Arc metallogeny: Regional and global perspectives

CIM Edmonton 2008
Abstract Subduction-related magmatic arcs are one of the pre-eminent metallogenic geodynamic environments (other major environments being related to mantle plumes and continental rifting). Mineral deposit types founds in arc settings range from seafloor base metal sulfide (in back-arcs and forearcs), porphyry Cu-Au, and epithermal Au in oceanic arc settings, porphyry Cu-Mo-Au, skarn, IOCG, and epithermal Au in more mature island or continental arcs, porphyry Mo and Ag-rich deposits in more distal continental arc settings, and syn- to post-collisional alkalic porphyry and epithermal Au deposits. The variety of deposit styles reflects the range of upper plate lithospheric conditions encountered in both space and time in subduction zones, which in turn control the style and volume of magmatism reaching the upper crust. In less mature island arc settings, thinner and denser upper plate lithosphere allows for less crustal-level evolution of mantle-derived magmas, and resultant more mafic, tholeiitic systems with limited potential for porphyry-style mineralization (e.g., island arc terranes in the SW Pacific). In mature island arc and continental arc environments, magmatism is characterized by more evolved calc-alkaline andesite-dacite-rhyolite (I-type) magmas, which commonly generate magmatic-hydrothermal (porphyry and epithermal) systems prospective for Cu-Au deposits (e.g., Papua New Guinea, Philippines, the Andes, SW USA, the Canadian Cordillera, Neo-Tethys). Regions of thickened continental crust limit the passage of primitive magmas, and eruption products are commonly felsic, with associated Mo and Ag enrichments (e.g., Bolivia). Arc collision potentially leads to lithospheric mantle +/- lower crustal delamination, with a resurgence of magmatism prospective for alkalic-type porphyry and epithermal deposits, as well as deposits of U and other rare metals associated with high-level felsic volcanism. Final closure of an ocean basin by continental collision may also lead to lithospheric delamination, but commonly also involves wholesale crustal melting to form felsic (S-type) magmas, with potential for Sn-W and other lithophile element enrichment (e.g., the Hercynides of western Europe). Thus, a wide variety of deposit types may be found in an arc depending on its age and maturity.
Keywords: volcanic arc, Porphyry, Global, Magmas, epithermal, Tectonics, Metallogeny
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