Browsing by Subject "Mineralogy"

Now showing 1 - 7 of 7
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    Fluvial facies, vertebrate taphonomy and palaeosols of the Teekloof formation (Permian) near Beaufort West, Cape Province, South Africa
    (1989) Smith, Roger M H; Minter, Laurie; Cluver, Mike
    The main Karoo Basin of South Africa contains a relatively continuous sequence of continental deposits that accumulated over a 100 million year period from Permo-Carboniferous (280 Ma) to early Jurassic (180 Ma). In the southwestern region of the basin the Karoo succession is approximately 4 000 m thick, the upper half of which consists of vertebrate fossil-bearing fluvial rocks of the Beaufort Group. This study deals with Lower Beaufort (Adelaide Subgroup) strata belonging to the Teekloof Formation which are exposed in the cast-west trending erosional escarpment between the towns of Beaufort West and Fraserburg in the central Cape Province. The 450-mctre succession consists mainly of vertically accreted floodplain mudrocks with interbedded continuous sheets of fine-grained sandstone that bear evidence of having accumulated by lateral accretion on the inner banks of meandering channels. The mudrocks contain numerous fossilized skeletons of therapsid "mammal-like" reptiles as well as more primitive cotylosaurs and a few amphibians. Rarely, impressions of Glossopteris leaves and equisetalcan stems are found although root moulds are relatively abundant. Several types of calcareous nodules and sheets occur in the mudrocks and arc interpreted as evidence of calcic palaeosols that formed under semi-arid climatic conditions. This is an interdisciplinary study that integrates a conventional sedimentary facies analysis with investigations of the taphonomy of in situ therapsid fossils and the nature and distribution of palaeosols. Such an approach has not previously been applied to any of the Karoo strata. The results contain descriptive and quantitative information on sedimentary processes, palaeohydrology, absolute time represented in the stratigraphic record and the topography, soils and habitats of the ancient landscape. These are summarized into a palaeoenvironmental synthesis of the Teckloof Formation.
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    Large particle effects in chemical/biochemical heap leach processes - A review
    (Elsevier, 2011) Yousef, Ghorbani; Becker, Megan; Mainza, Aubrey; Franzidis, Jean-Paul; Petersen, Jochen
    The application of heap leach technology to recovery of economically important metals, notably copper, gold, silver, and uranium, is wide-spread in the mining industry. Unique to heap leaching is the relatively coarse particle size, typically 12–25 mm top size for crushed and agglomerated ores and larger for run-of-mine dump leaching operations. Leaching from such large particles is commonly assumed to follow shrinking core type behaviour, although little evidence for the validity of this assumption exists. This review investigates the current state of knowledge with respect to the understanding of the characteristics and mineralogy of large particles and how these influence leaching in a heap context and the tools to characterize these. This includes the study of ore and particle properties, visualization techniques for ore characterization, the connection between comminution and leaching behaviour, as well as particle models within heap leach modelling. We contend that the economics of heap leaching are strongly governed by the trade-off between the slow rate and limited extent of leaching from large particles and the cost of crushing finer. A sound understanding of the underlying large particle effects will therefore greatly inform future technology choices in the area of heap leaching.
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    Large particle effects in chemical/biochemical heap leach processes – A review
    (Elsevier, 2011) Ghorbani, Yousef; Becker, Megan; Mainza, Aubrey; Franzidis, Jean-Paul; Petersen, Jochen
    The application of heap leach technology to recovery of economically important metals, notably copper, gold, silver, and uranium, is wide-spread in the mining industry. Unique to heap leaching is the relatively coarse particle size, typically 12–25 mm top size for crushed and agglomerated ores and larger for run-ofmine dump leaching operations. Leaching from such large particles is commonly assumed to follow shrinking core type behaviour, although little evidence for the validity of this assumption exists. This review investigates the current state of knowledge with respect to the understanding of the characteristics and mineralogy of large particles and how these influence leaching in a heap context and the tools to characterize these. This includes the study of ore and particle properties, visualization techniques for ore characterization, the connection between comminution and leaching behaviour, as well as particle models within heap leach modelling. We contend that the economics of heap leaching are strongly governed by the trade-off between the slow rate and limited extent of leaching from large particles and the cost of crushing finer. A sound understanding of the underlying large particle effects will therefore greatly inform future technology choices in the area of heap leaching.
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    The mineralogy and crystallography of pyrrhotite from selected nickel and PGE ore deposits.
