Geology and geochemistry of Linares-La Carolina Pb-ore field (southeastern border of the Hesperian Massif)

Base-metal late Hercynian vein and stratabound-type deposits occur in the Linares-La Carolina mining district (Sierra Morena, Spain). No other ore deposits than iron beds and a supergene iron-manganese karst-related deposit were found in the studied area. However, Upper Ordovician-Lower Silurian rocks show Ni, Zn, Pb content above the average values of sandstones. Upper Ordovician-Lower Silurian country rocks are grouped into two stratigraphical sequences that reflect sea-level rise-fall cycles in a basin developed in a passive margin. The duration of these cycles indicates that they were caused by a combination of eustatic processes and intraplate extensional tectonics. The Late Hercynian hydrothermal deposits hosted by metasediments and granitoids, comprise (Ba)-(Pb-Zn-Cu- [Ag]) vein and stratabound type deposits that were emplaced before the Ladinian, during an extensional stage starting in the Upper Permian. Three stages of ore deposition have been recognised, the first stage is characterised by the formation of pyrrhotite, arsenopyrite, Ag sulphosalts and minor arsenopyrite and Bi sulphides. In the second stage, pyrite, Cu sulphides, barite and Ni-Co mineral s precipitated. Main deposition of galena and sphalerite took place at the end of the first stage and the beginning of the second stage. There is no evidence of selective Ag enrichment. Hydrothermal alteration of granitic host rocks is characterised by argillic-phyllic, argillic-propylitic assemblages overprinted by a late alkai metasomatism. There is a strong relation between composition of secondary minerals, mineralogy of the alteration zone and whole-rock composition. Mass transfers of alumina appear to be important. There is a significant introduction of Si, AI, K, Na, Rb and Pb, together with a depletion in Ca and Sr. Chlorite and illite geothermometers indicate temperatures of 276.7-321.5 ·C. Three events of fluid entrapment at hydrostatic pressures have been recognised, with fluids evolved from low to moderate, locally carbonaceous hot fluids to highmoderately polysaline cooler fluids. Ore-lead was derived from Palaeozoic U-'enriched' country rocks, although some participation from the Hercynian granitoids can not be ruled out. The distribution of sulphur isotopes is not homogeneous in the scale of the district. Differences exist between those deposits at the El Centenillo-Santa Elena sector (where the dominant process was the mixing of 'magmatic'-derived sulphur and sulphur derived from the metasediments) and those occurrences at the Linares-La Carolina sector (where the dominant sulphur was 'magmatic'-derived)

Geoguía 2: Mazarrón, la minería olvidada del plomo, zinc, plata y alumbres

El distrito minero de Mazarrón (Murcia) constituye uno de los sitios de interés geológico y minero más importantes de España, y junto con los distritos de La Unión y Rodalquilar, constituye un extraordinario ejemplo de la relación entre el vulcanismo mioceno del sureste peninsular y los procesos metalogénicos. En Mazarrón podemos observar la presencia de cuerpos mineralizados (Pb-Zn-Ag, alunita) relacionados con aparatos subvolcánicos (pórfidos dacíticos) tipo domo del Mioceno. Existen tres zonas mineralizadas principales en el distrito de Mazarrón (de este a oeste): San Cristóbal-Perules, Pedreras Viejas y Coto Fortuna. El ejemplo más notable de domo mineralizado lo constituye San Cristóbal-Perules (adyacente al pueblo de Mazarrón)

Intraplate mafic magmatism, degasification, and deposition of mercury: the giant Almadén mercury deposit (Spain) revisited

