 413 (366) 564 357 Duplicate results Eu 63.0 73.0 (71.4) 103 63 are bracketed. Cd ((222) 240 162 392 306 Tb 32.5 (34.3) 35.8 (31.9) 67.6 26.6 Yb 6.65 (6.45) 7.39 (7.59) 7.42 6.02 La 1.55 (1.45) 1.57 (1.22) 2.27 1.75

3. Ia--; i 1P.TH6 IN THOLE 3L= T.Rk :SGR S3I E S07ITE P ID)F9 307I= PHOSCORīT3 P7 al. P12 Z Eli La 435 (439) 290 574 (535) 150 350 30.7 :. 378 194 210 Ce 1150 1381 (3a.4) 437 SO2 125 966 514 564 al 604 ((593) 413 644 .553) 221 348 40.9 475 252 313 Sa 111 (111) 76.1 123 (123) 50.5 74.4 9.92 109 57.2 60.5 Zu 17.3 (15.6) 11.3 23.8 (20.3) 9.4 14.2 1.85 19.7 9.62 11.2 Gd Tb 7.43 (7.73) 4.38 9.45 (8.06) 1.09 4.25 0.91 6.2 3.17 3.67 Ib 2.34 (2.12) 1.64 3.330 (3.44) 0.63 1.1 0.15 0.53 3.62 1.33 Lu 1.36 (1.55) 0.56 1.36 (1.35) 0.17 0.25 0.17 0.11 0.24 0.19

C. a:: EARTHS IN LT'_.i? 1•1iTai,Ls

CLLCīT3 CHCi92CDITE id)DEL YITE ,'CA P113 9203 Pli La 372 325 233 139 71 Ce 926 746 575 363 436 479 358 293 191 31 96.4 74.6 62.9 39.5 95.1 15.0 15.2 12.6 4.75 6.02 3d 94.0 61.1 51.3 13.93 Tb 4.50 4.52 3.96 1.33 14.52 2.26 3.17 3.03 60.15 Lu .24 .22 .46 .46 23.26

339 Values for Ho and Tm were below the detection limit of the method used. The gadolinium values are not quite as good as the others because of interference from other elements. Both Sm and Th interfere with the Gd peak used (see Table 30). The Sm decreases to insignificance after a few months and the remaining peak can be corrected for Th interference. The apatite samples were counted again for Gd two months after initial activation and the results obtained have been used. The high levels of Th in the apatite have been corrected for. Values of Gd for the whole rocks were not obtained since they were unnecessary for the study. 5D.2. The radiochemical neutron activation analysis (RNAA) of Au and PGM: The technique was not powerful enough to resolve the levels of PGM in the sulphides tested. The planned analytical programme was therefore abandoned. The method used for those analyses quoted in the text was a radiochemical extraction based upon that used by Nadkarni and Morrison (1974) and adapted by Parry (pers. comm.1978). The method of analysis for Au, Pd, Ir and Pt involves irradiation of the material, followed by dissolution of the samples and selective absorption on Srafion NMRR ion exchange resin and high resolution x-ray spectrometry. Experimental procedure: 1) Approximately 400mg. of dry hand picked sulphide concentrates were put into polythene ampoules and weighed. 2) Standard solutions were pipetted into ampoules and evaporated to dryness and weighed. 3) Samples and standards irradiated for 8 hours in a thermal neutron flux of approximately lx1012 n.cm s' ec-1' The samples were allowed to decay over night before processing. 4) Active samples were tipped into Ni crucibles. The empty ampoules were weighed to.determine the amount of sulphide in the crucibles by difference from 1) above.

5) The radiochemistry has been described in detail by Nadkarni and Morrison (1974). In brief, the irradiated

340. samples were fused with NaOH and Na202 in the presence of noble metal carrier solutions (non-active). This fusion was heated for 10 minutes to ensure isotopic exchange between the added carrier and the corresponding radio nuclide. The coded melt was dissolved in 75m1. water and acidified with HC1. The solutions were heated and oxidized with 2m1. HNO3. The excess peroxide was destroyed by boiling. The pH of the solutions was then adjusted to 1.5-2 using dilute ammonia. Each solution was passed through an ion exchange column at a rate of lml./min. The resin was washed in HC1, drained and tipped into small plastic flat bottomed containers. 6) The resins, samples and standards were counted for 10,000 seconds using a Ge(Li) detector and equipment as described for REE analysis. The isotopes and peaks used are shown in Table 32. 7) Corrections for the neutron flux variation, decay during counting and comparisons with standards were done using a programmable calculator.

TABLE 32: THE ISOTOPES AND THEIR PHOTON ENERGIES USED FOR PGM ANALYSIS

Isotope(s) Half life Principal x-ray Element produced of nuclide used KeV Au Au198 64.8h 412 Pt Pt197 19h 77 Pt199 ( - decay * 30m - Au199 of Pt199) 3.15d 158 Ir Ir192 74d 317 & 468 Ir194 17.4h 328 Pd Pd109 13.5h 88

Concentrations of Elements in Standard Solution Au 0.01319 mgm./100mg.solution Pt 7.389 Ir 0.09564 It 't " Pd 4.844 "

341. Results Despite the long counting times (2.778hr), the peaks for Pd, Pt and Ir could not be resolved above the background activity. The detection limits and results of two duplicate pairs are given below in ppm. Pd Pt Ir Au Palabora P50 <.15 <.85 <.08 <0.144 P5OR <.15 <.85 <.08 <1.266 Sokli 390/10 <.10 <.25 <.01 < .0015 390/10R <.10 <.25 <.01 < .0014

Only the Au analyses were above detection limit. Sokli material was orders of magnitude lower than Palabora, but Palabora material did not appear to be homogeneous. A fact supported by the appearance of native gold and silver in some polished sections. The PGM analysis precluded any further work.

342. BIBLIOGRAPHY

ALEKSANDROV, I.V., SIN'KOVA, L.A. & IVANOV, V.I. 1965 : An experimental study of the behaviour of rare earths and yttrium in the hydrothermal process. In: "Problems of Geochemistry" Izd.Nauka, Moscow. ALEKSANDROV, I.V., TRUSIKOVA, T.A. & TUPITSIN, B.P. 1971 : Effect of sodium and potassium on migration and precipitation of niobium. Geochem.Internat. Vol.8, No.2. 1972 : Geochemistry of niobium and tantalum in the carbonatite process. In: Tugarinov (Ed.) "Recent contributions to Geochemistry and Analytical Chemistry" pp.335-344. ALLEN, M.C. 1978 : Carbonatites; mineral deposits of the future. Unpub. MSc.thesis, Imperial College, London. ALTHAUS, E. & WALTHER, J. 1977 : Fluid inclusions in minerals from carbonatites. Jour. Geol.Soc. London, Vol.134, pp.385-397 (abstr.) AMLI, R. 1975 : Mineralogy and rare earth geochemistry of apatite and xenotime from Gloerheia granite pegmatite, Froland, S. Norway. Am.Mineralogist Vol.60, pp.607-720. ANDERSON, A.T. 1968 : Oxidation of the La Blacke Lake titaniferous magnetite deposit, Quebec. Jour. Geol.Vol.76, pp.528-547. ARGIOLAS, R. 1978 : Morphologie des cristaux d'apatite; influences des conditions experimentales et implications sur la petrogenese. PhD.thesis, Universitē de Nice. BAGDASAROV, Yu.A. 1971 : Types of apatite metasomatite in carbonatite complexes. Dokl.Akad.Sci.USSR, Earth Sci.Sect. Vol.199, pp.129-131. BAILEY, D.K. 1974 : Continental rifting and alkaline magmatism. In: H.Sorenson (Ed.) "Alkaline Rocks", Wiley, London. 1978 : Volcanism, earth degassing and replenished litho- sphere mantle. Roy.Soc. meeting Nov.1978 on "The evidence for chemical heterogeneity in the earth's mantle".

