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By Yueyue Ding, Yuanhui Li, Zhengrong Li, Pengfei Yu, Kunmeng Li, Zhipeng Xiong

The overburden responses in gently inclined orebody mining are different from those in horizontal orebody affected by the orebody dip angle. In particular, the mining-induced stress presents asymmetrical distribution characteristics spatially, resulting in stress concentration and large-scale pressure relief phenomenon in the surrounding rock. As a result, frequent ground pressure disasters such as roof collapse and barrier splitting occur frequently. Moreover, the ground pressure evolution law and the interaction between stopes in multistope mining are complex. The effective ground pressure control measures cannot be taken due to unclear understanding of the evolution of stress and displacement fields, justifying the investigation of the distribution and evolution of underground pressure for safe and efficient mining.

Jun 1, 2023

By Steve Wirch, Robert Jankowski

The issue of dust control in underground coal mines has been extensively studied by both government and industry. This research work has resulted in many techniques which control the dust or help miners avoid it. Control techniques either prevent the dust from becoming airborne or cleanse the air before it can be inhaled. Avoidance measures minimize the exposure of miners to the airborne dust by blowing the dust away from work areas or making it unnecessary for a miner to occupy a dusty region. One of several successful dust control measures in continuous miner sections is the use of a machine mounted scrubber which cleanses the air and helps to prevent the contaminated air from reaching areas frequented by mine personnel. Research on the application of scrubbers on longwall shearers began in the 1970s and continued into the 1980s. The most successful projects showed only moderate improvement when a scrubber system was mounted on a longwall shearer, and the less successful projects actually increased worker dust levels. There are many reasons that scrubbers have not been successfully applied on longwalls. The most significant of these is that longwalls have across the face ventilation and generally have high face air flows. Scrubbers tend to work best when they are the primary cause of ventilation. Therefore, their capture efficiencies on longwalls tend to suffer because of the exposure of the drums to the primary airflow. Other reasons scrubbers have not been implemented on longwall s include the successful application of an excellent water spray system, effective cutting techniques, and dispersion of dust sources. These techniques can help control drum generated dust, increase production, and limit the relative effectiveness of a scrubber.

Jan 1, 1995

When overburden depth exceeds economical recovery in openpit coal mines, the use of highwall mining systems has increasingly come into play. However, stability in the highwalls is always a major safety concern during such mining. The U.S. Mine Safety and Health Administration requires that highwall mining operators follow ground control plans that specify the pillar sizes necessary to prevent collapse that would threaten highwall stability.

Jan 1, 2006

By W. G. Willson, Y. L. Li, P. D. Rao, D. E. Walsh

The combination of high moisture and low heating value has restricted most low-rank coal (LRC) usage worldwide to mine-mouth power generation. The objective of this study was to subject two Alaska low-rank coals to hydrothermal drying to enhance their marketability in the Pacific Rim markets and to evaluate the chemical and physical properties of the dried products as a function of process conditions. Coals from Usibelli Coal Mine and the Beluga coalfield have a heating value of approximately 18.5 MJ/kg and contain about 28% moisture. Hydrothermal treatment (at 275° to 325° C) of lump coal, from the Usibelli Coal Mine and the Beluga coalfield, enhanced the heating value of the material, on an equilibrium moisture basis, from 18.5 MJ/kg to nearly 27.8 MJ/kg. The product coal, with a high heating value and only 0.2% S, is an environmentally-acceptable premium fuel; additionally, with the Hardgrove grindability index of the coal greatly improved, its value is even further enhanced. An increase in hydrothermal drying temperature promotes vesiculation of resinite. Also, ulminite reflectance increased to 0.92%, and ulminite was subjected to widespread vesiculation; this resulted in a coke-like structure indicative that the material went through the fluid stage.

Jan 1, 1993

By Bruce Geller

The 2005 Prospectors and Developers Association of Canada (PDAC) convention continued the upbeat mood found in 2004. The global mining industry is booming due to higher commodity prices in nearly every sector. Other factors include low commodity inventories, China’s strong resource demands, the weak U.S. dollar, the very strong Euro, global uncertainties, an almost overripe investment climate for natural resources and the highest mining exploration budgets in seven years. Even unglamorous commodities, like iron, uranium and zinc, received copious attention in talks, the investors’ exchange, the core shack and in certain hospitality suites. The following impressions were gathered at the convention and enhanced by conference handouts and some abstracts that are available on the PDAC’s Web site, www.pdac.ca. At least 119 papers were presented, almost twice last year’s number.

