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By G. Hausen, H. Micka

"Modern signal and power electronics made adjustable-speed AC drives technically feasible and reliable and economically attractive. Cycloconverters are discussed as a proven technology for mine hoists. \IntroductionUntil rather recent technical and commercial advances in power and signal electronics, DC motors were used almost exclusively for applications requiring continuously adjustable operating speeds and torques. More recently, the significantly higher efficiency and the accordingly lower operating costs of AC motors gained importance. An effective and efficient speed control of AC motors requires the control of AC voltage and frequency. Table 1 shows typical applications of adjustable-speed AC drives.CycloconvertersOf particular interest to the mining industry are cycloconverters for hoist drives. The cycloconverter represents by far the simplest, most efficient and most economical means of converting a constant-voltage, constant-frequency supply into an adjustable-voltage, adjustable-frequency supply as required for the speed control of AC drives operating in the frequency range to half of the utility frequency.Cycloconverters feeding synchronous motors or induction motors are ideally suited for slow-speed direct-coupled drives."

Jan 1, 1988

By J. M. Ortiz

Grade control and short-term planning are usually based on the samples obtained from blastholes. These samples may carry a large sampling and sample preparation error. At El Tesoro copper mine in northern Chile, an advance drilling grid is used for short-term planning and grade control. These drill holes are sampled well in advance, and a short-term model that incorporates several variables and sophisticated estimation methods can be prepared for decisionmaking. An additional advantage of the advance drilling samples is that reverse circulation can be used instead of conventional down-the-hole equipment, and a very careful sampling and sample preparation process can be implemented, reducing the total sampling error. Advance drilling can be performed on a wider grid than blasthole drilling, hence the decision about the grid requires assessing the economic benefit of different sampling grids. Furthermore, this process allows the cost of poor sampling and the effect of different estimation procedures to be quantified. We demonstrate the optimization of the drilling grid for short-term planning and grade control at El Tesoro mine by means of the economic evaluation of the performance of different drilling grids, with different drilling techniques (which differ in the sampling error). The methodology is based on creating dense (exhaustive) geostatistical simulations of the grade distribution over a volume defined for a production period in respect of the geological model, and assuming each simulation as the true grade distribution. Then, samples are obtained from the exhaustive simulations at a spacing similar to the advance grid to be evaluated, and a sampling error is added. The short-term estimation procedures used on the mine are applied to determine the destination of each block and the profit obtained. This profit can be compared with the maximum profit (unachievable) and with the profit under different sampling errors and grids. The results show that the current 8 x 8 m drilling grid is appropriate and by reducing the sampling error, misclassification is also reduced, leading to an increase in profit of about US$ 5 million in 4 years.

Jan 1, 2012

By L. F. Contreras

In open pit mine design, it is customary for geotechnical engineers to define the appropriate slope design angles within practical limits. The conventional approach to slope angle design is based on the comparison of calculated stability indicators, such as the factor of safety (FS) and the probability of failure (PF), with generic acceptability criteria not directly related to the impacts of failure. A major drawback of this type of approach is related to the difficulty of defining meaningful acceptability criteria. An alternative methodology of pit slope design is proposed, where the economic impacts of potential slope failures are calculated and used as the elements on which to apply the acceptability criteria for design. The methodology is based on the construction of a graph, referred to as a risk map, that relates the probability of exceeding the economic impact of slope failure to the magnitude of the impact measured in monetary terms. The process includes the analysis of a selected number of representative years of the mine plan and slope sections of the pit areas to define the required inputs for the construction of the risk map. The paper discusses the concepts used in interpreting the probability of slope failure, and describes the approach followed for the estimation of the economic impacts of slope failure and the construction of the risk map. Finally, the two main uses of the risk map are discussed, including the comparison with acceptability criteria for the evaluation of a specific open pit design and the comparative analysis of open pit design options in terms of value and risk to identify optimum pit layouts.

