The Platreef occurs at the base of the Northern Limb of the Bushveld Complex and is variably mineralised with PGE, Cu, and Ni. The Platreef varies in thickness from a few meters to a few hundred meters and rests on progressively older sediments of the Transvaal Supergroup and Archaean granite basement northwards. Recent studies have highlighted the importance of magmatic processes, contamination of the magma by footwall rocks and syn- and post metasomatic fluid activity on the observed mineralisation. Along the Platreef strike, the PGE grade profiles are generally top-loaded from Overysel to Tweefontein North and more variable and bottom loaded from Tweefontein Hill southwards emphasizing the importance of the change in mineralisation style at Tweefontein in relation to the whole Platreef. This study presents the first significant PGM data on the Tweefontein farm, including ten boreholes along strike, providing insight into the distinctly different PGE mineralisation styles observed. Samples were selected based on assay data, varying rock types, stratigraphic position and proximity to geological features. The selected samples were investigated using petrography, geochemistry and the automated SEM techniques of QEMSCAN and MLA. Over 9000 PGM were analysed forming one of the most comprehensive PGM studies on the Platreef to date. The lowermost footwall intersected along the Tweefontein strike is banded ironstone of the Penge Formation. This is overlain by a metasedimentary footwall package, of variable thickness, derived from the shales and dolomites of the Duitschland Formation. Iron-rich, recrystallised, noritic sills occur at the base of the Platreef and are thought to represent sills which intruded prior to the emplacement of the Platreef. A pre- and possibly syn-Bushveld structural control resulted in irregular floor topography defined by a topographic footwall high in the central Tweefontein area and topographic depressions at Tweefontein North and Tweefontein Hill. The depression areas at Tweefontein are similar to the footwall basins at Turfspruit to the south, in which the Platreef is more lithologically complex compared to the footwall high areas. The footwall basins at Tweefontein and Turfspruit contain basal massive and submassive sulphides, which may not necessarily carry significant PGE grade. The Platreef lithologies at Tweefontein are composed of pyroxenites and norites with minor harzburgitic lithologies and contain numerous cross-cutting granitic veins. Xenoliths/interlayers of metamorphosed Duitschland lithologies occur primarily near the base of the Platreef, but also in the middle and upper Platreef sequence reflecting roof pendants. Unlike the Platreef on the farms adjacent to Tweefontein, the Platreef and footwall lithologies are relatively unaltered, but localised serpentinisation and chloritisation occur within harzburgitic lithologies and metasedimentary interlayers. Based on the stratigraphy and geochemical characteristics, the Platreef at Tweefontein can be subdivided into the upper and lower Platreef. The upper Platreef subdivision occurs in the top 20-40 m of the sequence and is defined by higher Mg#, Cr, Cr (ppm)/MgO and Pt/Pd values compared to the lower Platreef. In addition, the majority of the grade and base metal sulphide (BMS) content is enriched in the upper versus the lower Platreef, particularly for the northern and central parts of Tweefontein. The upper and lower Platreef may have been derived from different magma sources based on the “R Factor” concept proposed by Campbell and Naldrett in 1979 whereby the abundance of the PGE relative to the BMS content is linked to the proportion of magma with which the sulphide ore equilibrated (Naldrett, 2005b). Previous detailed geochemical studies from Tweefontein Hill southwards highlighted compositional breaks in the Platreef sequence thought to represent distinct sill-like intrusions (Hutchinson and Kinnaird, 2005; Kinnaird, 2005; Manyeruke et al., 2005; Nyama et al., 2006). They reported a more primitive sill at the top of the Platreef, which correlates to the upper Platreef at Tweefontein. The