Jan 1, 2005

By Murdoch Mackenzie

"Organic Polymers used as gangue depressants are classified according to their chemical structure. Absorption mechanisms for these reagents at the mineral - water interface are reviewed. The method of selecting these reagents for a particular flotation system is discussed. Details are given of methods of reagent solution make-up and distribution. Plant addition policy is reviewed.”

Jan 1, 1986

By Richard D. Nichols

A new method of slaking lime has been developed by DENVER EQUIPMENT DIVISION of Joy Industrial Equipment Company and patented under U. S. Patent 4,261,953. The new method utilizes an attrition machine, commonly used in mineral processing circuits as a sand scrubbing device, to slake lime. The scrubbing effect of the attrition slaker continuously produces a fresh reactive surface so that further slaking may occur. This process allows for utilization of slaking all grades of burnt lime and most grades of dolomite lime. Testing indicates that poor grades of water usually not considered for this service can now be tolerated using the attrition slaker. The slaked lime produced is of higher quality, faster reacting and much less apt to produce scaling problems than previously experienced. The attrition slaker can be combined with a spiral classifier and ball mill to eliminate any need for grit handling or grit removal. The attrition slaker can be designed for all burnt lime tonnages up to the limit of 175 tph and 1" pebble lime size. Control can be maintained easily with minimal operator assistance. The equipment, the principals of process metallurgy, and the above topics will be presented.

Jan 1, 1982

By Daryl E. Radcliffe, Raymond M. Stateham

The Bureau of Mines, under a Cooperative Agreement with the Bear Coal Company, Somerset, Colorado, conducted a large scale evaluation of the effect of time lapse on roof stability. Time lapse in this study is the interval between exposure and permanent support of the mine roof. The study indicates that time lapse is not a critical factor in roof stability provided permanent support is installed before catastrophic failure begins. Concurrently with the time lapse study, investigations were made of stress distribution around resin-grouted bolts, the regional stress field, and anomalous geologic conditions. The behavior of the resin-grouted bolts, at least in the Bear mine, appears to fit the Coulomb-Navier Theory. Geologic conditions are primary factors in trends of roof stability that extend across the mine.

Jan 1, 1982

By Avula Rajashekar Yadav, Sreenivasa Rao Islavath

Barrier pillars and gateroads play a vital role for the safe exploitation of coal from the panel in the longwall workings. The barrier pillars and gateroads are subjected to the front abutment and side abutment loads during the retreat of the panel. These structures may fail if the developed load on them is higher than their strength. The stability of the longwall structures such as barrier, gateroads and face is paramount in extracting the coal from the panel safely. For this, a deep longwall mine in India is chosen for the study using a 3D numerical modelling technique. In this paper, three critical conditions such as scenario 1 (no side goaved-out panel), scenario 2 (with side goaved-out panel) and scenario 3 (with two side goaved-out panels) are taken. For each scenario, five retreat distances such as 100, 125, 150, 175 and 200 m are considered for detailed investigation. The development of vertical displacement in gateroads, vertical stresses on barriers, vertical stress concentration factor, abutment zone and yield zone for longwall face are extracted and analyzed. Also, the safety factor of the barrier and longwall face is estimated considering the Hoek–Brown rock mass failure criterion. From the study, it is observed that the maximum vertical displacement of 121 mm in TG3 at scenario 3 for a retreat distance of 200 m and a minimum vertical displacement of 33 mm in TG2 for a retreat distance of 100 m at scenario 2. The development of vertical stress on the barrier is found to be between 8.78 and 13.40 MPa, and the safety factor of the barrier lies in between 1.56 and 1.80. The study also revealed that the yield zone at the longwall face lies within 2 to 3 m.

Dec 29, 2023

By Hongjie Yu, Mike Mooney

Transitions between geological/geotechnical soil units have a critical impact on the operation and performance of a tunnel boring machine (TBM). Geostatistics-based probabilistic modeling is used to quantify the uncertainty in soil transition locations. This paper presents two unique soft-ground tunneling case studies where the results from the geostatistics-based probabilistic modeling are compared to the TBM data and as-encountered ground conditions derived from the actual TBM data. The assessment enhances the confidence in using geostatistics to improve ground awareness for efficient tunnel construction, minimizing different site condition (DSC) claims, and improving decision-making on tunnel projects.

