Mining and Environmental Geology

This study compares the energy consumption of high pressure grinding rolls with the laboratory rod milling tests and the pilot plant. Three types of minerals were used as test specimens namely: pyroxenite (I), pyroxenite (2) and pyroxenite (3). These test samples were ground using jaw and cone crushers to provide feed for laboratory milling test deposit and to evaluate a circuit comprised of high pressure grinding rolls comminution followed by laboratory milling. Attempts at improving the comminution machines generally have been directed towards increasing the performance efficiency, particularly increasing throughput rate and decreasing energy consumption. To evaluate the potential energy benefits of this novel circuit arrangement, energy consumption related to comminution was calculated for the circuit using power draw readings off the main motor and the throughput recorded during testing. To provide a basis for comparison, the energy requirements for laboratory rod milling tests, the high pressure grinding rolls tests and the piloting campaign were determined through high pressure grinding rolls pilot-scale testing.

This research focused on the mode of magnesite mineralisation within the host rocks in  Folovhodwe  deposit.  Two  hostrocks  and  the  hanging  wall  were  sampled  from Folovhodwe Mine. The investigation was undertaken to establish the way magnesite was  formed  within  the  hostrocks.  The  study  established  the following  rock  types: basalt (hostrock), dolerite sill (hostrock) and sandstone (hanging wall), as well as the magnesite ore occurrence in the study area.
Petrographic studies and geochemical analysis were used to establish the mode of magnesite  mineralisation  within  basalt  and  dolerite  sill.  The  major  rock-forming minerals  of  basalt  are  plagioclase  and  clinopyroxene,  and  of  dolerite  are  olivine,
orthopyroxene,  clinopyroxene  and  plagioclase.  Petrographic  studies  have  shown evidence of alterations of the hostrocks through the presence of sericite,  smectite, talc and serpentine.
The geochemical analysis of the hostrocks showed lower concentrations  of MgO in basalt (3.61%) as compared to dolerite (30.75%). The analysis also indicated 51% SiO2 in basalt and 41.14% SiO2 in dolerite. Geochemical analysis also showed that
the  magnesite  ore  hosted  in  dolerite  comprised  65%  MgCO3
and  in  basalt  it  was 16% MgCO3.
The magnesite mineralisation took place along the joints, cracks and crevices within weathered  basalt  and  dolerite,  resulting  from  the  carbonation  of  forsterite  and enstatite that were altered to amphibole, serpentine and talc in the presence of CO2
and H2O to produce magnesite, smectite, palygorskite and sepiolite. Forsterite and enstatite were the primary sources of the Mg2+ ion.
The high content of olivine and pyroxene in dolerite led to the abundance of the Mg2+ ion  during  alteration,  hence,  the  dominance  of  magnesite  in  dolerite.  However, further work is recommended  to ascertain  the  role  of  temperature  and pressure  in the formation of magnesite within basalt and dolerite in the study area.

Siloam village is well known for its hot springs that geologically lie in the Nzhelele Formation of the Soutpansberg Group rocks. About 1800 million years ago, the Soutpansberg depositional basin was formed as an east-west trending asymmetrical rift. These Soutpansberg group rocks were severely faulted which resulted in a number of major faults, like the Siloam fault. Faults provide channels through which the hydrothermal fluids can flow. These fluids are heat sources for the hot springs. With no evidence of recent volcanic activities in the Limpopo province, it is assumed that all the hot springs are of meteoric origin and the heating of the hot springs is due to the deep circulation along fault zones. The main objective of the study is to delineate the faults that are potential recharge zones of the hot springs above the ground at Siloam village using remote sensing, geological maps and aeromagnetic data. LANDSAT 8 (OLI, November 2015), scenes P69, R76 (path 69 and row 76) free of cloud cover were downloaded from the USGS website page. The data was reduced to remove excess noise. A number of processing techniques were done to further enhance the visibility of the image and locate the faults by the use of ERDAS IMAGINE software. The aeromagnetic data was used to locate the faults using the magnetic susceptibility of the rocks. Aeromagnetic data was acquired from the Council of Geoscience of South Africa, which collected it using a proton precession magnetometer mounted on a low plane flight at an average height of 150m. The traverses were oriented in the E-W direction, and the traverse separation was 1 km. The aeromagnetic data reduction was applied during the processing in order to produce a colour map using Geosoft Oasis Montaj. The geological data was obtained through digitizing and georeferencing of an existing geological map acquired from the Council of Geoscience of South Africa. The GPS was used to locate the hot springs at the Siloam village for correlation with the lineaments. The lineaments were interpreted from the remote sensing. The aeromagnetic data was correlated with the faults on the geological map. The main faults associated with the known hot springs were delineated along with the minor faults which were potential zones carrying hot water at the Siloam village. The results show that the two sets of data are capable of extracting lineaments in inaccessible areas and they can complement each other in locating faults. The results showed that the three known hot springs are associated with the major faults. Geologically the other faults are also playing a part in recharging the hot springs.

