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In situ thermochemical sulfate reduction during ore formation at the Itxaspe Zn-(Pb) MVT occurrence (Basque-Cantabrian basin, Northern Spain)
Piqué, À. (Universitat de Barcelona. Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals)
Canals, À. (Universitat de Barcelona. Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals)
Disnar, J.R. (Université d’Orléans. Institut des Sciences de la Terre d’Orléans)
Grandia, F. (Amphos 21)

Data: 2009
Resum: Organic matter is thought to play a role in the genesis of many Mississippi Valley-type (MVT) deposits, acting as a reducing agent during thermochemical sulfate reduction (TSR). Although TSR is an extremely slow reaction t low temperatures (<100ºC), under favorable conditions it may supply the necessary reduced sulfur during ore formation. To test this hypothesis, the Itxaspe Zn-(Pb) MVT occurrence in the Basque-Cantabrian basin (Northern Spain) was studied. Sphalerite, the main ore phase, is generally found disseminated in Urgonian (Lower Cretaceous) carbonates, and in close relationship with solid bitumen. The bitumen source rock was very likely deposited in a marine marginal setting. Differences in composition of the bitumen samples are attributed to a fractionation during hydrocarbon expulsion and/or migration. The fluids involved in ore deposition were low temperature (Th ~130ºC), Na-Ca-Cl-(K-Mg)-type brines (salinities ~12. 5 equiv. mass % NaCl). The origin of brine solutes (including sulfate) is related to the dissolution of Mesozoic evaporite units, although the contribution of evaporated seawater brines cannot be ruled out. The temperatures of ore deposition, the close relationship between the bitumen and ore phases, the presence of aromatic sulfur-bearing compounds and the d34S of sulfides and sulfates are consistent with an in situ TSR during ore formation in the Itxaspe Zn-(Pb) occurrence. Therefore, at least for small mineralizations like Itxaspe, our conclusion is that the necessary reduced sulfur can be supplied by TSR during ore genesis at the site of metal deposition.
Drets: Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l’obra i la creació d’obres derivades, fins i tot amb finalitats comercials, sempre i quan aquestes es distribueixin sota la mateixa llicència que regula l’obra original i es reconegui l’autoria de l’obra original. Creative Commons
Llengua: Anglès.
Document: article ; recerca ; publishedVersion
Matèria: Bitumen ; Thermochemical sulfate reduction ; Mississippi Valley-type deposits ; Basque-Cantabrian basin
Publicat a: Geologica acta, Vol. 7, Núm. 4 (Desembre 2009) , p. 431-449, ISSN 1696-5728

Adreça alternativa:
DOI: 10.1344/105.000001448

19 p, 3.6 MB

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