Gold Mines In South Africa Research Articles

Emergence and disappearance of very small repeating earthquakes on a geological fault in a gold mine in South Africa

We investigated the activities of very small (−5.10 ≤ MW ≤ −2.35) repeating earthquakes that occurred during 14 months on a geological fault at a 1 km depth in the Cooke 4 gold mine in South Africa. Out of 4214 acoustic emissions occurring on the fault, 1785 (42.36% of the total) were identified as repeaters on the basis of the waveform similarity and the proximity of hypocenters. Quite a few large groups, having up to 57 members, were recognized. Activities of some groups certainly continued throughout the 14 months, but we also found some repeater groups that newly emerged or disappeared during this period. Both types often coexisted within a distance as small as ~0.5 m, within which background fault creep should be coherent. Some disappearing groups showed a decrease in the event magnitude with time. These temporal changes of repeater activities may imply the formation and dissipation of topographical asperity contacts on the fault. Our results suggest that ultrasensitive observation of acoustic emissions can reveal the physical evolution of asperities.

Study of Earthquake Generation Process by Acoustic Emission Observation in Deep Gold Mines in South Africa

Study of Earthquake Generation Process by Acoustic Emission Observation in Deep Gold Mines in South Africa

Ecotoxicity of Mine Tailings: Unrehabilitated Versus Rehabilitated.

Earthworms are bioindicators of soil pollution. The ecotoxicity of tailings from selected gold mines in South Africa was investigated utilizing Eisenia andrei bioassays and biomarkers. Samples were obtained from unrehabilitated, rehabilitated and naturally vegetated sites. Biomass, neutral red retention time (NRRT), survival and reproduction were assessed using standardized protocols. Earthworm biomass, NRRT and reproductive success in rehabilitated tailings (comparable to naturally vegetated site) were significantly higher (p < 0.05) than in unrehabilitated tailings. In addition, significantly lower (p < 0.05) body tissue concentrations of As, Cd, Co, Cu and Ni contents were found in the rehabilitated tailings compared to the unrehabilitated. Further, significantly lower (p < 0.05) soil Mn and Zn concentrations were obtained in unrehabilitated tailings than the rehabilitated and naturally vegetated sites. Overall, reduced ecotoxicity effects were confirmed in rehabilitated compared to unrehabilitated tailings. This suggests that rehabilitation as a post-mining restorative strategy has strong positive influence on mine tailings.

Trials of the Garford hybrid dynamic bolt reinforcement system at a deep-level gold mine in South Africa

Trials of the Garford hybrid dynamic bolt reinforcement system at a deep-level gold mine in South Africa

Monitoring, Warning, and Control of Rockburst in Deep Metal Mines

Abstract This paper reviews the recent achievements made by our team in the mitigation of rockburst risk. It includes the development of neural network modeling on rockburst risk assessment for deep gold mines in South Africa, an intelligent microseismicity monitoring system and sensors, an understanding of the rockburst evolution process using laboratory and in situ tests and monitoring, the establishment of a quantitative warning method for the location and intensities of different types of rockburst, and the development of measures for the dynamic control of rockburst. The mitigation of rockburst at the Hongtoushan copper mine is presented as an illustrative example.

Detection of potential methane gas pathways in deep South African gold mines

At a number of gold mines in South Africa, methane gas has been encountered when drilling into faults and/or dykes extending to depths beyond 7000 m. Methane gas has been reported to migrate up through structures from within the basin to the mine working environments (∼3000 m depth) and caused explosions. The Booysens Shale is one of the possible source rocks for hydrocarbons and it forms the footwall to the gold-bearing Ventersdorp Contact Reef (VCR, ∼1.5 m thick). The Booysens Shale lies at depths between 3500 and 4500 m below the surface and can be best described as a base of the divergent clastic wedge, hosting the quartzite and conglomerate units that sub-crop against the VCR towards the west of the gold mining areas. Geometric attributes (dip and dip azimuth) and instantaneous attributes (phase, frequency and envelope) computed for the Booysens Shale and VCR horizons provide insight into structures that extend from the Booysens Shale into the overlying mining level (i.e. VCR). These attributes successfully mapped the structures (faults and dykes) that have displaced both the VCR and Booysens Shale horizons. The edge-detection attributes were particularly useful in delineating faults with throws below the traditional seismic resolution criteria (e.g. a quarter of the dominant wavelength) that were not visible in the conventional seismic interpretation. The structural analysis using seismic attributes gives a new visual representation of geological structures that may be probable conduits for hydrocarbons, particularly methane, migrating from the Booysens Shale to the VCR mining levels.

