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By C. L. Workmann Davies

Underground transport and communication in collieries was the theme selected for the 1983 mining school conducted by The South African Institute of Mining and Metallurgy. The response from the industry was so good that three separate schools of one week each were arranged, and a total of 222 delegates attended. Development of Mineral Resources The Institution of Mining and Metallurgy and The Department of Mineral Resources, Government of Thailand, with the cooperation of the Thai Mining Association and Chulalongkorn University, is to hold an international conference entitled 'Role of Government in Mineral Resources Development' in Bangkok from 5th to 8th Decembc -:" 1983. Electronics in Mining A symposium entitled 'Electronics in Mining', organized by The South African Institute of ElectriealEngineers, is to be held in Randburg, South Africa, from 18th to 20th September, 1984.

Jan 1, 1983

By C. H. Wyndham, N. B. Strydom, S. Benade

A group of 23 underweight men weighing less than 50 kg were subjected to an acclimatization procedure in which the work rate was gradually increased from 35Watts on the first day to 70Watts on the eighth day. Excessively high body temperatures and heart rates were observed on these subjects throughout the acclimatization period and on their performance they must be rated as heat-intolerant. It can be concluded that such underweight men should not be subjected to acclimatization at such high work rates and that they should not be allocated to tasks involving these rates in a hot environment. The fact that their body surface areas are inadequate to enable them to get rid of the internal heat produced during strenuous work plus their low work capacities are the major reasons for their inability to tolerate heat.

By K. M. Banks

Multiple-pass hot-strip-rolling schedules of carbon steels and niobium-microalloyed ferrite-pearlite steels were simulated on a Gleeble 1500 thermomechanical test apparatus. The effects of finishing temperature, coiling temperature, and chemical composition on the as-deformed ferrite grain size and hardness of the steels were determined. Low finishing temperatures and low coiling temperatures both contributed to ferrite grain refinement. Good agreement was found for the microstructure and hardness of the steels between the as-ruled condition and the results obtained from rolling simulations. The progress of recrystalization and precipitation was followed from examinations of the flow-stress curves during the hot-rolling simulations. The flow-stress behaviour during the finishing passes was consistent with the resulting changes in final ferrite grain size. It was found that the no-recrystalization temperature, TNR, is raised by increased additions of niobium.

Jan 1, 1993

Past work on the ignition of methane-air mixtures by coal-cutting picks is reviewed, with special reference to the factors that contribute to ignitions and ways of reducing them. The main conclusions obtained from this review are outlined for the following aspects: mechanisms of ignition, methane concentrations, and the roles of rock types, cutting parameters, cutting tools, and water. However, many of these factors have been investigated on a qualitative, rather than on a quantitative, basis. A considerable amount of effort over a long period has been expended in this area of research. It is shown that a number of the factors influencing ignitions by machine picks have been researched adequately, but that there is still work to be done. Research is continuing in this area, being concentrated primarily upon the ignition potential of the coal-cutting pick.

