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By K. F. Unrug

The concept of bolting mine roofs to prevent roof falls was initiated in the 1950's and was quickly accepted by the mining industry because it was inexpensive, effective and convenient. The principle regarding roof bolting were that: a) the loose and fragmented rocks were suspended from or clamped to more competent surrounding rock and b) generally, by clamping several layers of thin and laminated strata, a more competent monolithic beam is created.

Jan 1, 1991

By L. M. Chan, D. H. Carlson, J. H. Johnson

This paper discusses laboratory evaluation of a tailpipe emissions measurement apparatus (EMA) developed by Michigan Technological University (MTU) under contract to the Bureau of Mines. The apparatus dilutes diesel exhaust and measures the concentrations of diesel particulate matter (DPM), CO, C02, NO and NO2 at known dilution ratios. The EMA was evaluated by side-by-side comparison of its measurements with those by laboratory grade instruments. During the preliminary laboratory evaluation concentrations of DPM, CO and CO2 were measured. The concentrations of CO and CO2 measured by the EMA were usually within ±14 pct of laboratory-measured values for CO and ±20 pct for CO2. EMA DPM concentrations correlated well (r = 0.96) with the laboratory values, but were 29 pct lower on average. The CO and C02 differences were observed to be related to the method of calculating the EMAs' dilution ratio and the difference in DPM concentrations is attributed to thermophoretic and/or condensation losses related to the EMA's unheated sample probe. Preliminery analysis of data obtained with a heated sampling probe and modifications in the sampling procedures have indicated reduced variability in DPM and in the calculated dilution ratios.

Jan 1, 1991

By G. E. McKelvey

A group of gold deposits in southeastern Ecuador, near the town of Zamora, have become the focus of intensive mining activity, due to their extremely high gold grade (unconfirmed reports of about 50 g/t or 1.4 oz per st, or more). The deposits at Nambija and other prospects in the district are hosted by a sequence of sedimentary and volcanic rocks that are present within a large xenolith orpendant within alkalic phases of the Jurassic Zamora Batholith. The xenolith, unknown in size, is composed of various island arc lithologies (limestones, shales, sandstones, tuffs and flows). All have been altered to some degree by skarn-hornfelde alteration assemblages. Mineralized areas appear to be localized within a linear zone containing tectonic and intrusion breccias that cross-cut a complex calcic skarn assemblage developed within the xenolith. Although the nature of the host rocks appears to have exerted some control on mineralization, the high-grade ore is concentrated along north-northeast trending breccias, faults and dikes that crosscut the flat-lying stratigraphy and skarn alteration as suggested by the strong linear trend of workings in the district.

Jan 1, 1991

By F. N. Kissell, N. I. Jayaraman

Dust scrubbers on continuous miners are steadily gaining in popularity. Recent US Bureau of Mines research on scrubbers is reviewed, with emphasis on development of a new type of water-powered scrubber that can be retrofitted to existing miners; comparison of scrubber effectiveness with blowing and exhaust line ventilation; and improving the quartz dust collection of flooded-bed panels.

Jan 1, 1991

By Jiang Shuguang, Zhang Huicheng, Wang Xingshen

Based on the experience about determination of properties of the main fan in mine shaft, this paper relates at length how to reasonablly select test system, test methods and test instruments, how to appraise the reliability of determination results, and how to effectively control the adjusted air etc. The merits and demerits of the two methods of determining air with Nine- Anemometer and Pitot meter are compared.

Jan 1, 1991

By D. L. Petersen, C. R. Nelson, P. M. Bergson, B. K. Nelson

Membrane waterproofing systems in large tunnels cause the partial decoupling of the concrete liner from the rockbolted and shotcreted reinforced rockmass. This decoupling leads to a loose fit of the liner in the excavation when shrinkage from cooling and moisture loss occurs. This increases tensile stresses which require either the addition of reinforcing steel in excess of common European practice or the potential for liner cracking. Hot weather concrete placement and cold weather service conditions increase the magnitude of the problem, while creep of the rockmass reduces it. Contact grouting also reduces, but does not eliminate, the problem.

