Ore geology, fluid inclusion and isotope geochemistry of the Xunyang Hg–Sb orefield, Qinling Orogen, Central China

Abstract

The Xunyang Hg–Sb orefield, Shaanxi Province, containing two large (Gongguan and Qingtonggou) and tens of small to medium Hg–Sb deposits, is located in the southern Qinling Orogen. Ore bodies of the deposits are hosted in Devonian dolomite and controlled by a fault system. Ores are mainly present as massive veins, disseminations, breccias and fine veinlets, with cinnabar (Hg) and stibnite (Sb) being the dominant ore minerals. Gangue minerals include quartz, calcite and dolomite. Hydrothermal minerals (quartz and calcite) only contain aqueous fluid inclusions with low homogenization temperature (135–274 °C) and salinity (1.23–12.3 wt.% NaCl equiv.), supporting an epizonogenic hydrothermal origin. The carbon, oxygen and hydrogen isotope data indicate that the ore‐forming fluids were mainly sourced from epizonogenic to metamorphic devolatilization of the Sinian−Triassic strata that possibly underthrusted beneath the orefield, with inflow of the circulating meteoric water. Sulphur isotope ratios of stibnite and cinnabar range from 2‰ to 12‰, suggesting a contribution from sedimentary sulphate or sulphate‐bearing fluids potted in strata, which is coincident with the δ34S values (3.4–8.6‰) of diagenetic pyrite in the strata. The conclusion drawn from sulphur isotopes is fully supported by the Pb isotope signatures. In addition, the 87Sr/86Sr ratios gradationally increase from ore‐hosting dolostones, through ore‐barren calcite or low‐grade ores, to high‐grade ores, indicating that a portion of the fluids originated from a source with higher 87Sr/86Sr values than the host‐rocks, which is possibly composed of the Neoproterozoic−Lower Palaeozoic basement of the Xunyang Basin. Integrating the data from ore geology, fluid inclusion microthermometry and stable, radioactive isotope geochemistry, it can be concluded that the deposits in the Xunyang Hg–Sb orefield were formed by epizonogenic hydrothermal fluids mainly sourced from the strata via structural deformation during the North China−Yangtze continental collision. Copyright © 2014 John Wiley & Sons, Ltd.

Isotope and fluid inclusion geochemistry and genesis of the Qiangma gold deposit, Xiaoqinling gold field, Qinling Orogen, China

“…Fluid boiling and hydraulic fracturing commonly caused the uprising metamorphic fluids to mix with epizone fluids (Chen, 2010;Chen et al, 2009a;Zhang et al, 2014;Zheng et al, 2012;Zhou et al, 2014a,b) including circulating meteoric water. In the late stage, the fluid inclusions have low salinities and low temperatures, indicating cooling and dilution of the fluids, which is likely the result of the progressive inflow and mixing of meteoric water.…”

Ore geology and fluid inclusion study of the Donggebi giant porphyry Mo deposit, Eastern Tianshan, NW China

“…Mainland China, except for southern Tibet and Taiwan Island, has been entirely absent of marine sedimentation since the Jurassic but generally developed Late Palaeozoic marine strata, which strongly indicates that the final oceanic closure occurred around the Triassic, followed by continental collision, resulting in tectonic and geographic transformation from oceans to lands or mountains (Chen, ; Chen et al ., ). The Triassic marine strata are widespread in the areas south of the Central Orogenic Belt (COB: Kunlun–Altun–Qinling–Dabie), suggesting that the termination of the northernmost Palaeo‐Tethys occurred at the end of the Triassic (Deng et al ., ; Han et al ., ; Li et al ., ; Mao et al ., ; Zhang et al ., ; Zhou et al ., ). Recent studies show that the termination of the Palaeo‐Asian oceanic basins occurred diachronously in the time span of Late Carboniferous to Early Triassic, followed by continental collision resulting in the formation of the Central Asian Orogenic Belt (CAOB) and the majority of orogenic‐type and intrusion‐related hydrothermal mineral systems (Xiao et al ., , , ; Y.J.…”

Zircon geochronology and Hf isotope geochemistry of the granitoids in the Yangshan gold field, western Qinling, China: implications for petrogenesis, ore genesis and tectonic setting

“…), the greenschist facies metamorphosed Lower Palaeozoic assemblage, and the widespread Devonian–Triassic sedimentary sequence. The Precambrian basement is a metamorphosed submarine volcanic–sedimentary sequence with a thickness of >1000 m, unconformably overlain by the Lower Palaeozoic strata that comprises metamorphosed argillaceous clastic rocks, argillaceous carbonates, siliceous shales or cherts, and minor orthoschist, with a total thickness of over 5000 m (Zhang et al ., ). The Devonian–Triassic sequence unconformably overlies the Lower Palaeozoic strata and/or the Precambrian basement, and consists of littoral to shallow marine facies clastic sediments and carbonate rocks.…”