Person: Ortega Menor, Lorena
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First Name
Lorena
Last Name
Ortega Menor
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Geológicas
Department
Mineralogía y Petrología
Area
Cristalografía y Mineralogía
Identifiers
3 results
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Item Petrology and Geochemistry of Mafic-Ultramafic Fragments from the Aguablanca Ni-Cu Ore Breccia, Southwest Spain(Economic geology and the bulletin of the Society of Economic Geologists, 2006) Piña García, Rubén; Lunar Hernández, Rosario; Ortega Menor, Lorena; Gervilla, F.; Alapieti, T.; Martínez, C.Aguablanca (southwest Spain) is the first economic Ni-Cu-(PGE) deposit found in southern Europe. Two features make it an unusual example of magmatic sulfide ore: it is related to the development of an Andeantype continental magmatic arc, and it is hosted by a subvertical magmatic breccia. The structural style and the geodynamic context of the deposit contrast with most plutonic Ni-Cu-PGE deposits elsewhere, which occur at specific levels of layered mafic intrusions in rift environments. The Ni-Cu deposit is hosted by the Aguablanca intrusion, a mafic body composed of gabbronorite and minor quartz-diorite, gabbro, and norite. Sulfides are concentrated in a gabbronorite matrix along a subvertical (dipof 70º–80º N), funnel-like magmatic breccia that contains barren or slightly mineralized ultramafic-mafic cumulate fragments. Modal compositions of the fragments reflect a wide variety of rock types, including peridotite (hornblende-rich werhlite, dunite, and hornblende-rich harzburgite), pyroxenite (ortho- and clinopyroxenite), gabbro (gabbro, gabbronorite, and hornblende gabbro), and anorthosite. The primary silicate assemblage includes olivine (Fo91–Fo79), orthopyroxene (Mg no. 0.85–0.73), clinopyroxene (Mg no. 0.93–0.62), plagioclase (An99–An38), amphibole (Mg no. 0.87–0.68) and phlogopite (Mg no. 0.89–0.64). The wide range of rock types and the Fe-enrichment trends in the primary ferromagnesian silicates suggest magmatic differentiation processes from the parent melts, with the fragments representing different stages of cumulate formation. The ore-bearing breccia contains both semimassive and disseminated sulfides in the gabbronorite matrix. Textures vary between meso- and orthocumulate, and the rock-forming magmatic silicates are orthopyroxene (Mg no. 0.83–0.74), clinopyroxene (Mg no. 0.89–0.78), plagioclase (An50-An77), and intercumulus amphibole (Mg no. 0.86–0.70), phlogopite (0.84–0.69) and minor quartz. The gabbronorite in the matrix of the breccia is petrographically and chemically very similar to that of the unmineralized parts of the main Aguablanca intrusion and exhibits a similar differentiation trend, suggesting that the matrix of the ore-bearing breccia and the unmineralized rocks belong to a same magmatic suite. The local presence of mafic-ultramafic fragments in the barren Aguablanca intrusion supports this suggestion. The presence of highly Ni depleted olivine, whole-rock Cu/Zr ratios below 1, and the local occurrence of disseminations of magmatic sulfides in the peridotite fragments point to sulfide segregation before and/or during the formation of the peridotite cumulates. Mantle-normalized incompatible trace element patterns of the fragments along with published sulfur isotope data are consistent with crustal contamination, suggesting that addition of crustal sulfur from pyrite-bearing black slates led to sulfide saturation. These results support a model in which sulfides segregated and settled during the differentiation of an unexposed mafic-ultramafic complex, now sampled as fragments in the breccia, whereas the overlying silicate magma, most probably fed by successive fresh magma injections, underwent fractional crystallization, giving rise to this cumulate sequence. The emplacement of the ore breccia took place at temperatures above the (monosulfide solid solution (mss) solidus but below the olivine and pyroxene solidus, likely owing to the explosive injection of a new pulse of magma into the chamber, which mingled with the sulfide liquid and disrupted the overlying cumulate sequence. As a consequence, fragments reached their current position in the breccia, injected along with the sulfide and the silicate melts, which subsequently formed the sulfide-rich gabbronorite.Item Geochemical Constraints on the Origin of the Ni–Cu Sulfide Ores in the Tejadillas Prospect (Cortegana Igneous Complex, SW Spain)(Resource geology (Tokyo. 