South African Gold Research Articles

Optimizing the cut-off grade for tabular gold deposits, considering the South African gold tax and mineral resource royalty regime

The South African mineral resource royalty system, initiated in 2010, employs a hybrid ad valorem approach tied to profitability ratios. This rate is then applied to the total revenue from mineral sales. In this article we explore how the profitability ratio in the mineral resource royalty formulae interacts with the gold tax formula as applied to South African gold mines, devising a strategy for cut-off grade optimization. The study focuses on nine narrow, tabular-reef (Witwatersrand) gold mines. The approach involves a mixed-integer cut-off grade optimizer utilizing Excel Solver, incorporating relevant royalty and income tax formulae. Different mineral resource royalty cost scenarios were examined. Ignoring these costs in the break-even analysis lowers the cut-off grade but slightly boosts profits compared to considering expected costs. The developed optimizer model, recognizing the profitability aspect of the mineral resource royalty and income tax formulae, yielded a 6% lower cut-off grade than the base case. This is significant for increasing mine life. While the profit differences are marginal (0.2% compared to the break-even base case), substantial improvements were noted: a 6% increase in stope tons above cut-off grade, and a 4% rise in total revenue. Enhanced resource utilization (3% extra gold kilograms) reduces necessary development and overall costs, allowing for a reduction in the cut-off grade and ultimately, more profit.

Sustainability and South Africa’s mature mines: The innovation imperative

Given the current reserves, numerous South African Witwatersrand gold and Bushveld platinum mines have a shorter remaining lifespan than the period they have been in full production. This situation presents a paradox: while mines aim for sustainable development, the inherently unsustainable nature of mining poses challenges. A fundamental question emerges: how can mines approaching the end of their economic lives enhance sustainability? One approach is to extend their production lifespan. This approach is especially important in the context of South Africa with its already unacceptably high unemployment rate. Mature mines in established mining jurisdictions face sustainability issues. Thus, this study argues that innovative skills development, research, and partnerships can help sustain mining operations, although commodity prices fluctuate and mines near the end of their economic viability. The study presents novel ideas to assist mature mines in extending their life and reducing the vulnerability of affected mine workers.

Statistical analysis of gold production in South Africa using ARIMA, VAR and ARNN modelling techniques: Extrapolating future gold production, Resources–Reserves depletion, and Implication on South Africa's gold exploration

South African gold mining is one of the main contributors to the country's economic growth and employment creation. Assessment of future gold production is pivotal for positioning the country's supply security and contribution to the projected global demand. In this study, we modelled and forecasted South African and global gold production trends (1990–2022) using the Autoregressive Integrated Moving Average (ARIMA), Vector Autoregressive (VAR), and Autoregressive Neural Network (ARNN) techniques. The study also evaluated the impact of annual productions on the collated reserves (2008–2021) and the contribution of resource–reserve conversion in sustaining gold reserves within the South African goldfields. The ARIMA (1,1,0) model, based on root mean square error (RMSE), mean absolute error (MAE), and mean absolute percentage error (MAPE), outperformed both ARNN (1,1) and VAR (2) methods. The forecast of the ARIMA model showed an increase in South Africa's gold production, with a compounded annual growth rate (CAGR) of ∼0.6%. The model also predicted an increase in global gold production, with CAGR of ∼2.2%. The analyses of reserves–production trends showed that most South African mining companies have been depleting their gold reserves due to production and were minimally converting resources to reserves, averaging at ∼2%/year from 2017 till present. The minimal conversion may also reflect the challenging mining conditions (such as mining depths and underground flooding) and the mining industry's socio-political dynamics. We demonstrated that, if the resource–reserve conversion factor is maintained (at ∼2%/year and above), the forecasted production may sustain the current reserves (at > 2000 t Au excluding tailings) but deplete ∼27 % of the resources to reserves by 2040. However, if the conversion factor continues to decline (to <1 %), the forecasted gold production will reduce the reserves to < 500 t Au with ∼3% of the resources converted to reserves.

Profitability, Respectability and Challenge: (Re)Gaining Control and Restructuring the Labour Process while Maintaining Racial Order at South African Gold Mines, 1913–1922

The history of black labour at the South African gold mines has conventionally been punctuated by three great African strikes, in 1920 (often obscured by the great white mine-worker strike of 1922), 1946 and 1987. The strikes of 1920, 1946 and 1987 (as well as the great white strikes of 1913 and 1922) have all attracted considerable scholarly attention. Yet a more limited black strike in 1913 has seldom, if ever, been recalled, despite its crucial importance for formulating racial policy at the gold mines, buried as it was in the violent defeat of white miners and their cohorts. This paper takes up the challenge of understanding management and state responses to collective (black and white) mine-worker struggles during the decade from 1913 to the early 1920s and assessing outcomes for worker participants, white and black alike.

