Mode of occurrence of ore minerals and mineralization of the Dalingkou silver deposits, Tiantai County, Zhejiang Province, eastern China

Abstract

A Pb-Zn orebody with high Ag concentration is situated in the Cretaceous rhyolites in Dalingkou, Tiantai County, Zhejiang Province, eastern China. The orebody occurs in brecciated and fissured zones. Unlike many other shallow-seated hydrothermal gold-silver ore deposits in North America and Japan, the Ag/Au ratio of the ore is very high and ranges from 97 to 60, 000 (average: 970). Main silver minerals are polybasite, tetrahedrite, argentite, and pyrargyrite. The gangue mineral assemblage is characterized by abundant rhodochrosite and the absence of adularia. Chemistry of fluid inclusion suggests ore-forming conditions, such as salinity 0.2-4.1 wt.%, pH=3.4-5.6 and pressure 98.3-186.8 bars, which are not much different from those of the other Ag-Au deposits. The ore body is an epithermal fracture-filling, Ag-Au-bearing, base metal ore deposits.