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By Richard J. Ebens

The trace element geochemistry of the cherty, clay-rich carbonate residuum. Covering much of southern Missouri and adjacent parts of Arkansas was investigated during the early 1970's as part of a statewide geochemical survey of Missouri-1/2/3 The study was environmentally oriented and focused on the character of the "natural' geochemical environment of the state. A great deal of effort was made to collect samples that would represent the geochemical variability of the near-surface environment in an unbiased way. In general, this was accomplished by use of randomization procedures in both collection and analysis. Most of the sampling sites were selected randomly to prevent personal bias from entering into sample selection. In the laboratory, samples were analyzed in a randomized sequence to circumvent the effects of any systematic bias that may have entered into the laboratory procedures. Several residuum samples contained 1 000 parts per million (ppm) or more of Pb, Zn and Ba. All these samples were collected in Washington County in or near the barite district. The frequency distributions shown in figure 1 indicate just how unusual the residuum in Washington County is with regard to these three metals and copper. The shaded parts of the histograms represent the samples from Washington County. The histograms are based on analyses of 141 samples from 38 localities scattered over the subcrop of the Cambrian and Ordovician Formations of southern Missouri and northern Arkansas. Eight localities were selected randomly from over each of four bedrock units--Bonneterre Dolomite, Potosi and Eminence Dolomites, Roubidoux Formation, and the Jefferson City, Powell and Cotter Dolomites. Six localities were selected randomly from over the Gasconade Dolomite. The geochemical "background" for these elements in residuum is defined by samples from outside of Washington County (unshaded part of the histogram); lognormal distribution curves have been fitted to the corresponding parts of each histogram. Clearly, these lognormal models (curves) describe well the background

Jan 1, 1977

By S. N. Groudev

A process for the combined chemico-biological removal of iron present as oxide minerals in different mineral raw materials (quartz sands, kaolins, clays, etc.) was developed. In the process, mineral raw materials are leached at about 90 °C with lixiviant containing microbially produced oxalic and hydrochloric acids. The leaching is carried out in mechanically stirred acid-resistant reactors for periods of from 1 to 6 hours, depending on the iron content and the forms of iron in the raw materials being leached. The iron contents of some sands treated by this method were lowered from levels that were in the range of 0.035% to 0.088% Fe2O3 to less than 0.012% Fe2O3, making them suitable for the preparation of high-quality glass. The iron contents of different kaolins were lowered from levels that were in the range of 0.65% to 1.49% Fe2O3 to levels in the range of 0.44% to 0.75% Fe2O3. As a result, the whiteness was increased from values of 55% to 87% to values of 86% to 92%. The iron content of clay was lowered from 6.25% Fe2O3 to 1.85% Fe2O3, and this increased the “fireproofness" of the clay from 1,670°C to 1,750°C. A similar process was used for the leaching of aluminum from aluminosilicates, mainly clays and kaolins. However, in this case, the microbial fermentation fluid containing citric acid was acidified by means of sulfuric or hydrochloric acid or by means of different mixtures of mineral acids. For enhancing aluminum solubilization, the aluminosilicates were heated before leaching at 600° to 650°C for 1 to 2 hours. Over 90% of the aluminum present in different clays and kaolins were leached within 3 to 6 hours. "Silicate " bacteria related to the species Bacillus circulans were used to leach silicon from low-grade bauxite ores containing aluminosilicates as impurities. The bacterial action was connected with the degradation of the mineral structures (by means of microbial metabolites such as organic acids and exopolysaccharides), as well as with the selective separation of the rich-in-aluminum fine fractions, which were retained by the mucilaginous capsules of the bacteria. The solid residues after treatment were characterized by higher values of alumina and silicon module (A1203: SiO2 ratio), and they were suitable for processing by means of the Bayer process for recovering aluminum. The bending strength and other ceramic properties of kaolins were improved by contact with well-developed cultures of "silicate" bacteria. The improvement was caused mainly by bacterial metabolites (exopolysaccharides) that acted as resins during drying.

