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By Zhengya Lu, F. Lawson

The surface tensions of lead and lead alloys with very low concentrations of silver, tin and copper were measured by the sessile-drop method. The enrichment of silver and tin in the surface of liquid lead alloys at temperatures close to the freezing-point of lead was confirmed, which may explain the unusual behaviour of small amounts of silver and tin in lead bulllion during the sulphur-drossing step of the refining process. From the limited data available copper also appears to concentrate at the surface of the liquid alloy

Dec 1, 1991

By N. Powell, R. J. Pine

An algorithm is proposed for updating the probability of slope failure on the basis of sequential testing using Bayesian probability theory. The approach is novel and computationally straightforward since, unlike other methods, updating of the probability of failure is carried out directly. This is because the probability is treated as a random variable whereas other methods have considered it as a purely deterministic value or as a function of shear strength parameters that are updated individually. The prior information required for the Bayesian analysis is obtained by a conventional probabilistic analysis. An exponential distribution is then used for the probability of failure, applying the principle of maximum entropy. This distribution is continually updated for individual slope cells, where repetitive excavation creates several such cells and a corresponding series of Bayesian estimates of the probability of failure is obtained. The approach is applicable to most simulations but there are limitations on its use. A more mathematically rigorous refinement using the beta distribution is currently under development

Apr 1, 1996

By D. J. Buchanan

British Coal's mining research programme is directed towards the strategic objectives of reducing production costs, improving product quality and resolving health, safety and environmental issues. The strategy for R&D is described and selected parts of the programme are reviewed. Two major initiatives are directed towards reducing production costs: geotechnics and automation. Integrated exploration techniques are used to delineate geological structures as an aid to mine planning. Rockbolting is being rapidly introduced and the in situ stress field has been found to be of significant influence. Automation is the subject of a major programme. A strategy for coal quality has been devised. The health, safety and environmental programme concentrates on the traditional hazards together with surface environmental problems.

Jan 12, 1992

By J. E. Rouse, D. L. Buchanan

"During the emplacement of the Bushveld Complex in the Potgietersrus area magma reacted with the original floor rocks— Archaean granite or Malmani dolomite and overlying Penge handed ironstone or sedimentary rocks of the Pretoria Series. The complex sequence of sulphide-rich mafic rocks that formed along the contact is known as the Platreef. Associated with the sul­ phide mineralization are important concentrations of platinum-group metals, copper and nickel. Xenoliths of Malmani dolo­ mite have been incorporated into the Platreef and previous work has suggested that anhydrite is likely to have been present in the dolomite. The sedimentarv-derived sulphur thus introduced into the magma exercised an important control on the forma­ tion of the sulphides.Petrographic studies on the Platreef rocks from the Tweefontein area indicate that the original magma reacted with the banded ironstone to form iron-rich pyroxenites. In the Turfspruit area, to the south, the footwall rocks consist of sediments of the Timeball Hill Series. Original argillaceous rocks have been metamorphosed to cordierite-, corundum- and spinel-bearing hornfelses. Graphite was present in the contact zone in both the Tweefontein and Turfspruit areas. Anhydrite-bearing hornfels rocks are also present on Turfspruit.The Platreef rocks that overlie the corundum- and spinel-bearing hornfelses on Turfspruit are peridotitie, and pyroxenites are present in areas underlain by cordierite-bearing hornfels. The absence of orthopyroxene in the peridotite is probably indicative of low silica activity in the original magma. The pyroxenites have, however, undergone silica contamination from the underlying more siliceous cordierite hornfels.Carbon isotope studies indicate that the graphite in the Tweefontein and Turfspruit samples represents organic material orig­ inally associated with the footwall sediments. Sulphur isotope determinations on the anhydrite-bearing floor rocks indicate that this phase is clearly of sedimentary origin and was probably derived from an evaporitic unit within the carbonate sequence. This provides firm support for a model of ore genesis that involved the introduction of additional sulphur into the Bushveld magma. Isotope studies on sulphides associated with the banded ironstone and graphite indicate that these units were not the source of additional sulphur. Experimental studies predict, however, that a magma contaminated with iron- and carbon-rich material would have a high sulphur-carrying capacity. Where additional sulphur is available the magma would achieve saturation early in its crystallization history and precipitate an immiscible sulphide phase. Experimental work has also shown that sulphide precipi­ tation can be triggered by the introduction of salic material into a magma close to sulphur saturation. This mechanism probably played a role in the control of the sulphide mineralization in the Turfspruit area."

