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By A. K. Bakshi

Mineral suspensions show Newtonian flow properties at lower solid concentration, but change into non-Newtonian regime as the solids content is increased. For Newtonian fluids viscosity is independent of shear rate, but for non-Newtonian fluids it varies with rate of shear. Therefore, measurement of viscosity at a shear rate, different from the process will be futile unless the slurry is Newtonian. This is especially true for hydrocyclone operation, where the rate of shear is different at different points within the hydrocyclone. In this case, it is very important to determine the flow type of the suspension before attempting to establish any correlation between viscosity and process efficiency. A new technique to distinguish such changes in flow type has been developed. This involved a co-axial cylinder type viscometer which measured apparent viscosity at a low shear rate, and a vibrating sphere type viscometer which measured the apparent viscosity at a high shear rate. Special precautions were taken to allow measurements of viscosity of rapidly settling mineral suspensions. Because the vibrating sphere viscometer operated at a much higher shear rate than the rotating viscometer, the two instruments together could determine the shear-rate dependency of the viscosity. Ground silica of 80% passing 65~m size in water was used to prepare slurries at concentrations ranging from 1O-70wt% solids. Viscosity of each slurry sample was measured simultaneously by both the viscometers and the results were compared with each other. With this technique, it was found that all the silica slurry samples were in the Newtonian flow regime.

Jan 1, 1995

By Edita Vircikova

The best demonstrated available technology (BOAT) for the removal of dissolved arsenic and some heavy metals as reported by USEPA (Contaminants and Remedial Options at Metal Sites, Draft Report, August 1993) (1) is still the chemical precipitation. Coprecipitation with the excess of iron is usually practised because of the availability of iron at low/no cost and also in order to meet the stringent regulatory discharge limits. The arsenic is usually removed with iron because of its common occurence in the mined orebodies and the excellent adsorptive property of the precipitated hydrous ferric oxide compounds. There has been controversy, however, over the long-term stability of the arsenic-bearing ferrihydrite which is produced.

Jan 1, 1995

By M. C. Williams

The solution of the dynamic population balance model (PBM) of a closed grinding network consisting of a mill, sump, and cyclone is problematic. The fact that the dynamic PBM model equation solution to the Inverse Problem for grinding systems is degenerate or underspecified is demonstrated. Two numerical solution approaches to the Inverse Problem are used. These are: 1) providing additional constraints on breakage selection functions or 2) performing the Arbiter-Bhrany (or other) normalization of the selection functions. Actual experimental anthracite batch grinding data is used to demonstrate the non-unique functionality of the batch dynamic mill selection and breakage functions for a real physical system. The Levenberg-Marquardt algorithm for systems of constrained non-linear equations is used to solve the batch dynamic PBM grinding equations to obtain the grinding selection and breakage rate functions. Different solutions to the same PBM transport equations are provided. The mill, sump and hydrocyclone were modeled as a CSTR operating at various retention times. Batch dynamic PBM data was used to provide the mill kinetic and breakage selection function data. Two different solutions were obtained depending on the numerical solution approach. The severity of the non-uniqueness problem for dynamic grinding is demonstrated. Each solution approach to a dynamic PBM with transport, while giving the same prediction for a single batch grinding time, gives different solutions or predictions for mill composition for other grinding times. This fact makes dynamic nodal analysis and control problematic. The fact that the constraint solution approach gives a solution may suggest that normalization for closed networks is not necessary. Differences in solutions to the PBM cannot be excused away by inaccuracies in the data used to model the grinding phenomenon.

Jan 1, 1995

By Mohsen Sanai, Paul Gefken

"SRI International has developed and patented* a castable dilute explosive tile @ET) that offersunique advantages over conventional high explosive. The primary advantages of DET are that itsdetonation pressure can be adjusted over a wick range and its impulse can be controlled independently by adjusting its thickness and configuration. Because DET has a much lower detonation velocity than conventional explosives, the pulse duration produced by DET is as much as 10 times longer than the pulse duration produced by conventional explosives for equal explosive weights. These features of DET present several advantages to the mining industry. For example, DET can be tailored so as to control fragment size and distribution to enhance extraction of desired elements from ore or breakup of specific regions."

