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

2.1 INTRODUCTION When total extraction of an opening of sufficient size is reached in a horizontal coal seam, the roof strata in the overburden deform continuously to reach a new equilibrium condition. The severity of deformation decreases upward toward the surface. As the downward saggings of the strata propagate and reach the surface, there will be a depression zone on the surface directly above, but extending beyond the edges of the underground opening. This is the surface subsidence basin or surface subsidence trough. The surface subsidence basin is circular in plan view, if the coal seam is horizontal and the mined-out opening is square in shape. But it is rectangular with rounded corners or elliptical if the coal seam is horizontal and the mined-out opening is a long- and thin rectangle or a short-rectangular, respectively (Fig. 2.1). Most underground openings (e.g., longwall panel) assume rectangular shape when total extraction has been completed. Theoretically the edges of the subsidence basin are the points of zero subsidence. But it is difficult to exactly locate the points of zero subsidence. Therefore in practice the points with vertical subsidence of 0.4 in. (10 mm) are used. The final subsidence basin is that which exists long after the mining has been completed, because its magnitude and shape are quite different from the dynamic subsidence basin formed while the face is moving. 2.2 CHARACTERISTICS AND TYPES OF DEFORMATION IN THE FINAL SUBSIDENCE BASIN For a horizontal coal seam, every point in the subsidence basin moves toward the center of the basin. Subsidence is maximum at the center of the basin. Any cross-section that passes through the point of maximum subsidence and either parallel to AB or CD line (Fig. 2.1) is a major cross-section along which principal directions of surface movements occur. However among those infinite numbers of major cross-sections, two specific ones are of special significance, not only because the magnitudes of surface movements are the largest, but also because they are the most easily identifiable directions, i.e., one that is parallel to the faceline at the center of the basin (CD in Fig. 2.1) and' the other is that perpendicular to the faceline but parallel to the diction of face advance (AB in Fig. 2.1). Nearly all the subsidence data obtained in the US have been derived from these two cross-sections, although some cross- sections parallel to CD but near the edges of the panel have also been included. In addition to moving horizontally toward the center of the basin, every point in the basin also subsides vertically. The magnitude of subsidence increases toward the center of the basin. Therefore surface subsidence is a three-dimensional problem and should be treated so in all cases. On all the major cross-sections, only principal subsidence and principal displacement occur. Since subsidence and displacement vary continuously in every major cross-section, three additional deformation components are de- rived, i.e., slope, curvature, and strain. On all other non-major cross-sections on the other hand the five components are accompanied by two additional components, i.e., twisting and shear strain. The seven components of the surface movement are defined as follows (Fig. 2.2): 1. Subsidence, S. On any cross-section, the vertical component of the surface movement vector is called surface subsidence. It generally points downward. But sometimes it points upward in areas ahead of the faceline or beyond the edges of the opening. In such cases it is a surface heave which is usually less than 6 in. 2. Displacement, U. On any cross-section, the horizontal component of the surface movement vector is called surface horizontal displacement. It generally points toward the center of the subsidence basin. But in steep terrain, it moves along the downdip direction 3. Slope, i. On any cross-section, the difference in surface subsidence between the two end points of a line section divided by the horizontal distance between the two points is called the surface slope of the section. 4. Curvature, K. On any cross-section, the difference in surface slope between two adjacent line sections divided by the average length of the two line sections is called the surface curvature of those two line sections. There are two types of curvature: con- vex or positive curvature and concave or negative curvature. 5. Horizontal strain, e. On any cross-section, the difference in horizontal displacement between any two points divided by the distance between the two points is called horizontal strain. If the distance between the two points is lengthening, it is tensile strain with positive sign. Conversely, if it is shortening, it is compressive strain with negative sign 6. Twisting, T. On the surface of the subsidence basin, the difference in slope between two parallel line sections divided by the distance between the two line sections is called twisting. 7. Shear strain, y. Shear strain is the changes in internal angles of a square on the surface of the subsidence basin or on any major cross-section. It is the summation of the differences in incremental (or decremental) lengths between the two opposite sides divided by the original distance between the two opposite sides. More precisely, the surface deformation indices (i.e., slope, strain, curvature, twisting and shear) are defined by derivatives of surface movement components. For simplicity, the x- and y-axes of the cartesian coordinate system are set to be parallel and perpendicular to the cross-section of interest, respectively. In such a coordinate system, slope and curvature along x direction are the first and the second derivatives of the vertical components (S) of surface movement with respect to x, respectively, or i, = ds/dx and kx = d2s/dx2. Horizontal strain along x direction is the first derivative of the component along x direction of the horizontal displacement,

