PER-20
GEOCHEMICAL ASPECTS OF THE MEGACRYST SUITE FROM THE MONASTERY KIMBERLITE PIPE
by
W. R.O.JAKOB
| ATOMIC ENERGY BOARD I pelindal..) / i PRETORIA 30 i*~\'$'.- j Republic of South Africa August 1977 3
i •:>:'::. MiK!ëliitebai!!gi88u»<(á$: ATOMIC ENERGY BOARD GEOCHEMICAL ASPECTS Of THE MEGACRYST SUITE FROM THE MONASTERY KIMBERLITE PIPE by W.R.O. JAKOB* "Chemistry Division POSTAL ADDRESS: Private Rag X256 Pelindaba Preto.-ia August 1977 0001 ISBN 0 86960 667 0 GEOCHEMICAL ASPECTS OF THE MEGACRYST SUITE FROM THE MONASTERY KIMBERLITE PIPE W. R.O.JAKOB Thesis submitted in fulfilment of the requirements for the degree of Master of Science at the Department of Geochemistry of the University of Cape Town October 1977 2 CONTENTS Page SAMEVATTING 3 ABSTRACT 4 ACKNOWLEDGEMENTS 5 1. INTRODUCTION 6 2. SAMPLING AND LOCALITY DESCRIPTION 7 3. ANALYTICAL METHODS 9 4. ANALYTICAL RESULTS 9 4.1 Olivine 9 4.2 Orihopyroxene 10 4.3 Clinopyroxene 11 4.4 Garnet 12 4.5 llmenite 13 5. DISCUSSION 15 5.1 Clinopyroxene 15 5.2 Garnet 16 53 llmenite 18 5.4 Orthopyroxene 19 5.5 Olivine 22 6. GENERAL DISCUSSION AND CONCLUSIONS 26 7. REFERENCES 28 8. APPENDICES: 34 APPENDIX I: DIAGRAMS 34 APPENDIX II: PLATES 47 APPENDIX III: TABLES 11 TO 2B 51 3 5AMEVATTING 3 Die Monastery kimberlietpyp in die Distrik Marquard, Oranje-Vrystaat, Suid-Afrika, het groot belangstclling in kimberlietstudies gaande gemaak omdat dit groot enkelkristalle (2— 20 cm) van olivien, enstaiiet, diopsied, granaat, ilmeniet en flogopiet/vermikuliet bevat- Daar is vasgestel dat at die silikate (behalwe flogopiet wat nie bestudeer is nie) met ilmeniet verband nou. Hierdie studie handel oor die chemie van die megakristalgroep. Hierdie homogene kristalle het groot verskille in chemiese samestelling. Die silikate wat met ilmeniet vergroei is, is altyd ryker aan yste: en armer aan chroom as die diskrete megakrtstalte. Die o/nwn-megakristalle kan in twee samestellingstrekke verdeel word met gemiddeldes naby Fo86 (0,3 tot 0,4 % NiO) en Fo 80 (0,06 tot 0,11 % NiO). Die oliviene wat meer magnesium bevat, het dikwels klein kimberlietinsluitsels met n samestelling soortgelyk aan die hoofsteengroeftipe kimberliet vanaf Monastery. Die ensfat/et-megakristalle bestaan uit twee groepe met verskillende samestellings. Glasagtige, homogene enstatiete met groot verskille in chemiese samestelling kom die minste in Monastery voor. Growwe reëlmatige en onreëlmatige vergroeiings van enstatiet en ilmeniet het uiters beperkte chemiese samestellings en hulle val binne die strek wat deur die homogene enstatiete bepaal word. Hierdie twee tipes bepaal die enstatiete Groep I. Die volopste is die gelaagde enstatiete Groep II wat by laer temperature in ewewig gekom het en cKoomdiopsied ± yanaat laat uitkristalliseer het. Hierdie enstatiete het wisselende Mg/Mg+Fe-verhoudings, maar, in teenstelling met die enstatiete Groep I, het hulle baie beperkte verskille in chemiese samestelling. Die diopsied-megakristaHe is subkalsium-diopsiede, arm aan chroom, met ongeveer 10 mol % yster. Gelaagde diopsied-ilmenietvergroeiings het groter Ca/Ca+Mg-verhoudings as dia diskrete diopsiede. Die diskrete pranaaf-megakristalle is chroomarme, titaanryke pirope met peridootaffiniteite. Seldsame vondsc van klein granaatinsluitsels in ilmenietmegakristalle het 'n baie lae chroominhc (<0,23% Cr203). Diskrete ilmenietmegaknitaUe is die megakristalmineraal wat die meeste in Monastery voor kom. Hulle het groter verskille in chemiese samestelling as die ilmeniete wat met silikaatminerale vergroei is. *cl Die samestellings van die megakristalle dui daarop dat ol fopx+cpx+gnt ± ilmeniet gelyktydig met die temperatuurinterval 1 400 tot 1 1S0°c by 'n druk van 42,5 ± 2 kbar bestaan het. Die diopsied- en enstatiettermometer het 'n temperatuurstrek van ongeveer 1 400 tot 1 250 °C vir die diskrete megakriitalle verskaf, en 1250 tot 1 150°C vir die ilmenietsilikaatvergroeiing». Die megakristalle het buite die diamantbestendigheidsgebied in ewewig gekom. Tussenelementverhoudings van die megakristalminerale en die groot verskille in chemiese samestelling dui daarop dat die Monastery-megakristalle gedurende 'n magmatiese voorval in die Bomantel uit 'n klein hoeveelheid smeltsel gevorm het, waarskynlik aan die einde van die Karoo vulkanisme. 4 ABSTRACT The Monastery Kimberlite pipe, situated in the Marquard District, Orange Free State, South Africa, has evoked much interest in kimberlite studies because it contains large single crystals (2— 20 cm) of olivine, enstatite, diopside, garnet, ilmenite and phlogopite/vermiculite. All the silicates (except for phlogopite, which was not studied) have been found associated with ilmenite. Th»s study is concerned with the chemistry of the megacryst suite. These homogeneous crystals have large ranges in chemical compor-fion. The silicates intergrown with ilmenite are always more iron-rich and poorer in chrome than the discrete megacrysts. The olivine megacrysts fall into two compositional ranges, with averages near Fo86 (0,3 to 0,4% NiO) and Fo80 (0,06 to 0,11 % NiO). The more-magnesian olivines often have small inclusions of kimberlite with a composition similar to the main Quarry-Type Kimberlite from Monastery. The enstatite megacrysts fall into two compositionally different groups. Least abundant at Monastery are glassy, homogeneous enstatites which have large ranges itt chemical composition. Coarse regular and irregular intergrowths of enstatite and ilmenite have very restricted chemical compositions which fall within the range defined by the homogeneous enstatites. These two types define Group I enstatites. The most abundant are the lamellar Group II enstatite, which re equilibrated at lower temperatures and have exsolved chrome diopside t garnet. These enstatites have variable Mg/Mg+Fe ratios, but otherwise have very restricted ranges in chemical composition, unlike the Group I enstatites. The diopside megacrysts are chrome-poor subcalcic diopsides with about 10 mole % iron. Oiopside-ilmenite lamellar intergrowths have higher Ca/Ca+Mg ratios than the discrete diopsides. The discrete garnet megacrysts are chrome poor high-titanium pyropes with peridotitic affinities. Rare finds of small garnet inclusions in ilmenite megacrysts are very low in chrome « 0,33 % 0203). Discrete ilmenite megacrysts are the most abundant megacryst minerals at Monastery. These have wider ranges in chemical composition than the ilmenites which are intergrown with silicate minerals. ^DI'FT-MIIV' *or tne Monastery megacrysts is constant (garnet) or nearly constant (diopside, enstatite). The compositions of the megacrysts indicate that ol+opx+cpx+gnt ± ilmenite coexisted within the temperature interval 1 400 to 1 150 °C, at 42,5 ± 2 kbar pressure. The diopside and enstatite solvi give temperature ranges of about 1 400 to 1 250 °C for the discrete megacryst», and 1 250 °C to 1 150 "C for the ilmenite-silicate intergrowths. The megacrysts equilibrated outside the diamond-stability field. Inter-element relationships of the megacryst minerals and the wide ranges in chemical composition suggest that the Monastery megacrysts formed from a small volume of melt during a magmatic event in the Upper Mantle, possibly at the end of the Karroo volcanism. 5 ACKNOWLEDGEMENTS This work has benefitted from the assistance of the following members of staff of the University of Cape Town: Profs L. H. Ahrens and A.J tdank, tor permission 10 do this thesis on a part-time basis. J.J. Gurney for intioducing me to the field of kimberlite, for suggesting this project, and for most of the samples. This work could not have been compieted without his unfailing help, advice, encouragement and supervision. CJ- Hatton, for some of his computer programs. S.R. Rickaid for instructing me in the use of the microprobe, and for ensuring its efficient operation. Mrs D. Curney for typing the manuscript. Mrs S. Davids for the preparation of many grain mounts. D.G. Fraser of Oxford University, for discussions on Chapter 5.B. H.W. Fesq of NPRU, University of Witwatersrand, for many of his references. The Atomic Energy Board is thanked for permission to use its facilities during the final preparation of this work. In particular, I am indebted to the following: Mr P.E. Haskins for editing the manuscript. Reprograpnic Services for the final typesetting and reproduction. 6 1. INTRODUCTION Kimberlite is a volumetrically rare rock type, with its major occurrences on the stable shields of Southern Africa and Siberia. Two types of kimberlite am recognised. The hypabyssal facies kimberlite which intruded the surrounding rocks as dikes and sills, and the diatreme-facies kimberlite. Modern concepts visualise the latter to be emplaced as a cool (300 600 °C) crystal mush along fractures at depth, and to develop a gas-charged head during ascent, which results in an explosive breakthrough to the surface, forming a brecciated volcanic pipe. Due to adiabatic cooling resulting from expansion of the C02-rich phase, the diatreme-facies kimberlite consolidates in situ and shews little metamorphic effect on the surrounding rocks (Dawson, 1972). Kimberlite itself was most recently defined by Clement, Skinner and Scott (1977): "KIMBERLITE is a volatile-rich, potassic, ultrabasic, igneous rock which has a distinctively inequigranular texture resulting from the presence of macrocrysts set in an essentially microporphyritic matrix." Since the matrix consists mainly of calcite, phlogopite and olivine, with lesser amounts of apatite, diopside, monticellite, perovskite, ilmenite, magnetite, chromite and a wide range of secondary minerals, it is therefore enriched in the major oxides TÍO2, &2O3, CaO, KjO, P2O5, H2O and CO2, and is high in trace elements such as the alkaline earths, alkalis, Ni, B, V, Zr, Nb, Th, U and Pb (Dawson, 1972). Xenoliths of fragmented rocks are found in the kimberlite and these include (1) crustal rocks which were incorporated into the kimberlite during its ascent, and (2) ultramafic nodules from the earth's upper mantle. The latter are one of the main reasons for the wide interest shown in kimberlites. These ultramafic inclusions in kimberlite have been grouped into the following types (Harte, in press): (1) Peridotites are generally the most abundant Upper-Mantle nodules found in kimberlite. These include Iherzolites and harzburgites, and their garnet bearing equivalents. Upper-Mantle studies have been directed mainly towards this suite in recent years because the coexistence of garnet and two pyroxenes in many of the rocks has proved to be most suitable for providing information on the conditions of equilibration of the rocks. Several textural types have been recognised in the peridotite suite (e.g. Boullier and Nicolas 1975, Harte efa/1975, Harte 1977). (2) Garnet pyroxenitts which grade into peridotites with increasing modal olivine. (31 Eclogites (and grospvdites) which are abundant in only some kimberlites (e.g. Roberts Victor). (4) Megacrysti (Discrete Nodules). These are large monominerallic single crystals, much coarser (2 - 20 cm) than the minerals found in ultramafic nodules « 1 cm). These large crystals may consist of olivine, ortho- and clinopyroxene, garnet, ilmenite and phlogopite/vermiculite. Intergrowths of two of the above minerals, or inclusions of one mineral in the host of another, are also found. Most frequently the association is of ilmenite and a silicate. (5) Metasomatised Rocks. This group includes diverse rock types that may be rich in amphiboles or mica. The megacrysts in general have been known for a long time (e.g. Wagner 1914, Williams 1932) but little work was done on them. Only the diopside ilmenite lamellar intergrowths have received special attention in recent years. Clinopyioxuiie-ilmenilc intergrowths have been reported from Angola (Boyd and 7 Danchin, 1972), tht Frank Smith pipe (Williams, 1932), the Uintjesberg and Sonop kimberlite in South Africa; Kao, Mothae and Pipe 200 in Lesotho; the Mir pipe, Yakutia. USSR, the Stockdale and the Kentucky kimbetlites, USA, and from Rhodesian kimberlites (from Gurney eta/. 1973). This study is concerned entirely witli the megaciyst assemblage found at the Monastery M^ne, OFS, RSA. Previous studies on these megaoysts have suggested a paragenesis involving re-equilibration at low pressures of a single high-pressure phase, eithe' a Ti rich garnet (Ringwood and Lovering, 1969) or an/ ilmenite-structured pyroxene (Dawson and Reid, 1970). Other investigators prefer an origin by eutectic (Williams, 1932, MacGregor and Wittkop, 1970, Gurney et a/, 1973, Wyatt, 1977) or cotectic (Frick, 1973) crystallisation. The above conclusions were based on only a small number of samples. This study was initiated to conduct a systematic and comprehensive sampling of the megacrysts from one single kimberlite pipe. Sampling a single locality could be expected to minimise differences between various population groups which might obscure any chemical trends present. The Monastery Kimberlite pipe was selected, for it was well known that the full suite of megacrysts was present in greater abundance than is found at any other South African locality. These megacrysts include olivine ortho- and clinopyroxene, garnet, phlogopite and ilmenite, and these silicates in association with ilmenite. The Monastery Kimberlite is situated between Marquard and Clocolan in the south-eastern portion of the Winburg District of the Orange Free State. It is described by Wagner (1914) and more recently in some detail by Whitelock (1973). The present study was directed to establish the tull range in chemical composition of the megacrysts (except phlogopite), and to attempt to determine whether or not the different silicate minerals in the megacrysts formed in equilibrium with each other as assumed by F.R. Boyd and P.H. Nixon in a series of papers about megacrysts, chiefly fiom the Monastery Mine and N. Lesotho (e.g. Nixon and Boyd, 1973). At the same time it was hoped that the large geochemical survey envisaged would provide information on the origin and mode of formation of the megacrysts. Boyd and Nixon (1975) have suggested a possible genetic link between megacrysts and deformed high temperature Iherzolites in N. Lesotho, whilst an association of the Monastery meoacrysts and the Monastery Kimberlite was inferred by Gurney et al (1973). Since it would be important to know which megacryst minerals have been in equilibrium with each other, or with other phases including melts, special attention was paid to finds of minerals with visible inclusions. Large sample populations were taken in an attempt to define the full compositional range for each mineral- 2. SAMPLING AND LOCALITY DESCRIPTION The bulk of the samples available for this study were collected by J.J. Gurney, J.B. Dawson and P.J. Lawless in 1973, and are a good reflection of what is to be found at Monastery. This kimberlite is situated in the Winburg District, Orange Free State, Republic of South Africa, close to the north-eastern border of Lesotho. The intrusion is oval in shape, with a maximum width of 180 x 70 m. The country rocks are near-horizontal shales and mudstones alternating with feldspathic sandstones, all belonging to the Red Beds of the Stormberg Series. Fresh mica megacrysts in the Monastery Kimberlite gave a Rb-Sr age of 90 ± 4 Ma., Allsopp and Barrett (1975), and Davies et al 11976) obtained a zircon age of 90,4 Ma. This compares with ages found in other kimberlites in Southern Africa, listed in Table 1 below (Davies op. cit). 8 TABLE 1 I >c topic Ages For Some Kimberlites In Southern Africa Kimberlite Age in million years Urai-iu 93,0 HilUtulilcu'i 91,2 De Beeis 92,0 Wfcbielton 90,3 Kamfersdam 86,9 Fmsch 94,1 Mothdc 37,1 Monastery 90 - Whitelock 11973) gives a detailed description of the mining history and geology of the Monastery Pipe and recognises four types of kimberlite, of which two predominate: (a) The Quarry-Type Kimberlita. Th:s is ihe most abundant variety present. It is dark grey and very resistant to weathering. Most of the meijaciysu found are derived from this kimberlite. Diamond grades of 50 carats/100 tonnes were established ib) The Breccia-Type Kimberlite. This consists of up to 80% of medium sized sedimentary xenolithsina soft serpentinous, micaceous matrix, in which megacrysrs of garnet are common. (c) The East-End Kimberlite Hits Mi.ïberliUi is rich in carbonate xenoliths. Altered dunite nodules and sporadic ilmenite are cnaractenstic, while garnets and gem quality zircon may also occur. Id) The Fine-drained Kimberlite Type. This was mined only in the northern area. It lacks xenoliths. The heavy mineral concentrate from the mine dumps of the Monastery Mine has been investigated by Nixon and Boyd (1973b), with the observer abundances reported in Table 2. TABLE 2 Mineral abundances at Monastery ______Mineral wt.% llmenite nodules 47 Ultrabasic nodules 17 llrnenite diopside irttergrowths 13 Garnet nodules 10 Dunite nodules 7 Garnet diopside, diopsicle, bron/ite, phiogopite etc. 4 Basement gneiss 2 During a recent visit to tne Monastery Pipe the following abundances of ~tegacrysts were observed, in decreasing order: (1) llmenite (2) diopside/ilmenite (3) garnet (4) diopside (5) olivine (6) mica (7) orthopyroxene (8) garnet/ilmenite (9) orthopyroxene/ilmenite (10) orthopyroxene/diopside (11) raie finds of fiamet/diopside and olivine/ilmenite. 9 3. ANALYTICAL METHODS Megacryst samples with a maximum dimension larger than 2 cm were sorted into mineral groups, and up to 25 minerals were selected at random from the different populations. In rare instances small inclusions of another silicate phase in J megacryst were found. AM such examples were selected for analysis on the assumption that the minerals represent equilibrium assemblages. In view of the technical difficulties or havirg so many thin sections prepared, and as it was thought, on the basis of previous work, that the mineials were homogeneous, it was decided that in the first instance it would be sufficient to analyse two fragments from each crystal, one near the centre and one near the outer edge. Thus in some cases the crystals had to be broken. The grains obtained were mounted on glass slides, polished and analysed by electron microprobe analyser. The b»[tk of the analyses in this study were performed with the Micotcan 5 electron microprobe, manufactured by Cambridge Scientific Instruments Limited. This instrument, together with instrumental conditions, standards and data reduction as used in this study, have been described in detail by Lawless (1974). The average of the analyses from the two grains are used m this study. The differences between the two analyses from each mineral show that jil the megacrysts investigated in this study were apparently unzoned and homogeneous in chemical composition. The kimberlite inclusion in olivine RJ46S w?s anoiyie'i with a Techtron AA6 atomic Sorption spectrophotometer, according to the method of Van Loon artd Parissis (1970). 4. ANALYTICAL RESULTS 4.1 Olivine Tiie olivine megarr ysu found on ih. ;,oi.equate dumps art- maii'ly bro' ei; r.hips, 2 - 5 cm in largest dimension. Due to their neutral, light brown colour, they are difficult Ic recognise. For this reason their abundance ha* ynerally been underestimated. The meaacrysts in the hardebank are more easily recognised against the 'iq!