Geochemical and Volcanological Criteria in Assessing the Links between Volcanism and VMS Deposits: A Case on the Iberian Pyrite Belt, Spain

VMS deposits in the Iberian Pyrite Belt (IPB), Spain and Portugal, constitute the largest accumulation of these deposits on Earth. Although several factors account for their genetic interpretation, a link between volcanism and mineralization is generally accepted. In many VMS districts, research is focused on the geochemical discrimination between barren and fertile volcanic rocks, these latter being a proxy of VMS mineralization. Additionally, the volcanological study of igneous successions sheds light on the environment at which volcanic rocks were emplaced, showing an emplacement depth consistent with that required for VMS formation. We describe a case on the El Almendro–Villanueva de los Castillejos (EAVC) succession, Spanish IPB, where abundant felsic volcanic rocks occur. According to the available evidence, their geochemical features, εNd signature and U–Pb dates suggest a possible link to VMS deposits. However, (paleo)volcanological evidence here indicates pyroclastic emplacement in a shallow water environment. We infer that such a shallow environment precluded VMS generation, a conclusion that is consistent with the absence of massive deposits all along this area. We also show that this interpretation lends additional support to previous models of the whole IPB, suggesting that compartmentalization of the belt had a major role in determining the sites of VMS depositionThis research is supported by the research project “Caracterización y datación isotópicas de rocas ígneas y sistemas hidrotermales en la Faja Pirítica Ibérica Española” (BTE2003-04354, Plan Nacional I+D) Careful revisions by anonymous reviewers have importantly contributed to improve this work and are acknowledged with than

El poblamiento de la edad del cobre en la tierra llana de Huelva

Se presentan en este trabajo los resultados del Proyecto Tierra Llana de Huelva referidos a la ocupación de la Edad del Cobre. Proponemos una permanencia del sistema del poblamiento durante el Calcolítico y Bronce Pleno, y su ruptura hacia el Bronce Final, periodo en el que se estructura el territorio en turno a centros hegemónicos.____________________________They are presented in this work the results of the project Flat Earth of Huelva referred to the occupation of the Copper Age. We propose a permanency of the system of the settlement during the Calcolithic time and Middle-Bronze Age, and their rupture toward the Final Bronze Age, in the one that the territory appears structured to hegemonic centers

Succession of felsic volcanic sequences in the Volcano-Sedimentary Complex in the Iberian Pyrite Belt: discrimination between volcanic and subvolcanic models

A field study is presented on two selected areas in the Volcano-Sedimentary Complex (VSC) of the Iberian Pyrite Belt (IPB), the Odiel River section and the Paymogo Volcanic lineament. Field evidence has allowed to distinguish two major groups of felsic rocks, which successively appear in the stratigraphic column. Probably, this conclusion can be extended to other areas in the IPB. In addition, field, petrographic and geochemical evidence shows that at least the felsic rhyolitic succession in the Odiel River (and probably also in Paymogo) formed in a volcanic, environment, favouring a volcanic-pile model in the VS

Alteración hidrotermal asociada a los yacimientos de sulfuros masivos de la Faja Pirítica Suribérica

