Informatics Publishing Limited

T. C. Devaraju ¹, R. H. Sawkar ², R. P. Viljoen ³, T. L. Sudhakara ², M. G. Omkesh Murthy ², S. Vijaya Kumar ², R. G. Vijaya Vikram ²

Affiliations
1 Rajamangala', Saptapur, Haliyal Road, Dharwad - 580 001, IN
2 Ramgad Minerals and Mining Pvt. Ltd., Baldota Enclave, Hospet - 583 203, IN
3 School of Geosciences, University of Witwatersrand, Johannesburg, ZA

Abstract

The ultramafic-mafic rocks of the Archaean Holenarasipur greenstone belts of the western Dharwar craton in southern India has been explored for PGE and base metal mineralization. This initiative was prompted by the overall favourable geological setting and the presence of anomalies of Pt (10-27 ppb) and Pd (8-21 ppb) in several of the stream sediment samples collected from different parts of the belt. The exploration programme consisted of field examination and analysis of over 276 samples collected from a range of mafic-ultramafic rocks in four main exploration blocks of the belt viz. Yedegondanahalli, Bantaratalalu, Yenneholeranganabetta and Bettadasatenahalli. The investigation has revealed weak mineralization with 10 to 111 ppb Pt, 16 to 166 ppb Pd and 40 to 277 ppb of (Pt+Pd). Anomalies were located in serpentinite, amphibolite and sill/dyke-like bodies of hornblendite. Two small patches of sulphide mineralisation located in the belt, in the Yedegondanahalli and Yenneholeranganabetta blocks, are Cu dominated (>1.0 wt% Cu) and analyze up to 0.3 wt% Ni, 0.09 wt% Co, 40 ppm Ag and 0.5 ppm Au.

Keywords

Ultramafic-Mafic Rocks, PGE-Base Metal Exploration, Holenarasipur Belt, Dharwar Craton.

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M. J. Viljoen ¹, R. P. Viljoen ¹

Affiliations
1 Department of Geology, University of the Witwatersrand, P.O. Wits 2050, Johannesburg, ZA

Abstract

No Abstract.

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R. P. Viljoen ¹

Affiliations
1 School of Geosciences, University of the Witwatersrand, Johannesburg, ZA

Abstract

The paper attempts to compare the Kaapvaal and Zimbabwe cratons of southern Africa with the Peninsular Indian Cratons with special reference to kimberlite clan of rocks and incidence of diamonds. The applicability of Clifford's Rule, Host-Rocks, structural controls, presence of large igneous provinces In both the regions are analysed to underscore the parallels and to draw inferences of utility tn the renewed diamond exploration activity currently underway in India.

Keywords

Kimberlite Clan Rocks, Diamonds, Comparative Study, Exploration Targets, India, Southern Africa.

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T. C. Devaraju ¹, R. P. Viljoen ², R. H. Sawkar ³, T. L. Sudhakara ⁴

Affiliations
1 'Rajamangala', Haliyal Road, Saptapur, Dharwad - 580 001, IN
2 School of Geosciences, University of Witwatersrand, Johannesburg, ZA
3 MSPL Limited, 'Baldota Enclave', Abheraj Baldota Road, Hospet - 583 203, IN
4 Department of Applied Geology, Kuvempu University, Jnanasahyadri, Shankaraghatta, Shimoga - 577 451, IN

Abstract

Evidence of mafic and ultramafic magmatism exists in many parts of the Dharwar craton which is divided into two blocks, the West Dharwar Craton (WDC) and the East Dharwar Craton (EDC). The mafic-ultramafic rocks occur in supracrustal/greenstone belts and in numerous enclaves and slivers in the WDC. The oldest recorded maficultramafic rocks, which are mainly komatiitic in nature, are preserved in the Sargur Group which is more than 3.3-3.4 Ga old, the youngest being manifested by 63-76 Ma old mafic dyke magmatism, possibly related to Deccan volcanism.

In the Sargur Group, ultramafics rocks greatly dominate over mafic lithological units. Both extrusive and intrusive varieties, the latter in the form of differentiated layered complexes, occur. Mafic volcanics exists in all the greenstone belts of the eastern block and in the Bababudan and Western Ghats belts of the western block. In addition to the Sargur Group where stratigraphic sequences are unclear, mafic magmatism is recorded in three different formations of the Bababudan Group and two sub-divisions of the Shimoga and Chitradurga Groups where basaltic flows are conspicuous. In the well studied greenstone belts of Kolar and Hutti in the EDC, three to four different Formations of mafic volcanic rocks have been mapped. Isotopic dating has indicated that while mafic magmatism in the greenstone belts of the EDC covers only a short time span of between 2.65 to 2.75 Ga, those in the Dharwar Supergroup of the WDC cover a much longer time span from 3.35 to 2.5 Ga.

Mafic dyke magmatism has taken place repeatedly from 2.45 Ga to about 1.0 Ga, but, the peak of emplacement was between 1.8 and 1.4 Ga when the densely developed swarms on the western and south western portions of the Cuddapah Basin and in the central part of Karnataka, were intruded. Emplacement of potassic ultramafic magma in the form of kimberlite-lamproite which is confined to the EDC, is a later magmatic event that took place between 1.4 Ga and 0.8 Ga.

