Page 111 - Geochemical Anomaly and Mineral Prospectivity Mapping in GIS

110 Chapter 4

Fig. 4-18. Spatial distributions of background and anomalous populations of PC4 scores
representing an As-Ni association in stream sediments, Aroroy district (Philippines), based on
thresholds defined from the (A) continuous surface of PC4 scores (Fig. 4-17A) and (B) discrete
catchment basin surface of PC4 scores (Fig. 4-17C). L = low; H = high. Triangles represent
locations of epithermal Au deposit occurrences, whilst thin black lines represent lithologic
contacts (see Fig. 3-9).

situated along the intrusive contact of the Aroroy Diorite with the Mandaon Formation
(see Fig. 3-9), suggesting that such anomalies are possibly associated with
hydrothermally altered rocks.

Synthesis of multi-element associations
It is appealing to integrate the PC3 and PC4 scores of the point stream sediment
geochemical data because there are some parts of the area where anomalies of PC3
scores and anomalies of PC4 scores are spatially coincident (Fig. 4-18 and 4-19). For
example, the southern parts of the area where two epithermal Au deposits occur and the
northern part of the area below one epithermal Au deposit occurrence. In addition, in the
northwestern parts of the area where many epithermal Au deposits occur, there is spatial
coincidence between high background PC3 scores and anomalous PC4 scores. A simple
multiplication can be applied to integrate the PC3 and PC4 scores, although this will
create false anomalies from PC3 and PC4 scores that are both negative. This problem