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By J. van der Merwe, C. Phetolo, V. Matjeke

The mechanical properties and microstructure of AlSi10Mg alloy samples that were printed by selective laser melting (SLM) were studied to determine the effect of processing parameters and building orientation. After printing, the alloy was stress relieved at 250°C for 2 hours. The microstructures were analysed by optical microscopy and scanning electron microscopy (SEM) to determine the alloy phases and distribution. Phase transformation characteristics of the material were evaluated using differential scanning calorimetry (DSC). Mechanical properties were determined by subjecting the XY- and Z-built samples to tensile and nano-indentation testing. The samples from the tensile tests were then used to perform fractographic analysis by SEM. The microstructural properties in each orientation revealed a non-homogeneous microstructure which was characterized by a semi-elliptical tract and fine silicon precipitates, which were found to be softer along the fusion zone. The DSC thermograms revealed that the material underwent two phase transformations during the first heating cycle. The mechanical properties revealed a higher UTS, higher yield strength, and a lower percentage elongation in the Z orientation than in the XY orientation. Fractographic analysis showed that crack initiation in both orientations started from the surface in a brittle manner due to surface flows, and then propagated via microvoid coalescence.

Jul 1, 2021

By G. M. Evans, S. Mitra, G. J. Jameson, M. M. Hoque, E. Doroodchi, R. Moreno-Atanasio

In this study, the detachment behaviour of 314 μm diameter silica particles from a single 3 mm diameter bubble rotating in a confined cavity connected to a cross-flowing water channel was investigated. The liquid cross-flow generated a rotating flow inside the confined cavity, which was quantified using 2D particle image velocimetry (PIV) measurements. The fluctuating (x-y) velocity components inside the cavity for each cross-flow velocity, U, were then used to estimate the corresponding time/volume average turbulence intensity values, Ti. Turbulence intensity ranged from 9.3-16.2%. In the absence of a bubble, the rotating vortex within the cavity created a pressure field which decreased towards the centre of the vortex; wherein the lowest pressure zone was located at the centre of the cavity. The vorticity into the cavity was found to increase with increasing the turbulence intensity. A bubble, both without and with particles attached, was introduced into the cavity under different flow conditions and its motion was tracked using the shadowgraphy technique. Experimentally, it was found that the bubble-particle aggregate was trapped at the centre of the cavity (low-pressure region) following a spiral trajectory. An interface resolved 3D computational fluid dynamics (CFD) model was developed to predict the particle detachment conditions within the confined cavity. CFDpredicted vorticity in the absence of a bubble agreed well with experimental observation. The CFD analysis indicated that the vorticity inside the cavity was not significantly changed when a single bubble was introduced. On this basis, the computed vorticity was utilised in describing the force balance applied to the attached particle. Computationally, it was found that the critical turbulence intensity, beyond which the particle was detached from the bubble, was 14%. This value was consistent with the experimental observation of detachment at Ti at 15.7%, and above, but not at lower values. Keywords: Bubble, particle, turbulence intensity, vorticity, particle detachment, CFD, PIV

