Genesis of the Ballynoe Barite Deposit,Ireland,And

Home , Baryte, Bournonite, Microspherulite

GENESIS OF THE BALLYNOE BARITE

DEPOSIT,IRELAND,AND OTHER BRITISH STRATABOUND

BARI1E DEPOSITS.

A THESIS SUBMITTED FOR THE

DEGREE OF DOCTOR OF PHILOSOPHY OF THE

UNIVERSITY OF LONDON

JOHN RUSSELL BARRETT

Mining Geology Division, Department of Geology, Royal School of Mines, Imperiel College of Science and Technology,

The University of London. February 1975 IA curious grey rock'

A,B.Wynne 1861 -3-

ABSTRACT

This thesis describes the geology of a large,stratiform barite deposit located at Ballynoe (near Silvermines) Co.Tipperary,Ireland.The deposithas been investigated from the sedimentological,mineralogical and geochemical aspects in order to determine its probable genesis.

The bedded barite is a conformable,mineralised-horizon of Upper Tournaisian age.The barite horizon is associated with a non-sequence at the top of the Muddy Reef Limestone and marks the transition from a quiet water environment to one of dynamic sedimentation.In the footwall succession (Upper Devonian - Lower Tournaisian) a major sedimentary cycle is evident,a cycle which terminates in a non-sequence and is overlain by the barite horizon.Mass extinction of the fauna is associated with the non-sequence.

The geometry of the barite orebody correlates with the palaeo-topography of the footwall,the topography acting as an important control over the lateral extent,thickness and nature of the mineralisation.Sedimentary features within the barite horizon suggest that the barite was precipitated in the form of a cryptocrystalline mud.Lithification and diagenesis resulted in extensive stylolitisation,recrystallisation and remobilization of the barite.

The wallrock geochemistry suggests that the dispersion of anomalous barium is strictly confined to a mineralised- horizon directly overlying the Muddy Reef Limestone.Iron and silicon were associated with the initial emplacement of the barite.Sulphur and oxygen isotope values suggest that contemporaneous slavvater so played a significant role in the precipitation of the barite.

The barite was precipitated in a partially restricted marine lagoon (carbonate mudbanks controlling water circulation and the Eh and pH conditions),the ore forming solutions probably being chloride-brines debouching from fractures along the Silvermines Fault.The metals in the brines(migrating formation waters) were derived from the Lower Palaeozoic troughs to the north and south of Ballynoe.Some admixing with juvenile waters associated with contemporaneous volcanism probably occurred. ACKNOWLEDGEMENTS

This research project was formulated through the insight of Professor G.R.Davis who regarded the Ballynoe barite deposit as a possible 'genetic key' to the mineralisation of the Irish Carboniferous Limestone.The work was also supervised and edited by Professor G.R.Davis whose suggestions and constructive criticism is gratefully acknowledged.

The research was supported financially by the Natural Environmental Research Council,an award from the William Selkirk Scholarship fund and a grant from Dresser Minerals. I express my sincere gratitude to these bodies.

The field investigations were facilitated through Mr. Ovid Johnson,Jr.,Exploration Manager of Dresser Minerals, whilst sustained assistance in and out of the field was given by Staff geologists,Dr.R.W.Stewart and Mr.R.D.Turner. I offer them my sincere thanks.I am also grateful to Mr.R.B. Harrison,Managing Director,Magcobar (Ireland) Ltd., and to his staff at the Ballynoe Mine.

The co-operation received from Dr.W.W.Weber,Vice-Pres- ident of International Mogul Mines Ltd., and Mr.E.Grennan of Basin Exploration is gratefully acknowledged.

I express my gratitude to the technical staff of the Department of Geology at Imperial College for their considerable assistance,notably to Mr.Tony Thompson of the Applied Geochemistry Research Group and to Mr.B.Foster,Mr.R.Curtis, Miss T.Leslie,Mrs.K.Irving,Mr.N.Wilkinson,Mrs H.Richardson and to the late Mr.Jimmy Gee.

I record stimulating discussion with Dr.C.Halls,Dr.P. Garrard,Mr.J.McMoore and with my fellow research students, especially Mr.D.Pearson - many thanks to all.

Finally,I should like=to thank my parents for their long continued encouragement and assistance. -6-

Note : Units of measurement

All units in this work (with minor exception) are in Imperial units.These units are used by Magcobar and Mogul Mines and have been retained to avoid confusion.

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CONTENTS

is Page ABSTRACT 3 ACKNOWLEDGEMENTS 5 CONlhNTS 7 LIST OF FIGURES 12 LIST OF TABLES 15 LIST OF PLATES 16

CHAPTER ONE INTRODUCTION 1-1. Foreward 19 1-2. Location of the barite deposit 19 1-3. Geography 20 1-4. Historical background 21 1-5. The Magcobar operation 23 1-6. The role of barite in drilling fluids 24 1-7. Previous geological work at Ballynoe 26 1-8. The present investigation 30

CHAPTER TWO

THE GEOLOGICAL SETTING OF BALLNOE 2-1. Introduction 32 2-2. Regional stratigraphical setting 32 2-3. Regional structural setting 39 2-4. Stratigraphy of the Ballynoc Mine 41 Silurian L .1 Devonian (Old Red Sandstone) 44 Basal Fragmental L7 Lower Dolomite L.7 Muddy Limestone 49 Muddy Reef Limestone 49 Green Argillite 50 Upper Reef Limestone & Dolomite Breccia 55 Chert Horizon 57 Calp Limestone 59

2-5. Structural setting of the Ballynoe barite 59 -8-

Page 2-5a. Faulting 59 2-5b, Jointing 63 2-5c. Folding 63 2-5d. Structure of the footwall rocks 66 2-6. Summary 70

CHAPTER THREE THE BARITE HORIZON 3-1. Introduction 72 3-2. Form of the Ballynoe barite orebody 72 3-3. Stratification of the barite horizon 76 3-3a. The basal zone 80 Barite breccia 83 Bedded hematite formation 86 Replacement of the footwall by barite 94 3-3b. The siliceous barite zone 94 3-3c. The stylolitic and spherulitic barite 97 3-3d. Massive grey-black microcrystalline barite 103 3-3e. Massive sulphide 'cap' to ',-„he orebody 109 3-31. Macrocrystalline barite 'cap' to the orebody 111 3-4. Other barite occurrences within the mineralised- 117 horizon 3-5. Summary 119

CHAPTER FOUR THE MINERALOGY OF THE BARITE HORIZON 4-1. Introduction 121 472. Minerals associated with the barite horizon 122 4-3. Descriptive mineralogy 123 4-3a. -Pyrite and marcasite 123 4-3b. Partial trace element content of the pyrite 137 4-3c. Copper mineralisation_ 139 4-3d. Sphalerite and galena 142 4-4. Diagenetic and supergene modification of the 148 barite deposit Page

4-4a. Diagenesis 148 4-4b. Supergene alteration 149 4-4c. Mineral formation as a result of contemporary 151 weathering

4-5. Paragenesis of the barite deposit 154

CHAPTER FIVE GEOCHEMISTRY OF THE BARITE HORIZON 5-1. Introduction 159 5-2. Geochemistry of the wallrocks 159 5-2a. Wallrock dispersion in sub-economic areas of 160 the 'mineralised-horizon' 5-2b, Wallrock dispersion adjacent to the barite ore- 165 1 body 5-3. Element dispersion within the barite orebody 170 5-3a. Silicon 171 5-3b. Strontium 173 5-3c. Aluminium 175 5-3d. Magnesium 175 5-3e. Calcium 177 5-3f. Iron 178 5-3g. Copper 178 5-3h. Lead and zinc 178 5-3i. Other elements 180 5-33. Element dispersion between primary and secondary 180 barite 5-4. Barium content of rocks in the Silvermines region 181 5-5. Sulphur and oxygen isotope geochemistry 183 5-5a. Isotopic data for the Ballynoe barite 185 5-5b. Discussion of results 185 5-6. Summary 188 -10-

CHAPTER SIX Eage STRATABOUND BARITE IN THE BRITISH ISLES 6-1 . Introduction 190 6-2. Barite in a sedimentary environment 190 6-2a. Reported occurrences of sedimentary barite 191 Cambrian 191 Devonian 191 Carboniferous 193 Permian 1 96 Triassic 197 Jurassic 198 Cretaceous 198 Eocene 201 6-3. Distribution of Ba in English and Welsh stream 201 sediments Related to mining activity 201 Related to lithologies carrying a high .Ba. background 203 Related to diagenetic barite 204 6-4. The barium anomaly to the NE of Leeds,Yorks. 204 6-4a. Distribution of Ba in stream sediments 206 6-4b. Follow up investigation 206 6-4c. The stratigraphical range of barite mineralisation 213 6-5. Barite 'flatting' deposits 213 6-6. Discussion and conclusions 215

CHAPTER SEVEN DISCUSSION - GENESIS OF THE BALLYNOE BARITE DEPOSIT 7-1. Introduction 21 9 7-2. Geologic environment 220 7-2a. Sedimentary setting 220 7-2b. Fossil topography of the Muddy Reef Limestone 223 7-2e. Sedimentary characteristics of the barite orebody 224 7-2d. Sedimentary characteristics of the sulphide 'cap' 227 7-2e. Summary of the sedimentary features 228

7-3. Deposition of the barite 229

7-4. Nature and source of ore-forming fluid 232

7-5. Genetic model for the Ballynoe barite 236

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CHAPTER EIGHT

SUMMARY OF CONCLUSIONS Lam

8-1. - Conclusions 239

REFERENCES 242

APPENDIX 253 : Drill Coverage in the Silvermines Area 253 II : The Conolly Contour Method 254 III : The Direct Reading Spectrograph 255 IV The Optical Emission Spectrograph 259 -12-

LIST OF FIGURES

Page

1.1 Irish production of mined barite 1870 - 1973 25

2.1 Geological map of Ireland 34 2.2 Upper Tournaisian (Waulsortian) facies in Ireland 36 2.3 Stratigraphical column,Silvermines area 43 2,3A Regional geology around Silvermines 43 2,L1. Local geological map of Ballynoe 45 2.5 Devonian - Lower Tournaisian transition sequence 48 2.6 Plot of the diameter of crinoid ossicles in DDH 60-31 2.7 Brecciated zones in the hangingwall rocks 56 2.8 Development of breccia as observed in DDH 88 56 2.9 First and second faulting at Ballynoe 61 2.10 North - south faulting at Ballynoe 62 2.11 The southern limb of the Kilrnastulla valley 64 syncline (Ballynoe section) 2.12 Structure contour plot of the top of the Muddy 67 Reef Limestone

2.13 The footwall 'highs' and 'lows' 69

3.1 The extent of the Silvermines orebodies 73 3.2 East - west serial sections,Ballynoe barite 75 3.3 North - south serial sections,Ballynoe barite 77 3.4 North - south section along gridline 42.000E 81 illustrating differing mineral environments 3.5 Mineralogy of the basal 5ft of the mineralised- 82 horizon 3.6 Stylolite classification 100 3.7 Troughs in the stratiform sulphide horizon 109 3.8 The three types of white macrocrystalline barite 112 3.9 North - south section of the eastern periphery 113 of the barite 3.10 Barite occurrences in Mogul's '0' zone 118 -13—

Page

4.1 'Daisy pyrite' 131 4.2 Diagrammatic representation for the origin of 150 diagenetic 'secondary' barite 4.3 Paragenetic scheme for the Ballynoe barite 157 horizon

5.1 Dispersion of Ba,Sr,Fe in DDH 60 161 5.2 Element dispersion in DDH 60 (argillaceous 163 affinity) 5.3 Element dispersion in DDH 60 (mineralised- 164 horizon affinity) 5.4 Pb-Zn enrichment in the hangingwall 'Ba zone' 165 5.5 Remobilized barium over the 'eastern dome' 167 5.6 Comparative wallrock dispersion,orebody -DDH60 169 5.7 Orebody sample sites 170 5.8 Dispersion of silicon in the barite 172 5.9 Dispersion of strontium in the barite 174 5.10 Dispersion of aluminium in the barite 176 5.11 Dispersion of magnesium in the 'cap' barite 177 5.12 Dispersion of iron in the barite 179 5.13 Variation in trace element content :primary 180 barite - secondary barite 5.14 Distribution of Ba in the stream sediments of 182 the Silvermines - Toomyvara region 5.15 Variation in average isotope s34 values throughout 184 geologic time for contemporaneous seawater SO4 5.16 Isotope s34 and 018 values of barite from Ballynoe 186

6,1 'Sedimentary' barite localities mentioned in 194 the text 6.2 Mineralogy of Dactylioceras commune 199 6.3 Barite occurrences in the fullers-earth,Nutfield 200 6.4 Distribution of Ba in English and Welsh stream 202 sediments 6.5A Distribution of Ba in NE Leeds stream sediments 208 -14-

Page 6.5B Occurrence of barite in the NE Leeds area 208 6.6 Barite mineralisation,3arwick in Elmet 210 6.7 Stratigraphical range of barite mineralisation 213 6.8 North - south section, Nussey Knott 214 6.9 Barite associated with Coal Measure faulting 218

7.1 Eh-pH stability relations between iron and 230 barium minerals 7.2 Source of ore forming fluids,West Ireland 238

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Page

LIST OF TABLES

1.1 World production of mined barite 1968-72 25

2.1 Generalised Lower Carboniferous (Dinantian) 36 succession -in Ireland 2.2 Major periods of Irish Earth Movement 39 2.3 Strati graphical column,Silvermines region 42 2.4 Fault development at Ballynoe 60

3.1 Stratigraphy of the barite horizon 76 3.2 Eh-pH stability fields for iron 91

4.1 Partial trace element content of Ballynoe pyrite 138 4.2 Co :Ni ratios for table 4.1 138 4.3 Pyrite efflorescences: X-Ray Diffraction Data 155

5.1 Diamond drill holes sampled 160 5.2 Ba dispersion (T) in DDH 60 161 5.3 SrSO4 content of primary and diagenetic barite 175 5.4 Ba content of rocks in the Silvermines region 181

6.1 Sedimentary barite in the British Phanerozoic 192 6.2 Chemistry of Devonian authigenic & vein barite 193 6.3 Metallic mineral content of Upper Liassic 199 ammonites collected north of Nhitby,Yorks 6.4 Par.cial trace element content,Nussey Knott barite 214

7.1 The Tournaisian sedimentary cycle in the footwall 220 rocks to the orebody, -.16-

LIST OF PLATES Page

2.1 Looking to the NE of Ballynoe 46 2.2 Looking to the NW of Ballynoe 46 2.3 Coral and crinoid debris at the top of the 52 Muddy Reef Limestone 2.4 Replacement of a crinoid ossicle by silica 52 2.5 Crinoid ossicles in an accumulation of slump 53 debris at the top of the Muddy Reef Limestone 2.6 Drag folds developed in the Chert Horizon 58 2,7 Contact between solution pipe clays and the 58 Dolomite Breccia 2.8 Condensed sequence at the base of the solution 58 Pipe 2,9 Structure of the barite looking west 65 2.10 The 'eastern dome', as viewed from the SW 68

3.1 Barite stratification exposed in the eastern 78 end of the open-pit 3.2 Stratigraphy exposed in a vertical section of 79 the orebody 3.3 Barite breccia in a slump sequence 85 3.4 Barite breccia from the SE of Mogul's 'B' zone 88 3.5 Barite breccia from the SE of Mogul's 'B' zone 90 3.6 The bedded hematite formation 92 3.7 Slumping and faulting in the hematite horizon 93 3.8 Replacement of the footwall by barite 95 3.9 The development of jasper 96 3.10 Silica in the barite 99 3.11 Stylolite formation in the barite 102 3.12 Spherulitic barite 105 3.13 The microcrystalline barite zone 108 3.14 Stratiform sulphide 'cap' to the barite 110 3.15 Secondary cross-cutting barite veins 114 3.16 Macrocrystalline barite and orebody barite 112 3.17 Diagenetic 'secondary' barite 116 -17-

Page

4.1 Pyrite structures from the footwall 125 4.2 Pyrite in the hematite zone 126 4.3 Pyrite structures from the siliceous barite 128 4.4 Pyrite textures in the microcrystalline barite 130 4.5 Reniform pyrite associated with the 'cap' barite 132 4.6 Pyrite structures in the-l eap' barite 134 4.7 Framboidal pyrite from the sulphide 'cap' 136 4.8 Copper mineralisation 141 4.9 Sphalerite and galena in barite 144 4.10 Spheroidal sphalerite-galena fabrics 146 4.10A Spheroidal and colloform sphalerite 147 4.11 Supergene mineral formation 153 4.12 Oxidation products 156

6.1 Barite mineralisation around Bramham,Yorkshire 21 2

NOTE

0n many of the 'POLYFAX' black & white plates the fine detail of the original negative has not been reproduced. The original prints may be consulted in the Watts Library,Geology Department l Imperial College. -18- -1 9-

CHAPTER ONE

INTRODUCTION

1-1. Foreward

The names of Meggen and Ra-qmelsberg are associated in geological literature with the occurrence of large, stratiform,sulphidefsulphate orebodies and have stimulated a great deal of controversial discussion regarding their probable genesis.

In the early 1960's a new stratiform sulphide/sulphate ore deposit was discovered in west-central Ireland near the village of Silvermines.The bedded ore-horizon subsequently proved to be the first commercial orebody of this nature to be exploited within the British Isles.

This thesis is based on a study of the peripheral barite zone to the sulphide horizon at Silvermines and hopes to propound a model direcl,ed towards its genesis. A possible corollary to this work,is that a model applicable to the emplaceMent of the barite may also apply to the formation of the adjacent massive sulphide horizon.Such knowledge would be of aid in the prediction and location of virgin orebodies being sought in a similar provenance.

1-2. Location of the barite de osit

The barite deposit is located at Ballynoe (52°46'N, 8°151 W) half a mile SW of the village of Silvermines, County Tipperary,Ireland.The regional centre of commerce -20-

Limerickllies 20 miles SSW of the deposit,Shannon Inter- continental Airport,33 miles SW,and Foynes,a deep water port on the Shannon estuary,42 miles to the SSW.Well main- tained tarmac roads provide adequate access to the mine and bulk ore shipment is facilitated by a short rail spur to the main Dublin - Limerick railway line.

1-3. Geography

Situated on the northern flanks of Silvermines Moun- tain (elev.1609') the deposit lies at an average altitude of 450 feet and overlooks the broad,undulating two mile wide Kilmastulla valley.The Kilmastulla valley is bounded to the north-west by the rolling highlands of the Arra Mountains (elev.1517').All the streams draining the northern flanks of the five mile long Silvermines Mountain ridge flow into the river Kilmastulla and thence into the river Shannon just below Loch Derg.

The region supports animal husbandry,the rough veg- etated highlands and often water-logged valley being unsuitable for arable cultivation.(Consolidated Mogul Mines have utilized the poorly drained western end of the Kilmastulla valley in the construction of their mine tailings pond).Few exposures of bedrock are found in the valley due to an extensive spread of glacial drift,its thickness around Ballynoe ranging from between 3 feet to over 350 feet. The warm,moist North Atlantic airstream greatly influences the region's climate which has a mean annual air temperature of 10*C and a mean annual rainfall of some -21-

50 inches.In the prevailing westerly airstream the mass of Silvermines Mountain creates a local control over the weather.The deposit is situated in the mountain's rain shadow and the sun is often obscured by orographic-stratus cloud condensing in the lee of the 1,600 ft high ridge.

1-4. Historical background

In the first geological account of the Silvermines district WEAVER (1819) mentions,."superficial works between Knockeenroe and Gortnadine" which was a probable reference to the old Ballynoe copper mine situated 200 yards south of the barite outcrop.However,no mention was made of the barite horizon.

Credit for the discovery of the barite must be awarded to the officers of the Geological Survey of Ireland who between the years 1858 - 1860 mapped the entire Silvermines region.The officer responsible for the field survey was WYNNE (1860) who noted that in the township of Gortshaneroe, "some limestone beds contained a quantity of lead whilst others consist of a grey sulphate of barytes."

GAGES (1860) identified the mineral orpiment from Ballynoe and described, "a mass of sulphate of barytes interstratified with Carboniferous Limestone and traversed by a ser.es of filiform veins of galena and arsenial pyrites."

In the very comprehensive District Memoir,WYNNE (1861) described strata to the north of the old Ballynoe copper pit and remarks that "apparently overlying beds of dolomite and seen in two streams,there occurs a curious grey rock sometimes speckled with red spots and -22-

containing pyrites,orpiment etc.,but largely consisting of sulphate of baryta.As a consequence it is rendered very heavy because of this and although more solid looking, it is not unlike a limestone at a little distance." This accurate description of the original barite outcrop cannot be surpassed.

HALLISSEY (1923) based his description of the Ballynoe barite on Wynne's early work and commented that, "the deposit was not of very great economic importance,although of much scientific interest." Hallissey considered the possib- ility of mining the low grade zinc ores found at Ballygown, half a mile east of Ballynoe,in conjunction with the bedded barite and establishing a lithopone industry. (Lithopone is precipitated by the interaction of barium sulphide and zinc sulphate solutions and is used as an additive to white paint).

Exploitation of the deposit was initiated between the years 1956 - 1958 by the Silvermines Lead & Zinc Company, who quarried at outcrop and shipped some 3,800 tons of 80% BaSO to England as chemical grade barite,the ship- 4 ment however failing to make the required grade.

In 1959 the Silvermines Lead & Zinc Company drilled the now enlarged barite outcrop in the hope of finding an associated lead-zinc orebody,the drilling meeting with negative result.In the latter half of that year,the Magnet Cove Barium Corporation (Magcobar) examined the prospect as regards a potential source of barite for use in drilling muds,and were favourably impressed.A lease on the property was taken out from the Silvermines Lead & Zinc Company in -23-

1960 and diamond drilling commenced.The exploration of the deposit subsequently proved a multi-million ton barite orebody of 85% - 90% BaSO4 grade.

Openpit mining operations were commenced by Magcobar in 1963 and the production in 1964 amounted to 60,000 tons. Since that date the annual production figures have steadily risen and in 1974 the Ballynoe barite deposit ranked as one of the world's foremost producers of barite.

1-5. The Magcobar Operation

The mining operations at Ballynoe are conducted by Magcobar (Ireland) Ltd.,a wholly owned subsidary of Dresser Industries of Houston,Texas.The Dresser group of companies provide services and technology to the explor- ationl drjlling and production segments of the petroleum industry,Magcobar specializing in the many varied drilling fluid systems.

The gently dipping stratiform barite orebody is exploited by conventional openpit extraction methods, production control being simplified by well defined hangingwall and footwall contacts.After primary crushing at the mine the ore is railed to the port of Foynes on the Shannon estuary.At Foynes a percentage of the barite is ground and bagged for well drilling use in Europe,the remainder of the barite being shipped crude to the United States of America,Venezuela,Nigeria and Libya.Barite intended for the North Sea oil-field is shipped from Foynes to distribution points along the eastern seaboard of Scotland and stored in bulk silos ready for pneumatic -24-

transfer into the holds of the oil-rig support vessels.

The major expansion of Irish barite production in 1964 is primarily due to the commencement of mining operations at Ballynoe,see (figure 1.1),In. 1972 Ireland was the free world's fifth most important producer of mined barite (table 1.1).Production was increased in 1974 when Milchem (UK) Ltd. commenced treating the mine-tailings for barite at the Tynagh mine,Co.Galway.

1-6. The Role Of Barite In Drilling Fluids

Ground,non-chemical grade barite is used principally in drilling fluids because the mineral is heavy (4.5 density), chemically inert and relatively cheap.Barite is used in a finely ground form and must pass the U.S.standard 325 mesh sieve regulations (COLLINS 1972).The principal func- tions of a barite based drill fluid are to carry rock chippings to the surface,lubricate the drilling bit,stab- ilize the walls of the hole and to contain any sudden blowout effects when hydrocarbon bearing horizons are penetrated.

The actual consumption of a drilling fluid varies widely and is always dependent on the permeability of the wallrock and the regional/local geopressures encountered down the hole.More barite is consumed in drilling exploration holes than in production wells (BLIGH 1973).Drill fluids in exploration holes are over-weighted as a safety factor against any sudden blowouts when unknown sub-surface structures and formations are intersected. -25-

TABLE 1.1 : World Production of Mined Barite 1968-72

U.S.A. 841 977 775 748 816 W.Germany 456 473 413 409 408 Mexico 247 177 319 279 281 Italy 204 242 223 201 199 EIRE 135 160 160 160 165

(In x,000 sh.tons) Source : U.S.Bureau of Mines.

FIGURE 1.1 : Irish Production of Mined Barite 18 0-1

—350,000 tons

_300,000

_250,000

_200,000

_150,000

_100,000

50,000

18 70 19 1 d30 1 960 19E 0

Sources : HALLISSY (1923) O'BRIAN (1969) U.S.Bureau of Mines. -26-

For example,a 10,000 feet deep production well in Texas might only consume 40 tons, of barite,whilst 6,000 feet deep exploration holes in the North Sea often exceed 450 tons of barite per hole.One example is recorded from the Norwegian offshore sector of a gas well consuming over 3,000 tons of barite down the hole.Very high geopressures were encountered in this area.

Current European continental shelf demands for barite based drilling muds are in the order of 70,000 tons per annum,BLIGH (op.cit) forecasting a rise in demand in the next three years to over 100,000 tons of barite per annum.

1 —7 . ELTy:12-2.22221s2E122.114T2111AL... ..

Over the last half century active research work into the genesis of ore deposits has radically modified many of the existing concepts on ore deposition,a fact exemplified by thoughts on the Ballynoe barite.

Although WYNNE (1861) expressed no genetic ideas regarding Ballynoe in his Memoir,the deposit was described in the section dealing with the local lithologies as,"a curious grey rock." Did Wynne favour a syn-sedimentary origin for the barite?

In his general discussion on the origin of the Bally- noe barite HALLISSY (1923) postulated a metasomatic replacement of the Carboniferous Limestone and suggested that infiltrating solutions were derived from the Silver- mines Fault,The age of replacement was thought to be late Mesozoic or early Cainozoic. -27—

The very detailed work by RHODEN (1958) which dealt with the general mineralisation along the Silvermines Fault,included a short account on the barite deposit. Rhoden remarked on the lenses of strongly pyritized, "unreplaced shaley material" within the orebody and regarded the barite and the adjacent Ballynoe copper deposit to be remnants of a single and possibly much faulted ore-horizon. In Triassic or early Jurassic times,mineralising solutions diffused from the Silvermines Fault and were channelled beneath a hangingwall of chert into a carbonate host rock to form the stratiform,replacement deposit.Rhoden correctly predicted a northern and eastern extension to the barite horizon,away from the then,very small outcrop.

In late 1962 and early 1963 an intensive geophysical survey along a five mile strike length of the Silvermines Fault was carried out by International Mogul Mines of Canada.This survey resulted in the discovery of the eleven million ..on Garryard 'G' zone lead/zinc orebody,situated only of a mile to the NW of the Ballynoe barite.Some nine million tons of the 'G' zone orebody are stratiform in nature, and lie stratigraphically on the same horizon as the barite (WEBER 1964).Subse5uent exploration by Mogul resulted in the discovery of a second,stratform lead/zinc orebody,the two million ton 'B' zone,which is located of a mile to the NNE of Ballynoe.Further exploration to the north of the 'B' and 'G' zones in the Kilmastulla valley encountered low-grade,stratiform mineralisation and was deSignated the 'V' zone. -28-

The theories advanced by SNELGROYE (1966),PEREIRA (1967),RUSSELL (1968) and WEBER (1968) concerning the genesis of Mogul's stratiform sulphides are directly related to Ballynoe and will be more fully discussed in a later chapter.The above workers were in general agreement that the stratiform ores were deposited as colloidal gels in a restricted,shallow,marine basin adjacent to the active Silvermines Fault.Biogenic activity was thought to have played a major role in the deposition of the sulphides,the source of the metals being either from submarine hot springs (volcanic) or brines derived from the leaching of the underlying argillaceous sediments,

GRAHAM (1970) made some impol,tant observations regarding Ballynoe during his research into the mineralogy and genesis of Mogul's 'G' zone orebody.Graham noted that the barite horizon is contained in a succession very similar in detail to that enclosing Mogul's sulphide bodies and remarked that the 'soft sediment deformation' towards the base of the barite orebody was analogous to the gravity slumping witnessed in the basal part of the Upper 'G' zone, He interpreted the small scale interbanding of hematite,chert and barite at the base of the orebody as 'evidence pointing towards sedimentary deposition.' Graham postulates that the stratiform orebodies were formed by hot springs debouching metal bearing chloride brines into a fault controlled marine basin.The metals were precipitated. by sulphate reducing bacteria.Barium ions migrated outwards from the basin and were deposited as barite in the more freely circulating seawater. -29-

A series of lead and sulphur isotope determinations on material from both Mogul and Magcobar deposits led GREIG (1971) and his co-workers to discard the previous synsedimentary theories and to favour an hydrothermal- epigenetic origin for the orebodies.Isotope S34 values obtained from the sulphides progressively become 'lighter' upwards and away from the fault zone within the Upper 'G' zone. Greig found that the barite at the distal end of the stratiform 'G' zone and barite from the Ballynoe deposit had consistant isotope values of S34: +18°/oo.The trend in S34 values and the occurrence of barite in the peripheral areas of the sulphide zones was explained by an increase in the pH and Eh states of the hydrothermal fluids through reaction with the host rock carbonates.As the hydrothermal fluid moved upwards and away from the fault the reduced sulphur species Lecame less abundant and progressively more negati7e in S34 values whilst the oxidised sulphur species became more abundant and positive.Lead/lead dating suggested an age of 60 - 115 million years for the Silvermines mineralisation.

FILION (1973),although concerned mainly with a geo- statistical study of Mogul's 'B' and 'V' zones,noted the important role played by possible paleo-relief in controlling the geometry of the stratiform ore horizons.He envisaged unconsolidated mineralised muds meandering between 'massive islands' and strongly advocated a synsedimentary origin for the orebodies. -30--

In the latest sulphur and oxygen isotope study on the Ballynoe barite horizon COOMER (1974) found a progressive zonation of SS34 values ranging from +170/00 near the footwall through to +200/0o in the upper half of the orebody.Coomer postulates that the progressive biogenic precipitation of isotopically light pyrite in the adjacent t Gt and 'B' orebodies would leave the remaining SO in 4 the restricted basin progressively isotopically heavier.

1-8. The Present Investi ation

The aim of this thesis is to determine the geological parameters controlling the emplacement of a large stratiform barite deposit.A fundamental consideration in any genetic study of an orebody is a detailed knowledge of the geological environment.The first part of this thesis is devoted to the stratigraphical and palaeogeographical setting of the Ballynoe barite within the regional and local tectonic framework.A detailed mineralogical study of the barite horizon follows and a paragenetic scheme for the mineralisation is constructed.An integral part of the research is a geochemical study of the wallrocks and a determination of trace element trends within the barite. Differing types of stratabound barite deposits are then reviewed in the context of the geochemical cycle of barium to recognize preferential environments for the element.

The resulting data is 'objectively analysed and the results directed towards the construction of a genetic model for the Ballynoe barite,possibly enabling the prediction of extensions to the Silvermines stratiform ore horizon,and the selection of other favourable areas for -31- the exploration of barite.

