| Located in the Wulashan Mountain which belongs to the middlepart of the north edge of Huabei Craton, the Xishadegai molybdenum ore deposit which is a medium-sized porphyry type of ore deposit, is gripped by the Huhehaote-Baotou Fault and the Linhe-Jining Fault. For a long time, the previous researches on this ore deposit is mainly focused on the geological characteristics of the ore deposit and the ore geochronology, which is not comprehensively enough. The geochemistry and geochronology of the magmatic rock, the characteristics and the source of the fluid inclusion, however, has not been reported, which restrains the deep and peripheral prospecting work. Based on the detailed field work and gathering the samples, this research is mainly concentrated on the systematic laboratory research, including slides identifying and the research about the geochemistry, geochronology, fluid inclusion and the stable isotope geochemistry about the Xishadegai ore deposit. According to this research, the characteristics of the ore deposit has been investigated and deepen, the genesis of it has been ascertained. Furthermore, the metallogenic model has been established preliminarily.The Xishadegai molybdenum ore deposit is hosted by the Wulashan Mountain Group, Mesoarchean. Controlled by the fracture, ore bodies occur as NEE-EW trending vein. The quartz vein type of ore dominated with semi-euhedral granular texture and disseminated and vein types of structure. Molybdenum and pyrite is the main part of the metallic minerals. While the sphalerite, chalcopyrite, magnetite occupies a small part. And quartz, k-feldspar, plagioclase, fluorite and sericite dominated the non-metallic minerals. The alteration of the wall rock featured by the greisenization, k-feldspathization and pyritization with a small quantity of sericitization. The mineralization process can by identified as three stages, including ash black stage, smoky gray stage and oyster white stage.The geochemistry research for magmatic rock shows that it riches in silica and potassium but lacks in Na, which belongs to high-potassium cal-alkaline series and peraluminous. Riches in LILE such as Ba, K, Sr and HFSE, U, Th, for instance, the magmatic rock depletes in Ti and P which is HFSE. LREE weighs more in the rock, the chondrite-normalized REE patterns for Xishadegai magmatic rock is right inclined. Besides, it shows Eu negative-anomaly slightly. The magmatic rock of Xishadegai is highly differentiated I-type granite and syn-collision to post-collision entirely. The research for chronology by zircon U-Pb data shows that the rock occurred at 232.7Ma±4.1Ma, which derives from the magmatism of early-Triassic to middle-Triassic, Indo-china period.The petrography and micro-thermometry of fluid inclusion indicates that liquid-vapor two-phase aqueous inclusions and CO2-H2 O three phase inclusions dominates in the Xishadegai ore deposit. Combined with Laser Raman analysis, the ore-forming fluids featured by moderate-low temperature, moderate-low salinity and moderate density. Fluid immiscibility occurred in the mineralization process, which is the supreme system leads the formation of the Mo ore deposit, proofs demonstrated. The ore-forming fluid is a mixture of magmatic water and meteoric water, and the latter one contains more. Moreover, some phenomenon argures that severely degasification and δ18OH2O drift took place.In conclusion, the geological features, metallogenic background, geochemistry features and the characteristic and property mineralization fluid points out that the Xishadegai molybdenum ore deposit belongs to porphyry type of ore deposit, which controlled by stratigraphy, tectonics, magmatic rock and geochemistry. Furthermore, genetic type has been checked clearly, and theore genesis has been established. |
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