>t ijiey kimberlite, where the colour contrast is greater. I," the prewnt study, 30 olivine megaciy»is ivt;tj analysed, Vd. ot ;!iem in implicate. Another four published snWyw» (Boyd, 1973) are included h»e (fable 11). No zoning or mnomogeneity of the rmgacryst? was found, and none has been reported by Boyd (1973). Olivine seldom coexists with another mineral ;>mor,,j ihe megacrysts, either as host c inclusion. Thus only one olivine ;.',i g-jcryst coexisting with garnet and on'; with ilmenite were found, both bemg coarse intergrowths. Another coarse íntergrowth c' olivine and garnet from Monastery has been reported by Boyd (1973). The 3'} olivine megacrysts from the Monastery Kimberlite analysed in this study fall into two distinct populations tlvc. i ar.i 2 ind Table 3). 10 TABLE 3 LewF*C HighFtO Mean FeO (wt n.•- 13,61 1934 Hamje c.i FtO (wt ui 12,3 14.5 17,8-20.4 • i 23 7 Mg/.Vti* Fe Ul .<; 8VÓ S/.4 78,^-t1,1 Iron in the range 13 14 wi.% FeO jvas rieternmfcl w;th a precision of 1o = 0,22 wt.% FeO, n - 8. Nickel and manganese alio disorminaie the iwe ol,>/ioe poyul.'tions. The losw-Fe. high-Mg olivines have 0,3 wt.% NiO, whiie ti.t iron r.ch group have NiO contents between 0,06 ami 0,11 wt.%. The iron-rich olivine group »0,16 - Q,ZA vt.% MnO» has almost twice as much manganese as the Mg-rich population (0,06 - 0,15 wt-% WhO) Tho eo»K.-virations of TIO^ Cr2Oj and CaO are all below 0,1 wt.% ind near the detection iimit. AI2O3, hov/evei is yu:">e;ally above rh.» detection iimii ard may reach 0,13 wt-% AI2O3 or higher in either group which ;u high for Sumbcriitic olivine. The olivine: The single olivine ilnsemte intarqrowth urtalysai h*. sn Fe ich olivine composition fTabir; 20 and Plate i). Tf*e two minerals have different compositions along thei' corttfic*. compared to tho otfceri*tM homogeneous crystal themselves This is r,hown by a tíecre<»fe in iron and a.i increaM iri magnesium in the olivine where it is ir. comaot «virh the Hnwiifc. Tins d true only for a 1 mm zona where the olivine is in contact with ti.e ilmenitt; Th'-re is no evidence oi /cnincj in its fiue sense between the olivine and the ilmenite, b'->t .utlitr a limited in.oi.int '.1 if equilibration between the tw«> minerals a'or >i the points of contact. fHacjgerty and Bo»0 ('ú/h/ hav; described a-> olivine nugacrysr with spheroidal kimberlite inclusion». During a recent visit 10 Monastery at Uast »tn such samp'es have been found in olivines embed-lrcf in hardebank. They are therefoie iiuite common and n iy be preset.! in as many as 5% of ih# olivine m?gacrysts. iv>osl of the inclusion!) aie tubular features, up to 5 mm in diameter ?nt> with lengths a* up to 2 : 4 ? Orthopyrcxene Tire oithopyru^ cries are trie leas! aljur.rid'ti rney^crys's at Monastery, dii' i.hips (>2crn) of '.ngcr crystals were available for mis study, and ths m.jjo, ity of these i (1) The t.rsi are clear, {jla«y-tookiny crystal fragments, with cracks alonrj clai«vage (iliriu several millimtirsj a^art, giviirj a coliirnnar appearance. Thfesy ertstatitet are chi.actflr'sed by ^ei' high and variable AljOj and i.'^O, low Crj^j, inteimftdiale T'O-^ and variable FeO (Tsb't r7». Or.'y si* wero 'pund by us, plus orin v/hich co e*'st; with olivine, but it is in of he reseats idei.t.cal. 11 (2) Coarse intergtowths of orthopyroxent and ilmenite are more abundant at Monastery than discrete enstatites. For the present study, 18 intergrowths have been analysed (Table 19). These are both regular and Regular intergrowths (Plates 4 and 5) but have no cleavage fractures and are not as transparent and clc-ai as the discrti^ r:nstattes Enstatites associated with ilmenite are chemically similar to the discrete eiistdtites, except that they have more T1O2, and TÍO2, AI2O3, FeO and CaO are almost constant. (3) The third and most ahunda..i group or nrrliopyroxene meyacrysts which have not previously been reported from Monastery are dull-coloured enstatites. These have ;: onounced cleavage planes which give a lamellar appearance to the locks. Bright green chrome-dio, side lamellae ha''e been found along the cleavage olanes. Generally the dtopside is more abundant near the edges of the enstatite crystals. Since the surrounding kimbeiiite reacts with the enstatite mainly at the edges and along cleavage planes, the diopside is often alteied, difficult to detect an,' an analysis is not possible. For these reasons also bulk rock analyses would be difficult to interpret. In two of these enstatites garnet has been found apparently exsolved along cleavage planes, wh;|e in a third sample a 2 mm rounded garnet inclusion is present. These lamellar enstatites are chemically distinct. They have low and constant CaO, low T1O2, AI2O3 anil Nd20, l)ui nujh C12O3 and a high Mg/MgfFe ratio (Table 18 and Fig. 1). 4.3 Clinopyroxene Pale-green, partly serpentimsed clinopyroxene megacrysts and pyroxene-ilmenite. lamellar intergrowths are very abundant at Monastery, such ttut this is the classic locality for kimberlitic megacrysts. Intergiowths or inclusions of clinopyioxene with garnet, e.tstatite and ilmenite, but no olivine, have been found. In the present study 26 mononiineiallic clinopyroxene megacrysts have been analysed, 14 of them in duplicate. The results aie shown in Table 12, together with six analyses from the literature. These diopside megacrysts have a very restricted iron content (range 5,34 - 6,12 wt.% FeO) and a small range in Mg/Mg+Fe (83,7 - 87,6) with a low Ca content (13,37 - 15,75 wt.% CaO). As a result the Monastery diopside megacrysts are subcalcic with a relatively constant 10 mole wt.% Fe but variable Ca/Ca+Mg of 31,4 - 39,1. The chrome content is also low and restricted (0,10 -- 0,34 wt.% Cr203>. The diopside-ilmemte lamellar inlergrowths are very abundant and single pyroxene crystals of up to 20 cm in diameter may form. The diopside is often altered, especially where it is in contact with the ilmenitc. Within a single nodule there are often abrupt textural changes. In the central part, the lamellar intergrowth is often fine-grained and the lamellae form long thin slabs, whilst towards the outside the intergrowths become coarse grained and more irregular (Plates 6, 7 and 8). Ilmenite always forms lamellae in two crystallographic directions at an angle of 60 0 in the diopside matrix. inclusions of diopside and ilmenite, as compared to the lamellar intergrowths, are vory rare at Monastery and only out diopside inclusion in an ilmenite host has been found. Twenty three diopside ilmenite lamellar intergrowths were analysed (Table 11). Published analyses of diopside-ilmenite intergrowths from Monastery are sho Eight bright-green chrome-diopsides, present along the cleavage planes of the lamellar Group II enstatites, have been analysed (Table 13) They are calcic (Fig. 1) and are poor in iron and titanium (<' 0,1 wt.% T1O2) and net) in chromium Hit,"/ die thmefoie very similar to diopsides from peridotites, 12 Only two diopside yarnei meyaciysis were found (Table 20). Sample RJ 1 consists of a diopside megacryst (11 cm) wit1! a garnet meyacryst inclusion of 2 cm (RJ1) and another small 3 mm garnet inclusion (RJ 4) Both these garnets have a similar composition. Diopside megacyst RJ 1 is interesting in thai it is traveised by serpenimous matei ml ami contains, in addition to garnet, many altered inclusions. fiie jeni''ij >Ji(..ps,oe IJUI .it.i iii^a^v1! ai..--.ii .it an lb cm diopside crystal with a small 2 mm rounded garnet inclusion neoi ;c Luitft \Hi 400) tiuin diopside» K.J I and RJ 466 have a composition within the field ol the discrete diopsidc megac; ,. sti (t-iy I) 4.4 Garnet The garnet iney.iu, sis i> -.,• t \\ (weiuy so. iiioiiut.nm.-KiHii, .|«n:.ti III.SJJC. ysi» woe analysed, seven of them in duplicate. Three further samples weie checked tui hontuyeneitv for uon, magnesium and chromium, using polished thin sections, f-or all 10 duplicate analyses, nu zoning oi inhomoyene:ty was found. The electron microprobe analyses of the garnets are shown in Table lb. The second gi uup of yoi net:» uiiuly>ed ait gam^u that coexist with ilmenite. Their colours also range from orange to ied. In all iho samples that weie availaule foi this study, ilmenite was the host i.e. the megaciyst, and tl>' gamuts wete ))i-;si.-ut <:S >ounded inclusions, ranyi. orn 1 mm to 5 mm diameter. In no instance was the garnet obsewed to be the host, and no coarse i• i jrgrowths of garnet and ilmenite were found. A total of 20 gat net inclusion.) in iimanite were analysed, the results are given in Table 16. Also shown in the same Table are three ctses in which two separate garnat inclusions in the same ilmenite host megacryst were analysed. These duplicates ore of snnilai composition. Interyrowths of garnet with another silicate mineral are very r« A notable feature of the rrionommeiriilic gamHs and the garnet inclusions in ilmenite is their small range in Ca content (4,3 b, I wt.'•• (JaOi This is well illustrated in Fig. 1, which also shows that the garnets associated with nmenite are more iron rich (IV.r/MgfFe 68,4 - 73,6) than the monominerallic garnet megacrysts (Mg/Mgt Fe 71,1 81,5) The trend is continuous, with only a small overlap. The two garnets from the garnet -olivne inturgrowths n'a. among the most Mq rich garnets found (Mg/Mg+Fe of 79 - 80). The chiomium content o1 the Monasteiy garnets is low, with the garnet megacrysts having a range from 0 - 2 wt.% O2O3, while the garnets of the garnet imenite association are extremely low in chrome (below 0,33 wt%). The garnets coexisting with olivine have intermediate chromium contents (1,06 wt.% and 0,89 wt.% Cr^Oj for samples RJ 4/4 and PHN I8b9 M lespectively). 13 Tttarktm in tht garnets it rtiativtty high but variable (0.64 - 1,5 wt% TiOj) and thit variation it found in garnets which co-exist with iimanttt and thow which do not. 4.5llrntnita The Monastery Kimbertite Pipt is extremely rich in ilmtnita andtiws minera l is therefor» alio tht matt abundant heavy mineral present According to Ninon and Boyd (1973). ilmtnite constitute? about 47 % of tht coarse concentrate at Monastery. In the present study, 89 ilmtnitcs have been analysed (Table 21 - 24) and represent the following groups: llmenite megwrvsts 26 llmenitt/garnet 19 llmenite/enstatite 18 llmenite/diopside 25 llmenite/olivine 1 The ilmenites were not studied in detail since this study was directed towards tht silicate minerals, but tht following observations were made: The ilmenites with garnet inclusions, as well as tht ilmenite/olivine, consist of tingle homogeneous crystals. Among the other groups, including the monomineraJlic ilmenites, rtcrystaHistd polyeryttalline nodules are present These have bean analysed on duplicate grains which were found to be homogeneous. Some of tht i.menites art traversed by tubules, a phenomenon alto noted by Nixon and Boyd (1973). These tubules or spheres are filled by calcite or amorphous material. They have been noted only in tht monominerallic ilmenite megacrysts. Submicroscopic exsolution, too small to be resolved with the microprobe, has been noted in several ilmenites. The most important exsolution feature is an iron-rich mineral, probably magnetite, but Cr, Ca and Ti-rieh zones have also been noted. Aluminium-rich zones, containing up to 3 wt.% AJ2O3, arc a common feature in tht ilmenites occurring along fractures and around individual grains of tht rtcrystallittd polycrystalline nodules. This is probably a recryttallisation feature. The Monastery ilmenites are typically picro-ilmtnitts with a gsikielitt content of 20-40%. Although there art large variations of any element within a single group (Table 21 - 24), the averages of all the groups are quite similar except for the lower Cr contents of the ilmcnite/gamct and ilmenite/dioptide associations, and the slightly wider range of MgO and Fe2(>3 of the monominerallic ilmenites. 6. DISCUSSION 5.1 Clinopyroxmw The chrome-poor subcalcic discrete diopside megacryttt and the dioptide* of the diopside-ilmenitc lamellar intergrowths form a continuous trend (Fig. 1) suggestive of igneous differentiation, e.g. chromium decreases regularly with decreasing Mg/Mg+Fc (Fig. 3) and with increasing Ca/Ca+Mg (decreasing equilibration temperature) (Fig 4). The ilmenite intergrowths are always more Fe-rich and Cr-poor than the discrete megecrytti. Tht inverse linear relationship of Ca/Ca+Mg (temperature) and Mg/Mg+Fe (differentiation index ?) for dioptide megecrysts from Letteng-le-terae was also suggested by Nixon and Boyd (1973) to represent en igneous differentiation trend. It mutt be pointed out, however, that although Mg/Mg+Fe in Fig 5 decreases with increasing Ca/Ca+Mg, this does not represent en iron-enrichment trend, 14 since the iron content of the Monastery magscrysts is «cry restricted, and is similar to megacrysts from other localities. Monastery 5.34 - 6.12 wt% FcO Thsfaa Potso» 5.34 - 5,79 wt.% FeO Letiene>la-teree 4.96 - 5.92 wt.% FeO Similar restricted compositions have been reported for chrome-poor diopsides from the Iron Mountain Kimberlites, Wyoming (Smith, McCtttum and Eggler, 1976) and from the Sloan Pipes. Colorado (Eggler and McCallum, 1976). In addition to the restricted absolute iron content of the Monastery diopsides. the partitioning o* iron and magnesium between tiiopsidc and ilmenite u aisc nearly constant. The range for K0ilm-cp* for the 23 lamellar intergrowths is 7,6 -11,4. with 14 samples having a KD between 8 and 9. The largest error in 3 calculating KD is introduced by the assignment of Fe * in the ilmenrte structure. This is possibly responsible for much of the observed spread of KD. The restricted KD for the Monastery lamellar diopside intergrowths is in contrast with the experimental work of Rahe*m and Green (1974) and Green and Sobolev ,m cp (1974) who suggested that KD' ' * may be a potential geothermomettr. The most subcalcie diopsides from Monastery have compositions similar to the sheared Iherzolites from Northern Lesotho and this may indicate a genetic link. The diopside-ilmenite lamellar intergrowths, being the most calcic diopside megacrysts from Monastery, have chemical characteristics very similar to chrome-poor diopside megacrysts which are regarded to be basaltic accumulates (Fig. 6), as shown in Table Sheared Mnnailaiv Basalt megacrysts Utercolrte CpK cpx/ilm Elie Ness* Mt. Noorat* Ka« TI02 0,22 0,37 0,42 0,62 1,32 0,91 0,74 wt.% AI2o3 2,45 2,56 2,50 8.16 8,64 8,6 7,86 wt.% CT203 0,77 0.25 0,05 0,18 0,00 0,05 wt.% FeO* 4,19 5,73 6,31 6,26 5,59 7,1 6,77 wt.% Mg/Mg+Fe 87-92 84-87 83-85 82,6 81,6 80,0 81,4 "Total Fe as FeO (a) Chapman (1976) (b/Irving (1974) (c) Kakanui (Mason and Allen 1973) Chapman (1976) discussed the chemistry of the clinopyroxenes and ascribes the increase of TiOj in the late-formed pyroxenes to an increase in the Ti-Tschermacks molecule solid solution, since Ti-Ts becomes stable only at low pressures. Similarly, the increase in Al is ascribed to the increasing amount of Ca-Ts at low temperatures. The above author also found little iron enrichment until the late-stage groundmass augites. Quite generally, therefore, the Monastery diopsides are ir wrmediate in chemical composition to the sheared Iherzolites and to the megecrysts found in basaltic rocks. The diopside solvus (determined experimentally by Davis and Boyd, 1966) has received much attention in recent years. It has been redetermined by Nehru and Wyllle (1974), Warner and Luth (1974) and by Urtdsley and Dixon (1976). These later experiment» showed that the diopside solvus is not yet well established at 30 kbar*. The effect of pressure on the dlopside limb of the solvus has been determined by Mori and Green (1976), Lindsley and Dixon (1976), and Mysan (1976) and has been found to be significant Temperature and pressure are inversely related. Howells and O'Hera (1975) found the diopside *1 kbar = 100 MPa 15 solvus -feptndem on 'utAv- rr«?sure and si -..c. activity. The above . ithors «i.M state that temperature estimates of ?n aitv^e^at-r?*?-,! esse-nb , ,-• JV» -" be ccmpaitd only to a diopside sotvus determined in the presence or footer* je .^r •. « ,, ;U otf-u: < isons Hart* (in pre»* suggests ffil Ui-s^iraturesderived from thft diopside w'vu» should J« retarded nly as relative values within a single suna wf rocks Si:*» in* Wtoniiiery megaciysn for.r: „ «.hi vcally continuous/eries, it is probable that the diopside solvus can be used to estimate the re!»t>ve equilibrati'ir. temperatures, keeping the »*>-»vementionad limitations in mind. Two assumptions have to be made, firstly, in order to v*s; ;! ^oside solvus. n must b» assumed that the Monastery dopsidw equilibrate in thg presence cl *.i«.tu u- !•* second assumption is that an approximate correction tor th* 10 mole wt.% iron in thsd!i>i»u> n>j*>»íir\iís can be made from either the Wood and Banno (1973) correction, or ignored by txtiapolittmi lrv.it. the drops.d» composition in the Ca-Mg-Fe tetrahedron onto the Ca-Mg join- Temperatures for the d>scr»w diopside megacryst* range ftom 1 385 to 1 220 °C (using the average of the temperatures ob'.atr>«i from the dtowide sotvi mentioned earlier). The lamellar diopside-ilmenite intergrowths give a temperature range from 1 270 to 1 130 °C. Another temperature estimate can be made from the garnet inclusions in diopsides RJ 1 and RJ 466. Twc experimental studies can be used. The work of Raheim and Green (1974) is applicable for some eclogite assemblages and is pressure-dependent. In a diopside-enstatite-garnet assemblage the pressure-independent relationship between KD and temperature as determined by Akella and Boyd (1973) can be used: 4 "20 TK=—-— 2,31 + 8nKD For the present discussion on the Monastery megacrysts, the above Akella and Boyd equation will be used because diopside, garnet, enstatite and olivine are present. The temperatures obtained for RJ 1 from KD between 30 and 40 kbar agree well with those of the 30 kbar diopside solvus. This is also true for the second garnet inclusion in diopside RJ466 and suggests that the diopsi 'e-garnet imerg.owths represent equilibrium assemblages. If this is true, then the Akella and Boyd equation can be used to test if the Monastery megacrysts equilibrated in the presence of garnet. This has been done in the following manner: from a small cluster of diopsides on the Ca-Mg-Fe tetrahedron, an average temperature is obtained from the diopside solvus, using the average temperature as obtained from the work of Davis and Boyd (1966), Nehru and Wyllie (1974), Warner and Luth (1974) and Lindsley and Dixon (1976). This temperature is used in the Akella and Boyd equation which is then solved for the Fe/Mg ratio of the garnet. The process is repeated for the whole range of garnets; the results are given in Table 5 below. TABLE 5 Sample* used Temperatures °C Diopsides Garnets Raheim & Green (34 kbar) Akella & Boyd Di(en) sol. 216,224,246 70,72,112 1378 1380 1380 223,230 84,98,100 1 343 1344 1355 234,244 206,210 82,108 1 308 1309 1300 212,236 285,393 260 1 212 1 212 1 210 403,412 RJ1 1360 1362 1345 RJ466 1315 1315 1280 16 If tht diopftdt did >n fast equilibrate in tht prestnct of garnet, than tht tit-lint» obtained as described above should be reasonably parallel to thoaa of tht natural drapnaVgarntt assemblage» RJ1 and RJ 466. The slight deviation »t tht two «at» ot tit-lint» (fig. 7) can probably bt escribed to tht trron in selecting clusters of dtoptide* and garnets in order to gtt an average vehie. and to tht atsumption that the Aktlla and Boyd aquation and tht temperatures obtainad from tht "average" dioptidt solvus ghrt tht tama tamptraturt over tht ««holt tamparaturt rang» diaplayad by tht mtgacrytts. Tht tamperaturt range» obtained from tht extreme sample compotit'nn for both the Akttla and Boyd aquation and the dioptide solvus are also almott identical (252 and 256 «C respectively). Temperatures obtained from the KQ values art about 45 °C higher than those using tht average dioptide tonus. As tht calculated diopside-gsmet tie-lines do not grossly deviate from those of tht natural assemblages, and because the temperature range» obtained from the diopside solvut and 'St diopsidrgtmtt pairs art identical. H is concluded that tnt Monastery diopside megactyin coexisted with genet rragecryi». The bright-green, chrome-rich magnesian diopsides found along deevagt planes of the lamellar enstatitts art dissimilar to any diopside megecrysts from Monastery. Th-ir cxsohition suggests that tht tnstatitas re-equilibrated in response to a cooling history to which the other megacrysts have not reacted. The exsotvtd chrome diopsides art similar to the calcic diopsides from granular Iherzolites from Northern Lesotho, and to diopside in a phlogopitt-baaringgarnet Iherzolite FRB1 f.om Monastery (Table 25). They will be discussed in a later section together with their tnstatitt hosts. 