Rubén Piña

U-Pb age constraints on Variscan magmatism and Ni-Cu-PGE metallogeny in the Ossa-Morena Zone (SW Iberia)

New U–Pb zircon ages from the Santa Olalla Igneous Complex have been obtained, which improve the knowledge of the precise timing of Variscan magmatism in the Ossa–Morena Zone, SW Iberia. This complex has a special relevance as it hosts the most important Ni–Cu–platinum group element (PGE) mineralization in Europe: the Aguablanca deposit. U–Pb zircon ages have been obtained for seven samples belonging to the Santa Olalla Igneous Complex and spatially related granites. With the exception of the Cala granite (352 ± 4 Ma), which represents an older intrusion, the bulk of samples yield ages that cluster around 340 ± 3 Ma: the Santa Olalla tonalite (341.5 ± 3 Ma), the Sultana hornblende tonalite (341 ± 3 Ma), a mingling area at the contact between the Aguablanca and Santa Olalla stocks (341 ± 1.5 Ma), the Garrote granite (339 ± 3 Ma), the Teuler granite (338 ± 2 Ma), and dioritic dykes from the Aguablanca stock (338.6 ± 0.8 Ma). The Bodonal–Cala porphyry, which has also been dated (530 ± 3 Ma), comprises a group of sub-volcanic rhyolitic intrusions belonging to the Bodonal–Cala volcano-sedimentary complex, which hosts the igneous rocks. The knowledge that emplacement of the Aguablanca deposit was related to episodic transtensional tectonic stages during the Variscan orogeny will be fundamental in future mineral exploration in the Ossa–Morena Zone.

Platinum-group elements-bearing pyrite from the Aguablanca Ni-Cu sulphide deposit (SW Spain): a LA-ICP-MS study

Despite the fact that pyrite is a relatively common phase in Ni-Cu-Platinum-Group Elements (PGE) magmatic sulphide deposits, the trace element content of the pyrite has been neglected in the studies of these deposits with most attention being paid to the PGE concentrations of pyrrhotite, pentlandite and chalcopyrite. Pyrite in these deposits exhibits a range of textures, from euhedral to xenomorphic. The origin of the different pyrites is not always clear; they could have formed by exsolution from monosulphide solid solution (mss), by replacement of the existing minerals during cooling or metamorphism or directly from hydrothermal fluids. In order to provide data on trace element contents of pyrite in a magmatic sulphide deposit and to investigate the origin of the pyrite, we have measured the content of PGE and other chalcophile elements (Au, Ag, Co, Ni, Cu, Se, Sb, As, Bi and Te) by laser ablation ICP-MS in pyrite exhibiting different textures from the Aguablanca Ni-Cu deposit (Spain). The results show that 1) large idiomorphic pyrite is compositionally-zoned with Os-Ir-Ru-Rh-As-rich layers and Se-Co-rich layers; 2) some idiomorphic pyrite grains contain unusually high PGE contents (up to 32 ppm Rh and 9 ppm Pt); 3) ribbon-like and small-grained pyrite hosts IPGE (i.e., Iridium-group PGE, Os, Ir, Ru and Rh) in similar contents (100–200 ppb each) than the host pyrrhotite; and 4) pyrite replacing plagioclase is depleted in most metals (i.e., PGE, Co, Ni and Ag). Overall, the different textural types of pyrite have similar abundances of Pd, Au, Se, Bi, Te, Sb and As. Mineralogical and compositional data suggest that the formation of pyrite is the result of the activity of late magmatic/hydrothermal fluids that triggered the partial replacement of pyrrhotite and plagioclase by pyrite, probably due to an increase in the sulphur fugacity on cooling. During this episode, pyrite inherited the IPGE content of the replaced mineral, whereas other elements such as Pd, Au and semi-metals were likely partially introduced into pyrite via altering fluids. These results highlight that pyrite can host appreciable amounts of PGE and therefore it should not be overlooked as a potential carrier of these metals in Ni-Cu-(PGE) sulphide deposits.

