Polymetallic Sulfides and Sulfosalts of the Pongkor Epithermal Gold-Silver Deposit, West Java, Indonesia

The Pongkor gold–silver deposit, of Pliocene age (2.05 ± 0.05 Ma), is the largest low-sulfidation epithermal precious-metal deposit in Indonesia. It consists of nine major subparallel quartz – “adularia ” – carbonate veins with a very low sulfide content. The association of sulfides is the main gold carrier and is dominated by pyrite, chalcopyrite, sphalerite, ± galena (grey sulfide – quartz stage). Minor phases are silver-rich sulfides and sulfosalts, such as acanthite–aguilarite (Ag2S–Ag4SSe), polybasite– pearceite [(Ag,Cu)16(Sb,As)2S11], famatinite (Cu3SbS4), proustite (Ag3AsS3), and tetrahedrite. Gold occurs as Au–Ag alloy and uytenbogaardtite (Ag3AuS2). Chalcocite, native gold, stromeyerite (AgCuS), rare covellite and mckinstryite [(Ag,Cu)2S] are the latest phases, of supergene origin. Microthermometric data and the mineral association indicate the presence of a low-salinity fluid, evolving from low f(S2) at a temperature of about 220°C to higher f(S2) at a temperature below 200°C. Dendritic native gold probably formed from dissolution of Au–Ag alloy and reprecipitation of gold and stromeyerite – mckinstryite from a supergene copper-bearing fluid.