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 pyroxenitic 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-, clinopyroxene- 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.