The Acoje Block of the Zambales Ophiolite Complex (ZOC) is made up of upper mantle-crustal rocks represented by residual harzburgite, transition zone dunite, layered ultramafic cumulate (dunite, wehrlite, websterite, clinopyroxenite and lherzolite) and mafic cumulate (gabbronorite and olivine gabbronorite) rocks. Petrographic investigations of the upper mantle-crust sequence reveal the crystallization order, olivine +/- spinel—> clinopyroxene —> orthopyroxene—> plagioclase. Residual harzburgite and transition zone dunite exhibit protogranular and equigranular textures, respectively. Porphyroclastic texture, however, predominates the ultramaiic cumulate rocks,

Primary metallic suliides which include chalcopyrite, bornite and secondary sulfides (pentlandite, mackinawite) are found in the interstices of silicate minerals (olivine and pyroxene), within the boundaries and interstices of chromite grains. Pentlandite occurs as blocky and amoeboid while mackinawite, chalcopyrite and bornite occur as rims and mottles in the blocky pentlandite.

The Mount Matalisbong area covers the northern extension of the transition zone dunite and layered ultramafic cumulate rocks of the Acoje minesite. The layered ultramafic cumulate rocks include dunite, wehrlite, websterite, and clinopyroxenite. Mineragraphic investigations of layered ultramafic cumulate rocks show very minimal amount of metallic sulfides. Sulfides are also found in the interstices of serpentinized olivines. Platinum-group element and associated base metal mineralization is mainly confined heterogenously to the transition zone dunite and layered ultramafic cumulate rocks.

Cryptic variation and other pertinent binary diagrams suggest that fractional crystallization and immiscible sulfide segregation are important processes which may have controlled the distribution, mode of occurrence and genesis of precious and base metal mineralization in the study area.