Jan 1, 2000

By J. E. Murphy, Y. Topkaya, R. E. Johnson, B. R. Palmer, D. K. Dysinger, R. B. Bhappu, A. E. Clark

The U.S. Bureau of Mines utilized a central composite experimental design to investigate leaching kinetics of pure chalcopyrite in the sulfuric acid-oxygen system. The six factors studied were oxygen pressures of 150, 300 and 450 PSI, leach temperatures of 35O, 65O, and 95O C, oxygen-to-chalcopyrite mass ratios of 0.5, 1.0 and 1.5, leach times of 8, 16 and 24 hours, initial acid strengths of 0.6, 1.2 and 1.8 g H,SO,/g chalcopyrite and pyrite to chalcopyrite mass ratios of 0, 1, and 2. Chemical analysis and oxygen consumption measurements indicatedthat leaching occurs through three consecutive reactions. Temperature was the primary determinant of leach rate and solution acidity was the primary determinant of oxygen consumption, sulfur oxidation, and activation energy.

Jan 1, 1993

By Reynold Q. Shotts

Underground mines, penetrating well below the water table, quickly fill with water when abandoned. Ordinarily, these natural cisterns are not thought of as sources of industrial water. Under special circumstance, if chemically treatable, they might become valuable industrial water reservoirs. An example of a group of about 20 mines in a geological and structural setting insuring water entrapment, rapid recharge and a possible minimum of contamination, are the small, compact Belle Ellen and Piper basins in Alabama's small but second most productive coalfield, the Cahaba. The mines have been abandoned from more than 50 to less than three years. The county now produces about a million tons of coal annually, all from strip mining. Figure 1 shows an idealized cross section of the strata in the Belle Ellen syncline near West Blocton, Bibb County, Alabama. Figure 2, 3 and 4 are maps showing the location of the syncline, other structural features, the outcrop lines of the three principal coalbeds underlying the basin, and the mined-out areas on the three beds (1).

Jan 1, 1973

By M. Albrecht

I have been following the discussions on coal degradation started by the article "Degradation process in coal slurry pipe-lines," by M.G. Ayat and B.C. Scott. I agree with Mr. Dasher's comments in January that the title of the article was perhaps misleading as the information appeared to pertain more to processing the coal than to transportation. Specifically, the authors' conclude that the cyclone had an important impact on the degradation. Dr. Ferri's comments on degradation in other physical processes was very correct, handling of coal in a turbulent manner has an impact on the size distribution of the coal. This is one reason that when I design a coal system (mine to rail car) I try to minimize the total number of transfer and processing steps consistent with achieving the desired product specifications. Another area, mentioned in passing in the article, the impact of natural causes and the mining step, is of particular interest to me. A mine in West Virginia had a variation of 50% in the -6.35 mm (-0.25 in.) raw coal depending upon the direction of mining. Since it was a single unit mine, this significantly impacted the final product. Two articles on mining's impact on size distribution are: • Stefanko, R., Chopra, 1K., and Ramani, R.V., 1974, "Mining influence on size consistency and washability characteristics of coal," SME Fall Meeting, September; and • Albrecht, M., and Olsen, D., 1980, "Mining methods impact on coal preparation plant design," 1st International Mine Planning and Development Symposium, September. Both articles presented information on variation of size distribution and cleaning plant performance on a coal depending on the mining method used. Both articles considered a single coal seam at one mining operation. Stefanko's article considered continuous and conventional mining of coal in Pennsylvania. Albrecht's article considered surface, underground continuous, and underground hydraulic mining of a coal in British Columbia. Both concluded that mining methods do impact coal characteristics. I agree with Mr. Ayat's comments in reply to Dr. Ferri's discussion, "... degradation is a multi-faceted phenomenon involving many natural and man-made factors." As efforts are being made to produce a higher quality (lower sulfur) coal, this topic becomes even more important

Jan 1, 1989

By John Conway, Gerald Bennett, John Herrick

Research efforts which have led to reduced resin bolting costs at White Pine Mine are described. Key factor was development of the capability to drill small holes (1 1/8 in. diam) in the hard (20,000-30,000 psi) White Pine roof rock. Economic data comparing the 1 1/8 in fully-grouted Resin Bolt to the conventional 1 3/8 in fully-grouted bolt is also included. The development of a method which allows the Resin Bolt to hold itself in the hole thus removing the requirement for the operator to break his "work momentum" while he stops and waits for the resin to set is also described. This technique increased bolter productivity by 23% in a recent full-scale unit test.

