Search Documents

By D N. Castendyk, J L. Mauk

The world-class Waihi (>6.6 Moz Au, >41.8 Moz Ag) and adjacent Favona (>0.5 Moz Au) deposits are within a single volcanic-hosted epithermal Au-Ag district located in the southern Coromandel Peninsula, New Zealand. Gold and silver mineralised quartz veins at both deposits are hosted in porphyritic andesite flows of the Waipupu Formation. Both deposits have veins surrounded by intense widespread hydrothermal alteration that is characterised by the assemblage of quartz, pyrite, adularia, illite or interstratified illite-smectite, plus less common chlorite and albite, which is locally overprinted by minor calcite or rare kaolinite. Quantitative mass transfer calculations using Gresen's general metasomatic equation indicate that hydrothermally altered andesite at both deposits is enriched in silicon, potassium, rubidium, barium, sulphur, gold, arsenic and antimony, whereas sodium, strontium and calcium are mostly lost. Iron and magnesium show mixed gain and loss. Element gain or loss can be directly related to the prevailing alteration mineralogy. Addition of potassium, rubidium and barium coupled with the concomitant loss of sodium, strontium and calcium in intensely altered wall rocks corresponds to the replacement of plagioclase by adularia or illite. Partial retention of sodium and calcium reflects the presence of hydrothermal albite and calcite, respectively. Mass balance calculations show distinct element gain and loss that can be related to the intensity and type of alteration mineralogy. However, because most rocks are intensely altered and the progression into less altered peripheral rocks is not observed in this study, the lateral extent of elements gain or loss is unconstrained with anomalies extending at least 200 to 300 m away from major veins.

Jan 1, 2003

By L. J. E. Hofer, J. L. Snyder, J. N. Barn, J. E. Chilton, W. E. Thomas

Various silicone materials have been proposed for use in mining environments. The catalytic methane sensors now employed are poisoned by silicone vapors. Activated charcoal and carbon cloth adsorbents will increase the sensor lifetimes in an environment containing significant silicone vapor concentrations. The results of a study of catalytic methane sensor operation with adsorbent materials in hexamethyldisiloxane-air mixtures are reported. Sampling techniques developed for measuring silicone vapor content of mine atmospheres are described.

By G. S. Littlejohn

Following study of historical South African practice and a review of recent experience gained during the design, construction and testing of the high pressure plugs at the South Deep Water Barrier Project, this paper makes recommendations to improve practice. Initially, site investigation requirements are described with reference to geological, hydrogeological and seismic considerations, including site preparation and pre-grouting of the surrounding rock mass, if permeable. Structural and hydraulic aspects of plug design address topics such as residual permeability, aggressive mine water, plug materials, mortar strength and bleed. In situ thermocouples and piezometers are recommended to optimize the timing of plug tightening and monitor plug performance during service. Plug construction covers aggregate preparation, mortar quality control, plug tightening grouts, injection pressures, records and the overriding need for a method statement specification to control all aspects of plug construction. On completion of the plug, tests to establish surrounding rock stress regime, plug strength, and residual permeability are described to enable a comparison with original design assumptions. Monitoring and maintenance procedures are proposed to ensure satisfactory long-term performance of the plugs.

Jan 1, 2006

By T. I. Nelson

Natural aggregates, primarily stone, sand and gravel, are recovered from widespread, naturally occurring mineral deposits and processed for use primarily in the construction industry. They are mined, crushed, sorted by size, and sold either loose or in concrete products to build roads, houses, buildings, and other structures. Smaller quantities are used in agriculture, cement manufacture, and industries employing chemical and metallurgical processes. The growth of cities, their buildings and the highways that connect them have created demand for enormous quantities of aggregates. The aggregates industry is the largest mining industry in the United States in terms of production by weight, volume and by number of active operations.

