New data (U–Pb, K–Ar) on the geochronology of the alkaline-carbonatitic association of Fuerteventura, Canary Islands, Spain

Zircons from a nepheline-syenite of the Fuerteventura Basal Complex were dated by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). The age obtained from a total of 21 U–Th–Pb analyses is 25.4F0.3 Ma (2r) indicating a late Oligocene–early Miocene crystallization. This age is consistent with new K–Ar ages on nepheline-syenites and pyroxenites, and contradicts previously published 39Ar–40Ar (feldspar) ages that were interpreted to represent a late Cretaceous–early Paleocene, pyroxenitic–syenitic magmatic episode. These new geochronological data are consistent with both field observations and most of the previously published ages on alkaline silicate rocks and associated carbonatites of Fuerteventura. Therefore, they strongly support the existence of a single, late Oligocene–early Miocene event of alkaline–carbonatitic magmatism in the Basal Complex of Fuerteventura, taking place at approximately 25 Ma and comprising: alkaline-pyroxenites, melteigites-ijolites, nepheline-syenites and carbonatites, as well as their volcanic equivalents and associated dykes. These new data provide an estimate for the length of time that it took the island to grow, thus eliminating one of the major problems in explaining its development by a hot-spot model

A Geochemical and Geophysical Characterization of Sulfide Mine Ponds at the Iberian Pyrite Belt (Spain)

This work presents the results of a geochemical and geophysical characterization of the Monte Romero and La Naya mine ponds, belonging to the Cueva de la Mora and Riotinto mine districts, respectively, based on mineralogical, geochemical and geophysical techniques. In order to obtain a representative environmental characterization, two deposits showing different mineralogies, physico-chemical parameters, chemical compositions of tailings and pond conditions were selected. Monte Romero mine tailings showed an upper level mainly composed of silicates and a deeper level mainly composed of sulfides and barite. The toxic metal content was different in both levels but high enough to exceed the regional legal concentration limits for agricultural soils. An electrical resistivity tomography survey revealed a homogeneous upper unit (3 m thickness), which displayed low resistivity values, corresponding to water-saturated silt and clay materials with an abundance of sulfides which was interpreted as the pond infilling. The La Naya mine pond presented a homogeneous mineralogical composition made up of quartz as the main mineral and chlorite-smectite and jarosite as accessory phases. The absence of sulfide phases and the low contents of metal elements are directly related to the reworking processes of the sludge dumped in this pond. The geophysical survey revealed that the pond infilling did not have a constant thickness, but ranged between 15 and 20 m. An inner groundwater flow in the infilling was recognized. The low resistivity values allowed the presence of acid waters and related subsurface flows to be identified in both mine ponds, but no acid water drainage occurred across their vessels. When compared to the Aznalcóllar tailings spill, the La Naya pond is large enough to release a similar amount of sludge, but of a very low metal content. The Monte Romero sludge displays a similar, potentially toxic metal content to the Aznalcóllar sludge, but its size is significantly smaller

U-Pb geochronology of carbonatites from NW Fuerteventura revisited: new data and geological implications

En este trabajo se presentan nuevas edades U-Pb en circones de carbonatitas del sector NW de Fuerteventura. Los circones presentan características tanto texturales como composicionales que indican su origen ígneo y su cristalización a partir de magmas carbonatíticos. La edad obtenida, 24.2 ± 0.3Ma, es algo más joven que la existente para las carbonatitas del sector centro-occidental de la isla, por lo que se propone que habrían existido al menos dos intrusiones alcalino-carbonatíticas con cierta migración temporal en el sentido SW-NE, dentro de una zona de rift. Esta edad, además, restringe el episodio magmático alcalino-carbonatítico de la isla a prácticamente 1 Ma de duración. Sin embargo, este lapso temporal es significativo, en cuanto que representa la consecuencia de los cambios que ha sufrido la placa africana en su movimiento de divergencia con respecto a América del Sur y de convergencia con Eurasia.In this work, new U-Pb zircon ages in carbonatites from the NW sector of Fuerteventura are presented. The zircons show textural and compositional characteristics indicating its igneous origin and its crystallization from carbonatitic magmas. The obtained age, 24.2 ± 0.3 Ma, is slightly younger than the existing age for carbonatites in the central-western sector of the island. Therefore, we propose that at least two alkaline- carbonatitic intrusions would have been emplaced in a rift zone, with a certain degree of time migration from SW to NE. In addition, this age constrains the alkaline-carbonatitic magmatic episode in the island to an almost virtually 1 Ma span. However, this time lapse is meaningful, as it represents the consequence to the changes underwent by the African plate in its divergent movement with respect to South America and its convergence with Eurasia.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEMinisterio de Economía y Competitividad (MINECO)Universidad del País Vascopu