Dec 1, 2022

By L. T. Larson

Nothing in Turkey is simple. Its his¬tory is long and convoluted, its culture fascinating, its metallogeny diverse, and its geology very complex. This article will focus on the geology of western Anatolia and the precious metals poten¬tial of this third of Turkey. Any gold produced by mines in Tur¬key since the early 1900s has been a by-product of the mining for other met¬als, such as copper from the massive sulfide deposits of the Pontics. Archaeological records, however, prove that gold was mined from the Pactolus (present day Gediz) River and refined by Croesus at Sardis in about 550 BC. Other records and legends make it possible that gold was mined before 1200 BC for the Homeric City of Troy (Priams treasure?) about 25 km (15 miles) east of Canakkale at Mad¬endag and Kartaldag. A final legend of antiquity suggesting gold in what is now Turkey relates to King Midas. And, indeed, the city-state belonging to a king of that name has been recognized near the city of Eskise¬hir. More recently, precious metals have been mined at Madendag-Kartaldag in the late 1800s. Arapdag, near Izmir, remains the only "authenticated" epith¬ermal precious metal deposit in Turkey (Mosier et al., 1985). With this spotty record, why the sud¬den interest shown by at least five Euro¬pean-based, three or four US-based, and several other international mining firms and their Turkish subsidiaries? Like other aspects of Turkey, the complete answer is not simple but, reduced to its basics, has three parts. Turkey, relative to many developing nations, has a stable, democratic form of government (although it also has a for¬midable bureaucracy) whose currency exchange rate is premised on the US dollar. New laws promulgated since 1983 have opened the country and welcomed foreign investment. Some have even provided investment incentives. The Mining Law of August 1985 made sweeping reforms of the old land tenure system. This law made it possible for a foreign-based company to have a wholly-owned Turkish subsidiary en¬gaged in mining. Equally important is the belated recognition that western Anatolia, while geologically compli¬cated, is today basically a province Neogene extensional tectonics having many of the geologic attributes of the leading gold producing province of the US - the Basin and the Range. Geologic rationale for precious metals exploration Tectonic/lithologic framework: Alle¬gorically and simplistically, Anatolia during early Neogene (middle Miocene) can be likened to a tube of toothpaste with the cap off. It is squeezed in the vise formed by the Arabian plate mi¬grating north toward the southwest end of a stable Asian platform. The "tube" was compressed. It could not expand to the east because it was sealed by what is now southern Russia and Iran. The filling of the tube escaped to the west, in the direction in which the cap was miss¬ing (Fig. 1). So developed during the middle to late Miocene the western-most struc¬tural province of Anatolia. This was done by a process aptly termed tectonic "escape" by Sengor et al (1985). This province is dominated by exten¬sional tectonics much like the Basin and Range of the western US and has an estimated extension of between 30% and 50%. The most striking manifesta¬tion of this extension is the 10 to 11 major east-west trending grabens (Ge¬diz, Buyuk Mendares, Kocuk Mendares, etc.) and intervening horsts, although a much greater number of smaller, gener¬ally northeast-striking grabens and half

Jan 1, 1989

By L. S. McNickle

[Commonly accepted maintenance methods are being outdated by the rapid acceptance and use of more complicated hydraulic circuitry on modern mining equipment. It is no longer adequate to use the maintenance program to merely repair or sustain equipment operation. Ever increasing operating costs place a huge premium on lost production time. It has, therefore, placed the maintenance programs in the position of being required to alleviate equipment malfunctions on production shifts and still attain the maximum unit life from each component part.]

Jan 1, 1961

Although mineral commodities used to play and still play a very crucial role in the development of civilization over the centuries, their extraction, transportation, transformation and use are at present sources of great concern in terms of sustainability. Some of the most discussed environmental problems are in fact closely related to the utilization of minerals as materials and fossil fuels. The paper analyses the origins of sustain-ability weakness of mineral supply through Environmental Economics models, which have interpreted the phenomena of pollution and non-renewable resource depletion as a market failure. Conventional market tools have proved to be unable to perform an optimal allocation of those resources that are priceless or have open access. An external intervention is needed in order to reduce the excessive exploitation of environmental and natural resources. Some of the solutions proposed by policymakers and subsequently implemented by governments are briefly considered and the achieved results are discussed. In several cases the public intervention, where the attempt was to restore the sustainability conditions, has failed. Restrictive environmental protection regulations have resulted in severe limitations to the mining activity, without, on the other hand, achieving the expected results in terms of sustainability. Some of these regulations instigate unfair international competition practices among those producers who do care about the environment, but who have high production costs, and those who supply cheap raw material but whose low costs hide heavy environmental impacts. Nowadays, most of the world?s supply of minerals is being produced in developing countries, with severe global environmental impacts. As effective tools for monitoring the problem, sustainable development indicators could be used by policymakers to duly associate the comprehensive environmental impacts for each mining product, depending on its origin and extraction history.

