A new style of Ni-Cu mineralization related to magmatic breccia pipes in a transpressional magmatic arc, Aguablanca, Spain

Abstract

The Aguablanca deposit represents a new style of magmatic Ni Cu mineralization in discordant sulfide rich pyro xenitic breccia pipes. The orebody is hosted by Variscan calc alkaline diorites and gabbros which intruded during an oblique subduction/collision event. Transpressional transtensional left lateral structures facilitated the intrusion of primitive magmas to shallow depths in the crust. A two stage genetic model is proposed. In the first stage, a transitional deep magma chamber formed. The primitive magma interacted at depth with wall rocks, resulting in extensive crustal contamination, concomitant sulfide magma immiscibility and settling of orthopyroxene , clinopyrox ene and sulfide rich cumulates to form a layered magmatic complex. Geochemical and mineralogical evidence, including the virtual disappearance of olivine, heavy 34S values (7.4‰), distinctive Nd, Sr and Pb signatures, high Au contents, and the presence of spinel and graphite indicate a major interaction with the upper crust, probably with pyrite rich carbonaceous slates of Late Proterozoic age. The second stage was related with the emplacement of residual calc alkaline gabbroic to noritic melts and the development of an intrusive breccia containing fragments of the consolidated layered complex rocks and associated disseminated to massive sulfides