Jan 1, 1974

By Yu. A. Polozov, V. A. Lagunov, O. Yu. Lushinkova, Yu. I. Svirskiy, Eh. Ya. Kipko, Roy A. Williams

The reliable quality assessment of grouting operations is one of the key issues in establishing impermeable grout curtains around shafts, drifts and tunnels. Reliable opera¬tional information on the decrease in the permeability of rock during the grouting process facilitates the assessment of the effectiveness of the completed curtain and assures production quality. Quality control and assurance also fa¬cilitates the early detection and elimination of possible de¬fects in the grout curtain. Thorough control of the grouting process provides the capability to evaluate decreases in the permeability of water-producing fracture zones prior to the beginning or the continuation of excavation of the shaft, tunnel or drift. In order to achieve this objective, post¬grouting hydrodynamic investigations are conducted prior to the initiation or re-initiation of work on the underground workings to measure the decrease in the permeability coef¬ficient of aquifers during grouting operations. 8.1 QUALITY ASSURANCE AND CONTROL OF THE ISOLATION OF ROCK BY GROUTING THROUGH HOLES DRILLED FROM THE SURFACE Quality assurance and control are based on measuring the decrease in the permeability coefficient of water-pro¬ducing horizons as a result of injecting grout into the drill¬holes. For this purpose, the value of the acceptable residual permeability coefficient is calculated beforehand based on the acceptable value of ground water inflow into the shaft, drift or tunnel as specified by the "construction norm and integrated practice (SNIP)" (Anon., 1976). Having ob¬tained the values of aquifer thickness, permeability, and head distribution for each aquifer from flowmetric data (dis¬cussed in Chapter 3), the average value of the permeability coefficient of all aquifers intersected by the shaft is calcu¬lated as [ ] where Ki is the permeability coefficient of the "ith" aqui¬fer; Pi is the pressure of the "ith" aquifer; and M; is the thickness of the "ith" aquifer. The total expected inflow of ground water into the shaft is [ ] where RK is the radius of the contour of influence; RCFB is the radius of the shaft; and p is the coefficient of dynamic viscosity of the ground water. The necessary reduction of the coefficient of permeabil¬ity of the aquifer [ ] where Q is the expected inflow of ground water into the shaft from eq. 8.2; Q.-fin is the acceptable inflow of ground water; and a is the safety factor. By knowing the average permeability value of the rock and the permeability reduction coefficient, it is possible to determine the value of the acceptable residual permeability coefficient for all the aquifers [ ] The values of the permeability coefficient, pressure, and thickness for each aquifer are determined from the data gathered during the hydrodynamic investigations conducted in grout holes prior to beginning the grouting operations as discussed in Chapter 3. After injecting the grout into the first of the holes, the injection into each of the following grout holes is preceded by repeated hydrodynamic investi¬gations. Using the data obtained for each water-producing zone, a graph is constructed where the numbers representing the grout holes in their order of grouting are placed on the abscissa, and the values of the aquifer permeability coeffi¬cient are placed on the ordinate (Fig. 103). This curve char¬acterizes the change in permeability of the given hydro¬stratigraphic unit as grouting operations are completed, one hole at a time. The results of grouting operations are considered to be positive when each sequential observation records a steady decrease in the permeability of the aquifer. The permeabil¬ity measured prior to the injection of the grout into the last hole must be lower than or equal to the acceptable perme¬ability as determined by the application of eqs. 8.1 through 8.4. Table 8.1 presents illustrative data on the hydrogeo¬logic properties of aquifers at a mine shaft prior to the initiation of grouting operations. Data also are presented on the reduction in the permeability coefficient during the in¬jection of the grout. The shaft in question intersects eleven aquifers. Based on data concerning aquifer pressure, thick¬ness, permeability, and the expected inflow rate of water for each of the strata, the average permeability coefficient is calculated according to eq. 8.1 as K = 0.2 x 10-12 m2. The

