矿床地球化学国家重点实验室知识库

The Ciemas gold deposit is located in West Java of Indonesia, which is a Cenozoic magmatism belt resulting from the Indo-Australian plate subducting under the Eurasian plate. Two different volcanic rock belts and associated epithermal deposits are distributed in West Java: the younger late Miocene-Pliocene magmatic belt generated the Pliocene-Pleistocene epithermal deposits, while the older late Eocene-early Miocene magmatic belt generated the Miocene epithermal deposits. To constrain the physico-chemical conditions and the origin of the ore fluid in Ciemas, a detailed study of ore petrography, fluid inclusions, laser Raman spectroscopy, oxygen-hydrogen isotopes for quartz was conducted. The results show that hydrothermal pyrite and quartz are widespread, hydrothermal alteration is well developed, and that leaching structures such as vuggy rocks and extension structures such as comb quartz are common. Fluid inclusions in quartz are mainly liquid-rich two phase inclusions, with fluid compositions in the NaCl-H2O fluid system, and contain no or little CO2. Their homogenization temperatures cluster around 240 degrees C-320 degrees C, the salinities lie in the range of 14-17 wt.% NaCl equiv, and the calculated fluid densities are 0.65-1.00 g/cm(3). The values of O-18(H2O-VSMOW) for quartz range from +5.5 parts per thousand to +7.7 parts per thousand, the 5D(VSMOVV) of fluid inclusions in quartz ranges from -70 parts per thousand to -115 parts per thousand. All of these data indicate that mixing of magmatic fluid with meteoric water resulted in the formation of the Ciemas deposit. A comparison among gold deposits of West Java suggests that Miocene epithermal ore deposits in the southernmost part of West Java were more affected by magmatic fluids and exhibit a higher degree of sulfidation than those of Pliocene-Pleistocene.