Gold-bearing rocks of Mangalur greenstone belt, Gulbarga District, Karnataka

Transcription

1 Proc. Imhan Acad. Sci. (Earth Planet. Sci.), Vol. 96, No 2, September 1987, pp. 11) Printed in India. Gold-bearing rocks of Mangalur greenstone belt, Gulbarga District, Karnataka S G TENGINKAI and A G UGARKAR Department of Studies in Geology, Karnatak University, Dharwad , India MS received 12 December 1985; revised 20 August 1986 Abstract. The Mangalur greenstone belt of Dharwar Craton, South India, is an Archaean schist belt dominated by metavolcanic rocks. The gold mineralization occurs within the metavolcanics and the fabric, mineralogy and geochemistry of these host rocks indicate that they were tholeiitic basalts regionally metamorphosed under medium to low-grade greenschist facies. The basic metavolcanic rocks occur as tholeiitic metabasalts and amphibolites. The rocks have undergone some fractionation and appear to be derived from melts generated by 10 to 25% melting of the mantle at depths 30 to 35 km around temperature 1200~ and pressure 12 kb. The source of gold is mainly in the basalts and not in the surrounding granites. Keywords. Gold-quartz veins; metavolcanic rocks; tholeiites; geochemistry; petrogenesis; Mangalur greenstone belt. I. Introduction Gold mineralization of gold-quartz vein type in India is essentially confined to the eastern gold field province of the Dharwar Craton. This province includes the region lying to'the east of the N-S trending band of younger granites. A feature common to all greenstone belts falling within this province is the gold mineralization associated with the metavolcanics. Since these belts are largely made up of steeply inclined mafic volcanic rocks, they have been compared with the classical greenstone belts of South Africa, Canada and Western Australia (Radhakrishna 1983). There are four gold-bearing Archaean greenstone belts in this province namely, Kolar, Ramagiri, Hutti and Mangalur, the last one of which constitutes the subject of this paper (figure 1). The Mangalur greenstone belt (lat. 16o30 ' and 16o44 ' and long. 76~ '' and 76o40 ' ) has geological characteristics akin to the above gold deposits. The difference, however, lies in the size of the belt and in the mineralization characteristics. Bruce Foote (1875) first reported the occurrence of hornblende and micaceous schists of this belt as forming the northern continuation of Hutti-Maski belt in the hills of NW of Shorapur. Mahadevan and Krishnamurthy (1945) reported L611ingite in tile pegmatite vein exposed near Mavinmatti. Mahadevan (1945) described ripple marks in certain rocks of Mangalur belt ~and arrived at the conclusion that the Dharwars were originally sedimentary. The Mangalur gold mine is located at Mukangavi village. Exploration by the Geological Survey of India and development of the mines by Hutti Gold Mines during recent years have resulted.in establishing a sizable gold ore reserve of 70,000 metric tonnes of an average grade of 3 g/ton, and a strong plea was made by the 103

2 104 S G Tenginkai and A G Ugarkar Group tes Ldurga Group I~u dan Group sular Gneiss ~earing volcanic belts ~ockites ms Figure 1. Geological map of Eastern Gold Fields Province of the Dharwar Craton (after Ananta iyer and Vasudev 1979). Geological Survey of India for reopening the Mangalur Gold Mine (Ramachandra Rao 1980). The mine was reopened in 1981 and developed by the Hutti Gold Mines Co Ltd. Apart from this, there exists no literature on the detailed geological settin~ of the deposit, mineralogy, geochemistry, controls of mineralization and genetic aspects of Mangalur greenstone belt. Ugarkar (1986) opined that there exists a geochemical similarity of the Archaean gold-bearing metabasic volcanic rocks of Mangalur with the oceanic tholeiites generated at marginal basin tectonic environment. The present paper describes preliminary geology and geochemistry of the gold-bearing host rocks of this belt. 2. Geology of the Mangalur greenstone belt The Mangalur greenstone belt is composed of heterogeneous assemblage of metavolcanic and metasedimentary rocks. The metavolcanic rocks are predomi-

