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By W. H. Langer

At the start of the 20th century Denver?s population was 203,795. Most streets were unpaved. Buildings were constructed of wood frame or masonry. Transport was by horse-drawn-wagon or rail. Statewide, aggregate consumption was less than 0.25 metric tons per person per year. One hundred years later Denver had a population of 2,365,345. Today Denver is a major metropolitan area at the crossroads of two interstates, home to a new international airport, and in the process of expanding its light rail transit system. The skyline is punctuated with skyscrapers. The urban center is surrounded with edge cities. These changes required huge amounts of aggregate. Statewide, aggregate consumption increased 50 fold to over 13 metric tons per person per year. Denver has a large potential supply of aggregate, but sand and gravel quality decreases downstream from the mountain front and potential sources of crushed stone occur in areas prized for their scenic beauty. These issues, along with urban encroachment and citizen opposition, have complicated aggregate development and have paved a new path for future aggregate development including sustainable resource management and reclamation techniques.

Jan 1, 2009

By A. J. Romeo

The Old Hickory heavy mineral ore body, which lies within the Fall Zone of south central Virginia, has been mined since 1997. There are many differences in this deposit when compared to humate-laden mineral sands mines of southern Georgia and Florida. These differences include an abundance of kaolin-rich clayey sands, highly concentrated and iron-colored heavy mineral sand units, and a base of mineralization that is undulating. For these reasons, the selective approach of dry mining with track excavators is ideal. Grade control in this deposit uses traditional panning techniques and requires an intimate working knowledge of near-by drilling data. Mine geologists train equipment operators to recognize the base of mineralization by such characteristics as a stark color change, significant changes in grain size, and/or considerable, recognizable shifts in the concentration of heavy minerals. The regular pattern of mine site drilling does not always prepare the geologist and digging crews for occurrences of near-vertical contacts between the saprolite basement and the ore sands. These deformed areas, combined with undulating and pinching ore zones, require close monitoring and flexibility by the geologist and the mine operators.

Jan 1, 2005

By N. F. Sather

Results of comprehensive trace element analyses of samples of Illinois #5 and #6 seam coals and the unquenched ashes obtained from gasification of these coals in a Lurgi reactor are reported and discussed. Areas where additional background information is needed for assessment of the environmental impact of trace element emissions from coal gasification are identified.

Jan 1, 1976

By N. M. Levine

This work defines and systematizes the physical factors of the problem of leaching and demonstrates for the first time the utility of macropore volume, micropore volume, specific surface, pore size distribution and permeability as parameters of leaching based on a study of the recovery of uranium from the Top Black member of Chattanooga Shale.

Jan 1, 1962

By Ellsworth R. Spencer

An assessment of U.S. western hardrock miners? noise exposures was conducted as part of a multi-year National Institute for Occupational Safety and Health (NIOSH) survey of noise exposures in each sector of the mining industry. Noise from selected mining equipment and operator noise exposures were measured, analyzed and tabulated for dissemination to the participating sites and are being used to direct NIOSH research and interventions to address the greatest noise hazards. Eighty-two noise dosimeter measurements were obtained, along with time-motion studies as the miners operated hardrock mining machines. Of the operators, 96% had daily noise doses that exceeded the U.S. Mine Safety and Health Administration?s (MSHA) permissible exposure level. The average gold miner dosages while operating the following equipment were: haul trucks - 261%, load-haul-dumps (LHDs) - 235%, single boom drills - 221%, bolters - 214% and dual boom drills - 163%. The worst exposure level was a silver miner with a daily dose of 873%. Time-motion data showed that this miner?s exposure accumulated most rapidly while operating a jackleg drill. These results will be used to help prioritize noise control development by NIOSH and other partners.

