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By W. M. Ma, Daniel W. H. Su, K. Centofanti, Yi Luo, W. L. Zhong, Syd S. Peng

9.1 INTRODUCTION There are approximately 70,000 abandoned coal mines nation¬wide, which is about 35 times the number of underground coal mines presently operating. The US Bureau of Mines estimates that there are over 8 million acres of undermined land due to the extraction of coal, metals, and nonmetals. Subsidence has affected more than 2 million acres, and more than 99% of the subsidence is related to underground coal mining. There is reason to believe that some of the remaining 6 million acres of the undermined land have a high potential to subside. The expansion of housing, highways, commercial structures, and other facilities has required the use of many areas that are underlain by abandoned coal mines, and this growth will continue. Many subsidence problems are derived from the collapse of aban¬doned underground coal mines. There are numerous abandoned mine workings in the anthracite fields of northeastern Pennsylva¬nia, in the Appalachian bituminous fields, the Illinois Basin, the Rock Springs, Wyoming area, and other areas of the United States (Gray et al., 1976). Various room and pillar patterns of mining have been used in the dipping anthracite seams and the nearly flat-lying bituminous seams with considerable variation in the per¬centage of coal extracted. The progressive deterioration of pillars, mine floors, and mine roofs after long exposure to air and water may later result in the collapse of strata over the mine entries, the crushing of the remaining coal pillars, or the bearing failure of the mine floor beneath the coal pillars. Subsidence then results as the collapse reaches the ground surface in the form of differential strains, depressions, cracking of the ground, and sinkhole devel¬opment. Subsidence over active longwall mines, which occurs concurrently with mining or is completed within a short period following coal extraction, has been studied extensively over the past decade. On the other hand, subsidence over abandoned coal mines receives little attention by the researchers, mainly because it is difficult to predict and takes place decades after mining has ceased. The techniques of investigating the subsidence events over abandoned coal mines are similar to those employed for active mines except that at the outset, it is necessary to determine whether or not the subsidence events are mining-related (Chugh et al., 1986; Cummings and Singh, 1986; Peng and Hsiung, 1986). This calls for the identification and confirmation of abandoned mine workings under or near the affected surface structures. Gen¬erally old mine maps, if available, are acquired, the surface bore¬holes are drilled for confirmation of the accuracy of the mine maps and determination of the potential for continued subsidence. Sub¬sidence monuments are established and periodic surveys con¬ducted to determine the amount and trends of surface movement in and around the affected surface structures; surface boreholes are used to investigate the integrity of the underground structures (i.e., roof, coal pillars, and floor) by TV camera. They are also used for monitoring the vertical and horizontal movements of the subsur¬face strata by Sondex (FPBX) and inclinometer (PFBI), respec¬tively, for determining the continuity of the subsidence events. Tape extensometers, crackmeters, etc., are used to monitor the development trends of major cracks in the structures or on the ground. These data are used to identify the causes of the subsidence events. Finally, abatement methods are selected to stabilize the structures. It must be noted that most subsidence events over abandoned coal mines are reported after the fact, and investiga¬tions are begun some time after reporting, that the subsequent measured movements are generally much smaller than that at¬tained in the active mines, and that due to lack of knowledge about the damage conditions and the exact location of the abandoned mine workings with respect to the affected surface structures, the precise causes of surface subsidence or surface structural damages are in most cases very difficult to identify. 9.2 TYPES OF SURFACE SUBSIDENCE According to Gray et al. (1977), after examining 354 incidents of subsidence above abandoned mines in the Pittsburgh metropol¬itan area, the subsidence features have a mean diameter (i.e. the average of long and short dimensions) from less than 1 ft to 1600 ft, with 84% less than or equal to 15 ft; the subsidence features have a depth ranging from less than 1 ft to 48 ft, with 89% less than 25 ft; 66% of the subsidence features are deeper than they are broad. Nearly 59% of the subsidence features occur with overbur¬den less than 50 ft thick and 81% less than 100 ft thick. No subsidence features occur with overburden thicker than 450 ft (Fig. 9.1). Occurrence of subsidence incidents varies from imme¬diately to more than 100 years after mining (Fig. 9.2). In analyzing the characteristics of approximately 3000 chim¬ney subsidence features along the Colorado Front Range, Matheson and Eckert-Clift (1986) examined historical aerial photographs on 4- to 14-year intervals between 1937 and 1967 and found that the majority of observable surface subsidence features occurred within 30 to 40 years after mining. According to Gray et al. (1977), the most prevalent subsi¬dence features over abandoned mined land are sinkholes, with depths of more than 3 ft, and troughs or sags, usually less than 3 ft deep. Sinkholes are steep-sided pits, while troughs are shallow depressions much wider in area than sinkholes. A. SINKHOLE SUBSIDENCE A sinkhole is caused by the collapse of a mine roof that works its way upward. If it is not arrested during the process it will eventually reach the surface and emerge as a sinkhole. The process is governed by the thickness and character of the overburden, the width and height of the mine openings. Sinkholes are usually 3 to 20 ft deep and may be 2 to 40 ft in diameter, although most are fewer than 16 ft across (Gray et al., 1977; DuMontelle and Bauer, 1983). Newly formed sinkholes have steep sides with straight or bell-shaped walls. At times, they appear to be conical in profile with the apex upward. If the topsoil collapses, the top portion will widen to form an hour-glass shape. Sinkhole subsidence usually occurs over abandoned mines less than 165 ft deep (Hunt, 1979). Matheson and Eckert-Clift (1986) found that chimney sink¬holes are likely to occur when the ratio of overburden thickness to mining height (h/m) is less than 4 to 5. When h/m is between 5 and 10 to 11, the potential occurrence of chimney sinkholes decreases rapidly. When h/m is more than 10 to 11, less than 10% of the mine openings that collapse will induce sinkholes on the surface.

