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
13 results
Search Results
Now showing 1 - 10 of 13
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 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 María; 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 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.Item The graphite deposit at Borrowdale (UK): A catastrophic mineralizing event associated with Ordovician magmatism(Geochimica et cosmochimica acta, 2010) Ortega Menor, Lorena; Millward, David; Luque del Villar, Francisco Javier; Fernández Barrenechea, José María; Beyssac, Olivier; Huizenga, Jan-Marten; Rodas, Magdalena; Clarke, S.M.The volcanic-hosted graphite deposit at Borrowdale in Cumbria, UK, was formed through precipitation from C–O–H fluids. The δ13C 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. The structural features of the pipe-like mineralized bodies as well as the isotopic homogeneity of graphite suggest that the mineralization occurred in a very short period of time.Item Graphite morphologies in the volcanic-hosted deposits at Borrowdale (NW England, UK): preliminary raman and SIMS data(Macla, 2008) Fernández Barrenechea, José María; Luque del Villar, Francisco Javier; Ortega Menor, Lorena; Rodas, Magdalena; Millward, David; Beyssac, Olivier- Project number: 200
Item El Distrito Minero más importante de Europa, la Faja Pirítica (SO Península Ibérica): nueva colección de muestras y nuevas herramientas para la docencia práctica en Recursos Minerales(2022) Piña García, Rubén; Yesares Ortiz, María Dolores; Ortega Menor, Lorena; Luque del Villar, Francisco Javier; Iglesias Martínez, Mario Item Graphite morphologies from the Borrowdale deposit (NW England, UK): Raman and SIMS data(Contributions to mineralogy and petrology, 2009) Fernández Barrenechea, José María; Luque del Villar, Francisco Javier; Millward, David; Ortega Menor, Lorena; Beyssac, Olivier; Rodas, MagdalenaGraphite in the Borrowdale (Cumbria, UK) deposit occurs as large masses within mineralized pipe-like bodies, in late graphite–chlorite veins, and disseminated through the volcanic host rocks. This occurrence shows the greatest variety of crystalline graphite morphologies recognized to date from a single deposit. These morphologies described herein include flakes, cryptocrystalline and spherulitic aggregates, and dish-like forms. Colloform textures, displayed by many of the cryptocrystalline aggregates, are reported here for the first time from any graphite deposit worldwide. Textural relationships indicate that spherulitic aggregates and colloform graphite formed earlier than flaky crystals. This sequence of crystallization is in agreement with the precipitation of graphite from fluids with progressively decreasing supersaturation. The structural characterization carried out by means of Raman spectroscopy shows that, with the exception of colloform graphite around silicate grains and pyrite within the host rocks, all graphite morphologies display very high crystallinity. The microscale SIMS study reveals light stable carbon isotope ratios for graphite (δ13C = -34.5 to -30.2%), which are compatible with the assimilation of carbon-bearing metapelites in the Borrowdale Volcanic Group magmas. Within the main mineralized breccia pipelike bodies, the isotopic signatures (with cryptocrystalline graphite being lighter than flaky graphite) are consistent with the composition and evolution of the mineralizing fluids inferred from fluid inclusion data which indicate a progressive loss of CO2. Late graphite–chlorite veins contain isotopically heavier spherulitic graphite than flaky graphite. This agrees with CH4-enriched fluids at this stage of the mineralizing event, resulting in the successive precipitation of isotopically heavier graphite morphologies. The isotopic variations of the different graphite morphologies can be attributed therefore, to changes in the speciation of carbon in the fluids coupled with concomitant changes in the XH2O during precipitation of graphite and associated hydrous minerals (mainly epidote and chlorite).Item Key factors controlling massive graphite deposition in volcanic settings: an example of a self-organized critical system(Journal of the Geological Society, 2012) Luque del Villar, Francisco Javier; Ortega Menor, Lorena; Fernández Barrenechea, José María; Huizenga, Jan-Marten; Millward, DavidMassive graphite deposition resulting in volumetrically large occurrences in volcanic environments is usually hindered by the low carbon contents of magmas and by the degassing processes occurring during and after magma emplacement. In spite of this, two graphite deposits are known worldwide associated with volcanic settings, at Borrowdale, UK, and Huelma, Spain. As inferred from the Borrowdale deposit, graphite mineralization resulted from the complex interaction of several factors, so it can be considered as an example of self-organized critical systems. These factors, in turn, could be used as potential guides for exploration. The key factors influencing graphite mineralization in volcanic settings are as follows: (1) an unusually high carbon content of the magmas, as a result of the assimilation of carbonaceous metasedimentary rocks; (2) the absence of significant degassing, related to the presence of sub-volcanic rocks or hypabyssal intrusions, acting as barriers to flow; (3) the exsolution of a carbon-bearing aqueous fluid phase; (4) the local structural heterogeneity (represented at Borrowdale by the deep-seated Burtness Comb Fault); (5) the structural control on the deposits, implying an overpressured, fluid-rich regime favouring a focused fluid flow; (6) the temperature changes associated with fluid flow and hydration reactions, resulting in carbon supersaturation in the fluid, and leading to disequilibrium in the system. This disequilibrium is regarded as the driving force for massive graphite precipitation through irreversible mass-transfer reactions. Therefore, the formation of volcanic-hosted graphite deposits can be explained in terms of a self-organized critical system.- Project number: 230
Item Curso de nivelación de Química para los Grados en Geología e Ingeniería Geológica(2015) Campo Santillana, José Antonio; Álvarez Serrano, Inmaculada; Herrero Domínguez, Santiago; Ruiz González, M. Luisa; Torralba Martínez, M. Carmen; Sánchez Peláez, Ana Edilia; Ovejero Morcillo, Paloma; Hernando González, María; Varela Losada, Áurea; Ramírez Castellanos, Julio; Arroyo de Dompablo, Elena; Ortega Menor, Lorena; Luque del Villar, Francisco Javier; Arribas Mocoroa, José; Pieren Pidal, Agustín Pedro; Muñoz Martín, Alfonso; Ureta Gil, M. Soledad