lower Platreef is therefore likely to represent a different sill intrusion. A relatively homogenous pyroxenitic package characterises the upper Platreef, although a more heterogeneous package is observed close to and at Tweefontein Hill. At Tweefontein North, the base of the upper Platreef is often marked by a chromitiferous package comprising a pegmatoidal feldspathic pyroxenite unit, up to 6 m thick, capped by a chromitite layer. Due to similar stratigraphy and high PGE grades, this distinct horizon has been compared to the Merensky Reef found elsewhere in the Bushveld Complex. The predominant base metal sulphides (BMS) in the Platreef at Tweefontein are pyrrhotite, pentlandite, chalcopyrite with minor pyrite aligned with that found elsewhere along the Platreef strike. There is an increase in BMS content, primarily pyrrhotite, towards the base of the Platreef with massive and submassive sulphide development near the base and in the footwall, particularly at Tweefontein Hill. Sulphur isotopes and detailed mineralogical studies at Turfspruit have shown that the addition of S, As and Sb into the magma from the Duitschland footwall triggered the development of a PGE-poor sulphide liquid which was then able to mix, modify and dilute the magmatic sulphides (Hutchinson and McDonald, 2008). Due to the similarity in footwall between Turfspruit and Tweefontein, these proposed processes help to explain the increase in BMS towards the base and the development of basal massive and submassive sulphides, which are not necessarily associated with significant PGE grade. At Tweefontein North, the processes dominating the top-loaded PGE mineralisation were primarily magmatic. The PGM assemblage, hosted by base metal sulphides and magmatic silicates, is dominated by Pt-and Pd-bismuthides and -tellurides with minor PGE-sulphides and Pt-arsenides. PGE-sulphides occur in the Platreef where the chromitiferous horizon is developed, which may indicate an environment low in volatile activity and one of the most primary mineralisation styles along the Platreef strike. The footwall high, which separates the depressions at Tweefontein North and Tweefontein Hill may have kept the Platreef at Tweefontein North relatively protected from additional processes affecting Tweefontein Hill. In contrast, assimilation of the Duitschland footwall is thought to play a key role in the development of the variable but predominantly bottom-loaded PGE mineralisation at Tweefontein Hill. The PGM assemblage is Pd-dominant characterised by Sb-, As- and Bi-bearing PGM, reflecting the incorporation of Sb, As and Bi from the Duitschland footwall. The association of the PGE mineralisation with the extensive basal sulphide development implies that the mineralisation at Tweefontein Hill probably occurred due to the gravitational settling of a sulphide liquid containing a mix of sedimentary and PGE-hosting magmatic components. Due to a significant PGM-BMS association in the mineralised footwall and metasedimentary interlayers/xenoliths, a downward migrating sulphide melt is believed to be the main mechanism responsible for the redistribution of PGE, predominantly Pd, into the mineralised metasedimentary lithologies. Finally, the Platreef and footwall lithologies may be locally modified by late-stage felsic and hydrothermal fluids to form bismuthide- and arsenide-dominant PGM assemblages, primarily hosted in quartz and serpentine respectively. This study shows the PGM and sulphide mineralisation at Tweefontein to be multifaceted, involving magmatic processes, assimilation of the Duitchland footwall into the Platreef magma and late-stage hydrothermal and felsic fluid activity. Footwall composition and irregular floor topography, resulting in depression areas at Tweefontein North and Tweefontein Hill, are believed to play a key role in what processes become significant along the Tweefontein strike. This research represents a significant contribution to the understanding of the distinctly different PGE mineralisation styles at Tweefontein and allows for a complete comparison of the Platreef PGE mineralisation from Overysel to Turfspruit.

