Characteristics Of Geology, Geochemistry And Metallogenesis Of Sansegou Pb-Zn Polymetallic Deposit,Qinghai Province

The Sansegou Pb-Zn deposit is located in eastern Kunlun orogenic and metallogenetic belt, which is characterized by its complex tectonic settings and favorable ore-forming conditions. Based on detailed field study of geological features, wall rock alteration characteristics, and ore-controlling structures, associated with trace elements, REEs, stable isotopes, and fluid inclusions, we discussed the geologic structure background, ore genesis and mineralization mechanism.The magmatism is highly variable and characterized by high silicon, potassium, peraluminous calc-alkaline, high-K calc-alkaline, and has the same evolution series as crust remelting type granite of Southern China. The NE-NNE ore-bearing structures reflect the characteristics of mineralization that is extensional tectonic stress field. Then, the NW structures play a role of transform fault which is mainly shearing and accompanied by extensional. Except for Pb in metamorphic rhyolite, ore-forming elements in the strasta are rather low, and locally enriched in the alteration belts caused by magmatic hydrothermal fluids. Mineralization physico-chemical conditions changed from early large-scale acidic alteration to the alkaline alteration of final precipitation of the ore body.The main mineralized types in the deposit are veintype Pb-Zn mineralization and porphyrystyle copper mineralization, and the quartz-lead polymetallic sulfide stage is the main stage of Pb-Zn epoch. Pb-Zn ore bodies are controlled by altered fracture zone and the type of quartz-polymetallic sulfide which characterized by unhomogeneous mineralization and local enrichment.Sulfur and lead isotope composition of sulfide indicate that the metallogenic element S was derived from magma and Pb came from the deep crust or mantle source. Fluid inclusion studies indicate that the fluid inclusions are in three types:two phase aqueous inclusion (type Ⅰ), three phase CO2aqueous fluid inclusion (type Ⅱ) and pure CO2fluid inclusion (type Ⅲ). The ore forming fluids are characterized by low salinity, density. The Pb-Zn mineralizing temperatures range from178to209℃, low salinities range from0.3%to18.8%NaCl equivalent, and the calculated pressure ranges from50to143MPa; the porphyry copper mineralizing temperatures range from182to228℃, salinities range from3.5%to18.8%NaCl equivalent, and the calculated pressure ranges from71to164MPa. The immiscibility of oreformingfluids plays an important role in the metallogentic process of Pb-Zn Cu deposit.Associated with the tectonic settings, it is suggested that the porphyrystyle copper mineralization in the central part of the ore district which is related to magmatic hydrothermal activities is the result of the same tectionicmagmatic activities as Pb-Zn mineralization.