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By L. J. Cabri, J. M. D. Wilson, R Lastra

An image analysis program can search for gold minerals in polished sections by scanning about 100 x 100 back-scattered electron images at a magnification of x400, allowing gold grains as small as 1 micrometre in diameter to be detected. Typically, a c.15 h overnight search of a product smaller than 45 micrometres will scan c.1 500 000 particles, providing data that are not easily obtained through manual operation of an optical microscope. The program locates grains of the correct brightness, acquires gold X-rays from them by wavelength-dispersive spectrometry, filters the data to remove artefacts and record the images and stage locations for subsequent retrieval. At the end of the run, the program allows the operator to verify and identify the grains found. Industrial studies at Canmet have included determining the nature of gold in cyanidation tailings, checking the mineralogy and size of gold grains in samples from an Indonesian Cu-Au concentrator and locating and measuring gold liberation and grain sizes in an ore

Jun 21, 1905

By F. N. Voskoboyev

The suggested new method for control of geomechanical state of undermined rock mass ensures, as a safety measure for the earth surface protection, the decrease of deformations by 2,5 - 10 times in mining the single seam, and by 1,5 - 5 times - in mining bed series, i. e. approximately within the seam ranges as in the application of full packing with various compressive properties or partial extraction of resources over the area with different coefficients of extraction. It should be noted that this new method has the following advantages o\w rhr. conventional methods: a) the decrease of the packing area and packing works volume by 2 - 4 fold including the operating and productive expenses; b) the elimination of mineral losses due to the increase of extraction coefficient up to 100 5%; c) rock utilization from workings drivage by its placing in the mined - out space. Perspective field of application of this method: disconservation of mineral resources in the left protective pillars of various designation.

Jan 1, 1996

By J. D. Dixon

This Bureau of Mines report describes the results of an investigation for developing and applying procedures for stabilizing excavations openings in highly yielding ground. The approach developed in this report involves nonlinear modeling of the progressive relaxation of the zones of rock mass around the excavations opening where Coulomb criterion of failure is exceeded. Stresses are calculated by using a computer code; Coulomb-failure condition is examined for both intact rock and joints (using strength parameters [~] and c). The rock mass in the failed zones is relaxed by reducing the Young's modulus of the rock based on an empirical formulation that is a function of the shape of the opening and the extent of the failed zone. In addition, the material in the failed zone is assigned reduced strength paramters 0' and c'. The limiting (or convergent) relaxed zone is obtained through an iterative process by manually changing the rock modulus and the strength parameters between iterations. Support pressures are computed by applying forces normal to the excavation surface. The approach is applied to the analysis of stability and support requirements for an entry in a longwall coal mine.

Jan 1, 1985

By P. den Hoed, R. I. Rambiyana

"Four sulphide minerals - pyrite (FeS2), pyrrhotite (Fe1-xS), pentlandite ([Ni,Fe]9S8), and chalcopyrite (CuFeS2) - contain the base metals and most of the iron in concentrates of platinum group metals (PGMs). In the pyrometallurgical processing of PGM concentrates these sulphides form a matte during smelting, and iron and sulphur are removed from the matte during the converting process. This paper discusses the roasting of Merensky concentrate in air before smelting, with the purpose of reducing the matte load to the converter.Roasting tests were conducted in a bench-scale rotary kiln at temperatures from 350°C to 700°C. The concentrate tested contained 17.4% sulphur and consisted of 23% pyrrhotite, 16% pentlandite, 11% chalcopyrite, and 2% pyrite. The particles were fine (d50 = 22 µm), and all the sulphide particles were liberated. Roasting in air at 550°C and 650°C for 20 minutes removed respectively 60% and 70% of the sulphur. The iron in the sulphides was oxidized to Fe3O4 (magnetite) at temperatures below 500°C and to Fe2O3 (haematite) at temperatures above 550°C. At 700°C the bed sintered and copper oxides formed. At temperatures below 450°C oxidation was incomplete: pyrrhotite remained and only 30% of the sulphur was removed. Smelting tests were conducted to assess matte fall and the deportment of copper and nickel to matte. It was evident that roasting resulted in lower matte falls (a drop of approximately 60%) compared with matte falls from unroasted concentrate. The iron and sulphur levels in the matte were reduced to below 3.5% and 22% respectively.This paper also briefly describes the mechanisms by which pyrrhotite, chalcopyrite, and pentlandite are oxidized during roasting. For chalcopyrite, the mechanism proceeds through an intermediate solid solution phase, which extends from Cu1.02Fe1.04S2 to Cu2.04Fe0.72S2 to a copper-rich solid solution of bornite (Cu4Fe1.4S4-Cu2S). The oxidation of pentlandite proceeds through a monosulphide solid solution (Ni0.39Fe0.53S-Ni0.74Fe0.15S) to a solid solution of heazlewoodite ([Ni,Fe]3}xS2). These mechanisms are explored in relation to chemical thermodynamics and microstructures."