The base metal and platinum group metal extractive processes for two South African refineries were examined using x-ray powder diffraction. Base metal refinery matte contained nickel sulphide (Ni3S2), copper sulphide (Cu2S), nickel-copper alloy (Ni-Cu), iron oxide (Fe3O4) - nickel iron oxide (NiFe2O4) and nickel oxide (NiO). Nickel iron oxide and cobalt sulphide (CO3S4) were found in matte aeration cavities. Matte fast cooling caused alloy zoning. Alloy stoichiometry and weight percentages of matte constituents were calculated. Magnetic separation of the alloy phase was unfeasible due to high bulk and poor separation from Ni3S2. Sulphuric acid matte leaching produced residues containing copper sulphide (Cul.8S) and nickel sulphides (Ni3S4, NiS). Potassium cyanide residue leaching produced NiS-rich residues, while thiourea / hydrochloric acid leaching produced residues almost free of copper sulphide. PGM concentrates were examined. Base metals occurred as: copper sulphate pentahydrate; copper sulphate hydroxide hydrate (CU4SO4(OH)6'H2O); copper sulphide (CuS); copper platinum (Cu3Pt); nickel oxide (NiO); nickel iron oxide (NiFe2O4). Lead occurred as lead sulphate and silicon as quartz and enstatite ((Mg,Fe,Al)SiO3). Heating the concentrate to 260°C with sulphuric acid converted copper sulphide to copper sulphate. PGMs were mostly metallic. Overdrying concentrates caused pgm sintering. Drying with sulphuric acid reduced sintering. PGM oxidative leach solubility was examined. Platinum sulphide (Pt,Pd)S caused low platinum and palladium solubility. (Ru,Rh,Ir,Pt)AsS caused low rhodium and ruthenium solubility. Platinum-rhodium (Rh0.57Pt0.43), ruthenium-osmium (~Ru16Os), iridosmine (Os,Ir,Ru) also caused low pgm solubility. Silver chloride remained in residues. Concentrate overdrying produced insoluble sintered platinum, palladium monoxide, and ruthenium dioxide. In minor concentrates sintered platinum, rhodium selenide (RhSe2+x), ruthenium dioxide and possibly palladium monoxide lowered pgm solubility. Precipitates and salts were examined. Iron precipitated as iron oxide hydroxide (B-FeOOH); gold as metallic gold; lead as lead chloride. Common salts were: sodium chloride; sodium iron hydroxide sulphate hydrate (Na2Fe(SO4)2(OH)'3H2O); ammonium chloride; sodium carbonate monohydrate. PGM-Iead fusion was examined. Fusion produced the insoluble alloy Pb(Pd,Pt)3. Ruthenium dioxide reacted with lead carbonate forming lead ruthenium oxide (Pb2Ru2O6.5). Nitric acid insoluble residues also contained lead sulphate and iron oxide (Fe3O4). This study demonstrated that solution problems can be understood by identifying the crystalline insoluble phases in intractable residues. / Thesis (Ph.D.)-University of Natal, Durban, 1994.

Mineral hydration is known to result in low flotation recoveries and grades within primary platinum group element ores worldwide. This is because the phyllosilicate minerals derived from hydration reactions of silicate minerals (i) form electrostatic coatings on valuable minerals that in turn hinders collector adsorption, (ii) alter the viscosity of the slurry leading to poor gas dispersion and (iii) decrease the concentrate grade due to naturally-floating gangue. Sodium metasilicate was investigated because its dispersant, rheology modifying, and depressant properties could prove promising in combating the problems associated with these ore types. Quantitative evaluation by scanning electron microscopy (QEMSCAN) analysis revealed large quantities of serpentine and talc present within the ore sample used in this study, which led to a poor flotation response, as indicated by batch flotation tests. Using sodium metasilicate improved the recoveries and grades at high dosages (>1000 g/t). A suite of techniques was chosen to decouple sodium metasilicates' effects to answer why an improved flotation performance occurred. The zeta potential experiments indicate that improved recoveries are, in part, as a result of the reversal of serpentines surface charge, creating electrostatic repulsion between serpentine and valuable minerals which prevents the coating of valuable minerals by serpentine slimes. This corresponded with improved recoveries of a PGM proxy in the presence of serpentine slimes and a high sodium metasilicate dosage. Ore dilution and rheology tests indicate that decreased viscosity at high dosages also improved recoveries. This was supported by slower particle settling rates at high sodium metasilicate dosages during particle settling measurements. Talc micro-flotation tests revealed that the depression of talc occurred at higher sodium metasilicate dosages, which improved concentrate grade. This was supported by a QEMSCAN concentrate analysis of the sodium metasilicate batch flotation concentrates, which confirmed that talc, and other associated silicate minerals, were depressed at high sodium metasilicate dosages. The processing of near-surface altered ores is becoming an increasing problem worldwide and the use of sodium metasilicate proved valuable in mitigating the problems associated with the altered ore investigated in this study.

