Element And Isotope Geochemistry Of The Zhaxikang Sb-Pb-Zn Polymetallic Deposit, Tibet

The Zhaxikang Sb-Pb-Zn polymetallic mining area,located at 48km west of Lhunze County in the Shannan Prefecture of Tibet, belongs to the Laguigangri passive epicontinental basins of the Himalayan block in tectonic. This deposit is a typical deposit in the Sb-Au ore belt of Southern Tibet, but it has been less studied. After carrying on the detailed field geological investigation, using the methods of element geochemistry and isotope geochemistry, the ore deposit’s ore-forming fluids, the mineralization materials and its genesis have been initially studied in this paper based on analyzing and studying all previous achievements.The ore-bodies occured in the SN or NE striking faults with the shapes of vein and lens, and the ore-bearing wall-rocks are gray and black shale, calcareous slate, silty slate and quartz sandstone of Ridang Group in Lower Jurassic. The ore minerals are stibnite, sphalerite, galena, boulangerite, bournonite, freibergite, etc.; while the gangue minerals are quartz, calcite, kaolinite, chlorite, sericite and so on. The main types of alteration are silicification, ferritization, magnetite, pyritization, calcilization, clayzation, kaolinization, chloritization, sericitization, etc.. The mineralization can be divided into four stages as follows:â… ) the quartz - fine stibnite stage,â…¡) the polymetallic sulfide stage of quartz - galena - pyrite - sphalerite,â…¢) the quartz - coarse stibnite stage,â…£) the quartz - calcite stage.The studies of major elements, trace elements and rare earth elements in the mafic dikes of this mining area show that they have the characteristics of OIB-type basalt, their sources are the mantle peridotite of enriching garnet and clinopyroxene, and they may be related to the large early Cretaceous Comei igneous provinces in formation. In the formations of the mining area （the unmineralized calcareous slate）, the ore-forming elements such as As and Sb strongly enriched, it can be speculated that the enrichment of ore-forming elements may be related to the input of hydrothermal in the process of deposition, according to the composition features of major elements, REE, as well as Mo, Co, Cr and other trace elements. The element migration calculations of mineralized altered rock show that CaO, Ba and Sr are largely migrated out during the alteration process, reflecting the dissolution of carbonate compositions and sulfate components occurred. While, a larger number of SiO2 migrating into the mineralized altered rock is identical with the phenomenon of silicification, and a lot of As, Sb, Pb, Zn and other elements moving into the mineralized altered rock are related to the precipitation of arsenopyrite, stibnite, galena, sphalerite and other minerals.The studies of S-C-H-O isotope show that sulfur and carbon in the ore mainly come from the Ridang Group formations, and the research of H-O isotope show that the water in the ore-forming fluids derived from the meteoric water. The higherδ¹⁸O_H2O value of calcite suggests that it is likely to be the product of early mineralization stage, and there is a strong interaction between hydrothermal and formation where occurred a strong exchange of oxygen isotope to make theδ¹⁸O_H2O value of ore-forming fluids much higher. While theδ¹⁸O_H2O values of quartz and siliceous rocks are relatively lower, which may reflect they are formed later than calcite, and that because the water/rock ratio increases with the added geothermal water and result in reduction ofδ¹⁸O_H2O value .