Scielo RSS <![CDATA[Journal of the Southern African Institute of Mining and Metallurgy]]> vol. 116 num. 8 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Diamonds still Sparkling Conference 2016</b>]]> <![CDATA[<b>Goals, Systems, and Plans</b>]]> <![CDATA[<b>Johannes Paulus Hoffman the Technical Father of 3CR12</b>]]> <![CDATA[<b>Pioneering large diamond recovery at Karowe diamond mine</b>]]> Historically, the recovery of large diamonds in conventional treatment plant flow sheets has been associated with dense media separation (DMS). This is attributed mainly to DMS's highly efficient and proven track record in the concentration and separation of ores with variable solids densities. In most instances, DMS has been utilized as a pre-concentration step ahead of any recovery plant, due to its ability and versatility in reducing feed within a specific size range to manageable volumes for downstream X-ray processing and subsequent diamond recovery. The benefit of using carbon-signature-based detection equipment for retrieving large stones upfront in the flow sheet not only equates to earlier recovery of diamonds from the system, but also lessens the exposure of diamond-bearing ore to additional materials handling, pumping, and/or crushing, which has been known to damage or even break diamonds and decrease revenue. <![CDATA[<b>The CCUT block cave design for Cullinan Diamond Mine</b>]]> Petra Diamonds Cullinan Diamond Mine (CDM) is currently producing from two mining blocks that are nearly depleted and highly diluted. CDM is developing the CCUT mining block as a mechanized block cave with an advance undercut that would replace the current mining blocks and increase production to approximately 4 Mt/a. The CCUT block production level on 839 m level is approximately 200 m below the current production areas on the 630 and 645 m levels. The planning of the CCUT block with a lift height of approximately 194 m at CDM under Petra's ownership commenced in 2008. The access declines to the block started in 2009 and 2010. Most of the shaft deepening and waste development have been completed, with the planned 'deep' shaft and ground-handling system planned for commissioning in June 2016. The first undercut ring was blasted in July 2015. This paper reports on the design process and evolution of the project, including: ► Geotechnical design criteria ► Advance undercutting sequence and strategy ► Undercut advance rates, slot designs, and rings designs to achieve the undercutting objectives (of high early tonnages and high undercut advance rates) ► The production level development philosophy in utilizing advance undercutting, production level design and drawbell opening sequence.' <![CDATA[<b>Design and implementation of steeper slope angles on a kimberlite open pit diamond operation-a practical approach</b>]]> The steepening of slope angles on an open pit mining operation has a material impact on improving the economics of mining. Steepening of slope angles can also increase the risk of slope failure. Slope failures are inherently costly events, because they can be catastrophic, resulting in multiple fatalities, equipment damage, and temporary or permanent closure of a mine. The steepening of the basalt slope angles at Letseng Diamond Mine followed operational improvements that were introduced through improved blasting practices and geotechnical controls. The steeper slope design resulted in a 6 Mt/a reduction in the peak waste mining compared with the previous mine plan coupled with an increase in the net present value and life of mine. This paper is an outline of the steps that were taken at Letseng to increase slope angles in waste and the resulting improvements to the mine plan. <![CDATA[<b>Using the proportion of barren samples as a proxy for minimum grade in a diamondiferous linear beach deposit - an application of the Nachman model</b>]]> Over the past 80 years, the Namibian diamondiferous marine placer has been studied extensively to develop solutions for mining and sampling challenges. The types of studies include the statistical modelling of the distributions of the stone counts per sample; investigating the relationship between geology and the grade distribution; assessing the quality potential of the entrapment of the available diamond pulse; using predetermined acceptability of barren samples (zero proportion (Zp) samples) to model distributions; optimal sample sizes; and more. During early-stage project evaluation it is more important to find out if a particular area is likely to be above a specific cut-off grade than to focus on sampling for the purpose of accurate resource estimation. Previous work using mixed Poisson and Sichel distributions to model the abundant onshore diamond data has been very successful in modelling the long-tailed nature of these linear beach deposits. The means of these distributions are, however, sensitive to extreme values. Technical and cost constraints prevent a similar scale of sample collection in an adjacent, geologically equivalent, submerged beach environment. A method not sensitive to extreme values is thus required to make early-stage assessments of the likelihood that the grade of a particular target is above a minimum cut-off grade. The Nachman model describes the functional relationship between the mean population density and proportion of barren patches ( Zp) in a patchy environment. A prerequisite for using the Nachman model is that the underlying data must be modelled using a negative binomial distribution (NBD). The case study