NICKEL LATERITE

The Minahang Bayan area is underlain by ultramafic rocks composed of intensely serpentized harzburgite and dunite, which are part of the Dinagat Ophiolite complex dated as Late Cretaceous Age (84 million years old). The harzburgite, the most widespread in the area interlayered with the dunite, can be easily recognized due to very rough surface when deeply weathered, wherein the pyroxene stand out in relief. This rock is coarse grained, massive, with variable colour when altered, and contained dominantly of pyroxene mineral with minor amount of olivine. The dunite body is likewise massive but very fine grained and dark in colour when fresh but turns to chocolate brown when weathered. It consists of more than 90% olivine mineral with subordinate amount of pyroxene. The pyroxene exhibits a shiny appearance when exposed to sunlight. Both of these rocks contain minor amount of chromite and magnetite crystals. They are commonly transected by chrysotile veinlets, filling the constricted fractures. The chrysotile is fibrous, greyish green but becomes dark when altered. Due to re-current tectonic activities in the area, the rocks are severely shattered to fractured, producing serpentine minerals. The conservative estimated source of the nickel laterite within the minahang bayan license area is about 47.3 million tonnes with an average depth of 7.0 meters only. Manual auger drilling conducted by the members of the minahang bayan and small-scale miners along the southeast section of the area indicated a depth down to 8-9 meters only and is still open ended. The crest and slopes of the ridges are mantled with residual nickeliferous lateritic soil derived from extensive weathering of serpentized harzburgite and dunite. Associated with these laterite deposits are minor amount of disseminated chromite and magnetite grains. Concentration of black sand along the channels of the drainage systems dissecting the area is believed to be the result of weathering process of the underlying rocks.

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