Assessing environmental radon contribution by different sources near a South African gold mine tailings

Assessing environmental radon contribution by different sources near a South African gold mine tailings

Radiolytically reworked Archean organic matter in a habitable deep ancient high-temperature brine

Investigations of abiotic and biotic contributions to dissolved organic carbon (DOC) are required to constrain microbial habitability in continental subsurface fluids. Here we investigate a large (101–283 mg C/L) DOC pool in an ancient (>1Ga), high temperature (45–55 °C), low biomass (102−104 cells/mL), and deep (3.2 km) brine from an uranium-enriched South African gold mine. Excitation-emission matrices (EEMs), negative electrospray ionization (–ESI) 21 tesla Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and amino acid analyses suggest the brine DOC is primarily radiolytically oxidized kerogen-rich shales or reefs, methane and ethane, with trace amounts of C3–C6 hydrocarbons and organic sulfides. δ2H and δ13C of C1–C3 hydrocarbons are consistent with abiotic origins. These findings suggest water-rock processes control redox and C cycling, helping support a meagre, slow biosphere over geologic time. A radiolytic-driven, habitable brine may signal similar settings are good targets in the search for life beyond Earth.

An Ubuntu-based reflection on the public health impact of silica dust exposure in the South African mining industry

Issuing fitness certificates to South African mine workers with early and mild silicosis to continue risk work underground is a public health concern. This article draws on the view of solidarity to contend this practice. We employed a normative ethics approach and the concept of solidarity in African ‘Ubuntu’ philosophy to report and reflect on the public health implications of silica dust exposure among South African miners. We argued that since silicosis is irreversible, incurable, and could be progressive, leading to death, thus, issuing certificates of fitness to individuals who have early and mild silicosis, in many ways, is inappropriate and the practice ought to be rejected. We recommend more studies to reflect on the ethical management of silica dust exposure in the South African gold mining industry.

IFN-γ independent markers of Mycobacterium tuberculosis exposure among male South African gold miners.

The prevalence of tuberculosis among men who work in the gold mines of South Africa is among the highest in the world, but a fraction of miners demonstrate consistently negative results upon tuberculin skin test (TST) and IFN-γ release assay (IGRA). We hypothesized that these "resisters" (RSTRs) may display unconventional immune signatures of exposure to M.tuberculosis (M.tb). In a cohort of RSTRs and matched controls with latent TB infection (LTBI), we profiled the functional breadth of M.tb antigen-specific T cell and antibody responses using multi-parameter flow cytometry and systems serology, respectively. RSTRs and LTBI controls both exhibited IFN-γ independent T-cell and IgG antibody responses to M.tb-specific antigens ESAT-6 and CFP-10. Antigen-specific antibody Fc galactosylation and sialylation were higher among RSTRs. In a combined T-cell and antibody analysis, M.tb lysate-stimulated TNF secretion by T cells correlated positively with levels of purified protein derivative-specific IgG. A multivariate model of the combined data was able to differentiate RSTR and LTBI subjects. IFN-γ independent immune signatures of exposure to M.tb, which are not detected by approved clinical diagnostics, are readily detectable in an occupational cohort uniquely characterized by intense and long-term infection pressure. Further, TNF may mediate a coordinated response between M.tb-specific T-cells and B-cells. This work was supported by the US National Institutes of Health (R01-AI124348 to Boom, Stein, and Hawn; R01-AI125189 and R01-AI146072 to Seshadri; and 75N93019C00071 to Fortune, Alter, Seshadri, and Boom), the Doris Duke Charitable Foundation (Davies), the Bill & Melinda Gates Foundation (OPP1151836 and OPP1109001 to Hawn; and OPP1151840 to Alter), Mass Life Science Foundation (Fortune), and Good Ventures Fund (Fortune).