Jan 1, 2003

By Francisco J. Escandon V.

Numerous lead-zinc-barite-fluorite ore deposits, with simple mineralogy and roughly concordant with bedding, are found widely distributed all over the world, having been denominated and well described as "stratiform deposits" or "strata-bound ore bodies", not having any genetic relationship. During several years, its origin has been discussed, without getting to general agreement regarding the main mining districts of this type. Through studies made of large stratiform deposits in the United States, Europe and Russia, it has been found that there are, within this classification, syngenctic diagenetic and epigenetic ore bodies. During the Symposium about the genesis of the stratiform lead-zinc-fluorite-barite deposits, carried out in New York in 1966, Frank G. Snyder (1), presented an excellent analysis of the theories of the origin of these deposits and of the evaluation of the criteria regarding classification. As per his definitions (Table 1), "a deposit is syngenetic if formed by processes similar to and simultaneously with the enclosing rock, epigenetic if introduced into a pre-existing rock and a diagenetic origin implies deposition of metals with the host sediments but with recrystallization, rearrengement and limited migration".

Jan 1, 1974

By Cyrus W. Field

Chemical, mineralogical, and petrographic data have been obtained for suites of plutonic rock samples from the Guichon Creek Batholith of British Columbia and the Mineral-Iron Mountain-Sturgill Peak- Cuddy Mountain-Peck Mountain areas of western Idaho. Intrusions at these two geographically separate localities represent composite plutons ranging from early gabbro through quartz diorite to late grano- diorite and more silicic-alkalic phases. They are early Mesozoic (200 m.y.) in age, and contain porphyry-type mineralization in close spatial and temporal association with late-stage intrusions of porphyry, aplite, pegmatite, and (or) breccia. Country rocks are eugeo-synclinal assemblages of metasedimentary and metavolcanic greenstones of Permian, Triassic, and Jurassic age. The petrochemical evolution of these intrusions, and the effects of subsequent hydrothermal alteration and metallization, are illustrated by standard ternary diagrams of the major oxide and mineralogical data. Samples plotted on an AFM diagram suggest a calc-alkaline magma trend. However, their distributions on NKC and Qz-Kf-Pf diagram show well-defined trondhjemitic (Na20-rich) and tonalitic (quartz-rich) variants to this trend, which are similar in part to those reported for mineralized island arc plutons of the northern Caribbean and southwest Pacific, but which contrast markedly to those for continental plutons of the Bingham District, Boulder Batholith, districts of southern Arizona, and elsewhere.

Jan 1, 1975

By Russell L. Dahl

In a continuing effort to improve plant efficiency, United States Steel's Atlantic City Ore Operations completed the rubber lining of its balling drums in late 1982. This resulted in benefits of reduced bentonite consumption, reduced maintenance costs, improved production rates, and lower power consumption. These advantages far outweigh the disadvantages of increased oversize production and increased surging on the roll screen sizing devices. Certain operating characteristics and variables are discussed herein.

Jan 1, 1983

By Yoginder P. Chugh

Physical mine modeling and computer simulation techniques were used to conduct technical feasibility and economic analyses of selected pit configurations for surface mining a single coal seam dipping at about 15 percent to a maximum depth of 150 feet. The pit orientations along the dip (dipline), strike (strikeline) and along an apparent dip were studied. Physical models of each pit configuration were prepared first to delineate potential operational problem areas, and also to furnish a data base-for the computer simulation models. A dragline micro- simulation model (Fluor), a shovel/truck simulation model and a cost analysis model were used to conduct the study. Sensitivity analyses were conducted on variables such as the pit width, block length, and angle of dip. The productivity (Cu.yds/hour) of the mining equipment (dragline or stripping shovel) under each set of conditions was used to optimize the pit configuration. Both block length and panel width were found to significantly affect the dragline productivity larger size trucks were preferable to smaller size trucks in the pit configuration along an apparent dip. The cost analysis results showed that the pit configuration along the seam dip was more economical than the pit along the strike or along an apparent dip.

