Search Documents

By D. G. Krige

For the purpose of determining confidence limits for ore grade estimates, an extensive simulated data base was used, which included 1728 ore blocks with ‘actual’ grades and the corresponding estimates based on ordinary and simple kriging. The practical results show that conditional unbiasedness is essential and that acceptable confidence limits can then be set using Normal theory for the simulated error distribution based on the logarithms of the ratios of ‘actuals’/estimates with a variance related to the kriging variance. The mean of the data used to prepare the variogram and the estimated block grade are to be used properly in this approach. A practical analysis was also done of the actual point and block data from a very large mined out Carbon Leader area. The distributions of the actual grades for two levels of block sizes with different levels of variability were fitted using three models, ie. 2-. 3- and compound-lognormal. The trends of tonnages, grades and relative profits for a range of pay limits, as well as the usual tonnage-grade curves, show a practical insensitivity for the choice between the three lognormal models considered.

Jan 1, 2003

By K B. Holm

This paper deals with the advances made at Syferfontein Colliery in the calculation and control of dragline methodology. The high capital outlay and operating cost of a dragline necessitates strict control of all aspects of the dragline operation. Before purchasing a dragline, a complete evaluation of all the parameters that can affect the viability, now and in the future, of the dragline operation needs to be completed. Such parameters as thickness of burden, material properties (swell), “castability”, pit width and pit length, etc. need to be considered.

Jan 1, 1994

By C A. Locke, A B. Christie, J Cassidy, J L. Mauk

New and existing gravity and aeromagnetic data are used to determine the structure of the Waihi region and to investigate any relationship between structure, hydrothermal alteration and epithermal mineralisation. The 24 mGal, 10 km diameter, negative Bouguer gravity anomaly which occurs south of Waihi has been modelled as a I.5 km deep asymmetrical basin. This basin, the Waihi Depression, is interpreted to be infilled with low-density volcanic rocks of the Uretara Formation and Whitianga Group, overlying older andesites of the Waipupu Formation. To the north and west, the margins of the depression are defined by the Waihi and Mangakino Faults, which have been modelled with dips of 45 - 60¦ to the south and west respectively. The southern and eastern boundaries of the Waihi Depression are defined by smooth, shallow dipping (15 - 20¦) boundaries. The Waihi Depression is interpreted as a fault-angle depression, resulting from southeast extension in the early Pliocene. The Waihi Fault is modelled as an approximately E-W feature, located to the south of Waihi. Small 2 - 4 mGal positive Bouguer gravity anomalies occur north and west of the margins of the depression, and correlate with known areas of hydrothermal alteration and areas of low magnetic gradient.

Jan 1, 2003

By Kara A. Teacoach

Current regulations for fire suppression systems in underground coal mines to protect conveyor belt installations have been in place since the Coal Mine Health and Safety Act of 1969 was enacted. Over time, the coal conveyer equipment being used and ventilation conditions underground have changed significantly, particularly the width of the conveyor belts and the use of belt air at the face. The effect of these new conditions on the effectiveness of suppression systems during a fire is not known. The National Institute of Occupational Safety and Health (NIOSH) conducted a study to evaluate the effect of air velocity, water sprinkler activation temperature, and a limited water application time on the effectiveness of water sprinkler fire suppression systems to extinguish large-scale conveyor belt fires. The fire tests were conducted using both new and used 1.8-m-wide, fire-resistant rubber belt that met the Mine Safety and Health Administration (MSHA) flame resistant requirement specified in Title 30, Code of Federal Regulations, part 18, section 18.65 (also known as the 2G test). Tests were conducted using standard response sprinklers with activation temperatures of 68 °C and 141 °C at air velocities of 0.5 and 5.1 m/s. Two tests were conducted at both air velocities for each sprinkler activation temperature, one using a new belt and one with a used belt. The results showed that the suppression system was able to suppress the fires in ten minutes to the point that a miner could extinguish it with a fire hose. However, in several of the tests, the fire reestablished itself a few minutes after the sprinkler water supply was cut off and quickly grew out of control. This report discusses the large scale experimental configuration, the installation specifications of the fire suppression system, and the results and conclusions regarding the effect of air velocity, sprinkler activation temperature, and limited water application on the suppression system performance.

