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A novel learning intervention has been developed and tested in which honor's level Earth science students were tasked with conducting interviews with established geologists working in the Southern African minerals sector. The task was designed using Laurillard's conversational framework as a theoretical underpinning, which offers an iterative and communicative approach to learning. The teaching goals for the task were that students would come to understand the role of the geologist in the minerals sector, and that students would have exposure to developing professional networks. Data from student feedback surveys showed that the learning intervention was a success and that both goals were achieved. Because of the depth of knowledge accessed from the interviewees, students attained a much deeper level of understanding of the role of the geologist in the minerals sector. The success of the intervention is further discussed in terms of knowledge and social capital transfer across the university--industry interface and in terms of developing graduate attributes.

This study provides for the first time details of the mineralogy, petrography and mineral paragenetic relationships of manganese ores of the Avontuur deposit, a prominent northern outlier of the Kalahari Manganese Field in the Northern Cape Province of South Africa. Using a combination of light and electron microscopy and X-ray powder diffractometry on an extensive suite of exploration drill core samples, it is shown that the manganese ores comprise an exceptionally fine-grained assemblage of Mn2+-silicates (friedelite, tephroite, gageite), Mn2+/Mn3+-oxides (jacobsite, hausmannite) and Mn2+-carbonates (rhodochrosite, kutnahorite, Mn-dolomite and Mn-calcite). This mineral assemblage is a product of diagenesis and very low-grade regional metamorphism. Locally, this assemblage is overprinted by contact metamorphism or supergene alteration. Despite close geochemical and textural similarities, the manganese ores of the Avontuur deposit are surprisingly different in their mineralogy compared to the carbonate- and braunite-dominated mangano-lutites of the main Kalahari deposit. Distinctly higher concentrations of both SiO2 and Fe2O3 in the manganolutites of the Avontuur deposit as compared to the main Kalahari Deposit provide the reason for the markedly different mineralogy. Such marked differences in bulk chemistry are tentatively attributed to systematic lateral variations in the physicochemical conditions of mineral precipitation during the deposition of the Hotazel Formation. [ABSTRACT FROM AUTHOR]

Discordant iron-rich ultramafic pegmatites (IRUPs) intersect the UG2 chromitite at many places in the Bushveld Complex. The effects of IRUP interactions on the UG2 ore mineralogy and PGE grade are assessed at the Thaba mine, north-west Bushveld, based on a borehole profile through the UG2 layer and detailed analysis of mineral textures and compositional variations across the UG2-IRUP contacts using micro-XRF element mapping. The UG2-IRUP interaction operated at different scales and probably by different mechanisms. At the local scale (< 10 cm), a thin layer of Fe–Ti–Cr spinel and ilmenite formed on the IRUP side of the contact with UG2, whereas the UG2 chromitite developed grain coarsening, loss of interstitial silicates, and chemical gradients in Cr, Al, Fe, and Ti that extend a few centimeters from the contact into the seam. These local effects are attributed to the intrusion of IRUP melt into the solidified UG2 layer, followed by re-equilibration of the oxide minerals across the contact during cooling. On a larger scale, changes in the ore and gangue mineral assemblages in UG2 took place throughout the entire meter-thick main seam. Compared with regional UG2 compositions, chromite has higher TiO2 and lower Mg#, and there is an anomalously low abundance of interstitial plagioclase. The IRUP-affected UG2 shows relatively abundant secondary hydrous silicates, replacement of PGE sulfides by PGE alloys and PGE-As–Sb–Bi–Te–Pb phases, and formation of secondary Ni–Cu–Fe sulfides after pentlandite and chalcopyrite. These large-scale effects are attributed to hydrothermal fluids derived from IRUP melts. The IRUP bodies at the Thaba mine caused redistribution of PGE within the UG2 layer but did not significantly reduce the overall grade. However, significant changes in the ore mineral assemblage and an increased abundance of secondary silicates can reduce the efficiency of PGE recovery. [ABSTRACT FROM AUTHOR]

The Bredasdorp Basin covers the greater part of the larger Outeniqua Basin, representing a productive petroleum-bearing basin off the south coast of South Africa. However, uncertainty about the diagenesis, provenance, and their impacts on reservoir qualities of the sandstones has hindered further exploration, particularly in the southern Bredasdorp Basin. In this part of the basin, sandstones from the primary and secondary hydrocarbon targeted intervals within the 6At1 and 14At1 stratigraphic sequence were investigated using a combination of petrographic, mineralogical, and geochemical techniques. Petrographic studies show that the sandstones are largely subarkose. The provenance analysis indicates that the sandstones are largely derived from granites and granite-gneisses of a continental block tectonic provenance, suggesting that the sandstones were derived from stable shields and uplifted areas. Furthermore, the tectonic diagram suggests that the basin developed on a rift passive setting (trailing edge) of the stable continental margins. The main diagenetic processes that have affected the reservoir quality of the sandstones are cementation by authigenic clay, carbonate, and silica, growth of authigenic glauconite, dissolution of minerals and load compaction. The development of secondary porosity as a result of the partial to complete dissolution of calcite cement and some detrital grains (i.e., feldspar) has improved the reservoir quality of the sandstones. The scattered plots of porosity and permeability versus cement+clays show inverse correlations, signifying that the reservoir quality is mainly controlled by cementation and authigenic clays. In general, there is no particular diagenetic process that exclusively controls the type or form of porosity evolution in the sandstones. [ABSTRACT FROM AUTHOR]

Despite the wealth of Late Pleistocene archaeology that exists across southern Africa's open landscape, it is routinely neglected in favour of rock shelter (re)excavation, biasing interpretation of human–environment interaction. This is compounded by the scarcity of open-air studies that use geoarchaeological methods to investigate the history and processes involved in their formation. The open-air archaeology of the Doring River Valley is an example of this, despite nearly a decade of dedicated study and publication. Consequently, there remains a limited and untested understanding of the valley's formation history. This paper rectifies this by providing a sedimentary context for the surface archaeology exposed across one of the Doring River Valley's artefact-baring localities, Uitspankraal 7 (UPK7). Characterisation, particle size, mineralogical, morphometric, and geophysical analysis of UPK7′s sand mantle resulted in the identification of four artefact-bearing sedimentary units, the aeolian and pedogenic processes involved in their formation, and their proposed order of deposition. This provides a stratigraphic, taphonomic, and environmental context against which chronometric dating and an analysis of the taphonomic, spatio-temporal, and technological composition of UPK7′s surface archaeology can be compared. This work is the first vital step towards understanding the depositional and behavioural history of a landscape, irrespective of context type. [ABSTRACT FROM AUTHOR]

A characterization study of chromite ore from South Africa was conducted using bulk assays, X-ray diffraction, optical, scanning electron microscopy (SEM), automated electron probe microanalysis (EPMA) and quantitative evaluation of mineral by scanning electron microscopy (QEMSCAN) mineralogical techniques, and quantitative EPMA. The aim was to identify all major gangue impurities, the degree of chromite liberation, and possible beneficiation options. The bulk material assayed 40.5% Cr2O3 with the major impurities being Al2O3 (13.2%), MgO (12.1%), and SiO2 (7.5%). Quantitative mineral phase analysis showed that the sample mineralogy was dominated by a chrome-rich spinel phase with an average chemical composition (in wt.%) of: Cr2O3—47.8; FeO—26.0; Al2O3—15.4; and MgO—11.0. Contaminant phases included siliceous minerals enstatite, anorthite-rich plagioclase (bytownite), Cr-rich diopside (containing 1–2 wt.% Cr2O3), and phlogopite mica. QEMSCAN analysis of sized fractions indicated that (a) most silicate gangue species were in the +850 μm fractions, (b) the chrome-rich spinel in all fractions was >80% liberated, and (c) the most common mineral association for chromite was with enstatite. Based on the results, upgrading test work demonstrated that stage crushing followed by wet gravity concentration produced a chemical–metallurgical-grade 'chromite' product containing >46% Cr2O3 and <1% SiO2. [ABSTRACT FROM AUTHOR]

Limestone calcined clay cement (LC3) has considerable potential for large-scale implementation. We investigated three selected kaolinitic clays at different locations in South Africa. LC3 mortars were compared to Portland cement mortar as control, particularly the hydration phase mineralogy/content, microstructure, compressive strength, and 3D void structure. The investigation indicated that similar pozzolanic oxide (SiO2 + Al2O3) could be obtained from calcined clay of varied kaolinite content. While kaolinite content improves the pozzolanic activity, consistency, and compressive strength of the mortar, the void refinement at the microscale depends on the degree of limestone filling/hydration. The hydration phase contents, microstructure, mineralogy, and porosity of the processed kaolinitic clays were determined to be adequate. However, it is noted that the intrinsic content of limestone (and gypsum) in commercially available Portland cement should be considered for equivalent clinker, limestone, and gypsum contents of 50%, 15%, and 5%, respectively. [ABSTRACT FROM AUTHOR]

