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By H. K. Taylor

Ore reserves are inadequately defined. Geological reconnaissance and pre-feasibility mining work generate a broad range of valid tonnage estimates, many published for the benefit of various interests, who may view all figures as reserves. This work reviews the regular estimation of tonnages, grades and relevant factors for single deposits. A consistent framework of definition is suggested which, by conforming to the known structures of feasibility studies and long-range plans, avoids the pitfalls of over-categorisation and of unrealistic promises. Applications are based on North American experience but are intended for general use

Sep 1, 1991

By L Besra, A. R. Prasad, B. P. Singh

The role of surface-chemical phenomena and the physical processes that participate in the dewatering of a suspension of alumina trihydrate were subjected to a systematic investigation, which has increased understanding of the influence of surface tension, contact angle and adsorption in the process. The residual moisture content of the cake can be reduced significantly through the use of surface-active agents in slurry pretreatment or as wash-water additives. The effectiveness of a particular surfactant is hard to predict from any single parameter, but is dependent on its ability to reduce surface tension and possibly to modify the solid-liquid contact angle. If scaled up to industrial operation of the dewatering step of the Bayer process in India, the use of these chemical additives could substantially improve its process economics, reducing the fuel costs for thermal drying by a much as Rs 50/t

Jun 21, 1905

By L. J. Barnes

The process for bio-remediation of sulphidic slag (BROSS) operates at 45 degrees C in a neutral (pH 7), aerobic aqueous environment in which sulphide in the slag is converted to sulphate. A two-stage version has been developed that involves quantitative chemical pre-oxidation of total sulphide to thiosulphate, followed by complete biooxidation of thiosulphate to sulphate. Ferric hydroxide, also produced, acts as a flocculant in the bioreactor effluent, concentrating heavy metal precipitates in the thickener as a sludge which can be returned to the smelter. The process has a high sulphate production rate and low acid and nutrient consumptions. Microorganism growth is the rate-limiting stage, requiring a minimum liquid residence time in the bioreactor of about 7 h. Although large quantities of oxygen are needed, sufficient gas mass transfer can be attained in an air-lift reactor. Products are an aqueous stream containing sodium sulphate with only trace levels of toxic heavy metals and a benign, toxic metal-containing sludge

Jun 18, 1905

By G. Adachi, K. Machida, T. Ozaki, K. Murase

The chlorination rate with CCl4 was unexpectedly slower than carbochlorination using chlorine under the same reaction conditions. Chlorination with CCl4 was topochemical and the amount of monazite reacted after different periods suggested that the kinetic control step was the reaction between CCl4 and the monazite core at the interface. The kinetic order of the reaction was 0.5. The presence of a complex former, AlCl3, promoted the chemical vapour transport of rare-earth chlorides as complexes

Jun 18, 1905

By S. Kelebek

DETA exhibits a highly selective depressant action on pyrrhotite without adversely affecting the collectorless flotability of pentlandite and chalcopyrite in nickel-copper ores of the Sudbury region. A simplified Eh-pH diagram has been constructed to illustrate the extended stability of elemental sulphur and to explain the collectorless flotation of pentlandite and chalcopyrite. Cu and Ni ions, which are known to exist on the surface of pyrrhotite, promote the flotation of this mineral whether a collector is present or not. Thermodynamic calculations indicate that the action of DETA involves the sequestration of Cu and Ni ions from surfaces under a wide range of redox conditions; analysis of flotation test filtrate indicates as much as a 20-fold increase in the concentration of Ni and Cu ions. It appears that DETA may enhance the self-hydrophobicity of chalcopyrite and pentlandite by exposing more of the sulphur-rich surface sites for bubble contact in flotation. There are various possible explanations for its depression of pyrrhotite