Jan 1, 1992

By E. T. Pecina

Bioleaching is a viable option for the processing of auriargentiferous refractory ores with high arsenic content. The application of mesophilic (A. ferrooxidans and ?L. ferrooxidans?) and thermophilic bacteria of the genus Sulfolobus (S. solfataricus and S. acidocaldarius) as oxidant treatment before the cyanidation of an industrial arsenical pyrite concentrate is presented. The results show that extraction of gold and silver increases due to bio-oxidation caused by mesophilic bacteria and results in a maximum gold recovery of 68%. In all strains studied, biooxidation resulted in an average silver recovery of 50%. The results showed that all evaluated strains were sensitive to solids content (5 to 20%) and average particle size (75 and 38 µm) of the concentrate.

Jan 1, 2010

By C. R. Stephan

Explosion-resistant seals in underground coal mines isolate the environment within the sealed area from the active workings of the mine. The current United States Title 30 Code of Federal Regulations (CFR) requires these seals to be constructed of solid concrete blocks. The CFR also allows for alternative methods or materials to be used to create a seal if they can withstand a static horizontal pressure of 138 kpa (20 psi), provided the method of installation and the material used is approved in the ventilation plan. The purpose of this report is to identify those explosion-resistant seals that have been tested and meet or exceed all the requirements of the CFR.

Jan 1, 1997

By Felicia F. Peng

Using a fuzzy logic controller, a signal applied on the processes may be generated through a linguistic protocol expressing an operator's intuitive control strategies. In this work, fuzzy logic controller and PID controller imposed upon the feedback liquid level control systems for a stirred tank are studied and compared. The construction factors including the shape of membership functions, number of fuzzy variables, number of inputs, number of rules, and different defuzzification methods are considered in design and formulating the fuzzy logic control strategies and algorithms. From the analysis of the strategies and control performances, an optimum controller may be generated by making use of the best combination of these fuzzy construction factors.

Jan 1, 1997

By L. A. Henry

The island of Jamaica consists predominantly of Carbonate rocks which vary in chemical & physical characteristics. Currently these rocks are used for construction and road aggregate, landfill and as a raw material in the manufacture of cement. Over the past fifteen years the Geological Survey of Jamaica with assistance from a number of international aid agencies and the private sector have identified deposits of high calcium/high brightness limestones which have the potential to be utilized as a high quality filler and a number of other commercial applications. Geologically, these limestones are formed within the Eocene Swanswick Formation, the Oligocene Walderston-Browns Town Formation and to a lesser extent the Miocene Montpelier and Newport Formations.

Jan 1, 1998

By D. D. Harbuck

Previous studies at the U.S. Bureau of Hines have shown that only 70 to 80% of the germanium in domestic zinc process residues can be extracted during H2S04 leaching. To increase germanium extraction, the Bureau developed and researched the hypothesis that minor amounts of germanium and zinc silicate, both present in zinc calcine, dissolve during the leaching stages of zinc processing, forming soluble germanium and silica gel. This silica gel then selectively adsorbs germanium from solution, rendering the germanium insoluble. Testing showed that as the amount of silica gel formed increased, the amount of insoluble germanium in the zinc residue increased. Several processing alternatives are presented for overcoming this problem.