Jan 1, 1991

By J. P. Stone

The Mining Regulatory Affairs review arrived in time for the May issue. The Managing Editor inadvertently buried it in one of his paper piles. Regulatory developments at the federal level involving the minerals industry solid waste disposal under the Resources Conservation and Recovery Act (RCRA) remained at the forefront of concern. The Environmental Protection Agency (EPA) received public comments on two major documents. One was a strawman draft rule covering wastes from mining and beneficiation. The other was a report to congress covering selected mineral processing wastes. The regulation of minerals industry waste management is moving forward on parallel paths. Mining and beneficiation waste is somewhat further advanced.

Jan 1, 1991

By J. Baz-Dresch

A custom-designed shotcrete system, consisting of an 8-m3 (10-yd3) transit mixer and a shotcrete spray boom carrier, is used bya 2-man crew to transport and place up to 25 m3 (32 yd3) of steel-fiber reinforced, dry, silica fume shotcrete per II-hour shift. Shotcrete is custom blended by a local supplier and delivered predampened. Mix design and quality control is performed with a computer program that develops and graphs a properly balanced mix based upon the materials sieve analyses.

Jan 1, 1991

By M. S. Seehra, V. Suresh Babu, R. S. Pandurangi

Different mixtures of the three polymorphs of silica viz. quartz, cristobalite and tridymite are analyzed by x-ray diffraction (XRD) and their IR spectra are investigated by photoacoustic spectroscopy. It is observed that XRD provides a higher resolution to distinguish between the three polymorphs in a sample than IR spectroscopy. In the latter, a sharp band near 617 cm-1 is characteristic of both cristobalite and tridymite. A mine dust sample is quantitatively analyzed by XRD and it is shown to contain illite, quartz, kaolinite and calcite.

Jan 1, 1991

By A. Bhattacherjee

Industries in general and the mining industry in particular have become more safe than ever before. However, there is a need to increase the search for the causes of mining work-related injuries and to contribute to their reduction through job design, work procedures, and worker training. Mine accident and hazard control has to be practiced in a manner which is consistent with the overall objectives of the mine management, among which are the optimum allocation and effective utilization of the resources. The purposes of this paper are to (i) review the role risk analysis in safety management with references from mining and other industries; (ii) discuss the risk measures appropriate for injury analysis; (iii) present a set of analytical tools to injury experience data in under-ground coal mines; (i v) apply these tools on case study example; (v) discuss the results of the case study; and (vi) amplify the application limitations and the future research needs.

Jan 1, 1991

By G. L. Myers

The Fortitude skarn near Battle Mountain, NV is currently one of the largest producing gold skarns in the world. It contains about 11 Mt (12 million st) of minable ore grading 5.14 g/t (0.149 oz per st) and is the distal portion of a continuous skarn system in the Copper Canyon area centered on the Eocene Copper Canyon granodiorite porphyry. Calcsilicate compositions, opaque mineralogy, and the high gold grades are atypical of other base metal skarns (iron, Fe; copper, Cu; lead-zinc, Pb-Zn; or tungsten, W). The Copper Canyon skarn is systematically zoned from a garnet (AD 70-100) dominant, pyroxene (HD 20-45) subordinate zone, with major Cu mineralization, adjacent to the intrusive (West ore body), to a pyroxene (HD20-100) dominant, garnet (AD90-100 cores. AD 30-60 rims)subordinate assemblage, with major Au, near the distal marble front (Fortitude ore body). An extensive biotite ± diopsidic pyroxene ± kspar alteration halo surrounds the pyroxene > garnet gold-bearing skarn and represents the early stages of metasomatic alteration. Retrograde alteration is limited in areal extent and intensity, and consists of actinolite, chlorite, quartz, and prehnite. Economic gold mineralization begins in the pyroxene > garnet zone and continues to the marble front, a distance of 1 to 1.5 km (0.6 to 0.9 miles), respectively, from the plutonic contact. The opaque mineralogy in this gold zone includes pyrrhotite, arsenopyrite, marcasite, minor chalcopyrite, galena, sphalerite, argentite, hessite, hedleyite, volnyskite, and native bismuth and gold. The pyrite-pyrrhotite geothermometer yields temperatures that range from 450° C to 300°C (842° F to 582° F) and the electrum-argentite-sphalerite geothermometer yields temperatures which range from 290°C (554° F) at the marble front to about 420°C (788° F) more proximal to the intrusive. Log fS2 calculations from the sulfide assemblages yield values near - 10 with log fO2 values of about -30, in a solution of near neutral pH (5-6). Calculations of metal solubility suggest that the metals were transported as chloride complexes in the proximal skarn but that bisulfide complexes were predominant within the distal gold skarn. Relatively low oxidation states buffered by the carbonaceous to argilliceous, calcareous protolith and subsequent ferrous iron-rich skarn assemblages appear to have increased the gold carrying capacity of this large hydrothermal system.