All the research extending from November 1971 to December 1974 was conducted in the Mining Geology Division of the Geology Department,Royal School of Mines,Imperial College,London.A total of 25 weeks were spent in the field, with 17 weeks based at Ballynoe and the-_remainder spent sampling barite occurrences throughout the British Isles. -32-

CHAPTER TWO

THE GEOLOGICAL SETTING OF BALLYNOE

2-1. Introduction

The emplacement of a stratiform mineral deposit whether resulting from syn-sedimentation or a direct replacement of country rock,is the end product of an unusual combination of geological circumstances.Unless catastrophic, the evolution of these events is a slow process and would probably be reflected in the regional stratigraphic and tectonic history.

The footwall and hangingwall successions of a syngenetic stratifbrm mineral deposit may be indicative of the evolution and subsequent preservation of the mineralising environment:Conversly,these conditions would not apply to the emplacement of a stratabound epigenetic mineral deposit which would be more dependent on a favourable host structure and/or lithology.

With these concepts in mind a study is made of the regional and local geologic framework of the Ballynoe barite deposit.

2-2. Regj.onalS _n

The early geological history of Ireland from late Precambrian to the end of the Silurian,was dominated by a complex series of sedimentary basins within the overall framework of the Caledonian geosyncline.A variable range of sediments accumulated in these flucuating troughs,ranging from coarse greywackes through to mudstones which are in -33-, places intercalated with andesitic lavas and tuffs,the products of local volcanicity.At the close of the Silurian these sediments were strongly folded by the Caledonian Orogeny,and although a strong NE/SW regional trend was imposed on the strata,metamorphic effects were slight.The numerous hills arising from the south-central Irish plain have cores consisting of these folded Lower Palaeozoic rocks which are mainly Upper Silurian in age.(To the north of Silvermines some Caradocian and Ashgillian beds are exposed in the Slieve Aughty and Slieve Bernagh hills).

As a consequence of the Caledonian Orogeny the sedimentary basins were elevated into land of high,though quickly subsiding relief.The detritus from these weathering highlands was initially deposited in intermontane basins and great thicknesses of red,purple and grey-green sandstones interbedded with conglomerates and siItstones accumulated. The thickest development of these Devonian (Old Red Sandstone) beds are fm south-west Ireland,NAYLOR & JONES (1967) estim- ating a totally non-marine sequence of some 20,000 feet of sediment.DORAN (1973) working on the southern part of the Slieve Felim - Devilsbit inlier,12 miles SE of Baliynoe, suggests that when the effects of Hercynian folding are compensated for,the pre-Old Red Sandstone's surface is a peneplain devoid of relief.The lowest beds of Old Red Sandstone found in the Slieve Felim range are Upper Devonian and rest with marked unconformity on the folded Silurian strata dated at an Upper Wenlock (Cyrtograptus zone) age.Minor volcanic activity was evident in Upper Devonian times as witnessed by the flows of rhyolite lava south of Killarney

FIGURE 2.1 GEOLOGICAL MAP OF IRELAND

35 miles

(after Geol.Survey of Ireland)

. . • . • • • • • • • • • .. • .. . . .

Post Carboniferous Limestone in age

Carboniferous Lst.

0 : Mines & major prospects

Carboniferous ?re-Carboniferous' volcanic centres Lst.in age -35-

and numerous scattered tuff horizons.

Towards the top of the Devonian a transition from a fluviatile environment to a tidal regime occurs and many of these sediments based on microfossil faunal dating are regarded by MACDERMOT & SEVASTOPULO (1973) to be of a Lower Tournaisian,Carboniferous age.

The Lower Tournaisian succession strongly reflects the transition-of environments and consists of an alternating series of sandstones,silts and calcareous shales grading upwards into well-bedded,argillaceous limestones. These sediments termed the Lower Limestone Shales (table 2.1) are extensively developed over south-central Ireland and appear to be very uniform in character.South of the line running through Kenmare and Cloyne,the Lower Limestone Shales give way to a non-calcareous,shallow,marine sequence, deposited in a developing Hercynian trough (CHARLESWORTH 1963). Sedimentation in this trough continued to be of a dominently elastic nature throughout the Lower Carboniferous.Residual Caledonian highlands still formed positive areas to the east and north-west of Ireland,for example,the Longford Down,Leinster and Atlantean Massifs (GEORGE 1958).

Throughout the Upper Tournaisian (figure 2.2) the Carboniferous sea slowly transgressed to the north whilst carbonate mudbank complexes formed in the more stable shelf sea conditions developed in the south.The origin of these carbonate mounds or 'Waulsortian Reefs' has been investigated by DELEPINE (1951) and LEES (1961,1964).Basically they are a series of coalescing,calcilutite mounds bearing a rich fauna of fenestellid bryozoans and displaying

-Jb TABLE 2.1 Generalised Lower Carboniferous (Dinentian) Succession in Ireland

ZONE FORMATION SUB-STAGE THICKNESS D, 1,500 ft 1 Upper Limestone S . VISEAN 1,500 ft 2 Middle Limestone (Calp) 0 -3,000 ft C2S1 Waulsortian Limestone ZO TOURNAISIAN 1,000 ft 1 Lower Limestone K1 Lower Limestone Shale 150 ft

(compiled from various sources)

FIGURE 2.2 Upper Tournaisian (Waulsortian) Facies in Ireland 25 miles

•••

.v,VJ "c' cyan -0

ot ,,, - Pre-Upper 0.R.S

.....,4...--, /

oar' L,pc1g7;' -' -- 1Waulsortian Limestone

Isopachytes of Waul'ian Lst.

after LEES (1961) & MACDERMOT & SEVASTOPULO (1973) -37-

characteristic calcite filled stromatartis cavities.Crin- oidal and cherty limestones are often associated with the crests and flanks of these features.

Evidence suggesting an arid,tropical climate in Upper Tournaisian times is presented by SHERIDEN (1967) who reports the formation of evaporites along the transgressive northern shoreline exposed in County Fermanagh and by LLENELLYN (1969), who noted the occurrence of anhydrite along the southern margins of a trough parallel to St Georges Land,the easterly extension of the Leinster Massif.Recent borehole data from Derbyshire reveals sabka type anhydrite facies occurring at the Tournaisian Visean boundary and which DUNHAM (1973) interprets as e marine transgression over an arid landscape.

The Nassauian period of crustal instability heralded the Visean,and a major marine transgression submerged the Longford Down Massif and extended far to the north.The shallow-shelf,carbonate sedimentation established during the Tournaisian gave way to a deeper basinal facies and led to the formation of massive,argillaceous 'Calp' limestone.Along the shelf to basin transitional zone, reef-knolls are developed and display a marked east-west lineation.Their morphology is very similar in detail, to the reef-knolls of Craven in west Yorkshire.

Associated with the Nassauian instability are two periods of volcanic outbursts,the Lower Volcanic series intercalated with S2 Calp Limestone and the Upper Volcanic series interbedded with early D1 limestones (ASHBY 1939). The main eruptive centres were situated around Limerick and -38-

Pallas Grean,activity being focussed on a large number of minor vents.One such vent is near Annocotty and is situated only nine miles SW of Ballynoe.The Lower Volcanics are basic to intermediate in composition and range from olivine basalts through to trachytic lava and tuffs.Extreme differentiation is exhibited in the Upper Volcanics and from a number of vents ultra-mafic,picrite basalts are developed. A lens of trachyte interbedded with the earlier Tournaisian limestone was interpreted by TURNER (1952) as a lava and suggested a possible link With the volcanicity of SW England which started in Middle Devonian times and continued into the Lower Carboniferous.Ashby (op.cit),however,regarded the trachyte to be an intrusive sill of Visean age and not a lava.STROGEN (1973) demonstrated that many of the Limerick lavas were submarine in origin,the severe brecciation seen in many of the flows being attributed to the degassing after emplacement and to steam shattering effect3 arising from entrapped super-heated water.

Arid conditions continued throughout the Visean and WEST (1968) noted the occurrence of celestine nodules after gypsum and rare nodules of barite from the Sroduffy Form- ation in County Leitrim.Towards the end of the Visean, sedimentation began to outpace subsidence in the Lower Carboniferous basins and the deposition of calcareous sediments gave way to deposits of a more elastic nature.The sandstones,siltstones and shales which comprise the thick Namurian sequence are well developed west of Limerick and were the forerunners of the tropical,deltaic-swamp sediments of the Westphalian coal measures of the Upper Carboniferous. 7,397

The Nassauian earth movements culminated at the close of the Carboniferous in the Hercynian orogeny and all Palaeozoic sedimentation in the region was terminated.The succeeding Mesozoic and Tertiary strata has,with minor exception,not been preserved in the region under study and will only be discussed when relevent.

2-3. T11:2Regional Structural Setting

With reference to figure (2.1),two dominent structural trends are developed in the Palaeozoic rocks of Ireland, a NE/SW strike of Caledonian age and the E/W,WNW/ESE strike of Amorican (Hercynian) derivation.

Although the period of Caledonian compression had ceased by Mid-Devonian times(RAYNER , 1967),the effects of the orogeny are far reaching in the structural evolution of Ireland.Subsequent Nassauian and Amorican earth movements (table 2.2) reactivated many of the old Caledon- ian structures and although the E/W Amorican strike is well developed across Southern Ireland,structures across the central Irish Plain still bear the old NE/SW Caledonoid trend.

TABLE 2,2 Major Periods of Irish Earth Movement

Period of movement Extent Dominent trend

Caledonian U.Silurian-M.Dev. NE/SW (Caledonoid

Nassauian Lower Visean Caledonoid

Amorican (Hercynian) U.Carb-U.Permian E/W,WW/ESE & Caledonoid

Alpine M.Tertiary-Quatern. Caledonoid -40—

The NE/SW striking domes and periclinal inliers of Lower Palaeozoic rocks across the Irish Plain are good examples of Amorican compression resulting in a Caledonoid trend.Ballynoe is situated on the northern flanks of the largest inlier,the Slieve Felim - Devilsbit range of hills.

Major ENE/WSW striking faults often form tectonic contacts between the Silurian/Devonian strata of the inliers and the enclosing Lower Carboniferous rocks.These faults as typified by the 25 mile long Silvermines - Slieve Bernagh dislocation,normally dip to the north and often have downthrows in excess of 1,000 feet.It is relevant to note here that all the producing mines and larger prospects on the Irish Plain are located along faults of this nature.On the basis of some unusually low bouguer anomalies MURPHY (1962) postulated the existance of a major fault striking NE/SW and running a distance of 75 miles from Navan SW to Nenagh (5 miles NE of Ballynoe).Coarse greywackes of Silurian age are developed to the west of this suspected fault whilst argillaceous,shelf type sediments are found to the east (HARPER & BRENCHLEY,1972).This may imply a tectonic shelf to basin contact to a Silurian trough and that many of the dominent faults striking across the Irish Plain are in fact pre-Caledonian in age.Many of the faults associated with the Caledonian Orogenesis demonstrate complex histories of reactivation with continued movement extending into at least the Tertiary (McMANUS 1967). According to BLUNDELL (1968) Mesozoic and Tertiary (Alpine) earth movements may have reactivated Caledonian and Armorican structures throughout Ireland. The Strati r E2yOfThfm9eLina1

In Irish stratigraphy a degree of confusion exists in the nomenclature pertaining to the various stratigraphical units.Throughout the last century the Irish Geological Survey used a lithostratigraphical division for their mapping and this classification has subsequently been treated as a basis for chronostratigraphical division.Present day mining companies have often adopted these 'classical' names for similar successions found on their properties, although these rocks may differ markedly in age and lithology from the strata for which the names were originally coined.The terminology used in this thesis (table 2.3) is adapted from the stratigraphical nomenclature presented by FILION (1973) for the Silvermines area and is in common with that used by Consolidated Mogul Mines for their Silvermines operation.

With reference to figure (2.3) the Ballynoe barite deposit is located 300 yards north of the Silvermines Fault, a tectonic contact between the Silurian/Devonian rocks of the Slieve Felim inlier and the gentle-synclinal,Lower Carboniferous rocks of the Kilmastulla valley.

Silurian : Silurian shales and slates,the oldest rocks exposed in the Silvermines area,outcrop 300 yards due south of the barite deposit (figure 2.24) and are the footwall rocks to the main fracture comprising the Silvermines Fault zone.The beds strike ENE/WSW and display very steep isoclinal folding with an E/W sub-slatey cleavage being developed in the more argillaceous horizons.Varied lithologies are found ranging from very coarse gritstones,

-42-

TABLE 2.3 Stati ra shical Column Silvernines Region Lithology Name FmRal Era —Tr—Tr- limestone CALP S2 VISEAN cherts -- intercalated CHERT with limestone

\ 11 N 6

V \* dolomite breccia. IA 42 A a \ .e` DOLOMITE 02S1 dl \aVa- 7 BRECCIA IA reef limestone -7-77- barite BaSO ORE - ZONE I t 71 1168Eociethin . MUDDY REEF I shales in thin MUDDY 7-777 ,- bedded limestone LIMESTONE r 1 1 & dolomite . ' e

s\, \ dolomitic 1st. ' LOWER 6 ' vP \‘ \ & dolomite. DOLOMITE 4A V X ' Minor breccia vAtn \' X \ ,A \ horizons. 4A \ \ \'

\ 'Y \' t'ti argillaceous 7 lst.,shales with . c.c sandstone BASAL _ ..• .. , , FRAGMENTAL

.,: micaeous sand- OLD stone with silts RED Sc conglomerates SANDSTONE DEVONIAN if. '.z minor tuffs

shales Sc slate isoclinal folds WENLOCK SILURIAN

: Barite horizon Vert.Scale: 50ft = lcm. FIGURE 2e Regional Geolog d.Silvermines

BALLYNOE BARITE

RIVER SHANNON

X X X X Y x X X X Y. y'..„ Carb.valcanics

x x . X X X X x xx xx xxx x xx X x X X x X XX X X x X x x x x X x X XX X x x x XX X XX X X X X X XX X x x X X X X X xx x x X XX X x

SECTION A-B

Barite horizon -144-

arkose and grey sandstones through to a dominent succession of blue-green shales and siltstones.No identifiable fossil remains have been found by the writer although KINAHAN & WYNNE (1861) record favosites and COPE (1954) cyrtograptids and retiolitids from the district.This fauna is indicative of an Upper Wenlock age.The accompanying section to figure (2.3) illustrates the relationship of the Silurian strata to the younger rocks.

Devonian Old Red Sandstone : The angular unconformity between the Silurian shales and the overlying Devonian quartz-pebble conglomerate is well exposed on the crest and northern flanks of Silvermines Mountain.In the vicinity of the Magcobar deposit the Old Red Sandstone has beeh denuded from the Silurian by erosion and is only preserved to the west of Ballynoe,and as minor downfaulted wedges to the north of the Silvermines Fault.One such wedge forms a prominent break of slope 200 yards south-east of the barite outcrop and consists of well-bedded micaceous quartzites and minor conglomeritic horizons.Vein quartz,jasper, chaldedony and rare fragments of Silurian shale comprise the clasts in the conglomerate which are cemented in a fine matrix of indurated sandstone.Drill evidence along the southern boundary of the Magcobar property (figure 2.4) suggests that the sandstone wedges are extremely variable in composition and thickness and cannot be correlated with the more uniform Devonian succession intersected by Mogul to the north of Ballynoe ('B' & 'V' zone drill data). WEBER (pers.com) considers that the irregular sedimentation of the Old Red Sandstone sequence witnessed in this zone •

4100 N MR Muddy Reef Lst. - Pit Outline A

ti t I *11/4_ ML pf Muddy • 1st. •

. ,••••./ Lower Dolomite DoV)InIte • 9F ;=-1Basal Fragmental -•• r ecc‘c% /"/-

250 ft L oc a

old Cu/Pb l mine 0 /original

BARITE 1600 1600 ti •-• MR • • •''‘•■•••••

.•••••

.•••••• . M -- • • a io ML o. of B . . . e)

••• l 1f3 D yn tom . r) • • Devonian Sandstone .• oe • . V .. • • . • .. • • • 7.\- 'et ?... •• • • . . • . • . • • ol 4:!. • .• -'• • • • • - • . • ' Ea op • "•••• • ••••••..- CR copperper ileiaci • •• ••••■.- 8F . •. • . PL../ • . • - /V "'S./ • - - Silurian shales

4100 Looking NE of Ballynoe Plate 2.1 -Looking NE along the strike of the Slieve Pelim inlier.The hills are inliers of isoclinal Silurian shales and selvidges of Devonian Sandstone.Carboniferous Limestone lies to the left of the dashed line.(A) Devilsbit Mountain, 14 miles to the east.

a b

• .

- - ".• • 0. 1. • W • -• '

Looking NW of Ballynce Plate 2.2 -Viewing NW across to the Slieve Bernagh and Arra Mountain Silurian inlier.Note the Mogul Mine headframe and the tailings dam in the swampy Kilmastulla valley.(A) : Slieve Bernagh,14 miles NW. (B) : Arra Mountain,8 miles NNW.

-47-

is partly due to the penecontemporaneous fault movement effecting sedimentation in Upper Devonian times along an active margin to the Slieve Felim,Silurian massif,a statement with which the writer is in full agreement (BARRETT 1973).

The slow transition from the Devonian terrestrial - fluviatile conditions to the marine sedimentation of the Lower Tournaisian,renders the precise positioning of the base of the Carboniferous a matter of conjecture at Ballynoe, a typical transitional sequence being presented in figure (2.5).

Basal Fragmental (Lower Tournaisian} : The Basal Frag- mental series is the local name 01: the formation the Irish Geological Survey call the Lower Limestone Shales.The transition from an arenaceous to an argillaceous/calcareous succession is represented at Ballynoe by a series of thick black shales alternating with thin,nodular limestone horizons (figure 2.5).A marine fauna is developed in the black shales.Argillaceous limestones become more prominent towards the top of the succession in which rare colonial growths of syringopora may be found.The Basal Fragmental series thickens to the north away from the fault zone. Fossils found syTinFopora sp. (locality No.1,fig 2.14) spirifa sp. Porifera spicules ?

The Lower Dolomite : This horizon is essentially a well bedded,bioclastic limestone with partial or complete dolomitisation.The lower half of the formation is often completely dolomitised with an accompanying increase in grain size which obscures the original textural features. -48-

FIGURE 2.5 : Devonian - Lower Tournaisian transition se uence

[i 7861 DDH M.2 4095E DDH V.2 r381ya]9E

1080'

3. : Lower Dolomite (3) 2. : Basal Fragmental

1. : Devonian Sandstone

1 Scale : 1 cm = 25ft. S I t k t

t` I VI 1 1213' 4t TA-r17-1 1. I. 1' trt t /' : dolomite (2) -C-r-r 990'

: limestone

thin bedded : limestone I' I -10501

13501 nodular : limestone

:'argillite

(1) argillaceous : sandstone -1438

1150' : sandstone 464,...••■•■••

(Based on Mogul's drill data) Shale partings, importantin the lower half of the succession diminish at higher levels and thick units of either limestone or dolomite are found.Minor brecciated horizons are locally developed and are always recrystallised by dolomitisation.South of the barite deposit,the Lower Dolomite averages some 300 feet in thickness,the horizon thickening to the north where FILION (1973) reports a 490 feet thick sequence underlying Mogul's 'V' mineralised zone.An almost continuous exposure of Lower Dolomite may be traced in the stream bed forming the present western boundary to the open-pit and the following fauna was collected. flIrifa attenuatus (common) (locality No t s.21 314 fig 2.4) fenestella sp. (common) caninia gigantica (v.rare) syringopora sp. (rare)

woodocrinus SD. (common)

Muddy Limestone : This succession is a series of thin- bedded shales,argillaceous limestones and thicker limestone units,representing a gradual change to more muddy conditions.The series is partially dolomitised and contains abundant crinoidal debris.The unit is between 60 - 110 feet thick at Ballynoe and as with the Lower Dolomite,thickens considerably to the, north.

Muddy Reef Limestone : The Muddy Reef Limestone is the footwall formation to the stratiform sulphide/Sulphate orebodies developed at Silvermines and Ballynoe and may be used as an important and easily distinguishable marker horizon.The unit is composed of irregular bedded shales and thin,nodular,bioclastic limestones which bear a rich fauna.' The Muddy Reef Limestone is extensively replaced by chert in the upper part of the succession,and black chert lenses upto 15.feet thick are of common occurrence under the barite horizon.A similar thickness of chert is reported by GRAHAM (1970) underlying Mogul's 'G' zone orebody. Towards the top of the Muddy Reef succession,the diameters of individual crinoid ossicles tend to increase in size until are abrupt extinction of the crinoid population occurs. A plot of the ossicle enlargement trend is shown in figure (2.6).This size increase may be a direct consequence of changing physico-chemical environments during sedimentation,the crinoids reflecting these conditions until for some reason mass extinction occurred.Possible causes for this rapid termination of crinoidal growth will be discussed in a later section.

The upper Muddy Reef Limestone is well exposed in the open-pit and forms the southern face to the workings,When- ever unreplaced by chert,nodular shales are developed, interbedded with thin,argillaceous limestones and thick accumulations of crinoidal debris.The crinoidal lenses may exhibit severe slumping.Towards the top of the succession the argillaceous limestones may grade into calc- arenaceous beds,locally grading into thin sandstones at the top of the sequence. Fauna found : woodocrinus sp (abundant) fenestella sp (common) fragmentary corals

Green argillite : The Muddy Reef Limestone may be capped by an irregular development of green argillite which also -51-

FIGURE 2.6 : Plot of the diameter of crinoid ossicles DDH 60

0.5cm 1.5cm -150ft (ossicle diameter

-200ft

DOLOMITE BRECCIA (no crinoids in core)

-300ft

•-• - • - ._ 1 _ • • - - • - • - • - •-• _ • - • ^ Mineralised horizon

MUDDY REEF LIMESTONE -400ft

-450ft 0.5cm 1.0cm 1.5cm

Sampling interval : A 1ft section of core every 5ft.Each plot represents the 51 of 10 counts over the lft section. Location of DDH 60 : 41480E 17645N Plate 2.3 — Coral and crinoid debris developed near the top of the Muddy Reef Limestone succession.A slumped accumulation of debris. 23 X.

Plate 2.4 — Chert lens in the Muddy Reef Limestone. A complete replacement by silica of a crinoid ossicle in a matrix of chert after carbonate. 11 X. -53-

Plate 2.5 -Large crinoid ossicles in an accumulation of slump debris at the top of the Muddy Reef Limestone. Note the partial,marginal replacement of carbonate by auartz and the pressure dissolution along the contact of the two crinoid plates.The matrix between the organic debris is very carbonaceous. 23 X. interdigitates with the barite horizon.The thickest development of shale is found to occur in minor surface depressions at the top of the Muddy Reef Limestone,the shale's thickness ranging from a few inches upto a maximum of four feet.Slump structures are evident in the thicker shale lenses and rare,angular,micrc-fragments of bioclastic limestone are sometimes incorporated into the slumped argillite.On the basis of its constituent mineralogy (identified by optical and X-Ray Diffraction methods) the green argillite may be divided into two facies : a)a chlorite-illite-quartz shale J.: barite. b) a siderite-chlorite-illite-quartz shale.

Type (a) has the most widesp:vead distribution and also comprises the very important shale intercalations within the basal part of the barite orebody.Detrftal grains of quartz are readily identifiable and BERRY (pers.com) has identified rounded,detrital grains of zircon.Barite laminae and nodules whenever present in tie green shale are commonly diffuse in appearence and often fragmented by slumping,(fully discussed in chapter three).

Type (b) is defined by its siderite (FeCO 3) content and is very limited in extent,being centrally localised under the barite orebody in the surface irregularities at the top of the Muddy Reef Limestone,the shale is a paler shade of green than type (a),less laminated and not greatly effected by slumping. (Siderite is strongly developed to the north of the barite orebody,underlying Mogul's 'B' ore zone and will be discussed in chapter three). -55-

The Barite Horizon : The barite and its associated ferruginous rocks present a perfectly conformable horizon to the Muddy Reef Limestone and Green Argillite succession. and will form the basis of chapter three.

Upper Reef Limestone and Dolomite Breccia : This sequence of well bedded biomicrites and dolomite breccia forms, the hangingwall succession to the barite horizon.In the lower half of the succession the limestone has been dolomitised and heavily brecciated.This brecciation has been interpreted by GRAHAM (1970) as the product of soft sediment slumping,probably induced by gentle movements along the Silvermines Fault zone.The breccia is extremely variable in lateral extent and horizons of brecciation intercalate with massive dolomites and reef limestones (figure 2.7).. In many instances it is observed that the brecciation is initiated along angular,hairline cracks or stylolites in massive dolostone,the term t proto-breccia' being- applied to this development by the writer.A typical sequence from dolostone to a coarse dolomite breccia is tabulated in figure (2.8) where a series of diagrams cover an eight feet section of drill core.Above well developed slump planes,a multiple brecciation and graded bedding of the breccia clasts may be observed.According to FILION (1973) the dolomitisation and brecciation of the reef limestone lessens considerably to the north of the Silvermines orebodies.

A very distinctive and continuous horizon within the dolomite breccia at Ballynoe is a five to ten feet thick sequence of very thin,filamentous,dolomite laminae of a -56=-

FIGURE 2.7 : Brecciated zones in the hangingwall rocks

37 I:25ft 38 :60ft

65 4 4 4 66 4 4 • • 4 4 • 4 44 4 4 4 4 4 4 4 4 4 • 4 4 4 4 44 4 • 4 4 4 • 4 • 4 • • • 4 4 • 4 4 • • • • 4 • • • • • • 4 4 • 4 4 4 4 4 gr • A 4 4 4 4 4 4 • 4 • 4 4 4 4 4 4 44 4 4 4 4 4 4 • • • 4 4 • 4 • • • • 4 4 A a 4 4 4 •4 • 4 4 • 4 4 al& :Breccia in • 4 reef 1st. 4 44 4 • • 4 • 4 s 44 44 A A 4 • :stromatolitic band? • A A • 4 • (section along 41200E)

FIGURE 2.8 : Develo ment of breccia as observed in DDH 88

(-154')

Development of proto- breccia with well formed stylolites & Reef limestone with minor brecc- minor hairline- iation. cracks.

-i56') (-160')

Pronounced carbonaceous matrix between clasts. Repeated slumping results in a multiple brecciation. ....■•■•0•■■■•41.• -57- possible stromatolitic affinity (GURR pers.com).The stratigraphical position of this 'stromatolitic' horizon is plotted on figure (2.7),and is observed to pinch-out to the north,down-dip.

In the upper half of the succession,the Dolomite Breccia tends to become more argillaceous and is increas- ingly replaced by a black or grey chert.In many instances only the carbonaceous zones within the Dolomite Breccia are replaced,and examples are known of angular,dolostone clasts being set in a matrix completely replaced by a black, homogeneous chert. woodocrinus sp.

Fauna found : fenestel.la sp. rare corals. filamentous algae ?

The Chert Horizon : Only the basal part of this series is preserved at Ballynoe and consists of thin-bedded argillaceous limestones and shales intercalated with horizons of thick,black chert.The chert content of the succession varies between 10% - 80% in observed sequences. In the chertlfossils.are represented by cavities or a complete replacement by beekite,a variety of quartz.

In the western end of the open-pit at Ballynoe,a 20ft. thick sequence of the Chert Horizon has been down-faulted and subsequently preserved in a large,solutional collapse- pipe developed in the Dolomite Breccia.( See plates 2.6-2.8). The sequence is condensed with clay partings representing thicker,once calcareous layers.HARTRN-BRETZ (19L-0) has described identical bedded formations preserved in sink-hole

-58-

PLATE 2.6 Drag folds developed in the Chert Horizon due to its collapse into a solutional cavity developed in the underlying Dolomite Breccia.

!t> AIM

PLATE 2.7 Contact between the clays in the solution pipe and the Dolomite laSEF- 1"14211WIMIFINcilrirmiaweramezz■ Breccia.Note the typical solution weathering on the oxidised surface of the Dolomite.

PLATE 2.8 Detailed view of the condensed sequence of laminated clay and interbedded black chert. The sequence has coll- apsed a vertical dista-

nce of some 60ft from f its in-situ position -59- cavities developed in the Joliet Limestone of NE Illinois. gala L1122.912/11 This bioclastic,carbonaceous limestone succeeds the Chert Horizon and is only preserved at Ballynoe in the form of exotic blocks downfaulted in the solutional collapse pipe.The blocks which are upto 10ft. in breadth,are highly etched by solutional weathering and carry a rich fauna indicative of S2 Visean age (Middle Limestone). productus sp. orthis sp.

Fauna found : soleniscus sp. E2.112.41.21: sp. fenestella sp. syringopora sp. & crinoids

2-5. Structural Setting of the Ballynoe Barite

The Ballynoe barite horizon is contained in the southern limb of a north-easterly plunging syncline composed of Upper Palaeozoic rocks (0.R.S. & Carb.Limestone), laying between two elevated inliers of isoclinally folded Silurian shales and slates,see figure (2.3).The synclinal, Lower Carboniferous rocks are thrown against the Silurian, southern inlier (Silvermines Mountain) by an easterly extension of the 25 mile long Slieve Bernagh - Gallows Hill dislocation,locally called the Silvermines Fault,The term 'Silvermines Fault' is reserved for the entire system of major and tributary fractures found in the Silvermines, Ballynoe and Shallee area,whilst the term 'Main Fault' is used to describe only the larger and most continuous fracture.

2-5a. Faulting : The Main Fault strikes E/ENE in the vicinity of Ballynoe and outcrops 250 yards south of the -60- barite deposit,throwing basal Carboniferous shales against Silurian slates with a downthrow of at least 600 feet to the north.The Main Fault is well exposed in the open-cut at the old Ballynoe copper mine and dips to the north at 75'- 85' (table 2.4).Drill evidence (Mogul's 'Mt zone data) suggests that the dip of the fault plane grows arcuate at depth and pinches in the incompetent Silurian shales.

TABLE 2.4 FaultDeveloi tAtBalloe

Name trend 1.L throw Main Fault ESE - E/ENE 75'- 85' 300-600ft N. 2nd order en-echalon ESE 606- 85' 0-150ft N. tributary N/I\TNE 60'- 90° 50-100ft W. minor N or ENE 606 - 80* 1-4ft S or E.

Tc the north of the Main Fault in the more competent sandstone and limestone,a series of second order,en-echalon fractures strike E/ESE into the Main Fault (figure 2.9) and are responsible for the outcropping wedges of Devonian Sandstone seen faulted against Carboniferous Limestone,SE of the open-pit.McMAHON MOORE (pers.com) suggests that the pattern of these second order faults may be indicative of some wrench movement along the Silvermines Fault.Major wrench fault zones are often propogated in a series of 'pulsating' movements,the termination of these pulses often resulting in en-echalon fracturing.A very similar series of en-echalon faults are developed at the eastern end of the 30 mile long,North Craven Fault,Greenhow Hill,Yorkshire, the faults carrying lead-fluorite ores (BARRETT 1968).At Ballynoe the throws of the en-echalon faults quickly lessen 19

7 - 1 ...... - .., _. . • * 75 • . . .

. e • 71 ......