Jan 1, 1984

By M. J. Russell, W. E. Stephens, D. B. Mohamad, A. B. MacKenzie

Redox front processes in rocks are important in the context of both radioactive waste disposal and the development of orebodies. Results are presented from a study of the distribution of uranium and thorium and the natural decay series equilibrium about redox fronts in a granite at the Criffel pluton and Craignair quarry, Dalbeattie in southwest Scotland. The results are considered in the context of large scale uranium aqueous transport in the region and compared with those from a previous study of highly developed redox fronts at Pocos de Caldas, Brazil. Results show that the Criffel pluton has experienced a recent and rapid removal of uranium from the uppermost section of the granite whereas thorium has remained relatively immobile. The radium and uranium distributions indicate that diffusion processes probably control the distribution of radionuclides about the front. These processes are similar to those observed at Pocos de Caldas. The trends of concentration and activity ratio about the Dalbeattie redox front are less pronounced than those at Pocos de Caldas owing to the shorter time available for the process and the lower intensity of weathering at Dalbeattie.

Jan 12, 1992

By J. M. Smith

This resume provides an account of the work of the Bureau and it's establishment by an Act of Parliament in August 1916. The Medical Bureau is concerned solely with the administration of the medical provisions of the Act. Its main functions are to conduct and to direct or control the medical examinations provided for in the Act. The paper covers the changes in type of silicosis, classification into the three legal stages of silicosis, cancer of the lung and tuberculosis.

Jan 1, 1947

By J A. Hacked

This paper explores the potential to exploit controls over the outputs of the primary blasting operation, arising from the performance consistency benefits gained in using modern bulk emulsion explosives technology. The former, allied with the latest powerful blast predictive software and measuring tools, offers the user the opportunity to apply control over both cost and performance, which has not been possible in the past.

Jan 12, 1997

By NA NA

RJB completes purchase of second lease-licence mine, Miller buys Wimpey Mining, Point of Ayr Colliery in North Wales closes, jobs created at Lithgow Minerals Processing Park, Australia.

Jan 9, 1996

By D. G. Skinner, J. H. Griffiths, F. T. Williams, A. G. Withers

"The absence of homogeneity, in dust-clouds underground indicates the use of a method in which the volume of air sampled is an appreciable proportion of the total volume under consideration. Of the available methods, only the impinger and gravimetric techniques seem to comply with this requirement. In practice, greater efficiency of collection of the smaller particles is possible by the use of a gravimetric filter than with the impinger. For this reason if, as seems desirable, a standard method of sampling be sought, the adoption of a gravimetric technique is to be recommended.Provided that the amount of dust collected is reasonably large, the paper filter would seem to be preferable to the solid crystal type of filter on account of its greater convenience in use.Alternative methods of sampling are desirable to cover the wide range of practical conditions."