Jan 1, 1991

By Howard L. Hartman

To concede that I am the most surprised - not to mention the least likely - recipient of the Daniel C. Jackling Award is a true confession I must share with you. Quite honestly, I've asked myself, "Why me?" The Jackling Award has a well-deserved reputation of being a practitioner's, a doer's, a CEO's award - not kudos for a retired school teacher! While at least five of the previous recipients have taught in universities, to my knowledge I am the first to earn the award for "alleged" academic accomplishments. It is humbling enough to keep me livable for a long time. If you glance over the roster of Jackling Award lecture topics, you will spot another anomaly: The lectures last year and this deal with the subject of education - the only two in the 37-year history of the award. The two complement one another rather well, too, C. Allen Bom of Amax addressing critical needs of public education, while I am going to look at the post-high-school years. But I want to focus on more than engineering education. The training role of industry - the principal consumer of our product-also warrants examination. As I hope to establish, there is something unique about mining engineering - education and practice - that is both strength and weakness. We need to recognize that, if we are to cope with the weaknesses in order to capitalize on the strengths. We look at five premises that relate to the uniqueness of the mining engineer and his or her preparation for a professional career.

Jan 1, 1991

The thermal field of a frozen rockmass surrounding an airway is often disturbed due to thermal interaction with mine ventilation air. Outside air entering an underground mine changes the parameters of the physical state of the surrounding medium. The variations in air temperature result in stress redistributions around a tunnel or mine working. This paper examines the influence of fluctuations in air temperature on stress distribution around an airway, and approaches are suggested to minimize the impact of temperature- stress on the stability of mine openings in far northern mines.

Jan 1, 1991

By B. J. Arnold, F. F. Aplan

Prior laboratory work has demonstrated that much of the fine ash forming minerals entering a flotation froth are there as a result of water carryover- from the bulk contents of the flotation cell (Arnold and Aplan, 1986a). Using a bank of four 8.5 m3 (300 cu ft) Wemco flotation cells cleaning a well-liberated Lower Kittanning seam coal, test results show that the sulfur and ash content of the froth is directly related to the water content of the froth (or inversely related to the percent solids in the froth). Reagent changes that result in a watery froth produce a higher ash content in the froth. A direct comparison of laboratory and plant results show that the standard laboratory flotation test produces a product higher in sulfur and ash than that produced in the plant. Caution should be exercised when extrapolating laboratory test results to the plant situation. A method of estimating coal flotation product quality in the plant based on laboratory tests is given.

Jan 1, 1991

By R. P. Moran, B. C. Lewis

The objective of this article is to discuss the fundamentals for determining the value of a limestone reserve or operation. The general step-by-step procedure, while prudent, is subject to the various site-specific issues that influence the valuation calculation. The most common methods for determining fair market value of mining lands are: comparable sales, operational analysis, and royalty analysis. An overview of typical eastern limestone mines (both quarries and underground) is presented. Specifically, properties in West Virginia and Alabama are reviewed and the sample methodologies and valuation calculations are presented.

