Abstract
M.Sc. (Geology)
The study aims to provide a geometallurgical assessment, including an evaluation of the response of different facies types of the Merensky Reef to mineral processing, and the identification of critical characteristics that determine processing behaviour. This is accomplished by obtaining quantitative mineralogical information, combined with chemical assay, laboratory scale milling and flotation testing. Lonmin Platinum’s Marikana Mine is located on the Western Limb of the Bushveld Complex to the east of Rustenburg. Platinum group elements (PGE) occur in, and are mined from, a variety of facies types of the Merensky Reef, and the UG2. For the purpose of the present study, three facies types of Merensky Reef samples and one sample of UG2 were used. The Merensky facies samples comprise of the BK, RPM, and Western Platinum variants. The mineral assemblages of the various Merensky Reef facies types at this locality comprise varying amounts of orthopyroxene, clinopyroxene, plagioclase, olivine, talc, serpentine, chlorite, chromite, magnetite and sulphides (mainly pyrrhotite, pentlandite and chalcopyrite). Approximately 20 individual 10 cm channel samples were collected from each of the facies variants of the Merensky Reef, and the UG2. These are coarsely crushed, mineral modal abundances determined using the MLA, and then analysed for Co, Cr, Cu, Ni, S and 6 PGE. The samples were then combined per facies type, and each of these composites subjected to laboratory scale milling and flotation testing. Abundant sulphide typically occurs with (is associated with) thin chromitite stringers, as is commonly observed in the Merensky Reef throughout the whole of the Bushveld Complex. Chromitite stringers are characterized by high PGE concentrations. The milling behaviour of the various facies samples, as well as flotation behaviour, was observed to be a function of mineralogy. The influence of ore mineralogy on the various stages of flotation, the mineralogical makeup of the various flotation concentrates, and the level of recovery of the PGE’s during flotation, were also investigated. Ore facies having the most abundant anorthite required the longest milling time to achieve the target grind of 60wt.% passing 75μm; and the ore with the most abundant enstatite produced the largest mass pull on floating. The facies with higher PGE grade, modal abundance of base metal sulphides, higher degree of liberation of base metal sulphides and least enstatite abundance produced the most favourable set of characteristics for efficient PGE recovery.