A Geochemical and Geophysical Characterization of Sulfide Mine Ponds at the Iberian Pyrite Belt (Spain)

(The original publication is available at www.springerlink.com)This work presents the results of a geochemical and geophysical characterization of the Monte Romero and La Naya mine ponds, belonging to the Cueva de la Mora and Riotinto mine districts, respectively, based on mineralogical, geochemical and geophysical techniques. In order to obtain a representative environmental characterization, two deposits showing different mineralogies, physico-chemical parameters, chemical compositions of tailings and pond conditions were selected. Monte Romero mine tailings showed an upper level mainly composed of silicates and a deeper level mainly composed of sulfides and barite. The toxic metal content was different in both levels but high enough to exceed the regional legal concentration limits for agricultural soils. An electrical resistivity tomography survey revealed a homogeneous upper unit (3 m thickness), which displayed low resistivity values, corresponding to water-saturated silt and clay materials with an abundance of sulfides which was interpreted as the pond infilling. The La Naya mine pond presented a homogeneous mineralogical composition made up of quartz as the main mineral and chlorite-smectite and jarosite as accessory phases. The absence of sulfide phases and the low contents of metal elements are directly related to the reworking processes of the sludge dumped in this pond. The geophysical survey revealed that the pond infilling did not have a constant thickness, but ranged between 15 and 20 m. An inner groundwater flow in the infilling was recognized. The low resistivity values allowed the presence of acid waters and related subsurface flows to be identified in both mine ponds, but no acid water drainage occurred across their vessels. When compared to the Aznalcóllar tailings spill, the La Naya pond is large enough to release a similar amount of sludge, but of a very low metal content. The Monte Romero sludge displays a similar, potentially toxic metal content to the Aznalcóllar sludge, but its size is significantly smaller.Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Mineralogía y geoquímica de las sienitas nefelínicas de Montaña Blanca-Esquinzo, NO de Fuerteventura (Islas Canarias)

Nepheline-syenites from the northern, Montaña Blanca-Esquinzo sector of the Basal Complex in the island of Fuerteventura (Canary Islands) are the most differentiated rocks belonging to the alkaline-carbonatitic association in this area. These nepheline-syenites are peculiar when compared with their counterparts in other alkaline-carbonatitic bodies, due to their lack of hydrous minerals (amphiboles, micas) and their strong depletions in incompatible elements. In this work, we present both mineralógica! and geochemical data on these rocks in order to obtain information about their origin and relationship with the ultramafic and mafic terms (clinopyroxenites and melteigites-ijolites) of the alkaline silicate rocks belonging to this association of the Basal Complex. These data suggest that the Montaña Blanca-Esquinzo nepheline-syenites are the products of extensive fractionation + accumulation of the same magma that gave rise to the clinopyroxenites and melteigites-ijolites

Material audiovisual para el aprendizaje de métodos y conceptos básicos en Geología

El proyecto se centra en la elaboración de vídeos en los que se resuelven problemas prácticos relacionados con conceptos básicos de Geología General, principalmente relacionados con mapas topográficos y mapas geológicos. El objetivo es que estos vídeo-tutoriales sirvan de apoyo a los alumnos de los primeros cursos de las titulaciones de Grado en Geología y Grado en Ingeniería Geológica, para el estudio de los contenidos y ejercicios prácticos