...... • '

18 '7 ...... B ZONE • •

. n... • G ZONE ... -x_ -t....'. ...„. '.1.. -.. -t. •.. -,.. • co Cl. ••■.. \ % 5N. •'...• • . . .. •••■,.. . ••■.. •N„, ....,...... ,, . . . • "t... 17 .1,.. •fts,„„ ...,.. •••4„.. CD •••...... ‘,. 0 1. .1.• -...... BARITE -,.. ••• ••••• ••••• ".... 1••• I...... 6. • .11••• ...N. • •••••• ...... 1. .... s •N,•• • n... Q ''''. ...b. ab.. ••15. ..1,." '1•• ...... • .. •••■•• ••i... '1.. 1.. ■•••‘. • . 0 ....„„ ...,.„ ..,,,.. ‘,... •••■... 1. ..1 ..1.,. "...... ,••"1 1.. •••••••• • _ ...•••• •.. •• • (1011 ...../ ...... "V • CD . e fouli 16 --- -nev ....., p,'-',,trto Ft ."1- .....e,-:‘,4 e • .....%„.. N.„,, ....- ..., •••■,...... _ N.. , ...... „:"...... ,...... os. ...,.... ''''' 7•••• -•".. •• 1.-. •-••• ..4%., A...... ,e ...... ,,,, ••-•••• ...... ,.....• ....., •'''' '''''

_ 15 10 A re 41 44 45 46

H 1000 ft (I) : First order fault : orebodies 0 : Second order fault CD faults -62-

in value away from the Main Fault.A second order fault is well exposed in the eastern half of the open-pit, striking ESE and dipping to the north at between 606 -80'. In the extreme east of the open-pit,the footwall contact of the barite is downthrown 30 feet to the north,the throw pinching-out along strike when the fault is traced 100 yards to the WNW.

North-south striking faults are developed between the Main Fault and the second order fractures,throwing the wedges of Devonian Sandstone found SE of the pit, successively to deeper levels westwards (figure 2.10).With the exception of the afore mentioned en-echalon fault,the barite orebody is singularly uneffected by major faulting.Only minor N or ESE trending fractures affect the barite with throws of less than four feet.

The three fold fracture pattern (E/ENE,ESE & N) mapped at Ballynoe is comparable to the overall fault pattern developer: along the three mile strike length of the Silver- mines Fault from Shallee to Silvermines village,the theoretical aspects of this development being discussed by RHODEN (1959).

4090E 41 75E rt 200ft ML e_ e e . • P 116 • • • e " :200ft LOWER OOL0PAITE ,------e.- • • •

- -7 -1 -I. •• .045. ..? Drawn along BASAL GmENTAL gridline :

714A 15700N. • . S 1 71/A,

FIGURE 2.10 : North - south faulting at Ballyroe

7-7 -63-

2-5b, Jointing : The dominent joint directions at Ballynoe are directly related to the main fault trends.In the barite orebody and country rock the major joint trend is SE - ESE,a direction which correlates with the second order fault system.An important north-trending set of joints in the hangingwall is not developed in the orebody,a NE set being more apparent.This deflection from N to NE is a probable function of a differing competancy during stress between the barite and carbonate rock.A slight vertical movement is the norm for the N/S set of joints whilst horizontal and vertical movement occurs in the more important ESE set.Most of the joint planes carry secondary mineralisation and this will be discussed in chapter four.

2-5c. Folding : The main fold structure which effects the Upper Palaeozoic rocks in the Kilmastulla valley is a gently NNE plunging,asymmetrical syncline of probable Hercynian age.The northern limb dips SE at 10*-15' whilst the steeply dipping southern limb is truncated by the Silvermines Fault.In proximity to the fault the southern limb dips at 60'-85°N,the flexure diminishing to the north where gentle 10*-15°N dips are the norm.The barite horizon has an average dip of 25*-35'N (figure 2.11)although along the steep,south-western footwall,dips upto 85'N are developed.In this section,bedding-plane slip is evident with slickenside gouge two to three feet long indicating considerable slippage over the 'polished' chert of the footwall. FIGURE 2,11 : The southern limb of the Kilmastulla valley syncline (Ballynoe section)

North

250 ' Silvermines 501[ Fault

BARITE

Karst collapse fill

Silurian

001 ornite / / 8r eccio

Y Reeefef t st --,,---4

---,___

fT■ PLATE 2.9 Structure of the Magcobar open-pit locking west.

In the SW of the open-pit the footwall dips steeply north averaging 70°-85'N (A),diminishing to 30'N in the central part of the pit (B) and to 10°-15'N,further to the north. The haulage roadway (B) follows the hangingwall contact between the barite and Dolomite Breccia.At (C) the north- western flank of the 'eastern dome' is exposed dipping to the NW at 10'.

Karst Drift

Barite •

Section based on plate 2,9 2-5d. Structure of the footwall rocks : A structure contour map (figure 2.12) covering an area of five square miles over the southern limb of the Kilmastulla valley syncline has been constructed using the top of the Muddy Reef Limestone as a datum horizon.The relative elevation of the Muddy Reef Limestone to Ordnance Datum,was calculated with the aid of combined Mogul and Magcobar diamond drill- log data.The top of the Muddy Reef was selected as the datum horizon because : a) it forms the footwall horizon to the barite orebody and a considerable portion of the Upper 'G' and 'B' zone orebodies. b) the horizon is uniformly developed throughout the area under study. c) the abrupt transition in lithology at the top of the Muddy Reef.makes it easily identifiable in drill core sections. d) Magcobar drilling was normally terminated at the Muddy Reef Limestone. Although the southern limb of the Kilmastulla valley syncline is an E/ENE striking structure,it is evident from figure (2.12) that many important flexures complicate the general strike.For the purpose of this study,the flexures have been classified into 'highs' or 'lows',the 'highs' being anticlinal and the 'lows' synclinal flexures. The greater part of the barite orebody is situated in a 'low' and bounded to the SE by a prominent,NW trending t high'.This 'high' is partially exposed in the open-pit as a dome of highly-silicified,Muddy Reef Limestone,and -67-

figure 2.12, 19 19

18 18

1 17

•:•:;;;71._

••••‘.. •••16... 16

- , '10; /N. "h. ••••■•• etp.

38 '39 -68-,

is hereafter referred to as the 'eastern dome'.

In order to clarify the suspected relationship between the topography of the footwall and the geometry of the barite horizon the 'Conolly contour method for revealing ore structures' has been applied to the top of the Muddy Reef Limestone (CONOLLY 1936).This technique (described in the appendix) brings out the full significance of the relationship between the footwall structures and the bar_Lte horizon,see figure (2.13).The barite orebody is contained between the 'eastern dome' and a well developed NE - ENE trending 'high'.Although the NW segment of the orebody overlaps onto a 'high',the overall correlation between footwall topography and the configuration of the barite horizon is very good.

PLATE 2.10 : The 'eastern dome' as viewed from the SW Note the swing of strike in the orebody from NE to ENE around the dome structure.On the flanks of the dome the thickness of barite. thins rapidly and is underlain by hematite (note the red stained Muddy Reef Lst footwall). ss.

,e6) 6.e.cle-)..ov I I

-+1

possib_ connecti to the 'B' zo e

FIGURE 2.13 The footwall 'highs' & 'lows' 40 ----1 .250ft 2-6. Summary

(A brief conspectus is included at the end of each chapter which summarizes data relevant to the general discussion in chapter 7). a) The Caledonian orogeny had far reaching effects throughout the subsequent geologic history of the Ballynoe area.Many of the Caledonoid structures were remobilized by Hercynian and possibly Alpine earth movements. b) Movement along the Silvermines Fault was initiated in Devonian times and may even be related to pre-Caledonian fractures.The continuous fault movement during the Lower Carboniferous was probably intensified during the Nassauian period of instability (Visean). c) A regional volcanic setting.Minor activity in the Upper Devonian and Tournaisian culminated in major outbursts during the Lower Visean. d)The Upper Tournaisian had an arid climate and probably warm seas. e) The Muddy Reef Limestone - Green Argillite transition. possibly represents a diastem (non-sequence).Detrital quartz and zircon indicate a terrestrial derivation for the green shale. f)The rich faunal assemblage found in the Muddy Limestone and Muddy Reef Limestone reflect a shelf-sea environment. g) A changing physico-chemical environment at the top of the Muddy Reef Limestone may be reflected by the marked increase and sudden termination of crinoid growth at the base of the barite.Lenses of crinoid debris are very common at this level. h) The barite deposit is a conformable horizon to the Muddy Reef Limestone. -71-

i)The soft sediment slumping in the Dolomite Breccia was probably induced by tremors derived from movement along the Silvermines Fault. j)The karst solution al collapse pipe post-dates the Visean S2 'Middle Limestone' and may have similar age relationships to the Tynagh residual or•ebody. k) The topography of the top of the Muddy Reef Limestone correlates with the geometry of the barite orebody and a definate relationship is postulated. -72-

CHAPT.LiR THREE

THE BARITE HORIZON

3-1. Introduction

Barite (BaSO4) is an integral constituent of the * Silverminesl stratiform,mineralized-horizon and commonly occurs on the periphery of the mabsive sulphide zones. The barite mined at Ballynoe by Magcobar is the only peripheral deposit of barite to be of economic importance, the others being of low-grade or minor tonnage.Although this study is based on the Ballynoe barite,the work will encompass all known barite occurrences within the mineralized-horizon.

3-2. Form of the Ball noe barite orebody

The Silvermines mineralized-horizon contains three known orebodies : ** Mogul's Upper 'G' zone orebody 9,323,100 short tons 9.2% Zn,2.4% Pb (GRAHAM 1970) Mogul's 'B' zone orebody : 2,585,200 short tons 6.0% Zn,4.0% Pb (FILION 1973) Ballynoe barite orebody : 4,000,000 short tons 85% - 95% BaSO4 (BLIGH 1973)

The mineralized-horizon : This term describes the entire zone of stratiform mineralization found at Silvermines, including the low-grade mineralization between the orebodies. ** The Lower 'G' orebody : This. orebody,underlying the Upper 'G' zone is of a fissure vein configuration and contains 2,000,000 short tons, 3.4% Zn,4.5% Pb. (GRAHAM 1970) -73--

figure 3.1

▪

38 39 41 'V I ZONE FIGURE 3.1

THE EXTENT OF THE SILVERMINES OREBODIES

19 19r-

B' ZONE

AFTER FILLION 1973

UPPER 'G' ZONE • AFTER GRAHAM 1970 • • • •••

.0 18 18 F. t. S.

•••• • •••• •

. .0 1• . 0..0 • / I /•-• /.._ •

..— • ,40

••■• • ..••• • ...E. • • . I • a. .

% • • •••• 17 •• 4.e.g.: •••• • 17 •••• • .°'• 0•20 ALA. e.."2:" max. 4 •.6 • 40 •qc. . _ .— • ' • ••• . • • • S. 5, BALLYNOE •• if( .:• • • •• ••• ••• • •1' . „.;•er .• • • • '..-7N- ... • BARITE . I •••• ..• N" . ..• • .4.- .... .•--1... Jr . •.-. •.•...•.. /- ...• ... . Z A"- . • ostA

IL •

•••••••-•• •••• ti / • ..••• • -•• • 16 16 • •• • • • .. . • ..

; Barite orebody 11•44 ao.•••••

Sulphide orebodies ./•••■• .•-••'...... -:.•:.'•....-.••••• •.• .• . . •••••• • •*.-N- 200ft .•••-■■••• /••••• Ore-thickness in ft. Eirt=E- =74= 15 15 38 39 40 41 42 43 The three orebodies at Silvermines comprise part of a composite,mineralized-horizon which extends for 11- miles along strike and at least 4 of a mile,down-dip.The orebodies are linked by low-grade stratiform or disseminated mineralization,see figure (3.1).The Magcobar barite deposit is located between the Mogul orebodies,and is 500 yards to the SE of the Upper 'G' zone and 300 yards, SSW of the 'B' zone orebody.The barite deposit is connected to the 'G' zone by a lobe of low-grade,stratiform barite, whilst a mixed sulphide-barite horizon interdigitates NNE from Ballynoe into the southern 'B' zone.For a detailed description of the geology and mineralogy of the Mogul orebodies the reader is referred to the work of GRAHAM (1970) and FILION (1973).

As previously stated,the barite horizon is conformable with the -Lop of the Muddy Reef Limestone and is overlain by the Dolomite Breccia sequence.In both strike and dip sections (figures 3.2 & 3.3) the orebody is lenticular in shape,ore-grade barite quickly pinching out into low- grade material along the margin of the lens.Economic barite mineralization extends for 2,300 feet along strike and 1,300 feet down-dip from outcrop.The average thickness of the orebody is 35 feet of massive barite,with a maximum thickness of 66 feet being developed in the west-central part of the deposit.The configuration of the barite orebody is postulated to be a direct function of the fossil topography of the footwall rocks and will be discussed in a later section.

• ..4 -75-

figure 3.2

-76-

3-3. Stratification of the barite horizon

In contrast to the adjacent,massive-sulphide orebodies which present a relatively simple mineralogy,the Ballynoe barite deposit is a complex interstratification of sulphate, sulphidel oxide,silicate and carbonate minerals.The mineralized-horizon exhibits both lateral and vertical zonation which is of considerable genetic importance.On the basis of the vertical mineral and textural variation,seven,broad, zonal divisions have been established (table 3.1).

TABLE 3.1 Stratigraphy of the barite horizon average zone thickness.density

Dolomite Breccia (hangingwall) 7. Replacement in the hangingwall 10ft 4.0 6. Massive sulphides 3ft 5. White,crystalline 'cap' barite 5ft 4.5 4. Black,microcrystalline barite 3oft 4.3 3. Spherulitic barite 5ft 4.2 2. Siliceous barite 10ft 4.1 1. Basal zone 3ft 3.8

r Muddy Reef Limestone (footwall)

The above zonal divisions within the barite horizon are extremely variable in extent,and often co-exist.For example,the white,crystalline barite of zone 5 may be found as disseminations within zones 4 and 6,whilst layers of spherulitic barite may be developed throughout zone 4. Zones 2 to 4 carry ore-grade barite and normally constitute 85% of the total tonnage mined. -77- FIGURE 3.3 NORTH-SOUTH SERIAL SECTIONS BALLYNOE BARITE

40880E

(Symbols as fig 3.2)

JRQ -78—

PLATE 3,1 : Barite stratification exposed at the eastern end of the open-pit.

(View looking due east from No.5 level)

(A):Replacement of the hangingaall Dolomite Breccia by isolated masses of grey,tabular-cr2rstalline barite, (B):White,crystalline 'cap' barite dipping south at 20°. (0): Cryptocrystalline black,ore-grade barite. (D):Siliceous,hematitic barite. (E):Green argillite,masking cherty,Muddy Reef Limestone. (F):Pod of massive pyrite along the hangingwall contact. -79--

PLATE 3.2 Stratigraphy exposed in a vertical section of the ore-body.

(Strike section,looking north from No.6 level)

(A): Thin-bedded barite underlying massive sulphide at the hangingwall contact. (B): Well-bedded cryptocrystalline,grey-black barite. (C): Hematite-rich,spherulitic and stylolitic barite. (D): Siliceous barite zone ,* (Note hammer in zone (a) for scale) -80-

3-3a. The Basal Zone : The relationship between the Muddy Reef footwall and the basal sequence of the barite orebody is of considerable genetic importance and has been studied in detail.

The development of individual mineral species within the basal zone empirically demonstrates a close correlation with the footwall topography,the 'highs' and 'lows' (2.5d) appearing to be a controlling factor over the mineralising environment.A plot has been constructed (figure 3.5) of the dominant mineral species developed over the basal five feet of the mineralised-horizon.It is evident from figure (3.5) that an intimate relationship exists between the barite orebody at Ballynoe and the massive sulphide zones developed to the west and north-east.The peripheral nature of the barite to massive sulphide is only demonstrable in the basal zone of the mineralised-horizon.

A striking example of footwall topographical control over the Lineralising environment is presented in figure (3.4),a north-south section along gridline 42.00E. The mineralogy of the basal zone in this section suggests two chemical environments (basins?),one oxidising and the other reducing and possibly separated by a low threshhold.Hematite

(Fe203) is developed on the flanks of a high (the 'eastern dome') and overlain by barite whilst a pronounced 'low' along the western margin of the 'B' zone probably contained more reducing conditions and led to the formation of massive siderite (FeCO ).Siderite development in the 'B' zone is 3 strictly limited to this trough.The stability fields of hematite - siderite and the genetic problems involved will be discussed in a later section. FIGURE 3.4 : North - south section along gridline 42.000E illustrating differing

environments Magcobar Barite !Mogul's B Zone 40f t 1-70-7A- 46 42 32 30 36 !B 16 B 56 B57 58 59 a 60 , 61 612 DRIFT • - • / • e.r

DOLOMITE BRECCIA k-g-7 Pito barite

hematite .2114117:1/49-t r ‹,% Topv NF /

: siderite /

‘12 t Oki _61/041/0 : pyrite 6 4A9 -82-

figure 3.5

4t FIGURE 3-5 •

MINERALOGY OF THE BASAL 5 FEET OF THE MINERALISED HORIZON

X • X X

XXXX X • x x X x...xXX XXXX X XXI( K ( XXX' X XX X • X•X XX Xx x X X X ... X X X X X XX X. l X XX xx XX X XX X XXXX X X X XX X %XXX XXX Xx x X X K k. XX XX xX X X K X WIWI.. XX XX X X XXX 1t. XX X: X X XXX X X K 11 X X X le X X MK X X X X X X K X XX x X .XX X X X XX X X X X X X X a I X al X x X X' X f X X XX x. X XXXxx X X X XXX KKK% X X A X K X X X X X XX XX XXX X X X X X XX X XX X ',XX XX X XXXXX XXI. X XX XY XX X X X X X x Xx), X XXXXXXx x XX X X% X X X X X X X XX X XX XXX XX XXX X XX XXX. X X X XXx x XxX ••• X XXX XXXX X X X X XX XX K X X XX/ xx ...... xxxx XX KX XXX X X X K X XX XX.Xx. X X X XX x XX XXX XX X X X Mx), X X 11( K X11 X X XX Xx X Xi X XX Wig X x . x x ...x ., .K .x K .. XXXxX XXX X X xK x ...- x X XX X X x X XX XX K.. K x KKK XXX x X • X XX X X X XX C X K * * % X X X XX X XXX XX KX X x X*. ■ .•• X X XXXXXXXXX XX XXK X X X - x Xx X Xxxx X X . x xxxxxxxxxxxxxxxxxxx x Xxxxxxxxx x xx xxxxx xx x K K xxxxxx x xx X KMX XX XXX XX XXx X X KX N. XX X XX XX . • X XX X XX X XXX X X .K.X.X.Xx 111K X X xX XX X x K Xx X x X M 2. x=+ X BICK .. X Xx X XX X X x X x X"! X x XX K X xX \ Xx x XX X XX X X X ....x.KxxX • xX X K K K % X . X K x X . X.Xx x . X \ ,xx"xx%%xi'. K x X x X. XxXx XX XX X • X X X%K K K ix XxX X X XXX XX XX XX XX X XXX% X XXX XX. X; \ . . . s . . T• XX X XXX XXX XX X X XxXx X xx X XXX x XXX XX • • .xx1. x"ItxxwKx-XCig x X . ' ' m m, xxxxxXXX_..., x XXX XXX XXX X XXXX XX X X X XX XXX XX XX XX X . XXIt X XX XXX X XXX )(lex A x x XX X X • .xxxx ..xx XXX X XXXX XX X XXX XXX X XxX X x XXXX XXX X \ x X X XXX xX X xxx" XXXXXX X XXX XX X XXX XX X X XX X XX x XX XXX XXX K .9 40, K . x x.4 xx l ',i x ,im XX XX XX x X X X XX X X X.XXX x xx X X . x xx Xxxxx XXXX X xXX x XXX X ItxX XX 'Ix X .1 xXXxX XX XX - x Xi'' X X n x - x - X XX' W X K ... x X XXX Xx XIX X XK X X X XK % XX X xxxxxX X X X xxxx2. xXxxX xx Xx X 1 XX X X X X K XX XX XXX X x XX X xX xlax xXxx x. .% X X X1IX X XXX X X KY X X XX X XX X XX XxX X x XX K X XXX I ..XX XxX X XX X X X XX x X X X X X X XX X X XX • K X X XX XX X XX XX X X XX XX K X xX X Xx K X X XXX le X X X Xx X IK X Xxlel r x K • r 21 x X., • 1 ..X X x • s t X XX x X X XXX X x %XXX x XX XxxXX x X. XX x Xx.x • 141X.xxxxx xxxx xxxxx UK xx x • • 1XX lexxxx xxxxxx xX xx • • X X K xx xxx X Xx xX xxxxx xxxx xxxxxxxxx • . x .-X-xxxxxxxxxxxxxXxXx xxx It x xx N... X It. -x xxxXxx xxxxxxxxxxxxxxxxxxxxx xx - * X "X --k% * * X ,, k X * XXX XXX XXX XX XXX X xx A x x 1,,, *,, X XX X X k.,,,, X X X X X X X X X X X X X k M %Mx x*x ::::;\ X X X X X X X f X X X X X X X X X X X X X XKK XX XXX XX X K 11114K X% X XX XX • XX X Kjc • XX • X% X XXXXXXXx It% XX X X1(kft XXX). XXI, X If X X X X X XIfX X X X X X XXV X X KX K XX X X X U •K X x X >I x x X X X X X XX KK Xx X %XXX Id Kr x XX x X X %Mx X XX x x"' ••X K x •

100ft

•16 MASSIVE PYRITE

WEAK PYRITE

SIDERITE

BARITE

WEAK BARITE

HEMATITE _

BARITE BRECCIA

—APPROX. LIMIT OF MINERALISATION

15 38 40 41 -83-

The basal zone of the mineralized-horizon at Ballynoe may be sub-divided into the following types : i)barite breccia. ii)banded hematite-barite with massive jasper. iii)replacement of the footwall by barite and pyrite.

i) Barite breccia : The development of barite breccia is associated with local changes of slope in the footwall, and its formation may be exemplified on the flanks of the 'eastern dome'.0n the north-western flank of this footwall

I high',1ensoid masses of siliceous,crinoidal debris are overlain by pyritic,green shales and thence a thin,baritic breccia sequence.The barite breccia consists of scattered iclasts of brick-red to pink barite set in a matrix of highly-slumped,green argillite.Fragments of bioclastic limestone are not infrequent in the breccia.The barite' breccia clasts may be angular,rounded or diffuse.The diffuse barite occurs in zones of intense slumping and is often sheared and invaded by slivers of green argillite parallel to the plane of movement.The slumped material has been subjected to secondary silicification and pyritisation, see plate (3.3).The fact that the barite breccia is confined to the flanks of the 'eastern dome' suggests gravitational slumping and the existance of the topographical 'high' during early barite deposition.The barite breccia sequence rarely exceeds 20 inches in thickness.

Thin lenses of green argillite persist within the barite orebody for upto 12 feet above the footwall contact and are probably what RHODEN (1958) referred to as,'unreplaced shaley material parallel to the original -84--

PLATE 3.3 Barite brecciaLlaslialmjaLmllle

(A) Barite in the early stages of fracturing, almost pseudo-stylolitic in appearance. (northern flank of the 'eastern dome')

(B) Diffuse barite in slumped,green argillite. The structure of the barite is indistinct due to silicification. (NW flank of the 'eastern dome')

(D) Strongly sluped argillite with very sheared slivers of barite.Marginal replacement of barite by euhedral quartz at (a). (northern flnk of the 'eastern dome')

(E) Diffuse barite in slumped argillite. Extensive replacement of barite by quartz. (locality as B)

(F) Angular,red barite clasts in strongly slumped,green argillite.Note the carbonate clast at (a). (locality as B)

- 85-

PLATE 3.3

A - X 32 -

X 3? D

F X 0.8 -86- bedding.' No allothigenic barite fragments'have been identified from the interbedded shale lenses which are extensively replaced by barite,pyrite and jasper.

A zone of thick,barite breccia is developed in a 'low' situated in the south-east of Mogul's 'B' zone orebody.The brecciated sequence is upto 28 feet thick and consists of sub-angular clasts of micro-crystalline, brown barite,set in a muddy carbonate matrix.Typical morphologies are described in plates (3.4 - 3.5). ii) The bedded hematite formation : This very interesting,conformable,ironstone horizon is analogous to the Tynagh bedded ironstone formation (SCHULTZ 1966), although developed on a very much smaller scale.The bedded hematite at Ballynoe is unique to the barite deposit,no comparable formations being reported from Mogul's 'G' or 'B' zones.The hematite horizon averages 2 feet in thickness and is best developed under the southern half of the orebody,pinching out entirely down- dip to the north.The horizon consists of lenses of massive hematite (upto 1 ft thick) in a matrix of hematitic-barite and interlayered with goethite and jasper slivers.Rare magnetite has been identified (X-Ray Diffraction) from crushed samples of massive hematite.Evidence suggests that the hematite was laid down as a sediment in a dynamic environment. Soft- sediment slumping and penecontemporaneous micro-faulting (plate 3.6a) are of frequent occurrence throughout the horizon.Wherever the hematite horizon is underlain by green argillite the sequence is balled-up and highly brecciated.lt is possible that the -87-

ElAWILTIL : Barite breeeiq.122121112ZPSM2E1211 '13' zone orebody

(A) A very compact breccia composed of coarse and fine grained barite clasts,evidence for considerable slumping.

DDH B.71 -500 ft. X.22

(B) Angular,wedge of barite breaking away from a larger clast.The light brown smears in the barite wedge are due to replacement by iron- stained carbonate.The matrix to the breccia is very carbonaceous.

DDH B.71 -510 ft. X,22

). A muddy-carbonate slump plane separaiAng coarse crystalline barite from a finer grained variety.Note the truncation r)f the bladed barite crystals at (a).

DDH B.71 -520 ft. X.22 `7 ,VIXT, ?'M trxnema sraerin-wranomram-rffirrsm7pwrmeorata, - :-VG1s="77.., " .TAOLSows -89-

PLATE 3.5 : Barite breccia from the SE of Mogul's t B z9ne9222291y

(A) Strongly slumped slivers of barite in a muddy,carbonate matrix.Such diffuse barite clasts are rare from this locality. DDH B.71 -515 ft.

(B) Coarse and fine grained barite brought together by slumping.Minor pyrite is localised along the slump-plane contact. DDH B.71 -500 ft.

(0) Small,sub-angular barite clasts in a very carbonaceous matrix. DDH B.7I -517 ft.

(D) Highly contrasting barite fragments in juxtaposition.The white clast shows evidence of probable recrystallisation along its left-hand margin. DDH B.71 -502 ft.

(E) Diffuse barite bearing a similar morphology to the slumped barite developed in the Magcobar open-pit. DDH B.71 -515ft

(F) Slumped barite clasts acting as a nucleus for late stage,euhedral pyrite. DDH B.71 -505 ft PLATE 3.5

A - X 32--

- X32-

E - X 32 - -91-

upper surface of the green shale acted as a plane of decollement to the overlying hematite formation and initiated the slumping.This arguement may also apply to the brecciated hematite sequences found on the flanks of the 'eastern dome'.Further examples of slumped and faulted hematite are presented on plate (3.7).

Although a continuous ironstone horizon cannot be traced down-dip it is suggested that the hematite grades into siderite.Siderite is locally developed under the north- eastern margin of the barite orebody (see figure 3.5) and as previously noted a siderite sequence upto 30ft thick underlies the western segment of Mogul's 'B' zone (figure 3.4),If we accept the thesis that the hematite and siderite are of syn-sedimentary origin and were laid down in a marine basin,a restricted environment (partial stagnation) would be required for the formation of the siderite.Table (3.2) after GARRELS (1960) is a plot of the Eh-pH stability relations among iron oxides,siderite and pyrite at 25'0 and 1 atm. total 'pressure.it is possible that the water circulation in the basin may have been controlled by the palaeo- topography of the Muddy Reef Limestone. TABLE 3.2 0.8 0.6 1.:hematite Fe203 2.:siderite FeCO 3 0.4 3.:pyrite FeS2 (Eh) 0.2 4.:magnetite Fe 0 3 4 0 -0.2 -0.4 -0.6 (after GARRELS 1960)

10 12 (pH)

VIP -92-

PLATh 3,6 : The bedded hematite formation

(B) X.O.7 Slumped fragmental hematite in a green argillitic matrix.The white streak is secondary barite of a replacement origin.

(A) X.0,7 Banded hematite,goethite and hematitic barite.Minor slumping associated with penecontemporaneous faulting is developed in the hematite.

(C) .A four foot section of the Muddy Reef Limestone - barite orebody contact exposed in the base of the open-pit.The basal zone of the mineralised-horizon consists of 14" of massive hematite resting conformably on 2" of Green Argillite and thence cherty,Muddy Reef Lst.A minor fault downthrows the contact 2ft to the souLh.Hematitic-barite overlies the hematite. -93--

PLATE 3.7 : Slumping and faulting in the hematite horizon

Slivers of hematite in a matrix of hematitic barite.Marginal alteration of hematite to goethite (dark blue in colour).Note the secondary introduction of white barite which is free from iron colouration. crossed-nicols X.69

Hematite faulted by penecontemporaneous movement in a matrix of red,hematitic barite. crossed-nicold X.69 -94-

4 iii) Replacement of the footwall by barite : The morphology of barite which replaces the footwall rocks is very distinctive and under the microscope is easily differentiated from the allothigenic barite found in the basal argillite sequence.The replacement barite normally occurs as stellate crystal groups and is always white to translucent in colour (plate 3.8).Although the stellate barite crystals are developed in a very siliceous environment upto 10 ft. below the footwall contact with the mineralised-horizon,they are free from any silicification. This suggests an emplacement which post-dates the chertif- ication of the Muddy Reef Limestone.

3-3b. The siliceous barite zone : The gradual transition from'bedded ironstone into siliceous,iron-rich barite is marked by streaks and lenses of brilliant-red jasper.Two types of jasper have been identified and probably represent different generations.A colloform variety is associated with hematitic barite (plate 3.9a) whilst a second variety replaces pyrite euhedra (plate 3.9b).

The colloform jasper is composed of coalescing spherulites about 100 microns in diameter and enclose amorphous,vuggy jasper.Late-stage barite often infills the vugs.A feature common to the colloform jasper and not the replacement variety are dehydration (syneresis) cracks, often infilled with white barite.The cracks which are wedge shaped,pinch out towards the centre of the jasper lens and according to GROSS (1972) are typical of the texture when dehydration of a silica gel takes place.The thicker -95--

EL:4'1w : Replacement of the footwall by barite

(A): Typical radiating 'stellate' cluster of tabular barite crystals,The barite is replacing very cherty,Muddy Reef Limestone.Note the absence of silicification within the barite crystals. X.22

(B): Barite replacement in green shale from the flanks of

the 'eastern domel ,Compare the morphology of the fF ill replacement barite to that of allothigenic barite (plate 3,4) within the same type of sequence. X.22 -96-

PLATE 3.9 : The development of jasper

(A): Colloform jasper associated with hematitic barite.Note the iron-free barite (late-sage) infilling some of the vugs and cross-cutting the jasper. X.31 (B): Hematite clouded quartz or jasper? replacing and pseudomorphing pyrite crystals.From the basal,silicec_us barite zone. (in X-polars) -97-

lenses of red jasper whenever uneffected by syneresis cracking are almost of lapidary quality.