Integrated energy simulation of a deep level mine cooling system through a combination of forward and first-principle models applied to system-side parameters

Mine cooling systems typically account for around 25% of the total electrical energy consumption of deep level mines. Numerous energy saving strategies have been implemented, with various levels of success. Most of the previously implemented strategies involved load shifting, energy efficiency and demand reduction. To achieve this, some levels of control are often introduced to control chilled water consumption, water and air mass flow rates as well as scheduling cooling system operation in order to shift the load primarily to off-peak periods.To support and sustain further reduction of energy consumption and optimisation of savings, a simulation model of the integrated cooling system represented by smooth and continuous equations is needed to assist the optimisation computation. This study focused on developing such an integrated mine cooling system simulation model to mimic the thermal hydraulic behaviour along with the energy consumption of the complete mine cooling system. This was achieved by coupling various models representing the major cooling system components such as chillers, cooling towers, pumps and fans. Although various cooling system energy simulations were considered before, very few quantify the simulation accuracy on a component basis; furthermore, only limited cases were found where the entire system was considered. For these cases not all components were always based on explicit models which would eliminate the requirement for iterative computation which deter optimisation applications.The simulation model was used to predict the energy consumption of the integrated cooling system of a deep level gold mine in South Africa. The simulation model obtained an average error when compared to the mine’s system data of 3.5% for a selected dataset and 2.5% for another dataset one month later. The successful energy simulation of an integrated mine cooling system would allow for a holistic view on the total power consumption as one parameter or any combination of parameters of the system changes.

Trouble on the Rand: The Chinese Question in South Africa and the Apogee of White Settlerism

The importation of more than 60,000 Chinese laborers to work in the Witwatersrand gold mines in South Africa between 1904 and 1910 remains an obscure episode in the history of Asian indentured labor in European colonies. Yet the experience of the coolies on the Rand reverberated throughout the Anglo-American world and had lasting consequences for global politics of race and labor. At one level, the Chinese laborers themselves resisted their conditions of work to such a degree that the program became untenable and was canceled after a few years. Not only did the South African project fail: Its failure signaled more broadly that at the turn of the twentieth century it had become increasingly difficult to impose upon Chinese workers the coercive and violent exploitation that had marked the global coolie trade in the era of slave emancipation. At another level, the Chinese labor program on the Rand provoked a political crisis in the Transvaal and in metropolitan Britain over the “Chinese Question”—that is, whether Chinese, indentured or free, should be altogether excluded from the settler colonies. Following the passage of laws limiting or excluding Chinese immigration to the United States (1882), Canada (1885), New Zealand (1881), and Australia (1901), Transvaal Colony and then the Union of South Africa, formed in 1910, likewise barred all Chinese from immigration—making Chinese and Asian exclusion, along with white rule, native dispossession, and racial segregation the defining features of the Anglo-American settlerism.