Jan 1, 1991

By Frederick B. Henderson

On 10 August 1976, The Geosat Committee was organized in Denver to institute The Geosat Program. This program is an industry backed effort to evaluate and help select optimum space remote sensing systems for geological purposes. It is believed that the recommendations of The Geosat Committee can be supported by industry as additional exploration tools which can materially benefit industry and the Nation with respect to our energy and other natural resources needs. Appended is a general summary of The Geosat Committee Organizational Meeting and general review of The Geosat Program. The Geosat Workshop Report. The Geosat Committee, and The Geosat Program will be reviewed at a special afternoon session, Friday, 3 September.

Jan 1, 1976

By T. Zoltai

Asbestos is a generic term for industrially useful fibers recovered from exploitable deposits of the asbestiform varieties of five silicate minerals: chrysotile, anthophyl-lite, actinolite-tremolite, cummingtorute-grunerite, and rie-beekite. Asbestos and asbestiform fibers of some other minerals are known to be carcinogenic. Minerals crystallized in the asbestiform habit-are characterized by unique properties (morphology, strength and flexibility, physical and chemical durability, and defect-free surface structures). The key to the unusual properties, and health effects, of asbestiform fibers appears to be in their unusual surface structure. In contrast, non-asbestiform crystals of the same minerals, including the five so called asbestos minerals, do not have these properties and are not carcinogenic.

Jan 1, 1989

By Daniel G. Ganey

Kerr-McGee Coal Corporation has used diesel face haulage and support equipment at its dual-seam Galatia Mine in Southern Illinois since production activities commenced in 1983. The mine began production from its lower seam, the Harrisburg No. 5 coal seam, in October 1983 and from the upper Herrin No.6 coal seam in April 1985. Before production began, the company developed a program designed to make use of the flexibility offered by diesel equipment. While productivity was an important goal, the top priority of the program was to provide a safe and healthy work environment for the miners. Management believed that high productivity would naturally follow. History has proven this belief to be true.

Jan 1, 1990

By Jim Johnson

The purpose of this paper is to summarize and discuss a variety of site specific conditions which are typically evaluated as part of the engineering design process for heap leach pads, solution control ponds, and associated facilities. The following sections will focus primarily on the topographic, climatologic, hydrologic, and geotechnical evaluations critical to selection of heap leach sites, and selection of a preferred heap leach configuration or method. Other important considerations in the design of a heap leach project, including evaluation of ore properties and leachability, pregnant solution processing requirements, spent ore neutralization/disposal requirements, and other anticipated reclamation requirements are beyond the scope of this paper are not addressed in any detail.

Jan 1, 1998

By Dirk van Zyl

Three conditions are required for a risk to be realized: (1) a source of risk (i.e., hazard) must exists (2) some process must take place which will lead to the exposure of people, animals, and/or the environment to the hazard: and (3) as a result of the expense, undesirable effects are produced on the people, animals, and/or the environment. A comprehensive risk assessment addresses all three of the conditions through the following four steps: (1) risk source (hazard) characterization, (2) exposure assessment, (3) dose-response assessment, and (4) risk estimation. Although the terminology may differ, the overall approach of financial, public health, and environmental risk assessments is the same (National Science Foundation, 1985).

Jan 1, 1988

By R. J. Caine

Like most major firms engaged in project management, Dravo Corporation faces a constant challenge to keep its management systems in tune with the ever-increasing demands imposed by larger and more complex projects. This paper suggests that one of the key elements in meeting this challenge is more effective organization of project data. It reveals some of the details of a program at Dravo's Minerals 6 Metals Division which seeks, through better organization of project data, to improve Dravo's capabilities in estimating, cost control, scheduling, performance reporting and material control. In particular, this paper discusses ideas Dravo is developing for improved job numbering, codes of accounts, requisition and purchase order numbering, inventory cataloging, and employee/badge numbering.

Jan 1, 1980

By Joseph R. Hatch

During the past ten years detailed elemental analyses of approximately 8,000 well-documented samples of coils in the United States (including Alaska) have been produced by the U.S. Geological Survey and the various State geological surveys. Examples of data listings include Swanson and others (1976) Gluskoter and others (1977) Hatch, Affolter, and Davis (1979), and Wedge and Hatch (1980). These analyses serve as a basis for evaluating elemental abundances in coals from the various coal province, regions, and fields. When combined with additional geological and geochemical data, some of these analyses give insight into when certain elements were introduced into coals, and which physical and geochemical parameters are most important in determining coal elemental composition.

