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By N. Krauland, A. Nystrom, M. Board, S. Sandstrom

Several deep Swedish cut-and-fill mines experience severe ground control problems, including roof collapse and wall sloughing, as a result of variable rock quality and high in situ stresses. A project to examine the problem included two main areas. The first was prediction of mining conditions at depth and the adaptation of cut-and-fill mining to such conditions; the second was the assessment and improvement of support methods at present and future depths. Simple, elastic, mine-scale numerical models were used to optimise stope sequencing and more detailed, stope-scale models to simulate the failure processes around a stope and the interaction of rock mass and support. Kristineberg was chosen for testing and calibration of the predictive methods because of its long history of severe ground conditions and the large base of observational and monitoring data available for comparison. Horizontal cut and fill was found technically suitable to depths beyond 1 000 m and economically viable if ore value covers support costs. Stability can be achieved with the present support technology down to 1 000 m but the 7-strand 15.2 mm cables have poor deformation properties (5% failure strain) compared with rebar rock bolts (17%). Reducing the intervals between levels from 100 m to 50 m will cut support costs and improve production reliability and capacity. Simulation of sill-pillar mining indicated that conditions would be most severe when pillar height was reduced to 15-20 m; mining of a sill pillar has been carried out successfully to the last 3 m, whose extraction is planned for the near future

Dec 1, 1995

By J. Crummy, I. K. Anderson, A. J. Hall, R. S. Haszeldine

Bedrock gold mineralisation has been located in association with an extensive float train 25 km west of known alluvial gold. It is in the form of open, matrix-supported breccias comprising pyritic quartz/sericite clasts in a vuggy, cherty chalcedonic and crystalline quartz matrix. Fluid inclusions in pyritic clasts indicate trapping temperatures for gold mineralising hydrothermal fluid of 170-240 degrees C. This mineralisation could represent the upper part of a feeder zone to an exhalative hydrothermal system. It is possible that other high-level feeder zones could be preserved elsewhere in the area. Deep weathering of such a system could provide a source for the alluvial gold localities near Helmsdale. It is suggested that east and central Sutherland presents good prospects for exhalative epithermal gold mineralisation and the associated feeder zones

Jun 19, 1905

By C. A. Jeffrey

The Dirtlow Rake vein deposit, which is up to 12 m thick, contains a range of paragenetically linked replacement mineralisation styles typical of many Mississippi Valley-type deposit environments. The main ore zone lies within the solution collapse breccia domes, the more southerly of which has recently been well exposed, allowing its relationship to the associated mineral-hosting structures to be studied. The domes were largely formed during early silicification, propagated by dissolution collapse and infilled by subsequent fluorite-barite mineralisation. The location of pipes and pervasive replacement was also controlled by early silicification. Structurally controlled bow tie shears were formed as a result of fluid access at fracture-bedding plane intersections. The nature and distribution of the mineralisation styles indicate that the degree of fluid access, residence time of solutions in contact with the wallrock and susceptibility of the limestone to silicification each played a major role in dictating mineralisation

Jun 19, 1905

By D. M. Evans, D. L. Buchanan

Paper presented at the IAGOD international symposium on mineralisation related to mafic and ultramafic rocks, held in Orleans, France, 1-3 September 1993. The Zinca area was chosen as a suitable location for an investigation of the weathering and secondary dispersion of platinum group metals from the Zone. It was concluded that platinum is immobile while within weathered rock, its mineral phases tending to alter from primary sulphides and tellurides to secondary Pt-Fe alloys. Palladium is variably mobile in weathered rock. In stream sediments Pt occurs mainly as small, dense, discrete particles, giving rise to a nugget effect, whereas Pd probably occurs as much finer particles or chemically adsorbed on to a suitable substrate. Pt shows a rapid decrease in sediments downstream from mineralisation, whereas Pd has a much slower downstream decay

Apr 1, 1994

By E. Niehuis, J. Y. Kim, H. G. Cramer, S. L. Chryssoulis, K. G. Stowe, C. Bendel

