Department of Earth Sciences
Permanent URI for this community
Browse
Browsing Department of Earth Sciences by browse.metadata.advisor "Becker, Megan"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
- ItemDeveloping protocols for XCT scanning of dense mineral ore samples with applications to geology and minerals processing(Stellenbosch : Stellenbosch University, 2020-04) Bam, Lunga C.; Miller, Jodie A.; Becker, Megan; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.ENGLISH ABSTRACT: X-ray computed tomography (XCT) is a non-destructive technique capable of producing 3Dmineralogical and textural information from drill cores. The discrimination between mineralogical information of the drill cores was optimised by using the developed linear attenuation coefficient data bank that can automatically provide linear attenuation coefficient information. The discrimination between the minerals was further optimised by using the determined optimal scanning parameters. XCT technique is most effective when scanning low density samples or minerals with low linear attenuation coefficients. However, when scanning high density samples, the technique suffers from the lack of X-ray penetration which results in beam hardening. Beam hardening affects the true representation of mineralogical and textural information and this leads to the misrepresentation of the mineralogical and textural information. Beam hardening is not easily quantifiable because its impact on the sample information is not uniform and can result in a loss of sample information. To address this, it was proposed to use an aluminium standard when scanning high density samples which acted as a standard in order to quantify the degree of beam hardening in each slice of the sample volume. The aluminium standard sample not only quantified the degree of beam hardening but also determined the optimal sample size for scanning where no sample information is lost. The optimal sample size for scanning was determined to be 4mm when scanning samples with SG > 3. Even though the impact of beam hardening was minimised when using the optimal sample size the degree of beam hardening still affected the discrimination between minerals. This lead to the development of a simplified dual energy method in order to optimise the discrimination between minerals that are affected by beam hardening and result in high levels of noise within the images. The developed simplified dual energy method uses a combination of scanned volume data volume together with the simulated image. This combination has an advantage over the traditional dual energy method that uses two scanned volume data which is more time consuming. The simplified dual energy method effectively discriminated mineralogical information with no artefacts as compared to the traditional dual energy method which result in edge artefacts. The utilisation of the aluminium standard and the simplified dual energy method resulted in the reliable quantification of porosity information and 3D chalcopyrite grain size distribution (GSD). The quantified porosity information was largely in agreement with QEMSCAN results which show the importance of using the aluminium standard when scanning high density ore samples. The quantified 3D chalcopyrite GSD had a similar trend to the 2D QEMSCAN data but with coarser GSD as expected. This shows the effectiveness of the developed simplified dual energy method to optimise the discrimination of chalcopyrite in dense ore mineral samples. The reliable quantification of porosity and chalcopyrite information is important in minerals processing. Porosity is a component of texture and it is of relevance to physical processing where chalcopyrite is important in terms of inherent rock strength, its breakage, liberation properties and establishing geometallurgical units. The reliable quantification of the textural information using XCT shows that the technique can be adopted and adapted to any ore type with even more complex textures or mineralogies.
- ItemEvaluating the application and limitations of element to mineral conversion to predict modal mineralogy: the development of a framework for its application(Stellenbosch : Stellenbosch University, 2021-12) Cupido, Ivana; Miller, Jodie A.; Becker, Megan; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.ENGLISH ABSTRACT: The quantification of modal mineralogy has become increasingly important in the modern mining industry due to active mines being forced into mining lower-grade and mineralogically more complex parts of existing ore deposits. The value of a deposit not only depends on the overall grade of the valuable metals, but also on the proportions of its minerals. Since different minerals show different processing behaviour, the modal mineralogy of a deposit governs the liberation, extraction and concentration of the valuable metals. Advances in automated mineralogy technologies such as QEMSCAN has provided a faster and more statistically reliable approach for ore characterization than previous techniques of optical microscopy and point counting. However, automated techniques often require extensive sample preparation, is expensive and time consuming and thus is often only applicable in later stages of a mining project. There exists a need for a technique to determine modal mineralogy that is relatively fast, cost effective and statistically reliable. In this study, element-to-mineral conversion (EMC) has been proposed as an alternative. To apply the EMC approach, the bulk rock chemistry and mineral chemistry of a deposit is required, two measurements performed in the early stages of a mining project. Thus, EMC may provide mineralogical information at the early stages of a mining project where this was previously not possible. Despite being a known technique for decades, it is underused and very rarely applied in the mining industry. The lack of its application may be founded on the absence of a framework for its application in the current literature. In this study, a framework has been developed to guide the decision- making process when applying the EMC approach for modal mineralogy quantification. This framework has been developed through the study and application of the EMC approach to eight different deposits, as sourced from the literature. Where the devised framework was applied and the routine design was optimized, an improvement in the modal mineralogy results and residual elements was observed. From the data compiled from routines developed by the framework, 85.20 % of the data showed a percentage difference of ≤ 30% and a correlation coefficient of ≥ 0.85, compared to 63.07 % for routines where the framework was not applied or only partly applied.