• Mineral Liberation Analysis can readily determine rare earth-bearing mineral in particles and grains occurring coal ash. • Four rare earth-bearing minerals were determined, namely: monazite-REE, xenotime-REE, REE-cerium, and REE-silicate. • Understanding the detailed mineralogy of the rare-earth bearing minerals and/or mineral phases will guide the prediction of REE extraction method and efficiency. Critical raw materials, including rare earth elements (REE), are the cornerstone of modern technologies. Due to their unique properties, REE are in high demand, leading to the exploration and research of alternative sources. Coal combustion by-products, specifically coal ash, has been identified as a potential alternative source of REE, but more research is required. This study aimed to identify REE's occurring in power station and laboratory-derived coal ash. Results from Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and Mineral Liberation Analysis are presented herein, to gain insight into rare-earth-bearing minerals occurring in the ash samples. REEs were determined in both sets of ash samples at values higher than 600 parts per million (ppm) using ICP-MS. Critical REE occur in ranges from 203 to 406 ppm; uncritical REE from 179 to 256 ppm; and excessive REE ranging from 197 to 348 ppm in these samples. Laboratory-derived coal ash and power station-generated ash samples were prepared as polished blocks and coated for examination using a Mineral Liberation Analyser (MLA). A bright phase search mode was employed to detect rare earth-bearing mineral phases using the back-scattered electron detector (BSE).Energy dispersive spectroscopy (EDS) was used to determine elemental compositions in these phases. Four rare earth-bearing mineral phases were determined, namely: monazite-REE, xenotime-REE, Ce-REErium rich, and REE-silicate. The laboratory-derived ash samples had a greater proportion of liberated rare earth-bearing minerals, related to the lower proportion of aluminosilicate glassy phase, related to the low temperature ashing procedure. The detailed mineralogy provides insight into the design of REE extraction processes, targeting specific REE's hosted in the various minerals. This will be documented in a future paper. [ABSTRACT FROM AUTHOR]

Geological and geophysical models are essential for developing reliable mine designs and mineral processing flowsheets. For mineral resource assessment, mine planning, and mineral processing, a deeper understanding of the orebody's features, geology, mineralogy, and variability is required. We investigated the gold-bearing Black Reef Formation in the West Rand and Carletonville goldfields of South Africa using approaches that are components of a transitional framework toward fully digitized mining: (1) high-resolution 3D reflection seismic data to model the orebody; (2) petrography to characterize Au and associated ore constituents (e.g., pyrite); and (3) 3D micro-X-ray computed tomography (µCT) and machine learning to determine mineral association and composition. Reflection seismic reveals that the Black Reef Formation is a planar horizon that dips < 10° and has a well-preserved and uneven paleotopography. Several large-scale faults and dikes (most dipping between 65° and 90°) crosscut the Black Reef Formation. Petrography reveals that gold is commonly associated with pyrite, implying that µCT can be used to assess gold grades using pyrite as a proxy. Moreover, we demonstrate that machine learning can be used to discriminate between pyrite and gold based on physical characteristics. The approaches in this study are intended to supplement rather than replace traditional methodologies. In this study, we demonstrated that they permit novel integration of micro-scale observations into macro-scale modeling, thus permitting better orebody assessment for exploration, resource estimation, mining, and metallurgical purposes. We envision that such integrated approaches will become a key component of future geometallurgical frameworks. [ABSTRACT FROM AUTHOR]

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]

We studied diamond inclusions in the 133 Ma Lace kimberlite of the Kroonstad Group II kimberlite cluster (Kaapvaal craton) to compare them to diamonds beneath the adjacent coeval Voorspoed kimberlite. The studied 288 Lace diamonds are mostly colorless dodecahedral Type IaAB. Based on diamond inclusions (DI), 38 Lace diamonds were classified as eclogitic (44%, 19 samples), peridotitic (35%, 15 samples), and websteritic (9%, 4 samples). The diamonds formed from mantle carbon (δ13C = − 9.1 to − 2.5 ‰ for 18 samples), with the exception of one eclogitic diamond (δ13C = − 19.2 ‰). A rare zircon inclusion provides age constraints for the Lace eclogite protolith at 3.2 ± 0.4 Ga (Lu–Hf model age) and Lace eclogite diamond formation at 188 ± 37 Ma (U–Pb age). The eclogite protolith age suggests its formation contemporaneous with the lower crustal magmatism and metamorphism in the Central Kaapvaal craton, complementary to the tonalite–trondhjemite–granodiorite magmatism in the region and synchronous with the consolidation of the Eastern Kaapvaal Block. Two distinct kinds of eclogites are found to host Lace diamonds, (1) Fe-rich eclogites located at 160–190 km, and (2) more calcic–magnesian eclogites with mineral compositions identical to websteritic DIs, that derive from shallower lithospheric depths. Various thermobarometric methods applied to Lace diamonds and DIs constrain the Lace geotherm as reflecting a surface heat flow below or equal to 38 mW/m2 and a lithosphere thickness of at least 220 km, at the time of kimberlite eruption. These thermal parameters demonstrate an excellent match between the thermal state of the Voorspoed and Lace mantle segments that persisted from the Archean to Cretaceous times. The Lace peridotitic-to-eclogitic diamond ratio (5/4) does not differ much from the Voorspoed DI ratio (6/4), but a hot and spatially restricted carbonatitic metasomatism event affected the Voorspoed peridotitic mantle to create the majority of Voorspoed diamonds. The contrast in the mineralogy of DIs in Lace and Voorspoed diamonds highlights the very local (ca. 10 km) extent of the metasomatism and heating, as well as the variability of the diamond-forming processes at the same spatial scale. [ABSTRACT FROM AUTHOR]

This study aims to generate rock units based on core permeability and porosity of OW oilfield in the Bredasdorp Basin offshore South Africa. In this study, we identified and classified lithofacies based on sedimentology reports in conjunction with well logs. Lucia's petrophysical classification method is used to classify rocks into three classes. Results revealed three lithofacies as A (sandstone, coarse to medium-grained), B (fine to medium-grained sandstone), and C (carbonaceous claystone, finely laminated with siltstone). Lithofacies A is the best reservoir quality and corresponds to class 1, while lithofacies B and C correspond to class 2 and 3, which are good and poor reservoir quality rock, respectively. An integrated reservoir zonation for the rocks is based on four different zonation methods (Flow Zone indicator (FZI), Winland r35, Hydraulic conductivity (HC), and Stratigraphy modified Lorenz plot (SMLP)). Four flow zones Reservoir rock types (RRTs) were identified as RRT1, RRT3, RRT4, and RRT5, respectively. The RRT5 is the best reservoir quality composed of a megaporous rock unit, with an average FZI value between 5 and 10 µm, and HC from 40 to 120 mD/v3, ranked as very good. The most prolific flow units (RRT5 and RRT4 zones) form more than 75% of each well's flow capacities are supplied by two flow units (FU1 and FU3). The RRT1 is the most reduced rock quality composed of impervious and nanoporous rock. Quartz is the dominant framework grain, and siderite is the dominant cement that affects flow zones. This study has demonstrated a robust approach to delineate flow units in the OW oilfield. We have developed a useful regional petrophysical reservoir rock flow zonation model for clastic reservoir sediments. This study has produced, for the first time, insights into the petrophysical properties of the OW oilfield from the Bredasdorp Basin South Africa, based on integration of core and mineralogy data. A novel sandstone reservoir zonation classification criteria developed from this study can be applied to other datasets of sandstone reservoirs with confidence. [ABSTRACT FROM AUTHOR]

The trace element data pool for South African coals is limited. However, certain elements are reported as occurring in considerably higher concentrations than global average values. These elements include chromium (Cr), as well as manganese (Mn), cobalt (Co), and molybdenum (Mo), with Cr showing the most consistent enrichment. The aim of this study was to investigate the occurrence of Cr in South African coals sampled from five coalfields, and to assess the possible source of Cr. A total of 21 run-of-mine (ROM) coal samples from the Waterberg, Soutpansberg, Witbank, Highveld, and the Nongoma Coalfields were obtained from active mines. Coal characterization, mineralogy, and geochemical data were compiled. The Cr values for the Waterberg (23 to 28 ppm), Soutpansberg (4.7 to 43 ppm), Witbank (24 to 37 ppm), and Highveld (33 to 37 ppm) coal samples are higher than those for the Nongoma coals (1.2 to 2.5 ppm), and, in nearly every case, higher than the Clarke value for hard coals (17 ppm). Correlation coefficients, density fractionation, and selective leaching were used to infer (indirect) modes of occurrence. A dominant silicate (clay) affinity was determined with Cr, as well as an organic affinity in the ROM samples. The Nongoma coals, with illite and no kaolinite, have extremely low Cr values. The other samples are enriched in kaolinite and also have a high Cr content. Chromium values as high as 67 ppm were reported for 1.4 RD float fraction samples, indicating a positive correlation with organic matter. A Cr - silicate association was observed following selective leaching. These results imply multiple modes of occurrence of Cr in the South African samples, in agreement with studies conducted globally. Chromium in the South African coals could have originated from the Bushveld Complex (approximately two billion years old), the largest Cr reserve in South Africa, which predates coal formation (approximately 299 to 252 million years ago) and is proximal to the coalfields. The Cr, seemingly not associated with chromite, may have been redistributed in the peat swamps during peat deposition, accumulating in the sediments and organic material. The Nongoma Coalfield is the farthest distance from the possible Bushveld Complex Cr source, and these samples are depleted in Cr. [ABSTRACT FROM AUTHOR]