Operational energy minimisation for forced draft, direct-contact bulk air cooling tower through a combination of forward and first-principle modelling, coupled with an optimisation platform

Bulk air coolers (BACs) are extensively used in the deep-level mining industry to cool ambient air for underground use. BACs contribute significantly to the mine's chilled water requirements and it was therefore the purpose of this study to utilise a modelling method to predict the thermal performance of mechanically ventilated direct-contact bulk air cooling towers and perform energy optimisation. The model consisted of a combination of forward and first-principle methods based on underlying energy balance and heat transfer principles. The model allowed for the explicit estimation of the BAC outlet conditions for given inlet conditions, without the need for iterative calculations. This model was validated with operational data obtained from a bulk air cooler of a deep-level gold mine in South Africa. Average prediction errors of between 0.5 °C and 0.7 °C for the outlet water temperature were achieved. Subsequently, the model was coupled with an optimisation platform to optimise the electrical energy consumption of the BAC. Energy savings of 13% were obtained using the optimisation model for a period of high energy demand. This paper showed that such a modelling and optimisation approach could be useful to reduce the operation energy cost of thermal systems in general.

Acoustic Emission Monitoring for Mitigating Seismic Risks in Deep Gold Mines in South Africa

Acoustic Emission Monitoring for Mitigating Seismic Risks in Deep Gold Mines in South Africa

Discriminating Characteristics of Tectonic and Human‐Induced Seismicity

We analyze statistical features of background and clustered subpopulations of earthquakes in different regions in an effort to distinguish between human‐induced and natural seismicity. Analysis of end‐member areas known to be dominated by human‐induced earthquakes (The Geyser geothermal field in northern California and TauTona gold mine in South Africa) and regular tectonic activity (the San Jacinto fault zone in southern California and the Coso region, excluding the Coso geothermal field in eastern central California) reveals several distinguishing characteristics. Induced seismicity is shown to have (1) higher rate of background events (both absolute and relative to the total rate), (2) faster temporal offspring decay, (3) higher rate of repeating events, (4) larger proportion of small clusters, and (5) larger spatial separation between parent and offspring, compared to regular tectonic activity. These differences also successfully discriminate seismicity within the Coso and Salton Sea geothermal fields in California before and after the expansion of geothermal production during the 1980s. Online Material: Figures of examined regions, earthquake epicenters, and joint distributions of the time and space components of the nearest‐neighbor distance.

Characterization of rectorite from the Beatrix Gold Mine in South Africa

Three rectorite samples from the Beatrix Gold Mine, South Africa were characterized. Scanning electron microscopy revealed a layered morphology. High resolution transmission microscopy showed well distinguished light and dark layers of about 2.20nm consistent with the 1:1 interstratified mica-smectite nature. X-ray diffraction measurements confirmed the basal spacing d001 of 2.20nm consistent with a one-water-layer structure. Unit cell parameters, for a monoclinic unit cell with primitive lattice, refined to a=5.177Å; b=8.980Å; c=22.489Å and β=97.335° with mean crystallite size around 14nm and calculated cell volume of 1045Å3. The Greene-Kelly test suggested that the expandable smectite layers have montmorillonite-beidellite composition. Nuclear magnetic resonance spectroscopy indicated a high degree of Al substitution and the presence of two different Al sites corresponding to six- and four-fold octahedral and tetrahedral aluminum respectively. The chemical composition and diffraction data suggest that the mica is Na-Ca-rich, i.e. of paragonite-margarite series. The fixed interlayer regions (mica interlayers) contains proportionally dominant Na+ and Ca2+ and minor amounts of K+. The exchangeable smectitic interlayers contain almost equal amounts of Na+ and Ca2+ ions. The distribution of the interlayer Na+ ions was quantified by 23Na solid-state NMR spectroscopy. It points to a three component mixed-layer structure with considerable variation in the composition of the mica layer of the different samples.

Special Issue: The State, The Citizen and Power

Two decades ago, a cohort of key historians made an important intervention into understanding the workings of political violence and coercion in southern Africa. The essay col- lection was published on the cusp of the democratic transition in South Africa in 1992.2 They focused on coercion and paternalism in the labour market and cults of violence in Mozambique; violence on the gold mines in South Africa; political and masculinist domestic violence in the armed struggle; protests in informal settlements in South Africa; and, finally, they offered a look at war and the potential for social healing in Zimbabwe. Now, in this Special Issue, a new generation of historians make their mark.

Platinum and Gold Mining in South Africa: The Context of the Marikana Massacre.

