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By J. L. Liow

Studies have been carried out on the causes and effects of slopping in an annular cylindrical geometry such as the top submerged combustion reactor. Properties of standing waves formed such as the wave profile, period, pressure distribution and velocity have been derived analytically. The wear profile due to wave erosion was calculated based on the assumption of linear motion and that the wear is a dissolution process. The use of the j, factor showed that the wear was proportional to the square root of the wave velocity at any point. Using the dimensions of the lsasmelt reactor given by Errington et al. (1987)[11, the wear profile due to wave erosion was calculated using the analytical solution. The wear profile calculated was shown to have a maximum just below the initial bath surface. The wear was found to be concentrated in the region where the first asymmetric standing wave was most active. The results showed that the refractory near the bath surface will be affected by wave erosion, more so than any other parts of the reactor. The contribution of wave erosion on wear must be accounted for in assessing the total refractory wear of a vessel in which slopping exists.

Jan 1, 1991

By Q Liu, P D. Katsabanis

Dust explosions in underground sulphide and oil shale mines result from the detonation of explosives in the blasting operations. Explosive composition, oxygen balance, priming and ideality of detonation were examined theoretically and experimentally in the presence of reactive sulphide dust. It was found that the temperature as well as the chemical composition of the gaseous products of detonation are the controlling parameters related to the explosive. Non aluminized, oxygen balanced emulsion explosives were proven to be relatively safe, while explosives creating combustible products were proven to be extremely dangerous due to the secondary flame they generate. Since a large number of dusty orebodies are often very friable, low density emulsion explosives are also examined for application in production blasting.

Jan 1, 1991

By A. Ghosh

Commonly used predictors of ground vibration from blasting, being linear in log-log plot, do not model the underlying physics of wave attenuation. Amplitude of the wave decays with distance due to geometrical spreading and inelastic attenuation producing a nonlinear carve in log-log scale. The nolinear decay of seismic waves has also been observed from non-explosive sources, such as, pile driving, drop hammer, traffic, etc. The improved predictors, by explicitly taking these two mechanisms into consideration, model the data trend extremely well at all distance ranges. Actual field data from different studies have been used to validate the improved models.

Jan 1, 1991

By Walter E. McCulloch

Installation of flash flotation in the copper concentrator of Freeport Indonesia in late 1986 and 1987 increased gold recovery by about 13%, while also increasing concentrator throughput. Copper recovery remained essentially the same. Flash flotation has since been included in a recently completed mill throughput expansion to 32,000 t/d (35,300 stpd) as well as in a current expansion to 52,000 t/d (57,300 stpd).

Jan 1, 1991

By Peter J. Nicholson

The methods of reinforcement to be discussed in this paper are all insitu methods, ones that can be used on the soil structure as it exists in the ground, and do not rely on excavation and replacement of the soil. Current practice in the United States, as well as new ideas and methods, will be discussed as they relate to slope stability, retaining walls, and to other uses such as control of mine or cavity related subsidence and to liquefaction control under existing structures. The method is based on the concept of "nailing" or reinforcing the soil in place, and thereby causing a mass of soil to act as a coherent unit. When performed properly, a true gravity structure can be constructed, one that will remain intact under both horizontal and vertical loadings and that will also resist vibrational and seismic loadings.

Jan 1, 1991

By Victor F. Hollister

Skam deposits considered as porphyry copper deposits have been classified into three basic prospecting models: (I) the skam deposit associated with a mineralized intrusive (Pima-Mission), (2) the deposit associated with a barren igneous stock (Ertsberg), and (3) mineralized rock that seems to have no clear association with apluton (Phoenix). Pima-Mission, Christmas, and many other copper-bearing skarns developed in carbonate sequences near mineralized intrusives form an important part of the deposit. Historically, copper derived from the mineralized intrusion accounts for less than half of the metal produced by most porphyry mines, as most mineralization occurs in the intruded rocks. Skam mineralization is an important part of wall-rock metal deposition, because carbonate sequences are preferentially replaced by sulfide and skarn minerals. Exploration for skam mineralization is an important phase of porphyry copper exploration. Impure carbonate beds can become better host rocks for skam deposits than pure carbonates, and these in particular should be included in porphyry-exploration programs if the impure strata are cut by the stock. Skam deposits can also form near stocks that are barren of sulfide. In this model, the two best ore guides are strata favorable for mineralization (usually impure carbonate beds) and the intrusive contact. Faults can also act as important ore controls. Some skarn deposits form that have no clear genetic connection with a stock, although intrusive rocks are known in the district. In such cases, the best ore guides are strata and district-wide faulting. Dikes and sills are also common and mineralization can locally prefer their contacts even though the igneous rocks are barren. Skam minerals are influenced by the chemical composition of the carbonate. Forsterite, brucite, tremolite, and talc are common in skams developed in dolomitic beds. Skams derived from calcic beds often contain wollastonite, calcite, stilbite, or idocrase. Diopside, however, is a common accompaniment of copper sulfide in skam regardless of the original composition of the carbonates. Tremolite and possibly other amphiboles and chlorite can occur significantly in the zinc-lead portion of skams. Gamets occur in magnetite, copper, and zinc-lead zones of skams, but are not as diagnostic as diopside for the copper zone or tremolite for the zinc-lead zone. A general desciption of skam-deposit mineralogy can be used to construct prospecting models of porphyry copper skams. An abstract of such a description follows.

