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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 M. Bustillo, S. Ordonez

"Paper presented at the conference Economic geology in Europe and beyond II, models for mineral deposits in sedimentary basins, held in Keyworth, UK, 13-14 April 1994. The Mississippi Valley-type deposits occur in massive, homogeneous dolostones from which diagenesis has obliterated all primary sedimentary structures. The mineralisation forms irregular, lens-shaped stratabound bodies, mostly in the lower part of the dolostones. They are composed exclusively of sphalerite, galena, pyrite, marcasite and barite, with white sparry dolomite a common cementing phase. Mineral zoning can be recognised from pyrite and marcasite in the east to barite in the west. Sphalerite, the most common sulphide, occurs basically as colloform and banded crusts and galena as isolated cubic or skeletal crystals, mainly in the centre of the banded botryoidal sphalerite. The combined observations of the deposits' geology, geochemistry and ore petrology suggest a three-stage genetic model: carbonate sedimentation in a shallow-water environment; dolomitisation, probably after compaction, by fluids of connate origin and lateral evolution; and mineralisation by migrating solutions, perhaps related to oil-field brines, that originated in deep zones of the basin during diagenesis of the basinal mudrocks in the NE"

Apr 1, 1995

By M. T. Styles, E. Condliffe, R. C. Leake, R. J. Chapman, D. J. Bland

Paper presented at Mineralisation in the Caledonides, the Mike Gallagher memorial meeting held in Edinburgh, 27-28 June 1996. Quantitative point analysis and microchemical mapping identified 52 different types of mineral in inclusions, usually ranging in size from 5 to less than 1 micrometre, inherited from source bedrock. A combination of grain chemistry, heterogeneity and inclusions provides a grain signature reflecting the type and history of source mineralisation. Several grains from an alluvial site are needed, to allow for bedrock variation and the presence of inclusions in only 10-20% of grains. A total of 1 530 grains obtained from 30 localities in Scotland were of ten types, two of them minor variants. Two types in the Highlands may be related to centres of Caledonian igneous activity, but the most widespread is likely to have been of deep-seated origin and structurally controlled. Gold in the Ochil Hills is probably from a source associated with Devonian andesitic activity. In the Southern Uplands, grain types reflect two separate episodes of mesothermal lode gold mineralisation and relationships with Permian red beds/mafic volcanics and with Tertiary dykes

Jun 19, 1905

By S. P. Ball, A. J. Monhemius

In a laboratory study under acidic oxidising conditions, the thiocyanate system gave results at least as good as cyanide and considerably better than thiourea, with modest consumption of SCN (less than 1 kg/t ore). For both cyanide and thiocyanate lixiviants a residence time of about 24 h was required for maximum gold extraction, which was generally in the range of 92-96%. The adsorption of gold from thiocyanate leach liquors was found to be rapid, but activated carbon catalyses the autoreduction of ferric iron to ferrous iron in thiocyanate solutions, suggesting that ion exchange may be a better recovery route

Dec 1, 1995

By B. Denby

Paper presented at a meeting on: Artificial intelligence in the minerals sector, held in Nottingham, UK, 20 April 1993. The design and scheduling of open pit operations are consistent problems encountered by the surface mining industry. Numerous techniques and algorithms have been developed to assist the mining engineer in the creation of optimum development strategies. Virtually all the practical techniques that have been produced have concentrated on one of the aspects (limit definition or scheduling) at the expense of the other. It has long been recognised, however, that the two activities are intrinsically linked and thus solving either problem independently of the other can only ever produce sub-optimal results as a whole. This has been termed the "circular reasoning problem". It has also been recognised that, for all practical-sized situations, solving both problems simultaneously is virtually impossible using conventional techniques due to the massive size of the search space involved. A technique is presented which is based on a self-learning genetic algorithm, which provides a combined pit limit and extraction schedule simultaneously in order to maximise the NPV (net present value) of the extraction. The theory is developed in two-dimensions and a number of examples of its application are presented. It is proposed that this approach is a highly efficient, heuristic technique offering the potential to transcend the circular reasoning difficulties of separate pit limit and extraction scheduling systems. Extension of the technique into three-dimensions and its application to realistic problem sizes are discussed

