Page 239 - Geochemical Anomaly and Mineral Prospectivity Mapping in GIS
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Knowledge-Driven Modeling of Mineral Prospectivity 241
TABLE 7-XI
Principal components of fuzzified evidential scores (fS c ) of classes of proximity to geological
features in Aroroy district (Philippines) (see Table 7-X and Fig. 7-21B).
4
NNW 1 NW 2 NE 3 NA % of variance Cum. % of variance
PC1 0.528 0.592 0.177 0.582 42.70 42.70
PC2 -0.242 -0.207 0.937 0.145 24.47 61.17
PC3 0.743 -0.145 0.253 -0.603 17.76 84.93
PC4 -0.333 0.765 0.164 -0.526 15.07 100.00
2
1 NNW-trending faults/fractures. NW-trending faults/fractures. NE-trending faults/fractures.
3
4 Nabongsoran Andesite porphyry.
For the case study area, PC1 (explaining about 43% of the total variance of fS c values
in the input maps) indicates a strong spatial association between the NNW- and NW-
trending faults/fractures and the Nabongsoran Andesite porphyry, which is weakly
associated with the NE-trending faults/fractures (Table 7-XI). PC2 (explaining about
24% of the total variance of fS c values in the input maps) reflects mainly the NE-trending
faults/fractures, whilst PC3 (explaining about 18% of the total variance of fS c values in
the input maps) mainly reflects either the NNW-trending faults/fractures or the
Nabongsoran Andesite porphyry. PC4 (explaining about 15% of the total variance of fS c
values in the input maps) mainly reflects either the NW-trending faults/fractures or the
Nabongsoran Andesite porphyry. Thus, of the four PCs, PC1 is a multivariate
association that is the most plausible integrated spatial evidence of heat source and
structural controls on hydrothermal mineralisation in the case study area. A map of the
PC1 scores can thus be considered a geologically-constrained mineral prospectivity
model (Carranza, 2002).
The geologically-constrained wildcat model of hydrothermal mineral deposit
prospectivity represented by the map of PC1 scores (Fig. 7-22A), obtained from the PC
analysis of fuzzified evidential scores (Table 7-XI), shows intersecting linear patterns
(reflecting proximity to faults/fractures), which intersect with circular patterns (reflecting
proximity to mapped units of Nabongsoran Andesite porphyry) in the southwestern
quadrant of the case study area. The map patterns are different from those of the earlier
models of epithermal Au prospectivity in the case study area because the geochemical
evidence has not been integrated into the present model. The predictive performance of
the map of PC1 scores can be aptly compared only with the map of integrated Bel (Fig.
7-19A) because both of these maps have predictions for all locations in the case study
area. If 20% of the case study area is considered prospective, then the map of PC1 scores
delineates correctly six (or about 46%) of the cross-validation deposits (Fig. 7-22B).
This means that, based on 20% predicted prospective zones, the map of PC1 scores is
inferior to the map of integrated Bel (Fig. 7-19B). If 50% of the case study area is
considered prospective, then the map of PC1 scores delineates correctly 12 (or about
92%) of the cross-validation deposits (Fig. 7-22B). This means that, based on 50%
predicted prospective zones, the map of PC1 scores performs equally as the map of