U-Pb dating of scheelite, wolframite and apatite from the Woxi Au-Sb-W deposit, western Hunan Province and their geological significance

The Xuefeng Uplift in western Hunan is an important Au-Sb-W mineralization belt in South China, while the Woxi deposit is the largest gold deposit with a unique element association of Au-Sb-W in this region. As the ore -forming elements and mineralization stages of the deposit are relatively complex, there has been a long dispute about its mineralization ages. In this study, geological characteristics of scheelite, wolframite and pyrite ( the most important gold -bearing mineral) and stibnite in the Woxi deposit were observed in details, and U-Pb dating of scheelite, wolframite and apatite were conducted with a LA-ICP-MS method. The results show that the Woxi deposit was genetically related to several hydrothermal events happened during the Late Jurassic to Early Cretaceous. Among the dated minerals, the scheelite is the earliest, which has the intercept ages of 149.0 +/- 12Ma, 144.8 +/- 1.7Ma and 139.8 +/- 6.1Ma; and the wolframite was formed slightly later than the scheelite, with the intercept ages of 137.8 +/- 3.9Ma, 134.8 +/- 5.1Ma. Native gold and stibnite were mainly precipitated after the formation of scheelite and wolframite, and there was still a small amount of native gold occurred in the late quartz carbonate vein ( 125.8 +/- 5.6Ma, 123. 8 +/- 4.6Ma). Combined with the published geochronological data, two periods of mineralization are revealed in the Woxi deposit, i. e., the Caledonian intracontinental orogenesis and the Yanshanian extensional tectonic event, respectively. The fragments of earlier W -bearing quartz veins are usually in good collage and cemented by later Au-, Sb- bearing quartz veins, indicating that there was a succession of crack -seal processes which bring about hydraulic fracturing in the Woxi deposit. Such processes were conductive to the activation, migration, accumulation and precipitation of the ore -forming elements ( especially gold) in the deposit.