Oxygen isotope ratio of quartz veins from the auriferous Ramagiri-Penakacherla schist belt and surrounding granitoids in the Eastern Dharwar craton: A case for a possible link between gold mineralization and granite magmatism

摘要

In the Eastern Dharwar craton, among the many shear zone-hosted lode gold deposits, those at Ramagiri and Penakacherla are located near the western margin of the craton. Mineralized quartz (isulfide ± carbonate) veins are hosted by the schistose (metavolcanic and carbonaceous metasedimentary) rocks, in close spatial association with granitoids having quartz and quartzofeldspathic veins representing hydrothermal activities associated with them. Mineralized quartz veins from the ore zones (in Ramagiri and Penakacherla regions) and quartz (or pegmatitic) veins from the surrounding granitic terrane were chosen for δ~(18)O analysis. Samples from the schistose and granitic domains show δ~(18)O_(quartz) values in the range of 10.4-14.9 and 9.3-10.9‰ respectively. The ore-zone fluids from the Ramagiri and Penakacherla regions give δ~(18)O values of 7.9 ±1.5 and 5.1 ± 0.8‰, calculated at pressure-corrected temperatures obtained from fluid inclusion microthermometry. The late-magmatic fluid is relatively ~(18)O-poor with δ~(18)O values estimated at 4.5 ± 0.7%<> and the value is closer to what is obtained for the ore zones. Based on the δ~(18)O values reported and a possible magmatic contribution to ore fluid deciphered from fluid inclusion characteristics, a genetic relationship between granitic magmatism and gold mineralization is surmised. The observed increase in the ~(18)O/~(16)O ratio from the magmatic fluid to ore fluid in the shear zone is attributed to interaction of the magmatic fluid with host metasediments, that agrees well with the variation in the CO_2/CH_4 ratio of carbonic component in such fluids.