Geological Characteristics And Ore Genesis Of Baiyinnuoer Pb-Zn Deposit In Chifeng City, Inner Mongoiia

Baiyinnuoer Pb-Zn deposit is located in Baiyinwula town, Balin left banner,Chifeng, Inner Mongolia, and its geotectonic position belongs to the late Paleozoicorogenic belt, southern Great Hinggan Mountains. In order to fully explore old mineresource, solve the problem of deep ore exploration and genesis theory, extend themine service life as much as possible, and provide strong support for the localeconomic development, this paper mainly elaborates the type of ore-controllingstructure, the source of ore-forming material as well as the characteristics ofOre-forming fluid, and systematically summarizes and discusses the geologicalcharacteristics of ore deposit and the type of genesis in combination with the previousresearch results.Exposed strata in the mining area are relatively simple, mainly including EarlyPermian Dashizhai Formation and Zhesi Formation, Late Jurassic ManketoueboFormation and Manitu Formation and Quaternary deposits; Structure of the study areaobviously controlled by regional tectonic, and are relative development of folds andfaults, characterized by early distinctly deformed folds and advanced faults. Based onthe1:2000measurement of geological cross-section within the mining area andadjacent regions, as well as logging of the tunnel, it shows that the generation ofBaiyinnuoer Pb-Zn orebodies were controled by both folds and faults; Magmaticrocks are widely distributed in the mining area, according to the field geological dataand predecessors’ achievements, we can find that the igneous rocks, closely related tothe mineralization of Baiyinnuoer Pb-Zn deposit, mainly consist of granodiorite(porphyry), diorite porphyrite and quartz porphyry.Mining area can divided into north and south ore belts, which have differences inquantity, scale, occurrence, thickness and grade, etc. Based on the mineral associations, texturea and structure, and the cutting relationship between minerals ortheir aggregation, the hydrothermal mineralization of Baiyinnuoer pb-zn deposit isdivided into two metallogenic periods and five metallogenic stages. Based on theanalysis of the alteration type and its distribution rule, the distribution of chloritizationis extensive, and as the distance from the ore bodies shortening, the degree ofalteration has gradually decreasing trend. Skarn rocks, containing diopside, garnet andother different types of skarn minerals, commonly occur in centrally mineralized areasand the surroundings, indicating that the skarnization have obvious connection withthe mineralization. However, the skarn zones without mineralization in some areassuggest that the skarnization does not have a direct contact with mineralization,whereas the skarn zones with distinct carbonatization and silicification often producea certain scale of ore body, indicating that skarnization areas accompanied by a certaincarbonatization and silicification, is most likely obviously mineralized areas.The analysis of S and Pb isotopic elements from metal sulfide in the ore indicatesthat the ore-forming material mainly originated from the magma. Based on the studyof fluid inclusions, Ⅰ-1stage mainly developed Vapor-Liquid (VL-type), vapor-rich(LV-type) and NaCl-bearing Mineral (SL-type) fluid inclusions. The homogeneoustemperature of VL-type fluid inclusions ranges from375.4℃to479.8℃, and theirsalinity varies from10.73％to13.73％NaCleqv；the homogeneous temperature ofLV-type fluid inclusions ranges from415.2℃to458.4℃, and their salinity variesfrom5.32％to7.67％NaCleqv；and the homogeneous temperature of SL-type fluidinclusions ranges from434.6℃to497.5℃，and their salinity varies from42.15％to45.25％NaCleqv. The fluids of Ⅰ-1stage belong to the immiscible NaCl-H2Ohydrothermal system with medium-high temperature and high salinity. Ⅰ-2stagemainly developed VL-type and LV-type fluid inclusions. The homogeneoustemperature of VL-type fluid inclusions ranges from202.3℃to345.7℃, and theirsalinity varies from5.17％to11.22％NaCleqv；and the homogeneous temperatureof LV-type fluid inclusions ranges from265.7℃to381.9℃, and their salinity variesfrom1.98％to5.01％NaCleqv. The fluids of Ⅰ-2stage belong to the unevenNaCl-H2O hydrothermal system with medium temperature and medium salinity. Ⅱ-2stage (the main metallogenic stage) mainly develops VL-type fluid inclusions, thehomogenization temperature and salinity of which ranges from165.9℃-258.7℃and0.83％-5.62％NaCleqv, respectively, indicating that the fluids of Ⅱ-2stage belong to the uniform NaCl-H2O hydrothermal system with medium-low temperature andlow salinity. The above-mentioned indicate that metallogenic fluids underwent theevolution from the immiscible NaCl-H2O hydrothermal system with medium-hightemperature and high salinity to the uniform NaCl-H2O hydrothermal system withmedium-low temperature and low salinity, and in the process the system varied fromboiling to natural cooling, which should be the main mechanism of industrial orebodyenrich in Pb，Zn and other metal elements. Based on hydrogen and oxygen isotopicanalysis of the fluid inclusions, ore-forming fluid should be magmatic water in theearly stage of mineralization, while it is provided by a great deal of atmospheric waterat the end of mineralization, and mixing of atmospheric precipitation plays a promoterole in the process of mineral enrichment. In summary, we conclude that BaiyinnuoerPb-Zn deposits blong to skarn type Pb-Zn polymetallic deposit, which had beeninfluenced by two stages of mineralization, i.e., the main mineralization duringIndosinian period and the superposition of mineralization in Yanshanian period.