- ItemA geometallurgical study of the quartz dominant ore varieties in a polymetallic base metal sulphide deposit, Northern Cape, South Africa(Stellenbosch : Stellenbosch University, 2020-03) Stroebel, Graeme B.; Miller, Jodie A.; Becker, Megan; Corin, Kirsten; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.ENGLISH ABSTRACT: Geologically complex deposits require integrated approaches to characterisation, extraction and processing of ores in order to maximise the yield of the deposit. In this study, a complex polymetallic (Cu-Pb-Zn-Ag) base metal sulphide deposit was examined to evaluate whether the different ore bodies should be grouped into geometallurgical domains. Geometallurgy is the practice of incorporating the entire value chain, and in this case, means the incorporation of geological knowledge of a deposit with metallurgical/process mineralogical knowledge to create a predictive, all-encompassing, model of a deposit. This idea was investigated using a Cu-Pb-Zn deposit in the Northern Cape of South Africa. The deposit consists of three ore bodies, namely: the Upper Ore Body (UOB), the Garnet Quartzite Ore Body (GQOB) and the Lower Ore Body (LOB). The UOB consists of magnetite-dominated ores and the other two ore bodies are quartz-dominant ores. The two quartz-dominant ore bodies consist of three different ore types: (1) garnet quartzite (GQOB), (2) mineralised schist (LOB) and (3) sulphidic quartzite (LOB) (abbreviated as ores G, H and I respectively). In this study, an in-depth investigation into the feed mineralogy/morphology, minerals processing responses and flotation concentrate mineralogy/morphology was conducted to test the legitimacy of creating one quartz-dominant geometallurgical domain. Mineralogical analysis of the feed was performed using QEMSCAN on samples milled to achieve a P80 of 65% passing 75 μm. Mineralogical analysis of the feed showed that the three ores were not as similar as originally proposed. Ore G had a unique feed mineralogy compared to ores H and I (which were similar to each other). Ore G consists of high (5.3 wt. %) amounts of chalcopyrite compared to that of ores H and I (1.1 wt. % and 1 wt. % respectively). In contrast ores, H and I consist of far higher (9.9 wt. % and 10.1 wt. % respectively) modal amounts of galena compared to the low amounts found in ore G (0.7 wt. %). Together with the differences in modal abundances of economic sulphides (ES) in the three ores, the two ore bodies had distinct sulphide gangue (SG) and non-sulphide gangue (NSG) populations. The NSG component of the three ores was, as expected, dominated by quartz, however, ore G has high amounts of garnet (10.2 wt. %) and magnetite (23 wt. %), whereas ores H and I has high amounts of mica (8.5 wt. % and 12.8 wt. %, respectively) and barite (8.7 wt. % in ore I). The mineral liberations and associations of ore G is also unique from ores H and I. ore type, similar total solids vs water recoveries were obtained for each ore type. Further investigation into the flotation performance of the three ores was done by analysing the flotation concentrates using ICP-OES to create elemental grade vs. recovery and metal mass vs water recovery profiles. Through the analysis of these results, it was determined that the ores again showed a similar grouping to the feed mineralogy (GQOB ores distinct from LOB ores). The analyses of the flotation concentrate showed that the target elements in the quartz-dominant ores (Cu and Pb) were being recovered as expected (in chalcopyrite and galena, respectively). The high iron recovery in the flotation concentrate (in particular of ore G) was a result of true flotation concentration of pyrite. This concentrate analysis once again showed that the three quartz-dominant ores were not as similar as originally thought. Ore G had a far higher pyrite content (56.7 wt. %) than ores H and I (29.8 wt. % and 20.7 wt. %, respectively) which were similar. As expected, ore G had a high chalcopyrite content (30.7 wt. %) in the concentrate, whereas ores H and I had a high galena content (57.4 wt. % and 67.3 wt. %) in the concentrate. Based on the above information, it is proposed to make two geometallurgical domains from the three quartz-dominant ores, one made up solely of ore G and the other made up of the combination of ores H and I. Implementation of geometallurgical domaining of this Cu-Pb-Zn deposit would require further analysis of the feasibility of mining and processing ores in such a way to preserve the ore domaining throughout the mining chain. On existing mine sites this would likely prove challenging but the results of this study suggest that such an approach could improve the financial return on the mining activities. In the case of this deposit, the ore domaining proposed for the quartz-dominant ores needs to take into consideration the UOB which is magnetite-dominant. Should the difference between the ores of the UOB and the quartz-dominant ores be more significant than the difference between the two proposed quartz-dominant domains, then the subdivision of the quartz-dominant ores might not make economic sense. Nevertheless, this study proposes that the quartz-dominant ores should be split into two domains aimed at grouping together ore types that exhibit similar processing responses.