• Improved process mineralogy techniques is required for characterizing low-grade refractory gold ores. • Coupled approach by LA ICP-MS and an automated mineralogical technique fully characterize low-grade gold ores. • A case study on Witwatersrand tailings demonstrates practical applicability to the approach. • The approach gives information for optimization and remediation plans for the sustainable recovery of gold. Researchers have made notable progress in quantifying refractory components causing gold losses in traditional extraction methods. The potential for improving gold recoveries lies in targeted re-treatment of the 'invisible' gold fraction hosted within various ore minerals, even at low concentrations. This study presents a methodology for analysing the refractory components that cause gold losses in traditional extraction methods. The approach utilizes automated mineralogical techniques in conjunction with in-situ laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS) to characterize low-grade refractory ores and assess gold deportment. The methodology combines pre-concentration gravity separation, traditional chemical and mineral techniques, and LA ICP-MS to generate comprehensive datasets. To demonstrate the practical application of the methodology, a case study was conducted on historical tailings material from Witwatersrand's Evander Goldfield in South Africa. The case study aimed to determine the mineralogical distribution of gold that cannot be extracted through cyanidation. The results indicated that invisible gold is primarily hosted in pyrite (with an average concentration of 10.21 ppm representing 32 % of total gold), other sulphides (with an average concentration of 1.29 ppm representing 0.42 % of total gold), and oxides (with an average concentration of 0.50 ppm representing 1 % of total gold). The remaining gold is present in discrete fine cyanide amenable phases (with 28 % deportment) and silicate-hosted phases (with 39 % deportment). Environmental monitoring of the Witwatersrand tailings material revealed a net "acid-producing" nature, with high concentrations of heavy metals (such as As, Cu, Pb, Mn, Hg, and Ni) associated with sulphides (with over 78 % deportment). The deportment information obtained through this approach can optimize ore processing strategies and provide valuable insights for future remediation plans. By characterizing the refractory components causing gold losses and understanding the distribution of gold within the ore, this methodology offers the potential to enhance gold recovery and improve the efficiency of ore processing operations. [ABSTRACT FROM AUTHOR]

• Case study conducted on a Platreef ore – batch flotation testwork in combination with mineralogical characteristion were used as diagnostic tools. • Collector components evaluated – DTP or DTC in combination with SIBX. • Results highlighted that DTP versus DTC showed different affinities of mineral species, middlings particles and particle size. • This data can be utilised to tailor collectors based on ore mineralisation for various ores types as case studies highlighted. • Clearly demonstrating that one reagent type does not fit all flotation applications. Flotation is a complex physical chemical process in which flotation reagents play a vital role in valuable minerals recovery and concentrate grades. This study examines the performance of new generation AECI Mining Chemicals (previously named Senmin) collectors. They were developed to enhance the valuable minerals recovery and flotation selectivity by tailoring the collectors to target specific valuable mineral species present in an ore and thus create added value for concentrators treating PGM ores. The case study was conducted on a Platreef ore, where batch flotation tests were performed and the concentrates were mineralogically characterised for PGE and BMS using QEMSCAN. Further batch flotation testwork was conducted on Merensky and UG2 ores from various localities in South Africa to confirm the trends observed for Platreef ore. The results have shown that there is a strong correlation between PGE mineral type and AECI Mining Chemicals collector type. Clearly demonstrating that one reagent type does not fit all flotation applications. [ABSTRACT FROM AUTHOR]

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and electron microprobe analysis (EMPA) techniques were used to determine the mineralogy and chemistry of dominant sulphide and associated gold deposits at the Fairview Gold Mine of the Barberton Greenstone Belt (BGB). The rocks and ore mineral associations at the Fairview Mine indicate mesothermal (orogenic) conditions for the gold deposit. The whole rock chemistry of the Fairview Mine reflects calc-alkaline affinities, and felsic provenance is revealed by high SiO2, K2O, Al2O3, and TiO2, and low Fe2O3, MgO, Ni, and Cr contents. The mineral assemblages of the Fairview Mine rocks and ores indicate three phases of metamorphisms; regional prograde, thermal, and retrograde metamorphism, which caused zonation and heterogeneity of the ore minerals. The principal ore minerals in this deposit are pyrite, arsenopyrite, pyrrhotite, chalcopyrite, and rare sphalerite, as well as minor gold. The obtained results revealed that sulphides of the Fairview Mine are divided into two types (generations) varying in their morphology, association, and elemental composition. The old type 1 is porous, anhedral, heterogeneous, contains inclusions and rich in As, Ni, Co, and Au compared to type 2. Trace-element distribution and occurrence mode of gold at Fairview mine reflect two phases of gold mineralization. The first stage is associated with sulphides (mainly pyrite and arsenopyrite), whilst the second phase is free-lode hosted by silicates (mainly quartz). [ABSTRACT FROM AUTHOR]

The mineralogy of the ash and slag formed at typical UCG temperatures were investigated using a bituminous coal from the Theunissen UCG site in the Free State province of South Africa. The ash and slag samples were produced from the coal, and the surrounding roof and floor geological structures at 1000, 1100, 1200 and 1300°C. XRD results show an increase in crystalline phases, with a decrease in the amorphous content as the temperature increases, with mullite and quartz found to be the dominant minerals in the crystalline phase. FTIR spectroscopy results reveal the appearance of peaks related to the crystalline phase of mullite with increasing temperature. SEM results show the formation of spherical particles, with the appearance of cenospheres, as the temperature increases. The samples produced at 1000°C had significantly lower surface area and porosity values than the blended coal sample, but these values remain similar for the ash samples produced between 1000°C and 1300°C, where only slight decreases are observed with an increase in temperature. Results indicate that the higher the temperature in a UCG cavity, the less leaching of inorganic species should occur. [ABSTRACT FROM AUTHOR]

Gold production in South Africa is projected to continue its decline in future, and prospects for discovery of new high-grade deposits are limited. Many of the mining companies have resorted to mining and processing low-grade and complex gold ores. Such ores are technically challenging to process, which results in low recovery rates, excessive reagent consumption and high operating costs when compared to free-milling gold ores. In the Witwatersrand mines, options of blending low-grade gold ores with high-grade ores exist. Although it is well known that most of the Witwatersrand gold ores are highly amenable to gold cyanidation, not much is known on the leachability of blended ores, especially the effects of mineralogical and metallurgical variability between different gold ores. In this study, we apply a geometallurgical approach to investigate mineralogical and metallurgical factors that influence the leaching of blended ores in a set of bottle shaker and reactor column tests. Three gold-bearing conglomerate units, so-called reefs, i.e., Carbon Leader Reef, Ventersdorp Contact Reef and the Black Reef, all in the Carletonville goldfield, were sampled. The ores were prepared using a terminator jaw crusher followed by vertical spindle pulverizer (20 kg aliquot) and high-pressure grinding rolls (80 kg aliquot). Mineralogical analysis was conducted using a range of complementary tools such as optical microscopy, QEMSCAN and micro–XCT. The results show that Witwatersrand gold ores are amenable to the process of ore blending. Some of the ores, however, contain impervious inert gangue and reactive ore minerals. Leach solution can only access gold locked in impervious gangue minerals through HPGR-induced pores and/or cracks. The optimum ore blending ratio of the bottle shaker experiments (p80 = − 75 μm) comprises 60% Carbon Leader Reef, 20% Ventersdorp Contact Reef and 20% Black Reef and yields 92% recovered Au over a leach period of 40 h. Blended ores with high carbonaceous material (> 1 wt% carbonaceous material, (Black Reef = 36–60%) yield lower recoveries of 60–69% Au). Ore leaching at the mixed-bed reactor column (− 75 μm and − 5.6/+ 4 mm) yields about 70% over a leach period of two weeks. We therefore suggest that the feasibility of ore blending is strongly controlled by the mineralogy of the constituent ores and that a mixed-bed reactor may be a viable alternative method for leaching of the low-grade Witwatersrand gold ores. Material from certain reefs, such as the Black Reef, has synergistic/antagonistic (nonadditive) blending effects. The overall implication of this study is that ore blending ratios, effects of comminution on mineral liberation, an association of gold with other minerals, and gold adsorption behavior will greatly inform future technology choices in the area of geometallurgy. [ABSTRACT FROM AUTHOR]

• PGEs are a critical resource and usually not substitutable with other metals. • PGM flotation tailings represent a significant secondary resource. • Surface oxidation is one of the key causes of value minerals rejection to tailings. • Fine grinding in inert media provides opportunities to re-treat tailings. • Tailings grade of <0.5 g/t 4E is suspected not to be extractable by flotation. Flotation tailings from South Africa's platinum group minerals (PGM) represent complex polymetallic orebodies comprising a low-grade platinum group elements (PGE) content and complex mineralogical composition. Nevertheless, given the valuable mineral potential in the tailings, it is understandable that the substantial historic tailings deposits and sizeable annual production volume from primary processes represent a potential secondary resource. For several decades, valorising the PGM tailing materials received very little interest due to limitations associated with extractive metallurgical technology to achieve economically viable PGE extraction. The early 21st century saw the coming online of technologies, including but not limited to ultrafine grinding, suitable to meet challenges in primary metallurgical treatment processes to recover valuable minerals from ultrafine particle fractions, which could not otherwise be recovered. More so, such processes were critical in improving the liberation of partially liberated particles without compromising additional ultrafine generation. These technologies led to the development of re-treatment pilot tests and subsequent industrial re-treatment recovery processes. The current industrial re-treatment approach – via tertiary scavenging flotation circuits – renders profit in small increments up to 1 ∼ 2% additional recovery relative to the primary plant head grade. These small increments relate to about ∼12–30% PGE recovery of the feed grade to the re-treatment circuit, thereby enhancing the primary plant's overall economics as well as aiding the supply of critical metals to meet global demands. With a focus on South Africa, this review provides an overview of (a) the current and future drivers of the precious metals global demand; (b) proffers discussion on the PGM characteristic mineralogy and the metallurgical value chain; (c) relates the parent orebodies ("reefs") mineral characteristics to the inherent processed tailings; (d) estimates the economic potential these massive processed waste materials contain, (e) provides an overview of existing technologies that are industrially used in tailing re-treatment plants; and (f) outlines a comprehensive understanding of the nature of value minerals rejection to tailings. [ABSTRACT FROM AUTHOR]

