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