Jan 1, 2005

Efficiency, Economics, Energy and Emissions - Emerging Criteria for Comminution Circuit Decision Making

Sep 13, 2010

By L. R. C. Cairncross

In this study, the general case of semi-batch precipitation of nickel hydroxide, Ni(OH)2, is modelled. In practical terms, this precipitation may occur at high ionic strengths, and therefore the model for solution chemistry requires a thermodynamic model that is applicable for these non-ideal systems. The activity coefficient model used is the ELEC-NRTL. The simulation of the solution chemistry is performed using AspenPlusTM, which is a steady-state process simulation program. This allows for rigorous evaluation of the solution speciation, and hence the degree of supersaturation which dictates the precipitation kinetics. The solution chemistry provides the basis for predicting the formation of solids. The model consists of a solution chemistry part and a solids formation part. The inputs to the model include the initial concentrations of the streams entering the reactor, kinetic parameters for the precipitation processes, and a particle size distribution obtained from experiments. The solids formation part of the model employs the method of moments for the evaluation of the population balance. The population balance accounts for total particle number, and the formation and increase in size of particles across the entire particle size range. This balance requires kinetic parameters for the processes of nucleation, growth and agglomeration. Using optimization routines inherent in AspenPlusTM, parameters for the rate of nucleation, growth and agglomeration may be extracted from experimental particle size distributions. These are then used in the model to extrapolate to other conditions. Once an understanding of the kinetics of the precipitation processes is gained, the model provides a predictive tool for optimization of these kinetics, in order to increase the overall particle size and therefore improve solid-liquid separation. The work is deemed to be significant as it sheds some light on solids formation processes involved in precipitation?including nucleation, growth and aggregation?and develops a predictive modelling tool applicable to solutions of high ionic strength. We argue that this dewatering of suspensions is affected significantly by particle size distribution and surface properties of the solids formed by precipitation. This modelling tool should facilitate the design of solids formation processes where downstream dewatering is enhanced.

Jan 1, 1997

By H. John Head, Fred N. Kissell

In This Chapter [Gas reports from around the world Regulations for gassy mines in the United States Differences between metal/nonmetal mines and coal mines Monitoring for methane and taking action Diluting methane with additional ventilation Eliminating ignition sources What experienced mine operators say about methane control and Looking for methane when starting a new mine or expanding an existing mine] This chapter gives guidelines for preventing methane gas explosions during metal and nonmetal mine development and subsequent production operations.3 Emphasis is placed on recognizing the differences between coal mines, where the potential for methane hazards is relatively well understood, and metal/nonmetal mines, where methane may accumulate unexpectedly. Also, interviews with experienced mine operators add much to a complete understanding of what must be done to address methane problems in metal/nonmetal mines. METHANE GAS IN METAL/NONMETAL MINES Gas reports from around the world. The presence of methane gas in metal/nonmetal mines around the world is more common than one might imagine [Edwards and Durucan 1991]. For example: • The former Soviet republics have occurrences of methane and hydrogen in apatite, gold, and diamond ores, where solid or liquid bitumen occurs in the rock. • Scandinavian iron ore deposits include methane and other hydrocarbons in boreholes that intersect pitch and asphalt within the deposits, and methane and nitrogen in boreholes and fissures in arsenic and sulfide ores.

Jan 6, 2006

By S. H. Ash, E. M. Brooks

"Many of the hoisting slopes at the mines in the State of Washington are driven on extra steep dips. To facilitate hoisting they are driven wide enough to provide two tracks. The cars are handled by high-speed, first-motion electric hoists and the trips run in balance.The State mining laws a provide that special man-cars be provided on slopes of 20° or more and that no one be allowed to ride while any loaded car is being hoisted in any slope in a mine. Obviously, in addition to the fact that it is more or less hazardous to ride while an empty trip is being hoisted, considerable hoisting time is lost during the day if some one has to ride the trips in the slope.Owing to the locations of pumps and various types of equipment, more or less travel is required up and down the slope. Not only to provide a proper safety factor but also to comply with the law, some other means of transportation in an¬other passageway is desirable. This is sometimes recognized in large mines by pro viding separate hoisting shafts, or slopes, and necessary equipment, which are use for transporting men and material. The handling of material in itself would justify the system in most large mines.The following description of an automatic electric man-hoist was prepared from data furnished through the courtesy of Mr. Thomas Murphy, superintendent of the Northwestern Improvement Company's mines in the Roslyn-Cle Elum coal field.The special features of this hoist are that no hoistman is required and its operation is always under the control of the person or persons riding the trip.The hoist was installed at mine No. 5, Roslyn, Washington, to provide a means of entering and leaving the mine on idle days or at night when no hoistman was on duty and to make it unnecessary to use the main hoist for a man trip during working hours. It has been in operation for about two years and has given very satisfactory service.The hoist, with all accessories, is housed in a concrete building 200 feet back from and in direct line with one of the main airways. One car with a capacity of six men operates over a distance of 1,200 feet on a 38° pitch.The wiring details of the electric circuits which control the operation of the hoist are shown in Figure 1-a.The hoist is driven through a worm gear by a 500-volt shunt-wound direct-current motor at a car speed of 120 feet per' minute. A gravity friction brake with magnetic release is mounted on the- motor shaft and is wired in multiple with the motor field coils. The hoist drum is also equipped with emergency friction brakes, which operate by gravity and are released, in case of overspeed, by the governor geared direct to the drum shaft. When these brakes set the control circuit is opened at contact 2E-2C and the motor stops.If the descending car meets some obstruction and is stopped, the hoist continues to run and unwind the rope. To guard against this occurrence, a weighted sheave wheel rides the rope 4 feet from the drum, and if the rope becomes slack the rider drops downward and opens the contact 2C-2E which stops the hoist.Limit switches, S1 and S2, are located on the hoist indicator, which is connected to the drum shaft through sprockets and chain. The pointer P indicates the position of the hoist at all times."

