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The decrepitation technique is a rapid means of measuring abundances, temperatures and to some extent the fluid compositions, of fluid inclusions in transparent and opaque minerals. The method has been used to investigate the hydrothermal fluid systems associated with gold mineralisation in the Tennant Creek, Pine Creek and Halls Creek Goldfields. At the Enterprise Mine, Pine Creek, several different stages of quartz veining are distinguished and within these, gradational changes in fluid temperatures and compositions help to define the centre and nature of the thermal system responsible for the mineralisation. In the surrounding Pine Creek region and at Tennant Creek and Halls Creek, the results were applied on a regional scale to characterize outcrops and aid in the discrimination between potentially mineral- ized and barren outcrops. The decrepitation method involves the heating of a small (lgm) sample of crushed and sized grains up to as high as 800 degrees celsius. During the heating the fluid inclu- sions within the grains develop sufficient internal pressure to physically burst, the temperature of such bursting being dependent on the type of fluid and the prevailing tem- perature at the time the inclusion was originally trapped. The resulting tabulation of the number of inclusion bursts per 10 degree temperature interval is plotted as a histogram of decrepitations versus tempera- ture and called a decrepigram. The decrepi- grams frequently show several distinct peaks at different temperatures which are caused by different populations of inclusions in the sample. The areas of the peaks indicate the abundances of inclusions in each population while the shape and mean temperature of the peak provides a guide to the type of fluids involved. Of particular importance in this study is the presence of decrepitation peaks at fairly low temperatures (around 2000 C. These are characteristic of C02 rich fluids which build up internal pressure very quickly when heated. The Enterprise Gold Mine at Pine Creek comprises a number of overlapping quartz vein systems hosted by Burrell Creek Formation sediments. The geology of this mine has been described at this conference by Dann and Delaney, who have defined several distinct stages of quartz veining based on structural, mineralogical and physical features of the veins. For this decrepitation study, 19 quartz samples from the mine and environs, including some from each stage of veining were collected. These results suggest that there are 4 major vein types, within 3 of which additional small variations can be discerned which are due to gradational changes in the temperatures and fluid compositions in the mine area.

Jan 1, 1984

Traditional techniques for extracting pillars in thick underground coal seams in India are reviewed. Problems encountered are principally control of roof strata and low recovery. Recently developed mechanized methods and projected newer techniques are discussed.

Jan 1, 1986

By Mozley R

Contaminated sediments are a multinational problem. A crucial factor in solving an environmental problem is knowledge of, not only the amounts of polluted soil, the contaminants involved and their concentration, but also the historical background of the problem. Processing polluted soil is a tailor made activity based on rational decisions resulting from a detailed treatability study. Lack of information about characteristic properties of a specific sludge/pollution combination is the main obstacle in the route from first ascertaining that a particular harbour subsoil is polluted, to final identification of the full scale treatment plant. In the first instance, information must be generated regarding the distribution of pollutants in relation to the distribution of the original geophysical components. Based on this information rational decisions can be made on separation at a particular cutpoint and what sequential techniques should be involved for a certain fraction. For this purpose a `fingerprint method' is presented especially developed for investigation of polluted soil and sediments. The heart of the fingerprint method is a series of sequential hydrocyclone separations, by which a series of products is generated. The objective of the fingerprint method is to select an optimised treatment procedure in which the pollutants are concentrated in as small a volume of material as possible, leaving the bulk of the material clean. The pollutants can then readily be destroyed or isolated from the environment. The philosophy and advantages of the fingerprint method are demonstrated for a harbour sludge containing heavy metals as main pollutants. Hydrocyclone separation combined with flotation of both the coarse and fine fraction resulted in reusable and dischargeable products. Flotation of the fraction of fines was carried out by means of an experimental flotation cyclone enabling the selective recovery of mineral particles with diameters less than 10 microns. The overall conclusion is that design and engineering of treatment flow schemes for polluted dredged materials is a tailor made activity based on rational decisions resulting from the fingerprint information.

Jan 1, 1993

By Blair J. R

In the Bayer process, bauxite is leached with caustic soda, forming a solution of sodium aluminate, from which hydrated alumina is precipitated. The efficient operation of the continuous form of this process requires that the concentration of caustic soda be controlled. A computer simulation of the concentration of caustic soda has been conducted to provide information, regarding the dynamic behaviour of caustic concentration, which is not available from normal plant data. The basis of the simulation is a state- space model of an alumina refinery, linearized about the normal operating condition. The formulation of the model, with the relevant approximations and assumptions, is outlined. The simulation of the mudwash section of the. plant is described in detail. A continuous model of the mudwash, having time-varying coefficients, was driven using operating data from an alumina refinery. The modelled response showed reasonable agreement with the recorded plant response.