Jan 1, 2015

By D. F. Malan

This paper gives an overview of the difficulties associated with determining the strength of hard-rock pillars. Although a number of pillar design tools are available, pillar collapses still occur. Recent examples of large-scale pillar collapses in South Africa suggest that these were caused by weak partings that traversed the pillars. Currently two different methods are used to determine the strength of pillars, namely, empirical equations derived from back analyses of failed and stable cases, and numerical modelling tools using appropriate failure criteria. The paper illustrates that both techniques have their limitations and additional work is required to obtain a better understanding of pillar strength. Empirical methods based on observations of pillar behaviour in a given geotechnical setting are popular and easy to use, but care should be exercised that the results are not inappropriately extrapolated beyond the environment in which they are established. An example is the Hedley and Grant formula (derived for the Canadian uranium mines), which has been used for many years in the South African platinum and chrome mines (albeit with some adaptation of the K-value). Very few collapses have been reported in South Africa for layouts designed using this formula, suggesting that in some cases it might yield estimates of pillar strength that are too conservative. As an alternative, some engineers strongly advocate the use of numerical techniques to determine pillar strength. A close examination unfortunately reveals that these techniques also rely on many assumptions. An area where numerical modelling is invaluable, however, is in determining pillar stresses accurately and for studying specific pillar failure mechanisms, such as the influence of weak partings on pillar strength. In conclusion, it appears that neither empirical techniques nor numerical modelling can be used solely to provide a solid basis for conducting pillar design. It is therefore recommended that both these techniques should be utilized to obtain the best possible insight into a given design problem. Owing to the uncertainties regarding pillar strength and loading stiffness, monitoring in trial mining sections and in established mining areas is also an essential tool to test the stability of pillar layouts in particular geotechnical areas.

Jan 1, 2011

By G. S. Camm

Gwynfynydd is a small, high-grade black shale-hosted vein-gold deposit. The Chidlaw Link Zone is the only area being mined and contains 24 000 t ore grading 15.2 g/t gold. Within the Link Zone a complex vein structure occurs consisting of a mother vein up to 5 m thick and narrow (less than 0.5 m) leader veins. The former shows minor variations in dip, strike and thickness, whereas the latter show marked changes in all three. The leader veins are hosted within the footwall zone of the mother vein and both are composed of quartz with galena, sphalerite, chalcopyrite, pyrite and minor arsenopyrite. The vein system is transected by a series of cross-vein and intra-vein dip-slip faults. Pockets of gold occur at vein intersections or branches and within the complex footwall zone and are often related to variations in vein attitude and/or geometry. The Chidlaw Link Zone displays a complex, erratic distribution of gold mineralisation and a multi-stage history of structural activity, fluid flow and mineral deposition

Jun 18, 1905

By Belcher C. B

A procedure was required for the rapid determination of silicon in low-alloy irons and a suitable method used the formation and reduction of silicomolybdic acid at 50°C. The procedure gives results for elemental silicon and this enables the correct computation of oxidation requirements in basic oxygen steelmaking. The method could be useful in iron foundries which have not installed direct reading spectrometers.INTRODUCTIONOxygen steelmaking experiments required rapid determinations of 0,5-1,6 per cent silicon in iron (3-4 per cent C) within 10 min of sampling; a reproducibility better than ±0.03 per cent Si was desired. Only elemental silicon (Si°) is of interest as a fuel in basic oxygen steelmaking technology, and the proposed procedure determines exclusively this form of silicon. The method is described as it may prove useful to other workers although the interference study would be incomplete for some applications.The analysis of silicon in iron is frequently obtained using direct reading spectrometers, but for the proposed experiments the spectrometers could not be used because of the prohibitive distance from the furnace. It should be noted that spectrometers determine both the elemental silicon and that present as silicon dioxide in occluded slag and inclusions.The silicon content of iron and steel is determined in this laboratory by spectrophotometric measurement of a "molybdenum blue" colour. The reactions involved have been extensively investigated; Strickland (1952) showed that a...

