METALLOGENY OF MAJOR GOLD DEPOSITS AND BELTS IN THE NORTH AND SOUTH AMERICAN CORDILLERA

Past production plus reserves of the principal gold belts and isolated giant deposits in the western American Cordillera approximates 850 million oz in ten widely recognized main deposit types. These gold concentrations occupy substantially <1 % of the Cordilleran orogen. Most of the gold belts and giant deposits correspond to brief (typically <5-10 m.y.) metallegnic epochs of Jurassic through Miocene age, although Proterozoic and Carboniferous examples also occur. All the belts and deposits, except the one of Proterozoic age, formed during active subduction at paleo-Pacific margins.

High-sulfidation epithermal gold, some porphyry copper-gold, and pluton-related gold deposits linked to oxidized equigranular intrusions occur at different paleodepths in typical calc-alkaline magmatic arcs. Low-sulfidation epithermal gold deposits are related to either alkaline or bimodal volcanic rocks in extensional back-arc settings. The bimodal suites may be products of mantle plume activity. Two giant porphyry copper-gold deposits were also generated in back arcs, where either extension or contraction prevailed. Pluton-related gold deposits in and around reduced felsic intrusions are restricted to probable back-arc environments characterized by thick turbidite successions. Orogenic gold belts occur in fore-arc settings, where they are localized by brittle-ductile fault zones bounding accreted terranes, but near the oceanward margins of partly coeval calc-alkaline batholiths.

Although several belts and deposits formed above the landward extremities of shallowly dipping subduction zones, there is no systematic linkage to slab-flattening processes or to subduction of oceanic features, such as spreading centers and aseismic ridges. The tendency for two or more (six in the western US) gold belts or giant deposits of different types and ages to occupy restricted Cordilleran segments could suggest gold inheritance from long-standing, regional-scale anomalies, most probably at mantle depths.