Determining the cutoff between background and relative base metal smelter contamination levels using multifractal methods

For a specified, spatially distributed geoscience variable measure, log-log plots of contour interval versus cumulative contour area for all contours exceeding a specified contour value can provide insight into the nature of the multifractal spectrum; e.g. if there are sharp bends or breaks. These can be estimated graphically by plotting lines of best fit and finding their solution on a log-log graph of contour interval versus cumulative area per contour interval. The breakpoint between background and anomalous values is defined when the spectrum is relatively close to its minimum value. A new computer program using MAP INFO 4.1, VERTICAL MAPPER 1.5 and EXCEL 5.0 has been developed for the preceding method. As an example of application, variation in estimated background metal concentration cutoffs is illustrated using humus geochemistry in the vicinity of a base metal smelter near Flin Flon, Manitoba. Cutoffs between background and anomalous metal concentrations of copper, zinc and mercury are estimated using the multifractal area-concentration model. These metals return to background geochemical levels within approximately 142, 104 and 105 km from the source respectively. (C), 1999 Elsevier Science Ltd. All rights reserved.