Jan 1, 1965

By William E. Young

There are many large rhodonite-bearing veins containing manganese in the Eureka-Animas Forks area of the San Juan Mountains in Colorado. The Sunnyside vein is the largest known vein in the area. As observed on the surface, the vein is mineralized over 8,000 feet and attains a maximum width of 200 feet. The average width of the vein and its branches and ramifications is 58 feet in the area that was mapped in detail. The weighted-average analysis of surface and underground samples from the northeastern extension of the Sunnyside vein is 8 percent manganese. Most other known veins in the area have a similar manganese content. The Hidden Treasure vein lies southeast of the Sunnyside-No Name-Mastadon vein. The weighted average of the analyses of surface and underground samples from this vein is 13 percent manganese. Exposures of the Scotia-Silver Chord vein are visible over a strike length of 4,000 feet on Treasure Mountain. Diamond-drill holes show that the vein contains 10 percent or more manganese to a depth of 400 feet. The vein has an average width of 28 feet. The Independence vein is exposed on the surface for a distance of 600 feet and has an average width of 6 feet. Three cut samples taken across the vein had an average content of 20.7 percent manganese. Sampling of the outcrops of eight veins in the Placer Gulch area also indicates manganese. Numerous other veins cropping out in the surrounding area are similar to the outcrop of the Sunnyside vein system mineralogically and are worth investigating.

Jan 1, 1966

The refractory nature of residual gold in Kalgoorlie calcines is caused by occlusion in dense pyrrhotite formed by fusion within pyrite grains during decomposition. Fusion of pyrite increases as the rate of heating exceeds the rate of sulphur expulsion. By controlling these rates in relation to each other in a fluidised system fusion is limited and an expanded structure is formed. The increased area presented to cyanide solution, and the decreased diffusion distance, makes gold more accessible for extraction. Gold extraction from expanded pyrrhotite, before oxidation for porosity, is comparable with extraction from fully oxidised calcines from Edwards roasters. A method is suggested for standardised comparison of cyanidation residues.

Jan 1, 1957

By M Blanch

Gas management practices across the Australian underground coal industry have evolved significantly since the early nineties with the introduction of hazard management plans, directional drilling techniques, surface gas predrainage methods, and the widespread use of ventilation and gas reservoir simulation software.The improvements are evidenced by a substantial reduction in the occurrence of outbursts and gas related delays during a period where coal production rates have increased three to four fold. The development of effective gas predrainage strategies have been afforded by the use of reservoir simulators and a significant increase in the availability of measured gas reservoir data, in particular gas content and composition, adsorption isotherms and permeability. That said significant opportunities remain to optimise gas drainage designs and increase certainty in the gas predrainage design process through an enhanced understanding of coal seam permeability and how it is applied in the gas drainage design process.This paper describes the discrepancies between measured and actual seam permeability found during the recent assessment of two pilot predrainage programs executed in the coal measures of Queensland’s Bowen Basin. The results of those programs illustrate the need to better understand the validity of measured permeability data. The history match method employed in the pilot well assessments is proposed as an integral step in the routine gas drainage design processes that will ultimately lead to increased certainty and flexibility in gas predrainage practices.CITATION:Blanch, M, 2017. Coal seam gas predrainage optimisation through an enhanced knowledge of coal seam permeability, in Proceedings Australian Mine Vent Conference 2017, pp 73–78 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 28, 2017

By David A. Monaghan

On January 14, 1974 a fire occurred in the 3 East mains of the Joanne Mine of Eastern Associated Coal Corp. in Rachel, West Virginia. The mine was evacuated without injury and sealed completely at the surface within 24 hours. It was decided by the coal company along with the U, S, Bureau of Mines, the West Virginia Bureau of Mints and MESA that remote sealing of the fire zone would be attempted. This report summarizes the remote sealing effort and those activities directly related to the remote sealing effort. This chapter provides a brief history of previous remote sealing attempts, a description of the recently developed remote sealing system and a description of the Joanne Mine operation as it related to and affected the remote sealing effort.

Jan 1, 1975

This report summarizes the work performed and results achieved in the period from 18 June 1971 through 18 October 1971 under Phase I (Task 1: Literature and Industry Search; Task 2: Conceptual Design and Evaluation; and Task 3: Concept Selection and Preliminary Design) in substantiation of the drill/impregnation machine concept recommended for detailed design in Phase II. Also included as Task 5 are recommendations for an experimental investigation to be conducted during Phase II. The report is submitted for approval and authorization to proceed to Phase II.