Jan 1, 2020

By S. T. L. Harrison, M. A. Fagan-Endres, M. D. Odidi

This paper investigated the ability of eight common hydrodynamic models – tanks in series (TIS); three compartmental model configurations (Comp-1, Comp-2 and Comp-3); advection dispersion (AD); piston exchange (PE); piston exchange-diffusion variant (PE-D) and piston dispersion exchange (PDE) – to simulate residence time distribution (RTD) data generated from tracer tests conducted on a packed bed composed of different size fractions of malachite ore. The chosen materials were packed into 0.1 m internal diameter columns to a depth of 0.155 m and drip irrigated at 5.11 L/ m2.h. The four size fractions tested were: 1 – 2 mm, 2 – 2.8 mm, 4.75 – 5.6 mm and 13.6 – 16 mm. Step-up tracer tests were conducted using potassium chloride. The results showed that an increase in the particle size of the malachite ore had little effect on overall bed porosity but resulted in significantly lower values of liquid holdup. Two of the monoporosity models tested, TIS and Comp-2, were the most affected by the changes in bed size fraction due to their inherent inability to cope with high degrees of non-ideal flow present in the larger particle systems. The dual porosity models performed relatively better with the dominant trend being a reduction in dynamic to total liquid holdup as particle size increased. Of all the models tested, the PDE and TIS models were the best and worst performers respectively, with R2 values averaging at 0.997 and 0.679 across all experiments respectively. Though the Comp-1, Comp-3 and PE-D models also performed well, the addition of the dispersion coefficient to take the axial spread of fluid molecules into account added a layer of complexity that allowed the PDE model to perform relatively better than the other dual porosity models. Keywords: Heap leaching, packing material, hydrodynamics, malachite, PSD, modelling

Jan 1, 2020

By W. Soetaert, P. Dhar, H. R. Kota, M. Thornhill, S. Roelants, I. V. Chernyshova

Yeast-derived bola-amphiphiles have attracted considerable attention for their applications in various industrial sectors in recent years. However, only a few studies on this class of surfactant were reported to be relevant to mineral processing applications. In this paper, one of the novel surfactants, acidic glucolipid obtained from Candida bombicola sophorolipids and modified by using Penicillium decumbens naringinase substrate has been evaluated for its interaction with chalcocite and calcite minerals because of a new Cu-ore Nussir deposit in Norway containing calcite impurity. The interaction of glucolipid biosurfactant with copper sulphide and carbonate minerals was investigated with zeta potential, adsorption and FTIR studies, and also by Hallimond tube and bench scale flotation tests using pure minerals and Nussir copper ore, respectively. The results illustrate collector adsorption and flotation of copper sulfides at neutral pH. The bench-scale flotation results demonstrate that copper sulphides can be selectively floated from carbonate and silicate gangue minerals. This study underlines the glycolipid’s high potential for its use as collector for flotation of valuable copper sulphide minerals. Keywords: Flotation, biosurfactants, adsorption

Jan 1, 2020

By M. Rudolph, R. Tolosana-Delgado, G. van den Boogaart, M. Reuter, U. Peuker

This paper addresses the challenge to define a concept of entropy (state of order) for a textured particle system. Both the particle texture, the intergrowth respectively, and the particle size influence the order of a particle system. The smaller the particles become, the more particles form the solid system and the more permutations of the structure of the particle bed are possible. The texture within a particle is fixed, as long as it is not subjected to changes due to comminution, flocculation or agglomeration. The paper will present a definition of entropy, which is able to reflect qualitatively and quantitatively the intergrowth and the size (distribution) of the particles. Theoretical examples will show how different breakage mechanisms can be identified using the entropy definition. Furthermore, we will define the specifications for data sets to calculate the entropy of a particle system. Keywords: Milling, mineral liberation, intergrowth, statistical entropy, modelling

Jan 1, 2020

By N. Tatalias, P. Ilunga, M. Lampi, J. Edwards, K. Valkama, M. Nicolle, D. Samal