Jan 1, 1995

By Somerville M, Muray A, Bocking M

Australia has an extremely large total hot dry rock (HDR) resource above a depth of 5 km, equivalent to 7500 times its present annual energy consumption, of which 80 per cent underlies the Great Artesian Basin. The resources most likely to be exploited first are those residing in homogeneous granitic bodies beneath sedimentary basins containing insulating rocks such as shales and coal measures. In the Sydney Basin south of Muswellbrook, an area of high geothermal gradient corresponds to a gravity low thought to be a buried granite body at a temperature of possibly 250¦C. This locality is suspected to have the ideal geological characteristics for Australia's first hot rock test facility. Australia's high HDR potential is possibly unique in the world, in that the potential sites satisfy four independent, geological conditions, each considered as favourable for the creation of a resource, and for the ease of extracting that resource. They are: ò Higher crustal heat generating capacity than that of normal continental crust. ò Much of the Australian continent is covered by sedimentary basins which contain a high proportion of shales and coal measures that have low thermal conductivities, thus providing an insulating blanket for the heat being generated beneath. ò The sedimentary basins are in many places underlain by large untectonised granitic bodies that are not only a major contributor to heat generation, but also ideally suited to the establishment of HDR reservoirs. ò The crustal shortening stress field that is found in the majority of the Australian continental crust results in a vertical minimum principal stress orientation which should result in the development of favourably oriented horizontal stimulation cells necessary for maximising an HDR resource.

Jan 1, 1995

By Bearman R. A

The majority of published material regarding the operation of crushing machinery is concerned with simulation of performance rather than design of equipment. The reason underlying the bias in published material relates to why research is carried out and who undertakes the research. Two distinct types of research can be identified: 1. Internal research by crusher manufacturers - generally related to mechanical design, value engineering and to the commercial realities attached to sales demands. Any work on basic crusher geometry or rock/machine interaction is of a sensitive nature and rarely enters the public domain. 2. Academic research - mostly confined to modelling of crusher performance and simulation. This is not because of any bias, but crusher design requires access to manufacturers data or at least an in-depth understanding of crusher design, which is rarely available. The crushing of rock is a complicated problem. It involves three aspects; the machine geometry, the material composition (type of rock/feed size distribution) and the machine/rock interaction. The machine geometry is often ignored in empirical mineral processing simulations, while the response of different feed materials is only nominally addressed in machine specifications provided by manufacturers. The manner by which the machine produces a stress field and causes different types of breakage for different rocks (or the machine/rock interaction) is sadly neglected by both groups. All three aspects must be considered collectively to successfully understand and model the entire crushing process. 1. Centre for Mining Technology and Equipment, Julius Kruttschnitt Mineral Research Centre, University of Queensland, Isles Road, Indooroopilly 4068 Qld. The importance of crushing is often underestimated. In mining and mineral processing the invisibility of the crushing process is understandable as it merely provides a coarse reduction stage prior to the intricacies of mineral extraction. However in the quarrying industry crushing and screening basically provide the finished product. A brief overview of the quarrying industry shows the importance of crushing. Figure 1 gives production figures for most of the western European countries, Australia and the USA.

Jan 1, 1995

By David R. Hanson

Transient electrical noise events pose serious problems for data acquisition systems used in monitoring acoustic emissions in laboratory and field environments. The U.S. Bureau of Mines has designed and constructed a trigger discriminator circuit for use in ultrasonic acoustic emission studies. Designed for use with signals in the frequency range of 50 to 400 kHz, the instrument examines .incoming signals for frequency content, amplitude, simultaneity, threshold crossings, and number of channels above threshold. If preselected criteria on these properties are met, a plus 5-V pulse is output that may be used to trigger a data acquisition system, allowing rejection of noise events that do not possess useful information. The system was designed for four input channels, but may be expanded to more channels with minimal design changes.