Jan 3, 2010

By Joel K. Waterland

GENERAL DESCRIPTION Open cut-and-fill stoping for many years was prob¬ably the most widely used mining method in under¬ground metal mines. Then for a time this method was largely supplanted by the blasthole stope. It again be¬came popular as many mines reached depths or grades where methods requiring large open voids to remain open for extended periods of time became unsuccessful, often as a result of excessive dilution. The open cut-and-fill method is very flexible and is readily adaptable to almost any ore body. The standard application requires that a slice of ore usually 2.4 to 3 m (8 to 10 ft) thick be removed from the back of the stope, and as the ore is taken down, the back is dressed and rockbolted. After the back is secured, the broken rock is removed through rock passes to the level below. When the rock has been removed, the rock passes are extended upward the height of the ore removed, the stope is backfilled, and another cycle is mined. This method is best employed in plunging ore bod¬ies with considerable vertical extent, ore areas that re¬quire selective mining, ore areas where weak wall con¬ditions exist, and ore bodies that have an ore value that will carry this relatively expensive mining method. Blast¬hole stoping, shrinkage stoping, and other mining meth¬ods that do not employ rock passes in a stope are not efficient in plunging or flatly dipping ore bodies because the footwall makes ore removal quite difficult. Since mining is accomplished by taking down slices of the back, only small areas of the wall rock are exposed at any one time, and these only for short periods. Due to limited back height, areas of uneconomic rock may be left in place, or they may be mined and the material gobbed in the stope. Because the miners in the stope must work under freshly blasted areas, the amount of ground control is usually great. The volume of rock that is broken during one section of mining is relatively small and the amount of nonproductive work required is high. This results in limited productivity for the scope and, be¬cause of the nonproductive work that must be done on a regular basis, the production from the stope may be quite cyclical. SUITABLE ORE BODIES The open cut-and-fill method may be adapted to al¬most any type of ore body with a relatively high vertical extent. The ore body must be accessible at both top and bottom as well as at regular intervals throughout its vertical extent. Although adaptable to most ore bodies, the method is probably best employed where the ore has poor con¬tinuity and where most types of bulk mining would pro¬duce excessive dilution. In areas of poor ore continuity, the capability of continuous and extensive sampling dur¬ing the mining of each cycle makes this method very desirable. This capability also minimizes the amount of evaluation sampling that must be done before mining is started. Because of the extractive system used, the size and shape of the stope may be as readily changed as the sampling mandates. Probably the only ore characteristic demanded is that the ore has strength enough to be sup¬ported through the use of rockbolts or cable bolts dur¬ing the mining and backfilling cycles. Good planning, systematic sampling, and careful supervision will pro¬duce a product with less dilution than any other open stoping method. PLANNING Evaluation Planning Once it has been decided that the open cut-and-fill method would be the most efficient for mining a par¬ticular ore body, the next considerations would probably be the availability of an economical backfill material and the selection of an efficient transport system for this material. Although hydraulically transported mill tail¬ings are the most widely used product, this is not always practical due to mill location or the quality of the tailings. In such cases, backfilling may be used. The type of backfill and the type of equipment used will determine if a floor or capping on the backfill is required to minimize dilution during ore removal. The early selection of rock removal equipment is im¬portant since equipment usually determines the amount of development work required to bring a stope into pro¬duction and the size of the openings needed. The size and continuity of the ore body will usually determine the type of loading equipment. The use of slushers or load¬haul-dump (LHD) equipment captive in the stopes will minimize the amount of development. If the ore con¬tinuity is such that a ramp system for extraction can be used, the cost of development will be increased but the flexibility of continuous mining will minimize the cycli¬cal nature of the production. The height of the mining section usually is deter¬mined by the strength of the wall rock and the amount of back bolting required. Once this has been decided, the appropriate drilling equipment can be chosen. The number and sizes of the rock passes employed depends upon the type and size of the extractive equipment and the type of backfill that is to be used. Since the miners must enter and leave the stope each shift, the level inter¬val is usually maintained at approximately 45 m (150 ft). Access from the level above into the stope must be main¬tained at all times. The employees perform all the work in the stope and adequate ventilation must be provided. Stope Planning Due to the flexibility of the method and the vari¬ability of the ore zones, layout is usually done on a stope basis. In areas where continuity is a problem, the size of the stope is usually determined by the boundary of the ore (with all of the ore within that boundary being removed). In areas of good continuity where ramps are to be used, the length of the stope may be determined by the length of time each of the cycles (preparation, back¬fill, mining, and ore extraction) requires. The ramp work is then laid out so that access to the various parts