Jul 1, 1930

By M. Fan, M. Mankosa, G. Luttrell

"Column and other non-conventional flotation approaches continue to provide benefits where conventional flotation processes have exhibited limited success. This is particularly evident with respect to flotation of ultrafine and coarse particles. Advancements in air sparging technology have provided the ability to produce finer bubbles than previously possible. The generation of finer bubbles coupled with the froth washing capabilities of a flotation column has demonstrated improvements in ultrafine particle recovery while simultaneously producing a high-grade float product. On the other side of the spectrum, the use of these sparging technologies while applying flotation fundamentals to a fluidized-bed reactor has increased the maximum floatable particle size up to and in excess of 3 mm. Benefits of higher recoveries and reduced reagent consumption have resulted from the use of these technologies. An additional benefit includes a reduction in plant grinding requirements. As such, this paper describes the application of Cavitation-Tube sparger technology and fluidized-bed flotation (HydroFloat). A review of data from industrial and pilot-scale applications is also provided.INTRODUCTIONConventional (mechanical) froth flotation is considered the workhorse of the minerals processing industry. This low-cost process makes it possible to selectively recover minerals by exploiting the difference in surface characteristics (e.g., wettability) of the valuable component and the waste material. Unfortunately, the upper particle size limit for flotation rarely exceeds 0.600 mm, and is typically maintained at less than 0.300 mm for most industrial applications. For many commercial base metal plants, the particle size range for optimum recovery is typically between 0.01 and 0.1 mm (Lynch et al., 1981). This finding is not novel. In fact, the effect of particle size on flotation recovery was studied as early as 1931 by Gaudin et al. who showed that coarse (+0.250 mm) and extremely fine particles (-0.010 mm) are more difficult to recover than particles of an intermediate size. The loss of recovery is due to inherent limitations associated with the flotation process, including bubble-particle adhesion and collision, detachment, buoyancy, and transport."

Jan 1, 2010

By M. Ounpuu

"Gold, because of low head grade and recovery, is usually of minor importance in the economics of base metal flotation mills. Because of the above little metallurgical attention is usually provided to gold in these mills. But collectively, the gold losses can be significant. For instance, Noranda presently has interest in 13 base metal flotation mills with a collective gold recovery of only 50%. Gold losses are in the order of 150.000 oz per year!The Noranda Technology Centre, in cooperation with Noranda's milling operations, has been investigating the potential of gravity concentration of gold from base metal flotation mills. This paper outlines the pilot and plant testing conducted at three operations with distinctly different ore types; porphyry copper, complex massive sulphide and polymetallic semi-massive sulphide. Testing has been with the Knelson Concentrator which has proven to successfully recover fine gold in a simple, trouble free circuit. Discussion of issues which have risen from the testwork is included. INTRODUCTIONGold, because of low head grade and recovery, is usually of minor importance in the economics of poly-metallic base metal ores. TABLE I presents gold heads and recovery for some of Noranda's base metal mills. It should be noted that the stated recoveries are to payable concentrates, but does not reflect the actual payable gold recovery which in cases is significantly lower. Noranda's average gold recovery into a gold payable concentrates is about 45%. This equates to a collective loss in the order of $57 MM per year of gold"

