The relationship between large deep mafic sills, crustal contamination and the formation of Ni-(Cu) and IOCG deposits

Abstract

The Ossa Morena Zone (SW Iberia) hosts an unusual suite of ore deposits, including magmatic Ni-(Cu) and IOCG mineralization. These deposits are interpreted to have a relationship to a deep mafic sill intruded in the middle crust. Interaction of mafic magmas with crustal rocks produced immiscible sulphide-rich melts and water-rich melts. The latter exsolved large amounts of Fe- and CO2-rich brines that were responsible for widespread albite-actinolite alteration and IOCG mineralization.