Jan 1, 1991

By Thomas D. Kaufmann

Whether pursuing hedging or speculative strategies, gold miners can increase sales revenues 1 % to 6% by constantly pricing production forward. Unlike other commodities, gold futures prices are consistently higher than spot prices. A Colorado School of Mines study showed theoretically and empirically that in the 15 years since the price of gold was released from government control, the forward price for gold has been higher than the current price almost 100% of the time. The reason why Metal traders know that holders of metal earn a bonus selling forward when the metal is in "contango." "Contango" is a mysterious word that crept into the trading vocabulary a century ago. It designates a situation when the price of a metal on the futures markets is higher than the price in the immediate or spot market. If the spectrum of spot and futures prices remains static over time, the forward seller who has contracted at a higher than spot price can make a profit equal to the contango by redeeming his commitment at the lower spot price when the contract matures. Consequently, when a seller in a contango market hedges, he makes a profit on the transaction in addition to avoiding a price change risk. On the other hand, buyers of the metal who hedge in a contango situation will sustain a loss equal to the contango. Producers of gold, however, are sellers of gold. For most metals and oil, there is no inherent reason why futures prices should be higher than present prices. Buyers and sellers decide that the price of the commodity will be lower or higher than present values for a variety of reasons.

Jan 1, 1991

By E. G. Kelly

Many methods of evaluating the efficiency of mineral separations have been described in the literature. In most cases, these present the efficiency as a single number. This paper argues that single-number measures of efficiency are inadequate because they seldom allow reliable comparisons, and are unlikely to correspond to the optimum operating conditions. To realistically make comparisons, it is necessary to distinguish the particle-induced component from the equipment- induced component. In a number of situations where the separating property can be identified (such as in gravity concentration and classification), this can often be done. However, in more complicated systems, such as flotation, this has not been possible. A technique is described whereby particle and equipment contributions to efficiency can be distinguished without the need to define the separation property. Because smelter schedules define a boundary correlation between grade and recovery, they generate some of the better single¬-number measures of efficiency, but even these have limitations.

Jan 1, 1991

By LeRon E. Bielak

The marine minerals program of the Minerals Management Service (MMSI has undergone significant changes during 1991. Formerly the Office of Strategic and International Minerals, the program has been renamed and invested with additional responsibilities. The new name, Office of International Activities and Marine Minerals, (INTERMAR) reflects its dual mission. INTERMAR'S role in the international area was broadened in January 1991 to provide the MMS with a focal point for identifying and coordinating international opportunities of mutual interest and benefit. Opportunities include energy and nonenergy minerals and a broad range of areas such as resource and environmental assessment and management, structural and operational safety, royalty management, regulatory matters and public affairs. Cooperative efforts involving information exchanges, training programs, research, and similar arrangements are receiving particular emphasis. Australia, Canada, France, Japan, Sweden, the United Kingdom and the USSR represent a growing list of countries with whom arrangements have been established. Support has also been lent to other Federal Agencies and the United Nations in areas where MMS expertise and resources can impart a significant contribution. Opportunities will also be explored which involve Pacific insular areas.

Jan 1, 1991

By Randall Smith, Leslie Stayner

At the request of the Mine Safety and Health Administration, a quantitative assessment of the risk of lung cancer associated with occupational exposures to diesel exhaust was performed. This assessment was primarily based upon the results from a study of the effects of chronic inhalation exposure to diesel exhaust in Fischer-344 rats (previously reported by Mauderly et al., 1987). An adaptation of the Armitage-Doll multistage model, which allows for an age-dependent effect of exposure, was used to model the tumor response data. This model was fitted to all tumors (benign and malignant), and to malignant neoplasms alone. Estimates of unit risk (potency) were derived based upon a linear approximation to the results from the multistage model. A biologically equivalent dose was developed to scale the results from airborne exposure in rats to humans, which was adjusted for differences in weight, ventilation rate, deposition fraction, and the percentage of time actually exposed. Comparisons are made with risk estimates derived from modeling other rat inhalation bioassays and from applying different models to the study by Mauderly et al. (1987). We emphasize that our risk estimates are based upon a series of assumptions and carry a great deal of uncertainty. In particular, uncertainties regarding the effects of exposure on lung clearance mechanisms, the deposition rates in humans, and the relevance of our exposure index limit our confidence in these risk estimates. Because of these uncertainties, this risk assessment would best be viewed as an exploratory effort. Key words: Diesel, lung cancer, risk assessment

