THE GUNUNG-PONGKOR GOLD-SILVER DEPOSIT, WEST JAVA']JAVA, INDONESIA

The Gunung Pongkor gold-silver deposit in West Java is one of the most recent and largest gold discoveries in Indonesia, containing more than 100 tonnes of gold and 1000 tonnes of silver. It consists of several steeply dipping quartz-veins that formed within the epithermal environment, associated with Neogene calc-alkaline volcanism. The discovery and definition of the orebody resulted from a three year long exploration programme using a variety of geological, geophysical and geochemical techniques. Production is expected to commence in 1994 at an annual rate of 2 tonnes of gold. Vein textures (colloform banding and cockade textures) and mineralogy (quartz, carbonate, adularia) are typical of those encountered in low-sulphidation vein deposits. Mineralogical and fluid inclusion evidence suggests that the mineralizing fluids were dilute (around 1 eq.wt.% NaCl), near-neutral pH brines with a moderate gas content and temperatures of around 230-degrees-C, and that they were boiling under conditions which favoured gold deposition. There is little variation in mineralogy, fluid inclusion data and gold grade throughout the drill-tested portion of the vein systems.