3 Gold-bearing rocks of Mangalur 105 nantly represented by metabasalts and amphibolites. These rocks are exposed in the western part of the belt. Terrigenous metasedimentaries are exposed in the eastern part of the belt. The general strike of the formations varies from N-S to N 20~ with a westerly dip of 65 to 75 ~ The rock formations are tightly folded into isoclinal folds with axial planes dipping west. In addition, shear zones parallel to the strike of foliation are observed near Mukangavi and Mangalur villages, and in the Temple hill A 449. Migmatites are the oldest lithounits of the area. Although there are no direct field evidences to infer the migmatites to form the basement, the presence of a conglomerate horizon within the belt, with well-rounded pebbles of light-coloured quartzite that succeeds them, suggests a pre-existing sialic crust. The schistose rocks of Mangalur belt are intruded by granites, pegmatites, quartz veins and lastly by dolerite dykes (figure 2). The gold-quartz veins and lenses occur within the * * I~\ 4-4- ~ a GUOIF 4- "0" 4"1 ~ X GNUR 4" + 4- '.L,. # I t t-,,#- 4-,I,, P~NAHAL L ~,",~'e,i ',\\ ",4. % 9 9 "~z~ ~" ~" + + KARAD~.a -----to It, , -I- -I- ",H ~] Doler te 4- Granite AVL I J Metavolcanics [T~ Metasediments ~" ~CI Conglomerates Migmatites [~] Strike and dip Old work ings + '4",i! \ ~k~.cj~, dr l SOUTH,4- NDIA i..,, i\\~.~ + I j, \\l,, "t "4..I #, o 2000 i l 4- Mtrs ~ + ~- + 4, 4-,4, , ~! tadah ~,HALU 4- + Ir.~ 9 "r t- $horapur IGGANDODDI +,p ,R. 4- "P 4..~ 't- 4- "il- L \ AIM "P + ~, A.L Figure 2. Regional geological map of the Mangalur greenstone belt.

4 106 S G Tenginkai and A G Ugarkar narrow shear zones in the metamorphosed basic volcanic rocks. The volcanic suite shows well-developed pillow structures in the central and southern portions of the belt (figure 3). 3. Petrography and mineralization Mangalur gold-bearing rocks exhibit variation in grain size from medium to fine. The thin section studies reveal that the massive rocks exhibit slender porphyroblasts of actinolite/tremolite without any apparent alignment whereas in schistose variety, they show parallel alignment exhibiting segregation banding. Plagioclase occurs as slender, tabular crystals exhibiting polysynthetic twinning and saussuritization. Actinolite/tremolite are set in a ground mass of chlorite. Epidote and zoisite are the alteration products of earlier pyroxenes. Relic euhedral pyroxenes are seen occasionally. Hornblende grains sometimes exhibit preferred orientation in coarse-grained amphibolites. The host metabasic volcanic rocks in the shear zones are chloritized, biotitized and carbonitized and can be called chlorite-biotite schists and biotite-chlorite schists. In Mangalur deposit, gold occurs only in native state. Gold mineralization is represented by the presence of disseminated streaks and grains of sulphides in the schistose amphibolites associated with thin quartz veins parallel to the schistosity and the abundant occurrence of biotite, chlorite and influx of carbonates (ankerite + calcite) indicating wall-rock alterations suggests the broad mechanism underlying gold mineralization in the area. The dominated sulphide phase is pyrrhotite-pyrite assemblage with little amount of arsenopyrite, chalcopyrite and sphalerite. Figure 3. Pillow structure in Mangalur metavolcanic suite.

