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By H. A. D. Kirsten

The paper reports on loading tests conducted on shotcrete reinforced with mesh and various types of steel fibre, and compares the results with the energy absorbing capabilities of 16 mm rebar shepherd's crooks. It is concluded that mesh-reit1forced shotcrete has sufficient energy-absorbing capabilities to contain rockbursts of significant magnitude, having greater energy absorbing capabilities, even at a thickness of 50 mm, than 16 mm rebar shepherd's crooks. Fibre-reinforced shotcrete has energy absorbing capabilities of the same order as, or better than, those of 16 mm rebar shepherd's crooks, but its performance is erratic.

Jan 1, 1995

By Levent Ozdemir, Roy H. Spitzer, Don W. Deere, John B. Blyler

This paper documents the construction of the Stanley Canyon Tunnel, the geologic conditions encountered, boreability of the rock, and the impacts of the conditions encountered on the construction. The 5.05 kilometer long (3.1 miles), 3.47 meter (11.4 feet) diameter, tunnel was driven through granites with a refurbished tunnel boring machine (TBM). Difficult ground conditions encountered included shear zones, high groundwater flows, and hard, tough, and strong rock. Detailed geotechnical studies during construction revealed that microscopic changes in the rock grain boundaries due to contact metamorphism, resulted in the hard boreability. Originally scheduled for five months, the tunnel construction required nearly three years, including periods of project shutdown.

Jan 1, 1995

By L. A. Panek

A new pillar strength formula is presented. It incorporates a function [IF] of size and shape that takes into account the size-shape interaction effect as well as the enhanced strength exhibited by wide pillars. Existing pillar formulas, lacking these capabilities, are not suitable for extrapolating small-specimen test results to mine-pillar sizes and shapes. Interpreting compressive strength test results as function of [Y] reveals wide-pillar behavior in much old test data. Model relationships are discussed, along with their scaling implications.

Jan 1, 1995

By Aitchison J, Clarke G

A reappraisal of the stratigraphy, new regional kinematic analysis and thermobarometric data allow a new interpretation of the metamorphic zoning and tectonic structure of the Upper Eocene high-pressure metamorphic core complex of northern New Caledonia allow a three steps evolution to be proposed : 1) subduction and understacking of previously thinned continental crust elements; 2) subduction blocking due to the crustal thickening; 3) crustal thinning and extensional detachment during the diapir-like uplift and unroofing of the eclogitic core. Steps 2 and 3 may be partly contemporaneous. Such a model accounts for the thermobarometric and radiochronologic data, and also for the weakness of substratum deformation during the emplacement of the ophiolitic nappe.

Jan 1, 1995

Overland conveyor belts that exhibit tracking problems under loaded and unloaded conditions can be tested to' determine the root cause of the mistracking. Moveable conveyors are more prone to mistracking due to structure alignment requirements. In addition, belting quality, splice straightness and carcass condition has a dramatic effect on the performance of a belt in relation to tracking. Methods are discussed that are proven to reduce belt mistracking and improve the operational reliability of the conveyor system.

Jan 1, 1995

By Oliver Gutsche

High-pressure roll mill comminution of heterogeneous multicomponent feeds was simulated with artificial limestone-quartzite mixtures using a piston-die press. The influence of heterogeneous interactions between components of the mixture on grinding path, energy utilization and energy split have been examined. Primary fractures are governed by differential fracture strength and attrition resistance of the components at heterogeneous contacts; subsequent secondary and tertiary fracture events are governed by coarse-fine interactions in the particle-bed. The weaker component is preferentially ground out of the feed size fraction and concentrates in the fines. Energy split among the components in the mixture is a function of their relative fracture strengths. It doubles for limestone and decreases by a factor of 5 for quartzite over the entire range of the mixing ratio.

Jan 1, 1995

By Terence Day

The traditional approach to mineral resource development is to identify the resource and then to undertake an environmental impact assessment of the effects of developing the resource. However, the traditional approach tends to ignore or underestimate cumulative, indirect and synergistic effects (Therivel et al., 1992). Moreover, traditional environmental impact assessment puts the project proponent in a position where the environmental impact assessment is used to defend on environmental grounds, a decision which has already been taken on technical and economic grounds. An alternative approach is to undertake an area-wide or strategic environmental assessment, (United States Department of Housing and Urban Development, 1981; Kelly et al., 1987). Strategic environmental assessment consists of the compilation and analysis of environmental data and information on an area. The data and information includes physical and chemical oceanographic data, biological surveys, social and economic parameters such as recreation and resource use, and ecosystem stressors such as dumping areas and sewage outfalls. Strategic environmental assessment is being increasingly used in the U.S. to provide scientific information to evaluate national or regional objectives for development and conservation of coastal and oceanic resources (National Oceanic and Atmospheric Administration, 1991). The strategic environmental assessment process lends itself very well to an evaluation of offshore sand and gravel re- sources in Atlantic Canada, because although the potential resource is widespread, the environmental constraints on development are potentially serious, but highly variable. The approach has the merits of identifying areas which are least susceptible to environmental damage, and of concentrating the exploration efforts on that part of the resource which is most viable from the perspective of integrated resource management and marine conservation.