The backfill operations at the deep level gold mine consist of a Cyclone Classified Tailings (CCT) Plant as well as a Full Plant Tailings (FPT) Plant with both producing cemented backfill. Due to the high demand of backfill at the mine, including a backlog of voids that need to be filled, both the CCT and FPT Plants are being operated at the moment. The mine will require an increased capacity of backfill going forward, with monthly throughputs in the order of 200 000 to 250 000 tonnes being required. The current mining methods includes destress cuts, long hole stoping as well as drift and fill mining with cemented backfill as a support medium. These concerns have led to the review of the entire backfill operations of the mine with a need for optimising, reducing costs and reducing operational complexity going forward. The research provides strength test work (solids density, particle size distribution, slurry pH, temperature, conductivity, freely settled bed packing concentration, permeability, particle micrographs, water quality, mineralogy, boger slump tests, cement mortar tests (ISO bars), and unconfined compressive strength (UCS) tests) and audit the current backfill operations at the mine. The data showed that both materials had similar top particle sizes of approximately 500 μm. The CCT has a d30 and d10 of 63.4 and 18.2 μm, respectively, compared to the FPT with a d30 and d10 of 13.1 and 3.1, respectively, which is significantly finer. The freely settled bed packing concentration by volume was calculated from the volume of the freely settled bed formed by a known volume of solids. A slurry sample was allowed to settle for 24 hours in a measuring flask. The actual solids volume was determined from the dry mass of material and the solids density. The results were as follows: CCT 45.2 %v (69.1 %m) and FPT 40.0 %v (63.8 %m).

Carbonaceous shale is more topical than ever before due to the associated unconventional resources of methane. The use of FTIR, SEM-EDX, and mineralogical analyses has demonstrated a promising approach to assess methanogenesis potentials in a more rapid and reliable manner for preliminary prospecting. Representative core samples from the borehole that penetrated the carbonaceous Mikambeni shale Formations were investigated for methanogenesis potentials. The absorption band stretches from 1650 cm−1 to 1220 cm−1 in wavenumber, corresponding to C-O stretching and OH deformation of acetic and phenolic groups in all studied samples, thereby suggesting biogenic methanogenesis. The CO2 was produced by decarboxylation of organic matter around 2000 cm−1 and 2300 cm−1 and served as a source of the carboxylic acid that dissolved the feldspar. This dissolution process tended to release K+ ions, which facilitated the illitization of the smectite minerals. The SEM-EDX spectroscopy depicted a poly...

The issue of abandoned mine sites is a major environmental and social problem for the mining industry, communities and governments. Historical mine sites are characterized by significant environmental, health and safety problems. The aim of this study was to develop hazard maps that can assist in the prioritization of rehabilitation at Nyala Mine. The approach used involved site examination and characterization to establish the environmental conditions of the mine. Hazards at the mine were identified, scored, and rated using modified Historic Mine Site Scoring System. The scoring focused on source and exposure pathways. The developed hazard maps showed that the best approach of effectively reducing the physical and environmental hazards at Nyala Mine was to give priority to extremely and moderately hazardous pits; surface infrastructure and spoil dumps, and then to tailings dumps characterized with less physical hazards but extremely high environmental hazards. Pits and spoil materials which were found to be relatively less problematic in terms of physical hazards were to receive least attention. The use of this hazard-scoring and risk-ranking methodology coupled with the hazard maps would provide a more robust scientific basis for making sound decisions and prioritize actions that need to be taken to minimize or manage risks associated with various areas of the mine site.