5 Gold-bearing rocks of Mangalur Sampling and analytical techniques For our present study, samples have been collected from the ore-zones as well as least altered zones. Twentyfour least altered metavolcanic rocks have been analysed chemically (table 1). While collecting these samples, care was taken to sample rocks that are free from quartz, calcite and epidote veins, and intense chloritization and biotitization. These samples were collected from the surface outcrops and drilled cores. For petrogenetic consideration, the analyses of only these 24 samples are plotted on carefully chosen discriminant diagrams (figures 4 to 8). Five samples collected across the shear zone representing rich-ore to non-ore bodies in a cross-cut at 370' level have been analysed chemically (table 2). Pulverized (-300 mesh) and homogenized samples were analysed for major and trace elements by using an atomic absorption spectrophotometer (Schimadzu, AA:II~ I, Japan). Standardization was based on USGS natural rock standards, W-l, DR-N, AGV-1, PCC-1 and BCR-1 (Flanagan 1973). Gold contents were determined by fire assay techniques of Schuler (1971). 5. Geochemistry of metavolcanic rocks Analyses of Mangalur metavolcanic rocks (table 1) exhibit variations of SIO2( %) and K20 ( %), probably due to the alteration of these rocks. These rocks have high FeO (av %), low TiO2 (av. 0.95%), Al203 (av %) contents and low M (Mg/Mg + Fe) values (av. 0.30) when compared to MORB (FeO = 10.00%, TiO2 =-1-50% Al20 3 = 6.00% and M = 0.44) quoted by Condie (1976). FeO/MgO ratios of Mangalur metavolcanic rocks (av. 2-12) are higher than MORB (1.33) reflecting their iron-rich chemistry. Cr content (av. 189 ppm) is comparable and Ni content (av. 163 ppm) is slightly higher than MORB (Cr = 300 ppm and Ni = 100 ppm). Rb content (av. 4.5 ppm) is slightly less whereas Sr content (av. 127 ppm) is comparable to MORB (Rb = 10 ppm and Sr = 135 ppm). The K/Rb ratio (308) is less and Rb/Sr ratio (0-046) is more than MORB (K/Rb = 1160 and Rb/Sr = 0.007). 6. Petrogenetic discussion Mafic and ultramafic extrusive rocks of Archaean greenstone belts are generally tholeiitic and komatiitic (Rajamani et al 1985). From the geochemical criteria available for discriminating tholeiitic and komatiitic rocks, the gold-bearing metavolcanic rocks (least altered) of the Mangalur greenstone belt would be considered as tholeiite. Mangalur metavolcanic rocks are characterized by typical quartz/or hypersthenenormative mineralogy and total absence of normative olivine (Ugarkar 1986). The MgO content of metavolcanic rocks varies from 4.42 to 7.46% and CaO/AI203 ratios < 0.9, which would suggest a tholeiitic affinity. Similar opinions were expressed by Glikson (1983) for the Archaean tholeiites. On CaO-AI203-MgO ternary diagram (figure 4) of Viljoen and Viljoen (1969) and Condie (1981), all the metavolcanic rocks plot in the tholeiitic field.

6 108 S G Tenginkai and A G Ugarkar ox,,0 tt,j 00 "-d,.i ox ~o o~

7 Gold-bearing rocks of Mangalur 109 I ~- o~ Y.Z~ u e~

8 110 S G Tenginkai and A G Ugarkar Table 2. Major and trace element data for rich-ore to non-ore bodies across shear zone Si A l TiO FeO(t) MgO CaO NazO K MnO LOI Total Au Tr Ni Co Cu Cr Zr Sr Rb Samples 1 to 5 were collected from the rich-ore to non-ore bodies. MgO / I I i I i I I i I CaO o- Man~11ur Metavolcanic rc~k$ A1203 Figure 4. CaO-MgO-AI203 ternary diagram (after Viljoen and Viljoen 1969 and Condie 1981). PK refers to Barberton peridotitic komatiites; BK to basaltic komatiites, G to Geluk type, bd to Badplass type and bb to Barberton type; and TH refers to tholeiites. Komatiite-tholeiite trend is defined by ultramafic and mafic rocks of Archaean greenstone belts. Note the Mangalur metavolcanic rocks showing tholeiitic affinity.