The Impact of Basotho Migrant Labourers’ Retrenchment from South African Mines on Rural Development in Lesotho: The Post-Mine Livelihood Strategies of Former Basotho Miners at Koro-Koro in the Maseru District

The migration of Basotho men in search of employment opportunities in South African diamond and gold mines dates back to the 1800s. The South African mining industry has been the source of employment and livelihood for many Basotho families by remitting incomes for centuries. However, there was a downturn in events starting in the late 1980s and early 1990s, when many South African mines started to downsize their foreign labour force. This contributed to the loss of remittances that were invested in farming and the maintenance of many rural households in Lesotho. This study was conducted to investigate the post-mine livelihood strategies of former Basotho migrant labourers at Koro-Koro in the Maseru district. The research followed a descriptive research design where primary data was collected from a sample of 50 former Basotho mine workers using snowballing and simple random sampling techniques. Qualitative and quantitative data were collected using face-to-face interviews and observation. The collected data was analysed qualitatively and quantitatively using descriptive statistics, mainly percentages. It is argued in this paper that retrenchment and the loss of jobs by many Basotho men in South African mines were major blows to the livelihoods of many rural households. In addition, Basotho men who worked in South African mines are now confronted with unemployment as well as futile exertions while engaging in alternative income generating activities, both farm and non-farm.

Enzymatic degradation of carbonaceous matter in contrasting South African refractory gold ores using cell-free spent medium from Phanerochaete chrysosporium

Two carbonaceous gold ores (ZAFB and ZAFV) underwent sequential biotreatment to expose gold and minimize preg-robbing before cyanidation. These included comparable organic carbon contents (6.0%wt in ZAFB and 4.4%wt in ZAFV) but were contrasting in the graphitic degree of the carbonaceous matter. Based on Raman spectra, the carbonaceous matter in ZAFB was more physically and chemically disordered than the ZAFV. To reduce extraneous factors, ≥ 90% of sulfides in both samples were oxidatively dissolved by the thermophilic mixed culture. Afterwards, the secondarily-formed minerals (mainly jarosite) were dissolved by oxalic acid washing. The carbonaceous matter was then treated for 15 days with a cell-free spent medium (CFSM) with lignin-degrading enzymes produced from a Phanerochaete chrysosporium culture. The enzymatic treatment reduced the carbonaceous matter content in the ZAFB by 0.73%wt from an initial value of 7.56%wt, while the ZAFV was unchanged. Raman and 3D-fluorescence analysis of the carbonaceous matter showed that the CFSM treatment was much more effective on the ZAFB sample. This indicates that the graphitic degree of the carbonaceous matter is a significant factor when applying crude enzymes derived from P. chrysosporium. The lignin-degrading enzyme treatment improved the gold extraction of ZAFB from 88% to 93%. It was found that Raman spectroscopy could serve as a handy tool for determining carbonaceous gold ores that are suitable for enzymatic treatment.

Exploration, Storytelling and Frontier-Making in the Colombian Andes

This chapter shows how the speculative (pre-)lives and afterlives of resource extraction are put together through corporate narrative and imaginative practices. It shows that the expansion of extractive frontiers is not merely driven by abstract and asocial market forces, but that deeply social practices of storytelling and imagination are also vital for making mining exploration possible. Drawing on 15 months of fieldwork in Colombia, it discusses the spectacular narratives surrounding the exploration campaign of South African gold mining corporation AngloGold Ashanti (AGA) across the Colombian Andes. The chapter examines how corporate storytelling unfolds through corporate processes and individual narratives, and shows it to be integral to conjuring Colombia as the ‘last Andean frontier’ for gold exploration in the international investor’s imagination. Corporate narrative and performative practices were not only crucial to attracting and sustaining investor interest, but also served an important internal function in shaping the professional identity of exploration geologists and corporate identity more broadly. At the same time, the chapter shows that frontier expansion and the capitalisation of mineral finds are uneven and speculative processes, with room for alternative stories.

Mining Migrant Worker Recruitment Policy and the Production of a Silicosis Epidemic in Late 20th-Century Southern Africa.

Between the 1980s and 2000s, an epidemic of silicosis was identified in migrant black gold miners, many from neighbouring countries, who had worked in the South African gold mines. This study uses the newly available employment database of a large gold mining company to demonstrate how a sustained rise in employment duration in a new cohort of black migrant workers resulted from changes in recruitment policy, and it examines the implications for current surveillance and redress. Contract data of 300,774 workers from the employment database of a multi-mine gold mining company were analysed for 1973-2018. Piecewise linear regression was applied to determine trends in cumulative employment, including South African versus cross-border miners. The proportions with cumulative employment of at least 10, 15, or 20 years, typical thresholds for chronic silicosis, were also calculated. Five calendar phases were identified between 1973 and 2018. During the second phase, 1985-2013, mean cumulative duration of employment rose fivefold, from 4 to 20 years. Cumulative employment continued to rise, although more slowly, before peaking in 2014 at 23.5 years and falling thereafter to 20.1 years in 2018. Over most of the 1973-2018 period, miners from neighbouring countries had greater cumulative employment than South African miners. Overall, the proportion of miners exiting with at least 15 years of cumulative employment rose from 5% in 1988 to 75% in 2018. This report identifies a number of fundamental changes in labour recruitment policy in the gold mining industry in the 1970s which provide an explanation for the subsequent rise in cumulative exposure and associated silicosis risk. These new data support the hypothesis of a silicosis epidemic driven by increasing cumulative silica dust exposure in a new cohort of circular migrant workers from the 1970s. They inform current programmes to improve surveillance of this neglected population for silicosis and related disease and to provide medical examinations and compensation to a large number of former gold mines. The analysis highlights the lack of information on cumulative employment and silicosis risk among migrant miners in previous decades. The findings have global relevance to the plight of such migrant workers in hazardous occupations.

