Wenchao Su

Continental hydrothermal sedimentary siliceous rock and genesis of superlarge germanium (Ge) deposit hosted in coal: A study from the Lincang Ge deposit, Yunnan, China

There are abundant hydrothermal sedimentary structures and plant fragment fossils in the siliceous rocks from the Lincang Ge deposit. The major element compositions of these siliceous rocks are characterized by high content SiO2, low TiO2 and Al2O3 concentrations, and low Al/(Al+Fe+Mn) ratios (0.010 on average). The siliceous rocks are distinctly enriched in Ge, Sb, As, W, and secondly enriched in Cs, U, Mo and Tl. Their total REE content are generally less than 1μg/g, LREE relatively concentrated, and the values of Eu anomaly and Ce anomaly vary from 0.452 to 5.141 and 0.997 to 1.174, respectively. Their NAS-normalized REE patterns are plain or left-inclined. The Oxygen isotope compositions of these siliceous rocks are similar to those of the hydrothermal siliceous sinter. The above characteristics, as well as the geological setting of the deposit, indicate these siliceous rocks formed in continental hydrothermal environment. As the interlayer or cliff of the Ge-rich coal seams, siliceous rocks tightly contacted with ore-body, and the contents of Ge in siliceous rocks vary from 5.6 to 360 μg/g (78 μg/g on average). The Ge content increased in coal which close to the siliceous rocks. With the increase of Ge content, the typical trace element ratios (i.e., Ge/Ga, Nb/Ta and U/Th) and REE patterns of Ge-rich coal are more close to those of the siliceous rocks. The Ge concentrated in coal seams of the Lincang Ge deposit might be transported by the hydrothermal water, which demonstrated by the siliceous rocks, during the coal-forming processes.

Lower cambrian metallogenesis of south China: Interplay between diverse basinal hydrothermal fluids and marine chemistry

The lowermost Cambrian metalliferous black shales of southern China represent a unique metallogenic province. The shales host a wide range of world-class synsedimentary metal deposit types. The diverse metal assemblages in these deposits are best explained by venting of multiple hydrothermal fluids including reduced H2S-rich brines, petroleum, and oxidized brines into the basin. Coinciden formation of shales that are extraordinarity rich in organic carbon and metals suggest a rapid increase in bioproductivity and anoxic/dysoxic conditions during ore formation. We propose that basinal fluids were the source of bioliming nutrients that caused eutrophication and basin-wide anoxia. The dramatic geologic and geochemical changes in this basin demonstrate the possible impacts of hydrothermal systems on the generation and sequestration of organic matter, formation of black metalliferous shales, and chemical changes of seawater.

Metallogenic model and prognosis of the Shuiyindong super-large strata-bound Carlin-type gold deposit, southwestern Guizhou Province, China

The Shuiyindong deposit is one of the largest (more than 100 tonnes of Au) and highest grade (more than 7×10−6–10×10−6), strata-bound Carlin-type gold deposits in southwestern Guizhou Province, China. The deposit is controlled by both structure and favorable lithology. It is situated near the axis of the striking Huijiabao anticline and is hosted in bioclastic limestone of the Permian Longtan Formation. Gold mineralization occurred under low temperature with Th of 220°C ± and is closely associated with decarbonation, silicification, sulfidation and dolomitization. The deposit has a characteristic elemental assemblage of Au-As-Hg-Tl. Studies of geochemistry and isotope compositions indicated that the ore-bearing materials and fluids of the gold deposit mainly originated from a plutonic source, and possess a mixing feature with the strata matter during transportation from mantle to crust. Fluid inclusions in vein quartz from the gold deposit are rich in volatile flux, indicating that metallogenic fluid is an overpressured one. The activity and geothermal state of the Earth’s crust in the long period of time are favorable for the formation of overpressured fluids in a large area, and extensive structures would drive the fluids into ore-forming system and make gold deposits formed. The complexity of structural movement in the upper crust of southwestern Guizhou Province resulted in complicated gold mineralization. Through metallogenic prognosis and exploration, the proven reserves of the deposit increased by tens of tonnes of Au and the deposit has become a super-large strata-bound Carlin-type gold deposit.

