| Baoshan Cu-Pb-Zn polymetallic deposit is located in the north edge of the middle section of the east-west the Nanling Mountain tectonic magmatic metallogenic belt in China,and in the west of the intersection of the Leiyang Linwu north-south fault metallogenic belt and the Chenzhou Linwu north-east deep fault belt.It is a typical representative of the skarn type Cu-Pb-Zn polymetallic deposits in this area.Based on the field geological survey of the deposit and combined with the study of the geological characteristics of the deposit,a large-scale(1:100)fine measurement of the typical cross vein(165+169 exploration lines)in the middle level of the exploration and mining face with the lowest elevation in the mining area was carried out.Through the analysis of rock and ore control structures,the rock and ore control laws of the Baoshan deposit were summarized;By comparing the differences of mineralization alteration between horizontal and vertical ore-forming rocks and carbonate rocks,and combining the geochemical zoning characteristics of trace elements and mineralization elements,the mineralization alteration zoning rules are summarized,and the mineralization alteration zoning model is established.LA-ICP-MS was used to carry out in-situ micro analysis of calcite and garnet,and extract their indicator information for structure alteration.Comprehensive structural alteration mineralization information,construct a structural prospecting model for the Baoshan copper lead zinc polymetallic deposit,propose deep exploration directions,and provide a basis for the deployment of 3000 m deep drilling in the southern Hunan section of the National Deep Ground Plan project,which has achieved verification results.The main achievements and understandings are as follows:(1)The study of rock and ore controlling structures shows that the Pingbao ore field and Baoshan ore deposit are respectively in the form of "well" structural assemblage and composite structural assemblage,and there are four structural assemblages in the ore body(vein),namely,inverted ―entering‖ structural assemblage and structural breccia,silica calcium surface,hydrothermal breccia and magmatic intrusive breccia assemblage.The structural classification and rock and ore control laws correspond to the scale and structural combination style of the deposit,ore bodies,ore veins,and structural combination styles,showing the characteristics of equidistant distribution of ore control faults;(2)Characteristics of mineralization alteration zoning: taking granodiorite porphyry as the center on the whole,it presents the change law of altered granodiorite porphyry zone(I zone)→mineralized skarn zone(II zone)→marlite limestone zone(III zone)→calcite limestone zone(IV zone).The REE characteristics of the skarn are highly similar to those of the granodiorite porphyry,which may suggest that the ore-forming fluid mainly originates from the granodiorite porphyry;(3)The study of characteristic mineral calcite shows that calcite(type I),calcite(type II)of ore body and calcite(type III)of rock body are exposed in the deep part of the mining area,and calcite varies from type I to type II to type III,The gradual increase of ΣREE,LREE,and HREE indicates that the ore-forming fluids mainly come from magmatic hydrothermal fluids,with the addition of atmospheric precipitation in the later stage.The fluid evolution undergoes a transition from reduction to oxidation to reduction;(4)The study of characteristic mineral garnet shows that type I andradite(Grt-Ⅰ)and type II cadherin aluminum garnet solid solution series(Grt-Ⅱ)have the same origin;Grt-I is formed in a Fe rich,high oxygen fugacity alkaline environment,while Grt-II forms a weak oxidation weak reduction weak alkaline environment.The oxygen fugacity gradually decreases from Grt-I to Grt-II,and changes from oxidation to weak oxidation weak reduction environment;Its compositional characteristics are similar to garnet in typical skarn type copper deposits in the world,and are closely related to mineralization of Cu,Fe,Mo,Zn,Sn,etc.The Sn content of the ore-forming element shows a trend of increasing towards the deep,indicating potential for mineralization;(5)Based on the study of tectonic alteration zoning rules,combined with the relationship between rock and ore controlling structures and the deep extension of ore bodies,a structural prospecting model for Baoshan Cu-Pb-Zn polymetallic deposit was established,and two prospecting prediction areas,I-1 and I-2,were proposed. |
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