343. BALASHOV, Yu.A. & POZHARITSKAYA, K.L. 1968 : Factors governing the behaviour of rare earth elements in the carbonatite process. Geochem.Internat. Vol.5, pp.271-288. BALDOCK. J.W. 1967 : The geology and geochemistry of the Bukusu carbonatite complex, S.E.Uganda. PhD. thesis, University of Leeds (unpub.) 1969 : Geochemical dispersion of copper and other . elements at the Bukusu carbonatite complex, Uganda. IMM Trans. Vol.78, pp.B12-B27. BARBER, C. 1974 : The geochemistry of carbonatites and related rocks from two carbonatite complexes, S.Nyanza, Kenya. Lithos, Vol.7, No.1, pp.53-63. BARONNET, A., AMOURIC, M., CHABOT, B. AND CORNY, F. 1978 : Solubility of phlogopite in basic aqueous solutions under hydrothermal conditions. Jour. Cryst. Growth, Vol.43, No.2, pp.255-263. BARNES, H.L. & CZAMANSKE, C.K. 1967 : Solubilities and transport of ore minerals. In: H.L. Barnes (Ed.) 'Geochemistry of Hydro- thermal Ore Deposits', pp.334-381; Holt, Rinehart & Winston Inc., New York. BARTON, P.B. & SKINNER, B.J. 1967 : Sulphide mineral stabilities. In: H.L.Barnes (Ed.) "Geochemistry of Hydrothermal Ore Deposits", pp.236-333; Holt, Rinehart & Winston Inc., New York. BELL, P.M., MAO, H.K., ROEDDER, E. & WEIBLEN, P.W. 1975 : The problem of the origin of symplectites in olivine bearing rocks. Proc. Sixth Luna Sci. Conf. Geochim. Cosmo Acta. BJORLYKKE, H. & SVINNDAL, S. 1960 : The carbonatite and per-alkaline rocks of the Fen area. Mining and Exploration work. Geol. of Norway. Norg. Geol. Unders. No.208, pp.1O5-110. BLOOMFIELD, K. 1973 : Economic aspects of Uganda carbonatite complexes. Overseas Geol. Min. Rec. No.41, pp.139-167. BORLEY, G. 1979 : Pers. Comm. Geol.Dept. Imperial College.

344. BORODIN, L.S. 1957 : Types of carbonatite deposits and their connec- tion with ultrabasic-alkaline rock complexes. Izv. Akad. Nauk. SSSR, Ser.Geo1..Vol.5,pp.3-16. 1958 : The chemistry of aegirinization and nephilini- zation of pyroxene in the formation of metasomatic nepheline-pyroxene rocks (ijolites). Geochem. Vol.5, pp.637-640. BORODIN, L.S. LAPIN, A.V. & KHARCHENKOV, A.G. 1973 : 'Rare metal Camaphorites". Nauka Press, Moscow (in Russian). BOUWER, R.F. •1957 : The carbonatite member of the Palabora Igneous Complex. PhD thesis, University of Cape Town (unpub.) BOWEN, N.L. 1924 : Fen area in Telemark, Norway. Am. Jour. Sci. Vol.8, pp.1-11. BOWEN, N.L. & TUTTLE, 0.F. 1949 : The system Mg0-Si02-H20. Bull. Geol.Soc.Amer. Vol.60, No.3, pp.439-460. BOWLES, J.F.W. 1976 : Distinct cooling histories of troctolites from the Freetown layered gabbro. Min. Mag. Vol.40, No.315, pp.703-714. BRETT, R. & YUND, R.A. 1964 : Sulphur rich bornite. Am.Min. Vol.49, pp.1084-1098. BROGGER, W.C. 1921 : Die Eruptivgesteinen des Kristianiagebietes IV. Das Fengebiet in Telemark, Norwegen. Ngl. Norske. Vid.Selskab. Skr. Hat.Naturwis.No.9. BROOKINS, D.G., TREVES, S.B. & BOLIVAR 1975 : Elk Creek, Nebraska; Carbonatite:Sr Geochemistry. EPSL, Vol.28, No.1, pp.79-82. BUCHANAN, D.L. 1978 : Personal communication, Dept. of Geology. Univ. Wits. Johannesburg, South Africa. BUDDINGTON, A. & LINDSLEY, D. 1964 : Iron titanium minerals and synthetic equivalents. Jour. Pet. Vol.5, pp.310-357. CARMICHAEL, I.S.E. 1967 : The iron titanium oxides of salic volcanic rocks and their associated ferro-magnesian silicates. Contrib.Mineral. and Pet. Vol.14, pp.36-64.

345. CARTWRIGHT, A.P. 1972 : "Palabora, Mining City of the Future" Cape Town, Purnell. p.160. CLOCCHIATTI, R., HAVETTE, A. & NATIVEL, P. 1978 : Petrogenetic relations between transitional basalts and oceanites from trapped melts in olivine and chromospinel phenocrysts of Piton de la Fournaise (Reunion Island, Indian Ocean). Centiēme Anniversaire de la Soc.Franc.de Min. et Crist. Colloque "Mineraux et Minerais". p.41 abst. COETZEE, G.L. 1963 : Carbonatites of the Karema Depression, Western Tanganyika. Trans.Geol.Soc.S.Afr. Vol.66, pp.283-340. COETZEE, G.L. & EDWARDS, C.B. 1959 : The Mrima Hill Carbonatite, Coast Province, Kenya. Trans. and Proc. Geol.Soc. S.Afr. Vol.62, pp.373-395. COUSINS, C.A. & VERMAAK, C.F. 1976 : The contribution of Southern African ore deposits to the geochemistry of the platinum group metals. Econ. Geol. Vol.71, No.l. CRERAR, D.A. & BARNES, H.L. 1976 : Ore Solution Chemistry V: Solubilities of chalcopyrite and chalcocite assemblages in hydrothermal solution at 200°C to 350 C. Econ. Geol. Vol.71, pp.772-794. CURRIE, K.L. & FERGUSON, J. 1972 : A study of fenitization in mafic rocks with special reference to the Callander Bay complex. Can.J.Earth Sci. Vol.10, pp.1253-1261. CURRIE, K.L. 1976 : The Alkaline Rocks of Canada. Geol. Surv.Can. Bull.239. CURTIS, G.D. 1964 : The application of crystal field theory to the inclusion of trace elements in minerals during magmatic differentiation. Geochim.Cosmochim. Acta Vol.28, pp.389-403. DAWSON, J.B. 1962 : Sodium carbonate lavas from Oldoinyo Lengai, Tanganyika. Nature 195, pp.1075-1076. 1966 : Oldoinyo Lengai - an active volcano with sodium carbonatite lava flows. In "Carbonatites" Ed. Tuttle & Gittins, Wiley.

