Geology and Alteration‐Mineralization Characteristics of the Cibaliung Epithermal Gold Deposit, Banten, Indonesia

Abstract

. The Cibaliung gold project is located at the central portion of the Neogene Sunda‐Banda magmatic arc. Gold‐silver mineralization in the area is hosted in a thick sequence of sub‐aqueous basaltic andesite volcanics with intercalated sediments intruded by sub‐volcanic andesite to diorite plugs and dykes, and subsequently cut by a cluster of diatreme breccias. These host rocks are unconformably overlain by dacitic tuffs, younger sediments and basalt flows. The gold prospects in Cibaliung occur within a NW‐trending structural corridor that is 3.5 km wide by at least 6 km long. It is fault‐bounded and is considered to be a graben. Two aligned NNW‐trending sub‐vertical shoots, Cikoneng and Cibitung, host the currently defined resource within the steeply dipping vein system with a minimum strike length of 1,300 m. As of July 2001, exploration has defined an inferred + indicated mineral resource of approximately 1.3 million tonnes at 10.42 g/t gold and 60.7 g/t silver at a 3 g/t Au cut‐off. This equates to approximately 435,000 ounces of gold and 2.54 million ounces of silver. Gold‐silver mineralization occurs as quartz veins characteristic of the low‐sulphidation epithermal adularia‐sericite type. Progressive dilation with a general increase in gold grade has produced multi‐stage veining and brecciation that grades from early to late stages as: pre‐mineral fluidized breccia, quartz vein stockwork, massive vein, crustiform vein, colloform‐crustiform vein with progressive increase in chloritic clay bands, clay‐quartz milled matrix breccias with a progressive increase in clay content, and synto post‐mineral fault gouge with vein clasts. Wall rock alteration is characterized by pro‐grade chlorite+adularia flooding that is locally overprinted by a low temperature argillic alteration (smectite, illite and mixed layered clays). Generally, the argillic alteration becomes weak with depth. The major mineral constituents of the veins are quartz, adularia and clay. In the early gold‐poor hydrothermal stages, quartz and adularia dominate with minor calcite and clay (smectite, poorly crystalline chlorite, interlayered chlorite‐smectite and illite‐smectite). In the later gold‐rich hydrothermal stages, clay with variable amounts of carbonate increases whereas the abundance of quartz and adularia decreases. Gold occurs mainly as electrum while silver occurs as argentite‐aguilarite‐naumannite and electrum, and rarely as native silver, sulphosalts and tellurides. Sulphides generally comprise <1 vol % of the vein, with pyrite as the most common species. Together with pyrite, traces of very fine‐grained base metal sulphides dominated by chalcopyrite, sphalerite and galena are in most cases intimately associated with electrum and silver minerals. Partial supergene oxidation generally extends down to about 200 m below the surface at Cikoneng and further down to more than 300 m at Cibitung. The hydrothermal system responsible for the gold‐silver mineralization in the area may be related to rhyolitic magmatism focused on a volcanic i...

Characteristics of Gold Mineralization at the Ciurug Vein, Pongkor Gold-Silver Deposit, West Java, Indonesia

“…Ore deposits associated with volcanism in West Java include epithermal gold deposits within and on the flanks of the Bayah Dome, such as Cikotok, Cirotan and Cikidang (Marcoux and Milesi, 1994;Milesi et al, 1999;Rosana and Matsueda, 2002), as well as that at Cibaliung (Angeles et al, 2002;Harijoko et al, 2004). The Bayah Dome consists of shale and sandstone basement overlain by the central volcanic belt of Oligocene to early Miocene age, which is composed of largely coarse volcaniclastic rocks, with intercalated limestones and sandstones.…”

Timing of the Mineralization and Volcanism at Cibaliung Gold Deposit, Western Java, Indonesia

“…The volcanic rocks are overlain by sedimentary rocks more or less equivalent to the Pliocene Cipacar Formation (Angeles et al, 2002;Sudana and Santosa, 1992). The sedimentary rocks consist of conglomerate, calcareous sandstone and limestone.…”

“…The geology of the Cibaliung deposit was described by Angeles et al (2002). The host rock of Cibaliung deposit is the Honje Formation, which comprises basaltic andesite lava and volcanic breccia intercalated with tuffaceous sedimentary rocks (Fig.…”

“…HARIJOKO, K. SANEMATSU, R. A. DUNCAN, S. PRIHATMOKO and K. WATANABE Angeles et al (2002). The outlined area is the location of the Cikoneng and Cibitung shoots.…”

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).…”