Pugo formation was previously designated by Schafer (1954) as Pugo Series probably in reference to the exposures within the Pugo claims of Benguet Consolidated, Inc. in the Baguio District. This is a sequence of basaltic and andesitic flows and breccias with minor interbeds of sandstones, argillites and chert, as well as pyroclastic rocks. Pillow lava structures in the volcanic rocks have been noted in some places. This formation underlies a large part of the eastern part of the Baguio District which is intruded by later igneous rocks, notably the Central Cordillera Diorite Complex as well as by a variety of dikes, including lamprophyres.
In places, the rocks exhibit considerable effects of low-grade metamorphism (greenschistfacies) and even mapped separately as Dalupirip Schist. This metamorphic effect is localized along narrow shear zones (up to 1.5 km wide) near contacts with quartz diorite bodies as in Ambalanga River and portions of Agno River, especially near barrio Dalupirip in Itogon, Benguet from where it derives its name.
The total thickness of the Pugo Formation in the Cervantes-Bontoc area is Lepanto Metavolcanics, so named for the basement rocks in the area by the geologists of Lepanto Consolidated Mining Company. This unit occupies a narrow N-S trending belt on both sides of the Abra River Fault. The volcanic rocks include massive flows and pillow basalts, which are highly fractured and epidotized. They are commonly weakly metamorphosed into greenschists, although they rarely exhibit distinct foliation. Intercalated with these volcanic flow rocks are volcanic breccias and green and red tuffaceous sandstones, siltstones and mudstones with some chert. In places, the volcanic flows are intruded by numerous diabasic dikes (Ringenbach, 1992). Reports of small outcrops of gabbro and gabbro float, in addition to the occurrence of dikes evoking a sheeted dike complex, have led Ringenbach (1992) to consider this unit as part of an ophiolitic basement. This unit may also be correlated with the volcanic flows constituting Maieterre’s (1989) Pingkian Ophiolite farther east.
Radiometric dates of samples of volcanic rock from Mankayan, Benguet, range from 39 Ma to 42 Ma (Sajona, 1999, unpublished report). A limestone clast in the upper member of the Malitep Formation, which unconformably overlies the Lepanto metavolcanics, was dated Late Eocene. The Lepanto is presumably of Cretaceous-Eocene age.
- Uncomformably overlain by its equivalent in the Baguio District by the Zigzag formation, and in the Bontoc area by the Malitep formation.
- Over 1,000 m and may each 1,600 m.
- Pugo series (Schafer, 1954)
- Peña (1970)
- Lepanto Metavolcanics (Lepanto Consolidated Company)
- Succeeded by - Malitep formation