Geostatistical and Mineralogical Insights on Some Nickel Prospects in the Philippines

Carlo Arcilla

Director
National Institute of Geological Science

Cherisse R. Ferrer, Engielle Mae R. Paguican, Meryl Y. Calibo, Mark John S. Africa, Zaymon Calucin, Justin Vidamo and Mary Jane B. Moral

National Institute of Geological Science
University of the Philippines

With the prices of Nickel in historical highs, deposits with close to 1% Ni content are now viable mining targets.  Since the Philippines is host to several ophiolite deposits with ultramafic sections exposed, large areas with these rocks as bedrocks and exposed to rain-induced chemical weathering can be exploration targets. We examine some marginal deposits that have been sampled extensively, and try to delineate the mineralogical residence of Ni and Cr, using polarized and transmitted light microscopy,  combined X-Ray Diffraction, X-Ray Fluorescence and Atomic Absorption Spectrophotometer methods. The mineralogical residence of Nickel is important not only for extraction but also for the mode of chemical analysis used in determining concentrations. For example, iron oxide and hydroxide-dominated laterites can easily be dissolved by three acid digestive process prior to quantitative chemical analysis; however, saprolite and garnierite-rich portions of the Nickel deposit contain nickel-bearing silicates that can only be dissolved completely with hydrofluoric acid. The implication is that Nickel values could be underestimated in saprolitic and garnieritic zones if the chemical analysis does not involve HF. Important geostatistical relationships between Ni, Cr, and Fe are also important tools in delineating areas which are probable ore horizons. We have documented that a "chromite-based" approach to nickel exploration could miss out nickel orebodies because the denser chromitites do not host substantial amounts of nickel. These observations have profound implications for exploration and chemical analysis of nickel laterite and saprolite ores.