Jan 1, 1985

By W. Lin, H. Endo, M. Kwasniewski, A. Kamei, M. Takahashi

Uniaxial tension tests were conducted on specimens of eleven granitic rocks which came from eastern Japan, and included a granite, four granodiorites, four tonalites and two gabbros. The axial and transversal deformability of these rocks was determined based on strain measurements using wire strain gauges. The experimental test results revealed that deformational properties of the rocks investigated varied depending on their petrographic features. However, the axial strain and the lateral strain characteristics showed a similar trend for all the rocks, i.e. the stress-strain curves were non-linear throughout the whole stress range from the initial point of loading to the point of ultimate failure. Moreover, the tangent Young's modulus and the ratio of the lateral strain to the axial strain decreased monotonously with the increasing of the axial stress. Still, the deformational properties were different for individual rocks in a quantitative sense. In particular, the difference in the lateral strains among different rocks was more distinct than that in the axial strains. For example, the Poisson's ratio at a stress level equal to 50% of the ultimate strength of a granodiorite was very low, close to zero. Furthermore, the Poisson's ratio of a tonalite was lower than that of a granodiorite, and assumed a negative value. This effect occurred because the lateral strain became positive as it changed from contraction at the initial stage of loading to extension at higher stress levels. There is no ready explanation for this phenomenon; it is believed, however, that it occurs due to microcracks pre-existing in rock materials and/or weak bonds between the adjacent mineral grains. Les essais de traction directe ont été conduits sur les échantillons de onze roches granitiques provenant de la région Est du Japon: un granit, quatre granodiorites, quatre tonalites et deux gabbros. Déformabilité axiale et transversale de ces roches s’était déterminée en utilisant des jauges extensométriques à fil. Les résultats obtenus à partir des essais montrent que la déformabilité des roches examinées varie selon leurs propriétés pétrographiques. Cependant, à partir des essais, une tendance semblable était observée dans les paramètres de la déformation axiale et la déformation latérale de toutes les roches; c'est-à-dire chaque courbe de contrainte-déformation était non-linéaire dans tout l'intervalle de contraintes à partir de l’état initial jusqu’à l’état d’une rupture finale au cours du chargement. De plus, le module tangent de Young et le rapport de la déformation latérale sur la déformation axiale a diminué de manière monotone avec l'augmentation de la contrainte axiale. Cependant, les différences quantitatives de propriétés de déformation sous traction étaient observées entre des roches individuelles. Particulièrement, la différence de déformations latérales était plus notable que celle-là de déformations axiales entre des roches différentes. Par exemple, le coéfficient de Poisson à un niveau de contrainte égal à 50 % de la résistance d'un granodiorite était très bas, près du zéro. En outre, le coéfficient de Poisson de la tonalite était inférieur que celui du granodiorite et a assumé une valeur négative. Cet effet est apporté parce que la déformation latérale est devenue positive en passant de la contraction dans l'étape de chargement initiale à l'extension sous les contraines plus hautes. Il n'y a aucune explication prête de ce phénomène; on prétend, cependant, qu'il est induit par des microfissures préexistantes dans des matériaux rocheux et/ou des joints faibles entre les grains minéraux adjacents. Einaxiale Zugversuche wurden auf Probestuecke von elf frischen, in Ostjapan vorkommenden, granitartigen Gesteinen durchgefuehrt, welche einen Granit, vier Granodiorite, vier Tonalite und zwei Gabbros umfassten. Die axiale und transversale Verformbarkeit von diesen Gesteinen wurde durch Verformungsmessungen mit Drahtdehnungsmessstreifen geklaert. Die experimentellen Versuchsergebnisse offenbarten, dass Verformbarkeitseigenschaften des untersuchten Gesteins in Abhaengigkeit von ihren petrographischen Eigenschaften variierten. Jedoch zeigten die axialen und die lateralen Spannungsdehnungslinien eine aehnliche Tendenz bei allen Gesteinen, d.h. die Verformungskurven waren nicht linear im ganzen Bereich vom Ausgangspunkt des Belastens bis zum Punkt des entgueltigen Bruchs. Ausserdem verringerten sich das tangentiale Elastizitaetsmodul und das Verhaeltnis der lateralen Verformung zur axialen Verformung monoton mit der Erhoehung der axialen Spannung. Dennoch waren die Verformbarkeitseigenschaften der einzelnen Gesteine in der quantitativen Wahrnehmung unterschiedlich. Insbesondere war der Unterschied bezueglich der lateralen Verformungen zwischen verschiedenen Gesteinen eindeutiger, als der in den axialen Verformungen. Z.B. war die Querkontraktionszahl auf einem Spannungsniveau, das 50% der Zugfestigkeit eines Granodiorits entspricht, sehr niedrig und nah an Null. Ausserdem war die Querkontraktionszahl eines Tonalits negativ und deshalb niedriger als die eines Granodiorits. Dieser Effekt trat auf, weil die laterale Verformung, als sie sich von der Kontraktion am Ausgangsstadium des Belastens bis hin zur Ausdehnung auf den hoeheren Spannungsniveaus aenderte, positiv wurde. Es gibt keine fertige Erklaerung fuer dieses Phaenomen; es wird jedoch angenommen, dass es wegen der Mikrorisse auftritt, die vorher im Gesteinsmaterial und/oder in den schwachen Bindungen zwischen den angrenzenden Mineralkoernern existieren.

