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Black Mountain Quartz Diorite    


Quartz diorite porphyry

Stratigraphic relations

Intrudes Pugo Formation and Zigzag Formation in the Baguio area


Black Mountain, Camp 6, Kennon Road


Late Miocene  – Pliocene

Named by   

Balce and others (1980)


MGB (2004)

The unit was previously named Black Mountain Porphyry Complex by Balce and others (1980) for the porphyritic quartz diorite stocks and small bodies intruding Pugo Formation and Zigzag Formation in the Baguio area.  The type locality is at the former copper mine of Black Mountain Inc. at Camp 6 through which the Kennon Road passes.  The quartz diorite consists mainly of plagioclase, hornblende and quartz some occurring as phenocysts ranging from 0.5 mm to 12 mm set in a fine-grained groundmass of the same minerals.  These quartz diorite bodies are associated with porphyry-type copper deposits in Black Mountain mine in Camp 6 below Bued River, Philex Mine, Sto. Nino Mine as well as in Lepanto Mine (Far Southeast Deposit) and other places.  A Late Miocene to Early Pliocene age (3.8 – 5.9 Ma) for the quartz diorite porphyry in Baguio area is indicated by K/Ar and fission track dating (Wolfe, 1981; Teledyne Isotopes, 1988).  The Guinaoang quartz diorite stock and other quartz diorite bodies in Lepanto mine area are associated with dacites.  K/Ar dating indicates a range of 2.5 Ma to 3.5 Ma (equivalent to Pliocene) for the Lepanto quartz diorites, which is later than those for the Baguio area (Arribas and others, 1994; Sillitoe and Angeles, 1985).

Formation sequence[]