The Aguablanca Ni–(Cu) sulfide deposit, SW Spain: geologic and geochemical controls and the relationship with a midcrustal layered mafic complex

The Aguablanca Ni–(Cu) sulfide deposit is\udhosted by a breccia pipe within a gabbro–diorite pluton.\udThe deposit probably formed due to the disruption of a\udpartially crystallized layered mafic complex at about 12–\ud19 km depth and the subsequent emplacement of melts and\udbreccias at shallow levels (<2 km). The ore-hosting breccias\udare interpreted as fragments of an ultramafic cumulate,\udwhich were transported to the near surface along with a\udmolten sulfide melt. Phlogopite Ar–Ar ages are 341–\ud332 Ma in the breccia pipe, and 338–334 Ma in the layered\udmafic complex, and are similar to recently reported U–Pb\udages of the host Aguablanca Stock and other nearby calcalkaline\udmetaluminous intrusions (ca. 350–330 Ma). Ore\uddeposition resulted from the combination of two critical\udfactors, the emplacement of a layered mafic complex deep\udin the continental crust and the development of small\uddilational structures along transcrustal strike-slip faults that\udtriggered the forceful intrusion of magmas to shallow\udlevels. The emplacement of basaltic magmas in the lower\udmiddle crust was accompanied by major interaction with\udthe host rocks, immiscibility of a sulfide melt, and the\udformation of a magma chamber with ultramafic cumulates\udand sulfide melt at the bottom and a vertically zoned mafic\udto intermediate magmas above. Dismembered bodies of\udmafic/ultramafic rocks thought to be parts of the complex\udcrop out about 50 km southwest of the deposit in a\udtectonically uplifted block (Cortegana Igneous Complex,\udAracena Massif). Reactivation of Variscan structures that\udmerged at the depth of the mafic complex led to sequential\udextraction of melts, cumulates, and sulfide magma. Lithogeochemistry\udand Sr and Nd isotope data of the Aguablanca\udStock reflect the mixing from two distinct reservoirs, i.e.,\udan evolved siliciclastic middle-upper continental crust and a\udprimitive tholeiitic melt. Crustal contamination in the deep\udmagma chamber was so intense that orthopyroxene\udreplaced olivine as the main mineral phase controlling the early fractional crystallization of the melt. Geochemical\udevidence includes enrichment in SiO2 and incompatible\udelements, and Sr and Nd isotope compositions (87Sr/86Sri\ud0.708–0.710; 143Nd/144Ndi 0.512–0.513). However, rocks\udof the Cortegana Igneous Complex have low initial\ud87Sr/86Sr and high initial 143Nd/144Nd values suggesting\udcontamination by lower crustal rocks. Comparison of the\udgeochemical and geological features of igneous rocks in the\udAguablanca deposit and the Cortegana Igneous Complex\udindicates that, although probably part of the same magmatic\udsystem, they are rather different and the rocks of the\udCortegana Igneous Complex were not the direct source of\udthe Aguablanca deposit. Crust–magma interaction was a\udcomplex process, and the generation of orebodies was\udcontrolled by local but highly variable factors. The model\udfor the formation of the Aguablanca deposit presented in\udthis study implies that dense sulfide melts can effectively\udtravel long distances through the continental crust and that\uddilational zones within compressional belts can effectively\udfocus such melt transport into shallow environments