Jun 18, 1905

By S. G. Beattie, N. Mojtabai

A study was carried out which aimed to: determine the effects of blasting on excavation perimeters and nearby slopes; establish a low-cost blast monitoring and field observation programme to determine peak particle velocities and blast damage; and to develop criteria for observable blast damage that are based on the peak particle velocity. Full-scale production blasts in a large open pit copper mine were monitored and studied to develop damage criteria for various rock types. Better blast designs can be achieved by correlating the results of blast monitoring with field observations of damage at the pit walls and on benches. Back-break and damage are related to blast-induced ground vibration. Peak particle velocity is accepted as a reliable measure for the prediction of ground vibration levels. Empirical models for the estimation of rock damage can be developed and used for blast design. The models are used to determine the zones of damage within the rock face. Rock damage models can also be used to design trim shots to achieve further reduction of back-break in more critical areas

Apr 1, 1996

By R Lastra, J. A. Finch

An artificial standard material has been developed and used to examine the robustness of some of the procedures for correcting stereological bias. Different mineral liberation distributions were constructed from the standard material. The particles were mounted, sectioned and the sectioning data measured with an electron microscope interfaced to an image analyser. Four correction procedures were used and the corrected and true liberation distributions compared. It was found that the large-sections correction provided a simple, uncorrupted correction. Hill's fast approximation performed well except in cases of narrow liberation distributions; the sectioning data appeared to support the assumption that the locked section and locked particle distributions are identical. Barbery's correction performed well in most cases, having difficulty only with the very irregular liberation distribution. The PARGEN correction was able to provide a good estimate of the true amount of free material, but had difficulty in predicting the locked particle distribution

Jun 21, 1905

By R. D. Dukimo, M. V. Sevian

The nature of fracture and factors that control the extent of fracture in the tumble-drum and drop-tower tests have been identified. The product-size distribution, on which the standard strength indices for these tests are based, and the breakage rate constants depend on a number of factors other than the strength of the lumps. The standard indices and rate constants are meaningful only in a comparative context and for events whose loading mechanism is similar. The results of experiments on three Australian ores, from Yandi, Koolan and Mount Whaleback, are used in combination with fracture mechanics theory to explain why different tumble-drum standards have been found to be fully consistent. A more meaningful measure of strength could be the parameters of the Weibull function, scatter and average strength

Jun 19, 1905

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. S. Coats, G. E. Patts, N. Hughes

Conventional sampling methods are known to suffer from the variable loss of fine gold by elutriation. Freeze sampling yields representative and quantitative data that, when combined with information on the sedimentology of gravel-bed rivers, may facilitate the development of improved dispersion models for source detection. It is suggested that freeze sampling may have particular application to the orientation stage of a large gold exploration survey

Jan 1, 1991

By B. Gazea, A. Kontopoulos, A. Kourtis, K. Adam

Static tests give a measure of the balance between acid-producing and acid-neutralising mineral components in a material, while kinetic tests determine acid generation and neutralisation over a long period. Drill-core samples from the amphibolite and gneiss host rocks of the Stratoni lead-zinc sulphide deposit in Greece and mine/mill waste samples from Stratoni and Olympias were examined by the standard acid base accounting, BCR and net acid production tests. Mineralogical data on the materials and resulting residues were used to illustrate the differences between the methods and establish their ranges of applicability. BCR seems to simulate most closely the conditions prevailing during generation of acid mine drainage but is time-consuming and requires elaborate equipment. Acid base accounting is suggested for standard screening; net acid production might be used in the field or for solids with less than 10% S

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 S. A. Sayed, M. N. M. Ahmed, M. A. Doheim

The performance of a 12.7 cm hydrocyclone was investigated by considering the effect of design variables (diameters of the vortex finder and apex) and operating variables (pressure drop and solids content of the feed) at a medium feed solids concentration of mixed minerals. Cut-size was found to be the most important parameter in hydrocyclone design and operation. The effect of feed pressure in reducing hydrocyclone cut-size is less pronounced at medium feed solids concentration with a mixed mineral feed. The choice of vortex finder diameter and apex diameter becomes more sensitive at medium feed solids concentrations. The effect of feed solids concentration in increasing the cut-size becomes less marked at higher concentrations. Predictions of an empirical model were found to be in good agreement with experimental data. Comparison of results obtained from the model with those predicted by theoretically derived models showed the latter to be more promising, with the turbulent two-phase model giving closer agreement with the experimental data

