MODEL GENETIK ENDAPAN EMAS-PERAK EPITERMAL DAERAH CIBODAS-CIKIDANG KABUPATEN LEBAK JAWA BARAT

• Main Author: Idrus, Arifudin
• Format: Theses
• Language: Indonesia
• Subjects: Teknik (Rekayasa, enjinering dan kegiatan berkaitan)
• Online Access: https://digilib.itb.ac.id/gdl/view/4413
• Institution: Institut Teknologi Bandung

<b>Abstract : </b><p align=\"justify\">Cibodas Au-Ag epithermal deposit is a prospectous deposit, which is located in southern part of Cikidang Au-Ag mining area, Lebak District, West Java. <br /> <br /> The hidrothermal alteration in the area, consists of three mineral assemblages. These are; (1). Quartz-chalcedony- yrite zone, overprintlenvelope with adularia-clay-sericite (silicicF (2). C1ayquartz-sericite zone, with adularia-chlorite-pyrite (argillic), (3). Carbonate-chlorite-epidote zone, with quartz-adularia-sericitepyrite (prophylitic). XRD analysis indicates clay types in silicic and argillic alteration such as montmorillonite, illite and kaolinite. The ore minerals consist of sulphide, oxide minerals as well as metals (gold, silver). There are two stages of mineralization; (1). Hipogene mineralization marked by the presence of magnetite, stibnite, proustite, pyritee chalcopyrite, sphalerite, gold (electrum) and silver at T 20th-300 C, (2). Supergene enrichment marked by Pe presence of super gene sulphide (covelite, cinnabar) at T < 150 C. Oxide minerals (hematite, goethite, limonite) were formed in oxidation zone. High grade Au-Ag mineralization generally found in silicic alteration associated with shear zones and the mentioned clay minerals. <br /> Physio-chemistry conttions of Cibodas deposit indicates temperature of 200-210 C, lowyalinity of 0.149-0.868 wt.% NaCi <br /> eV, density of 0.75-0.95 gr/cm and pressure of 25-30 bar. The deposit is not formed under boiling condition at depth of 180-225 m below paleo surface and according to Buchanan model, it is still in upper part of the precious metal zone. This means, at depth 22525 m below paleo surface (lower part of the precious metal zone) or approximately at 986-1,186 m elevation may be still found potential Au-Ag ores and boiling zone that usually is rich in precious metals. <br /> <br /> At the beginning, Cibodas deposit is guessed a tension gash fracture that infilled by Au-Ag bearing hidrothermal fluid, forming quartz vein and altered the wall rocks. The major fracturing is developed to became a synthetic R shear with north-south trend, which caused the shearing (brecciation) of the vein. The Cibodas oblique fault with minor faults (normal and reverse faults) were formed during the post mineralization stage, which influenced the geometry of the deposit.