Jan 1, 1992

By S. A. Lolon, J. F. Brune

"INTRODUCTION In underground longwall coal mining, the mined-out areas or gobs frequently contain methane which can form explosive methane-air mixtures. Historically, there have been many events of mine fires and explosions recorded in the United States and other countries that have demonstrated the existence of such explosive mixtures, herein referred to as Explosive Gas Zones (EGZs), inside and around the perimeter of bleeder-ventilated longwall gobs (Loane et al., 1975; Lynn et al., 1986; Elkins, et al., 2001; McKinney et al., 2001; Dziurzynski and Wasilewski, 2012; Brune, 2013). The risk of mine explosions can increase if the EGZs migrate out from the gob into the surrounding mine entries. Several factors can induce EGZs outflowing from the gob, but the most common cause is the fluctuating barometric pressure. Atmospheric pressures change regularly every day but can fluctuate abruptly and become increasingly hazardous in adverse weather conditions. Other sudden pressure changes can result from roof falls, failing ventilation controls and fan outages. Any such fluctuation of mine ventilation pressure will disturb the pressure differential between the gob and the surrounding mine workings and may cause EGZs to outgas from the gob. The correlation between major mine explosions and abrupt barometric pressure changes has been studied and confirmed for explosions in coal mining countries including the United States, South Africa, Australia, and Poland (Hosler, 1948; Boyer, 1964; Kissell et al., 1973; Fauconnier, 1992; Hemp, 1994; Wasilewski, 2014; Belle, 2014; and Lolon, 2017). Disastrous mine explosions appear to happen more frequently during stormy weather, which, in the United States, typically occurs during the late fall and winter seasons. ROOT CAUSE AND EFFECT OF GOB BREATHING Gob breathing is the result of the pressure differential between gob internal and external pressures caused by external atmospheric pressure fluctuations that occur naturally as a result of gravitational and thermal forces in the atmosphere (Lindzen and Chapman, 1969). Other major and sudden pressure changes may be caused by fan failures, failures of ventilation controls or roof falls can also cause an unexpected gob breathing. Normal barometric fluctuations occur every day but usually do not pose an explosion risk as they occur gradually so gob pressures have sufficient time to equilibrate. More extreme fluctuations associated with cyclonic weather systems and storms often result in more rapid and larger drops or rises in barometric pressure (Hosler, 1948; Fauconnier, 1992). A study by Lolon (2017) found that the timing of historical mine explosions showed consistency with the occurrence of abrupt and intense barometric variations."

Jan 1, 2018

By S. K. Nicol

Flotation, water-washing cyclones (hydrocyclones) and spiral concentrators are the three process units most commonly utilised in fine coal preparation. The results of testwork conducted on these three units will be presented and their performance and separation characteristics examined in detail. In particular, the dependence of the separation characteristics of each unit on particle size and the constraint this places on product quality (ash and sulphur levels) will be discussed. This dependence will be shown to be a critical criterion in the selection of fine coal circuits.

Jan 1, 1986

By X. Cheng

A series of batch flotation tests was performed on chalcopyrite-quartzite, pyrrhotite-quartzite, and on chalcopyrite-pyrrhotite-quartzite mixtures. Pulp potential measurements in the flotation tests of single sulfide minerals indicated that each sulfide mineral had its own optimum potential range for flotation. When these results were used to select the potential ranges for the separation of the two minerals from their mixture, their flotation responses changed and the selectivity of separation was adversely affected. A possible mechanism involving surface alteration through galvanic interaction is discussed. A method to improve the selectivity of flotation separation was proposed.

