Liu J.,China University of Geosciences |
Liu J.,Chinese Academy of science |
Dai H.,China University of Geosciences |
Zhai D.,China University of Geosciences |
And 8 more authors.
Ore Geology Reviews | Year: 2015
Located in thewestern part of the Min-Li metallogenic beltwithin thewestern QinlingMountains, the Zhaishang gold deposit is a giant Carlin-like disseminated gold deposit discovered recently. The ore deposit is present both in rocks of lowgrademetamorphic 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 ofmineral in the ores and the existence of microscopic visible native gold constitute the outstanding features of the gold deposit. Webelieve that the mineral source of the ore deposit has a close connectionwith the host rocks, because all samples show the light of the REE distribution patterns. The S, C, Pb, H and O isotopic compositions showthat the oreforming elementsweremainly 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 lowwater/rock ratio. Ore-forming temperatures are estimated to have been in the range from120 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 themost important depositionalmechanisms for the existence of microscopic visible gold grains but also favorable conditions for gold enrichment in the Zhaishang gold deposit. © 2014 Elsevier B.V.
Liu K.,China University of Geosciences |
Liu J.-J.,China University of Geosciences |
Li J.-X.,China University of Geosciences |
Yang S.-S.,China University of Geosciences |
And 2 more authors.
Geology in China | Year: 2014
Located in the western part of the Min-Li metallogenic belt within the West Qinling Mountains, the Mawu gold deposit is a medium Carlin-type disseminated gold deposit discovered in recent years. The orebody is controlled by the NW-trending faults and hosted in the Devonian phyllite and limestone. Two main types of fluid inclusions, i.e., CO2-H2O inclusions and aqueous fluid inclusions, are trapped in the gangue minerals. The homogenization temperatures range from 135 °C to 389 °C, while the salinities range from 4.4% to 15.9%, indicating medium-low temperature and medium-low salinity. The trapping pressures are 34.6 MPa to 219.8 MPa. The gold mineralization occurred at the depths of 1.3 km to 8.1 km. Fluid inclusion analyses show that the gas phase is mainly composed of H2O and N2, with minor CO2 and O2, while the liquid phase is mainly composed of Ca2+, Na+, C1- and SO4 2-. The ore-forming fluid belongs to the N2-H2O-Ca2+-C1- system. The hydrogen and oxygen isotopic compositions of fluid inclusions show that δ18Oh2o values range from 5.3‰ to 10.5‰, while δ D values range from -123‰ to -93‰. The ore-forming fluid came from the geothermal brine. An analysis of the fluid evolution shows that the variation of the stability of the fluid system caused by the structural transition and the boiling action played vital roles in the precipitation of gold.