Jan 1, 2003

By H. M. Wells

The investment decision under uncertainty by H. M. WELLS, Pr. Eng., M.Se. (Fellow) The future outcome of a proposed investment is uncertain at the time the decision must be made to accept it or reject it. This uncertainty can be expressed in the form of a probability distribution. An attempt is made to rationalize the investment decision under these circumstances, especially when the range of possible outcomes extends into both the acceptable and unacceptable domains. A rigorous definition of risk is proposed, and a criterion of risk aversion is developed that forms the boundary between acceptable risk and unacceptable risk (called the loss limitation line). It is shown that this decision criterion can also serve as a quantitative yardstick in the evaluation of various possibilities for 'tailoring' the proposal to mlke it more compatible with the particular financial circumstances of the company concerned.

Jan 4, 1976

By R. H. Steel

Ingot casting and wire drawing In Iron Age Southern Africa by R. H. STEEL (Visitor) This paper describes the experiments that were conducted in 1974/1975 on two related aspects of Iron Age copper technology in Southern Africa: ingot casting and wire drawing. Three types of ingot were successfully cast: the St Andrew's Cross ingot, the marale ingot, and the musuku. It is suggested that the 'studs' on the musuku are not the remains of broken-off rods as previously proposed by other investigators, but that the ridged pattern is an ornamental feature. Copper wire was successfully drawn with similar tools and according to the procedures described in the literature on African Iron Age wire drawing. It is concluded that these accounts are generally accurate and that the pre-European metal workers are worthy of respect for the results they achieved with primitive methods.

Jan 11, 1975

By L. A. Vermeulen

A simple argument shows that it is impossible for the flight of a rod in contact with a litter bar in a rotary mill to be initiated at that point on the upside of mill rotation when all the forces acting on the rod are in equilibrium. The argument was confirmed experimentally in a study showing that the lift of litter bars is a function of their height, that the rod velocity at the point of departure has a significant radial component, and that the subsequent flight of a rod is along a parabolic trajectory as predicted by elementary mechanics. A quantitative account of the observed effects, which is based on a dynamic theory of the sliding interaction between rods and litter bars, revealed interesting properties of the motions of rods down the surfaces of litter bars when the latter are in uniform circular motion during the rotation of a mill.

Jan 1, 1985

By J. H. van Dalen, P. J. Brandt, F. W. Wessels

A maximum of ten process streams (Merrill barren solutions) can be monitored sequentially with this on-line analyser, and gold concentrations as Iow as 0,005 mg/I can be determined. The design is a further development of the Tell-tale analyser constructed by the Corner House Laboratories during the period 1965-69. The barren solution is preconcentrated automatically by solvent extraction, the solvent being a solution of I per cent Aliquat 336 in di-isobutyl ketone. An aqueous-to-solvent ratio of 40: I is maintained. The extracted gold in the organic phase is determined by flame atomic absorption, each analysis taking approximately II minutes. The long-term reproducibility of the absorbance readings over a 24-hour period of repetitive sampling of four simulated process streams varied from 6,9 to 4,1 per cent relative standard deviation for gold concentrations of 0,0 I to 0,05 mg/I.

Jan 1, 1980

By K. R. Vost

Most theoretical methods for the prediction of air-temperature gradients in underground airways always assume that the temperature of the entering air either remains constant or has only a slow seasonal variation. Large changes of temperature, caused by variations in atmospheric conditions on the surface, were measured in a fourteen-day period in air entering a horizontal airway. The changes in wet-bulb temperature were damped along the airway less uniformly than the dry-bulb changes; significant variations occurred in the wet-bulb temperature of the air leaving the airway. The damping was .associated with large variations in air-temperature gradients. Other causes of rapid changes In temperature are discussed. These changes must be taken into account in predictions of the frequency with which undesirable conditions can be exceeded at critical points in the ventilation circuit of a mine to allow proper planning of ventilation and refrigeration requirements.