Jan 1, 1992

By G. L. Gates

The waters used to waterflood the Wilmington oilfield were studied by the Bureau of Mines, in cooperation with the city of Long Beach, Calif. Increases in the pressure of the injection wells indicated that they were being plugged by materials suspended in the waters. This study was made to identify the suspended materials, determine their origin, and find methods of preventing their formation. The suspended oil-coated materials were iron sulfide, barium sulfate, calcium carbonate, clay, and sand (or silica). Results indicated that the sulfide, which was as high as 90 milligrams per liter, was the product of sulfate-reducing bacteria. The injection of ocean water increased the sulfate content of the waters in the petroleum reservoirs from 3 to 250 milligrams per liter, thereby furnishing sulfate for growth of the bacteria. The waters were supersaturated with barium sulfate. Laboratory tests showed that sulfide could be removed from the waters by adding iron at a cost of 1 to 2 mills per barrel. The solubility of iron sulfide and calcium orthophosphate in the injection waters was also determined.

Jan 1, 1975

By Scott A. Stebbins

Cost evaluation models constructed specifically to evaluate the economic potential of an individually motorized railcar system of ore and waste transport demonstrate that the approach may be considerably more cost effective than traditional rubber-tired haulage methods. The system design places a motorized drive unit on each railcar, as opposed to the more common configuration in which a series of un-motorized cars trail behind a single locomotive. These motorized railcars are directed to various load and dump points by a computerized dispatch system, and as such have the advantage of operating unmanned. In addition, the tractive effort of the rail-type drive system is noticeably more efficient than that of the rubber-tired mode of transport. The savings are realized primarily through comparative reductions in the requirements for labor and, to a lesser degree, energy.

Nov 1, 2011

By R. J. Durrheim

The seismicity of the Witwatersrand Basin and Bushveld Complex has been analysed, revealing significant differences in source and damage mechanisms. A comparison of mining taking place at similar depths and extraction ratios indicates that the seismic energy release rate is considerably lower in the Bushveld Complex. Technologies introduced in the past decade to manage the risk of rockbursting are reviewed and assessed. These include geophysical methods to detect hazardous structures ahead of mining, new mining layouts and support systems, and the mechanization of in-stope processes. Despite important differences in geology, in situ stress, mining layouts and methods, there are many opportunities for the reciprocal transfer of knowledge, experience and technology between the gold and platinum mining sectors to improve the management of the rockburst risk.

Jan 1, 2005

This Bureau of Mines report concerns two subjects important in the application of electric power in mining systems. Electrical transients and their suppression are discussed, and several considerations are explored with regard to the use of explosionproof or other electrical enclosures.

Jan 1, 1979

By F. T. Cawood

?It is in the interest of stability and investor confidence that the healthy and necessary debate on such a (minerals) policy should soon find its way to consensus.? (President Nelson Mandela at the104th (1995), AGM of the South African Chamber of Mines) Inauguration of the new political dispensation in South Africa initiated a dynamic period in the historical development of its minerals policy. The process of substituting the current South African mineral policy framework with an acceptable ?post apartheid? system, started soon after the 1994 election of the African National Congress (ANC) government. The Green Paper on a Minerals and Mining Policy for South Africa released for public discussion in February 1998, calls for radical transformation in mineral rights ownership. A shift towards exclusive state ownership of mineral rights, away from the present dual system of private and state ownership, is the most significant proposal. The current holders of mineral rights, or their nominees, who lawfully enjoyed security of tenure under past and present mineral laws are opposed to this transformation because mineral rights were often acquired at considerable cost. The situation is compounded by poor public record-keeping and passive mineral rights administration over a very long period. This paper represents a summary of the historical developments leading to the current legislative environment and forms the basis for any discussion on which future sculpturing of South Africa?s policy regarding mineral rights can take place. One cannot plan for the future without considering the past!

Jan 1, 1998

Atlas Copco Construction and Mining Australia identified a number of issues in regard to the skill levels, labour turnover and productivity of our service technicians. In 1994 we were experiencing a labour turnover rate of 42 per cent per annum amongst our technicians. Exit interviews were held with each individual and one of the major areas of dissatisfaction was the degree of product training provided on our equipment, compared to what is required to be competent across the range of our products. These tradespersons were prepared to accept the reduced remuneration that an OEM offers, for the benefit of comprehensive, professional training that, in theory, could be provided. The truth is that we were achieving approximately 40 per cent of our target for training hours because of the demands of field service, pre-deliveries, etc. So, the summary was the same as the industry was experiencing at that time because of skilled labour shortages, production demands, etc people were employed and thrown in at the deep end. A recipe for failure that will be successful every time.