TOF-SIMS was used to detect, identify from parent molecular ions and determine the relative concentrations of collectors sorbed on the surface of mineral particles in concentrate and tailings samples from three Canadian concentrators. In the Kidd Creek Zn circuit, sphalerite lost to tailings carried on average a quarter of the amount of isobutyl xanthate present on that recovered to Zn concentrate; amyl xanthate, which is not reported as added to the circuit, was also detected on floated sphalerite and pyrite. At Brunswick, sphalerite particles lost to the scavenger tailings had ten times less amyl xanthate and isobutyl xanthate than those recovered to the Zn final concentrate, while both xanthates were detected on sphalerite floated to the Cu-Pb cleaner circuit. At Matagami, significantly more isopropyl xanthate and isopropyl dithiophosphate were detected on sphalerite recovered to the final Zn concentrate than on that lost to the Zn rougher tailings

Dec 1, 1995

By R. O. Suominen, P. A. Taskinen, K. R. Lilius, A. T. Jokilaakso

Chalcopyrite concentrate was flash-oxidised in a laminar-flow furnace in oxygen-nitrogen atmospheres that ranged in composition from N2 to N2 + 50 vol% O2. Gas pre-heating temperatures were 500-1100 degrees C and four particle-size fractions were studied: 28-38, 38-44, 44-62 and 62-74 micrometres. The effect of the residence time of the particles on sulphur removal was studied in the range 0.1-0.35 s. Scanning-electron microscopy combined with energy-dispersive analysis and back-scattered electron analysis was used to determine the morphology and mineralogy of the reacted particles. Total desulphurisation was achieved under the most oxidising conditions. Particles were observed to undergo fragmentation during oxidation, the violence of this depending on the iron and sulphur contents and the original particle-size fraction. The melting and/or reaction stages of the particles under different conditions were studied in powder samples. Polished sections were examined to follow the development of porosity and the mineralogy of the particles. A model for the fragmentation process is described

Jul 1, 1991

By B. S. Terry, C. L. Harris

After measuring the kinetics of Ni reduction from a SiO2-saturated fayalite slag into a Cu-based metallic phase on a laboratory scale, a general model was developed that is capable of simulating mass transfer to and from metal-slag, slag-gas and metal-gas interfaces for multiple species. The model was used to simulate the reactions that occur when Cu and Ni are reduced from fayalite-based slags into a Cu-based metallic phase. Good agreement was achieved between model predictions and experimental data

Aug 1, 1995

By G. B. Harris, A. R. Laplante

Fine tungsten was used to mimic gold and fine and coarse silica and magnetite to mimic gangue. The optimum flow rate of fluidisation water varied from 1.7 l/min for fine silica to 5.6 l/min for coarse magnetite. Overloading at optimum flow rate was then investigated. With fine silica gangue no overload occurred under any of the conditions studied, and there was very little overload with fine magnetite. Coarse silica caused appreciable overload, but only after a significant bed of tungsten had been formed; with fine magnetite gangue the onset of overloading occurred earlier. Finally, with coarse magnetite severe overloading occurred almost immediately. Overloading was modelled using a first-order kinetic rate constant for erosion of the concentrate bed and a critical mass of constant above which it takes place. The results clearly demonstrate the importance of removing oversize to maximise recovery, particularly with a high-density gangue

Jun 18, 1905

By C. A. Pickles, J. M. Toguri

The refining of two molten Ag-Cu alloys, containing 7.5 and 11.2 mass% Cu, with a borosilicate slag was investigated using both air and pure O2 to determine the effects of the following variables: flow rate of oxidising gas; injection time; mass of sodium borosilicate flux; and injection of the oxidising gas into either the slag or the metal. The results demonstrate that more than 90% of the Cu can be removed with Ag losses of less than 5% and that refined metal with a Cu content of less than 0.5 mass% can be produced. Ag losses to the slag increased with the amount of Cu removed, and a mechanism is proposed to account for this

Dec 1, 1995

By D. C. Bailey, D. I. Hodson

Paper presented at the annual joint meeting of the IMM and IMinE held in Harrogate, 31 January 1991. The Neves-Corvo copper-tin mine is the highest-grade large-tonnage copper operation in the world and is now arguably the most significant producing base-metal mine in Europe, rating in the top ten world producers of both copper and tin. A description is given of the initial exploration work and the development of the project from the orebody discovery in the Iberian Pyrite Belt of southern Portugal in 1977 to full operating capacity in 1990. The chronological account includes discussion of the main organisational, financial, technical and environmental decisions and of the various difficulties encountered, and the challenges of the future are identified. The project was brought in on schedule and within budget

Jan 1, 1991

By A. E. Tercan, D. Mamurekli

Ordinary kriging on the assumption of a gaussian error distribution and indicator kriging were used to derive the probability that a given calorific value would or would not be exceeded by coal from an area of a deposit. The two techniques led to similar probability maps despite local differences; the lack of an absolute reference makes it impossible to judge which method is better for this particular application

