The effect of shearing on the quality of some coals in the southeastern Canadian Cordillera

CIM Bulletin, Vol. 75, No. 841, 1982

P.M. BUSTIN, Department of Geological Sciences and Coal Research Centre, The University of British Columbia, Vancouver, B.C.

Extensive deposits of tectonically sheared coal of the Mist Mountain Formation occur in the southeastern Canadian Cordillera. The quality of the coal varies markedly; it is commonly partially oxidized even far from the present weathering horizon and locally has a disproportionately large amount of ash and poor washability characteristics.Oxidation of the sheared coal has been promoted by its fine grain-size and by fractures in adjacent rocks which have facilitated penetration of atmospheric oxygen and circulation of oxygenated waters. Oxidation has resulted in a loss of coking power, a decrease in vitrinite reflectance, and an increase in oxygen and decrease in carbon content.The relatively low clean coal yields of the sheared coal are primarily the result of the greater volume of mineral matter present, which in turn reflects both the greater susceptibility to shearing of coal with abundant rock partings and the shearing and dissemination throughout the coal of formerly discrete rock partings. The high ash content of some sheared coal seams may be artificial, resulting from the difficulty in distinguishing and separating sheared roof rock and floor strata from the coal seam during mining. There is little variation between the quality of the washed sheared and unsheared coal, with the exception of the somewhat higher ash content of the clean sheared coal compared to clean unsheared coal. This poorer separation of the ash from the organic fraction of the sheared coal is considered to be a product of the large amount of fines present as well as the local formation of aggregates of organic material and ash resulting from plastic flowage of the vitrite and clarite during shearing.
Keywords: Coal structure, Shearing, Cordillera, Mist Mountain Formation, Comminution, Eagle Mountain, Tent Mountain, Washability, Coal petrography, Vitrinite reflectance.