submitted partial fulfilment of the requirements for the degree of MASTER OF SCIENCE in the Faculty of ENGINEERING in the University of the Witwatersremd, Johannesburg August 1991 \

Extraction of platinum group elements (PGE) is a major source of revenue in South Africa and the reserves represent about 75 per cent of world reserves. Most of the remaining Platinum Group Mineral (PGM) reserves are located in the UG-2 chromitite layer of the Bushveld Igneous Complex. Platinum concentrators experience significant losses of PGE in their secondary milling circuits due to insufficient liberation of platinum-bearing particles. The chromium oxide (Cr2O3) content in UG-2 concentrates is typically 3%, which results in operational problems in the downstream smelting process. Ways of improving the design of the secondary milling circuit were investigated, with the purpose of improving PGE recovery and reducing Cr2O3 entrainment in the subsequent flotation stage. Batch-scale laboratory and pilot plant tests were carried out to investigate the optimal design of a secondary milling circuit configuration. The optimal design consisted of a conventional hydrocyclone to de-slime the feed, followed by gravity separation with a spiral concentrator circuit to separate the ore into lights (silicates-rich) and heavies (chromite-rich) fractions. Separate milling of the light and heavy fractions made it possible to grind the silicate-rich fraction finer and to avoid over-grinding of the chromite. The total milling energy was redistributed between the silicates and chromite ball mills with 88% of the energy input to the silicates mill and 12% to the chromite mill thus reducing chromite over-grinding. The effects on the recovery of PGE, and the entrainment of Cr2O3 were measured in combined batch rougher flotation tests. The results indicated a 2% improvement in the secondary rougher flotation PGE recovery for the densifier underflow sample as compared to the standard MF-2 circuit, and most significantly the Cr2O3 entrainment was reduced by over 30% overall. Attritioning of the chromite-rich heavies fraction and ball milling of the silicates-rich lights fraction resulted in a 52% reduction of Cr2O3 in the rougher flotation concentrate and a 0.4% increase in PGE recovery (0.4%) as compared to the standard circuit. The improved reduction in chromite entrainment may be attributed to the lower fines generation with attritioning (52.8%- 106μm) as compared to ball milling with a 12% energy input (83.6% -106μm). Over 50% of the chromite minerals remained in the +106μm of the attritioned heavies product as compared with 21% for the ball milled spiral heavies stream. This accounted for a significant proportion of the overall chromite reduction in the flotation concentrate and supported the motivation for the inclusion of a separate grinding circuit for the chromite and silicate particles. Pilot plant testwork on a VHG (very high grade) spiral concentrator circuit followed by laboratory milling and rougher flotation tests confirmed the above conclusions. A 3.7% improvement in PGE recovery was noted with a 32% Cr2O3 reduction in the secondary rougher flotation concentrate as compared to the standard circuit. The statistical reliability of the laboratory and pilot plant data were quantified at various stages of the testwork due to the heterogeneous nature of the feed material and representative sampling. The repeat analyses on selected flotation tests for the high grade ore revealed that the variances were below 0.5%, 4%, and 7% for the head grades, PGE and Cr2O3 recoveries respectively. The flotation results for the standard and significantly improved milling circuits had variances in the 4E recoveries for the low grade ore and pilot plant ore of below 5.5% and 1% respectively. Low variances (<1%) in the Cr2O3 recoveries were noted for the low grade and pilot plant ores. A preliminary cost estimate was undertaken based on the pilot plant data to determine what value the proposed circuit could add for an additional 3.7% PGE recovery. An additional revenue of approximately R50 000 per day could result based upon the platinum mineral recovery only. The other precious metals, i.e. palladium and rhodium were neglected and would further increase the overall revenue. The minimum payback period for the estimated capital investment would be approximately 4 years. This confirmed the benefit of this improved secondary milling circuit design as a viable option. A closed-circuit operation of the silicates mill should offer more significant benefits compared to the open circuit option; however, this was not considered in the current testwork. This project has confirmed the benefit of separate ball milling and the use of a spiral concentrator as an effective gravity separation device in the secondary milling circuit for a chromite-rich (>50%) UG-2 platinum ore. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2011.

This project is an investigation of the UG2 cyclic unit of the Upper Critical Zone at Lebowa (Atok) / Thesis (M. Sc.)-University of KwaZulu-Natal, Westville, 2008.

