HE Ming-qin1, LONG Cheng-xiong2, WANG Gan-lu1
(1. College of Resources and Environmental Engineering, Guizhou University, Guiyang 550025, China;
2. 105 Geological unit of the bureau of Geology and Mineral Resources of Guizhou Province, Guiyang 550018, China)
Abstract: Pingqiu Au ore deposit is one of the most representative Au ore deposit in Jinping County, Southeastern Guizhou Province, China, where both quartz vein and altered rock type Au gold ore deposit being respectively controlled by Neoproterozoic Qingbaikou Group Fanzhao Formation and interlayer-gliding or in-sequent fault. However, the systematic and comprehensive geologic studies have not been carried out and especially the special studies on the origin of ore-forming fluids are still lack. Because of the quartz vein type ore bodies are now being mined, our study is focused on this type ore body. By sampling and selecting the pure quartz and arsenopyrite in the ore of metallogenic epoch, we carried out isotopic analysis of H-O and He-Ar of quartz and arsenopyrite, respectively, and the origin of ore-forming fluids was also studied. Results show that the values of 18Oquartz and DH2O range from 17.2‰ to 17.7‰ and from -66‰ to -62‰, respectively. The calculated 18OH2O values with the mean value of homogeneous temperature for fluid inclusions in quartz by the oxygen isotopic equilibrium equation between quartz and water range from 17.2‰ to 17.7‰, suggesting that the H2O in ore-forming fluids was originated from metamorphic water. Additionally, the values of 3He/4He range from 0.0483×10-6 to 0.1087×10-6 and the values of 40Ar/36Ar range from 1046.3 to 6929.3, the calculated R/Ra and 40Ar/36Ar ratios range from 0.0345 to 0.0776 and 1046.3 to 6929.3, respectively, indicating that the rare gas in ore-forming fluids was derived from the crust. Therefore, it is indicated that the ore-forming fluids of Pingqiu Au Deposit were originated from the metamorphic fluids, most likely being derived from low metamorphic rocks from Fanzhao Formation.
Keywords: H-O; He-Ar; isotope; ore-forming fluid; Pingqiu; Au ore; Jinping County; Guizhou Province
ACTA MINERALOGICA SINICA Vol. 35, No. 4, 2015, Page 497-501