Use of cavitation to enhance the leaching kinetics of refractory gold ores

ABSTRACT The cyanidation process for refractory gold ores has been the subject of numerous investigations aimed at improving gold recovery and leaching kinetics. From recent literature investigations, hydrodynamic cavitation has been found to be a promising new approach which may modify the cyanidation processes. In this study, this approach results in the enhancement of mass transfer kinetics in multiphase fluid streams due to impacting two pulps streams against one another in a vessel called the Jetleach reactor. In this work, the Jetleach reactor was applied to a flotation concentrate from a South African gold tailings processing plant (Ergo) where an improvement of almost 10% in gold recovery was obtained while decreasing cyanide and oxygen consumption by almost 8% and 50%, respectively. The main reason for the improvement is surmised to be due to the generation of micro-cavitation which improves the mass transfer of oxygen and cyanide within the slurry.

The Penetration of European Banking into Ottoman Lands During the Second Half of the Nineteenth Century

ABSTRACT We discuss the development of ‘modern’ banking in core Ottoman lands during the latter half of nineteenth century. We present evidence showing considerable local financial sophistication prior to European entry around 1856. Drawing on the ‘constitutional commitment’ literature we maintain its success was related to enhanced security of life and property European financial ties provided to Ottoman decision-makers. We argue international relations substituted for missing domestic institutions. We describe the conflictual process ending around 1900, with the domination of Ottoman capital markets by European banks, particularly the Banque Impériale Ottomane, or BIO. The competition pitting BIO against ethnically based local banking networks opens a different window into the economic and fiscal occurrences of that epoch. We consider the role of London based ‘South African Gold Panic of Autumn 1895’ and its interactions with the unfolding ‘Armenian Crisis’ of Istanbul and Anatolia in bringing about this final outcome.

Evaluation of pre-treatment methods for gold recovery from refractory calcine tailings

The South African gold mining industry has a legacy of abundant tailings dams, which have attracted the attention of investors because of their potential as a cheaper secondary gold resource. In this we investigate study gold recovery from a refractory calcine tailings dam. Bulk mineralogy of the tailings indicated silicates and iron oxides to be the most abundant phases. Scanning Electron Microscopy (SEM) showed gold to exist in submicrometre and micrometre sizes, as free gold, and associated with arsenic, sulphur, and silicates e.g. quartz and talc. Gold recovery by direct cyanidation was low at 17.3%. Mechanical (ultra fine grinding P80 -16µm) and chemical (alkaline, NaOH) pre-treatment and microwave roasting and microwave-assisted cyanide leaching were investigated to increase gold recoveries. Ultrafine grinding was the most effective, producing recoveries of 66.5%. NaOH pre-leaching of ultrafine milled material increased recovery to 71.5%. Alkaline pre-leaching overall increased recoveries for non-pre-treated material, making this process the most preferred because it is less costly than ultrafine grinding. Microwave roasting and microwave-assisted leaching did not achieve higher recoveries than alkaline pre-treatment or fine grinding. The investigation highlights and confirms that chemical treatment with NaOH is a powerful tool for gold extraction from refractory tailings.

Mine closure, women, and crime in Matjhabeng, South Africa

AbstractResearch from the Global North suggests that crime increases during a mining boom but not during mining decline. Our evidence from the South African gold mining town of Matjhabeng (formerly Welkom) shows that crime increases during mining decline and affects women in particular. We use social disruption theory to explain women’s experiences of crime and also their involvement in it. We find that criminal activities harm women in particular, that crime has become entrenched within female‐headed households, and that women are conflicted in their roles as parents and become participants in crime and beneficiaries of criminal activities. It is a matter for concern that research generally ignores the sociospatial nature of mine closure and its effects on women.

Accuracy of Computer-Aided Detection of Occupational Lung Disease: Silicosis and Pulmonary Tuberculosis in Ex-Miners from the South African Gold Mines.

