Petrology and Geochemistry of Subbituminous Coals from the Red Deer River Valley, Alberta Plains, Canada

Abstract

Coals and associated carbonaceous strata along the Red Deer River Valley in Alberta have a wide variation in boron concentrations (10–628 ppm). Boron concentrations decrease from bottom to top of the coal-bearing succession, closely reflecting changes in depositional environment conditions. These changes range from subaquatic deposition in the delta plain area and influence of brackish waters due to a marine transgression, to deposition in areas removed from any brackish water influence. There is good agreement between boron variation and depositional environment as interpreted from regional geology. However, the relation between boron and sulfur is not clear; samples with high boron concentrations are high in sulfur while low boron samples also have high sulfur. Compared to mean concentrations in world coals, some of the highest elemental concentrations measured in coals of this study are: As (38.0 ppm), Ba (2800 ppm), Cr (91.0 ppm), Mn (232 ppm), and V (209 ppm). There is a similarity in the vertical variation of the elements Th and Hf while bentonite layers are enriched in Ba and Sr, pointing to the presence of gorceixite. No enrichment of REEs was observed in the bentonite layers. A comparison of elemental concentration to world mean values for coab shows that the RDRV coals are elevated in As (up to 4×x), Cr (up to 12×), Mn (up to 4×), Mo (up to 12×), Th (up to 5×), V (up to 12×), and Zn (up to 5×). Compared to coals from the eastern Alberta Plains of similar rank, age, and depositional environment, the RDRV coals have higher or similar concentrations of all elements of environmental significance, with the exception of Be and Pb. When compared to coals of similar rank in the western Alberta plains deposited under freshwater conditions, the RDRV coals have higher concentration of As, B, Ba, Sb, and Sr, similar concentrations of Be, Co, Cu, Mn, Pb, Se, Th, and U, and lower concentrations of Ni.