GEOCHEMICAL STUDIES OF GRANITOIDS AROUND THE NEOARCHEAN GADAG GOLD FIELD, SOUTHERN INDIA: IMPLICATION TO THE SOURCE OF AURIFEROUS ORE FLUIDS

The Orogenic Gold Deposits in the granite greenstone terrains are hosted in the supracrustal rocks of greenstone belts traversed by crustal scale shear zones [1].There are many hypothesis given for the source of ore fluid & a critique narrowed down these choices to metamorphic devolatilisation,granitic magmatism or metamorphism alone [2].Studies have also indiacated involvement of mantle derived fluids[3].Based on fluid inclusion & mineral chemistry, granitic magmatism can be inferred to be the most possible cause for mineralisation.The supracrustal & granitoids of Gadag were classified into different granitic domain[4]. Therefore,studies of these granitoids can be a major step to know the role of granitic magmatism in gold mineralization. The REE pattern of these granitoids shows a characteristic U shaped ,negative Eu anomaly with LILE enrichment & negative HFSE anomalies (Nb-Ta, Zr-Hf &Ti) and positive Th & U suggesting intracrustal melting of crust, without involvement of mantle & those of gold bearing QCVs of GGF show LREE enrichment with positive Eu-anomaly [4]. The mass balance principle requires that, if ore bearing fluids would have derived from any of these granites,there should be a similarity in REE pattern of the two.This indicates,fluid responsible for gold mineralisation may not have been derived from any of these granitoids.In addition to this,reported SHRIMP U-Pb ages of granites are in the range of 2552±6Ma to 2568±5Ma [5,6 & 7] occurring in the vicinity of GGF,predate mineralization age 2522±6Ma by 30-46 Ma.In addition,water-rock interaction model of isotope data of these QCVs do not indicate involvement of granitic magmatic fluids in the generation of auriferous fluids[3]. Based on the geochemical studies of these granitoids & the comparison of their reported ages with reported age of gold mineralisation, we infer that the source of auriferous fluids for gold deposits of GGF have not originated during the emplacement of any of these granitic bodies. [1] Goldfarb et al. (2005) Econ Geol,407-450 [2] Goldfarb & Groves (2015) Lithos,233, 2-26 [3] Swain et al. (2015) OGR 70,305-320 [4] Chadwick et al.(2003) GSI 61 [5] Chadwick et al.(2007) GSI 69,5-24 [6] Sarma et al. (2011) Mineral Deposita 46,273-288 [7] Ram Mohan et al (2014) Precambrian Res 243.