346. DAWSON, J.B., POWELL, D.G. & REID, A.M. 1970 : Ultrabasic Xenoliths and Lava from the Lashaine Volcano, Northern Tanzania. Jour. Petrology. Vol.2, pp.519-549. DEANS, T. 1966 : Economic Mineralogy of African Carbonatites. in "Carbonatites" Ed. Tuttle and Gittins, Interscience, (Wiley). DEANS, T., SUKHESWALA, R.N., SETHNA, S.F. & VILADKAR, S.G. 1972 : Metasomatic feldspar rocks (potash fenites) associated with the fluorite deposits and carbonatites of Amba Dongar, Gujarat, India. Trans. Inst. Min.Metal. Section B Applied' Earth Sci. Vol.81, Feb.1972, pp.Bl-9. DEINES, P. & GOLD, D.P. 1973 : The isotopic composition of carbonatite and kimberlite carbonates and their bearing on the isotopic composition of deepseated carbon. Geochim. et Cosmochim. Acta 37, pp.1709-1733. de KUN, N. 1961 : Die Niobkarbonatite von Afrika. Neues Jahr B. Mineral. Mh., 1961 (6). 1962 : The economic geology of columbium and of tantalum. Econ. Geol., Vol.57. de VAAL, P. 1976 : Personal communication; Mineralogical Staff, Palabora Mining Company. DERNOV-PEGAROV, V.F. & MALININ, S.D. 1976 : Solubility of calcite in high temperature aqueous solutions of alkali carbonate and the problem of formation of carbonates. Geoch. Internat. Vol.13, No.3, pp.1-13. DONALDSON, C.H. & DAWSON, J.B. 1978 : Skeletal crystallization and residual glass compositions in a cellular alkalic pyroxenite nodule from Oldoinyo Lengai. Contrib. Min. Pet. Vol.67, pp.139-149. DONTSOVA, Ye.I., KONONOVA, V.A. & KUZNETSOVA, L.D. 1978 : The oxygen-isotope composition of carbonatites and similar rocks in relation to their sources and mineralization. Geochem. Internat. No.4, pp.1-11. du TOIT, A.L. 1931 : The genesis of the pyroxenite-apatite rocks of Palabora, Eastern Transvaal. Trans. Geol.Soc. S.Afr., Vol.34, pp.107-127.

347. EASTOE, C.J. 1978 : A fluid inclusion study of the Nanguna porphyry copper deposit, Bougainville, Papua, New Guinea. Econ. Geol. Vol.73, No.5. pp.721-748. EBY, G.N. 1975 : Abundance and distribution of the rare earth elements and yttrium in the rocks and minerals of the Oka carbonatite complex, Quebec. Geochim. et Cosmochim. Acta 39, pp.597-620. ECKSTRAND, O.R. 1975 : The Dumont serpentine: a model for control of nickeliferous opaque mineral assemblages by alteration reactions in ultramafic rocks. Econ. Geol. Vol.70, pp.183-201. EDWARDS, A.B. 1947 : Textures of the ore minerals and their significance. Australian Inst. Min. Metal. Melbourne, 1947. Revised Ed. 1954. ELLSWORTH, H.V. 1928 : Thucolite and uraninite from the Wallingford Mine near Buckingham, Quebec. Am.Mineralogist, Vol.13, pp.442-448. ERDOSH, G. 1977 : Personal Communication. The Cargill Phosphate Company, N. Ontario. ERICKSON, R.L. & BLADE, L.V. 1963 : Geochemistry and petrology of the alkalic igneous complex at Magnet Cove. U.S. Geol.Surv. Prof. Pap. 425. ERIKSSON, S.C. 1978 : Geochemical and isotopic studies on a Pre- cambrian carbonatite from Palabora, S.Africa. G.S.A. Ann. Meeting Abstr. p.397. 1978 : Personal Communication. Univ. Witwatersrand, S .Africa. EUGSTER, H.P. & MILTON, C. 1957 : Mineral assemblages in the Green River formation. Carnegie Inst. of Washington Yearbook. Annual Report 1957, p.153. EVZIKOVA, N.Z. & MOSKALYUK, A.A. 1964 : Gas liquid inclusions in carbonatite from carbonates. Dokl. Akad, Nauk. SSSR 159, 1964 pp.98-101; Dokl. Akad. Sci. SSSR, Earth Sci. Sect.159, pp.108-111. FICK, L.J. & van der HEYDE, C. 1959 : Additional data on the geology of the Mbeya carbonatite. Econ. Geol. Vol.54, 1959. FISHER, J.R. 1976 : The volumetric properties of H20; a graphical portrayal. U.S.Geol.Surv.Res. Vol.4,pp.189-194. 348. FORSTER, I.F. 1958 : Paragenetic ore mineralogy of the Loolekop Palabora carbonatite complex, E.Transvaal. Trans. Geol. Soc. S.Afr. Vol.6l,pp.359-365. FRANZ, G.W. & WYLLIE, P.G. 1967 : Experimental studies in the system CaO-Mg0-Si02- 0O2-H 0 in Ultramafic and related rocks. (P.J. 7yllie,ed), pp.323-326 New York: John Wiley and Sons. FRICK, C. 1975 : The Palabora Syenite Inclusions. Trans.Geol. Soc.S.Afr. Vol.78, pp.201-213. FRIEL, J.J. & ULMER, G.C. 1974 : Oxygen fugasity geothermometry of the Oka carbonatite. Am.Mineral Vol.59,No.3-4,pp.314-318. FROLOV, A.A. 1971A: Vertical zonations in deposition of ore as in ultrabasic alkaline rocks and carbonatites. Int.Geol. Rev.13, 4, pp.685-695. 1971B: A carbonatite type of lead zinc ore deposit. In: Geologiya Rudnykh Mestorozhdeniy (Geol.of Ore Deposits) Akad.Sci.SSSR. Ed.V.I. Smirnov May- June '71 Vol.13,No.3,pp.91-93 (in Russian) see reviews in Econ.Geol. Vol.69,1974,pp.153-154. 1974 : Depth of mineralization in the massifs of ultrabasic-alkalic rocks and carbonatites. Geol.Rud.Mestorozhd. Vol.16, No.6,pp.89-96. 1975 : Structure and Ore Deposition in Carbonatite Massifs. Nedra, Moscow p.160. FROLOV, A.A. & EPSTEIN, E.M. 1962 : Geological formation of carbonatite massifs. In: Geol.Formation & Mineralogical, Geochemical Characteristics of Rare Metal Carbonatites. Gosgeol. Izdat. pp.38-69. GAIDUKOVA, V.S. & ZDORIK, T.V. 1962 : Geological formation and mineralogical, geochemical characteristics of rare metal carbonatites. Gosgeol.Izdat. (in Russian). CARSON, M.S. 1959 : Stress pattern of carbonatite and alkaline dykes at Tundulu ring structure, S.Nyasaland. Intern.Geol.Congress, 20 sess. Asoc.Serv.eeol. Africanos, pp.309-323. GASPARRINI, E. 1976 : The energy-dispersive spectrometer attached to the electron microprobe: a new tool of investigation for the earth scientist. Min.Sci. and Eng. Vol.8, No.1, pp.3-22.

