Geochemical Characteristics And Source Of Ore-forming Materials For The Xishanwanyangchang Ag-Pb-Zn Deposit, Inner Mongolia

Xishanwanyangchang Ag-Pb-Zn deposits located in the east margin of Mesoproterozoic-neoproterozoic rift groove of Lang mountain-Zhaertaishan in the north China margin, belonging to Zhaertaishan mountain regions in the central and western Inner Mongolia Autonomous Region, where is a favorable metallogenic band. The previous geological datas of the research area are based on full collection, in order to analysis into the source of minerals that combines with petrology, geochemistry and mineralogy other multi-disciplinary research methods, systematic research of its geochemical characteristics.Ag deposits are mainly occured in the acidic volcanic rocks of lower series of Cretaceous Bainvyangpan Formation(K1bn). Host rock mainly is rhyolite, rhyolite porphyry and rhyolite breccia. Pb-Zn deposits are hosted in deep tonalite rock of Precambrian. The desposit is obviously affected by fractures. Local faulted structure is well-developed and it provides adequate structural conditions for hydrothermal activity and forming ore material enrichment.The tonalite host rocks of the Pb-Zn ore in the deposit, are characteristic of rich Si, Al, Na, poor Ca and Mg. It is a metaluminous-peraluminous calc alkaline rock. Meanwhile the rock possesses geochemical characteristics of adakitic rocks. The total REE content is higher, ∑REE=105.32×10-6~298.07×10-6, LREE are strong enrichment, LREE/HREE=11.78~38.44, the REE show strong positive europium anomaly and weak negative cerium. La/Nb, Nb/U, Nb/Ta show the crust-mantlemixing characteristic.Trace element characteristics indicate that ore minerals pyrite enriched in LILE Rb, U and loss of high field strength elements Nb, Ta, Zr, Hf etc. REE is total lower and its pattern is right-wing, LREE is displayed enrichment type and shell source type with mineral coming from the lower crust. Pyrite has obvious positive Eu anomaly, Ce does not have obvious abnormalities indicating Pb-Zn mineralization(greater than 250 ℃) in a higher temperature and relative reduction of fluid characteristics. Meanwhile, pyrite Hf / Sm, Nb / La, Th / La were less than 1 indicating that the ore-forming fluid lost HFSE, enrich Cl. Pyrite with Y / Ho(26.24 ~ 29.35), Zr / Hf(10.46 ~ 29.43), Nb / Ta(6.36 ~ 20.50) changes in a large range. Therefore, pyrite mineralization may be subject to late stage hydrothermal activity at the time and metasomatism associated interference.Sulfur isotope composition delta is 4.0 ‰ ~ 6.1 ‰ which is changes in the scope of the narrow. it shows a tower distributional effects, which reflects the comparison of the total sources of sulfur in ore and the characteristics of magmatic sulfur. With the low μ(9.28~9.74) and high ω(38.57-43.61) characteristics of the Pb isotopic composition of the ore, which indicates from the source region of the enriching Th and deficiting U, it shows the characteristics of the lower crust. Pb isotope tectonic environment diagram and Pb isotope tectonic model both shows that Pb is mainly from the lower crust.Geochemical characteristics show that the mine ore-forming substances of Pb-Zn ore body are mainly derived from the lower crust. In the process of upward migration of hydrothermal solution, ore bearing minerals of tonalitic were enriched.