Jan 1, 1977

By Aziz N. I

Examination of the geology and support performance at two site leads to development of an under tanding of the influence of caving on powered support rating. The two site represent the current extremes in support rating, i.e. 6/260 tonne supports operating in the Hirst seam at Solsgirth Colliery, Scotland, and 4/900 tonne supports operating in the Bulli seam, West Cliff Colliery, Australia.A conceptual model considers the coal ahead of the face, the powered support, and the caved waste to be three yielding foundations which interact to control the subsidence of the roof strata.The caving mechanisms identified for the strata of the Hirst and Bulli seams, are different. These mechanisms being related to rock properties - the palaegeography and depositional conditions at each site-produce caved wastes with different yield characteristics.An analysis of the results obtained for convergence and support reaction during production cycles at both sites shows the manner in which support reaction is developed, indicating the importance of higher setting load densities in the Bulli seam.Evaluation of the work done on the subsiding roof strata during typical production cycles by two of the yielding foundations the powered support and the caved waste immediately behind the powered support - further demonstrates the influence of caving mechanisms on support rating.

Jan 1, 1989

By Zenari L, Kent D

As our mines introduce more sophisticated production technology into their operations, the dependence on communication systems is markedly increased to allow the management of the technology. However the attention given to the communication systems has lagged that given the production equipment - namely LHDs, trucks and jumbos. At times it was treated as after thought. However, this is changing as the degree of automation increases in our mines. The communication system is now being given much more priority and is genuinely becoming a part of the mine design. The transfer of information around underground, as well as between the surface and underground, is an essential day-to-day activity, with the aim being a smoothly run operation. However the mine environment is far from static, and situations arise - such as breakdowns or other incidents - that require swift analysis of the issue, its cause and its remedy. Also, as communication systems become more sophisticated their use in areas, other than direct data flow, become available. The importance of communication, its development, and new areas being impacted by communication is the subject of this Paper.

Jan 1, 1997

By Laajalehto K

The basic condition necessary for flotation is hydrophobicity of the surface of the mineral to be floated. For sulphides, this condition usually requires treatment with a collector solution. The conditions for this treatment have until recently usually been chosen by the trial and error principle which has indeed been working relatively well under favourable conditions; ie for simple homogeneous ores. However, the present tendency to increasing use of complex and often relatively lean ores sets increasing requirements for the control of the flotation process. This development is the reason for the present rapid development of process control methods in flotation. In addition to the already well-established practices of pH and reagent feed controls, the importance of measuring and controlling the electrochemical potential of the ore particles to be floated is recognised in the case of sufficiently conductive minerals. In fact, the electrochemical potential seems to be the basic quantity determining the flotation behaviour of such relatively well-conducting minerals as sulphides. Since the hydrophobicity of the mineral and, hence, its flotation properties are ultimately determined by the composition and structure of its surface, information on these under different process conditions is important for design and operation of efficient flotation processes. The basic requirement set for the methods used for obtaining this information is high surface sensitivity of the method. The recent rapid development of surface characterisation has produced several methods which fulfil this requirement. Their application to the problem of characterising surfaces of mineral samples in contact with collector solution is, however, often complicated. The main reason for this is the vacuum environment necessary for the measurement. In the case of flotation experiments this means that in most of these methods the measurement cannot be made in situ, but the sample must be extracted from the liquid and subsequently evacuated in the vacuum chamber of the instrument. It is essential to carry out these steps so as to avoid to the extent possible changes in the sample surface. For the purpose of establishing whether this has been accomplished it is important to compare the results of methods operating in vacuum with some available in situ method. An optimal choice of methods seems therefore to be a combination of the available powerful vacuum methods with in situ measurements. The most usual combination seems to be X-ray photoelectron spectroscopy (XPS or ESCA), Fourier transform infrared spectroscopy (FTIR) and electrochemical measurements. This choice combines the unique possibilities for direct elemental and chemical characterisation offered by XPS (Cecile, 1985) with the in situ capability of FTIR and electrochemistry. In the XPS measurements, it is essential to apply a special sample handling technique to avoid loss or damage of some sensitive species of the collector-based layer on the mineral surface. In the following will be given some examples of the application of the XPS technique in combination with electrochemical methods of sample treatment to studies of the layer formed on sulphide substrates in ethyl xanthate (EX)

Jan 1, 1993

By Polthier K

A short discussion of the salient aspects of a dispersed flow model in relation to the gas flow in blast furnaces is given. The use of the theory in assessing vessel performance is mentioned. Tracer results of a blast furnace (688 m3) from three furnace levels and different radial positions are analysed and results presented as D/ud values. The significance of the shapes of experimental tracer curves are included and comparison is made with results obtained on other furnaces.

