Genesis And Metallogenic Regularity Of Kengdenongshe Au-Pb-Zn Polymetallic Deposit, Maduo County, Qinghai Province

ABSTRACT:Kengdenongshe Au-Pb-Zn polymetallic deposit is located in eastern area of Eastern Kunlun orogenic belt with Paleozoic subduction complex where is a joint of two third-grade tectonic units, the area of which is characterized by complex tectonic settings, favorable metallogenic conditions, and it belongs to the metallogenic subzone of East Kunlun metallogenic belt. The metallogenic regularities and metallogensis of Kengdenongshe deposit has been studied, and metallogenic mode has been established, as well as targets of prospecting prediction, based on field geological investigation, identification of thin sections, fluid inclusions, stable isotope, zircon dating, rocks and ores’ geochemistry analysis, etc..The magmatite is characterized by high potassium, peraluminous calc-alkaline and high-K calc-alkaline, reflecting high degree of differentiation. Volcanic rocks are considered to be formed at246±3.0Ma, and belong to Hongshuichuan group of Lower Triassic, based on zircon dating. The geological characteristics of the deposit shows that ore bodies were mainly formed within and adjacent the contact zone of volcanic and carbonate rocks, with apparent mineralization belts, and two types of mineralization porphyry type and epithermal type have been found.3epochs and6stages have been divided according to characteristics of the deposit, in which the main mineralization stages are Pb-Zn (Cu) sulfide stage and barite sulfide stage. In terms of wall-rock alteration, baritate, silicification, and carbonation have been identified, among which barite is closely related to gold mineralization.The metallogenic material are mainly derived from intermediate-acid magma with a marginal proportion from strata related to later hydrothermal activities properly, relying on research of ore-forming elements. Ore sulfur and lead isotope composition indicate that the metallogenic material S are mainly originated from magma of the crust, partially from strata, Pb from mixture of crust and mantle with dominated crust material. Hydrogen and oxygen isotope show that ore-forming fluids are mainly derived from magmatic fluid, mixed with metamorphic water and groundwater. Wallrocks, magmatite and orebodies have been considered to share the same metallogenic system in accordance with their similar REE characteristics.One type of fluid inclusions has been identified based on Petrographic and microthermometric criteria, which a type of two-phased aqueous inclusions is. The ore-forming fluid is characterized by low salinity (0.17～11.34(wt%. NaCl equiv)), and low density (0.50～1.06g/cm3), with low-medium temperature of porphyry mineralization ranging from139to320℃, while the temperature of epithermal mineralization concentrated in two interval, ranging from150to250℃. Metallogenic depth is estimated to range from0.2km to0.9km.This deposit was formed in the orogenic belt of post collision, with the evident control of strata, magmatic, and structure. Intermediate-acid magmatite is considered to be the ore-forming rock, part of metallogenic material originated from strata. It is estimated to that the cryptoexplosive breccia played an important role in mineralization, and the NW-NWW trending faults are the main ore-controlling structures in this mining district.Finally, the metallogenic model of Kengdenongshe deposit has been established, in which the deposit is a compound of porphyry type and epithermal type.