Apr 1, 1994

By I. D. Nock, R. M. Parkin

Paper presented at a meeting on: Artificial intelligence in the minerals sector, held in Nottingham, UK, 20 April 1993 (original title: Knowledge-based condition monitoring of cone crushers). A large proportion of the electricity used by the quarrying industry is consumed in the comminution and sizing process. In most cases aggregate processing plants operate with minimum control features resulting in limited operational efficiency. Improved control is required to increase operational efficiency with concomitant savings associated with reduction in re-circulating load and improved resource utilisation. Development work has suggested that a combination of adaptive control and process condition monitoring could improve control of comminution plants. Many commercial process control and condition monitoring systems are available, but none were deemed suitable due to the domain specific characteristics of the application. An assessment of the particular characteristics of cone crushing concluded that the application was best suited to the use of small domain specific process control combined with bespoke condition monitoring. The processing power of the control system for the project is a function not of the academic requirement, but rather the economic and practical constraints imposed by the application. As a result of the constraints a high-end PC system has been designed in preference to a workstation. Within the research project work packages are sub-divided into novel wear sensor development, knowledge based control/condition monitoring and the investigation and mathematical modelling of the wear mechanisms inherent in cone crushing. Numerous strategies were considered to implement the control system outlined. The system currently under development is a modular design which utilises intelligent novel sensors to provide a variety of data inputs

Apr 1, 1994

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 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 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 T. G. Carter, R. I. Miller

First, the influence of variation in the

Apr 1, 1995

By P. H. Morris

The exponential delta profile equation matches the profiles of a wide range of coal and metalliferous subaerial tailings deltas well, but the original model implies unrepresentatively low solids concentrations. A revision, based on analysis of the governing equations of mobile bed flows with high concentration values, has shown that for exponential delta profiles to form there must be quasi-steady, slowly varying flow and slow deposition as well as tailings with a log-uniform sorting-parameter distribution. Deposition on tailings deltas is slow and the flow in many natural streams and, by analogy, tailings deltas is quasi-steady and slowly varying; the assumption of such flow is justified by the strong congruence of the revised model and the available data. The predictions of the theoretical model are essentially unchanged but concentration and flow Froude number are now not explicitly limited

Jun 19, 1905

By A. J. Davidson

A Cu-conducting solid electrolyte was used to develop the sensor. Instead of measuring the potential across the electrolyte from the reference material to the Cu-containing phase, a potential was applied and the stable current measured. This gave reasonable readings for copper-tin alloys, which agreed with the theoretical calculations, but was less satisfactory in the case of mattes because the surface area of electrolyte presented to the matte phase varied from sensor to sensor. To overcome this problem the potential was applied, the current was measured and then reversed and remeasured and the ratio of the currents was calculated. The current ratio is shown to be independent of the resistance of the electrolyte and the surface area of the electrolyte offered to the melt, but strongly dependent on the activity of the copper

Jun 21, 1905

By L. Villa, O. Suarez, D. Arias, L. G. Corretge

The deposit comprises two vertical, lenticular bodies emplaced in the allochthonous block of a Variscan thrust. Epigenetic mineralisation occurs as replacement of carbonated volcaniclastic rocks of Cambro-Ordovician age. The dominant sulphide minerals are sphalerite and galena with minor chalcopyrite; the main non-metallic mineral is quartz and there is hydrothermal silicification, chloritisation and sericitisation. Sulphur isotope values for sphalerite and galena are heavy and reflect the fundamental relationship between delta-34S in ZnS and in PbS, suggesting isotopic equilibrium. Four sphalerite-galena pairs yield temperatures between 163 and 218 degrees C, in good agreement with the 187-207 degrees C estimated by the Ga/Ge-sphalerite geothermometer. The ore sulphide was leached by the hydrothermal solution from diagenetic pyrite in the host rocks and disseminated sphalerite and galena in Cambrian carbonates

Jun 19, 1905

By M. C. Ruiz, M. E. Godoy, J. B. Rivarola, M. W. Ojeda

The amount of Pd recovered from an exhausted olefin hydrogenation catalyst was found to depend on mixing technique, particle size, carbon percentage, chlorine flow, reaction time and temperature. Pd extraction was total when a sample in the 125-175 micrometre particle size range was chlorinated for 60 min at 723 K with 20 cm3 Cl2/min, for 60 min at 748 K with 30 cm3 Cl2/min and for 30 min at 773 K with 30 cm3 Cl2/min. No C addition was needed; the initial C content of the catalyst was sufficient for total recovery. Pd extraction was also affected by heat treatment in different atmospheres before chlorination. Treatment with O2, N2 and N2 with traces of O2 led to different degrees of oxidation of C and permitted the formation of oxidised Pd species. Thermal pretreatment in N2 with traces of O2 was most conducive to Pd extraction