"Developing a greenfield mining project is a complex exercise: doing so in an increasingly volatile, uncertain, and ambiguous global economy adds significantly to this complexity. In the context of an elevated cobalt price, this paper outlines the metallurgical and process development of the Mutoshi copper–cobalt project for copper cathode and cobalt hydroxide production in the Democratic Republic of Congo. Chemaf has a long production history on the Copperbelt, a region widely perceived to be tough to operate in. This history stretches back to 2001, during which time the company has developed two copper–cobalt processing facilities. The experience gained in the development and operation of these two facilities has been used extensively in the Mutoshi copper–cobalt project. The metallurgical test work, process design, and project delivery approach are presented. Additionally, the decisions taken to minimize risk and maximize upside to the project are discussed. IntroductionChemaf (Chemicals of Africa), a mining company located in Katanga province of the Democratic Republic of Congo (DRC), has been operating since 2001 with two major copper– cobalt processing facilities: the Usoke and Etoile plants. In 2016, Chemaf acquired the Mutoshi mine, which belonged to Gecamines and had been explored by Anvil Mining since 2004 under a joint venture with Gecamines. Chemaf appointed African Mining Consultants Ltd (AMC) to undertake a preliminary economical assessment, then develop a JORCcompliant Mineral Resource estimate and finally a full life-of mine feasibility study. Both a Mineral Reserve and Mineral Resource were developed and the final life-of-mine feasibility study is to be published shortly. A metallurgical test work programme was initiated and carried out by Chemaf’s research and development laboratory with assistance from the Chemaf process team. After completion of the initial test work, Chemaf developed a process design criteria document for a 20 kt/a copper cathode and 8 kt/a cobalt in hydroxide production plant, followed by a flow sheet and supporting METSIM mass balance. As the drilling progressed, the plant design capacity was revised to 16 kt/a cobalt production. The life of the mine at this production rate is over 40 years."

Nov 1, 2018

By D. T. Jordan, L. C. Coetzee, G. Kalenga, T. Mahlangu, W. J. Shipman

Although online free cyanide analysers are widely available and used in gold leaching operations worldwide, reliable automated free cyanide concentration control is not consistently achieved in many of these operations. Effective cyanide concentration control is complex owing to amongst others, the long residence times and ore feed variations. Model Predictive Control (MPC) has been proven to provide superior cyanide concentration control over traditional proportional-integral-derivative (PID) control, leading to savings in operational costs and reduced leachable gold losses. In the first example reported in this paper, MPC has improved control of the free cyanide concentration by keeping it within the required range 73% of the time during testing, compared to the previous PID controller that only achieved this target 30% of the time. This represents a 143% improvement. Another example demonstrates a 22% reduction in cyanide usage as a result of using MPC. MPC functionality is rarely available on the programmable logic controllers (PLCs) and control systems installed at gold plants, hence it is implemented on a personal computer (PC) networked to the cyanide analyser and plant infrastructure. Mintek has developed an embedded MPC that installs into the Mintek Cynoprobe analyser, adding MPC functionality without the need for additional PC and network infrastructure, reducing installation costs. This allows plants to minimise their expenditure on additional infrastructure while gaining the benefits of superior MPC technology for multiple cyanide dosage points. This paper will present results showing that the embedded MPC performs as well as Mintek’s existing PC-based StarCS MPC controller, making it a viable alternative for infrastructure-constrained gold plants. Keywords: Model predictive control, gold cyanidation

Jan 1, 2020

By M. Rudolph, E. Schach

Tecflote is a new group of nitrile-based collectors for sulfide flotation. Water insolubility results in some interesting implications for the actual mechanism. It is not yet understood if Tecflote is directly adsorbed on the mineral surface as emulsion droplets or if it is only active at the air-water interface, affecting the interfacial rheology or electrostatic- and Van der Waals interactions, which have a direct impact on the bubble-particle contact. Different investigations including contact angle measurements, AFM studies and micro-flotation experiments are conducted to obtain a better understanding of the actual mechanism of Tecflote. Due to the reagent’s insoluble character, the Langmuir-Blodgett technique is used to investigate its behaviour in the air-water interface and to deposit defined layers of Tecflote on mineral substrates for the above-mentioned studies. An interferometric set up is used to investigate the influence of Tecflote on the film thinning between an air bubble and a mineral substrate. In addition, possible synergistic effects for the combination of Tecflote and conventional frothers (e.g. MIBC) are studied. Keywords: Sulfide flotation, insoluble collector

