The Onca Puma mine is built on lateritic nickel deposits of saprolitic laterite ore.

Lateritic weathering profiles at Onca and Puma can be classified according to protolith mineralogy and the accumulation of quartz. Protolith mineralogy, the presence of significant chlorite and/or vermiculite in the serpentine #3 host at Puma distinguishes that deposit from Onca where the dominant Serpentinite #2 host is largely serpentine and chromite.

Each of the deposits has a saprolitic zone overlaid by a limonitic zone (if it has survived erosion). Nonsiliceous or normal profiles consist of serpentinite saprolite overlain by thin layers of limonite and in rare cases by some form o f ferricrete. Siliceous profiles are defined as having greater than 15% quartz in both siliceous saprolite and siliceous limonite. The limonite zones overlying tire On9a and Puma saprolites are generally thin, discontinuous, and from their chemistry consist of goethite, chromite, several manganese oxide phases, and sporadic amounts of quartz.

The principal minerals in the Onca saprolite in decreasing order of importance are serpentine, limonite, quartz, chromite and vermiculite. Ni occurs in solid solution largely in serpentine with subordinate amounts in goethite (=limonite) and vermiculite. Minor amounts of various green silicates, “gamierites” intergrown with chalcedonic quartz, are seen locally in Onca saprolite; grains of possible nepouite contained 13-19 wt% Ni have also been identified in mineralogical studies. Nickel and Cobalt also occur in manganese oxide phases but not in significant amounts of the saprolite unit. Intergrowths of a Mn-Al oxide phase have also been observed (typically this would be lithiophorite) and tamaite, (K,Ba)3Mn24(Si,Al)40(O,OH)u22*(H2O), with - 10% contained Ni.

Nickel in the Puma serpentinite is associated with narrow zones of fine-grained serpentine micro-breccia and centimeter-scale subhedral patches of very fine-grained polycrystalline chlorite and vermiculite. Locally significant amounts of chlorite and vermiculite are cut by millimeter to centimeter thick garnierite ± chalcedony veinlets controlled by a structural event which has cross-cut the igneous-layering. Vermiculite and chlorite are strongly enriched in nickel in the saprolite zone. Because both are more insoluble than serpentine, they persist upward in the laterite profile and are present in limonite and siliceous limonite.

The operation produces ferronickel via the rotary kiln-electric furnace process, currently operating with a single line, with nominal capacity estimated at 27,000 metric tons per year.