Jan 1, 1995

By J C. Carlile

Many low sulphidation epizonal gold and zinc-lead vein deposits within magmatic arcs are situated on basement highs, and post-date both the main volcanic episode and porphyry copper (gold) mineralisation. These features are best explained by emplacement of a flat batholith a few kilometres beneath each mineral district, as recently demonstrated by geophysical data in the Baia Mare district of Romania. The batholith provides heat for the hydrothermal system, and results in extensional faulting both through up-doming of the overlying rocks, and in some arcs through incipient collapse of the thermally weakened crust under regional extensional stress. More water-rich magmas emplaced at greater depths could explain some deep epizonal and mesothermal gold deposits situated outside magmatic arcs.

Jan 1, 1995

By David M. Spatz

Ore deposit models are defined largely by physical geologic features that relate conveniently to remote sensing. New Landsat, SPOT, RADARSAT and other multispectral and hyperspectral sensors with improved spatial resolution are currently in development. Near-infrared and thermal airborne hyperspectral scanners hold outstanding promise for both mineral exploration and feasibility stage mapping at potential new mining projects. These scanners are capable of identifying silicification, differentiating silicate alteration types, and mapping compositional variations within igneous and metamorphic complexes. Research in 'mineral and rock spectrometry is helping to advance applications of remote sensing. Hyperspectral scanners are capable of differentiating compositional variations within individual mineral species. Innovative data processing techniques continue to enhance computer software applications and facilitate imagery analysis by the geologist. Today, . remote sensing imagery is commonly integrated with multiple data sets in GIS format to form the core data base for regional exploration programs.

Jan 1, 1995

By William Petruk

The primary requisite for a successful extractive metallurgy operation is to grind an ore fine enough to liberate the minerals so that they can be concentrated, or to expose mineral surfaces so that the minerals can be leached. The ease or difficulty of liberating or exposing the mineral grains is dependent upon the mineral textures such as grain size, crystallinity and bonding between mineral grains. In particular, mineral grains with straight grain boundaries and a weak bonding to other minerals are easily liberated and readily concentrated into high grade concentrates. In contrast mineral grains that have re-entrant boundaries and are strongly bonded to their neighbours are not easily liberated and will not produce high grade concentrates, even with regrinding. Similarly, inclusions that occur along fractures and grain boundaries can be readily exposed and leached. Whereas minute random inclusions in large grains will not be liberated or exposed unless they occur along planes of weakness.

Jan 1, 1995

By K. Rainer Massarsch

In some parts of the world, vibrators are used extensively for different types of foundation engineering projects. If used correctly and in suitable soils then vibratory pile driving for example is very efficient. However, soil conditions and the installation procedure have great significance for the driving resistance and affect the bearing capacity of vibrated piles. Also the intensity of ground vibrations which are transmitted to the surrounding soil is affected by the vibration process. In spite of the increasing use of vibrators and the rapid development of vibrator technology, many aspects of pile-soil interaction are not yet understood. In order to asses the importance of factors, which govern pile installation (and extraction), it is necessary to consider the entire chain of vibration energy transmission from the vibration source to the pile, the interaction between the vibrating pile and the soil and the wave propagation in the subsoil, Fig. 1. [ ] Fig. 1. Transfer of vibration energy from the vibrator through the pile into the ground In the present paper, some important aspects of vibratory driving and their significance for pile installation and soil compaction will be discussed.

Jan 1, 1995

By Chen Bingchen, Zhang Jian, Liu Jiaxiang

The influence of various installation angles of hydrocyclone on its operation indexes was investigated, and the correspondent mathematical models were established in this paper. The models developed in this paper can be used to the optimizing control of hydrocyclone and make the hydrocyclone as a particle size sensor.