Los depósitos de sulfuros masivos de Masa Valverde y Aznalcóllar-Los Frailes se localizan en el sector SE de la Faja Pirítica Suribérica (FPS). Estos depósitos se encuentran encajados en una secuencia vulcanosedimentaria carbonífera denominada Complejo Vulcanosedimentario (CVS). Más específicamente, ambos depósitos aparecen a techo de la primera secuencia volcánica félsica, generalmente referida como V1. Estos yacimientos tienen una morfología aproximadamente lenticular y se encuentran sobre una secuencia compleja de rocas alteradas hidrotermalmente. Las rocas encajantes son pizarras negras que yacen sobre rocas volcanoclásticas y coherentes de composición dacítica-riolítica. La mineralización consiste principalmente de pirita con cantidades accesorias de calcopirita, esfalerita, galena, arsenopirita y pirrotina. El objetivo de este estudio es caracterizar la mineralogía, petrología y geoquímica del muro de la mineralización, integrando todos los datos disponibles para distinguir las diferentes zonas de alteración y sus características físico-químicas. Finalmente, se sugiere un escenario geológico plausible para la génesis de las mineralizaciones, antes de la deformación Varisca. Se han identificado tres zonas en base a su mineralogía, textura y características geoquímicas. La zona más interna se caracteriza por una alteración penetrativa que ha destruido la mayor parte de las texturas volcánicas originales. En esta zona prácticamente no quedan minerales relictos. La asociación mineral consiste en clorita + cuarzo + sericita ± carbonato ± sulfuros. Se caracteriza por un intenso lavado de álcalis y un aumento en el contenido en Fe y Mg. Esta zona, generalmente denominada clorítica, está rodeada por otra zona de intensa alteración caracterizada por sericitización, sulfidización y silicificación, en la que la asociación mineral más común está compuesta por sericita + clorita ± cuarzo ± sulfuro. En esta zona el incremento en Fe y pérdida en Mg es menos significativo que en la zona interior. Por otra parte, existe una alteración periférica caracterizada por presentar sericitización y albitización con evidencias menores de silicificación. Geoquímicamente, esta zona se caracteriza por presentar un enriquecimiento en Na y K en relación a otras zonas. Todas estas facies de alteración se sobreimponen a la Alteración hidrotermal regional. La distribución de la alteración es aproximadamente concéntrica y tiene un desarrollo irregular. Las evidencias isotópicas obtenidas a partir de datos de isótopos de carbono, oxígeno y deuterio, junto con el estudio de inclusiones fluidas, indican que la circulación hidrotermal relacionada con la formación de los VMS estuvo dominada por agua marina en la que progresivamente la temperatura aumentó desde los 200 hasta los 350 °C. En algunos casos, los fluidos podrían haber llegado a su punto de ebullición. Los datos disponibles son consistentes con la presencia de un sistema hidrotermal convectivo propiciado por un ascenso mantélico asociado a un estrechamiento cortical. Éste habría fundido progresivamente niveles corticales más superficiales en un ambiente geodinámico extensional/transpresivo. La actividad hidrotermal queda marcada por un progresivo aumento de temperatura que favoreció los procesos de lavado y facilitó los procesos de alteración hidrotermal, sostenida a lo largo de un período de tiempo prolongado. El lixiviado fue particularmente intenso en las zonas internas del sistema, donde fueron movilizados incluso los elementos “inmóviles”. En esta zona clorítica, se ha descrito la precipitación de circón hidrotermal significativamente enriquecido en TRR. El régimen hidrotermal evolucionó desde un sistema hidrodinámico difuso a uno focalizado de alta temperatura durante la etapa de alteración hidrotermal más intensa. Esta evolución provocó un cambio progresivo en la mineralogía y geoquímica de los VMS, evolucionando desde una mineralización polimetálica a cuprífera.The Masa Valverde and Aznalcóllar-Los Frailes massive sulphide deposits are located in the SE sector of the Iberian Pyrite Belt (IPB). The deposits are hosted by a Carboniferous, Volcano-Sedimentary succession named Volcano-Sedimentary Complex (VSC). More specifically, both deposits occur at the top of the first felsic volcanic sequence, generally referred to as V1. Both deposits have a roughly lenticular morphology and overlie complex sequences of hydrothermally altered rocks. The host rocks are black shales, directly overlying volcaniclastic and coherent rocks of dacitic-rhyolitic composition. The mineralization consists mainly of pyrite and accessory amounts of chalcopyrite, sphalerite, galena, arsenopyrite and pyrrhotite. The aim of this study is to characterize the mineralogy, petrology and geochemistry of the footwall of the mineralization, integrating all the available data in order to distinguish alteration zones and their physicochemical characteristics. We finally suggest a plausible geological scenario for the genesis of the mineralization, prior to the Variscan deformation. Three alteration zones have been identified on the basis of their mineralogical, textural and geochemical characteristics. The innermost zone is characterized by a penetrative alteration that has destroyed most of the original volcanic textures. In this zone there are virtually no relict minerals. The mineral assemblage consists of chlorite + quartz + sericite ± carbonate ± sulphide. It is characterized by an extensive leaching of alkalis and an increase in the content of Fe and Mg. This zone, generally described as chloritic, is surrounded by another intense alteration area characterized by intense sericitization, sulphidation and silicification, in which sericite + chlorite ± quartz ± sulphide constitute the commonest assemblage. Here, both increase in Fe and loss of Mg are less significant than in the inner zone. The outer, peripheral alteration zone is characterized by sericitization and albitization with minor silicification. Geochemically, this zone is characterized by an enrichment in Na and K relative to the other zones. All these alteration facies are superimposed to regional hydrothermal alteration. The distribution thereof is approximately concentric and have an irregular development. Isotopic evidence obtained from carbon, oxygen and deuterium isotopic data, coupled with fluid inclusion study, indicate that the hydrothermal circulation related to the VMS formation was dominated by seawater in which temperature progressively increased from 200 to 350 °C. In cases, fluids could have been reached the boiling point. The available data are consistent with a model of convective hydrothermal circulation triggered by a mantle rise associated with cortical thinning. This would have led to melting of progressively more shallow crustal levels in an extensional/ transpressive geodynamic environment. Hydrothermal activity was marked by a progressive increase in temperature which stimulated leaching processes and triggered hydrothermal alteration, sustained along a protracted time span. Leaching was particularly intense in the inner zone, where even “immobile” elements were mobilized. In these chloritic zones, precipitation of hydrothermal zircon, significantly enriched in REE, has been described in detail. The hydrothermal regime evolved from a predominantly diffuse to focused, high-T hydrodynamic regime during the most intense hydrothermal stage. This evolution caused a progressive change in the VMS mineralogy and chemistry, evolving from polymetallic to cupriferous