Mining is a source of extraordinary wealth, but its benefits often do not accrue to the workers and communities most involved. This paper presents two case studies of mining in South Africa to reflect on the history and legacy of mining both through observation and through the voices of affected communities. Interviews and observations on field visits to the platinum and gold mining areas of South Africa in the immediate aftermath of the Marikana massacre highlight this legacy--including vast quantities of tailings dumps and waste rock, lakes of polluted water and a devastated physical and social environment, high unemployment, high rates of occupational injury and disease including silicosis with co-morbidities, absent social security, and disrupted rural and agricultural communities. Exploitative conditions of work and the externalization of the health and environmental costs of mining will require international solidarity, robust independent trade unions, and a commitment to human rights.

Unexpectedly frequent occurrence of very small repeating earthquakes (−5.1 ≤ Mw ≤ −3.6) in a South African gold mine: Implications for monitoring intraplate faults

AbstractWe observed very small repeating earthquakes with −5.1 ≤ Mw ≤ −3.6 on a geological fault at 1 km depth in a gold mine in South Africa. Of the 851 acoustic emissions that occurred on the fault during the 2 month analysis period, 45% were identified as repeaters on the basis of waveform similarity and relative locations. They occurred steadily at the same location with similar magnitudes, analogous to repeaters at plate boundaries, suggesting that they are repeat ruptures of the same asperity loaded by the surrounding aseismic slip (background creep). Application of the Nadeau and Johnson (1998) empirical formula (NJ formula), which relates the amount of background creep and repeater activity and is well established for plate boundary faults, to the present case yielded an impossibly large estimate of the background creep. This means that the presently studied repeaters were produced more efficiently, for a given amount of background creep, than expected from the NJ formula. When combined with an independently estimated average stress drop of 16 MPa, which is not particularly high, it suggests that the small asperities of the presently studied repeaters had a high seismic coupling (almost unity), in contrast to one physical interpretation of the plate boundary repeaters. The productivity of such repeaters, per unit background creep, is expected to increase strongly as smaller repeaters are considered (∝ Mo −1/3 as opposed to Mo −1/6 of the NJ formula), which may be usable to estimate very slow creep that may occur on intraplate faults.

Draft Genome Sequence of Thermus scotoductus Strain K1, Isolated from a Geothermal Spring in Karvachar, Nagorno Karabakh.

The 2,379,636-bp draft genome sequence of Thermus scotoductus strain K1, isolated from geothermal spring outlet located in the Karvachar region in Nagorno Karabakh is presented. Strain K1 shares about 80% genome sequence similarity with T. scotoductus strain SA-01, recovered from a deep gold mine in South Africa.

Can the use of natural biostimulants be a potential means of phytoremediating contaminated soils from goldmines in South Africa?

ABSTRACTBiostimulants offer great potential in improving phytoremediation of contaminated soils. In the current greenhouse-based study, Brassica juncea seedlings grown on soils collected from Krugersdorp Goldmine and the adjourning areas (a Game Reserve and private farmland) were supplemented with different biostimulants (Kelpak® = KEL, vermicompost leachate = VCL, smoke-water = SW). Indole-3-butyric acid (IBA) was included in the study for comparative purposes because these biostimulants are known to enhance rooting. Prior to the pot trial, concentrations of elements in the three soil types were determined using Inductively Coupled Plasma-Optical Emission Spectroscopy. Plants were harvested after 105 days and the growth and concentrations of elements in the various plant organs were determined. TheB. juncea seedlings with and without biostimulants did not survive when growing in soil from the Krugersdorp Goldmine. The Game Reserve and private farmland soils supplemented with KEL produced the highest plant biomass and the lowest accumulation of metals in the organs of B. juncea. High concentrations (>13 000 mg kg−1) of zinc and aluminium were quantified in the roots of IBA-supplemented soils from the Game Reserve. Generally, IBA and SW enhanced the phytoremediation of B. juncea due to elevated levels of elements that accumulated in their different organs.