Howiesons Poort (HP) sites, over the past decades, have provided exceptional access to anthropogenic remains that are enhancing our understanding of early modern human behaviour during the Middle Stone Age in southern Africa. Here, we analyse the technological and typological trends in the lithic record that form part of these behaviours, based on the HP sequence recently excavated at Klipdrift Shelter, located on the southern Cape coast of South Africa. This study contributes to enhance knowledge on the mechanisms of changes that occurred during the transition to the post-HP. Despite patterns of continuity observed, notably for core reduction methods, the seven successive lithic assemblages show significant changes in the typological characteristics and raw material selection but also in the relative importance of blade production over time. However, these changes are not necessarily synchronic and occur either as gradual processes or as abrupt technological shifts. Consequently, we cross-examine the association between the lithic phasing and other anthropogenic remains within the HP sequence at Klipdrift Shelter. We explore the implications of these patterns of changes in terms of cultural behaviours and population dynamics during the HP and we highlight the relationship between the different phases of the HP sequence at Klipdrift Shelter and those from other South African HP sites. [ABSTRACT FROM AUTHOR]

In the past few decades, a diverse array of research has emphasized the precocity of technically advanced and symbolic practices occurring during the southern African Middle Stone Age. However, uncertainties regarding the regional chrono-cultural framework constrain models and identification of the cultural and ecological mechanisms triggering the development of such early innovative behaviours. Here, we present new results and a refined chronology for the Pietersburg, a techno-complex initially defined in the late 1920’s, which has disappeared from the literature since the 1980’s. We base our revision of this techno-complex on ongoing excavations at Bushman Rock Shelter (BRS) in Limpopo Province, South Africa, where two Pietersburg phases (an upper phase called ‘21’ and a lower phase called ‘28’) are recognized. Our analysis focuses on the ‘28’ phase, characterized by a knapping strategy based on Levallois and semi-prismatic laminar reduction systems and typified by the presence of end-scrapers. Luminescence chronology provides two sets of ages for the upper and lower Pietersburg of BRS, dated respectively to 73±6ka and 75±6ka on quartz and to 91±10ka and 97±10ka on feldspar, firmly positioning this industry within MIS5. Comparisons with other published lithic assemblages show technological differences between the Pietersburg from BRS and other southern African MIS5 traditions, especially those from the Western and Eastern Cape. We argue that, at least for part of MIS5, human populations in South Africa were regionally differentiated, a process that most likely impacted the way groups were territorially and socially organized. Nonetheless, comparisons between MIS5 assemblages also indicate some typological similarities, suggesting some degree of connection between human groups, which shared similar innovations but manipulated them in different ways. We pay particular attention to the end-scrapers from BRS, which represent thus far the earliest documented wide adoption of such tool-type and provide further evidence for the innovative processes characterizing southern Africa from the MIS5 onwards. [ABSTRACT FROM AUTHOR]

Petrographic and mineralogical studies of samples of the Normal (or undisturbed) Merensky Reef from Frank Shaft No. 1 at Rustenburg Platinum Mine revealed the presence of a Pt-Fe-alloy, probably isoferroplatinum (58 vol.% of total precious metal minerals), arsenides (21 vol.%), bismuthotellurides (10 vol.%), electrum (9 vol.%) and platinum group element- (PGE-) sulfides and stannides (2 vol.%), associated predominantly with base-metal- and iron-sulfides. A Pt-Fe-alloy-dominated facies has been known for considerable time from potholes and discordant bodies and has been attributed to fluid activity with high fO₂ and low fS₂. Our petrographic results indicate that the normal thin reef has also undergone hydrothermal alteration. For the first time, the rare mineral troilite (stoichiometric FeS) was found as intergrowths with masses of Pt-Fe-alloy, together with Fe-rich pyrrhotite, secondary hydrous silicates, magnetite and calcite. The observed mineral assemblage and texture is interpreted as the product of partial desulfurization, caused by migrating S-undersaturated fluids, which led to the exsolution of Pt-Fe-alloy from pyrrhotite (Fex-1S) with the latter approaching a stoichiometric composition. Overall our new observations provide convincing support for the importance of metasomatism in the secondary modification of ore mineralogy and textures even in the undisturbed Merensky Reef. [ABSTRACT FROM AUTHOR]

Olivine phenocryst chemistry is a useful tracer of mantle source lithology as olivine is typically the first mineral to crystallize in a range of mafic to alkaline magma types and contains geochemical information about the primary parent magma composition. It is particularly useful in discriminating between pyroxenite (i.e.,recycled crustal component) and peridotite mantle source lithologies. Radiogenic isotope studies of HIMU basalts have shown the important role of a recycled crustal component in the source. However, olivine chemistry of HIMU basalts suggests a dominantly peridotitic mantle source with a subduction-derived metasomatic carbonate component. To further investigate how olivine chemistry can be used to understand the source of HIMU magmas, I present major and trace element data for olivine megacrysts related to the 89 Ma Cr-poor megacryst suite from the Monastery kimberlite (South Africa), which have previously been interpreted to crystallize at high P-T conditions of ~1400 °C and ~5 GPa from a magma sourced from a HIMU reservoir. Olivine megacrysts have high-Ni concentrations at a given Fo (forsterite) content, overlapping ocean island basalts (OIB) interpreted to have formed from pyroxenite-dominated sources but are distinct from typical olivine in HIMU basalts. However, they have low 100*Mn/Fe (0.8–1.1) and no correlation is observed between Ni and trace elements indicative of recycled components such as Co, Li, or Zn. The olivine megacryst chemistry is similar to that of aillikite olivine interpreted to be controlled by phlogopite in the source rather than pyroxenite. Comparison with olivine chemistry from orangeites/Group II kimberlites (sourced from phlogopite-rich mantle lithologies) supports a phlogopite controlon low 100*Mn/Fe in olivine. Further comparison with olivine phenocryst chemistry of HIMU melilitites (76–58 Ma) in southern Africa suggests a mineralogically heterogeneous HIMU reservoir formed by metasomatic modification of the lithospheric mantle in southern Africa. Thus, olivine megacryst chemistry supports interpretations for the recycled component of the HIMU reservoir as mineralogically complex metasomatic lithologies formed by the infiltration of subduction-derived melts into the base of the lithospheric mantle. In addition to carbonate-richHIMU mantle lithologies in southern Africa and worldwide, Monastery kimberlite olivine megacrysts and olivine in melilitites suggest that a phlogopite-richHIMU lithology is present in southern Africa. An important question arising from this study is in reconciling the homogenous isotopic ratios of HIMU basalts worldwide with an apparent heterogeneous lithological source indicated by olivine chemistry. [ABSTRACT FROM AUTHOR]

The Waterberg platinum deposit is an extraordinary example of a vein-type hydrothermal quartz-hematite-PGE (platinum-group element) mineralization. This study concentrates on the geochemical character of the ores and the platinum-group mineral (PGM) assemblage by application of reflected-light and scanning electron microscopy followed by electron probe microanalysis. The PGM-bearing quartz veins show multiple banding indicating numerous pulses of fluid infiltration. Mineralization was introduced contemporaneously with the earliest generation of vein quartz and hematite. High oxygen and low sulfur fugacities of the mineralizing fluids are indicated by hematite as the predominant opaque mineral and the lack of sulfides. The 'Waterberg type' mineralization is characterized by unique metal proportions, namely Pt>Pd>Au, interpreted as a fingerprint to the cradle of the metals, namely rocks and ores of the Bushveld Complex, or reflecting metal fractionation during ascent of an oxidized, evolving fluid. The PGM assemblage signifies three main depositional and alteration events. (1) Deposition of native Pt and Pt–Pd alloys (>90% of the PGM assemblage) and Pd–Sb–As compounds (Pt-rich isomertieite and mertieite II) from hydrothermal fluids. (2) Hydrothermal alteration of Pt by Cu-rich fluids and formation of Pt–Cu alloys and hongshiite [PtCu]. (3) Weathering/oxidation of the ores producing Pd/Pt-oxides/hydroxides. Platinum-group element transport was probably by chloride complexes in moderately acidic and strongly oxidizing fluids of relatively low salinity, and depositional temperatures were in the range 400–200°C. Alternatively, quartz and ore textures may hint to noble metal transport in a colloidal form and deposition as gels. The source of the PGE is probably in platiniferous rocks or ores of the Bushveld Complex which were leached by hydrothermal solutions. If so, further Waterberg-type deposits may be present, and a prime target area would be along the corridor of the Thabazimbi-Murchison-Lineament where geothermal springs are presently still active. [ABSTRACT FROM AUTHOR]

