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By Bangerter PJ

The use of gravity concentration is, and has always been, the conventional primary method for gold recovery from alluvial deposits. The development of high capacity cone concentrators and metallurgically efficient wash-waterless spiral separators has had some impact in the technology for alluvial gold processing, but perhaps more significantly has led to the relatively recent use of this gravity concentration technology in grinding circuits of hard rock ore for "coarse" gold removal and for scavenging gold locked in sulphides from cyanidation tailings streams.Gravity concentration systems are relatively low-cost, non-polluting and energy efficient; and their judicial use in gold treatment plants can significantly reduce overall capital and operating costs.The application of modern gravity concentration technology to hard-rock and alluvial gold ore treatment is discussed. Flowsheets and test and operating data from a number of gold processing operations incorporating gravity concentration treatment are presented.

Jan 1, 1984

By J. F. Labuz

Fracture tests were conducted on subsize specimens of Charcoal granite to demonstrate that the extent of the nonlinear region at the crack tip can be significant. The model of the fracture process considers an effective crack length as a traction free portion plus a process zone where closing stresses act; this zone is identified by microcracking and interlocking. A singularity is allowed at the effective crack tip. The effective stress intensity factor is the superposition of the stress intensities due to the effective crack and the process zone. By assuming that the closing stress is a linear function, it is shown that a process zone length of approximately one-third the effective crack is needed to match the compliance-determined crack length.

Jan 1, 1984

By D. D. Bolstad, S. M. Dar, T. W. Smelser, H. C. Pettibone

The use of roof bolt supports has reduced the number of fatal and nonfatal roof fall accidents in coal mines. Roof fall accidents, however, still occur far too frequently. Roof bolting plans are based almost entirely on trial and error, which inevitably leads to underdesign or overdesign with regard to bolt length, spacing, tension, and bolt type for the specific conditions. Underdesign poses safety problems, and overdesign leads to unnecessary costs. Guidelines are needed to select and design optimum roof-bolt plans that will maximize safety and minimize cost. Despite the use of 100 million roof bolts per year, the theory of roof bolting remains underdeveloped. Underground tests designed to provide this knowledge have been only partially successful owing to the many uncontrollable geologic variables present in underground mining situations. The Bureau of Mines believes that the best approach is to conduct a laboratory model study in correlation with finite-element analysis (FEA) and field verification, where these variables can be tightly controlled and measured. A physical model allows precise performance measurement of different bolt types as a function of a wide range of precisely measured parameters. Although the model being used is idealized and limited in size, it serves as a reliable basis for confirming the mechanism of rock reinforcement by bolting and the accuracy of the computer FEA approach to modeling mining problems.

Jan 1, 1984

By Slechta JJ

The performance of a hydrocyclone treating fine coal has been examined over a wide range of feed and operating conditions.The results were expressed in terms of partition curves from which the water split to the oversize flowstream,the corrected separation size and reduced partition curves were determined-.The following conclusions were obtained. (a) The water split to the oversize flowstream was found to be dependent upon the vortex finder and spigot diameters of the cyclone and the flowrate and solids content of the feed slurry. (b) The corrected separation size was dependent on the solids content of the feed,and the vortex finder and spigot diameters.The hydraulic pressure (or flowrate) of the feed slurry did not have a significant effect.This phenomenon could be explained in terms of crowding of the particles at the Spigot.

Jan 1, 1984

By Jacob H. Masliyah

The dynamic simulation of a gravity separation vessel (a high throughput classifier) has been developed. The feed slurry was assumed to contain light (oil droplets) and heavy (mineral solids) particulates of various size. The feed slurry was characterized by the particle size distribution of both the light and the heavy particles. The equations describing the slip velocity for each specie and those defining the time variation of each specie concentration were solved implicitly using Runge-Kutta algorithm. The dynamic simulation was capable of predicting the movement of the froth layer and the density variation of the under- flow. Field data are in agreement with the simulation model and it is shown how this model could be used to develop a control strategy.