9 Gold-bearing rocks of Mangalur 111 Ringwood (1975) has shown that quartz or olivine tholeiites are generated from the basaltic magma formed by a high degree of partial melting of the mantle under low pressure at shallow depths. The quartz-normative nature of the metavolcanic rocks of the area might indicate their formation around temperature 1200~ and pressure 12 kb, as suggested by Ewart (1981) for similar rocks of Central Queensland, Australia. Several workers have utilized the theta (0) index of Sugimura (1968) to estimate the depth of magma genesis (Please refer Naqvi et al 1974). The 0 values of the Mangalur metavolcanic rocks range from 30 to 35 with and average of 34, and suggest that the depth of magma generation was about 30 to 35 km. The quartz tholeiitic nature of the Mangalur metavolcanic rocks and their geoizhemistry would suggest their derivation from a magma generated under the above conditions. The low M values (av. 0.30) could have been generated through the fractional crystallization of Mg-rich phases. Wilkinson (1981) suggested that basaltic melts with low M values relate to the degree of partial melting and to mantle heterogeneity. Hanson and L angmuir (1978) developed a model based on major elements, particularly MgO and FeO (figure 5), to obtain such quantitative petrogenetic information for mafic and ultramafic rocks. All the samples of Mangalur metavolcanic rocks plot well below the melt fields (0% melting line) in the figure at temperatures < 1300~ suggesting that they do not represent primary melts from a pyrolite mantle. From the plot it is clear that these rocks have been derived by 10-25% melting of the mantle. These conclusions are substantiated for the Mangalur metavolcanic rocks on the MgO-Ni diagram (figure 6) of Hanson and Langmuir (1978), as they plot near the field of primary melts, and on the (Mg) % vs (Fe) % diagram (figure 7) of Ford et al (1983) wherein they fall well below the field of melt. The total range in (Fe) % of Mangalur metavolcanic rocks is more than 4%. If the mantle sources were homogeneous, the large range in (Fe) may be due to ranges in the extent of melting and depths of melting as suggested by Rajamani et al (1985) for Kolar tholeiites. Samples with the highest incompatible element abundances (Zr = 68 ppm), i.e. those formed at lowest extents of melting, have both higher and lower (Fe) contents. This could result in a homogeneous source only as a result of higher and lower melting pressures respectively. For example, if the parent magmas of samples 8 and 18 were generated at similar depths and temperatures and had similar differentiation histories, then sample 8 with cation % '(Fe) would represent a magma generated by a lower extent of melting than would sample 18 with 11.45% (Fe). If the mantle source had been heterogeneous, some variation in the FeO abundances of the rocks of Mangalur could be attributed to variations in the FeO/MgO ratios of their source region. Due to the apparent large extent of fractionation involving olivine, pyroxene and plagioclase, it may be difficult to evaluate the relative importance of extents of melting, temperatures of melting and FeO/MgO ratios of the source regions in causing observed spread in the FeO contents of these rocks. Zr and Ni abundances are plotted in the Zr vs Ni diagram (figure 8). Using the criteria suggested by Rajamani et al (1985) to evaluate the melting, the plots of Mangalur metavolcanic rocks in the diagram indicate that these rocks could be derived by 10 to 30% melting of a mantle with 7.8 ppm Zr and 2000 ppm Ni.

10 112 S G Tenginkai and A G Ugarkar , RESIDUE PYROLITE OLIVINE 164-4" o o 30 1,5o oo~ ~"r 5Kb q9 o-mangalur Metavolcanic rocks OL FeO % Figure 5. Plot of MgO against FeO (cation mole%) abundances in Mangalur metavolcanic rocks. Melt and residue fields are contoured for temperature and extents of melting of pyrolite (38.9 wt% MgO and 7.6 wt% FeO) at 1 atm. (Hanson and Langmuir 1978). The two curves with tics indicate the liquid line of descent for fractional crystallization of olivine. Each tic represents 5% fractionation from the previous tic. Mantle solid at 5, 20, 35 and 50 kb are those given by Langmuir and Hanson (1980). The plots of Mangalur metavolcanic rocks indicate that these rocks have been derived by 10-25% melting of the mantle at about 10 kb. 7. Metamorphism Actinolite/tremolite, epidote, plagioclase, chlorite, biotites, sericite, quartz and carbonate are the typical minerals found in the basic igneous rocks which have been metamorphosed under greenschist facies of regional metamorphism (Deer et al 1962). Typically, the gold-bearing rocks of Mangalur are devoid of either the traces of olivine or its alteration products and hence they can be very well compared with the Karroo lavas which are known to be olivine free. The authors feel that the pyroxenes and plagioclases of the volcanic rock of basaltic character have been broken down to yield actinolite/tremolite, chlorite, biotite and epidote under greenschist facies to lower amphibolite facies conditions of metamorphism. All the analysed rocks contain modal quartz whose percentage varies from 7 to 23. In spite of this silica percentage in these rocks decreases towards the quartz veins suggesting

11 Gold-bearing rocks of Mangalur In %' 9 RE~DI.JE. ~,4:)_c~.,# E 5o 15s4 / / 9 MELT FIELDS [~]1 arm 20 / ff130~.-u...,,.. ~. "--Mangalur I 0 P]10~ Metavolcanic rocks 1000" O t I I Ni ppm Figure 6. Ni-MgO diagram for batch melting of a pyrolite mantle with 1800 ppm Ni (after Hanson and Langmuir 1978). Fields for melting at 1 arm. and 30 kb are shown. Curves for fractional crystallization of olivine at 1 atm. are shown with marks at intervals of 5% fractional crystallization of olivini~. The residue and melt fields are contoured for temperature and fractions of batch melting. The plots of Mangalur metavoicanic rocks do not represent primary melts from a pyrolite mantle. 60 o- Mangalur Metavolcanic rocks 50 o 40 SOkb Z 2O 10 1~SKb / I arm 4 ~ 10~ o, o~ ol V ~ o* ,2,B [Fe] ~ Figure 7. Plot of (Mg) % against (Fe) % (cation mole%) for, the Mangalur metavolcanic rocks after Ford et al (1983). Three melt fields are shown for melting of pyrolite (38.9 wt MgO and 7.6 wt% FeO) with isotherms at different pressures. On the 0% melt line for each melt field the square symbol is the estimated location of the solidus for melting of an hydrous mantle (Langmuir and Honson 1980). The arrows from the square symbols labelled A, B and C are adiabatic paths of melting starting at 50 kb, for mantles with 38.9 wt.% MgO and 7.6, 9.0 and 10.2 wt.% FeO respectively.

