Abstract

The concentrations of all platinum-group elements and gold in monthly composited samples of mined ores have been determined by neutron activation analysis. Average values from a typical medium Ni tenor ore shoot (10% Ni in 100% sulfides) are: Os, 480; Ir, 230; Ru, 980; Rh, 320; Pt, 1,650; Pd, 2,050; Au, 500 (all values are in ppb and are recalculated to 100% sulfides). These values are similar to those reported from other komatiite-hosted ores. Os, Ir, Ru, Rh, and Pd correlate strongly with Ni (r = 0.63 to 0.92) whereas Pt (r = 0.50) correlation with Ni is only moderate. Au does not correlate with Ni (r = -0.28).Geochemical profiles of platinum-group element values recalculated to 100 percent sulfides through typical ore zones show that Pt, Pd, and Au are lower in massive ore relative to overlying matrix and disseminated ores, whereas other platinum-group elements have a more uniform distribution through these ore types. Pt, Pd, and Au are strongly concentrated at the footwall metabasalt-massive ore contact and in small sulfide-filled fractures within the footwall metabasalt. Other platinum-group elements are concentrated to a lesser extent at this position. Some magnetite-rich selvedges immediately above massive ores are depleted in Os, Ir, and Ru.Pt, Pd, and Au largely occur in discrete mineral phases (Hudson and Donaldson, 1984) and Os, Ir, Ru, and Rh are interpreted to occur in solid solution in pentlandite. The present concentration of Pt, Pd, and Au at the base of massive ores in late fractures is attributed to metamorphic remobilization although this does not preclude an original magmatic concentration of platinum-group elements at the base of the massive ore. The variation in the platinum-group element content of bulk ore samples is similar to that of Ni, Cu, and Co and is controlled by a variation in Fe content at constant sulfur levels.

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