Jun 19, 1905

By D Macdougall, J Otto

The financing of large mining projects in developing countries is often achieved, at least in part, by limited-recourse financing methods. Financing agreements are affected by the basic accord that is struck between the host government and the sponsors of the project. It is concluded that governments and project sponsors should take into account the requirements of lenders when structuring such mineral development agreements to maximise the potential for attracting project financing. Lenders are likely to be most interested in aspects such as fiscal arrangements, calculation of taxable income and general accounting rules, royalties, transferability of payments/dividends overseas, corporate structure and control, staged development, financing, loan support and state guarantees/approvals, political risk, provisions for default, product marketing, settlement of disputes and environmental issues

Aug 1, 1994

By G. Kill

Although other energy commodities have developed successful futures contracts, long-term contracts still dominate the coal market. To establish whether coal markets will develop in the same way, coal price and volume data are tested against a set of criteria considered to represent some of the factors contributing to the development of a successful futures contract. Coal meets only some of the criteria: market players are subject to little risk in quite a stable market, have strong preferences for the specific nature of long-term contracts and profit from product uniqueness, each trade being individually negotiated. Potential structural changes in the western European market are not felt to be sufficient to create demand for a coal futures contract, but an empirical model has been developed that could form the basis of a further study to predict the potential for success

Aug 1, 1994

By J. K. Brimacombe, F. D. Richardson

Studies have been made of interfacial turbulence occurring in reactions in which indium, zinc and cadmium, dissolved in amalgams, are oxidised into aqueous phases by ferric or mercurous ions. It has been found that this turbulence occurs when the concentrations of oxidising ions in the aqueous phase become sufficiently great. These concentrations are the same as those at which the mass-transfer coefficients in the aqueous phase increase sharply when both phases are stirred by gas bubbles rising through them. The effects of gas flow rate on the mass-transfer coefficients for zinc in mercury have been established, and the oxidation of pure mercury has been investigated. The relevance of the work to processes involving liquid metals is discussed

Dec 1, 1971

By V. Krupa, E. Lazarova

A method is proposed for the continuous calulation of a rock mass in real time while tunnelling with a TBM. Rock properties are investigated through models of the fracture stress under the disc cutters, the quasi-shear stress between the disc cutters and the specific energy of cutting under the disc cutters. Comparison of theoretical and monitored data of cutting specific energy can be used to determine theoretically the prevailing shape and size of the bulk debris. The shape and size of the chips from a given rock vary with the boring parameters. Introducing shape and volume corrections into the models of the evaluated stresses suppresses the influence of the boring regime and allows the rock properties to become dominant

Dec 1, 1996

By J. A. Every-Brown

Case studies are presented of three derelict sites in Kent and Essex that provide a good cross-section of opportunities for second-generation commercial uses of former chalk, limestone, clay and gravel workings. A 240 ha abandoned chalk quarry at Grays in Essex, now known as Chafford Hundred, is undergoing mixed development to include leisure facilities, a range of housing and commercial areas and an enhanced environment. The 120 ha of Stone Marshes now comprises the Crossways business park and the Dartford international ferry terminal. Reclamation and servicing required more work than had been anticipated and the fact that the area was within the green belt added to the delays, but Blue Circle was eventually able to provide a comprehensive development of the entire area to a high environmental standard. Stone Pit 1 landfill, at Dartford in Kent, is a former chalk quarry 40 ha in area and with an original average depth of 35 m. Landfilling commenced in 1976 and during the period 1979-1984 the site operator designed, developed and installed a gas collection and flaring system. From 1986 a gas plant supplied up to 5 000 000 therm/yr of landfill gas to a local cement works and in 1989 a 1 MW power generation scheme, later expanded to 3 MW, was commissioned. Gas is currently also supplied to a metal refining company for use in internal combustion engines

