GOLD DEPOSIT IN THE LOWER SILURIAN BLACK ROCK SERIES IN NORTHERN SHIQUAN-HANYIN, SHAANXI PROVINCE

The gold deposit belt of black rock series of Lower Silurian Meiziya Formation in Northern Shiquan-Hanyin is tectonically located in the north margin of Niushan Old Land in the west of South Qinling Orogenic Belt. The ore belt is about 100 km long in E-W direction and 10-50 km wide in S-N direction. The early exploration has ascertained that the Lower Silurian Meiziya Formation was the ore-bearing layer of the gold deposits in this region. Based on the lithological assemblage characteristics, it is divided into six lithologic members and four ore-bearing sub-layers. More than ten gold deposits have been found in this ore belt. The gold deposits in this belt, controlled by stratigraphic, lithologic, paleogeographic and paleo-structural conditions, are homologous with the black rock series. The gold occurs mainly in particles and is unevenly distributed. The isotopic data show that the sulfur was originated from the strata. The characteristics of hydrogen and oxygen isotopes indicate that the aqueous media of the ore-forming fluid are mixed water containing mainly metamorphic-hydrothermal solution and atmospheric precipitation. The REE features reveal that the material source of gold deposits is similar to the Devonian sedimentary rocks in Qinba area. Ductile shear zone is not the necessary indicator for the existence of gold orebodies. Therefore, the gold ore in Meiziya Formation is a kind of sedimentary deposit.