Jan 1, 1995

By X. Wu

A quantitative damage evaluation caused by ground motions associated with strong roof caving is presented. The strong roofs are modeled as either cantilevering or bridging beams over continuous elastic foundations subject to an exponentially distributed vertical stress. Major factors influencing roof caveability and strain energy buildup are identified and investigated. A methodology to evaluate the strain energy accumulation caused by overhanging roof is presented. The potential for mine tremors is determined in terms of the local Richter magnitude ML which depends on the seismic energy transformed from the stored strain energy released when the roof fails. A particle velocity model is applied to estimate the damage area associated with roof collapse. A case study from a Utah coal mine shows that estimations of bump severity and damage area agree well with the field observations.

Jan 1, 1995

By R. L. Grayson, M. P. Miano, S. Yuan

Matching the productivity gains of continuous mining machines with the increasing performance levels achieved by longwall units has required creative thinking to assure that development is completed in time for uninterrupted longwall production. By using management information systems to coordinate support operations, the most productive planning decisions can be made. This paper focuses on the role of computer technology tools in achieving improved productivity from both longwall and continuous miner sections. The primary emphasis is on the planning process and the methodology developed to guarantee the best allocation of management and manpower resources.

Jan 1, 1995

By K. Olsen

As aluminum alloy usage in automobiles grows, there are increasing demands on recycling processes and facilities to deal with mixed alloy automotive aluminum scrap. These processes and facilities strive to produce near virgin aluminum stock, which can be relatively costly and difficult. One alternative is to use physical processing methods to upgrade the scrap properties instead of chemically refining the scrap. The Impulse Atomization Process (LAP, patent pending) is a new process for making metallic and ceramic powders. It can produce fine homogeneous microstructures in scrap aluminum alloys due to high undercooling and rapid solidification. The particles have a very narrow size distribution and are in a convenient form for consolidation. This paper compares and contrasts the microstructural features of Impulse Atomized. and quenched Impulse Atomized powders,' for both AL6061 and a scrap aluminum alloy composition.

Jan 1, 1995

By Chris J. Conway, Bruce W. Atkinson, Graeme J. Jameson

The flotation of coal in the fie and coarse particle size ranges presents particular problems. Fine or ultra-fine coal less than 100 microns presents a challenge to conventional flotation machines because the rate of capture of the coal particles can be very low, so longer residence times are needed. Also, conventional mechanical cells are not normally designed with froth properties in mind. Froth drainage may be inadequate, leading to excessive entrainment of ash. The upper limit of flotation of coal is normally put at about 500 um (30 mesh). It appears that, in mechanical cells, coarser particles tend to be torn away from bubbles in the turbulent environment created by the impeller. In this paper, results are presented from plant trials of a high-intensity flotation column of novel design, namely the Jameson cell. Extensive trials have been conducted on coal slurries with a top size of around 1 mm. Size-by size analysis shows that it is possible to achieve high yields of low ash product over the whole particle size range.

Jan 1, 1995

By R. L. Nielsen

The thematic mapper (TM) aboard Landsat II records image data at seven wavelength intervals or bands. Three record the visible region; three record reflected IR energy. A false color image combining bands 7, 4 and 2 rendered as red, green and blue respectively provides maximum discrimination of rock types in arid regions. Structural analyses and interpretation defines regional structures, large volcano-tectonic features intrusive complexes, all which localize mineralization. Special digital processing using the ratio: Band 3 / Band 1 can identify limonites and other iron minerals. The ratio: Band 5/ Band 7 identifies clays and alunite. These ratio images show features and patterns of hydrothermal mineral systems: ?patterns of sulfide and alteration zoning in large porphyry systems, and zones of strong silica, quartz-alunite-illite, and pyrite-sericite in epithermal centers. Thus, digitally processed Landsat TM images are a cost effective and rapid means to recognize altered areas and define targets for large mineralized systems.

