Trace element geochemistry of coals from the Southern Cantabrian Zone (NW Spain): preliminary results

Abstract

Trace element geochemistry of coals from the Southern Cantabrian Zone (NW Spain): preliminary resultsBituminous to anthracite coals from three small Stephanian intramontane coal-bearing basins (La Magdalena, Cinera-Matallana and Sabero) located along the Sabero-Gordón fault line strike-slip systems of the Southern Cantabrian Zone (SCZ) were examined. Coal rank expressed as mean vitrinite reflectance values of these Stephanian coals is in the range 0.72-3.96%. The vitrinite maceral group exceeds 72 vol. % in all of the coals. The coals are characterized by relatively variable contents of mineral matter and coal-ash. The mineral matter comprises, in the main, clay minerals, carbonates, sulphides and quartz. The coals exhibit medium-high concentrations (see for comparison Ronov et al. 1990; Kabata-Pendias, Pendias 1999; Ketris, Yudovich 2009) of the following elements (in ppm): ΣREE (53-205), Ba (300-900), As (11-57), Zn (<50-150), Cr (10-160), Rb (50-145), Co (5-26), Sc (2-24.6), Ce (17-99), Yb (1.3-4.5), Th (2.4-11.9) and U (1.1-8.1), Br (<1-14), Cs (<2-9), Eu (<0,3-1.5), Lu (0.11-0.85) and Sb (0.8-4.8), and relatively low concentrations of Sm (0.6-6.6) and Ta (<1-2). They are also characterised by relatively high Th/U values (1.31-2.29). LREE/HREE values fall in the range 24-44 (average - 30). In contrast, concentrations of Au, Ag, Hg, Ir, Ni, Se, Sn, Sr, and W are below detection limits for the applied INAA method. As the concentrations of elements are significantly higher in coal-ash, most are likely related to mineral matter in the coals.