Effects of Magmatic Fluids in Coals of São Pedro da Cova Coalfield, Douro Carboniferous Basin, Portugal: Insights from Inorganic Geochemistry

Abstract

The Douro Carboniferous Basin (DCB), aged from Gzhelian, is an important coal-bearing basin occurring in Northern Portugal. While the coals and the sedimentary sequence of the DCB have been deeply studied, the inorganic geochemical data are scarce. This study intends to provide major and trace element contents and discuss their modes of occurrence and origins using a set of twenty-four coal samples from the São Pedro da Cova Coalfield taken from different sectors/outcrops. Thus, an integrated approach using petrographic, geochemical, both organic and inorganic, and mineralogical data was used to achieve these purposes. The main results demonstrated that these coals are anthracite A and vitrinite is the main organic component. Most of the elements have inorganic affinities and are associated with aluminosilicates, while the other elements have affinities with sulfides. Illite and muscovite are the main phyllosilicates occurring in these coals and pyrite is the most common sulfide. However, cinnabar, together with phosphates (fluorapatite, monazite, xenotime and gorceixite), were also identified. The enrichment of most elements as well as a heterogenous rare earth elements (REE) distribution pattern in the tectono-sedimentary unit (TSU) samples are related to magmatic fluids. On the other hand, on the Eastern Outcrop (EO), a tectonic slice, the subparallel trend of the REE distribution patterns, and a depletion of all the elements are related to the sedimentary contribution. The occurrence of cinnabar and gorceixite epigenetic mineralizations is interpreted as the action of a porphyry intrusion identified in this area of the DCB, between the TSU B1 and TSU D1.

Phytotoxicity of coal waste elutriates (Douro Coalfield, North Portugal) in Lactuca sativa

“…This study was carried out in the Fojo coal mine waste pile, located in the Pejão Coalfield (Douro Carboniferous Basin, North Portugal). As a result of coal mining between 1920 and 1994, several waste piles were geographically dispersed (Caetano 1998 ; Costa et al 2022 ). In October 2017, a wildfire caused the ignition and self-burning of coal waste, and between 2017 and 2019, an effort to extinct the fire was done by remobilizing the coal-waste material, using water mixed with a cooling accelerator agent.…”