Jun 21, 1905

By P. H. Morris

Nineteen field trials of the co-disposal of fine coal tailings and coarse coal wastes were conducted at the dual Goonyella-Riverside mine in Queensland and at the Hunter Valley No. 1 and Warkworth mines in New South Wales, Australia. The profiles of and the sorting that occurred on the co-disposal deltas are described and an existing theory of subaerial deposition, originally developed for mine tailings alone, is shown to apply to the co-disposed wastes. This enables the dimensionless profiles of large deltas, which may take years to deposit, to be predicted from data obtained from a small delta formed in a few days or even hours

Jun 19, 1905

By G. E. Christidis, P. W. Scott

The deposits were formed from low-temperature alteration of pyroclastic rocks. Properties investigated include their cation exchange capacity, swelling capacity, pH, rheological properties, the green and dry compressive strengths, shatter index, wet tensile strength, compactability and permeability. It was found that deposits with abundant opal-CT have poor physical properties. The rheological and swelling properties were found to be influenced by the bentonite grade (smectite content) and the degree of disaggregation of the smectite quasi-crystals. The only deposits of high grade which had good foundry properties were those with no opal-CT. Hydrothermal alteration was detrimental to the physical and chemical properties of bentonites in that it decreased the smectite content and the pH and changed the smectite layer charge and the lattice dimensions

Jun 18, 1905

By J Kokado, N Hatta, S Yabushita

A theoretical model is described for prediction of the capacity of fines from porous ores, such as cokes and sintered ores, to be removed by a pneumatic, horizontal-type classifier prior to charging into a blast furnace. First, the influence of variation in the apparent density and drag coefficient of porous ores on removal efficiency is analysed from a stochastic standpoint. The effect on efficiency of collisions between particles in the classifying region is then examined analytically in relation to the ratio of the mass flow rates of particles and air (the loading ratio). Finally, a theoretical model is constructed that takes these factors into account. Theoretical and experimental results are compared and classifying efficiency is discussed from both experimental and theoretical viewpoints.

Dec 1, 1993

By Seong-Taek Yun, Chil-Sup So, Seung-Jun Youm

The greisen-bordered quartz veins are spatially, temporally and genetically associated with a late Cretaceous granite intruding an early Palaeozoic, limestone-rich formation. Paragenetic data indicate three stages of hydrothermal mineralisation, the first typically in or within 500 m of the granite stock and showing vertical zoning between deeper Mo and higher W, the other two more abundant in the upper and outer parts of the mineralised area. Fluid inclusion and stable isotope data indicate that hydrothermal veins formed over a temperature range of 120-395 degrees C from low-salinity fluids. Early wolframite and molybdenite deposition in stage I occurred at temperatures of 300-395 degrees C from magma-derived, low-salinity, CO2-rich fluid, mainly as a result of fluid boiling and associated CO2 effervescence. Progressively larger volumes of local meteoric water entering the system led to the successive deposition of scheelite in stage I vugs, stage II base-metal sulphides and stage III fluorite-carbonates. Remobilisation of W and its later deposition of scheelite in the outer and shallower portions of the system occurred at 215-275 degrees C and stage II and III mineralisation from lower-temperature fluids that became progressively lighter in stable isotopes. It is concluded that the influx of meteoric water increased with distance from the cooling pluton

Jun 18, 1905

By D. M. A. Flight, G. E. M Hall, P. R. Simpson

theoretical viewpoints.

Apr 1, 1994

By R. H. T. Garnett

N.B. This paper provoked much (positive!) discussion in later issues, with responses from the author (and thanks also for the many private contributions he had received) - see under Garnett R.H.T. Expanded version of a paper originally presented at the Alluvial mining conference, London, 11-13 November 1991 and published in Alluvial mining, Barking: Elsevier Applied Science for IMM, 1991, p.115-156. The usual measure of performance in gold and tin dredging is the R/E factor. It compares actual production or recovered grade for a given period with that estimated from the original sampling. The factor is a multiple of four component factors, each ideally approaching 1.00. The factors are concerned with estimation, selection, excavation and treatment. The estimation factor reflects the errors involved in determining the grade and depth of single drill-holes or pits. An optimum selection factor is achieved by a higher drilling density. The excavation factor is affected by failure of the dredge to excavate the total volume contained within its course. The required dredge throughput rate influences not only the success in digging recovery but also the treatment factor. No two alluvial deposits are the same, but, in general, the greatest divergence from 1.00 is invariably demonstrated by the estimation factor. A major divergence in one of the other factors may also be the cause of the R/E factor being significantly different from 1.00. The component factors are examined in detail and historical trends in R/E factors are discussed

Sep 1, 1991