Jan 1, 1992

By Peter L. Siems

Humid tropical environments pose many problems for mineral exploration. The problems result from thick lateritic soils, dense vegetation, seasonally heavy rains, deep chemical weathering, few outcrops and thick saprolites. Although geochemical exploration should be potentially a useful technique in these environments, it appears from the scarcity of reports in the literature that insufficient attention has been paid to developing procedures that are specific to the needs of humid tropical areas. For this reason, the authors believe that this account of a geochemical study in a tropical coastal area on the edge of the Brazilian shield is of general interest and importance for potential geochemical exploration surveys in similar areas within the tropics. The objective of the geochemical study was to develop a practical technique of reconnaissance geochemical prospecting for copper deposits in Brazilian tropical coastal lowland areas. In order to achieve this objective, information concerning the secondary dispersion of copper in these areas was required. Consequently, an orientation survey was designed to provide this information. The present account contains details of the geochemical study and the information about the secondary dispersion of copper that was acquired during the course of the orientation survey. Location and Climate The field area is on the Atlantic coastal lowland of Brazil at latitude 13°S. It lies approximately 10 kilometers south of Maragojipe, a city of 15,000 inhabitants; this city is on the western side of the Bay de Todos os Santos about 45 airline kilo¬meters northwest of Salvador. (See Fig. 1) A good gravel road from Sao Felipe to Sao Roque do Paraguay crosses the southern part of the field area. The climate of the area is hot and moist, and is without prolonged dry periods. The mean annual rainfall is about 1600 mm (63 in.) and the greatest precipitation occurs during the winter months of May and June and the summer months of December

Jan 1, 1972

By Robert A. Westman

The INRED process has been developed step by step by Boliden since 1972 at MEFOS, the Foundation for Metallurgical Research, at Lulea in Sweden. The demonstration - plant is number five in this series. The purpose of this plant, which has a nominal capacity of 60,000 tonnes per year of hot metal is to: 1) prove the process on a sufficiently large scale to provide the basis for construction of production plants, 2) test various kinds of raw materials on behalf of licensees, 3) train operators of the first production plant, 4) develop the process further for special applications.

Jan 1, 1983

By Robert C. Salak

The era of low-seam mining with continuous haulage has been here for quite some time. Typical tonnages in companies such as Terry Glenn Coal are currently averaging 405 tonnes per shift in .8m coal. JoAnn Coal has averaged 453.6 tonnes per shift in .775m to .825m coal for the past four years. John Chaney of Chaney Coal has averaged 297 tonnes per shift in .6m to .65m coal. There are many other mines that are experiencing similar success and with maintenance costs that are averaging $.10 to $.40 per tonne. These figures have been documented and can be verified by the operators.

Jan 1, 1981

By George W. Parker

The ever increasing costs of labor and supplies have made it imperative that operators of open pits look for some way in which to cope with these increases. One of the most logical ways to increase the efficiency of an operation is by the introduction of larger haulage equipment, as generally haulage costs are the greater portion of the over all expenses. These larger haulage units require larger shovel units. In the late 1930's and the early 1940's large mining, quarrying and heavy construction operations had more or less standardized on the 4 to 6 cubic yard shovels. During this same period the haulage units were generally 22 to 27 tons. Some ten years ago 9 - 13 cubic yard shovels along with plus 50 ton haulage units were introduced by manufacturers in an effort to enable operators to decrease costs.

Jan 1, 1962

By M. Rodgers

Dow Water & Process Solutions (DW&PS) was approached by ASARCO Inc. to attempt to recover cobalt and copper from their copper solvent extraction (SX) raffinate. Cobalt is added to many copper electrowinning tankhouses to help to prevent lead electrode corrosion. With cobalt?s high price this can be a large expense. ASARCO has ore that contains a small amount of naturally occurring cobalt. Currently they have no way of capturing this high value metal from their leach or raffinate streams. DW&PS has some chelating resin technologies that should be able to help solve this problem.