Jan 1, 2015

By A. C. Legg, M. T. Malema

Keywords: Pyrometallurgy, flash, smelting, furnace, nickel, copper, Botswana BCL Limited operates the only Flash Smelting Furnace on the African continent, at Selebi-Phikwe, situated in north-eastern Botswana. The furnace was commissioned in 1973 and produces a high-grade sulphide matte containing nickel, copper and cobalt, which is shipped to refineries in Zimbabwe and Norway for further processing. This paper outlines the recent process improvements and plant expansions that have resulted in a capacity increase from 40 000 to 60 000 tons per annum of metal production.

Jan 1, 2006

Several economic factors have caused the surface mining industry to require large-capacity shovels and trucks for efficient, high-production, low-cost operations. Some of those factors include technological advancements in equipment, commodity market depressions, increased labor and maintenance costs, contractural obligations and harsh operating conditions. The difficult operating conditions in surface mines, however, pose challenges to the use of high-capacity equipment. They include space limitations, weak over-burden, and weathered soils and rocks. So mining companies face major challenges in selecting appropriate shovels to meet the technical, operating, safety, environmental and economic requirements of their mines.

Jan 1, 2003

By Dana C. Reinke

A job analysis is a written list of the tasks associated with doing a particular job. In drilling, describing the steps associated with adding rod to the drill steel would be an example of a task associated with the job. How to hammer casing or fish a lost drill bit out of a hole would also be job tasks. Develop a written list of job tasks. Ask drillers in your company if the tasks listed are correct and accurately reflect how to perform the job. While each driller may do the job a little differently, some tried?and?true methods are required to perform certain tasks safely and correctly. You may find a separate analysis is needed for different drilling jobs (e.g., a residential well or a monitoring well). Also remember to include the tasks of both the helper and the driller.

Jan 1, 2005

By B. W. Dunning

This paper describes studies conducted by the Bureau of Mines to achieve its goal of developing methods for increased recovery and utilization of valuable constituents in a wide variety of domestic and industrial wastes, In this particular study, 36 units of obsolete electronic equipment from military aircraft were disassembled into their modular components by hand to determine materials distribution. Further modular disassembly into individual parts was used to identify metal composition. After identifying the metals in some of the more difficult to dismantle modules, similar modules were grouped together, shredded, mechanically separated, and using metal composition data from hand separation, classified along with the hand-separated materials. Although this equipment is normally classified as law-value iron-bearing aluminum, data were obtained that indicated the potential for moderately higher value classification. The electronic units were classified as to precious metals, copper, iron, and aluminum contents, and scrap values were estimated.

Jan 1, 1980

By Won C. Park

Experiments showed changes in the mineral content of dolomitic oil shale at temperatures and exposure times which bracket conditions encountered during in situ retorting. Laboratory results correlate with cores from a spent in situ retort at Occidental's Logan Wash test site at Garfield County, Colorado. Dolomite, CaMg(CO3)2, decomposes rapidly to form periclase, MgO, calcite, CaCO3, and CO . Both calcite and periclase are intermediate products that can be stabilized by CO atmosphere at lower temperatures, while steam accelerates the formation 2 of silicates. The decarbonation of calcite appears to involve a direct reaction with both quartz and periclase in forming these silicates. Decarbonation preceeds the formation of akermanite, Ca2 MgSi 207, and diopside, CaMgSi 206, within several hours of heating and is followed by the nucleation of forsterite Mg2SiO4, and monticellite, CaMgSiO4. Under in situ retorting conditions, akermanite and diposide are the major minerals above 800°C. Equilibrium is not attained within 200-300 hours. In situ retorting temperatures above 800°C for extended periods of time should reduce potential ground water leaching by the formation of silicate minerals. These silicates are less soluble than free lime, magnesium or alkali oxides. There is a corresponding decrease in the natural pH of these silicates from approximately 12 down to 7.5 to 9:

