Magmatic-hydrothermal ore-forming processes and metal enrichment mechanisms of the large Yangchuling porphyry W-Mo mineralizing system in South China

Abstract Porphyry-type tungsten (W) deposits are of significant economic importance; however, their enrichment and precipitation mechanisms are still unclear. We studied the Yangchuling, South China, W-Mo deposit to uncover the ore-forming processes and metal enrichment mechanisms using scheelite geochemistry. Scheelite is the primary tungsten ore mineral in the Yangchuling deposit, which exists in three generations (e.g., Sch1, Sch2, and Sch3). The earliest Sch1 formed in veins and was disseminated in monzogranite and granite porphyries. Sch1 exhibits homogeneous blue luminescence, high total rare earth element (ΣREE) + Y content (1471–4059 ppm), and light REE (LREE)-enriched patterns with negative Eu anomalies. Sch1 precipitated directly from the earliest magmatic-hydrothermal fluid. Sch2 occurs in veinlets within the monzogranite porphyry and displays distinct oscillatory zonation, fluorescent yellow under UV light, and a range of complex cathodoluminescent (CL) images, from dark green to dark blue. Sch2 is notably enriched in Mo and shows dextral-inclined patterns of LREE enrichment with strong positive Eu anomalies. Trace element mapping of Sch2 indicates variations in Eu concentration, which suggest ore-forming fluids in an open hydrothermal system. Sch3 is commonly found in quartz-scheelite ± molybdenite ± pyrite ± calcite stockworks and veins, which can be subdivided into Sch3a, Sch3b, and Sch3c. Their variable REE profiles are influenced by the changing composition of the hydrothermal fluid, particularly its salinity, and its affinity for the Na-REE coupled substitution mechanism in scheelite. Plagioclase dissolution in intrusive rocks helps to provide calcium for the precipitation of scheelite during subsequent hydrothermal mineralization processes. The dissolution of plagioclase contributed to the presence of Eu.