349. GENKIN, A.D. VASIL'EVA, Z.V. & YAKOVLEVSKAYA, T.A. 1961 : The occurrence of apatite in copper-nickel sulphide ores of the Norv'sk deposit. Geol.Rud. Mestorozhd. 2, No.2, p.196. GERASIMOVSKII, V.I. 1973 : The geochemistry of East African Rift Zone carbonatites. Geochem. Int. Vol.10, No.6, pp.1300-1308. GERASIMOVSKII, V.I., BALASHOV, Yu.A. & KARPUSHINA, V.A. 1972 : Geochemistry of rare earth elements in the extrusive rocks of the East African Rift Zones. Geochem. Int., Vol.9, pp.305-319. GEVERS, T.W. 1948 : Vermiculite at Loolekop, Palabora, N.E.Transvaal. Trans. Geol.Soc. S.Afr. Vol.51, pp.133-178. GINZBERG, A.I. (ED,) 1962 : Geology of rare element deposits 17; geological structure and mineralogical characteristics of rare metal carbonatites. Gosgeollekhizat, Moscow. GINZBERG, A.I. & EPSTEIN, E.M. 1968 : Carbonatite deposits. In: The Origin of Endogenic Ore Deposits, pp.152-219. Nedra Press, Moscow. GIRAULT, J. 1966 : Genese et Geochimie de 1'apatite et de la calcite dans les roches lie ou complex carbonatitique et hyperalcalin d'Oka (Canada). Bu11.Soc.Franr,. Min. Grist. V.89, pp.496-513. GITTINS, J. 1966 : Russian views on the origin of carbonatite complexes. In: Carbonatites, Ed.Tuttle & Gittins, Intersci., Wiley, pp.379-384. 1978 : A comment on the paper: An estimation of temperatures of intrusion of Indian carbonatites using calcite-dolomite geothermometry, by S.F. Sethna and S.G. Viladkar, Jour. Geol. Soc. Ind. Vol.118, pp.275-280. GITTINS, J., ALLEN, C.R. & COOPER, A.F. 1975 : Phlogopitization of pyroxenite; its bearing on the composition of carbonatite magmas. Geol.Mag. Vol.112, No.5, pp.503-507. GLAGOLEV, A.A. 1962 : Example of metasomatic zoning around the apatite- magnetite rocks and the carbonatites. Doklady Akad. Nauk SSSR, Geol.Ser. Vol.147 No.3. 1965 : Apatite-magnetite rocks in the Kola Peninsula. Geol. Rudn. Mestorozhd. No.3.

350. GOLD, D.P. 1963 : Average Chemical Composition of Carbonatites. Econ. Geol. Vol.58, pp.988-991. GOLD, D.P. VALLEE, M. & CHARETTE, J.P. 1967 : Economic geology and geophysics of the Oka alkaline complex, Quebec. Can. Min. Metal.Bull. 60, pp.1131-1144. GOLDSMITH, J.R. & HEARD, H.C. 1961 : Subsolidus phase relations in the system CaCO3 - MgCO3. Jour. Geo1.75, pp.45-74. GRANT, J.N.M. 1979 : A study of ore genesis and geochronology it the subvolcanic tin belt of the Eastern Andes, Bolivia. Unpub. PhD Thesis, Imperial College, London. GREENLAND, L. & LOVERING, J.F. 1966 : Fractionation of fluorine, chlorine and other trace elements during differentiation of a tholeittic magma. Geochim. & Cosmochim.Acta, Vol.30, pp.963-982. GRINENKO, L.N, KONONOVA, V.A. & GRININKO, V. 1970 : Isotopic composition of sulphide sulphur in carbonatites. Geochem. Int. Vol.7, No.1, pp.45-53. GURNEY, J.J. 1978 : Chemical variations in mantle nodules in kimberlites from Southern Africa. Royal Soc: Meeting on the Evidence for chemical heterogeneity in the earth's mantle. Abstr. (full publication in press). HAAPALA, I. 19.78 : Fluid inclusion studies in apatite from the Sokli carbonatite, Northeastern Finland. I.A.G.O.D. Meeting, .5th Symposium Utah, U.S.A. programs & abstracts, p.94 (abst.) HALL, A.L. 1912 : The crystalline metamorphic limestones of Lulukop and its relationship to the Palabora plutonic complex. Trans. Geol. Soc. S.Afr. Vol.15, pp.18-25. HAMILTON, D.L., FREESTONE, I.C., DAWSON, J.B. & DONALDSON, C.H. 1979 : The origin of carbonatites by liquid immiscibility. Nature Vol.279, pp.52-54. HANEKOM, H.J., van STADEN, C.M.vH., SMIT, P.J. & PIKE, D.R 1965 : The Geology of the Palabora Igneous Complex. S.Afr. Geol.Surv. Mem.54, p.179.

351. HARTE, B. & GURNEY, J.J. 1978 Magmatic and metasomatic compositional variations in Matsoku garnets, peridotites and pyroxenites. Royal.Soc. Meeting on the Evidence for chemical heterogeneity in the earth's mantle. Abstr. (full publication in press). HASKIN, L.A., WILDEMAN, T.R. & HASKIN, M.A. 1968 : An accurate procedure for the determination of rare earths by neutron -activation. Jour.Radiochem. Chem., Vol.1,pp.337-348. HAUGHTON, D.R., ROEDDER, P.L. & SKINNER, B.J. 1974 : Solubility of Sulphur in Mafic Magmas. Econ. Geol. Vol.69, No.4, p.451. HEINRICH, E.W. 1966 : The Geology of Carbonatites. Rand McNally & Co. Chicago. 1970 : The Palabora Carbonatite Complex - A Unique Copper Deposit. Can. Min. Vol.10, pt.3, pp.585-598. 1976 : Personal Communication. University of Michigan. HEINRICH, E.W. & LEVINSON, A.A. 1961 Carbonatitic niobium - rare earth deposits, Ravalli County, Montana. Am. Mineral.Vol.46. 1976 : Personal communication. University of Michigan. HELZ, G.R. & WYLLIE 1979 : Liquidus relationships in the system CaCO - Ca(OH) - CaS and the solubility of sulphur in carbonaatite magmas. Geochim.et Cosmochim. Acta Vol.43, pp.259-265. HENDERSON, P., FISHLOCK, S.J., LAUL, J.C., COOPER, T.D., CONRAD, R.L., BOYNTON, W.V. & SCHMITT, R.A. 1976 : Rare earth element abundances in rocks and minerals from the Fiskenaesset complex, W.Greenlānd. Earth & Planetry Sci.Letters, 30, pp.37-49 HEWITT, R.L. 1938 : Experiments bearing on the relations of pyrrhotite to other sulphides. Econ.Geol.Vol.33, pp.305-338. HEWITT, R.L. & SCHWARTZ, G.M. 1937 : Experiments bearing on the relation of pyrrhotite to other sulphides. Econ.Geol.Vol.32, p.1070. HIEMSTRA, S.A. 1955 : Baddeleyite from Palabora, E.Transvaal. Am.Min.Vol.40, pp.275-282.

352. HOEFS, J., NIELSEN, H. & SCHIDLOWSKI, M. 1968 : Sulphur isotope abundances in pyrite from the Witwatersrand conglomerates. Econ.Geol.Vol.63, pp.975-977.

