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

The copper endowment of the North and South American Cordillera, from Alaska to central Chile, is almost entirely confined to porphyry and genetically related but subordinate skarn deposits. Isolated major deposits and principal metallogenic belts contain ~850 million tonnes of fine copper -some 85 % of the total estimated for the American Cordillera- and range in age from latest Cretaceous to early Pliocene. The premier Cordilleran copper concentrations are located in northern and central Chile (e.g., Chuquicamata; El Teniente) and southwestern North America (e.g., Morenci; Cananea).

All the major deposits and belts formed during subduction-related contractional tectonism that resulted in crustal shortening and thickening that gave rise to high rates of regional uplift. The contractional events coincident with major porphyry copper formation within restricted segments of the Cordilleran orogen are inferred to have been responses to flattening of orthogonally subducted oceanic slabs. Slab flatenning may be linked to either rapid convergence or subduction of buoyant oceanic features. However, there is no clear evidence to support a direct one-to-one relationship between subduction of oceanic topographic anomalies and giant porphyry copper generation.

The arc segments devoid of major copper deposits, such as the central Andean and North American regions during the Mesozoic, developed during periods of regional extension in either continental or oceanic island-arc environments (e.g., British Columbia). Andean-type extensional settings, including the Great basin of western North America, also appear to have inhibited major copper deposit formation. Nevertheless, isolated giant deposits at Cerro Colorado, in the Panama island arc, and Bingham, Utah emplaced during the transition from regional contraction to extension caused by slab removal at the landward margin of the North American Cordillera, are clear exceptions. The tectonic setting of the major Pebble copper deposit in Alaska remains ill defined.