Jan 1, 1972

By Gilles Landry, Mohamed Ourriban, Pierre Pelletier, Ahmed Bouajila, Claude Gagnon

"This paper summarizes the work carried out to develop and implement the gold cyanidation by size class (CSC) process, a novel concept aiming to reduce cyanide consumption.First, the authors will present the methodology and results of laboratory tests conducted to evaluate the response and the expected gains for the selected ore when submitted to the CSC processing. In the second part, focus will be on the methodology behind the CSC scheme development prior to its implementation at Sleeping Giant Mine concentrator. Finally, the evaluation of the modified circuit performance (operating since July 2007) will be addressed as a reduction of cyanide consumption by more than 30% and of free NaCN in the tailings by more than 50% is confirmed.INTRODUCTIONCyanidation is the most widely used technique to extract gold from hard rock ore. Its use of oxygen as an oxidant still makes it the cheapest process available after more than a hundred years. Unfortunately, gold cyanidation is known to be a slow process that requires high consumption of cyanide. In fact, cyanidation plants are designed with very long residence times (Habashi, F., 1967). Drawbacks of long cyanidation times are, among others, loss of gold in tailings, high reagent consumption and high capital investment and maintenance costs.Responding to their members expectations for the improvement of cyanidation process, COREM undertook a challenging R&D program covering the development of alternative concepts (processes) and the understanding and solving of mass transfer, gold passivation and process water chemistry problems. One of the interesting findings of the R&D program is a patent pending process technology based on the cyanidation by size class (CSC) concept (Côté and Ourriban, 2004; Gagnon and Ourriban, 2007; Gagnon and Ourriban, 2004).The new technology was tested at the Sleeping Giant concentrator, a plant member of COREM. The existing flowsheet was modified in order to implement the CSC process in the full-scale plant. The plant has been operated using the modified CSC based process since August 2007. Laboratory testwork was conducted prior to the industrial application in order to properly design the new process scheme. The modifications included:1) Reclassification of the grinding circuit product through an hydrocyclone2) Leaching of the coarse size fraction3) Addition of the fine fraction to the coarse leaching circuit tails."

Jan 1, 2009

By J. Konnerup-Madsen, T. Unlu, H. Stendal

Paper presented at the conference Economic geology in Europe and beyond II, models for mineral deposits in sedimentary basins, held in Keyworth, UK, 13-14 April 1994. The region includes the Deveci siderite/goethite deposit and the Hasancelebi, Karakuz and Kuluncak magnetite/goethite deposits; Deveci is the only mine in operation. The area consists of a serpentine-gabbro complex overlain by a volcano-sedimentary sequence hosting the iron ores. At least three generations of hydrothermal alteration have affected all rock types except the latest trachytic dykes. The Deveci deposits occur in a pyroclastic volcano-sedimentary sequence with shales and carbonates equivalent to the main mafic sequence, whereas the other three deposits formed contemporaneously with the intrusion of trachytic dykes. The deposits are of the volcanic-exhalative type, with syngenetic siderite in pillow lavas or stratiform layers the primary and main Fe-bearing mineral. In the west hydrothermal alteration has replaced siderite in pillow lavas with magnetite or has remobilised sideritic iron into magnetite veins