No description available.

North Range low-sulfide mineralization is dominantly hosted by Sudbury breccia, with amphibole-plagioclase equilibrium metamorphic temperatures of 440 to 533 ± 75oC, produced by the SICs thermal aureole. Mineralization led to increases in the bulk halogen content of the host Sudbury breccia and the formation of Ni-enriched ferromagnesian silicates. South Range low-sulfide mineralization is typically hosted by metabasalts of the Huronian Supergroup. Garnet-biotite-plagioclase-quartz geothermobarometry produced equilibrium metamorphic conditions of 513 to 645 ± 50oC and 2.0 to 7.7 ± 1.0 kbar, probably corresponding to a late-Penokean overprint of peak Blezardian/Penokean metamorphism. Silicates associated with South Range mineralization are compositionally similar to the host rock equivalents and no alteration selvage is commonly observed due to subsequent recrystallization. Platinum-group minerals (PGM) from the North Range comprise platinum and palladium tellurides and bismuth-tellurides, with Sb-bearing palladium bismuth-tellurides and sperrylite from the South Range. Kotulskite-sobolevskite from the North Range shows a previously unreported Ag-Pd substitution, with michenerite from irregular veinlet style mineralization showing the substitution of Se and Sb for Bi. Two unknown PGMs were identified from the South Range, along with kotulskite-sobolevskite-sudburyite crystals displaying extensive Te-Bi-Sb solid-solution not noted before at Sudbury. A new Se-bearing variant of pilsenite was identified at McKim. Polyphase aggregates from both Ranges indicate that Bi-Te melts may have been widespread at some stage postdating the emplacement of the main magmatic sulfides. Normalized plots for low-sulfide mineralization show enrichments in the precious and semimetals relative to contact and sharp-walled vein mineralization. This enrichment has resulted in elevated concentrations of Ag and Se in chalcopyrite and Pd+Ag and Se in pentlandite from the North Range. The mass balance for North Range samples found that a significant fraction of Ag and Se occurs in sulfides with all other elements preferring discrete phases. A substantial fraction of Pd is hosted by pentlandite on the South Range, with gersdorffite also a major host despite its low abundance. The enrichments observed reflect the formation of low-sulfide mineralization from a fractionated sulfide liquid and hydrothermal fluids that have interacted with a fractionated sulfide source, and suggest that the precious and semimetals behave incompatibly with crystallizing sulfide.

