The Hanshan gold deposit in the Caledonian North Qilian orogenic belt, NW China |
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Authors: | Mao Jingwen Zhang Zuoheng Yang Jianmin and Zhang Zhaochong |
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Institution: | (1) Institute of Mineral Deposits, Chinese Academy of Geological Sciences, Beijing 100037, China e-mail: mjw@cags.cn.net; Fax: +86 10 68310894, CN |
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Abstract: | The recently discovered Hanshan gold deposit in northern Gansu Province, northwestern China, is hosted by a WNW-striking
shear zone in Ordovician andesite and basalt. Mineralization consists of surface to near-surface oxidized ore (the yellow
sandy gossan type) and three types of primary ore, i.e. early-stage quartz-sericite-pyrite ores in stockworks, early-stage
disseminated ore, and the most important late-stage quartz ± calcite-sulfide veins. The ore system is characterized by variable
degrees of potassic and silicic alteration. Late-stage gold-related fluid inclusions have homogenization temperatures between
170 to 310 °C, with a peak around 260 °C and low salinities. The ore fluids had high contents of CO2, CH4, and N2. Sulfur isotope measurements of −1.9 to +1.7 per mil for hydrothermal pyrites could be consistent with a hydrothermal fluid
source from the mantle, but the oxygen and carbon isotope data from calcite and quartz suggest mixing between mantle and crustal
fluid sources. K-Ar ages for hydrothermal sericite from ore zones are 213.9 ± 3.1 and 224.4 ± 3.2 Ma. Due to the arid Cenozoic
climate, a yellow gold-bearing gossan developed, which consists of jarosite, gypsum, and relict quartz. It could be a widespread
and useful prospecting guide for gold in northwestern China.
Received: 1 February 1999 / Accepted: 1 August 1999 |
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