Alteration and Vein Textures Associated with Gold Mineralization at the Bunikasih Area, Pangalengan, West Java

Abstract

The Bunikasih vein system in the Pangalengan district of West Java is a low-sulfidation, adularia sericite epithermal gold deposit. It is hosted by Late Miocene andesitic volcanic and volcanoclastic rocks occurring in the south western margin of Malabar Volcano complex. Gold ore and alteration minerals related to deposition of gold in Bunikasih deposits superimposed on Late Tertiary-Quaternary andesitic formation that were altered and mineralized by some hydrothermal events. The veins consist almost entirely of quartz, with small amounts of adularia, bladed calcite, pyrite, and gold. Gold ore shoots are vertically restricted and are more continuous horizontally. The veins display complex and multi episodic filling with texture characteristics of open space precipitation such us colloform, lattice bladed, crustiform banding, vugs, breccia, and cockade and comb texture. The presence of bladed calcite and silica pseudomorph after bladed calcite suggests that the hydrothermal fluids boiled. In the Cibaliung section of the area, anomalous gold is related to veins trending northeast -southwest, milky quartz with dark grey to black manganese staining is found intermittently for a length of about 800m. The mineralized andesite ore bodies exhibit broad alteration patterns adjacent to mineralization, passing from fresh rock into anargillic, chlorite zone, and then sericite-silica close to mineralization. An argillic assemblage composed of kaolinite with fine-grained pyrite bulb is present in the upper portions and surrounding of the quartz vein system. The veins range from centimeter to meter in size. Of 24 vein samples collected, gold averages up to 0.3 grams per tone ("g/t"), to a high of 24.6 g/t. The Bunikasih epithermal gold deposit was mined by people for more than 10 years, mainly for the gold ore. SariUrat-urat yang terdapat di Bunikasih, Kecamatan Pengalengan, Jawa Barat, merupakan bagian dari suatu endapan emas tipe epitermal adularia serisit, sulfidasi rendah. Endapan emas tersebut terdapat dalam batuan vulkanik andesit dan batuan klastik vulkanik berumur Miosen Akhir yang terdapat di barat daya kompleks gunung api Malabar. Emas dan mineral alterasi penyerta dijumpai mengubah satuan batuan andesit Tersier Akhir -Kuarter yang telah mengalami alterasi hidrotermal. Urat-urat yang dijumpai tersusun oleh kuarsa dengan sedikit adularia, bilah-bilah kalsit, pirit, dan emas. Endapan emas dalam urat penyebarannya terbatas secara vertikal, dan relatif lebih menyebar secara horizontal. Urat-urat kuarsa memperlihatkan tekstur kompleks yang menunjukkan pengendapan berulang secara episodik dalam ruang terbuka seperti koloform, mineral berbentuk bilah, perlapisan crustiform, breksi, dan tekstur cockade and comb. Dijumpainya bilah-bilah kalsit dan pseudomorph silika hasil ubahan bilah kalsit menunjukkan kemungkinan terjadinya pendidihan (boiling) pada larutan hidrotermal. Di daerah Cibaliung, keterdapatan emas berasosiasi dengan urat-urat kuarsa berwarna putih susu berarah timur laut -barat daya sepanjang sekitar 800 m, dengan ...

Mineral Potential Mapping Using Geographic Information Systems (Gis) for Gold Mineralization in West Java, Indonesia

“…(after van Bemmelen, 1949and Martodjojo, 1984in Suparka et al, 2007. Syafrizal et al, 2011;Subandrio et al, 2010;Suparka et al, 2007;Utoyo, 2007 andIsmayanto et al, 2005). (b) Lithology map of the study area (lithology map is derived from digital version of many geology maps sheets, scale 1:100,000 by Geology Agency of Indonesia, Unpublished data).…”