Jan 1, 1993

By James R. Taylor

24.1-BASIC PRINCIPLES JAMES R. TAYLOR The basic principle involved in maintenance is protection of a company's investment through the care and upkeep of machinery and equipment, buildings and properties. Maintenance is justified through making available to the maximum extent possible the facilities, machines and services required by the operating and production departments in their function of insuring optimum return on investment. As the size, cost and complexity of the equipment used in modern mining and related industries increase, operating and production personnel become proportionately more dependent upon maintenance engineering for its contribution to the overall profit picture. A greater part of the total cost now is charged to maintenance and the maintenance group becomes a major company unit. Basic maintenance concepts have changed very little over the years, but the advances in methods and technique have brought about tremendous challenge and have in consequence assumed a greater influence and importance. The older "sledge- hammer" methods have given way to engineered and scientific systems, while the accelerating development of intricate equipment and machinery, and the instrumentation essential for control, demand an ever-increasing upgrading of maintenance personnel. Regardless of this growth in importance, cost and complexity of the maintenance function, it is important to remember that it is not an independent and self-sufficient unit, but is a necessary facet of the entire plant operation and is subject to the company's total production effort. As one part of a team, maintenance is successful only when functioning cooperatively wit11 the other departments it serves Close collaboration in all areas served by n maintenance group is essential if it is to function fully to protect the company's investment, whether the assets are in machinery, materials or people. 24.1.1-MAINTENANCE SCOPE Maintenance functions may be grouped into the two general classifications of primary and secondary. This grouping constitutes a basic division although, in practice, the scope of the maintenance activity varies in each mine or plant and is subject to differences in size and type of operations and company policy, plus the influence of precedent, which may be sectional or industry-wide. The primary functions supply the justification for the maintenance engineering department. while secondary functions are variable according to plant conditions and needs. The primary functions may be categorized as follows: 1. Maintenance of existing machinery and equipment. 2. Maintenance of existing buildings and grounds. 3. Inspection and lubrication of equipment and machinery. 4. Utilities generation and distribution. 5. Alterations to existing equipment and facilities. 6. Installation of new equipment and facilities. 7. Instrumentation.

Jan 1, 1973

By J. A. Brierley, S. N. McIntosh, C. L. Brierley, E. G. Baglin, E. G. Noble, D. L. Lampshire

The U.S. Bureau of Mines investigated column bioleaching as a means of recovering manganese from a domestic low-grade oxide ore. Manganese was solubilized from the ore using indigenous heterotrophic microorganisms and molasses as the nutrient source. The effects of medium flow rate, molasses concentration, and frequency of medium replacement on the rate of manganese extraction were examined. Results showed that flow rates between 0.4 and 8.1 L/min/m2 had little impact on manganese extraction, while an increase in the total amount of molasses applied during leaching directly affected the extent and rate of manganese extraction. Manganese extractions of more than 90% were achieved in 12 weeks of bioleaching in column tests using 500 g charges of ore. Sugar utilization by the microorganisms and formation of organic acid metabolites were monitored by high performance liquid chromatography (HPLC). Two methods were evaluated to recover manganese from the sugar- depleted bioleaching medium: (1) adsorption onto weak cation exchange resin, followed by stripping and precipitation techniques; and (2) direct precipitation of the manganese as MnCO, using ammonium carbonate. Both recovery methods removed at least 95% of the solubilized manganese from the medium as a carbonate salt. The stripped molasses medium was replenished with fresh molasses and recycled back through the bioleach column, successfully leaching more manganese.