Jan 1, 1975

South Africa is the world's largest producer of gold. The survival of its gold mining industry is dependent, to a large extent, on the successful implementation of new mining technology which reduces the operating costs. Gold mines of the country have a record of a high operational cost per tonne of rock excavated. The geology of the gold-bearing rock, in addition to the mining depth and the gold recoverable grade, profoundly affect the profitability of the industry. Among the other mining operations, drilling and blasting take a fair share of the mining cost. It is therefore proper to implement a dynamic approach of technological review aimed at combating the escalation of mining costs. Over the years, the industry has moved away from labour intensive activities. Mechanised operations are introduced where possible. Management techniques are oriented more towards better utilisation of human resources and machinery so as to enhance productivity in the stopes. This paper addresses the issue with particular reference to blasting operations in the stopes of deep gold mines. It reviews the conventional drilling and blasting techniques. It outlines some innovative changes brought about in the course of recent years with the aim of optimising productivity and the stope efficiency in particular. It focusses on the peculiarities of the blasting technology in deep mines. It discusses the issue of interaction between the high stress fields underground and the blasting generated stresses on rock fragmentation, as well as their impact on the remaining excavations. It anticipates the concept of the new technology of selective blasting in stoping. Finally it puts forward the crucial role played by management of the human factor underground.

Jan 1, 1995

By Daxian Z, Youdi Z, Shucai Y

The Huolinhe surface mine is a very large-scale surface coal mine, located in the north-east area of China with a production rate of 1.2 Mtpa. Its coal haulage system has a large capacity, long transportation line and high degree of automation. The system comprises two crushing plants, many belt conveyors, four surge bunkers, one loading bunker, one coal storage and five end product bunkers. In this paper, the network patterns of semi-continuous systems in surface mines are studied, the reliability calculation methods and a simulation model are established and the software for computing the reliability of a semi-continuous system is worked out. By considering the whole coal haulage system in the Huolinhe surface mine, the authors developed the system reliability-numerical simulation method. The steps and the computing results of this method are described in detail. Through the calculation, we can master the present situation of system reliability and the main factors impairing system reliability, expose the system weak links, put forward the ways of enhancing system reliability and furnish the basis for improving the system and equipment. The way of increasing capacity and methods of enhancing system reliability are further raised.

Jan 1, 1995

When a thin film of volatile matter is deposited under vacuum on a polished coal surface, and the coated surface is examined microscopically in piano--polarized reflected light, colour changes are observed characteristic of the various macerals present. The colour changes appear to be mainly due to interference between light reflected at the upper surface of the film and at the film/coal interface. A variety of source materials for the volatile matter required have been tested, including powdered bituminous coal, coal tars, boron oxide, and certain resins.

Jan 1, 1969

By C Hertle

GHD-Black & Veatch (GHD-BV) have completed design and specification of the ash thickening plant at Tarong Power Station, including operation of a pilot plant. Construction of the plant is in progress and commissioning is planned for early-2004. The objective of the new plant is to convert the low concentration (lean phase) ash slurry currently generated by the power station into concentrated slurry which will then be pumped to the existing ash dam. Water recovered from the lean slurry will be returned to the power station for reuse. The drivers behind this project are to extend the life of the ash dam and to reduce water pumping costs. A maximum flow of 1000 litres per second is expected in the thickening plant. The process involves a screening phase, which removes large material that could cause blockages or equipment damage. A 50 metre diameter thickener then concentrates the screened lean ash slurry to 55 - 60 per cent w/w solids. In addition, the thickener plant will allow the harvesting of floating cenospheres (hollow, spherical ash particles) from the lean slurry. Cenospheres are currently collected from the surface of the ash dam and drained on a pad adjacent to the dam. The new system will use a surface skimmer to remove the cenospheres from the thickener and transfer them to settling ponds for further classification. The settling ponds simulate the detention on the existing ash dam, and allow entrained fine ash and slow settling cenospheres time to settle. As settling occurs in ponds, the slow settling cenospheres can be completely recovered whereas when they settle in the dam, the opportunity for recovery is lost. Cenospheres are a valuable by-product produced during the combustion process, and recycling of this material reduces the waste generated by the power station. Water recovered from the thickener drains to a three megalitre reservoir. Water is drawn from the reservoir for thickener plant service water and various other uses in the power station. The bulk of the water is used to sluice ash from the power station to the thickening plant. In the current configuration, surface water from the ash dam is reused but must be pumped several kilometres back up to the power station. The dam also holds an inventory of several thousand megalitres of water and has significant evaporative losses. Therefore the current raw water make up demand is substantial. In addition, some areas of the power station traditionally using raw water will be modified as part of this project to allow the use of recovered water, further reducing the raw water demand. The design incorporates many features of sustainable water management. By more effectively recovering water from the lean ash slurry, the amount of raw water make up required by the system will be significantly reduced. This method of water recovery provides a more sustainable and energy efficient ash-transport mechanism.

