Formation of Gold Alloys during Crustal Differentiation of Convergent Zone Magmas: Constraints from an AU-Rich Websterite in the Stanovoy Suture Zone (Russian Far East)

Gold is typically transported by mafic and evolved magmas into the upper crust to be deposited in shallow oxidized porphyry epithermal environments. However, magmatic behavior of gold still poorly understood warrants further attention. Additional insights evolution other noble metals can provided investigations primitive convergent zone products their differentiation that contain primary-textured Au-alloys. One best examples such Au-rich ultramafic cumulates Triassic (232–233 Ma) Ildeus intrusion, which was emplaced within Mesozoic Stanovoy subduction Russian Far East. Some websterites from representing crystallized a magma, are enriched Au (up 596 ppm) abundant Cu-Ag-Au micro-particles. Most these Au-alloy micro-particles display compositions similar those previously found explosive pyroclastic rocks Lesser Khingan iron district, mantle wedge peridotites Kamchatka Cretaceous adakites suture zone. Textural compositional characteristics suggest alloys precipitated calc-alkaline melt during its crustal paleo-subduction large grains an internal honeycomb-like structure with alternating Cu-rich Cu-poor zones. Heating experiments under atmospheric conditions recorded substantial loss Cu primary alloys, appears process characteristic hydrothermal ore systems. We later-stage alteration differentiated igneous conduits containing results formation Cu-free mineralization comparable