Geochemical evidences of sedimentary-exhalative origin of the shale-hosted PGE-Ag-Au-Zn-Cu occurrences of the Prades Mountains (Catalonia, Spain): Trace-element abundances and Sm-Nd isotopes
Por:
Canet C., Alfonso P., Melgarejo J.C., Belyatsky B.V.
Publicada:
1 ene 2004
Resumen:
The Llandoverian black shales of the Prades Mountains, SW Catalonian Coastal Ranges, contain several metamorphosed stratiform sulfide deposits. The mineralized interval, up to 30 m in thickness, consists of interbedded sulfide-rich (mostly pyrrhotite) shales, feldspar-rich layers and apatite beds. The ore contains Zn, Cu, Pb, Au, Ag and PGE. Whole-rock trace-element analyses were performed by ICP-MS, and the results were normalized to NASC reference standard. The REE patterns show enrichment in Eu (La) and a strong depletion in Ce. This distribution is compatible with REE mostly inherited from seawater, but a significant hydrothermal component is inferred for Eu. Profiles of redox-sensitive trace elements show great V, Cr, Ni, Co, Mo and U enrichments with respect to NASC standard. Part of this enrichment could derive from a direct precipitation from seawater, favoured by the euxinic conditions of the Silurian basin. Nevertheless, V (up to 5444 ppm) and Cr (up to 640 ppm) contents would require additional sources. These elements could be scavenged from seawater by exhalative particles in a hydrothermal derived plume that finally accumulated on the seafloor. In contrast, high Ni, Co and Mo values could be of hydrothermal origin. Sm-Nd isotopic analyses of feldspar-rich layers yielded an isochron age of 437 ± 57 Ma (Llandoverian). These results, as well as the fine-grained textures, the lack of evidences of replacement and the pre-deformational and pre-metamorphic character support the syngenetic origin of the mineralization. Trace-element geochemistry and Sm-Nd isotopes are consistent with a submarine-exhalative origin of the mineralization processes, and suggest that the feldspar-rich levels are metaexhalites. © 2004 Elsevier B.V. All rights reserved.
Filiaciones:
Canet C.:
Departamento de Recursos Naturales, Instituto de Geofísica, Univ. Nac. Autonoma de México, Del. Coyacan, México DF 04510, Mexico
Alfonso P.:
Dept. de Cristallografia, Mineralogia i Diposits Minerals, Universitat de Barcelona, c. Marti i Franquès s/n, Barcelona 08028, Spain
Melgarejo J.C.:
Dept. de Cristallografia, Mineralogia i Diposits Minerals, Universitat de Barcelona, c. Marti i Franquès s/n, Barcelona 08028, Spain
Belyatsky B.V.:
Inst.ofPrecambrianGeol./Geochronol., RAS, nab. Makarova 2, St. Petersburg 199034, Russian Federation
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