However, the high silica content of the basal barite is not only due to jasper which is normally restricted to areas of hematitic barite but primarily due to the extensive replacement of barite by free quartz.The pattern of quartz replacement is strongly controlled by the crystalline fabric of the barite and as a consequence a tabular meshwork of barite and quartz is often developed (plate 3.10),In the siliceous barite zone the quartz content of the barite maybe as high as 10% by volume.The intensity of quartz replacement quickly diminishes above the ± 10ft.thick siliceous zone although isolated,prismatic quartz crystals may be found throughout the upper orebody.The dispersion of silicon in the Ballynoe barite is graphically presented in figure (5.8).

33c. St lolitic and S herulitic barite : Stylolitic and spherulitir! barite is confined in development to the central and thickest section of the orebody,the zone being very poorly defined in the east where the barite thins rapidly over the 'eastern domei .An empirical relationship is observed between the formation of stylolites and the occurrence of spherulitic textures in the barite.Zones of extensive stylolitisation in fine grained,grey-black barite tend to be overlain by layers of coarse,spherulitic barite crystals, the spherules often being pink to dark red in colour due to tiny inclusions of hematite.

Using the stylolite classification established by PARK & SCHOT (1968) the stylolites developed in the barite -98-

PLATE 3.10 Silica in the barite

A. : Red jasper (j) replacing hematite in the basal,interlayered barite/hematite formation. Quartz is partially replacing the barite (Ba).

B. : Jasper completely replacing hematite in the basal barite formation. Jasper :(j)

C,D : Extensive replacement of barite by quartz. The tabular crystallisation of the barite is controlling the geometry of quartz replacement. In the siliceous barite zone the quartz is always amorphous and never crystalline.Minor prismatic quartz crystals are only found in the upper orebody ond white 'cap' barite.

E. : (Slide etched by hydrofluoric acid) Major quartz replacement of barite and strongly controlled by the barites fabric. Quartz : black Barite : white

PLATE 3.10

• •••

'1'74 47

1 ! -^ I "t, 1, P4-71tir •• - 4 • .4k '

A -X32-- B

X 32 - 0

X32 r100-

orebody fall into two classes : i) horizontal-simple. ii) horizontal-sutured. Horizontal-simple stylolites (plate 3.11 a,c,e) tend to be independent of the original barite fabric which is truncated at random.The very carbonaceous composition of the stylolites probably represents the insoluble residue left from the original barite.In contrast to the simple stylolites,the horizontal-sutured variety are narrower in width,display a greater amplitude and have a tendency to be localised along the margins of megacrystalline barite 'fans' (plate 3.11 FIGURE 3.6 : Itylolite classification

X.69 Horizontal-simple X.69 Horizontal-sutured

According to PARK & SCHOT (1968) the simple and sutured classes of stylolites are,"most frequently found in layered sedimentary rocks which are little affected by tectonic activity." The occurrence of stylolites in barite was first reported by PARK (1962) in material from the Cave In Rock district,Illinois,followed by ZIMMERMANN & AMSTUTZ (1965) who described stylolitic barite from Arkansas.A comparable stylolitic fabric to that of the Ballynoe barite is reported from the Meggen,stratiform barite deposit,Germany.According to ZIMMERMANN (1970) -101—

PLATE 3.11 : St7lolite formation in the barite

A,B Simple-horizontal stylolites developed in

spherulitic barite.The stylolites are parallel to the bedding and occur at crystal interfaces.

C. : Simple and sutured stylolite formation.Note the differing barite fabric between the stylolites.The simple stylolites have thicker carbonaceous partings than the sutured type.

D,E : Modes of occurrence,simple-stylolites.

F,G : Well formed sutured-stylolites truncating plumose barite.The continuity of individual stylolites is well illustrated on plate 'G'. PLATE 3.11

A X32-

C -X32-

F - X32 -103- fine grained barite is separated from nodular and coarsely granular barite by stylolitic layering,a sequence which is identical in detail to Ballynoe.The diagenetic implications leading from the presence of stylolites within the barite orebody will be discussed in chapter four.

Layers of 'spherulitic' and coarsely-crystalline, nodular barite are associated with the zones of stylolitisation.Aggregations of 'spherulites' form thin,colloform layers of red barite which are conformable with the bedding and maybe followed along strike for tens of yards (plate 3.12c).The radiating crystal groups have cores of grey-black barite which progressively becomes hematite rich towards the outer margin of the crystal (plate 3.12d).The colloform layering is occasionally replaced by mega-crystalline, cream coloured barite which is often banded by the incipient growth of iron-rich 'spherulites' (plate 3.12b).Associate. with this type of barite ar•e clots of 'zebra' textured barite,consisting of alternating,spherulitic layers of white/grey or pink/grey banding.The bands are upto one inch in thickness and present a very striking texture. Identical 'zebra' textures have been found by the writer developed in barite nodules which replace the Lower Magnesian Limestone (Permian) at Bramham,west Yorkshire. The above textures are considered to be derived from a diagenetic,recrystallisation of primary barite and will be discussed in chapter four.

3-3d. Massive grey-black microcr stalline barite : The greater part of the orebody consists of well-bedded,grey to black barite of a very fine and uniform texture.In

v.- -1oL-

PLATE 3.12 : Spherulitic barite

(A) Spherulitic barite development.Red,iron-rich spherulites in a matrix of grey-black barite. (18 ft above the footwal1,4100E,1645N).

(B): Crystalline white barite associated with the spherulitic zone.Note incipient growth of iron rich banding and its displacement by micro-faults. (22 ft above the footwal1,4150E11500N).

(C): A two feet thick,conformable,spherulitic zone overlying the siliceous barite horizon (streak of red jasper near the contact at the lower left). Note the thicker-bedded,siliceous barite horizon in compari-ion with the gently flexed and thinner- bedded barite above the spherulitic zone.

(locality as Pi),

(D): Photomicrograph of the iron-rich (hematite inclusions) margin to a spherulite.Note how the cores of the crystal 'plumes' are iron-free, X.32

(E): A similar fabric to (D) showing an almost total replacement of a barite crystal 'plume' by iron enrichment. X.69 -105- PLATE 3,12: LEherulitic barite

D -106— appearance specimens are not unlike a dark anhydrite or a bituminous limestone.The fabric of the barite consists either of a compact aggregate of microplumose crystals (with no preferred orientation) or looser aggregates of microspherulites (plate 3.13a).The micrspherulites .(not to be cCifused with the 'spherulitic texture' described in 3-3c) are upto 0.5mm in diameter and commonly exhibit a cruciform extinction (plate 3.13b),The microspherulites represent the primary crystalline state of the barite,a stage which is often obscured by diagenetic-recrystallisation. A comparable texture is again found in the Meggen barite depodit and according to ZIMMERMANN & AMSTUTZ (1971), spherulites are an indication of a possible 'sedimentary origin.' Spasmodically replacing the above mentioned fabric are patches of a coarser,plumose barite (plate 3.13c) which exhibits an undulose strain extinction.Associated with these plumose 'fans' is a definate recrystallisation fabric which takes the form of anhedral barite grains developed along 'fan' terminations or bladed crystal boundaries (plate 3.13d).Within the plumose 'fans' the crystal boundaries have a tendency to be stylolitic and the anhedral barite grains may represent reprecipitated material from stylolitic solution. Stylolite formation in the crystal 'fans' is shown in plate (3,13e).

Rare 'clots' of carbonate are disseminated along strike within the lower half of the microcrystalline barite zone,the carbonate being partially replaced by a coarse meshwork of acicular barite crystals (plate 3.13 e,f).This carbonate (calcite) may have been derived by ex-solution -107-

PLATE 3.13 : The microcrystalline barite zone

(A): A compact aggregate of microsherulites, the typical fabric of massive,grey- black barite. (15 ft.below the hangingwall, 4130E.1645N).

(B): Well developed cruciform extinction in a microspherulite. (22 ft.below the hangingwall, 4130E.1645N).

(C): Plumose barite crystal,note the strain extinction marked at 's'. (10 ft.below the hangingwall, 4135E.1625N).

(D) Terminati-m Of a plumose crystal group,with the development of a recrystallisation fabric marked at 'x'. (locality as iCP.

(E): Stylolite development along the margins of barite crystal laths,with minor recrystallisation. (locality as Ci).

(F & G) Acicular barite crystals replacing 'clots' of carbonate within massive barite. (28 ft below the hangingwall, 4115E,1620N). PLATE 3.13

A X32

- X32- C

r) -X69-

•••

-69X- ▪ • . -109-

during the primary crystallisation of the barite horizon.

3-3e. Maasjae heorebod. : The microcrystalline barite zone is rarely in direct contact with the hangingwall dolomites and is normally overlain by a sequence of massive,stratiform sulphide and/or a macrocrystalline,white barite.The stratiform sulphides which are. upto 4 ft.in thickness,are best developed over the western end of the barite orebody.The sulphide horizon which consists of massive pyrite and disseminated galena/ sphalerite,attains its maximum thickness in 'troughs' controlled by the very undulose,upper contact of the barite orebody (plate 3.14).The barite-sulphide contact at the base of the 'troughs' consists of laminated,plumbiferous argillite grading upwards into massive pyrite carrying disseminated galena and sphalerite mineralisation.The thinner development of pyrite overlying the crests of the Undulations,tends to carry less galena/sphalerite than the pyrite in the 'troughs',see figure (3.7).

FIGURE 3.2 : 'Trou hs' in the stratiform sulphide horizon V 7PV1' It vurP u r r DOLOMITE r v r r I BRECCIA •• • ' • :1 ft ; '• • • • -• .• • • - '• • 0 •• •. • • •• • • A 04' • 'MASSIVE . * : • • "' • . .- • • •. • SULPHIDE

Pb & Zn muds BARITE OREBODY

Wher the stratiform pyrite horizon is traced eastwards along strike,the pyrite gradually pinches out into a thin, 2 to 3 inch thick layer of laminated,pyritiferous argillite carrying visible galena mineralisation.Although very thin, the plumbiferous argillite is remarkably consistent along -110—

PLATE L.:LL : Stratiform sulphide 'cap' to the barite

(A): Stratiform pyrite,1 1 to 3' LI thickness overlying the microcrystalline,orebody barite.Note the very undulose contact between the barite and sulphide.The downfaulted chert horizon in the solutional collapse pipe is exposed in the bench above the pyrite and marked 'c).

(B): Sulphide trough in detail.The trough is 4' thick and contains a 4" rib of massive galena along its lower contact. Note the blue,iron sulphate efflorescences on the barite derived from the weathering pyrite.The upper surface of the pyrite has been altered to goethite. strike and was traced for over 30 yards,the contact with the overlying Dolomite Breccia being sharp and well defined. Downdip,the sulphide horizon thickens considerably and a 12ft.thickness of massive pyrite has been intersected along the northern margin to the barite orebody (see figure 3.3c).

3-3f. Macrocrystalline barite 'cap' to the orebody In marked contrast to the stratiform sulphides,a white and highly crystalline barite overlies the eastern segment of the orebody.Three facies of macrocrystalline barite have been differentiated : i) barite conformable with the stratification and capping the orebody barite. ii) irregular patches of white barite replacing the black, microcrystalline barite within the orebody. iii) extensive hangingwall replacement by the white barite.

The macrocrystalline (type i) barite is hereafter described as the 'cap' barite.The 'cap' barite is pure white in colour and is composed of a coarse aggegate of macroplumose crystals upto 3" in length.The horizon varies between one to four feet in thickness and was originally best developed near the surface over the 'eastern dome' (STEWART pers.com). Masses of reniform pyrite are not uncommon within the basal development of the 'cap' barite (see chapter four).

Where the orebody is gently flexed along strike over the 'eastern dome',1arge,irregular patches of macrocrystalline, white barite replaces the black,orebody barite (figure 3.8). The replacement is a transitional process,the original barite initially being replaced by a 'porphyritic texture' of white,tabular crystals,the crystals gradually coelescing -112-

FIGURE .8 : The three types of white,macrocrystalline barite

-T--1 1 11 11 ec2 , . t

v (ff cOT

(reniform pyrite : conformable white barite (type i) orebody barite : irregular repl.in Muddy ?..eef Lst Footwall the orebody (type ii) . 1 Oft : repl.of the hang- : ingwall (type iii) I EAST

The actual occurrence of white,macrocrystalline barite along grid-line 42.300E is presented on figure (3.9),The section illustrates the eastern periphery of the orebody.

PLATE 3.16 : Macrocr stalline white & orebody barite

X. 02_2 (A): Highly crystallirie,white barite found replacing the Dolomite Breccia in the hangingwall. (B) Microcrystalline,grey-black orebody barite. FIGURE 3.9 16050N NORTH -SOUTH SECTION OF THE EASTERN PERIPHERY

OF THE BARITE -114- until the original fabric is completely replaced.

Over the north-eastern and eastern periphery of the orebody,the hangingwall is extensively replaced by a greyish-white,highly crystalline barite (plate 3.16).This barite is characterised by a high calcium and magnesium content,in part,due to inclusions of calcite and dolomite (plate 3.17 b,c,d),Irregular replacement of the hangingwall by barite may extend for upto 50 ft. above the orebody.

It is suggested that the white,macrocrystalline barite is of a secondary origin and probably represents remobilized barium liberated from the parent barite deposit. Agents resulting in remobilization and the obvious control played by the 'eastern dome' are discussed in chapter fol'r.

Associated with the development of secondary barite are crosscutting veinlets of thin barite (1" wide) which extend across the orebody from footwall to hangingwall,a vertical distance of 30 ft.plus (plate 3.15).The veinlets trend NE/S7: (a dominent joint trend) and invariably dip to the east at between 70' - 85'.The vein barite carries no sulphides.

Plate 3.1 5 Two barite veins cross- cutting well-bedded barite.The oxidised surface of the barite is coloured by hydrated ferric oxide waters derived from the overlying sulphide 'cap' -115-

PLATE 3.1/ : Diagenetic t secondaryLlarite

(A): Typical mega-bladed crystals in the 'cap' barite.Unlike the crystal boundaries within the orebody barite no stylolites are developed.

(B) Rhombohedral dolomite crystals replacing secondary' barite.The barite is from the 'cap' zone.

(C): Stringers of calcite veining 'secondary' barite which is developed in the hangingwall. (The slide has been etched with 10% HC1).

(D) Megacrystalline barite 'fan' replacing the hanginuall carbonate (Dolomite Lreccia). Compare the nature of crystallisation with the stratiform 'cap' secondary barite (A). i 6-

PLATE 3Q17 : Dia enetic 'secondary' barite

• A. • , • ir

• frir. • A.. • • !. 1 •••• •••

, ' Attr • ■ - ••, .; 1 :Ot• •Ye • ,4t-••••• • • A x.31 •4 B x.31

C x.31

••• -117—

3-4. Other barite occurrences within the mineralised-horizon

It may be seen on figure (3.5) that barite is periph- erally related to the massive sulphides of Mogul's Upper 'G' and 'B' zones.To determine if this relationship has any genetic connotations with respect to the Ballynoe barite, the nature of the occurrences are categorised.Barite mineralisation intersected by drilling in the Upper 'G' zone falls into three groups : i)stratiform barite denoted on fig. 3.10 as tt ii)barite disseminated in pyrite as A iii) barite disseminated in the wallrock as 0

Group i) : The NW trending lobe of thin,stratiform barite which intersects the eastern margin of the Upper 'G' zone is directly related to the Ballynoe deposit and consists of microcrystalline,hematitic to grey-black barite.Barite of a similar nature occurs as an isolated lens along the northern extremity of the 'G' zone where a 9ft thickness is developed, see figure (3.10). Group ii) : Barite is very rare within the stratiform,massive sulphides.Exceptions to this statement occur on the northern and western margins of the zone of 30ft thick pyrite and is found disseminated throughout the basal zone of the sulphide or in association with brecciated sulphide sequences. Group iii) : Barite is weakly disseminated throughout the wallrock on the western and north-western periphery of the Upper 'G' zone.The barite may overlay or underlay the sulphide horizon.

In the 'B' zone the occurrence of thick-barite breccia under the SE segment of the deposit has already been documented -118-

FIGURE 3.10 : Barite occurrences in the Upper 'G' zone

600ft m --. limit o 'G' zo e / 0 ! or-body / 162 n ! - . 0 i . s Airgi- • lr 0 ..,..../ 1 1 , -, 104 149 .„, Ar ,-. I'S --. 11- 4.y. m N. m '8i,—. 'r -IL A n ,:•..! - . 19 . --,,_ "X- -.,,,

--1:: "N... ::

(stratiform) - -,_ . , pyrit .., thicker than 60ft. --._ --1,_ 37 -,, 38 3 9 -, qp

1,1 : stratiform barite barite below sulphide 76— . barit() above sulphide, A : barite in sulphide

(Numbers refer to core sections depicted below)

e_t,crt keft

1 -.v4

D A A G. G.162 G.10 G.60 149 G.70 G.104 (Muddy Reef Limestone contact)

(Barite : red, Sulphide : black) -119-

(plates 3.4 & 5). To the north of the 'B' zone sulphides a considerable amount of white,megacrystalline barite disseminated in the Dolomite Breccia and is considered by the writer to be 'secondary barite' in origin.

With the exception of the stratiform (type i) barite the minor barite mineralisation in Mogul's sulphide zones is probably related to the outward migration of BaS (Ba would be soluble in the environment needed to precipitate sulphide) and precipitation of BaSO4 occurred in areas of higher redox-potential ie., the flanks of the basin.

3-5. Summary

1. Barite is an integral part of the Silvermines,stratiform,

mineral-horizon,economic tonnages and grade only occurring within the Ballynoe deposit. 2. The barite horizon may be divided into stratified zones, from the hematitic basal zone through to the cryptocrystalline barite in the upper half of the orebody.A considerable amount of white,m-igacrystalline 'secondary' barite is emplaced in the hangingwall. 3. Many sedimentary features are evident in the barite horizon : slumping,brecciation,de-watering structures, stylolitisation and recrystallisation.

4. The black,cryptocrystalline barite is overlain by a massive pyritic 'cap' with laminated Pb and Zn rich muds marking the contact. The pyrite thickens on the northern margin of the barite whilbt to the east it pinches out on the flanks of the 'eastern dome', 5. Megacrystalline 'secondary' barite is developed over the 'eastern dome' and occurs in three distinct facies. 6. Most of the barite occurrences in Mogul's sulphide deposits are related to the formation of 'secondary' barite.Exceptions are the barite breccia sequences underlying the SE of the 'B' zone and the stratiform barite lens to the NE of the Upper 'G' zone. -1 21 -

CHAPTER FOUR

THE MINERALOGY OF THE BARITE DEPOSIT

4-1. Introduction

This chapter is devoted to the mineral assemblage associated with the Ball,ynoe barite and to the roles these minerals played in the paragenetic evolution of the deposit.

Previous work by GRAHAM (1970) and FILION (1973) has fully described the mineralogy respectively contained in Mogul's 'G' and 'B' zone orebodies.Both writers stressed the genetic significance of the sulphide flow structures and colloform sulphide growths developed within the ore- zones.Graham (op.cit) paid particular attention to the abundant framboidal pyrite textures associated with the 'G' zone sulphides.

At Ball3inoe,a close correlation is appak.ent between the structural habit of the sulphides and their relative position within the 'stratigraphic' barite zone established in chapter three.Within the orebody,sulphide textures are so characteristic of a particular barite zone that their presence under the microscope may be used as a diagnostic feature of that zone.

Of the 30 plus mineral, species presently identified associated with the barite deposit,only pyrite is the ubiquitous accessory mineral,comprising some 5 - 10% by volume of the barite horizon.

-122-

4-2, Minerals associated with the barite horizon

The following mineral species have been identified from the Ballynoe barite deposit

SULPHATES CARBONATES ** Barite BaS0 Calcite Ca00 3 Gypsum * CaSO4 Dolomite (CaMg)CO3 Anglesite * PbSO4 Ankerite Ca(MgFe)C07 Melanterite FeSO4.7H20 Siderite FeCO 3 Pisanite (FeCu)SO4.7H20 Cerrusite • PbC0 3 * Rozanite 24.H 0 FeS04' 2 Malachite • Cu2(CO3)0H2 * Smithsonite ZnCO 3

SULPHIDES OXIDES Pyrite FeS2 Goethite • FeH2O

Melknikovite FeS2 Hematite Fe203 Marcasite FeS2 Magnetite Fe3O4 Galena PT'S Psilomelane (BaFe)2Mn5O10 Sphalerite ZnS ChalcopyrIte CuFeS2 SILICATES Chalcocite Cu2S Quartz SiO2 * Covellite CuS Beekite SiO2 Arsenopyrite FeAsS Jasper Si02 Orpiment As2S3 (1865) Chlorite • (MgFeA1)6(A1S1)4

010(OH)8 FLUORIDES SULPHOSALTS Fluorite CaF Bournonite PbCuSbS 2 3

* secondary supergene minerals ** = both primary and secondary mineral generations present -123-

4-3. Descriptive mineralogy

The following section is based on a detailed reflected light microscopy study of specimens collected from the Ballynoe barite horizon.A total of 65 polished sections and 30 polished-thin sections were prepared.

4-3a. pyrite & marcasite As noted in the previous section,pyrite is ubiquitous throughout the entire barite horizon and presents a diverse range of textural habits.These textural variations may be related to particular barite fabrics or wallrock lithologies and are classified as below :

Type ofyrite structure Barite fabric or lithology

10. Framboidal and/or anhedral Dolomite Breccia repl. of carbonate 9. skeletal 'fans' barite disseminated in the hangingwall

8. framboidal,tube-like, stratiform sulphide 'cap' granular.

7. atoll structures and/or white 'cap' barite syntaxial overgrowths. 6. reniform and botryoidal base of 'cap' barite

5. zoned spherulites and/or microcrystalline barite granular aggregates.

4 cruciform,dendritic,stellate siliceous barite acicular or spherical aggregates 3. 'slump-zone' replacement hematite horizon 2, massive granular footwall contact of barite 1. euhedral,granular veins. Muddy Reef Limestone

The above tabulated pyrite structures are described in the following sequence of photomicrographs. -124-

PLATE 4.1 : P rite structures from the footwall

Pyrite is widely disseminated throughout the immediate footwall to the barite and locally gains importance over the crest of the 'eastern dome' where black cherts are replaced by a massive pyrite lens,upto 4 ft. in thickness.

(A): Euhedral pyrite crystals in footwall chert (silicified Muddy Reef Limestone).The orientated strings of crystals tend to be parallel with the bedding.

(B): Two generations of euhedral pyrite in chert.

(C): Lateral spread of granular pyrite from a vertical vein of pyrite.The micro-flatting horizons. of pyrite are controlled by the fissility of the chert.

(D): Radiating crystals of barite in green-argillite acting as a nucleus for euhedral pyrite.

(E & F) : Granular pyrite from the massive pyrite lens capping the 'eastern dome'.The 'ghost' fabric consists of pyrite replacing bladed barite crystals.

(G) : Vugs within the massive pyrite lens are partially infilled with late stage sphalerite and galena. Sphalerite is marked by the symbol tsp'. P1 ATE 4.1

4-1 - x 31 -

C - x31 -

E x69 -

G x31 -126-

PLATE 4.2 : Pyrite in the hematitic zone • (DIEL_)

Pyrite pseudomorphing 'slump textures' is restricted to the once dynamic environment of the hematitic horizon. The 'slumping' consists of aggrega -es of euhedral and subhedral crystals of pyrite which replace in detail the original slumped fabric of the hematite.

In plate (4.2) pyrite replacement outlines the slumped and contorted hematite which sits conformably on grey chert. The chert - hematite contact is marked by a sub-angular clast of red jasper (veined by pyrite) and slivers of hematite. -127-

PLATE 403 : P rite structures from the siliceous barite zone (Type L1)

The morphology of pyrite from the siliceous barite zone is restricted in development to this particular horizon and presents a marked contrast to other types of pyrite structure found at Ballynoe.

(A,B) : Spherical aggregates of anhedral :pyrite in a fabric of siliceouS barite.The concentrically banded appearence of the spherulites is derived from a variable packing frequency of pyrite crystals which are equidimensional in size.No pyrite spherulites have been identified from the spherulitic barite zone.

(C,D,E) : Stellate masses cf acicular pyrite (marcasite ?) radiating from a nucleus of euhedral pyrite.Due to the high magnification needed to resolve the crystals no confirmatory tests for marcasite were possible. Acicular marcasite was reported by MORRISSEY (1970) from a siliceous and baritic segment of the Tynagh residual orebody and is identical in morphology to plate 'E'.

(F): A dendritic growth of 'bush' type pyrite which tends to be developed in areas of free Quartz within the barite.

(G): A cruciform configuration resulting from the coelesced growth of euhedral pyrite.As with the the 'bush' pyrite this structure is restricted to very siliceous barite.

(H) : The general relationship between acicular, dendritic and euhedral pyrite.

ea' 28- PLATE 4.3

A x31 x69

C x200 0 x69

• '

E x380 F x200

G x69 H x31 -129-

PLATE 4.4 : Pyrite textures in the microcr stalline barite (Type 5)

This barite zone is characterised by its accessory sphalerite and galena content rather than by pyrite which is restricted to minor disseminations and veinlets.

(A & B) : Late-stage pyrite veins (near vertical) cross cutting earlier pyrite.The black margin to the pyrite veins is a selvedge of secondary (white) barite.

(C &D) : The emplacement of structureless pyrite being controlled by the microcrystalline barite fabric.Note the complete absence of pyrite in the surrounding barite fabric.

(E) : Structureless pyrite cross cutting an earlier,granular pyrite generation.Note how the late-stage pyrite margins are controlled by the barite's fabric whereas the earlier pyrite is unaffected.

(F & An unusual development of concentrically zoned, spherical pyrite.The nuclei of the spherules may be circular or pyritohedral in shape.GRAHAM (1970) has reported similar pyrite spherules from the upper 'G' zone. A x31

111. r e • • et. 4 41,4„ Y

• 1 - x31 - 1)

E x31

4 4,... . Nik . • 144 y

F x31 x380

-131—

PLATE : Reniform rite associated with the 'ca ' barite

Reniform pyrite is associated with the megacrystalline white barite which overlies the main orebody barite in the eastern segment of the deposit.Whenever freshly exposed the botryoidal masses of pyrite are iridescent,although they quickly tarnish with continued exposure.Vugs within the pyrite carry large,translucent crystals of tabular barite. Occasionally in certain sections of reniform pyrite,groups of stellate pyrite spherules may be observed with a morphology resembling 'daisy gypsum',see figure (4.1)

FIGURE 4.1

'Daisy pyrite'

(A,B,C) : Radiating,concentrically banded pyrite.The black banding consists of sub-parallellfibrous crystals of possible melknik-:vite composition.Melknikovite is described by RAMDOHR (1969) as being,"colloform in nature and characteriseu by a fine blackish powder which cannot be polished.The mineral is indicative of a low temperature formation." The black banding was examined by X--Ray Diffrac- tion analysis and gave very anomalous 'd' spacings which were pyritic in rature.According to Ramdohr,this is typical of melknikovite.The cores of the radial structures are composed of an anhedral mosaic of pyrite,with minor sphalerite replacement,

(D) : Radiating marcasite associated with reniform pyrite.

(E,F) : Concentric melknikovite/pyrite fractured by late-stage granular pyrite.(F) is a magnification of (E).

(G,H) : Late-stage pyrite and sphalerite veining;minor dislocation, PLATE 4.5

- x31 - A B

C - x69 - D

E x31 F x69

- x31 - H G -133-

PLATE 4.6 : pyrite structures in the 'ea barite (Type 7)

The white,crystalline barite 'cap' to the orebody carries a very low sulphide assemblage,consisting of widely disseminated pyrite and rare galena/sphalerite.

(A) : A general assemblage of euhedral pyrite crystals and minor sphalerite (grey).Note the atoll structures which rim many of the larger pyrite crystals.Some replacement of sphalerite by pyrite.

(B,C,D,E) : Typical euhedral crystal forms developed in pyrite.Octahedral,trapezohedral and cube faces are represented.It is of interest to note that no pyritohedral crystal forms are developed,a ubiquitous form for pyrite in the footwall rocks (plate 4.1). The granular pyritic rim to the euhedral pyrite crystals (atoll structure) is a probable 2emobil- ization texture.The colloform aggregate of pyrite seen in the upper left of plate 'C' has no rim of atoll pyrite and probably post-dates the euhedral pyrite.

(F) : Pyrite atoll structures without a euhedral crystal nucleus.The structures tend to be cruciform in shape and are associated with strings of framboidal pyrite (top left corner).Similar atoll structures are reported from the Meggen barite deposit by EHREHBERG et al (1954).

(G,H) : Strings of framboidal pyrite in white,crystalline barite.In diameter they range from 10 - 25 microns. - PLATE 4.6

A x31 x69

x69 C x31 D

x200 F x69

x200 x69 H -135-

PLATE 4.7 : Framboidal puite from the sulphide 'cam' (

The massive pyrite capping the western segment of the barite orebody (3-3e) is very rich in framboidal structures. The framboidal spherules are abundant in the galena and sphalerite bearing laminated muds at the base of the sulphide horizon.In the more massive sulphide,pyrite may develop tube- like structures which are upto 4" long by ill in diameter.The morphology of these tubes strongly resembles pyritic crinoid stems

(A,B) : Pyrite framboids and subhedral pyrite in a sphalerite matrix.Note the wide packing variation in the constituent crystals comprising the framboid spherules.The diameter of a single framooid averages 14 - 16 pyrite grains,the grain size increasing proportionally with the size of spherule.

(D): Coalesced,pyrite framboids controlling the emplacement of galena (gn).No actual replacement of framboids by late stage sulphides has been observed and is a probable function of the high resistance of spheres to penetration.

PLATE 4.7 : Pyrite textures in the hangingwall (Types 9 & 10)

(E,F) : Pyrite is commonly associated with the secondary barite which replaces the Dolomite Breccia.Granular pyrite is being controlled by the large,bladed barite crystals. (G,H) Framboidal pyrite developed in carbonaceous partings within the Dolomite Breccia. , 6 PLATE 4.7

- x380 8

4Io

141. 9^

11411C

- x380 - r)

E - x31 -

G x69 H x380 -137-

4-3b. Partial trace element content of the etrite

Table (4.1) demonstrates a close correlation between the trace element content of the pyrite and the zone within the barite horizon from where the specimens were collected.The massive pyrite 'cap' to the orebody is markedly enriched in ColNi,Cu,Pb and Zn with respect to all other forms of pyrite found at Ballynoe.Of note are the high Cu values (450-860ppm) which are found in the stratiform pyrite cap' in comparison with the pyrite strings from mid-orebody (25-55ppm) and the massive footwall pyrite from the 'eastern dome' (6ppm).

The cobalt-nickel ratio in pyrite is of value in determining its probable genesis.According to DAVIDSON (1962) sedimentary pyrite may be differentiated from magmatic-hydrothermal pyrite by a Co/Ni ratio which is less than one.This was supported by LOFTUS-HILLS & SOLOMON (1967)who noted a relatively high Ni content in sedimentary pyrite and low Co/Ni ratios.

