Geochemical Characteristics and Genesis of Copper and Nickel Minerals in the Fule Pb-Zn Deposit, NE Yunnan Province

The Fule deposit, which is located in the southeastern part of the Sichuan, Yunnan and Guizhou Pb-Zn polymetallic ore cluster in China, is a typical disseminated element-rich Pb-Zn deposit. In this study, a few nickel and copper-bearing sulfides were recognized in the ores of this deposit, including vaesite, gersdorffite, zinc-bearing vaesite, zinc-tetrahedrite, zinc-tennantite, and chalcopyrite. The nickel-bearing sulfides are radially distributed in the hydrothermal dolomite veins containing sphalerite and galena. Microscopic observation reveals that these minerals are commonly ring-banded, i.e. the core is gray irregular vaesite, the transition zone is white irregular gersdorffite, and the rim is zinc-bearing vaesite. The EDS data show that (1) the vaesite contains 45.4% to 47.3% Ni, 51.1% to 53.1% S, and 0.30% to 0.70% Fe; (2) the gersdorffite contains 31.1% to 34.3% Ni, 17.1% to 27.3% S, 35.4% to 42.2% As, and from 5.3% to 14.1% O; (3) the Zn-bearing vaesite contains 39.0% Ni, 44.2% S, 12.6% As, and only 3.4% Zn. Most of the fahlore group minerals occur inside of or along the edge of sphalerite, and less in hydrothermal dolomite veins or fissures; and their morphology is mostly irregular patchy, star-shaped and vein-like. EPMA data show that the zinc-tetrahedrite has Cu contents of 35.89% to 37.99%, Zn of 6.92% to 8.10%, Sb of 25.19% to 26.92% and As of 1.61% to 2.36%, while the Cu contents of zinc-tennantite range from 38.38% to 40.70%, Zn from 5.02% to 10.81%, As from 9.43% to 20.00%, and Sb between 0.12% and 14.44%. The δ34S values of nickel-bearing sulfides vary widely from –6.0% to 14.5%0, and the δ34S values of fahlore vary from 0 to 4.0%0. Combined with the geologic and geochemical characteristics of this deposit, it is suggested that Cu and Ni in the Fule Pb-Zn deposit might have derived from the Cambrian black rock series. Vaesite and gersdorffite were formed during sedimentary diagenesis, while Zn-bearing vaesite, zinc-tetrahedrite, and zinc-tennantit were formed during the Pb-Zn metallogenic stage, specifically zinc-bearing vaesite was formed through metasomatism of preexisting sulfides by Zn-rich fluids. The ore-forming hydrothermal fluids may interact with the Cambrian black shale and leach Ni and Cu as they migrate along the Mile-Shizong deep fault, and concentrate these ore metals in the fracture-rich part of the Permian Yangxin Group. © 2022 Science Press. All rights reserved.