Jan 1, 1995

By Quan Li, Xiang Ren, De Lui, Yumin Zhang

SL-type continuous centrifugal separator with injection flow (Injection Flowing Film Centrifugation, IFFC) for separating fine and ultra-fine minerals has been developed recently in China and it is capable of recovering particles down to one micron in size. In this paper, the principle of its separation is discussed. IFFC is a special transient pulsating film which combines both thin film jigging and thin film concentration functions. It not only can intensify the looseness and stratification of the settled particles, but also create a hydraulic weir effect to improve recovery of fines and ultra- fines and significantly improve the performance of thin film separation. In a Chinese tin gravity concentrator, SL devices, SL-1200s (capacity 1.5-2.0 ton/hr) and SL-600s (capacity 0.5 ton/hr) were applied to treat -1 0 micron cassiterite slime(removed as tailings at the past) and to replace the old tin flotation system(-74+10 micron slime). The plant results show that 50-60% of the cassiterite can be recovered from -10 micron slime with an enrichment ratio of 10-12. Particle down to one micron were recovered. Under optimal conditions, the recovery from -74+10 micron slime can reach more than 85%. The recoverable size range can be determined by calculation.

Jan 1, 1995

By R. S. Conti, C. D. Litton

This U.S. Bureau of Mines (USBM) report discusses the results of research conducted in the USBM experimental mine at its Lake Lynn Laboratory to determine the alarm times of smoke and carbon monoxide(CO) sensors, and a point type heat sensor (PTHS) to slowly developing coal-conveyor belt fires. The tests were conducted at air velocities of 0.44 and 0.97 m/s. The data clearly indicate that smoke sensors provide earlier warning of fire than 10 ppm CO sensors, and that 10 ppm CO sensors provide earlier warning than PTHS. A success rate of 1.0 (indicating detection of every test fire) was obtained for both smoke and CO sensors. For the PTHS, the success rate was 0.57 at the lower air velocity, decreasing to 0 at the higher air velocity. Data are also presented showing the sequence of fire events and detection events at the two air velocities as a function of time. Results show that early detection and warning of underground mine fires will improve the probability of miners’ escape.

Jan 1, 1995

By Robert J. Timko, R. Lincoln Derick

This U.S. Bureau of Mines study examined spontaneous heating episodes in coal mine pillars in an active underground coal mine. The information obtained from these incidents was then analyzed to learn which sampling methods provided the earliest indication of pillar heating. The objective of this study was to discover if the location of future events of pillar spontaneous heating could be inferred from the available information. The spontaneous heating-prone area in this evaluation involved pillars located just in by the mine portals. Several detection methods were used to determine gas levels outside as well as inside the affected pillars. It was hoped that, by incorporating external and internal sampling methods into an organized program, locations undergoing spontaneous heating could be determined more readily. This study found that by drilling small-diameter boreholes into the pillars, then obtaining gas samples from the affected pillars, the ability to locate early spontaneous heating episodes was improved. However, the ability to accurately predict future spontaneous heating events remains in question.

