Summary:
Mineral Property Geology
The project area is in Barangay Dimaluade, Municipality of Dinapigue, Isabela Province, Philippines. It is underlain by the ultramafic rocks that is attributed to the Isabela Ophiolite. Andal et al. (2005) reported that peridotites in Dinapigue is divided into two varieties, the homogeneous lherzolites and layered peridotites.
Lithologies in the MPSA are predominantly peridotites, dunites and pyroxenite. Patches and lenses of dunites and pyroxenites are scattered within the MPSA. A dunite body in Area 4 hosts chromite which is already mined out. Serpentinites are observed within the joint planes of the host ultramafic rocks. No mafic rocks like gabbro have been mapped in the MPSA, although there are gabbros identified adjacent to the MPSA in Area 5 and in Area 3.
Weathering of these ultramafic rocks produced the laterite ores being mined. The laterite has elevation ranges from 300 to 600 m above sea level. The limonite which is iron (Fe) rich lies on top of the saprolite which is nickel (Ni) rich. The laterite occupies the plateau area and roughly oriented north-south within the property.
The geological model of Dinapigue Nickel Laterite Deposit as confirmed from geologic mapping, drilling and assay data interpretation is based on the ideal nickel laterite profile composed of distinct conformable layers of the weathered zone overlying the parent rock.
The primary zones are limonite, saprolite and bedrock. The transition zone is poorly developed and not distinct Saprolite zone can be further divided into an upper soft saprolite zone and rocky saprolite portion near the bedrock. Photo 1 shows roughly the Limonite and Saprolite horizons in Area 1.
Mineral Deposit
Type Nickel deposits are formed from the chemical and mechanical weathering of ultramafic rocks. These rocks are present in ophiolite complexes as harzburgite and dunite. Pervasive weathering disintegrates the susceptible minerals. Their chemical components are being diffused and transported in groundwater that may result to new minerals that is much stable in a new environment. The Ni-Fe Laterites have been classified based on their weathering profile and their mineralogical characteristics (USGS – Marsh et.al, 2013). Three major types of NiFe Laterite deposits – hydrous MG-silicate, clay, and oxide.
The nickel laterite deposit within the tenement of DMC can be classified under the oxide subtype. It is formed through the weathering of the minerals harzburgite and dunite. In an environment of low relief and heavy rainfall, the olivine, clinopyroxene, and antigorite of the partially serpentinized ultramafic rocks were gradually leached of their most soluble elements, Mg and silicon (Si), whereas the less-soluble components, Fe, Ni, Co, Al and Cr, were enriched (USGS – Marsh et.al, 2013).
Style of Mineralization
Mineral Deposit Model
The deposit is classified as laterite which is divided into 2 domains- limonite which is Fe-rich and saprolite which is Ni-rich. The laterite is the product of the weathering of ultramafic rocks and usually follows the topography of the area.
Wall Rock Alteration, Zoning, and Paragenesis
Wall Rock Alteration, Zoning, and Paragenesis are not applicable in nickel laterite deposit since these features are usually observed on base metal deposits such as gold and copper.
Localization of the Deposit and Continuity of Mineralization
The deposit is developed within the weathered soil horizon and the continuity of the mineralization is confined within this layer. This zone is usually located within the plateau and on tops of ridges.
The ore controls for the Dinapigue Nickel Laterite Deposit are the following :
• Lithological Control – the bedrock should be ultramafic, otherwise the weathered profile will not develop high nickel and iron grades
• Favorable Topography - gentle to flat elevated topography allows for the significant accumulation of limonite and saprolite. Areas with very steep
• Structural Control – wide zones of highly fractured zone associated with faults in a favorable topography can increase the thickness of the nickel laterite. However, this has not been observed in the Valencia deposit; and
• Tropical Climate – alternating wet and dry conditions enable differential leaching and concentration of mobile elements such as Ni, Co, Si, and Mg, and immobile elements such as Fe, Cr, and Mn thereby creating limonite and saprolite zones.