Abstract

There is commonly a close spatial relation between porphyry Cu (± Au) and high-sulfidation epithermal Cu-Au deposits throughout the world, although a genetic association has not been proven. Nowhere is this spatial association better seen than in northern Luzon, Philippines, where the Lepanto epithermal Cu-Au deposit overlies the Far Southeast (FSE) porphyry Cu-Au deposit, both world-class orebodies. Fresh rock and hydrothermal mineral separates yield K/Ar ages indicating that premineralization and postmineralization volcanism occurred at 2.2–1.8 Ma and 1.2–0.9 Ma, respectively, and that the hydrothermal system was active from ∼1.5 to ∼1.2 Ma. K/Ar ages of alunite from Lepanto have the same range as those of hydrothermal biotite and illite from the FSE deposit, indicating that both epithermal and porphyry mineralization formed from an evolving magmatic-hydrothermal system that was active for about 300 ka. This temporal relation strengthens the argument for a genetic link between these two styles of ore deposit, and has implications for exploration. Where one style of mineralization is found, there is potential for the other nearby.

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