Jan 1, 2003

Vaal Reefs Mine annually produces some 75 tonnes of gold. Stoping operations, using a scattered mining method, are conducted on several reef horizons within Witwatersrand Supergroup metasediments of the Klerksdorp Goldfield. Current grades average 7.19 g/t Au over a 133cm stoping width. The reef horizons, of which the Vaal Reef is the most important, consists of 2.9Ga palaeoplacer deposits at the base of low angle unconformities. Typically, a reef comprises a mature quartz and chert conglomerate with a siliceous matrix and intergranular pyrite and carbon. Geologists are primarily responsible for underground mapping and supervising of drilling programs. To a lesser extent they are involved with sampling, grade control, ore reserve estimation, mine planning and rock mechanics. Due to a general decline in grades of gold mines, an escalation of production costs, and with the current weak gold price, it has become essential to improve production efficiencies. Consequently the role of the mine geologist has moved away from that of simply keeping the mining people "on reef'. Greater emphasis is being placed on refining geological models to assist in selective mining of the reef and investigations of secondary reef horizons are encouraged. Exploration within fault losses and re-evaluation of pillars is important, and geologists are becoming more involved with sampling and grade control exercises.

Jan 1, 1990

By White A, Price G

The main assets of a mining company are its orebodies; the second are the people who find and use them.The graphs in Figure 1 were derived from a paper by Rob Macdonald of Rothschild Australia presented to The AusIMM Centenary Conference in Adelaide earlier this year. They show that the value of the industry on the Australian Stock Exchange halved over the past decade, despite the re-investment of capital equivalent to its full market capitalisation. Why is this so? The average dividend yields for the ASX Mining Index was never above five per cent during that period and barely averaged 2.5 per cent. Why then is $Ai million capital re-investment per employee since 1960 not enough to generate a rate of return to investors better than lousy bank interest? Do the investing public no longer regard our industry's assets to be world class?

Jan 1, 1993

BHP Steel International's Newcastle blast. furnaces have operated since their caimissioning on cake based on local low rank coals. In the early 1960's Newcastle coke was believed to be the weakest in the world. Newcastle coke now supports a blast furnace operation with a productivity of 2.1 t/d.rn IV, a fuel rate of 490 kg/t and a coke rate of 415 kg/t. This coke is nuudv from blonds of lcxni and southern Sydney basin coals with blend Ro nex in the range 0.94 - 1.01. Blast furnace performance in periods of differing coal blends is conjured. The relationship between coal aril coke quality indices and blast. fin-mice perforrnarcc.e is discussed as well as the relevance of conventional coke tests. New BHP coke tests are referred to.

Jan 1, 1987

By Khosia NK, Ravishankar SA, Sankar TAP

Alumina reduction in Rajhara iron ore slimes essentially involves separation of hematite from gibbsite in relatively coarser fraction and from kaolinite in the finer fraction. Selective dispersion flocculation studies on synthetic mixtures clearly indicated that while it was possible to achieve almost perfect separation of hematite from kaolinite using starch and PAMX (modified polyacrylamide containing hydroxamate functional groups) flocculants, no selectivity was observed in iron oxide-alumina system. A schematic flowsheet suggested on the basis of this work for the beneficiation of Indian ore slimes thus consists of classification in a hydrocyclone, followed by selective dispersion of coarse fraction (underflow) and selective flocculation of the overflow fraction. Starting with a feed assaying 46 per cent Fe and 11.6 per cent A1203, a concentrate assaying 60 per cent Fe and 4.7 per cent A1203 could be produced at an overall iron recovery of 60 per cent using conventional Reagents.

