Alkaline Porphyry Copper Deposits and IOCG – What is the link?

Abstract

The geotectonic setting (cratonic or back-arc) of IOCG deposits, and the nature of their associated magmas is not consensual. Alkaline porphyry deposits and IOCG’s show the same high temperature Na-Ca alteration and both occur in extensional tectonic settings. These two similarities contribute to the definition of the IOCG’s source magmas. Magmas and volatiles extracted from the asthenosphere are able to metasomatise and fertilize the SCLM (Sub-continental Lithosphere Mantle) at specific depths (metasome). The metasomes are mantle portions enriched in Fe+3, Ti, K, Nb, C, H, Cl, F, Cu, Ni, P, LREE, U, Th, Na and LIL. The metasomatism in the mantle occurs when the C-O-H peridotite solidus curve intercepts the cratonic geotherm. The IOCG deposits result directly from extensional periods in the SCLM (rifting), associated with partial melting of the metasome and the production of alkaline magmas rich in volatiles (O-H-C-S-CL-F). These melts are rich in compatible and incompatible elements and rarely reach the upper portions of the crust. In general the copper porphyry and IOCG deposits have more differences than similarities