With reference to table (4.2) the Co/Ni ratios determined, from the Ballynoe pyrite are under 0.5 in value, with the stratiform 'cap' pyrite averaging only 0.12. These Co i ratios are slightly lower than those determined by GRAHAM (1970) for the 'G' zone.The stratiform 'cap' pyrite has high Ni values (280-320ppm) and enriched Co values (30-45ppm).KRAUSKOPF (1956) found that in a sedimentary environment,Ni and Co are concentrated by the action of organisms rather than by adsorption or sulphide precipitation,a process which may be applicable to the stratiform sulphides at Ballynoe. -138-

TABLE 4.1 : Partial trace element content of pyrite from Ballynoe

(in ppm) Specimen location Co Ni Cu Pb Zn

.Repl.in Dolomite Breccia 25 70 55 1550 14500 .Repl.in Dolomite Breccia 25 60 34 1500 9000

stratiform 'cap' 30 280 450 2000 43000 stratiform 'cap' 45 320 860 1450 20000

vein in black barite 20 50 24 400 600 vein in siliceous barite 20 45 55 385 540

euhedral crystals in f/wall 20 65 70 2450 500 • euhedral crystals in f/wall 35 155 5o 1400 270

• massive lens,'eastern dome' 20 750 6 1300 1800

(Analyses by Atomic Absorption) by Tony Thompson.

TABLE 4.2 : Co/Ni ratios for table (4.1)

Spec.No. 22ZE1 1. 0.357 2. 0.416

3. 0.107 4. 0.140 5. 0.400 6. 0.W1

7. 0.307 8. 0.225

9. 0.026 -139-

4-3c. Copper Mineralisation

The copper mineralisation exposed in the south-west corner of the openpit is associated with a SSW attenuation of the barite orebody.Lenses of chalcopyrite/marcasite upto one foot thick occur in a coarse,grey-white barite gangue (plate 4.8) which is localised along the faulted, footwall contact to the orebody.The average copper content of the barite orebody is less than one part per million (see 5-4g)l all copper mineralisation being limited to the fault plane.

The extension of the copper bearing fault may be traced for 300 yards to the west of the openpit (fig.2.4) by a string of old shaft craters and where,to quote WYNNE (1861)," white lead ore was raised at some remote period." Superficial examination of the spoil heaps produced small nuggets of malachite and minor intergrowths of cerrusite and limonite,evidence for the cupriferous and plumbiferous nature of the fault.This mineralisation is spatially related to the copper occurrences 250 yards due south of the openpit where," excavations removed a great bunch of copper ore out of the containing dolomite rock which is brought against the Silurian by. the Silver- mines Fault " WYNNE op.cit).

The occurrence of chalcopyrite in a gangue of probably secondary' barite and the neglible copper content of the barite orebody suggests that the copper mineralisation post-dates the emplacement of the barite horizon.This has interesting genetic implications regarding the age of the Silvermines 'fissure vein' mineralisation and will be discussed in chapter seven. -140-

PLATE 4.8 : Copper mineralisation

(A): Massive chalcopyrite veined by stringers of secondary chalcocite (grey) and covellite (blue). Covellite alteration is always marginal to the chalcocite.The black voids are inclusions of barite. X.31 (B): Chalcopyrite (yellow) replacing fractured marcasite and pyrite (white-pink).Note the major alteration of chalcopyrite to chalcocite (grey). X.31

(0) Marginal replacement by covellite (blue) of a chalcopyrite grain.The matrix is grey,crystalline barite which is veined by covellite. X.200 (D) : Twinned marcasite being partially replaced by

- chalcopyrite.The photomicrograph has been taken with slightly crossed polars to accentuate the marcasite. X.68

Specimens 'A - DI were obtained from the chalcopyrite lens along the SW footwail of the orebody, 4080E,1600N. -141-

PLATE 40 8 Copper Mineralisatinn

B C

-142-

4-3d. Sphaleritetigalena

Disseminated sphalerite and galena mineralisation is found throughout the barite horizon and is strongly developed in the stratiform pyrite which overlies the orelody. With the possible exception of the sphalerite and galena rich muds at the base of the stratiform pyrite,the lead/zinc mineralisation post-dates the emplacement of the barite and is described in plates (4.9,10).

It is of interest to note that the barite horizon may have been explored for lead in the past.The 'old men' drove a series of levels through the clays of the solutional collapse pipe towards the massive sulphide 'cap' of the barite.On occasions, the old mine timbers still packed with dry grass and heather are revealed during quarrying operations.MNNE (1861) briefly alluded to these old trials which were abandoned before 1820.

Galena displays a greater mobility than sphalerite within the barite horizon and in most cases post-dates the mineral.This relationship may be observed in the hangingwall where joints in the Dolomite Breccia carry weak mineralisation.Honey-yellow crystals of sphalerite are confined to calcite coated joints* which are subsequently invaded by pink dolomite veinlets carrying galena.The galena partially replaces the sphalerite and is also disseminated in the immediate country rock to the veinlets.Vugs within the veinlets display the following paragenetic sequence of crystallisation : 1. barite (secondary) 5. dolomite 2. calcite 6. galena

3. pyrite 7, quartz 4. sphalerite North-south trending joints often carry a deep purple fluorite with no associated sulphides. PLATE 4.9 : Sphalerite/galena in barite

(A,B) : (Microcrystalline grey-black barite zone). Galena replacement controlled by the fabric of the barite.The galena highlights the crystalline structure of the barite,a role never adopted by sphalerite.Compare the stubby-bladed barite crystals developed in this zone to the more plumose 'fan' barite of secondary origin,plato 'C & DI .

(C,D) (Macrocrystaliine 'cap' barite zone). Skeletal textured galena controlled by plumose barite crystals.In plate 'C' the galena highlights a complete crystal plume of barite.

(E,F) (Microcrystalline grey-black barite zo.,.e). Typical sphalerite - galena relationships in the barite.In plate 'E' late-stage galena is replacing the barite matrix between the sphalerite crystals. In plate 'F' galena atoll replacement structures are developed in sphalerite,a texture according to SCHOTT (1971) to be indicative of a hydrothermal- sedimentary environment. Sphalerite (grey). Galena : (white). Barite : (black).

(G,H) : (Microcrystalline grey-black barite zone). Sphalerite-galena-pyrite relationships.In plate 'G' pyrite rims the sphalerite crystal until in the south it replaces with an 'explosive burstl .In plate 'H' a a vein of pyrite is replaced by sphalerite and thence by galena. PLATE 4.9

A x31 B x69

WA „ • *.d • ■ 1 1 . . ' . ' •

• p,,,t, .i , ..., , L., .,••I: ' .' . .1 ,, . . , . . , .,-,./,.., ,-....y. ... ., • - - ., ..--;...- ;I.? ...-..,,,‘. . -.. i lii• .4.; • ,4;•• / .•.- ,iii 4-.et. . „, .. I • . ; i ; :: . - :..,,,, w-, . f ' i P. i*- If • "Sr . , ir 11 i. ..4/..

/ &

- x31 -

E x31 F x69

G - x69 - -i 5-

PLATE 4.10 : Spheroidal afabrics

(A,B) : 'Spheroidal' galena replacing sphalerite.The galena is probably pseudomorphing the original spheroidal fabric of sphalerite as seen in plate 'C'.

(C): Spheroidal sphalerite replacing a large crystal of pyrite.The outer rim of the sphalerite spheroid at (a) is replaced by galena.

(D) Galena replacing spheroidal sphalerite and also invading subhedral pyrite.

(E): A veinlet of euhedral pyrite with a marginal replacement by spheroidal sphalerite which in turn is almost completely replaced by galena. Note the strings of galena invading the pyrite at (a).

(F): A sphalerite spheroid replacing pyrite.The nucleus of the spheroid is replaced by galena.

(The above textures occur in microcrystalline barite).

(G) A string of granular sphalerite replacing a growth boundry in reniform pyrite.

(H) Spheroidal sphalerite replacing reniform pyrite along a growth boundry.Galena is very rare in the reniform galena crystals. -146- PLATE 4.10

x 6 A x31 R

x200 D x 6L

F x31

1 •

•

- x69- PLATE 4.10a : Spheroidal and colloform sphalerite in barite

(A) : A nest of sphalerite spheroids controlled between large tabular barite crystals in the 'cap' barite. Compare this sphalerite fabric with 'uhe skeletal galena in the same environment (plate 4.9c). (cap barite,eastern end of the openpil.,, X.31).

( B ) : Colloform sphalerite banding associated with the base of the 'cap' barite.The innermost sphalerite cores are richer in iron than the peripheral banding. X.200

r -148-

4-4. Diagenetic and supergene modification of the barite deposit

211aantall t is evident that the barite horizon has undergone considerable diagenetic modification since its original emplacement.The extensive recrystallisation fabrics,zones of stylolitisation and the development of macrocrystalline,white barite bear testimony to this statement.The localisation of the white 'cap' barite above the 'eastern dome' suggests that this structure had a probable control over the development of the secondary barite.

Discussion : At normal temperatures and pressure barite is extremely insoluble .its solubility product constant (Ksp ) being only 1 x 1 0-10 ,falling to 1 x 10-958 at 100'C (SILLEN & MARTELL 1964).The solubility of barite increases strikingly with a rise in the salinity and temperature of the environment,especially so in NaCl solutions (TEMPLETUN 1960).PLUMMER (1 971) stated that below the water-table barite may be extremely soluble.

The solubility of the Ballynoe barite deposit may have been enhanced by factors which were a direct result of diagenesis.If we accept the pressure solution theory proposed by PARK & SCHOTT (1968) for stylolite formation, the stylolitisation of the barite horizon must have been initiated during the early compaction and lithification of the deposit.The increasing compactional pressure and the resultant rise in temperature could be attributed to a progressive burial under the overlying carbonate sequence.According to GORNITZ (1972) barite crystals -149-

(cm) -6 with a diameter of 4 x 10 ,are upto one thousand times more soluble than coarsely crystalline barite under the same conditions.This marked increase in solubility as a direct consequence of a microcrystalline fabric may be applicable to the Ballynoe barite where stylolitic solution is restricted to the microcrystalline zone.No stylolites have been observed in the coarsely crystalline 'secondary' barite.If for the sake of this discussion we make the early assumption that the barite horizon is of syn-sedimentary, marine origin (fully discussed in chapter seven),entrapped connate sea-water would be expelled during the compaction of the barite.This connate water,rich in chloride ions would act as a strong solvent of barite and coupled with the rise in temperature due to compaction,would greatly lower the (Ksp ) of BaS0 .Figure (4.2) shows how the escape path for the Ba bearing connate waters may have been controlled by the fossil topography of the eastern dome, the overlying carbonate rocks providing an excellent host for the re-precipitation of the barite.It is of interest to note that chloride_ bearing fluid inclusions have been reported by MORRISSEY (1970) from the barite at Tynagh, the barite carrying upto 1)#OOppm Cl.To date,no fluid inclusions have been identified from the Ballynoe barite. The important differences in trace element content and isotope geochemistry between the orebody and 'secondary' barite are discussed in chapter five.

4-4b. Supergene alteration : The most obvious zone of supergene alteration is along the footwall contact of the orebody which acted as a natural conduit for descending meteoric waters.

-150-

FIGURE 4 2

DIAGRAMMATIC REPRESENTATION FOR THE ORIGIN

OF DIAGENETIC 'SECONDARY' BARITE

Primary barite

Direction of compactionaJ. pressure ==4. Direction of.connate water flow

^10*VI : Stylolite formation

Diagenetic 'secondary' barite

: Muddy Reef : Eastern Dome Lst.

Dolomite Breccia -151-

Along the footwall contact,the most common form of alteration is the progressive replacement of hematite by goethite.Amorphous masses of black goethite (plate 4.11a) are relatively common and stringers of the mineral often extend into the hematitic barite zone, (plate 4.11b). Associated with the development of goethite are dendritic fronds of psilomelane.Many of the joints within the basal barite zone are coated with apple-green slivers of chlorite and is probably derived from a remobilization of the chloritic Green Argillite horizon.

Wherever the basal clays of the solutional collapse pipe are in contact with the sulphide 'cap' of the barite orebody extensive oxidization has taken place (plate 3.14b). Pyrite is altered to limonite (goethite),an alteration• which often results in beautiful,colloform banded forms (plate ..11f,g).Acicular crystals of cerrusite (upto 2" in length) are abundant throughout the basal clays of the pipe and are accompanied by rare anglesite and smithsonite. Two sulphates are of common occurrence.Gypsum is found in the form of translucent,stellate crystal masses upto 3" in diameter whilst concretions of 'gritty' barite upto 6" in breadth occur.The poorly sorted chert fragments within the clay are coated with a thin film of psilomelane. In some respects the high base metal content of the clays ) is analogous with the Tynagh residual orebody to which it is possibly related in age.

4-4c., Mineral formation as a result of contem orar weathering

When the stratiform pyrite 'cap' is exposed by quarrying in the open-pit,the sulphide quickly begins to -152-

PLATE 4.11 : SuperEpne mineral formation

(A): Alteration of hematite by goethite (gt). The goethite is amorphous and vuggy. X.31

(B): Stringers of goethite invading the hematitic barite zone.The stringers are provably derived from the underlying hematite horizon. X.69

: Alteration of pyrite to goethite (gt) in the siliceous barite zone. X.69

(D,,E) : Dendritic fronds of psilomelane in the hematitic zone.The hematite has be -m partially replaced by pyrite and thence both minerals by goethite. under oil X.69

(F,G) : Development of reniform limonite (goethite) by the replacement of stratiform 'cap' pyrf_te. Note the unreplaced pyrite in the outer colloform bands of plate §F§ : X. 31 OG§ : X.69 PLATE 4 11

F weather,a common weathering product being efflorescences of pale blue to green,hydrated iron sulphate.With the aid of X-Ray Diffraction,three species of iron-sulphate have been identified : Melanterite FeSO4.7H20 (table 4.3a) Pisanite (Fe,Cu)SO4.7H20 (table 4.3b) Rozanite FeS0 411,0 4* , Melanterite is extremely soluble and its development is restricted to pyrite whichis sheltered from direct precipitation.Copper bearing pisanite is associated with the weathering of the chalcopyrite lenses described in section (4.3e).

Acidic waters derived from the weathering pyrite readily attacks the orebody barite and seepage along joint planes results in a very soft and 'rotten' BaSO4.

4-5. Paragenesis of the barite de osit

The paragenetic scheme for the barite horizon may be divided into eight stages, see figure (43).

. The primary stage of barite mineralisation at Ballynce was accompanied by high concentrations of iron and silicon. In this environment hematitic barite,massive hematite, siderite and jasper were emplaced.A waning of the iron phase heralded the bulk of the barite mineralisation (stage 2) which initially was still very siliceous.The micro- spherultic fabric of the barite suggests a rapid crystallisation.With the possible exception of minor pyrite (biogenic?) the barite was free of accessory mineralisation.A gradual cessation of barite mineralisation (stage 3) witnessed the introduction of sphalerite and galena muds which were -155-

TABLE 4.3 : Pyrite efflorescences•X-Ra Diffraction data table 4.3a 1. Melanterite FeSO4.7H20 Rio Tinto,Huelva,Spain. 2. Pale-blue efflorescence on massive pyrite. Stratiform pyrite 'cap',Ballynoe open-pit. No.1 No.2 0 dA

4.90 100 4.91 100 3.78 64 3.80 7o 3.23 20 3.22 30 2.63 16 2.59 20 5.52 13 5.50 15 2.75 ii 2.75 10 2.31 10 2.35 10 4.55 8 4.61 10 4.02 8 4.11 5 2.01 8 2.05 5 1.96 8

table 4.3b 1.Pisanite (Fe,Cu)SO4.7H20 Flin Flon,Manitoba,Canada. 2.greenish-blue efflorescence on cupriferous pyrite. Chalcopyrite/Pyrite lens,SSW corner of the open-pit. No.1 No.2 0 0 dA 1 dA I • 4.86 100 4.81 100 3.77 50 3.70 85 5.37 3o 5.36 4o 3.24 30 3.22 30 2.70 30 2.70 25 2.63 30 2.60 25 2.32 20 2.35 15 2.00 20 2.05 10 1.96 20 1.95 10 1.85 20 1,82 5

-156-

PLATE 4.12 : Oxidation products

(A): Melanterite FeSO4 7H,0 ' 4 X. 0.5 A typical efflorescence on pyrite from the stratiform, pyritic 'cap' zone.The mineral is very soluble and its formation is restricted to pyrite which is sheltered from direct precipitation.

(B) Malohite e cerrusite & limonite X. 0.5 Cerrusite (acicular white crystals) intergrown with colloform malachite in a matrix of limonite.The material was collected from the cupriferous fault zone SSW of the barite orebody. 4055E,1604N. -157—

FIGURE LI .3 : Paragenetic Scheme for the Ballynoe Barite Horizon

1 2 6 Primary BARITE •4W2i4 Secondary BARITE Hematite 4111alato- Siderite Magnetite Jasper -- Quartz ---- Calcite Pyrite Sphalerite Galena --- Marcasite Bournonite - - - Dolomite Fluorite --____ Chalcopyrite Arsenopyrite ...... - Chalcocite Covellite Gcethite -=;:, Psilomelane Cerrusite Smithsonite ------Malachite Anglesite Chlorite Gypsum Melanterite Pisanite Rozanite

(1)Primary Ba & Fe mineralisation (5) Diagenetic stage

(2)Main Ba mineralisation (6) Epigenetic Cu stage (3)Waning Ba stage and early sulphide(7) Supergene stage (4)Sulphide stage (8) Weathering stage -158— the forerunners of the stratiform,sulphide t capt to the orebody (stage 4).

The compaction of the barite horizon and the resultant diagenetic modifications ie,extensive recrystallisation, stylolitisation and remobilizationsculminated in the formation of secondary,macrocrystalline,white barite (stage 5). The introduction of sulphides into the orebody barite and the minor mineralisation of the country rocks was probably associated with this stage.

The copper mineralisation which post-dates the emplacement of the stratiform barite is possibly related to the fissure-vein type mineralisation found along the Silvermfnes Fault zone from Ballygown to Shallee.

Subsequent mineral formation at Ballynoe is the product of supergene alteration end open-pit, weathering of the mineralised-horizon. -159-

CHAPTER FIVE

GEOCHEMISTRY OF THE BARITE HORIZON

5-1, Introduction

In the preceding chapters it has been established that the Ballynoe orebody is : i)a stratiform mineral deposit located at the top of the Muddy Reef Limestone and is concordant with the stratification within the Lower Carboniferous succession. ii) a composite rather than homogenous deposit and consists of layers of hematitic,siliceous and pure barite.Diagenetic modification has resulted in extensive recrystallisation and remobilization.

The aim of this chapter is to determine if these geologically based statements can be substantiated with the aid of geochemical data.The barite orebody and wallrocks of the 'mineralised-horizon' are chemically analysed and the results discussed.An additional geochemical parameter is provided by a series of sulphur and oxygen isotope determinations from the barite horizon.

5-2, Geochemistraf the wallrocks

A direct-reading emission spectrographic technique was applied in the analysis of the argillaceous,siliceous and carbonate wallrocks of the deposit.A computer programme thence converted the raw spectrographic output into element concentrations.(See appendix for analytical details). Cores from 4 diamond drill holes (see table 5.1) were selected for analysis,with a 3" long,split core sample being taken at 5' intervals,

-160-

TABLE 5.1 : Diamond Drill Holes sam led

Magcobar DDH No : 60 _65_ 38 30 Location : 41480E 41200E 41200E 41900E 17645N 16760N 16650N 16670N Elevation 372' 474' 487' 497' Angle 90' 90' 90' 90' Total length 485' 209' 216' 120' Thickness of drift 160' 12' 9' 13' II " of the HW 186' 148' 138' 87' II II of orebody : 0' 35' 60' 29' tt " of the FW : 139' 1-4.' 6' 5' Sampling interval : DDH No's 60,65 & 38 one sample every 5 ft. of core.In DDH 30 every 2 ft. Sample size : Split Bx half-core, 3" in length.

5-2a. Wallrock disrNersion in sub-economic areas of the 'mineralised-horizon'

Diamond drill hole 60 is located midway between the barite orebody (300 yds to the north) and Mogul's 'B' zone. It is the deepest Magcobar exploration hole drilled to date and intersects the full thickness of the Muddy Reef Limestone (85ft) and some 55ft of Muddy Lime.Aane.Although the 'mineralised-horizon' was intersected,the hole failed to prove any ore-grade barite.

In figure (5.1) the dispersion profiles for barAum, strontium and iron have been plotted throughout the 325 ft. core length of DDH 60.Barium values in the footwall Muddy Reef and Muddy Limestone are very consistent with a mean of 805 ppm Ba (28 samples).A marked enrichment in Ba is observed in a 10 ft.thick section of core laying directly above the upper contact of the Muddy Reef Limestone.This 10 ft.section which is the base of the Dolomite Breccia series -161-

FIGURE 5.1 Dispersion of Ba,Sr,Fe in DDH 60

Chert horizon

Dolomite (BA-ltIUM) (STRONTIUM (IRON)

proto ~ breccia 2000ppm 2000ppm

breccia

Muddy Reef Lst

slump

Muddy Lst

slump - shale I: 20ft. ~~~ ______~ ____~ ______~~ ______~ ____~ ____~~R,a

TABLE 5.2 Barium dispersion (Arithmetical Means)

Range No of samQles Mean (i) i I Chert Horizon 143:ppm 80-310ppm 5 I; Dolomite Breccia 609ppm 250 -3000ppm 30 tBa zone' 2%+ above calibration 4 Muddy Reef Lst. 726ppm 350 -965ppm 18

Muddy Limestone 884ppm 155 -1170ppm 11 -162- averages 2% Ba and is subsequently referred to as the 'Ba zone'.(In DDH 60 the 'mineralised-horizon' is 20ft.thick and comprises the 10ft.thick 'Ba zone' plus a further 10ft. thickness of Fe,Pb & Zn enrichment).The 150ft.thick sequence of Dolomite Breccia above the 'mineralised-horizon' averages 609 ppm Ba,l,his value falling to only 140 ppm Ba in the Chert Horizon.Iron has a antipathetic relationship to barium and strontium,enrichment occurring in the immediate hangingwall and footwall to the 'Ba zonei .This situation is analogous to the barite orebody which is overlain by stratiform pyrite and has strong,disseminated pyrite along its footwall.

To test the hypothesis that the 'Ba zone' is perfectly conformable with the top of the Muddy Reef Limestone,analyses of elements with a definite affinity towards rocks of an argillaceous nature have been plotted (figure 5.2).The abrupt termination of the dispersion profiles for K,A1,Si, Ti,Cr,V and Ga at the lower contact of the 'Ba zone' strongly emphasizes the stratigraphic position of the 'mineralised- horizon'at the top of the Muddy Reef Limestone.Of lesser consequence,the profiles differentiate also between the Muddy Reef Limestone and the more argillaceous Muddy Limestone. Besides Ba,Sr and Fe other elements enriched in the the 'mineralised-horizon' are Mn,Pb,Zn and Ag.Manganese forms a narrow halo to the 'mineralised-horizon',enrichment being more pronounced in the footwall than hangingwall.On a regional. scale RUSSELL (1974) noted a Mn aureole with a radius,of 7km surrounding the Tynagh ore deposit.Most of the samples collected from carbonate rocks within 1km of Tynagh carried Mn values of 1,000 ppm pius,a feature not comparable to Ballynoe where the Mn content of the walirocks quickly falls'

FIGURE 5,2 Element Dispersion (Argillaceous Affinity) In DDH.60

Potassium Aluminium Titanium rC V Gallium hert Zone

Silion- --

nd *0.7% --._ nd 1 nd

....___, Dolomite L.% 1 0Oppm 50ppm I Oppm nd= not 2% 10% 1 0Oppm Breccia detecte nd nd *.0% nd * = detec- nd tion *1PPm *5PP * O. 2pp

. ._._._._._._._._._._._._. _._._._._ .

scale 1cm Muddy Reef 10ft Lst

1111-

Muddy Lst

-.MMUnMirIM=WMaTsla, imsstsf-mrsmsrammarommi.

FIGURE 5.3 Element Dispersion DDH 60 ('Mineralised et Aff init )

Manganese Lithium Scandium Copper Lead Zinc Silver _ _ Chert Zone *2ppm *5PPm *I ()ppm ' 1006ppm ,ruuTim Tuvpm "5-U5pm ITUDIppm ILIOUTZpm 1-r015fom

*=detecti o. limit Dolomite nd= not nd Breccia detected *0.3ppm

...•- • - ._. _.

Muddy Reef Let.

nd nd nd Muddy Lst.

AR -165-

below 800 ppm within 100ft. of the 'mineralised-horizon',see figure (5.3).

It is of considerable interest that the strong zone of lead-zinc enrichment in DDH 60 is restricted to the pyritic, hangingwall contact of the 'Ba zone' (figure.5.4} and is only feebly developed below this level.This suggests that

the period of barium enrichment was not accompanied by lead- t, zinc and that the latter probably post-dates the former.

FIGURE 5.L1. Pb/Zn enrichment above the Ba horizon combined Pb+Zn% 1cm=1%

15f t

Horizon enriched in barium

based on Mactoobar data The dispersion of copper is uniform throughout DDH 60 (25ppm mean) and only a slight and expected enrichment was detected in the more argillaceous rocks of the Muddy Limestone series.

5-2b. Wallrocl dispersion the barite orebod

To determine the element dispersion profiles in the wallrocks of the barite orebody,cores from diamond drill holes 65,38 and 30 were analysed.All three drill holes intersected at least 25ft.of ore-grade barite (table 5.1) and may be taken as being representative of the deposit.

The dispersion of barium in the hangingwall of DDH 65, in comparison with the Ba profile for DDH 30, illustrates the- -i66- statement made in chapter 4-4,where it is postulated that secondary barite of diagenetic origin has been preferentially emplaced in the wallrocks over the 'eastern dome'.DDH 30 is located over the northern flanks of the 'eastern dome' whilst DDH 65 is sited to the west,just north of the central part of the orebody.Figure (5.5) is a diagrammatic,east-west section across the orebody and presents the dispersion of barium in the wallrocks of drill holes 65 and 30.The mean barium content of the wallrocks above the central part of the orebody is 695ppm (30 samples over a 148ft.range) a value which differs very little from the Ba content found in the wallrocks of DDH 60 (609ppm).This suggests that over the central part of the orebody,barite mineralisation is strictly confined to the horizon of stratiform barite and that no vertical remobilization and subsequent replacement of the hangingw?:11 has taken place.

The dispersion of barium in the hangingwall• over the 'eastern dome' (DDH 30) contrasts markedly with the Ba proile determined in DDH 65.In DDH 30 the wallrock is greatly enriched in barium and one 25ft. section of core averages over 4,000ppm Ba (the limit of instrument calibration),It i9 suggested that this high content of Ba in the hangingwall is directly related to the development of diagenetic 'secondary' barite over the 'eastern dome' and exemplifies the hypothesis, presented in 4-4.

With the termination of Magcobar drilling 4-6ft.below the footwall contact of the barite orebody only this limited thickness of footwall was available for sampling.ln the immediate footwall to the barite orebody, element dispersion is comparable with DDH 60 (figures 5.2 & 5.3) and the only

-167-

FIGURE 5.5 : Remobilized Ba over the 'eastern dome'

The remobilized Ba is strictly localized over the 'eastern dome' suggesting the model presented in figure (4.2) i6 correct.

I: 10ft

Ba: 695 ppm

.. - s x X X x .4> , x X '''' x X% x% x ., x x x •so x x x o x x xx Barite flexed over the 4.P % x xx xx , x, x xx x x x /x ,x x xx ,. xx x xx x x x x x xxxx. x x % x x x Barite orebody xx x . xx x_...,x x xx xx x x*x xx

Muddy Reef Limestone -168- elements to be enhanced in value are Si,Fe and Mn.

The footwall 'to the ,orebody is characterised by very high silicon values.The footwall rocks average 31.2% (9 samples over a 6ft. range in DDH's 65,38,30) and contrasts with DDH 60 where the mean silicon content over the same vertical range is only 6.6% Si.It is suggested that strong barite mineralisation is associated with a major silicification of the footwall and the converse applying to weak barite mineralisation (as in DDH 60).

Iron is enriched in the immediate footwall to the orebody with a mean value of 8.3% (over a 6ft.range) and is comparable to DDH 60,see figure (5.6),In contrast to the footwall,the hangingwall is not enriched in iron,the initial 15ft above the orebody averaging 1.6% (15 samples).Over the same range in DDH 60 iron averages 5.1%.This supports other evidence in suggest4ng that when the barite horizon fades out downdip, its place is taken by disseminated and massive pyrite.

The pattern of Mn dispersion at Ballynoe correlates with the iron content of the wallrocks.The iron enriched footwall 1 rocks carry a mean-Mn content of 3,100ppm (10 samples over a 6ft. range) falling to 960ppm Mn in the initial 15ft of hangingwall.(In DIE 60 over the same range of hangingwall the Mn content is 2,550ppm and correlates with the high Fe content),In the hangingwall no Mn halo is developed as found by RUSSELL (1974) at Tynagh.

No footwall or hangingwall enrichment was detected in the Cu,Pb or Zn profiles. FIGURE 506 : Comparative wallrock dispersion rofiles Barite Orebody — DDH 60

SILICON Rs\\1 MANGANESE IRON

111 1 000ppm qi\m] 1% \\ n R of DDH's I 65,38,30 not detected, DOLOMITE detection limit 4% DDH 60 BRECC IA (hangingwall)

vertical scale,

. lem = 5ft. ••••■••••••••■••••••••••• •••••••• •■••• • immom • ••■••• • MT* • Imam* • •■•• • R.. . CL. . . . .

BARITE OREBODY (Ba Zone in DDH 60)

MUDDY REEF LsT. (fOotwall) -170-

5-3, Element dis ersion within the barite orebody

The element dispersion profiles within the barite orebody were determined by optical emission spectrography, quantitative results being obtained with the aid of a projection comparator-densitometer (see appendix for analytical details).Barite intersections from five diamond drill holes were selected for sampling and were supplemented by two vertical sample suites collected from the exposed orebody in the openpit.Sample site and sampling details are presented in figure (5.7).

Thirty-five trace elements were sought in the barito and from this total,fifteen occurred in measurable concentrations,the most important being Si,Sr,A11 Mg,Ca,Fe,Pb and Zn.

FIGURE 5.2 Orebody sample sites

17 * 65 ® : DDH number & 30 .41 location 031 e • 0 0 A : open-pit sample m 16 • 16 suite location L------J 500ft 40 41 42 43

Sample site : 38 a 11 Bs Thickness of barite sampled : 29' 60' 35' 10' 38' 40' 35' Elevation of HW contact : 410' 337' 299' 367' 386' 4.60'_435' Elevation of FW contact : 381' 277' 264' 357' 348' 420' 4001 Sampling interval : every 2ft. Sample size (drill core) : split Bx half core, 3" in length (openpit) : chip sample,approx. 3" in length -1 71 -

To clarify the trace element dispersion determined in the barite horizon (figures 5.8 - 5.11) the variable true thicknesses of the sampled sections have been standardised to fit a uniform section of barite,3Oft.in thickness. It is important to note however,that the relative position of an individual sample in relation to the footwall contact remains the same.