Aug 1, 1994

By H. Forster, F. H. Koenemann, U. Knittel

The greenstone belt developed along the Sandawana line, an anastomosing, transcrustal shear zone. The lode gold is concentrated in veins and along brittle-ductile shear zones and other faults. Gold contents of 200 rock samples were found to be well below economically significant levels, excluding purely syngenetic deposit formation. Average gold content of unmineralised banded iron formation decreases from 7.3 ppb in the east (Manica) to 1.6 ppb in the west (Odzi), where depletion reflects hydrothermal leaching. The mineralising fluids may have been generated during deep crustal deformation, metamorphism and magmatism. Gold was hydrothermally deposited during carbonatisation and sericitisation of ultramafic and mafic rocks and during hydrothermal overprinting of banded iron formation and felsic rocks. It is present in native form and as microscopic to submicroscopic inclusions in pyrite, arsenopyrite and pyrrhotite. Argentiferous galena and other sulphides are commonly observed. Rezende, which produced over 38 t Au, is hosted by a granodiorite stock. By-product gold was produced from Cu-Ni sulphides at Mundonguara. The deposits are related to the older, but not the younger, of the granitoids intruding the belt's supracrustal sequences; the estimated age of mineralisation is 2700-2600 Ma. Odzi district, with 61 mines, has produced only 3.5 t Au as its higher-level host rocks have apparently been eroded. Mutare (formerly Umtali) district, with 133 mines and 9 placers, has produced 68 t Au (65 t from Rezende and adjacent deposits), and Manica district, with 23 mines and 8 placers, 12 t Au. Estimated reserves for the Rezende area are 20 t Au and for Manica district 4 t lode Au and 19 t placer Au

Apr 1, 1996

By A. Sutton-Pratt

The African continent has been the most prolific producer of gold since mining began. Although most of this gold has come from South Africa, other countries have also been important contributors in the past. There is currently little production outside South Africa, Ghana and Zimbabwe, but the gradual globalisation of the industry over the past decade has resulted in growing interest in the region which bodes well for its future development. An outline is given of prospects and activity (or lack of it) in South Africa, Lesotho, Swaziland, Zimbabwe, Mozambique, Madagascar, Botswana, Namibia, Zaire, Tanzania, Kenya, Uganda, Rwanda, Burundi, Zambia, Malawi, Angola, Congo, Central African Republic, Gabon, Equatorial Guinea, Ethiopia, Eritrea, Djibouti, Somalia, Sudan, Chad, Libya, Tunisia, Egypt, Algeria, Morocco, Ghana, Ivory Coast, Liberia, Sierra Leone, Guinea, Senegal, Guinea-Bissau, Gambia, Mauritania, Mali, Burkina Faso, Togo, Benin, Niger, Nigeria and Cameroun

Apr 1, 1996

By P. H. Carr, G. G. Marino, K. A. Patel

Extensions to a correctional institution at Wabash Valley, Indiana, required development over abandoned coal-mine workings, at 90 m depth, where subsidence was possible at surface. Backfilling of the flooded mine in critical areas was determined to be the most cost-effective method of limiting the risk of damage to the buildings. Containment grout was first placed in selected entries and cross-cuts of each mine area; the remaining volume was then filled with a readily flowing infill grout. Where a high proportion of an area was taken up by rubble, calcium lignosulphonate was used as a retarder and plasticiser to increase penetration. Grout movement was monitored from adjacent boreholes with an electrical resistivity probe during grouting, while after the work was finished core samples were obtained from verification holes drilled in the backfilled areas

Jun 19, 1905

By G. Zhan, P. Mousset-Jones, G. Danko, J. J. K. Daemen, C. Mezei

Paper presented at the conference Risk assessment in the extractive industries, held in Exeter, 23-24 March 1994, and first published London: IMM, 1994, preprint volume. 18pp., 12 refs. (Originally entitled: Tunnel roof diagnosis using a robotic sensor test bed.) An integral roof diagnosis method is proposed to assist in assessment of risk regarding the stability of an excavation. A Robotic Sensor Test Bed (RSTB) is being developed for the characterisation of roof stability. The sensor test bed consists of a sonic/ultrasonic wave response sensor, a laser surface profiler and a surface temperature sensor. These sensors are mounted on an articulated robot manipulator for performing remote-controlled or fully automated diagnoses. A number of laboratory and field sonic/ultrasonic tests were conducted. A high-energy ultrasonic transducer and an impact device were used to resonate rock slabs. The fracture depths of the slabs were found to be inversely related to the measured resonance frequencies. The agreement between identified and actual dimensions was acceptable. Field tests also showed that loose rock on the surface can be clearly distinguished from solid formation by comparing their wave responses. The robotic laser profiler part of the RSTB was used to measure surface geometry. Different scanning methods are being developed to achieve the fastest and most precise measurements and to provide pertinent information about rock joints and major fractures

Dec 1, 1994