Jan 1, 1977

By J. P. Coetzee

Dr. K. Gebhard In his excellent and comprehensive survey on the future development of the Iron and Steel Industry in South Africa, Mr. Coetzee has also mentioned the direct reduction processes as a possible method of converting iron ore to iron. Mr. Coetzee has made it quite clear that at this stage one should not consider these processes as a 'magic formula' which herald a 'break through'. I agree entirely with this point of view. Once upon a time I held the opposite view, but in the meantime I have revised my views. To do so, I had 40 years at my disposal. In 1930 I had the privilege of being connected with the first commercial sponge iron plant in Germany1 - a plant which was capable of producing 40 tons of sponge iron a day. We were determined to prove that the blast furnace would become obsolete in the near future. We considered it as an unnecessary detour to convert iron ore first into an iron-carbon alloy, which contained further quite a number of undesirable elements, and to remove this carbon by an endothermic process. Direct iron-making seemed to be a logical short cut. Unfortunately, we were not able to establish this 'short cut,', but the life of our sponge iron plant was cut short. We had solved all technical but not the economic problems. Basically the positon is still the same today - mainly economic and to a lesser degree technological aspects determine the rate at which sponge iron plants are installed. More has been said and written than done about direct reduction plants. I think that there are two main reasons for this stagnation in the introduction of direct reduction processes. The first reason is that modern blast furnaces are just too good and too economic ever to be replaced by direct reduction processes on a large scale. This, of course, already limits the field of application for direct reduction plants. The second reason is that sponge iron production and utilisation is based on technical considerations, which increase not only the production cost of sponge iron but also the conversion cost to steel to such an extent that under special conditions only are direct reduction plants an economic proposition. Are these technical considerations still as forceful and valid today as they were when 'direct steelmaking' was first contemplated? The development of sponge iron production as a method of direct

Jan 3, 1971

By N. B. Strydom

The data on heat stroke cases reported during the past five years were examined to determine the influence of age on the incidence of heat stroke. Relating the age distribution of these cases to that of the total number of Bantu mine workers showed clearly that the older men run a significantly higher risk of developing heat stroke than the younger men. Although the number of Bantu over 40 years of age in the industry is less than 10 per cent of the total they nevertheless accounted for 50 per cent of the fatal heat stroke and 25 per cent of the nonfatal heat stroke cases during the period under review. Age must, therefore, be recognised as a causal factor in heat stroke and the worker over 40 years of age should be allocated to work on surface, or in cool areas or to non-strenuous and supervisory tasks in hot areas.

By A. L. Hinde, A. A. Bradley, K. H. Stanton, P. J. D. Lloyd, G. K. Schymura

As part of its programme to develop methods for concentrating minerals underground, the Chamber of Mines of South Africa in conjunction with Lurgi evolved and tested a I MW centrifugal mill. The machine is capable, in the autogenous mode, of grinding more than 25 t/h of minus 75 plus 44 mm hard quartzite to a minus 3 mm product containing over 50 per cent minus 75 µm material, and as a ball mill of grinding more than 60 t/h of minus 19 mm quartzite to a minus 3 mm product containing over 35 per cent minus 75 µm material. Extrapolation of computer models of the process suggests that these limits can be comfortably exceeded. Long-term continuous testing is in hand, aimed at proving that this I m in diameter by I m long mill is in every respect the equivalent of a conventional 4 m by 6 m ball mill.

Jan 1, 1982

By V. J. Moore

Introduction Although months have passed since APCOM 87, held from 19th to 23rd September, 1987, the vivid memories of all aspects of its activities remain as clear in one's mind as if it all happened only yesterday. The Symposium, which was held at the Johannesburg Sun Hotel, was organized by The South African Institute of Mining and Metallurgy in collaboration with the Council for Mineral Technology (Mintek), supported by The Geostatistical Association of South Africa, The Operations Research Society of South Africa, and the Computer Society of South Africa, and was backed financially by the Chamber of Mines of South Africa. The total number of registrants amounted to 375 delegates and 50 affiliates: 100 of the delegates were from outside the Republic of South Africa and represented 15 countries, namely Australia, Brazil, Canada, Chile, France, Great Britain, Greece, Italy, Namibia, Phillipines, Sweden, Turkey, United States of America, West Germany, and Zimbabwe.