Jan 1, 1982

During the last 20 years, more than 80 km (50 miles) of tunnels have been constructed in the Los Angeles, CA area. Recent projects include The East Central Interceptor Sewer (ECIS), completed in 2004. It spans more than 18 km (11 miles). The Northeast Interceptor Sewer (NEIS), completed in 2005, spans 11 km (7 miles). And the 2-km (1.3-mile) Metropolitan Transportation Authority?s Gold Line Eastside Extension (MCGLEE) was completed in 2006. All of the tunnel routes lay beneath heavily populated urban environments so minimizing ground surface settlement was critical to the success of the projects. Previous tunneling efforts in the Los Angeles area using open shield methods resulted in significant settlement that damaged roads, utilities, buildings and other structures. Earth pressure balance (EPB), or slurry machines, were specified for these projects to reduce subsidence risk. The contractors chose EPB tunnel boring machines (TBM) for the work. The closed and pressured face of the EPB TBM reduces loss of ground at the tunnel face and, when the machines are used in combination with gasketed pre-cast tunnel liners and backfill grout behind the installed segments, losses from over-cut of the excavated surface are also reduced.

Jan 1, 2008

By A. M. Gaudin

In a recent paper we have reviewed principles and applications of measurement methods for contact angles and their hysteresis (22). In this paper we apply these methods to a system consisting of rutile, an organic liquid (benzene, decane, or dodecane) and water. Surfactant (dodecylamine hydrochloride) was used at various concentrations and various pH values.

Jan 1, 1964

By R. V. Huff

An in-situ leaching technology was developed for copper oxide minerals at the Van Dyke deposit at Miami, Arizona. This paper discusses the process developed and the activities that occurred. Specifically, the activities of well installation, deposit data acquisition, leach testing and equipment development are reviewed. Installation and operation of the test facility are described.

Jan 1, 1988

In order to ensure safe mining and reduce surface damage in shallow multiple-seam mining, the failure characteristics of interburden strata with different coal pillar offset distances between pillars in the upper and lower seams, the distribution characteristics of stress concentration in coal pillars, and the development characteristics of stratum cracks and subsidence were physically investigated and also using UDEC2D software. Meanwhile, the effect of different coal pillar offset distances on the stress concentration of coal pillars and development of stratum cracks were studied. Based on those results, a formula for safe mining and reducing surface damage was established, which provided a theoretical basis for safe and environmentally friendly mining in shallow multi-seams. According to the results of the study, the optimal coal pillar offset distance (the side-to-side horizontal distance of the upper and lower coal pillars) between the upper and lower coal seams was developed to reduce the stress concentration of coal pillars and surface damage. The results of this study have been applied in Ningtiaota coal mine and have achieved good results in safe and environmentally friendly mining.

Jul 28, 2020

By J. O. Marsden

Parts I and II in this series of papers presented the chemistry of medium-temperature pressure leaching of copper sulfide concentrates and reviewed the metallurgical development of a process to effectively recover copper using medium-temperature pressure leaching and direct electrowinning (DEW). Part III reviewed the large-scale demonstration of the MT-DEW-SX process at Bagdad, Arizona. Key features of the process were the use of superfine grinding of the concentrate (to a P98 of 12 to 15 µm and a P80 of 6 to 7 µm), pressure leaching at 160ºC with 1,380 kPa (200 psig) oxygen overpressure, DEW to produce LME Grade A cathode, recycling some of the lean electrolyte to the pressure leaching step, and treatment of a lean electrolyte bleed by solution extraction (SX). Recycling of lean electrolyte provided all of the acid required to effectively dissolve copper and convert approximately 65% to 70% of the sulfide sulfur to elemental sulfur, resulting in an acid-autogenous process for pressure leaching. This paper (Part IV) discusses the development and design of a full-scale commercial application for the Morenci operation in Arizona.

