THE SEPARATION OF GEOCHEMICAL ANOMALIES FROM BACKGROUND BY FRACTAL METHODS

Lithogeochemical data (major oxides and trace elements) from 1233 surface samples in the Mitchell-Sulphurets precious-metal district (almost-equal-to 120 km2 in area), British Columbia, were analyzed using fractal and multifractal models. Log-log plots for element concentration-area and perimeter-area relations were employed to separate geochemically anomalous areas from background. The values used for perimeters and areas are the lengths and enclosed areas of geochemical isopleths obtained by interpolation. Elements and oxides, including Au, Cu, As, Ag, K2O and SiO2 within alteration zones associated with copper and gold porphyry system(s) in the district, show power-law type element concentration-area and perimeter-area relations, which can be fitted as straight lines on the log-log graphs. Separate relations inside and outside the potassic, sulphidic and silicic alteration areas can be used to delineate the anomalies. The slopes on the graphs show that Au is much more irregularly distributed than Cu and As in the porphyry systems.