Quantitative spectrometric borehole logging techniques for coal mining

Three spectrometric borehole logging techniques, γ-γ, prompt neutron-γ and natural-γ, were investigated for practical application to coal mining. The performance for quantitative coal ash measurement of the γ-γ technique was tested in both dry and waterfilled boreholes at four coal deposits in eastern Australia while that of the neutron-γ technique was tested only in water-filled boreholes at six coal deposits. The diameter of the boreholes varied between 96 (nominal) and 175 mm. The r.m.s. deviations for ash determinations in coal strata ranging from 45 to 260 cm thick ranged from 1.5 to 2.8% ash for both techniques. The corresponding errors in measured ash content include the errors due to sampling and chemical analysis. The spectrometric natural-γ technique showed that intersedimentary strata could be identified from the ratios of the K, Th and their daughter peaks. (author)