Concentration of heavy minerals by panning and its interpretation

La prospección aluvionar, también conocida como prospección con batea, se centra en buscar minerales pesados en acumulaciones de tipo placer. Los placeres son depósitos de minerales en grano de alta resistencia resultantes de la denudación de un macizo rocoso y que han sido concentrados por agentes mecánicos exógenos como, por ejemplo, el agua en cursos fluviales o playas. La búsqueda de algunos de estos minerales, principalmente oro y gemas, siempre ha despertado el interés del hombre. Esto puede usarse como un reclamo para introducir conceptos geológicos y mineralógicos en alumnos de Educación Secundaria y Universidad. En este trabajo, se propone un taller didáctico que enseñe a usar la batea como técnica de prospección aluvionar, a la vez que permita a los estudiantes disfrutar de una actividad respetuosa con el medioambiente y que actualmente es un deporte.Aluvionar prospecting, also known as prospecting with a pan, focuses on finding heavy minerals in placer accumulations. Placers are deposits of mineral grains with high resistance resulting from the weathering of a rock massif, which have been concentrated by exogenous mechanical factors such as, for example, water in fluvial courses or beaches. The search for some of these minerals, mainly gold and gems, has always aroused man’s interest. This can be used as a decoy to introduce geological and mineralogical concepts to students of Secondary Education and University. In this paper, we propose a didactic workshop that teaches how to use the pan as a technique of aluvionar prospecting, which also allows the students to enjoy themselves with an environmentally friendly activity that is now a sport

Hydrothermal fluid evolution during the genesis of the Aznalcóllar massive sulphides (Iberian Pyrite Belt): fluid inclusion evidences

Fluid inclusion data from Aznalcdllar and Los Frailes stockworks indicate that hydrothermal fluids changed continuously in temperature and salinity, both in time and space. Th values change from 140 to 380 °C and salinity from 0.4 to 12.4 NaCI eq. The highest values for both parameters ha ve being found for central stockworks and later fluids. Statistic population analysis of fluid inclusion data points to three stages of hydrothermal activity, at low (<200 °C), intermediate (200-300 °C) and high temperatures (300-400 °C). Salinity values show similar variation trend with higher values for the last hydrothermal stag

Geochemical and Volcanological Criteria in Assessing the Links between Volcanism and VMS Deposits: A Case on the Iberian Pyrite Belt, Spain

VMS deposits in the Iberian Pyrite Belt (IPB), Spain and Portugal, constitute the largest accumulation of these deposits on Earth. Although several factors account for their genetic interpretation, a link between volcanism and mineralization is generally accepted. In many VMS districts, research is focused on the geochemical discrimination between barren and fertile volcanic rocks, these latter being a proxy of VMS mineralization. Additionally, the volcanological study of igneous successions sheds light on the environment at which volcanic rocks were emplaced, showing an emplacement depth consistent with that required for VMS formation. We describe a case on the El Almendro–Villanueva de los Castillejos (EAVC) succession, Spanish IPB, where abundant felsic volcanic rocks occur. According to the available evidence, their geochemical features, εNd signature and U–Pb dates suggest a possible link to VMS deposits. However, (paleo)volcanological evidence here indicates pyroclastic emplacement in a shallow water environment. We infer that such a shallow environment precluded VMS generation, a conclusion that is consistent with the absence of massive deposits all along this area. We also show that this interpretation lends additional support to previous models of the whole IPB, suggesting that compartmentalization of the belt had a major role in determining the sites of VMS deposition