The Gaosongshan epithermal gold deposit in the Lesser Hinggan Range of the Heilongjiang Province, NE China: Implications for Early Cretaceous mineralization

Abstract

The newly discovered and large ca. 99Ma Gaosongshan gold deposit is located in the Lesser Hinggan (or Xinggan) Range to the west of the Jiamusi Massif. The deposit is located at the border of the Great Hinggan Range–Mongolian Orogen with the Circum-Pacific tectonic belt and has a resource of ~22t @ 6.3g/t Au. Gaosongshan is classified as an adularia–sericite epithermal deposit associated with the large tensional Shaqihe Fault and has a low-sulfide content with a high concentration of gold hosted by pure chalcedonic quartz, which makes the deposit both unique and economically important in the area. Early Cretaceous volcanic rocks host the deposit as well as other gold deposits in the region. The mineralization at Gaosongshan includes Au, Ag, Mo, Sb, As, Pb and Hg. Stable isotope studies of fluid inclusions associated with the mineralization suggest that the mineralizing fluid had a meteoric origin (DV-SMOW: −129 to −111‰; 18Ofluid: 7.9 to 13.8‰). Fluid inclusion thermography indicates that the mineralized fluid was between 150° and 310°C and had a low salinity (0.7–3.71wt.% NaCl), low density (0.48–0.94g/cm3), shallow metallogenic depth (430–1270m), and a large amount of reducing gaseous components (CH4, C2H6, CO, N2, and CO2). The presence of large quantities of flaky quartz, adularia, gas-rich fluid inclusions, low-sulfide minerals and pure gold-bearing chalcedonic quartz suggests that fluid boiling was the principal mechanism for the gold precipitation. Sulfur isotopic data (δ34S: ~ −2.4 to 2.9‰) indicate a deep magmatic origin for the mineralization, and the Pb isotopes (206Pb/204Pb: 18.14–18.46; 207Pb/204Pb: 15.51–15.57; 208Pb/204Pb: 38.01–38.40) also indicate that the metallogenic source of the deposit contained a significant mantle component. The mineralizing fluid interacted with a Late Paleozoic (ca. 260–253Ma) substrate and ca. 141–91Ma volcanic host rocks. The geological and geochemical characteristics of the deposit, and the Tuanjiegou, Dongan, Sandaowanzi and other large gold deposits represent an Early Cretaceous (114–80Ma) epithermal mineralizing events in the Lesser Hinggan Range. The belt is controlled by the volcanic Sunwu–Jiayin Basin formed in a back-arc extensional setting along an active continental margin in East China, and the gold deposits in the belt have the same genesis as porphyritic Au(–Cu) deposits along the continental margin in eastern Jilin and Heilongjiang provinces. It is here proposed that the mineralization in both regions is related to the subduction of the Paleo-Pacific plate.