The mining industries in South Africa generates huge amounts of mine waste that includes tailings; waste rocks and spoils. The tailings materials are dumped in surface impoundments that turn to be sources of hazards to the environment and the surrounding communities. The main environmental hazards posed by these tailings facilities are associated with their chemical constituents. Exposure to chemical constituents can occur through windblown dust, erosion to surface water bodies, inhalation by human beings and animals and through bioaccumulation and bio magnification by plants. Numerous un-rehabilitated tailings dumps exist in Limpopo province of South Africa. The communities found around these mines are constantly exposed to the environmental hazards posed by these tailing facilities. Development of a cost-effective technology that can beneficially utilize these tailings can reduce the environmental hazards and benefit the communities. This paper presents the initial evaluation of the copper and gold mine tailings in Limpopo, South Africa with a view to assessing the suitability of conversion into beneficial geopolymeric materials. Copper tailings leachates had alkaline pH (7.34–8.49) while the gold tailings had acidic pH. XRD confirmed presence of aluminosilicate minerals. Geochemical fractionation indicates that majority of the major and trace species are present in residual fraction. A significant amount of Ca, Cu and K was available in the mobile fraction and is expected to be released on tailings contacting aqueous solutions. Results from XRF indicates the tailings are rich in SiO 2 , Al 2 O 3 and CaO which are the main ingredients in geopolymerization process. The SiO 2 /Al 2 O 3 ratios indicates the tailings would require blending with Al 2 O 3 rich feedstock for them to develop maximum strength. Moreover, the tailings have particle size in the range of fine sand which indicates potential application as aggregates in conventional brick manufacture. [ABSTRACT FROM AUTHOR]

Heat treatment was one of the first transformative technologies in the southern African Middle Stone Age (MSA), with many studies in the Cape coastal zone of South Africa identifying it as an essential step in the preparation of silcrete prior to its use in stone tool manufacture. To date, however, no studies have investigated whether heat treatment is necessary for all silcrete types, and how geographically widespread heat treatment was in the subcontinent. The aim of this study is to investigate experimentally whether heat treatment continued further north into the Kalahari Desert of Botswana and northernmost South Africa, the closest area with major silcrete outcrops to the Cape. For this we analyse the thermal transformations of silcrete from both regions, proposing a comprehensive model of the chemical, crystallographic and ‘water’-related processes taking place upon heat treatment. For the first time, we also explore the mobility of minor and trace elements during heat treatment and introduce a previously undescribed mechanism—steam leaching—causing depletion of a limited number of elements. The results of this comparative study reveal the Cape and Kalahari silcrete to respond fundamentally differently to heat treatment. While the former can be significantly improved by heat, the latter is deteriorated in terms of knapping quality. These findings have important implications for our understanding of the role of fire as a technical solution in MSA stone tool knapping, and for the extension of its use in southern Africa. Silcrete heat treatment—at least in the form we understand it today—may have been a strictly regional phenomenon, confined to a narrow zone along the west and south coast of the Cape. On the basis of our findings, silcrete heat treatment should not be added as a new trait on the list of behaviours that characterise the MSA of the southern African subcontinent. [ABSTRACT FROM AUTHOR]

[Display omitted] • The African continent hosts a large number of vanadium ore resources. • The most important V resources are associated with magnetite layers in layered mafic–ultramafic magmatic intrusions. • Economic potential can be found in: vanadate districts, V-bearing graphite bodies, V-bearing uranium deposits. • In historical vanadate district of Namibia and Zambia, re-processable old tailings and slags are widespread. As part of the critical metals group, vanadium is an essential commodity for the low- and zero-CO 2 energy generation, storage and transport. This contribution aims to carry out a review of the known vanadium ore sources and mineralizations located in Africa, which are highly diversified in their geological and mineralogical characteristics, and can be classified in: 1. Vanadiferous (titano)magnetite deposits; 2. Sandstone-hosted (U)-vanadium deposits; 3. Calcrete-hosted (U)-vanadium deposits; 4. Vanadate deposits; 5. Graphite-associated vanadium deposits; 6. Vanadium occurrences associated with laterite, bauxite, and phosphate ores. The economically most significant vanadium sources in Africa are associated with titanomagnetite layers in mafic–ultramafic layered magmatic intrusions (e.g., the Bushveld Complex in South Africa and the Great Dyke in Zimbabwe). Vanadium has been historically mined also in vanadate deposits deriving from the supergene alteration of Pb-Zn-Cu sulfide ores in Namibia and Zambia. Several areas in these countries, where potentially re-processable old tailings and slags have been accumulated, still have economic potential. Vanadium mineralizations are associated with graphite bodies in the Mozambique Metamorphic Belt. Vanadium is also enriched in uranium ores occurring in the Upper Paleozoic-Mesozoic Karoo continental sediments: typical examples are found in Botswana, South Africa, and Zimbabwe. Significant uranium-vanadium concentrations (where carnotite prevails) occur in relatively recent (Tertiary-Quaternary) calcrete duricrusts in paleo-fluviatile beds, which are widespread throughout the African continent. These derive from the weathering of U-(V)-fertile source rocks, which under favorable paleoclimatic conditions resulted in the vanadium precipitation in the critical zone. Variable vanadium amounts have been also recorded in iron ore deposits, phosphorites, and laterites, even though the phosphate deposits seem to have the most favorable characteristics for potentially economic vanadium concentrations. On the whole, South Africa holds the most significant vanadium ore resources globally. However, also many other African countries, where this metal could be profitably extracted as a by-product from other economic ores, will probably be at the forefront of vanadium production in the near future. [ABSTRACT FROM AUTHOR]

• Synchrotron µXRD resolved the microscale mineralogy in this manganiferous soil. • Manganese and Fe mineralogy change along the transect of redoximorphic concretions. • Calcium can stabilize Mn-oxides in acid soils by aggregation and structural changes. • Silica is important for Fe stability and nodule preservation. • Carbonate nodules are preserved in this acid soil and may form pedogenically. Manganese-oxides are one of nature's strongest sorbents and oxidants which often occur in trace amounts in soils as amorphous coatings and crusts. Thus, not much is known about their microscale mineralogy in soils and concretions. We collected soils enriched in pedogenic manganese-oxides and concretions from Graskop, South Africa to determine the mineralogy of naturally occurring manganese phases from soils with varying degrees of pedogenic alteration. Bulk X-ray diffraction (XRD) demonstrates the dominance of lithiophorite and the presence of todorokite in the less altered wad soil compared to the more pedogenically altered soils enriched in gibbsite and birnessite. The mineralogy inside concretions is elucidated with synchrotron µXRD paired with X-ray fluorescence (XRF). Synchrotron XRF mapping shows critical insight into the mechanisms stabilizing manganese and iron in these dolomite-derived yet acid soils. Manganese and calcium are found in consistent ratios in the solum and nodules, and calcium is important for manganese persistence and nodule aggregation/flocculation. Similarly, silicon and iron distribution are strongly correlated, and silica enhances iron stability by altering the crystalline structure and cementing mineral surfaces. The µXRD elucidates the mineralogical gradient across a concretion transect. With birnessite occurring in the outermost layer and todorokite, gibbsite, lithiophorite, and maghemite becoming more abundant in the concretion middle layers. µXRD also indicates mineral phases obscured in the bulk XRD like anatase and ramsdellite and minerals typically from metamorphic or hydrothermal origin including periclase, wüstite, manganosite, and spinel. These novel results quantify the mineralogy and nanoscale distribution of pedogenic manganese-oxides. [ABSTRACT FROM AUTHOR]

South African coastal lake sediments provide an excellent opportunity to investigate environmental changes such as sea level and climate variability during the Holocene period. In this study we present a sediment record from the coastal lake Groenvlei located in the southern Cape region which is part of South Africa's year-round rainfall zone. In order to improve the understanding of palaeoenvironmental changes in this region, we provide a high-resolution multi-proxy data set derived from geochemical, mineralogical, isotopic and granulometric analyses. The age-depth model is based on 14 C and 210 Pb dating and reveals a basal age of 4210 + 200 / − 120 cal BP. Differences in the mineralogical composition of deposited carbonates reflect changes in the past lake water chemistry, probably caused by variations in both sea level and climate. Compared to the present, mostly drier conditions and a greater marine influence due to a higher sea level are inferred for the period between 4210 and 2710 cal BP. However, the record also indicates the occurrence of short humid phases during this time, which were probably associated with heavy rainfall events. A transition layer was deposited between 2710 and 1210 cal BP, probably as a result of reworking of sediment. During this time, the lake passed through a major change finally turning into a freshwater system from at least 1210 cal BP until the present. Our data indicate that the marine influence on the lake decreased due to a lower sea level and climate became generally more humid after 1210 cal BP probably resulting in a greater lake-internal and -external bioproductivity. Based on a comparison with other palaeoenvironmental studies from South Africa, our record suggests a prevailing winter rainfall seasonality at the southern Cape coast between 4210 and 2710 cal BP and a stronger influence of summer rainfall from 1210 cal BP onwards. [ABSTRACT FROM AUTHOR]

Non marine clastic sediments from the Late Permian – Early Triassic Balfour Formation of the Karoo Supergroup were studied to infer the composition, provenance and influence of weathering conditions. Petrographic studies based on quantitative analysis of the detrital minerals reveal that these sediments (mainly sandstones) are mostly composed of quartz, feldspar and sedimentary and metamorphic rock fragments. There is no significant petrographic variation across the sandstone succession of the study. The sandstones are dominantly feldspathic litharenite and ultralithofeldspathic in composition indicating a metamorphic source area. Modal analysis data plot in the dissected and transitional arc block provenance fields of QmFLt (quartz-feldspar-lithic fragments) diagram suggesting an active margin and magmatic arc signature preserving a recycled provenance. [ABSTRACT FROM AUTHOR]

