Density of Coals from the Telkwa Coal Property, Northwestern British Columbia

INTRODUCTION It is important, for mining feasibility studies, to be able to accurately convert in situ coal volumes to tonnages using coal densities. The density of coal of c”nstant rank varies depending on the am”unt of included rock (mineral matter), water, and void porosity. Actual measurements of density often require adjustment because data are needed at different ash, water or porosity values. Data from the Tclkwa Coal property are used t” validate a density equation. The equation predicts density given per cent ash or, per cent ash given the density. It requires the following constants to be defined: density of dry zero-ash coal (DC), density of dry mineral matter (DMM), weight per cent water (TM), v”Iume per cent void porosity (VP) and the ratio weight of mineral matter divided by weight “f rewltant ash (WTLOS). The equation (Equation I, Table S-6-l) has the form; BD = 100XDCXDMM/[DCXDMMX(TM+VP)+MMX (DC~DMM)+DMMXtIUO~TMI1: MM is the weight of mineral matter, and is given by; MM = WTLOS X per cent ash. The Telkwa coal property is located in northwstem British Columbia, IS kilometres south of Smith.%. In the area, Cretaceous sediments of the Skeena Group conl~ain a coalbearing succession which includes ten seams over approximately 300 metres of section (Figure 5-6-l). Exploration on the property by Crows Nest Resources Limited (geological assessment reports submittzd to B.C. Ministry of Energy, Mines and Petroleum Resources. 1981 to 1989) has culminated in a submission to the provincial government seeking approval to develop an open-pit coal mine on the property. The data discussed in this study were collected as part of the mining feasibility study for one of the proposed “pen pits which is located on the north side of the Telkwa River (Pit 7). One hundred and eighty seven samples of NQ diamond-drill core from Seams 2 to 8 (Figure 5-6-l). repre.senting approximately 50 metres of section, were analyzed on an air-dried basis (ADB) for apparent specific grwity (AX), per cent ash, per cent sulphur and per cent moisture. The apparent specific gravity was measured “n 60.mesh sized particles, using ASTM procedure Dl67. Previous discussions of coal density versus a,sh relationships have taken two general directions. Some fit mathematical curves to data sets of ash and density msasurements (Ward, 1984). This approach lucks ilexibility and requires a new set of sample analyses if rank or moisture content of coal change. Other papers take a more theoretical approach and develop equations which predict coal density using real variables such as per cent ash and per cent moisture (Smith, 1989). This paper takes the latter approach; Equation I was developed over a number “f yean; while worki”;; in industry and is similar to, though less r~.g”rous than that used by Smith.