Geology
The Pujada Peninsula is occupied by west dipping ophiolite sequence of peridotite, gabbro, diabase, and basalt. Thin discontinuous belt of marble and schist overlain the ophiolite sequence to the west. The marble and underlying basalts of the ophiolite sequence are overlain structurally by a west dipping peridotite slab with a metamorphic sole of amphibolites and kyenite schists. Eocene limestone locally lies unconformably on the ophiolite. Miocene- Pliocene clastic and sedimentary rocks overlie the western peridotite along the west coast. The eastern peridotite thrust over greenschist-facies metamorphic rocks which are separated from basaltic wackes to the northeast by a strand of the Philippine Fault.
The geologic setting is reflected on the regional geomorphology of the Mindanao Island. This is manifested on the offshore and onshore geomorphic features (e.g. structural basins and highs), contrasting lithologic units (e.g. unconformable contacts between older igneous rocks and younger sedimentary and volcanic rocks) and superposition and reactivation of older fault structures by younger ones coupled with a divergent sense of displacement.
The oldest rock units are slightly metamorphosed inter-bedded volcanic flows, siliceous sandstones and carbonates belonging to the Iba Formation. It is overlain unconformably by the Tagugpo Schist. Amphibolite facies occur at the basal (i.e. Ansuwang) and upper (i.e. Bitaogan) portions of the schist. At least two (2) ophiolite slices were distinguished – the Surop Ultramafics and Nagas Ultramafics.
Bedding attitudes of the sedimentary units suggest a broad anticlinal structure whose axis straddles the length of Mati Gulf. The most prominent fault structures in the region consist of the older north-south trending west- dipping thrust faults along the central portion of the peninsula, and a younger northwest trending left-lateral strike-slip fault associated with the southern extension of the Philippine Fault.
The Pujada Ni-Co laterites have formed on the southeastern rim of the Philippine archipelago and are believed to be an extension of the prominent Bicol-Eastern Mindanao Ophiolite Belt.
Basement rocks in the region are comprised of suites of peridotite with local metamorphics, which are interpreted to have been emplaced during Paleocene. Post-Ophiolite units are of early Tertiary to Recent age and include metavolcanics and meta-sediments, gabbroic dikes, volcanics, limestone, clastics, etc. The predominant structural orientation is NNW-SSE, which is almost parallel to the Philippine Fault.
At the prospect area, basement to the laterite is predominantly harzburgite with occasional dunite. Serpentinization of the harzburgite is common, especially near major fault zones. Gabbroic dikes up to five (5) meters wide and meta-sediments were reported to have been mapped in the area.
Mineralization occurred in the weathered ultramafic basement rock. Transition from saprolite to the overlying limonite may be sharp but is often identified as a transitional zone of one (1) meter or more. It is identified as a mixture of saprolite and limonite material types. The formation of lateritic weathering over the Project Area is typical of many other humid lateritic environments. The laterization process of the parent rocks at AALMC involves the dissolution of the original rock mineralogy, the leaching of certain elements, and the eventual deposition of those elements elsewhere. The most soluble of the compounds, such as magnesium oxides, are thus removed, increasing the relative concentration of the remaining minerals, which include iron oxides and any contained nickel and cobalt. Five (5) laterite ore deposits have been delineated within the project area namely Catmonan, Magum, Tumagdo, Alog and Masanlog.