Jan 1, 1984

By J. C. Wynn

This paper outlines research conducted by the US Geological Survey on the geophysical signatures of chromite. Results of the chromite study highlight the importance of a laboratory research Phase (petrophysical and petrographic studies) at the beginning of work on a new commodity; a realistic ore deposition model to serve as a conceptual framework, and the necessity to continually test, refine, and modify it during the study; and indirect geologic/geochemical indicators, secondary associations, and the use of multiple physical properties. The keystone to the success of the study is frequent and substantive dialogue among geologists, geophysicists, and geochemists.

Jan 1, 1984

By Reginald E. Reid

Mining on Bureau of Land Management (BLM) administered lands is affected by Federal laws and regulations requiring the mining industry to plan for the environmental consequences of surface disturbance. Regardless of the requirements for obtaining a claim, permit, lease or contract to mine, a notice or a mining and reclamation plan will be submitted and an acceptable environmental document must be prepared prior to mining. A bond may be required based on the results of the environmental evaluation, public interest and the operator's past history of compliance. In several areas, Federal requirements are different from California's requirements under their Surface Mine and Reclamation Act (SMARA). Therefore, the BLM is negotiating with the State in order to work out problem areas of responsibility and duplication of effort.

Jan 1, 1984

By W. A. Rickelton

Trialkylphosphine sulphides, in contrast to their well known oxide analogues (1,2,3,4), have received comparatively little attention as metal extractants and previous studies have been biased toward analytical rather than commercial solvent extraction applications (5,6,7). The sulphides are soft Lewis bases and only from complexes readily with the limited number of metals in the periodic table which can be classified as soft acids (8) e.g. Ag+, Hg2+ and Pd2+. Consequently, these compounds tend to be more selective than the broad-spectrum, hard-base, phosphine oxide extractants such-as TOPO (trioctylphosphine oxide). The purpose of this paper is to describe a potential application of one phosphine sulphide, CYANEX® 471X extractant, in the selective recovery of silver from base metal sulphate solutions. CYANEX 471X is triisobutylphosphine sulphide (TIBPS).

Jan 1, 1984

By B. H. Smith

"Most of the discoveries of nickel sulphide deposits in Western Australia have followed the search for gossans. The chances of further discoveries depend on improving our understanding of the cover of strongly leached and transported materials that obscure approximately 85% of the area of the Yilgarn Block that has nickel sulphide mineralization potential. The lateritic profiles that are observed on the Yilgarn Block today were formed over a period of more than 100 m.y. of warm and humid climates. This lateritized land surface has been preserved by induration during subsequent arid climates as well as by the structural stability of the Yilgarn Block.In geochemical surveys of lateritied terrain samples have to be taken from at least the saprolite zone usually by drilling so that confident predictions can be made of the significance of analytical data. Account must be taken of the mineralogy of samples, as well as the nature of the horizon of a laterite profile that is being sampled, owing to the concentrating effects on trace elements of Fe and Mn oxides.Multivariate techniques have been applied successfully to analytical data in gossan recognition when textural evidence is ambiguous. Pathfinder geochemistry has also been used in gossan recognition and the most significant recent advance has come from studies of platinum group metals in nickel sulphides and their dispersion during weathering."

Jan 1, 1984

By R. J. Shaffer

Hydraulic fracturing in rock masses involves complex and coupled processes of fractures propagating in discontinuous media and of fluid flow in discrete channels. The Unconventional Gas Program at LLNL is actively developing numerical models to gain insight in the physics of these coupled processes. This paper describes the current status of the FEFFLAP code, which models fluid-driven discrete fracture propagation in jointed media. We also discuss the results of a preliminary series of physical tests in which hydrofractures were driven across slanted interfaces between dissimilar materials, in blocks loaded in biaxial compression.

Jan 1, 1984

By Robert J. Evans

An in-seam tester, which is a hydraulically activated single-pick instrument to measure and record pick cutting forces, was designed and fabricated to establish criteria necessary for the design and development of a water-jet-assisted rotary drum cutting system using moderate-pressure jets (3,000 to 10,000 psi). Data are presented for cutting trials in a simulated coal block and underground in the Pittsburgh coal seam for water-jet assist and dry cutting. Data analysis indicates that water-jet assist significantly reduces pick forces.