Source of ore fluids in Carlin-type gold deposits, China: Implications for genetic models

Fluid inclusion and isotopic data on quartz, carbonate, and clay minerals from Carlin-type deposits in two gold grovinces of southwest China suggest the deposits formed at epizonal levels where metamorphic fluids discharged into foreland fold and thrust belts, reacted with sedimentary rocks, and mixed with local meteoric ground waters.

Geochemistry and δ34S of ores and ore stage iron sulfides in Carlin-type gold deposits, Dian-Qian-Gui area, China: Implications for ore genesis

The relative enrichments of Au, trace elements, S, and Fe in gold deposits in the Dian-Qian-Gui area are nearly identical to those of Nevada Carlin-type deposits. Pyrite, marcasite, and arsenopyrite of the ore stage typically occur as disseminations, and locally in open spaces, and have high concentrations of Au, As, Sb, Hg, and Tl, and low Ag and base metals. These elements are soluble in H2S-rich fluids and precipitated by sulfidation of ferroan minerals in the host rocks or Fe in a contrasting fluid. δ34S data indicate reduced S was derived from sedimentary rocks. These data and the absence of subduction-related plutons in the area are consistent with amagmatic models for these deposits.

Geochemistry and Metallogenic Model of Carlin-Type Gold Deposits in Southwest Guizhou Province, China

Carlin-type gold deposits, also known as sediment-hosted gold deposits are among the largest hydrothermal gold deposits in the world, currently being sought and mined in the United States and China (Tretbar et al., 2000; Hu et al., 2002). The region of southwestern Guizhou (SW Guizhou), which is a region where the Carlin-type gold deposits were found for the earliest time in China, is an important component of the Yunnan-Guizhou-Guangxi “gold triangle” province. Carlin-type gold deposits in SW Guizhou, China, are hosted in late Paleozoic and early Mesozoic sedimentary rocks along the southwest margin of the Precambrian Yangtze craton. They can be classified as two types, i.e., the fault type and the strata-bound type, on the basis of their occurrence, shape and structural controls (Zhang et al., 2003; Xia, 2005). The former type includes the Lannigou, Yata, Banqi, Zhimudang (the upper orebodies), etc. with gold ores mostly occurring in high-angle compresso-shear faults. The ore-hosted strata are generally Middle and Lower Triassic in age, ore-bearing rocks are dominated by muddy siltstones and silty mudstones. The strata-bound gold deposits include the Shuiyindong, Taipingdong, Zhimudang (the lower orebodies), Getang, Nibao, etc. Gold ores are hosted mainly in the interbeded rupture zone at the karst discontinity surface of the Upper-Lower Permian and the Upper Permian strata. The deposits are mostly concealed ones at depth, the orebodies occur as stratiform, stratoid and lenticular ones and are developed along the strata, characterized by multi-layer distribution. Ore-hosted rocks are mainly impure bioclastic limestones and carbonate rocks in organic-rich coal series formations, with obvious anticline ore-controlling features. They have characteristics similar to Carlin-type gold deposits in Nevada, including notable enrichment in As, Sb, Hg, and Tl (Hu et al., 2002; Xia, 2005). Typical characteristics include impure carbonate or calcareous and carbonaceous host rock that contains disseminated pyrite and arsenopyrite. Gold occurs either as submicrometer-sized particles or invisibly as solid solution in As-rich rims of pyrite and arsenopyrite. Late stibnite, realgar, and orpiment fill fractures on the periphery of gold mineralization. Hydrothermal alteration caused decarbonation, silicification, argillization, and sulfidation, similar to Carlin-type gold deposits in Nevada (Hofstra and Cline, 2000; Emsbo et al., 2003; Kesler et al., 2003). Detailed studies in recent years have shed much light on the geochemistry and metallogenic mechanisms of the Carlin-type gold deposits in the