The mining and milling operations at Raglan, northern Quebec, treat an ultramafic, pervasively serpentinised nickel ore, and produce a final nickel concentrate by grinding and sulphide flotation. A final tailings stream is discarded. A study was made of the nickel chemical assays of the Raglan final tailings stream, using a data mining technique of operational measurements. A distribution model and probability plot using nickel chemical assays were produced from this study. It was found that the nickel assay values formed a residually lognormal bimodal distribution. By using a lognormal probability plot, this distribution may be semi-quantitatively decomposed into two subordinate distributions by using either visual interpretation or the TRIPOD software. It is proposed that these two subordinate distributions represent two different degrees of nickel mineral liberation. Independent QemSCAN mineral measurement of one of the two tailings studies shows agreement with these graphical interpretations. Repetition of this method after flowsheet changes that produced metallurgical performance improvements shows that this model responds to concentrator performance improvements, and may be used as a monitoring tool to interpret concentrator behaviour. The study opens up potential for further work. This has been identified and will be pursued. (c) 2007 Elsevier Ltd. All rights reserved.