5.2 Garnet The Monastery garnet megacrysts display affinities towards the peridotite-pyroxenite trend (Fig. 8, Gumey, 1974). They have only a slightly higher calcium content than the garnet xenocrysts from tht Kimberley area, u oudined by Raid and Honor (1970). Most of the garnet megecrysts fall into the field defined by die Matsoku garnet peridotites (Cox, Gumey and Harte, 1973) but there are differences between ihe two groups. The Monastery garnets have high titanium, low chromium « 2 wt.% 0203) and a small range in CaO (4,1 - 5,2 wt.% CeO). The Matsoku garnets are low in titanium, high in chromium, and have more variable Ge/£r ratio). The Monastery garnets differ from ttw granular and sheared Iherzolites (Nixon and Boyd 1973a) m being mora iron-rich. The inverse Fe-Cr (and also Mg/Ma+Fe-Cr) relationship for garnet* of intermediate Cr content noted by Gumey, Few and Kábte (1973) is quite general for kimberfite garnets. This also applies to the Monastery garnet» which show a well-defined trend at low Cr contents (Fig. 9). The garnets in the garnet Iherzoiitt» 1589 N and FRB 1 from Monastery (Table 25, Boyd and Nixon, 1973, 1975) are the most magnesium-rich garnets; tftty ado heva the highest chrwmium content wrn> 9J0O wt.% and 5,00 wt.% &2O3 respectively. The iron-rich garnets that coexist with ilmenitt art varytow in Cr, below 0,33 wt.% CrjOa. The garnet-silicate intargrowths investigated in this study (Tabid 20) follow the Mg/Mg+Fe-Cr relationship well. Among these intergrowths ên two coarse gernet-otivine intcrgrowths, viz. sample RJ 474 from this study and sample PHN 1859 M (Boyd, 1973). Both garnets have high but similar Mg/Mg+Fe ratios and Cr contents (Fig. 9), and the coexisting olivines both have similar Mg/Mg+Fc ratios and Ni content» (Table 20). fna MCOIMJ apsis) ft |*n»TfHfcate intergrowdw ara two femes Utttn^m H» diopiida megacrysts (Table 20), whit* |sjw already Bagn described. Both follow tht IBjnwj+fVQ rtletionsnip (Fig. 9), and the equilibration temparauir» for tfw magnesium and «hrgnM-riaf) dlapH6V|gmai RJ1 (using either the , n diopsida lefvui or H 09 «-4»w| it higher than for #w low chroma farnet-diopside assemblage RJ 466 (RJ1 = 1 3450c, RJ406* 1 2B0OC). The titanium content of the Monastery garnet megecryiti varies between 0,64 wt.% and 1,46 wt.% T1O9, the higher values being the maximum found among kimberlitic garnets (Gurney, Fesq and 17 Kabte, 1973) except for recent data on Premiei (Danchin and Boyd. 1976). This classifies the rmgacrysts as high-titanium pyropes (Dawson and Stephens. 1975). The titanium content of the garnets also shows * weakly defined relationship with iron and, an essentially similar one, with Mg/Mg+Fe. Rg. 10 really indicates two trends, viz. one in which Ti increases with decreasing Mg/Mg+Fe. but with a large scatter in the data, and a second trend of decreasing Ti with decreasing Mg/Mg+Fe. This trend is s The distribution coefficient for coexisting ilmenite-garnet pairs is defined as K Mm-ea (Fe++/Mg)ilm DIF.-Mgi (Fe+t/Mg)^ For silicates of the present study, total iron has been taken as Fe+ + , although structural formula calculations of the Monastery garnet megacrysts indicate Fe2(>3 contents from O to 2 wt.% F^Os- Rost tt aV (1975) lieve also shown Fe3+ to be present in pyropes of the Stockdale Kimberlite. Green and Sobolev lm 9 (1975) determined K0' ' * experimentally over the range Mg/Mg+Fe of 41 - 62 and 73,8 - 77.2 at.% for garnet and 15,3 - 27,6 and 41,7 - 47,9 at.% for iimenite The above authors found KD to be constant at 4,0 i 0,5. This compares well with a value of 4,6 ± 0,5 for 19 samples as determined in the present study, over the ranges 68-74 at.% Mg/Mg+Fe for garnet and 32 - 38 at.% for iimenite. Only sample RJ 294 1 1 9 with KD = 5,61 falls outside the range. Ko' " ' * is therefore independent of temperature, pressure or bulk lm 0a composition. In addition, FejOg in iimenite (5.7-12 wt.%) is independent of KD' ' and the Cr content of the garnets is only weakly dependent on Fe2C>3 in the iimenite, contrary to the suggestion of Green and Sobolev (1975). The experimental work of the above authors indicates in addition that the titanium content of garnets that coexist with iimenite increases at higher temperatures. Fig. 10 shows that both titanium and chromium increase with increasing Mg/Mg+Fe of the garnet inclusions in ilmer/te. As a result of the constant Ko',m'9*, the MgO content of the iimenite also increases regularly with increasing Mg/Mg+Fe of the garnet (Fig. 11). This is consistent with the experimental work of Green and Sobolev (1975) and with published mineral analyses from the Excelsior Pipe (Boyd and Dawson, 1972) and the Frank Smith Pipe (Boyd, 1972) for coexisting garnet-ilmenite megacrysts (Fig. 12). Titanium and chrome in the garnet, and MgO in the coexisting iimenite, thus increase with increasing Mg/Mg+Fe of the garnet. Boyd and Nixon (1973) and Boyd and Dawson (1972) regard the trend which the Monastery garnets define in the Ca-Mg-Fe tetrahedron to be due to igneous differentiation. Further evidence supporting this comes from the Cr-Mg/Mg+Fe relationship and from the decreasing equilibration temperatures for the diopside-garnet intergrowths in Fig. 9. The present results therefore indicate that the Monastery garnets display an igneous fractionation trend towards decreasing Mg/Mg+Fe. Because of the constant Ko',m'9*, the MgO content of the iimenite is dependent on the Mg'Mg+Fe of the garnet. The experimental work of Akella and Boyd (1972) indicates that garnet coexisting with iimenite or rutile will dissolve up to 1,5 wt.% T1O2 at 1 100 OC and 15 - 40 kbar. Garnets falling in the diamond stability field (Gurney and Switzer, 1973) or diamond inclusions (Meyer and Boyd, 1972) are Ti-poor (Fig. 8), but it is known that these almost certainly do not coexist with iimenite. Boyd (1974) and Boyd and Danchin (1974) have described garnet megacrysts and some gernei-ilmenite intergrowths from other localities than Monastery. These have chemical compositions very similar to those described here. The garnet megacrysts and garnet-ilmenite intergrowths from different localities are therefore very similar in composition. In Table 6 below they are compared to granular and sheared peridotites and to megacrysts found in the basaltic lavas. 18 TABLES Monfry Basalts gmislar *~* game* g>X/ilm EKeNess(i) Kafcamriiii) HO: 0.1 0.7 1.19 1.00 0,40 0,51 wt.% 0/203 6 2.5 0.65 0.09 0.07 - wt.% FeO 6.5 7.2 11,0 12.7 10.4 10,8 wt.% CaO 6.5 5 4.64 4.52 5.5 5.1 wt% Mg/Mg+Fe 83-86 81-86 753 713 76 75,4 at.% Total Ft as FeO (i) Chapman (1976) Average of Samples 1,6, EN (ii) Kakanui (Mason and Allen, 1973) At Monastery both the discrete megacrysts and the small garnet inclusions in ilmenite hosts are higher in titanium and lower in calcium than peridotite garnets or basalt megacrysts. Chromium in the discrete megacrystt is of intermediate range, but iron and the Mg/Mg+Fe ratios are the same as from megacrysts found in basalts. The small garnet inclusions in ilmenite have chromium contents similer to basalt megecrysts. The Monastery garnets therefore have both higher and lower ranges of composition than displayed by the basalt megacrysis, and to a large extent overlap that field. Garnets which equilibrated in the presence of orthopyroxene and clinopyroxene have a Ca/Ca+Mg ratio dose to 0,13 (ffHara and Yoder, 1967). Both the Monastery garnet megacrysts and the garnet inclusions in ilmenite have calcium contents falling within the range 4,17 - 5,13 wt.% CaO. Consequently their Ca/Ca+Mg ratios range from 0,13 - 0,16. Gurney and Hatton (In Press) suggest that orthopyroxene buffers the calcium content of garnets in the system gnt-cpx-opx-ol by the reactions: 3CaMgSi20e -I- Mg3Ala^Oi 2 *» Ca3AI2Si30i2 + 6MgSi03 and 3CaFcSi20e + Ft3Al2Si3012 * Ca3Al2Si30i2 + 6FeSi03 A small 2 mm garnet inclusion has been found in the ilmenite from the coarse enstatite-ilmenite intergrowth RJ 460. Both the garnet and the enstatite have compositions which fall within the ranges defined by the gernet-ilmenite and enstatite-ilmenite intergrowths (Fig 7). This, together with the constant calcium content mentioned above, suggests that the garnets coexisted with orthopyroxene (and clinopyroxene) and display an igneous differentiation trend. Sállmtnrtt The present investigation on the Monastery megacrysts indicates the following to be the most important cburecteristlc* of the ilmenite: 1. Ko(Fe-Mg) for the ilmtnite-silfcste intergrowths is constant (garnet) or nearly constant (opx, cpx). 2. The monomirwrirflic ilmenite megscrysts have a wider range in magnesium content than the ilmenite-silicate intergrowths (Fig 13). 3. The similar compositions of the ilmenitfs intergrown with all the silicates is consistent with these minerals being in equilibrium with each other. 4. Only on» ílmenite-olívlne Intergrowth has been found. These »rt therefore very rare. 19 Since the silicate megacrysts are considered here to have formed by igneous differentiation. Fig. 13 suggests that the MgO content of the ilmenite decreases during differentiation, and may therefore be temperature-dependent The diopside-ilmenite intergrowths appear to have crystallised over a temperature range of 140 ©C, (from 1 270 to 1 130 »C). Assuming a lirmr relationship of MgO in the ilmenite with temperature, then the ilmenite with the highest MgO content has an equilibration temperature of 1 390 °G This compares well with the beginning of crystallisation of the coexisting silicates, i.e. 1 385 °C However, the MgO(ilmenite)-Ca/Ca+Mg(diopside) relationship is poor and there is no evidence from the experimental work of Green and Sobolev (1974) that the MgO content of the ilmenite is temperature dependent. The most-magnestan ilmenite which coexists with garnet has a lower MgO content than the most-magnesian ilmenite that is intergrown with diopside or enstatite (Fig. 13). This is consistent with what is seen in Fig. 7, which shows that whilst the diopfide from the natural diopside-gtrnet intergrowth RJ 1 lies on the boundary between the discrete diopsides and the lamellar intergrowths, the coexisting garnet RJ 1 lies well into die field of monominerallic garnet megacrysts. This may indicate that diopside and enstatite formed intergrowths with ilmenite before garnet. This could also be indicated by the lower chrome content of the ilmenite megacrysts with garnet inclusions, shown below. average wt.% &2O3 range Cr203 discrete ilmenite 0,26 0-1,16 ilmenite-garnet 0,10 0 - 0,42 iimenite-enstatite 0,25 0,1 -0,45 ilmenite-diopside 0,19 0,02 - 0,48 Garnet, unlike clinopyroxene and orthopyroxene, does not form a coarse intergrowth with ilmenite but has been found only as small inclusions in ilmenite hosts. 5.4 OrthopyroxtM The Monastery orthopyroxenes fall into two groups. The glassy discrete enstatites and the dull-coloured enstatite-ilmenite intergrowths have similar chemical compositions and constitute one group (Group I). Among these the discrete nodules have a wider r. nge of compositions and resemble enstatites from Northern Lesotho sheared Iherzolites (Fig. 14). The second group (Group II) consists of the lamellar enstatites with exsolved chrome diopside. These have chemical affinities with the Northern Lesotho granular Iherzolites. The linear relationship of CaO with Mg/Mg+Fe for the first group of discrete enstatites and the enstatite-ilmenite intergrowths is well illustrated in Fig. 14. CaO is temperature-dependent, and Fig. 14 shows the large range in equilibration temperatures of the discrete enstatites. Aluminium is both temperature- and pressure-dependent- There is therefore also a good C8O-AI2O3 relationship for the glassy enstatites and the enstatite-ilmenite association (Fig. 15). The chrome content of the Monastery enstatite megecrysts decreases regularly with decreasing Mg/Mg+ Fe (Fig. 16) and is similar in this respect to the garnets and diopsides. The distribution coefficient Kp^f jj?'. was suggested by Green and Sobolev (1975) to be a possibly useful geothermometer. The Monastery intergrowths have a small range in KD (8,3 - 10,5), with an average KD of 9,5 and a small temperature range of 50 °C (obtained as described below). No relationship between KD and temperature was noticed in the present study, possibly because of the small range found in KD. The enstatite-ilmenite intergrowths have a higher KQ than the garnets (Ko=4,6) or the diopsides (K0 = 8,5) which are also associated with ilmenite. Boyd and Nixon (1973) constructed an empirical enstatite geothermometer from coexisting ortho and clinopyroxenes from the Northern Lesotho Iherzolites. The diopside solvus of Davis and Boyd (1966) is 20 used to estimate the temperature of the diopside and this temperature is then assigned to the Ca/Ca+Mg ratio of the coexisting enstatite. This geothcrmometer has been verified experimentally in the system opx+cpx+gnt for the pressure range 26-44 «bar by Akella (1976), who found, on average, slightly lower temperatures for a given Ca/Ca+Mg ratio of the enstatite. The same author notes that the Ca/Ca+Mg ratio decreases as pressure increases. Nehru (1976) summarises the experimental work on the enstatite limb of the diopside soivus and points out its large temperature dependence. The work of Hensen (1973) shows that the Ca/Ca+Mg ratio of an enstatite containing iron increases considerably over that of the iron-free systems, which complicates the picture even turner. At the present time, therefore, the available experimental data cannot be used for temperature estimates, and the empirically formulated enstatite soivus of Boyd and Nixon (1973) has to be used. Temperatures derived from the enstatite soivus for the six glassy discrete enstatites have a range of 1 190 - 1 410 °C This is very similar to the temperature ranges for the diopsides and garnets which are 1 130- 1 385 °C for the "average" diopside soivus and 1 175- 1 427 °C for coexisting diopside and garnet pairs (Akella and Boyd, 1973). The temperature ranges obtained from the above geothermometers are in dose agreement (220 ©C, 255 °C and 252 °C respectively). The temperature range of the enstatites is slightly lower, but is extended to 230 »C if the enstatite-ilmenite intergrowths are also considered. Seventeen intergrowths have a temperature range from 1 250 - 1 300 °C and only one sample gives a temperature of 1 190 oc The six glassy enstatites available for this study therefore cover almost the whole temperature range represented at Monastery. One analysis from the literature (Table 17, Boyd and Nixon, 1975) falls within this range. The similar temperature ranges and. to a certain degree, the absolute temperatures derived from the abovementiored geothermometers further suggest that opx+epx+garnet coexisted. The TiQ2-Mg/Mg+Fe relationship of the silicate-ilmenite intergrowths also suggests that thes^ minerals coexisted (Fig. 17). The constant Kotilmenite-silicate) has already been mentioned. A small garnet has been found enclosed in the ilmcnite of the enstatite-ilmenite intergrowth RJ 460. Both the garnet and the enstatite have compositions which fall within the ranges defined by the garnet-ilmenite and enstatite-ilmenite intergrowths (Fig. 7). It is therefore concluded that the Monastery enstatites coexisted with diopside and garnet over their whole compositional range. The solubility of aluminium in orthopyroxene has been used to estimate equilibration pressures. As the pressure is increased at constant temperature on a garnet-pyroxene assemblage, the pyroxene becomes less aluminous and more garnet is formed. The effect of pressure on the solubility of aluminium in orthopyroxene has been determined experimentally by McGregor (1974) in the system MgSi(>3-Al203, and by Akella (1976) in the system CaSi(>3-MgSi03-Al203. These authors found that the AI2O3 isopleths have steep positive slopes in the garnet-peridotite field. At constant temperature, therefore, a pressure decrease increases the solubility of AI2O3, while at constant pressure a temperature decrease decreases the aluminium solubility of the orthopyroxene. The aluminium isopleths of these two experimental studies cross just above 1 200 °C, and the data of McGregor (1974) indicate a higher solubility of aluminium in enstatite. The AI2O3 content of the Monastery enstatites is much lower than that of the experimental systems, and large extrapolations have to be made. Since this study stronly suggests that the Monastery enstatites coexist with diopside and garnet, tamperature estimates from the extreme compositions of the diopside and garnet can be made by using both the diopside soivus and the distribution of iron and magnesium between diopside and garnet. If these extreme temperatures are then superimposed onto the data of Akella (1976) they fall between the 0,74 wt.% and 1,31 wt.% AI2O3 isopleths which »ra applicable for Monastery, over the pressure range 60-65kbar. The steep diopside soivus of Nehru and Wyllie (1974) gives a slightly wider temperature range. The Monastery enstatite-ilmenite intergrowths have aluminium contents between 0,80 wt.% and 1,1 wt.% AI2O3 end enstatite soivus derived temperatures between 1 101 and 1 300 °C. These extreme temperatures also fall between the 0,80 and 1,1 wt.