    (Society of Economic Geologists, 2010) Becker, Megan; De Villiers, Johan; Bradshaw, Dee
    The nonstoichiometric sulfide pyrrhotite (Fe(1–x)S) common to many ore deposits occurs in a variety of crystallographic forms and compositions and occasionally is also intergrown with stoichiometric troilite (FeS). In this study, the mineralogy of pyrrhotite derived from several different nickel and PGE ore deposits in South Africa, Botswana, and Canada was examined in detail in terms of pyrrhotite association, crystallography, and mineral chemistry. Pyrrhotite samples were subdivided into two-phase 6C Fe11S12 pyrrhotite intergrown with 2C FeS troilite, two-phase 4C Fe7S8 pyrrhotite intergrown with 5C Fe9S10 pyrrhotite, single-phase 5C Fe9S10 pyrrhotite and single-phase 4C Fe7S8 pyrrhotite. None of the pyrrhotite samples analyzed were classified as two-phase 4C pyrrhotite intergrown with pyrite due to the scarcity of pyrite in these samples. Average solid solution Ni contents of NC pyrrhotite (0.75 ± 0.10 wt % Ni) in this study were found to be greater than in 4C pyrrhotite (0.43 ± 0.10 wt % Ni), but only when the pyrrhotite occurred as two-phase 4C pyrrhotite intergrown with NC pyrrhotite. For single-phase pyrrhotite occurrences in this study, 4C pyrrhotite was more Ni rich (up to 2 wt % Ni) than NC pyrrhotite (0.75 ± 0.19 wt % Ni). The average atomic metal/S ratios obtained for 4C Fe7S8 pyrrhotite was 0.869 ± 0.013 (n = 699), for 5C Fe9S10 pyrrhotite was 0.895 ± 0.013 (n = 316) and for 6C Fe11S12 pyrrhotite was 0.918 ± 0.017 (n = 101). The histogram comparing metal/S ratios of all the pyrrhotite samples analyzed showed a continuum of metal/S ratios, although with frequency maxima corresponding to the ideal compositions of 4C, 5C, and 6C pyrrhotite. The presence of the continuum however, was interpreted to be representative of nonstoichiometry in the pyrrhotite structure.
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    Open Access
    Sugilite and associated metamorphic silicate minerals from Wessels Mine, Kalahari manganese field
    (1988) Dixon, Roger; Reid, A M; Moore, J M
    Sugilite, a purple mineral belonging to the milarite group, occurs in the lower manganese orebody at Wessels Mine, in the Kalahari Manganese Field. This orebody was formed in the lowermost manganiferous horizon of the Hotazel Member of the Voelwater Jasper Formation, part of the volcanogenic sedimentary iron formation of the Griqualand West Sequence. At Wessels Mine, which is located northwest of Kuruman in the northwestern Cape Province, evidence of a widespread and pervasive hydrothermal event which took place around 1300 Ma is found in the form of upgrading of the manganese-ore horizons and the formation of zoned silicate-mineral assemblages. The presence of unusual minerals such as glaucochroite, iron akermanite, xonotlite and hydrogarnets of various types constrains the main phase of metamorphism to between 400 and 450 °C in a low pressure, hydrous environment with XCO2 ≤ 0,02. All the minerals which occur in these assemblages are described and discussed in terms of their chemistry and formation.
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    Towards the development of an integrated modelling framework underpinned by mineralogy
    (2018) Ntlhabane, Sithembiso; Becker, Megan; Charikinya, Edson; Schouwstra, Robert; Bradshaw, Dee
    The mining industry is under increased pressure from many stakeholders to be forward thinking in its approach to sustainability. This requires a holistic approach to address techno-economic, environment and social issues, rather than just focusing on individual aspects of sustainability practice. The ability to do so requires an integrated modelling framework, underpinned by mineralogy so that the effect of ore variability on one or more of these factors can be simultaneously evaluated and optimised. This study focuses on the steps towards the development of this proposed framework using a case study of a polymetallic sulfide ore flotation circuit. The initial focus in the framework development is on integrating the techno-economic and the environmental aspects of sustainability. Thereafter the framework is used to consider a variety of scenarios evaluating the balance between techno-economic value and environmental burden. A sampling exercise was conducted around the intermediate and terminal streams of the flotation circuit processing polymetallic sulfide ore. All samples were characterised using both chemical assays and mineralogy (QEMSCAN). This formed the input data for the development of an ore specific element to mineral conversion (EMC) recipe that converts chemical assays to mineral grades. The EMC technique has the advantage of being fast, inexpensive and can be used on a routine basis. The recipe for this specific polymetallic sulfide ore was designed to calculate nine minerals in four different rounds, using least square method in the first two rounds and non-negative least square in the last two rounds. Sulfide minerals (chalcopyrite, galena and sphalerite) were calculated in the first round, barite was estimated in the second round, silicate minerals (garnet, biotite and quartz) were determined in the third round and pyrrhotite and magnetite were calculated on the last round. Data validation for EMC was performed by comparing calculated mineral grades against the measured mineral