Geological and geochemical characteristics and formation mechanisms of the Zhaishang Carlin-like type gold deposit, western Qinling Mountains, China

Located in the western part of the Min–Li metallogenic belt within the western Qinling Mountains, the Zhaishang gold deposit is a giant Carlin-like disseminated gold deposit discovered recently. The ore deposit is present both in rocks of low grade metamorphic Middle Devonian and Lower Permian clastic formation, which is composed of quartz sandstone, siltstone, calcareous slate and argillaceous limestone. Gold mineralization is strictly controlled by a fault zone. Minerals in ores are quite complex and consist of sulfides, sulfosalt, oxides, sulfate, carbonate, tungstate, telluride, native metals, and polymetallic alloys. The diversity of mineral in the ores and the existence of microscopic visible native gold constitute the outstanding features of the gold deposit. We believe that the mineral source of the ore deposit has a close connection with the host rocks, because all samples show the light of the REE distribution patterns. The S, C, Pb, H and O isotopic compositions show that the ore-forming elements were mainly derived from the country rocks, the underlying rocks, and partially deep sources. Data obtained suggest that the ore-forming fluids were derived predominantly from an active meteoric groundwater system. Mineralization and related alteration have features of a low water/rock ratio. Ore-forming temperatures are estimated to have been in the range from 120 to 240 °C. The dissolution of ferruginous limestone in the host rocks and the sulfidation of the dissolved iron by H2S introduced by ore fluids constituted not only the most important depositional mechanisms for the existence of microscopic visible gold grains but also favorable conditions for gold enrichment in the Zhaishang gold deposit.