Jan 1, 1995

By M. Phylli Bray

"Mining has the reputation of being a very ""macho"" industry. Recently, wider educational opportunities for women in nontraditional occupations and changes in mine technology have combined to make mining a viable career choice for women also. To benefit from this new resource, the mining industry faces the challenge of developing a different work environment from the one now burdened with sexism. Management supported initiatives are needed to facilitate such a transformation. The same rethinking of gender attitudes might also be extended to mining women in their traditional role as ""wife of"". The assumption that the male worker's wife is an unpaid adjunct is being questioned. It is suggested that women's separate concerns both as helpmate and as part of the mining workforce should be considered when planning for mining into the 21st century.IntroductionI must confess that, during the preparation of this paper, there have been many moments when I questioned my temerity. After all, I am not male, I am not an engineer, and I have never had a position in mine management. But as the wife of a mining engineer and a long-time resident of Northern Ontario mining towns, I do have an interest in the mining industry. This interest has had little to do with the technical and management aspects of the industry. Instead my research has been concerned with the impact the mining industry has on the people involved, particularly women, whether directly as employees or indirectly as wives. As I look toward the 21st century, I believe that the whole question of gender relations in the mining industry is one of the critical management issues smouldering below the surface."

Jan 1, 1995

By M. J. Beus, M. K. Larson, J. K. Whyatt

U.S. Bureau of Mines researchers reviewed an in situ stress estimate developed from measurements of overcore strain taken at test sites on the 7300 and 7500 levels of the Star Mine near Mullan, ID. Although the field measurements of overcoring strain were found to be useful, significant deficiencies were found in the stress estimation procedure. A new stress estimate was developed incorporating statistical methods and an improved understanding of stress concentration factors for interpreting overcore strains recorded by doorstopper cells. Spatial variability of overcore strains and the implications for stress field variability were explored.

Jan 1, 1995

By M. O. Woodburne

The Mojave Desert province is comprised of a diverse group of mountains that range in elevation from about 2,000' (600 m) to 3,000' (900 m), separated by tracts of alluvial cover. The province is bounded on the southwest by the San Andreas fault, on the north by the Garlock fault, on the east by the Death Valley- Granite Mountains fault. Rocks preserved in the Mojave Desert Province collectively record a rich assemblage of Precambrian crystalline basement' ranging in age from ca. 1.8 to 1.35 Ga, upper Precambrian and Paleozoic Cordilleran miogeoclinal sediments and platform rocks, Mesozoic backarc and interarc shallow marine and continental sequences, locally emplaced Permian- Triassic syenitic plutons, extruded hypabyssal volcanic rocks of the ?Jurassic "Sidewinder Volcanic Series," and regionally intruded late Mesozoic granitoid batholithic rocks (Dokka et al., 1988). The Mojave block apparently was a high-standing element for much of the early Tertiary, with strata of Late Cretaceous or early Tertiary age preserved only on its margins. Beginning about in the late Oligocene an intense episode of regional north-south extension was developed in a roughly east- west trending belt that traversed the central part of the province. This extensional belt has been termed the Mojave Extensional Belt. The extensional regime lasted from about 22-17 Ma, and is generally divided into two phases. The first, from about 22-20 Ma records intense extension via the activity of crustal-scale, simple shear, low- angle normal faults, high-angle normal faults, and extensional fracturing, along with intrusion of intermediate to silicic volcanic rocks, including episodes of explosive volcanic activity. The Peach Springs Tuff, a major regional marker unit that extends across the Mojave from Arizona to about Barstow, forms an effective stratigraphic lid on the extensional interval, (i.e., is not rotated) and is dated isotopically at about 18.5 Ma. The extensional episode was followed by an interval of high- angle normal faulting and dike emplacement from about 19 to 17 Ma, and was accompanied by at least local uplift and volcanism. Most volcaniclastic and epiclastic sedimentary units of the central Mojave block post-date the interval of extension and normal faulting, and occur as a complex of marginal alluvial and more interior lacustrine facies that formed as recently as late Miocene (ca 13 Ma). Local sequences (e.g., Lava Mountains) record deposition up to about 8 Ma, but there appears to be a regional "gap" from then until at least local successions record Pleistocene deposition. Magnetic and isotopic age studies indicate a complex history of crustal rotations, distributed across a number of discrete domains, during the past 10 Ma. Some of the youngest volcanic and geomorphic features apparently developed at "holes" formed at the edges of rotated blocks.

Jan 1, 1995