Jan 1, 2007

Because of its small interburden thickness, concentrated stress distributions, high coal seam metamorphism, and complex geological conditions, mining the five coal seams (Nos. 5, 7, 8, 9 and 12) of Kaiping coalfield is difficult. Kaiping coalfield is located within 80 m in the Kailuan Group. The overburden caving caused by mining the five coals seams was measured using ZTR12 geological penetration radar (GPR) survey combined with borehole observations. The development characteristics of full-cover rock fractures after mining were obtained from the GPR scan, which provides a measurement basis for the control of rock strata in close multiple-seam coal mining. For the first time, it was found that the overburden caving pattern shows a periodic triangular caved characteristic. Furthermore, it is proposed that an upright triangular collapsed rock pile and an inverted triangular area with larger fragments piled up alternately appear in the lower gob. The research results show that the roof structure formed in the gob area can support the key overlying strata, which is beneficial to ensure the integrity and stability of the upper coal seams in multiple-seam mining of close-coal seams.

Jan 7, 2020

This paper presents the results of a unique study conducted by the National Institute for Occupational Safety and Health (NIOSH) from 2016 to 2019 to evaluate the effects of longwall-induced subsurface deformations on shale gas well casing integrity and underground miner safety and health. At both deep and shallow cover instrumentation sites, surface subsidence measurements, subsurface in-place inclinometer measurements, and underground pillar pressure measurements were conducted as longwall panels were mined. Comparisons of the deep and shallow cover test site results with those from a similar study under medium cover reveal an interesting longwall-induced response scenario. Under shallow and medium covers, measured horizontal displacements within the abutment pillar are one order of magnitude higher than those measured under deep cover. Conversely, measured vertical compressions under deep cover are one order of magnitude higher than those under shallow and medium covers. However, FLAC3D simulations of the casings indicate that, in all three cases, the P-110 production casings remain intact under longwall-induced deformations and compressions, which has serious implications for future mine design in areas where shale gas wells have been drilled ahead of mining.

Jan 7, 2020

By Roger K. McLimans, Venkatramaiah N. Vasudev, Christian Knudsen, Stefan Bernstein, Dirk Frei

Computer Controlled Scanning Electron Microscopy (CCSEM) analyses of sediment samples from coastal regions of Kerala and Tamil Nadu states and the heavy mineral deposits of Chavara, South India, show large lateral differences in the titanium content in ilmenite due to varying degrees of iron leaching. As the depositional environments for the sands with varying degrees of ilmenite alteration are comparable, the cause for the different degree of alteration is due to differences in the primary source of the ilmenite or to differences in the geochemical history of the ilmenite grains during transport from source to deposit. The CCSEM analyses of the heavy mineral fractions show that source of sediments with a high content of titanium-enriched ilmenites, mainly the heavy mineral deposit around Chavara, resides in the khondalite belt of South India (granulite facies metasediments). The less titanium-enriched ilmenites are sourced from other rocks in the area such as the charnokites. Those conclusions are based on the high MgO content in the leached ilmenites, chemical composition of the accompanying garnets (low CaO and high MgO), and the concentration of aluminum-rich minerals in the sands.

Jan 1, 2005

By John Addison

Experimental animal studies comparing asbestos and non-asbestos varieties of tremolite indicate tremolite asbestos is markedly more carcinogenic. By direct analogy, the differences in carcinogenicity between tremolite asbestos and non-asbestos prismatic tremolite should be the same for the other types of amphibole that also crystallize in the asbestos and non-asbestos habits. The earliest of the experiment animal studies, done more than 25 years ago, have design limitations by modern standards including the use of injection or surgical implantation as the route of administration rather than the more relevant route of inhalation. However, the differences in the carcinogenicity of amphibole asbestos and non-asbestos amphiboles are sufficiently large to be clearly discernable even with the study limitations. Together with later studies on these and related minerals, there is strong evidence of a much lower hazard associated with the shorter, thicker fibers of the non-asbestos amphiboles, than is found for the asbestos analogues of the same mineral. It is possible that the non-asbestos amphiboles are no more hazardous than other silicate minerals widely considered nuisance dusts. © 2007 Elsevier Inc. All rights reserved. Keywords: Amphibole; Asbestos; Tremolite; Carcinogenic

Jan 1, 2007

By J. D. Christensen

In August 1987, we marked the tenth anniversary of the Surface Mining Control and Reclamation Act. Anniversaries are supposed to be times of celebration, and I truly believe that we have something to celebrate on this anniversary. For, after ten years, there has been much progress in the implementation of the surface mining law.