Jan 1, 2010

By T. O. Llewellyn

The Bureau of Mines conducted batch-?scale tests on a sample of parphyry copper mill tailings as part of a study to determine the feasibility of rutile recovery from this source. The tailings that were tested contained 0.75 percent titanium dioxide (Ti02), with about two-thirds of the Ti02 values occurring as rutile. Mineralogical studies indicated that about one-half of the Ti02 content could be considered recoverable. Beneficiation studies of the tailings showed that best flotation results were obtained when sulfides and carbonates were removed by bulk flotation prior to rutile flotation. Rutile flotation was most effective when a petroleum sulfonate collector was used in an acid circuit. From this basic method of flotation, two alternative procedures were developed. The first procedure was to size and grind the tailings to minus 200 mesh; deslime the total pulp; and then float the sulfides, carbonates, and rutile. The second procedure was the same, except that it did not include sizing and grinding. Flotation of the sized and ground tailings yielded rutile concentrates containing 43.1 percent Ti02 and 75.7 percent of the recoverable Ti02. Rutile concentrates floated from the tailings that were deslimed but not ground contained only 34.7 percent Ti02 and 69.4 percent of the recoverable Ti02.

Jan 1, 1980

By R. M. Goktan

Point-attack picks are one of the most widely used tools for the mechanical excavation of rock and coal. In the literature, some practical formulas have been developed to estimate their performances under varying cutting conditions such as the pick geometry, cutting depth and cutting geometry. In this study, it is shown that Evans?s theoretical model, the most cited in the literature, has serious limitations concerning the changes in the cutting geometry. Analysis of the two independent full-scale linear rock cutting experimental data reveals that both his theory and its recent modification can not fully explain the mechanism of rock breakage under asymmetrical attack. The cutting force predictions made by employing such models are shown to be too significantly weak to be of any service in practice. In this study, a semi-empirical approach was followed by means of which cutting forces under varying cutting geometries could be made. By analysing the full-scale rock cutting test data, prediction equations of the peak cutting force and mean cutting force have been developed. Comparisons of laboratory determined and predicted force values indicate that the suggested prediction equations are applicable to quite different rock materialsm which have uniaxial compressive strength in the range of about 30?170MPa, and valid for different cutting geometries. It is also shown by regression analysis that the established prediction equations are statistically significant.

Jan 1, 2005

By Carolyn Kenney, Jianjun Liu, Zhenghe Xu

"The flotation of fine particles has been a challenge to scientists and engineers in mineral processing. A novel concept of reactive oily-bubbles as carrier to float fine particles is described in this paper. The reactive oily bubble flotation is considered attractive for fine particle flotation. In addition to the role of fine particle agglomeration by oily films, the surface properties of air bubbles coated with a thin oil film can be better controlled for the desired selectivity by adding certain types and concentrations of water insoluble collectors into the oil phase. This approach can eliminate the addition of collector to the aqueous phase, avoid undesired synergetic interactions among collectors, activators, depressants and dispersants present in slurry, minimize undesired activation of gangue particles and significantly reduce the amount of collectors needed.The concept of using reactive oily-bubble to achieve selective flotation was demonstrated in contact angle measurement and by microflotation tests with fine sulphide minerals: sphalerite and galena in this paper. The flotation behavior of sulfide minerals can be radically modified with adjustment of solution pH, addition of depressant and activator as in conventional flotation. The successful separation between PbS/SiO2, ZnS/SiO2 and PbS/ZnS was demonstrated using mixed mineral systems. Compared with conventional flotation, the reactive oily-bubble flotation showed a stronger collecting power.INTRODUCTIONThe challenge for fine particle flotation has long been recognized and well documented (Fuerstenau, 1980). Because of drastic changes in surface properties of fine particles and associated physicochemical and hydrodynamic conditions of flotation systems, fine particles responded poorly to the conventional flotation processes. For instance, the small mass and hence low inertia of fine particles would result in a low efficiency of collision and attachment of fine particles with flotation bubbles. Large specific surface area of fine particles, on the other hand, would cause an increased reagent consumption. Dominating colloidal forces of fines may cause slime-coating, accompanying a low selectivity (Somasundaran & Arbiter, 1979; Fuerstenau, 1980; Sivamohan, 1990)."