Violations of Gutenberg–Richter Relation in Anthropogenic Seismicity

Anthropogenic seismicity (AS) is the undesired dynamic rockmass response to technological processes. AS environments are shallow hence their heterogeneities have important impact on AS. Moreover, AS is controlled by complex and changeable technological factors. This complicated origin of AS explains why models used in tectonic seismicity may be not suitable for AS. We study here four cases of AS, testing statistically whether the magnitudes follow the Gutenberg–Richter relation or not. The considered cases include the data from Mponeng gold mine in South Africa, the data observed during stimulation of geothermal well Basel 1 in Switzerland, the data from Acu water reservoir region in Brazil and the data from Song Tranh 2 hydropower plant region in Vietnam. The cases differ in inducing technologies, in the duration of periods in which they were recorded, and in the ranges of magnitudes. In all four cases the observed frequency–magnitude distributions statistically significantly differ from the Gutenberg–Richter relation. Although in all cases the Gutenberg–Richter b value changed in time, this factor turns out to be not responsible for the discovered deviations from the Gutenberg–Richter-born exponential distribution model. Though the deviations from Gutenberg–Richter law are not big, they substantially diminish the accuracy of assessment of seismic hazard parameters. It is demonstrated that the use of non-parametric kernel estimators of magnitude distribution functions improves significantly the accuracy of hazard estimates and, therefore, these estimators are recommended to be used in probabilistic analyses of seismic hazard caused by AS.

Delineation of large localized damage structures forming ahead of an active mining front by using advanced acoustic emission mapping techniques

We applied advanced mapping techniques to 291 230 acoustic emission (AE) events as small as around M −4 that were recorded over 50 days by an ultra-high resolution network close to the active front of a tabular mining stope being advanced northward at 1km depth in the Cooke 4 Gold Mine in South Africa. We first applied joint hypocenter determination (JHD) to improve absolute locations, and then applied the double-difference relative location algorithm to the JHD output. These steps resolved the seemingly continuous, dense cloud of AEs that extend about 20m ahead of the stope front into several discrete, steeply dipping tabular clusters a few meters thick and 10–30m in dip extent, separated by quiet intervals a few meters thick. The clusters have a strike parallel to the stope face and a dip of about 65°, resembling commonly observed large shear fractures along the plane of maximum shear (Ortlepp shears). In general, the activity of the clusters changed in similar ways as the stope face advanced, but each cluster remained stationary and the gaps between clusters were impressively quiet. This study demonstrates that high-resolution AE mapping can delineate the formation of large structures of localized damage in the highly stressed intact rock mass ahead of the stope face, a process that may culminate in hazardous seismic events.

Nucleation process of an M2 earthquake in a deep gold mine in South Africa inferred from on‐fault foreshock activity

AbstractUsing a network of sensitive high‐frequency acoustic emission sensors, we observed foreshock activity of an Mw 2.2 earthquake (main shock) in a deep gold mine in South Africa. Foreshock activity, which selectively occurred on a part of the rupture plane of the forthcoming main shock, lasted for at least 6 months until the main shock. Rock samples recovered from the main shock source region showed evidence of ancient hydrothermal alteration on the main shock rupture plane, suggesting that the foreshock activity occurred on a preexisting weakness. The foreshocks during 3 months before the main shock were concentrated in three clusters (F1–F3), which we interpret as representing localized preslip at multiple sites. While the location of mining area, the source of stress perturbations, changed with time, the locations of foreshock clusters did not change, suggesting that the preslip patches were controlled by strength heterogeneity rather than stress distribution. Activity over the entire foreshock area was generally constant, but the largest cluster (F2) showed accelerated activity starting at least 7 days before the main shock, while mining stress did not increase in this period. The main shock initiated at a point close to F1, away from F2. All the six foreshocks during the final 41 h occurred in F1 and F2 and in‐between. These suggest that in the last stage of the preparation process of the main shock, preslip patches interacted with each other through the stress concentration ahead of the expanding preslip patch (F2), which should be the only driving force of the preparation process under the constant external load.