Pustaka Ilmiah Universitas Padjadjaran

Abstrak

The Arinem Te-Bearing Gold-Silver-Base Metal Deposit, West Java, Indonesia

The vein system in the Arinem area is a gold-silver-base metal deposit of Late Miocene (8.8-9.4 Ma) age located in the southwestern part of Java Island, Indonesia. The mineralization in the area is represented by the Arinem vein with a total length of about 5900 m, with a vertical extent up to 575 m, with other associated veins such as Bantarhuni and Halimun. The Arinem vein is hosted by andesitic tuff, breccia, and lava of the Oligocene- Middle Miocene Jampang Formation (23-11.6 Ma) and overlain unconformably by Pliocene-Pleistocene volcanic rocks composed of andesitic-basaltic tuff, tuff breccia and lavas. The inferred reserve is approximately 2 million tons at 5.7 g t-1 gold and 41.5 g t-1 silver at a cut-off of 4 g t-1 Au, which equates to approximately 12.5t of Au and 91.4t of Ag. The ore mineral assemblage of the Arinem vein consists of sphalerite, galena, chalcopyrite, pyrite, marcasite, and arsenopyrite with small amounts of pyrrhotite, argentite, electrum, bornite, hessite, tetradymite, altaite, petzite, stutzite, hematite, enargite, tennantite, chalcocite, and covellite. These ore minerals occur in quartz with colloform, crustiform, comb, vuggy, massive, brecciated, bladed and calcedonic textures and sulfide veins. A pervasive quartz-illite-pyrite alteration zone encloses the quartz and sulfide veins and is associated with veinlets of quartz-calcite-pyrite. This alteration zone is enveloped by smectite-illite-kaolinite- quartz-pyrite alteration, which grades into a chlorite-smectite-kaolinite-calcite-pyrite zone. Early stage mineralization (stage I) of vuggy-massive-banded crystalline quartz-sulfide was followed by middle stage (stage II) of banded-brecciated-massive sulfide-quartz and then by last stage (stage III) of massive-crystalline barren quartz. The temperature of the mineralization, estimated from fluid inclusion microthermometry in quartz ranges from 157 to 325°C, whereas the temperatures indicated by fluid inclusions from sphalerite and calcite range from 153 to 218 and 140 to 217°C, respectively. The mineralizing fluid is dilute, with a salinity 4.3 wt% NaCl equiv. The ore-mineral assemblage and paragenesis of the Arinem vein is characteristically of a low sulfidation epithermal system with indication of high sulfidation overprinted at stage II. Boiling is probably the main control for the gold solubility and precipitation of gold occurred during cooling in stage I mineralization.