Background: Computer-aided detection (CAD) of pulmonary tuberculosis (TB) and silicosis among ex-miners from the South African gold mines has the potential to ease the backlog of lung examinations in clinical screening and medical adjudication for miners’ compensation. This study aimed to determine whether CAD systems developed to date primarily for TB were able to identify TB (without distinction between prior and active disease) and silicosis (or “other abnormality”) in this population. Methods: A total of 501 chest X-rays (CXRs) from a screening programme were submitted to two commercial CAD systems for detection of “any abnormality”, TB (any) and silicosis. The outcomes were tested against the readings of occupational medicine specialists with experience in reading miners’ CXRs. Accuracy of CAD against the readers was calculated as the area under the curve (AUC) of the receiver operating characteristic (ROC) curve. Sensitivity and specificity were derived using a threshold requiring at least 90% sensitivity. Results: One system was able to detect silicosis and/or TB with high AUCs (>0.85) against both readers, and specificity > 70% in most of the comparisons. The other system was able to detect “any abnormality” and TB with high AUCs, but with specificity < 70%. Conclusion: CAD systems have the potential to come close to expert readers in the identification of TB and silicosis in this population. The findings underscore the need for CAD systems to be developed and validated in specific use-case settings.

Characteristics of Fault Rocks Within the Aftershock Cloud of the 2014 Orkney Earthquake (M5.5) Beneath the Moab Khotsong Gold Mine, South Africa

AbstractCores recovered during the International Continental Scientific Drilling Program project “Drilling into Seismogenic zones of M2.0 to M5.5 earthquakes in deep South African Gold Mines” include fault breccia from within the aftershock cloud of the 2014 Orkney earthquake (M5.5). The breccia and surrounding intrusive rocks, probably lamprophyres rich in talc, biotite, calcite, and amphibole, had high magnetic susceptibilities owing to the presence of magnetite. All of these characteristics can be attributed to fluid‐related alteration. Both the breccia and the lamprophyres had low friction coefficients and showed evidence of velocity strengthening, which is inconsistent with the occurrence of earthquakes. Variable amounts of talc, biotite, calcite, and amphibole within the lamprophyres might have produced complex frictional properties and spatial heterogeneity of fault stability. The altered lamprophyres may be the host rocks of the 2014 Orkney earthquake, but frictional complexity may have governed the magnitudes of the main‐ and aftershocks and their distributions.

An In Toto Approach to Radon Dispersion Modelling from a South African Gold Mine Tailings.

The USA Environmental Protection Agency’s (EPA) Industrial Source Complex Short Term 3 (ISCST3) dispersion modelling code was used to evaluate radon transport and the effects of local variations around tailings dam using a Gaussian plume model. The tailings dam was modelled as point, flat ground and top level, total emitting surface area (true geometry) and volume source geometries. The true area geometry was considered as the baseline source geometry. To improve the accuracy of the model predictions as compared to traditional approaches, the true geometry area source term was corrected to account for cracks and fissures on the tailings and the geometry of tailings dam was modelled by considering all emitting surfaces as sources. Compared to the baseline, the model overpredicted the flat ground area source by up to 274% and underpredicted the top-level area source by up to 50%. The volume emission source was overpredicted by up to 300% in 60% of the modelling runs and underpredicted by 55% in 40% of the volume model runs. While the top-level area source term produced lower concentrations at near-field ground-level receptors, accounting for the wakes effect increased the radon concentrations from the top-level area source of the tailings dam by up to 239%. From the modelling results, the highest concentration predicted by the model from the true geometry source was found to be 0.843 Bq m−3, which corresponds to the dose of 0.012 mSv/y to the public due to radon from the tailings. This value is less than the 1 mSv/y dose constraint stipulated by the National Nuclear Regulator.

86Kr excess and other noble gases identify a billion-year-old radiogenically-enriched groundwater system

Deep within the Precambrian basement rocks of the Earth, groundwaters can sustain subsurface microbial communities, and are targets of investigation both for geologic storage of carbon and/or nuclear waste, and for new reservoirs of rapidly depleting resources of helium. Noble gas-derived residence times have revealed deep hydrological settings where groundwaters are preserved on millions to billion-year timescales. Here we report groundwaters enriched in the highest concentrations of radiogenic products yet discovered in fluids, with an associated 86Kr excess in the free fluid, and residence times >1 billion years. This brine, from a South African gold mine 3 km below surface, demonstrates that ancient groundwaters preserved in the deep continental crust on billion-year geologic timescales may be more widespread than previously understood. The findings have implications beyond Earth, where on rocky planets such as Mars, subsurface water may persist on long timescales despite surface conditions that no longer provide a habitable zone.