A study of five diamonds containing mineral and fluid inclusions, selected among forty-nine specimens from the Cullinan Mine, South Africa, was carried out to better document the origin and formation of N-absent B-poor (type IIb) diamonds. The combination of several in-situ non-destructive techniques was used to identify the mineralogy and the chemical composition of primary and secondary inclusions. These include breyite, larnite, graphite, Fe-Ni-Cu native metallic alloys, sulfides of the pyrrhotite group, Ni-rich oxide and potential hydrous ferric sulfates. A common and abundant hydrous fluid containing H 2 O + CH 4 was also identified. From the various observations, we suggest that these type IIb diamonds grew in an aqueous oxidized fluid reacting with a reduced mantle characterized by low oxygen fugacity. Remnant pressures recorded in primary breyite by Raman shifts and XRD measurements enabled the calculation of minimal entrapment pressures of inclusions using elastic geothermobarometry. Applying pressure corrections caused by elastic relaxation, minimum trapping pressures from 4.9 GPa to 5.6 GPa were calculated, suggesting lithospheric depths consistent with the occurrence of numerous graphite inclusions. The association of breyite and larnite, which is often considered as an indicator of sublithospheric origin, also occurs at pressures of 6 GPa or lower in a H 2 O-rich and carbonate/Ca-rich environment. The B-poor and N-absent features of type IIb diamonds do not require the classic subduction-related model of their formation. Whereas high-pressure minerals would host boron in cold subducting slabs, slabs are also important carriers of nitrogen into the deep mantle, with this latter element mostly absent in these diamonds. In our alternative model, the mantle is proposed as an alternative source of boron, whereby metallic alloys or N speciation between fluid and melt would still prevent the incorporation of nitrogen, leading to the expression of the blue, boron-related and N-absent features of type IIb diamonds. The observed mineralogical assemblage neither proves sublithospheric origin nor does it exclude lithospheric depths of formation for these diamonds. Hence, we propose that type IIb diamonds form in a mantle continuum, from sublithospheric to lithospheric depths. • N-free type IIb blue diamonds from Cullinan Mine studied for mineral/fluid inclusions. • A unique association of C graphite + H 2 O + CH 4 fluids and Fe Ni alloys has been found. • Minimum trapping pressures of 4.9–5.6 GPa from breyite suggest a lithospheric origin. • Type IIb grows at low f O 2 at any mantle depth in aqueous fluids ± metal alloys. • Metals prevent nitrogen trapping while boron might sourced from the mantle. [ABSTRACT FROM AUTHOR]

Archaeomalacological analysis is generally undertaken on recovered macro-remains to characterize the overall composition of faunal remains in a deposit. Given the susceptibility of shell middens to a variety of taphonomic processes, it is assumed that the prior presence of shell in deposits may therefore occasionally be missed. Deteriorated micro-remains can mix indistinguishably into surrounding sediments and make their analyses and identification difficult, particularly in older deposits and in environments that experience rapid rates of weathering. This paper explores whether microscopic remains of deteriorated molluscs can be distinguished from other microscopic remains at the coastal rock shelter site of Waterfall Bluff in Mpondoland, South Africa. The methodology uses a multi-scalar approach integrating shell mineralogy and microstructure using the taxonomic distinctiveness of these features. The diagnostic features (e.g., morphology, hinges, spires, and apertures) used for identifying macro-remains are absent in micro-remains, therefore unique methods of identification are needed to identify these microscopic mollusc fragments. Through mineralogical analyses and scanning electron microscope (SEM) imaging, the nacreous remains of Mytilidae shell were identified from previously unidentified degraded shell remains as well as sediment samples from Waterfall Bluff. These methods thus recovered 'invisible' evidence of shellfish remains providing further evidence of continued coastal foraging from Marine Isotope Stage 3 to the early Holocene (ca or ⁓ 40 ka to 10 ka) on the south-eastern African coast. • Multi-scalar approach integrating shell mineralogy and microstructure to taxonomically identify micro-shell remains. • Highly fragmented and degraded shell remains at WB due to acid dissolution from drip water under the dripline. • Nacre tablets identified by Scanning Electron Microscopy in an aggregate with no macro shell evidence. • Ostreidae and Mytilidae mollusc shell microstructure and composition examined. [ABSTRACT FROM AUTHOR]

Petrological and mineralogical features are key for inferring palaeoenvironmental and sedimentary conditions of coal-bearing sediments. Following the logging of a borehole core, this study reports on the organic petrology and mineralogy of the A and B Seams, Ermelo Coalfield, Main Karoo Basin (MKB), South Africa. Seventeen coal samples collected from the core, differentiated based on changes in lithotypes, were assessed using detailed petrography (macerals, microlithotypes, and mean random vitrinite reflectance), quality analyses (proximate, elemental, and gross calorific value), and mineralogy in order to deduce depositional environments for the Ermelo coals. The lithologies present in the core were typical of the MKB, and the coals were inertinite- and mineral matter-rich, apart from samples occurring at the base of the seams. The latter samples also had a higher proportion of structured inertinite macerals (fusinite and semifusinite) and lower ash yields. The rest of the samples had higher inertodetrinite contents, occurring in association with detrital quartz and kaolinite, resulting in higher ash yields. The formation of each coal seam thus commenced with the prevailing conditions conducive to the preservation of structured macerals and concluded with the accumulation of predominantly inertodetrinite. Select samples from the B Seam also had durite, an association of inertodetrinite and liptinite (including alginite). The co-occurrence of inertodetrinite and the detrital minerals alongside alginite suggests two depositional episodes. The first episode relates to the formation of primary inertinite macerals through charring, followed by fragmentation and redeposition as inertodetrinite. This latter process likely also reflects seasonal flooding, resulting in fluctuating water levels within the palaeomire. The second episode was quieter, occurring in deeper waters, and conducive for the growth of algae. An allochthonous origin is thus proposed for inertodetrinite and the associated detrital minerals, whereas alginite deposition was autochthonous. The cyclical upward-fining and upward-coarsening facies of the MKB were observed in the core, indicative of fluvial and deltaic palaeoenvironments, respectively. The fluvial facies were generally associated with the occurrence of structured vitrinite and inertinite macerals, suggesting in-situ formation, and mostly occur at the base of the coal seams. In contrast, the inertodetrinite-rich samples appear to be related to the overlying deltaic deposits. • An Ermelo core intersecting the A and B Seams is described. • Inertinite is common in the coals, though vitrinite is higher at the base of the seams. • In some B Seam samples, alginite occurs with inertodetrinite reflecting autochthonous and allochthonous deposition. • Structured macerals are associated with fluvial facies and inertodetrinite with deltaic facies. [ABSTRACT FROM AUTHOR]

Erratum to: Contrib Mineral Petrol (2017) 172:72 DOI 10.1007/s00410-017-1390-9. [ABSTRACT FROM AUTHOR]

An unusual oxide body, enriched in Ni and the platinum-group elements, was found in the north-western part of the Barberton greenstone belt, South Africa, in the 1920s. With mineralogy and geochemistry which are extremely anomalous, and do not conform to that of any other Ni-rich crustal rocks, it has been interpreted as either an Archaean paleo-meteorite or of terrestrial deep-mantle origin. Cr isotopic ratios were used to evaluate the merits of these two possibilities. Isotopic analyses returned values for ε(53) of 0.00 epsilon units, within a 2 s error, relative to a terrestrial standard. We interpret this information, together with trace element data from the surrounding peridotites, as pointing to a terrestrial origin for the body, and conclude that the current dataset is not inconsistent with a deep-mantle origin, as a remnant of core formation, with subsequent transport to and emplacement in the lithosphere by a mantle plume. [ABSTRACT FROM AUTHOR]

Abstract: Paleosol–sediment sequences at the West Coast Fossil Park in Langebaanweg, South Africa have a stratigraphy extending over ten units occupying a total depth of 18m ranging in age from Mid-Miocene to Holocene. Six of these units qualify as paleosols. The mineralogical assemblages and micromorphology of the paleosols and pedofacies have been studied with the objective of interpreting and reconstructing the paleoenvironments of the area. Physico-chemical parameters, mineralogical properties and micromorphology (described from thin sections) of the paleosols and pedofacies were analyzed using routine laboratory methods. The units are named following the FAO and Soil Survey Staff classification systems. An alternating stack of paleosols and sediments preserve repeated phases of paleoenvironmental changes. Rhizoliths in the Pleistocene Ck layer lend credence to a shallow standing paleowatertable during the Pliocene. Remarkable differences are observed in the mineralogy of the paleosols and sediments. Paleosols of the Middle Miocene have mixed clay mineralogy of halloysite, chlorite, muscovite mica, and kaolinite — an indication that the clay sources could have either formed pedogenically or from different parent materials which may have taken place during transportation. Allophane and imogolite in the Early Pliocene paleosols are most likely to be stream-deposited while palygorskite and sepiolite indicate dry paleoclimates. Vertic properties of the paleosols were observed from their open porphyric c/f-related distribution, blocky microstructure and striated b-fabrics. Properties including calcareousness, vertic, gleyic, illuviation suggest cyclic patterns of erosion and deposition, which correlates with paleoenvironmental and climatic changes. The observed pedofeatures indicate the reddish Mid-Miocene paleosols and Pliocene pedogenic carbonates possibly formed under subtropical and Mediterranean climate conditions, while the pedosediments reflect a (semi) arid climate. [Copyright &y& Elsevier]

