THE AGUABLANCA NI-(CU) SULFIDE DEPOSIT, SW SPAIN: GEOLOGIC AND GEOCHEMICAL CONTROLS AND THE RELATIONSHIP WITH A MIDCRUSTAL LAYERED MAFIC COMPLEX

Abstract

The Aguablanca Ni-(Cu) sulfide deposit is hosted by a breccia pipe within a gabbro-diorite pluton. The deposit probably formed due to the disruption of a partially crystallized layered mafic complex at about 12-19 km depth and the subsequent emplacement of melts and breccias at shallow levels (<2 km). the ore-hosting breccias are interpreted as fragments of an ultramafic cumulate, which were transported to near surface along with a molten sulfide melt. phlogopite ar-ar ages 341-332 ma in breccia pipe, and 338-334 layered mafic complex, similar recently reported u-pb host aguablanca stock other nearby calc-alkaline metaluminous intrusions (ca. 350-330 ma). ore deposition resulted from combination two critical factors, emplacement complex deep continental crust development small dilational structures transcrustal strike-slip faults that triggered forceful intrusion magmas shallow levels. basaltic lower middle was accompanied by major interaction rocks, immiscibility melt, formation magma chamber cumulates melt at bottom vertically zoned intermediate above. dismembered bodies rocks thought be parts crop out about 50 km southwest deposit tectonically uplifted block (cortegana igneous aracena massif). reactivation variscan merged depth led sequential extraction melts, cumulates, magma. lithogeochemistry sr nd isotope data reflect mixing distinct reservoirs, i.e., evolved siliciclastic middle-upper primitive tholeiitic crustal contamination so intense orthopyroxene replaced olivine main mineral phase controlling early fractional crystallization geochemicalevidence includes enrichment sio2 and incompatible elements, and Sr and Nd isotope compositions (87Sr/86Sri 0.708-0.710; 143Nd/144Ndi 0.512-0.513). However, rocks of the Cortegana Igneous Complex have low initial 87Sr/86Sr and high initial 143Nd/ 144Nd values suggesting contamination by lower crustal rocks. Comparison of the geochemical and geological features of igneous rocks in the Aguablanca deposit and the Cortegana Igneous Complex indicates that, although probably part of the same magmatic system, they are rather different and the rocks of the Cortegana Igneous Complex were not the direct source of the Aguablanca deposit. Crust-magma interaction was a complex process, and the generation of orebodies was controlled by local but highly variable factors. The model for the formation of the Aguablanca deposit presented in this study implies that dense sulfide melts can effectively travel long distances through the continental crust and that dilational zones within compressional belts can effectively focus such melt transport into shallow environments. © Springer-Verlag 2006.