Estudo geoquímico dos coques naturais da Bacia de Peñarroya-Belmez-Espiel (Espanha)

Abstract

The natural cokes that occur in the eastern sector of the depocentre I of the Peñarroya-Belmez-Espiel Basin (Spain) resulted from the contact metamorphism induced in coals by the emplacement of a doleritic sill parallel to the stratification. In this study, geochemical data of three coke samples are presented and complemented with petrographic data. Organic particles exhibit circular and elliptical devolatilization pores, isotropic and, occasionally incipient anisotropic to fine mosaic texture pointing out that, at the time of carbonization, these coals should have reached a rank equivalent to a vitrinte random reflectance between 0.70% and 0.85%. The maximum reflectance for the coke particles close to the dolerite sill contact suggested a paleotemperature for the intrusion > 390 ºC. The alignment and folding of the devolatilization pores indicate that the emplacement of the doleritic sill was simultaneous to the folding of the sedimentary sequence. The ash yield is variable, the C content high and total sulfur content low. The composition in major and trace elements revealed that two of the samples are very enriched. The enrichment in Hg can be related to magmatic fluids and also to a secondary enrichment after volatilization of the original coal. The occurrence of the REE seems to be linked to the sedimentary mineralogical composition.