Facies Architecture of the Volcanic Sedimentary Complex of the Iberian Pyrite Belt, Portugal and Spain

摘要

The Iberian Pyrite Belt is the richest massive sulfide province in the world. The massive sulfideudore deposits occur in a felsic volcanic and sedimentary succession (VS Complex) of lateudFamennian (Upper Devonian) to late Visean (Middle Carboniferous) age. Volcanic faciesudanalysis has been carried out on three areas in Portugal, including the Neves Corvo mine, andudfive sections in Spain. In all sections studied, the depositional setting during accumulation of theudVS Complex was submarine and below wave base.udThe principal felsic volcanic facies are: (1) coherent rhyolite and dacite, associated withudmonomictic breccia; (2) fiamme-rich breccia (with variable amounts of dense volcanic andudsedimentary clasts), fiamme-rich sandstone and fiamme-bearing mudstone; and (3) crystal-richudsandstone and mudstone. Mafic units are minor, dominated by coherent facies and haveuduncertain mode of emplacement (intrusions or lavas). Fiamme typically have lenticular shapeudand quartz- or quartz- and feldspar-phyric texture, and are interpreted to be altered andudcompacted pumice clasts. The volcanic facies are typically interleaved with, and regionally lessudvoluminous than, the non-volcanic facies, which are dominated by mudstone.udThe felsic volcanic facies are interpreted to be the products of numerous, relatively smalludintrabasinal volcanic centres that generated abundant lavas, domes and pyroclastic units. Someudvolcanic centres are dominated by lavas, whereas others have similar proportions of lavas andudpyroclastic units. The domes and lavas are more voluminous but less laterally extensive than theudpyroclastic units. A sediment-matrix breccia typically occurs at the top contact of the felsicudlavas with sedimentary units. This sediment-matrix breccia formed from the infiltration of fineudsediment into interclast spaces in previously formed hyaloclastite, and could be misinterpretedudas peperite. Felsic intrusions are less voluminous than lavas, and were emplaced as cryptodomesudand partly extrusive cryptodomes, late in the evolution of the VS Complex. The architecture ofudthe different study areas reflects differences in the eruption style, emplacement processes andudproximity to source. Parts of the succession interpreted to be proximal are dominated by thickudlavas/domes and intrusions, and coarse pyroclastic deposits. Medial parts compriseudresedimented autoclastic facies derived from the lavas and domes, and relatively thin pyroclasticudunits. Distal parts comprise relatively thinly bedded crystal-rich sandstone and siliceousudmudstone. Regional correlations in the VS Complex are impossible, as none of the volcanicudfacies are regionally extensive and each of the volcanic centres has a unique internaludarchitecture.udAt Neves Corvo mine, the massive sulfide ore deposits are close to one of the felsic volcanicudcentre(s), occurring immediately above the rhyolitic lavas/domes.udIV