Jan 1, 1947

Jan 1, 1947

By E. H. W. Hornbrook, P. W. B. Friske

Paper presented at the 28th International Geological Congress, Washington DC, July 1989 (International geochemical mapping sessions). The objective of the programme is to establish and maintain a nationally consistent geochemical drainage database. Towards this end systematic surveys have been conducted since 1973. To date more than 200 surveys have been completed to the required standards, representing 180 000 sites and covering about 2 100 000 km2 throughout Canada

Jun 13, 1905

By Tawsaporn Nuchanong, Ian Nichol

Investigations of the dispersion of gold in soils and stream sediments associated with three gold deposits in Thailand indicate the existence of different geochemical dispersion patterns in the three areas, demonstrating the need for the adoption of a variety of exploration techniques. The three gold deposits which were investigated were the Phu Tham Phra-Phu Thong Daeng copper-gold prospect, the Doi Tung and the Huai Hin Lab gold prospects. Overall the investigations at the three localities demonstrate clearly that the chances of exploration success can be significantly enhanced if composite soil samples are analysed to ensure a more reliable estimation of the gold content in soils and if both the 63 micrometre fraction and the field-panned concentrates of stream sediments are analysed because of the variable grain size of the gold characterising different gold deposits and surface environments.

Jan 4, 1992

By Winmill T. F.

(Paper presented at the Institution of Mining Engineers' general meeting held in London on 8th June 1916.) The conclusions reached in this paper may be summarized briefly as follows: (1) The method of estimating moisture in coal by determining the loss in weight of a sample heated to 105°-110° Cent, in an air-bath for an hour is untrustworthy, the results so obtained being too low. (2) Dried coal has a very considerable power of absorbing moisture, and a sample, after being dried, must be protected instantly if it is to remain free from moisture. (3) A fairly accurate estimation may be made by heating the coal in a current of dry air at 105° to 110° Cent., and collecting the moisture evolved. (4) In cases in which it is proposed to use the dried coal for any further experiments, the drying must be done in the absence of oxygen, and this can be done simply and quickly by the vacuum method now described

Dec 1, 1916

By Y. L. Ding, N. A. Warner

Cylindrical pellets made from graphite and chromite mixtures were reduced in high-carbon ferrochromium melts at 1 600-1 695 degrees C, under an atmosphere of almost pure CO. The reduction rate, as measured by gas evolution, increased with increasing melt temperature and graphite addition and with decreasing pellet diameter or height, although reductant particle size had a very limited effect on kinetics. At a pellet size, heat and mass transfer were significant in controlling the early stages of reduction of large pellets while at chromite grain size, gas diffusion was probably a rate-controlling step. The time required for dissolution of unfluxed pellets into the melts was significantly longer than that for reduction. This indicates that pellet dissolution may be the limiting factor in determining the operating parameters for a proposed new process to produce high-carbon ferrochromium using melt circulation

Jun 19, 1905

By R. Winand, P. Harlet

he cathodes produced are of electrorefined grade; metallographic structure and surface roughness are controlled to a depth of 1.3 cm (single-side deposits); silver levels in the cathode are regulated by the presence in solution of Cl- and Br- ions; organics must be used at very low concentrations (around 0.1 mg/l with a consumption of about 0.01 mg/l/hr). The required concentrations of additives were established according to a well-defined strategy based on the consumption of organics at the cathode by a mass transfer limited-process.