5-3a. Silicon (figure 5.8)

The siliceous nature of the basal barite has already been described In chapter 3-3b where -it was demonstrated that amorphous and/Or crystalline silica selectively replaces the fabric of the barite.In the dispersion profile for silicon throughout the barite orebody a marked diminishment in Si content from footwall to hangingwall is detected.A mean footwall value of 6% Si progressively reduces to a mean of 200ppm Si in the proximity of the hangingwall.The secondary

'cap' barite is further diminished in Si with a mean content of only 65ppm Si.The anomalous re,,ult marked (A) on fiqure 5.8 (2,200ppm) is due to the development of minute,prismatic quartz crystals in the basal part of the 'cap' barite.The white 'secondary' barite disseminaf.ed in the hangingwall is differentiated from the 'cap' barite by a slightly higher silicon content,with a mean of 280ppm Si as opposed to 65ppm Si. The high silicon content of the basal barite layers is a continuation of the very strong Si profile determined at the top of the Muddy Reef Limestone (figure 5.6).Evidence presented in chapters 3 and 4 suggests that the silicification was contemporaneous with the emplacement of the primary barite. -172-

FIGURE 5.8 Silicon

A A A A 'secondary' A A barite zone A A A A 'AAA A 'cap' barite AA A A

upper half of orebody

lower half of orebody

basal & hematitic barite

0 10 100 1000 1% 10% (in ppm

secondary' barite 15 280ppm 55PPm 85PPm 'cap'barite : 20 65PPm 30Plom 1 5PPm upper half of orebody : 50 900ppm 260ppm 200ppm lower half of orebody : 55 1.2% 2.0% 0.7% hematitic barite 10 2.6% 1.0% 0.1i%

number of samples R = arithmetical mean standard deviation L 8- = standard error of mean

-173-

5-3b. Strontium figure 5.9)

The strontium sulphate content of the barite orebody is remarkably uniform and averages 2.33% SrSO4.However,in the basal hematitic and white,'secondary' barite,lower SrSO4 values (1.7%) have been detected.

In all known cases barite contains certain amounts of isomorphous strontium and according to STARKE (1963) the mean SrS0 b. content of barite is 2.13 mole per cent.In rare cases vein barite may contain upto 15% SrSO4.GUNDLACH (1959) suggested that the Sr content of barite may be used as a possible indicator for the temperature of formation and that different generations of barite in a single deposit can often be distinguished by their Sr contents.

The apparent lower value of SrSO4 in the hematitic barite may be explained by the high Si02 and Fe304 content of the ore (upto 15% plus combined) which correspondingly reduces the BaS0 content and proportionally the SrS0 4 content.The low SrSO4 content found in both groups of 'secondary' barite (see figure 5.9) suggests that the Sr content may be directly related to the mode of formation of the mineral.In chapter 4-4a it was postulated that the migration of chloride. bearing connate waters carrying Ba in solution led to the emplacement of the 'secondary' barite.Work by STARKE (1964) showed that when the Ba/Sr ratio is constant in a solution,the presence of sodium chloride results in a lower incorporation of Sr in (Ba,S0SO4 crystals.Starke also proved that Sr content of (Ba,Sr)SO4 crystals increases when the temperature of the ore forming solution is increased.The low SrS0 content of the 4 diagenetic barite found at Ballynoe maybe applicable to Starke's work.Within the orebody,no marked difference is

-174-

FIGURE Strontium as SrS0 ) 5.9 4

0.1% 0.5% 1% 2% 3% 5% 10% (per mole %) A a I 'A I As I 4 1 I A' 1 barite in the A : 1 A: 1 hangingwall A I AA: Ft s A AA IA& : i 'cap' barite :A AAA: A; i • ----h-----r--AT,Al • AA& I : . 4 0 AsisiikAil ; /s I Allidi 41 , 1 upper half of I : Atha * tI 1 fI orebody I I , • : : ► : A Ikilik 1• • s ► le A:AlskA : :• 4 s Ati At # ; : t Alimi, : ; : • s lower half of o A A /AL ; : : s 4 4 _ odik 4 , A e-l , orebody 4 8 4 1 AA :AA : :

s AAA A; : I 4 1 i Atti -19A 1, : ■ basal & hematitic All 1 : Ad k' : : AMA : " barite L 1 Is A 4A _iI 4 1 I I III s- N x hangingwall barite : 15 1.62% 0.24% 0.33% 'cap' barite : 20 1,8% 0.31% 0.41% orebody,upper half : 50 2.45% 0.68% 0.49% orebody,lower half : 55 2,21% 0.72% 0.53% hematitic/basal b'ite: 10 1.96% 0.52% 0.31%

mean SrS0 content of orebody (105 samples) 4 : 2.33% -175-

observed between the SrSO content of the microcrystalline 4 barite and the coarser,recrystallised material (table 5.3).

TableJ.J SrSO4 content of orebody primary & diagenetic barite

14.2..1121 Range Black,micrXtalline barite : 2.41% 1.8-3.2% 25 Red,mega-epherulitic barite (D) 2.32% 1.6-3.0% 15 Grey,plumose Xtalline barite (D): 2.36% 2.1-2.7% 10

(D)= diagenetic

Although the SrSO4 content of the remobilized barite tends to be lower than the primary barite at Bailynoe,recent work by CUNDLACH et al (1972) on the partition of Ba and Sr in barite at different temperatures suggested that, as yet, no reliable genetic conclusions may be drawn using the Ba/Sr ratio.

5-3c. Aluminium (figure 5.10)

Aluminium has a sinuous dispersion throughout the orebody,the relatively high basal value of 1750ppm Al decreas- ing to less than )400ppm around mid-orebody and thence increasing to 1000ppm Al towards the hangingwall.The remobilized cap' barite carries a negligible Al content and contrasts with the secondary barite in the hangingwall which has a mean aluminium content of 700ppm.The possible genetic connotation of the sinuous Al trend is discussed in chapter seven.

5-3d. Magnesium

The orebody barite contains negligible magnesium (a mean of only 8ppm) and contrasts with the Mg rich secondary barite disseminated in the hangingwall.The dispersion profile -176-

FIGURE 412 ALUMINIUM r AI I I 0 At A I A t 0 A I I secondary' A I 1 0 1 barite zone A A 1 A I A AA IA A 'cap' barite AA AAA A • A A4& I 0 A A AA 41 I 1 1 I AAA I I 1 • ALA A Al t f AAA 1 o I upper half of i • AA A A IA I I 1 orebody • I AA 14. I 0 • A Ai AA t 0 0 t • i A I AA A • 1 0 A I AA • A i + AA AI 0 f i A I A AA ,A I i • • Atilo. A 1 I lower half of 1 I AA Ati • • o 0 1 0 A A 1 AA o 1 o orebody t I • A AAA o 1 1 1 1 001 AAA basal & hematitic o I I baritb I A 1 AL 10 100 1000 1 10% (in ppm)

N S sR

'secondary' barite .• 15 70C 260 310

'cap' barite .• 20 40 10 orebodyyupper half .• 50 1100 195 270 orebody,lower half . 55 14o0 180 360 hematitic barite : 10 1750 90 220

(Al content in ppm) -177-

for Mg in the 'cap' barite is very interesting (figure 5.1 1) and suggests that Mg enrichment of barite only occurs when the mineral is in direct contact with the hangingwall dolomites.If this is the case,the emplacement of the 'secondary' barite post-dates the dolomitisation of the hangingwall rocks.In the hangingwall,the 'secondary' barite averages 1% Mg (range : 0.4 - 6.5%)

FIGURE 5,11 Dispersion of M 1 1

0 10 100 1000 10000 in ppm Mg) 1 1 _L

* eS vert.scale icm = 5ft. 0® •

• 0 0

5-3e. Calcium

The dispersion of calcium in the barite is analogous to the dispersion of magnesium.With the exception of certain anomalies,no calcium has been detected in the orebody barite (detection limit for Ca is 100ppm),In the hangingwall):_the magnesium rich 'secondary' barite carries a mean Ca content of 1.15% (range : 0.5 - 8.2%).The anomalous Ca values detected in the orebody occur in microcrystalline barite (see plate 3.13f,g) and give rise to Ca values upto 9400ppm.It is of considerable importance to note that no magnesium is associated with these high Ca values,which are possibly derived from the exsolution of calcium during the primary crystallisation of the barite.

to. -178-

5-3f. Iron (figure 5.12)

Iron in the form of FeS2 and Fe203 is the dominant accessory element found in the barite horizon and the wide spread of analytical values is,in part,due to the unavoidable contamination of samples by pyrite or hematite.The bifurcation of values plotted at the base of figure (5.12) contrasts the hematitic barite developed in the southern half of the orebody with iron free,basal barite found to the north in DDH's 65 & 30.The two trends merge above the hematitic horizon when the hematite content of the barite gives way to disseminated pyrite.Above the hematite horizon the orebody barite averages 4175ppm Fe,this value falling to only 525ppm Fe in the remobilized,I secondary' barite.

5-3g. Copper

Although the spectrographic detection limit for copper is less than ippm,no trace of Cu eras detected in the orebody barite.The uniform copper profiles determined from the wallrocks (a mean o.f 18ppm Cu) and the lack of any copper enrichment in the orebody suggests that the chalcopyrite lens along the SSW footwall (ch.4-3c) is not genetically associated with the barite and post-dates its emplacement.

5-3h. Lead & Zinc

Any enrichment of lead and zinc detected in the barite (local values upto 3% Zn,1.9% Pb) is primarily due to disseminations of galena and sphalerite.Enrichment is confined to the upper half of the barite horizon and correlates with ore microscopy observations (ch.4-3d).No trace of Pb or Zn was detected in the basal hematite zone. -179-

FIGURE 5,12 IRON

'secondary' barite

cap' barite

Upper orebody

Lower orebody

Hematitic barite

0 10 100 1000 1% 10% (in ppm)

x secondary' barite 15 600 220 300 'cap' barite 20 450 300 320 orebody,upper half • 50 4200 4800 1000 orebody,lower half : 55 4150 3900 920 hematitic barite • 10 5% 1% 2%

-180-

5-3i. Other Elements

Mn, Ti and. Be were- only detected in= the hematitic barite horizon.In this zone Mn averages 200ppm with minor anomalous values upto 2400ppm (probably due to the development of psilomelane dendrites,plate 4.11).Titaneum and beryllium occur as traces (less than 2Oppm) and are restricted to hematitic barite carrying over 5% Fe.

Silver values (range 1 - 2307,:pm) are associated with plumbiferous barite.

The following elements were sought but not found : 0o,CrINi,Li,V,MolGa,Ge,Sn & Bi.

5-3j. Element dispersion between primary barite - 'secondary' barite

Figure (5.13) presents the variation in trace element dispersion found within the orebody and 'secondary' barite development.A clear distinction between barite types is established.

FIGURE 5.13 :

1000ppm

100ppm

I Oppm 1 2 3 4 c 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 SILICON SrS 04 IRON ALUMINIUM

1. Hematitic barite 4. 'cape barite

2, Orebody,lower half 5. hangingwall barite 3. Orebody,upper half -1,81-

5-4. Ba content of rocks in the Silvermines region

Devonian sandstones and Silurian shales collected within three miles of the Ballynoe barite deposit were analysed for barium (table 5.4).The Silurian shales were found to carry high and very constant Ba values whilst the Devonian sandstones were more erratic and subject to marked fluctuations in barium content.

TABLE 5.4 Lithology N. R Ba range (in PPm) Silurian shale,Silvermines Mtn.ridge 5 828 609-1120 " shale,Mulkeir river bed (2m SSW of mine)4 741 659- 878 et " mudFtone,Keeper Hill (3m S of mine) 2 910 840- 980 Devonian Sandstone,Silvermines Mtn.ridge 6 550 264-1430 tt tt sandstone,400 yds SW of mine 2 320 220- 420 " tt sandstone, 250 yds W of mine 4 885 511-1740

A geochemical,stream sediment survey (centred on SilvermineE village)was carried out along the 25 mile strike length of the CarbL,niferous Limestone — Sil/Devonian contact (figure 5.14).A-80 mesh stream sediment was collected,crushed and thence analysed by atomic absorption.

Of considerable interest is a 16 sq.mile barium anomaly delimited_ north of Toomyvara,fourteen miles NE of Ballynoe. The streams draining an area of Devonian sandstone are aalL191:Lialy enriched in Ba with values ranging from 1350ppm upto 1.3% Ba.This anomaly and its possible genetic implications regarding Ballynoe will be discussed in chapter seven. FIGURE 5,14 : Distribution of barium in strum sediments in the Silvermines area

Nenagh

pT :5000 + ppm Ba 21- miles * :1000 - 5000ppm Ba

dashes : Silurian C :300 - 10C0ppm Ba stipple : Devonian 0 : 0 - 300ppm Ba white : Lower Carboniferous -183-

5-5. Sulphur and oxygen isotope geochemistry

For a comprehensive account of sulphur isotope fractionation the reader is referred to the work of AULT & KULP (1;959), THODE,MONSTER & DUNFORD (1961) and HOLSER & KAPLAN (1966). Briefly,the above workers found that in sedimentary rocks, sulphates are enriched and sulphides are depleted in the isotope S34 with respect to meteoritic aulphur.(The meteoritic standard in use is from the Canon Diablo meteorite,where the 02/04 ratio equals 22.22 ).

In a submarine environment sulphate reducing bacteria (for example Desulfovibrio desulfuricans) consume seawater sulphate and produce H2S,the sulphide being depleted in isotope S34 with respect to the original seawater sulphate. Corresponding to the reduction of S34 in the sulphide there is an increase in isotope S34 in the coexisting sulphate. Howeverl because of the vast reservoir of sulphate ions in seawater the amount of S340 4 produced by bacterial activity will not perceptibly change the isotope ratio of the seawater sulphate (unless contained in a restricted basin).Sulphates which are precipitated from seawater will thus have isotope S34 values equal to the original seawater sulphate at the particular time of formation,The value of isotope S34 4 0 from seawater has varied throughout geologic time,see figure (5.1 5).

An account of oxygen isotope fractionation is given by TAYLOR & EPSTEIN (1962).Three stable isotopes of oxygen are found in,ocean water : 016 : 99.763 o17 : 0.037 % o18 : 0.1,99 % -1814.—

FIGURE 5.15 : Variation in avera e 6 s34 values throu hout eoloaic time for contem oraneous seawater sul hate

Tertiary

100my Cretaceous

Jurassic

200my Triassic

• Permian (approx age of Waulsortid,n Lst 300my •Carb —-11'

L.Carb • \ •

• Devonian • 400my Silurian

Ordovician 500my

Cambrian 0 600my

••• ( os34 0/00)

•: data after THODE & MONSTER (1965: •: data after HOLSER & KAPLAN (1966; -185-

The 018/016 ratio in natural materials varies over a range of 10%,this variation being due to equilibrium and kinetic fractionation.For example in sample 'A',any enrichment or depletion of 018 relative to the standard is reported in terms of the isotope permil notation le,

A = [RA - 1000 std.

R = 018/016 std. = SMOW (Standard Mean Ocean Water)

5-5a. Isotopic data for the Ballynoe barite

The sulphur and oxygen isotope data for the barite horizon presented in figure (5.16) formed part of a larger study including Mogul's 'G' and 'Is' ore-zones and was carried out by COOMER (1973-4 pers.com).

The isotopic values for the orebody barite (figure 5.16) are clustered in the range oS34 +18.6 - 19°Ao 018 +13.0 - 14.5°Ao A marked variance from orebody istopic values was obtained from samples of 'secondary' barite.This barite gave very high 6 018 values of +17.4 - 17.8°Ao.The white 'cap' barite (sample No.9) is only slightly differentiated from the orebody barite with the isotope values,SS34 +19o/oo 6018 +14.5°/00

5-5b. Discussion of results

Recent research on the sulphur and oxygen isotopic ratios of stratabound ore deposits (BUSCHENDORF et a1,1963;SANGSTER 1968;SAKAI et a1,1970;KAJIWARA & DATE,1971) suggests that contemporaneous sea water played a significant role in controlling the distribution pattern and isotopic variation, in the inferred syngenetic ore deposits. -186-

34 FIGUPE 5,16 : OS and 3018 values of the barite from

5S34°/oo...... +20 CI•Da . ' 0 0 8b 10 . . .• • ' . +19 CI")613

+18 • 1 • . • :04 •- . • 02 +17 .: (;) - 6, : . .: .: +16 (data after Coomer 197L +12 +13 +t4 +15 +16 +17

6018oApo

Sample Not Ft above footwall Sample Description 10 50 ' secondary' bari•Ge 9 42 'cap' barite 8a massive grey/black 39 8b ' secondary Ba . ve in 7 39 massive grey/black 6a massive grey/black 6b 33 spherulitic pink 6c spherulitic pink 5 32 massive grey/black L. 28 massive grey/black 3 20 spherulitic 2 10 red jaspilitic Ba. 1 1 hematitic barite The SS34 values for orebody barite fall within the range obtained by THODE & MONSTER (1965) for contemoraneous,Lower Carboniferous,seawater sulphate.This suggests that the sulphate ions of Lower Carboniferous seawater origin (connate or contemporaneous) were the predominant sulphur species in the barite forming solutions.The original 3 S34 value of the sulphate ions remained virtually unchanged during mineralisation,whether or not biogenic exchange took place between sulphate and sulphide.

As previously postulated,the formation of 'secondary' barite at Ballynoe is the result of expelled connate water from the massive barite horizon during diagenesis.Bacterial reduction of the sulphate in the connate water to H2S woulu be reflected by isotopically heavier sulphate remaining in the water.This isotopic fractionation is developed at Ballynoe. A definite increase in BS34 values is observed from primary barite through to diagenetic 'secondary',for example :

secondary': 6S34 +19.80/00

F-1 'cap' barite: 304 4-19.1°Ao

primary barite : 604 +18.5°Ao

A similar enrichment in SS34 values was determined from secondary gypsum ores in the Noto Mine,Japan by SAKAI et al (1970).

The oxygen isotopic compositions of sulphate according to SAKAI et al (1970) are largely determined by the isotopic composition and temperature of the original water.SOLOMON (pers com) suggests that fluid - rock interaction is also an important factor.These factors may account for the wide -188-

variation of 6018 values determined in the primary and 'secondary' barite,reflecting the differences in the nature and temperature of the waters which operated in primary barite deposition and diagenetic processes.The higher 6018 values of the 'secondary' barite may be due to the re-equilibration of oxygen isotopes during the expellation and the subsequent fluid - rock interaction of the diagenetic,connate orebody waters.A similar re-equilibration of oxygen isotopes was determined by SOLOMON et al (1971) in barite from the North Pennine Orefield...At the Settlingstones Mine,both primary and secondary barite generations were analysed :

Settlingstones primary barite : SO18 +12.9Voo (Ballynoe primary barite) : 6018 +1 3.2°/00

Settlingstones secondary barite : 6018 4-18.5°Ao (Ballynoe 'secondary' barite) : 5018 +17.8°/oo

The above results suggest that the SO4 anion in the Ballynoe barite is of marine origin (connate or contemporaneous), The source of the barium cation is discussed in chapter seven.

5-6. Summary

1.The barite mineralisation is exactly conformable with the top of the Muddy Reef Limestone as proved by the geochemical 'unconformity'. 2. Barium enrichment is still intensified at the top of the Muddy Reef Limestone well to the north of the barite orebody. 3. The wallrocks to the barite horizon carry negligible barium (excluding the remobilized Ba). 4. Secondary remobilization of Ba into the hangingwall is -189- controlled by footwall structures ie., the 'eastern dome'. 5. Strong barite mineralisation is accompanied by a correspondingly high silicification of the footwall,the converse applying to weak barite mineralisation. 6. The main period of lead-zinc mineralisation is not associated with the emplacement of the barite.Copper mineralisation also post-dates the barite.The only elements of importance to be caplaced with the barite were iron and silicon (as hematite/siderite, jasper and quartz). 7. Trace element dispersion within the barite differentiates between the different generations (see figure 5.13). 8. A major barium anomaly has been delimited in an area of Devonian sandstone around Toomyvara. 9.Isotope evidence suggests that contemporaneous Lower Carboniferous seawater or Lower Carboniferous connate water was the source of the sulphur in the BaO.4 10. The sulphur and oxygen isotopcs differentiate between primary and secondary barite. -1 90-

CHAPTER SIX

STRATABOUND BARITE IN THE BRITISH ISLES

6-1, Introduction

Stratabound barite occurrences are distributed throughout most of the Phanerozoic rocks in Britain,the host strata ranging from Cambrian shales through to clays of Eocene age. The deposits of stratabound barite may be divided into two arbitrary groups : i)Sedimentary barite : emplaced by synsedimentation (chemical or elastic) and modified by diagenetic processes. ii) Barite 'flatting' deposits : emplaced by the direc:, metasomatic replacement of a favourable host horizon by epigenetic fluids. Because of the diverse nature of stratabound barite in Britain a comparative study with the Ballynoe barite horizon is not possible or indeed intended. The aim of this chapter is to be a complimentary exercise,to marshal the significance of geological similarities or dissimilarities found between the deposits concerned and to plot the dispersion of barium throughout the Phanerozoic time-scale.Such an understanding will provide a broader base for the construction of a genetic model for the Ballynoe barite.

6-2. Barite in a sedimentary environment

Although barite is normally classified as an important gangue member in metalliferous fissure veins,the mineral is widespread in other lesser known environments,particularly in -.191—

thick sedimentary rock piles,In a sedimentary environment barite may occur as syngenetic precipitates,nodular and oolitic concretions and detrital accumulations.During sediment consolidation,diagenetic processes often modify and remobilize the aforementioned deposits,giving rise to baritic cements, authigenic crystal growth,diagenetic nodules and minor vein formation.

It would be instructive to review the recorded occurrences of 'sedimentary' barite within the Phanerozoic time-scale,where barite may be found in rocks spanning some 500 million years., The occuirences of barite have been tabulated in the form of a atratigraphic column (table 6.1),the table being a compilation of localities reported in literature and new ones discovered by the writer.

6-2a. Reported occurrences of sedimentary barite

Cambrian : Although large barite veins (probably remobilized barite,HALL 1922) truncate Pre-Cambrian rocks in Shropshire,the oldest reported authigenic barite occurs in Lower Cambrian shale sequences, interbedded with thick sandstone units at Nuneaton,Warwickshire.Large,crystalline barite blades are found in the shales (FLEET 1925) with minor baritic cementing in the adjacent sandstones. Devonian : Authigenic barite is widespread throughout the Devonian sandstones of the West Midlands and Welsh Borders and according to FLEET (1926) horizons in the Downtonian and Dittonian series carry abundant, "large sized, clear,angular plates of barite." The mineral is very common in the Ledbury and Tr•impley fish-zones and acts as a cement in certain Cornstone horizons (a concretionary,earthy limestone). -192-

TABLE 6.1 'Sedimentar barite in the British Phanerozoic

ABC DE

EOCENE E MI ondon Clay PALAEOCENE

Nature of Barite CRETACEOUS ❑ Chalk A: syngenetic pi

p! reensand Palden B: nodules,septaria C: authigenic crystals JURASSIC m -i-- .Lias D: c emen t m la ,Lias .Lias E:allothigenic ■ euper vein,replacement etc TRIASSIC - iii -- anter F: . -- U

PERMIAN _-_ ,Magnesian Lst. asal Sand,Marl Slate ®® m 0 , oal Measures CARBONIFEROUS__ ...... _

: m - amurian o inantian Relative abundance II ffi pper DEVONIAN m liddle 0 rare

E n ❑ ower m minor widespread SILURIAN in major

Ballynoe barite horizon ORDOVICIAN 1

Stratigraphic Scale: CAMBRIAN I = 20 million years E ®

1 E ower

AB CD EF - -193-

The Lower Devonian sandstones of eastern Scotland, so well exposed along the Arbroath coastline (see figure 6.1) carry innumerable stringers and veinlets of barite and are postulated by the writer to be of a probable diagenetic origin.The open pored textures of sandstones make the rock an excellent medium for migrating diagenetic fluids.The chemistry of the Arbroath barite almost identical to that of barite from the Welsh Borders (table 6.2).Barite strings and veins are also relatively common from the Middle Devonian strata of Caithness,Orkney and SW Ireland.In many instances the barite is associated with minor Pb and Cu mineralisation.

TABLE 6.2 Chemistry of Devonian authi enic & vein barite Sample Sr Si Mg Mn Pb Cu Fe Al Ca 'A' 0.9% 1100 - - 350 1300 - 'B' 0.7% 1•2% - 280 1 050 - Sample 'A' : Tabular authigenic barite crystals. Lower Devonian Sst. Ledbury, Herefordshire. 4 Sample 'B' : Massive pink barite. (mean of samples) Lower Devonian Sst. Forbidden Cave Headland, Auchmithie,Angus. (mean of 5 samples)

Carboniferous : Minor barite is associated with an Upper Visean tidal flat,evaporite facies in County Leitrim,Irelard (WEST et a1,1968).The barite occurs as veinlets and nodules, in part replacing gypsum and celestine. Overlying the Visean,the Namurian Millstone Grit series of Yorkshire and Lancashire(a deltaic complex of sandstones, grits and shales) often carries concentrations of allothigenic

(detrital) barite.GILLIGAN (1919) separated barite in quantity from the Great Almscliffe,Follifoot and Slaidburn Grit sequences found to the north of Leeds.The writer has collected -194- J I

£:IGURE 6.1 Sedimentar;}T" bari te locali ties mentioned in the text

~A~_--- - Orkney ~ .

______Caithness J

x : Eocene

7r .• Cretaceous a : Jurassic 8 : Triassic ______Arbroath w: A <1>: q> : A : Devonian BaC12 n : / brlnes

o q> Leitrim

.", BALLYNOE

0A Ledbury o Forest· of Dean I 7ro N .,./ T Nutfield Dover 50m. Wight , ------~, I -195-

translucent,authigenic barite crystals from the Almscliffe and Slaidburn Grits which confirms Gilligan's early work. (Very rare 'cockscomb' barite was observed along bedding planes in the Almscliffe Grit).A barium geochemical anomaly outlined in this area by DAVIES (1971) was tentatively related to mineralisation in the underlying Carboniferous Limestone.A detailed examination of this barium anomaly is described in section 6-4.

Numerous authigenic and detrital barite occurrences have been reported from the Coal Measures of Britain.Sandstone horizons are the predominant host formation and examples' occur in the Midland Valley of Scotland (GREENSMITH 1971), West Cumberland (LEWIS 1931),the Keele Beds of Staffordshire (FLEET 1925) and in south Yorkshire (VERSEY 1925).A more substantial deposit of barite was found in No.3 Pit,Manvers Main Colliery near Rotherham,where a sandstone bed above a coal seam carries a lens of barite 15ft long by tft wide (FINN 1930).in the same region ELLIOT (1972) has reported thin veins of barite cutting the Coal Measures at Bevercotes Colliery whilst at the same mine,barite was precipitated on the walls of a recently sunk sheft.Ironstone nodules frequently carry barite in the Coal Measures,examples being reported from the Overseal Marine Band,Leicestershire (FORD 1972) and in sideritic nodules from the Forest or Dean coal- field.

Of considerable interest are the barium bearing,chloride brines associated with the Coal Measures of north-east England.The brines were first reported by BEDSON (1877) and

CLOWES (1889) who noticed that water-boxes carrying the brine ti -196- became choked with precipitated barite.ANDERSON (1945) records 12 barium chloride brines which averaged 1700ppm Ba (range: 710ppm 3430ppm Ba).Barite (blanc-fixe) was once commercially produced at a rate of over 100 tons per week by precipitating the brines with sulphate bearing waters at Backworth Colliery, Northumberland.According to DUNHAM et al (1945) the considerable tonnage of vein barite (& witherite) localised along the Deer-less Fault and Great Spar Dyke in the Durham Coal Measures is not genetically related to the barium brines. Similar Ba brines in Germany have been recorded by BEYSCHLAG (1914) from the Coal Measures (Carboniferous) of Westphalia. Recent work by SCHERP & STRUBEL (1974) suggests that the barite veins in the Ruhr and Rheinisches Schiefergebirge are related to these brines.

Permian : Along the angular Carboniferous/Permian unconformity in south Yorkshire and Derbyshire,irregular, eroded hollows in the Coal Measures are infilled with sand (Permian Basal Sand).From these sand pockets LEWIS (1923) separated angular to rounded grains of detrital barite, regarding the source of barite to be local veins in the Coal Measures.

The Marl Slate formation which overlies the Basal Sand is the English stratigraphical equivalent of the German Kupferschiefer which carries probable syngenetic base metal mineralisation (DEANS 1950,HIRST & DUNHAM 1963),In Co.Durham minor barite is associated with low grade Pb and Zn mineralisation from this horizon.Above the Marl Slate,the Lower Magnesian Limectone is an important host for extensive barite mineralisation centred around Ferryhill•in Co.Durham (HIRST -197-

& SMITH 1974) and at Bramham in west Yorkshire,see

Triassic : Sandstones of Triassic age carry some of the largest concentrations of stratabound barite in Britain and in the future these 'low grade - high tonnage' deposits will possibly attain commercial significance.

Barite occurrences have been documented from the Bunter Pebble Beds at the base of the Trias through to the Keuper Marls at the top of the system.The predominant host horizons for barite are the Mottled and Lower Keuper Sandstones which are well developed around the Cheshire Plain.Normally soft sandstones are cemented into resistant ledges by crystalline rosettes of barite.At Stapleford in Nottinghamshire,barite cemented Bunter Sandstone forms two conical hills,the valley between the hills containing the famous Hemlock Stane.The Hemlock is a 40ft high pillar of Bunter Sandstone cemented by barite and according to CLOWES (1889) averages over 30% BaSO4.The petrography of the sandstone consists of rounded .grains of quartz cemented in a matrix of crystalline barite. A recent study of the area by TAYLOR & HOULDSWORTH (1973) detected the presence of barite in the underlying Coal Measure sandstones and a genetic link with the barite in the Bunter appears probable.A war time economic survey of the Stapleford area calculated a barite reserve of at least 2 million tons (DUNHAM et al 1945). The barite enriched sandstones are strongly developed along the southern and western periphery of the Derbyshire Dome,the Mid-Cheshire Ridge (POOLE & WHITEMAN 1966) and even in the Scottish Trias at Elgin,Morayshire (MAXIE 1901).At one locality on the Cheshire Plain the writer surveyed a 25 ft thick section of barite cemented Mottled Sandstone -198- carrying an estimated grade of 20% BaSO4.

In the south of England THOMAS (1909) reported barite cemented Triassic sandstones intersected at a depth of 1000ft in a bore hole near Lyme Regis in Dorset.

Jurassic : Barite is commonly found in the argillaceous Liassic sediments within the lower half of the System.Nodular barite in the form of flattened discs have been found in the Lower Lias shales of Dorset (RICHARDSON 1923) whilst septarian nodules veined by barite are of common occurrence from the Amaitheus mar anitatus zone of the Middle Lias in Rutland (TAYLOR 1,950).From the Middle Lias in NE Yorkshire ironstone bands are often veined by barite and in one instance fossil wood has been partially replaced by the mineral XSTEAD 1909). From the Alum Shales of the Upper Liassic DANBREE (1871) noted, "the occurrence of barytine on the surface of fossils at Whitby.tt ln the Jet Rock and Alum Shales to the north of Whitby, the writer has examined a large number of ammonites for barite and the results are presented in table (6.3).Barite is a very rare constituant in the ammonites examined,the mineral either infilling a core of a calcitic body chamber or synerecis cracks in the outer whorl (figure 6.2).11 is of interest to note that iron rich sphalerite is very common in the outer body whorls of the ammonites and is a ubiquitous constituant of the genus Hildoceras bifrons,

Cretaceous : At Nutfield in Surrey the Sandgate Beds (Lower Greensand) contain economic deposits of fullers earth, the host horizon for translucent,nodular barite.In the montmorillonite clay beds which have long been worked,WEBSTER (1821) recorded finding nodules of a yellow,crystalline -199-

TABLE 61.1 : Metallic mineral content of Upper. Liassic Ammonites collected north of Whitby.Yorks.

