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
MineralogÃa y PetrologÃa
Area
CristalografÃa y MineralogÃa
Identifiers
19 results
Search Results
Now showing 1 - 10 of 19
Item Evidencias de fraccionación en el yacimiento intramagmático de Ni-Cu-EGP de Aguablanca (Badajoz)(Cuadernos do Laboratorio Xeolóxico de Laxe, 2000) Ortega Menor, Lorena; Lunar Hernández, Rosario; GarcÃa Palomero, F.; MartÃn Estévez, J.R.Item Conditions of graphite precipitation in the volcanic-hosted deposits at Borrowdale (Cumbria, UK)(2009) Ortega Menor, Lorena; Luque del Villar, Francisco Javier; Barrenechea, Edurne; Beyssac, Olivier; Huizenga, Jan-Marten; Millward, D.; Rodas, MagdalenaItem Edades de cristalización U-Pb en circones del complejo Ãgneo de Santa Olalla de Cala: implicaciones en la edad del yacimiento d e Ni-Cu-EGP de Aguablanca (Badajoz)(Macla, 2004) Rombo, I.; Lunar Hernández, MarÃa Del Rosario; Capote Del Villar, Ramón; Quesada, C.; Dunning, G. R.; Piña GarcÃa, Rubén; Ortega Menor, Lorena; Sociedad Española de MineralogÃaItem Fluid composition and reactions of graphite precipitation in the volcanic-Hosted deposit at Borrowdale (NW England): evidence from fluid inclusions(Macla, 2008) Ortega Menor, Lorena; Luque del Villar, Francisco Javier; Fernández Barrenechea, José MarÃa; Millward, David; Beyssac, Olivier; Hizenga, Jan Marten; Rodas, MagdalenaItem Contrasting Mineralizing Processes in Volcanic-Hosted Graphite Deposits(Smart Science for Exploration and Mining, Proceedings of the Tenth Biennial SGA Meeting, 2009) Luque del Villar, Francisco Javier; Barrenechea, José F.; Ortega Menor, Lorena; Rodas, Magdalena; Millward, David; Williams, Jean-PierreThe only two known graphite vein-deposits hosted by volcanic rocks (Borrowdale, United Kingdom, and Huelma, Southern Spain) show remarkable similarities and differences. The lithology, age of the magmatism and geodynamic contexts are distinct, but the mineralized bodies are controlled by fractures. Evidence of assimilation of metasedimentary rocks by the magmas and hydrothermal alteration are also common features to both occurrences. Graphite morphologies at the Borrowdale deposit vary from flakes (predominant) to spherulites and cryptocrystalline aggregates, whereas at Huelma, flaky graphite is the only morphology observed. The structural characterization of graphite indicates a high degree of ordering along both the c axis and the basal plane. Stable carbon isotope ratios of graphite point to a biogenic origin of carbon, most probably related to the assimilation of metasedimentary rocks. Bulk į13C values are quite homogeneous in both occurrences, probably related to precipitation in short time periods. Fluid inclusion data reveal that graphite precipitated from C-O-H fluids at moderate temperature (500 ºC) in Borrowdale and crystallized at high temperature from magma in Huelma, In addition, graphite mineralization occurred under contrasting fO2 conditions. All these features can be used as potential exploration tools for volcanic-hosted graphite deposits.Item Mineralogy and geochemistry of platinum group elements in the Aguablanca Ni-Cu deposit (SW Spain)(Mineralogy and petrology, 2007) Piña GarcÃa, Rubén; Gervilla, Fernando; Ortega Menor, Lorena; Lunar Hernández, RosarioThe Aguablanca Ni-Cu-(PGE) magmatic sulphide deposit is associated with a magmatic breccia located in the northern part of the Aguablanca gabbro (SW, Iberia). Three types of ores are present: semi-massive, disseminated, and chalcopyrite-rich veined ore. The principal ore minerals are pyrrhotite, pentlandite and chalcopyrite. A relatively abundant platinum-group mineral (PGM) assemblage is present and includes