Jan 1, 2003

The modelling of lithological domains is a critical step in mineral resource and reserve evaluation. Deterministic models rely on an interpretation of the available drill hole data and expert knowledge, but do not account for the uncertainty in the spatial extent of the lithological domains. Instead, probabilistic models based on conditional simulation can be used to map the probabilities of occurrence of the domains within the deposit, which reflect the uncertainty in their presence or absence at unsampled locations. The mineral grade model is then obtained by weighting the predicted grades associated with each lithological domain by the probability of occurrence of this domain. Such an approach accounts for the continuity of the grades proper to each lithological domain and for the uncertainty in the spatial extent of these domains within the deposit. An application to a porphyry copper deposit is presented. Keywords: spatial uncertainty; plurigaussian simulation; geological control; kriging; geostatistics.

Jan 1, 2007

By Ren G. Dong, Richard McCormick, Dan E. Welcome

Vibration exposure at workplaces is generally multi-axial. The health effects of vibration exposure also likely depend on the vibration direction. Therefore, there is a wide interest in the simulation of multi-axial vibration in laboratory experiments. Advances in technology have led to the development of a new 3-D test system for studying hand-transmitted vibration exposure and health effects. The purposes of this paper are to introduce the system and to present the results of its preliminary evaluations. Test System As shown in Figure 1, the system is basically composed of three vibration generators, a multi-axis vibration control system, instrumented handle, handle fixture, and shaker-fixture linkages (stingers). [ ] Figure 2 shows the array of three vibration generators (MB Dynamics, Energizer BLACK-500 lbs) and their associated support bases and foundation developed by MB Dynamics (Cleveland, USA), which create the 3-axis simultaneous motion. These electrodynamic exciters are powered by power amplifiers which provide current proportional to the analog drive signal from a controller. The controller (JAGUAR Multi-Input/Multi-Output closed-loop vibration controller) was provided by Spectral Dynamics, San Jose, California, USA). NIOSH-designed instrumented handle was equipped on the system.

Jan 6, 2006

By R. M. Imhof, M. J. G. Battersby, G. Ciernioch

Pneumatic flotation is rapidly becoming accepted in the main stream of flotation techniques. Imhoflot is a pneumatic flotation process that in recent years has undergone progressive development. It combines short flotation times with excellent selectivity by employing intense pre-aeration and dispersion. K+S GmbH (K+S), Germany, has installed a complete Imhoflot flotation plant at its Sigmundshall plant. The plant treats hard salt consisting of sylvine, halite, anhydrite and kieserite. The reason for selection was that Imhoflot achieves the required grades of plus 60 weight percent K2O whilst offering lower operating costs than conventional flotation installations.

Jan 1, 2002

A paper presenting an overview of legislative and best practice approaches to the management of OHS&E and business risk for Australian tunnelling operations. Best practice can be achieved in Australian tunnelling through ærisk awarenessÆ by decision-makers and line personnel. This will identify problems before they occur and lead to implementing controls appropriate to avoiding loss throughout the life cycle of the underground opening. The author draws on legislative approaches from all Australian states together with practical experience from risk management and risk engineering work from six recent tunnelling projects. This describes a process that:commences with concept risk assessment,involves quantification of major hazards,conducts assessments of operating risks, andleads to implementation of an integrated management system that keeps construction activities connected with the controls identified in the design and planning phases and minimises the losses sustained as a result. Key points addressed include:where the industry is going with respect to risk û methods and considerations,how tunnelling risks are perceived by the industry and legislation,how tunnel constructors and owners can minimise exposure by using proper risk engineering ætoolsÆ, andreflections on best practice methods for transferring knowledge from designers to contractors/operators.

