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By P. G. Flood

A simplified conceptual model shows how the arc flank to arc fringe areas adjacent to ignimbritic centres form a prospective zone for natural zeolites. Large alkaline lakes that serve as the repository of voluminous ash-fall tuffaceous material provide the ideal chemical setting for pervasive alteration of silicic glass to zeolites. The unusually old age of the Escott deposit demonstrates that any silicic volcanic province that contains low-temperature, unmetamorphosed sequences is a potential zeolite exploration target and that age should not be used as a criterion to exclude potential areas. It has also been demonstrated that heulandite and mordenite, formed by diagenetic alteration of silicic glass, do not always change to analcite and albite through the ageing process

Jan 1, 1991

By B. M. England, M. V. Swain, N. Bristow, R. D. Dukino

The toughness and fracture mechanisms of ores with significantly different microstructures from Yandi, Koolan and Mount Whaleback were studied with a view to understanding their degradation behaviour. Bulk fracture toughness was determined by the 3-point single-edge notch beam test and the results interpreted using Weibull statistical analysis; indentation fracture mechanics was also used to measure fracture toughness of the different mineral forms and to understand their response to contact fracture

Apr 1, 1995

By R. Ciccu, P. P. Manca, A. Bortolussi, G. Massacci

Tool performance and the unit cost of cutting depend on a number of operational variables (peripheral velocity, pull-back force, water injection rate, angles of the sections of wire outside the rock) as well as on the geometric features of the cut itself (area and shape). Cutting rate and wire productivity are also influenced by the type and number of diamond beads per unit length of wire and by the characteristics of the rock (granite or marble). A computer program aimed at handling a problem of this complexity has been developed and tested with the use of available field and laboratory data and has been found acceptably reliable. Discrepancies between current industrial data and some of the results suggest future lines of research, while the simulation should also be extended to include different types of rock and tool and a variety of bench face geometries

Aug 1, 1994

By F. T. Da Silva

Concentrates of titaniferous minerals containing around 30 wt% Ta2O5 are processed hydrometallurgically by hydrofluoric acid leaching and solvent extraction, followed by the precipitation of hydrated potassium heptafluorotantalate. A fundamental study of the thermodynamics of this precipitation and recrystallisation was undertaken to increase understanding of the conditions most conducive to the production of pure, well-crystallised K2TaF7. Activity-pH diagrams for the Ta-K-F-H2O system explained the dissolution of Ta2O5 in fluoride solutions quite well and also the precipitation-recrystallisation of K2TaF7.H2O. X-ray diffraction and scanning electron microscopy confirmed the thermodynamic observations. It was concluded that the best precipitating agent for K2TaF7 from fluoride solutions is KF but a recrystallisation step in a HF environment produces purer, well-crystallised K2TaF7.H2O, eliminating oxy-salts and other impurities

Jun 21, 1905

By J. L. Robson, C. M. Bristow

mass flow rates of particles and air (the loading ratio).

Dec 1, 1994

horizontal-type classifier prior to charging into a blastfurnace.

Apr 1, 1995

By R. G. Kidel, S. C. Doming

The project has shown that it is feasible for a junior company to reopen a narrow vein-style gold mine and successfully take it into production. An intimate understanding of the mineralisation and a flexible approach to mining are crucial, as are stringent cost control and efforts to keep overheads low. The project has confirmed the geological complexity of the Main Lodes, which consist of highly sheared quartz-sulphide infill in strongly sericitised granodiorite. The existence of discrete high-grade zones within the Hangingwall Lodes has also been confirmed. Broad low-grade zones continue to be recognised and require the local application of bulk longhole mining methods. The initial mine plan called for predominantly longhole stoping, but adverse ground conditions have meant that a switch to air-leg mining has produced higher run-of-mine grades. The excess capacity at the processing plant can best be used by batch processing, with its reduced maintenance requirements

Jun 21, 1905

By G. D. Schena, M Zanin

A numerical approach is presented for predicting the liberation of phases during comminution, with direct calculation of a liberation spectrum giving the fraction of the particulate system in each narrow size-composition class. The numerical model uses a Poisson flat process for stochastic generation of the non-convex three-dimensional Poisson polyhedral textures and the system of fractures that give rise to convex fragments. With this numerical approach, there is no need to assume random uniform isotopic fracture (lack of selective liberation); only computational geometry primitives are exploited for the derivation. The agreement with relationships obtained previously under the random uniform isotopic fracture hypothesis demonstrates that the approach is capable of deriving full liberation spectra directly. Both volumetric and superficial composition can be calculated

