The deposition of volcanics and pyritite in the Iberian Pyrite Belt

Abstract

Stratiform pyritic deposits occur interbedded with sedimentary and volcanic rocks and may be considered to consist of sulphidic rock, called "pyritite". In the Iberian Pyrite Belt such deposits are found at different levels and settings in the Volcanic-Siliceous Complex of Lower Carboniferous age, which comprises sediments and felsic to mafic volcanics. The felsic volcanics range from dust tufts to lapilli tufts of quartz-keratophyric to rhyolitic composition, and are interpreted as submarine ashflow tufts laid down by sliding and flowing down volcanoes at the eruptive centres in the Hercynian geosyncline. The pyritite bodies are likewise regarded as redeposited: they originated on the volcano flanks from emanations towards the end of the felsic vulcanicity, to slump and move down into deeper water among tufts or muds.Les gisements pyriteux stratiformes se trouvent intercal& dans des roches s6dimentaires et volcaniques, ce qui m~ne ~ les consid6rer comme constitu6s d'une roche appel6e >>pyritite<c Dans la Ceinture Pyriteuse Ib6rique, ces d6p6ts se pr6sentent dans des niveaux et des milieux vari6s, dans le Complexe VulcanoSiliceux, d'fige Carbonif&re inf6rieur, qui comporte des s6diments et des roches volcaniques acides et basiques. Les volcanites acides sont des tufs variant de tr~s fins A grossiers, de composition quartz-k6ratophyrique ~ rhyolitique. Nous admettons un mode de d@6t par des coul6es sous-marines de cendres, ~t la suite d'6boulements sur les volcans aux centres ~ruptifs dans le g6osynclinal hercynien. Nous estimons 6galement que les masses de pyritite se sont d6pos6es en deux 6tapes : engendr6es par des exhalations sur les flancs des volcans, vers la fin du volcanisme acide, elles glissaient et coulaient dans des eaux plus profondes, parmi des tufs ou des boues.

Metallogenesis in the Iberian Pyrite Belt

“…Most felsic rocks in the area were originally rhyolitic, often high-silica rhyolites (Munha 1981;Barriga 1983). Their present composition is mostly quartzkeratophyric to quartz-kalikeratophyric (Schermerhorn 1970(Schermerhorn , 1973Salpeteur 1976;Barriga 1983). These cumbersome terms obscure the fact that they are simply hydrothermally altered rhyolites (felsic spilites according to .…”

Geology of massive sulphide deposits in the Spanish-Portuguese Pyrite Belt

“…Since the geology of Lousal, with special reference to its pyrite deposits, was described by STI~AVSS (1965, 1970, an intensive geological, geophysical and diamond drilling exploration program confirmed the earlier results but yielded slight modifications concerning the stratigraphy and tectonics.…”

Silicate facies iron-formation and strata-bound alteration; tuffaceous exhalites derived by mixing; evidence from Mn garnet-stilpnomelane rocks at Redstone, Timmins, Ontario

“…Sato (1972) proposed that the metals may be transported as a high-density saline brine which flowed downslope from the discharge vent area and precipitated in sea-floor depressions. Schermerhorn (1970) recognized sedimentary structures, such as graded and crossbedding, in some of the pyrite ores of the Iberian pyrite belt and described these ores as exhalative resedimented types. Although a mechanism of elastic sedimentation does overcome some of the problems of transporting the sulfide ores away from the vent area into distal settings, it does not account for metal zoning within these ores.…”