Zircon petrochronology and chemistry reveal the formation of the giant tungsten deposit at Dahutang in South China by multi-stage tungsten enrichments

Abstract

Tungsten enrichment during the formation of giant W deposits is thought to be related to magmatic and hydrothermal processes. However, the mechanisms of W enrichment and their role in controlling ore formation remain unclear. Zircon is a ubiquitous accessory mineral that can provide a record of the physicochemical conditions during mineralization. Dahutang in South China is a giant W deposit (1.89 Mt WO₃ at 0.18%) associated with the late Mesozoic granites. In this study, we report new zircon morphological, geochronological, and chemical data for the most evolved Li-mica albite granite in the Dahutang deposit, in order to determine the processes of W enrichment. We classified the zircons into three types based on their appearance and composition. Type-IA and -IB zircons (ca. 145 Ma) successively crystallized from metasedimentary-derived magmas (δ¹⁸O = 8.9 ± 0.3‰) at 786–732 °C. Type-II zircons formed by interaction between volatile-rich melts and Type-I zircons at 669 ± 39 °C. Type-III zircons formed by autometasomatism of earlier Type-I and -II zircons, which involved exsolved hydrosilicate fluids. Our numerical model shows that the granitic melts have undergone > 95% fractional crystallization and experienced metasomatism by hydrosilicate fluids, during which the rare-metals (W, Nb, and Ta) were extensively enriched. Furthermore, we compiled data for ten W deposits across South China to investigate the key factors controlling the formation of giant W deposits. The strong correlation (R² = 0.79) between WO₃ tonnage and zircon Hf content indicates that an extensive and multi-stage evolution may be the key factor controlling the formation of giant W deposits.