ENRICHMENT OF IPGE’S IN CHROMITITE OF THE NUGGIHALLI SCHIST BELT, WESTERN DHARWAR CRATON, INDIA

English Abstract:

An attempt has been made to understand the PGE in chromitite hosted rocks in Nuggihalli Schist belt, Dharwar craton, India. The chemical composition suggests an unusual enrichment of IPGE’s in chromite. The geochemical data with inter elemental plots suggest, that i.e.Ir and Ru could be present as alloys in laurite grains in chromites.The PGE data generated for limited representative samples from Rangapura (RNG), Byrapura (BYR) , BHMC (Bhakatarhalli) and TGR ( Tagadur ) areas. The PGE binary plot Fig .1a Ru vs Ir imply a positive correlation signifying Ir and Ru could be present as alloys in laurite grains in chromites. In Fig. 1b the binary plot between Ir+Ru vs sulphur reflect no correlation exist, although Ir and Ru values are very high. In Fig 1c Pt+Pd vs S also shows no correlation rather external sulphur addition could be due to post magmatic effect or intense overprinting due to peak metamorphism stages . In Fig.1d Ir+Ru vs Pt+Pd reflect presence of high temperature PGMs, which may have crystallized simultaneously with the chromite at magmatic temperatures, while Pt + Pd are more likely to be concentrated by formation of tiny amounts of sulphide melt at a later stage of magma evolution. The Cr/Fe ratio is affected by ferrit-chromite formation, and these overprinting phenomena may cause enrichment in the more mobile Pt and Pd.The PGE show a strong correlation with each other than Cr suggesting that metals occur as discrete phases rather than solid solution in chromite. Although the data set presented here is limited, the high Ir, Ru and Rh contents in our samples were corroborated with abundant presence of laurite grains in chromite. The severe overprinting and peak metamorphism upto amphibolites facies and presence of chromite as ferrit chromite (magnetite) restrict a localized PGE enrichment in chromites rather than potential economic grade PGE resource. This limited study still infancy stages and need detailed multidisciplinary studies including air mag data, ground magnetic, and electrical methods and detailed core log for any future prospective studieThe external sulphur has no significant influence of enrichment of PGE in Nuggihalli schist belt.The entire belt is severely overprinted by metamorphism and difficult to assess the potential of PGEs.