Geochronology and geochemistry of garnet from Tongguanshan skarn Cu deposit, Tongling, eastern China: insights into ore-forming process

Skarn Cu deposits are one of most important deposit-type in Middle-Lower Yangtze River region, eastern China, but skarn formation process remains unclear. Mineralogical, morphological and in situ geochemical data from the skarn stage of Tongguanshan skarn Cu deposit in Tongling region are systemically investigated, to reveal the timing, physical-chemical conditions, and fl uid evolution during the skarn formation. The Tongguanshan garnets can be identified fi ed homogeneous and unzoned early generation garnet (GrtI), and oscillating zoned late generation garnet (GrtII) with the Fe-rich core (GrtII-Fe) and Al-rich edge (GrtII-Al). Garnet U-Pb - Pb dating results show that the Tongguanshan Cu mineralization was formed in 145.6 +/- 4.4 Ma. In situ elemental composition results of the garnet samples indicate that they belong to grossular-andradite solid solution series, and are a magmatic-hydrothermal origin. The distinctly geochemical characteristics (e.g., Sn and U contents, (La/Yb)N, N , delta Eu and Y/ Ho values) reveal that the physiochemical conditions from GrtI to GrtII-Fe, and GrtII-Fe to GrtII-Al stages in the Tongguanshan skarn formation were an increase and a decrease of fl uid salinity and oxygen fugacity, closed to open and then to closed of fl uid environment, and neutral-weakly acidic to acidic and acidic to neutral-weakly acidic of fl uid pH, respectively. A comprehensive discriminant analysis indicates a fl uid boiling occurred in the GrtI to GrtII-Fe stage of the Tongguanshan skarn Cu deposit, and there is little or no external fl uid mixed during the skarn stage. (c) 2024 Guangzhou Institute of Geochemistry, CAS. Published by Elsevier BV. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).