% AI2O3 isopleths of Akelle (1976), at constant 21 pressure. Individual data points indicate a positive slope for the enstatite-ilmenite intergrowths and a negative slope for the discrete glassy enstatites. The temperature estimates for the Monastery enstatites as derived from the empirical enstatite solvus of Bayd and Nixon Í1973) are regarded with some confidence, since the coexisting diopsides and diopside-garnet pairs give similar temperatures and temperature ranges. The temperature range of the Monastery enstatites can fully account for the whole range of AI2O3 in the enstatites, at constant pressure. This is as a consequence of the temperature dependence of the AI2O3 content of the enstatite. Pressures of 60 — 64 kbar, as indicated by the aluminium content of the enstatites for the Monastery enstatites from the experimental studies of McGregor (1974) and Akella (1976) are almost certainly too high. In these two experimental systems, iron-free compositions were used. These are not applicable to silicate phases that coexist with ilmenite, cs is the case at Monastery. Wood and Banno (1973) propose a simple mixing model to estimate the pressure from the solution of garnet in enstatite. Balancing of the charge distributions in the enstatite (Wood 1974) using the data of McGregor (1974) results in a decrease in the pressure estimate (Fraser and Gurney, in prep.). These calculations show that the pressure estimate for the Monastery enstatites is reduced by 20 kbar from those obtained using the experimental systems. Pressure estimates obtained for the Group I enstatites are constant at 42,5 ±2 kbar. Th s is strong evidence that the Group I Monastery megacrysts have equilibrated by isobaric cooling over a temperature range of 250 oc, from about 1 150 to 1 400 «C. The megacrysts therefore represent a thermal event in the Upper Mantle, and define a vertical geotherm over a very restricted depth range. The equilibrium conditions of the Group I megacrysts (1 400 to 1 150 °C, 42,5 ±2 kbar) are above the graphite-diamond stability curve outside the diamond-stability field. The Group II lamellar enstatites with exsolved chrome diopside have so far been excluded from the discussion since these magnesium-rich enstatites are compositionally very different from Group I enstatites. The mineral compositions suggest that these lamellar enstatites have equilibrated in the temperature range 920 - 960 OC (except for one sample giving a temperature of 1 090 °C). Whole-rock analysis of the lamellar enstatites is not practical because of the alterations along cleavage planes by the enclosing kimberlite, but calculations show that if less than 10 % chrome diopside is added to the respective enstatite hosts, the resulting concentrations of CaO, AI2O3 and Na20 would fall into the range displayed by the discrete enstatites and the enstatite-ilmenite intergrowths. While T1O2 and FeO would still be lowr in the mixed enstatite-diopside, chromium would be even higher and the trend shown in Fig. 16 would be maintained. The physical appearance of the exsolved diopsides and their unusual characteristic in having a higher Mg/Mg+Fe ratio than the coexisting enstatite suggests that they are a recrystallisation, and not a primary feature. This assumes that the exsolved diopside must at one stage have been dissolved in the enstatite host. The higher Mg/Mg+Fe ratio of the Group II enstatites (Fig. 14) and the position of the break in the Group I and II trends suggests that the Group II enstatites are genetically linked to the Group I enstatites. It is possible that the lamellar enstatites formed a continuation of the Group I trend shown in Fig. 14, but whether it was a linear relationship is not known. The small amount of garnet along cleavage planes of the lamellar enstatites, mentioned earlier, also appears to be due to exsolution. Only two garnets could be analysed (Table 20) but small and sometimes altered grains are quite frequent. It is therefore assumed that the lamellar enstatites formed a continuous but not necessarily linear trend in Figs. 14 and 15; the chrome diopside (and garnet) exsolution can thus be explained by chemical oversaturation during isobaric differentiation: mixed pyroxene (high T, high P) -»opx + cpx i garnet (low T, high P) Thi; reaction can take place during or after the isobaric differentiation proces.. Only the chemically least stable, early formed minerals are re-equilibrated. The equilibrium temperatures of the lamellar enstatites (using the enstatite solvus) aid of the exsolved diopsides (using the diopside solvus) indicate 22 re-equilibration temperatures of 920 -960 °C However, the diopside solvus is insensitive at these temperatures and even lower temperatures are possible. These temperatures are lower than those that prevail at the end of the major differentiation process labout 1 150 OC). This seems to indicate that the lamellar ensiatites exsolved diopside and re-equilibrated only after further cooling, when the differentiation process came to an end. The lamellar enstatite RJ 337 has a higher equilibrium temperature than the other enstatites that have exsolved diopside. The temperatures derived from the diopside solvus (1 090 °C) agrees closely with that derived from the exsolved diopside and garnet (1 076 °C), using the Akella and Boyd equation. This suggests that the diopside, garnet, and the enstatite host are in equilibrium. The re-equilibration must therefore have occurred in the mantle, since a time interval and slow cooling are necessary for the diopside to exsolve and lo migrate to the boundaries of the enstatite crystal, and yet for the phases to remain in equilibrium. Such stable conditions may have been reached when the megacrysts cooled down towards the normal shield geotherm during and after isobaric differentiation. Along the geotherm, re-equilibration can take place, possibly under conditions different from those which prevailed during the differentiation, e.g. under more water-rich conditions. The Monastery Group I discrete enstatites and the enstatite-ilmenite intergrowths have Mc'Mg+Fe ratios and iron contents similar to basaltic enstatite megacrysts, as shown in Table 7 below. TA3LE 7 Northern Lesotho Monastery Basalts (1rving , 1974) Iherzolites Group 1 Group II Mt.Noorat The Anakie* granular sheared opx opx/ilm opx/cpx Al203 0,9 0,8-1,4 0.74-1,3 1,0 0.77 4,5 5wt.% &2O3 0,36 0,18-0,45 0,04 0 0,21 0,27 0,20 wt.% FeO 4,3 5,6 9.5 9.5 6,3 9,4 10,0 wt.% CaO 0,4 1-1,7 0,79-1,53 1,1 0,26 1,8 1,7 wt.% Mg/Mg+Fe 94 91 85,5 85,5 91 85,1 84,2 at% Total iron as FeO The Monastery enstatites, except for the Group II enstatites, are characterised by their low chrome contents. The biggest difference between the Monastery and the basaltic megacrysts is the high aluminium contents of the latter. This indicates equilibration pressures within the spinel Iherzolite field. 5.5 Olivine The Monastery olivine megacrysts are unrecrystallised and unstrained crystals. They form two populations with Mg/Mg+Fe ratios near 0,80 and 0,86 (Figs. 1 and 2). Boyd (1974) analysed twelve olivine megacrysts from Monastery covering the range of Mg/Mg+Fe 0,80-0,88 but published only three analyses, including the extreme values. These fall into the ;wo populations established in this study. The magnesium-rich olivine megacryst population has a nickel content of between 0,3 and 0,4 wt.% NiO. This is identical to the euhedral groundmass olivines analysed by Boyd (1974). These are partially serpentinised olivines with original dimensions of 200- 400 ^/m found in the kimberlite matrix surrounding olivine megacryst FRB 183. These small olivines have variable chemical '.ompositions which cover the whole range found for the magnesium-rich olivine megacryst population. Boyd and Nixon (1974) have shown that some dunite nodules from kimberlites other than Monastery have similar compositions to the discrete nodules, inasmuch as their Mg/Mg+Fe ratios are also in the range 0,80-0,87. It is therefore possible that the olivine meqacrysts from Monastery represent true discrete 23 nodules or that they formed by the disintegration of coarse grained dunites. Howe»* ih* rtstiftct chemical differences of the two olivine populations as found in inis study requite the different oltvme groups to be considered separately. The similai composition ot the Mgnch olivine yioup and the yroundmass olivines, both in their Mg/Mg+Fe ratio and their Ni content», suggest* a genetic link. During the present study all sizes of olivines with Mg/Mg+Fe ratios near 0,86 have been found in the kimtxrlite enclosing some of the megacrysts. This may suggest that these and the groundmass olivines analysed by Boyd and Nixon 09741 may have formed by fragmentation of the megacrysts during eruption of the kimberlite or that all sizes of olivines were present at the place of origin of the megacrysts. The composition of the olivine in the two Iherzolites from Monastery (Table 25) is more magnesium-rich than any megacrysts or grouitdmass olivines analysed. If the two Iherzolites in Table 25 are representative of the ultrabasic nodules at Monastery, then the megacrysts could net have formed by fragmentation of coarse-grained Iherzolites, nor were the groundmass olivines formed by such a process. Use has been made of the IIon magnesium distribution coefficient in an attempt to predict the olivine compositions which would be in equilibrium with certain liquids (Roeder and Enslie 1970, Roeder 1974). KQ for olivine/liquid has been shown to be near 0,3 (Roeder and Enslie 1970, O'Hara 1975) and to be relatively insensitive to pressure, temperature an^ oxygen fugacity (D.G. Fraser, personal communication). 3 + The calculation of KD does not take any Fe present into consideration, and this will be in addition to the FeO indicated. Various liquids can be tested to determine whether they could be considered as possible parental liquids for the Monastery megacryst olivines. For a constant KQ of 0,30 the calculated liquids in equilibrium with the Monastery olivine megacrysts are shown in Table 8 below. TABLE 8 Magnesian Olivines Calculated liquid FeO/MgO Fo88 0,80 Fo84 0,97 Iron-rich olivines FoBI 1,39 Fo 78,3 1,65 These liquid compositions are much more iron rich than those produced from two garnet Iherzolites from kimberlite (Kushiro, 1973b), which are shown in Table 9 below. TABLE 9 JJG352(Fe/Mg+Fe 0,09) 1611 (Fe/Mg+Fe = 0,13 20 - SO % melt 10 - 25 % melt Pkbar 10 10 15 20 10 15 20 Toe 1 350 1 375 1 430 1 490 1 375 1 450 1 475 FeO/MgO 0,50 0,30 0,34 0,22 1,1 1,2 1,0 The large partial melt produced from JJG 352 is of picritic character and is too magnesian to be in equilibrium with the megacrysts. Sample 1611, being more iron-rich than Sample JJG 352, gives a basaltic liquid. This has the required inteimediate FeO/MgO ratio required by the megacrysts. In another experiment Kushiro (1973a) produced a 20% melt from a spinel Iherzolite, to which 1 % phlogopite was added. This melt was produced at 1 475 °C and 20 kbar pressure. If all the iron is taken as Fe2 +, this partial melt has an FeO/MgO ratio of 0,40 This is similar to the picritic melt obtained from sample 24 JJG 352 and n> therefore too-magnesian to ha.e b«t*n in equilibrium with the rr.e-jac^ystï. Myser. and Boettcher, (1975; produced a t;art>ai rrwit f-.om a spsnei Iher/olite at ! !•>> °C and 20 kbar. This has an FeO/MgO latio of 0,54 and is also too-magi lesian A whole-rock analysis of a round*) k-mberiite inclusion (to be discussed) in a magn«siar olivine ine^acryst (Fo 85) has beeu obtained. This inclusion was too vnail to allow determination of the V*1 ' Ft;-5 • ist.o if all imn is taken as ft* *, ifvs Inclusion h?s an FeG/MgO ratio of 0,53 and would he expecteó to be in equilibrium w>th olivine ot FeQ/MgO tatio 0,16. This i* much lower than that expected for the Monastery megacrysts and is close to the olivine (Fo 91) in the garnet Iherzolite FRB 1 (Table 25) which has olivine with an FeO/MgO ratio of 0,17, and which should be in equilibrium with a liquid with an FeO/MgO ratio of 0,57. Yet Haggerty and Boyd (1975) analysed olivines in a kimberlite inclusion in an olivine and found these small olivines to have compositions ranging from Fo 88 to Fo 86. Olivine of tin:, composition should be in equilibrium with melts of FeO/MgO ratios between 0,80 and 0,88. This is much higher than was found for the incl' *ion in the present study (FeO/MgO- 0,16). However, this need not necessarily indicate disequilibrium or a different KQ, but may merely indicate variability among the inclusions. Karroo tholeiites (Walker and Poldervaart, 1949) have FeO/MgO ratios near 1,3. This corresponds to a liquid composition in equilibrium with more rr.jonesian ol.vines of the iron-rich megacrysts I Table 11). Some olivine microphenocrysts from Kanoo dolerites (Le Roux, Personal Communication, 1977) are also of composition Fo 80. Several Karroo basalts from the Nuanetsi Province of Rhodesia (Cox and Jamieson, 1974) have FeO'MgO ratios up to 0.94, and these correspond to liquids in equilibrium with the magnesian megacrysts (Table 11). Mysen (1975) uses total iron in the calculation of the distribution coefficient KQ1. Because the amount of Fe3r present is dependent on the pressure, temperature, oxygen fugacity and the composition of the starting material, KD is also dependent on these variables and is not useful for the present discussion. N, An alternative approach would be to use KD lol I iq) but this may also be dependent on other variables, e.g. Hakli and Wright (1967), Irvine (1974), Leeman (1973) and Bannoand Matsui, (1973). For this reason Sato (1977) normalises the nickel partition coefficient to that of magnesium, and in this way Nl obtains a constant KD. KD is generally taken to assume a value between 10 and 17 for melts of basaltic compositions, but O'Hara et al (1975) argues that KpN> is probably close to unity for melts of perldotltic composition and increases as the Fe/Mg ratio of the melt increases. Because the Monastery megacrysts are not ioned, they were a!,nost certainly in equilibrium with any coexisting liquid. If perfect equilibrium prevailed then S.rf-U c° lf(D~1H-l/ where cs and c° are the nickel concentrations in the solid and liquid respectively, D is the partition coefficient (solid/liquid) and f is the increment of solidification. Using cs - 0,36 wt.% NiO, 0=17, and f is small, then the magnesium-rich olivines would have crystallised from a melt containing 210 ppm NiO, or from a melt containing more NiO if D is smaller than 17. When D is near unity in a peridotitic melt (0'L'ara, 1975) of large volume (f is small), the concentration of NiO in the melt approaches the concentration of nickel in the olivines of the Monastery Iherzolites. This implies that the olivine in the Iherzolites must have contributed significantly to the melt, since the concentration of nickel in the other Nl mineral phases of the Iherzolite are low. KD would have to be near 3,6 or higher to give a concentration of 0,1 wt.% NiO or less in the melt. This is a likely concentration in a melt produced from garnet Iherzolite, since the 20% partial melt in Kushiro's (1973b) experiment has a nickel content of 0,1 wt.% NiO. Since diopside (0,054 wt.% NiO, c,to, 1977) is probably the first major phase to disappear on partial melting, a concentration of less than 0, i wt.% NiO can Ur. expected trom less than 20% partial melt of a spinel 25 Iherzolite. Basalts are Generally regarded as partial melt products. For the magnesian olivine megacrysts to have crystallised frorr. a basaltic melt of 250 - 800 ppm NiO, KD will assume a value between 16 and 5, which falls into the range expected foi KD The iron-rich olivine megacrysts would require a KQ of 3,2 to 1,0 to have crystallised from a melt of 260 - 800 ppm NiO. This range of KQ is lower than that expected from the iron-rich nature of the olivines. K and N 65 tnat The above considerations of the Distribution coefficients D°j:é-Ma) Ko '(ol-liq) SUM * the magnesian olivine megacrysts are likely to have been in equilibrium with a basaltic melt with an FeO/MgO ratio of 0,80 to 0,88 and a nickel concentration of 250 - 800 ppm NiO. The experiments of Kushiro (1973bi indicate that this magma could be produced by a 10 — 25% partial melt of mantle peridotites with Fe/Mg-f Fe ratios near 0,13. The bimodal distribution of the Monastery olivine megacrysts is shown in Fig. 2. Mitchell (1974) also noted a similar distribution of olivines from the Wesselton kimberlite, and ascribes the two populations to be of xenocrystic and phenocrystic origin. Two olivine populations of olivine have also been noted in melilite basalts (A.J. Moore, personal communication). Fig. 7 shows that the Monastery olivine megacrysts define two ranges, with a compositional gap between Fo 84,6 and Fo 81,1. Extrapolations of tie-lines of coexisting minerals in Fig. 7 suggest that the compositional gap of the olivines corresponds to the crystallisation range of the other silicate-ilmenite intergrowths. Therefore only one olivine-ilmenite intergrowth has been found. The absence of olivine in the range in which ilmenite crystallises together with other silicates suggests either that olivine stopped crystallising, or that it undergoes a chemical reaction with the liquid. There are several possibilities in which olivine can react. It is unlikely that olivine of composition Fo 81 — 85 was consumed by the liquid when olivine of Fo 85 - 88 was not consumed. For olivine, ir. the presence of a large amount of titanium, to react fayalite + geikielite ^ forsterite + ilmenite is also unlikely because the composition of the crystallising olivine is independent of whether ilmenite crystallises or not. The olivine is in equilibrium with the liquid and consequently changes only when the liquid changes. A third, and perhaps the most likely, reaction is suggested by the hematite content of the ilmenite (5 - 27 % He). As the oxygen fugacity increases during differentiation, the Mg/Mg+SFe ratio of the liquid decreases but, due to an increase in Fe3^, the Fe2"*/Mg ratio does not increase much or may even decrease. As a consequence the Mg/MgtFe2 * ratio of the olivine may decrease very slowly, remain constant, or even increase. All these reactions do not explain the presence of the olivines with lower Fo content, although compositional gaps in olivine composition are quite frequent in differentiated rock series. One possibility is that the two olivine populations are derived from two different kimberlite intrusions at Monastery. A kimberlite inclusion in olivine megacryst RJ 469 has been analysed. This was a circular inclusion 4 mm in diameter, but the length could not be determined because the olivine was a broken chip and only part of the inclusion was found (Plates 2 and 3). The whole-rock composition of this inclusion is very similar to that of the Quarry Type Kimberlite from Monastery, but the inclusion has slightly higher iron and lower sodium and volatile contents (Table 26). Several minerals crystallised from within the inclusion, but no detailed work was done on them. Some minerals in another inclusion have been analysed by Haggerty and Boyd (1975) and are compared to the Monastery megacrysts and Iherzolites in Table 10 below. 26 TABLE 10 Inclusion Megacrysts Lhtrzolites* Olivine Mg/Mg> Ft dt % 86 88 84,6 87,4 91,3,93,8 Garnet Ti02Wt.% 0,89 0,6- 1,5 0,48; 0,09 Cr203Wt.% 1,28 0-2 3,07; 5,00 Mg/Mg+Feat.% 31,6 71 -81 85; 87,9 a: FRB 1 and 18b9 N respectively. Table 25 The similarity of the minerals in the inclusion and the Monastery megacrysts is noteworthy. Haggerty and Boyd (1975) favour an entrapped-liquid hypothesis to that of infilling by a later kimberlite. The entrapped-liquid hypothesis assumes that liquids of composition of the inclusion (i.e. kimberlitic) were present during crystallisation of the olivine megacrysts. 