HOLLAND, H.D. 1952 : The potash ankaratrite-melaleucitite lavas of Nabugando and Mbuga craters, south-west Uganda. Trans.Geol.Soc., Edinburgh, Vol.15,pp.187-213. 1959 : Some applications of thermochemical data to problems of ore deposits I: stability relations among the oxides, sulphides, sulphates and carbonates of ore and gangue minerals. Econ.Geol. Vol.54,pp.184-233. HOLMES, A. & CAHEN, N.L. 1957 : Geochronologie Africaine 1956; mem.Acad. Roy. Beige. Cl. Sci.Vol.8, (15,1) (1-169). HOWD, F.H. & BARNES, H.L. 1975 : Ore Solution Chemisry IV. Replacement of Marble by Sulphides at 450'C. Econ.Geol. Vol.70, pp.968-981. HUTCHEON, I. 1978 : Calculation of metamorphic pressure using the sphalerite-pyrrhotite-pyrite equilibrium. Am.Min. Vol.2, p.87. JACOBSEN, J.B.E. 1975 : Copper deposits in time and space. Min.Sci.Eng. Vol.7, No.4, pp.337-371. 1977 : Personal Communication. Univ. of Witwatersrand, S.Africa. JACOBSEN, J.B.E. & McGARTHY, T. 1976 : An unusual hydrothermal copper deposit at Messina, S.Afr. Econ. Geol.Vol.71,pp.117-130 JAMES, T.C. & McKIE, D. 1958 : The alteration of pyrochlore to columbite in carbonatites in Tanganyika. Min.Mag. Vol.31, pp.889-900. KAPUSTIN, Yu.L. 1965 : Sulphide Mineralization in Carbonatites of the Kola Peninsula. In: The Petrology and Geo- chemical Characteristics of Complex Ultrabasites, Alkaline Rocks & Carbonatites. Nauka Press, Moscow (in Russian). 1966 Geochemistry of REE in Carbonatites. Geochem. Int.6, pp.1054-1064. 1971 : The Mineralogy of Carbonatites (in Russian) Nauka Press. 1977 : Distribution of Sr, Ba and the rare earths in apatite from carbonatite complexes. Geochem. Int. No.4, pp.71-80.

353. KAPUSTIN, Yu.L., LAPITSKII, E.M., POGREBNOY, V.T., STORCHACK, P.N. & KOCHANOV, Ye.N. 1978 : The carbonatite zone in the Ukranian Shield. Int. Geol. Rev. Vol.20, No.10, Oct.'78, pp.1131-1140. KHITAROV, D.N., SOKOLOV, S.V. & KHARLAMOV, E.S. 1978 : The inclusion minerals of carbonatite formations. I.A.G.0.D.5th Symposium, Snowbird, Utah. Programs & Abstracts, p.114. (abstr.) KING, B.C. & SUTHERLAND, D.S. 1960 : Alkaline rocks of eastern and southern Africa, Parts I,II and III. Sci.progress 48, pp.298-720. KIRK- OTHMER 1968 : The Encyclopaedia of Chemical Technology. Ed. A.Standen. Vol.16,p.389. J.Wiley & Son, U.S.A. KNOERR, A.W. 1971 : Palabora's Amazing Expansion Programme. Eng. and Min.- Journal, May 1971. KOGARKO, L.N. 1975 : Behaviour of volatile components in alkali rocks. In: Recent Contributions to Geochemistry and Analytical Chemistry, pp.189-198. KONONOVA, V.A. & TARASHCHAN, A.N. 1970 : Thermoluminescence of carbonates from carbonatites. Int. Geol. Rev.12, pp.272-280. KOSHITZ, K.M. 1934 : The alkalic rocks of the Eusk region and related ore formations. Bull. Leningrad Geol.Trust,No.1, p.13 (in Russian). KOSTER van GROOS, A.F. 1975 : The effect of high CO2 pressures on alkalic rocks and its bearing on the formation of alkalic ultrabasic rocks and associated carbonatites. Am.Jour.Sci. Vol.275, pp.163-185. KOSTER van GROOS, A.F. & WYLLIE, P.J. 1966 : Liquid immiscibility in the system Na20 - A1203- Si02 - CO2 at pressures to 1 kilobar. Am.3our.Sti. Vol.264, pp.234-255. 1968 : Liquid immiscibility in the join NaAlSi 0 - Na2CO3 - H2O and its bearing on the gendsts of carbonatites. Am.Jour.Sci. Vol.266, pp.932-967. 1973 : Liquid immiscibility in the join NaA1Si3O8 - CaAl2Si208 - Na2CO3 - H2O. Am.Jour.Sci. Vol.273, pp.465-487 (June).

354. KOTOV, N.V., ROGOZIN, M.P., SHINKAREV, N.F. & DOMINA, M.I. 1978 : Experimental Na-carbonate metasomatism in the subsolidus range for haplogranite systems under pressure. Int. Geol. Rev.Vol.20, No.10, pp.1203-1213. KRAUSKOPF, K.B. 1967 : Introduction to Geochemistry. McGraw-Hill Book Co.., New York. KUKHARENKO, A.A. & DONTSOVA, E.I. 1964 : A contribution to the problem of the genesis of carbonatites. Econ.Geol.(USSR) Vol.1, Nos.3,4, pp.31-46 (in English). KUKHARENKO, A.A. & ORLOVA, M.P. 1965 : The caledonian complex of ultrabasic alkaline rocks and carbonatites of the Kola Peninsula and N.Karelia. Nedra Press, Moscow (in Russian). KULLERUD, G. 1953 : The FeS - ZuS system: a geological thermometer. Norsk Geol. Tidsskr.Vol.32, pp.61-147. LANCELOT, J.R. & ALLEGRE, C.J. 1974 : Origin of carbonatite magma in the light of the Pb-U-Th isotope system. Earth & Planet Sci. Lett. Vol.22, No.3, pp.233-238. LARSEN, E.S. 1942 : Alkalic rocks of Iron Hill, Gunnison Co.Colorado. U.S.G.S. profess. Paper 197-A. LE BAS, M.J. 1976 : Personal communication, University of Leicester. 1977 : Carbonatite-nephelinite volcanism. J. Wiley, London. LOMBARD, A.F., WARD-ABLE, N.M. & BRUCE, R.W. 1964 : The exploration and main geological features of the copper deposit in carbonatite at Loolekop, Palabora complex. In: Haughton, S.H. Ed. The Geology of some Ore Deposits in Southern Africa, Vol.2, Johannesburg, Geol.Soc.S.Afr.pp.315-337. LOUBET, M., BERNAT, M., JAVOY, M. & ALLEGRE, C.J. 1972 : Rare Earth Contents of Carbonatites. E.P.S.L. 14, pp.226-235. MacLEAN, W.H. 1969 : Liquidus Phase Relations in the FeS-Fe0-Fe304- Si02 System and their Application in Geology. Econ.Geol.Vol.64, pp.865-884.

