Some key features and possible origin of the metamorphic rock-hosted gold mineralization in Buru Island, Indonesia

Abstract

This paper discusses characteristics of some key features of the primary Buru gold deposit as a tool better understanding of the deposit genesis. Currently, about 105,000 artisanal and small-scale gold miners (AS are operating in two main localities, i.e.Gogorea and Gunung Botak by digging pits/shafts following gold-be quartz vein orientation. The gold extraction uses mercury (amalgamation) and cyanide processing. The field s identifies two types/generations of quartz veins namely (1) Early quartz veins which are segmented, sigmoidal continous, and parallel to the foliation of host rock. The quartz vein is lack of sulfides, weak mineralized, crysta relatively clear, and maybe poor in gold, and (2) Quartz veins occurred within a 'mineralized zone' of about 1 in width and ~1,000 m in length. The gold mineralization is strongly overprinted by an argillic alteration zone mineralization-alteration zone is probably parallel to the mica schist foliation and strongly controlled by N-S or SW-trending structures. The gold-bearing quartz veins are characterized by banded texture particularly collo following host rock foliation and sulphide banding, brecciated, and rare bladed-like texture. The alteration t consist of propylitic (chlorite, calcite, sericite), argillic, and carbonation represented by graphite banding and ca flakes. The ore mineralization is characterized by pyrite, native gold, pyrrhotite, and arsenopyrite. Cinnabar, stib chalcopyrite, galena, and sphalerite are rare or maybe absent. In general, sulphide minerals are rare (< 3%). Fifteen samples were collected in Wamsaid area for geochemical assaying for Au, Ag, As, Sb, Hg, Cu, Pb, and Zn. Elev fifteen samples yielded more than 1.00 g/t Au, in which six of them are in excess of 3.00 g/t Au. It can be noted all high-grade samples are originally or containing limonitic materials, that suggest the role of supergene enrichm Interestingly, most of the high-grade samples contain also high grade As (up to 991ppm), Sb (up to 885 ppm), an (up to 75 ppm). Fluid inclusions in both quartz vein types consist of four phases including L-rich, V-rich, L-V and L1-L2-V (CO2)-rich phases. Mineralizing hydrothermal fluid is typified by CO2 -rich fluid, moderate temper of 300 - 400°C and a typical low salinity (0.36 to 0.54 wt.% NaCl eq). Based on those key features, gold minera tion in Buru Island meets the characteristics of LS epithermal or orogenic gold deposit types; however, it tends fitter with orogenic gold deposit rather than another type.