Page 212 - Introduction to Mineral Exploration

TABLE 9.6 Calculated weights and contrasts for patterns in generating a probability map. The mineralisation
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9: MINERAL EXPLORATION DATA
2
pattern was known gold occurrences as 1 km cells.
Patterns W j + W j − C
Landsat lineaments NE–SW 250 m buffer −0.222 0.025 −0.248
Landsat lineaments NW–SE 250 m buffer 0.247 −0.039 0.285
Landsat lineaments NW–SE 500 m buffer 0.298 −0.119 0.417
Landsat lineaments NW–SE 750 m buffer 0.315 −0.245 0.560
Landsat lineaments NW–SE 1 km buffer 0.259 − − − − −0.339 0.598
Landsat lineaments NW–SE 1.25 km buffer 0.143 −0.276 0.419
Landsat lineaments NW–SE 1.5 km buffer 0.052 −0.145 0.197
Landsat lineaments NW–SE 1.75 km buffer 0.002 −0.009 0.011
Landsat lineaments NW–SE 2 km buffer −0.003 0.023 −0.027
Felsite 3.739 − − − − −0.059 3.797
Dartmouth Slate 1.050 − − − − −0.618 1.668
Anomalous catchments with Au >> >> > 5 ppb 0.844 − − − − −0.689 1.533
Contact (Dart – Mead ) 2 km buffer 0.625 − − − − −0.741 1.366
Dolerite 1.184 − − − − −0.017 1.201
Thrust 250 m buffer 0.784 − − − − −0.062 0.846
Contact (Mead – Stad ) 750 m buffer 0.548 − − − − −0.199 0.746
Contact (Mead – Mdev ) 750 m buffer 0.605 − − − − −0.084 0.689
For each lineament set a series of buffers were calculated and an example of the results for different buffers of the NW–SE
lineaments is shown. Otherwise only the final results are shown. The significant features (shown in bold) were used to
calculate the final probability.
+
−
W j , positive weight; W j , negative weight; C, contrast.
Dart, Dartmouth Slate; Mead, Meadfoot Group; Stad, Staddon Grits; Mdev, Middle Devonian Slates.

55,000

50,000

45,000
5
N km
250,000 255,000 260,000 265,000 270,000 275,000 280,000
Probability

Legend 0.075–0.125
No data
Prospect
Coast 0–0.025 0.125–0.175

0.175–0.9
0.025–0.075

FIG. 9.13 Posterior probability map resulting from a weights of evidence analysis of geological and
geochemical data discussed in the text. Note the general good correlation with known occurrences with the
exception of that at ~2,72000E, 52,000N, which is probably of different origin. (Source: Wang 1995.)