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

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Rosa, CJP (2007) Facies Architecture of the Volcanic Sedimentary Complex of the Iberian Pyrite Belt, Portugal and Spain. PhD thesis, University of Tasmania.

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Abstract

The Iberian Pyrite Belt is the richest massive sulfide province in the world. The massive sulfide
ore deposits occur in a felsic volcanic and sedimentary succession (VS Complex) of late
Famennian (Upper Devonian) to late Visean (Middle Carboniferous) age. Volcanic facies
analysis has been carried out on three areas in Portugal, including the Neves Corvo mine, and
five sections in Spain. In all sections studied, the depositional setting during accumulation of the
VS Complex was submarine and below wave base.
The principal felsic volcanic facies are: (1) coherent rhyolite and dacite, associated with
monomictic breccia; (2) fiamme-rich breccia (with variable amounts of dense volcanic and
sedimentary clasts), fiamme-rich sandstone and fiamme-bearing mudstone; and (3) crystal-rich
sandstone and mudstone. Mafic units are minor, dominated by coherent facies and have
uncertain mode of emplacement (intrusions or lavas). Fiamme typically have lenticular shape
and quartz- or quartz- and feldspar-phyric texture, and are interpreted to be altered and
compacted pumice clasts. The volcanic facies are typically interleaved with, and regionally less
voluminous than, the non-volcanic facies, which are dominated by mudstone.
The felsic volcanic facies are interpreted to be the products of numerous, relatively small
intrabasinal volcanic centres that generated abundant lavas, domes and pyroclastic units. Some
volcanic centres are dominated by lavas, whereas others have similar proportions of lavas and
pyroclastic units. The domes and lavas are more voluminous but less laterally extensive than the
pyroclastic units. A sediment-matrix breccia typically occurs at the top contact of the felsic
lavas with sedimentary units. This sediment-matrix breccia formed from the infiltration of fine
sediment into interclast spaces in previously formed hyaloclastite, and could be misinterpreted
as peperite. Felsic intrusions are less voluminous than lavas, and were emplaced as cryptodomes
and partly extrusive cryptodomes, late in the evolution of the VS Complex. The architecture of
the different study areas reflects differences in the eruption style, emplacement processes and
proximity to source. Parts of the succession interpreted to be proximal are dominated by thick
lavas/domes and intrusions, and coarse pyroclastic deposits. Medial parts comprise
resedimented autoclastic facies derived from the lavas and domes, and relatively thin pyroclastic
units. Distal parts comprise relatively thinly bedded crystal-rich sandstone and siliceous
mudstone. Regional correlations in the VS Complex are impossible, as none of the volcanic
facies are regionally extensive and each of the volcanic centres has a unique internal
architecture.
At Neves Corvo mine, the massive sulfide ore deposits are close to one of the felsic volcanic
centre(s), occurring immediately above the rhyolitic lavas/domes.
IV

Item Type: Thesis (PhD)
Date Deposited: 22 Oct 2007 01:37
Last Modified: 11 Mar 2016 05:53
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