Origin and emplacement of the Aguablanca magmatic Ni-Cu-(PGE) sulfide deposit, SW Iberia: A multidisciplinary approach

A model is proposed for the origin and emplacement of the ca. 341 Ma Aguablanca magmatic Ni-Cu-(platinum group element [PGE]) sulfi de deposit (SW Iberia) integrating petrological, geochemical, structural, and geophysical data. The Aguablanca deposit occurs in an unusual geodynamic context for this ore type (an active plate margin) as an exotic , magmatic subvertical breccia located at the northern part of the coeval gabbronorite Aguablanca stock (341 ± 1.5 Ma). Structural and gravity data show that mineralized breccia occurs inside the inferred feeder zone for the stock adjacent to the Cherneca ductile shear zone, a Variscan sinistral transpressional structure. The orientation of the feeder zone corresponds to that expected for tensional fractures formed within the strain fi eld of the adjacent Cherneca ductile shear. Two distinctive stages are established for the origin and emplacement of the deposit: (1) initially, the ore-forming processes are attributed to magma emplacement in the crust, assimilation of crustal S, and segregation and gravitational settling of sulfi de melt (a scenario similar to most plutonic Ni-Cu sulfi de ores), and (2) fi nal emplacement of the Ni-Cu sulfi de-bearing rocks by multiple melt injections controlled by successive opening events of tensional fractures related to the Cherneca ductile shear zone.

Liquid immiscibility between arsenide and sulfide melts: evidence from a LA-ICP-MS study in magmatic deposits at Serranía de Ronda (Spain)

The chromite-Ni arsenide (Cr-Ni-As) and sulfide-graphite (S-G) deposits from the Serranía de Ronda (Málaga, South Spain) contain an arsenide assemblage (nickeline, maucherite and nickeliferous löllingite) that has been interpreted to represent an arsenide melt and a sulfide-graphite assemblage (pyrrhotite, pentlandite, chalcopyrite and graphite) that has been interpreted to represent a sulfide melt, both of which have been interpreted to have segregated as immiscible liquids from an arsenic-rich sulfide melt. We have determined the platinum-group element (PGE), Au, Ag, Se, Sb, Bi and Te contents of the arsenide and sulfide assemblages using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to establish their partitioning behaviour during the immiscibility of an arsenide melt from a sulfide melt. Previous experimental work has shown that PGE partition more strongly into arsenide melts than into sulfide melts and our results fit with this observation. Arsenide minerals are enriched in all PGE, but especially in elements with the strongest affinity for the arsenide melt, including Ir, Rh and Pt. In contrast and also in agreement with previous studies, Se and Ag partition preferentially into the sulfide assemblage. The PGE-depleted nature of sulfides in the S-G deposits along with the discordant morphologies of the bodies suggest that these sulfides are not mantle sulfides, but that they represent the crystallization product of a PGE-depleted sulfide melt due to the sequestering of PGE by an arsenide melt.

Ore-Forming Processes in the Aguablanca Ore Deposit

The high sulfur content and the low concentrations of PGE (0.47 g/t, evaluation by Rio Narcea Recursos, SA) of the Aguablanca mineralization indicate that this deposit belongs, according to the classification of Naldrett (Magmatic sulfide deposit: Geology, geochemistry and exploration. Springer, Berlin, p 728, 2004), to those magmatic sulfide deposits valuable due to their primary Ni and Cu contents with PGE recovered as by-products.

The Santa Olalla Igneous Complex (SOIC)

The SOIC is a subrounded (up to 7 km long) calc-alkaline plutonic group structurally located in a wedge bounded by two main faults (Romeo et al. in J Struct Geol 28:1821–1834, 2006a, Romeo et al. in Geol Mag 145:345–359, 2008): the Cherneca Fault to the north, and the Zufre Fault to the south.

The Aguablanca Ni–Cu–(PGE) Sulfide Deposit

The Aguablanca Ni–Cu sulfide mineralization occurs in form of a poorly exposed subvertical mineralized breccia in the northern part of the Aguablanca stock, near to the sedimentary host rocks. The mineralized breccia consists of unmineralized (or very weakly mineralized) mafic-ultramafic fragments embedded in a variably mineralized matrix.