Table 3.

Range of potential iron sulphide content in the Luarca slate depending on the voxel threshold value

SampleAnalysed CT volume (mm3)Voxel resolution (µm)CT thresholdDetermined content of iron sulphides in samples (%)
Average valueStandard deviationCoefficient of variability (%)
11692.16.115463.90.34–0.44
13673.96.29322.40.26–0.36
14718.56.113753.50.30–0.38
224043.113.011043.70.30–0.46
243905.113.010522.30.28–0.36
264188.213.011054.60.23–0.39

A lower limit of iron sulphide content listed in the last column always corresponds to the threshold value at the level of its arithmetic mean plus standard deviation. An upper limit of this content corresponds to the threshold value equivalent to mean threshold minus standard deviation.