Jan 1, 2008

By Kari Moen, John Rasmus Leinum, Jarle Hjelen, Terje Malvik

"Industrial minerals may contain the same elements in approximately the same amount. In these cases backscatter electron imaging or chemical analysis are not sufficient to identify the minerals. Another problem arises when micro textures are not detectable in traditional imaging or the grain size is smaller than the X-ray spatial resolution.As a supplementary technique in these cases, application of crystallographic information by electron backscatter diffraction (EBSD) in the scanning electron microscope (SEM) may be a suitable method. The technique has been demonstrated on three Norwegian mineral raw materials and one Italian marble and shows that it has some advantages compared to traditional techniques.• quantitative measurements by ebsdCommon automatic techniques describing the mineral contents and the occurrence of minerals in free and locked particles, are based on optical-, backscattered electron (BSE)- or X-ray-signals. There are various commercial software systems on feature analysis by backscattered and X-ray signals in combination with image analysis (e.g. Oxford Inca Feature, CSIRO QemScan).Especially in silicates, the occurrence of similar elements in the different minerals is common. Sometimes the various minerals not only contain the same elements, but also approximately the same amount of each element. In these cases BSE imaging and chemical analysis are not always sufficient for identification."

Jan 1, 2003

By Timothy D. Stark

Jet grouting has increasingly become one of the ground improvement technologies used to address seepage concerns and to provide strength improvement of soils. The technique of jet grouting uses high pressure/velocity jet fluids to erode the existing soil and then to mix the cuttings with cement slurry to form soilcrete. Excess slurry or spoil is ejected to the surface. If the native soil is not completely mixed with slurry, the resulting columns will have soil inclusions which can reduce the strength of the column and/or increase the permeability of the column. A jet grout test program at Tuttle Creek Dam shows that the completed large diameter columns contain perhaps 40 to 50% or more of native soil that was not broken up and mixed during the jet grout process. The test program included excavation of full-scale columns to a depth of 35 ft (10.7 m) for visual inspection and testing. Additionally, six of the columns were cut or sectioned to investigate the interior of the columns. The observed inclusions include significant amounts of both fine grained (silts and clays) and coarse grained (fine sands and sands) soils. Evidence suggests at least two explanations: (1) fine grained soils can be difficult to erode and break up into small enough particles that can be ejected to the surface, especially if at low natural water content, and (2) when large diameter columns are being excavated, the excavated roof of the cylindrical cavity may be unstable and may collapse. With this roof instability large slabs of material can break off, fall into the slurry and escape the cutting and mixing action of the rotating jets. This paper describes the Tuttle Creek Dam test program, inclusions observed in the completed columns, and suggests potential causes of the inclusions.

Jan 1, 2009

Extraction of copper from a chalcopyrite concentrate by means of a cupric chloride leach is described. Initially the concentrate is mixed with sulphur in a 9: 1 ratio, and heated to 350-400°C. This converts the chalcopyrite into more readily soluble sulphides, while the iron rejected from the chalcopyrite is transformed to pyrite, which is insoluble in the leach solution employed. A two-stage countercurrent leach using a leach solution of 1 M cupric chloride, 3.5 M sodium chloride, and 1 M hydrochloric acid extracts 98 per cent of the copper, if conducted at 105°C. Iron extraction is relatively low, the mole ratio of iron to copper extracted being 0.17, compared to 1.0 for unreacted chalcopyrite. After dissolution, copper can be recovered by electrolysis, cupric chloride leach solution being regenerated at the anode.Electrolytic power requirement is low, being approximately 0.5 kWh per kg of copper. The sulphur and, most of the iron entering as feed are rejected from the process in the form of pyrite, which remains in the leach residue.

Jan 1, 1974

By R. N. Hambright

Gaseous and particulate exhaust emissions are characterized for a 1200 Bhp two-stroke cycle diesel, a 1000 Bhp four-stroke cycle pre-combustion chamber diesel, and a 900 Blip four-stroke cycle, direct injection diesel using steady-state modal testing and a versatile exhaust dilution-collection system. In addition, a 1.50 Bhp four-stroke cycle, pre-combustion chamber, turbocharged diesel was characterized for use in experimental water injection evaluations. Water injection downstream of the turbocharger compressor and upstream of the turbocharger exhaust turbine are evaluated for their particulate removal effectiveness on the small turbocharged diesel engine. The water droplets are inertially separated using cyclone separators designed for minimum pressure drop and outsize, lip to 50 percent of the total particulate mass generated was removed using a combination of both inlet and exhaust water injection techniques.