Jan 1, 1993

By Rebecca S. Stanevich

BACKGROUND Diesel exhaust is an animal carcinogen, although evidence of the carcinogenicity in humans is "limited". (World Health Org. , 1989) Of the eight cohort studies in the 19808, five found an increased risk for lung cancer among workers who may have been exposed to diesel exhaust (RR from 1.3-1.5, SMR from 101-132). (Howe, et al., 1983) Only two studies accounted for smoking indirectly. Of the ten case-control studies in the 1980's, eight reported increased risk of lung cancer among those populations purportedly exposed to diesel exhaust. (Benhamou, et al. , 1988) All but one of these adjusted for smoking and other occupational exposures. The odds ratios ranged from 1.2 to 2.1. In two of these studies, miners experienced a two to three fold risk. (Benhamou, et al., 1988) Bladder cancer has also been linked to diesel exhaust in cohort and case-control studies. Excesses of approximately 50% were observed among truck drivers in studies by NCI. (Hoar, et al., 1985) In the National Bladder Cancer Study, risks for truck drivers rose with duration of employment. A study by NIOSH in Ohio also found an excess of bladder cancer among truck drivers, particularly among those with 20 or more years of employment. (Steenland, et al, 1987) Despite the large number of studies in which the relation between diesel exhaust exposure and lung cancer has been examined, exposure to diesel exhaust has been quantitatively estimated only in the studies of railroad workers and truck drivers. (Woskie, et al., 1988) The excess lung cancer risk experienced by workers in these two occupational groups was modest, ranging from 40 to 90% for those with long-term employment. However, diesel exhaust exposure among railroad workers and truck drivers is lower than that seen among miners. Several markers of diesel exhaust have been utilized in these studies. Diesel exhaust is a complex mixture of particulates, vapors and gases. One group of these gases, the nitrogen oxides, react with polynuclear aromatic hydrocarbons, forming mutagenic and possible carcinogenic nitrated derivatives. (World Health Organization, 1989) For this reason, and because it is easy to measure and analyze, NO, was frequently used as a marker of diesel exhaust exposure. As part of the Garshick (Garshick, et al., 1988) study of railroad workers, Woskie measured NO, exposures of 477 railroad workers. (Woskie, et al., 1988) Geometric mean exposures of 13 job groups ranged from 12 to 80 ppb. In a New Mexico potash mine, (Attfield, et al. , 1982) exposures of from 100 to 3300 ppb nitrogen dioxide

Jan 1, 1992

By A. L. Mular

Steady-state material balances calculated from data measured at various locations around process units are useful for many purposes, such as metallurgical accounting, on-line control, and the development of mathematical models. Often it is possible to calculate material balances by several independent procedures when excess measurement information, i.e., redundant data, is available. Clearly, if the data were collected without measurement errors, a theoretical condition never found in practice, all material balances calculated from redundant data would be in agreement. The real situation is that error exists in practical measurements, so that the results of material balances determined from available optional procedures differ. Consequently, best fit computational procedures to improve the material balances by taking measurement errors into account have been formulated. Such procedures can be used also to judge whether measurements are grossly in error due to either faulty observations or defective data sensing devices. A variety of mathematical techniques are available which serve to adjust raw data. The adjusted data permit mass balancing that does not depend on the computational method. To illustrate the need for an adjustment procedure, Table 1 shows a raw data set acquired around the Brenda Mines Ltd. No. 4 grinding circuit shown schematically in Fig. 1. At least seven optional ways to calculate a circulating load ratio may be employed. These are shown in Table 2 where, depending upon the calculation [ ]

Jan 1, 1979

By Kenneth R. Ware

I INTRODUCTION The Washington Metropolitan Area Transit Authorities (WMATA) rapid transit system (METRO), currently under construction, will have a total length of 98 miles. Forty-eight of these miles are underground and require either open cut excavations or tunnels. Despite stringent construction controls, it is inevitable that some ground settlement will occur adjacent to the deep open cut earth excavations and large diameter earth tunnels. It is therefore essential to underpin nearby important structures to prevent excessive differential settlements and Fig. 1 presents the METRO criteria for this underpinning. This paper describes the underpinning methods currently used on METRO and evaluates the effectiveness of each method. II DESCRIPTION OF SUBSURFACE STRATA The foundation materials in the Washington, D.C. area are extremely variable. Fig. 2 presents an idealized profile showing typical subsurface strata. The engineering properties of each stratum have been determined by extensive exploration and testing programs. Fill: Washington, D.C. fills consist of every variety of soil and rubble. They are not important to this study because no underpinning is founded on fill material. Terrace Deposits: Formed in outwash plains during the glacier period, these deposits are composed of random layers of either sand 1 The writings and opinions expressed herein are solely those of the author and do not necessarily reflect those of WMATA.