Jan 1, 2020

By L. A. Cisternas, A. Lopez-Valdivieso, Y. L. Botero, L. Cortes

In the processing of sulfidic ores, pyrite is usually depressed and ends up in the tailings. However, pyrite is the most common species responsible for acid mine drainage (AMD) due to its spontaneous oxidation. This AMD affects the tailing chemical stability by dissolving some toxic or heavy metals species such as As, Cd, Co, Pb, and Zn, which can migrate into the surrounding ecosystems. Therefore, the strategies to reduce pyrite’s environmental impacts are a crucial point to produce more chemically stable tailings. Consequently, numerous studies have been made to find procedures that could inhibit or restrain AMD. This work aims to develop a procedure for designing conceptual flotation circuits that can produce tailings with low content of pyrite and to assess this type of circuit with traditional flotation circuits. The method consists of applying optimal flotation design where three products are considered: metal concentrate, pyrite concentrate, and tailing with low content of pyrite. Two approaches are considered; in the first, a flotation circuit is designed to generate a concentrate rich in all sulfide minerals and to obtain a tail with low pyrite content. Then, a second flotation circuit is designed for the selective separation of the bulk into metal concentrate and pyrite concentrate. This is called fractional separation design. In the second approach, a flotation circuit design is realised that generate the three products simultaneously. This is called integrated separation design. Both fractional separation design and integrated separation design are assessed in this paper. This methodology is focused on cleaner production (waste prevention and resource minimisation) rather than end-of-pipe technology (treat existing waste). The methodology was applied to a copper sulfide ore from a local company in the Antofagasta region (Chile). This ore contains chalcocite, covellite, iron oxides, and pyrite. Keywords: Flotation, tailing, pyrite, cleaner production

Jan 1, 2020

By M. Krasowska, W. Skinner, R. K. Asamoah

Understanding chemical interactions at solid-liquid interfaces have played a pivotal role in improving mineral flotation performance, increasing the rate of mineral crystallisation and profitable leaching of valued minerals and metals. This paper highlights gold leaching with links to surface and interfacial chemical processes occurring, and opportunities to maximise extraction while reducing usage of more recent scarce resources. From the review, there is a significant link between surface and interfacial processes and gold leaching performance. Evidently, gold leaching kinetics could be increased by changing leaching conditions, including manipulating the surface and interfacial interactions. Control of surface and interfaces during gold extraction could enhance rapid, smarter gold extraction and mitigate formation of passivation layers. Keywords: Surface and interfaces, refractory ores and concentrates, gold leaching, reaction mechanism and kinetics

Jan 1, 2020

By K, J. MAUNDERS

This paper briefly describes a computerised model of the South African electricity system which has been developed jointly by the Atomic Energy Board and the Electricity Supply Commission. The results of an analysis of this system have been subjected to a fairly extensive sensitivity analysis which reveals that up to the year 1990 between 680 and 700 million tons of coal will be required for electric power generation, together with between 7 000 and 10 000 tons of uranium. This result is fairly insensitive to data variations, but the prediction of a cumulative requirement up to the year 2000, of between 1 300 and 1 800 million tons of coal and 25 000 to 70 000 tons of uranium, proves to be very data-sensitive.

Jan 1, 2014

By R. Degel

Submerged arc furnaces and electric smelters are applied in numerous metal and slag production lines. Particularly in ferroalloy and non-ferrous metal production, like silicon metal, platinum group metals, calcium carbide, and copper, the units are an essential part of the production technology. Most of these electric furnaces are considered to be highly energy-intensive units. The high level of required electrical power is defined by the process. SMS developed several measures to reduce the overall electrical energy consumption of these metal production lines. In particular, the following measures contributes to a lower energy consumption: improved electrical efficiency with intelligent design and application of components, minimizing the heat losses from the furnaces with a balanced cooling/refractory systems, minimization of process steps (such as elimination of agglomeration), recovery of energy, process optimization (resulting in higher metal yield) and the achievement of higher recovery rates, enlarging furnace capacity to reduce heat losses, and maximizing the power-on time. This paper gives an overview of the above-mentioned solutions.

