Two‐Stage Sulfide Mineral Assemblages in the Mineralized Ultramafic Rocks of the Laowangzhai Gold Deposit (Yunnan, SW China): Implications for Metallogenic Evolution

Abstract

The Laowangzhai gold deposit, located in the Ailaoshan gold belt (SW China), is hosted in various types of rocks, including in quartz porphyry, carbonaceous slate, meta‐sandstone, lamprophyre, and altered ultramafic rocks. In contrast to other wall rocks, the orebodies in altered ultramafic rocks are characterized by the occurrence of a large amount of Ni‐bearing minerals. The ore‐forming process of the orebodies hosted by altered ultramafic rocks can be divided into two stages: pyrite‐vaesite‐native gold and gersdorffite‐violarite stages. The contents of As and Sb increased during the evolution of ore‐forming fluid based on the mineral assemblages. Thermodynamic modeling of the Ni‐Cu‐As‐Fe‐S system using the SUPCRT92 software package with the updated database of slop16.dat indicates the fS2 in ore‐forming fluid decreases significantly from stage I to stage II. The decreases of fS2 due to crystallization of sulfides and fO2 due to fluid–rock reaction were responsible for ore formation in altered ultramafic rocks of the Laowangzhai gold deposit. Geological evidence, the in situ sulfur isotope values of pyrite, and the other published isotopic data suggest that the ore‐forming fluid for ultramafic rock ores was dominantly composed of evolved magmatic fluid with the important input of sediments.

Geology and Geochemistry of K‐feldspar Veins in Lamprophyre at the Zhenyuan Gold Deposit, Yunnan, Southwest China: Implications for Gold Mineralization

“…Abundant Cenozoic lamprophyres and hydrothermal gold deposits are widely distributed in the Ailaoshan tectonic belt, SW China. Previous studies focused on the alteration, ore mineralogy, and ore fluid compositions of these hydrothermal gold deposits (Deng et al, 2015b;Zhang et al, 2019;Wang Y et al, 2020;Yang et al, 2023), and considered that these gold deposits have intimately temporal and spatial relationships with lamprophyres (Chen et al, 2014;Wang Q et al, 2020). Sulfides-bearing K-feldspar veins, which connect lamprophyres and hydrothermal gold deposits, have not been reported in the Ailaoshan tectonic belt.…”

Geochronology and Geochemistry of the Granite Xenolith within the Lamprophyre at the Zhenyuan Gold Deposit (Yunnan Province, SW China)

“…Therefore, the occurrence of xenoliths in the mine should be paid close attention. As an important part of the Sanjiang Tethyan metallogenic region, the Ailaoshan tectonic belt underwent multi-stage geological evolution and hosts a number of large gold deposits including Zhenyuan, Mojiang, Chang'an, and Daping (Zhang et al, 2014;Hou and Zhang, 2015;Zhang et al, 2019;Wang Q et al, 2020). In the Zhenyuan gold deposit, the geological setting, features of mineral assemblage and alteration, and ore-controlling structures have been previously studied (Zhang et al, 2012;Deng et al, 2015;Li et al, 2019a, b), but the sources of ore-forming materials and the relationship between gold mineralization, shearing, and magmatism remain poorly understood.…”