grades obtained from QEMSCAN. The accuracy was determined by evaluating the R2 value, the results were comparable as the R2 value was above 0.95 for all minerals. Mineral grades obtained from EMC of the assayed streams were used to carry out a mineral mass balanced of the flotation circuit. From the results, mineral grade and recovery were calculated and were used to evaluate metallurgical performance across the flotation circuit. The chalcopyrite (copper) concentrate was diluted with pyrrhotite (26 wt. %). The sphalerite concentrate (zinc) had the highest grade (94 wt. %) followed by galena (lead) with a concentrate grade of 85 wt. %. Sphalerite and galena achieved high recoveries over 90 %. From analysis of the flotation performance of the circuit, the results demonstrate an opportunity to improve the copper (chalcopyrite) concentrate quality. The diluted concentrate is likely to attract penalties during downstream processing (e.g. smelter) due to the presence of impurities (pyrrhotite). The concentrate can be upgraded by rejecting pyrrhotite in the first stage of the copper circuit. In addition, the mass balanced mineralogy results were used to calculate a theoretical potential of the final tailings to generate acid rock drainage (ARD). The ARD method used is based on the relative abundance of acid generating sulfide minerals (chalcopyrite, galena, sphalerite and pyrrhotite) and other minerals with the theoretical potential to neutralise the acid generated. The net mineralogically calculated acid producing potential was estimated as 46.4 kg H₂SO₄/ton. To further demonstrate the usefulness of the framework, a mineral splitter function was used to model the flotation circuit and test different hypothetical scenarios. Two hypothetical scenarios were investigated relative to the current operating condition of the flotation circuit. A sensitivity analysis on both scenarios was conducted to assess the effect of feed ore variability. The pyrrhotite feed grade was varied between 10 and 100 % of the base case and all sulfide mineral recoveries were kept constant. Scenario I considered improving Cu (chalcopyrite) concentrate grade in the Cu circuit by rejecting pyrrhotite. A Monte Carlo simulation was carried out by varying the pyrrhotite recovery to concentrate from a minimum of 2 % to a maximum of 18 % in the mineral splitter function. The results showed an increase in pyrrhotite grade in the final zinc tailings and an increase in the mineralogically calculated ARD potential (up to 53.9 kg H₂SO₄/t for tailings). Scenario II considered the installation of a magnetic separator to concentrate pyrrhotite in the final tailings and achieved a net acid producing potential of 15.2 kg H₂SO₄/t, which was lower than scenario I. The sensitivity analysis of scenario I showed a correlation between increased pyrrhotite feed grade with mineralogically calculated ARD potential (89.6 kg H₂SO₄/t). The results from sensitivity analysis of scenario II were lower were than scenario I (28.6 kg H₂SO₄/t). This shows that installation of a magnetic separator has the potential to mitigate ARD formation and produce a potential economic magnetite concentrate by-product. In conclusion this study has shown how mineralogy can be integral in developing an integrated modelling framework for simultaneously assessing techno-economic and environmental performance. The developed framework demonstrated the possibility of simultaneously balancing the trade-off, improving grade and mitigating the risk of ARD formation. It is a conceptual starting point for a new approach to traditional process mineralogy studies to start implementing sustainable development aspects on the operational level.
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    Use of X-ray computed tomography to investigate crack distribution and mineral dissemination in sphalerite ore particles
    (Elsevier, 2011) Ghorbani, Yousef; Becker, Megan; Petersen, Jochen; Morar, Sameer H; Mainza, Aubrey; Franzidis, J-P
    As the trends in mineral processing move towards the beneficiation of finer grained and more complex ore bodies, so too do the methods needed to understand and model these processes. During the heap leaching of low-grade ore bodies, the crack distribution and mineral dissemination in ore particles are important characteristics that determine the performance of sub-processes, such as the diffusion of reagents in and out of particle pores. Recent developments in X-ray computed tomography (CT) as an advanced diagnostic and nondestructive technique have indicated the potential for the technology to become a tool for the acquisition of 3-D mineralogical and structural data. The spatial distribution of cracks and mineral dissemination in particles derived from a sphalerite ore in the Northern Cape, South Africa, was characterized using a high-resolution industrial X-ray CT system. This paper describes the use of image analysis techniques including image segmentation, which uses a combination of thresholding and other methods to characterize and quantify crack and mineral dissemination in the sphalerite particles. The results are validated with those obtained using traditional techniques such as physical gas (with N2) adsorption, mercury intrusion porosimetry, SEM and QEMSCAN. A comparison of the effect of different comminution devices (HPGR and Cone crusher) on crack generation is also given.