North Range low-sulfide mineralization is dominantly hosted by Sudbury breccia, with amphibole-plagioclase equilibrium metamorphic temperatures of 440 to 533 ± 75oC, produced by the SICs thermal aureole. Mineralization led to increases in the bulk halogen content of the host Sudbury breccia and the formation of Ni-enriched ferromagnesian silicates. South Range low-sulfide mineralization is typically hosted by metabasalts of the Huronian Supergroup. Garnet-biotite-plagioclase-quartz geothermobarometry produced equilibrium metamorphic conditions of 513 to 645 ± 50oC and 2.0 to 7.7 ± 1.0 kbar, probably corresponding to a late-Penokean overprint of peak Blezardian/Penokean metamorphism. Silicates associated with South Range mineralization are compositionally similar to the host rock equivalents and no alteration selvage is commonly observed due to subsequent recrystallization. Platinum-group minerals (PGM) from the North Range comprise platinum and palladium tellurides and bismuth-tellurides, with Sb-bearing palladium bismuth-tellurides and sperrylite from the South Range. Kotulskite-sobolevskite from the North Range shows a previously unreported Ag-Pd substitution, with michenerite from irregular veinlet style mineralization showing the substitution of Se and Sb for Bi. Two unknown PGMs were identified from the South Range, along with kotulskite-sobolevskite-sudburyite crystals displaying extensive Te-Bi-Sb solid-solution not noted before at Sudbury. A new Se-bearing variant of pilsenite was identified at McKim. Polyphase aggregates from both Ranges indicate that Bi-Te melts may have been widespread at some stage postdating the emplacement of the main magmatic sulfides. Normalized plots for low-sulfide mineralization show enrichments in the precious and semimetals relative to contact and sharp-walled vein mineralization. This enrichment has resulted in elevated concentrations of Ag and Se in chalcopyrite and Pd+Ag and Se in pentlandite from the North Range. The mass balance for North Range samples found that a significant fraction of Ag and Se occurs in sulfides with all other elements preferring discrete phases. A substantial fraction of Pd is hosted by pentlandite on the South Range, with gersdorffite also a major host despite its low abundance. The enrichments observed reflect the formation of low-sulfide mineralization from a fractionated sulfide liquid and hydrothermal fluids that have interacted with a fractionated sulfide source, and suggest that the precious and semimetals behave incompatibly with crystallizing sulfide.

Ni-laterites have the potential to become unconventional ore deposits for platinum group elements (PGE). This study was conducted to determine enrichment trends of PGE as a result of the Ni-laterization process. 6 samples were selected by mine workers from the protolith, saprolite, and limonite horizons of the Ni-laterite profile from the Acoje ophiolite block, Luzon, Philippines, and sent to Luleå University of Technology (LTU). 2 samples representing the protolith are described as dunite having undergone serpentinization, 1 sample is a massive chromitite from the saprolite layer of the laterite profile, 1 sample is a massive chromitite from the limonite layer of the laterite profile, and 2 samples are limonitic soils. Total PGE contents of the investigated Acoje samples range from 161-1180 ppb with the highest contents of PGE occurring in the limonite hosted chromitite, and the lowest contents in the saprolite hosted chromitite. C1 chondrite-normalized patterns reveal distinct trends of the PGE in the different sample types: dunite samples have a positive trend from Ir-Pd, the chromitite samples have a negative trend from Ru-Pd with a negative Ir anomaly and the limonite samples have a strong positive trend from Ir-Pd. Rare earth elements (REE) chondrite-normalized patterns of the samples show a negative Ce anomaly in the limonite while the dunite and saprolite-hosted chromitite have negative Eu anomalies. Cr# (Cr/[Al+Cr]) and Mg# (Mg/[Fe2++Mg]) were analyzed using automated mineralogy and produced Cr# values ranging from 0.67 – 0.77 and Mg# values from 0.46 – 0.59.  17 platinum group minerals (PGM) were identified from the Acoje samples: 9 from the dunite, 1 from the saprolite-hosted chromitite, 6 from the limonite-hosted chromitite and 1 from the limonite. Laurite ((Ru,Os)S2) was identified in samples A-02 and A-07 and is the only primary mineral identified. Secondary PGM, thought to have formed due to alteration processes during serpentinization, were identified as alloys composed of: Cu-Pd, Cu-Pt, Pt-Ni-Cu, Pt-Fe, Ir-Ni-(Pt,Fe), and Cu-Pt-Au-(Pd-Ag). PGM are small, measuring consistently <10 µm in diameter. Laurite occurs as inclusions in unfractured chromite. PGM alloys in the dunite samples occur along the boundary of sulfide minerals or within serpentine. PGM identified in the limonite-hosted chromitite occur along interstitial fractures within chromitite or in a Fe-Al oxide matrix within pore spaces.

