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By Bernhard J. Ralph

In refractory gold ores much of the gold occurs in sub-microscopic form in sulfide minerals, most commonly pyrite and arsenopyrite Bacterial leaching is being developed as a pretreatment for these minerals to aid the liberation of gold and a variety of extracting reagents. This paper reviews the nature of the principal micro-organisms involved, the effects of various physico-chemical factors on the rate and extent of extraction, and likely mechanisms involved.

Jan 1, 1989

By M. Timucin

Phase relations within the condensed Cu-Cu2S-PbS-Pb region of the Cu-Pb-S ternary were investigated. The boundaries of the ternary liquid-miscibility gap were redrawn, and the directions of the tie-lines were established by the quenching of samples equilibrated in evacuated and sealed silica capsules at 1473 K. The activities of lead in sulphur-saturated Cu-Pb alloys along the boundary of the miscibility gap were measured by the dew-point technique at 1473 K. From the tie-line distributions, measured lead activities, known activities of the Cu2S-PbS join, and the ternary Gibbs-Duhem integration, consistent sets of activities for lead and copper and partial pressures of sulphur were obtained along the ternary miscibility gap at 1473 K.

Jan 1, 1989

By T. O. Kuhl

The Royal-Mountain King Project is 7.2 kilometers (4.5 miles) northwest of Copperopolis, California. Reserves of 8,250,000 t (9,100,000 st) at 2.32 g/t (0.068 oz/st) gold will be processed at 2500 t/d (2750 st/d) from three pits. Production is scheduled to begin the first quarter of 1989. District geology consists of northwest trending sequences of Jurassic meta-sedimentary and meta-volcanic rocks. Three ore bodies are located along the Hodson fault which trends northwest and dips 40 degrees northeast. The Gold Knoll and North Pit ore bodies are hosted in carbonate and silica altered meta-volcanic rocks whereas the Skyrocket ore body is hosted in quartz stockwork zones in meta-sedimentary rocks. Gold is present as inclusions and micro-veinlets in pyrite.

Jan 1, 1989

By H. R. G. Steeghs

Recently developed organic binder systems have the advantage of eliminating bentonite contamination. This results in better chemically reactive taconite pellets. Both acid and fluxed pellets show increased R40 reducibilities, whereas mechanical and physical properties of the taconite pellets are not adversely affected. Blast furnace performance of these pellets is excellent, and substantial economic benefits are achieved.

Jan 1, 1989

By C. T. Christensen

The paper gives an outline of the design, installation and performance of a series of mooring and berthing dolphins for a major ferry berth outside the port of Elsinore, Denmark. The Dolphins are large cylindrical bottle shaped and open ended steel piles vibrated into the sandy seabed. They are subsequently equipped with prefabricated fender units. Vehicle access to the ferry is via a fixed ramp and a semi-submerged linkspan. Supplementary passenger access is via a covered gangway steel bridge from an existing gangway facility to a midship door in the ferry«

Jan 1, 1989

By R. E. Brewer

Pilot scale flotation tests were conducted with a 1-ft-diam column at the Barrick Resources (USA) Mercur mine, Tooele County, UT, to scavenge unleached (0.01 to 0.018 oz/st) gold values from the tailings of a carbon-in-leach (CIL) circuit. The optimal recovery was 35 pct of the unamenable-to-leaching gold, at a grade of 0.353 ounces of gold per short ton, using a mixture of dithiophosphate, xanthate, and diesel fuel as a collector. This was achieved by floating approximately 1.6 wt pct of the CIL tailings. The gold values are believed to be contained in arsenic-bearing minerals, attrited carbon, and carbonaceous material in the ore. Redox potentials were measured with a gold electrode during the conditioning stage prior to flotation. The correlation between flotation recovery and redox potential values could be used to control reagent additions. Treatment of a previously leached and weathered tailings material, averaging about 0.055 ounces of gold per short ton, was also investigated using the column. The tailings were first water leached at approximately 600 C, and the water-leached tailings, which contained approximately 0.03 ounces of gold per short ton, were then fed to the column flotation unit. The effects of pH and sodium sulfide addition on gold flotation recovery and redox potentials were examined. maximum gold recovery, 36 pct, was achieved at pH 8.5 with a sodium sulfide addition of 0.18 lb/st.