1998), 2012) Piña García, Rubén; Gervilla, Fernando; Ortega Menor, Lorena; Lunar Hernández, RosarioAfter the discovery of theAguablanca ore deposit (the unique Ni–Cu mine operating in SW Europe), a number of mafic-ultramafic intrusions bearing Ni–Cu magmatic sulfides have been found in the Ossa–Morena Zone of the Iberian Massif (SW Iberian Peninsula). The Tejadillas prospect is one of these intrusions, situated close to the border between the Ossa–Morena Zone and the South Portuguese Zone of the Iberian Massif. This prospect contains an average grade of 0.16 wt%Ni and 0.08 wt%Cu with peaks of 1.2 wt%Ni and 0.2 wt%Cu. It forms part of the Cortegana Igneous Complex, a group of small mafic-ultramafic igneous bodies located 65 km west of the Aguablanca deposit. In spite of good initial results, exploration work has revealed that sulfide mineralization is much less abundant than in Aguablanca. A comparative study using whole-rock geochemical data between Aguablanca aand Tejadillas shows that the Tejadillas igneous rocks present a lower degree of crustal contamination than those of Aguablanca. The low crustal contamination of the Tejadillas magmas inhibited the assimilation of significant amounts of crustal sulfur to the silicate magmas, resulting in the sparse formation of sulfides. In addition, Tejadillas sulfides are strongly depleted in PGE, with total PGE contents ranging from 14 to 81 ppb, the sum of Pd and Pt, since Os, Ir, Ru and Rh are usually below or close to the detection limit (2 ppb). High Cu/Pd ratios (9700–146,000) and depleted mantle-normalized PGE patterns suggest that the Tejadillas sulfides formed from PGE-depleted silicate magmas. Modeling has led us to establish that these sulfides segregated under R-factors between 1000 and 10,000 from a silicate melt that previously experienced 0.015% of sulfide extraction. All these results highlight the importance of contamination processes with S-rich crustal rocks and multiple episodes of sulfide segregations in the genesis of high-tenor Ni–Cu–PGE ore deposits in mafic-ultramafic intrusions of the region.Item Platinum-group elements-bearing pyrite from the Aguablanca Ni-Cu sulphide deposit (SW Spain): a LA-ICP-MS study(European journal of mineralogy, 2013) Piña García, Rubén; Gervilla, Fernando; Barnes, Sarah-Jane; Ortega Menor, Lorena; Lunar Hernández, RosarioDespite the fact that pyrite is a relatively common phase in Ni-Cu-Platinum-Group Elements (PGE) magmatic sulphide deposits, it has been neglected in the studies on PGE distribution in favour of pyrrhotite, pentlandite and chalcopyrite. An example of this is the Aguablanca deposit, where although pyrite is an important phase in the semi-massive ore and an early study has revealed that it hosts traces of PGE, the presence and origin of PGE into the pyrite has not been investigated in detail. With this in mind, we have measured by laser ablation ICP-MS the content of these and other chalcophile elements (Au, Ag, Co, Ni, Cu, Se, Sb, As, Bi and Te) in pyrite exhibiting different textures. The results show that 1) large idiomorphic pyrite is compositionallyzoned with Os-Ir-Ru-Rh-As-rich layers and Se-Co-rich layers; 2) some idiomorphic pyrites contain unusually high PGE contents (up to 32 ppm Rh and 9 ppm Pt); 3) ribbon-like and small-grained pyrites host IPGE (i.e., Iridium-group PGE, Os, Ir, Ru and Rh) in similar contents (100-200 ppb each) to the host pyrrhotite; and 4) pyrites replacing to plagioclase are depleted in most metals (i.e., PGE, Co, Ni and Ag). Overall, the different textural types of pyrite have similar abundances in Pd, Au, Se, Bi, Te, Sb and As. Mineralogical and compositional data suggests that 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 during cooling. During this episode, pyrites inherited the IPGE content of mineral to that was replaced, 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.