Papers by LORENA ORTEGA MENOR
Mineralogical Magazine, Jun 1, 1991
Economic Geology, 2013
The partition coefficients of platinum group elements (PGE) and chalcophile elements Au, Re, Ag, ... more The partition coefficients of platinum group elements (PGE) and chalcophile elements Au, Re, Ag, Se, Bi, Te, and Sb, between arsenide and sulfide phases (DAs/sulf) have been estimated by measuring in situ concentrations of these elements using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) in coexisting arsenide and sulfide minerals from the Beni Bousera Cr-Ni mineralization (North Morocco). Previous experimental studies and observations on the distribution of PGE in a number of As-rich, Ni-Cu-PGE ore deposits have shown that arsenide minerals may play an important role controlling the distribution of these metals in magmatic sulfide systems. However to date, there is no comprehensive study quantifying the partitioning behavior of these elements when arsenide minerals crystallize either directly from a sulfide melt or from an arsenide melt previously segregated by immiscibility from a sulfide melt. The Beni Bousera mineralization represents an excellent natu...
Mineralium Deposita, 1998
Un correcto análisis de los datos adquiridos durante la investigación geológica es fundamental ta... more Un correcto análisis de los datos adquiridos durante la investigación geológica es fundamental tanto para la interpretación de los mismos como para su posterior comunicación a la comunidad científica. Por ese motivo el aprendizaje de una metodología de análisis de datos debe formar parte de la preparación de todo geólogo a lo largo de su formación. En este trabajo se desarrolla una metodología de análisis de datos como parte principal de dicha preparación. Las técnicas propuestas no requieren conocimientos avanzados de estadística por parte del geólogo y tienen como principal objetivo el establecimiento de relaciones entre datos y la elaboración de hipótesis sobre las mismas que deberán ser formalizadas en una fase final de tratamiento estadístico aplicado.
Applied Clay Science, 2016
Two textural types of chlorite are identified in the mineralised veins at the Patricia Zn-Pb-Ag e... more Two textural types of chlorite are identified in the mineralised veins at the Patricia Zn-Pb-Ag epithermal ore deposit (NE, Chile): massive and oscillatory-zoned radiated chlorites. Three main stages of mineralisation have been defined in the Patricia deposit: (1) pre-ore stage, (2) base-metal stage which is divided into two substages: substage 2a and substage 2b and (3) post-ore stage. Both types of chlorite are classified as chamosite and occur coeval to the sphalerite precipitation during the substage 2a. Massive chlorite shows an average content of 33 wt.% FeO, 4.9 wt.% MnO, and 4 wt.% MgO. Oscillatory zoning in radiated chlorites consists of concentric bands with different contents on FeO (from 26.45 to 41.41 wt.%), MgO (from 1.7 to 5.44 wt.%) and MnO (from 1.7 to 9.32 wt.%). Four different chlorite geothermometers based on the system SiO 2-Al 2 O 3-FeO-MgO-H 2 O were applied to both types of chlorites. The temperature estimations are in agreement with temperatures data of fluid inclusions previously measured in sphalerite of the sub-stage 2a. Despite the high content in Mn of chlorites, the study confirms the applicability of the chlorite geothermometers without the knowledge of the Fe 3+/ Fe ratio in low-pressure paragenesis and its usefulness as an important tool for characterising the thermal conditions in epithermal ore deposits.
Geoscience frontiers, Mar 1, 2012
Stable carbon isotope geochemistry provides important information for the recognition of fundamen... more Stable carbon isotope geochemistry provides important information for the recognition of fundamental isotope exchange processes related to the movement of carbon in the lithosphere and permits the elaboration of models for the global carbon cycle. Carbon isotope ratios in fluid-deposited graphite are powerful tools for unravelling the ultimate origin of carbon (organic matter, mantle, or carbonates) and help to constrain the fluid history and the mechanisms involved in graphite deposition. Graphite precipitation in fluid-deposited occurrences results from CO 2-and/or CH 4-bearing aqueous fluids. Fluid flow can be considered as both a closed (without replenishment of the fluid) or an open system (with renewal of the fluid by successive fluid batches). In closed systems, carbon isotope systematics in graphite is mainly governed by Rayleigh precipitation and/or by changes in temperature affecting the fractionation factor between fluid and graphite. Such processes result in zoned graphite crystals or in successive graphite generations showing, in both cases, isotopic variation towards progressive 13 Cor 12 C enrichment (depending upon the dominant carbon phase in the fluid, CO 2 or CH 4 , respectively). In open systems, in which carbon is episodically introduced along the fracture systems, the carbon systematics is more complex and individual graphite crystals may display oscillatory zoning because of Rayleigh precipitation or heterogeneous variations of d 13 C values when mixing of fluids or changes in the composition of the fluids are the mechanisms responsible for graphite precipitation.