Jan 1, 2010

By B. K. Baird

The application of cutoffs during and after pit optimization is examined for a lower-grade multi-metallic copper deposit. Pit optimization requires calculation of the net revenue associated with each mining block, incorporating parameters such as metal prices, grades and expected recoveries, mining and processing costs, smelting and refining charges, and penalty element and royalty charges. Sensitivity analysis during pit optimization reveals which of these parameters have a significant effect on the total contained resource tonnage and total contained non-discounted revenue in the optimized pit. The cumulative effect of changing several of the more significant parameters is investigated. Application of a copper cutoff grade to a block inside the optimized pit could result in the less than optimal extraction of the resource. A block with copper grade below the applied cutoff could be economic due to the presence of other metals. Conversely, a higher copper grade block may be sub-economic. The relative merits of applying a copper grade cutoff, "equivalent grade" cutoff and dollar value per ton cutoff to blocks inside the optimum pit are discussed.

Jan 1, 1999

By R. J. Sweigard

Stabilization of slopes on abandoned mine land (AML) invariably involves some channelization to control surface drainage. Typically, these channels are lined with riprap or gabions, depending on gradient and expected flow rate. The conventional treatments pose a problem since they require frequent maintenance and replacement at times. Soil bioengineering presents an alternative to the conventional measures. In soil bioengineering, living woody plant material forms the main structural component in systems designed to prevent shallow mass slope failures, surface erosion, and channel bank erosion. An experimental application of soil bioengineering techniques was designed and implemented at an AML site in eastern Kentucky. The design consisted of live fascines and live stakes using willow branches installed with coir geotextile. Channel gradient, length, and cross-section were considered in the design.

Jan 1, 1998

By I. O. Otunniyi

The natural hydrophobic response flotation method for beneficiation of printed circuit board comminution fines (PCB CF) still requires many studies to further basic understanding of the process and the flotation traits that the PCB CF presents. Varying particle size distribution (PSD) and water recovery under the scheme show that higher mass pull, obtained at the finer PSD, gave lower water recovery but higher value loss. The reverse also holds: the least mass pull at the coarsest PSD used, -106 + 75 µm, gave the highest water recovery per unit mass pull with the highest reverse recovery. This is unlike what obtains in primary resources processing, where higher water recovery is often with increased fines entrainment. The reverse recovery loss here is, therefore, more due to entrapment with the heavy mass pull characteristic of the method than to the entrainment of value with water. Other peculiarities of the system observed are discussed, with the goal of improving the performance of the process, and broadening the general knowledge of flotation systems.

By Atsushi Sainoki

Induced seismicity is deeply related to various engineering projects entailing anthropogenic in-situ stress change in deep underground. Hence, there is a persistent demand for estimating and mitigating the risk. Significant efforts have been made in simulating induced seismicity with a variety of numerical simulation techniques; however, there are still discrepancies between characteristics of induced seismicity numerically simulated and observed in the field. One of such discrepancies is the simulation of triggered seismicity defined as seismic events caused by an infinitesimal amount of anthropogenic stress change, which is frequently observed in geological structures. The present study aims to develop a methodology to simulate triggered seismicity whilst reproducing a complex stress state in a fault zone. For the purpose, a discrete fracture network within a fault damage zone is first generated. Then, an equivalent continuum model, in which each zone has a different anisotropic compliance tensor, is constructed by employing the crack tensor theory. A fault core is simulated at the center of the model with interface elements. Using the equivalent continuum model, an initial stress condition is simulated with the boundary traction method, which results in a very complex stress state with stress anomalies due to the stiffness anisotropy and heterogeneity. Subsequently, the effective normal stress on the fault plane is decreased in a stepwise manner to induce slip. The result demonstrated that many seismic events are induced on the fault plane with a slight decrease in the confining stress, thus being regarded as triggered seismic event. Further analysis on this seismic activity shows that the magnitude of triggered seismic events is inconsistent with the amount of shear stress drop, implying that a relatively small triggered seismic event could produce a large stress drop, generating locally intense ground motions and thus inducing severe damage to the nearby rock mass.