Production of platinum and associated metals is a major source of revenue for South Africa. Significant losses occur in the concentrating stage (10 to 15 per cent) and this research is focused on optimising platinum flotation. Research begins by conducting laboratory batch flotation tests. However, subsequent pilot-plant tests often produce different results. It is believed these differences arise from the artificial nature of laboratory techniques. This project was focused on improving flotation techniques in the laboratory. The largest source of platinum in South Africa is the UG2 reef and two samples of this ore were used for testing: ‘good’ and ‘bad’ ore. These had different characteristics with regards to the recovery of PGMs and the presence of talc. The latter is an unwanted floatable mineral, which must be depressed to prevent excessive recovery. The conventional laboratory test procedure makes use of batch tests in various sizes of flotation cells. The procedure was made more realistic, by using four stages of flotation, rather than just two, to mimic a typical platinum flotation plant. The use of four stages made it possible to separate the fast-floating and slow-floating stages and to control froth conditions accordingly. Attention was also given to the fact that in laboratory tests, water is often added to the ‘cleaner’ stage of flotation, to make up the level. Experiments showed that this dilution, which does not take place in practice, had a significant impact on overall efficiency. A method of measuring frother concentration was developed and used to determine the realistic level of frother in cleaning tests. Tests at these levels of frother concentration showed that significant improvements could be made to plant performance, by making use of a thickener to reduce the frother concentration in the cleaning stages. The improved test procedure was used on both good and bad ores, and the effect of regrinding was also tested. A combined solids recovery of 2 % over both cleaners was targeted for all test work. At this recovery, the regrinding of the bad ore increased the PGM recovery from 67 to 76 per cent at the cost of an additional 8 g/t depressant. An investigation of the effect of frother concentration in the cleaning stage, using good ore, demonstrated that that rejection of chromite could be improved significantly by reducing frother concentration. The tests mimicked the use of a thickener to separate some of the water with a high concentration of frother. Tests conducted on the good ore showed that use of two thickeners, as opposed to none, reduced the Cr2O3 content of the final concentrate from 4.2 to 3.2 per cent for the equivalent concentrate mass and PGM recovery. The depressant requirement was also reduced from 67 to 55 g/t. These tests provided insight on how to improve performance on a platinum flotation plant, particularly when floating the bad ore.

From the abstract: In the layered sequence of the Bushveld Complex a number of distinct, but possibly genetically related groups of transgressive, postcumulus, ultramafic and mafic rock are recognised. The main part of this thesis investigates a suite of postcumulus rocks for which the name iron-rich ultramafic pegmatite is proposed. The majority of iron-rich ultramafic pegmatite bodies examined are from the upper critical zone of the layered sequence at Rustenburg Platinum Mines Amandelbult Section, in the northern sector of the western Bushveld Complex. Field relationships imply that the iron-rich ultramafic pegmatites should be considered as an integral feature of the layered sequence, even though they transgress the cumulates. Consequently, this thesis also includes a study of the cumulate sequence at Amandelbult. A second group of postcumulus, ultramafic rocks which is investigated comprises latiniferous ultramafic pipes; the Driekop pipe has been selected as a case­ study. This thesis is presented in four sections, namely, an introduction and verview, and studies on the Driekop pipe, the cumulate sequence at mandelbult and the iron-rich ultramafic pegmatite suite. A new classification scheme of discordant bodies of postcumulus, ultramafic rock in he Bushveld Complex is proposed (see also Viljoen & Scoon, in press). In he scheme presented here, two main varieties of postcumulus, ultramafic rock re recognised, namely, non-platiniferous magnesian dunites and iron-rich ltramafic pegmatites.

