Fluid Evolution of the Mosabani and Rakha Copper Deposits, Singhbhum District, Jharkhand: Evidence from Fluid Inclusion Study of Mineralized Quartz Veins

摘要

Fluid inclusions in quartz from the mineralized quartz veins from the Mosabani and Rakha copper deposits were investigated. On the basis of petrography, two distinct types of primary inclusions were identified. These are low saline aqueous biphase inclusions and high saline halite-bearing polyphase inclusions. The halite-bearing inclusions mostly homogenized by halite dissolution, barring instances where homogenization was manifest by disappearance of the vapour bubble. Minimum entrapment pressure values were estimated by intersection of the halite liquid with the corresponding inclusion isochores. The ranges in P-T at the temperatures of halite dissolution are: 2.6 kb/370 ℃-0.8 kb/263℃ for Mosabani and 2.1 kb/270 ℃-0.65 kb/217 ℃ for Rakha. Temperaturesalinity plots for both the deposits is suggestive of restricted mixing (and simple cooling) of a hot saline magmatic fluid with cooler low saline meteoric water that caused precipitation of sulphide minerals. Stable isotope data (δ~(18)O and δD) from Changkakoti et al. (1987) are re-interpreted in the present study, leading to the conclusion that the main fluid component for Mosabani mineralization was either of magmatic/metasomatic parentage or an evolved meteoric water at a low water/rock ratio, after its interaction with a granitic pluton. The observed high saline nature of fluids in both the deposits compels us to choose an initial magmatic/metasomatic fluid that evolved by restricted mixing and simple cooling.