merenskyite, melonite, michenerite, moncheite and sperrylite. Moreover, concentrations of base and precious metals and micro-PIXE analyses were obtained for the three ore-types. The mineralogy and the mantlenormalised chalcophile element profiles strongly suggest that semi-massive ore represents mss crystallisation, whereas the disseminated ore represents an unfractionated sulphide liquid and the chalcopyrite-rich veined ore a Cu-rich sulphide liquid. Palladium-bearing minerals occur commonly enclosed within sulphides, indicating a magmatic origin rather than hydrothermal. The occurrences and the composition of these minerals suggest that Pd was initially dissolved in the sulphides and subsequently exsolved at low temperatures to form bismutotellurides. Negative Pt and Au anomalies in the mantle-normalised chalcophile element profiles, a lack of Cu-S correlation and textural observations (such as sperrylite losing its euhedral shape when in contact with altered minerals) suggest partial remobilisation of Pt, Au and Cu by postmagmatic hydrothermal fluids after the sulphide crystallisation.Item Origen de los fragmentos máficos-ultramáficos de la brecha mineralizada del yacimiento de Ni-Cu-EGP de Aguablanca (Badajoz)(Macla, 2004) Piña GarcÃa, Rubén; Lunar Hernández, MarÃa Del Rosario; Ortega Menor, Lorena; Gervilla, F.; Alapieti, T.; MartÃnez, C.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 GarcÃa, Rubén; Lunar Hernández, Rosario; Ortega Menor, Lorena; Gervilla, F.; Alapieti, T.; MartÃnez, 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 CaracterÃsticas texturales y geoquÃmicas de la pirita en la mineralización intramagmática de Ni-Cu-PGE de Aguablanca (Badajoz)(Cuadernos do Laboratorio Xeolóxico de Laxe, 2000) MartÃn Estévez, J.R.; Ortega Menor, Lorena; Lunar Hernández, Rosario; GarcÃa Palomero, F.Item Assimilation, Hydrothermal Alteration and Graphite Mineralization in the Borrowdale Deposit (UK)(Smart science for exploration and mining : proceedings of the 10th Biennial SGA Meeting, Townsville, Australia 17th-20th August 2009, 2009) Ortega Menor, Lorena; Luque del Villar, Francisco Javier; Barrenechea, Edurne; Rodas, Magdalena; Millward, David; Beyssac, Olivier; Williams, PatrickThe volcanic-hosted graphite deposit at Borrowdale was formed through precipitation from C-O-H fluids. The G13C data indicate that carbon was incorporated into the mineralizing fluids by assimilation of carbonaceous metapelites of the Skiddaw Group by andesite magmas of the Borrowdale Volcanic Group. The graphite mineralization occurred as the fluids migrated upwards through normal conjugate fractures forming the main subvertical pipe-like bodies. The mineralizing fluids evolved from CO2-CH4-H2O mixtures (XCO2=0.6-0.8) to CH4-H2O mixtures. Coevally with graphite deposition, the andesite and dioritic wall rocks adjacent to the veins were intensely hydrothermally altered to a propylitic assemblage. The initial graphite precipitation was probably triggered by the earliest hydration reactions in the volcanic host rocks. During the main mineralization stage, graphite precipitated along the pipe-like bodies due to CO2 -> C+O2. This agrees with the isotopic data which indicate that the first graphite morphologies crystallizing from the fluid (cryptocrystalline aggregates) are isotopically lighter than those crystallizing later (flakes). Late chlorite-graphite veins were formed from CH4-enriched fluids following the reaction CH4 + O2 -> C+ 2H2O, producing the successive precipitation of isotopically lighter graphite morphologies. Thus, as mineralization proceeded, water-generating reactions were involved in graphite precipitation, further favouring the propylitic alteration.