- ItemA mineralogical approach to quantifying ore variability within a polymetallic Cu-Pb-Zn Broken Hill-type deposit and its implications for geometallurgy(Stellenbosch : Stellenbosch University, 2019-12) Gordon, Henry Justinian Jnr; Miller, Jodie A.; Becker, Megan; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.ENGLISH ABSTRACT: A detailed two-part mineralogical study was undertaken on a polymetallic Cu-Pb-Zn ore from the Aggeneys-Gamsberg Ore District to quantify which mineral characteristics of the lithological ore types are problematic during flotation. The first part involved quantifying the bulk mineralogy, grain size distribution and textural characteristics from five primary lithological units (Quartz-Magnetite, Amphibole-Magnetite, Mineralised Schist, Sulphidic-Quartzite and Garnet-Quartzite) in order to propose early-stage geometallurgical domains prior to flotation testing. Strong bulk mineralogical and chalcopyrite grain size distribution patterns were selected as the partition between three early-stage geometallurgical domains. These domains were, the least variable Cu-rich quartz dominated Garnet-Quartzite domain, the Cu-Pb-rich quartz-dominated Lower Ore Body domain (consisting of the Mineralised Schist and Sulphidic Quartzite) and the most variable Cu-Pb-Zn rich magnetite dominated – Upper Ore Body domain (consisting of the Amphibole Magnetite and Quartzite-Magnetite). Six bulk samples that represent the magnetite-dominated Upper Ore Body domain were selected to test the process mineralogical variability of the Quartz-Magnetite and Amphibole-Magnetite subordinate lithological units, and thereby prove or disprove the proposed early-stage Upper Ore Body geometallurgical domain. Distinct metal zonation (head grade), liberation and mineral association configurations within these ores proved to be the defining variables that influenced their respective flotation responses. From this approach, the Cu-Pb Quartz-Magnetite domain (medium grade, best liberated and most straightforward), the Zn-Cu-Pb Pyroxmangite-Quartz-Magnetite domain (highest grade, moderately liberated and most complex) and the Cu-Pb Amphibole-Magnetite domain (lowest grade, poorest liberated and poorest quality) were resultant. However, provisions should be made to counteract the negative implications associated with the economic sulphide -, gangue sulphide - and non-sulphide gangue mineralogies of the three magnetite-dominated geometallurgical domains, if processed individually. Problematic process mineralogical features of the magnetite-dominated ores are: Slow floating sphalerite minerals (implications for Zn recovery); chalcopyrite disease (implications for selectivity between chalcopyrite and sphalerite); varying chalcopyrite and galena head grades (implications for Cu and Pb recovery); varying hardness and concentration ratios (implications for ore throughput); locked economic sulphide minerals (implications for recovery of gangue minerals) and fine-grained manganese minerals (implications for manganese entrainment). These problematic process mineralogical characteristics can potentially be neutralised through finer grinding (increased liberation and recovery of economic sulphide minerals), blending of Mn-rich and Mn-poor ores, and follow up quantitative mineralogical test work to ascertain the lower limit grain size at which manganese entrainment can be minimized. Integration of the above-mentioned domain considerations back into the geological block model is challenging due to limited mineralogy data and the incompatibility of the mineralogy and chemical assay data that define geological block models. As a result, an elemental proxy, the Cu:S ratio was presented as a quantitative variable that could be used to illustrate the differences between these domains in a 2-D and 3-D manner to inform the geologist and metallurgists about the expected variability. Secondly, a geometallurgical matrix was presented as a qualitative approach to ensure that the domains are accurately identified by the underground geologists and the variability of the mined feeds are efficiently communicated to the metallurgists. The approach of this study can contribute to the way in which the geometallurgical domains within other deposits are formulated.