355. MAKELA, M. & VARTIAINEN, H. 1978 : A study of sulphur isotopes in the Sokli multistage carbonatite (Finland). Chem.Geol. Vol.21, pp.257-265. MELCHER, G.C. 1966 : The Carbonatites of Jacupiranga, Sao Paulo, Brazil. In: Carbonatites, Ed. Tuttle & Gittins, pp.169-182. Wiley. METZGER, F.W., KELLY, W.C., NESBITT, B.E. & ESSEN, E.J. 1977 : Scanning electron microscopy of daughter minerals in fluid inclusions. Econ.Geol.Vol.72,pp.141-152. MILLER, J.P. 1952 : A portion of the system calcium carbonate-carbon dioxide-water, with geological implications. Am. Jour.Sci.Vol.250,pp.161-203. MITCHELL, R.H. & BRUNFELT, A.O. 1975 : Rare earth element geochemistry of the Fen Alkaline Complex, Norway. Contrib.Mineral. Petrol. Vol.29,pp.247-259. MITCHELL, R.H. & KROUSE, H.R. 1971 : Isotopic composition of sulphur in carbonatite at Mountain Pass, California. Nature, Vol.231, p.182. 1975 : Sulphur isotope geochemistry of carbonatites. Geochim.et Cosmochim.Acta.Vol.39,pp.1505-1513. MOORE, A.C. 1973 : Carbonatites and kimberlites in Australia: a review of the evidence. Min.Sci. & Eng.Vol.5, No.2, pp.81-91. NADKARNI, R.A. & MORRISON, G.H. 1974 : Determination of the noble metals in geological materials by neutron activation analysis. Analytical Chem.Vol.46, No.2,pp.232-236. NALDRETT, A.J. & CABRI, L.J. 1976 : Ultramafic and related mafic rocks: their classification and genesis with special reference to the concentration of nickel sulphides and platinum group elements. Econ.Geol.Vol.71,•pp.1131-1158. NASH, W.P. 1972 : Mineralogy and petrology of Iron Hill Carbo- natite complex, Colorado. Geol.Soc.Am. Bull. Vol.8, p.1361. NESBITT, B.E. & KELLY, W.C. 1977 : Magmatic and hydrothermal inclusions in carbo- ratite of the Magnet Cove complex, Arkansas. Contrib.Min. & Petrol.Vol.63,pp. 271-294.

356. NEWHOUSE, W.H. 1927 : The equilibrium diagram of pyrrhotite and pentlandite and their relations in natural occurrences. Econ.Geol.Vol.22, pp.288-299. NORRISH, K. & HUTTON, J.T. 1969 : An accurate x-ray spectrographic method for the analysis of a wide range of geological samples. Geochim.Cosmochim.Acta.Vol.33,pp.431-453. OHMOTO, H. 1972 : Systematics of sulphur and carbon isotopes in hydrothermal ore deposits. Econ.Geol.Vol.67, pp.551-578. OLSEN, J.C., SCHAWE, D.R. PRAY, L.C. & SHARP, W.N. 1954 : Rare earth mineral deposits of Mountain Pass District, San Bernadino Co.California. U.S.G.S. Profess.Paper, 261. P.M.C. Ltd., MINE GEOLOGICAL & MINERALOGICAL STAFF 1976 : The Geology and the Economic Deposits of Copper, Iron and Vermiculite in the Palabora Igneous Complex; a brief review. Econ.Geol. Vol.71,No.1, pp.177-193. PAARMA, H. 1970 : A new find of carbonatite in north Finland, the Sokli plug in Savukoski. Lithos 3, pp.129-133. PAARMA, H. & TALVITIE, J. 1976 : Deep fractures: Sokli carbonatite. Dep.Geophys.Univ.Oulu, Contrib.,p.65. PAARMA, H., VARTIAINEN, H. & PENNINKILAMPI, J. 1977 : Aspects of photogeological interpretation of Sokli carbonatite massif. In: Prospecting in Areas of Glaciated Terrain, I.M.M. 1977, pp. 25-29. PANINA, L.I. & SHATSKIY, V.S. 1973 : Traprock and ultramafic rocks of the Yessay carbonatite intrusion. Dokladii, Vol.209, pp.184-187. PARKER, R. 1979 : A computer based system of XRF analysis and its application to the geochemistry of Vulcini volcano, central Italy. Unpub.PhD Thesis, Imperial College, London. PARRY, S.J. 1978 : Personal Communication. Univ.Lond.Reactor Centre, Ascot.

357. PHILLIPS, K.A. 1955 : Some notes on the carbonatite at Nkumbwa Hill, Isoka District, N.Rhodesia. Rhod.Geol.Surv. 'Records for 1953, pp.20-23. PHILPOTTS, A.R. 1967 : Origin of certain iron-titanium oxide and apatite rocks. Econ.Geol.Vol.62, pp.303-330. PHILPOTTS, J.A., SCHNETZLER, C.C. & THOMAS, H.H. 1972 : Petrogenetic implications of some new geochemical data on eclogitic and ultrabasic inclusions. Geochim.et Cosmochim.Acta.36, pp.1131-1166. POLYAKOV, E.A. 1965 : Eelctrical resistivity and density of aqueous salt solutions under high pressure and temperature. Prikl.Geofizika, USES. Nauchno- Issled. Inst.Geofiz.Metodov Razvedki Sb.Stadei No.41, pp.163-180 (in Russian). POTTER, R.W. 1977 : Pressure corrections for fluid inclusion homogenization temperatures based on the volumetric properties of the system NaCl-H2O. J.Res. U.S. Geol.Surv. Vol.5, pp.603-607. POTY, B.P., STADLER, H.A. & WEISBROD, A.M. 1974 : Fluid inclusion studies in quartz from fissures in the Western and Central Alps. Schweitz.Min.Petr.Mitt. Vol.54,pp.717-752. POZHARITSKAYA, L.K. 1962 : Mineralogical-petrographical characteristics of carbonatites. In: Geology of Rare Element Deposits, Vol.17, Pt.6. POZHARITSKAYA, L.K. & SAMOYLOV, V.S. 1972 : The petrology, mineralogy and geochemistry of the carbonatites of Eastern Siberia. Nauka Press, Moscow. PRINS, P. 1972 : The composition of magnetites from carbonatites. Lithos 5, pp.227-240. 1973 : Apatite from African Carbonatites. Lithos 6, pp.73-133. PUUSTINEN, K. 1973 : Tetra-ferri-phlogopite from the Siilinjarvi carbonatite complex, Finland. Bull.Geol.Soc, Finland, Vol.45, pp.35-42. 1975 : Dolomite exsolution textures in calcite from the Siilinjarvi carbonatite complex, Finland. Geol.Soc.Finland Bull. Vol.46, No.2, pp.151-159.

