Alkaline magmatism related hydrothermal gold systems

Alkaline rock, as a rare type of magmatic rock, exhibit significant economic importance for their hydrothermal gold mineralization systems. In recent years, global discoveries of alkaline rock related high-grade magmatic-hydrothermal gold deposits have demonstrated a close genetic relationship between alkaline rock and gold mineralization. They predominantly occur in the tectonic transition zones of active continental margins, with their spatial and temporal distribution controlled by post-subduction or post-collisional extensional tectonic regimes. The alkaline-related gold mineralization mainly occurs in the Mesozoic-Neogene, with a minor subset forming during the Paleozoic. The parental alkaline magma for these deposits is derived from the partial melting of the metasomatized mantle wedge or lower crust cumulate, characterized by high volatile content and high oxygen fugacity, which facilitate efficient metal extraction from the metasomatized mantle. Shallow emplacement and the alkali-rich nature of alkaline magma together promote the efficient release of magmatic fluids and the efficient partitioning of gold from magma to fluid. Gold migrates within the ore-forming fluid in the form of [Au(HS)2]- and [AuCl2]- complexes. The primary mechanisms for gold precipitation are fluid boiling and mixing. Although water-rock interaction can induce intense and widespread potassic alteration, its contribution to gold precipitation is still controversy. And gold enrichment process of deep magma origination, the partitioning behavior of gold during magma fluid release, and the evolution of alkaline hydrothermal system are still unclear.