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The Pongkor fold-silver epithermal deposit is located 80 km at South-west of Jakarta, Indonesia, contains more than 98 tons of gold and 1030 tons of silver, with average grades of 18.7 g/t Au and 188.3 g/t Ag. It consists of four main steeply dipping quartz veins located close to the internal border of a Miocene volcano tectonic depression due to an explosive ignimbritic eruption. Mineralized bodies are thick, usually banded, quartz-carbonate-adularia veins due to tectonic extension. GSQ facies is the sulfide-richest and related to the highest gold and silver grades of the veins. Sulfides are dominated by pyrite, with common acanthite-aguilarite and polybasite-pearceite. Electrum is common also, with gold values ranging from 48-74 wt% Au. Sphalerite, galena, chalcopyrite and hessite are fairly uncommon, moreover present within the CQ facies. A strong weathering has affected the ore deposit, down to 250 m below the surface. This supergene action is thus responsible for appearance of manganese oxides layers gold enrichment. |