Jan 1, 2012

By J. Yianatos, P. Vallejos

In the last decades, the exponential increase in the cells’ volume resulted in significant advantages such as investment costs, footprint and energy savings. However, in larger size cells, despite the increased diameter/height ratio, new constraints arose related to the need for decreasing the larger froth transport distances to enhance the froth recovery. Thus, the use of froth crowders and internal launders became compulsory to maintain the froth transport distances but decreasing the ratio between gas and collected mineral flowrates. Consequently, the bubble load will increase until reaching a critical bubble surface coverage. In this paper, the concentrate carrying capacity (tph/m2) is described in terms of the bubble surface coverage (bubble loading) at the pulp-froth interface and the froth recovery (froth transport) and is evaluated as a function of the cells’ volume and operating variables. A sensitivity analysis, based on industrial operating and design conditions, such as superficial gas rate, particles size, froth crosssectional area and cells’ volume, was developed for evaluating the metallurgical performance of cells from 100 to 630 m3. Results show that limiting carrying capacity can arise for the whole range of cells’ volume, depending on critical operating conditions, particularly in first rougher cells and cleaning stages of industrial flotation circuits. The increase in cells’ volume consistently increases the bubble loading (bubble surface coverage) under all conditions, approaching the limiting conditions more rapidly in the case of cells without internal launders. Otherwise, the limiting condition was achieved when the particle size DPS decreased from 50 to 20 (μm) and for superficial gas rates significantly less or larger than 1 (cm/s). The use of internal launders allows for increasing the range of the operating conditions needed to reach a certain carrying capacity. Keywords: Bubble carrying capacity, flotation cells, bubble surface coverage, cells’ volume

Jan 1, 2020

By C. C. Pretorius, S. Ramjee, R. J. Mostert

The study investigates the effect of prior corrosive exposure on crack growth resistance behaviour of thin sheet (3 mm thick) aluminium alloy 2024-T3 at slow strain rates. Compact tension specimens were exposed to standard corrosive environments that simulate accelerated atmospheric corrosion attack. Two corrosive environments were considered – an exfoliation corrosion (EXCO) solution and a 3.5 wt% sodium chloride solution. The unloading compliance R-curves of the two-hour EXCO-exposed specimens revealed a significant degradation of approximately 11% in the crack growth resistance behaviour (Kc_e values) compared to the baseline (air-exposed) values. Furthermore, secondary intergranular crack formation was also revealed in the plastic zone ahead of, and adjacent to, the crack tip of these specimens; which formed during the crack growth resistance loading. It is postulated that the observed degradation of the Kc_e values of the EXCO-exposed material is due to hydrogen embrittlement since the exposure times for the EXCO evaluation were limited to ensure that uniform corrosion dominated; that is, significant penetration of corrosion damage and pitting due to localized corrosive attack did not occur. The sodium chloride-exposed specimens revealed a similar degradation (13%) after 24 hours exposure. However, slight intergranular corrosive attack and isolated pitting were observed on the exposed surfaces prior to crack growth resistance loading, resulting in notch effects that could assist in crack growth. Pitting and intergranular corrosion were, however, not observed at the pre-crack tip. The relative contributions of the notch effects and the hydrogen embrittlement during the degradation of the KR performance are, therefore, unclear.