Jan 1, 1989

By A. W. Khair

This paper presents an analysis of fracture depth and intensity due to subsidence over the longwall panel. Sonic reflection techniques were utilized to determine fracture depth, and a variation of p-wave velocity was used as an indication of the fracture intensity. Instrumentation has been tested for consistency and accuracy first in the laboratory using small scale models, then applied in the field in two mine sites with different mining geometry and geologic conditions. A new sonic viewer was utilized for sonic velocity measurements. Regular hammering method was on acoustic source. The results were concurrent with monitored horizontal strain profiles and measured open fractures over the longwall panels.

Jan 1, 1989

By Gary Kahn

In this document the VODR is discussed from a technical point of view and is intended to give the reader a feel for the design of the instrument, its technical specifications, and its limitations. It is not intended as a tutorial on the use of the instrument in the field.

Jan 1, 1989

By Harold R. Newman

The performance of Ecuador's mineral industry continued to be affected not only by depressed oil prices in recent years but also by natural disasters. In March 1987, Ecuador canceled foreign debt payments for the rest of the year and appealed for international aid because of a series of earth-quakes that destroyed villages and crippled the nation's oil industry. The earthquake destroyed a key section of the country's main oil pipeline and forced a halt to production and shipment of Ecuador's most important export product. Ecuador produces 240,000 barrels of oil per day and exports 144,000 barrels daily. Oil accounts for 60% of the nation's hard currency earnings. The Government of Ecuador asked the Organization of Petroleum Exporting Countries and other oil-producing countries to assume Ecuador's oil sales commitments. Ecuador agreed to pay the countries back in an equivalent amount of oil when it was able to resume exports.

Jan 1, 1989

By S. P. Mehrotra, P. C. Kapur

A phase-species classification is suggested for the mathematical models of flotation kinetics. Important models are discussed and the structure of their rate constants and parameters is analyzed. Split or enhancement factors are formulated for different kinetic models. The steady state dynamics of the flotation circuits can always be described in terms of these factors. For simulation of circuits, feed is characterized in a formal manner starting from a multivariate distribution of particles in flotation rate, size and mineral content. Synthesis of optimum circuits which simultaneously searches for the best process variables and structural parameters from a generalized master network is described. Trends in the areas of search algorithms, role of middlings and feed identification etc. are indicated.

Jan 1, 1989

By Jackson E

The general level of awareness amongst members of the professions that they are faced with an increasing number of claims for breaches of their professional duty was dramatically heightened by the decision of Rogers J. at first instance in Cambridge Credit Corporation v Hutcheson (1985) 3 ACLR when the auditors of the failed company were found liable for breach of contract and faced a damages award of $145 million - well in excess of their insurance cover. No comfort should be found in the fact that this decision was overturned on appeal, for that result rested on the issue of whether there had been a causal connection between the breach of contract which had occurred and the loss suffered rather than on the fundamental principle of auditors' liability.

Jan 1, 1989

By G. K. Rogers

The portal, which is the near-horizontal, surface point of entry to an underground excavation, can often be an exceedingly difficult area in terms of ground control. Surface and subsurface failures at portals, as discerned during a study involving over 300 case histories, are unfortunately, common. To aid in the engineering evaluation of portals, the Geomechanics Classification System was appended with discontinuity orientation assessment values and support/excavation guidelines. Also, a design model utilizing RMR predicted rock loads in conjunction with half-dome theory is proposed for the most common type of portal failure. Other pertinent comments and recommendations relating to portal stability are included.

