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Balabac Andesite    

Lithology

Andesites, lamprophyres, appinites

Stratigraphic relations

Intrudes Pugo Formation and Zigzag Formation

Distribution

Baguio District

Age

Late Miocene  – Pliocene

Previous Name   

Emerald Creek Complex (Schafer, 1954)

Renamed by

Balce and others (1980)

Late Tertiary andesites occurring as dikes and small intrusive bodies in the Baguio District was previously named collectively as Emerald Creek Complex by Schafer (1954).  The Balacbac Andesite was designated by Balce and others (1980) for the hornblende andesite at Balacbac, at the Western Minolco Mine area.  This is probably contemporaneous with the deposition of the pyroclastics and associated volcanics of the Baguio Formation.  They are generally mappable, although they may be so numerous in some areas, such that they are mapped as dike complexes.  Thus, the Emerald Creek Complex of Schafer (1954) and Camp 4 Complex (Malicdem, 1971) indicates areas in which these late Neogene intrusive bodies occur as dike swarms.  These rocks include lamprophyres and appinites and other porphyritic rocks, which exhibit prominent pyroxene and hornblende phenocrysts as well as ordinary andesite porphyry with varying sizes and amounts of plagioclase phenocrysts.

Dating of two samples of andesite by K/Ar was reported by Maleterre (1989) to be 5.1 Ma and 3.5 Ma.  Radiometric dating of volcanic clasts from the Malaya Formation ranges from 6.2 Ma to 3.7 Ma, while that of a volcanic clast from Baguio Formation gave 3.57 Ma.  These suggest volcanic activity during Late Miocene – Early Pliocene time, probably contemporaneous with the deposition of Baguio Formation.

A later phase of andesite emplacement is suggested by Plio-Pleistocene dates for some samples.  Dating of samples of andesite porphyry by radiometric (K/Ar) and fission track methods reported by Lovering (1983) indicates an age of 1.9 Ma and 1.8 Ma, respectively, equivalent to latest Pliocene.

Formation sequenceEdit

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