Role of Mantle Carbon in Archaean Gold Genesis in South India : Evidence from Carbon Stable Isotopic Composition of Fluid Inclusions

Ore fluids in the gold-quartz veins in Kolar (Champion Reef) and Wynad (Nilambur) are characterized by CO₂-bearing systems of low salinity and moderate density. Step-wise heating of auriferous quartz, and the isotopic analyses of CO₂ extracted from fluid inclusions yield a tightly constrained δ¹³C range of -5.9 to -9.4%0, providing the first direct evidence for the involvement of mantle carbon in the genesis ofthese Archaean gold deposits. The similarity in the range of carbon isotopic compositions of CO₂ trapped within the Archaean granulites and gold deposits suggests a common source for the fluids. The isotope data are consistent with the derivation of CO₂ from an outgassing sub-lithospheric mantle.