Jan 1, 1984

By I. A. Lange, A. M. Richardson

Although methods for determining shaft lining thickness are well documented, little attention has been given to the design of station breakouts and other related shaft ground support structures. This paper discusses design of selected shaft structures for the Cathedral Bluffs project, a planned 54-kt/d (60,000-stpd) oil shale mine in western Colorado. Design philosophy and construction sequences used in the three completed 520-m (1700 ft) deep, 4.6-m (15 ft) to 10.4-m (34-ft) diameter shafts are described.

Jan 1, 1984

By Pollard D, Meadows N

The presence of impurities which are electropositive to zinc in acid zinc electro- lyte causes changes to deposit morphology and reduced current efficiency. Glue may be added to control some impurity effects, but assaying for animal glue concentration is difficult and seldom done. Measurement of the activation overpotential for zinc deposition by cyclic voltammetry is used in some plants to monitor electrolyte quality and control glue additions. The deposit morphology and current efficiency of zinc deposition from commercial electrolyte were investigated for various glue additions in the presence of increased levels of antimony. Cyclic voltammetry was invest- i,ated as a method of optimizing glue additions in the presence of antimony. Scanning electron microscopy showed deposits characteristic of the impurity element present and the glue addition rate. Cyclic voltammetry measurements showed some correlation between current efficiency and activation polarization potential. The importance of using tankhouse electrolytes where results are to be related to tankhouse operation was noted.

Jan 1, 1984

By S. J. Mitchell

An analysis of bolting reinforcement of several large [approximately 18 m (60 ft) cube] pillars was performed. The many overcoring stress profiles in pillars at the mine were used to produce generalized stress distributions at various stages in pre- and post-failure. A complete stress-deformation curve was estimated from this data. The effect of pillar bolting on the load-deformation behavior was extrapolated from the observed unbolted behavior. Bolting can increase pillar strength by up to 10 percent. The effect of bolting on general mine stability was examined with a short computer analysis. The computer model was calibrated against measurements performed at the mine, and produced good agreement between measured and modeled stresses. The analysis indicated that bolting increases the bolted pillar safety factors in the event of additional pillar failure by a small amount (approximately 5 percent). Progressive pillar failure is unlikely, because arching transfers most load from yielding pillars to large unmined abutments rather than to the smaller panel pillars.

Jan 1, 1984

By M. J. Ferrante

Relative enthalpies of CuBr from 298.15 to 1,301 K were measured at the Bureau of Mines to provide thermodynamic data needed for the advancement of mineral technology. The temperatures of transition were measured by differential scanning calorimetry (DSC) and the standard enthalpies of transition[ (IlH~r) by drop calorimetry. The combined results gave reversible transitions at 657 K with llH~r= 1.10 kcal/mol, at 741 K with lm~r == 0.51 kcal/mol, and at 759 K with an enthalpy of fusion (AH~) of 1.22 kcal/moL ] An anomalous increase in heat capacity preceded the first crystal transition at 657 K. Tabulated values are listed for the standard relative enthalpy, heat capacity, entropy, and Gibbs energy function from 298.15 to 1,500 K. Standard relative enthalpies are also given in equation form and combined with thermodynamic data from the literature to derive values of standard enthalpies of formation and Gibbs energies of formation.

Jan 1, 1984

By W. A. Yuill

A process has been developed for increasing the grade of chalcopyrite concentrates from about 25 percent copper to about 60 percent copper. The concentrates are treated with two steps of autoclaving and then by flotation. Because of the lower associated weight, copper in the concentrates could be shipped and smelted at less cost than untreated concentrates. Use of the process can also increase overall yield from an orebody if a lower grade concentrate is sent to enrichment than would be sent to a smelter. Potential applications of the process would be for treating concentrates that must be transported a long distance for smelting or for treating concentrates so as to increase the capacity of a smelter.