Apr 1, 2021

By J. Saunders, N. Pretorius, G. Krafft, T. P. Katakwa

Imagine being able to see all the future planned mining activities in real time. This is exactly what SIMS (Short Interval Management System) will enable you to do. SIMS is a real time short interval control system that continuously measures and sets optimised plans for mining production processes. The system utilises algorithm-based software that takes resources (people, equipment, tasks, and workplaces) and gives you the best achievable plan. The algorithm was developed using methods found in the field of metaheuristics. A metaheuristic is a strategy to designed to efficiently search for optimal or near optimal solutions to problems that are very complex computationally. (Glover, 1986) There are several algorithms that have been developed to solve optimisation problems which are difficult to solve using traditional techniques. This has given rise to a field called evolutionary computing. (Simon, 2013) Examples of these techniques are genetic algorithms, particle swarm optimisation, and ant colony optimisation. These methods are used to solve problems in a variety of fields. As an example, Kok and Lane (2012) used particle swarm optimisation for equipment allocation in a mechanised underground mining environment. The first SIMS deployment took place in a platinum underground tabular mechanised mine near Burgersfort (province?) from 2017-2019. This included the development from a paper-based system to a fully operational online system. SIMS then moved to a second site and is currently being tested in a second platinum underground tabular mechanised mine in South Africa. Full deployment of the system is currently being phased in. SIMS was built in response to issues that have been plaguing the mining industry for years. These issues are all aligned into one major problem statement: how can we optimise mining production processes without compromising safety? This product was developed by combining years of mining experience with software development. SIMS is based on a four-pillar concept. Safety, productivity, accountability, and business improvement. SIMS uses a set of pre-configured mining and production rules, and with the resources that are available, to determine valid short term production plans. A background algorithm then determines the optimum plan to be executed. The system continuously produces a set of job cards that are pushed to respective operators on their allocated tablets. The management portal component allows you to view and manage all current and planned work on any connected device available. This allows real time visibility of completed, current, and planned work to operators, service departments and management, i.e., seeing into the future.

Sep 1, 2021

"Chairman: Dr W. S. RAPSON Rapporteur: Mr J. W. WILSONPapers:Computer applications in rock mechanics by F. H. Deist, E. Georgiadis and J. P. E. Moris Rock mechanics in the design of mine layouts by K. Hodgson and N. G. W. Cook Automated regulation of mine ventilation by P. NiskanenThe rock mechanics papers, because of their complementary nature, were presented in succession and discussion on both followed directly. The paper on automated ventilation control at a mine in Finland was then presented and the session was closed with several contributions to this paper.By and large the papers and discussions which followed in this session showed how a classic tie-up had developed between the use of computing techniques in important fields of mining, and their practical application. In fact, the dis-cussion following the rock mechanics papers showed clearly that without the aid of high-speed digital computers the rate of progress in applied research in deep-level hard-rock mines, would have been severely hindered. Furthermore, it became apparent from the comments made by several contributors that the rock mechanics techniques and computer progress described in Deist's and Cook's papers could be used to provide useful data in the solving of rock mechanics and design problems on mines other than flat dipping deep tabular deposits.The paper by Niskanen, which described an automated ventilation control system at a mine in Finland, showed how effective computers could be in areas where the reversal of mine ventilation occurs due to severe seasonal temperature ranges. Although the system described in the paper could not be introduced easily in complex underground mines, several contributors gave examples of similar ventilation problems that could be solved mechanically,In introducing his paper, Dr Deist said that the purpose of the paper was to give a brief account of some of the programs designed by himself and his co-authors to aid in the solution of rock mechanics problems,The first system presented by Dr Deist was known as MINSIM in the South African mining circles. This system was designed specifically to aid in the solution of rock mechanics problems in the South African gold mining industry. It was particularly designed to handle tabular deposits at great depth but it has been used satisfactorily on a number of occasions to obtain at least approximate solutions in other mining situations. Dr Deist said that the principles embodied in the programs were easily extended and, in fact, there was a project in progress at that time which was aimed to do this. He said that the principles could easily be extended to shallow-depth mining at steep or very steep inclinations."

Jan 1, 2014

By B. P. Watson

The discussion written by Dr de Frey suggests that mine design should be based on closely spaced stability pillars. However, this concept leads to low extraction ratios at depth. The concept of `crush' pillars in conjunction with more widely, appropriately spaced stability pillars allows for significantly larger extraction ratios, particularly at depth. It should be noted that the rock conditions in many areas of South African platinum and gold mines are good, allowing significant spans to be mined safely between stability pillars. `Crush' pillars are cut small enough to fail stably near the face under stiff loading conditions, and their residual strength is intended to support about 10 m rock height between stability pillars. While this support resistance cannot be achieved by conventional support, crush pillars have been proven to have the required capacity for this purpose. The concept of leaving smaller crush pillars with appropriately positioned stability pillars has been used successfully for more than 30 years in areas of South African platinum and gold mines.

