Metallogenic Characteristics And Metallogenic Mechanism In The Wurinitu W-Mo Deposit In Inner Mongolia, China

The Wurinitu W-Mo deposit, located in the northwestern of the Wurinitu Village, Chagan’aobao County, Sunid zuoqi, Inner Mongolia, is a large scaled deposit which is discovered in recent years. The orebodies, in stratiform-like, tabular shape, veinlet and dissemination structure, mainly occurred in Yanshannian granite rock body and the nearby contact zone.Based on the study of the historical research data and geological features of ore deposit, the author carried out a LA-ICP-MS U-Pb chronological study of zircons. The U-Pb dating results from the granites are 139 Ma, respectively, indicating that they were formed in early Cretaceous, late Yanshanian stage. The character of rock geochemistry shows that the granites belongs to high K calc-alklline magama, strongly peraluminous. Chemically,the granitoid belong to A-type, implying that they formed under an extensional tectonic setting.The fluid inclusion microthermometry, Laser Raman spectroscopic, inclusion groups components and hydrogen oxygen isotopes studies suggest that the main types of fluid inclusions for Wurinitu metallogenic fluid system are two-phase vapor-liquid inclusions, vapor-rich phase inclusions, liquid-rich phase inclusions and pure liquid phase inclusions, occasionally two bubbles occurs in some fluid inclusion. The ore-forming fluid is a fluid system of medium-low temperature,medium-low salinity, low density, medium-low pressure and medium-low depth. The liquid composition of the ore-forming fluid are maily Ca²⁺, Na⁺, SO₄^2-, Cl^-, some K⁺, F^-, Mg²⁺ and NO₃^-, and less Br^- and Li⁺, While the gas composition are mainly H₂O and CO₂, some N₂ and O₂, and less CO, CH4, C₂H₂, C₂H₄ and C₂H₆. The ore-forming fluids belong to the H₂O-NaCl-CO₂ system and came from the mixing of magma water and meteoric water.The sulfur isotopic compositions of pyrite in the deposit show the δ34SV-CDT values（0.6‰ to 4.1‰）varies in a very limited range, which suggests the character of magmatic sulfur. The lead isotope isotopic compositions indicate that the mineraliation may be induced by the magmatism, and ore-forming materials is characterized by the source of lower crust and show crust-mantle mixing. The carbon and oxygen isotope analysis shows that the calcite forms in two minealization stages. The CO2 in the earlier stage is mainly related to the magma, and the later hydrothermal ore fluids show the characteristics of mixture fluids of meteoric water with magmatic water as the meteoric water add. When the ore-forming fluids migrated along the structure and wall rock crack, it experienced immiscibility or the boiling action, also mixed with meteoric water in the later ore-forming stage. As the physicochemical conditions changed in the ore-forming fluid system, the W-Mo complexes decomposed and caused the precipitation and enrichment of ore-forming materials in appropriate space.