data is from an analogous area adjacent to the exploration target and meets the NBD requirement. It is thus appropriate to apply the Nachman model. The Nachman model provides an opportunity to use the observed Zp to predict the mean grade for an area at the very early stage of an exploration project. In future, early-stage exploration data from a homogenous geological zone exhibiting characteristics of the Nachman model assumptions can thus be used to rank and target those areas that show potential to be above the minimum required grade cut-off for follow-up sampling and inclusion in the mine planning cycle. <![CDATA[<b>Microdiamond analysis - a method for estimating the size frequency distribution of the macrodiamonds</b>]]> Estimating the size frequency distribution of the macrodiamonds on a new deposit is important for both economic reasons and for the design of the processing plant. Millions of dollars can be lost due to incorrectly sized comminution circuits. This report analyses an alternative methodology for macrodiamond grade estimation using the cumulative results from small parcels of microdiamonds and plotting them on a log-log scale. The method was first evaluated mathematically for diamond populations to assess the confidence for data extrapolation. Macrodiamond size distributions and grades were predicted using microdiamond data from three kimberlites, and the actual macrodiamond grades compared to the the predicted grades. The predicted grades were found to replicate the actual grades closely, showing that a high degree of confidence can be ascribed to the results from this method of analysis. This analysis can be used both for resource estimates and for predicting the diamond size distribution information needed for designing a new operation. <![CDATA[<b>Extension of the Cullinan Diamond Mine No. 1 Shaft underneath the existing operating shaft, with emphasis on rock engineering considerations</b>]]> In 2012, Cullinan Diamond Mine began an expansion programme with the shaft deepening and development of access to the C-Cut 1 block at approximately 839 m below surface. The expansion programme is funded by a combination of bank loans and retained operating profit generated by the mine. Continuous production during deepening of the No. 1 Shaft, which is the rock hoisting shaft, was therefore critical for sustainability and efficiency as well as overall funding of the project. The deepening method, support design and verification, as well as learning outcomes pertaining to the extension of the No. 1 Shaft underneath the existing operating shaft are summarized, with emphasis on the importance of gaining some understanding of the shaft's host rock mass. <![CDATA[<b>Fracture banding in caving mines</b>]]> The Duplancic model of caving is widely accepted in industry and is the framework within which most monitoring and numerical modelling results in caving mines are interpreted. As a result, the damage profile ahead of the cave back is often interpreted as continuously decreasing damage with increasing distance ahead of the cave back. Physical modelling of the caving process performed in a centrifuge did not support this expected behaviour, but instead suggested a discontinuous damage profile ahead of the cave caused by fracture banding. Some support is found in the literature to suggest that the behaviour observed in the models may also be present in the field. This notion is further supported by banding behaviour observed from microseismic monitoring at two block cave mines. Combining the information from the physical models, field observations referred to in the literature, and the microseismic analyses, it is concluded that the Duplancic model needs to be extended to include the phenomenon of fracture banding. It is also reasonable to expect that fracture banding may play a more important role in the caving process than has previously been recognized. <![CDATA[<b>Estimating specific energy from the brittleness indexes in cutting metallic ores</b>]]> Specific energy (SE) is a very useful parameter for assessing rock excavation by machine. Predicting the SE from the brittleness will be practical, especially for preliminary studies, due to the fact that determining the SE from cutting tests is difficult and expensive. In this study, the predictability of the SE from different brittleness concepts was investigated for metallic ores such as chromite, haematite, galena, and smithsonite. Uniaxial compressive strength, Brazilian tensile strength, impact strength, and small-scale cutting tests were carried out in the laboratory. The SE values were calculated from the cutting tests and correlated with three different brittleness concepts. A significant correlation could not be found between the SE and the brittleness B3(the ratio of compressive strength minus tensile strength to compressive strength plus tensile strength). However, strong correlations were found between the SE and the both brittleness B5 (the product of percentage fines in the impact strength test and compressive strength) and brittleness B8 (half of the product of compressive strength and tensile strength). The validations of the derived equations were also checked. It is concluded that the SE in ore cutting can be reliably estimated from the brittleness concepts B5 and B8. <![CDATA[<b>The globalization of the South African mining industry</b>]]> In 1990 the South African mining industry was predominantly domestically based and was dominated by six mining houses, which all had their head offices in