358. RAMDOHR, P. 1969 : Ore Minerals and their Intergrowths. Int. Series of Monographs on Earth Sciences, Pergammon Press, 3rd Edition. RANKIN, A.H. 1973 Fluid inclusion studies in apatite from some E.African carbonatites and ijolites. Unpub. PhD Thesis, Univ. Leicester. 1975 : Fluid inclusion studies in apatite from carbonatites of the Wasaki area, W.Kenya. Lithos, Vol.8, No.2, 1975. 1977 : Fluid inclusion evidence for the formation conditions of apatite from the Tororo carbonatite complex of Eastern Uganda. Min.Mag: Vol.41, pp.155-164. 1978 : User school on fluid inclusion equipment and methods, course notes. Applied Mineralogy Group (Min.Soc.U.K.) at Imperial College,London. RANKIN, A.H. & ALDOUS, R.T.H. 1979 : Tritolyl phosphate - a suitable immersion oil for fluid inclusion freezing stage studies. Min.Mag. Vol.43, No.326, pp.315-316. RANKIN, A.H. & Le BAS, M.J. 1974A: Liquid immiscibility between silicate and carbonate melts in naturally occurring ijolite magma. Nature 250, pp.206-209, 1974. 1974B: Nahcolite (NaHCO ) in inclusions in apatites from some E.African ijolites and carbonatites. Min.Mag. Vol.39, p.564. RAZIN, L.V. 1971 : Problem of the origin of platinum metallization of forsterite dunites. Int. Geol. Rev. Vol.13, No.5. REZNITSKII, L.Z. & VOROBYOV, E.I. 1978 : Exsolutional microinclusions of sulphates and sulphides in endogenic calcites. Gen.Meeting Int. Min.Assoc. Novosibirsk, Abstr. Vol.II, p.70. RIMSKAYA-KORSAKOVA, 0.M. 1964 : The Genesis of the Kovdo.r Iron Ore Deposit (Kola Peninsula) Int.Geol.Rev.Vol.6,p.1735. RIMSKAYA-KORSAKOVA, O.M. & SOKOLOVA, E.P. 1964 : On ferro-magnesian mica with a reverse scheme of absorption (in Russian). Zap.Vsesoyuz. Min. Obsts. 93, pp.411-423.

359. ROEDDER, E.W. 1965 : Liquid CO inclusions in olivine bearing nodules aid phenocrysts from basalts. Am. Mineralogist 50, pp.1746-1782. 1967 : Fluid inclusions as samples of ore fluids. In: Geochemistry of Hydrothermal Ore Deposits, Ed. H.L.Barnes, pp.515-574. New York, Holt Rinkhart & Wilson. 1970 : Application of an improved crushing microscope stage to studies of the gases in fluid inclusions. Schweizer Mineralog, Petrog.Mitt. Vol.50, Pt.1, pp.41-58. 1972A: The composition of fluid inclusions. In: Fleisher, M.Ed. Data of Geochemistry, 6th Edn. U.S.G.S. Prof.Paper 440 p.164. 1972B: Fluid inclusion research, proceedings of C.O.F.F.I. (annual summary of world literature privately printed and available from the editor). 1978 : The Origin and Significance of Magmatic Inclusions. Centenary Meeting of French Soc. of Min.et Grist., Nancy. ROEDDER, E.W. & COOMBS, D.S. 1967 : Immiscibility in granitic melts indicated by fluid inclusions in ejected granite blocks from Ascension Island. Jour.Petrol.Vol.8,pp.417-451. ROEDDER, E.W., INGRAM, B. & HALL, W.E. 1963 : Studies of fluid inclusions III: extraction and quantitative analysis of inclusions in the milligram range. Econ.Geol.Vol.58,pp.353-374. ROLLINSON, H.R. 1979 : Ilmenite-magnetite geothermometry in trond- hjemites from the Scourian complex of N.W. Scotland. Min.Mag.Vol.43,pp.165-170. ROMANCHEV, B.P. 1972 : Inclusion thermometry and the formation conditions of some carbonatite complexes in East Africa. Geochem.Internat.Vol.9,pp.115-120. ROWE, R.B. 1958 : Niobium (columbium) deposits of Canada. Can. Geol.Serv. Econ.Geol. Ser.18. RUSSELL, H.D. HIEMSTRA, S.A. & GROENEVELD, D. 1954 : The mineralogy and petrology of the carbonatite at Loolekop E.Transvaal. Trans.Geol.Soc. S.Afr. LVII 1954, pp.197-208. SAMOYLOV, V.S. 1974 : Influence of T and P on the acidity-alkalinity of carbonatite forming fluids. Akad.Nauk SSSR Dokl. Vol.218, No.2, pp.452-455.

360. SCHNEIDER, A. 1970 : The Sulphur Isotope Composition of Basaltic Rocks. Contrib.Mineral.Petrol.Vol.25, pp.95-124. SCHWARTZ, G.M. 1931 : Intergrowths of Bornite and Chalcopyrite - pp.186-201. Textures due to unmixing of solid solutions - pp.739-763. Econ.Geol. Vol.26, 1931. SHAND, S.J. 1931 : Granite-syenite-limestone complex of Palabora, E.Transvaal and the associated apatite deposits. Trans.Geol.Soc.S.Afr. XXXIV 1931, pp.81-105. SHCHERBINA, V.V. 1963 : Differences in geochemical processes occurring with the participation of potassium and sodium. Geochem.No.3, p.245. SHIMA, H. & NALDRETT, A.J. 1975 : Solubility of sulphur in an Ultramafic Melt and the relevance of the system Fe-S-0. Econ,Geo1.Vol.70, pp.960-967. SILLITOE, R.H. 1977 : Personal Communication, c/o Imperial College, London. SINE, N.M.T., TAYLOR, W.O. & WEBBER, G.R. 1969 : Third report of analytical data for CAAS sulphide ore and syenite rock standards. Geochim.et Cosmochim. Acta Vol.33, pp.121-131. SIN'KOVA, L.A. & TURANSKAYA, N.V. 1968 : Differences between the effects of K and Na on the migration tendencies of rare earth elements. Geochem. Internat. Vol.5, No.3, p.481. SKINNER, B.J. & PECK, D.L. 1969 : An immiscible sulphide melt from Hawaii. Econ.Geol.Monograph 4, p.310. SMIRNOV, V.I. (Ed.) 1976 : Geology of Mineral Deposits. Chap.6,pp.138-152, MIR Publishers, Moscow (brig;pub. in Russian 1962). 1977 : Ore Deposits of the USSR. Transl.D.A. Brown & Canberra Pitman Publ.Ltd., Vols. 1,2,7. SORENSEN, H. 1974 : The Alkaline Rocks. Wiley, London. SPRINGER, G. 1968 : Electron probe analyses of mackinawite and valleriite: Neues Jahrb.Mineralogie, Montash. No.8, pp.252-258.

361. STANTON, R.L. 1972 : Ore Petrology. McGraw-Hill. STEINFINK, H. 1962 : Crystal structure of a trioctohedral mica: phlogopite. Am.Mineralogist, Vol.47,pp.886-896. STRICKER, S.J. 1978 : The Kirkland-Larder Lake Stratiform Carbonatite. Mineral. Deposita (Berl.) Vol.13,pp.355-367. STUMPFL, E.F. & TARKIAN, M. 1976 : Platinum Genesis: New Mineralogical Evidence. Econ.Geol.Vol.7l,pp.1451-1460. SUWA, K., OANA, S., WADA, H. & OSAKI, S. 1975 : Isotope geochemistry and petrology of African carbonatites. Physics & Geochemistry of the Earth, Vol.9, No.47, p.735. Eds.Ahrens,L.H., Dawson, J.B., Duncan, A.H. & Erlank, A.J. TATSUO TATSUMI 1967 : Sulphide minerals from Palabora carbonatite deposit. Trans.I.M.M. p.76B(Abstr.) Univ. Tokyo, Japan. TAYLOR, P., FRECHEN, J. & DEGENS, E.T. 1967 : Oxygen and carbon isotope studies of carbonatites from Laacher See district, West Germany and Alno district, Sweden. Geochim.et Cosmochim.Acta Vol.25,pp.159-174. ' TSAI, H. SHEIH, Y. & MAYER, H.O.A. 1977 : Mineralogy and S34/S32 ratios of sulphides associated with kimberlites, xenoliths and diamonds. 2nd Int.Kimberlite Conf., New Mexico (extended abstrs.) VALYASHKO, V.H. & KOGARKO, L.N. 1965 : Inclusions in apatite of the Khibiny and Lovozero plutons. Akad.Sci.SSSR. Dokl.Earth Sci.section Vol.166,pp.146-149. VAN de VEEN, A.H. 1963 : A Study of Pyrochlore. Verh.Kon.Nedl.Geol. Minjb.Gen. Geol.Ser., 22. Van WAMBEKE, L., BRINCK, J.W., DEUTZMANN, W., GONFIANTINI,R., HUBAUX, A., METAIS, D., OMENETTO, P., TONGIORIGI, E., VERFAILLIE, G., WEBER, K. & WILMMENAUER, W. 1964 : Les Roches Alkalines et les Carbonatites du Kaiserstuhl. Euratom 1827. VARTIAINEN, H. 1977 : Personal Communication. Rautaruukki Oy,Finland. VARTIAINEN, H. & PAARMA, H. 1979 : Geological characteristics of the Sokli Carbo- natite Complex, Finland. Econ.Geol. Vol.74, pp.1296-1306.