The Platreef is a platinum group element (PGE) and base metal enriched mafic/ultramafic layer situated along the base of the northern (Potgietersrus) limb of the Bushveld Complex. It represents an important resource of PGE which is only in its early stages of exploitation. The present study contains a detailed petrographic and geochemical investigation of a borehole core drilled on the farm Townlands. At this locality, the Platreef rests on metasedimentary rocks of the Silverton Formation of the Transvaal Supergroup, and is comprised of three medium grained units of gabbronorite/feldspathic pyroxenite that are separated by hornfels interlayers. I refer to the three platiniferous layers as the Lower, Middle and Upper Platreef. The Middle Platreef is the main mineralized layer, with total PGE contents up to 4 ppm. The Lower and Upper Platreefs are less well mineralized (up to 1.5 ppm). Trace element and S-isotope data show compositional breaks between the different platiniferous layers suggesting that they represent distinct sill-like intrusions. The study also reveals a reversed differentiation trend of more primitive rocks towards the top of the succession. For example, pyroxene shows an increase in Cr2 O3 with height couples with a decrease in TiO2 . Olivine from the Upper Platreef has Fo contents between 80-83 (averaging Fo81) and those from the Middle Platreef have Fo from 78-83 (averaging Fo79 ). The Upper and Lower Platreefs have <FONT FACE="SYMBOL">d</FONT> 34S values averaging 80/00 while the Middle Platreef has <FONT FACE="SYMBOL">d</FONT> 34S values averaging 4 0 /00. All three Platreef layers have elevated <FONT FACE="SYMBOL">d</FONT> 34S values, indicating addition of 34S-enriched crustal sulphur. The model of contamination is supported by elevated K, Ca, Zr and Y contents in the Platreef relative to Critical Zone rocks from elsewhere in the Bushveld Complex, and by high Zr/Y ratios. Well defined correlations between concentrations of the individual PGE, and between the PGE and S suggest that the concentration of the PGE was controlled by segregating sulphide melt. Alteration of the rocks, possibly due to infiltration by fluids derived from the floor rocks, caused localized redistribution of Cu and, to a lesser degree, the PGE. A model is proposed whereby the Platreef magma assimilated calcsilicate and hornfels from the country rocks. The hornfels and calcsilicate of the Silverton Formation that forms the floor rocks to the Platreef on the farm Townlands constitute a possible source of the crystal sulphur. Release of S from the floor rocks caused S-supersaturation in the magma, followed by segregation of an immiscible sulphide melt. The sulphide melt scavenged the PGE from the silicate magma. The sulphides and the xenoliths were entrained by successive, metal-undepleted magma flows, causing high metal tenors in the sulphides and undepleted Ni contents in associated olivine / Dissertation (MSc)--University of Pretoria, 2006. / Geology / unrestricted

The Townlands iron-rich ultramafic pegmatite is a relatively large pipelike body situated in the western corner of Rustenburg Section, Rustenburg Platinum Mines. It is characterised by a strong negative magnetic signature and transgresses the noritic layered sequence of the upper critical zone of the Bushveld Complex. The layered rocks are downwarped in the vicinity of the pipe and are in sharp contact with the pegmatitic material. The pegmatite varies in composition between dunite and wehrlite, with the marginal zones being more wehrlitic in composition. Olivine (Fo₃₀ - Fo₅₂) and clinopyroxene (Wo₄₅En₃₀Fs₂₅ - Wo₄₅En₃₇Fs₁₈) are the dominant constituents and accessory phases include ilmenite, Ti -magnetite, apatite, amphiboles, chlorite-group minerals, biotite, ilvaite and a host of unusual ore minerals. The Fe-Ti oxides exhibit exsolution textures typically found in slowly cooled igneous rocks and temperatures of formati on are consi dered to be in excess of 800°C. The UG2 chromitite leader layers intersected by borehole TLP.l are enriched in Fe and Ti and exhibit compositions intermediate between chromite and Ti-magnetite. The ore mineral assemblage includes a primary sulphide assemblage consisting of troilite, chalcopyrite, cubanite and pentlandite, and an array of unusual phases formed by late-stage secondary processes. The unusual sulphides mooihoekite and haycockite, that occur in certain parts of the pegmatite, are considered to have formed by partial replacement of the primary assemblage and a possible paragenetic sequence is discussed. Mineral compositions and whole rock geochemical data are consistent with an origin for the pegmatite by crystallization from a fractionated melt. It is suggested that intercumulus fluids, trapped during the crystallization of the noritic layered sequence, accumulated in an area of structural weakness, in response to an increasing overburden pressure and/or tectonic activity. Evidence is also presented that indicates that the Townlands pegmatite may consist of at least two separate, but adjoining pegmatite bodies. / KMBT_363 / Adobe Acrobat 9.54 Paper Capture Plug-in

Ph.D. (Geology) / Please refer to full text to view abstract