Fractals - Geomathematics: Theoretical Foundations, Applications and Future Developments - page 373

Fig. 10.4 Mitchell-Sulphurets mineral district, northwestern British Columbia. Four plots origi-
nally constructed by Cheng ( 1994 ): (a) Simplified geology after R.V. Kirkham (personal commu-
nication, 1993), including outline of alteration zones; (b) Sampling sites and (smoothed) isopleth
for 200 ppb gold concentration value; (c) Lognormal Q - Q plot (Au determinations below 2 ppb
detection limit are shown as horizontal line); (d) Log-log plot for area enclosed by isopleths
(including circumference of pattern for 200 ppb in Fig. 10.4b). Straight lines are least-squares fits
(log base 10; gold in ppb) (Source: Agterberg 1995a , Fig. 3)
The Geographic Information System (GIS) used to obtain the contour maps of
Fig. 10.5 (“Spatial Analysis System” or SPANS; cf . Cheng 1994 ) allowed several
interpolation procedures, including 2-D Kriging and so-called “potential mapping”.
The latter method consisted of the calculation of simple weighted moving averages
with a moving circular window with adjustable parameters to control the weighting
of values at neighboring points ( cf . Sect. 1.4.1 ). The parameters include radius of
the circular window, decay ratio of the weighting function, and maximum number
of samples to be included within each window. For the example ( cf . Cheng
et al. 1994 ) parameters selected were: radius of 0.8 km, decay ratio of 0.5
(corresponding to a linear weighting function with weight 0 for samples located