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The mineralogy and texture of Ni-sulfide ores at the Nkomati nickel mine are highly variable, and this results in often erratic nickel recovery at the mine. The variability of the ore presents an opportunity to study the influence of grind size on the flotation-based recovery of Ni in highly heterogeneous sulfide ores, which would be applicable to this ore type at many other mines worldwide. In view of this, a process mineralogy investigation was conducted on thirteen mineralogically and texturally different nickel-sulfide ores from the Nkomati Nickel Mine, with a view on the influence of grind size on the flotation performance of pentlandite. Ore types presented include medium- and high-grade variants of the bleb, disseminated, massive, semi-massive, and net-textured sulfide ores of the Main Mineralized Zone (MMZ), as well as disseminated chromite-rich nickel sulfide ore and massive chromitite ore of the Peridotitic Chromitite Mineralized Zone (PCMZ). Laboratory scale metallurgical test work, comprising of sequential grinding and bench-top flotation testing of the ores, was conducted in combination with quantitative mineralogical investigation of the flotation feed and associated flotation products, using a FEI 600F Mineral Liberation Analyzer. The ore types under consideration require a variety of grind sizes (i.e., milling times) in order to attain optimal recovery of nickel through flotation. This is predominantly controlled by ore texture, and also partly by the abundance of the major constituent minerals in the ore, being pyroxenes, base metal sulfides, and chromite. Liberation of pentlandite is directly correlated with grind size (milling time), which is also positively correlated with the level of nickel recovery through flotation. A grind size of P80 at 75 µm results in the highest concentrate nickel grades of 7.5–8.1% in the PCMZ ores' types which is the current grind for the PCMZ ores at Nkomati. A grind size of P77 at 75 µm yields the best overall pentlandite liberation, Ni recoveries of 84–88% and grades of 5.3–5.6% in the MMZ ores. This holds the potential to produce the best overall pentlandite liberation, nickel grades, recoveries from blending the MMZ and PCMZ ore types, and milling the composite ore at a target grind of P80 at 75 µm. [ABSTRACT FROM AUTHOR]

Froth flotation process is an important process that involves solid-solid/solid-liquid separation of minerals from gangue. However, the performance of froth separation is affected by the types of frothers. The purpose of this study, therefore, was to determine the effect of different frothers in the flotation of low-grade nickel sulphide obtained in South Africa. Sodium isobutyl xanthate was used as a collector in this investigation. The mineralogy analysis showed that the samples of the ores contained 0.33 and 2.45% nickel feed grade for ore samples A and B, respectively. Batch flotation tests were performed on the ore samples using two different frothers namely Senfroth XP 200 and 516. Some of the nickel was found to be associated with the gangue minerals present in these ores and recoveries were based on the total nickel value. It was observed that 0.24 and 0.29% of the total 0.333% of the feed ore were recovered from sample A by Senfroth XP 516 and 200, respectively. The results also revealed that 1.77 and 2.13% of the total 2.45% of the feed ore were recovered from sample B by 516 and XP 200, respectively. Analysis of the results revealed that 0.07 and 0.04% of the nickel were recovered from the tailing by Senfroth XP 516 and 200, respectively from the ores grade sample A, while 0.53 and 0.30% of nickel were recovered from the tailing of sample B. It can be deduced from this work that Senfroth XP 516 is more selective for the recovery of nickel from nickel sulphide ore as compared to the Senfroth XP 200. The better performance of Senfroth XP 516 can be attributed to the better adsorption capacity and level of interaction of the Senfroth 516 and the dispersant employed in this study. [ABSTRACT FROM PUBLISHER]

