Geochemical Studies of Rare Earth and Redox Sensitive Elements in Meta-exhalites Associated With Sedex Deposits of the Southern Catalonian Coastal Ranges, NE Iberian Peninsula

The Paleozoic series from the Southern part of the Catalonian Coastal Ranges contains several SEDEX deposits. The most important are hosted in Lower Silurian black shales and in Lower Carboniferous gray shales and sandstones. In the Silurian deposits the mineralized interval attains 30 m in thickness and consists of interbedded sulphide-rich shales (mostly pyrrhotite), feldspar rich layers and apatite beds. The ore mineralization is rich in Zn, Cu, Pb, Au, Ag and PGE (up to 0.6 ppm of Pd). The Carboniferous orebodies (up to 5 m in thickness) consist of massive sulphides (pyrrhotite, sphalerite and galena) interbedded within feldspar rich layers and chlorite beds. The ore mineralization is rich in Cu, Ag and Bi bearing minerals. The feldspar rich layers consist of fine-grained metasediments of cherty aspect, made up essentially of Ca-feldspar, quartz and chlorite. Feldspar layers and chloritites, are in all cases related with sulphide mineralization, and have been interpreted as meta-exhalites. Trace-element geochemical studies of these meta-exhalites are reported here. The REE content of Silurian and Carboniferous deposits has been normalized to NASC values. In the Silurian deposits, the REE patterns show a strong depletion in Ce and a low enrichment in La-Eu. Ce depletion reveals a major marine origin of REE, although there is a possible hydrothermal source for Eu-La. The defining characteristic of the REE profiles in the carboniferous deposits is a pronounced Eu enrichment. This fact suggests a hydrothermal origin for REE. Similarly, the content of some redox sensitive elements (V, Cr, Mn, Co, Ni, As, Mo, Th and U) and other related elements has also been normalized. In the Silurian deposits RSE profiles show great enrichments in V, Cr, Co, Ni, Mo and U. Part of the enrichment of these elements could arise from a direct precipitation from seawater, favored by the euxinic conditions of the Silurian basin. However, to explain the high V (up to 5444 ppm) and Cr (up to 640 ppm) it is necessary to consider additional sources. V and Cr could be scavenged from seawater by exhalative particles in a plume that accumulated on the seafloor. This hyppothesis is supported by the absence of feeder zones, suggesting distal deposition of the mineralization. RSE patterns in Carboniferous deposits show enrichment in Co, Mo, Th and U, and a depletion in V and Mn. Co and Mo enrichments could be explained by a hydrothermal supply. The higher solubility of V in non-euxinic environments (like the Carboniferous basin) could explain the absence of this element. Elsewhere, Mn is found in synsedimentary deposits of the Carboniferous basin, formed far away from sulphide deposits.