Jan 1, 1991

By Jerry Olson

The Bureau of Mines (Bureau) conducted a mineral resource investigation of the French Creek-Patrick Butte study area, in west central Idaho during 1989. No mineral resources or significant occurrences were identified. Other than small scale placer gold, no mineral production is known or recorded. At least 100 lode and 150 placer claims have been located in the study area. Most of the area was examined by ground or areal surveys, and 110 lode and 60 placer samples were taken. Four lode prospects were examined in detail, and all placer claim locations were sampled.

Jan 1, 1991

By David M. Mchaina, Michel Grenier, Stephen G. Hardcastle

An airborne dust survey was conducted at the Arthur W. White mine of Dickenson Mines Limited by CANMET/MRL and Dickenson Mines Limited Staff in April 1990 for the purpose of evaluating environmental conditions underground and in the surface mining plants. The survey was designed to measure respirable silica, total arsenic and lead concentrations at several workplaces. In addition, settled dust and rock samples were collected from workplaces and analysed for total arsenic content. More importantly, arsenic exposure data were needed to evaluate the impact of Ontario Regulation 176/86 as amended by Ontario Regulation 23/87. A total of 165 area and personal air filter samples were collected during the study. Of these, 85, 67 and 13 samples were for arsenic, silica and lead respectively. Sampling aid analyses were performed according to the Ontario Ministry of Labour Regulations. More than 90% of the workplaces sampled for respirable silica, total arsenic and lead were below the Ontario Ministry of Labour Regulations; and 10% of the workplaces sampled for arsenic shaved concentrations above the Threshold Limit value (TLV) proposed in the Ontario Regulation 176/86 as amended by Ontario Regulation 23/87. These results were used to identify occupations and/or workplaces where more sampling and control measures were required respirable silica, total arsenic and lead. This paper describes the results of the dust sampling program conducted at Dickenson Mines Limited.

Jan 1, 1991

By R. Kramer

During foundry sand reclamation process development, molds formed from reclaimed chromite sand showed a rapid decline in tensile strength during thermal cycling tests. Because this characteristic could limit reuse of chromite sand in the. foundry, the sand was examined in detail Scanning electron microscopy, x-ray mapping, magnetic susceptibility, and x-ray diffraction were utilized to evaluate processed chromite sand. It was found that process variables such as binder composition, reclamation temperature, and processing method had a significant effect on the chromite sand particle surface. X-ray diffraction indicated a crystallographic change in the processed sands. Magnetic susceptibility also increased after processing. Diffusion of iron to the particle surface and increased surface roughness were identified as potential causes of the decreased tensile strength in the molds.

Jan 1, 1991

By John F. Parmeter

On August 29, 1989, the Department of Labor, Mine Safety and Health Administration (MSHA), published a Federal Register concerning a new proposed rule on air quality, chemical substances and respiratory protection standards. As of this writing, their proposed rule has not become a standard. However, with little revision it could be expected to become a standard, and we in the mining industry will be expected to adhere to and enforce it.

Jan 1, 1991

By A. D. Fowler, M. T. Anderson

A phenomenological model is presented that relates Pb-Zn mineralisation to proximal geopressure zones. Typically, geopressure zones (GPZ) consist of masses of undercompacted sediment encapsulated within impermeable shales and are characterised by high formation fluid pressures. Heat flow is perturbed in some GPZ on account of their insulating properties. Geothermal gradients as high as 150 degrees C/km have been observed over short distances in the sediments of the US coast of the Gulf of Mexico. Some modern geopressure zones are known to reach temperatures of 120-150 degrees C at depths of 2.5-3.5 km. It is demonstrated that the zones may act as proximal sources of hydrothermal fluids, thus explaining the high temperatures of mineralisation observed in the deposits, which are hosted in basins characterised by thick, rapidly deposited, shale-rich clastic sequences

Jan 1, 1991

By I. M. Arbuthnot

Over the last five years, a large number of small to medium sized carbon-in-pulp gold treatment plants have been built in Australia, most designed to treat between 250,000 -1,500,000 tpa of ore. In many cases, the primary requirement was to get a plant built and operating in a short period of time and at minimal capital cost, relating to the limited capital resources and tight cash flow positions of these relatively small mining companies. Since the inclusion of both pre-leach and tailings thickeners resulted in an obvious and significant capital cost, most plants were built without thickeners, without doing a detailed cost-benefit analysis on their inclusion, However, the increasing use of High Rate Thickener?s (HRT s) in the mineral processing industries resulted in a reassessment, in some cases, because of their considerably lower cost. This reassessment was triggered primarily by the need to conserve water in arid mining areas, where borefields were costly to install and water was limited. It has become apparent, though, since startup and operation of these installations, that the savings in cyanide consumption is also a very significant factor and can be used as a primary justification for the installation of a HRT in many cases.