6. GENERAL DISCUSSION AND CONCLUSIONS Evidence suggests that the Monastery megacrysts formed from only a small volume of liquid: The megacrysts show a large range in chemical composition and few samples cluster around the same composition. This is well illustrated for the diopside, garnets and the six glassy enitatites (Fig. 1). The chrome content of the garnet (Fig. 9), diopside (Fig. 3), enstatite (Fig. 16) and ilmenite megacrysts is low and is rapidly depleted in the melt as differentiation continues. The abundance of ilmenite megacrysts and ilmenite intergrowths suggests a very titanium-rich melt. It seems unlikely that such a melt was ever of large extent i,. the Upper Mantle. This may indicate that the megacrysts formed from a relatively small volume of liquid which was changing continuously, though not fast enough to result in zoning of the megacrysts. The distribution of Fe-Mg and nickel between olivine and liquid, and the similar compositions of the olivines, diopside (Fig. 6) and garnet megacrysts (Table 7) to phenocrysts or megacrysts found in basalts, suggest that the megacryst protomelt that gave rise to the high-temperature megacrysts was a slightly undersaturated melt, but rapidly changed toward a basaltic composition. This liquid could have formed from a 10-25 % partial melt of Upper Mantle Iherzolite, as the experiments of Kushiro (1973b) indicate. Lead-isotope studies on megacrysts from the Kimberley area (Kramers, Personal Communication, 1977) indicate young ages for the megacrysts. This may make it possible to relate the melting event that gave rise to the megacrysts to the Karroo volcanism. A large partial melt produced by the increase in heat flow during the breakup of Gondwanaland is regarded by Cox (1970) to have produced the Karroo volcanism. Large volumes of this melt differentiated on the way up to shallower depths, and gave rise to the Karroo tholeiites. Small pockets of this melt might have been trapped at depth, and this could have given rise to the megacrysts while the melt cooled towards the geotherrri. Mitcheli «nd Brunfelt (1975) suggest that the decreasing heat flow after the breakup of Gondwanaland results is small degrees of melting of partially depleted Upper-Mantle material, after the basaltic melts that gave rise to the Karroo volcanism were removed. These small degrees of partial melts will give more undersaturated basaltic and alkaline melts. Partial melts produced from Iherzolites when diopside is the major phase to melt (together with any hydrous phases present), are also compatible with the rare-earth element pattern found for the diopside and diopside-ilmenite intergrowths at Monastery (Gurney, Fesq and Kable, 1973; Mitchell, Cars well and Brunfelt, 1973). The diopside megacrysts have light rare-earth element enriched pattern, consistent with having formed from a liquid produced by a partial melting event. The low chrome content of the megacrysts (e.g. garnet, ilmenite) and the LREE enrichment restrict any melting of garnet Iherzolite to a partial melt in which diopside is the most important contributor. A partial melt incorporating substantial amounts of garnet would increase both the HREE and chrjme content of the melt. It may therefore be 27 suggested that the melt from which the rnegaciysts foimed was a small volume of slightly undersaturated basaltic liquid with an FeO/MgO ratio of 0,80. This may have been derived 'rom entrapped pockets of melt that gave rise to the Karroo volcanism. or it may have been a later event when the waning heat flow gave rise to smaller degrees of partial melts from partially depleted Upper Mantle material. The kimbeilite IIK.IH»IUI« H> LIIC uiuiiic niujuv-iyst HI 4bu suggests that the melt present during crystallisation of the megacrysts v- Crystallisation of magnesian enstatite and possibly of some magnesian ilmenite continues while the melt cools down towards the geotherm. At a temperature near 1 400 °C (obtained from the diopside solvus and the Akella and Boyd equation), diopside, garnet and olivine, together with enstatite and some ilmenite become liquidus phases. With falling temperature the melt becomes more iron-rich, and chrome in the melt decreases rapidly (Figs. 9 and 16). The amount of i'menite crystallising at this stage is apparently small, since the amount of titanium in the megacrysts increases (Fig 17) Crystallisation of all the megacryst phases continues with falling temperature until a temperature of about 1 250 °C is reached. At this stage silicate-ilmenite intergrowths start to form There is some evidence that the more-magnesian ilmenites formed before the magnesium poor ilmenites Í Fig. 13). Of twenty-six analysed ilmenite megacrysts, only four have magnesium contents highei than those observed for the ilmenite-silicate intergrowths. This, together with the abundance of ilmenite inteigrowths, suggests that the amount of ilmsnite removed from the melt increases rapidly when the ilmenite-silicate intergrowths start to form. This is seen in Fig. 17 from a drastic decrease in the titanium content of the megacrysts as the rnelt becomes less magresian. During crystallisation of the ilmenite-silicate intergrowths, the oxygen fugacity of 'he melt is likely to increase, because anhydrous phases are removed. More Fe3 ' is therefore formed and the relative amount of Fe2 + decreases. This buffers the olivine composition above Fo 84,6, as was discussed earlier. The similar composition jnd the small range displayed by the enstatite-ilmenite intergrowths also suggest a buffering action. Crystallisation of the megaciysts (except tor the iron rich olivines) terminates at about 1 150 °C. During this long period of crystallisation the volume of the melt decreases and its composition changes continuously due to megacryst fractionation anil possibly also by reaction with the wall-rocks. The continual increase in water may cause the solidus to be progressively lowered as crystallisation and cooling of the melt takes place (Boettcher, Mysen and Modreski, 1975). Wyatt (1977) also suggests hydrous conditions during diopside-ilmenite intergrowth crystallisation. This may be one reason for the exceptionally large crystallisation range (250 °C) displayed by the megacrysts. A temperature of 1 150 °C, as suggested for the termination of megacryst fractionation, is likely to be still above the temperature of the shield geotherm at depths of 1 70 km or less. Further cooling of the megacrysts and the small amount of interstitial liquid therefore takes place, until the geotherm is reached. On the geotherm the most-magnesian enstatites, which formed first and do not belong to the opx^cpx fgnt + ol equilibrium assemblage, are chemically the most unstable megacrysts present, and consequently exsolve diopside with or without garnet. As is suggested by the Fe-Mg t istribution, the exsolved diopsides and garnets are equilibrium assemblages. This equilibrium was most likely reached under stable conditions such as may have been present on the geotherm. The exsolved diopsides indicate re-equilibration temperatures for the lamellar enstatites of 920 - 960 °C The megacrysts other than the lamellar enstatites did not re-equilibrate and still display their igneous character. This indicates that they were not excessively unstable when they cooled towards the geotherm. 28 Boyd and Nixon (19/3, 19,'b) suggested that the Monastery megacrysts are equilibrium assemblages and formed in a crystal mush in the low-velocity lone. This model is similar to the one suggested here, inasmuch as only a small volume of liquid is thought to be dispersed among the megacrysts. However, the model suggested by the above authors requires the megacrysts to be present along a large vertical section in the mantle, while the present model suggests isubai ic ditfeientiation ot a small volume of melt, at probably lower pressures than weie suggested by trie abuve autnurs. hvme (19/4) discusses mechanisms of megacryst formation and states that "the implications are compelling that pyroxene megacrysts are fragments of loosely cemented, pegmatitic polycrystalline aggregates precipitated from basaltic magma...". A pegmatitic intergrowth can also be suggested for the Monastery megacrysts, where only a small amount of liquid with kimberlitic affinities is dispersed among the megacrysts. Except for the 2 cm garnet intergrowth with an 11 cm diopside in Sample RJ 1, no other evidence of a pegmatitic intergrowth at Monastery has been observed. Because of die action of the kimberiite on the megacrysts, and because the minerals in a pegmatitic intergrowth would be disrupted along their mineral boundaries, it is questionable whether an intergrowth would be preserved during the eruption ot the kimberlite. The small volume of interstitial liquid of kimberlitic character might not be sufficient to give rise to the Monastery kimberlite. Further additions of kimberlitic liquids eg metasomatic fronts, could be necessary to give the liquid its Quarry-Type kimberlite charactei, and to increase the volume of kimberlitic fluid. However, it is also unlikely that a large volume ot kimberlitic material ot the Quarry Type ever accumulated, since the Monastery Kimberlite pipe is small, 'solated and dissimilar to other kimberlites from the adjacent Northern Lesotho Kimberlite province. 7. REFERENCES Akella, J. (1976). Garnet-pyroxene equilibria in the system CaSiG3 McjSiC^ AI2O3 and in a natural mineral mixture. Artier. Mineralogist 61 pp 589 - 598. Akella, J. and Boyd, F.R. (19721. Partitioning of Ti and Al between pyroxenes, garnets and oxides. Carnegie Inst. Year Book 71 pp 378 - 384. Akellj, J. and Boyd, F.R (19/4) Petrogenic Grid for the Garnet Peiidotites. Carnegie lint. Year Buok 73 pp 269 - 273. Allsop, H.L. and Barrett, D.R. (1975). Rb - Sr Age Determinations on South African Kimberlite Pipes Phys. Chem. Earth 9 pp 605 - 618. Banno, S. and Matsui, Y. (1973). On the formulations of partition coefficients for trace element distribution between minerals and magma. Chem. Geo/. II pp 1 15 Boettcher, A.L, Mysen, B.O. and Modreski, P.J. (19/5). Melting in the mantle: phase relationships in natural and synthetic peridotite H2O and peridotite - H2O - CO2 with application to kimberlite. Phys. Chem. Earth 9 pp 855 - 867. Boullier, A.M. and Nicolas, A. (1975). Classification of Textures ami Fabrics of Peridotile Xenuhths from South African Kimberlites. Phys. Chem. Earth 9 pp 467 - 4/6. Boyd, F.R. (1971). Enstatite - ilmenite and diopside ilinenite inteigtowths horn the Monastery Mine. Carnegie Inst. Year Book 70 pp 134 138. 29 Boyd, F.R. (1973). A Pyroxene geotherm. Geochimica et Cosmochimica Acta 37 pp 2533 — 2546. Boyd, F.R. (1974). Olivine Megocrysu ttoir, ttce ^inUieilues ot ttit Monastery diid frank Smith Mines, South Africa. Carnegie Inst. Year Book 73 pp 2ti2 2tib. Boyd, F.R. and Danchin. R V (19?4). Discrete Nodules from the Artur De Paiva Kimberlite, Angola. Carnegie Inst- Year Book 73 pp 278 — 282. Boyd, F.R. and Dawson, IB (1972) Kimberlite garnets and pyroxene ilmenite intei growths. Carnegie Inst. Year Book 71 pp 373 — 378. Boyd, F.R. and Nixon, P.H. (1973) Origin of the llmenite-Silicate Nodules in Kimberlites from Lesotho and South Africa, in: Lesotho Kimberlites pp 254 - 268. Chapman, NA (1976) Inclusions and Megacrysts from Undersaturated Tuffs and Basamtes, East Fife, Scotland. Journ. Petrol. 17(4) pp 472-496. Clement, C.R., Skinner, E M.W. and Scott, B.H (1977). Kimberlite Redefined, Second International Kimberlite Conference, Santa Fé 1977. (Long abstract). Cox, K.G., Gurney, J.J. and Hatte, B. (1973). Xenoliths from the Matsoku Pipe, in: Lesotho Kimberlites pp 76 -- 100. Cox, K.G. and Jamieson, B.G. (1974). The Olivine - rich lavas of Nuanetsi. a Study of Polybaric Magmatic Evolution. Journ. of Petrology 15(2) pp 269-301. Danchin, R.V. and Boyd, F.R (1976). Ultramafic nodules from the Premier Kimberlite Pipe. Carnegie Inst. Year Book 75 pp 531 - 538. Davis, B.T.C. and Boyd, F.R. (1966). The join Mg2Si20g — CaMgSi206 at 30 kb pressure and its application to pyroxenes from kimberlite. J. Geophys. Res. 71 pp 3567 - 3576 Davis, G.L, Krogh, T.E. and Erlank, A.J. (1976). The ages of Zircons from Kimberlites frorr. South Africa. Carnegie Inst. Year Book 75 pp 821 - 824. Dawson, J. B. (1967). Geochemistry and Origin of Kimberlite in: Ultramafic and related rocks ed. Wyllie, P.J. New York, J. Wiley and Sons. Dawson, J.B. (1972). Kimberlites and their relation to the mantle. Phil Trans. R. Soc. London. A. 271 pp 297 — 311. Dawson, J.B. and Reid, A.M (19/0). A pyrovene - ilmenite intergrowth from the Monastery Mine, South Africa. Contrib. Mineral. Petrol. 26 pp 29b -301. 30 Eggler. D. (1974). Quoted in: D.G. Frazer. Thermodynamics in Geology. 1977 D Reidel Publ. Co. Holland. Eggler. O.H. and McCalli'm, ME. (1976). A Geotherm from Megacrysts in the Sloan Kimberlite Pipes, Colorado. Carnegie Inst. Year Book 75 pp 538 - 541. Frick, C. (1973). Intergrowth o' Orthopyroxene and llmenite from Frank Smith Mine, near Berkley West, South Africa. Trans. Geol. Soc. S. Afr. 76 pp 195 - 200. Green, D.H. and Sobolev, N.V. (1975). Coexisting Garnets and llnnenites Synthesized at High Pressures from Pyrolite and Olivine Basanite and their Significance for Kimberlitic Assemblages. Contrib. Mineral. Petrol. 50 pp 217 - 229. Gurney, J.J. (1974). The Origin of Kimberlite: Modern Concepts. Trans. Geol. Soc. S. Afr. 77(3) pp 353 - 361. Gurney, J.J. and Ebrahim, S. (1973V Chemical Composition of Lesotho Kimberlites. in: Lesotho Kimberlitei pp 280 - 284. Gurney, J.J.; Fesq, H.W. and Kable, E.J.D. (1973). Clinopyroxene - llmenite Intergrowths from Kimberlite: A Re-appraisal, in: Lesotho Kimberlites pp 238 - 253. Gurney, J.J., Harte, B. and Cox, C.G. (1975). Mantle Xenoliths in the Matsoku Kimberlite Pipe. Phys. Chem. Earth. 9 pp 507 - 524. Gurney, J.J. and Hatton, C.J. (in press). Gurney, J.J. and Switzer, G.S. (1973). The discovery of garnets closely related to diamonds in the Finsch pipe, South Africa. Contrib. Mineral- Petrol. 39 pp 103- 116. Haggerty, S.E. and Boyd, F.R. (1975). Kimberlite inclusions in an olivine megacryst from Monastery. Long abstracts. Kimberlite Symposium, London, July 1975. Hakli, T. and Wright, T.L. (1967). The fractionation of nickel between olivine and augite as a geothermometer. Geochim. Cosmochim. Acta. 31 pp 877 - 884. Harte, B. (1977). Rock Nomenclature with particular Relation to Deformation and Recrystallization Textures in Olivine-bearing Xenoliths. Journ. Geol. 85(3) pp 279 - 2S8 Harte, B. (in press). Kimberlite nodules, Upper Mantle Petrology and geotherms. Harte, B„ Cox, K.G. and Gurney, J.J. (1975). Petrography and Geological History of Upper Mantle Xenoliths from the Matsoku Kimberlite Pipe. Phys. Chem. Earth 9 pp 477 - 506. 31 Hensen, B.J. (1973). Pyroxenes and Garnets as Geothermometers and Baromttajrs. Carnegie Inst. Year Book 72 pp 529 - 534. Howeflt, & and CHara. M.J. (1975). Palaeogeotherms and the diopside - enstatite solvus. Nature 254 pp 406 - 408. Irving, A.J. (1974). Megacrysts from the Newer Basalts and Other Basaltic Rocks of Southeastern Australia. Geol. Soc. Amer. Bull. 85 pp 1503 -1514. Irving, A.J. (1976). On the validity of paleogeotherms determined from xenolith suites in basalts and kimberlites. Amer. Mineralogist 61 pp 638 - 642. Kramers, J. (1977). Personal Communication. Kushiro, I. (1973a). Origin of some magmas in oceanic and circum-oceanic regions. Tectonophysics 17 pp 211 - 222. Kushiro, I. (1973b). Partial Melting of Garnet Lherzolites from Kimberlite at High Pressure, in: Lesotho Kimberlites pp 294 - 299. Lawless, P.J. (1974). Some Aspects of the Geochemistry of Kimberlite Xenocrysts. Unpubl. M.Sc. thesis. University of Cape Town pp 121. Leeman, W.P. (1973). Partitioning of Ni and Co between olivine and basaltic liquid: an experimental study. EOS 54,1222. Lindsley, C.H. and Dixon, S.A. (1976). Diopside - Enstatite Equilibria at 850 o to 1400 °C, 5 to 35 kb. Amer. Joum. of Science 276 pp 1285 - 1301. MacGregor, I.D. (1974). The System MgO - AI2O3 - SiOj: Solubility of AI2O3 in Enstatite for Spinel and Garnet Peridotite Compositions, Amer. Mineralogist 69 pp 110 - 119. MacGragor, I.D. and Witlkop, R.W*. (1970). Diopsidt - ilmenite xenoliths from the Monastery Mine, Orange Free State, South Africa (abstract). Abstr. with Program» for 1970. Geol. Soc. Amer. 2 p 113. Mason, & and Allan, ftO. (1973). Minor and trace «lament» In augitt, hornblende, and pyrope megacrysts from Kakanui, New Zealand. New ZealmtdJeur. Geology and Geophysics 16 pp 935 - 947. Mitchell, R.H. (1973). Composition of olivine, silica activity and oxygen fugacity in Kimberlite. Lithos 6 pp 65 - 81. Mitchell, R.H. (1977). Geochemistry of magnesian ilmenites from kimberlites in South Africa and Lesotho. Lithos 10(1) pp 29 37. 32 Mitchell. R.H.. Brunfelt, A.O. and Nixon. P.H. (1973). PART II Trace elements in Magnesian llmenites from Lesotho Kimberlites in: Lesotho Kimberlites pp 230 - 235 Mitchell, R.H.. Carswell, D.A. and Brunfelt A.O. (1973). PARTI llmenite Association Trace Element Studies, in: Lesotho Kimberlites pp 224 - 229. Mori, T. and Green, D.H. Subsolidus equilibria between pyroxenes in the CaO — MgO — SiC«2 system at high pressures and temperatures. Amer. Mineralogist 61 pp 616 — 625. Mysen. B. (1975). Partitioning of Iron and Magnesium between Crystals and Partial Melts in Peridotite Upper Mantle. Contrib. Mineral. Petrol. 52 pp 69 - 76. Mysen. B. (1976). Experimental determination of some geochemical parameters relating to conditions of equilibration of peridotite in the upper mantle. Amer. Mineralogist 61 pp 677 - 683. Mysen, B.O. and Boettcher, A.L. (1975). Melting of a hydrous mantle: II. Geochemistry of crystals and liquids formed by anatexis of mantle peridotite at high pressures and high temperatures as a function of controlled activities of water, hydrogen and carbon dioxide. J. Petrol. 16 pp 549 - 593. Nehru, C. E. (1976). Pressure dependence of the enstatite limb of the enstatite — diopside solvus. Amer. Mineralogist 61 pp 578 -581. Nehru, C.E. and Wyllie, P.J. (1974). Electron Microprobe Measurement of Pyroxenes Coexisting with H2O - undersaturated Liquid in the Join CaMgSijOe - MgjSijOg - H2O at 30 Kilobars, with application to Geothermometry. Contrib. Mineral. Petrol. 48 pp 221 - 228. Nixon, P.H. and Boyd, F.R. (1973a). Petrogenesis of the Granular and Sheared Ultrabasic Nodule Suite in Kimberlites in: Lesotho Kimberlites pp 48-56. Nixon, P.H. and Boyd, F.R. (1973b). Notes on the Heavy Mineral concentrates (from Monastery), in: Lesotho Kimberlites pp 218 - 220. CHara, M.J., Saunders, M.J. and Mercy, E.L.P. (1975). Garnet - Peridotite, Primary ultrabasic Magma and Eclogite; Interpretation of Upper Mantle Processes in Kimberlite. Phys. Chem. Earth 9 pp 571 - 604. Raheim, A. and Green, D.H. (1974). Experimental Determination of the Temperature and Pressure Dependence of the Fe - Mg Partition Coefficient for Coexisting Garnet and Cfinopyroxene. Contrib. Mineral. Petrol- 48 pp 179 - 203. Reid, A.M. and Hanor, J.S. (1970). Pyrope in Kimberlite Amer. Mineralogist 66 pp 1374 - 1379. 33 Ringwood, A.E. and Lovering, J.F. (1970). Significance of Pyroxene - ilmenite intergrowths among Kimberlite Xenoliths. Earth Planet. Science Letters 7 pp 371 - 375. Sato, H. (1977). Nickel content of basaltic magmas: identification of primary magmas and a measure of the degree of olivine fractionation. Lithos 10 pp 113 - 120. Smith, CB., McCallum, M.E. and Eggler D.H. (1976). Clinopyroxene - ilmenite intergrowths from the Iron Mountain Kimberlite District, Wyoming. Carnegie Inst Year Book 75 pp 542 - 546. Van Loon, J.C. and Parissis, CM. (1969). Scheme of silicate analysis based on the Lithium Metaborate fusion followed by atomic-absorption spectrophotometry. The Analyst 94(1125) pp 1057 - 1062. Wagner, P.A. (1914). The Diamond Fields of Southern Africa. The Transvaal Leader, Johannesburg. Second impression 1971. Cape Town, Strink (Pty) Ltd. pp 355. Walker, F. and Poldervaart, A (1949). Karroo dolerites of the Union of S. Africa. Bull. Geo/. Sec. America 60 pp 591 - 706. Warner, R.D. and Luth, W.C. (1974). The diopside - orthoenstatite two — phase region in the system CaMgSi206 - Mg2SÍ2C<6 Amer. Mineral 59 pp 98 -109. Whitelock, T.K. (1973). The Monastery Mine Kimberlite Pipe, in: Lesotho Kimberlites pp214 - 218. Williams, A.F. (1932). The Genesis of the Diamond. London, E. Benn Ltd., 2 vols. Wood, B.J. (1974). The solubility of alumina in orthopyroxene coexisting with garnet. Contr. Mineral. Petrol. 