The Geochemical Characteristics And Diagenesis Of Ore-forming Diorite-porphyrite From Shuangjianzishan Ag Polymetallic Deposit In Inner Mongolia

Shuangjianzishan Ag polymetallic deposit is a hultra-huge hydrothermal vein type deposit in the middle-southern part of Da Hinggan Mountains including an Ag polymetallic vein group and two orebodies in different trends. Orebodies were hosted in silty slate and argillite of Dashizhai formation in lower permian system and mineralization was in ductile shear zone or inside of diorite-porphyrite, metallogenic belts were in thin veins and disseminated. Orebodies were pyritized、silicified and being chloritization. Ores are mainly consist of pyrite、 galena、sphalerite and so on. Gangue minerals are quartz、calcite、chlorite、muscovite、epidote and so on. Silver minerals mainly are argentite、native silver、canfieldite、polybasite. Ore textures are automorphic-hypautomorphic granular、allotriomorphic granular、structural residual、influnced by stress action and including structure. Ore structure are block、veinlet and banded structure.Geochemistry characteristics show: The left elements such as Rb、Ba、Th、U is enriched relatively, HSFE is dificited. Rb/Sr is 0.72~3.50, average value is 2.42>2; Sr/Ba is 0.06~0.35, average value is 0.15<0.5; Zr/Y is 2.17~20.69, average value is 14.30>5; radioactive elements Th/U is 2.50~3.94, average value is 3.40>3; Nb/Ta is 8.77~28.88,average value is 16.23; Sr is(37.60~110.90)×10-6, belongs to deficit type of Sr.The curves of rare earth dictribution slant right, belongs to the LREE enrichment type. The fractionation of LREE and HREE is significant. δEu is 0.22~1.23 which belongs to negative Eu anomacies, δCe is 1.02~1.14 belongs to positive Ce anomalies. LREE/HREE and ΣREE were curvilinear showing that magma source were a mixture of remelting of mantel and crust. δEu and LREE/HREE were also curvilinear showing the same conclusion.According to the results of SHRIMP U-Pb the ore-forming diorite-porphyrite was emplaced and crystalized in the early Triassic(249.1Ma).