Jan 1, 1995

By John A. Mavrogenes

The Texaco gasification system developed at the Monte Bello pilot plant efficiently bums petroleum-coke thereby producing syn-gas and electricity. This system produces more electricity than conventional burners, yet the only by-products are pharmaceutical grade sulfur and V -rich slag. Vanadium is known to exist in multiple valence states in compounds which possess a wide range of melting points and physical properties. Consequently, it becomes important to carefully regulate oxygen fugacity throughout the system in order to control vanadium valence state. Vanadium phase equilibria is presently poorly understood, in large part because of the multiple oxidation states of vanadium (-I, 0, +2, +3, +4, and +5) and the difficulty of unequivocally identifying the valence state(s) in many compounds. The operation of these gasifiers at approximately 1400°C is well above the melting point of V20S but considerably below the melting temperature of V02 and V 203. If J02 can be regulated to keep the burner within the V 205 field, slag material would more likely remain molten and more easily flow out of the bottom of the burner. In pure V oxides. the oxidation state is readily determined by microprobe analysis. where V20S (V+5) is 56% V, V02 (V+4) is 61.4% V, and V203 (V+3) is 68% V. However, V valence in multi-element phases (especially phases containing other elements of variable valence) cannot be resolved by microprobe analysis alone. Petroleum-coke gasification slags collected from within the gasifier under different oxidation conditions were studied by electron microprobe analysis (EMPA). X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Raman spectrometry in conjunction with microprobe analysis was found to resolve the valence of vanadium in the phases of these slags. Raman spectra collected from homogeneous single phase V-oxide standards in vacuum at low temperatures (-150°C) yielded peaks characteristic to each valence state. Gasifier slag samples are, however, much more complicated. Oxidized samples contain: fine grained (Ca. Mg, Fe. V) oxide matrix of variable composition, (Fe. V, Ni) spinel. (Fe, AI, V, Ni, Mg) spinel, V205laths, AI-Si glass blebs and Ni sulfides. Reduced samples contain: crystalline Ca-siIicate matrix, subhedral to euhedral (V, Fe, Mg, AI) spinel, subhedral V02, Fe and Fe-Ni sulfides, Fe-Ni alloys, and complex Ca-oxide matrix. The different spinel assemblages, the characteristic V-oxides and the distinctly different character of the matrices makes the oxidized and reduced slags readily discernible.

Jan 1, 1995

By G J. Corbett, T M. Leach

Although hosted within an Ordovician magmatic arc, the Peak Hill high sulphidation system displays features typical of youngerPacific Rim high sulphidation epithermal gold deposits. Regional NW trending transfer structures are inferred to localise the magmatic source at their intersection of the NS trending arc. Fluids have migrated from the magmatic source along NW structures and thence exploited permeable horizons, which have become silicified. Alteration displays typical zonation from silicification through assemblages characterised by alunite, pyrophyllite and kaolinite and is followed by breccia/fracture controlled sulphide and gold deposition. Sinistral rotation on the NS arc has dilated NW trending fractures to produce the WNW to EW dilational fractures which host the higher grade ore. Mineral assemblages are typical of formation distal to the magmatic source in an epithermal environment. The combination of alteration and mineralisation zonation with structure provide fluid vectors which target a magmatic source to the SE of Peak Hill.

Jan 1, 1995

By A. J. Hyett, N. Hedrick, J. Blackall

The Garford bulb anchor is a modified cable geometry developed and patented by Garford Ply Ltd. of Australia, and which has recently become widely available in Canada. It is produced by deforming the seven wires (including the central kingwire) of a standard cable into a bulb" (Fig. 1). Laboratory cable pull tests indicate that the bond capacity of the 25 mm Garford bulb anchor is comparable to the nutcase cable, in excess of the birdcage cable, and significantly higher than standard 7-wire strand. Its comparative advantage over the latter is most significant for tests at low radial confinement and high water:cement ratio grout, which corresponds to operational conditions of low quality rock (i.e. weak, highly fractured rock masses, foliated hanging walls, failed ground, etc.) and poor installation quality control (perhaps the most common explanation for cable bolt failures). It is under such conditions that cable bolting is often ineffective. The most impressive result is that for a reduction of the effective rock mass modulus by a factor of five, the Garford bulb cable capacity remains virtually unchanged.

Jan 1, 1995

By Robert Rautenberg, Ted Budd

The paper will discuss the successful construction of the largest dollar value ($194.5 million, U.S.) TARP (Tunnel and Reservoir Plan) project built to date for the Metropolitan Water Reclamation District of Greater Chicago. The mining and lining of the 18.5km (11.54 miles) tunnels will be emphasized. The tunnels were driven utilizing three TBMs ranging in size from 9.85m (32.33 ft) to 3.70m (12.16 ft) in diameter. The operations surrounding the 11,546m (37,876 ft) long 9.85m (32.33 ft) diameter tunnel will be highlighted. A total system concept was utilized to attain mining rates up to 29.3m (96 ft) per shift and lining productions of 58.5m (192 ft) per day. The reliability of these systems was instrumental in the completion of the project more than a year ahead of schedule.