No.containing Genera No.examined barite ZnS PbS CuFeS

Dactylioceras commune 580 ' 16 360 11 2 Hildoceras bifrons 46 2 46 0 0 Phyllocer--.s sp. 10 0 0 0 0

(collected from the Jet Rock — Alum Shales) , 1

FIGURE 6.2 : Mineralogy of Dactylioceras commune

sphalerite barite in syneresis cracks

bladed sphalerite & minor galena

crystals on outer surface

zoned Fe rich calcite

barite in core of calcitic body chamber

A polished section through the ammonite,true scale

••■•■■■•■ -200- barite upto 112 pounds in weight.The geology of the deposit has been described by MANTELL (1841) and more recently by DINES & EDMUNDS (1933) who considered the nodules to be, 'apparently indigenous'. In a recent exposure of fullers earth at the Laporte Industries open-cut,Nutfield,the formation of honey-yellow barite crystals (associated with quartz and pyrite) tend to be restricted to the top of the clay bed which is overlain by glauconitic sandstone.Below the barite nodules and extending the full thlckness of the clay horizon (15ft) are thin,near vertical veinlets of fibrous barite,see figure (6.3).The veinlets,which are upto truck- • possibly acted as feeders to the barite nodules at the top of the bed.Fibrous barite has also been reported from the Cretaceous,Wealden Marls of the Isle of Wight. OSBORNE-WHITE (1921) noted lentjcular veins of 'beefy heavy spar' culting the Marls.The occurrence is unusual as the Marls are overlain by a conglomeritic bed containing pebbles of barite derived from the underlying veins.According to SE ADMAN (pers.com) the occurrence of fibrous barite is extremely rare.

Minor baritic nodules have been reported from the Chalk formation near Dover (RUDLER 1905).

FIGURE 6. : Barite occurrence in fullers-earth Nutfield

Glauconitic Sst.

barite nodul C44t:;› : 10ft.

'feeder vein

'fullers- J earth'

Fl -201-

Eocene : Some of the youngest authigenic barite in Britain occurs as stellate crystals coating septarian nodules from the London Clay formation.The radiating crystal sheaves are pale yellow in colour and are very abundant in the London Clay exposed in the Thames estuary around Southend and the Isle of Sheppy. •■•

6-3. Distribution of Ba in En lish & Welsh stream sediments

(This section is based on data collected by the Imperial College Applied Geochemistry Group under the leadership of Professor J.S.Webb in preparation for the 'Geochemical Atlas of England and Wales (in prep.)).

The ('',istribution of barium anomalies in England and Wales are plotted on figure (6.4).The anomalies may be classified into three groups : i)stream sediment contamination by mining activity (metalliferous and coalmining). ii)lithologies carrying a high Ba background content (this group is allied to group iii). iii)priarily due to diagenetic barite in sediments.

The fcllowing barium anomalies (figure 6.4) are directly or indirectly related to mining activity : No,2a. Colliery spoil heaps,Northumberland Coal Measures. 3. Colliery spoil heaps,NW Cumberland Coal Measures. 4. Waste tips,West Cumberland hematite mines. 5 Barite mining along the Pennine Escarpment. 6. Barite mining (& Pb/Zn),Teesdale. 8. Pb/Zn mining,Wensleydale. 9. Pb/fluorspar mining,Wharfedale and Greenhow Hill,Yorks. 12a. Colliery spoil tips,S.Yorkshire & N.Derbyshire 13a. Pb/barite mining,southern Derbyshire orefield. -202--

FIGURE 6,L : Distribution of Ba in English and Welsh stream sediments

500 + pprr

Based on data compiled by the Applied Geochemistry 300-500ppm Research Group, Imperial College. 0 -300ppm

D 2 0 a 22

‘-'29

50m1s. -203-

No.21a. Pb/Zn and barite mining,Shelve,Shropshire. 23a. Colliery uoil heaps,Monmouthshire.

ii) The anomalies related to lithologies carrying a high Ba background extend over a larger area than the more restricted barium haloes found around mining fieids.The pattern of barium dispersion in this group often reflects the strike and regional extent of the host rock.Illustrating this statement are the synclinal shaped Wealden anomalies (no.31) and the concentric Ba anomaly developed in the Cheviot volcanics (no.1).The following high Ba background anomalies are plotted on figure (6.4):

No.1. Cheviot volcanics (andesite lava),Northumberland. 7. Silurian shales,southern Lakeland. 11. Permo/Triassic,west Lines. 12b. Coal Measure shales,Notts,Derbyshire and S.Yorkshire. 14. Ordovician volcanics (andesite lava and ash),Snowdon. 15. Cambro-Ordovician shales and extrusives,Harlech Dome. 19. Coal Measure shales,N.Warwickshire. 20. Cretaceous Gault Clay,Cambridgeshire. 21b. Silurian shales,Shelve,Shropshire. 22. Basaltic intrusives,Pembroke. 23b. Keuper Marls - Lower Liassic shales,Glamorgan. 24. Keuper Marls and Jurassic Waterstones,Gloucestershire. 26. Keuper Marls,Somerset. 27. Keuper Marls - Lower Liassic shales,Watchet,Somerset. 28. London Clay,Essex. 29. Gault Clay,Oxfordshire. 31. Weald Clay, Kent. 32. London Clay,Hampshire. 33. Oligocene clay,Isle of Wight. 34. Eocene clays,Hampshire. 35. Lower Liassic clays,Dorset.

Related to the group (ii) barium anomalies are the anomalies derived from diagenetic barite formation within -2042

the sediments.Many of the barite occurrences described in section (6-2) comprise the group (iii) barium anomalies plotted on figure (6.4) : No.2b. Barite precipitated from Ba brines,Co.Durham & Northu'nd. 10. Barite veining in the Millstone Grit,Coal Measures and Magnesian Limestone,West Yorkshire.(This anomaly is described in section 6-4). 13b. Bunter and Keuper Sandstones cemented and veined by barite,South Derbyshire and Staffordshire. 16. *Bunter Sandstone cemented and veined by barite,Cheshire Plain. 17. Bunter Sandstone cemented by barite,Stapleford and Beeston,Notts. 18. Bunter Sandstone and Keuper Marl,west Midlands. 25. Authigenic barite in Devonian Sendstone,Herefordshire. 30. Barite in the Sandgate Beds (fullers-earth),Nutfield, Surrey. *The Ba anomaly over the Cheshire Plain is partly due to the dispersion of barite enriched Keuper Sandstones by glacial action (DAVIES 1971).

6-Li.. The barium anomaly to the north-east of Leeds Yorkshire

The Ba anomaly (no.10,figure 6.4) lies an average of six miles to the NE of Leeds and trends from the southern outskirts of Harrogate,SSE to beyond Castleford,a distance of 20 miles.

The region is drained by a river system flowing eastwards off the Pennines to form part of the river Ouse catchment basin.Three topographic belts coincide with the outcropping geology : a) The Millstone Grit country rises to over 650ft in the NW of the region (figure 6.5A) and has been strongly disected by the river Wharfe and its numerous tributaries.The differential -205-

erosion of gritstones and shales give rise to an undulating landscape.

b) The Coal Measures developed in the south of the region have a topography similar though less pronounced than the Millstone Grit,rising to 400ft within the boundries of figure (6.5A).

c) The Permian rocks in the area terminate in a west facing escarpment,the dip-slope shelving eastwards towards the Vale of York.The gently undulating surface of the Permian rises to 300ft along the escarpment,the dip-slope being masked by extensive spreads of boulder clay.

The geology of the region has been described in detail by MITCHELL & WHITEHEAD (1950) and a brief summary will suffice. The oldest exposed strata is the Millstone Grit (Namurian) and consists of a 4,000ft thick sequence of rythmically bedded sandstones and shales with minor coal horizons.Sedimentation is considered to be of deltaic origin with minor marine incursions. The Millstone Grit is conformably suceeded by the Coal Measures which outcrop to the south of the Grit and continue eastwards under the younger Permo-Triassic cover.Thick shale sequences alternate with thiner sandstone horizons and coal seams upto 9ft thick are found (ie,the Beeston Seam).Broad, irregular folding effects the Carboniferous rocks with an E-W axial trend. The Permian rocks rest with a marked N-S trending unconformity on the Carboniferous strata.The thin,loosely cemented Basal Permian Sand is overlain by the Lower Magnesian Limestone, a well bedded dolomitic limestone (porcellanous to oolitic in texture).The Magnesian Limestone dips east at 1 in 50 and -206-

varies between 150-300ft in thickness.The overlying Upper Permian and Triassic rocks are not developed in the region under study.

6-4a. Distribution of Ba in stream sediments

The regional geochemical map for Ba (figure 6.5A) presents a complex distribution pattern for the element, ranging from a medium anomaly over the Millstone Grit strata (550-8000ppm Ba) to very strong 1% + Ba anomalies developed over the Coal Measures and Magnesian Limestone.Seven anomalous areas of Ba enrichment have been delimited in the study region (the area no's refer to4ocalities on figure 6.5A).

Area 1 : Kirby Overblow Rigton (Millstone Grit).Very consistent Ba values in the stream sediment in the range 550- 1200ppm Ba (the background Ba value for the area is 150ppm Area 2 : Spofforth (Millstone Grit/Mag.Lst).High Ba values in the sediment of the river Crimple,5000-8200ppm. Area : Sicklinghall House (Millstone Gritilmag.Lst). An isolated value of 1% + Ba. Area 4 : Bardsey (Millstone Grit).High and consistent Ba values in the range 2500-6000ppm. Area 5 : Bramham (Lower Magnesian Lst),A major Ba anomaly with four of the main streams carrying in excess of 1% Ba. Area 6 : Barwick in Elmet (Coal Measures/Mag.Lst).A large anomaly over the Coal Measures and outliers of Magnesian Lst. Area 7 : Hayton (Lower Magnesian Lst).Four streams carrying a spread of values from 650ppm to over 1% Ba.

6-4b.Follow up investigation : A detailed field examination of the Ba anomalies proved the existance of widespread barite mineralisation and the results are presented on -207-

figure (6.5B).

Area 1 : The Millstone Grit in this area is veined by numerous stringers of pink to white barite (up to 4" thick) and examples may be observed along the crest of Stainburn Hill (locality no.1 on figure 6.5B).Across the valley of the river Wharfe barite veins up to 2ft thick truncate the Lower Follifoot Grits near Stockton Farm (2) and in Harewood Park (3).The Follifoot Grit was widely used as a building stone and barite strings are often observed in the walls of farm buildings !

Area 2 : This anomaly is derived from authigenic barite within the Plumpton Grit.10 grit samples were analysed for barium and the results were : Plumpton Grit, 7 samples : R 210ppm Ba (range 90-320ppm) 3 samples : x = 3600ppm Ba (range 1050-6300). The residual gritstone 'tors' in the Spofforth area may have certain horizons cemented by barite.

Area j : This anomaly is contained between two outliers of Magnesian Limestone.Both limestone and the underlying grits carry barite.Barite veining gritstone is exposed near Caristonhill Farm (4) whilst lenses of barite are very common in the basal Magnesian Limestone to the east of the West Plantation (5).From the river Wharfe at Ox Close (6) a concen- trate of 75% barite and 25% almandine garnet was panned and in exceptionally low water conditions,barite nodules up to 12 lbs in weight were recovered from the river bed.Above Ox Close a faulted outlier of Magnesian Limestone carries abundant barite in the form of stratiform lenses upto lft thick. To the west of the outlier (8) an exposure of Millstone Grit is veined by weak barite with marginal baritic cementing of the gritstone. -208-

FIGURE 6.5 : Distribution of Ba in NE Leeds stream sediments A : 1% Ba

: 5000-10a WETHERBY A : 1000-5000 • : 300-1000 o : 0 -300 (in ppni)

• Millstone Gri 1-15

TADCASTER

• • •

.••• . ..- •

:areas in text. . •

•• barite float W10 :Ba outcrop

40. L '71'0 Cl' 8 o O ,...(' P-'.f. . t Ay .. 9 ,...., ...." ° . • 0 .-t•.. ds. 012 013 - '. ..., ft, • . es. 4, • 1,15 . • '.°11' s.,!, k Y t , • .. !es lil - t • 1. ' - - • - •- '41

• . . . 1pqw ir 6 ;':, • .. .. -- . , 22■ 97 ..,:...,.,..— — • •

• e t 9 1 •.; 0 20 -209-

Area 4 : The Ba anomaly to the west of Bardsey village (9) is probably related to barite veining within the Lower Follifooti Grit Horizon.One mile SE of Bardsey in Barkers Plantation (10) minor barite veining was observed in the East Calton Grits, the overlying Magnesian Limestone carrying nodular barite mineralisation (11),In this area barite float (derived from Mag.Lst) was noted in the top soil of many fields.

Area 5 & 7 : Barite mineralisation in the form of nodules and veins has long been known around Bramham village (12),the Lower Magnesian Limestone being the host rock (VERSEY 1925). To the east of Bramham along the slight rise of the Oglethorpe Hills (13) extensive spreads of barite float has been found by the writer,with the odd boulder attaining a breadth of 3ft Copper staining is evident in some of the barite and chalcocitelcovellitel azurite and malachite have been identified. It is of interest that at Newton Kyme (14) 12 miles NE of the Oglethorpe Hills a 'green carbonate of copper' was recorded by MARSHALL (1829),an occurrence not verified by the Geological Survey (EDWARDS & MITCHELL 1950).Barite is abundant around Bramham village coating joint planc., s in the Magnesian Limestone, and occurring along faults in veins up to 2ft wide.Stratlform lenses and nodular replacements of barite are very common, see plate (6.1).Below Bramham Lodge (15) a large mass of crystalline barite is exposed in a cutting of the Al trunk road.In the Bramham Park Carboniferous inlier,cockscomb barite 'veins Millstone Grit (16) and pink barite the Coal Measures (17).1 The Ba anomaly around area 7 is derived from from a SE trending train of barite float carried in glacial drift (18), the barite being derived from the Bramham mineralisation. -210-

Area 6: The unconformity between the Coal Measures and the Lower Magnesian Limestone is exposed along the north-south trending escarpment above Cock Beck (20),Barwick in Elmet. The exposure presents the only example known to the writer of barite veining cross-cutting the Carboniferous-Permian unconformity.Barite veins up to 6" thick are common in the Coal Measure sandstones below the unconformity (see figure 6.6) and in rare cases extend across the plane of unconformity into the basal Permian strata.In both formations barite is abundant.In one case a micro-flatting horizon of barite was developed along the plane of unconformity.Evidence suggests the barite veins were derived from ascending and not descending' fluids.Barite float is abundant in the fields to the SW and SE of Aberford (19) and is derived from the mineralisation of the Lower Magnesian Limestone.

FIGURE 6.6.: Barite mineralisation,Barwick in Elmet

0 0 DISSE:UNATED BARITE IN DOLOMIT - BARITE IN THIN MARL

BARITE INVADING JOINT PLANES

' PERMIAN BASAL SAND •

*3 VEINS IN COAL Mii;ASURES

AUTHIGENIC BARITE CRYSTALS IN SANDSTONE *5

*1 : 957ppm Ba *3 : 2423ppm Ba *2 : 4370ppm Ba *4 : 14871)pm Ba *5 : 3987ppm : iFt. L_ -211—

PLATE 6.1 : Barite mineralisation around Bramham Yorkshire

A,B : An extensive spread of barite float in a ploughed field one mile due east of Bramham village,in the the Oglethorpe Hills.Boulders of white,crystalline barite (in Magnesian Limestone) are clearly visible in the foreground of plate B.

C,D : Nodular barite float in a ploughed field directly above the village of Bramham.Note the hammer for scale in plate D.

E,F Stratiform lenses of thin barite in well bedded Magnesian Limestone (exposed in Bramham Quarry). In the fields above this exposure,mole hills carry abundant fragments of barite.

G. : Detailed view of a stratiform barite lens from Bramham Quarry.

H. : Nodular barite replacing Lower Magnesian Limestone exposed in a. road cutting for the Al. PLATE 6.1

h A

G -211 3—

6-4c. 1122 .ical range of barite mineralisation

The lowest horizon of the Millstone Grit series to carry barite in the Leeds area is the Almscliff Grit horizon of

E2 age (Silsden Moor Group).Above this horizon all the successive Grit horizons carry barite,the most important being the Follifoot Ridge Grits (H1 ,Middleton Grit Group), the Plumpton Grit (Ri ,Kinderscout Grit Group) and the East Carlton Grit (R2,Middle Grit Group).At Barwick in Elmet, the Elland Flags of the Lower Coal Measures are the youngest Westphalian rocks to be mineralised by barite.Barite is present in the Permian Basal Sand above the Carboniferous/ Permian unconformity and is strongly developed in the Lower Magnesian Limestone.No barite mineralisation has been detected in the overlying Middle Permian Marl or Upper Magnesian Lime- stone. FIGURE 6,7 Stratiaphical range of barite mineralisation

1. Mq Lst

6-5. Barite 'flatting' deposits Barite 'flat' deposits are not strictly related to stratabound,'sedimentary' barite occurrences and are only briefly considered in this section.A barite 'flatting' is formed by the direct metasomatic replacement of a favourable host horizon.DUNHAM (1948) suggested that 'flats' formed in association with strongly mineralised veins in places where for some reason the formation of fissure veins was inhibited.

-214-

Barite 'flat' deposits are developed along the Pennine escarpment and replace the Lower Carboniferous Limestone strata.Examples are known at the Silverband Mine (a replacement of Great Scar Limestone) and at the Murton and Hilton Fell Mines (replacement of Melmerby Scar and Smiddy Limestones

In Wharfedale,Yorkshire,a series of barite flatting beds are developed at Nussey Knott.The beds dip at 12'N in

Lower Carboniferous (S2) Limestone and are intersected by N-S trending fissure veins (VARVILL 1920).Three flattings are known and carry massive barite in a heavy clay fill.The beds vary in thickness from between three to eight feet,the maximum thickness being near intersections with the N-S trending faults.lhe barite is amorphous to crystalline in nature and has a density of 4.45.Unlike the chemistry of the Ballynoe barite trace amounts of Cu,Ni and Cr was detected in the barite from Nussey Knott,see table (6.4).

TABLE 6.4 : Partial trace element content Nusse Knott barite Cu Ni Cr Brown,amorphous barite from the 'Middle Flat' Nussey Knott. 25ppm lOppm trace (A .mean of 10 samples over a 4ft R :(65-3) (17-tr) range ).

FIGURE 6. : North - south section Nussey Knott

South North Nussey Knott

rite 'flats'

MILL5ToNE GR IT

Craven Fault - (North) -215-

6-6. Discussion and conclusions

The distribution of 'sedimentary' barite throughout the Phanerozoic rocks of the British Isles suggests a strong genetic affinity with argillaceous formations.In local sedimentary sequences Ba-rich argillites are overlain by sandstone and carbonate horizons which often carry barite in the form of cements,authigenic crystals,veins and irregular replacement.This relationship may be developed on a regional scale,the host formations to barite mineralisation being adjacent to or underlain by sedimentary basins carrying a major shale fraction.It is evident that shales play a major role in diagenetic barite formation.

Why does barium become concentrated in shales ? Barium is a ubiquitous trace element in the earth's crust and averages 480ppm in igneous rocks and 430ppm in sedimentary. The Ba content in igneous rocks normally increases with increasing Si02 concentration.An ultra-basic dunite may carry only 0.4ppm Ba (TUREKIAN & 7JEDEPOHL,1961) whilsL at the other end of the scale alkalis rocks average over 1000ppm Ba.When the host rocks are broken down during the weathering process,barium is transported to the site of deposition. In the sedimentary basins barium is readily adsorbed from solution by clays,hydroxides and organic matter.Thus the silt and clay fractions of a sediment are often considerably enriched in Ba,FENNER & HAGNER (1967) correlating the amount of Ba in the clay with the illite content (the Ba++ ion may substitute for K+).Black shales often carry more barium than 'normal' shales DUNHAM(1961) suggesting a relationship between high Ba and organic matter. In the Lower -216-

Cambrian Mn shales of the Halech Dome,MOHR (1959) determined Ba values of over 2000ppm.He suggested that Ba entering the basin of deposition was rapidly precipitated close inshore and adsorption on clay minerals occurred.NICHOLLS (1962) reported that Coal Measure siitstones carried over 1000ppm Ba and that a constant K/Ba ratio implied that the Ba ion was associated with illite.In the Lower Cretaceous shales of the Carnawan Basin in Western Australia beds of barite up.'6o one foot thick are widespread (CONDON 19614).The shale is of a dark marine nature and contains many pelagic forams and radiolaria.According to SAMOILOV (1917) dark shales of Upper Jurassic age in the Soviet Union are enriched in Ba and carry extensive development of nodular barite.

GOLDBERG & ARRHENIUS (1958) noted Ba enrichment in the clay sediments under the Pacific.The greatest enrichment was in the equatorial zone and this was related to high biological productivity in the surface layers of the water.Several planktonic organisms are known to accumulate Ba in their tests for example the Rhizopod XeLIELLI2E122m.Recent clay sediments in the SE Atlantic carry upto )#000ppm Ba (TUREKIAN & TAUSCH,1964).

Formation waters derived from shale sequences frequently carry very high Ba values.In the Soviet Union the Ba content in formation waters has been successfully used for the correlation of stratigraphic horizons (KOZIN 196L-).The occurrence of the barium chloride brines in the NE of England and the Ruhr have already been described and are associated with the Westphalian Coal Measures.In America some brines of Pennsylvanian age (U.Carb),also derived from coal-measures 217-

may carry upto 1500ppm Ba (POTH 1962).

Oil-field brines may be enriched in Ba (DAVIDSON 1966) and one such brine from the Saratogo oil-field,Texas,readily precipitates oolitic and pisolitic barite (MOORE 1914).

The occurrence of Ba in formation waters indicates that the water is deficient in sulphate.In waters derived from an organic rich environment (black shales,coal formations etc) the SO 4 may have been lost through bacterial activity during diagenesis.The mixing of barium-rich formation waters with near surface SO4 waters would result in the precipitation of barite.It is postulated that argillaceous formations (preferably organic in nature) would act as a reservoir for barium ions,the metal being remobilized during diagenesis and precipitated in a receptive,SO4 bearing formation.

BEALES & JACKSON (1966) suggested that metalliferous brines are largely the result of the expulsion of formation. waters from shales in which the metals have accumulated during sedimentation.FORD & KING (1968) in postulating an origin for the Triassic mineralisation in the English Midlands consider that the migration of oil from a sedimentary basin may have flushed base metal complexes through the porous Triassic sandstone.HIRST & SMITH (1974) describing the distribution of barite in the Lower Magnesian Limestone at Ferryhill,Co.Durham suggest that BaCl2 brines derived from the Coal Measures were localized into positive features at the base of the Permian and precipitated barite on mixing with locally derived SO4 waters.

The writer considers that the extensive barite mineralis- -218—

'ation in the NE Leeds region (section 6—Lb) is attributable to the migration of Ba-rich formation waters derived from the west Yorkshire Coal Measures.The physical and chemical expulsion of the formation water during the compaction and diagenesis of the Coal Measures may have been the prime driving force behind the migration.The locus of barite mineralisation in this area is where the N-S trending Permian outcrop cross-cuts the SW-NE trending Leeds -

Osmondthorpe - Cross Gates fault belt (see figure 6.9). It is suggested that the migrating wa'Gers were controlled by these fractures which acted as conduits into the Lower Maguesian Limestone.The well bedded carbonate formation facilitated the lateral spread of the Ba-waters and gave rise to the statiform barite lenses.The occurrence of copper mineralisation within the barite near Bramham supports an argillaceous source for the metals. The detrital barite found in the Millstone Grit pre-dates the main barite mineralisation whilst the fissure:yeins in the Grit below the Permian unconformity,suggests a formation derived from downward flow of waters

FIGURE 6.9 Barite associated with Coal Measure faulting

OSMONDTHORPE FAULT BELT (1( t ( ( tt

MAGNESIAN Let 0.)COALMEASUI S MILLSTONE GRIT • • Migration of Ba ions out of Coal Measure basin and ppt at the base of the LML. -21 9-

CHAPTER SEVEN

DISCUSSION - GENESIS OF THE BALLYNOE BARITE DEPOSIT

7-1. Introduction

The Ballynoe barite deposit is a stratiform orebody of sedimentary affiliation.This simple statement of fact leads the writer into the complex subject of ore genesis, a controversial problem among mining geologists ever since 1546 when Agricola proposed his 'lateral secretion' theory for ore formation.

A model for the genesis of the Ballynoe barite must attempt to answer the following questions a) What was the geological environment at the time of ore deposition ? b) Why were the Upper Tournaisian carbonates at Ballynoe a locus for barite mineralisation ? c) What was the mechanism of ore emplacement or precipitation ? d) What was the source of metals (especially Bo) and the mode of transport for the metal bea,2ing fluids ? e)How important was diagenesis and remobilization ?

In the previous discussion concerning the origin of the stratiform orebodies at Silvermines,workers in.the field have postulated either a synsedimentary origin- for the mineralisation (WEBER 1968),(GRAHAM 1970),(FILION 1973) or an hydrothermal-epigenetic origin for the ore horizon (GREIG et al,1971).A genetic model for the Ballynoe barite deposit will provide yet another link in this chain of discussion, -220--

7-2. Geologic environment

a) Sedimentary setting : The great variety of sedimentary characteristics observed in and around the barite orebody provide strong lines of evidence towards its mode of emplacement.

One important feature is the abrupt change in lithology which occurs at the top of the Muddy Reef Limestone (the base of the bedded barite horizon) ie.,from quiet water to dynamic sedimentation.The thin bedded argillites and impure carbonates (Muddy Reef Limestone) are overlain by a patchy development of green shale and thence,(excluding the barite horizon) the heavily brecciated Dolomite Breccia sequence.The formation of green shale at the top of the Muddy Reef Limestone marks the termination of a major sedimentary cycle (elastic - carbonate - clastic),a cycle which began with the fluviatile - muddy marine transition at the base of the Carboniferous,see table (7.1).The overlying Dolomite Breccia series is not part of this sedimentary cycle.

TABLE 7.1 : The Tournaisian sedimentary cycle in the footwall rocks to the barite horizon

(1) Green argillite (elastic) (2) calcareous argillite (Muddy Reef Limestone) (3) muddy carbonate (Muddy Limestone) (4) pure carbonate (Lower Dolomite) (3) muddy carbonate (Upper Basal Fragmental) (2) calcareous argillite (Lower Basal Fragmental) (1) elastic (Devonian/Carboniferous transition) -221-

It was noted in chapter two that the fossil populations, especially the crinoids,apparently met with mass extinction at the top of the Muddy Reef Limestone.This extinction was associated with a definate trend of crinoid ossicle enlargement towards the top of the succession (figure 2.6).Although figure (2.6) is based on data from only one drill core section, it is tentatively suggested that the enlargement trend reflects changing physico-chemical conditions in the marine basin. Whether this was a consequence of muddier sedimentation,an increase in water temperature or an influx of trace metals into the marine basin is problematical.The large lenses of fossil debris at the top of the Muddy Reef Limestone may have been brought about by a drop in sea level or a toxic inflow of metals,barium,silicon and iron for instance

The top of the Muddy Reef Limestone is overlain by a green shale which carries a elastic mineralogy of detrital quartz,zircon,carbonate and barite.On the flanks of the 'eastern dome' the shale is highly slumped and carries diffuse fragments of allothigenic barite whilst in less dynamic areas,siderite formation is evident.The high chlorite content of the shale suggests a derivation from either the erosion of exposed Silurian shale: and slate or an accumulation of waterlain volcanic ash.(Waterlain volcanic tuffs have been identified from Lower Tournaisian successions in Co.Clare and Tipperary,one example being the Ballyvergin Shale, ROMER per•s.com).However,the presence of detrital quartz and zircon within the green shale suggests that the erosion of Silurian sediments is the more plausible hypoth-

esis. The green shale is regarded by the writer to cap a -222-

non-sequence ( a diastam) which is developed at the top of the Muddy Reef Limestone.During this depositional break it may be noted that layers of sediment already laid down may have been removed by erosion.The diastem was capped by a sluggish (?) influx of mud from a terrestrial source (the Green Argillite).

The Dolomite Breccia sequence overlying the Green Argillite (8c orebody) is a marked reversal of the sedimentary environment.Muddy,detrital sedimentation gave way to marine, carbonate deposition in a turbulent setting.The brecciation and horizons of graded-bedding within this carbonate succession may be explained by the gravity slumping of semi- consolidated sediments,the slippage initiated by tremours along the Silvermines Fault.To the north and away from the fault zone the carbonate succession is less effected by brecciatIon.The suggestion that the brecciation was pene- Contemporaneous with carbonate deposition is confirmed by the occurrence of continuous beds of thin shale between the brecciated horizons.The relatively fast deposition of the Dolomite Breccia series would facilitate the uick preservation of any synsedimentary mineral deposit which was developed at the top of the Muddy Reef Limestone.Along the hangingwall contact of the Upper 'G' zone pyrite,GRAHAM (1970) presents evidence of upward projecting tongues of pyrite which he attributes to the weight of the Dolomite Breccia on the still plastic sulphides.A succession very similar in detail to that developed at Ballynoe is described by SCHNEIDER (1964). In the Mesozoic,Ladinian geosyncline of the Eastern Alps, layered 'bleiberg' ores are associated with a lagoon type -223-

sedimentation and are overlain by an highly brecciated sequence.MAUCHER & SCHNEIDER (1967) drew attention to this sudden change from a monotonous and uniform carbonate succession to one of dynamic brecciation.As at Silvermines, stratiform lead/zinc/barite mineralisation is found at the base of the brecciated succession.

7-2b. Fossil topography of the Muddy Reef Limestone

The 'Conolly technique' applied in the analysis of the footwall structure (figure 2.13) suggests that the top of the Muddy Reef Limestone had a marked topographical variation which was subsequently overprinted by Amorican folding.The geometry of the 'highs' and 'lows' correlate extremely well with the configuration of the barite orebody and lateral extent of none ore-grade barite.A definate relationship between the topography of the footwall and the thickness of barite is postulated.The 'highs' which developed in the Muddy Reef Limestone shelf-sea environment w)re possibly mounds of carbonate mud and accumulations of crinoid debris.The basins ('laws') between the mounds were interconnected by wide, meandering channels which were possibly kept open by scouring. Scouring and erosion may haVe been active throughout the period of non-sequence at the top of the Muddy Reef.The gravitational slumping which effe'ts the Green Argillite on the flanks of the 'highs' was probably initiated by earth tremors induced by the Silverminec Fault which had been active since at least Upper Devonian times.

A reconstruction of the palaeogeographic conditions at this time envisages a shallow,fault controlled,marine lagoon -224-

with mounds of carbonate mud restricting free marine circulation.If perchance the interconnecting channels between the basins became choked,a more restricted environment would result.In these partially restricted basins the environment was not conducive to sustain the growth of marine fauna,the water either becoming too warm,too shallow or contaminated by a high metal content.To the south of the fault controlled shoreline remnants of the old Caledonian massif were possibly still exposed,the Green Argillite being derived from this source.