Jun 21, 1905

By P. J. Rowsell, M. D. Waller

Paper presented at a meeting on: Artificial intelligence in the minerals sector, held in Nottingham, UK, 20 April 1993. The applications of artificial intelligence systems in the upstream petroleum industry are reviewed. Particular emphasis is placed on current and potential applications in drilling engineering. Several recent advances in drilling technology have led to a large increase in the quality and volume of data available. This combined with the escalating cost, particularly of off-shore operations, is testing the traditional reliance on the skill and judgement of rig operators. AI systems offer enormous scope in enhancing and aiding the performance of these operations

Apr 1, 1994

By G. S. Camm

Gwynfynydd is a small, high-grade black shale-hosted vein-gold deposit. The Chidlaw Link Zone is the only area being mined and contains 24 000 t ore grading 15.2 g/t gold. Within the Link Zone a complex vein structure occurs consisting of a mother vein up to 5 m thick and narrow (less than 0.5 m) leader veins. The former shows minor variations in dip, strike and thickness, whereas the latter show marked changes in all three. The leader veins are hosted within the footwall zone of the mother vein and both are composed of quartz with galena, sphalerite, chalcopyrite, pyrite and minor arsenopyrite. The vein system is transected by a series of cross-vein and intra-vein dip-slip faults. Pockets of gold occur at vein intersections or branches and within the complex footwall zone and are often related to variations in vein attitude and/or geometry. The Chidlaw Link Zone displays a complex, erratic distribution of gold mineralisation and a multi-stage history of structural activity, fluid flow and mineral deposition

Jun 18, 1905

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 J. D. T. Capocchi, M. B. Mourao

The rate of reaction between iron oxides and carbonaceous materials, agglomerated as pellets, was studied experimentally by measuring the weight loss as a function of time. The effects of temperature, carbon type, inert gas flow rate, pellet size and additions (sodium. carbonate and Portland cement) were determined. It was shown that the value of the apparent activation energy can display large deviations under different experimental conditions; in the present work it was found to be 226.6 kJ/mol. The reaction with coke is slower than with charcoal, and the rate increases as the flow of inert gas in the reaction vessel decreases. Comparison of the rates for pellets of different sizes has shown that for small pellets the initial rate is faster but that it slows down at high conversions owing to the penetration of inert gas into the pellet. Additions of sodium carbonate and Portland cement increase the rate; sodium. carbonate promotes the catalysis of the Boudouard reaction, which is the slowest of the partial reactions. The increase in the rate with Portland cement is attributed to the release of water vapour

Jun 18, 1905

By R. Venugopal, T. C. Rao, N. Suresh

Experiments were carried out using the cyclone to treat coal in the size range -2.0+0 mm. The diameters of the cyclone outlets (vortex finder and spigot) were varied to study their effects on cyclone performance. The cyclone products were deslimed over a screen with an aperture of 0.075 mm. The performance of the separator was studied for washing coarse coal (-2.0+0.075 mm) and fines (-0.075 mm). Performance curves were plotted for the separation of -2.0+0.075 mm coal. The concept of a generalised distribution curve was adopted to predict cyclone performance. A mathematical representation was derived from the generalised distribution curve. The specific gravity of separation for individual size fractions showed a decreasing trend with decreasing particle size down to 0.85 mm, beyond which a reverse trend was noted. It was also found that the fine size fraction (-0.075 mm) does not separate on the basis of size or specific gravity but follows the water distribution

Apr 1, 1995

By I. R. Hanby

A simple solution to the problem of whether to round the calculated number of trucks up or down to the nearest whole number is to adopt as criterion the minimum cost per unit volume/mass moved, assuming all trucks in the fleet are of the same type. When the effects on journey time of varying haul-road slope are calculated for several rolling resistances, it is shown that the optimum angle of 7.5 degrees is moderately independent of both rolling resistance and height climbed; the lower the resistance, the lower the sensitivity to ramp angle, but if haul-road gradients do not exceed 1 in 10 (5.7 degrees) for safety reasons then travelling time will never be more than 7% greater than its theoretical minimum. Further calculations result in a graph of the maximum payload values to incur the minimum cost, for different values of total effective resistance

Jan 1, 1991

Errors in ore reserve estimation can occur during drilling and sampling, sample preparation and analysis, geological logging and modelling, database construction, statistical or geostatistical evaluation, selection of economic parameters, selection of ore reserve method and assessment of mining constraints. Core sample recovery can be a major source of error, and it is proposed that the modelling of grade, metal accumulation and thickness should be accompanied by the modelling of core recovery (or core loss) so that for each ore block a weighted block recovery factor is obtained. This gives a good indicator of the reliability of a reserve estimate. It is suggested that a resource reliability rating (RRR) system be established to quantify what is meant by geological assurance and to combine this with an estimate of the precision of estimation as gained by geostatistical analysis. Proven and probable minable reserves would be those with an RRR better than 50% and a precision of estimation better than 20%

