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The native gold in the Woxi Au–Sb–W deposit is characterized by remarkably high purities (99.9%), called as super-pure native gold. The deposit can thus be used as the suitable application example for analyzing ore-forming conditions by using the thermodynamic calculation of AuxAg1 – x-fluid equilibria. According to experimental results of minerals and fluid inclusions, some physicochemical conditions are assumed in the thermodynamic calculation of the fluids equilibrated with Au–Ag solid solutions of XAu = 0.999. Calculated results in log fO2-pH diagrams show dissolved gold and silver concentrations, as well as stability fields of pyrite and sericite associated with the super-pure native gold. On the other hand, LA-ICP-MS analysis indicates that both Au and Ag concentration are determined in the fluid inclusions of scheelite, showing varied Au/Ag ratios with different homogenization temperatures. The calculated results assumed by different data of inclusions in scheelite, indicate two fluid inclusions showing higher homogenization temperatures (303°C and 356°C) and higher Au/Ag ratios are possible for precipitation of the super-pure native gold coexisting with pyrite and sericite, whereas one fluid inclusion showing a lower homogenization temperature (198°C) and a lower Au/Ag ratio is impossible for the super-pure native gold. Therefore, the super-pure native gold in the Woxi deposit was probably formed by the hydrothermal fluid with higher Au/Ag ratios and high temperatures in the mineralization stage of scheelite. [ABSTRACT FROM AUTHOR]

We investigated the ecological restoration problems of dehydration river reaches, which are downstream of diversion-type hydropower station in medium and small watersheds. Based on this information, we calculated the ecological flow using the following five methods: the minimum monthly ecological flow method, the dynamic calculation method of ecological water demand, the Northern Great Plains Resource Program method (NGPRP), and the monthly frequency method. Then, we combined Matter Element Analysis (ME) and Tennant method to construct a ME-Tennant model. Furthermore, the ecological flow process of a river was evaluated with ME-Tennant model. The case study was performed at the Liujiaping Hydropower Station in Hunan Province, China. In this study, ME-Tennant evaluation model was applied to determine the ecological flow process, and the results were used to verify the validity and the applicability of the model. The study provides a basis for the ecological restoration of dehydration river reaches, which are downstream of the diversion-type hydropower stations. The proposed evaluation model does provide a new way to reasonably determine the ecological flow process of a river. [ABSTRACT FROM AUTHOR]