Jan 1, 1995

By George P. Jr Schivley

Data is presented showing Penetration Rate (PR) versus Force-on-the Bit (FB) and Bit Angular Speed (N). Using this data, it is shown how FB and N each uniquely contribute to the PR for any particular drilling situation. This data represents many mining situations; including coal, copper, gold, iron ore and limestone quarrying. The important relationship between Penetration per Revolution (P/R) and the height of the cutting elements of the bit (CH) is discussed. Drill performance is then reviewed, considering the effect of FB and N on bit life. All this leads to recommendations for the operating values of FB and N for drilling situations where the rock is not highly abrasive and bit replacements are because of catastrophic failure of the bit cone bearings.

Jan 1, 1995

By Robin J. Batterham, Stephen H. Algie

It is often stated that innovation is central to the economic survival of mining and mineral processing in the face of global competition, and yet technology is often far from a core strategy in our industry - hence the concerns that are often voiced about the apparent slow rate at which new technology is applied. Much of the discussion stems from a lack of understanding of the role of technology in innovation, and of the role of R&D within the innovation process. To a large extent this has all been said, however, the messages are clear and deserve repetition. This paper expresses the personal views of the authors, based on experience in government-funded (CSIRO and universities) research, and in CRA Ltd, a large mining and mineral processing company. Further than this, it explains how our own development unit within the CRA Group has come to see its key roles as including the transfer of technology, and the training of technologists to move into the operating business units. We conclude that these critical tasks are the keys to creating the environment that will allow us to maximise the contribution of technology.

Jan 1, 1995

By P. R. A. Andrews

"Garnet occurs in schists and gneisses in all provinces of Canada, all mainly in Quebec and Ontario. There is currently a renewed interest in exploration for economic sources of garnet for abrasive applications because of the inherent dangers from exposure to ground silica from sandblasting operations.High-quality garnet is used for lapping and grinding of glass and ceramics; for coated and bonded products such as sandpaper and cloth; and abrasive wheels for grinding and finishing various metals, woods, rubber and plastics. Low-quality garnet is used for cleaning and conditioning aluminum and other soft mewls, particularly by aircraft manufactures. Garnet may be added to grouting cements for oil-well drilling applications, and it has also been used for low- to medium-level radiation shielding. Garnet has been studied extensively by CANMET and its predecessor, Mines Branch, between 1917 and 1990. Twenty-nine studies relating 10 various aspects of beneficiation are presented and a review of the more important studies is presented. The information includes mineralogy, beneficiation methods, product sizes and analyses."

Jan 1, 1995

By P. I. Prescott

Ground calcium carbonate (GCC) is used in the paper, plastics, paint, rubber, caulks, and sealants industries. The favorable properties of GCC include high whiteness and brightness, low hardness, and outstanding rheology in water systems. The quality of calcitic GCC ores, which include chalk, limestone, and marble, is dependent on calcite purity and the nature and quantity of ancillary minerals. Wet and dry grinding is used in the manufacture of GCC. Ore processed by optical sorting, flotation, and/or particle size classification has higher brightness and lower abrasion. GCC markets are a function of the product's properties, purity, and cost.

Jan 1, 1995

Production scheduling is an important element of the mine planning process. The production schedule specifies the quantities of mineral to extract, the source of this ore, the timing of extraction and, where necessary, the quantity and timing of backfill placement. These details are important in linking long-term strategic goals to short-term operational planning. Mine scheduling techniques form the basis for communicating information concerning the overall impact of design and planning changes to a wide range of people at many levels within an organisation. Consequently the techniques used for mine scheduling must support the decision-making process by consistently providing high quality schedules in response to revised and updated data. A new mixed integer programming (MIP) model has been developed to generate optimal production schedules for underground stoping operations. The model maximised the before-tax Net Present Value of the production schedule while satisfying constraints such as contained metal tonnage, hoisting capacity, stope geometry relationships and stope backfilling demands. Zero-one variables were used to represent the decision to extract or backfill each stope in a particular time period. Continuous variables, capable of having non-integer values, were used to denote the quantity of ore or backfill associated with a specific stope in a given time period. A case study is presented to demonstrate the significant improvement in before-tax NPV over a comparative manual production schedule in a large underground mine. The MIP model allows for further modification to reduce solution times and meet the needs of individual mines.

Jan 1, 1995

The quality of life in many countries of both the developed and the developing world is strongly affected by the products and processes of mining industries. The first Issue in this new series brings together a set of review articles by leading authorities in the field which, taken together, provide a thorough and detailed survey of many of the key topics of current concern relating to the environmental impact of mining. The level of treatment of most topics is at first introductory but evolves through to the advanced level of current research, backed up by extensive citations of relevant primary literature and other sources. Thus the Issue as a whole will be found equally valuable by students of environmental science and those actively engaged in research related to this theme.

Jan 1, 1995