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

摘要

The recently discovered Hanshan gold deposit innorthern Gansu Province, northwestern China, is hosted by aWNW-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 quartzI calcite-sulfide veins. The ore system is characterized byvariable degrees of potassic and silicic alteration. Late-stagegold-related fluid inclusions have homogenization temperaturesbetween 170 to 310 deg C, with a peak around 260 deg C andlow salinities. The ore fluids had high contents of CO_2, CH_4,and N_2. Sulfur isotope measurements of - 1.9 to + 1.7 per milfor hydrothermal pyrites could be consistent with a hydro-thermal fluid source from the mantle, but the oxygen and carbonisotope data from calcite and quartz suggest mixing betweenmantle and crustal fluid sources. K-Ar ages for hydrothermalsericite from ore zones are 213.9 +- 3.1 and 224.4 +- 3.2 Ma.Due to the arid Cenozoic climate, a yellow gold-bearing gossandeveloped, which consists of jarosite, gypsum, and relict quartz.It could be a widespread and useful prospecting guide for goldin northwestern China.