Jan 1, 1991

By X. Wu, M. Karfakis, E. Topuz

The generalized ventilation network problems encompassing both natural and controlled splitting networks, is formulated using a nonlinear nonconvex programming model, which has not yet been solved satisfactorily. This paper presents a methodology which can deal with the problem. The proposed methodology converts the nonlinear problem into a linear problem, by using special ordered sets of variables, and optimizes it by a modified branch and bound technique. The global optimality of the methodology and its applicability to different cases are investigated

Jan 1, 1991

By R. Sandrik

Northwestern Resources Co. (NWR) was established in 1972 as a wholly-owned subsidiary of Western Energy Company of Butte, Montana, to acquire, explore, develop, and produce energy resources outside the state of Montana. Western Energy is a coal mining company with successful operations in Montana and Wyoming. In 1974, NWR acquired its first lignite lease in Texas. NWR eventually acquired a large leasehold in central Texas, which was identified as having a high potential for future production. In 1979. NWR contracted to supply lignite to Utility Fuels, Inc. (UFI), a fuel affiliate of Houston Lighting and Power Company (HL&P). This project, together with leases held by UFI, became the Jewett Mine. Lignite from the Jewett Mine is used as fuel at the adjacent HL&P Limestone Electric Generating Station, at an annual rate of approximately 7.3 Gkg (eight (8) million tons) per year.

Jan 1, 1991

By John H. Archibald, Arthur L. Miller, George A. Savanick

As part of its continuing research on selective mining, the Bureau of Mines has made progress toward developing a tool capable of remotely extracting hard minerals through a borehole. As the successor to the successful borehole miner, which extracted soft materials through a straight borehole, this new device has several innovative features: 1) it can propel itself in and out of an 8-inch borehole; 2) it can cut hard rock with an abrasive jet and transport the cuttings to the surface; and 3) it can negotiate deviated boreholes--the feature that enables it to follow a vein and extract only the values. This paper describes the development and feature testing of the reamer/miner.

Jan 1, 1991

By Carl S. Vender

Knife River Coal Mining Co.'s Beulah Mine is a multiple-seam lignite operation located in western North Dakota. The mine began production in 1963 with annual production of 450 kt (496,000 st). It now produces 2.2 Mt/a (2.4 million stpy). As development progresses, operations advanced into more complex geologic areas. Various techniques have been analyzed to maximize coal recovery in a cost-effective manner. Additional studies are ongoing to determine what changes will be implemented as deep, wet sands are encountered in the reserve area. Knife River Coal began as an underground operation in 1924 at Beulah, 120 km (75 miles) northwest of Bismarck. In 1950, the operation converted to a combination underground and surface mine. The underground segment was closed in 1952. Development of the existing reserve area south of Beulah began in 1963. About one-fourth of the acreage under permit (Fig. 1) is sufficient for 10 years at current production rates.

Jan 1, 1991

By C. O. Brawner

Geotechnical theory is reasonably well developed to evaluate the stability of rock slopes for surface mining projects. It is recognized widely that structural geology, groundwater pressures and seepage, and blasting are key factors that influence the stability of such slopes. However, our capabilities to model the structural geology, to determine rock strength along discontinuities and to model groundwater pressures and profiles are still very approximate. Plus, practical experience of the rock mechanics engineer is one of the most important inputs to the design of open pit mine slopes. To emphasize the use of practical experience, a number of case examples are reviewed here to illustrate key factors that must be evaluated. These case examples comprise a continuation of other examples presented in the Jackling lecture to the SME in 1986 by the author (Brawner, 1986). Example no. 1 In situations where the orientation of geologic discontinuities will not influence rock slope stability, extremely steep slopes can be developed, providing blasting and groundwater are controlled adequately. An excellent example of this condition is the Republic Pit of Cleveland Cliffs in Michigan. The rock slope in Fig. 1 isover400fthigh with a face angle of approximately 80". The rock is hard and massive, and blasting was carefully controlled. The original design of this slope was at45", a standard design angle at that time. The competency of the rock and the lack of critical geologic structure subsequently was recognized, and the much steeper slope angle was developed successfully. The rock proved to be so competent and the slope sufficiently stable that an underground crusher station was developed with entrance and exit tunnels excavated at the toe of the steep wall.

Jan 1, 1991