Statistical Evaluation of the Significance of Categorical Field Parameters in the Interpretation of Regional Geochemical Sediment Data

Abstract

Matysek, P.F., Fletcher, W.K. and Sinclair, A.J., 1983. Statistical evaluation of the significance of categorical field parameters in the interpretation of regional geochemical sediment data. In: G.R. Parslow (Editor), Geochemical Exploration 1982. J. Geochem. Explor., 19: 383–401. In an attempt to study the value and utilization of categorical data collected during regional stream-sediment surveys, we have taken data from the Canadian Uranium Reconnaissance Program in S.E. British Columbia. After initial classification of the data into six subsets on the basis of catchment geology, probability plots were constructed for each of 11 elements (Zn, Cu, Pb, Ni, Co, Fe, Mn, Mo, W, Hg and U) and used to select thresholds to reject anomalous samples. The remaining background populations then were successively subdivided into groups according to their classification with respect to four sediment characteristics (abundance of fines, sand, organic matter and sediment colour) and six environmental parameters (physiography, water flow rate, stream class, drainage pattern, bank type and contamination). After calculation of log means for each group and a pooled common standard error, differences between group means were tested for significance using Duncan's Multiple Range Test. The relative degree of confidence in the significance of difference between categorical means for any single field parameter were determined using a ratio method. Results of Duncan's Multiple Range Test, show that, many field observations can be related systematically to metal content of drainage sediments. Some elements are more susceptible than others to environmental factors and some factors influence few or many elements. For example, in sediments derived from granites there are significant relationships between bank type and concentration of 8 elements (Zn, Cu, Ni, Pb, Co, Fe, Mn and Hg). In contrast, the texture of these sediments, using estimates of fines content as an index, did not significantly affect the concentration of any of the elements studied. In general, results indicate that groups of environmental factors acting collectively are more important than any single factor in determining background metal content of drainage sediments.