Investigating The Mineralogy Of An Oxidised South African PGM Ore From The Western Limb

Abstract

- In this paper, the mineralogical characteristics of a weathered Platinum Group Minerals (PGMs) ore of Middle Group (1- 4) was investigated with the main objective of proposing a processing route for the ore. The oxidised PGM ore supplied was 60% passing 710µm and the major elements present were:Cr(27,03%), Fe(20,57%), Si(5,417%), Ca(5,43%), Mg(3,87) and Al(2,17 %). The ore was analysed for 4Es (Pt, Pd, Rh and Au) content using fire assaying followed by inductively coupled plasma - optical emission spectrometry. The results indicated that the grades of the 4Es were as follows: Au (0.04ppm), Pd (0.94ppm), Pt (1.98) and Rh (0.32). The Pd content is much lower than that of Pt, indicating Pd remobilization from the weathered zone to the lower zone which reduces the flotation efficiency by changing Pt:Pd ratio. The X-ray diffraction results indicated that the oxidised PGM ore sample was dominated by chromite, quartz, iron oxide minerals such magnesium/ferric iron, trevorite (nickel iron oxide) and secondary minerals such as covellite which is generally found in zones of secondary enrichment (supergene) of copper sulphide deposits. More mineralogical investigation is recommended such as Mineral Liberation Analysis in order to investigate the PGM’s grain size distribution, liberation and their associations. The body of work presented in this paper shows strong evidence that the PGM ore studied is weathered ore. The mineralogical study done on material showed oxidation and weathering as the probable causes of the low metallurgical performance of the ore. The results indicated there is an abundance of host minerals showing iron oxides minerals such as magnesium/ferric iron, trevorite (nickel iron oxide) and secondary minerals such as covellite which is generally found in zones of secondary enrichment (Supergene) of copper sulphide. The deposit has abundant amount of chromite and quartz. The fire assaying results indicated that the ore is low-grade and the Pd content is much lower than Pt, indicating Pd remobilization from the weathered zone to the lower zone which reduces the flotation efficiency by changing Pt:Pd ratio. More mineralogical investigation is recommended such as Mineral Liberation Analysis (MLA) to investigate the PGMs grain size distribution, their liberation and association.