Jan 1, 1984

By Richard J. Stoehr

Man has mined in all his time on earth about 3 billion ounces of gold. About one-half of this has been mined in the past 35 years. This gold is roughly in 3 large holdings: one-third held as reserves in Central Banks; one-third held as personal reserves; and one-third is in jewelry or other fabricated products. The world per capita availability of mined gold is increasing and there are many factors and forces shaping gold's future. Currently, gold has a favorable exchange ratio and this is encouraging many new gold-mining developments. Production is increasing and new techniques are surfacing. The use of gold in the financial markets is increasing in some unique ways and gold is again fulfilling its role as a universal money, making gold's future predictable. Currently, man is mining gold at the rate of approximately 44 million ounces annually and is therefore adding to the total supply of gold approximately 1.5% of newly mined gold each year. This current production plays a small role in the pricing mechanisms since a very large part of the 3 billion ounces mined in all of history is available to the market in one form or another.

Jan 1, 1984

By Edgar O. McAlister

Associated with cordilleran intrusives of intemediate to acidic composition, gold/silver ores are generally found in the intruded host rocks which are adjacent to these intrusives. Generally precious metal deposits lie further from the intrusives than allied base metal deposits. For vented intrusives, the associated volcanics may constitute the intruded rock and form the host for precious metal accumulation. Potential field methods, particularly magnetics, can help to define unseen boundaries of intrusive systems and thus can point to generalized prospecting targets. Other clues arise from the intrusive system type, its emplacement fracturing, the host rock type and local magnetic changes caused by mineralization processes.

Jan 1, 1984

By H. Ikeman

"The highly specialized communication systems used in the mining industry place exacting demands on equipment and transmission media. Safely and reliability of services are perhaps the two most important factors. Fibre optics is ideally suited 10 meet these stringent requirements. Aside from being an intrinsically safe, non-sparking and EMI/RFI immune medium , fibre optics offers greater reliability , higher quality of services and superior flexibility over conventional copper or radio-based communication systems.This paper wilt show how fibre optics can be applied in mining industry applications. Emerging trends and concepts will be presented to show how fibre-optic-based integrated service communication networks and local distribution systems can be implemented.IntroductionCommunication requirements in today's mine s are varied and extensive. The communication system must be rugged , safe and reliable, yet provide an ever increasing amount of high quality services. Presently, these systems are implemented using conventional copper cable. As mining method s and technology advance and the demand for better and more communication services increases, traditional systems quickly reach their limitations. It is under these circumstances that we turn to fibre optic communication systems.Fibre optics is a mature technology which is finding its way into more and more applications worldwide. A fibre optic communication system can provide a level of performance unattainable by conventional cable systems yet ca n be cost competitive. As is well known, fibre optics provides a noise-free, noise-immune, high -capacity communications channel. Glass fibre, being dielectric and non-sparking, is an intrinsically safe communications medium. Clearly, it is ideally suited to the harsh environment present in a mine.From a communication systems point-of-view, the topology of a deep mine is unique. The objective of the systems engineer is to implement a total communications capability throughout this wide spread area. Ideally all classes of services should be accessible throughout the network-an integrated network concept. Recent advances in communications technology combined with fibre optics make this realizable."

Jan 1, 1984

By Toguri JM

A solid electrolyte technique has been used to measure the activity of cobalt in liquid cobalt-gold alloys containing between 0.085 and 0.50 mole fraction of cobalt, and for temperatures from just above the liquidus to around 1550 K. The system exhibits positive deviation from ideality, both in the activities of cobalt and gold, and in the enthalpy and excess entropy of mixing. The results agree with previous measurements using a Knudsen cell - mass spectrometer technique, but differ from those reported for a gas equilibration method. The data have been used to calculate the activity coefficient of cobalt oxide in silica saturated iron silicate slags and to express the solubility of cobalt in such slags as a function of cobalt activity and oxygen pressure.

Jan 1, 1984