Jan 1, 1982

By J. Jeremy Burden, Bruce S. Brown

A major question in the design and permitting of a tailings storage facility is the quality and quantity of seepage which will occur from the base of the tailings facility into the underlying foundation and groundwater regime. A corollary to this is what liner system, if any, is necessary to protect the groundwater regime from unacceptable contamination. Modern tailings storage facilities are generally designed as drained tailings deposits whereby all free water is removed from the facility by decant, drainage and evaporation. This removes the source of on­going seepage and allows for efficient and timely reclamation of the facilities. Quantifying the residual seepage from the base of the tailings deposit is complicated due to the following factors:

Jan 1, 1992

By C. H. Bucknam, A. M. Raichur, M. Misra

Simultaneous dissolution of mercury along with gold occurs during cyanidation of gold ores. A method has been found for the efficient removal of mercury from the gold cyanide solution by treating with dithiocarbamates which form stable compounds with mercury. The mercury concentration in the leach solution can be brought down to low levels by adopting this treatment. Furthermore, it is also possible to stabilize the mercury in the ore heap itself by addition of this reagent so that mercury does not dissolve in the cyanide solution during heap leaching. Only trace amounts of mercury were detected in the pregnant solution obtained from a heap treated with dithiocarbamates. In this paper, process parameters are discussed in detail.

Jan 1, 1997

By James H. Lammers

Over the years, the chemical processing industries have con­tinued to move from batch to continuous processing in order to obtain better quality control, simpler designs, and often reduced capital and operating costs. One exception to this trend has been the carbon elution circuits in the gold industry. Although some successes have been achieved on a pilot scale, no continuous elu­tion circuit using Anglo American Research Laboratory (AARL) methods has ever been used on a commercial scale until now. This paper describes the continuous elution circuit which was recently commissioned at a major gold project. The paper also presents the economic justification for the selection of the process over conventional batch technology.

Jan 1, 1998

By Bruce W. Cavender

There is a tendency for managers of mining companies to regard the performance of a process plant as essen­tially fixed, with only incremental improvements to be realized by optimizing individual unit operations. However, a number of op­erations management methods are available that will substantially improve plant performance, through both productivity increases and cost reductions. Known collectively as "world-class manufac­turing" techniques, these include total quality control, just-in-time production and inventory management, the systematic develop­ment of innovative plant practices, and progressive management accounting and business control systems. The implementation of these techniques by plant managers and operators will enable the plant's performance to exceed levels that are currently believed to be maximized.

Jan 1, 1993

By J. H. Heintz

This paper discusses the law as it relates to appraising operational mining properties in the context of a takings claim. Topics include the need for valuation expertise, the differences between de jure and de facto takings, an overview of the law of condemnation, including jurisdictional issues, and defining your strategic options according to the controlling statute. State condemnation law varies by jurisdiction and just compensation can be calculated by comparable sales unit-times-price, before ¬after-valuation, capitalization of income and discounted cash flow methods. Takings under Federal laws are reviewed, as is the necessity of assembling a team including attorneys, valuation experts including a mineral appraiser, a real estate appraiser, economists and geologists.

Jan 1, 2002

By William R. Bond, Jim V. Rouse, Laura L. Damon

As noted by Damon (1990), "The time that a heap (of gold ore) is on the reusable leach pad is of critical economic importance." The Interim Neutralization Study, conducted by Brohm Mining Corporation (Brohm), at the request of the South Dakota Department of Water and Natural Resources and reported by Damon indicated that improvements could be made in leaching and pointed out the need for a better understanding of the gold ore leach procedures. To provide data on an actual heap, personnel from Brohm and GEOCHEM installed a series of pressure/vacuum lysimeters in an active Brohm heap, and conducted subsequent testwork to evaluate the efficiency of leaching. The objectives of the testwork included efforts to:

Jan 1, 1992

By R. Z. Pyrih

Pressure/ ,acuum lysimeters were used to instrument column tests containing several lifts of tailings slurry, and to sample pore water as the tailings lifts dried. The results of the column testwork demonstrated that air oxidation of sulfide minerals associated wilh the tailings residue neutralized the alkalinity of the tailings pore water. Neutralization of the alkaline pH volatilized cyanide which, in turn, destabilized copper-cyanide complexes and caused the precipitation of insoluble copper from solution. Analyses of pore water samples for microbial activity indicated high plate counts. The presence of viable microorganisms in the pore water implied that degradation of cyanide was enhanced by growth and activity of cyanide-consuming microorganisms in the tailings material.

Jan 1, 1991