The Study On Metallogenic Geological Background And Ore Genesis Of Erdaohezi Pb-Zn Deposit, The East Slope Of The Great Xing’an Range

Erdaohezi Lead-Zinc deposit belongs to Derbugan metallogenic belt lying in the northwest of Hailaer-Genhe Mesozoic volcanic basin which is located in the north of the Great Xing’an Range, northeast of China. The exposed strata of mining areas are Late Jurassic-Cretaceous stratas of terrestrial volcanic-volcaniclastic rocks and quaternary deposition. Magamtism strongly occurred in this area. It mainly exposed with early Yanshanian granites, most of whose scale is not large but complicated in form. Tectonic framework is widely developed in this area, it includes NE-trending faults and the secondary strutrue of NW-trending faults.Tamulangou Formation intermediate-mafic volcanic rocks and space accompanied, time connected acidic pyroclastic rocks and is controlled by the NW-trending and NNW-trending faults. These ore bodies with lenticular and vein-shape. The type of ore contains mainly dalena and sphalerite. Metallic minerals in Erdaohezi Pb-Zn deposit are mainly dalena, sphalerite, pyrite, moreover, there are chalcopyrite, tetrahedrite, argentite and covellite. Wall-rock alteration is mainly silicification, propylitization, carbonation and sericitization. The mineralization can be devided into two period:the hydrothermoal period and the supergene period, and the hydrothermal period can be devided into quartz-pyrite stage, quartz-polymetallic sulfide stage and quartz-carbonate stage.This deposit occurs in the Middle Jurassic Tamulangou Formation intermediate-mafic volcanic rocks and space accompanied, time connected acidic pyroclastic rocks. The host rocks are bedded trachyandesite, rhyolitic crystal-lithic tuffs and basaltic andesite. LA-ICP-MS zircon U-Pb dating of trachyte andesite and rhyolitic crystal-lithic tuffs indicates that their ages are (167.0±2.0) and (164.8±1.6) Ma, respectively. Element geochemical characteristics reflect that Tamulangou Formation intermediate-mafic volcanic rocks, SiO2=56.76%-72.69%, Na2O=3.64%-6.44%, K2O=1.88%-3.87%, They have right-leaned chondrite-normalized rare earth element (REE) patterns, light rare earth element (LREE)/heavy rare earth element (HREE)=10.75-15.28, (La/Yb) N= 16.95-26.70, 8Eu=0.61-0.90, and charactered by enrichment of large ion lithophile element (LILEs)(Rb, Th, U, LREE, etc) and depletion of high field strength elements (HFSEs) (Nb, Ta, Ti, HREE, etc); the (87Sr/86Sr)i, ratios negative εNd(t) and Nd model ages (TDM) range of 0.705007 to 0.705240, and 699 to 883Ma, respectively. Referring to the formers’ achievement in research, we concluded that trachyandesite and the basaltic andesite was derived from the partial fusion of lower crustal material assimilated by a depleted lithospheric mantle that had subsequently been metasomatized by subducted salb-derived fluids. While the rhyolitic crystal-lithic tuffs are featured by negative Eu anomalies (the average of 8Eu is 0.64) and the loss of Sr is strong, which are likely originated from the partial melting of accreted lower crust. Combined with previous reasearches, this paper considers the diagenesis and mineralization of Erdaohezi deposits occurred in the Late Jurassi.The study of fluid inclusion show indicates fluid inclusions have mainly liquid-rich inclusions and vapor-rich inclusions with a small amount of daughter mineral-bearing inclusions; The homogenization temperature, salinity and density of fluid inclusion are 160-220℃,5.55-11.95 wt% and 0.74-1.08 g/cm3, respectively. Fluids pressure is between 6.51-37.75Mpa and mineralization depth is between 0.65-1.12km. The studies of fluid inclusion showed that the ore-forming fluids have characteristics of low salinity and low-temprature. Reference regional data of S, Pb isotope speculate that forming materials comes from the mantle and the involvement of crustal material.The research demonstrates that the Erdaohezi Pb-Zn deposit which is occupied by fault and closely related to volcanic and subvolcanic hydrothermal, is a middle temperature hydrothermal Pb-Zn deposit formed in continental intaraplate extensional tectonic environment formed in extensional tectonic environment.