Granitic magmatism and metallogeny of southwestern North America

In this area, late Palaeozoic to Cainozoic granitic rocks and their related mineral deposits show consistent patterns that can be interpreted in terms of combined provincial, exposure and process controls. Voluminous Cordilleran magmatism began in the Permian and reached maximum fluxes in the Mid-Jurassic, late Cretaceous and Oligocene. Two distinct types of broad-scale igneous suites formed: calc-alkaline to alkaline suites that vary regularly with time from early intermediate-mafic centres to late felsic centres over intervals lasting 20-50 m.y., and a compositionally varied suite showing no obvious secular variation in composition. The first type formed during periods of stable convergence and compressional tectonics whereas the second type formed during neutral to extensional tectonics. Contrasting types of intrusive centres formed in the same lithospheric columns, suggesting that variability reflects thermal and stress regimes, subcrustal magma flux and crustal thickness. Igneous-related mineralization is ubiquitous where epizonal environments are preserved, thus preservation (and exposure) form the first-order filter on metallogeny. Metal contents and alteration styles correlate closely with igneous compositions and are broadly independent of setting. Ore element suites vary from Cu-Au-Fe associated with (quartz) dioritic to monzonitic intrusion centres through Cu-Zn-Mo-Pb-Ag-Au associated with broadly granodioritic centres, and finally to F-Mo-Zn-W-Ag-Be associated with metaluminous to strongly peraluminous granitic centres. Key features of a model are mineralogical controls on fluid compositions and the efficacy of magmatic processes in producing voluminous ore-forming aqueous fluids.