Fluid Inclusion, Rare‐Earth Element and Stable Isotope Study of Carbonate Minerals from the Pongkor Epithermal Gold–Silver Deposit, West Java, Indonesia

Abstract

Abstract The Pongkor gold–silver deposit is the largest low‐sulfidation epithermal precious metal deposit in Indonesia, and is of Pliocene age. The deposit consists of nine major subparallel quartz–adularia–carbonate veins with very low sulfide content. Vein infill records five paragenetic sequences, dominated by calcite in the early stage and quartz in the later stage of the hydrothermal evolution. Fluid inclusions in hydrothermal calcite and quartz of all stages indicate a temperature ranging from 180 to 220°C and a meteoric water origin (very low salinity close to 0 wt% NaCl equivalent). Carbon isotope data on calcite display a narrow range from −6.5 to −3.0‰δ 13 C. The oxygen isotope values have a wider range of +4.6 to +10.1‰δ 18 O. The broadly positive correlation of the δ 13 C versus δ 18 O plot suggests that the carbon species, which equilibrated during the formation of calcite, is dominated by H 2 CO 3 not far from equilibrium with HCO 3 − . The abundance of rare earth and yttrium (REY) in carbonate samples is very low (>REY mostly <2 ppm). However, there is always a positive Eu anomaly, which indicates a deeper fluid reservoir at >250°C.