Jan 1, 1974

By N. Colvin, J. W. Gulyas

HISTORY The Surigao Nickel Refinery of Marinduque Mining and Industrial Corporation is located on Nonoc Island off the northwestern coast of Mindanao in the Philippines. Nonoc Island is part of the Surigao Mineral Reservation which had been identified as early as 1912. Initial interest in these deposits was due to their iron content, and their value as a nickel deposit was not seriously entertained until the late 1950's. The Philippine government undertook extensive test pitting and sampling programmes at that time and in the early sixties Marinduque became involved in helping to establish firmer ore reserves. Evaluations of the test pitting programme indicated reserves of 75,000,000 tonnes of ore averaging 1.22% Ni, 0.1% Co and 38.5% Fe. The Philippine government called for bids on the reservation in 1962 and Marinduque and Sherritt Gordon carried out some feasibility studies for the recovery of nickel from the deposit. However, it was not until 1968 that Marinduque was granted proper authority to exploit the Surigao deposits. Marinduque and Sherritt then entered into an agreement which allowed Marinduque to utilize a process developed by Sherritt for treating lateritic ores. During 1968, a 25 st/d pilot plant was erected in Fort Saskatchewan, Alberta for the purpose of modelling all process steps. A 10,000 tonne ore sample was sent from Nonoc as feed stock for the pilot plant.

Jan 1, 1979

By B. J. I. Adair, K. R. Weller

The bulk scavenger tailing from Aberfoyle's Hellyer Concentrator, which represents about one-third of the total tailing, runs about 2.5-3 g/t gold and 140-200 g/f silver. Both values are very finely disseminated, particularly the gold. Aberfoyle wished to establish whether ultra-fine grinding followed directly by cyanide leaching could be applied to the tailing for recovery of gold and silver. The work comprised the determination of gold and silver recoveries as a function of grind size and leaching time, the specific energy consumption required for continuous wet grinding of the tailing to the specified product size in a small horizontal continuous stirred mill, and an estimate of the rate of media consumption. The maximum extraction of gold, 23.3% was obtained from the finest product, with the highest cyanide concentration and longest leach time, confirming earlier work. A similar result was obtained for silver. The specific energy requirement for milling rose from 27.7 kWh/t for a P80 of 8.1 um to 219 kWh/t for a Pea of 2.3 um. The consumption of ceramic media was about 1.6 g/kg of final product. An extensive QEM'SEM Trace Mineral Search on the unground tailing failed to identify any gold-bearing particles but did identify silver-bearing particles which displayed a variety of textural associations and liberation characteristics.

Jan 1, 1998

By Jim M. Johnson

INTRODUCTION The facility water balance and maintenance of sufficient excess storage volume in the solution control system are often amongst the most critical facets of design and operation of heap leach facilities in cold, snowy climates. The purpose of this paper is to summarize and discuss climatic and operational factors which have a significant impact on heap leach water balance evaluations in high snowfall climates. Example water balance simulations are presented for proposed heap leach projects located in areas subject to high snowfall in the northwestern United States. The climatic data input to these simulations represent both net evaporative and net precipitation climates. FACTORS AFFECTING WATER BALANCE EVALUATIONS The combined effects of seasonal operations, re1atively low evaporative losses, and potentially large inflows to the solution control system from snowpack and spring storms require an enhanced awareness of the factors which impact facility water balance. Unlike operations at mines in more arid climates, seasonal excess water rather than a shortage of make-up water is the rule. A thorough understanding of a number of factors, including regulatory constraints, climatic influences, and impact of operating philosophy and techniques, is critical to successful development of an incident-free heap leach operation under high snowfall climatic conditions. A process water circuit schematic for a typical heap leach operation is shown on Figure 1.

Jan 1, 1988

By Robert G. Woolery

Union Carbide_ began looking seriously at heap leaching in 1971. At that time some 1.6 million tons of mineral averaging 0.040% U308 were stockpiled at various sites around the Gas Hills, Wyoming, uranium facility. Several alternatives for economically exploiting these reserves were considered and heap leaching seemed the most attractive. At the time, Western Nuclear Inc. was operating a heap leach project nearby in which the low-grade ore was leached with sulfuric acid, the product liquor treated in an on-site solvent extraction circuit, and the stripped product liquor re-acidified and recycled. They were most generous in allowing us to visit their site, answering our questions, and were helpful in discussing the problems associated with heap leaching. They confirmed our belief that, it was possible to operate a heap leach profitably on material too low grade for. conventional milling. Based largely on what we had learned from Western Nuclear's experience, a program was set up involving a laboratory study to determine the characteristics of the mineral stockpiles as related to heap leaching and to conduct a pilot heap leach adjoining our Gas Hills mill. Basically, the pilot heap construction and leach procedure were similar to those described in the literature(1,2) with certain modifications to permit detailed monitoring of the operation. In May, '1972, the decision was made to construct a test heap. The UCC plant at Gas Hills, Wyoming was selected as the most appropriate site for the follow¬ing reasons:

