SULFUR ISOTOPE AND REE GEOCHEMICAL STUDIES OF AURIFEROUS QUARTZ CARBONATE VEINS FROM CENTRAL LODE SYSTEM, GADAG GOLD FIELD, DHARWAR CRATON, INDIA: IMPLICATIONS ON SOURCE OF ORE FLUIDS

The southern Indian Neoarchaean Dharwar greenstone belts are designated as the auriferous belts of India. The world famous Kolar Gold Fields in these belts, share the common characteristics of orogenic gold deposits [1]. The source of mineralising fluids for these deposits has been debated. While some authors have favored metamorphic origin for the mineralising fluids [2,3], others magmatic and/or juvenile mantle source [4,5]. In this work, we present stable isotope evidence and REE geochemistry of the Gadag Gold Field (GGF) in Chitradurga greenstone belt-to adress the problem of the source of the mineralising fluids. Gold in GGF occur in quartz carbonate veins (QCVs) in the form of sulfides mainly pyrite and arsenopyrite. The δ³⁴S values of pyrite and arsenopyrite (2.06±0.82‰) and the fluid δ³⁴S_H2S values (calculated from [6]) (0.88±0.82‰). Such narrow δ³⁴S ranges are consistent with the isotopic composition of mantle derived fluids (0 ± 2‰ [6, 7]). Therefore, the δ³⁴S and δ³⁴S_H2S values of the central lode of GGF indicate mantle/magma derived auriferous fluids. Chondrite normalized REE plots of the carbonates of the host auriferous QCVs show LREE as well as HREE enrichment and a distinct positive Eu anomaly in the range 0.92 to 3.38 (average Eu/Eu*: 1.91±1.29). QCVs with strong positive Eu anomaly have been reported from Sovetskoye orogenic gold deposits, Russia [8] and Ajjanahalli gold deposit, Chitradurga Schist Belt, India [9]; both have been formed from reducing auriferous fluids enriched in Eu²⁺that migrated along crustal scale faults tapping fluids from lower part of continental crust or mantle.

We conclude based on S-isotopic composition of sulphides, REE study and our earlier conclusion based on C and O isotopic study of carbonates in the host quartz-carbonate veins [5] that the hydrothermal fluids for GGF were derived from juvenile magmatic or mantle source. [1] Groves, et. al (2003) Econ. Geol. 98, 1-29; [2] Pal & Mishra (2004) Gondwana Res. 6, 531–540; [3] Kolb, et. al (2004) Econ. Geol. 99, 743–759; [4] Sarangi,et. al (2012) J. Asian Earth Sci. 52, 1–11; [5] Swain, et.al (2015) Ore Geol. Rev. 70, 305-320; [6] Ohmoto & Rye (1979) Geochem of Hydrothermal dep. pp. 509–567; [7] Thode, et. al (1961) GCA 25:159-174; [8] Tomilenko, et. al (2010) Econ. Geol. 105, 375-394; [9] Sarangi, et. al (2013) Geosci. Front. 4, 231–239.