Highlights: [•] Good conversion from leachate to carbonates for Ca (96%), Mg (59%) and Fe (98%). [•] Low overall conversion to carbonates for Ca (30%), Mg (3%) and Fe (9%). [•] Low extraction of Mg (5%) and Fe (9%) during dissolution stage. [•] Plagioclase and clinopyroxene are main reacting minerals. [•] Mineralogy of PGM tailings suitable for mineral carbonation. [ABSTRACT FROM AUTHOR]

Abstract: This study presents an integrated mineralogical–geochemical database on fine-grained sediments transported by all major rivers of southern Africa, including the Zambezi, Okavango, Limpopo, Olifants, Orange and Kunene. Clay mineralogy, bulk geochemistry, Sr and Nd isotopic signatures of river mud, considered a proxy of suspended load, are used to investigate the influence of source-rock lithology and weathering intensity on the composition of clay and silt produced in subequatorial to subtropical latitudes. Depletion in mobile alkali and alkaline-earth metals, minor in arid Namibia, is strong in the Okavango, Kwando and Upper Zambezi catchments, where recycling is also extensive. Element removal is most significant for Na, and to a lesser extent for Sr. Depletion in K, Ca and other elements, negligible in Namibia, is moderate elsewhere. The most widespread clay minerals are smectite, dominant in muds derived from Karoo or Etendeka flood basalts, or illite and chlorite, dominant in muds derived from metasedimentary rocks of the Damara Orogen or Zimbabwe Craton. Kaolinite represents 30–40% of clay minerals only in Okavango and Upper Zambezi sediments sourced in humid subequatorial Angola and Zambia. After subtracting the effects of recycling and of local accumulation of authigenic carbonates in soils, the regional distribution of clay minerals and chemical indices consistently reflect weathering intensity primarily controlled by climate. Bulk geochemistry identifies most clearly volcaniclastic sediments and mafic sources in general, but cannot discriminate the other sources of detritus in detail. Instead, Sr and Nd isotopic fingerprints are insensitive to weathering, and thus mirror faithfully the tectonic structure of the southern African continent. Isotopic tools thus represent a much firmer basis than bulk geochemistry or clay mineralogy in the provenance study of mudrocks. [Copyright &y& Elsevier]

Highlights: [•] Copper slag dumps at Okiep in South Africa total ∼5million metric tons. [•] All economic metals are associated with discrete spheroidal prills. [•] Variable prill size suggests grinding to −45μm will improve the historic poor copper recovery. [•] Recovery of metals from slags can assist environmental rehabilitation of dumps world wide. [ABSTRACT FROM AUTHOR]

Highlights: [•] Rheologically complex behaviour of ore slurries at high vol.% solids. [•] Rheologically complex behaviour attributed to particle size and mineralogy. [•] Phyllosilicate minerals (talc and serpentine) responsible for complex behaviour. [•] Great Dyke ore more rheologically complex than UG2 platinum ore. [Copyright &y& Elsevier]

Abstract: The Kalahari Manganese Deposit (KMD) is the largest land-based manganese deposit, hosting approximately 80% of the world''s known, mineable manganese resources. The deposit, located near Kuruman in the Northern Cape Province of South Africa, is one of five erosional relics of the Paleoproterozoic (ca. 2.2Ga) Hotazel Formation, with sedimentary manganese ores occurring as up to 50m thick beds interbedded with banded iron-formation (BIF) and hematite lutite. The study focuses on the manganese ores of the Nchwaning–Gloria mining area of the northern KMD. In this area, pronounced mineralogical and major element alteration was imparted on the sedimentary manganese ores by a structurally-controlled hydrothermal fluid flow event. Most notable effects of hydrothermal alteration are the decomposition and leaching of Ca- and Mg-carbonate, and marked residual enrichment of manganese. On the basis of mineral assemblage, grade, texture and geochemical characteristics, three ore types were distinguished in the studied sample set, classified into least altered (LA), partially altered (PA) and advanced altered (AA) types. Advanced altered ores may be further classified into five different types, based on mineral assemblages that contain hausmannite and/or braunite as significant minerals. The rare earth element (REE) geochemistry of these fundamental ore types was studied in detail, to document REE mobility during hydrothermal alteration. Total REE concentrations in LA ores were found to be very low (14–22ppm) and remarkably uniform, within the range typically observed for BIF. Hydrothermal alteration results in residual enrichment and a much larger scatter in REE contents. A small Ce anomaly observed in the protolith remains similar in magnitude when observed in PAAS-normalised REE plots. The data define, however, a power trend in the (Ce/Ce*) vs (Pr/Pr*) diagram. Such behaviour is interpreted in terms of a conservative system that was predominantly protolith-buffered. Local remobilisation of REE during hydrothermal alteration is attributed to the dissolution of diagenetic apatite and redistribution of hydrothermal trace minerals, including neoformed apatite, monazite and cerianite. [Copyright &y& Elsevier]

The mineralogy of the platinum-group elements (PGE), and gold, in the Platreef of the Bushveld Complex, was investigated using an FEI Mineral Liberation Analyser. Polished sections were prepared from 171 samples collected from two boreholes, for the in-situ examination of platinum group minerals (PGM). PGM and gold minerals encountered include maslovite (PtBiTe, 32 area% of total PGM), kotulskite (Pd(BiTe), 17 %), isoferroplatinum (PtFe, 15 %), sperrylite (PtAs, 11 %), cooperite (PtS, 5 %), moncheite (PtTe; 5 %), electrum (AuAg; 5 %), michenerite (PdBiTe; 3 %), Pd alloys (Pd, Sb, Sn; 3 %), hollingworthite ((Rh,Pt)AsS; 2 %), as well as minor (all <1 area% of total PGM) merenskyite (PdBiTe), laurite (RuS), rustenburgite (PtPdSn), froodite (PdBi), atokite (PdPtSn), stumpflite (PtSb), plumbopalladinite (PdPb), and zvyagintsevite (PdPb). An observed association of all PGM with base metal sulfides (BMS), and a pronounced association of PGE tellurides, arsenides and Pd&Pt alloys with secondary silicates, is consistent with the remobilisation and recrystallisation of some of the PGM's during hydrothermal alteration and serpentinisation subsequent to their initial (primary) crystallisation from BMS (e.g. Godel et al. J Petrol 48:1569-1604, ; Hutchinson and McDonald Appl Earth Sci (Trans Inst Min Metall B) 114:B208-224, ). [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 central Vredefort Impact Structure is characterised by impact melt rocks, known as the Vredefort Granophyre dikes, the mode of emplacement of which is not well known. Whole-rock and petrographic analyses of two dikes were conducted and compared to published geochemical data to elucidate the mode and timing of dike formation. The dikes are characterised by compositional and textural heterogeneity between, and within, individual dikes. Specifically, central dike portions are felsic and rich in wall rock fragments, whereas marginal dike phases are more mafic and fragment-poor. Collectively, this suggests that melt was derived from compositionally different parental melts and emplaced in at least two pulses. In addition, the chemical heterogeneity between fragment-rich and fragment-poor dike zones can be explained by variable assimilation of a mafic component, notably Ventersdorp basalt, at the base of the impact melt sheet, from which melt of the Granophyre dikes is derived. This scenario accounts for the mafic and fragment-poor character of melt emplaced first in the dikes and the more felsic and fragment-rich nature of melts of the following emplacement pulse, i.e., when the impact melt was less hot and thus less capable of digesting large quantities of (mafic) wall rock fragments. Differences in geometrical, textural, chemical and fragment characteristics between the Granophyre dikes and pseudotachylite bodies can be explained by the same process, i.e., impact melt drainage, but operating at different times after impact. [Copyright &y& Elsevier]

This article reports a study of chromitites from the LG-1 to the UG-2/3 from the Bushveld Complex. Chromite from massive chromitite follows two compositional trends on the basis of cation ratios: trend A-decreasing Mg/(Mg + Fe) with increasing Cr/(Cr + Al); trend B-decreasing Mg/(Mg + Fe) with decreasing Cr/(Cr + Al). The chromitites are divided into five stages on the basis of which trend they follow and the data of Eales et al. (Chemical Geology 88:261-278, ) on the behaviour of the Mg/Fe ratio of the pyroxene and whole rock Sr isotope composition of the environment in which they occur. Following Eales et al. (Chemical Geology 88:261-278, ), the different characteristics of the stages are attributed to the rate at which new magma entered the chamber and the effect of this on aAlO and, in the case of stage 5, the appearance of cumulus plagioclase buffering the aAlO. The similarity of PGE profiles across the MG-3 and MG-4 chromitites that are separated laterally by up to 300 km and the variation in V in the UG-2 argue that the chromitites have largely developed in situ. Modelling using the programme MELTS shows that increase in pressure, mixing of primitive and fractionated magma, felsic contamination of primitive magma or addition of HO do not promote crystallization of spinel before orthopyroxene (in general they hinder it) and that the CrO content of the magma was of the order of 0.25 wt.%. Less than 20% of the chromite in the magma is removed before orthopyroxene joins chromite, which implies a >13-km thickness of magma for the Critical Zone. It is suggested that the large excess of magma has escaped up marginal structures such as the Platreef. The PGE profile of chromitites depends on whether sulphide accumulated or not along with chromite. Modelling shows that contamination of Critical Zone magma with a felsic melt will induce sulphide immiscibility, although not chromite precipitation. The LG-1 to LG-4 chromitites developed without sulphide, whilst those from the LG-5 upwards had associated liquid sulphide. Much of the sulphide originally in the LG-5 and above has been destroyed as a result of reaction with the chromite. [ABSTRACT FROM AUTHOR]