The giant Almadén mercury deposit (Spain) is hosted by the Lower Silurian Criadero Quartzite; in turn this ore-bearing rock unit is cross-cut by the so-called Frailesca unit, a diatreme body of basaltic composition. The geochemical characteristics of the Silurian to Devonian Almadén District volcanic units indicate that these rocks originated from an enriched, evolving mantle source that ultimately yielded basanites?nephelinites to yolites, through olivine-basalts, pyroxene-basalts, trachybasalts, trachytes, very scarce rhyolites, and quartzdiabases. The Silurian intraplate alkaline volcanism developed in submarine conditions which triggered widespread hydrothermal activity resulting in Hg ore formation and pervasive alteration to carbonates. The #948;18O, #948;13C, and #948;34S isotopic signatures for carbonates and pyrite suggest different sources for carbon and sulfur, including magmatic and organic for the former and magmatic and sea water for the latter. The most important and efficient natural source of mercury on Earth is by far the volcanic activity, which liberates mercury via quiescent degassing and catastrophic (Plinian) events when eruptions can overwhelm the atmospheric budget of Hg. Thus, we suggest that CO2 degasification and coeval distillation of mercury from the volcanic rocks fed the huge hydrothermal system that led to massive deposition of mercury at Almadén. Build up of Hg0 gas in magmatic chambers during waning rifting in the Late Ordovician, followed by renewed volcanism in the Early Silurian, would have resulted in massive degasification of the accumulated mercury. Part of this mercury went into the Criadero Quartzite leading to formation of the huge Almadén deposit and others (e.g., El Entredicho) along the same stratigraphic level. Progressive depletion of the deep seated magmatic Hg stock would have resulted in a drastic reduction in ore deposit size after the Lower Silurian when smaller deposits formed (e.g., Las Cuevas)

Geoguía 1 : el oro de Rodalquilar

El distrito minero aurífero de Rodalquilar es único en la península ibérica por sus características geológicas. El cuerpo mineralizado principal del Cinto es un yacimiento epitermal de alta sulfurización asociado a caldera volcánica. El distrito se localiza en la Provincia de Almería, dentro de los terrenos del Parque Natural de Cabo de Gata - Níjar. El Parque, declarado como tal en 1987, recibió además el status de Reserva de la Biosfera por parte de la UNESCO en 1997 y tiene unos 457 km de tierras y costas protegidas. Esta reserva se encuentra en la región más árida de Europa. La zona posee además una alta diversidad florística que constituye una prioridad para la conservación en Europa. El clima es de tipo Mediterráneo semi-árido, con precipitaciones de unos 200 mm y una temperatura media de 18ºC. Bajo un punto de vista fisiográfico el distrito de Rodalquilar se localiza en un sector caracterizado por escarpados montes que sin embargo no superan los 360-380 m de altitud. Los valles se juntan para formar grandes ramblas que permanecen secas la mayor parte del tiempo aunque pueden inundarse durante episodios tormentosos. El clima semi-árido de la región puede haber empezado hace unos 4500 años, con una transformación importante del paisaje que se refleja en las condiciones esteparias que se observan hoy en día

Environmental assessment of the arsenic-rich, rodalquilar gold-(copper-lead-zinc) mining district, se Spain: soils and wild plants species.

The Rodalquilar mineral deposits (SE Spain) were formed in Miocene time in relation to caldera volcanic episodes and dome emplacement phenomena. Two types of ore deposits are recognized: (1) the El Cinto epithermal, Au?As high sulphidation vein and breccia type; and (2) peripheral low sulphidation epithermal Pb?Zn?Cu?(Au) veins. The first metallurgical plants for gold extraction were set up in the 1920s and used amalgamation. Cyanide leaching began in the 1930s and the operations lasted until the mid 1960s. The latter left a huge pile of *900,000?1,250,000 m3 of abandoned As-rich tailings adjacent to the town of Rodalquilar. A frustrated initiative to reactivate the El Cinto mines took place in the late 1980s and left a heap leaching pile of *120,000 m3. Adverse mineralogical and structural conditions favoured metal and metalloid dispersion from the ore bodies into soils and sediments, whereas mining and metallurgical operations considerably aggravated contamination. We present geochemical data for soils, tailings and wild plant species. Compared to world and local baselines, both the tailings and soils of Rodalquilar are highly enriched in As (mean concentrations of 950 and 180 lg g-1, respectively). Regarding plants, only the concentrations of As, Bi and Sb in Asparagus horridus, Launaea arborescens, Salsola genistoides, and Stipa tenacissima are above the local baselines. Bioaccumulation factors in these species are generally lower in the tailings, which may be related to an exclusion strategy for metal tolerance. The statistical analysis of geochemical data from soils and plants allows recognition of two well-differentiated clusters of elements (As?Bi?Sb?Se?Sn?Te and Cd?Cu?Hg?Pb?Zn), which ultimately reflect the strong chemical influence of both El Cinto and peripheral deposits mineral assemblages