12 114 S G Tenginkai and A G Ugarkar 160 II Metavolcanic rocks ~ 100 o. ~ 8O 60 IF" 4O 20 0! I 100 1,000 10pO0 Ni pprn Figure 8. Plot of Zr against Ni abundances in Mangalur metavolcanic rocks. Curves I and II are calculated batch melting curves at 1850~ 50 kb and 1575~ 25 kb respectively, and are marked with percentages of melting. Curves I!I and IV refer to olivine fractionation trends at 1 arm. with tics marking increments of 5% olivine fraction from the previous tic (Rajamani et al 1985). Mantle source is assumed to have 7-8 ppm Zr and 2000 ppm Ni (Taylor and Mclennan 1981). Zr is assumed to be incompatible. the formation of quartz veins from the silica released during the breakdown of pre-existing minerals. Since quartz veins are found occupying the fractures and schistosity planes, it is suggested that the silica released during~metamorphism moved towards low pressure sites and formed veins and lenses. 8. Origin and enrichment of gold The origin of gold in gold-quartz vein type deposits has been a long-standing question. The Mangalur deposit occurs in the schist belt, which is surrounded by granites. This setting would suggest that the gold deposit is of hydrothermal origin and that the solutions had their source in the granite intrusions. Geological relationship between the metavolcanic rocks and granites indicates that these granites have invaded. It seems possible, therefore, that the intrusion of granite plutons has indirectly played an important role in the concentration of gold. The gold content of a number of various rock types originating from granite-greenstone terraines.of the Kaapvaal and the Rhodesian Cratons quoted by Meyer and Saager (1985), indicate that volcanic rocks (Komatiitic and tholeiitic) contain gold ranging from 0.1 to 372 ppb and granitic rocks of the basement from 0-3 to 7.8 ppb. Gold contents of least altered basic metavolcanic rocks of the nearby Hutti greenstone belt quoted by Vasudev (1980) range between 8 and 56 ppb. With the available facilities at the disposal of the authors, it was not possible to analyse

13 Gold-bearing rocks of Mangalur 115 gold contents (in ppb) of the least altered metavolcanic rocks of Mangalur. However, the gold contents of Hutti metabasic volcanic rocks mentioned above are considered for the least altered metavolcanic rocks of Mangalur as background values for the present purpose, keeping in view the similarities in these two belts (Ugarkar 1986). Chemical changes of major elements are characterized by an appreciable gain of K20 and volatile contents (S + LOI) and loss of Na20 and SiO2 towards the gold-quartz veins i.e. from non-ore to rich-ore bodies (table 2). Many of the elements like Au, Cu, Zr, Co and Ni show gradual enrichment towards the gold-quartz veins in the shear zones. Mineralogical and geochemical studies of wall-rock alterations of Mangalur have shown that the gold and other gangue elements, initially present in the basic country rocks, were mobilized by metamorphically derived hydrothermal solutions and concentrated in a suitable tectonic structures and chemical traps during metamorphic overprinting. Similar opinions were expressed earlier for the gold-quartz type deposits elsewhere in the world (Wanless et al 1960, Boyle 1961, 1979; Kerrich and Fyfe 1981; Saager et al 1982; Fyfe and Kerrich 1984; Bernasconi 1985; Phillips 1986; Meyer and Saager 1985). A number of papers followed dealing with the relation between gold mineralization and volcanic rocks; many authors concede that the volcanic locks are the sources of gold in the greenstone belts and that the intrusive granites did play an important role in producing the heat energy requirement and structural environments necessary for the migration and concentration of gold to form the gold-quartz vein deposits (Anhauesser et al 1975; Hutchinson 1976; Keays and Scott 1976; Kwong and Crocket 1978; Fryer et a11979; Boyle I979; Kerrich and Fryer 1981; Fyfe and Kerrich I984; Saager and Meyer 1984; Phillips 1986; Meyer and Saager 1985). The chemical and mineralogical rearrangement associated with gold-quartz mineralization in the Mangalur belt has resulted in end products that are apparently similar to the products of magmatic hydrothermal activities, and the features like geological setting, shear zones and wall-rock alterations viz chloritization and biotitization are suggestive of hydrothermal deposits and a thousand fold concentration (in ppm) in the shear zones compared to the background values in the metavolcanic rocks (in ppb) compel the authors to doubt whether the hydrothermal solutions of magmatic origin also, though not mainly atleast partially, have taken part in contributing the gold concentrations in the Mangalur greenstone belt. 9. Conclusion Gold mineralization in the Mangalur greenstone belt occurs within the metavolcanic rocks which were tholeiitic basalts regionally metamorphosed under medium to low-grade greenschist facies. These rocks are characterized by the presence of pillow structures and relic pyroxenes indicating their earlier basaltic nature. From the petrogenetic discussion, it seems that the metavolcanic rocks of Mangalur have undergone fractionation and appear to be derived from melts generated by 10 to 25% melting of the mantle at shallow depths (30 to 35 km) around temperature 1200~ pressure 12 kb.

