The Aguablanca Cu-Ni ore deposit (Extremadura, Spain), a case of synorogenic orthomagmatic mineralization: age and isotope composition of magmas (Sr,Nd) and ore (S)

The Aguablanca Cu-Ni orthomagmatic ore deposit is hosted by mafic and ultra mafic rocks of the Aguablanca stock, which is part of the larger, high-K ca lc-alkaline Santa Olalla plutonic complex. This intrusive complex, ca. 338 Ma in age, is located in the Ossa-Morena Zone (OMZ) of the Iberian Variscan Belt. Mineralization consists mainly of pyrrhotite, pentlandite and chalco pyrite resulting from the crystallization of an immiscible sulphide-rich li quid. Isotope work on the host igneous rocks (Sr, Nd) and the ore (S) sugge sts that contamination with an upper-crustal component took place at some d epth before final emplacement of the plutons (epsilon Nd-338 = -6 to -7.5-, Sr-(338) = 0.7082 to 0.7100; delta S-34((sulphides)) near +7.4%). Assimila tion-fractional crystallization (AFC) processes are invoked to explain earl y cumulates and immiscible sulphide-magma formation. Intrusion took place a t the beginning of the type-A oblique subduction of the South Portuguese Zo ne under the Ossa-Morena Zone and was probably driven by transpressive stru ctures (strike-slip faults). The mineralization is thus synorogenic. Aguablanca is probably the first case referred to in the literature of a ma gmatic Cu-Ni ore deposit hosted by calc-alkaline igneous rocks. (C) 2001 El sevier Science B.V. All rights reserved.