Jan 1, 1977

By Herb Wilson

The Klondike symbolized one of mankind's driving forces - the desire to lay one's hands on a scarce resource, gold, in that case - and in doing so to make some money along the way. It can be argued that construction aggregates - a once lowly and ignored sector of the natural resource industries - have become the desired targets of their own "Klondike." This began in the 1970s and accelerated to a frantic pace in the 1980s. The scope of industrial minerals is very wide. It ranges from high value minerals such as talc, bentonite and kaolinite to the truly humble minerals of sands and gravels, limestones and granites. Their major end uses are in construction aggregates. A rich variety of different mineral types all make good construction aggregates. However, those successfully used have two fundamentals in common: • Their technical characteristics are appropriate for the requirements of their end use. • They are located within an economic distance from the market. The North American market This is the largest construction ag¬gregate market in the world. Consumption in 1990 reached 2.2 Gt/a(2.5 billion stpy). This rate of consumption has grown steadily over the past decades. In the United States, from 1963 to 1989, it averaged a 1.6% compound growth rate. Within this long-term trend, there are business cycles, because aggregate demand is closely linked to economic strength or weakness. The North American market also displays the greatest per capita demand for aggregates when compared to the major industrial economies (Table 1).

Jan 1, 1993

By T. S. Golosinski

Most of the 154 t (170 st) truck fleets that were predominant in large surface mines in the 1970s and 1980s are approaching the end of their economic life. One replacement option considered by mine operators is a change to the 2 18 t (240 st) trucks. A comparison of load capacities between the 1.54 t (170 st) and the 2 18 t (240 st) trucks indicates a large productivity advantage in favor of the 218 t (240 st) trucks. This advantage, however, is often reduced by a number of site-specific factors. Therefore, a careful evaluation is required to define the actual benefit of changing to the large trucks. This article discusses some important factors that have an impact on truck size selection, based on several different studies. 218 t (240 st) trucks The 2 18 t (240 st) rear dump trucks were first introduced for surface mine service almost 10 years ago. However, it is only during the last few years that this equipment has gained acceptance in the surface mining industry. About 250 units were employed in surface mines worldwide at the beginning of 1992, and further purchase commitments are being made. Encouraged by the mining industry’s interest, all major off-highway mining truck manufacturers now offer 218 t (240 st) models (Table 1). At present, the existing 218 t (240 st) truck fleets are dominated by electric drive trucks. However, recent introduction of a 2 18 t (240 st) mechanical drive truck rounds out the development of this truck size.

Jan 1, 1992

By Don L. Jensen

With the successful implementation of supervisory control on the Bagdad concentrator grinding circuits, steps have been taken to expand supervisory control to the flotation circuits. This paper discusses the design and installation of the slurry delivery systems, analyzing instruments, level control devices, reagent pumps and supervisory software. Emphasis is placed on the design and installation of a reliable slurry transport system to feed the Courier 30 online analyzing instruments. Total system availability has been measured at plus 95%. Phase 1 acceptance testing of the supervisory software indicates a notable increase in copper recovery with no significant change in final copper grade.

Jan 1, 1999

By William J. Attwooll

The development of gold heap leach projects in the Cripple Creek, Colorado, mining district has required utilization of heap leach pad sites other than relatively level natural ground. This paper describes the construction of a heap leach pad adequate to accommodate 907,000 tonnes (1,000,000 st) of ore over the surface of a tailings pond constructed during previous milling activities at the site. Based on the design parameters and the observed behavior to date, it has been found feasible to construct a major heap leach pile on the surface of a conventional tailings pond.

Jan 1, 1987