Apr 1, 1995

Objective To reduce dust generated from soiled floors within enclosed operator cabs. Background Enclosed operator cabs are widely used on mobile excavation equipment in the mining and construction industries. They protect the operator from bad weather, noise, and airborne dusts. The inside cab environment usually must be kept at very low dust concentrations because of quartz dust generated from the excavation of silica-bearing rock. For cabs to be effective in controlling airborne respirable dust, they must have an efficient air filtration system, while providing a positive pressurization of the cab interior. Ideally, the recirculated and exterior makeup air filtration should provide at least 99% capture efficiency for dust particles as small as 0.3-µmaerodynamic diameters. Many of these enclosed cabs use heating units mounted or directed along the floor (see figure 1), which can cause dust entrainment problems. Prior studies by the National Institute for Occupational Safety and Health (NIOSH) of enclosed cabs have shown that these floor heaters can generate notable amounts of dust within the cab enclosure (see Technology News 486). Multiple-shift dust levels measured inside a drill cab increased on average from0.04 mg/m3 during the summer months to 0.68 mg/m3 during the winter months. Additional dust level measurements, made with optical particle counters during a nondrilling time period, verified that dust levels inside the cab increased from 0.03 to 0.26 mg/m3when the floor heater/fan was turned on. Dust levels within the cab also became greater than the ambient air dust levels outside of the cab when the floor heater was turned on during the nondrilling time period. This shows that the floor heater was a notable dust source problem. Cab floors are commonly soiled from operators tracking dirt inside the cab upon entering from the mine or construction site. Interior cab dust levels can be increased by (1) airflow disturbance of the soiled floor or (2) operator disturbance of the soiled floor. Approach During prior NIOSH surveys of surface coal mine drills, several drills with very low cab dust levels (#0.1 mg/m3) were observed to have floor sweeping compound spread out over the cab floor during the working shift. This initial observation led to a more controlled A-B study of the effect of the sweeping compound on the interior cab dust levels. This study involved dust sampling with and without sweeping compound inside the cabs of a bulldozer and two drills. Sweeping compounds commonly use sawdust or cellulose as the main bulk material, with oil or wax added for dust adhesion purposes. Sand is sometimes added to increase bulk density. Sweeping compounds with sand are commonly used to sweep up concrete floors. Those without sand (usually referred to as "gritless") are used to sweep up smooth finished floors. Most of the oils and waxes used for the adhesive ingredient are petroleum-base and can have an irritating odor. People sensitized to petroleum distillates could have allergic reactions to these sweeping compounds. A few companies offer non petroleum-base sweeping compounds, using either a natural oil or chemical additive for dust adhesion. During this study, it was decided that only the gritless sweeping compound (without sand) would be used, eliminating the addition of another potential silica source inside the cab. Since the sweeping compound would be applied on the enclosed cab floor for the duration of the shift, it was decided to use a canola oil-base sweeping compound to eliminate irritating odor from the petroleum-base sweeping compounds. The natural canola oil-base sweeping compound had a slight woody scent. The three pieces of equipment used in this study had notably different cab layouts. The bulldozer had a small cab with vents discharging air-conditioned or heated air from adjustable louvers at operator waist level and floor level. The bulldozer also had a cloth fabric seat and a carpeted floor. Drill A had a large cab with the heat directed from adjustable louvers at operator knee level and the air-conditioned air directed from cabin ceiling louvers. This drill had a vinyl fabric seat and a steel plate floor. Drill B had a small cabin with the heat directed across the floor (see figure 1) and the air-conditioned air directed down from the ceiling. It had a vinyl fabric seat and a worn rubber mat on a steel floor.

May 1, 2001

By J. T. Nel

The establishment of a pilot plant for the continuous production of titania pigment and nano-titania is discussed. The plant was designed, constructed and operated on the Necsa site. The TiO2 production capacity is 7?10 kg.h-1 by the reaction of TiCl4 and O2at>1000°C. Liquid TiCl4 is sprayed under pressure into a plasma reactor where it evaporates and reacts with O2 to form TiO2. Process optimization has allowed for continuous production without any clogging or blockages. The primary advantage of the plasma-assisted process is the possibility to recover and recycle the chlorine values in high yield as Cl2 for use in the manufacture of TiCl4. The HCl formed in most conventional fossil-fuelled processes makes Cl2 recovery and recycling much more difficult. Particle size distribution analysis of the fine, white product revealed a d50= 125 nm. The raw product consisted of 60% rutile that could be increased to 80?100% rutile by post-annealing. The specific surface area (SSA) of the pigment was 8?20 m2?g-1(BET). According to the CIE colour index the ?whiteness? (L*>95) of the plasma-produced pigment was better than that of several commercially available pigments. The particle size could be manipulated by controlling the TiCl4 feed rate, gas flowrates, and the particle quench rate and residence time. Nano-sized TiO2 powders with a particles size (d50) as small as 50 nm were also successfully produced in this way.

Jan 1, 2010

By P. Fauvel, V. Nasri

In January 2001, French and Italian governments signed an agreement for the construction of a new Lyon-Turin railway line. This project includes a tunnel of 53.1 km length and a maximum of 2500 m overburden to be designed for a reference speed of220 km/h. The tunnel crosses major part of the West Alpine geological formations, which are very complex and contrasted in terms of the nature of rocks and the mechanical and hydrogeological conditions. In addition to the twin single-track tubes, numerous intermediary shafts, security station and intervention sites and cross passages should be built to respond to the security, operational and construction requirements. This paper describes the results of the preliminary engineering design and multiple challenges of this very long and deep railway tunnel.