Jan 1, 1998

By M. R. Geer

Information on the performance of coal-cleaning equipment is necessary to provide a basis for evaluating the performance of existing plants and projecting that of new plants. Performance data can contribute greatly to the wise selection and effective use of coal-washing equipment. The Bureau of Mines has published information on the performance of several commercial plants, as well as of some laboratory-scale equipment, 5 (2-9, 11, 12, 17-12, 21-25) from time to time for a number of years. A more intensive program to provide such information for all the principal types of cleaning equipment is underway. The present evaluation of table performance is part of this program.

Jan 1, 1962

By Stephen Gerard Sawyer

This report presents a Fortran IV computer program for the structural analysis of space-frame protective canopies used in underground mines to protect equipment operators from falls of roof, face, or rib. This program entitled CANOPY permits rapid calculation of the elastic strength of a canopy for a variety of static loading conditions. Stresses in, and displacements of each structural member are computed and printed out. Additionally, identification of all members that have commenced yielding, weight of the canopy, total loads on the canopy, and maximum loads that the canopy can sustain elastically are output. Program description, input instructions, program listing, and two example problems are included.

Jan 1, 1972

By Nuno Cruz, Saúl Rodríguez

"When executing offshore bored piles there are several specific factors and problems to consider in order to guarantee excavation stability. One of the methods employed to carry out this type of work consists in setting up a floating work platform, typically a barge, and implementing a soil stabilization system that combines a partial steel guiding casing with third generation polymeric drilling fluids. The main aspects to take into consideration when performing offshore pile boring works are soil stabilization, project design, work methodology and operational aspects. An example of a work methodology problem arises before any pile boring work takes place as the steel guiding casing contains water, sometimes salt water. What to do with this water in order to replace it by an adequate polymer fluid will determine the stabilization capacity as soon as the shaft advances below the protection of the casing. Another example of operational problem may derive from barge movements while executing boring activities. This study is the result of extensive field data collection and concrete logging analysis from marine projects using polymers in different continents. The bored pile stability target was set ranging between 2% to 15% of concrete overbreak. Values above 15% or below 2% mean that there is a stability problem. Then the off-target pile’s data is collected, analyzed and classified under categories. Thus, a direct correlation is established between the problem category and the final results. Modifying steps in the pre-established construction methods or operational variables guarantees target results without the need to replace the approved construction methods. As a general conclusion, the worldwide experience in large diameter marine works, allows to provide truthful information and solutions for these problems. In knowing how to follow a logical sequence of work and applying adequate work methodology will be the key for success.GENERALBackgroundTo carry out the drilling process of offshore bored piles there are two main options to take into consideration: drilling the pile by using full guiding casing until final depth; or using a combined system of partial steel guiding casing and support drilling fluids.The knowledge and situations described in this paper come from the experience acquired in different projects where the second method was employed. This construction method consists in installing a steel guiding casing by vibration and thus covering the water table and further stabilizing the soil below it with polymeric fluids until reaching the pile’s final depth. The Fig. 1 schematic shows an example of this method where H corresponds to the length of the steel guiding casing whereas the remainder of the shaft’s length is stabilized by polymer fluid. The entire bored length is full of slurry up to top of casing.In most cases this kind of civil works results from the need to build a bridge or executing port structures in places where the creation of temporary artificial peninsulas with fill material is impracticable or not allowed. Hence the need to use floating work platforms, commonly referred to as barges."

Jan 1, 2017

By Charles L. Kimbell

Virtually every available measure of total world mineral industry activity demonstrated that 1982 was little, if any, better for the industry than 1981 had been. Levels of production, trade, and consumption for virtually every major commodity declined; unit prices for most commodities fell, particularly in terms of constant dollars, and as a result of cutbacks in output and lower prices, capital available for investment within the industry was reduced. These conditions, coupled with the existence of considerable idle capacity, tended to retard investment, although there was an upturn in U.S. oil industry investment overseas. Despite the overall depressed situation of the world's mineral industry, there were indications of possible improvements in market economy countries near yearend, as output of some materials increased marginally and as prices for some mineral commodities reversed their downward trends. The downturns in total world mineral industry activity were not universal from the viewpoint of individual countries. Indeed, output of a number of commodities increased in centrally planned economy countries, and these gains were insufficient to offset declines in market economy countries, thereby sharply altering the proportion of total world output accounted for by each of these two groups of countries. There was a similar shift in consumption on a percentage basis.

Jan 1, 1984