Jan 4, 1992

By A. J. Naldrett

"Synorogenic mafic intrusions are a common feature of the northern Appalachians. Two sulphide-bearing intrusions in central Maine that have been investigated revealed a number of important features that illustrate sulphide-silicate interaction that relates to magmatic sulphides. The Moxie Pluton is a large mafic intrusion emplaced during the Devonian Acadian orogeny. The Katahdin gabbro is a small mafic body that is probably genetically and temporally related to the Moxie Pluton. Both intrusions were formed bv the intrusion of variably fractionated magmas into irregular chambers and feeder zones. The southern half of the Moxie Pluton contains three small sulphide accumulations, whereas the Katahdin gabbro hosts a large, predominantly massive, sulphide body. Textural evidence clearly documents the magmatic origin of these sulphides.The three Moxie Pluton sulphide bodies are located at or very close to the intersection between the intrusion and the sulphidebearing Hildreths Formation. Sulphur assimilation, suggested by this relationship, is supported by the isotopically light (634S = —8 to —25) and the selenium-poor (S/Se - 25 000-48 000) character of the Moxie sulphides and correlation with the Hildreths Formation sulphides (S34S = —25, S/Se = 25 000-48 000). Isotopically light sulphur (534S = —20 to —21) and high S/Se ratios indicate that the majority of sulphur in the Katahdin sulphide body was also derived from an unexposed country rock source. The volume of sulphide in this example illustrates the potential efficiency of the sulphur assimilation process—so efficient in this case that marked dilution of the economic chalcophile elements resulted from the addition of so much external sulphur.The three Moxie Pluton sulphide occurrences are all impoverished in Ni and Cu (1.87-0.44% Ni; 0.72—0.32% Cu in massive sulphide), but contain normal Co contents (0.22-0.13%) relative to typical magmatic sulphides. The Katahdin sulphides show a greater Ni and Cu impoverishment (0.2% Ni; 0.1% Cu in massive sulphide) with similar Co (0.17%). The Ni content of the Moxie Pluton olivines document the fractional removal of sulphides during crystallization of the host magma, which resulted in the progressive depletion of the chalcophile metals in this magma. Modelling that involved the fractional crystallization of the magma coupled with the fractional removal of a specified proportion of sulphide has successfully duplicated the Moxie Pluton sulphide compositions. A similar magmatic model has been postulated for the Katahdin sulphides with a greater degree of sulphide fractionation. This latter model is again supported by extremely low Ni/forsterite ratios in olivines, though the compositional range is insufficient to document fractionation. These magmatic models are not unique, but they provide a relatively constrained and consistent explanation for the sulphide compositions.The Ni contents of olivines are the most important indicator of sulphide-silicate interaction in mafic magmas and have exploration potential. They provide a means of assessing the timing and extent of sulphur saturation in an intrusion and are a guide to the Ni content of a sulphide accumulation in equilibrium with olivine. In the Maine examples they provide strong evidence of the magmatic origin of the sulphide accumulations and justification for magmatic modelling."

Jan 1, 1984

By F. Boudreault, M. J. Scobie, J. Szymanski, C. Hendricks

The development of new stoping methods and more effective control over dilution, recovery and fragmentation depends on improved accuracy in blasthole drilling. The mechanisms and factors which control accuracy are poorly understood. Canadian blasthole stoping and the practices adopted for monitoring and controlling drilling accuracy are reviewed. The techniques and problems associated with blashole set-up and trajectory surveying are discussed. Four new blasthole trajectory survey systems are evaluated on the basis of their performance in recent underground trials. Conclusions are drawn as to the technological developments required so that more precise control over drilling accuracy can be achieved.

Jan 12, 1992

By A. Paulin, A. W. D. Hills

The work has shown that packed-bed behaviour can be predicted from the results of single-particle experiments, total reaction times being predicted somewhat more accurately than gas and solid temperatures and gas compositions. A small laboratory packed-bed reactor was built and used to study the decomposition of beds of specially prepared CaCO3 spheres, steps being taken to minimise the effects exerted by the walls of the bed on processes occurring within the bed. Gas and solid temperatures and gas compositions were measured at various points in the bed and compared with theoretical predictions based on kinetic data determined in previous single-particle experiments. The measured solid temperatures and total reaction times agreed remarkably well with the values predicted theoretically. Gas and solid temperatures measured after the reaction had finished at any point in the bed did not agree with the theory. This was because solid temperatures in the bed rose very rapidly once the reaction was completed and the walls of the bed could not be heated at a sufficient rate for their temperatures to rise as rapidly; thus some loss of heat from the bed to the walls was inevitable, and this could not be accounted for in the theory. In addition, the theory did not allow for the conduction of heat within the bed, and this resulted in some further slight discrepancy between the measured and predicted values, particularly after the reaction was completed. Gas compositions measured in the bed were rather scattered, but, even so, they agreed moderately well with the predictions of the theory.