Abandoned mines and mine tailings pose a hazard to communities that live around these sites. Here we report on the environmental risk assessment and risk management strategies of an abandoned New Union Gold Mine that is located in Ka-Madonsi village, Malamulele district, South Africa. The visual assessment was done through visits to the mine sites and the levels of heavy metals in the mine tailings soil and stream sediments was analysed with atomic absorption spectrometry. The hazards were then rated based on the probability of reoccurrence and the severity of the impact. The risk management strategies were suggested based on the severity and the probability of the impacts and the geographical setting of the area. The heavy metals: Cu, Co, Cd, As, Zn, Ni and Mn were found in the mine tailings soil and in the stream sediments. The mine tailings soils and stream sediments were acidic, within pH ranges of 3.93 to 4.45 and 4.18 to 6.28 respectfully. The acidic soils can pose as a problem to the growth of plants and grass should they be used for revegetation of the mine tailings.Environmental impacts identified at the mine site were: soil erosion, sedimentation, land subsidence deep open voids and land scarification. Thus for each of the environmental impact that was identified, risk management strategies were then proposed. The re-vegetation of the exposed mine tailings was found to be the most practical way of solving the problem of soil erosion and sedimentation. Presence of plants and grass on the mine tailings may reduce the rate of soil erosion caused by either water and/ or wind. The deep openings need to be safeguarded and backfilled. The drainage lines and storm water infrastructures need to be established to channel water in order to prevent storm water from transporting sediment to the stream.

The study focused on assessment of safety status of open pit and suitability of water in Nyala Mine Pit Lake for domestic uses. The approach used in the investigation involved field description of the lake, modelling of surface runoff to the pit and chemical analysis of the water. It was found that the pit accumulates runoff water from high grounds along the northern part of the excavation. The water in the pit was found to be alkaline (pH ±9.6) with F-(±1.1 ppm), Cl-(±169.6 ppm), Mg 2+ (±67.85 ppm) and K + (±87.16 ppm) concentrations that were all above the standards permissible for domestic use.

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In order to improve the safety status and the quality of the landscape affected by surface mining, it is important that practical strategies for dealing with the excavations are identified. The aim of the work presented in this paper was to carry out an appraisal of the strategies for addressing the physical hazards of abandoned surface mine excavations in two mines in the Limpopo Province, South Africa. The method used involved carrying out field characterization of the current state and uses of the excavations, as well as their physical hazards of the surface mine excavations in the study area. The characterization took into consideration. Possible strategies for addressing the physical hazards of the excavations are identified, and their strengths, weaknesses, opportunities, and threats (SWOT) analyzed. The Quantitative Strategic Planning Matrix (QSPM) was performed on each of the identified strategies with the purpose of determining their attractiveness based on their SWOT facto...

The rise in demand for natural gas has spurred the need to investigate the inland sedimentary basin for more potential sources. In response, the petrophysical parameters of the carbonaceous shale samples from two deep boreholes of Anambra Basin were evaluated. The gas-prone nature of Nkporo shale showed a thermal evolution of a Type III kerogen with initial HI value between 650 and 800 mgHC/gTOC, S2/S3 < 1, a maximum Tmax value of 488°C and have a low hydrocarbon generation potential ranging from 0.07 to 0.15. However, the average TOC content (2.21 wt%) indicated a good source rocks for hydrocarbon since it exceeds threshold limit of 0.5%. The plot of HI against Tmax shows that the organic matter belongs to the Type-III kerogen which reflects the capability of the Npkoro Formation to generate more natural gas than oil compared to Type-II kerogen. The high values (>3) of pristane/phytane ratio in both wells indicated that the organic matter belongs to terrigenous source deposit...

Abandoned mines and mine tailings pose a hazard to communities that live around these sites. Here we report on the environmental risk assessment and risk management strategies of an abandoned New Union Gold Mine that is located in Ka-Madonsi village, Malamulele district, South Africa. The visual assessment was done through visits to the mine sites and the levels of heavy metals in the mine tailings soil and stream sediments was analysed with atomic absorption spectrometry. The hazards were then rated based on the probability of reoccurrence and the severity of the impact. The risk management strategies were suggested based on the severity and the probability of the impacts and the geographical setting of the area. The heavy metals: Cu, Co, Cd, As, Zn, Ni and Mn were found in the mine tailings soil and in the stream sediments. The mine tailings soils and stream sediments were acidic, within pH ranges of 3.93 to 4.45 and 4.18 to 6.28 respectfully. The acidic soils can pose as a proble...