362. VARTIAINEN, H., KRESTEN, P. & KAFKAS, Y. 1978 : Alkaline lamprophyres from the Sokli Complex, N.Finland. Bull.Geol.Soc.Finland, Vol.50 (1-2) pp.59-68. VARTIAINEN, H. & WOOLLEY, A.R. 1974 : The age of the Sokli carbonatite, Finland and some relationships of the N.Atlantic alkaline igneous province. Bull.Geol.Soc.Finland A6, pp.81-91. 1976 : The petrography, mineralogy and chemistry of the fenites of the Sokli carbonatite intrusion, Finland. Geol.Survey.Finland, Bull.280,p.87. VASILJEV, Yu.R., SOBOLEV, A.V..& CHMEL'NIKOVA, O.S. 1978 : The composition of olivines from ultramafic rocks of Siberian platform. Gen.Meeting Int. Mineralog.Assoc. Novosibirsk Vol.1 (abs.),p.45. VASILJEVA, Z.L. 1978 : On Apatite Heterogeneity. Gen.Meet.ing Int. Mineralog. Assoc.Novosibirsk, Vol.II (abs.), p.77. VERWOERD, W.J. 1964 : South African carbonatites and their probable mode of origin. Ann.Univ.Stellenbosch, Series A, Vol.41, pp.115-233. 1967 : The Carbonatites of South Africa and South West Africa. Geol.Surv. S.Afr. Hnbk,6.. VLASOV, K.A. 1966 : Geochemistry and Mineralogy of rare elements and genetic types of their deposits. Vol.2 Mineralogy of Rare Elements. VOLOTOVSKAYA, N.A. 1958A: Magmatic complex of ultrabasic, alkaline and carbonatitic rocks in the massif of Vuori-Yarvi. Zap.Vses.Mineral Obshuch.87, pp.290-300. 1958B: The Kovdor Massif. Geol.of USSR. T.27.(in Russian). von COTTA, B. 1858 : Geologische Fragen. J.G. Engelhardt, Freiburg. von ECKERMANN, H. 1948A: The alkaline district of Alno Island. Sver.Geol.Undersokn, Ser. Ca.36. 1948B: The Genesis of the Alno Alkaline Rocks. Int. Geol.Congr.l8th Sess.Gt.Britain III,pp.94-101. 1958 : The alkaline and carbonatitic dykes of the Alno formation on the mainland north-west of Alno Island. Kg1.Svenska Vetenskapsakad.Handl.,7(2)

363. von GEHLEN, K., 1967 : Sulphur isotopes from the sulphide bearing carbonatite of Palabora, South Africa. Trans. I.M.M. p.76B (abs.) WAGER, L.R., VINCENT, E.A., SMALES, A.A. & BARTHOLOME, P. 1957 : Sulphides in the Skaergaard intrusion, East Greenland. Econ.Geol.Vol.52,pp.855-895. WASS, S.Y., HENDERSON, P. & ELLIOTT, C.J. 1978 : Chemical heterogeneity and metasomatism in the upper mantle: evidence from rare earth and trace element abundances in apatite rich xenoliths in basaltic rocks of New South Wales, Australia. Royal Soc.Meeting on the evidence for chem.heterogeneity in earth mantle. (abs.) Full publication in press. WEBBER, G.R. 1965 : Second report of analytical data for CAAS syenite and sulphide standards. Geochim. et Cosmochim.Acta.Vol.29,pp.229-248. WENDLANDT, R.F. & HARRISON, W.J. 1978 : Rare Element partitioning between co-existing immiscible carbonate and silicate liquids and CO2 in the system K20 - A1203 - Si02 - CO2. Joint Ann.Meeting.GAC, MAC, GSA, Vol.3 (abs.) p.514. WOOLLEY, A.R. 1973 : Contributions and discussions on: Deans et al. 1972, Metasomatic feldspar rocks of Amba Dongar. Trans.Inst.Min.Metal.Sect.B, Vol.82,pp.B35-B39. 1978 : Personal communication. British Museum of Natural History, London. WYLLIE, P.J. 1966 : Experimental Studies of Carbonatite Problems: The Origin and Differentiation of Carbonatite Magmas. In: Carbonatites, Ed.Tuttle & Gittins, pp.311-352. 1978 : Influence of Volatile Components on the Upper Mantle Process. Gen.Meet.Int.Min.Assoc. Novosibirsk (abs.) Vol.II, p.55. WYLLIE, P.J. & BIGGAR, G.M. 1966 : Fractional Crystallization in the "carbonatite systems" Ca0 - Mg0 - CO2 - H2O and CaF2 - P205 - CO2 - H2O. Min.Soc. India, I.M.A. Vol.92-105. WILLIE, P.J., COX, K.G. & BIGGAR, G.M. 1962 : The habit of apatite in synthetic systems and igneous rocks. Jour.Petrology, Vol.3,pp.238-243. WYLLIE, P.J. & TUTTLE, O.F. 1960 : The system Ca0 - CaO, H,0 and the origin of carbonatites. J.Petr81. V81.I, pp.1-46.

.r / YEGOROV, L.S. 1975 : Camaforites or Phoscorites and Nelsonites? Geol.Rud.Mestorozhd. Vol.17,pp.117-121 (in Russian). YUND, R.A. & KULLERUD; G. 1966 : Thermal stability of assemblages in the Cu-Fe-S system. Jour.Pet. Vol.7, pp.454-488 ZHABIN, A.G. 1967 : Carbonatitic Kimberlites from Arbarasta. Doklady Akad. Nauk, Vol.177, No.3 (in Russian). ZLATKIND, Tz.G. 1948 : The Kovdoro Lake pluton of alkali and ultrabasic rocks. Doklady Akad, Nauk SSSR, Vol.117, pp.659-661. ZLOBIN, B.I., KRAVCHENKO, S.M. & LAKTIONOVA, N.V. 1973 : Distribution of copper in the extrusive basaltic series of different alkalinity. Geochem. Int. Vol.10, No.2, pp.270-276.

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