Interpretation of geochemical soil surveys by block averaging

In many cases the spatial distribution patterns of elements in soils - especially where geochemical response is weak - is erratic and incoherent and poorly defines underlying mineralized zones; frequency distributions of elements are characteristically positively skewed. Geochemical soil survey data for Cu, Pb, and Zn from around the Key Anacon massive sulphide deposit in New Brunswick, Canada, are used to illustrate an interpretative technique useful in these situations. Calculation of mean element values of all samples within non-overlapping blocks eliminates random background noise and enhances significant spatial trends. Frequency curves of the block means tend to normality if the spatial distribution is random; the frequency curves emphasize the skewness or become polymodal if the spatial distribution is systematic. The only critical step in this simple interpretative procedure is the determination of the appropriate block size for the particular sample density relative to the areal size of the geochemical response to the target.