Coal quality, coal rank variation and its relation to reconstructed overburden, Upper Cretaceous and Tertiary plains coals, Alberta, Canada

Near-surface coals in the Alberta plains occur in Upper Cretaceous and Tertiary sediments, the former represented by the Belly River Group, Horseshoe Canyon Formation, and Wapiti Formation, and the latter by the Scollard Member of the Paskapoo Formation. Statistical techniques were used to document both the distribution of and the interrelationships among the components of proximate and ultimate analysis and calorific value determinations. The coals discussed range in rank from subbituminous C to high-volatile bituminous C. These coals are variable in ash content and low in sulfur content. The relationships among calorific value (dry basis, in kJ/kg) and ash (dry basis, in %) and calorific value (moist mineral-matter-free basis, in kJ/kg) and equilibrium moisture (MEQ, in %) were determined to be CVD = 29,677 - 315.17 ashD, and CVMMMF = 31,816 - 442.05 MEQ, respectively. The maximum depth of coal seam burial (DOB, in m) was reconstructed on the basis of previously published graphs, relating the equilibrium moisture loss to depth of coal seam burial, using the relationship: log10MEQ = 1.865 - 0.000416 DOB. A least-squares regression analysis of calorific value (MMMF basis, in kJ/kg) on the calculated depth of burial (DOB, in m) yielded the equation, CVMMMF = 14,748 + 6.25 DOB, indicating a coalification gradient, determined on the reconstructed overburden, of 6.25 kJ/kg/m (0.82 Btu/lb/ft) of depth (or overburden). Near-surface coals in the Alberta plains increase in rank toward the west-southwest (toward the foothills and mountains region) because of progressively greater amounts of overburden that existed in that direction during the Tertiary. Erosion has since removed between 900 and 1,900 m (3,000 and 6,200 ft) of sediment, with the greatest amount of removal occurring in a west-southwest direction.