Apr 1, 1995

By H. Y. Sohn, Hang Goo Kim

Computer simulations were carried out using calcium ferrite slags containing 25 wt% CaO, and the results compared with those obtained using fayalite slags. There was little difference in overall elimination of Pb and Bi, but elimination of Sb and As was much lower with calcium ferrite slag. When calcium ferrite slag is used only in the converting stage and fayalite slag in the smelting stage, as in the Mitsubishi process, the contents of Sb and As in the blister copper can be kept to reasonable levels. This allows advantage to be taken of the considerably higher iron oxide-holding capacity of calcium ferrite slag than of fayalite slag at the high oxygen potential under converting conditions, thus preventing precipitation of magnetite. Satisfactory agreement was obtained between predicted values and observed data from a Mitsubishi converter

Jun 18, 1905

By B. J. Breen, C. S. Mogg

Considerable borehole investigation work has been completed at a proposed site at Sellafield in Cumbria, supplemented by seismic surveys, other geophysical sensing and geological mapping. The focussing of investigation on the rock mass itself will be achieved by means of the planned underground rock characterisation facility, giving access to depths of about 800 m in the strong, low-permeability basement rocks of the Borrowdale Volcanic Group. Characterisation work undertaken during the sinking phase and interaction with continuing surface-based exploration and monitoring should permit a firmer assessment of the long-term safety of a repository. Key considerations in the choice of a design for the repository include the waste handling method, underground inlet cell, underground vaults, vault environment and environmental effects

Aug 1, 1994

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 R. A. Lord, H. M. Prichard

Paper presented at Mineralisation in the Caledonides, the Mike Gallagher memorial meeting held in Edinburgh, 27-28 June 1996. The complex exemplifies a class of olivine-rich, platiniferous ophiolite complexes generated by unusually high degrees of hydrous melting above a subduction zone. Crystallisation of abundant olivine from unusually picritic magmas produced an exceptionally thick sequence of crustal dunite cumulates. Significant (1-4 ppm) concentrations of Pt+Pd occur where sulphide-bearing dunites are spatially associated with podiform chromite concentrations. In the area north of the Balta Sound, the chromitites appear to lie in distinct stratigraphic zones. A detailed programme of lithogeochemical and soil-rock interface geochemical exploration led to the intersection by diamond drilling of three stratiform horizons of sulphide-bearing dunites and associated precious-metal mineralisation. Patterns of cryptic geochemical layering, at scales from 200 m to less than 1 cm, suggests open-system fractionation

Jun 19, 1905

By J Hadijigeorgiou, R. W. Lawrence, R Pouling

The layered co-mingling method involves the disposal of waste rock with the addition, at predefined construction stages, of layers of dewatered mine tailings. The resulting waste structure displays bulk properties that are more favourable to acid rock drainage (ARD) control than the constituent materials alone. A laboratory test programme was conducted to examine the potential of this method. Columns containing different configurations of waste rock and tailings were percolation leached for 40 weeks and the leachates examined for various parameters. In the short term the chemical reactions that result from the introduction of dewatered tailings into rock waste can significantly improve the quality of the drainage. Columns with co-mingled material produced leachate with pH levels of 8, whereas leachate from the control column containing waste rock alone had a pH of 4. Larger-scale field tests are planned to determine the effect of the disposal method over the longer term

Apr 1, 1996

By S. P. Godby, S. P. Sharples

Wind-tunnel tests were carried out of the conditions under which nuisance dust particles (100-1 000 micrometres) become entrained by wind. A laser entrainment monitoring system (LEMS) was used, and was found to provide an accurate means of assessing nuisance dust emissions from a surface. Accurate determination of the threshold entrainment velocity of dusts using the LEMS gives a baseline against which the performance of dust control techniques can be evaluated. Minerals tested included coal, petroleum coke, limestone, sand and pulverised fuel ash. Pilot field trials of a portable wind tunnel equipped with the LEMS have been successfully completed, providing a means of validating laboratory results in the field

Jun 19, 1905

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