Dec 1, 1971

By K. C. Misra, W. Wrightson Jr.

The Lick Fork prospect shows appreciable nickel sulphide mineralization in a narrow, steeply dipping, layered sequence of metamorphosed hornblende peridotite, gahhro and hornblende gahhro, intrusive into the Pedlar Formation (charnockitic pyroxene granulite) of the Virginia Blue Ridge Complex (Precambrian). Rocks of the intrusion have equilibrated to granulite- facies metamorphism, as indicated by pervasive polygonal texture of silicate aggregates, development of biotite- and hornblende-preferred orientation, compositional equilibration of the silicate minerals, the Mg-Fe2+ (orthopyroxene-dino- pvroxene) distribution coefficients (average 0.57), (MgO + FeO + Fe20 3)/Al20 3ratios in orthopyroxenes, and Ti contents and AI(i\)/A I(\i) ratios of hornblendes. The sulphides, consisting of pyrrhotite-pentlandite (with up to 4 wt% Co)-chalcopyrite-pyrite-marcasite-violarite- bornite—mackinawite, are virtually restricted to the ultramafic unit of the intrusion and constitute 20-30% of the samples of hornblende peridotite studied. Although the basal accumulation of the sulphides may suggest magmatic segregation, sulphide- silicate textures typical of sulphide liquid immiscibilitv are not present, even in the sparsely mineralized gahbro units. On the other hand, the transgressive and relict textures are strongly suggestive of replacement of the silicate minerals by sulphides. These include chaleopyrite ± pyrrhotite ± pentlandite (violarite) ± pyrite ±magnetite veins crosscutting silicates, sulphide penetration into silicates at silicate-sulphide contact zones, rounding of silicate grains against sulphide matrix, and islands of silicate minerals (olivine, hornblende, pyroxene, biotite) in sulphide masses. Metamorphic mobilization of pre-existing sul­ phides is a possibility, but involvement of post-metamorphic, hydrothermal fluids is suggested by the following features: paucity of annealing and deformation textures in the sulphides, replacement of metamorphic and deformed silicates, lack of differential sulphide mobilization and the common occurrence of sulphides along grain boundaries and triple junctions of poly gonal silicate aggregates. The consistent association between sulphides and hydrothermal alteration products of silicates suggests that they are cogenetic. The hydrothermal fluids may have merely mobilized and concentrated the pre-existing, disseminated, magmatic sulphides, or there may have been significant addition of sulphides during this process. This question cannot be resolved unequivocally with the existing data.

Jan 1, 1984

By A. H. G. Mitchell

Gold-poor and gold-rich porphyry and epithermal gold-silver deposits of Caenozoic and Cretaceous age in the western Pacific and central and eastern Europe are confined to predominantly andesitic continental margins and island arcs. The arc volcanic rocks overlie a complex non-oceanic basement of stacked nappes, the uppermost of which is often ophiolitic. The emplacement of ophiolite triggered a reversal of tectonic polarity, subduction and arc magmatism. Andesitic volcanism and the formation of a strato-volcano were followed by the ascent of magma and porphyry copper mineralisation. Regional propylitic alteration came from convecting, predominantly meteoric fluids. Magmatic degassing caused advanced argillic alteration. This is commonly unmineralised in perched water tables, but may sometimes host high sulphidation gold or enargite gold at deeper levels within the propylitic zone. The onset of extensional stress after the andesitic volcanism allowed meteoric water to circulate to depths of 5 km or more, with consequent cooling of an ascending magma body at depth and the development of low sulphidation epithermal gold mineralisation near and immediately above the sub-volcanic basement surface. All andesitic arcs are mineralised. Regional controls on their ore potential include the level of erosion and geological features in the basement that focus the ascent of fluids. Differences between the mineralisation of the European and the western Pacific arcs may reflect the presence of older, more granitic basements in many of the European arcs.

Jan 12, 1992