Historic mining of magnesite at Nyala Mine left behind terrain characterized by scattered mine waste dumps and open excavations that pose threat to public safety. These are aesthetically unpleasant. In this work conceptual terrain models that depict areas of cut and fill for rehabilitation of the landscape of the Nyala Mine and improvement of the safety status of the mine pit lake were created. The models were used to analyze the slope angles of the pit lake and rain water accumulation in the lake. Based on the study it has been established that the most stable slope angle that has potential of reducing erosion considerably was 14° (≈24.99% grade). In order to reduce the amount of sediments deposition at the pit lake floor, approximately 20m length pit slope was designed with gabion protected reverse bench of 1m width and the steepness of up to 1.72°. The 3D surface models that depicts areas to be graded to create flat topography around the pit lake and the entire mine was developed...

Erosion is a serious problem at mine tailings disposal sites, particularly if the surface is left unprotected. Dust from the tailings dams can be harmful to human, animal, and plant life. Water erosion of the slopes of tailings dams is a considerable and costly maintenance and pollution problem. At present, erosion prevention and control in the short term is very often a process of trial and error and very little information exists on performance of erosion protection measures for long periods. The purpose of this study was to conduct a field-scale investigation into effectiveness of different erosion control measures. This involved creating erosion control panels on a typical slope of tailings dam with surface treatments ranging from simple vegetative techniques to fairly civil engineering erosion protection covers using fragments of rock. A series of measurement of erosion rates were made using measurement of sediment trapped in catchment paddocks and measurement by means of steel...

Understanding of clayey materials properties continues to elude brick manufacturers, hence unsure of their application for brick making purposes. The raw materials were assessed geochemically, mineralogically, physically and technologically. The geochemical result showed that the fluxing oxides K2O, N2O, CaO, MgO and MnO are generally low in content with average abundance ranging from 0.06% to 1.78%. The Fe2O3 content varies (4.8-25.5%) thus reflects heterogenous stability in tonality. Most of the studied samples have relatively high Al2O3 content which suggest the bauxitic composition from which kaolinite minerals might have resulted from. The XRD analysis revealed the presence of kaolinite and chlorite as the major clay minerals while quartz, feldspar, talc and hornblende were present as non-clay minerals. For DTA, the threshold of new crystallization processes were attained at 1000 °C. The SEM analysis revealed the presence of some stroma in all samples although with sizes >50...

ABSTRACT
Geotechnical site investigation is the process of collecting data and evaluating the conditions of the site for the purposes of obtaining earthworks design and earth-fill material which is suitable for foundation stabilization. The main purpose of a site investigation is to determine sufficient site information that is used to select a site with suitable earth-fill material for foundation stabilization.
The objectives of this site investigation were to determine texture, consistency, shear strength, bearing capacity and settlement properties of the material. The methodology used includes material sampling, sieve analysis, Atterberg limit tests, compaction test and California Bearing Ratio test.
Laboratory test results indicates that gravel particles dominate the material within the Tswinga area with an average percentage of about 74%. The site investigation also indicates that the Tswinga borrow pit material has an average liquid limit of about 30% with the plasticity index of about 11%, therefore the material tends to have medium plasticity index due to the abundance of clay shows expansion ability. The material is classified as clay, sandy and gravel (A-2-6) as according to the AASHTO classification system. The material samples maximum dry density at modified AASHTO compaction effort was within the range of 2122 kg/m3 to 2147 kg/m3 at optimum moisture content of 6.9% and 9.3% respectively. Material with this compaction effort has the settlement properties and bearing capacity suitable for foundation stabilization due to their great strength, therefore are classified as gravel. The CBR values at compaction efforts between 90% and 100% of the modified AASHTO varied from 11 to 49. The results showed that the have CBR values ≥ 25 at 95% modified AASHTO. This confirm that the material is of high bearing capacity.
This investigation of the earth-fill material from indicates that the material within Tswinga area are excellent too good which is suitable for foundation stabilization. It is strongly recommended that the earth-fill material from Tswinga area can be used to replace unsuitable soil for foundations stabilization.