From a mineralization perspective, mafic magmatism of the supracrustal groups of the WDC and the greenstone belts of the EDC are the most important. V-Ti-magnetite bands constitute the most common deposit type recorded in the mafic-ultramafic complexes of the Sargur Group with commercially exploitable chromite deposits occurring in a number of belts. PGE mineralization of possible commercial value has so far been recorded in a single mafic-ultramafic complex, while copper-nickel mineralization occurs at certain localities in the Sargur and Chitradurga Groups. Gold mineralization hosted by mafic (occasionally ultramafic) rocks has been noted in many of the old workings located in supracrustal groups of rocks in the WDC and in the greenstone belts of EDC. Economically exploitable mineralization, however, occurs mainly in the greenstone belts of the Kolar, Ramagiri-Penkacherla and Hutti-Maski and along the eastern margin of the Chitradurga belt, where it is associated with a major N-S striking thrust zone separating the WDC from the EDC. Gold deposits of the eastern greenstone belts are comparable to those of the younger greenstone belts of Canada, Zimbabwe and Australia where the mineralization is associated with quartz carbonate veins often in iron-rich metabasic rocks. The gold was emplaced as hydrothermal fluids, derived from early komatiitic and tholeiitic magmas, and injected into suitable dilatent structures.

The other common type of mineralization associated with the ultramafic rocks of the Sargur Group and supracrustal belts, particularly of the WDC, are asbestos and soapstone, related to autometamorphism/metasomatism. Ruby/Sapphire deposits occur in places at the contacts of ultramafic rocks with the Peninsular Gneiss, and are related to contact metamorphism and metasomatism. Mineable magnesite deposits related to low-temperature hydrothermal/lateritic alteration exist in the zone of weathering, particularly in the more olivine-rich rocks. Recent spurt in diamond exploration is offering promise of discovering economically workable diamondiferous kimberlite/lamproite intrusions in the EDC.

Keywords

Mafic Magmatism, Mafic Dykes, Kimberlite-Lamproite, Mineralization, Dharwar Craton.

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T. C. Devaraju ¹, T. L. Sudhakara ², R. J. Kaukonen ³, R. P. Viljoen ⁴, T. T. Alapieti ³, S. A. Ahmed ², S. Sivakumar ⁵

Affiliations
1 'Rajamangala' Saptapur, Haliyal Road, Dharwad - 580 001, IN
2 Department of Applied Geology, Kuvempu University, Jnanasahyadri, Shankaraghatta - 577 451, IN
3 Institute of Geosciences, University of Oulu, P.O.Box 3000, FIN-90014, Oulu, FI
4 School of Geosciences, University of Witwatersrand, Johannesburg, ZA
5 Ashapura Minechem Ltd., 'Sita Kunj', # 4-119C, Kunjibettu, Udupi - 576 102, IN

Abstract

Late Archaean Supracrustals of the Goa-Dharwar sector (GDS) are composed of a thick sequence of greywacke sequence with narrow intercalations of quartzite, BIF and carbonates. Mafic volcanics occupy the base of the sequence. The greywackes are predominantly tuffacious containing chlorite-sericite and hornblende. Arkosic variations containing biotite dominate the western part of the sector. Fine-grained variations occur as isolated narrow lenses within other types of greywackes. The conglomeratic greywackes are localized along the western and the eastern margins of the sector. All of the greywackes are all typically immature containing coarser clasts of mostly plagioclase (18-23%) and quartz (32-34%). Lithic fragments of felsic volcanic rocks are common. The matrix is dominated by mafic material. Biotite and amphibole are related to metamorphic recrystallization. Chlorite, sericite, epidote, carbonate and chert are products of the interplay of diagenesis and low-grade metamorphism. Fe-Ti oxide, sphene, apatite and zircon are usual accessories. But for slight enrichment in K₂O, the major element chemistry of the GDS greywackes is similar to the chemistry of Late Archaean greywackes. They also compare in respect of V, Co, Hf contents, K₂O/Na₂O, SiO₂/Al₂O₃, Na₂O/Al₂O₃, Ba/Rb, Th/U, La/Th, Sm/Nd ratios, steep REE patterns with distinct LREE enrichment and HREE depletion. The GDS greywackes however are distinctly enriched in Rb, Ba, Sr, Th, U, Cu, Zr, Ce/Ce^* and depleted in Cr, Ni, and Zn. The conglomeritic and biotite bearing verities contain considerable proportions of clasts derived from the basement tonalitic/granitic terrain. The common tuffacious greywackes containing hornblende and biotite-sericite however include only volcanic clasts and bear evidence of derivation from submarine weathering of predominantly felsic volcanics erupted on a large scale to form a magmatic arc in the later stages of geosynclinal deposition. Geochemical data suggest that the GDS greywackes were laid down in progressively changing basin geometry from a passive to active continental margin and island arc setting.

Keywords

Greywackes, Felsic Volcanic Source, Continental Island Arc, Submarine Weathering, Goa-Dharwar Sector.

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