Scielo RSS <![CDATA[Journal of the Southern African Institute of Mining and Metallurgy]]> vol. 108 num. 7 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[<b>Comparative study of the influence of minerals in gas sorption isotherms of three coals of similar rank</b>]]> This investigation compares the gas adsorption behaviour and capacity of three bituminous coals from South Africa, of similar rank, by assessing the characteristics of the raw coal, as well as the resulting float and sink fractions (at 1.80 cm3/g) obtained by density separation of crushed coal samples. Calculations were also made to obtain the raw coal gas storage capacity from the weighted contribution of both float and sink fractions results, thereby permitting comparison with the analysed results of the raw coal. The study demonstrated that the clean fraction of a coal has the highest capacity to retain gas in the sorbed state, followed by raw coal, and lastly the sink fraction, and re-confirmed previous investigations that showed minerals to be inhibitors of gas adsorption and retention. <![CDATA[<b>The 2007 South African Mineral and Petroleum Resources Draft Royalty Bill: An independent analysis</b>]]> This paper reviews the third Draft Mineral and Petroleum Resources Royalty Bill of 2007, and this analysis identifies potential areas for further consideration by the National Treasury before the new regime becomes official. At its basic level, a royalty regime consists of two elements: the base and the rate that must be applied to the base. Deciding on an acceptable royalty rate is complex and can be done only after understanding the base and after an extensive analysis of all variables affecting the competitiveness of the regime. The proposed royalty rate of the third Draft is calculated by means of a formula that provides for a sliding rate depending on the profitability of the mine. The base is a sales revenue definition that approximates net smelter return. The regime proposed in the third Draft Bill is a significant improvement on previous drafts and, with minor refinements, should stand the test of time. <![CDATA[<b>A new model for mining method selection of mineral deposit based on fuzzy decision making</b>]]> One of the main tasks in exploitation of mines is to select a method suitable for the deposits, specific features including geometric, geomechanical and geological features. The purpose of selecting a mining method at this stage is to choose one or more method(s) having the most coordination with the deposit's conditions and external factors, including the allocated budget and local technology for detailed feasibility studies. Several methods have been developed in the past to evaluate suitable mining methods for an ore deposit, based on its physical characteristics. These approaches can be classified into three groups: (1) profile and checklist methods, (2) numerical ranking (scoring) methods, and (3) decision-making models. Most of these methods have shortcomings. Considering the fact that most of the specifications of mineral deposits, such as dip and depth, are linguistic variables, absoluteness of the explaining parameters by previous methods can be mentioned as the most important disadvantage of these methods. This paper discusses the Fuzzy technique for order performance by similarity to ideal solution (Fuzzy TOPSIS) to determine the mining method. The fuzzy decision making (FDM) software tool is employed to develop a Fuzzy TOPSIS based model. Application of this model with various values (crisp, linguistic and fuzzy) of the deposit eliminated the existing disadvantages of other methods. Two empirical illustrations demonstrate the effectiveness and feasibility of the evaluation procedure. These show that the proposed model performs better than its alternatives. <![CDATA[<b>Ground support strategies to control large deformations in mining excavations</b>]]> SYNOPSIS Tunnelling under squeezing ground conditions poses significant challenges. There are fundamental differences in the choice of support for mining as opposed to civil engineering. This paper reviews ground support strategies that have been used to control large deformations in mining excavations based on field data from five different mines in Australia and Canada. Recommendations are made for improved ground control strategies in squeezing rock conditions. <![CDATA[<b>Seismic monitoring of the Northparkes Lift 2 block cave - Part I undercutting</b>]]> Caving of the second lift of the E26 orebody at Northparkes Mines was monitored with a comprehensive package of instrumentation, including an ISS seismic monitoring system. Seismicity was collected by an array of 19 triaxial accelerometers and 9 uniaxial geophones, giving a high quality seismic data set. The seismic response to block caving at Northparkes has been divided into two papers. The first paper focuses on the seismicity during undercutting. The second paper deals primarily with the seismicity during cave propagation during initial cave production. In this paper, traditional seismic monitoring concepts are applied to seismicity during cave mining. More than 40 000 seismic events were recorded during cave undercutting between February and January 2004. Events up to local magnitude +1.3 were recorded near the mine during undercutting, with event rates of up to 500 per day. Analysis of frequency-magnitude distributions, S-wave to Pwave energy, and temporal variations in event magnitude all gave insight into the seismicity recorded. In addition, a new technique, called apparent stress time history, was shown to be sensitive to stress change from undercut blasting, and useful to identify significant periods during cave development. A significant difference was identified between the cave back location and the halo of seismic events above the cave. Throughout the undercutting, the aseismic zone of loosening was typically 50 to 70 metres in vertical thickness. Based on the seismicity, a stress driven rock mass failure model is proposed. Early in the undercutting, seismicity and movements in the seismogenic zone were directly triggered by stress change from undercutting. Towards the end of undercutting, seismicity was virtually uncorrelated with undercut blasting, and likely due to the onset of cave initiation. <![CDATA[<b>Seismic monitoring of the Northparkes Lift 2 block cave - Part 2 production caving</b>]]> Production caving started for Lift 2 at Northparkes in August 2004. In a period of less than 3 months, more than 10 000 seismic events were recorded. Events up to local magnitude +2.9 were induced near the mine during caving, with event rates of up to 500 per day. This paper documents the seismicity related to cave initiation and cave propagation during the initial production of Lift 2. The seismogenic zone of events initially moved at a rate of about 0.5 metres per day, accelerating to 2 to 3 metres per day after a few months of cave production. Seismic data analysis infers that the crown pillar between Lift 1 and Lift 2 was destressed over a vertical height of about 100 metres. As the seismogenic zone approached the crown pillar, a macroseismic episode occurred, with more than 20 events of at least local magnitude +1 occurring in a two-week period. Based on the seismicity recorded for Lift 2 at Northparkes Mines, a caving mechanics model is proposed. Comments and suggestions are made for seismic data analysis and design of seismic monitoring systems in block caving mines.