46 pp 1 - 15. Wood B.J. and Banno, S. (1973). Garnet — orthopyroxene and orthopyroxene — clinopyroxene. Relationships in Simple and Complex Systems. Contr. Mineral. Petrol. 42 pp 109 - 124. Wyatt, B.A. (1977). The melting and crystallization behaviour of a natural clinopyroxene - ilmenite intergrowth. Contr. Mineral. Petrol. 61 pp 1 - 9. 34 « DISCRETE MEGACRYSTS • ILMENITE ASSOCIATION • GARNET- DIOPSIDE • GARNET-OLIVINE • OIOPSIOE EX SOLVED FROM OPX » GARNET IN OPX-ILMENITE Mg o Fig. I Ternary diagram for diopsides (topi, garnets (centre) and enstatites (bottom) from Monastery. The olivine compositions are indicated by two brackets on the Mg-Fe join 35 z 5 xiflíwi. .flllnÍn . «. 78 80 82 84 86 88 90 92 Mg/Mg* Fr a OLIVINE MEGACRYSTS G OLIVINE GARNET INTERGROWTHS • OLIVINE ILMENITE INTERGROWTH • LHERZOLITE FRB1 *r D • OBBDO o 2- z QD D D • _L _L J_ _L _L _L _L X _L _L X _L J 78 79 80 81 82 83 84 85 86 87 89 90 91 92 Mg/Mg • Fe OLIVINES Fig. 2 Nickel oxide plotted against Mg/Mg+Fe at.% for the Monastery olivine megacrysts, and histogram (top) 3 r x DIOPSIDE MEGACRYSTS • DIOPSIDE ILMENITE INTERGROWTH o DIOPSIDE EXSOLVED FROM OPX 2 - o CM L. o 8° l I 60 82 84 86 88 90 92 94 96 Mg/Mg+ Fe DIOPSIDE Fig. 3 Per cent Cr2C>3 plotted against Mg/Mg'i Fe al% for the Monastery diopsttles 36 45 r x DIOPSIDE MEGACRYSTS • DIOPSIDE ILMENITE INTERGROWTH cn 40» • o • • x o o o x xx X X 35 X X X XX XX x x ** x X 30 % Cr2 03 DIOPSIDES Fig. 4 Ca/Ca+Mg at.% plotted against % CrzO^ for the Monastery diopsides t DIOPSIDE MEGACRYSTS • DIOPSIDE ILMENITE INTERGROWTH o DIOPSIDE EXSOLVED FROM OPX 50 h 5 00 ™ *5 NORTHERN LESOTHO GRANULAR • MATSOKU o 40 N O o 35 NORTHERN LESOTHO SHEARED THEBA PUTSOA 30 AND S0LANE LETSENG-LA-TERAE 25 -L J I I L 60 82 84 86 88 90 92 94 96 Mg/Mg *Fe DIOPSIDE Fig. 5 Ca/Ca+Mget% plotted against Mg/Mg+Fe at.% for diopsides from Monastery. Also shown are diopside compositions from Northern Lesotho localities (Nixon and Boyd, 1973; Cox, Gurney and Hartc, 19/31 37 Ca 10 "7T- Fe Fig. 6 Diopside megecrysts plotted in part of the Ca-Mg-Fe ternary diagram. I: Monastery discrete diopsides (open area) and diopside-ilmenite lamellar intergrowtfis (black area). Diopside megacrysts found in basalts; 2: Mt. Noorat; 3,4,6: Elie Ness; 5: Mt. Franklin; 2 and 5: from Irvine (1974); 3,4 and 6: from Chapman (1976) 38 DISCRETE MEGACRYSTS ILMENITE ASSOCIATION GARNET- OIOPSIDE GARNET- OLIVINE DIOPSIDE EXSOLVED FROM OPX GARNET IN OPX-ILMENiTE Mg 0 Fig. 7 Ternary Ca-Mg-Fe diagram for diopsides (top), garnets (centre) and enstatites (bottom) from Monastery. Olivine compositions are shown by the two brackets on the Mg-Fe join. Natural (solid lines) and calculated (dashed lines) equilibrium assemblages are also shown Co -V x DISCRETE MEGACRVSTS Mg • ILMENITE INCLUSIONS NORTHERN LESOTHO / / GRANULAR / SHEARED MATSOKU (COX. GURNEY C HARTE, 1973 ) ( BOYD AND NIXON. 1973) / XENOCRVSTS, KIMBERLEY / - (REID G HANOR, 1970) DIAMONO INCLUSION FIELD i. — (LAWLESS. 1974) Mg -x—»- Fe 10 15 20 25 30 35 40 45 GARNETS Fig. 8 Ternary Ca-Mg-Fe diagram for garnet inegacrysts and garnet inclusions in ilmenite from Monastery. Also plotted are the fields for Northern Lesotho Iherzolites (Boyd and Nixon, 1973; Cox, Gurney and Harte, 1973), xenocrysts from the Kimberley area, and inclusions in diamonds 40 * LHERZOLITE FRB1 • GARNET MEGACRYSTS o GARNET-ILMENITE ASSOCIATION 30 & GARNET-DIOPSIDE ASSOCIATION x GARNET-EXSOLVE IN ENSTATITE a GARNET-OLIVINE ASSOCIATION x 1.0 - a . '£ D 1.. 68 70 72 % 76 78 80 82 84 Mg/Mg* Fe GARNETS Fig 9 Chrome plotted against Mg/Mg+Fe at.% for the Monastery garnets • GARNET MEGACRYSTS 15 - 60 0 ILMENITE ASSOCIATION 54.* V.Crj 03 xtOO INDICATED »55 6£ »'63 *55 .34 57 •72 87 .6655 * n 47»»21 .96 ,J 5, o 9o 025 5 ,5S • 68 • 103 • „O08 °35 5 * 0n '3°o OI3 10 9 Oo 5 < 1 1 1 1 I 1111 66 70 72 74 76 78 80 82 Ms / Mq . Ft GARNET.» Fig. 10 Titanium plotted against Mg/Mg+Fe at.% for thu ,',fnn*uer>/ garnet megacrysts and garnet inclusions in ilmenite hosts. Per cent O2O3 is also indicated 41 10 - •111 %Ti0 INDICATED 109 2 • •1111bK 109%116 78« 1.16 « QQ* •yofi LU LU • 81 •103 at 0 ••64 1 ± 1 1 I J 66 68 70 72 1U 76 78 Mg/Mg + Fe in GARNET GARNET INCLUSIONS IN ILMENITE MEGACRYSTS Fig. II The titanium content of garnet inclusions in ilmenite megacrysts increases with increasing Mg/Mg+Fe at' of the garnet and increasing magnesium content of the coexisting ilmenite host 42 U r- •16 • PYROLITE(1000-1100°C.21-31Kb. 0.3% H2O) 13 .13 (GREEN AND S0BOLEV. 1974) D 90 D EXCELSIOR 7 -11 12 ~ (BOYD AND DAWSON. 1972) • 9 x 74 x FRANK SMITH (BOYD. 1972) UJ 11 o MONASTERY D60 %TiO INDICATED UJ 5 io n 1 1 l l 1 I i 66 66 70 72 74 76 78 80 Mg/Mg • Fe IN GARNET GARNET COEXISTING WITH ILMENTE Fig. 12 The titanium content of garnet inclusions in ilmenite megacrysts increases for increasing magnesium in the ilmenits and for increasing Mg/Mg+Fe at.% of the garnet. This is consistent for both experimental i ork and natural intergrowths from Northern Lesotho. The titanium content for the Monastery garnet int growths is shown in Fig. 11 13r • ENSTATITE-ILMENITE INTERGROWTHS A DIOPSIDE - ILMENITE INTERGROWTHS e GARNET - ILMENITE INTERGROWTHS D OLIVINE - ILMENITE INTERGROWTHS UJ t 11h UJ — RANGE OF MgO IN z 10 o A,* * DISCRETE ILMENITE o MEGACRYSTS ± _L _L _L 60 65 70 75 80 85 90 Mg/Mg *Fe (at.%) OF SILICATE ILMENITE-SILICATE INTERGROWTHS Fig. 13 Per cent MgO in ilmenite plotted against the Mg/Mg+Fe at.% of the coexisting silicate. Note the large range of MgO in the discrete ilmenite megacrysts. 43 e> OPX MEGACRYST • OPX-ILMENITE INTERGROWTH x OPX- CPX EXSOLUTION 20 16 o\ NORTHERN LESOTHO SHEARED \ o / ° 1 2 o •.'i 2? o Oo -MATSOKU -NORTHERN LESOTHO GRANULAR #x * M **x _J I _L 82 84 86 88 90 92 94 96 Mg/Mg+Fe ORTHOPYROXENE Fig. 14 The Monastery enstatite megacrysts are compared to Northern Lesotho sheared and granular Iherzolites (Nixon and Boyd, 1973) and to enstatites from Matsoku Iherzclites (Cox, Gurney and Harte. 1973). Since the calcium content ofensiatites is temperature-dependent, the large range of equilibration temperatures of the Group I enstatites is evident. The lamellar Group II enstatites exsolved diopside ± garnet during a later re-equilibration process 44 1.6 o OPX MEGACRYST • OPX-ILMENITE INTERGROWTH x OPX-CPX EXSOLUTION -\Á 1.3 ©• <«. 1.0 o <5 8 o o x **f**Jíf 8 .9 1.0 1.2 1.3 U % Al203 ORTH0PYR0XENE Fig. 15 The composition of enstatites can be used to estimate equilibrium conditions. Calcium in the enstatite is temperature-dependent, while aluminium is both temperature- and pressure-dependent 45 o OPX • OPX-ILMENITE INTERGROWTH x OPX-CPX EXSOLUTION .3 - xx o fN X X x # X A J_ -L J- 82 84 86 88 90 92 94 96 Mg/Mg+Fe ORTH0PYR0XENE Fig. 16 Chromium oxide plotted against Mg/Mg+Fe at.% for the Monastery enstatites 46 ENSTATITES 0 1 t 1 1 1 ..i i i 82 83 84 85 86 87 88 89 Mg/Mg*Fe (DO O 4 |- • • * 3 1- DIOPSIDES Í: _i i i i 82 83 84 85 86 87 88 89 Mg/Mg*Fe 15 • • O 0 O 68 70 75 80 84 Mg/Mg*Fe • DISCRETE MEGACRYSTS o ILMENITE ASSOCIATION & OLIVINE ASSOCIATION a GARNET- DIOPSIDE ASSOCIATION Fig. 17 Titanium plotted against Mg/Mg+Fe at.% for the Monastery megacrysts and intergrowths. The Mg/Mg+Fe ratio is considered to be a good differentiation indicator for the megacrysts. Titanium in the silicate phases increases during differentiation until ilmenite starts to precipitate, when the titanium content of the melt decreases rapidly 47 Plate 1. (.' Plate 2. hnir>, ,,';i, :••< hi\,nr m nhiim nuihurwl II / /<>'', nitulvsn Inhh 2h. Si ulr X11>. Sole rrm lion rim inn! ,-« ÍII/. / <;' .,.'..• ' 48 Plate 3. himln rlilr iiiilmitin in uln im ini-gai rwt from Monustrrx. Xoti• Iruniliit oil nirhnnnic ruh niulrit i ontiiiniiifl »mall i rwln/s, n a< lion rim uiul vrinli I. Si ulc XI). Plate 4. Irrrgiilur uihl n-guttir i nslnlilr mi,/ ilntrnilc Iwhilrj inlirgrowlh. Stair XI. 49 Plate 5. Irrcgulur cnstatite and ilmenitc (white) inter/growth from Monastery. Scale XJ. Plate 6. Regular and irregular diopside and ilmenite (while) intergrowth. Scale X2. 50 Plate 7. Regular diupúde and ilmenite (white) lamellar intergrowth. S'ote central fine-grained intergruwth. Se.de A'U. Plate 8. Id enhir i/iii/i\nl iiid 'hneiiite ítehite) iiilergrnu'lh. S'nle out\ide enar\e intergroietll. Scale ,V i. I'he .//../i.;.,, /< , iiiii/d, I, I ,,' • i '! In , id, it . TABLE 11 ANALYSES OF IRON-POOR OLIVINES WT ?! RJ «*J «J PJ PJ "J P.J °J RJ PJ PJ RJ RJ 9 13 17 19 21 23 29 31 33 35 38 44 46 S102 39.56 39.51 39.69 39.61 39.89 39.77 39.58 39.09 ?9.27 39.39 39.84 39.70 40.43 Tin? 0.0? 0.03 0.05 0.04 0.0« 0.02 0.0C 0.0* 0.0« 0.05 0.07 0.00 0.03 AL23? 0.09 0.09 0.06 0.0« 0.1? 0.10 0.09 0.05 0.07 0.06 0.06 C.06 0.06 CR233 0.0? 0.00 0.0 2 0.02 0.0? 0.01 0.02 0.00 0.01 0.00 0.03 0.00 0.00 FEP * 14.26 13.30 13.19 13.R* 1«. 17 14.19 12.99 1«.«9 13.11 13.8« 14.01 13.20 13.60 mo 0. 0° 0.!« 0.1"» 0.1« 0.!? 0.11 0.06 0. 1« 0. 12 0.10 0.12 O.in C.15 «•so «5.23 «6.00 «5.14 «6.31 «5.95 «5.78 «6.56 ««.81 «6.85 46.35 46.56 45.47 45.96 C&n 0.08 0.11 0.08 0.06 0. 10 0.08 0.12 0.07 0.11 0.1« 0.08 0.10 0.08 NIO 0.38 0.36 0.35 0.36 0.39 0.?0 0.36 0.36 0.36 0.36 TITAL 99.38 99.56 98.72 100.«] 100.78 100.06 99.8" 99.01 99.58 100.29 101.13 98.99 100.67 NUMBE" OF CATIONS FOP 4 OXYGENS S! 0.996 0.99? 1.003 0.989 0.993 0.993 0.990 0.993 0.982 0.985 0.988 1.001 1.003 U 0.001 0.001 0.001 0.001 0.001 0.000 0.001 0.001 0.001 0.001 0.001 0.000 0.001 AL O.OO? 0.00? 0.002 0.00! 0.00« 0.003 O.OO"» 0.001 0.002 0.002 0.002 0.002 0.002 C3 0,000 0.000 0.000 0.000 0.000 0.000 0.000 n.000 0.000 0.000 0.001 0.000 0.000 F = 0.300 0.279 0.279 0.289 0.295 0.296 0.2V^ 0.308 0.274 0.289 0.291 0.276 0.282 »»"4 0.002 0.00? o.co? 0.003 0.003 0.002 0.00] 0.003 0.003 0.002 C.C03 0.002 0.003 M~ 1.697 1.722 1.701 1.723 1.705 1.705 1.726 1.696 1.747 1. 727 1.721 1.705 1.7C0 C4 0.002 o.oc 0.002 0.001 0.00? 0.002 0.003 0.002 0.00* 0.004 0.002 0.003 0.002 M 0. OOP 0.007 0.007 0.007 0.008 0.006 0.007 0.007 0.007 0.007 MG/"G«-FE 85.0 36.0 85.9 85.6 85.? 85.2 86.4 84.6 86.4 85.7 85.ó 84.0 85.8 * T°TAL !*0N AS F?0 TABLE 11 CONT. ANALYSES OF IRON-POOR OLIVINES WT x RJ RJ RJ RJ RJ RJ RJ RJ RJ RJ FRB FRb ED 47 51 55 57 60 65 469 470 473 475 183 220 SI02 40.36 39.72 39.86 40.42 39.53 39.89 39.47 39.80 39.62 39.82 39.5 40.3 39.6 TI02 0.04 0.04 0.06 0.05 0.03 0.03 0.06 0.00 0.05 0.00 0.04 0.03 0.05 AL203 0.10 0.13 0.05 0.08 0.06 0.04 0.00 0.00 0.04 0.00 0.08 o.os 0.06 CR203 0.00 0.03 0.01 0.01 0.02 0.03 0.02 0.01 0.02 0.02 0.03 0.03 0.0 3 FEO * 14.28 13.61 13.94 12.27 13.91 12.27 14.22 13. 18 14.38 12.48 12.3 11.7 12.8 MNO 0.14 0.12 0.12 0.09 0.10 0.13 0.06 0.C8 0.12 0.10 0.13 0.13 0.1 3 MGO 45.47 45.84 4S.99 47.68 46.48 46.01 45.62 47.17 45,19 48.03 46.8 48.8 46.2 CAC 0.10 0.24 0.11 0.09 0.08 0.13 0.10 0. C8 0.07 0.08 0.10 0.09 0.1 1 NIO 0.32 0.36 0.31 0.40 0.35 0.40 0.34 0.36 0.36 0.37 0.33 TOTAL 100.81 100.09 ICO.45 101.09 100.36 98.93 99.89 100.32 99.85 100.53 99.3 101.53 99.3 NUMBER OF CATIONS FOR 4 OXYGENS S! 1.002 0.993 0.993 0.994 0.986 1.003 0.991 0.988 0.995 0.985 0.989 0.«84 0.993 TI 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.000 0.001 0.000 0.001 O.OQl 0.001 AL 0,003 0.004 0.001 0.002 0.002 0.001 0.000 O.COO 0.001 o.oco 0.C02 0.002 0.002 CP 0.000 0.001 0.000 0.000 0.000 0.001 0.001 0.000 0.000 0.000 0.001 0.000 0.001 FE 0.297 0.285 0.291 0.253 0.290 0.256 0.299 0.275 0. *03 0.258 0.257 0.239 0.2 70 MN 0.003 0.00? 0.003 0.002 0.002 0.003 0.001 0.002 o.oo: 0.002 0.003 0.003 0.003 MG 1.684 1.709 1.708 1.749 1.728 1.725 1.706 1.745 1.692 1.769 1.747 1.775 1. 727 CA 0.003 0.007 0.003 0.002 0.002 0.004 0.003 0.002 0.002 0.002 0.003 O.OOt 0.003 Nl 0.006 0.007 0.006 0.008 0.007 0.008 0.007 0.007 0.C07 0.007 0.007 WG/*G*FE 85.0 85.7 85.5 87.4 85.6 87.0 85.1 86.4 84.8 87.3 87.2 38.1 86.5 * TCTAL IRON AS FEO TABLE 11 CONT. ANALYSES OF IRON-RICH OLIVINES WT t RJ RJ RJ PJ RJ RJ SI02 38.92 38.87 38.27 38.55 38.45 38.16 38.61 33.6 TIC2 0.02 0.02 0.03 0.04 0.03 0.02 0.03 0.03 AL203 0.17 0.00 0.08 0.05 0.06 0.04 0.03 0.04 CR203 0.00 0.02 0.00 0.03 0.00 0.00 0.02 0.03 FEO * 17.78 1 TOTAL 100.00 100.87 99.15 99.85 99.93 100.21 99.66 100.93 NUMBER OF CATIONS FOR 4 OXYGENS SI 0.991 0.990 0.990 0.991 0.985 0.983 0.996 0.982 TI 0.001 0.000 0.001 0.001 0.001 0.000 0.001 0.001 AL 0.C05 0.000 0.003 0.002 0.00C2 0.001 0.001 0.001 CR 0.000 0.000 0.000 0.001 0.000 0.000 0.000 0.000 Ft 0.378 0.421 0.420 0.416 0.402 0.439 3.427 0.403 MN 0.003 0.004 0.004 0.004 0.004 0.004 0.004 0.005 MG 1.624 1.591 1.5 86 1.590 1.616 1.5G6 1.570 1.623 CA 0.001 0.001 0.002 0.001 0.002 0.001 0.002 0.001 NI 0.002 0.001 0.002 0.001 0.001 0.001 0.001 MG/HG+FE 81.1 79.1 79.1 79.2 80.1 78.3 78.6 80.1 * TOTAL IFON AS FEO TABLE 12 ANALYSES OF CLINOPYROXENES *T Ï RJ RJ «J PJ PJ RJ RJ RJ «J RJ PJ PJ RJ RJ R J 5 J 205 20fc 208 210 212 214 216 218 220 223 224 226 228 230 2?2 234 SIQ2 54.97 55.05 55.75 54.97 54 .78 54.89 55.10 53.89 54.71 55.21 £4. 88 55.30 55.39 54.54 55. 55 5. 34 TIC2 0.37 0.39 0.34 0.39 0 .41 0.40 0.3 6 0.44 0.34 0.34 0. 26 0.29 0.35 0.31 0.30 0.33 AL203 2.52 2.60 2.54 2.54 2 60 2.58 2.54 2.58 2.43 2.57 2. 61 2.59 2.66 2.56 2.59 2.55 CR203 C.28 0.22 0.29 0.21 0 21 0.28 0.29 0.24 0.29 0.32 0. 32 0.30 0.22 0.30 0. 30 0. 3C FEO * 5.66 5.94 5.71 5.e3 6 .03 5.75 5.47 5.65 5.53 5.5? 5. 56 5.53 5,e7 5.57 5.59 5.67 0.10 0.09 0.12 0.12 0 11 0.10 0.09 0.09 0.09 0.12 0. 13 0. 11 0. 13 0.12 0. 11 0. 10 «ISO 19.M 18.69 19.77 19.05 18 .87 19.55 2 0.89 19.64 20.18 20.11 20. 94 20.29 19.56 Z0.51 20.52 9.97 CAO 14.31 15.04 14.32 15.16 15 22 14.82 13.73 14.64 14.04 14.35 13. 60 14.12 15.07 14.45 14.02 4. 15 NA2J 1.63 1.68 1.60 1.71 I .77 1.71 1.64 1.33 1.61 1.62 1. 47 1.66 1.83 1.64 1.63 1. 51 K20 COS 0.03 0.04 0.04 0 05 0.04 0.02 0.C2 0.03 0.02 0. 0? 0.03 0.01 0.Ú? 0.04 0.03 01 TJTAL 99.30 99.75 100.48 100.02 100.05 100.12 100.13 98.52 99.25 100.19 99.82 100.23 101.09 100.06 10G.65 100.46 J> NUKBEP OF CATIONS FOP 6 CXYGENS SI 1.987 1.987 1.990 1.980 1.976 1.974 1.971 1.967 1.976 1.977 1.970 1.979 1.974 1.9ol 1.978 1.991 TI 0.010 0.011 0.009 Q.011 0,011 0.011 0.010 0.012 0.009 0.009 0.007 0.008 0.009 0.009 c.coe 0.009 AL 0.107 0.111 0.107 0.108 0.111 0.109 0.107 0.111 0.106 0.108 0.110 0.109 0.112 0.109 0.109 0.107 CR 0.008 0.006 0.008 0.006 0.006 0.008 0.008 0.007 0.008 0.009 0.009 0.009 0.006 0.009 o.ooe 0.008 Fi 0.171 0.179 0.170 0.176 0.182 0.173 0.164 0.172 0.167 0.166 0.167 0.166 0.175 0.168 0.166 0. 169 «N 0.003 0.003 0.004 0.004 0.003 0.003 0.003 0.003 0.003 0.004 0.004 0.003 0.004 0.004 0.033 0.003 *G 1.046 1.006 1.052 1.023 1.015 1.048 1.115 1.C69 1.087 1.074 1.121 1.082 1.039 1.099 1.090 1.062 ca 0.354 0.582 0.548 0.585 0.588 0.571 0.526 0.573 0.543 0.551 0.523 0.541 0.5 75 0.557 C.53E 0.541 M. 0.114 0.118 0.111 0.119 0.123 0.119 0.116 0.C94 0.113 0.113 0.102 0.115 0.127 0.114 0.113 0.104 K 0. 002 0.002 0.002 0.002 0.003 0.002 0.001 0.001 0.002 0.001 0.002 0.001 0.000 0.001 0.002 0.001 CA 31.3 32.9 31.0 32.8 32.9 31.9 29.1 31.6 30.2 30.8 26.9 30.2 32.1 30.5 29.9 30.5 M3 59.1 56.9 59.4 57.3 56.9 58.5 61.8 58.9 60.5 60.0 61.9 60.5 5 8.5 60.2 60.9 59.9 FE 9.6 10.1 9.6 9.9 10.2 9.6 9.1 9.5 9.3 9.2 9.2 9.3 9.8 9.2 9.2 9.5 /«4G*FE 85.9 84.9 86. 1 85.3 84.8 85.8 87.2 86.1 86.7 86.6 87.0 86. ' 8 5.6 86. 6 86.7 86. 3 /CA»*G 34.6 36.6 34.2 36.4 36.7 35.3 32.1 34.9 33.3 33.9 31.8 33.3 35.6 32.9 32.9 33.7 » TOTAL IRCN AS FEO TABLE 12 CONT. ANALYSES OF CLINOPYROXENES WT ? RJ RJ RJ PJ PJ RJ RJ RJ RJ FRB FRB FRE 236 238 240 242 244 246 250 252 255 353 5 t ZtbO 2661 26É2 SI02 55.82 55.35 54.77 54.29 55.61 55.02 54.47 55.26 54.68 54,34 55.8 54.6 54.63 55.44 54.85 TI02 0.41 0.36 0.43 0.46 0.42 0.36 0.41 0.49 0.42 0.49 0.35 0.32 0.04 0.34 0. 33 At 203 2.62 2.57 2.58 2.30 2.58 2.55 2.62 2.52 2.45 2.43 2.4b 2.43 2.54 2.51 2.55 CR203 0.23 0.30 0.19 0.22 0.26 0.29 o.ie 0.10 0.16 0.18 0.34 0.34 0.21 0. 30 0.30 FEO * b.OO 5.60 5.84 5.85 5.71 5.75 5.82 6.12 6.C8 5.94 5.34 5.48 5.69 5.4"! 5.36 HMO 0.12 0,13 0.10 0.10 0.12 0.09 0.10 0.14 0.12 0.14 0.14 0.18 0.16 0.16 0.14 HGO 19.02 19.92 20.10 19.53 20.49 20.95 19.43 17.63 18.00 18.70 21.1 20.9 19.72 2C.44 20. 71 CAO 15.18 14.46 14.63 14,58 14.23 13.37 14.24 15.75 15.60 15.49 14.0 13.5 14.61 14.02 13.88 NA20 1.74 1.69 1.78 1.57 1.63 1.68 1.94 1.36 1.70 1.66 1. 58 1.57 1.68 1.56 1.50 K20 0.03 0.03 0.02 0.03 0.00 0.02 0.04 0.10 C. 02 0.00 NO ND ND ND ND TOTAL 1C1.19 100.43 100.47 98.94 101.05 100.08 99.25 99.47 99.27 99.37 101.1 °9. 3 99.64 100.20 99.62 NUMBER OF CATIONS FOR 6 OXYGENS SI 1.986 1.979 1.964 1.976 1.975 1.971 1.975 2.002 1.989 1.975 1.976 1.97C 1.9 72 1.982 1.972 Tl 0.011 0.010 0.012 0.013 0.011 0.010 0.011 0.013 0.012 0.013 0.009 0.009 0.011 0.009 0.009 AL 0.110 0.108 0.109 0.099 0.108 0.108 C. 112 0. IC8 0.105 0.104 0.103 0.103 0. 108 0. 106 0. 10b CR 0.006 0.009 0.005 0.006 0.007 o.ooe 0.005 0.003 0.005 0.005 0.010 0.010 0.006 0.006 0.009 FE 0.179 0.167 0.175 0.178 C.170 0.172 0.176 0.185 0.185 0.181 o.i 5e 0. 165 0.172 0.162 0.161 *N 0.004 0.004 0.003 0.003 0.004 0.003 0.003 0.004 0.004 0.00* 0.004 0.00b 0.005 0.005 C. 004 "3 1.009 1.062 1.074 1.059 1.085 1.119 1.050 0.952 C.976 1.013 1.113 1.122 1.062 1.089 1.110 CA 0.579 0.554 0.562 0.568 0.541 0.513 0.553 0.611 0.608 0.603 C. 532 0.524 0.565 0.577 0.535 NA 0.120 0.118 0.124 0.111 0.112 0.117 0.136 0.096 0.122 0.117 0.109 3.110 0.118 O.lOti 0.105 K 0.002 O. OOl 0.001 0.001 0.000 0.001 0.002 0.004 0.001 0.000 ND ND NP MO ND CA 32.8 31.1 31.0 31.5 30.1 28.4 31.1 34.9 34.4 33.5 29.5 28.9 31.4 30.0 29.6 *G 57.1 59.6 59.3 58.7 60.4 62.0 59.0 54.5 55.2 5b. 4 61.7 62.0 59.0 60.9 61.5 FE 10.1 9.3 9.7 9.8 9.5 9.5 9.9 10.6 10.5 10.1 8.8 9.1 9.6 9.1 e.9 MG/NG+FE BS.O 86.4 86.0 85.6 86.5 86.7 85.6 83.7 84.1 84.9 87.6 87.2 86.1 37.0 87.3 CA/CA*MG 36.4 34.3 34.4 34.9 33.3 31.4 34.5 39.1 38.4 37.3 32.3 31.8 34.T 33.0 12. t * TOTAL IFCN AS FEO FRB 353 F.R.BOYD UNPUBL1SHE0 FRB5.6 30Y0 U975I 26 60,2661.2662 NIXON AND BOYD (1973) 56 TABLE 13 ANALYSES OF DIOPSIDES EXSOLVED FROM LAMELLAR ENSTATITES HT % RJ RJ RJ R.> RJ RJ RJ RJ 126 319 320 322 330 332 335 337 SID2 53.62 54.08 54.22 54.74 53.94 54.38 54.68 55.12 TI02 0.11 0.13 0.10 0.01 0.05 0.01 0.09 0.02 AL203 1.68 1.72 1.76 2.37 1.67 2.52 1.60 2.98 CR203 0.90 0.86 0.90 2.04 1.22 1.92 0.74 2.51 FEO * 2.74 2.97 2.97 1.20 1.55 1.61 2.32 1.91 MNO 0.08 0.06 0.06 0.O7 0.05 0.02 0.05 0.08 MGO 16.43 16.41 16.51 16.24 17.00 16.00 16.93 16.73 CAO 21.88 21.69 22.19 20.83 22.52 21.24 22.62 18.50 NA20 1.39 1.37 1.37 1.86 1.17 1.87 1.12 2.37 K20 0.00 0.01 0.02 0.02 0.00 0.00 0.01 0.00 TOTAL 98.83 99.30 100.10 99.38 99.17 99.57 100.16 100.22 NUMBER OF CATIONS FOR 6 OXYGENS SI 1.972 1.978 1.972 1.984 1.970 1.974 1.979 1.978 TI 0.003 0.004 0.003 0.000 0.001 0.000 0.00? 