Jan 1, 1988

By Y. Hwang, C Kang

To understand the effect of thermal loading from HLW on the groundwater flow nearby, the coupling of TH in an equivalent porous medium is studied. Results indicate that under given conditions the alteration of groundwater flow by decay heat is localized phenomena. More comprehensive studies are underway for THM coupling. Zum Verstandnis fur die Wirkung der thermischen Belastung von HLW in der Nahe von Grundwasserstrom, ist die Verbindung von TH in den entsprechenden porigen Medium erarbeitet. Die Ergebnisse zeigen, dass unter vorgegebenen Bedingungen die Anderung von Grundwasserstrom durch Zerfallwarme lokalisiert wird. Zusatzliche umfassende Arbeiten sind fur die THM Kupplung auf dem Wege. Pour comprendre l'effet du chargement thermique de HLW sur l'écoulement d'eaux souterraines tout près, l'accouplement du TH dans un milieu poreux équivalent est étudié. Les résultats indiquent que dans des conditions données le changement d'écoulement d'eaux souterraines par la chaleur d'affaiblissement est des phénomènes localisés. Des études plus complètes sont en cours pour l'accouplement de THM.

Jan 1, 2003

By E. P. Gush

Diamonds, an enigma in a mineral resource sense. Chemically, diamonds are no more than carbon crystals in a cubic system-formed one might add under conditions of great pressure and temperature. They have certain physical properties which are fairly unique. They are very hard, they have a high refractive index, they luminesce, some of them fluoresce, they have a high specific gravity, they don't wet and they are a good conductor of heat. In a way, a rather clinical set of qualities. Of course, these qualities are what give diamonds their use and their beauty. It is on the emotional side that they get complex and stir memories of legends, of beauty, of wealth and romance, of war, happiness, bad luck and curses. It is on the emotional side that the value of a diamond is established, if such a thing is possible. Diamonds are extremely varied, there are more than 5000 categories into which they are sorted, so there is room at each point across the spectrum for their individualities to emerge, and accordingly their attractiveness to each buyer is unique.

Jan 1, 1994

By H. M. Friede

Notes on the composition of pre- European copper and copper-alloy artefacts from the Transvaal by H. M. Friede. Ph.D. (Visitor) Seven copper artefacts (five ingots and two ornaments) found at prehistoric sites in the Transvaal were submitted to analysis. All the artefacts showed a high copper content and a relatively Iow level of impurities. A little-known ingot type from the Limpopo Valley ('nail' ingot) is described, and its analysis is given. The analysis of two copper ornaments that come from sites dated to the 5th Century AD. and the 11th Century AD. showed the constancy of the composition of copper articles over long periods. The well-known 'Blaauwberg Ingot' was re-analysed, and the results showed that this ingot cannot be regarded as a true bronze. Analytical values for the composition of three brass artefacts from Bambandyanalo (Mapungubwe), Northern Transvaal, are given. Some aspects of pre-European bronze manufacture and brass smelting, and of early metal trade from the East Coast into the interior of South Africa, are discussed.

Jan 2, 1975

By R. R. Mankowski

The work described in this paper is an attempt to increase present-day knowledge of fatigue in mine hoisting cables, particularly the internal energy loss arising from interwire/strand friction in a cable undergoing periodic non-planar transverse vibration. Such frictional energy loss is known to be one of the major influences limiting useful working life of hoisting cables in use today, and is responsible for the large capital outlay required to maintain the high safety factors prescribed by the mining industry. The experimental method employed identifies two mechanical characteristics of cables that are independent of amplitude and frequency, and are primarily attributed to the type of cable construction. Interest is focused the time rate of change of curvature as the major parameter influencing the internal damping mechanism. Empirical results confirm that amplitude and mode number play an important role in quantifying the internal losses, and also reveal that a critical radius of curvature exists below which damage due to vibration fatigue rises exponentialy to potentially high levels.