Dec 1, 1996

By O. R. Eckstrand, M. Asif, P. L. Schwann, A. J. Naldrett, R. J. F. Scoates

Paper presented at the IAGOD international symposium on mineralisation related to mafic and ultramafic rocks, held in Orleans, France, 1-3 September 1993. PGE-bearing sulphide mineralisation is contained in the lower 600 m of the Upper Central Layered Zone of the intrusion. There are four regimes with distinctive crystallisation characteristics. PGE content is low, both in bulk rock and in terms of metal in 100% sulphides, in the sulphide-rich cumulates but increases sharply in the sulphide-poor cumulates at the base of regime 1. Increases in regime 2 have no such clear relationship with incoming cumulus sulphides. PGE contents are low throughout regime 3, but regime 4 has sulphides with high PGE content, decreasing rapidly upwards, at the base of many of its cyclic units. The observations are interpreted as indicating that sulphide saturation occurred in the middle of a cyclic unit in regime 1, after which fractional segregation of sulphide caused a systematic decrease in PGE content. The resulting contrast between 40 000 ppb PGE in sulphides below the mineralised zone and less than 1 000 ppb above is of practical importance in exploration for such zones. In regime 2 the magma chamber was open to fresh influxes and PGE content was not so sensitive to sulphide saturation. In many regime 4 units influxes of new magma caused immediate sulphide saturation and PGE depletion, so that PGE-rich cumulates do not underlie PGE-bearing sulphide zones. Theoretical analysis indicates that regime 1-type behaviour is likely to characterise intrusions below the level at which plagioclase has entered as a cumulus phase and regime 4-type behaviour above

Apr 1, 1994

By G. G. Barbante

Anode slimes produced during copper electrorefining are a valuable source of silver, gold, selenium and tellurium. The conventional pyrometallurgical process for treating slimes involves preliminary leaching in sulphuric acid followed by smelting in a reverberatory furnace with fluxes, but it is slow and has many recycle streams. The chemistry of the phases and the reactions that occur in slimes smelting are poorly understood and and this prevents major improvements to the process. Laboratory-scale experiments were conducted using unleached slimes, with and without the addition of fluxes and under neutral, oxidising and reducing conditions. Results show that selenium is readily removed as gaseous selenium dioxide and that molten Cu-Ag-Se-O phases form when fluxes are added. Oxidation-refining of these phases by air injection and flux addition can result in the formation of silver suitable for further electrorefining

Aug 1, 1995

By D. C. Goldring

Many high-grade iron ores are considered to result from the supergene enrichment of banded iron formations. The secondary processes may be related to either present-day or ancient erosion cycles and may reach a considerable depth. Other high-grade ores hosted by banded iron formations are regarded as either sedimentary or metamorphic in origin although often also subjected to the secondary processes. The evidence for this multiplicity of origins is reviewed with descriptions of selected deposits: Kedia d'Idjil and M'Haoudat in Mauritania, Bomi Hills and the Nimba Range in Liberia, the Itabira district in Minas Gerais, Brazil, and El Pao in eastern Venezuela. Emphasis is placed on the recognition of textures that show that some ores are tectonites, the precursor materials having undergone pervasive deformation accompanied by metamorphism. The question whether such ores are pre- or syntectonic is difficult to resolve, the evidence being inconclusive, but a diagenetic/early deformation origin is preferred. The possible range of origins has to be taken into account in exploration, particularly as regards the depth of drilling, and in the characterisation of ores for metallurgical use

Jul 1, 1991

By N. A. Warner, R. K. Manna

Physical modelling of liquid-phase oxygen mass transfer in a water model of part of a proposed new polymetallic smelter has been achieved. A study of solute mass transfer caused by multiple, subsonic air jets contacting superoxygenated water flowing in a channel model of the smelter converting hearth has been carried out. For a wide range of channel flow rates the rate of mass transfer was found to be independent of water velocity. The water model has been used to compare mass transfer for both open-packed and close-packed multiple-lance arrays with circular nozzles of diameters 2.26, 4.95, 10.95 and 24.40 mm. It was found that with fewer of the larger-diameter nozzles a reduction of up to 58% in liquid-phase mass transfer occurred, especially for the close-packed lance configurations. This restriction of liquid-phase mass transfer would result in reduced metal losses in the analogous smelting situation. The larger nozzles, however, exhibited more jet-jet and jet-channel wall interference effects than their smaller counterparts, resulting in an effective reduction in the momentum fluxes of the impinging jets

Jul 1, 1991

By T. G. Carter, R. I. Miller

First, the influence of variation in the

Apr 1, 1995