Abstract: Spherules in the S3 bed of the Barberton greenstone belt, South Africa are distal fallout formed within an impact plume after a large impact event at 3.24Ga. Since that time, diagenesis and lower greenschist grade metamorphism of the spherules has changed the mineralogy, though shape and texture are largely preserved. Alteration of the S3 bed has resulted in spherules composed of quartz, phyllosilicates, Ti- and Fe-oxides, and some Ni-rich chromites. Initially, glassy spherules were palagonitized and silica cementation of the spherules began during low-temperature interaction with seawater. Further alteration by Si- and K-rich fluids resulted in a mineralogical assemblage of quartz, feldspar, and clays. Crystalline minerals were replaced by dissolution-precipitation processes, preserving relict textures. Further silica cementation resulted in complete lithification of the bed. Most of this alteration occurred at the seafloor and during shallow burial. With continued burial, amorphous silica recrystallized to microcrystalline quartz. Later recrystallization of clays to micas occurred during regional metamorphism at peak temperatures of 300–320°C. Late-stage shearing and mineralization preferentially affected the northern region of the belt. Samples from different sections record highly variable local conditions. Water depth, the amount of pre-depositional transport, location within the belt, and proximity to igneous dikes all affect the diagenesis of the S3 spherules. Silica and barite concentrations are lower, and carbonate concentrations are higher in the deep-water depositional environments. Element mobility during diagenetic and lower greenschist grade metamorphism can be inferred based on studies of multiple sections throughout the BGB. The most immobile elements are Al, Zr, Ti, Sc and the high field strength elements and present element ratios can be used to infer original composition of the spherules. The large ion lithophile elements are highly mobile, as are the light rare earth elements (REEs), which are particularly susceptible to mobilization during carbonate diagenesis and phosphate authigenesis. Of the REEs, Ce and Eu show the largest variability, suggesting significant mobilization during diagenesis and low-grade metamorphism. Consistent Cr/Ir ratios, particularly in the high concentrations suggest limited mobility, and segregation of platinum group elements into Ni-rich chromite-bearing spherules. Sulfide mineralization has not affected the Ir concentration in the S3 layer. [Copyright &y& Elsevier]

A study of kite Paleozoic Witteberg Group rocks (Cape Supergroup) near Kirkwood, Eastern Cape was carried out to determine the viability of extracting silica for solar cell production. Mineralogical, geochemical and structural analyses of selected outcrops of quartz-arenites showed that source rocks in the study area do not possess the appropriate chemical attributes to warrant extraction of silica. Despite this finding the study presents valuable information on strata composition and structural data which are compared and interpreted with known regional structural patterns of the Cape Fold Belt in the Eastern Cape. Samples from the Witpoort Formation were analyzed using petrographic light microscopy, scanning electron microscopy and X-ray fluorescent spectroscopy. Analyses indicate that samples are composed almost entirely of quartz, with accessory biotite, muscovite, sericite, baryte, apatite, rutile and, monazite. Haematite occurs most frequently along fractures, and is more prevalent in the Rooirand Member than the Perdepoort Member, giving the former a reddish brown colour on outcrop. The presence of chemical impurities is thought to be partly controlled by the original depositional environment, namely, near-shore and beach environments. Strata in the study area display a range of fold styles, mostly showing northward vergence. Low angle thrust faults dip south and some thrusts clip north. In general, the orientation of fore-thrusts and folds in the study area indicate a northward-directed compression event during the Late Palaeozoic. This pattern conforms to the structural development in other parts of the Cape Fold Belt in the Eastern Cape. South-dipping normal faults and strike-slip faults post-date thrust faulting, and formed during the breakup of Gondwana, during the Mesozoic, transecting all other structures in the study area. [ABSTRACT FROM AUTHOR]

Abstract: Hypotheses proposed to explain the origin of pseudotachylite bodies formed during impact cratering include: (1) frictional heating, (2) shock loading, (3) decompression or (4) drainage of impact melt into target rocks. In order to differentiate among these processes, we conducted detailed geochemical and petrographic analysis of the matrices in pseudotachylitic veins and dikes and of their respective wall rocks. Our analyses indicate that the chemical compositions of matrices locally deviate significantly from their immediate wall rocks and that assimilation of wall rock has substantially modified the pseudotachylite matrix compositions in places. Variable magnitudes of assimilation can be explained by the surface area of wall rock or its fragments in contact with melt, as well as the initial temperature and cooling rate of the pseudotachylitic melt. Chemical trends observed can be explained either by admixture of an exotic melt component with immediate wall rock or by mixing of melts derived from local lithologies. Trends in the compositional deviation of centimetre to metre-wide pseudotachylite dikes from their immediate wall rocks are consistent with the presence of a primary melt component having granitoid composition akin to the average composition of Vredefort Granophyre dikes. Within veins, melt transport can be geochemically and petrographically traced for distances of centimetres to metres, with the direction of melt transport from larger pseudotachylite veins toward smaller ones and into apophyses. Sulphide and silicate mineralogy indicates that the initial temperature of pseudotachylitic melt must have been at least 1200–1700°C. Collectively, these characteristics point to an allochthonous origin of pseudotachylitic melt. We advocate the possibility that impact melt from the initially superheated impact melt sheet contributed to the formation of pseudotachylite bodies at Vredefort. [Copyright &y& Elsevier]

Abstract: The Gamsberg zinc deposit, located in the Northern Cape Province, represents South Africa’s greatest and most important unexploited base metal resource. Yet, in spite of its size, the low zinc grade combined with the high manganese content of the sphalerite continues to prohibit development of the deposit, as the high manganese content makes the zinc concentrates unsuitable for processing by conventional smelting methods, i.e. roasting, leaching/solvent extraction and/or electrowinning. Although numerous published investigations of the Gamsberg deposit have been undertaken, few have focused on the correlation between petrography and mineral chemistry of sphalerite and their implications on mineral processing. In accordance, the aims of this investigation are to highlight the importance of conducting a detailed geometallurgical investigation, as well as provide some new constraints on the metallurgical behavior of sphalerite and zinc concentrates from the Gamsberg deposit. Detailed analysis of sphalerite by petrographic and various microanalytical techniques reveal a marked absence of correlation between crystal morphology and mineral chemistry, necessitating a chemically based classification scheme. As such, six sphalerite populations where identified. They are: zinc-, cobalt-, iron- and manganese-rich, as well as manganese-enriched and manganese-poor. The zinc- and cobalt-rich populations display high zinc contents and low concentrations of iron and manganese, while the iron-rich population displays higher iron contents. Dominating the sphalerites of the mineralized pelitic schist is the manganese-enriched population. Of volumetrically lesser importance are the manganese-poor and -rich populations. The manganese-rich population contains high levels of iron, manganese, cobalt and cadmium relative to the zinc-rich population. In contrast, the manganese-poor population displays similar concentrations of cobalt and cadmium to the zinc-rich population, with iron and manganese intermediate between the zinc- and iron-rich populations. Comparisons between the sphalerite populations and milling size fractions reveal a consistent correlation between sphalerite mineral chemistry and size fractions with the coarser-grained concentrates being economically less favorable compared to the finer-grained concentrates, which display higher zinc contents. Combined with other lines of evidence, this suggests that the sphalerites of mineralized pelitic schist exhibit extensive solid solution that will have an effect on process optimization. For instance, it suggests that milling to a finer grain size will not remove or reduce the iron and manganese content. Another concern to processing will be the variable mineral chemistry of sphalerite, which might cause some sphalerites to display a delayed response during flotation or misreport to the lead concentrate. In spite of this, using solvent extraction, the elevated manganese content of the concentrates could be controlled, while simultaneously recovering zinc and manganese for sale. Hence, the recovery of manganese metal as a by-product could potentially enhance the economics of the deposit. Alternatively, other forms of mineral processing and metal extraction must be evaluated to meet the target grades and recoveries. [Copyright &y& Elsevier]

Abstract: The Mkuze Wetland System, forming part of the iSimangaliso World Heritage Site, is South Africa’s largest freshwater wetland area and is known to act as a sink for naturally occurring solutes within the landscape. The chemistry of groundwater and porewater samples, collected from two transects on the Mkuze River floodplain, was investigated to identify processes involved in the control of solute concentrations. Results show that solutes in the groundwater become increasingly concentrated under the influence of evapotranspiration, resulting in the saturation, precipitation, and accumulation of less soluble compounds. Trends in porewater chemistry and calculated saturation indices support previously documented mineralogical and sediment geochemical investigations, with CaCO3 and silica precipitation, and Fe-rich smectite neoformation identified as the major controls on solute concentration. The association of these mineral phases with zones of high salinity suggests that mineral precipitation is an active process on the floodplain which results in the progressive development of salinity, particularly in areas dominated by deep-rooted trees. Similarities between geochemical processes documented in the Okavango Delta (Botswana) and those identified in this study suggest that evapotranspiration-induced chemical sedimentation is an important process in southern African wetlands, which has the potential to influence vegetation distribution, hydrological flows, and local topography. [Copyright &y& Elsevier]