The Baoshan-Zhenkang terrane is one of the important lead-zinc polymentallic orefields in the southern part of the Sanjiang metallogenic belt, with complex geology and tectonics as well as very favorable Pb-Zn mineralization conditions. Two large-size Pb-Zn deposits were recently discovered in the Hetaoping and Luziyuang ore districts, which are apparently controlled by approximately NE-trending faults, anticlinal axis and strata. Marbleized limestone of Upper Cambrian Hetaoping and Shahechuang Formation is the ore-bearing horizon in this area, with proximal strong skarnization. Based on a comparative study of geochemical characteristics of fluid inclusions, lead, sulfur, hydrogen and oxygen isotopic compositions and trace elements from the two Pb-Zn deposits, the authors have reached the follow conclusions: The Hetaoping and Luziyuan Pb-Zn deposits have expe- rienced medium-temperature and high-temperature ore-forming stages; Compared with lead isotope compositon of the Luziyuan Pb-Zn deposit, lead isotope composition of the Hetaoping Pb-Zn deposit has a relatively high ratio and a wide range. Both ore districts, however, have radiogenic Pb isotopic ratios and are characterized by high μ values, suggesting a dominant input of Pb from crustal sources;Sulfur isotopic composition of the Hetaoping and Luziyuang deposits is characterized by lower positive δ 34S values and tower-type distribution, showing an involvement of deep magmatic sulfur; both ore deposits have not been subjected to the effect of biotic thermo-chemical reduction of sulfate, and has reached fractionation equilibrium of sulfur isotope; Hydrogen and oxygen isotope composition of quartz coexistent with sulfides indicates that the ore-forming fluid from the Hetaoping deposit was mainly derived from magmatic water with the mixture of meteoric water and stratigraphic water; The characteristics of trace elements of the two deposits are consistent with those of magmatic hydrothermal deposits, and do not resemble those of VMS type and MVT type Pb-Zn deposits. Therefore, both deposits belong to high-medium temperature skarn type Pb-Zn deposits associated with deep concealed intrusion, and the emplacement of the deep concealed intrusion in the ore districts was followed by the addition of Pb-Zn rich magmatic fluid into the intersection of anticline axis and NE-trending faults and the mixing with stratigraphic water and meteoric water, thus resulting in the formation of this type of ore deposits.%保山镇康地块是“三江”南段重要的铅锌多金属成矿区之一,地质构造复杂,铅锌成矿地质条件优越,其中核桃坪与芦子园是近年发现的两个大型铅锌矿床,矿床受近NE向断裂、背斜轴部和地层控制明显,上寒武统核桃坪组与沙河床组大理岩化灰岩为主要赋矿地层,近矿围岩矽卡岩化强烈,流体包裹体,Pb、S、H、O同位素和微量元素等地球化学对比研究表明:核桃坪和芦子园铅锌矿床均经历了中温、高温两个矿化阶段；核桃坪铅锌矿床矿石铅同位素较芦子园铅锌矿床有较高的比值和较大的变化范围,均以高μ值为特征,属于放射性成因铅,暗示其成矿物质以壳源铅为主；硫化物硫同位素均多为较低正值并呈塔式分布,具有岩浆硫特征,两者均无生物硫酸盐热化学还原作用的参与,其中硫同位素分馏已达平衡；与硫化物共生的石英δDH2O(-109‰～-91‰)和δ 18OH2O(-4.3‰～2.3‰)同位素研究表明核桃坪矿床成矿流体主要来自深部岩浆水,并遭受后期大气降水或地层水的混合；核桃坪矿床与芦子园矿床的微量元素具有岩浆热液型矿床特征,不同于VMS型、MVT型铅锌矿床.因此,笔者认为两个矿床应属于与深部隐伏岩体有关的中-高温矽卡岩型铅锌矿床,矿区深部隐伏岩体的侵入产生岩浆热液并携带Pb、Zn等成矿物质与地层水或大气降水混合,在背斜轴部与NE向断裂的交汇处形成该类型矿床.
展开▼
