2-D and 3-D Trend Analysis - Geomathematics: Theoretical Foundations, Applications and Future Developments - page 272

Fig. 7.32 Two-dimensional power spectra (a and b) and phase maps (c and d) for distribution of
copper (N-S set only) and gold occurrences in east-central Ontario (gridded area in Fig. 3.4 ). Dots in
a and b denote P -values selected for constructing phase maps (Source: Agterberg 1974 ,Fig.81)

oversimplification of those shown in Fig. 7.28 but existence of zones with alter-
nately high and low copper was correctly predicted.

7.4.3 East-Central Ontario Copper and Gold
Occurrence Example

The final example of harmonic trend analysis is concerned with the distribution of
copper and gold occurrences in the western Abitibi volcanic belt (Fig. 4.12 ) . The
pattern of copper deposits in Fig. 4.13 was coded as an array with 28 columns and
20 rows with numbers of copper deposits per cell. All data were corrected for their
mean and the array was augmented to size (32

32) by zeros. The inverse Fourier
transform was computed with the resulting 2-D power spectrum shown in Fig. 7.32 .
Individual P -values are distributed as chi-square with a single degree of freedom.
A. moving average for four P -values was contoured of the 95-% and 99-% fractiles