Gold in high-grade metamorphic belts: a review of deposit styles, controls on mineralisation and exploration implications

Résumé fourni par la source

Gold deposits in mid-amphibolite- to granulite-facies metamorphic belts are globally significant yet remain understudied and underexplored compared with those in lower-grade terrains. This disparity stems from a longstanding perception that high-grade metamorphic crust is inherently unfavourable for major gold mineralisation. This review challenges that paradigm through a synthesis of 22 relatively well-documented gold systems from high-grade metamorphic terrains across Australia, North America, Africa and Asia where mineralisation survived, formed or was superimposed on high-grade environments. These systems confirm that elevated metamorphic grade does not preclude substantial gold endowment but instead profoundly influences how mineralisation is preserved or expressed. Based on timing relationships relative to peak metamorphism, a threefold framework is recognised. Pre-peak systems were emplaced prior to peak conditions and subsequently overprinted or upgraded during prograde metamorphism. Rare syn-peak systems formed at or near peak conditions, likely involving high-temperature fluids and, locally, liquid-metal collectors in which molten metal droplets scavenged gold. Post-peak systems were introduced or remobilised during retrograde reactivation and renewed fluid ingress during exhumation. Comparative analysis identifies the ‘index mineral paradox’, whereby primary hydrothermal alteration modifies bulk-rock chemistry and suppresses expected metamorphic indicator minerals, effectively camouflaging mineralised zones. Network analysis further suggests that pre-peak systems commonly preserve sulfide-rich, Fe–As–Cu dominated signatures, whereas post-peak systems display more variable and commonly polymetallic signatures. High-grade metamorphic belts therefore represent an important and comparatively underexplored frontier for major gold discovery. Successful targeting requires a shift toward integrated mineral systems approaches centred on crustal architecture, rheological contrasts, reactive lithologies, structural reactivation and sensitive multi-element geochemical vectors.