Primary study on lead-zinc mineralization of Yangla copper polymetallic deposit, northwest Yunnan province, China

The Yangla copper deposit which is located in the middle of Jinshajiang tectonic belt, is the most typical copper deposit in the northwest of Yunnan province. In recent years, Pb-Zn orebodies were newly discovered in the depth of Yangla copper deposit, Pb-Zn orebodies mineralization and its genetic relationship with copper ore bodies have become a new scientific problem. In this paper, the rare earth elements and C-O, S, Pb and Zn isotopes geochemistry of Pb-Zn orebodies were mainly studied, on the basis of tunnel geological logging and rock-mineral identification. The Pb-Zn ore bodies of Yangla deposit are mainly of skarn type, which are distributed in the edge of skarn type copper bodies in the form of stratiform, irregular veins and lenticular, and co-produced with skarn type copper bodies. It is obviously characterized by branch-compound and ore bodies' reappearing after disappearing. The second is hydrothermal vein type, which filled in the structural fracture zone with irregular veinlike shape. Calcite associated with Pb-Zn orebodies can be divided into early mineralization stage calcite (Ⅰ) and late mineralization stage calcite (Ⅱ). The early mineralization stage calcite (Ⅰ) mainly occurs in the Pb-Zn orebodies in irregular clumps, and anhedraal crystal, ΣREE of calcite (Ⅰ) is between 24.05×10-6 and 104.50×10-6, δEu shows positive anomalies, δCe displays weak negative anomalies, chondrite-normalized REE patterns are LREE-rich. The δ13CPDB and δ18OSMOW of calcite (Ⅰ) are between -6.52‰--4.07‰ and 5.04‰-9.94‰, respectively, indicating that the metallogenic materials are mainly from granitic magma. The late mineralization stage calcite (Ⅱ) is produced veins in the Pb-Zn orebodies, ΣREE of calcite (Ⅱ) is between 28.71×10-6 and 114.60×10-6, δEu shows positive anomalies, δCe displays weak negative anomalies, chondrite-normalized REE patterns are LREE-rich. The δ13CPDB and δ18OSMOW of calcite (Ⅱ) are between -3.81‰--3.53‰ and 14.36‰-17.30‰, which proves that the ore-forming material comes from the mixing of granitic magma and marine carbonate rocks. Calcite in early and late metallogenic stages are of hydrothermal origin, and there is no significant difference in the content of rare earth elements. The δ34S of sulfide (n=38) in Pb-Zn orebodies are between -2.48‰ and 2.32‰, total sulfur isotope is close to zero, indicating that the metallogenic materials are derived from mantle and deep crust. The lead isotopic variation range of sulfide (n=15) is small, the 208Pb/204Pb, 207Pb/ 204Pb and 206Pb/204Pb range from 38.7501 to 38.7969, 15.7159 to 15.7248, and 18.3640 to 18.3874, respectively, indicating that the lead in Pb-Zn orebodies mainly comes from the upper crust. The δ66ZnJMC of sphalerite (n=5) is between 0.31‰ and 0.44‰, which is obviously higher than other skarn type Pb-Zn deposits, and it also reveals that the metallogenic Zn mainly comes from magma. There is no significant difference between the Pb-Zn orebodies and Cu orebodies in terms of host-rock layers, orebodies attitude, mineral association, ore fabrics, wall rock alteration, ore-controlling factors and isotope composition of C-O, S, Pb, which shows that the Pb-Zn orebodies and the Cu orebodies are of the same origin and are the products of the same metallogenic process. Pb-Zn orebodies is later than the Cu orebodies, which is the product of the late metalogenic stage and distributed at the edge of Cu orebodies. Based on the above research data, the Cu-Pb-Zn metallogenic pattern of Yangla deposit is established in this paper. © 2021, China Science Publishing & Media Ltd. All right reserved.