14 116 S G Tenginkai and A G Ugarkar The main source of gold is found in the basic metavolcanic rocks. In competent basic volcanic rocks, structural deformation might have led to the development of shear zones which acted as links for gold and other elements transported by migrating metamorphically secreted hydrothermal solutions. It is reasonable to assume that the magmatic hydrothermal solutions might have also taken part, atleast partially, in contributing the gold concentrations in the Mangalur greenstone belt, in addition to the major basaltic source. Acknowledgements The authors express their sincere thanks to the authorities of Hutti Gold Mines Co. Ltd., for all the facilities and help extended by providing the gold-bearing ore specimens for study. The authors are specially thankful to Dr V N Vasudev (Mines and Geology Department, Bangalore) and C Chakrabarthi (Geological Survey of India, Bangalore) for useful discussion and suggestions. One of the authors (AGU) thanks the Karnatak University authorities for financial assistance towards his Ph.D. programme. References Ananta lyer G V and Vasudev V N 1979 Geochemistry of the Archaean metavolcanics of Kolar and Hutti Gold Fields, Karnataka, India; J. Geol.Soc. India Anhauesser C R, Fritz K, Fyfe W S and Gill R C O 1975 Gold in primitive Archaean volcanics; Chem. Geol Bernasconi A 1985 Archaean gold mineralization in Central Eastern Brazil: a review; Miner. Deposita Boyle R W 1961 The geology, geochemistry and origin of the gold deposits of the Yellowknife district; Geol. Surv. Can. Mere Boyle R W 1979 The geochemistry of gold and its deposits; Geol. Surv. Can. Bull Bruce Foote R 1875 Geology of Southern Maharatta country; Geol. Soc. lnd~ Mem. XII pt. 1 Condie K C 1976 Plate tectonics and crustal evolution; (New York: Pergamon Press) Condie K C 1981 Archaean greenstone belts; Developments in Precambrian geology (Amsterdam: Elsevier) vol. 3, pp Deer W A, Howie R A and Zussman J 1962 Rock-forming minerals (London: Longman) vol. 5 pp Ewart A 1981 Petrochemical aspects of the tertiary anorogenic volcanism of Southern and Central Queensland, Australia. In: Deccan volcanism and related basalt provinces in other parts of the world (eds) K V Subba Rao and R N Sukheswala Geol. Soc. India Mem Flanagan F J 1973 Values for international geochemical reference samples; Geochim. Cosmochim. Acta Ford C E, Russel D G, Craven J A and Fisk M R 1983 Olivine-liquid equilibria: temperature, pressure and composition dependence of the crystal/liquid partition coefficients for Mg, Fe 2+, Ca and Mn; J. Petrol Fryer B J, Kerrich R, Hutchinson R W, Peirce M G and Rogers D S 1979 Archaean precious-metal hydrothermal system, Dome Mine, Abitibi Greenstone Belt. I. Patterns of alteration and metal distribution; Can. J. Earth Sci i-439 Fyfe W S and Kerrich R 1984 Gold: Natural concentration processes. In Gold 82; The geology, geochemistry and genesis of gold deposits (ed) R P Forster Geol. Soc. Zimbabwe Sp. Pub. 1 (Rotterdam: Balkema) Glikson A Y 1983 Geochemistry of Archaean tholeiitic basalt and High-Mg to peridotite komatiite suites, with petrogenetic implications in Precambrians of South India (eds) S M Naqvi and J J W Rogers; Geol. Soc. India Mere

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