Jan 1, 1981

By Jason Rrno

The emergence of Impact and Benefit Agreements (IBAs) in the Canadian mining sector has been read by many as a positive governance innovation. Negotiated directly between mineral resource developers and Aboriginal communities with limited government interference, IBAs serve to manage impacts associated with a mining project and deliver tangible benefits to local communities. Notwithstanding their increasing use and significance, limited systematic analysis has been undertaken to determine whether they are, in fact, working. This paper reports on the effectiveness of a number of IBAs negotiated in support of three northern Canadian diamond mines, drawing on evidence from time-series data, key informant interviews, and focus group meetings in Yellowknife and Dettah, NWT, and Kugluktuk, NU. While some deficiencies were apparent and perceptions of effectiveness varied somewhat by Aboriginal community, the IBAs were generally found to be meeting their objectives, especially with respect to the delivery of benefits. For Aboriginal communities affected by mineral development in the Canadian North, this represents a significant change to typical outcomes of the past. Moving forward, research on IBA effectiveness needs to adopt a longer timeframe and begin to gauge the degree to which IBAs are able to address long-standing concerns associated with hinterland resource extraction beyond their agreement-specific objectives.

May 1, 2010

By A. Lawley S. Schuster

The tensile behavior of copper foils prepared from rolled bulk material has been studied over the thickness range 2 to 53 , and for a range of pain sizes. For foils of comparable grain size, having the cube texture and tested along (100), yield strength increases with decreasing foil thickness t below -26p, with a corresponding decrease in ductility. Deformation occurs in the form of localized slip clusters distributed throughout the gage section. To the extent that the tensile strength (10 to 18 kg mm-) is unaffected by foil thickness, and that the foils possess fair ductility, the stress-strain behavior resembles that of bulk material rather than that of whiskers or evaporated films of comparable dimensions. The dependence of yield strength o on foil thickness t below -26p is of the form: oy = oo + kt-1/2. Possible explanations for the stress increase are considered based on 1) the dependence of active dislocation source length on foil dimensions, 2) the locking of surface sources, or the blocking of mobile sources at the surface due to surface film. It is now well-established that filamentary whiskers of many materials show exceptionally high strength compared with bulk crystals.'-11 As the diameter of the whiskers decreases to -1, the observed fracture strength approaches, and in certain cases exceeds, the calculated shear stress for the nucleation of slip in a perfect crystal.' In general, the stress-strain curve is entirely elastic, with strains at fracture approaching 1 pct. Similarly, thin films12-24 of evaporated or electrodeposi-ted material have been shown to possess tensile strengths three to seven times that of bulk material, with total strains at fracture -1 to 2 pct. In the present study, attention has been directed to the room-temperature tensile behavior of thin foils of copper over the thickness range 2 to 53, prepared from rolled bulk material. Yield stress, ultimate tensile strength, elongation to fracture, and work-hardening behavior are measured as a function of grain size and foil thickness. Structurally such foils are superior to either evaporated or electrodeposited films, and in the recrystallized condition exhibit considerable ductility. Apart from preliminary work by Sumino and Yamamoto25 on the work-hardening behavior of rolled and recrystallized copper foils, no systematic tensile studies have been carried out on material of this form. EXPERIMENTAL PROCEDURE Tensile specimens were prepared from 99.995 pct purity rolled copper foils of thickness 2, 6, 12, 26, and 53, obtained from the Hamilton Watch Co., Lancaster, Pa. Irrespective of specimen shape, it is necessary to use tensile foils with edges free from notches or tears. To this end, any form of cutting operation was excluded, and the tensile foils prepared using a photoengraving process, the details of which are described elsewhere.26 Since tensile data are required under conditions of uni-axial stress, the specimen shape is extremely important. Ideally, the foil should be infinitely long, allowing a gradual taper from the grip area to the gage section; however, from a practical standpoint, long foils are easily damaged during testing. A modified tensile specimen was therefore selected having a parallel gage section 1.25 by 0.20 in. with a tapered shoulder section increasing to 0.5 in. at the grips, and an over-all length between grips of 4 in., Fig. 1. In practically all tests, these foils fractured within the parallel gage section. By approximating the foil contour (Fig. 1) to a hyperbola it is possible to analyze the stress distribution in the tensile foil using two-dimensional elasticity