Jan 1, 1993

Shear-flocculation is one of a munber of potential processes for upgrading deposits of finely-grained minerals and, more generally, for separating different types of particles suspended in a fluid.The smaller the particle the more likely it is to follow the fluid streamlines, or be entrained within turbulent eddies, and the less likely it is to deviate from the streamline and attach to bubbles (froth flotation), other particles (selective flocculation) or magnetic poles (wet magnetic separation). As shown in Figure I, a number of ingenious ideas have been proposed to overcome this effect. The suspended particles are assumed to be 1 - 10 µm.Thus, the efficiency of attaching ultrafme particles of the valuable component (solid circles) to air bubbles, as in process A, is poor. The efficiency may be improved by attaching the particles to oil droplets (Ralston, Kart and Newcombe, 1984) to form agglomerates that rise or sink (B), to magnetic particles (C) (Parsonage, 1988) to allow recovery in a magnetic separator (D), to other particles to form aggregates (E) that are then either attached to bubbles (F) or recovered by sedimentation (G) (Warren, 1992), and to pieces of polyethylene (Rubio and Baltar, 1991) that rise or sink (H).In A, C, E, F and H, the forces that are generally used to ensure collisions result in adhesion are hydrophobic forces, hydrodynamic forces and inertial forces (Warren, 1992). These drag particles from the streamlines to allow particle-particle adhesion. In B and E, soluble polymeric molecules have been added to bridge between particles as they approach closely during a collision.The second major consideration is selectivity. Selective adsorption of the hydrophobe or polymer onto the valuable particles is the key. Many subtle effects of surface chemistry are involved in obtaining adequate selectivity. A complication in real systems is that the initial suspension is often naturally coagulated and needs to be dispersed before being selectively flocculated.

Jan 1, 1993

By Beattie MJV

Widely diverse mechanisms exist for the action of a range of selective sulphide flotation depressants. Collector desorp- tion, leaching, competitive adsorption, formation of hydrophilic reaction-product coatings, action as reducing agents, and action as lattice-oxidizing agents are discussed. Detailed attention is focused on the latter two mechanisms. Recent works on copper depressants particularly for copper-molybdenum separations, and oxidizing agents enabling arsenopyrite- pyrite separations, are presented and discussed.

Jan 1, 1984

By Phillips D. N, Herbert H. K, Fletcher A. C, Lewis R. K

Quartzite is a common feedstock used for the production of silicon by reduction at high temperatures in a submerged electric arc furnace. Silica fume, formed as a by-product in this process, contains crystalline silica in the respirable fraction. The crystalline silica in the fume represents entrained quartz derived from unreacted quartzite raw material within the furnace. A knowledge of the fragmentation of quartzite feedstock, in response to thermal disaggregation in the furnace, is important in feedstock selection to help minimise (a) the amount of crystalline silica in fume, critical from an occupational health and safety perspective, and (b) impurity levels necessary to achieve the highest possible purity of product silicon. In this study, a series of quartzites has been assessed in terms of the above requirements and correlations drawn between mineralogical and chemical characteristics. Alkaline solubility correlates with grain-size and level of stored strain in the quartz matrix. Grain-size affects the surface area available for attack while stored strain enhances the chemical reactivity of the strained matrix as well as profoundly influencing the disaggregation and microfracturing characteristics of strained grains and, hence, available surface area for chemical reaction.

Jan 1, 1995

The underground coal mining industry in Australia has, in the last 30 years, undergone a revolution in production methods, techniques and results probably unparalleled elsewhere in the world. It can lay claim not only to leading the fight against pneumoconiosis and setting high safety standards generally, but has at the same time recorded comparatively high rates of increase in output per man shift. The latter has been achieved as a result of progressively matching the latest in production and underground transportation equipment with significant changes in seam development and extraction techniques and the introduction of stress-relieving extraction methods unique to the world scene. However, the seam recovery factor is still too low. Apart from the overall objectives of maximising production and commercial returns with the greatest safety, there must be a concentration towards maximising seam recovery, particularly in high seams. The search will continue for systems which are more completely continuous mining operations than the present stop-go operations, with longwall having long term potential in this regard, but as yet not sufficiently developed to engender confidence for its more general use. Techniques developed in the last 10 years make the development and extraction of deeper seams, perhaps to 2500 feet or more, feasible with continuous miners as well as longwall. The future will see a greater use of continuous shifts at mines, larger mines with more sophisticated management organisation, extensible belts at the face, better systems of immediate roof support at the face, remote operation of face equipment, greater use of roof bolts and the longer roof cables. With commercial confidence in coal mining now virtually assured to at least the turn of the century, the stage is set for heavy capital development in the industry which will undoubtedly include major research into the whole area of mining methods and equipment. We must ensure that our contribution to such research equitably matches other coal producing countries.

Jan 1, 1975