Jan 1, 1984

By Kenneth A. Rogers, Richard F. Hill

Introduction A number of processes for deriving more convenient liquid and gaseous fuels from coal are commercially available or in final stages of development. Generally, synfuels from coal processes have efficiencies ranging from 50 to 70%. Considerable engineering design and development work are necessary to bring forth commercial plants using the various technologies-but technological breakthroughs are not expected or needed. Gasification While a variety of solids handling, gas contacting, and gas quality upgrading techniques may be employed in the various gasification processes, the primary goal is the same-to convert a sulfur-containing solid to an essentially sulfur-free gaseous product. The gaseous product may be a mixture of hydrogen and carbon monoxide with nitrogen. Definitions are not rigorous, but high-Btu gas is generally over 900 Btu/scf(33 534 kJ/m3) and low-Btu gas is generally below 350 Btu/scf(13 041 kJ/m3). Medium or intermediate gas falls between these values. High-Btu production is more difficult, as it requires additional upgrading of a low- or intermediate-Btu gas stream to produce a commercially acceptable product. The carbon/ hydrogen ratio is adjusted either by rejecting a portion of the carbon, increasing the hydrogen, or a combination of both. The chemical processing steps include production processing gas containing carbon oxides and hydrogen by the reaction of carbon and steam (gasification); reaction of hydrogen and coal to form methane (a hydrogasification process); reaction of hydrogen and carbon monoxide to produce methane (methanation); and the removal of impurities. The gasification processes share a number of common techniques. The coal received at the plant site must be further cleaned and crushed or ground before it can enter the gasifier. Conventional cleaning methods are used to remove extraneous materials such as metal, rocks, etc. For some processes the coal must be finely ground so it may be fluidized or entrained in a flowing gas stream. For other processes crushing and sizing only are required. Agglomerating coals may be pretreated by heating, mild oxidation with air, or other procedures to assure smooth gasifier operation and to avoid reactor plugging. Nonagglomerating coals Such as lignite and subbituminous coal normally do not require pretreatment. Feeding a solid material such as coal to a higher pressure reactor is a difficult task. Dry feeders using a series of pressurized lock hoppers, or wet systems in which a slurry is pumped into the reactor, are used. The gasification step is the heart of the process. Here, the solid feed material is contacted with synthesis gas (carbon monoxide and hydrogen). The coal is devolatilized and a portion of the fixed carbon converted to methane. The gas-solids contacting methods used include fixed beds, fluidized beds, moving beds, entrained beds, and free-fall systems. The gasification process, overall, is endothermic and the heat required to maintain reaction rates is usually supplied by burning a portion of the coal feed. External heat sources such as electric resistance heating, molten salt or solid heat carriers, and the introduction of a hot hydrogen stream also have been tested. Following the gasification step the particulate materials and heavy hydrocarbons contained in the reactor effluent are removed by a water quench and solids separation system. If low-Btu gas or synthesis gas is the desired product, the raw gas is scrubbed to remove carbon dioxide and sulfur compounds and then is used directly. However, if high-Btu gas is desired, methanation is necessary. In most gasification processes, the hydrogen content of the gasifier

Jan 2, 1980

By R. L. Virta

Common clay is a natural, fine-grained material composed of hydrous aluminum silicates. Shale is a laminated sedimentary rock that is formed by the consolidation of clay, mud or silt. Production About 160 companies produced common clay and shale in 41 states. In states not reporting production, common clay and shale probably was mined and sold for construction applications by companies not participating in the U.S. Geological Survey’s canvass of producers.

Jan 1, 2005

By T. P. Meloy

Media mills operate by having energy transferred to the media which in turn grinds the feed material in a packed bed. Regardless of the mill type, the media energy density per unit surface area is constant. Since for optimum grinding conditions, both peak pressures and particle number of the bed depth are constant, the frequency of energy input is inversely proportional to feed size. As the particle size decreases the voles energy density increases linearly necessitating cooling in stirred mills. Grinding finer particles therefore, requires moving from rotary to vibratory mills, and the finest, the stirred mills.

Jan 1, 1987