Jan 1, 1964

By G. G. Roy, R Shekhar

Pachuca tanks are extensively used for the cyanide leaching of gold and the carbonate leaching of uranium, processes in which oxygen mass transfer plays a very important role. Experiments were carried out to clarify the effect of design and operating parameters on oxygen mass transfer. Parameters such as the ratio of tank height to tank diameter, the ratio of draught-tube diameter to tank diameter and the tank design were found not to influence oxygen mass transfer. Results also showed that equal superficial gas velocities may be used as a criterion for scaling up oxygen mass transfer in both full-centre-column and free-air-lift Pachuca tanks with clear water. A volume-averaged, volumetric gas-liquid mass-transfer coefficient (k'av) was used to characterise oxygen mass transfer in full-centre-column tanks. The axial dispersion model was used to determine k'av. The resulting model used only tank geometry and air flow rate as inputs for the prediction of k'av in industrial-scale tanks. Predictions from the model show clearly that "local" mass-transfer coefficients, measured at one or two locations, may not adequately represent gas-liquid mass transfer in industrial tanks. It is therefore necessary to obtain an estimate of k'av

Jun 18, 1905

By A. Adu-Acheampong

A geotechnical study was conducted to identify the cause(s) of stope instability at the Ashanti Mine (Obuasi, Ghana). As part of the investigation, laboratory testing of rock was performed and the rock mass was classified according to the Q-System (Barton et al., 1974).Numerical analyses were performed using the computer program FLAC (Itasca, 2001). The observed failure zone around the stopes was simulated using both Mohr-Coulomb and Hoek-Brown (Sheorey,1997) models. Yielding along peripheral graphite bands and tensile failure were clearly identified to be the major contributors to stope instability.

Jan 1, 2003

Detrital gold in the Greymouth-Hokitika area has been won from: (a) gravel of the Pliocene Old Man Group, (b) glacial outwash gravel of Middle and Late Quaternary age, (c) raised shoreline deposits of Middle and Late Quaternary age, (d) deposits resulting from the erosion of (a) to (c). The source of the gold was probably widely dispersed quartz veins in great thicknesses of greywacke and low-grade schist eroded from east of the Alpine Fault, with a contribution from veins in Greenland Group greywacke in the south. At times of high interglacial and post-glacial sea level, gold was concentrated along marine shorelines, and subsequent progressive uplift has resulted in a set of sub-parallel beach leads up to 100 m above present sea level. During glaciations, gold was concentrated in outwash streams close to moraines, especially where ice forming one moraine penetrated and destroyed an older one. Worked deposits in the Old Man Group may also be associated with glaciation. Apart from workings that are essentially extensions of past workings, significant new prospects may depend on inferences as to where prospective deposits are completely obscured by younger ones.

Jan 1, 1996

By Davies S. G, Mackey L. C

The oxidation of iron and nickel sulphide concentrates, and the dominant sulphide minerals which comprise them, has been studied under ignition conditions using thermogravimetry (fG). The concentrates were derived from various minesites and they showed differing tendencies to ignite. Ignition temperatures ranged from 416 to 488°C and the extents of reaction, measured at 500°C, varied from 64 to 88 percent. The reactivity of the least reactivematerial was improved significantly by grinding. Particles <63/lm showed 85 percent oxidation compared with 55 - 65 percent for particles >63/lm.Examination of the individual sulphide minerals revealed that these materials also have significantly different degrees ofreactivity and are subject to particle size effects. For particles <45/lm, the ignition temperatures were as follows:ò pyrite and violarite 380 - 385°C; pentlandite 425 - 430°C; and pyrrhotite 470 - 475°;ò for particles >90 /lm, the ignition values were: pyrite 395 - 400°C;ò violarite 430 - 435°C; pyrrhotite 540 - 545°C; and pentlandite 560 - 565°C.Using the data on the individual minerals it was possible to rationalise the differing degrees of reactivity of the concentrates. The role of the most reactive constituent in initiating the ignition reaction has also been discussed.Finally, the results of this work were found to compare. favourably with the behaviour ofthe concentrates in industrial and pilot-scale flash smelters.