Apr 26, 2022

By L. F. McHugh

Molybdenum conversion operations discussed in this paper encompass all major operations commercially used to upgrade molybdenite concentrates to various refined products. More emphasis is placed on discussion of key pyrometallurgical unit operations. These operations conducted at Metec include roasting, sublimation, and hydrogen reduction

Jan 1, 1986

By Y. B. He

The effect of the stability and rheological properties of magnetite dense medium on the separation performance of a 6" dense medium cyclone (DMC) is studied with the use of fine density tracers. The tests in which different size fractions of magnetite are used to prepare the dense media reveal that at low medium densities (<1.5 s.g.), the best separation is achieved when using the magnetite with intermediate particle sizes (du3.2=18 11m). At medium densities above 1.5 s.g., however, it is beneficial to use coarser magnetite. With the fine magnetite dense medium, an increase in medium density results in a decrease in separation efficiency. With the coarse magnetite, an opposite trend is observed; the separation efficiency is improved with increasing medium density. An accurate cutpoint control is critical in gravity separation. The cutpoint shift for coarse feed particles is found to decrease with increasing medium stability (density). It assumes values close to zero in a highly stable fine dense medium. When the size of the treated particles is small (<0.5 mm), the cutpoint shift is mainly determined by medium rheology. With increasing medium density, a continuous increase in cutpoint shift is observed.

Jan 1, 1993

By R. A. Hill

A brief explanation of the theoretical functioning of a regenerative system followed by its application to firstly, shuttlecars and then continuous miners and its effect on performance thereof with regard to handling, production and safety.

Jan 1, 1986

By D. G. Feuerbacher

Maximizing production of oil from sandstone petroleum reservoirs is aided by use of non-damaging drilling and workover/completion fluids. Various tests, such as X-ray diffraction, scanning electron microsccpy, petrographic microscopy, porosity and permeability are conducted on core samples. Several fluids are selected, on the basis of these results, for return permeability tests. A report is then written giving the results of all tests, potential reservoir problems, and recommended practices for exploiting the reservoir.

Jan 1, 1983

Room-and-pillar mining at White Pine started in 1953 from a sub-outcropping orebody that gently dips to 1000 m depths in a distance of about 6 km. High horizontal stresses were recognized in the mid-1960s which had obvious stability impacts when viewed in combination with the increased overburden stresses. Modifications in conventional room-and-pillar design were introduced through the years on a trial-and-error basis to help overcome stability and resource recovery problems. These modifications were based on pressure arch concepts using pillar yielding and/or pillar recovery, and on mine layout orientation to minimize stress impacts. While some of these modifications were successfully applied in some areas, they failed in others. Through the years, visual observations played a major role in panel design with contributions from stress measurements and analyses. However, the down slide in the copper economy during the 1970s and early 1980s resulted in a loss of interest in the application of these concepts. This paper reviews ground control problems and presents the results of recent stress measurements and computer analyses. They shed light on the importance of using yield pillars and mine layout orientation to control stresses at depth.

Jan 1, 1993

By E. F. Young

An integrated steel company is an industrial complex ranging from raw materials mining, through pyrometallurgical smelting and refining, and hot shaping, to product finishing and coating. Within this complex is a great variety of operations which use vast quantities of water, and a variety of water uses which can result in pollution of many different types. The industry has recognized most of its problems for some time, and has spent a great deal of money and effort in reducing and eliminating pollution. A recent survey by AISI showed that the industry has spent, within the last 15 years, two hundred forty millions of dollars on water pollution control, and has authorized spending eighty-seven millions more on this type of non¬productive facilities. While much still remains to be done, I think the record to date is one we can be proud of. In this presentation, we will attempt to outline a number of the water pollution problems encountered in an integrated steel company and to show what types of corrective action have been and are being taken, using Jones & Laughlin Steel Corporation as an example.

Jan 1, 1968

By K. Thomson

The Mule Canyon gold deposit, located 14 miles ESE of Battle Mountain, Nevada, was discovered in 1986 as the result of a GFMC grass-roots exploration program. Drilling to date has identified six discrete orebodies which contain a demonstrated gold reserve of 8.487 million tons at an average grade of 0.136 oz/ton, totaling 1,152,000 ounces. Mineralization is associated with argillic alteration and silicification, localized along NNW trending high-angle faults within Miocene basaltic andesites. Trace element geochemistry at Mule Canyon is typical of upper level hot spring precious metal systems, displaying elevated Ag, As, Sb, Hg, and Se.

Jan 1, 1993