Geochimica et Cosmochimica Acta, Apr 1, 2010
The volcanic-hosted graphite deposit at Borrowdale in Cumbria, UK was formed through precipitatio... more The volcanic-hosted graphite deposit at Borrowdale in Cumbria, UK was formed through precipitation from CO -H fluids. The 13 C 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 CO 2-CH 4-H 2 O mixtures (XCO 2 =0.6-0.8) to CH 4-H 2 O 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 CO 2 → C+O 2. 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 CH 4-enriched fluids following the reaction CH 4 + O 2 → C+ 2H 2 O, 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.
Journal of the Geological Society, May 1, 2012
Massive graphite deposition resulting in volumetrically large occurrences in volcanic environment... more Massive 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: Borrowdale, UK, and Huelma, Spain. As inferred from the Borrowdale deposit, graphite mineralization resulted from the complex interaction of several
Economic geology and the bulletin of the Society of Economic Geologists, Jun 1, 2006
Introduction ECONOMIC Ni-Cu-PGE deposits associated with mafic-ultramafic rocks are uncommon in E... more Introduction ECONOMIC Ni-Cu-PGE deposits associated with mafic-ultramafic rocks are uncommon in Europe. With the exception of the world-class Noril'sk and Pechenga deposits in Russia (Barnes et al., 2001), most occurrences are restricted to Finland-in the Portimo, Penikat, or Koillismaa complexes (Alapieti and Lathinen, 2002), which are currently being evaluated by the Artic Platinum Partnership, and the Vammala,
Mineralium Deposita, Sep 22, 2013
Graphite deposits result from the metamorphism of sedimentary rocks rich in carbonaceous matter o... more Graphite deposits result from the metamorphism of sedimentary rocks rich in carbonaceous matter or from precipitation from carbon-bearing fluids (or melts). The latter process forms vein deposits which are structurally controlled and usually occur in granulites or igneous rocks. The origin of carbon, the mechanisms of transport, and the factors controlling graphite deposition are discussed in relation to their geological settings. Carbon in granulite-hosted graphite veins derives from sublithospheric sources or from decarbonation reactions of carbonate-bearing lithologies, and it is transported mainly in CO 2-rich fluids from which it can precipitate. Graphite precipitation can occur by cooling, water removal by retrograde hydration reactions, or reduction when the CO 2-rich fluid passes through relatively low-fO 2 rocks. In igneous settings, carbon is derived from assimilation of crustal materials rich in organic matter, which causes immiscibility and the formation of carbon-rich fluids or melts. Carbon in these igneous-hosted deposits is transported as CO 2 and/or CH 4 and eventually precipitates as graphite by cooling and/or by hydration reactions affecting the host rock. Independently of the geological setting, vein graphite is characterized by its high purity and crystallinity, which are required for applications in advanced technologies. In addition, recent discovery of highly crystalline graphite precipitation from carbon-bearing fluids at moderate temperatures in vein deposits might provide an alternative method for the manufacture of synthetic graphite suitable for these new applications.