Jan 1, 1989

By J. Osterberg

A new device has been developed for load testing driven piles and drilled shafts which consists of an hydraulic jack or bellows which has a telltale rod fastended to the bottom. The rod extends upward to the surface through a pressure pipe. When pressure is applied, the jack or bellows expands, applying an equal upward and downward load at the bottom. The downward movement at the bottom is indicated by the rod and the upward movement is indicated by the movement at the top. Thus, upward and downward load-deflection curves can be drawn. As load increases, failure will occur either in end bearing or friction. Results of field installations are described. Total loads of up to 1,100 tons metric have been used. The method obviates the need for the reaction load required for the conventional pile loading test and separates friction and end bearing. It is especially advantageous for use over water, in crowded spaces and for inclined piles.

Jan 1, 1989

By H. Mori

Construction of cast-in-place piles with enlarged bases has become popular in the cities in Japan facing to the sea coast, where the subground soil is soft alluvium deposited to depths often exceeding 30 m. The groundwater table is a few meters below the ground surface. Skin friction of piles may become negative due to ground subsidence or reduced due to liquefaction of loose sand during an earthquake. To support highrise buildings, depths of bearing strata to which piles are embedded often exceed 50 m. Due to such geotechnical conditions, methods and equipment to build cast-in-place concrete piles mainly built by the reverse circulation method have been developed since the 1970s. In the first half of this paper, the authors review the cur-rent practise of building cast-in-place piles with enlarged bases. Then they introduce the TFP system developed in recent years, and discuss about the procedures to control and monitor enlarging of bases.

Jan 1, 1989

By H. Haas

European coal mines are facing a very difficult situation. Despite a steadily increasing world energy consumption, the sales of European coal mines have been going down and production has to be adapted. The reason is the collapse of energy prices aided by the decreasing rate of U.S. $ to Deutschmark in the last few years. The problems are not due to the development of European mines themselves. Assured energy supplies are an important condition for the health of a nation's economy. Contribution of domestic energy production ensures some degree of independence from world market fluctuations as to supply volumes and price, and maintaining jobs and should be achieved within the framework of economic constellations. Governmental energy programs are planned towards meeting this end.

Jan 1, 1989

By Syd S. Peng

Coal mine ground control is the science of the application of rock mechanics principles to coal mining operations. More acceptance of ground control techniques by the US coal mining industry has been seen in the 1980s. It has been demonstrated many times that a proper ground control design is key to a successful coal mining operation. However, numerous in-mine applications of various ground control techniques by the author indicate that cur¬rent techniques need improvement. The biggest problem in coal mine ground control is that miners are dealing with materials of rapidly varying properties and occurrence. And only the exposed surface can be identified positively. Thus, in attempting to solve the ground control problems, many unknown factors are assumed. Some of these problems deriving from such assumptions are discussed here. Coal pillars There are two types of coal pillars - barrier and chain pillars - depending on the purpose. Barrier pillars are those located between panels or sections or mines. Their objective is to isolate the mined-out effects of one from the other. Chain pillars are characteristic of room-and-pillar mining. They are designed to support the overburden load and protect the surrounding entries and crosscuts. Pillar design is the most popular and, frequently, the only ground control technique employed by coal operators for mine design. There are many pillar design formulae available (Bieniawski, 1983; Peng, 1986). Nearly all consider both size and width/height effects. Specifically, pillar strength decreases with increases in pillar size and increases with increase in the ratio of width to height. However, the manner of those changes varies with investigators. Consequently, the pillar size determined varies considerably from investigator to investigator. And the variation grows much more pronounced as the seam depth increases (Fig. 1). The question, then, is which one should be used? One may say each formula is developed for a particular coalfield. A particular formula may have been used to design a pillar, which has not failed. Does that mean it was over designed? Not necessarily, because no one can confirm its stated "safety factor." Recent case studies (Peng, 1986; Tang and Peng, 1988) show that all pillar formulae are too conservative for chain pillar design in room-and-pillar mines due to the following two problems: • Uncertainty about in situ pillar strength. All formulae employ uniaxial compressive strength of selected samples tested in the laboratory and scaled to that for underground pillars. The scaling factors are not well proven. In situ testings by Bieniawski (1969) suggested that 1.5 m (5 ft) pillars are representative of in situ pillars that, after being tested in various US coal mines, are not universally applicable. • Uncertainty about the actual loading on the pillar. The most frequently used tributary loading theory defines the loading as total overburden weight tributary to each pillar (from roofline to surface). This is too conservative when it applies to coal measure rocks. The overburden consists of layered strata of different stiffness. Many stiffer strata will self-support over small roof spans. Depending on the location of these strata above the coal seam, it will reduce pillar loading in various proportions. It follows that total structural analysis using, for instance, finite element method is more appropriate. It can take into account the interaction of roof and floor strata with coal. This has been demonstrated by Peng et al. (1986,1988) on several case studies. However, the validity of the finite element structural analysis depends on the accuracy of in