Jan 1, 1989

By W. E. Tournay

In accordance with a cooperative agreement between the Bureau of Mines, United States Department of the Interior, and the Linde Air Products Co., an investigation was made at the Bureau Explosives Testing Station, Bruceton, Pa., to develop suitable test methods for evaluating the performance and sensitivity characteristics of liquid-oxygen explosives. This report presents the results of the investigation. The unique nature of liquid-oxygen explosives necessitated both modification of standard techniques and development of entirely new test methods. The latter requirement was due to the fact that differences exist in the kind of information that must be developed for studying relative safety and performance properties of these explosives compared to that of fixed explosives.

Jan 1, 1949

Reduce the respirable dust exposure of the roof-bolter operator when downwind of the continuous miner, particularly in mines where respirable dust standards are more stringent because of silica in the respirable dust. Dust Sources If roof-bolter dust levels are excessive, the bolter dust collector should first be checked to ensure that it is operating properly. (Technology News No. 219 provides information on how to spot and repair bolter dust collector problems). If the roof-bolter dust collector is operating properly and dust levels are still excessive, then the source is most likely a continuous mining machine operating upwind. In many sections, the roof-bolter operator must work on the return side of the continuous miner during part of the production cycle. In three-entry longwall developments with single split ventilation, this may happen as much as one-third of the time. Factors which pro-mote high quartz dust exposure are:

Jan 1, 1985

By Ingrid Hann

The Triple Bottom Line ? Economic Sustainability ? Creation of Joint Venture companies ? Planned evaluation of other kimberlites ? Social Sustainability ? Impact Benefit Agreement and Participation Agreements ? Education and training initiatives ? Environmental Sustainability ? Environmental management ? Mine closure planning

May 1, 2008

By L. A. Cornish, S. N. Prins, R. Süss

The work is being done using the Thermo-CalcTM software, and the database is being built up by obtaining good thermodynamic descriptions of all of the possible phases in the system. The database supplied did not cover all of the phases, and these had to be gleaned from literature, or modelled using experimental data. Similarly, not all of the experimental data were known, and where there were gaps or inconsistencies, experiments had to be undertaken. A preliminary version of the database was constructed from assessed thermodynamic data-sets for the binary systems only. The binary descriptions were combined allowing extrapolation into the ternary systems, and experimental phase equilibrium data were compared with calculated results. Very good agreement was obtained for the Pt-Al-Ru and Pt-Cr-Ru systems, which was encouraging and confirmed that the higher-order systems could be calculated from the binary systems with confidence. Since some of the phase models in databases were different, these phases had to be remodelled. However, more work is ongoing for information concerning the ternary phases present in the Al-Cr-Ru, Pt-Al-Ru (two ternary compounds in each) and Pt-Al-Cr (possibly more than three ternary compounds) systems. At later stage of the work, problems with the thermodynamic descriptions of the Cr-Ru and Pt-Cr binary systems were found. A programme of experimental work to overcome these has been devised, and is being undertaken. Keywords: Pt-based alloys, phase diagram calculations.

Jan 1, 2006

By M. England

Test equipment has been developed to record automatically both the displacement of the pile head and the load applied during a conventional maintained load pile test. Some systems also have, in addition, been fitted with the facility for maintaining the applied load, as set by the operator, at very constant levels. The advantages are both commercial and technical, but a well trained operator has to be in attendance to control the test. Since typical test specifications in the UK require more than 19 hours to complete, it became inevitable that at least one equipment operator remained on site to expedite the test for its duration. Although electronic measurement and data logging of load tests may be more safe than previous direct observation of dial gauges. A single person remaining on a construction site alone is not to be recommended, even if they are just supervising the test. Further development of the testing system produced equipment which will perform the entire test specification as required without operator intervention. To achieve this, full automation is employed. The patented method particularly addresses the safety requirements and by using additional sensors, detects any uncharacteristic behaviour of the pile under test or of the reaction system and the equipment takes appropriate action in a controlled and safe manner. The quality of test data returned from these automated systems is a key element when analysing pile behaviour with models such as CEMSOLVE? and TIMESETTM. These analysis methods often indicate ground disturbance resulting from installation technique and have allowed pile design to be optimised using actual field data rather than theoretical considerations alone. An additional feature is remote access, this allows the data recorded to be transferred and the progress of the test to be viewed from practically any location. This permits experts to view the data 'live' and allows rapid diagnosis of any problems with the expected pile behaviour.

Jan 1, 2002