A Dissertation submitted to the Faculty of Engineering, University of the Witwatersrand Johannesburg, in fulfillment of the requirements for the Degree of Master of Science in Engineering / High extractions of the platinum group metals' from a refractory tailings concentrate (PGM Concentration : Pt 81.5ppm, Pd 21.5ppm, Rh 17.5ppm) was achieved after short. low-temperature roasting and subsequent leaching with a zinc chloride based leach reagent containing nitric acid under atmospheric pressure at temperatures from 105-C to 120-C. [Abbreviated Abstract. Open document to view full version] / AC2017

Modeling gravity recovery of platinum group minerals (PGMs) in the grinding circuit is based on three components: Ore characterization of gravity recoverable platinum group minerals (GRPGM), their behavior in grinding mills and hydrocyclones, and the performance of the gravity recovery units. This thesis focuses on the first two components. / A laboratory methodology to characterize gravity-recoverable platinum group minerals (GRPGMs) in an ore with four incremental liberation and recovery stages was developed. It was applied to quantify GRPGM content of four ore samples from Canada. To measure the behavior of GRPGMs in the grinding circuit, a methodology to characterize the already liberated (or available) GRPGMs in the circuit streams was developed. The availability of GRPGM in streams, such as ball mill discharge, was used to model the behavior of the GRPGMs in the ball mills and hydrocyclones. Combining with the potential GRPGM in an ore, they can be used for design and/or optimization of platinum group mineral recovery circuit. / The GRPGM content measured by this methodology varied from 5 to 81% depending on the ore. The GRPGM size distribution varied from fine (most GRPGM below 37mum) to coarse (significant content above 212 mum). The stage size-by-size recovery and the total GRPGM content indicate that the methodology can quantify the GRPGM content of ores. / Based on the measurement of the availability of GRPGM in process streams, the behavior of PGMs in ball mills and hydrocyclones is characterized in terms of the less common cumulative selection functions and conventional classification efficiency curves. Mineralogical analysis indicates that sperrylite (PtAs 2) is the dominant platinum mineral at the Clarabelle mill. Its classification efficiency is similar to that of gold, despite its lower density, while grinding rate is significantly higher than gold. The cumulative selection function of platinum and palladium is 1.3 times higher than the ore for size classes above 212 mum and 50 to 70% of the ore below 212 mum. / As a result, sperrylite accumulates in finer sizes than native gold in the grinding circuit. The cumulative selection function of the platinum group minerals was calculated for the Clarabelle grinding circuit based on the survey data and the GRPGM contents in the ball mill discharge, cyclone underflow, and overflow. / The methodology of characterizing the content of GRPGMs in an ore also offers a way to concentrate the minerals for mineralogical study. The use of secondary electron microscopy (SEM), variable pressure SEM and QEM*SEM for qualitative analysis of platinum group mineral mineralogy is presented and discussed. Most of the GRPGMs recovered are well liberated. Qualitative mineralogical analysis of the GRPGM and its associations in ore samples are also discussed.

A method for the determination of platinum group elements (PGEs) in natural tree samples was developed. An alumina column in-line with inductively coupled plasma mass spectrometry (ICP-MS) achieves the separation of interferents as well as pre-concentration of the analytes. The application of this proposed method on tree top samples displayed an effective separation of Ru, Rh, Re, Pd, Ir and Pt from the interferents, Ni, Cu and Zn for quantitative analysis of the analytes. The concentration data was compared to ICP-HRMS data and while it was difficult to determine whether the concentrations were in agreement or not, as both methods have a large degree of error. However, both methods displayed elevated concentrations of PGEs in areas over geological conductors in Rock Lake, Manitoba. This proposed method offers distinct advantages over previous on-line methods, as it is extended to include multiple PGEs as well as reduces sample consumption to a more suitable volume for natural samples. While the detection limit is higher than previous methods due to the lowered sample volume, it is still lower than the detection limits reported in commercial laboratories. / Thesis (Master, Chemistry) -- Queen's University, 2008-01-30 19:40:54.673 / Anglo American