This quasi-stable environment would have been very receptive to the formation of a synsedimentary mineral deposit given an adequate supply of ore forming fluids.

7-2c. Sedimentary characteristics of the barite orebody

As described in section 7-2b,there is is a definate relationship between the topography of the footwall and the geometry of the barite horizon,The thickest development of barite is contained in a basin between the 'eastern dome' and a NE - E trending 'high',see figure (2.13).0n the flanks of both these 'highs' brecciated barite and hematite sequences are developed (figure 3.5).A lobe of barite which extends NE into the Upper 'G' zone is controlled by a well defined footwall trough.A similar connection is made to the 'B' zone via a NNE trending channel.

At the base of the barite orebody a layered hematite - hematitic barite - jasper succession is developed.This basal sequence exhibits slumping,brecciation,penecontemporaneous faulting and dewatering structurcs.Gel textures are developed -2.25- in the massive jasper with features pointing towards syneresis.According to ELLISTON (1963) syneresis crack patterns occur in the diagenesis of plastic sediments when water is expelled during the shrinkage of the gel phase.

The thin lenses of green shale which interdigitate the lower half of the barite orebody are related to the Green Argillite which caps the Muddy Reef Limestone.Although RHODEN (1958) referred to these lenses as 'unreplaced shaley material within the orebody' the writer considers the lenses to be a contemporaneous deposit associated with the emplacement of the barite.

Despite the fact that diagenetic recrystallisation has extensively modified the original fabric of the barite, zones of primary microspherulitic texture may still be identified. Microspherulites suggest a period of rapid crystallisation in a 'hostile' anvironment.An interesting comparison may be made with the crystallisation of barite from a stratabound 'flat' deposit.A tabular crystal of barite was recovered from the Dufton Fell mine,Westmorland weighing over one cwt and is believed to be the largest barite crystal ever found in the British Isles (BRAMALL 1921).The formation of large crystals requires slow and steady growth in a stable environment (BERRY & MASON 1959),a condition which is not applicable to the formation of microspheruli.kic barite as found at Ballynoe ! Barite spherulites are recorded from the stratiform Meggen deposit (ZIMMERMANN & AMSTTJTZ,1971),Rammelsberg and many of the stratiform,Nevada barite occurrences (ZIMMERMANN 1969) and are taken to be indicative of a probable sedimentary origin. -226-

Another important sedimentary characteristic observed in the barite horizon are the widespread occurrence of stylolites.According to PARK & SCHOT (1968) stylolites are of diagenetic origin and were formed by pressure solution during the lithification of a still plastic sediment.Solution is initiated along crystal grain boundary contacts when the solubility is enhanced by unidirectional pressure.Diffusion of the grain to areas of lower pressure takes place and reprecipitation occurs as crystal overgrowths (see plate 3.13) The composition and temperature of the pore fluid is also of importance during the formation of stylolites (GILBERT 1949). It is suggested that the barite horizon after its deposition was still in a plastic state and had a. relatively high porrsity and permeability.Compactional pressure induced by the overlying Dolomite Breccia series initiated stylolite formation,a process 1,Clich was aided by the migration of possibly chloride- charged,connate waters.This resulted in extensive recrystail- isation within the orebody and a remobilization of barium which was reprecipitated as 'secondary' barite in the hangingwall.When various generations of diagenetic crystallisatiall may be recognized,as at Ballynoe,AMSTUTZ & BUBENICEK (1967) apply the term lanalagerungstextureni.TWENHOFEL (1932) suggested that lit seems probable that there is much redistribution of. material in some sedimentary bodies before consolidation.' How well this statement applies to Ballynoe,

Stylolites appear to be very common in barite of a sedimentary affiliation with examples being reported from Nevada (KETNER 1963),Illinois (PARK 1962) and Meggen (ZIMMER-

MANN & AMSTUTZ 1965).A thorough search of the literature -227--

failed to record any examples of stratabonnd-replacement barite or fissure-vein barite which had been subjected to stylolitisation.Hence the occurrence of stylolites in barite may be a useful tool in distinguishing between either a synsedimentary or hydrothermal-epigenetic origin for the deposit.

7-2d. Sedimentallycharacteristics of the sulphide 'cap:

The trough-like depressions at the base of the sulphide 'cap' may have formed by the heavier massive sulphides sinking into the semi-consolidated barite horizon.Associated with the 'cap' sulphides are the laminated sphalerite and galena muds.Similar sulphide muds which are developed on a larger scale in the Upper 'G' zone display evidence of slumping,brecciation and graded-bedding (GRAHAM 1970). Supported by the work of LOFTUS-HILLS & SOLOMON (1967) the very low Co/Ni ratio (0.12) of the pyrite suggests that the sulphide was precipitated in a sedimentary environment.

Although not indicative of a sedimentary setting the abundant framboidal-pyrite spherules within the 'cap' sulphides suggest a low temperature of formation.The upper temperature limit for framboid formation is 200'0 (RICKARD 1970) whilst SWEENEY & KAPLAN (1973) have synthesized pyrite framboids in the laboratory at tenperatures between 60°C - 85ec.Tne widespread occurrence of melknikovite (gel-pyrite) is also indicative of a low temperature of formation.

According to SCHOTT (1971) the presence of galena atoll replaCement in sphalerite (plate 4.9f) is a strong indication of low temperature emplacement. -228-

7-2e. Summary of the sedimentary features

In the introduction to chapter two it was postulated that the footwall and hangingwall successions of a synsedimentary mineral deposit may be indicative of the evolution and subsequent preservation of the mineralised horizon.

The stratiform,Ballynoe barite deposit is associated with a probable diastem which marks the transition from a quiet water environment to one of dynamic sedimentation. In the footwall sequence a major cycle of sedimentation is evident,a cycle which terminates in a diastem and is overlain by the barite horizon.Mass extinction of the fauna is associated witri the non-sequence.The base of the barite horizon is marked by a detrital green-shale which carries fragments of slumped,allothigenic barite.This shale horizon also interdigitates the basal layers of the barite orebody.

The geometry of the barite horizon correlates with the palaeo-topography of the rootwall.The 'highs' (carbonate mudbanks ?) control the lateral extent and nature of the mineralisation and act as barriers between the respective orebodies (the barite,Upper 'G' & 'B' zones).Along the flanks of the 'highs' the basal layers of barite/hematite are slumped and brecciated.

The microspherulitic texture of the barite suggests a precipitation in the form of a cryptocrystalline mud which was still in a plastic state when overlain by the hangingwall carbonate succession.During the lithification of the barite mud stylolite formation was induced and accompanied by extensive diagenetic recrystallisation and -229-

remobilization within the deposit.

The sedimentary features displayed by the Ballynoe barite strongly suggests that the ore-deposit is an integral member of the Tournaisial. sedimentary succession.

7-3. Deposition of the barite

The evidence presented in tin preceding section implies that the barite was deposited subaqueously as a chemical sediment in a partially restricted lagoon at the top of the Muddy Reef Limestone.

The wallrock geochemistry at Ballynoe indicates that the dispersion of anomalous Ba values is strictly confined to a mineralised horizon overlying the Muddy Reef Limestone.The stratiform nature of the Ba anomaly is still evident in areas well away from the effects of the main mineralisation (DDH 60),Iron and silicon were the only major elements to be associated with the emplacement of the barite.Assuming that barium and iron were precipitated from an aqueous solution in the presence of amorphous silica,the stability field boundaries of the respective mineral generations are presented in figure (7.1).

According to BAAS-BECKING et al (1960) the pH value of a partially restricted,marine basin would be 7 - 7.5, falling to 6 - 6.5 in more confined conditions.The limits of Eh in near surface environments are set by the values at which water decomposes to form oxygen and hydrogen and is in the range 0.1 - 0.4 (the estimated pH and Eh field range for a marine lagoon is plotted on figure 7.1). In the plotted environment barium and iron would be co-

■.• -230-

FIGURE 7,1 : Eh-pH stability relations between Fe & Ba minerals

(:): likely environment for a marine Hematite Barite basin open to free circulatio

Siderite

Iron after Siderite'.. GARRELS 1960.

Ferrous Barium after silicate ROSS 1959.

2 4 6 8 10 12 VA_ PH Eh-pH stability relations at 25°C,latm total pressure in the presence of Ba,Fe and amorphous silica.

precipitated as barite and hematite.A drop in the Eh to below zero would lead to the co-precipitation of siderite and barite although with Eh values of -0.1 barite would be approaching the limits of its stability field.In the Ballynoe deposit siderite is interlayered with barite to the north of the basal hematite zone,see figure (3.5).The absence of barite associated with the massive siderite in -231-

Moguls 'B' zone trough and its occurrence on the periphery of the deposit suggests that the siderite was precipitated in Eh conditions below the stability of barite.Any Ba present would have been in the form of BaS,a completely soluble compound.Barium as BaS would have migrated to zones of higher redox potential (on the flanks of the 'highs') before precipitating as barite.

In the above hypothesis no allowance has been made for

the probable low Eh and pH state of the ore-forming fluid which on entering the 'lagoon' would tend to modify the original oxidation and pH state of the water.This suggests that the Ballynoe basin was open to free marine circulation or had periods of constant marine flushing.

The sinuous dispersion of aluminium throughout the orebody (figure 5.10) may reflect an initial muddy period of barite/hematite deposition and a r'.turn of these conditions with the cessation of the mineralisation.This is supported by the Occurrence of green shale lenses within the basal part of the barite horizon and that the upper contact of the barite is overlain by plumbiferous muds.

The model for the subaqueous precipitation of the barite is supported by the sulphur and oxygen isotope data which suggests that contemporaneous seawater SO4 (Upper Tournaisian) played a significant role in the deposition of the barite. Any biogenic enrichment of S34 was quickly diluted by marine circulation.

(The origin of the stratiform pyrite is not discussed,the writer supporting the theory advocated by GRAHAM (1970) and FILION (1973) in that bacterial reduction of seawater SO4 -232-

to H2S played a major role in the deposition of the pyrite. The restricted environment necessary for the precipitation of biogenic pyrite may have been brought about by the original lagoon becoming choked by a semi-consolidated barite mush and the outlet to the sea being cut-off.In these almost stagnant conditions BaS0 would be unstable and 4 form the soluble compound BaS).

7-4. Nature and source of ore-forming fluid

The geochemistry of the barite horizon suggests that the initial ore-forming fluid carried Ba,Fe and Si and was deficiant in Pb,Zn and Cu.In a synsedimentary mineral deposit three sources of metal are feasible : a)metals derived from the body of the sea. b) metals derived from a terrestrial source via local drainage patterns. c)metals derived from exhalative hot springs (volcanic or geothermal brines). a) The estimated mean barium content of seawater.is only 2Oppb (with a concentration range upto 78ppb),In most cases surface layers of seawater are depleted in Ba with values of less than lOppb (TUREKIAN & JOHNSON 1966). b)DUFOR & BECKER (1964) have determined a barium range in rivers from between 3ppb to 340pPb (R 75ppb),Ionic Ba in solution is quickly adsorbed into clays and organic matter or in the presence of sulphate is precipitated as barite. Thus the amount of Ba in surface run-off is negligible. In many respects the bedded hematite at Ballynoe is similar to the Tynagh Iron Formation.SCHULTZ. (1966) considers the -233- iron at Tynagh was deposited by chemical precipitation in the well oxygenated waters of a marine lagoon.The iron and silicon were derived from intense weathering of Lower Carboniferous and Devonian sediments uplifted by local earth movement.A significant feature of the Tynagh Iron Formation is the low barium content with a maximum of only 470ppm.Whilst the low Ba would support Schultz's terrestrial theory ftr the origin of the iron,his theory would not be applicable to the bedded hematite/'barite succession at Ballynoe unless separate sources for the Fe and Ba were considered.This is unlikely.DERRY et al (1966) whilst agreeing that the hematite and chert at Tynagh were chemical sediments suggested a volcanic spring origin for the metals.

Thus the sources of Ba considered in 'at and 'b' are unable to contribute the large quantities of ionic Ba required for the precipitation of a major Larite horizon. c) Volcanic hot springs are normally associated with the waning stages of volcanism and are often situated some distance away from the volcanic centre.Barium is not very common in present day fumarolic sublimates although minor traces have been reported from the Klyucherskoy volcano in the USSR (NABAKO 1945) and from Vesuvius (MINGUZZI 19148),In Italy layered barite/fluorite mineralisation has recently been discovered associated with volcanic tuffs in a lacustrine sediment.Large amounts of barite are associated with the 'Kuroko' type ore deposits which formed contemporaneously with Miocene basalt-andesite-dacite type volcanism (SAKAI et al 1970).An important feature of the 'Kuroko' deposits is that the ore bearing horizons are often restricted to one stratum ie.,the metals being precipitated over a short, period of time. **

Iron and silicon are often abundant in volcanic springs. Siliceous and iron rich sediments are presently forming in the sheltered bays of the Kameni Islands within the Santorini caldera (PUCHELT 1973),It is of interest that in the deeper layers of sediment gel seawater SO4 is considerably enriched relative to chloride.The normal seawater ratio of 0.14 increases to 0.72 in the sediment gel.The pH range of the sediments is 5.6 - 6.3.Under the ferrous hydroxide layer of the sediments a water rich,ferrous silicate gel is forming.The observed precipitation of Fe and Si at Kameni may be a present day analogue of the sedimentation of hematite and jasper at Ballynoe.Puchelt presented no analytical results for barium,the sediments however being very low in Pb ana Cu.

WILLIAMS (1971) suggested that the palaeo-geography of the Irish Lower Carboniferous resembled the volcanic, New Hebridean Island Arc,an environment where hot springs are abundant.

The volcanic association with the Ballynoe deposit is tenuous although as STANTON (1972) suggests 'by the time extrusive and pyroclastic activity have ceased,the ore- bearing beds contain little to suggest a volcanic affiliation.' The numerous tuff bands reported from the Upper Devonian and Tournaisian successions around Silvermines indicate a sustained period of volcanic activity in the areal Ballynoe probably being some distance from the eruptive centres. This activity culminated during the Nassauian instability in the Limerick volcanic episodes.If the barium mineralisation **(Considerable auantitities of barite are being deposited on the flanks of the East Pacific Rise by volcanism, BOSTROM & PETERSON 1966). -235-

was derived from volcanic hot springs,are the springs related to spasmodic Tournaisian volcanicity or were they a prelude to the major volcanism in the Visean ? On one point we can be fairly certain,with a long and continued history of volcanism the area would have had an increased geothermal gradient.

Geothermal brines (including formation waters) may also be considered as a potential source of barium.As described in section (6-6) water expelled from sedimentary basins during diagenesis are enriched in chloride and depleted in sulphate and act as agents to transport soluble metal complexes. Two outstanding examples of geothermal brines are the Salton Sea brine (SKINNER et a1,1967) and the Red Sea brine pools (DEGEN ROSS,1969).The Salton Sea brine carries upto 260ppm Ba.According to TOOMS (1970) the waters are meteoric in origin,the metals being derived from evaporite sequences. CRAIG (1963) classified geothermal waters into two types a)near-neutral chloride waters wllich. have experienced various amounts of oxygen isotope exchange with rocks through which they have circulated.Their deuterium content is similar to that of the local rain or snow.Examples of this type are Steamboat Springs,the Salton and Red Sea brines and Doughty Springs (which are actively precipitating barite !). b) Acid type hot springs which differ from local precipitation in both their oxygen and hydrogen compositions.Examples are the Yellowstone and Lassen Park sr,rings.

If the Ballynoe barite was precipitated from a geothermal brine the waters were probably chloride rich (enabling the transport of BaC12),a volcanic associated geothermal gradient providing heat for convection. -236—

7-5. Genetic model for the Ball-noe barite

MORRISSEY et al (1971) suggested that ore genesis in Ireland was probably not due to a single process acting at a specific geological tirne,but to superimposed processes that interacted over a long period of geological time.The writer is in full agreement with this statement.

A great thickness of shale,siltstone and greywackes were laid down in the Lower Palaeozoic troughs.During the diagenetic lithification of these sediments the Ba content of the shales and silts may have been partially leached by a process of membrane filtration leading to a concentration of Ba in the formation waters.Although a considerable amount of original formation water would have been lost during the Caledonian Orogeny,metamorphism was not severe and within the thicker sedimentary piles the Ba-rich formation waters may have been retained in a closed-system (with a further concentration of Ba ?),In. Devonian times a tremendous thickness of arenaceous sediments accumulated in rapidly developing basins along the old Caledonian trend,for example the 20,000ft thick sandstone sequence in Co.Kerry.With the increasing overburden the underlying Lower Palaeozoic rocks would have been subjected to increasing pressures and heat,factors which may have reactivated the migration of the formation waters. Contemporaneous with the developing sedimentary basins was the occurrence of minor volcanism,the crustal instability perhaps triggering the magmatism.It is possible that a mixing between the migrating formation waters and juvenile waters occurred at this stage,see figure (7.2).The flanks of a major Silurian - Devonian sedimentary trough is represented -237--

by the Slieve Mish - Galty Mountains hinge line,this feature perhaps controlling the migratory path of the ascending formation waters.(The copper mineralisation at Gortdrum is developed in close proximity to the Galty hinge line). The flushing of the brines through the porous Devonian sandstones may account for the widespread Ba/Cu mineralisation developed in this formation throughout Ireland.In.Lower Tournaisian times the rapid,arenaceous Devonian sedimentation gave way to slower,carbonate deposition and it is possible that the ascending brines outpaced sedimentation and reached the surface.Th.e Silvermines Fault would have been a natural conduit for the Ba-rich waters.Whether the brines were purely of sedimentary origin or had been admixed with magmatic fluids is problematical,the initial high Fe and Si content however,suggesting some volcanic addition.The occurrence of a major Ba anomaly 14 miles NE of Ballynoe at Toomyvara, suggests that the dispersion of Ba was of wide extent and that the Ballynoe orebody represents a mere fraction of the liberated brines.The localisation and preservation of the Ballynoe orebody was a function of the sedimentological setting as described in section '(7-2e).At some later date the synsedimentary barite and massive pyrite in the Silvermines area was overprinted by lead,zinc and copper mineralisation.

DUNHAM (1970) posed the question,'Is ore genesis in sediments merely a special case of diagenesis under the influence of formation waters ?' It is possible that the genesis of the Ballynoe barite answers this question.

FIGURE 7,2 Source of the ore-forming fluids, SW Ireland

SOUTH NORTH

SLEIVE MISH GALTY Mtn KERRY BASIN HINT LINE GORTDRUM BALLYNOE

1 V

I 4- 1 4-- I -I .Tournaisian 4.... I .J. . . . . sediments 5000ft :Devonian

15000ft :Lower Palaeozoics / -5

25000ft ARCHEAN BASEMENT HIGH

:Precambrian Volcanicity associated Basement 35000ft with basin margin

•11.% X N. 7, 45000ft voL Migration paths for formation waters --239-

CHARTER EIGHT

SUMMARY OF CONCLUSIONS

The Ballynoe barite deposit is a conformable,mineralised- horizon of Upper Tournaisian age.The barite deposit is associated with a diastem at the top of the Muddy Reef Limestone and marks the transition from a quiet water environment to one of dynamic sedimentation.In the footwall succession a major cycle of sedimentation is evident,a cycle which terminates in a diastem and is overlain by the barite horizon.Mass extinction of the - fauna is associated with the non-sequence.

The geometry of the barite orebody correlates with the palaeo-topography of the footwall,the topography acting as an important control over• the lateral extent,thickness and nature of mineralisation.

Sedimentary features within the barite horizon suggest that the barite was precipitated in the form of a cryptocrystalline mud which underwent major diagenetic modification. Diagenesis resulted in extensive stylolitisation,recrystallisation and remobilization.The remobilized barite may be differentiated from the primary barite by a coarser texture, differing mode of habit and geochemistry (both trace element and isotopic).

The wallrock geochemistry at Ballynoe suggests that the dispersion of anomalous Ba values are strictly confined to a mineralised-horizon directly overlying the Muddy Reef Limestone.Iron and silicon were the only major elements

-4 -240- which were associated with the initial emplacement of the barite.Barium and iron were co-precipitated from an aqueous solution in the presence of amorphous silicon in a semi- restricted marine lagoon.The subaqueous precipitation of barite is supported by sulphur and oxygen isotope data which suggests that contemporaneous seawater sulphate (Upper Tournaisian) played a significant role in the deposition of BaSO4.In the more restricted areas of the lagoon (cut-off by carbonate mudbanks),lower Eh and pH conditions led to the precipitation .of iron as siderite or pyrite.In these conditions Ba would exist as BaS and would have migrated to zones of higher-redox potential.

The stratiform barite deposit was probably laid down over a short period of time from the action of warm,chloride- rich springs debouching fro311 from the Silvermines Fault fracture zone.The source of the metals was probably the thick,Lower Palaeozoic troughs which are developed to the south and north of Ballynoe.The metals were carried in migrating formation waters the circulation being facilitated by a high regional heat flow (contemporaneous volcanism) and compaction by the overlying Devonian-Tournaisian sediments. The general flushing of formation water through the Devonian sediments led to the widespread BajOu mineralisation found in this formation.The migrating formation waters were concentrated on the flanks of the sedimentary troughs and at this level some admixing with volcanic solutions occurred. As the rising waters outpaced sedimentation hot springs developed at the surface and in receptive environments mineral deposits were laid down in shallow,marine, basins, ie., Ballynoe.

-249

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APPENDIX I

Drill GoveraasinLhe Silvermines Area

■•••■••••••••••••111

(Magoobar concession iL RED)

10 19 lo 17 to E - llfill 43 43 1 -T- 1

42 II I I H 71 L 1,". AIA III 11 11 1 ,-., II 41 Wi , 41 w _1 z 0 N iql In NM- 4o 4o MI Ii .z__ o W N 0 N TTi t,-.,--. I I I 1111j1 _ 39 1 II

3 3

LIE ETE rEg if i 3? 3? 19 18 17 16

1' -254-

APPENDIX II

The Conoll- Contour Method

The Conolly Contour Method (CONOLLY 1936) is the simple expedient of contouring the geometry of geological structures with reference to inclined planes which are approximately parallel to the average strike and dip.The angle and position

of the reference plane in relation to the structure being

analysed is arbitrary and must be carefully chosen to illustrate the structure to its best advantage.The distance between the reference plane and (as in the case of Ballynoe) the footwall is measured perpendicular to the reference plane (see figure II/1.

(A). A simple dip section based on a structure contour map.

A-% _14 ■ 44411.2- (B). Lines to footwall contact drawn perpendicular to the reference plane.

Reference plane

(C). A contour map of the resulting positive and negative values. For a contour map with actual numerical values the reference plane must have a fixed datum altitude which is common to all RP's drawn on the dip sections. -255-

APPENDIX III

DIRECT READING SPECTROGRAPHIC TECHNI UE

A direct reading emission spectrograph (ARL MODEL 29000B gliANT0i4ETER) was applied in the analysis of the wallrock,the raw spectrographic output being processed into element concentrations with the aid of an analogue computer.The spectrographic

technique (SYSTEM C) is almost identical with that used for the Imiserial College A.G.R.G. Regional Geochemistry Atlas project and is fully described in the A.G.R.G. publications 'Users guide to System C', Imperial College 1973.

DATA QUALITY CONTROL

Precision (within batch of samples) is gauged by the analysis of 10 - 15 samples in duplicate during the daylthe duplicates being separated by a random interval.On the analogue computer print out,the values are presented side by side and a statistical analysis made on the basis of a predetermined standard of precision. Between batch precision is assessed by the use of standards which are burned in every daily batch of sainples,and the deviation calculated.The values obtained for each standard are also compare with the grand mean values for each element in each standard (see table 111/2 and the deviation calculated).

OPERATING CONDITIONS

Sample : A fraction of approximately 10 gms of -80 mesh.

Preparation : Sample (o.lgm) mechanically mixed with buffer (0.15gm 0 Buffer : Sodium fluoride (1 part w/w) carbon powder (2 parts w/w). Excitation DC arc at 8.0 ampsscathode excitation in air.

Time of burn : 60 seconds for :: GalBisCds PbsZnsGesLis Mo and As.

90 seconds for :: PdsAlsFelK,MgsSilTi,MnIAgIBas Bes

Ca,Cr,Cu,Ni,Se,Sn,Sr. -256-

Sample weight : 15mg. Packing : Repeated pressing of inverted electrodes into a. heap of sample/buffer mixture followed by wiping flush to electrode walls. Electrodes : Rd 403, 6mm rod.

Geometry :

3mm

3mm t/-

6mm -257- APPENDIX III/1

Lines in use with System C.

Line Element Wave length Intens ity Slit Filter Known interfering lines*

Co 3453.5 x 2 50 U.V. Ni 3414.7 x 2 1000R 50 Glass Bg 3389 x 2 75 U.V. Zn 3282.3 x 2 500R 75 U.V. Mo 3170.3 x 2 1000R 50 U.V. Be 3130.3 x 2 200 50 U.V.. 6261.0 Ti 300 Bi 3067.7 x 2 3000hR 75 u.v. 3067.9 Fe 15, 3068.1 Fe Li 6103.6 2000R 75 Glass 150, 3067.2 Fe 300, Ge 3039.1 x 2 1000 75 U.V. 2947.0 x 2 20 50 U.V. Mn 2933.1 x 2 8o 75 U.v. Sn 2840.0 x 2 300R 50 U.V. 2840.0 Cr 25 Pb 2833.1 x 2 500R 50 U.V. Mn 2798.3 x 2 800R 75 U.V. Si 2435.2 x 2 150 75 U.V. As 2349.3 x 2 250R 37 Prism Sr 4607.3 1000R 50 Glass Ba 4554.0 1000R 50 Glass V 4379.. 2 200R 75 Glass Cr 4254.4 5000R 50 Glass Bg 4116 75 K 4044.0 800 75 Glass

Sc • 3907.5 125 50 Glass Ti 3653.5 500 75 Pd 3404.6 2000R 15 Ag 3382.9 1000R 75 _-_ Cu 3273.9 75 Ca 3158.9 100 75 Hog 2779.8 .40 75 Fe 2739.6 200 75 Al 2378.4 40 75 Cd 2288.0 1500R 75 - 2288.1 As 250R Zn 2138.6 800R 75 Bg 2098 75 Ga 2943.6 100 75 - 2943.9 Ni 50r

-258- APPENDIX III/2

System C Analysis of USGS standards. Means of'results obtained on nine successive days, with accepted values in brackets (ppm except where shown).

AGVI BCRI G2 GSPI GI WI Al % 8.9 6.2 7.8 7.2 7.4 7.4 (9.0) (7.2) (8.1) (8.0) (7.3) (7.7) Be 0.9 (0). 2.2 1.5 2.6 1.7 (2) (0) (2) (0.8) (-) (-) Ca % 2.4 3,3 1.0 0.9 0.6 5.0 (3.6 (4.9) (1.4) (i.5) (1.0) (7.8) Co 25.6 48 6.7 10.0 3.8 54 (15.5) (35) (4.9) (7.5) (2.2) (51) Cr 11.5 11.3 9.4 11.7 21 124 (12) (16) (9) (13) (22) (120) Cu 77 24 12 40 14 127 (64) (22) (11) (35) (13) (110) Fe % 3.2 5.4 1.1 1.t 0.5 4.1 (4.7) (9.4) (i.9) (3.0) (1.3) (8.2) Ga 20 24 22 21 20 20 (18) (21) (20) (19) (18) (16) K % 3.3 2.4 3.8 4.5 4.3 1.2 (2.4) (1.4) (3.7) (4.5) (8.2) (1.0) Mg % 1.3 2.0 0.7 0.8 0.4 3.0 (0.9) (2.0) (0.5) (0.6) (0.2) (3.7) Mn 914 1154 283 322 223 1380 (72$) (135o) (265) (326) (210) (1300) Mo 1.5 1.0 0.1 0.3 3.4 0.2 (3.7) (3.9) (1.2) (1.6) (-) (0.5) Ni 15 7 2 6 0.3 64 (17) (15) (6) (to) (1.1t) (82) Pb 63 31 44 83 31 27 (35) (18) (28) (52) (50) (7) Sc 16 37 5.2 7.1 3.4 45 (13) (16) (3.9) (9,2) (-) (-) Si % 29 24 30 29 32 21 (27) (25) (32) (31) (34) (24) Sn 10 8 0 7 I 9 (3) (1) (1) (8.5) (2) (2) Sr 570 298 448 211 (657) (345) (463) (247) (-) (-) Ti 5068 11115 1349 2059 738 3110 (6400) (13400) (2900) (3900) (1498) (6594) V 137 370 51 61 20 238 (121) (384) (37) (52) (21) (240) Zn 117 142 102 99 84 92 (112) (132) (74) (143) (-) (-) -259-

APPENDIX IV

OPTICAL EMISSION SPECTROGRAPH

An HILGER & WATTS LARGE QUARTZ PRISM emission spectrograph was applied in the analysis of the barite samples.Element concentrations were calculated with the aid of an A.R.L. PROJECTION-COMPARATOR.

Technique : A 10 gram sample (-80 mesh) was ignited in a furnace at 450.0 for three hours to oxidise any organic matter

(if any) and to remove H20. A 100mg quantity of sample was then weighed into a plastic tube containing a mixing ball and 200mg of spec pure carbon.(The carbon contained 400ppm

Pd as an internal standard).The 1:2 mixture was homogenised for three minutes in a Wig-L-Bug.A small quantity was packed into pre-drilled carbon electrodes (Rd 403) and ignited in. a 10 amp DC arc.The sample was always burned to completion, a time which varied from between 9 - 12 seconds.The resulting spectrum was recorded on a photographic plate ( 9 spectrums per plate).

Geometry of electrodes : cup depth 2mm

internal dia. external dia. 2.38mm 3.1mm

Analytical Control : Analytical control was retained by confirming that the Pd 400 ppm standard was 400ppm on the photographic plate,the blank samples were indeed blank and that the exact procedure was applied to all sample burns.With a poor sample burn the internal Pd standard was indistinct -260-

and the sample was burned again; a poor burn was normally caused by the sample being blasted out of the electrode on igniting the arc. Element standards were prepared in a spec-pure BaSO4 base with a Concentration range from 10% - 1ppm and a series of analytical calibration curves prepared for each element.The element standard was initially burned 10 times in order to obtain mean 'working curvet and thence every 50 samples to ensure adequate analytical control.A standard deviation at each element concentration in the standard was calculated and the results are presented in table IV/1.

Table IV /1

Standard deviation at set concentrations on the element standard 'working curves' 0 Element A 10% 1% 12222p2 1°°11211 12112 .1.21 Si 2881 12% 10% 8% 14% Sr 3380 14% 4% 6% Fe 1 3020 - 11% 16% 12% 8% 6% Fe 11 2929 6% 12% - - - -

Ca 3180 10% 10% 15% 17% - - Ag 3383 8% 7% 7% 12% 6% 10% Cu 3274 7% ,10% 12% 11% 14% 18% Mn 2801 18% 16% 21% 15% 12% - Pb 2833 12% 12% 15% 12% - - Mg 2795 7% 8% 6% 14% 10% 4

* Standard deviation calculated from the x of 10 burns.When certain samples were crossed checked by Atomic Adsorption there was a close reproducibility of results between Emission Spec. & A.A.