Volatiles associated with granitoid intrusives around orogenic gold deposits in Ramagiri and Penakacherla regions of Eastern Dharwar Craton, South India

The nature of magmatic fluid has been tested well in varied type of auriferous deposits. However, in context of orogenic gold deposits, there are not many studies that clearly point out the nature of fluids exsolved out of crystallizing granitoids. This study compares the fluid of late-stage magmatic origin with that causative for mineralization in gold camps of Ramagiri and Penakacherla in Eastern Dharwar Craton. Various types of fluid inclusion assemblages (FIAs) were identified in granitoid matrix quartz, pegmatites, quartz segregations and greenstone-hosted goldquartz veins. The aqueous-carbonic (CH4-poor) and carbonic (CH4- and H2O-poor) inclusions are most common in pegmatites and quartz segregations, while the matrix quartz grains are generally devoid of CO2-bearing inclusions. On the other hand, auriferous veins in greenstone rocks show predominance of low to moderate salinity, aqueous-carbonic (variably CH4-bearing) inclusions. Inconsistencies in H2O/CO2 ratio and final homogenization properties of aqueous-carbonic inclusions within individual FIAs, apart from common occurrence of the FIA comprising aqueous-carbonic, carbonic and aqueous biphase inclusions, point to immiscibility in the ore fluid regime. Based on estimated microthermometric results, we attempt to deduce the evolution path of magmatic fluid with respect to that of fluid in ore zone. On this basis, a case for magmatic derivation of the ore fluid has been put forward. The difference in magmatic and auriferous fluid in terms of CO2/CH4 ratio are justifiable and allows us to visualize that aqueous-carbonic composition of orogenic gold fluid does not signify its exclusive origin through any particular process (or source), for example metamorphism.