川滇黔接壤地区铅锌矿床成矿物质来源:方铅矿原位Pb同位素制约

位于扬子板块西南缘的川滇黔铅锌矿集区,是我国以碳酸盐岩为容矿岩石的铅锌矿产最为集中发育的区域,在我国铅锌成矿区/带中占有重要地位。尽管以往研究取得了丰硕的理论认识和找矿成果,但是对研究区铅锌矿床的成矿物质来源一直存有争议。以9个赋存于震旦系(乌斯河、赤普、银厂沟和茂租矿床)、泥盆系(火德红、毛坪和猫榨厂矿床)和石炭系(毛坪、会泽、亮岩和猫榨厂矿床)中的铅锌矿床为例,进行了较为系统的方铅矿原位Pb同位素地球化学综合研究。结果表明:①乌斯河、赤普、银厂沟、茂租、火德红、毛坪、猫榨厂、会泽、亮岩矿床原位Pb同位素组成的线性关系明显,其Pb-Pb等时线年龄约为2.5 Ga((2 574±30)Ma),暗示这些矿床的成矿物质来源相同,且太古代—古元古代结晶基底岩石是最可能的主要金属源区; ②在赋矿地层时代上,Pb同位素组成由老(震旦系)至新(石炭系)逐渐增加; 在赋矿层位空间上,Pb同位素组成由北(西)部的乌斯河、赤普矿床向南(东)部的猫榨厂、亮岩矿床逐渐增加; 这些特征暗示其是同一成矿流体不同演化阶段的产物,且在区域尺度上来源或流经结晶基底岩石的成矿流体由深部向浅部、由北(西)向南(东)方向运移演化。

Source of Ore-forming Materials for the Carbonate-hosted Pb-Zn Deposits in Sichuan-Yunnan-Guizhou Adjacent Area,SW China: Constraints of Galena In-situ Pb Isotopes

The Sichuan-Yunnan-Guizhou Pb-Zn metallogenic province, located in the southwestern margin of the Yangtze Block, is the most intensively developed region of carbonate-hosted Pb-Zn deposits in China. Both the number of Pb-Zn deposits/spots(more than 500)and the amount of Pb and Zn metal reserves(more than 2 000×10⁴ t)play an important role in the Pb-Zn metallogenic regions/belts of China. Although the previous research has made fruitful theoretical understanding and prospecting achievements, there has been a dispute on the source of ore-forming materials of the Pb-Zn deposits in the study area. A systematic In-situ Pb isotope analysis of galena from nine Pb-Zn deposits hosted in the Sinian(Wusihe, Chipu, Yinchanggou and Maozu deposits), Devonian(Huodehong, Maoping and Maozachang deposits)and Carboniferous(Maoping, Huize, Liangyan and Maozachang deposits)carbonate rocks was carried out. The results show that ① the In-situ Pb isotopes of galena in all deposits have an obvious linear relationship, and their Pb-Pb isochron age is about 2.5 Ga((2 574±30)Ma); it is suggested that the sources of ore-forming metals for these deposits are the same, and the Archean-Paleoproterozoic crystalline basement rocks are the most likely major metal source; ② in the age of ore-bearing strata, the Pb isotopes gradually increase from the old(Sinian)to the new(Carboniferous); in the space of ore-bearing horizon, the Pb isotopes gradually increase from Wusihe, Chipu deposits in N(W)to Maozachang, Liangyan deposits in S(E); it is indicated that they are the evolvement products of the same ore-forming fluids in different stages, and the crystalline basement-derived and/or flowed ore-forming fluids evolve and migrate from deep to shallow, and from N(W)to S(E)on a regional scale.