The Hanshan gold deposit in the Caledonian North Qilian orogenic belt, NW China

The recently discovered Hanshan gold deposit in northern Gansu Province, no rthwestern China, is hosted by a WNW-striking shear zone in Ordovician ande site and basalt. Mineralization consists of surface to near-surface oxidize d ore (the yellow sandy gossan type) and three types of primary ore, i.e. e arly-stage quartz-sericite-pyrite ores in stockworks: early-stage dissemina ted ore, and the most important late-stage quartz +/- calcite-sulfide veins . The ore system is characterized by variable degrees of potassic and silic ic alteration. Late-stage gold-related fluid inclusions have homogenization temperatures between 170 to 310 degrees C, with a peak around 260 degrees C and low salinities. The ore fluids had high contents of CO2, CH4, and N-2 . Sulfur isotope measurements of -1.9 to + 1.7 per mil for hydrothermal pyr ites could be consistent with a hydrothermal fluid source from the mantle, but the oxygen and carbon isotope data from calcite and quartz suggest mixi ng between mantle and crustal fluid sources. K-Ar ages for hydrothermal ser icite from ore zones are 213.9 +/- 3.1 and 224.4 +/- 3.2 Ma. Due to the ari d 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.