- ItemMineralogical characterisation of chromite in the UG2 Reef from Waterval Mine, Western bushveld : implications for minerals processing(Stellenbosch : University of Stellenbosch, 2010-03) Opoubou-Lando, Serge-Driver; Becker, Megan; Miller, Jodie A.; Viljoen, Fanus; University of Stellenbosch. Faculty of Science. Dept. of Earth Sciences.ENGLISH ABSTRACT: The Bushveld Complex of South Africa contains three of the most important platinum deposits in the world namely the Merensky Reef, the Upper Group Two (UG2) chromitite reef and the Platreef. These three ore bodies are principally beneficiated by froth flotation. During the beneficiation of chromite hosted PGE’s by froth flotation, chromite represents the principal gangue mineral. This is particularly true for the UG2 main seam. An excess of more than 3% in mass of chromite in the PGM concentrate is known to result in significant problems in the downstream processing and extraction of PGEs. The variability in texture and composition of chromite due to its primary crystallization and subsequent modification by the development of potholes or through IRUP intrusions are thought to influence the flotation behaviour of the UG2 main seam chromitite ore. This study conducted at Waterval Mine investigated the role of mineralogical characteristics of chromites on the flotation performance of three different environments for the UG2 main seam: (1) “normal” UG2 main seam; (2) UG2 main seam affected by pothole formation; and (3) UG2 main seam affected by IRUP intrusion. This was achieved through an extensive petrographic investigation of the chromites from each environment, to individually characterise their primary textures. This was followed by compositional characterisation of the chromite from each environment. Finally the flotation performance of the ore from each environment was investigated, using small scale batch flotation experiments, to establish any linkage between the textures, the composition and the flotation performance of the chromite from different environments. In this study it was found that the UG2 normal reef and the UG2 reef affected by pothole formation are both principally characterised by primary mineralogical features comprising mainly fine‐grained chromite as the cumulate phase and orthopyroxene and plagioclase as intercumulate phases. These two reef types were also found to be identical in the composition of the chromites present. In addition, in both of these almost unaltered reef types it was found that chromite showed small recoveries by flotation. On the other hand, it was found that the UG2 affected by IRUP intrusion was affected by post‐magmatic alteration that had overprinted primary textures and compositional features. This resulted in the replacement of primary minerals by secondary alteration assemblages. Orthopyroxene was iii replaced by serpentine, chlorite, amphibole and talc, while plagioclase is replaced by sericitic alteration. Furthermore, this alteration also resulted in modification of the chromite compositions. The compositional change in the chromites from the IRUP reef type resulted in Fe and Ti enrichment of chromite with increasing magnetic properties, and Cr, Al and Mg depletion. The alteration also resulted in the coarsening of chromite in the IRUP affected main seam reef particularly at the bottom and the top of the main seam. These compositional and textural modifications, principally the post‐magmatic alteration of intercumulate orthopyroxene, resulted in a greater recovery of chromite by flotation in the concentrate from the IRUP affected ore compared to the two other two ore types where there was small amount of chromite recovered. The characterisation of the recovered chromite revealed that the principal reason for chromite flotation was caused by the mineral association of chromite with hydrophobic Si, Mg, Fe rich phases, principally altered orthopyroxene and associated serpentine, chlorite, amphibole and talc. This investigation showed that the difference in mineralogical and flotation performances of chromite from the different UG2 main seam reef types was caused by the postcrystallisation alteration of cumulate and intercumulate phases due to the emplacement of IRUPs. Although IRUP affected UG2 main seam ore is not currently processed, it could be processed much more rapidly than the other two types of UG2 main seam ores because of its softer character resulting in shorter milling times. This is most likely a function of the presence of alteration phases and the presence of coarser chromite grains, as well as already brecciated chromite grains. Savings associated with the shorter milling time of this ore type are perhaps offset by the cost of the higher dosages of depressant required to suppress the floatable chromite in this ore type. However, given the energy cost of longer milling times, the cost of the depressant is likely to be insignificant. Moreover, the processing of the UG2 main seam ore affected by IRUP intrusion would also require a different approach to extraction of the ore to keep it separate from the normal reef ore.