0.001 AL 0.073 0.074 0.076 0.101 0.072 0.108 0.068 0.126 CR 0.026 0.025 0.026 0.059 0.035 0.055 0.021 0.017 FE 0.084 0.091 0.090 0.037 0.047 0.049 0.070 0.C57 MN 0.002 0.002 0.002 0.002 0.002 0.001 0.002 0.002 MG 0.899 0.894 0.893 0.878 0.926 0.866 0.914 0.895 CA 0.865 0.852 0.864 0.809 0.881 0.826 0.877 0.711 NA 0.099 0.097 0.097 0.131 0.083 0.132 0.079 0.165 K 0.000 0.000 0.000 0.001 C.000 0.000 0.000 0.000 CA 46.8 46.4 46.8 46.9 47.5 47.3 47.1 42.7 MG 48.6 48.7 48.3 50.9 49.9 49.6 49.1 53.8 FE 4.6 4.9 4.9 2.1 2.5 2.8 3.8 3.4 MG/MG+FE 91.4 90.8 90.8 96.0 95.1 94.6 92.9 94.0 CA/CA+MG 49.0 48.8 49.2 48.0 48.8 48.8 49.0 44.3 * TJTAL IRON AS FEO TABLE 14 ANALYSES OF DIOPSIDES COEXISTING WITH ILMENITE wr x RJ RJ RJ RJ RJ RJ RJ RJ RJ RJ f SI02 54.50 53.89 54.53 54.87 54.24 54.47 54.35 54.66 54.06 54.66 53.55 54. 15 TI02 0.45 0.49 0.42 0.43 0.45 0.44 0.44 0.44 0.45 0.34 0.44 0.38 AL203 2.57 2.47 2.57 2.48 2.44 2.54 2.56 2.49 2.48 2.43 2.51 2.40 CR203 0.08 0.12 0.02 0.03 0.07 0.03 0.04 0.10 0.06 0.02 0.11 0.01 FEO * 6.46 6.49 6.42 6.20 6.34 6.23 6.28 6.43 6.27 6.33 6.43 6.24 UNO 0.07 0.10 0.12 0.13 0. 11 0.13 0.14 0.12 0.38 0.14 0.09 0.11 MGO 18.46 18.22 17.55 18.32 18.05 17.73 18.17 18.31 17.66 17.05 18.79 17.26 CAO 16. 54 15.28 16.62 16.43 16. 19 16.31 16.21 15.80 16.38 16.99 15.81 16.73 NA2Q 1.86 1.77 1.97 1.97 1.71 2.03 2.08 1.96 1.91 2. OS 1.85 2.01 K2G 0.04 0.03 0.02 0.02 0.03 0.03 0.02 0.C5 0.03 0.01 0.05 0.04 99.94 100.29 100.36 99.68 100.05 99.63 99.33 nu iDtR ur i A i iurii run c u ATutNi <1 SI 1.960 1.974 1.976 1.972 1.974 1.977 1.967 1.974 1.971 1.985 1.953 1.980 TI 0.012 0.013 0.012 0.012 0.012 0.012 0.012 0.012 0.012 0.009 0.012 0.010 AL 0.109 0.107 0.110 0.105 0.105 0.109 0.109 0.106 0.107 0.104 0. 108 0. 103 CR 0.002 0.003 0.000 0.001 0.002 0.001 0.001 0.003 0.002 0.000 0.003 0.00 0 FE 0.194 0.199 0.194 0.186 0. 193 0. 189 0.190 0.194 0.191 0.192 0.196 0.191 MN 0.002 0.003 0.004 0.004 0.003 0.004 0.004 0.004 0.012 0.004 0.C03 0.003 MG 0.989 0.995 0.948 0.981 0.979 0.959 0.980 0.986 0.960 0.923 1.021 0.941 CA 0.637 0.600 0.645 0.633 0.631 0.634 0.628 0.611 0.640 0.661 0.618 0.656 NA 0.130 0.126 0.138 0.138 0.120 0.143 0.146 0.137 0. 124 0.146 0.131 0. 143 K 0.002 0.001 0.001 0.001 0.001 0.001 0.001 0.002 0.001 0.000 0.002 0.002 CA 35.0 3 3.5 36.1 35.1 35.0 35.6 34.9 34.2 35.7 37.2 33.7 36.7 MG 54.3 55.4 53.0 54.5 54.3 53.8 54.5 55.0 53.6 52.0 55.6 52.6 FE 10.7 11.1 10.9 10.4 10.7 10.6 10.6 10.8 10,7 10.8 10.7 10.7 MG/*G*FE 83.6 83.3 83.0 84.0 83.5 83.5 83.8 83.5 83.4 82.8 83.9 83.1 CA/CA^MG 39.2 ?7.6 40.5 39.2 39.2 39.8 39.1 38.3 40.0 41.7 37.7 41.1 * TOTAL IRON AS FEO TABLE 14 CONT. ANALYSES OF DIOPSIDES COEXISTING WITH ILMENITE UT % RJ RJ RJ RJ RJ RJ RJ RJ RJ RJ RJ 403 405 407 409 412 414 416 418 420 448 449 SI02 54.12 54.64 54.60 54.64 54.92 54.45 54.81 55.CI 54.84 54.97 55.31 TI02 0.43 0.43 0.33 0.46 0.43 0.39 0.46 0.44 0.40 0.42 0.39 AL203 2.45 2.45 2.48 2.51 2.46 2.54 2.52 2.50 2.54 2.57 2.53 CR203 0.01 0.10 0.00 0.08 0.01 0.00 0.09 0.04 0.02 0.06 0.02 FEO * 6.29 6.18 6.23 6.04 6.34 6.42 6.17 6.26 6.33 6.35 6.36 MNO 0.1<» 0.14 0.12 0.09 0. 13 0. 16 0.12 0.11 0.12 0.18 0. 13 MGC 17.99 18.48 17.27 18.51 17.77 17.29 18.48 18.03 17.80 17.13 16.91 CAO 16.70 15.74 17.28 16.15 16.65 16.87 16.12 16.18 16.83 16.42 17.29 NA20 1.94 1.97 2.13 1.83 2.00 2.10 1.99 2.10 2.08 1.83 1.84 K2Q 0.02 0.03 0.01 0.04 0.03 0.04 0.02 0.03 0.01 0.02 0.02 TOTAL 10O.O9 100.16 100.45 100.35 100.74 100.26 100.78 100.75 IOC.97 99.95 ICO.83 NUMBER OF CATIONS FOR 6 OXYGENS SI 1.978 1.975 1.977 1.971 1.979 1.9^5 1.970 1.979 1.973 1.992 1.991 TI 0.012 0.012 0.009 0.012 0.012 0.011 0.012 0.012 0.011 0.012 0.011 AL 0.104 0.104 0.106 0.107 0.104 0.109 0.107 0.106 o.ioe 0.110 0.107 C* CR 0.000 0.003 0.000 0.002 0.000 0.000 0.002 0.001 0.000 0.002 0.000 oo FE 0.189 0.18? 0.189 0.182 0. 191 0.195 0.185 0.188 C.190 0.192 0.192 M*4 0.004 0.004 0.003 0.003 0.004 0.005 0.004 0.003 0.004 0.006 0.004 MG 0.962 0.935 0.932 0.995 C.954 0.935 C.990 0.969 0.954 0.925 0.907 CA 0.642 0.610 0.670 0.624 0.643 0.656 0.621 0.624 0.649 0.637 0.667 NA 0.135 0.138 0.150 0.128 0.140 0.148 0.139 0.146 0.145 0.129 0.129 K 0.001 0.001 0.000 0.002 0.001 0.002 0.001 0.001 0.000 0.001 0.001 CA 35.8 34.0 37.4 34.7 36. C 36.7 34.7 35.0 36.2 36.3 37.9 MG 53.7 55.6 52.0 55.2 53.4 52.4 55.0 54.4 53.2 52.7 51.3 FE 10.5 10.4 10.5 10.1 10.6 10.9 10.3 10.6 10.6 10.9 10.9 NG/MG+FE 83.6 84.2 83.2 84.5 83.3 82.8 84.2 83.7 83.4 82.8 82.5 CA/CA+MG 4G.0 38.0 41.8 38.6 4C.2 41.2 38.7 39.2 40.5 40. 3 42.4 TOTAL IRON AS FEO TABLE 15 ANALYSES OF GARNETS WT % RJ RJ RJ PJ PJ RJ RJ RJ RJ 10 68 70 72 74 76 78 80 82 SI02 41.32 41.11 41.39 42.18 41.30 41.55 41.62 41.31 41.61 TI02 1.46 1.47 \.ll 0. 83 1.34 1. 20 1.30 1.36 1.26 AL203 21.42 21.43 21.61 22.07 21.66 22. 12 21.73 21.30 21.65 QRZQ3 0.54 0.60 1.03 0.96 0.34 0.21 0.72 0.55 0,62 FEO * 11.82 11.65 9.11 9.25 11. 51 11. 75 10.20 12.13 11.2? MNO 0.27 0.25 0.20 0.23 0.26 0.29 0.23 0.26 0.24 MGO 18.88 1 8.73 20. 36 20. 56 18.78 18.8! 19.77 18.50 19.32 CAO 4.70 4.66 4.58 4,33 4.65 4.61 4.66 4.72 4.70 T3TAL 100.32 99.91 99.39 100.42 99.86 100.53 100.25 100. 13 100. *-9 NUMBER OF CATIONS FOR 12 OXYGENS SI 2.972 2.973 2.976 2.995 2.983 2.980 2.979 2.986 2.976 TI 0.079 0.08 0 0.060 0.044 0.073 0.065 0.070 0.074 0.06P. At 1.820 1.827 1.831 1.847 1.844 1.870 1.833 1.815 1.827 CR 0.031 0.034 0.059 0.054 0.020 0.012 0.041 0.C31 0.035 FE 0.713 0.7 05 0.548 0.549 0.695 0.704 0.611 0.734 0.676 *N 0.016 0.015 0.012 0.014 0.016 0. 018 0.014 0.016 0.015 MG 2.029 2.020 2.181 2.176 2.022 2.011 2.109 1.996 2.063 CA 0.363 0.361 0.353 0.329 C.360 0.354 0.358 0.366 0.'61 CA 11.7 11.7 11.4 10.8 11.7 11.5 11.6 li.e u.6 MG 65.-'. 65.5 70.8 71.2 65.7 65.5 68.5 64.5 66.6 FE 23.0 22.8 17.8 18.0 22.6 22.9 19.9 23.7 21.8 MG/MG+FE 7<».0 7 4.1 79.9 79.8 74.4 74.1 77.5 73.1 75.3 CA/CA+MG 15.2 15.2 13.9 13.1 15.1 15.0 14.5 15.5 14.9 * TOTAL IRON AS FEO TABLE 15 CONT. ANALYSES OF GARNETS WT % RJ RJ RJ RJ RJ RJ RJ RJ RJ 84 86 88 90 92 94 96 98 100 SI02 42.02 41.32 41.26 40.67 41.13 41.41 41.25 40. C6 42.18 TIC2 1.23 1.14 1.06 1.11 1.29 1.20 1.11 1.18 0.90 AL203 21.46 22.08 21.94 21.96 21.38 20.63 21.53 21.69 21.13 CR2Q3 0.87 0.05 0.05 0.05 0.47 0.47 0.55 0.98 0.94 FEO * 9.87 13.09 13.35 12. 79 11.98 11.69 11.40 9.56 9.55 MNO 0.23 0.32 0.33 0.26 0.27 0.24 0.24 0.25 0.21 MGO 19.97 18.04 17.87 18.04 18.56 18.46 18.94 20.21 20.29 CAO «».74 4.58 4.55 4.71 4.72 4.79 4.62 4.53 4.59 TOTAL 100.40 100.62 100.41 99.58 99.80 98.90 99.64 98.46 99.78 NUMBER OF CATIONS FOR 12 YGENS SI 2.^98 2.977 2.984 2.962 2.981 3.024 2.984 2.921 3.021 TI 0.066 0.062 0.053 0.061 0.071 0.066 0.061 0.065 0.049 AL 1.805 1.876 1.870 1.885 1.825 1.776 1.836 1.864 1.785 CR 0.049 0.003 0.003 0.003 0.027 0.027 0.032 0.056 0.053 FE 0.589 0.789 0.808 0.779 0.726 0.714 0.690 0.'J83 0.572 MN 0.014 0.020 0.020 0.016 0.017 0.015 0.015 0.015 0.013 MG 2.124 1.^.40 1.9 26 1.961 2.007 2.011 2.045 2.197 2.166 CA 0.362 0.354 0.3 53 0.368 0.367 0.375 0.358 0.344 0.352 CA 11.8 11.5 11.4 11.8 11.8 12.1 11.6 11.3 11.4 MG 69.1 62.9 62.9 63.1 64.7 64.9 66.1 70.1 70.1 FE 19.1 25.6 25.6 18.6 18.5 25.1 23.4 23.0 22.3 MG/NG+FE 78.3 71.1 70.5 79.0 79.1 71.5 73.4 73.8 74.8 CA/CA+MG 14.6 15.4 15.5 13.9 14.0 15.8 15.5 15.7 14.9 * TOTAL IRON AS FEO TABLE 15 CONT. ANALYSES OF GARNETS WT t RJ RJ RJ RJ RJ RJ R.f RJ RJ 102 104 108 110 112 114 116 118 454 SI02 41.33 41.37 41.35 41.24 41.66 42.11 41.58 41.95 41.38 TI02 1.40 1.22 1.31 1.08 0.88 0.95 1.12 1.28 1.37 AL203 21.30 21.52 21.57 21.45 20.66 22.02 21.66 20.51 20.52 CR2Q3 0.55 0.65 0.57 0.66 2.09 0.33 0.68 0.52 1.63 FEO * 11.41 10.27 11.05 10.35 8. 11 10.69 10.45 11.79 9.80 MNO 0.28 0.26 0.28 0.26 0.31 0.22 0.23 0.22 0.29 MGO 19.21 19.78 19.22 19.53 20.02 19.86 19.65 19.02 19.52 CAO 4.75 4.44 4.48 4.57 5.06 4.17 4.50 4.64 5.13 TOTAL 100.23 99.51 99.84 99. 14 98.80 100.35 99.86 99.93 99.65 NUMBER OF CATIONS FOR 12 OXYGENS SI 2.978 2.982 2.981 2.986 3.012 3.004 2.987 3.C30 2.990 TI 0.076 0.066 0.071 0.059 0.048 0.051 0.060 0.070 0.075 AL 1.807 1.829 1.833 1.631 1.761 1.852 1.835 1.747 1.747 CR 0.031 0.037 0.032 0.038 0.120 0.019 0.039 0.030 0.093 FE 0.687 0.619 0.667 0.627 0.491 0.638 0.628 0.713 0.592 MN 0.017 0.016 0.017 0.016 0.019 0.013 0.014 0.013 0.018 MG 2.063 2.126 2.068 2.109 2.157 2.113 2.105 2.050 2.103 CA 0.367 0.343 0.346 0.355 0.392 0.319 0.347 0.360 0.397 CA 11.8 11.1 11.2 11.5 12.9 10.4 11.2 11.5 12.8 MG 66,2 68.8 67.1 68.2 71.0 68.8 68.4 65.7 68.0 FE 22.1 20.0 21.6 20.3 16.1 20.8 20.4 22.8 19.1 MG/MG+FE 75.0 77.4 75.6 77.1 81.5 76.8 77.0 74.2 78.0 CA/CA+MG 15.1 13.9 14.3 14.4 15.4 13.1 14.1 14.9 15.9 * TOTAL IRON AS FEO TABLE 16 ANALYSES OF GARNETS COEXISTING WITH ILMENITE WT % RJ RJ RJ RJ RJ RJ RJ RJ RJ 25 7 260 262 265 268 271 274A 2 74B 282 SI02 41.50 40.86 41.13 40.94 41.26 41.46 41.57 41.23 41.46 TI02 0,98 0.81 0.64 0.86 1.16 0.99 1.16 1.04 1.09 AL203 22.29 21.90 21.99 21.72 21.51 22.01 21.87 21.92 22.10 CR2Q3 0.00 0.02 0.00 0.03 0.09 0.03 0.13 0.13 0.11 FEO * 13.20 13.61 14.19 12.99 12.23 12.88 12.50 12.64 12.82 MNQ 0.30 0.31 0.32 0.31 0.27 0.31 0.28 0.31 0.27 MGO 18.13 17.32 17.22 17.81 18.51 18.18 18.29 18.55 18.72 CAO 4.51 4.50 4.34 4.42 4.56 4.63 4.71 4.54 4.53 TOTAL 100.91 99.32 99.83 99.09 99.59 100.49 ICC.50 100.36 101.10 NUMBER OF CATIONS FOR 12 CXVGENS SI 2.980 2.990 2.999 2.995 2.993 2.988 2.991 2.974 2.969 0) TI 0.053 0.04 5 0.035 0.047 0.063 0.054 0.063 0.057 0.059 to AL 1.887 1.890 1.890 1.873 1.840 1.870 1.855 1.864 1.866 CR 0.000 0.001 0.000 0.002 0.005 0.002 0.007 0.007 0.006 FE 0.794 0.833 0.865 0.795 C. 743 0.777 0.753 0.763 0.769 MM 0.018 0.019 0.020 0.019 0.017 0.019 0.017 0.019 0.016 MG 1.943 1.890 1.872 1.942 2.004 1.956 1.965 1.996 2.002 CA 0.347 0.352 0.339 0.346 0.355 C.357 0.363 0.351 0.348 CA 11.3 11.5 11.0 11.2 11.4 11.6 11.8 11.3 11.2 MG 63.0 61.4 60.9 63.0 64.6 63.3 63.8 64.2 64.2 FE 25.7 27.1 28.1 25.8 23.9 25.1 24.4 24.5 24.6 MG/MG+FE 71.0 69.4 68.4 71.0 73.0 71.6 72.3 72.4 72.2 CA/CA+MG 15.2 15.7 15.3 15.1 15.0 15.5 15.6 14.9 14.8 * TOTAL IRON AS FEO TABLE 16 CONT. ANALYSES OF GARNETS CO-EXISTING WITH ILMENITE WT t RJ RJ RJ PJ RJ RJ RJ RJ RJ RJ RJ 285 287 290 A 290B 294 298 304A 304B 308 311 314 SI02 40.62 41.34 41.10 41.50 41.31 41.31 41.17 41.16 41.55 41.49 41.54 TIC2 1.03 1.09 1.16 1.23 1.03 1.11 0.93 0.88 0.78 0.96 0.99 AL203 22.47 22.02 21.43 21.62 22.01 21.78 22.19 21.86 22.34 22.45 22.25 CR203 0.09 0.08 0.25 0.27 0.13 0.33 0.05 0.03 0.02 0.03 0.00 FEO * 12.14 12.56 11.76 12.00 11.93 11.99 12.89 12.66 13.04 12.40 12.78 NNO 0.30 0.31 0.27 0.26 0.28 0.28 0.28 0.30 0.32 0.32 0.31 MGO 18.21 18.49 18.42 18.74 18.42 18.50 18.07 18.17 17.86 18.41 18.02 CAO 4.35 4.52 4.63 4.7? 4.44 4.61 4.51 4.43 4.42 4.50 4.43 TOTAL 99.21 100.41 99.04 100.38 99.55 99.91 100.09 99.49 100.32 100.56 100.32 NUMBER OF CATIONS FOR 12 OXYGENS SI 2.956 2.978 2.995 2.989 2.992 2.986 2.978 2.992 2.997 2.980 2.993 s> TI 0.056 0.059 0.064 0.067 0.056 0.06 0 0.051 0.048 0.042 0.052 0.054 CO AL 1.927 1.870 1.841 1.834 1.879 1.855 1.893 1.873 1.900 1.900 1.890 CR 0.005 0.004 0.015 0.015 0.007 0.019 0.003 0.002 0.001 0.002 0.000 FE 0.740 0.747 0.717 0.723 0.723 0.725 0.780 0.771 0.787 0.745 0.771 MN 0.018 0.019 0.017 0.016 0.017 0.017 0.017 0.018 C.020 0.020 0.019 MG 1.978 1.989 2.003 2.012 1.990 1.995 1.952 1.972 1.923 1.973 1.938 CA 0.339 0.349 0.362 0.365 0.344 0.358 0.350 0.346 0.342 0.347 0.343 CA 11.1 11.3 11.7 11.8 11.2 11.6 11.4 11.2 11.2 11.3 11.2 MG 64.7 64.2 65.0 64.9 65.1 64.8 63.3 63.8 63.0 64.4 63.5 FE 24.2 24.5 23.3 23.3 23.6 23.6 25.3 25.0 25.8 24.3 2 5.3 MG/MG+FE 72.8 72.4 73.6 ">3.6 73.4 73.3 71.4 71.9 7C.9 72.6 71.5 CA/CA*MG 14.7 14.9 15.3 15.4 14.8 15.2 15.2 14.9 15.1 14.9 15.0 * TOTAL IRON AS FEO 64 TABLE 17 ANALYSES OF GLASSY DISCRETE ENSTATITES WR % RJ RJ PJ RJ RJ RJ FRB 122 124 130 138 150 328 4 SI02 5 5.49 56.39 57.31 55.51 56.19 56.01 55.3 TI02 0.16 0.13 0.20 0.27 0.16 0.25 0.15 AL203 0.75 0.82 1.30 1.16 0.74 1.31 0.70 CR203 0.02 0.00 0.12 0.04 0.00 0.08 0.03 FEO * 10.94 10.57 7.30 9.02 10.88 8.37 10.7 MNO 0.13 0.13 0.10 0.13 0.19 0.13 0.20 MGO 30.89 30.32 32.12 31.80 31.71 31.89 32.3 CAO 0.80 0.88 1.53 1.22 0.79 1.35 0.68 NA20 0.26 0.26 0.27 0.31 C.20 0.28 0.15 K20 0.07 0.02 0.00 0.00 0.00 0.00 0.00 TOTAL 99.51 99.42 100.25 99.46 100.86 99.67 100.2 NUMBER OF CATIONS FOR 6 OXYGENS SI 1.970 1.992 1.984 1.957 1.966 1.963 1.948 TI 0.004 0.003 0.005 0.007 0.004 0.006 0.004 AL 0.031 0.034 0.053 0.048 0.031 0.054 0.029 CR 0.000 0.000 0.003 0.001 0.000 0.002 0.001 FE 0.325 0.314 0.211 0.266 0.318 0.245 0.316 MN 0.004 0.004 0.003 0.004 0.006 0.004 0.006 Mu 1.634 1.597 1.656 1.671 1.653 1.666 1.698 CA 0.030 0.033 0.057 0.046 0.029 0.051 0.026 NA 0.018 0.018 0.018 0.021 0.014 0.019 0.010 K O.COO 0.000 0.000 0.000 C.OOO 0.000 0.000 CA 1.5 1.7 2.9 2.3 1.4 2.5 1.3 MG 82.1 82.1 86.1 84.2 82.6 84.9 83.2 FE 16.3 16.2 11.0 13.4 15.9 12.5 15.5 MG/MG+FE 83.4 83.6 88.7 86.2 83.8 87.1 84.3 CA/CA+MG 1.8 2.0 3.3 2.7 1.7 3.0 1.5 * TOTAL IRON AS FEO 65 .i) _- r\* L/> rr\ m .^ n _* o r-OfOCTOCD — OO í>OQO—Or-OO• ••••••••O• .*• r-* r*- i^oooao^ooo —«OOOOO^OCJO o^c * O *o coooo-*o*r>ooc f1 —*C30000-*C300 ^ r í vT. O r^ .ri T1 *f O p- ou <*» o <& r» o» o o c cr o o o —• o r-- o T.i o -i ^- cr • ••••••••• • • • » O o o o -* o *- c o o .n ,.. a, O ^ í fl1 c. ï J* -T •-* CT> O O O -•* O CO O O 3 u-i « j- t •* o * o (_i o .-• o o a o o -* o CJ O n n- 4Í r^ O P- r- ci "j -n C i^ O xnoo^OTiooo OOOC)—'O^OOn if rvj c. aj O o o »J O i (MOOOOO—• O O O O O CJ* IÍI -i |.j 4 4 nt^OdiQ •X O r>-. £3 f O *"J -* Cï 'J p-• a • r- • —• * «-•» «O• f*•i O• *"•3 ajOOrjONOOO p. r; o o c O f-1 O O O -*oacoo--'cjou Of--. tO fJ r«j o r«- Ul r- m o o er -£"> U O) -- 'Ví -* O <*SJ 000>-> — 000--1O >n *• ••• K t* r*i utl lO O O r-i 1-1 "4ooooo«-,o*,o Offy •i< o o r*> a o t<- co 1 1 cO r>j Í*^ -í i"j ^ i ^» T «^ r-* Uz) P~ i-yj •C ^ •t r>- ^ O Ti .-i "H -. QO r> o o a. íii •a O CJ O -0 O " O o o r»l UJ-> -»ïí »> 1« -. .f :n H ^ O- tf « -i T -5 r i O O ^Jr-t^ irt >f «1 O (? i-í O i^í íOniMaocrNoo ^« p-naor^or^ooo ^ H « lí N m O O Ci N vf lf O O) (\J O N K lf ^ tromo— O ffO^Cr'OíOOo CTGOO'-'O^OO• *••«•*••O• iil •••* • tO O O O -f Of r* O O O O O ^ O U O C^Ji i-i ^ooo^oir>ooo .-i ^ O • r ru cu CE r- CO rvj oon o "' o a M o o ^t r-ooocroi*jOOO f\íOOO0O—"000 O^r^J ^H S O ^ O O) O C> O O O K ^OOOOO^OO• # • O» c*l AJ if» IT ^ r»i <-* O >f iM <}> O t^ n ~* *Z rj 1« o o O O O' ^ -/ O i f i <-J O '•> CJ C, ^j n . _t <í u, ? O < ^T --, < o u > T (. i' «- j- '_J a n « • • o o O O •" • a n o ( O O < • (-1) Q O -* <*• • 0 o t » • • • - o o o o a •- -* f") rv n o o oco»-ooooo»- j O Í O H G ff O M wv «-• rj O O U u1 f J L.' í rj * * C (D ï CJOO»-OOCOO»- O J »- *- O iC*--O0 QW ^ ^i- ' C) O O O O * >j Q * o - o a ooof*OMOOo,n 0«-i wOCDL J'O-J O -D O C» i*J O O u> -J '•" • O O O O O * CjO*-"*-t-' £ O •- O -W CJ CD f O O O <*• O r-J CJ O O • ••*•••«* « • ••*•«•••• ^T>1_ J^ Mao 0OO^Ot\)OOO^3 i'j *j 'jJ -j -i .,.. o — -O •* r*> -< CO •^ *, j- .t fo ^ o -g *v- i' m > *- ff- J* C> Xs ju O *- ÍT UJ «CD "C m CJ O O •-* Ci ,_>OOC«- w u O o c •— •- CJ -a o <- c- a '-^ •*' m -* 1 £T •— -* f r »000.0 ••••••••«• \J<- x » O c- O 0 O o f-j •- i-"— iJ o O r J c* i — fj I- ^ IS, J "* W < Ult^ UUwu^si CO z a .-a OOO^-OOC'U'—» CC'—»-OJJO»-O0 '•>' $ • • • or^ - 1 f-OOO'Of^kJoCiX C I\J O r> •-• -y n c, f ' -* 'J (-- 3 O - *• M O * U i- ij IL O «D *•" t?" *• *• CJ fo O — r~ s \J1 • • ••••••••«• OOHMOJIOfCj i- Z ii u1 NJ O O O T O **• O O O £ Qf^»— o*— ^ O O f- i- 'OL JI* C •- Í- ^ C ï O Í O 0. O O H r G ^ o H o -g ^>J • •«•>••••• r»u o o o <* o ^J o o c- x O'vl- Nj •— ..J !_) O *••> O *-t_ O •— *• M O N O i- C ts CJ iT) r^ ^ i_> «-• i w •-• TI r-j ooo*-ooooo*- GO<-^0 £G« Off tu OOCSJ-ONJOOOC t G - g " 'O C D 'J f '• *- t- o •*- v* O -J c X-O-j ^- r-.i _- o c. -c —• r*j j' o C Q f,J -J "J fo O fJ -J -T l>- if ooo^-ooooo*- • ••«••••*• on ODO^OfvjOOOJD Oi^J^-fc-G>T'Cof,J'\J '^C_ & >C M i jiro»-»— -xCT- n o *° J* - '»' o T»J -J 0(_)OOO«-00C---J <- • •*•••*••• lull -w X *• O0O^O'»JO0OX G i) 'j t i- rj o 3i »• * 'x t_ t; D N Jl Li IvJ O J O Í • v» rj .** . ^j -* o c J *- n o -4 ti i- v." ri w i- 4- lfc a. *- x C3 o o •- o o n o o •- • ••••••••. ff r 1*1 ^"> CD M U OCOf OlMOOO'C Q »\J o •**•-• ** •> «c t^-» \JI r" c Civ (T M^- -J w TO •— J- C -.J1 O X ^ Í C) il T ^ f* i* i- rvj O0O»-0C>COO — O O •— "o O Xi C O O iji * ...... ,..• o- t) O C O -y C ra & O O J GrjC.,>h- GG Jl'v)» ^ t_ Ci*-2-c5CJC O 4- O J* ONS'jf-g.v-: •- -* i_j ti ^-"VVWO COO" ^ O C- tj •- C. O C3 O O — C D C"1 •— O "~ l"i C C i_' UJ — c c n ^ o»*JCno.r O r- •* .- 99 f TABLE 20 ANALYSES OF SILICATE INTERGROWTHS OiJPMCES b»o\fTs CLIV[\- ".i-N;V. ''LIVINi -NS1ATIT = 2« I'PX/IL* I'.ftP^2'!rt'*- -J460 5J Pr-N íj PHN *»?*- i J 5 en* •W*. 19^9" I- : 5i. 1* !>*. JR *1.3 7 *i.ao *I. 52 rW.bJ *..).C *1,27 «.2. 0 * 9 . <. r, ').C 1 •ico 3. 3o c.*t- I.Of Q.<)? 1.C1 0.0? O.C3 0.99 i,;o 2. OS 0, 'I J , 0 2 'Jl.I' • 0. Ji AL:.IÍ I.a? :.*•> 21.7? 21.71 21.*' 3.0^ O.CS 21.3' :i.«. U, 2*t 1,17 0. 24 C, ' e H?11 G.2o 0.13 0, r nai ioo.±r 99,éc IOO.ÏS 99,»*.: •iS.OT 131, ? 9S.f: U0.9 lOo.LO I.),- \ = 1 1.930 t .S7G 2.988 2.9*-> 3.CCt C.94u 3.9SI 2. »#9** 2 973 C,t-tib 1 *>t;'j O.Sfí*, 0 . C '. 0 2 . -*; T 0. 010 a.on 0.057 0.C52 0.055 0,001 0.C01 COS*. JS. 0.0^1 0 00 M c,:;i O.-i'l O.t02 0.112 0.107 1.828 i.63r 1.837 0.001 0.001 1 . «Ofc M1 T89 0.00! 0 C11 0. 001 0.01- 0.1*2 o.oo? J.CO". 0.052 0.0*8 0.027 0.001 3,001 C. 06u 0 05 0 0.0 00 0 0 02 0.30 0 ".1.1/ Ï . H 7 3 r 0.168 0.16« 0.575 0.583 0.68* 0.760 1.?oC C.570 0 e St G. \J~* 0 2Í c 0.3ÍÍ :. t hs ^. ft ? - . 1 - tí v.304 0.00? 0.01* 0.016 0.01* 0.00* O.CQ* 0,012 o 017 coo* 0 CO- 0.007 u i..05o 1. 0! 0 ?.!»5 2.168 2.01* 1,7*1 l.TfcC t.lHl „ 2--.1 1,^2 1 r72 0.5*8 o. to* 0.5-u 0.32* 0.371 0,002 o.co^ 0,3b1. c >i? 3 • 0 " 2 J i.M 0.1?^ 0.1.-7 0 PI 2 0.«. 02 0.C01 30. J »5.. 5 10. •» 10. 6 12.1 11.2 59.c St.. C 7 j. * 70.' 65. fc 71.1 i.c '-0.5 is.? 13.<• 2 2. * 1 7. ' TABLE 21 ANALYSES OF ILMENITES WT % RJ RJ RJ PJ RJ RJ RJ PJ RJ RJ RJ RJ aj RJ RJ 152 154 156 158 160 163 164 167 169 170 172 174 176 178 18C SI02 0.02 0.08 0.03 0.10 0.04 0.08 0.18 0.04 0.06 0.02 0.10 0.03 C.15 0.12 0.11 TI02 48.90 48.57 48.87 51.91 47.67 48.84 50.84 52.96 50.15 52.82 4B.00 50.68 51.82 53.87 52.71 AL203 0.23 0.70 0.86 0.43 0.76 0.74 0.51 0.43 0.55 0.59 1.44 0.66 1.13 1.08 0.84 CR203 0.87 0.04 0.25 0.13 0.03 0.03 0.20 1.16 0.04 0.00 0.06 0.06 0.03 0.36 0.23 FEC • 41.97 41.37 40.19 38.10 44.35 41.49 37.74 31.87 40.59 37.42 38.81 41.04 38.18 35.80 36. C4 UNO 0.23 0.17 0.17 0.18 0.18 0.20 0.16 0.2* 0.14 0.20 0.18 0.17 0.18 0.17 0.18 MGO 7.69 8.53 9.41 9.63 7.58 7.90 9.56 11.87 9.26 8.67 11.08 7.60 7.78 9.46 9.60 CAC 0.02 0.11 0.04 0.05 0.04 0.05 0.04 0.01 C.01 0.01 0.11 0.01 0.05 0.05 C.04 TOTAL 99.94 99.57 99.83 100.53 100.65 99.33 99.23 98.58 100.80 99.73 99.78 100.26 99.32 100.91 99.75 > FE203» 13.27 14.58 14.68 9.68 16.87 13.14 10.07 6.24 13.43 6.15 17.30 10.18 6.13 4.80 6.51 FEC • 30.03 28.25 26.98 29.38 29.18 29.66 28.68 26.25 28.51 31.85 23.20 3i.ee 32.66 31.48 30.18 NUMBER OF CATIONS FOR 3 OXYGENS ** 05 00 SI O.COO 0.002 0.001 0.002 0.001 0.002 0.004 0.0C1 0.001 0.000 0.002 0.001 0.004 0.003 0.002 TI 0.870 0.859 0.8 56 0.906 0.840 0.870 0.898 0.928 0.874 0.936 0.828 0.899 0.925 0.937 0.926 AL 0.006 0.019 0.024 0.012 0.021 0.021 0.014 0.C12 0.015 0.016 0.039 0.018 0.032 0.029 0. C23 C<* 0.016 0.001 0.005 0.002 0.001 0.001 0.004 0.021 0.001 O.COO O.C01 0.001 0.000 0.006 0.004 FE3* 0.236 0.258 0.257 0.169 0.279 0.234 0.178 0.109 0.234 0.110 0.299 o.iei 0.110 0.084 0.114 FE2* 0.594 0.555 0.526 0.570 0.571 0.588 0.563 0.512 0.552 0.628 0.445 0.629 0.649 0.609 C.590 NN 0.005 0.003 0.003 0.004 0.004 0.004 0.003 0.C05 0.003 0.004 0.003 0.003 0.004 0.003 0.003 PG, 0.271 0.299 0.327 0.333 0.265 0.279 C.335 0.412 0.320 0.305 0.379 0.267 0.275 C.326 0.334 C4 0.001 0.003 0.001 0.001 0.001 0.001 0.001 O.COO C. 000 0.000 0.003 O.COO 0.001 0.001 0.001 GK 24.6 26.9 29.4 31.1 23.4 25.3 31.1 39.9 28.9 29.2 33.7 24.8 26.6 32.0 32.2 IL 53.9 49.9 47.4 53.2 50.4 53.4 52.3 49.5 49.9 60.2 39.6 58.4 62.7 59.8 56.8 HM 21.5 23.2 23.2 15.7 26.2 21.3 16.6 10.6 21.2 10.6 26. 