Genetic Mineralogy Of Garnet And Sphalerite In Baiyinnuo'er Lead-Zinc Deposit,Inner Mongoli

The Baiyinnuo'er Pb-Zn deposit located in the eastern portion of the Xing-Meng orogenic belt,is one of the largest Pb-Zn deposit in the Daxing'anling region or even the northeastern China.Detailed study on its metallogenic timing processes,and genetic stlye is of vital to gain new insights into the regional metallogenic regular and ore prospecting in deep.The Baiyinnuo'er Pb-Zn deposit is a skarn type Pb-Zn deposit.according to petrography and the spatial cutting relationship of rock mass,three mineralization stages can be identified:pre-mineralization stage?gart-clinopyroxene-magnetitesulfide?;main ore-forming sta ge?sulfide-epidote-quartz-calcite?;post mineralization stage?calcite-chlorite-quartz-fl uorite?.In this paper,EPMA analysis and LA-ICP-MS in-situ trace element analysis were carried out on garnet in the pre-mineralization stage and sphalerite in the main ore-forming stage,thus revealing the fluid and its evolution characteristics.The NE-trending structure is the main ore-controlling structure of the Baiyinnuo'er Pb-Zn mine,and the existence of silica-calcium surface provides a good environment for ore-hosting.Since the ore-forming geological body in the mining area has not yet been revealed,it is particularly important to determine the location and age of the ore body.Therefore,zircon U-Pb dating is carried out to define the ore-forming age for magmatic rocks in the mining area,and derived some results and conclusions as follows:?1?The erupting age of the debris tuff lava crosscut by ore body,is constrained at 149.9±2.5Ma by the method of LA-ICP-MS zircon U-Pb dating,and the emplacement age of diorite porphyrite cut across the ore body is constrained at140.3±2.6Ma,reflecting the metallogenic timing is in the range of 149¹40Ma.?2?EPMA results of garnet from the Baiyinnuo'er ore show that garnet is mainly almandine and a small amount of Almandine-andradite.In situ LA-ICP-MS trace data analysis results show that garnet is deficient in LREE,enriched in HREE,and Eu is abnormal.The electron probe results of garnet from another ore deposit?Kaiyuan Lead-Zinc Mine?in the mining area show that it is mainly andradite.In-situ LA-ICP-MS trace data analysis results show HREE deficiency,LREE enrichment and Eu positive anomaly.During the further analysis of the main trace data,the linear relationship between Y and?REE was used to know that the metallogenic environment was unstable and the fluid composition changed.The Y/Ho-La/Ho diagram and Y/Ho value show that the magmatic hydrothermal fluids of the two deposits are similar.The growth process is not only affected by magmatism,but also affected by hydrothermal fluids.The ore-forming environment of the Kaiyuan deposit is alkaline oxidized contrastingly,the ore-forming environment of the Baiyinnuo'er deposit is acidic reduced.?3?The chemical composition of sphalerite In the Kaiyuan-Baiyinnuo'er Pb-Zn deposit is mainly characterized by enrichment of element of Mn,Fe,Cu,Se,Cd,In,but relatively depleted in Ga,Ge and Tl.For the scattered elements Cd/Fe in the Kaiyuan-Baiyinnuo'er deposit are 0.03-0.11,0.01-0.19 respectively,with average values of 0.06 and 0.07;Cd/Mn are 0.26-1.4 and 0.46-3.20 respectively,with average values of 0.60 and 1.48,indicating that a large amount of magmatism took part in the ore-forming process,and the characteristics of Ga-poor and Ge-poor deposits also meet the standards of skarn deposits.The maximum values of Ga/In in the two deposits are 0.031 and 0.20 respectively,with average values of 0.11 and0.04.The maximum values of Ge/In are 0.04 and 0.12 respectively,and the average values are 0.01 and 0.03.The Ge content in the ore concentration area is less than5×10^-6,which indicates that the mineralization temperature is high temperature mineralization,and the temperature of open source deposit is higher.?4?Summarize the content of the above research and the metallogenic re gularity of the Huanggangliang Fe-Sn ore and the Haobugao Cu-Zn?Sn?ore i n the region,and determine that the Kaiyuan deposit is the deep part of the Baiyinnuo'er deposit,and establish the metallogenic model of the Baiyinnuo'e r Pb-Zn deposit,and provide the possibility for prospecting and prediction ac cording to the Sn mineralization characteristics found in the mining area and the Sn content measured in garnet.