Johannesburg with their primary listings on the Johannesburg Stock Exchange (JSE). However, radical changes in the domestic and international political and economic environments during the 1990s resulted in the demise of the domestic mining house system and the two largest mining houses, Anglo American and Gencor (which was incorporated into Billiton) moved their head offices and primary listings to London. Unfortunately, this move led to massive disinvestment from South African mining and industrial assets by both Anglo American and BHP Billiton. It also resulted in a loss of financial and technological capacity, which during the last century had made a massive contribution not only to the mining industry but also the development of the manufacturing industry. After their London listings both these companies placed their international interests well above the national interests of the host country, South Africa. This raises serious questions regarding foreign ownership of the South African mining industry. Thus, although foreign-owned companies are still playing an important role, the history of our mining industry during the new century suggests that South Africa should not place excessive reliance on foreign-based companies to develop its mining industry and national economy. <![CDATA[<b>A systems approach to mining safety: an application of the Swiss Cheese Model</b>]]> Achieving zero harm in the mining industry is still a big challenge worldwide. A potential major step towards remedying the situation is a good understanding of the processes that lead to accidents in the industry. The Swiss Cheese Model has had a significant impact on the understanding of the causes of accidents in high-risk industries. In this paper, an accident analysis framework based on the Swiss Cheese Model is developed and tested against a previous mining disaster. The developed framework has the potential to enhance the understanding of the factors that contribute to accidents in the mining sector. <![CDATA[<b>Optimizing seat selection for LHDs in the underground mining environment</b>]]> Whole-body vibration (WBV) occurs when the human body is supported on a surface that is vibrating. Operators and passengers in mobile machinery are exposed to vibration transferred from the seatpan to the body. Excessive vibration exposure is strongly associated with low back pain, therefore seat selection is important for reducing vibration exposure. Recently, we developed an efficient neural network (NN) algorithm that identified the dynamic properties of suspension seats, and then interrogated the models to predict seatpan vertical accelerations for a variety of skidders in the forestry sector. We have expanded this approach to evaluate the influence of different seats on the WBV exposures from load-haul-dump vehicles in the underground mining environment. Of the five seat models that we tested, our results demonstrated that one particular seat model was best able to attenuate vibrations based on the equivalent daily exposure, Λ (8), and the corresponding working hours to reach the upper limit of the ISO 2631-1 health guidance caution zone for 8hour operation. We performed a sensitivity analysis to evaluate the influence of the individual vibration frequency components on the Λ (8) results for each of the seat models. This analysis revealed that each of the industrial seats responded differently to specific vibration frequencies and explained why the seat selection algorithm matched particular seats to specific vibration environments <![CDATA[<b>The prediction of penetration rate for percussive drills from indirect tests using artificial neural networks</b>]]> Percussive drills are widely used in engineering projects such as mining and construction. The prediction of penetration rates of drills by indirect methods is particularly useful for feasibility studies. In this investigation, the predictability of penetration rate for percussive drills from indirect tests such as Shore hardness, P-wave velocity, density, and quartz content was investigated using firstly multiple regression analysis, then by artificial neural networks (ANNs). Operational pressure and feed pressure were also used in the analyses as independent variables. ANN analysis produced very good models for the prediction of penetration rate. The comparison of ANN models with the regression models indicates that ANN models are the more reliable. It is concluded that penetration rate for percussive drills can be reliably estimated from the Shore hardness and density using ANN analysis. <![CDATA[<b>Where to make the transition from open-pit to underground? Using integer programming</b>]]> The transition from open pit (OP) to underground (UG) operation is one of the challenging mining engineering issues. Mines that have the potential to transition from OP mining to UG mining will eventually come to a 'transition point' where the decision needs to be taken whether to extend the pit or switch to UG mining. In this paper we present a new integer programming (IP) formulation to obtain the optimal transition point from OP to UG mining. The proposed model is implemented on a three-dimensional (3D) gold deposit and a two-dimensional (2D) case study is used to demonstrate the validity of the model. Due to the large number of variables, strategies are proposed to shorten the solution time. The proposed model has successfully determined the optimal transition point and generated a significantly better undiscounted profit than that of the traditional approach.