6 16.8 10.6 8.2 11.0 NG/NG»FE 31.3 35.0 38.3 36.9 31.7 32.2 37.3 44.6 36.7 32.7 46.0 29.6 29.8 34.9 36.1 (AT tï * TOTAL IRON AS FEO • FE203 AND FEO IS CALCULATED FROM THE TOTAL FE AND FROM THE ILMENITE STRUCTURAL FORMULA AB03» ASSUMING ATOMIC PROPORTION OF R2*=R4* *» CATION TOTAL NORMALIZED IN THE COURSE OF FE3* CALCULATION TABLE 21 CONT. ANALYSES OF ILMENITES UT t RJ RJ PJ RJ RJ RJ RJ RJ RJ RJ RJ 183 185 187 188 190 192 194 196 199 200 202 SI02 0.20 0.06 0.04 0.00 0.03 0.10 0.04 0.02 0.02 0.09 0.01 T102 47.53 48.80 47.31 50.02 49.88 47.36 55.37 50.44 49.45 49.66 47.80 AL203 0.70 0.35 0.51 0.27 0.79 0.58 0.61 0.87 0.68 0.78 0.74 CR203 0.06 0.82 0.06 0.84 0.13 0.55 0.51 0.05 0.03 0.05 0.04 FEO * •4.33 38.81 45.22 39.59 38.65 43.08 29.45 39.22 39.77 41.49 43.82 MHO 0.17 0.32 0.17 0.25 0.15 0.17 0.22 0.17 0.16 0.16 0.16 MGO 7.29 11.12 7.06 8.36 9.41 7.12 12.71 9.36 9.37 8.83 7.3 7/ CAO 0. 06 0.08 0.02 0.02 0.04 0.03 0.06 0.01 0.02 0.03 0.10 TOTAL 100.34 100.36 100.39 99.35 99.10 98.96 98.97 100.14 99.50 101.10 100.04 FE203* 16.22 16.79 17.13 10.88 11.93 14.70 2.86 11.90 13.52 14.08 15.84 FEO* 29.73 23.70 29.81 29.80 27.91 29.80 26.88 28.51 27.60 28.82 29.57 NUMBER OF CATIONS FOR 3 OXYGENS ** SI 0.005 0.001 0.001 0.000 0.000 0.002 0.001 0.000 0.000 0.002 0.000 TI 0.842 0.eA2 0.839 0.891 0.882 0.852 0.961 0.883 0.871 0. 664 0.848 05 AL 0.019 0.009 0.014 0.008 0.022 0.016 0.016 0.024 0.019 0.021 0.020 «> CR 0.031 0.015 0.001 0.016 0.002 0.010 0.009 0.001 0.001 0.001 0.C01 FE3* 0.28 7 0.2 0 0.304 0.194 0.211 0.264 0.050 0.208 0.283 0.245 0.281 FE2* 0.585 0.455 0.5 88 0.590 0.549 0.596 0.519 0.555 0.540 0.558 0.564 MN 0.003 0.006 0.003 0.005 0.003 0.003 0.004 0.003 0.003 0.003 0.003 MG 0.2 56 0.380 0.248 0.295 0.330 0.254 0.437 0.325 C.327 0.305 0.2 59 CA 0.C01 0.002 0.001 0.001 0.001 0.001 0.001 0.000 0.001 0.001 0.002 GK 22.7 33.8 21.8 27.3 30.3 22.8 43.5 29.8 29.6 27.5 23.1 IL 51.9 40.4 51.6 54.7 50.3 53.5 51.6 51.0 48.9 50.4 51.9 HM 25.4 25.8 26.6 18.0 19.4 23.7 4.9 19.2 21.5 22.1 25.0 MG/MG*FE 30.4 45.5 29.7 33.3 37.5 29.9 45.7 36.9 37.7 35.3 30.7 (AT t) * TOTAL IRGN AS FEO • FE203 AND FEO IS CALCULATED FROM THE TOTAL FE ANO FROM THE ILMENITE STRUCTURAL FORMULA AB03, ASSUMING ATOMIC PROPORTION OF R2*=R4* ** CATION TOTAL NORMALIZED IN THE COURSE OF FE3* CALCULATION TABLE 22 ANALYSES OF ILMENITES CO-EXISTING WITH CLINOPYROXENE WT * RJ RJ RJ RJ RJ PJ BJ pj RJ 371 373 375 377 379 381 383 385 387 SIQ2 0.06 0.04 0.06 0.04 0.00 0.04 0.04 0.00 0.00 TI02 50.63 49.61 50.16 52.17 50.57 48.70 50.50 50.66 5C.ll AL2C3 0.78 0.70 0.94 0.63 1.00 1.05 0.71 0.74 0.49 CR203 0.25 0.*8 0.22 0.06 C. 07 0.27 0.03 0.12 0.46 FEO * 37.85 38.47 38.90 37.85 38.61 40.18 39.56 38.21 39.01 MNO 0.00 0.08 0.18 0.17 0.14 0.19 0.17 0. 17 o.ie MGO 9.86 9.52 9.72 9.56 9.75 9.75 8.61 9.15 9.84 CAO 0.05 0.04 0.05 0.12 0.04 0.02 0.04 0.02 0.04 TOTAL 99. 47 98.94 100.23 100.69 100.18 ICO.20 99.6 7 99.06 100.13 F 203 + 10.99 12.13 12.55 9.ie 11.90 15.49 1C.75 10.18 13.03 FEO* 27.96 27,55 27.60 29.59 27.90 26.24 29.89 29.04 27.28 NUMBER OF CATIONS FOR 3 OXYGENS ** SI 0.001 0.001 0.001 0.001 0.000 0.001 0.001 0.000 0.000 TI 0.889 0.879 0.874 0.910 0.881 0. 84 7 0.894 0.898 0.87c AL 0.021 0.017 0.026 0.017 0.C27 0.029 0.020 0.02C 0.01'4 C» 0. 0O5 0.009 0.004 0.001 0.001 0.005 0.000 0.002 0.006 FE3* 0.193 0.215 0.219 0.160 0.208 C.27C 0.190 0.181 0.278 FE2* 0.546 0.542 0.535 0.5 74 0.541 0.508 0.. S8 0.57? 0.530 MN 0.000 0.002 0.004 0.003 0.003 0.004 0.0u3 0.003 0.004 MG 0.343 0.334 C.336 0.330 0.337 0.336 0.302 0.322 0.341 CA 0,001 0.001 0.001 0.003 0.001 0.000 0.001 0.000 0.001 GK 31.7 30.6 30.8 31.0 31.0 30.2 28.0 29.9 31.0 1L 50.5 49.7 49.1 53.9 49.8 45.6 54.4 53.3 48.3 HM 17,8 19.7 20.1 15.0 19.1 24.2 17.6 16.8 20.7 MG/MG+FE 38.6 38.1 38.6 36,5 38.4 39.8 33.9 36.C 39.2 (AT.I) * TOTAL IRON AS FEO • FE203 AND FEO IS CALCULATED FROM THE TOTAL FE AND FROM THE ILMENITE STRUCTURAL FORMULA AB03, ASSUMING ATOMIC PROPORTION OF R2*=P4» ** CATION TOTAL NORMALIZED IN THE COURSE OF FE3* CALCULATION NOIlVirmvD +Z3Ú dO 3S«Í103 3H1 NI 032nwwaON 1V101 NOI1V0 ** •*a=+Za 40 NOIlMOdOad 0IWO1V 9N1W0SSV '£09V VlflwaOJ ivarUDPblS 31IN3W11 3Hi WOad ON* 3d 1V101 3H1 WOad a31Vin31VD SI 03d ONV E023J • 03d S» NOHI 1V101 * (flVI 0*9E 6*8£ I*SE 5*0*/ 8*t* 8*6* S*l£ 3d*0k/9N 1*81 6*81 l*2t 9*91 */*22 2*81 1*02 WH 0*25 9*6*/ 5*95 1*6* 2*5* **6* 5*6* "II E*62 5*1E **1E 8*££ **2E **?E 8*62 X9 tO0*O 100*0 100*0 100*0 100*0 000*0 100*0 VO ete'o £ *» SN30AX0 £ dOd SN011VO JO aagwnN 16*82 01*12 2**0£ *S*12 *8*S2 tZ'LZ 80*12 • 03d ESMI 18*11 92*1 22*01 92**t 21*11 09*21 •£0233 68*66 20*001 56*66 81*001 12*001 62*66 2E*86 IViOi 50*0 *0*0 -70*0 50*0 50*0 *0*0 50*0 OVD £1*6 16*6 8**6 05*01 0**0t £0*01 Et*6 Q9W 61 *0 81*0 61*0 81*0 91*0 *l*0 11*0 CNW 62*6fc £E*8£ S6*9£ *1*9E 89*8E £2*1E 2V8E • 03d 90*0 60*0 E0*0 52*0 6£*0 9£*0 £0*0 £02aD £9*0 91*0 1E*0 *i*0 26*0 11*1 *0*T E021V *S*OS 11*05 68*25 21*15 19*6* 2E*0S 8**8* 2011 00*0 00*0 00*0 00*0 00*0 00*0 00*0 20IS 6*/*/ 8** 02*/ 91* 11* 60* 10* ra ra ra ra ra ra ra 2 1M 3N3XOtíAdONnO HUM DNI1SIX3-O0 S31IN3W1I dO S3SA1VNV 1N03 ZZ 318V1 Nouvinoivo *£34 40 asanoD 3m NI oaznvwaoN ívioi NOUVO ** •va«*2M jo Nonaodoad DIHOIV ONIHDSSV 'COSV VinHDOd IVbniDflrJiS 31IN3H1I 3H1 H0rj4 QilVinDIVD SI 034 QNV £0334 • 034 SV NOal "IV10X * U*1V» 2*2* E*i£ 0*8E •/*!* 8*9E A*9E 9*6E £**£ 6*8E 3J+9M/DH 5*12 1*11 T*6I i#ll 1**1 9*81 6*61 0*L\ 0*81 HH **s* 0*25 2*05 2*8*/ £*¥S S*tS **8* 0*25 1*05 11 I*EE 6*0E 1*0E T*¥€ 9*IE 6*62 i.*ï£ 0*1£ 6*IE X9 100*0 100*0 100*0 tOO'O 100*0 200*0 100*0 200*0 000*0 VD S9E*0 ZEE'O *EÊ*0 89E*0 SE£*0 S2£*0 S*E*0 2EE*0 **E*0 9M €00*0 *00*0 £00*0 £00*0 *00*0 £00*0 £00*0 •/00*0 £00*0 NH OOS'O 655*0 9*5*0 125*0 9*5*0 095*0 925*0 855*0 0*5*0 • 234 i£2*0 *8ï*0 i02*0 161*0 6M *0 eo2*o 912*0 281*0 *6Ï*0 • Ê34 100'0 200*0 500*0 £00*0 •00*0 200*0 200*0 £00*0 900*0 113 810*0 220*0 120*0 610*0 ZIO*0 210*0 1E0*0 220*0 •/20*0 IV 898*0 £68*0 288*0 168*0 M6*0 688*0 •/i.8'0 568*0 188*0 U C- 100*0 £00*0 100*0 200*0 100*0 200*0 100*0 100*0 100*0 IS *• SN39AX0 E HOd SN0UV3 do aagnriN SS*S2 6E*82 ÍL'LZ 86*92 0V62 12*82 12*12 60*82 6SV2 • 034 s**et 0**01 69*11 10*11 S**8 •/£•11 2»*21 02*01 00*11 +E02 34 91*66 S6*86 16*86 80*001 95*66 i.2'86 51*001 £0*86 12*66 "IV101 •/0*0 *0*0 20*0 SO'O 20*0 60*0 •/0*0 90*0 20*0 0*3 iVOl ev6 2S*6 U'OI 65*6 81*6 10*01 8£*6 98*6 OSN il*0 81*0 L\'0 *t*0 81*0 Z1*0 91*0 22*0 11*0 ONN 99*/E Sl'iE S2*8E 68*9£ 10*A£ I**8E 6E*8E *2*i£ b*t'Lt * 03 4 6E*o £1*0 82*0 91*0 02*0 ET*0 01*0 IT*0 SE*0 £02X0 99*0 Bi.*0 9/.*0 01*0 E9*0 £•/•0 £1*1 8i*0 88*0 E021V ÍL'6* />*05 88*6* 2E*tS 68*15 11*6*/ 92*05 U*0S o**os 2011 •/0*0 21'0 *0*0 11*0 *0*0 60*0 90*0 •/0*0 M)*0 20 IS 6S£ 9SE *SE 1SE 8*£ S*E EVE 0*/E 8EE r» r» Pb ra ra Pb ra ra ra t 1H 3N3XOUAfJOHldO HUM 0NI1SIX3-OD S31IN3W1I 40 S3SA1VNV £2 aiavx TABLE 23 CONT. ANALYSES OF ILMENITES CO-EXISTING WITH ORTHOPYROXENE HT * RJ RJ RJ RJ RJ RJ 1860 FRe BD 362 364 365 366 367 363 D 352 1636 SI02 0.00 0.04 0.02 0.10 0.02 0.02 0.14 0.11 0.05 TI02 50.03 51.48 48.87 49.62 50.27 50.84 51.88 46.66 48.30 AL203 0.72 0.47 0.90 1.33 0.65 0.88 0.88 0.64 0.61 CR2Q3 0.19 0.33 0.45 0.26 0.30 0.30 0.38 0.45 0.01 FEO * 38.71 37.60 38.68 38.76 37.88 37.53 37.23 42.75 40.70 MNO 0.14 0.20 0.16 0.17 0.18 0.18 0.20 0.21 0.20 MGO 9.42 9.76 10.11 9.82 9.77 9.58 10.57 7.82 8.52 CAO 0.04 0.02 0.02 0.04 0.06 0.07 0.05 0. C3 0.01 TOTAL 99.25 99.90 99.21 100.10 99.13 99.40 101.33 98.67 98.4 FE203* 11.90 9.88 14.36 13.06 11.48 10.16 10.58 16.52 14.0 FEO* 28.00 28.71 25.76 27.01 27.55 28.39 27.71 27.89 28.1 NUMBER OF CATIONS FOR 3 OXYGENS ** SI 0.000 0.000 0.000 0.002 0.000 0.000 0.003 0.C03 0.001 T! 0.683 0.903 0.857 0.863 0.886 0.895 0.890 0.836 0.865 AL 0.020 0.013 0.025 0.036 0.018 0.024 0.024 0.016 0.017 CR 0.004 0.006 0.008 0.005 0.006 0.006 0.007 0.008 C.000 FE3* 0.210 0.173 0.252 0.227 0.202 0.179 0.182 0.296 0.251 FE2* 0.550 0.560 0.502 0.523 0.540 0.556 0.529 0.556 0.559 MN 0.003 0.004 0.003 0.003 0.004 0.004 0.004 0.004 0.C04 MG 0.330 0.339 0.351 0.339 0.342 0.334 0.360 0.278 0.302 CA 0.001 0.000 0.000 0.001 0.001 0.002 0.001 0.001 0.000 GK 30.2 31.6 31.B 31.1 31.5 31.3 33.6 26.3 27.2 IL 50.5 52.2 45.4 48.0 49.8 52.0 49.4 56.6 50.3 HM 19.3 16.2 22.8 20.9 18.7 16.7 17.0 15.1 22.5 MG/MG*FE 37.5 37.7 41.1 39.3 38.8 37.5 40.5 33.3 35.1 (AT.t) * TOTAL IRON AS FEO • FE203 AND FEO IS CALCULATED FROM THE ILMENITE STRUCTURAL FORMULA AB03, ASSUMING ATOMIC PROPORTION OF RZ*=R4+ *' CATION TOTAL NORMALISED IN THE COURSE OF FE3 + CALCULATION 18600 BOYO ANO NIXON 1973 FRB 352 F.R.BOVO,UNPUBLISHED BO 1636 BOYD 1971 TABLE 24 ANALYSES OF ILMENITES CO-EXISTING WITH GARNET WT X RJ RJ RJ RJ RJ RJ RJ RJ ;j 257 260 262 265 268 271 274 278 282 SI02 0.00 0.00 0.03 0.00 0.04 0.05 0.02 0.01 0.04 IIC2 51.0* 51.16 49.24 50.66 51.07 51.11 50.85 51.17 52.21 AL203 0.73 0.00 0.73 0.77 0.71 0.65 0.53 0.97 0.45 CR203 0.03 0.00 0.02 0.05 0.11 0.06 0.15 0.17 0.00 FEO * 38.72 39.67 40.71 38.71 38.59 38.71 38.3 6 37.88 37.80 MNO 0.18 0.1b 0.1B 0.17 0. 16 0.18 0.15 0.14 0.16 MGO 8.90 8. 42 7.93 a. 85 9.62 9.14 9.31 9.60 9.60 CAC 0.02 0.00 0.03 0.05 C. 04 0.04 0.04 0.03 0.05 TOTAL 99.62 99.41 98.38 99,26 100.34 99.95 99.42 99.98 100.31 FF203* 9.89 9.82 11.95 10.19 11. C9 10.24 10.46 10. 17 9.C5 FCO* 29.82 30.83 29.96 29.54 28.61 29.49 28.95 28.73 29.66 NUMBER OF CATIONS FO» 3 OXYGENS ** SI 0.000 0.000 0.001 0.000 0.001 0.001 C.000 0.000 0.001 TI 0.902 0.912 0.882 0.898 0.891 0.899 0.89 8 3.896 C.91* AL 0.020 0.000 0.020 0.021 0.019 0.018 0.015 0.027 0.012 C« 0.001 0.000 0.000 0.001 0.002 0. 001 0.OO3 0.003 0.000 FE3* 0.175 0.175 0.214 0.181 0.194 0.180 0.185 0.178 0.158 FE2* 0.586 0.611 0.596 0.583 0.555 0.577 0.569 0.559 0.577 MN 0.003 0.003 0.004 0.003 0.00? 0.003 0.003 0. C03 C.003 MG 0.312 0.298 0.282 0.311 0.333 0.319 0.326 0.333 C.333 CA 0.001 0.000 0.001 0.001 0.001 0.001 0.001 0.001 0.001 GK 29.1 27.4 2 5.8 28.9 30.8 29.6 30.2 31.1 31.2 IL 54.6 56.4 54.6 54.2 51.3 53.6 52.7 52.2 54.0 HM 16.3 16.2 19.6 16.9 17.9 16.8 17.1 16.6 14.8 Mo/MG»FE 34.7 32.8 32.1 34.8 37.5 35.6 36.4 37.3 36.6 (AT.tl * TOTAL IRON AS FEO • FE203 ANO FEO IS CALCULATED FROM THE TOTAL FE ANO FROM THF ILMENITE STRUCTURAL FORMULA AB03, ASSUMING ATOMIC PROPORTION OF R2*=K4* ** CATION TOTAL NORMALIZED IN THE COURSE OF FE3-» CALCULATION I QL TABLE 25 COMPOSITION OF MONASTERY LHERZOLITES FRB 1 (BOYD & NIXONt 1975) 1589N (BOYD f. NIXON, 1973) MT % OL EN DI GT OL EN DI GT SI02 40.5 56.3 55.2 42.9 41.11 58.12 54.67 41.86 TI02 0.03 0.10 0.15 0.48 0.01 0.05 0.27 0.09 AL203 0.06 0.92 2.09 20.8 0.02 0.80 3.28 2 0.50 CR203 0.03 0.22 0.88 3.07 0.04 0.37 2.89 5.00 FEO 8.59 5.14 3.14 6.90 6.20 3.76 1.90 5.42 MNO 0.12 0.11 0.13 0.28 0.09 0.09 0.06 0.32 MGO 50.8 35,9 19.3 21.9 52.28 36.70 15.82 22.10 CAO 0.07 1.07 18.2 4.82 0.03 0.43 17.85 5.15 NA20 0 .8 1.55 0.03 0.17 3.22 0.04 NIO 0.39 0.37 TOTAL 100.6 99.9 100.6 101.2 100.46 100.49 99.96 100.47 -a NUMBER OF CATIONS FOR N OXYGEN N 4 6 6 12 4 6 6 12 SI 0. 984 1. 943 1. 972 3. 014 0.992 1.973 1.971 2.966 TI 0. 000 0. 003 0. 004 0. 025 0.000 0.001 0.007 0.005 At 0. 002 0, 037 0. 088 1. 720 0.000 0.032 0.139 0.712 CR 0. 001 0. 006 0. 025 0. 171 0.000 0.010 0.082 0.280 FE 0. 175 0. 148 0. 094 0. 406 0.125 0.106 0.057 0.321 HN 0. 002 0. 003 0. 004 0. 017 0.001 0.003 0.002 0.019 MG 1. 842 1. 848 1. 030 2. 296 1.881 1.858 0.850 2.335 CA 0. 002 0.,03 8 0. 698 0. 363 0.000 0.016 0.689 0.391 NA 0. 012 0. 107 0. 004 0.011 0.225 0.005 NI 0. 008 0.007 MG/MG+Ffc 91.3 92.6 91.6 85.0 93.8 94.6 93.7 97.9 CA/CA>MG 0.020 4C.4 0.009 44.8 77 TABLE 26 K [MHfcRl ITE MONASTERY INCLUSION QUARRY TYPE IN OLIVINE KIMBERLITE RJ469 1870 * SI02 31.4 27.98 TI02 5.5 4.22 AL203 2.63 2.64 CR203 0.15 0.14 FEO * 13.9 11.58 MNO 0.15 0.18 MGO 25.9 26.17 CAO 8.97 9.16 NA20 0.38 0.64 K20 1.45 1.78 H20- NO 0.40 H20+ ND 7.33 P205 NO 0.94 C02 PRESENT 5.83 S NO 0.09 TOTAL 91.8 99.86 * TOTAL IRON AS FEO NO NOT OETERMINEO # FROM GURNEY AND EBRAHIM (1973) 78 TABLE 2/ ANAL YSES OF CLINOPYROXENES COEXISTING WITH ILMENITE (LITERATURE VALUES) *T % JJG JJG JJG JJG PUN R R BD 80 201 207 214 216 1859GL 1115B 1115C 1374 1634 SI02 54.30 54.34 54.50 54.49 54.3 54.41 54.42 55.19 54.8 TI02 0.45 0.42 0.3 9 0.51 0.39 0.17 0.30 0.38 0.34 AL203 2.65 2.75 2.73 2.7C 2.52 2.62 2.74 2.76 2.58 CR203 0.03 0.05 0.04 0.06 0.05 0.03 0.06 0.01 FE203 1.72 FEO * 5.46 5.46 5.60 5.57 6.23 6.36 5.18# 5.76 6.35 MNO 0.08 0.C9 0.07 0.06 0.16 0.07 0.07 0.17 0.14 MGO 17.59 17.31 17.51 18.28 17.5 16.60 18.09 17.10 17.8 CAO 17.14 17.46 17.61 16.71 16.6 17.52 16.34 17.C3 16.4 NA20 1.75 1.74 1.89 1.82 2.48 1.76 1.71 1.28 1.88 TOTAL 99.45 99.62 100.34 100.20 100.2 99.51 100.63 100.12 100.3 NUMBER OF CATIONS FOR é CXYGENi SI 1.976 1.975 1.970 1.967 1.970 1.986 1.959 1.998 1.980 TI 0.012 0.011 0.011 0.014 0.011 0.005 0.008 0.010 0.009 AL 0.114 0.118 0.116 0.115 0.108 0.113 0.116 0.118 C.110 CR O.C01 0.001 0.001 0.002 0.000 0.001 0.002 0.000 FE3 + 0.047 FE2» 0.166 0.166 0.169 0.168 0.189 0.194 0.156 0.174 0.192 MN 0.002 C*002 0.002 0.002 0.005 0.002 0.002 0.005 0.004 MG 0.954 0.938 0.943 0.983 0.949 0.903 0.971 0.922 0.959 CA 0.668 0.680 0.6 82 0.646 0.646 0.685 0.630 0.660 0.635 NA 0.123 0.123 0.132 0.127 0.175 0.125 0.119 0.090 0.132 CA 37.4 3 8.1 38.0 35.9 36.2 38.4 35.9 37.6 35.6 MC 53.4 52.6 52.6 54.7 53.2 50.7 55.3 52.5 53.7 FE 9.3 9.3 9.4 9.3 10.6 10.9 8.9 9.9 10.8 MG/MG+FE 85.2 85.0 84.8 85.4 83.4 82.3 86.2 84.1 83.3 CA/CA+MG 41.2 42.0 42.0 39.7 40.5 43.1 39.4 41.7 39.8 * TOTAL IRON AS FEO § DETERMINED CHEMICALLY JJG 201-216 MONASTERY GURNEY ET.AL. 1973 f>HN 1859 GL/1 MONASTERY BOYD AND NIXON 1975 R1115 B AND C MONASTERY RINGWOOD ANO LOVERING 1969 BO 2374 MONASTERY DAWSON AND RE1D 1970 BO 1634,BD 1635 MONASTERY BOYD 1971 BO 1971 UINTJESBEPG BOYD AND DAMSON 1972 KEN 1 RILEY COUNTY,KENTUCKY,U.S.A. GUFNEY ET.AL. 1973 1L 527 MIR PIPE,VAKUTIA ILYUPIN ET.AL. 1973 IL 528 MIR PIPE,YAKUTIA ILYUPIN ET.AL. 1973 79 TABLE 27 CONT. ANALYSES OF CLINOPYROXENES COEXISTING WITH ILMENITE (LITERATURE VALUES) WT * BD BD KEN IL IL IL 1635 L971 1 527 528 528 SI02 54.4 54.9 55.15 53.80 55.1 55.9 TI02 0.43 0.6 0.50 0.50 0.09 0.09 AL203 2.60 3.1 2.52 1.67 2.26 5.25 CR2U3 0.03 0.05 0.32 0. 32 0.03 0.04 FE203 3.29 FEO 6.16 5.8 4.93 4.02 5.88 5.78 MNO 0.14 0.2 0.19 0.17 MGO 17.9 18.1 18.54 17.73 17.4 16.9 CAO 16.4 16.1 17.12 16.29 15.1 14.6 NA20 1.80 1.6 1.42 1.70 1.5 1.5 TOTAL 99.9 100.4 100.69 99.49 97.36 100.06 NUMBER OF CATIONS FOR 6 OXYGENS SI 1.974 2.032 1.975 1.963 2.030 1.992 TI 0.012 0.016 0.013 0.014 0.002 0.002 AL 0.111 0.131 0. 1C6 0.072 0.098 0.220 CR 0.001 0.001 0.009 0.009 0.001 0.001 FS3* 0.090 FE2* 0.187 0.174 0.148 0. 113 0.181 0.172 MN 0.004 0.006 0.006 0.005 MG 0.968 0.969 0.990 0.964 0.955 0.897 CA 0.6 38 0.620 0.657 0.637 0.596 0.557 NA 0.127 0.111 0.099 0. 120 0.107 0.104 CA 35.6 35.2 3 6.6 37.2 34.4 34.2 MG 54.0 55.0 55.2 56.2 55.1 55.2 FF 10.4 9.9 8.2 6.6 10.4 10.6 MG/MG*FE 83.8 84.8 87.0 89.5 84.1 83.9 CA/CA»MG 39.7 39.0 39.9 39.8 38.4 38. 3 * TOTAL IRON AS FEO * DETERMINED CHEMICALLY JJG 201-216 MONASTERY GURNEY ET.AL. 1973 PHN 1859 GL/1 MONASTERY ROYO AND NIXON 1975 R1115 8 AND C MONASTERY RINGWOOO AND LOVERING 1969 BD 2374 MONASTERY DAWSON AND REID 1970 BD 1634,BD 1635 MONASTERY BOYD 1971 BO 1971 U1NTJFSUEP0 BOYD ANC DAWSON 1972 KEN 1 RILEY COUNT Y ,KENTUCKY ,IJ. S. A. GURNf Y ET.AL. 19H IL 527 M1P PIPt,YAKUTIA ILYUPJN ET.AL. 1973 IL 528 MIR PIPF,YAKUTIA ILYUPIN ET.AL. 1973 so rAfiLt 2i> ANALYSE", Or MOIMASï' il.Mf !\'iTfcC TO EXISTING WITH CtJNOPYROXENE iLiTEHAIURt VALULS) WT % JJG JJG JJG JJG PHN S R BO 201 207 214 216 1859GL 11159 1115C 1374 1635 S102 0.03 0.08 0.09 0.08 0.10 0.04 0.04 0.C4 C. 11 TI02 50.44 49.96 50.11 51.46 49.5 48.27 48.77 50.22 49.3 AL203 0.53 0.51 0.53 0.55 0.25 0.56 0.5C 0.55 0.61 CR203 0.14 0.13 0.13 0.22 0.05 0.G5 0.08 0.07 NO FEP * 37. 74 38.04 38.63 36.32 38.8 37.86 37.3? 37.65 38.7 MNU 0.22 0.23 0.24 0.22 0.23 0.23 0.2 3 0.23 C.20 MGO 9.20 9.26 8.50 9.43 9.16 10.65 11.82 8.21 9.64 CAO 0.10 0.09 0.12 0.09 0.03 0.08 O.Oi» 0.02 TOTAL 99.4 99.4 99.3 99.1 99.4 97.73 99.8 97.C7 98.6 FE203 10.04 10.97 10.03 7.89 12.00 15.26 9.63# 8.32 12.06 FEO 28.70 28.16 29.61 29.22 28.03 24.13 28.65 30.16 27.05 NUMBER OF CATIONS FOR 3 OXYGENS ** SI O.0O2 0.002 0.002 0.002 0.002 0.001 0.001 O.0C1 0.002 TI 0.900 0.892 0.899 0.918 0.886 0.856 0.848 0.915 0.874 AL 0.015 0,014 0.015 0.015 0.007 0.016 0.014 0.016 0.017 CR 0.003 0.002 0.002 0.004 0.001 0. 001 0.001 0.001 NO FE3* 0.179 0.196 0.180 0.141 0.214 0.270 0.168 0.152 C.230 FE2* 0.569 0.559 0.591 0.580 0.558 0.476 0.554 0.611 0.533 MN 0.004 0.005 0.005 0.004 0.005 0.004 0.004 0. 005 C.004 MG 0.32 5 0.328 0.302 0.333 0.325 0.374 0.407 0.300 0.339 CA 0.002 0.002 0.003 0.002 0.001 0.002 0.002 0.000 0.000 GK 30.3 30.3 28.2 31.6 29.6 33.4 36.0 28.2 30.7 IL 53.0 51.6 55.0 55.0 50.9 42.5 49.1 57.5 48.4 HM 16.7 18.1 16.8 13.4 19.5 24.1 14.9 14.» 20.9 MG/MG*FE 36.4 37.0 33.8 36.5 36.8 44.0 42.4 32.9 38. 9 * TOTAL IRON AS FEO * FE203 ANO FEO IS CALCULA ED FROM THE TOTAL FE AND FROM THE ILHENITE STRUCTURAL FORMULA AB03, ASSUMING ATOMIC PROPORTION OF R2»*R4« •* CATION TOTAL NORMALIZED IN TFft COURSE OF FE3» CALCULATION * DETERMINED CHEMICALLY JJG 201-216 GURNEY ET.AL. 1973 PHN 1859 GL/1 BOYO AND NIXON 1975 K111S B AND C RING WOOD AND LOVERING 1970 BD 1374 CANSON ANO REIO 1970 1635 BOYD 1971 81 TABLE 28 CON i. ANALYSES OF II MtDI 1 F>; CO I TltViG WITH CI INOPYROXENE FROM OTHER OCCURRENCES (LITERATURE VALUES) MT % BD KEN A IL IL IL IL 1635 1971 1 265 527 528 528 52e SI02 0.11 0. 1 0.08 0.16 1.40 0.1 0.1 0.1 TI02 49.3 52.4 50.92 48.52 50.10 49.3 49.9 49.8 AL203 0.61 0.7 1.08 0.44 0.85 0.17 0.15 0.17 CR203 NO 0.2 1.24 0.24 0.28 0.15 0.15 0.16 FEO * 38.7 35.5 29.8 39.21 36.02 40.2 41.15 40.8 M^O 0.20 0.2 0.20 0.21 0.28 0.1 0.1 0.1 MGO 9.64 10.7 15.30 9.20 9.74 8.89 8.62 8.92 CAO 0.02 0.05 0.07 0.36 0.05 0.05 0.05 TOTAL 98.6 99.8 98.7 98.34 98.67 99.0 100.2 100.1 FE203 12.06 8.45 12. 76 13.85 7.71 13.07 12.99 13.30 FEO 27.05 27.90 18.32 26.75 29.08 28.44 29.46 28.83 NUMBER OF CATIONS FOR 3 OXYGENS •* SI 0.0O2 0.002 0.002 0.004 0.033 0.002 0.002 0.002 TI 0.874 0.913 0.864 0.864 0.885 0.877 C.680 0.877 AL 0.017 O.019 0.029 0.012 0.024 0.005 0.004 0.005 CR ND O.0O4 0.022 0.004 0.005 0.003 0.003 0.003 FE3* 0.230 0.147 0.217 0.247 0.136 0.2 33 0.229 0.234 FE2* 0.533 0.540 0.346 0.530 0.571 0.563 0.577 0.565 MN 0.004 0.004 0.004 0.004 0.006 0.002 0.002 0.002 MG 0.339 0.369 0.515 0.325 C.341 0.314 0.301 0.3U CA 0.000 O.0O1 0.002 0.009 0.001 0.001 0.001 GK 30.7 35.0 4 7.8 29.5 32.5 28.3 27.2 28.0 IL 48.4 51.1 32.1 48.1 54.5 50.7 52.1 50.9 HM 20.9 13.9 20.1 22.4 13. 0 21.0 20.7 21.1 MG/MG*FE 38.9 40.6 59.8 38.0 37.4 35.8 34.3 35.5 * TOTAL IROfc AS FEO • FE203 AND FEO IS CALCULATED FROM THE TOTAL FE AND FROM THE ILMENITE STRUCTURAL FORMJ'.A AB03, ASSUMING ATOMIC PROPORTION OF R2*»R4* •* CATION TOTAL NORMALIZED IN THE COURSE OF FE3+ CALCULATION BD 1"71 UlNTJEJBERG BOYD AND DAWSON 1972 KEfil RILEY COUNTY,KENTUCKY,U.S.A. GURNEV ET.AL. 1973 A 265 MIR KIMBERLITE,YAKUTIA ILYUPIN ET.AL. 1973 IL 527 MIR KIMBERLITE,rAKUTIA ILYUPIN ET.AL. 1973 IL 528 MIR KIMBERLITE,YAKUTIA ILVUPIN ET.AL. 1973