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

Abstract

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 OligoceneMiddle 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-kaolinitequartz-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.

Genesis and origin of Te–bearing gold–silver–base metal mineralization of the Arinem deposit in western Java, Indonesia

“…Investigations of the fluid inclusions in the Arinem samples (Yuningsih et al, 2012) revealed that the main-stage quartz vein was deposited at the average homogenization temperature (T h ) of 194-267°C, with a general decrease in temperature with decreasing depth and advancing paragenetic time (Table 1). However, one quartz sample belonging to stage IA shows evidence of boiling; this sample contains both gas-rich and liquid-rich inclusions along the same growth band.…”

“…It should be noted that not all stages of mineralization can be recognized in every part of the Arinem vein. A general description of these mineralization stages was made by Yuningsih et al (2012) and for the purposes of further interpretation, detailed mineral paragenetic sequences are presented below. …”

“…The Arinem vein forms an extensive braided pattern around lenses of andesitic host-rock. The K-Ar age of illite associated with the vein mineralization in Arinem is Middle Miocene (9.4-8.8 Ma, Yuningsih et al, 2012).…”

“…Petrographic, geochemical, and fluid inclusion data from Arinem samples have been studied by Yuningsih et al (2012), but there still exists a lack of information on the conditions of ore formation, such as pH and f S 2 . The aim of the present study is to constrain the physicochemical conditions of the Te-bearing Arinem mineralization, based on mineral associations and the likely origin of hydrothermal fluids as suggested by the stable isotopic studies of sulfur, oxygen, and hydrogen.…”

Epithermal Gold-Silver Deposits in Western Java, Indonesia: Gold-Silver Selenide-Telluride Mineralization

“…Studies of ore mineralogy and geochemistry were carried out within the epithermal ore deposits of western Java by previous authors such as Pongkor (Basuki et al, 1994;Marcoux and Milesi, 1994;Sukarna et al, 1994;Milesi et al, 1999;Sukarna, 1999;Warmada et al, 2003;Syafrizal et al, 2005;Syafrizal et al, 2007;Warmada et al, 2007), Cikidang (Rosana and Matsueda, 2002), Cibaliung (Sudana and Santosa, 1992;Marcoux and Milesi, 1994;Marjoribanks, 2000;Angeles et al, 2002;Harijoko et al, 2004;Harijoko et al, 2007), Cisungsang (Rosana et al, 2006), Cirotan , Arinem (Yuningsih et al, 2012), and Cineam (Widi and Matsueda, 1998).…”