Jan 1, 1989

By T Guiliani, F Ottuonye

Explosives casting is gaining increasing popularity as an overburden removal method in strip mining because the coats of using explosives to cast a percentage of the overburden to the spoil are lower than the costs of using stripping shovels or draglines to do all the overburden removal. This is due to the rising capital and operating costs of draglines and shovels.

Jan 1, 1989

By F. L. D. Cloete, M. C. Coetzee

This study was aimed at a comparison of the efectiveness of a new axial-flow type of mixer impeller (the Prochem design) with the traditional inclined-blade turbine. The intended application of the mixers was in carbon-in-pulp plants for the extraction of gold from cyanide-leached pulps. The first part of the project involved water and ion-exchange resin, and measurement of the power drawn by the various sizes of impeller to fully suspend the resin. The rate of reaction between the resin and the solution was measured as a function of the power input to the mixer. In the second part of the project, use was made of activated carbon, silver cyanide solutions, and ore pulps. The rate of absorption of silver from the solutions and pulps was determined, as well as the rate of attrition of the activated carbon caused by the various impellers in clear water. The Prochem design of axial-flow impeller was shown to fully suspend solids at only one-quarter of the power requireabyan inclined-blade turbine of similar size. The axial-flow pattern produced was responsible for the more uniform vertical concentration profile of suspended beads produced by the Prochem design. These measurements verified the observations of other researchers that the rate of reaction is not affected by the ;design of impeller provided that al the solids are fully suspended. The Prochem design of impeller therefore achieved the same reaction rate as the conventional turbine at a quarter of the power input. The atrition rates of activated carbon could be correlated, in terms of the energy absorbed, by the same equation for al the impellers. Higher concentrations of activated carbon increased the amount of carbon fines produced. These results emphasize the importance of designing mixers for minimum power consumption.

Jan 1, 1989

By H. J. Handewith, W. D. Coski

This paper describes the development and testing of the RAMEX excavation system. Incorporating a synergy of low velocity, high energy impact and kerf cutting, this machine offers a competitive alternative to drilling and blasting in hard rock. It is a boom mining machine that incorporates the features of a lightweight roadheader and it can mine nearly any shape opening in hard rock. The RAMEX Tunneler has been developed to satisfy industry demands for a non-explosive, flexible, continuous and rapid underground rock excavation system. It will produce minimum ground vibration in the urban environment and allow the flexibility necessary for thin seam mining conditions. It will also reduce initial ground support costs and has a minimum impact on rock integrity. Developed by RAMEX Systems with cooperative research provided by the U.S. Bureau of Mines, this system, could produce the next step in the continuing evolution of mechanical mining systems.

Jan 1, 1989

By Mark C. Williams, Thomas P. Meloy

Particle shape characterization is a complex task made more difficult because of the human eye's sophisticated recognition of shapes, giving rise to the assumption that shape analysis is considered a simple problem. Further exacerbating the problem is the question of whether particles have a general shape. Old and new shape measuring techniques are discussed, particularly the new image analysis methods techniques such as Fourier, Haar, Walsh and Delta. Problems with the current image analysis equipment and future research equipment needs are presented.

Jan 1, 1989