Jan 1, 2005

By L. A. Thompson, A. J. Linington

"Copper–cobalt extraction is a reagent-intensive process resulting in acid consumption greatly contributing towards production costs, which in the current market conditions curtail profitability. Nanofiltration (NF) membranes have become an attractive approach in the mining and minerals industry for product concentration and reagent recovery based on the ability of the membrane to separate monovalent ions from divalent ions. NF membranes can selectively separate acids from metals and salts allowing acid to be recycled as well as the concentration and purification of product streams. Membrane technology in the field of copper–cobalt processing focusses on the concentration of Cu2+ and Co2+ in the pregnant leach solution, recovery of acid from waste streams to neutralization, recovery of valuable metals from waste ponds and process water recovery. This paper aims to provide insight into the potential applications of NF membranes in copper–cobalt processing circuits as well as a brief overview of the effects of process conditions on membrane performance and process development. INTRODUCTION The copper–cobalt industry commonly uses inorganic acids, such as sulfuric acid, in large quantities for primary leaching of copper–cobalt oxide ores and releaching during product purification (Stuurman et al., 2014). This results in numerous acidic intermediate streams containing high metal concentrations and acidic waste streams with low metal concentrations. Acid consumption typically accounts for 10–15% of the operating costs of mines in the Democratic Republic of Congo (DRC) and Zambia (Acid Plant Database, 2015). Due to remote mine locations, poorly maintained roads and cross-border conflict, the cost of sulphuric acid can range between USD 300 and 400 per ton. The pivotal role of acid in the copper–cobalt extraction process has driven many mines to build sulphuric acid plants on site to ensure a reliable acid supply, however elemental sulphur still needs to be imported which faces similar logistical challenges and contributes towards operating costs."

Jan 1, 2015

By Janis A. Shandro

The mining sector is a major economic driver for Canadian, and British Columbian communities. In parallel strong commitments have been made by industry to the well-being and sustainability of associated communities. However, these dimensions are the least understood. Especially lacking are focused regional investigations that compare the well-being and sustainability of communities dependent on different resources sectors. It is hypothesized that this type of comparative analysis will help to foster a greater understanding of what makes a resource or mining community healthy and sustainable. This paper describes research that examined community-level indicators associated with well-being (e.g. education, income and employment) and sustainability (e.g. economic diversity). The indicators were derived from Canadian Census data for 31 British Columbia resource-based communities (with a focus on mining) during a period of time (1991 to 2001) when resource sectors experienced an economic downturn. Our findings identify that during this decade, mining communities differed significantly from other resource-based communities, and comparative analysis of census derived indictors illuminate challenges that mining communities in British Columbia face with respect to wellbeing and sustainability (such as economic diversity, unemployment, and population loss). To contribute to the mining sector?s efforts towards meeting their commitments to communities, this paper concludes by proposing strategic opportunities aimed at the enhancement of mining community sustainability for policy-makers, communities, and the mining industry to consider.

May 1, 2011

By Herbert A. Franke

ANY analysis of the aluminum situation, particularly of the factors involved in the current shortage of the metal, must consider the rapid march of events since the Munich fiasco of September 1938. At the end of 1938, the sole domestic producer of aluminum had more than a year's supply of metal on hand, having added 50,500 tons of output to stocks during the year. Not until war had been declared between the United Kingdom and Germany in September 1939 did the United States begin to make serious preparations for defense and a limited national emergency was proclaimed. Congress reflecting popular opinion, was not disposed to spend huge sums for armaments in 1939, and although 31,413 tons of aluminum was withdrawn from stocks. 107,500 tons was still on hand at the end of the year. When the President initiated a 50,000-airplane program in May 1940 the country was astounded, as previous Congressional authorizations of approximately 6000 planes for the Army by July 1911 and 3000 for the Navy by 1914 had been considered adequate.

Jan 1, 1941

By Don W. Lake

Of all the blast monitor& instrumentation systems and techniques av&able today, highspeed photography and videography remain as the most valuable, stand alone, diagnostic techniques to evaluate full scale blasts in the mining and explosives industries. Highspeed image data, coupled with information from other instrumentation systems, such as continuous VOD records, seismographs, laser surveying systems, refraction seismographs, etc. can eIiminate many assumptions about what actually took place in a blast. Thus, diagnostic confidence in evaluating both good and bad blasts is increased, and optimum blast designs are achieved considerably faster when compared to the trial and error approach or relying on just the experience factor.

Jan 1, 1992