Abstract: The Uitkomst Complex is a satellite intrusion of the Bushveld Complex and contains the only mine currently producing Ni as the main product in South Africa. Previously reported sulfur isotopic data suggest that externally derived sulfur was important for the generation of sulfide mineralization in harzburgite units that comprise the lower portion of the Complex. We have determined oxygen isotopic compositions of minerals and variations in pyroxenes and plagioclase compositions, and analyzed fluid inclusions in quartz from highly altered zones in order to evaluate the importance of country rock assimilation and hydrothermal processes in the evolution of the complex. Oxygen isotopic compositions of pyroxene and olivine from the sulfide-bearing harzburgite in the Complex range from 5.2 to 5.9‰ and suggest that bulk assimilation of high-18O country rocks by parental magmas did not occur or was minimal. Sulfur transfer to magma was accomplished via a fluid which did not perturb the oxygen isotope composition of the magma. Harzburgite, pyroxenite, and gabbronorite that overlie the ore-bearing harzburgites contain minor amounts of sulfide minerals that are characterized by mantle-like δ 34S values of 0±2‰. Low abundances of sulfides in these units are consistent with segregation of cotectic proportions. Hydrothermal alteration is pronounced in the upper and lower marginal zones of the Complex. Secondary quartz and albite are common in the upper portion of the Main Gabbronorite unit. Measurements of fluid inclusion in quartz indicate that alteration took place at ~500 °C and involved a moderately saline fluid of 20 to 25 eq. wt.% NaCl. Oxygen and hydrogen isotopes of secondary silicate minerals are most consistent with the involvement of an evolved, long path-length meteoric water that infiltrated the upper and lower contacts zones of the Complex. [Copyright &y& Elsevier]

The main approach to PGE target selection west of the Pilanesberg was to use the geological models for the setting of PGE mineralisation (together with their associated geophysical and geochemical signatures) in the southwestern lobe of the Bushveld Complex where abundant information is available. A small gravity anomaly to the west of tile Pilanesberg could represent stratigraphic thickening of the Bushveld stratigraphy or a local magma feeder zone. If the Merensky Reef is present in this area then it could be expected to be of the narrow, pegmatoidal, potholed (including contact type) and high-grade variety, as in the southwestern and northwestern lobes of the Bushveld Complex. High precision, airborne magnetic and radiometric surveys over the area, carried out by the Council for Geoscience, demarcate Upper Zone stratigraphy and a range of dykes, faults and probable scattered bodies of iron-rich ultramafic pegmatites (IRUPS). Of particular significance are a set of northeasterly trending dykes and/or faults of the Vlakfontein swarm, which could host Ni (PGE) sulphide bodies of the type already known from the area. Anomalously low radiometric signatures were used to demarcate areas of unequivocal mafic/ultramafic rock outcrops or sub-outcrops. Higher radiometric signatures reflect Transvaal floor rocks while extremely high signatures occur over the Pilanesberg alkalic rocks. In terms of soil geochemistry, chromium is a good indicator of the Lower and Lower Critical zones of the Bushveld Complex. The transition from a high to a low chromium signature in the Rustenburg area is broadly coincident with the base of the Upper Critical Zone, which contains the important UG2 and Merensky Reef platiniferous layers. The same high to low chrome transition is seen to the west of the Pilanesberg and is considered to be an important PGE target indicator. Anomalously high nickel values occur over the Lower Zone rocks to the west of the Pilanesberg, although in the Rustenburg sector the most pronounced nickel geochemical anomalies are shown to be related to the impact of mining including tailings dams, smelters etc. The expansive nickel anomaly west of the Pilanesberg probably reflects the greater abundance of altered (including birbiritized) olivine-bearing rocks (harzburgites) and the presence of nickeliferous pipes. The transition area from a high-nickel (>220ppm) to a low-nickel signature, as in the case of chromium, defines a good PGE target area. Vanadium and titanium as expected show an anomalous build-up in the Upper Zone rocks of the Bushveld Complex. V also shows anomalous values over the upper chromitite zone and over IRUPS. The zone east of the vanadium anomalies to the west of the Pilanesberg therefore emerges as one with PGE potential. By integrating the interpretations of the above data sets, six main PGE target areas emerge to the west of the Pilanesberg. The most important targets include a well-defined zone of probable Critical Zone rocks as well as east-northeasterly trending linear targets along the Vlakfontein and related fault/dyke sets. Possible fault-, basal- and offset-style mineralisations are identified in the northwestern part of the area. [ABSTRACT FROM AUTHOR]