Ore Geology Reviews, 2016
The Patricia ore deposit represents an unusual example of economic Zn-Pb-Ag mineralization at the... more The Patricia ore deposit represents an unusual example of economic Zn-Pb-Ag mineralization at the northernmost end of the Late Eocene-Oligocene metallogenic belt in Chile. It is hosted by volcanosedimentary units, which are typically tuffaceous and andesitic breccias. The ore body consists of a set of subvertical E-W vein systems developed under a sinistral strike-slip regime that included transtensive domains with generalized extensional structures where the ores were deposited. The deposit is divided into two blocks by a set of NNW-ESE-trending reverse faults, which uplifted the eastern block and exhumed thicker and deeper parts of the deposit. At least 200 m of volcano-sedimentary pile hosting the mineralization has been eroded in this block. By contrast, the western block exposes a shallower part of the system where cherts, amorphous silica and jasperoids occur. Three main stages of mineralization have been defined: (1) pre-ore stage is characterized by early quartz, pyrite and arsenopyrite, (2) base-metal and silver stage; characterized by sphalerite (6 to 15 mol.% FeS), galena, chalcopyrite, pyrrhotite and Agbearing minerals (freibergite, polybasite, stephanite, pyrargyrite, freieslebenite and acanthite) and (3) post-ore stage; characterized by late quartz, kutnohorite and minor sulfides (arsenopyrite, sphalerite,
Boletín de la Sociedad Española de Mineralogía, 1987
AGUFM, Dec 1, 2013
ABSTRACT
Macla: revista de la Sociedad Española de Mineralogía, Sep 1, 2008
The only two known graphite vein-deposits hosted by volcanic rocks (Borrowdale, United Kingdom, a... more The 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 13 C values are quite homogeneous in both occurrences, probably related to precipitation in short time periods. Fluid inclusion data reveal that graphite precipitated from CO -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 fO 2 conditions. All these features can be used as potential exploration tools for volcanic-hosted graphite deposits.
Boletín de la Sociedad Española de Mineralogía, 1994
Las mineralizaciones de antimonio de mari rosa y el juncalon son depositos filonianos encajados e... more Las mineralizaciones de antimonio de mari rosa y el juncalon son depositos filonianos encajados en el nucleo de anticlinales hercinicos constituidos por rocas precambricas pertenecientes al complejo esquisto-grauvaguico. Se encuentran situadas en la parte meridional de la zona cantro-ibarica del macizo hesperico. En mari rosa la mineralizacion se presenta en dos tipos de venas: vp, paralelas a la esquistosidad principal y vo, oblicuas a la misma. Estas ultimas corresponden a zonas de dilatacion en cabalgamientos de bajo angulo y concentran la mineralizacion masiva de estibina. En el juncalon la mineralizacion se localiza en fallas subverticales de desgarre. La paragenesis mineral se desarrolla en tres etapas hidrotermales. En mari rosa esta caracterizada por: 1) arsenopirita 2) estibina-(oro) y 3) pirita-pirrotina y diversos sulfoantimoniuros de plomo y cobre. De estos solo el segundo episodio es relevante y dio lugar a la precipitacion de estibina masiva. En el juncalon solo el segundo episodio dio lugar a la formacion de estibina, mientras que el primero y el tercero fueron esteriles (cuarzo). La alteracion hidrotermal es de menor importancia y consiste fundamentalmente en sericitizacion, junto con cloritizacion y carbonatizacion en mari rosa. Desde un punto de vista quimico, la alteracion esta caracterizada por un aumento en la relacion k20/na20, disminucion de si02/volatiles, aumento de sb, mo, au y n en la proximidad de la mineralizacion. Se observa ademas una correlacion alta entre sb y mo. Los fluidos hidrotermales asociados pertenece al sistema composicional h20-nac1-co2-ch4-n2, con la excepcion del co2, ausente en el juncalon. Su evolucion se caracteriza por un paulatino enfriamiento desde 400 a 150, junto con un aumento progresivo en la proporcion de h20 y de n2 en la fraccion volatil. En mari rosa, la precipitacion masiva de estibina tiene lugar a 300 c y 1 kb de presion por la ebullicion del fluido, estimandose una profundidad de formacion de 3,5 4 km. En el juncalon la precipitacion de estibina ocurre en torno a 250 c por enfriamiento progresivo del fluido
Macla: revista de la Sociedad Española de Mineralogía, 2004
Cadernos do Laboratorio Xeolóxico de Laxe: Revista de xeoloxía galega e do hercínico peninsular, 2000
Uploads
Papers by LORENA ORTEGA MENOR