CONTEMPORANEOUS FORMATION OF ADJACENT PORPHYRY AND EPITHERMAL CU-AU DEPOSITS OVER 300 KA IN NORTHERN LUZON, PHILIPPINES

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 s patial association better seen than Tn northern Luzon, Philippines, wh ere the Lepanto epithermal Cu-Au deposit overlies the Far Southeast (F SE) porphyry Cu-Au deposit, both world-class orebodies. Fresh rock and hydrothermal mineral separates yield K/Ar ages indicating that premin eralization and postmineralization volcanism occurred at 2.2-1.8 Ma an d 1.2-0.9 Ma, respectively, and that the hydrothermal system was activ e from similar to 1.5 to similar to 1.2 Ma. K/Ar ages of alunite from Lepanto have the same range as those of hydrothermal biotite and illit e hom the FSE deposit, indicating that both epithermal and porphyry mi neralization formed from an evolving magmatic-hydrothermal system that was active for about 300 ka. This temporal relation strengthens the a rgument for a genetic link between these two styles of ore deposit, an d has implications for exploration. Where one style of mineralization is found, there is potential for the other nearby.