Jan 1, 2011

A decision by joint-venture partners Anglo American, Gencor, and the Industrial Development Corporation to proceed with the expansion of the Columbus Stainless Steel plant in Middelburg will contribute significantly towards the economic growth that South Africa needs so desperately. The expanded facility, expected to come on-line in 1995, will be the largest single-plant producer of stainless steel in the world, and the company will rank sixth overall in world production.

Jan 1, 1993

By R. D. Cromarty, J. Du Toit

"Penetration of matte into tap-hole bricks causes detrimental refractory wear, which can lead to furnace breakouts. The ability of the tap-hole clay to form a protective layer on the brick, thereby limiting matte penetration was investigated by examining the interaction between platinum group metal (PGM) matte, tap-hole clay, and alumina-chrome refractory bricks on a laboratory scale.Samples containing clay and brick as well as samples containing clay, brick, and matte were heated to different temperatures to establish the clay-brick interaction and the extent of matte penetration. The greatest degree of physical contact between the brick and clay was achieved at curing temperatures of 600°C. Poor clay-brick contact was observed in the sample that was heated to 900°C.Matte displaced the clay in the clay-brick-matte sample that was heated to 1350°C, with significant matte penetration into the brick. Less matte penetration was observed when the clay-brick-matte sample was heated to 1500°C. Less matte penetration was also observed in the claybrick- matte sample in which the clay and brick were pre-baked at 800°C, and the sample then reacted with matte at 1350°C. IntroductionFloatation concentrate from ore from the eastern Bushveld Complex of South Africa, specifically the Platreef, Merensky, and UG2 reefs, forms the feed to the Polokwane platinum smelter (Hundermark, De Villiers, and Ndlovu, 2006). The ore from the UG2 Reef has a high chromite content, which requires high operating temperatures (1500–1700°C) to avoid chromium spinel build-up in the furnace hearth. These high operating temperatures lead to matte superheats in the vicinity of 500– 600°C, which put increased demands on the refractory materials (Nelson et al., 2005).Upon tapping, the matte moves through the tap-hole, which consists of an aluminachrome refractory brick-lined tapping channel (Hundermark, De Villiers, and Ndlovu, 2006). The flow of molten matte is stopped by the injection of tap-hole clay to form a plug in the tap-hole. The tap-hole clay hardens and strengthens during curing to obtain the required hardness and refractoriness against penetration, corrosion and erosion (Nelson and Hundermark, 2014)."

Jan 1, 2016

The AK6 kimberlite is situated 25 km south of the Debswana Orapa Mine in Botswana and was discovered by De Beers geologists in 1969 during the follow-up of geophysical targets in the Orapa area. The kimberlite was not extensively pursued at the time as the initial bulk sampling indicated it to be of limited size and low grade, factors largely contributed to by the basalt breccia capping. Completion of high resolution integrated geophysical techniques and drill bulk sampling to depth recovered 97 tons of kimberlite during 2003 and 2004, which led to the increased size and grade estimates. Bulk sampling by Large Diameter Drilling (LDD, 23 inch diameter) commenced in 2005; 13 holes were drilled to a cumulative depth of 3,699 m and 689 carats of diamonds were recovered. In July 2006 the De Beers Mineral Resource Classification Committee classified these Phase I LOO results at a High Inferred level with an average grade of 24 carats per hundred tonnes (cpht) at a bottom cut-off of +1 mm, and a modeled average diamond value of 150 dollars per carat. A second phase of LDO drilling was initiated in 2006, and bulk sampling by trenching commenced in 2007 in order to deliver a resource estimate at indicated level. An Indicated Resource of 11.1 million carats at an average grade of 22 cpht was declared for the deposit mining lease application lodged in 2007.

Jan 1, 2010