Jan 1, 1991

By J. Owens

Advanced materials development ranks as one of the most important high-tech industries of the future in the United States. Recent breakthroughs can be attributed to advanced computer technology, powerful mathematical models, and more precise analytical tools that enable scientists to examine and control properties of materials as never before. Discoveries now being made are providing many industries with opportunities to improve product lines, fabrication techniques, product reliability, and so forth. More¬over, industries, such as space, medicine, and defense, which require stringent: design and perfomance specifications in highly competitive world markets, increasingly demand these new materials. The definition of advanced materials used here is one that has been adopted by the U. S. Bureau of Mines: Those materials which have been developed over the past 30 years or so, and which are being developed at present, that exhibit greater strength, higher strength-density ratios, greater hardness, and/or one or more superior thermal, electrical, optical, or chemical properties, when compared with traditional materials.

Jan 1, 1991

By Carras S, Kelsey P, Caccetta L

An important problem in open pit mine planning is that of detennining the optimum ultimate pit limits of the mine. These limits are that contour which is the result of extracting the volume of material which provides the total maximum profit while satisfying certain practical operational requirements such as safe wall slopes. The determination of the optimum pit contour provides information that is essential in the evaluation of the economic potential of the mineral deposit. A number of optimisation techniques are available for determining this contour with the Lerchs-Grossman and the Network Flow methods being the most favoured. Unfortunately, direct application of these techniques to large ore-bodies may cause considerable difficulties because of the computational time and storage requirements. In this paper, we present a strategy for resolving these problems, and the associated pit design software PITOPTIM (incorporating a fast network flow technique) and a data reducer, BOUND. The results presented highlight the speed and power of the software package rivalling the popular Lerchs-Grossman technique. An application of the software for a sensitivity analysis is also presented and discussed.

Jan 1, 1991

By Frank A. Aplan, Barbara J. Arnold

INTRODUCTION Coal flotation is a fine cleaning process usually present in all but the older preparation plants. It is typically used to clean either the -28 mesh (-500 pm) or - 100 mesh (- 150 pm) raw coal fines, and it is the only commonly used preparation method that can effectively recover coal particles finer than, say, -200 mesh (74 pm). To place coal flotation into its proper context, it should be noted that the bulk of the raw coal sent to preparation plants is treated by gravity concentration. On a worldwide basis, from 0 to 40% of the raw feed to a preparation plant is treated by flotation, while in the US only about 10% of the raw coal feed is floated. Roughly, 50% of US preparation plants use flotation to process at least a portion of the raw coal feed, although most of the newer plants incorporate flotation into their flowsheet. Historically, the process has only been used to treat the raw coal fines naturally occurring after mining and a minimal amount of crushing at the preparation plant. This is in sharp contrast to ore flotation where, typically, the entire tonnage is first ground and then floated. As a consequence, of the approximately 500 Mt of raw coal treated by preparation in the US yearly, it is estimated that only about 40 Mt are sent to the flotation circuits (producing -30 Mt of clean product).'O1 This small tonnage compares with about 400 Mt of ores treated annually in the US by flotation. By analogy to ore flotation, where it is an effective, large tonnage, low cost, easy to operate process, its potential in coal preparation should be great. Reasons why it has not achieved a greater potential in coal preparation have been attributed by Aplan 102 to: 1. Indifferent results in removing sulfur and ash. 2. Difficulty in floating low rank and oxidized coals. 3. Inability to make clean separations with the finer sizes. 4.Inability to clean slurries with a high percentage of clay. 5. Problems with water chemistry. 6. Competition with effective, gravity coarse-cleaning methods. 7. Low value of coal historically. 8. Dewatering problems. 9. Transportation and storage problems with coal fines. 10. Marketing problems with coal fines. 11. Inadequate attention to the process in the plant. 12. Inefficient use of capital and operating monies. Inadequate attention to procedures, machines, and processes.

Jan 1, 1991

By L. E. Mercando

The proposed Flambeau Mining Project is based on a high grade copper deposit located approximately one mile southwest of Ladysmith, Wisconsin. The project involves only the mining, crushing, and shipping of ore to facilities outside of Wisconsin for processing. The Wisconsin environmental regulations include provisions for identifying wetlands, the requirements for minimizing the disturbance of wetlands, and the need to establish new wet-lands to replace any wetlands which have to be disturbed.

Jan 1, 1991