The Philippine deposits are divided into two main groups based on their locations in the arc-trench system, namely frontal arc and third arc. Deposits occurring in the frontal arc are characterized mainly by the predominance of nickel, laterite, chromite and cupriferous massive sulfide, under a geologic setting distinguished by ultrabasic and basic volcanics and subordinate intermediate intrusive-metamorphic (schist) rocks. These regional rocks are adjacent to deep troughs or trenches.Deposits belonging to the third arc are primarily characterized by the gold-bearing copper sulfides with pyrite and minor magnetite and molybdenite. The mineralizations are closely related to intermediate intrusives and intermediate-basic volcanics with occassional ultrabasics.Southeastern Luzon could probably exhibit the features of both the frontal and third arcs. It is suggested that the Sulu Sea Basin could probably have been formed as a result of the extensional rifting of a part of the frontal arc.
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