Jan 1, 1988

By P. E. Venteer

The Grootegeluk coal-processing plant treats 3 kt of raw coal per hour to produce a middlings fuel coal and a coking coal fraction with ash contents of 35 and 10 per cent respectively. The plus 0,5 mm fraction is treated by heavy-medium processes, the final top size of the coal being 15 mm. About 400 t of minus 0,5 mm coal per hour is subjected to froth flotation. The routes originally considered for the processing of this fine coal were froth flotation, shaking tables, heavy-medium cyclones, and water only cyclones in combination with froth flotation. The results from tests on the fines arising from a small-trial open-cast mine are discussed. When the froth flotation route was decided upon, further tests were conducted on the selection of the equipment most suited to the particular requirements of this coal and the rest of the plant. Tests using different types of flotation cells and dewatering equipment are discussed. During the commissioning, several operational problems were encountered, and the work done to find the best solutions is discussed.

Jan 1, 1984

By deur R. R. Mears

The expected curtailment of activities within the gold-mining industry by the closure of the more marginal mines, and the shortening of the life of the industry as a whole as a result of rising costs and/or an uncertain gold price, are factors that are bound to harm the South African economy in a number of ways. The industry has no option but to regard the gold price, which is determined on the world market, as a given quantity. The remaining ore reserves al tend to be of a lower grade and/or to be found at greater depth. Therefore tighter control of working costs would seem to be almost the only option open to the industry. Working costs can be divided into two broad categories: costs emanating from the environmental characteristics of the orebody, and costs emanating from the general inflationary environment in which the industry has to purchase its inputs. Working costs stemming from the physical environment also fall into two categories: those relating to the grade of the orebody, and those resulting from working at increasing depth and temperature, together with the need to pump increasing quantities of water. The industry is both capital- and labour-intensive in absolute terms, since it requires large inputs of labour as well as of capital. It is limited in its scope to adjust its production function by becoming more labour- or more capital intensive, and is dependent on a large labour force, which cannot easily be replaced by capital inputs. On the other hand, large amounts of capital are required for investment in shafts, development, machinery, and equipment. Since the early seventies, the working costs of the South African gold-mining industry have increased at an annual rate that was significantly higher than the general rate of inflation. This rapid rise in working costs has caused some mines to find themselves in a difficult profit position. At times, the gold-mining industry has even been compelled to restructure its cost/revenue relationship rather fundamentally by revising the grade of ore worked sharply upwards or downwards, as the case may be. The rise in the gold price since 1972 has made it possible for the industry to introduce significant changes in its Black wage policy. The main aim was to increase the permanency of the Black labour force and to encourage local Black workers to join the industry. At the same time, significant increases were also experienced in the cost of machinery and stores, as well as of capital, mainly as a result of inflation. In the study on which this paper is based, the author attempted to measure the influence of environmental factors on working costs, using the physical consumption of electricity as a criterion for measurement. He found that the usefulness of this criterion in relation to factors such as depth, temperature, and water quantities pumped was invariably more than neutralized by the effects of greater productivity and economies of scale. The effects of these environmental factors on the working costs of the industry could therefore not be determined to any degree of accuracy. It seems that good progress is being made with the development of capital-intensive forms of technology aimed at coping with rapidly rising working costs and other effects of increasing depth. Techniques are also being developed to improve rock-cutting procedures and to eliminate the use of explosives in order to introduce a continuous mining process. On the whole, the gold-mining industry seems to be more sensitive to general inflationary pressures than to the cost effects that are associated with depth, temperature, and water quantities pumped. Greater control is possible over physical environmental factors such as the grade of ore mined, temperature, rate and nature of development of a mine, and adaptation of the daily working cycle to a continuous mining process. Wolfe and others hold the view that the industry will lose control over labour costs as a result of the 'sharp increase in wages and the growth of Black trade unions. However, the use of more capital-intensive technology will allow the industry to reduce its labour force, and a smaller, better-trained, and more permanent labour force will enable the industry to cope with the increasingly difficult physical environment and higher wages.

Jan 1, 1987