Heterogeneity in fluid characteristics in the Ramagiri–Penakacherla sector of the Eastern Dharwar Craton: implications to gold metallogeny

Abstract The auriferous Penakacherla–Ramagiri schist belt is a part of the granite-greenstone terrain of the Eastern Dharwar Craton. It is surrounded by gneissose basement and has a close spatial association with the younger granitoid units. Fluid inclusion assemblages studied from quartz veins in schists, quartz veins in granites and matrix quartz in granite indicate heterogeneity in fluid characteristics with methane-poor aqueous-carbonic, methane-rich carbonic, low salinity aqueous and high salinity aqueous fluids. Coexisting aqueous and carbonic inclusions do not seem to be the product of phase separation of a parent aqueous-carbonic fluid on all instances. This is corroborated by the fact that the pure carbonic fluid is richer in methane than the carbonic component of the aqueous-carbonic inclusions. This warrants a separate source of carbonic fluid during deposition of the gold-quartz ± sulfide veins. A high salinity component in the fluid in the schist belt is unlikely to be contributed by metamorphism of the host volcanic units rather it is comparable to the high salinity fluid present in the closely associated granites. Thus it may be surmised that the heterogeneous fluid characteristics in the auriferous Penakacherla–Ramagiri schist belt raises the possibility of fluid derivation from diverse sources, including the granitoids, rather than from a single metamorphogenic source.