Low-sulfidation epithermal gold deposits in Java, Indonesia: Characteristics and linkage to the volcano-tectonic setting

Abstract

Java island, a part of the eastern Sunda magmatic arc, is becoming an emerging part of the region for gold and copper endowment. A total of 15.4% of 1044 tons of Java gold endowment is originated from Low Sulfidation (LS) epithermal deposit type. As a matter of fact, the mineralization type that has given a significant credit to the gold endowment of Java is intriguing to be geologically evaluated. This paper is aimed to document some data-information and summarizing the characteristics of selected 10 LS epithermal gold deposits in Java including Cibaliung, Kerta, Cisoka, Cikidang, Pongkor, Gunung Peti, Cihar, Cijaringao, Petungkriyono and Dalang Turu, as well as discussing their relationship with the volcano-tectonic setting.The formation of 10 LS epithermal deposits took place in the time span between Early Miocene and Pleistocene, which is coincident with the Mio-Pliocene magmatic arc activities, and even probably continue on to Pleistocene. All deposits show typical LS epithermal characteristics, i.e. quartz veins with crustiform-colloform textures, relatively high Au (Ag/Au ratio <15.8), less sulfides and base metals, low salinity fluids (commonly <1 wt% NaCl eq.), some deposits containing Mn-oxides and pseudomorph bladed carbonates. Metal signature is mostly Au and Ag, but some prospects contain elevated As and Sb.The Cibaliung veins seem to have genetic linkage with the dioritic intrusion and diatreme (phreatomagmatic) breccias, as well as with rhyolitic domes. In Kerta the veins exhibit close relationship with the rhyolitic/rhyodacitic plugs. The Pongkor and Cisoka veins are genetically related to rhyodacite dome/plugs within caldera setting, which is controlled by extensional structures. Cikidang and Gunung Peti may be related with the andesitic sub-volcanic plugs. Cihar and Cijaringao might be related to andesite dykes. Petungkriyono is linked with andesite and dacite plugs as well as diatreme breccia, formed in an extensional basin with few calderas developed. The Dalang Turu has been considered having a close linkage with andesite (plug) at extensional structures.In relation to the volcano-tectonic setting, six deposits (Cibaliung, Kerta, Pongkor, Cisoka, Cikidang and Gunung Peti) are obviously emplaced in Bogor Trough, a back arc rift/basin related to the Mio-Pliocene arc. The presence of rhyolitic to dacitic magmatism that could be related with caldera systems (e.g. in Kerta, Pongkor, Cisoka), and the common association with subvolcanic plugs (e.g. Kerta) are evidences of their linkage to the back arc rift/basin setting. The basaltic rocks in close proximity with the rhyolite-rhyodacite, as identified in Cibaliung and Kerta suggest the bimodal volcanism, which is commonly occurred in the back arc rifting environment. Exploration for LS epithermal prospects, therefore, should be targeted along the back arc rifting/basins (e.g. Bogor Trough) preferably over the areas with bimodal magmatism. The Bogor Trough is reported extending to East Java as Kendeng Trough/Basin, which is also reasonably targeted for exploration.