Jan 1, 1981

By J. Kang

To obtain microbial cultures with the ability to efficiently leach copper ion from chalcopyrite, microbial samples from acid mine drainage sites were mixed and then subjected to mutation using sodium nitrite (NaNO2), diethyl sulfate (DES), ultraviolet light (UV) and their combinations. Mixed cultures with a much stronger ability to leach copper ion (identified as mixed cultures A, B, C, D and E) were obtained by screening on leaching media. Leaching tests showed that mixed culture E had the best leaching performance and increased the Cu2+ content by 120.5% in 20 days, compared to a control without mutation treatment. Mixed culture E grows well on Leathen leaching medium supplemented with Cu2+ (at a final concentration of 32 g/L), reaching 3.2 × 107 cells/L after 15 days, while the unmutated control culture cannot survive beyond 15 days, indicating that mixed culture E is more tolerant of high concentrations of Cu2+. In addition, continuous leaching by mixed culture E is very effective at a pulp density of 1%. These results suggest that it has the potential for industrial applications.

Jan 1, 2008

By D. Nutakor

The ability of computers to create synthetic representations of the real world in virtual reality offers a number of opportunities to enhance training methods used in the mining industry. Unfortunately, the training effectiveness of virtual reality systems currently used in the mining industry has received only limited testing. Miner Simulation (MinerSIM), an augmented reality system with integrated hypermedia suitable for training underground miners in the basics of using a jackleg drill to install rock bolts in a virtual mine environment is in its evaluation process at the University of Missouri-Rolla Experimental Mine. This paper discusses evaluation methodologies of the MinerSIM system, which consists of experimental and control groups with control students learning via traditional lecture and text formats. Preliminary results from usability tests of the first part of MinerSim, which is an online tutorial on underground rock bolting, are presented.

Jan 1, 2008

By Larry Rayburn

Design of cost effective engineered solutions to complex problems requires the team efforts of the owner, the designer and the specialty construction contractor. The basic ingredients of success required to remain competitive and still produce a quality product are creative design based on experience and sound engineering principles, plus practical aspects of constructibility. The three case histories describe creative design/construct approaches that benefited all parties. 1. Introduction The increasing demand placed on specialty contractors to provide cost effective buildable solutions to complex construction problems compels us in the industry to be highly innovative. The practice of geotechnical engineering is considered more of an "art" than perhaps the other disciplines within civil engineering largely because of the basic nature and variability of soil and rock. The geotechnical design engineer must have the knowledge of the components of his design and know the limitations of his equipment and labor force. Thus, for the design/build specialty contractor the potential for creation of unusual solutions to difficult problems is quite high.

Jan 1, 1991

By A. Nieto

A vehicle proximity warning–collision avoidance system is being developed using GPS and wireless local area networks to improve safety of off-highway trucks in open pit mines. After two-and a-half years of research, software development, and laboratory testing, field tests were carried out at operating limestone quarries and open pit mining operations to evaluate GPS accuracy and overall system effectiveness under rugged operating conditions. This article describes the progress made on this NIOSH-funded project and discusses the GPS accuracy tests and overall system tests that were carried out during the year 2001 at the Colorado School of Mines Survey Field and at the Morenci open pit copper mine in Arizona. Keywords: GPS, Advanced Mining, Virtual Reality, Wireless Networks, Proximity Warning

Jan 1, 2003

By M. Zhang, M. Menabde, R. Middleton

Whilst mine planners almost universally assume deterministic forward commodity prices when undertaking valuations of mining projects, historical data well demonstrates that those prices are quite volatile. This paper seeks to understand and quantify how this forward price uncertainty will impact mining project valuation. This paper will also present a way of computing an upper bound on the expected Net Present Value (NPV) of a mining project given forward commodity price uncertainty.

Jan 1, 2007