Jan 1, 1988

By Russell G. Slayback

Feasibility investigations for prospective gold mines too often neglect to consider ground water. Simple observations and tests during drilling exploration can provide useful data on probable water conditions. As the prospect becomes more serious, more detailed investigation of ground water and dewatering needs may be warranted. Ignoring ground-water conditions can lead to costly mistakes.

Jan 1, 1987

The concept of classification in wet, closed circuit ball milling is expanded beyond the performance of the classifying equipment to include all aspects of the fines removal system of the grinding circuit. Design and operating parameters that effect fines removal are identified and discussed, and a quantitative index for circuit classification effectiveness is presented.

Jan 1, 1987

By Lawrence K. Nordell, Vinit Sethi

Published standards and specifications do not adequately cover engineered class pulleys for modern high strength steel cord belt conveyors. This paper discusses the Conveyor Dynamics, Inc. (CDI) design criteria and stress analysis techniques emphasizing the finite element method (FEM), fatigue failure criteria, design limits and manufacturing requirements to ensure successful and safe pulley installations.

Jan 1, 1993

In 1981, North American Degerstrom Contracting began gold mining on the Little Rocky Mountain Range, near Zortman, MT. In the past four years, the price of gold has fluctuated from a high of $16/g ($500 per oz) to a low of $9.60/g ($300 per oz). With that kind of a moving target, profitability presents a management challenge. Based in Spokane, WA, Degerstrom employs 85 people at the mine. It is one of the largest heap leach operations in the nation. Last year, 8 Mt (9 million st) of low-grade ore was moved to the leach pads in a two-shift, five-day operation. The current pit being worked produces 218 kt/m (240,000 stpm) of leaching ore. Ore fragmentation critical The gold bearing ore has no defined patterns or seams. It is an igneous intrusion resulting from volcanic activity. It occurs spontaneously throughout the range. To recover the gold, areas are staked out and core samples are taken and analyzed. These data determine if the ore is rich enough to mine. Once mining begins, an average of 150 holes are drilled and blasted on a two-day rotation. Five Ingersoll-Rand T4s drill on a 4- x 4.5-m (14- x 15-ft) spacing to a 7.6-m (25-ft) depth. "When we first came to this site, we drilled on a 3.6- x 3.6-m (12- x 12-ft) pattern," said Paul Baker, superintendent for N.A. Degerstrom Contracting. "We did some experimenting using a high density emulsion in the bottom of the hole and filling the rest with regular Anfo." The high density emulsion saved the company on overall drilling and blasting costs since the holes could be spaced on a wider pattern and still achieve the high degree of fragmentation needed for leaching. Blasting is important because the gold lays in the natural strata of the rock. Also, the ore is not crushed before it goes to the leach pads. So complete fragmentation is critical. Terrain dictates loading/hauling system The shot ore is worked in 6 m (20 ft) benches by two Caterpillar 245 front shovels equipped with 3 m3 (4 cu yd) buckets, a 992C wheel loader with a 12.6-m3 (16.5-cu yd) bucket, and a 988E high lift fed by a D9H. A Caterpillar D10 tractor trap dozes to the loader. According to Baker, the 6 m (20 ft) bench is an efficient lift for the front shovel and the wheel loader. In tight quarters or in a pocket of ore, Degerstrom uses the 245s. For high production areas, the wheel loader is used. The hauling fleet includes 28 Cat 773 off highway trucks. The 45 t (50 st) trucks are seven pass loaded by the 245s with a 25-second cycle time per bucket load. The 992C loads the trucks in two passes in less than 30 seconds. The cycle time is four to five minutes for a 1.2-km (4000-ft) haul on grades that average 10%. Grades, in some places, exceed 16%. "We use the 773s because they have a low weight-to-horsepower ratio - that's what you need in steep country," Baker said. The trucks haul the shot ore to the leach pad. Currently, Degerstrom is working a pad that has a capacity for 5 Mt (5.5 million st) of ore. Building the leach pads The base of the pads resemble a large drainage basin. They take about one month to construct. A 0.3-m (1-ft) layer of impervious bentonite clay is hauled in and leveled by a Cat D9H tractor. A 30-mm (1.2-in.) PVC liner is then laid in place on top of the clay base. It, in turn, is covered with tailings from an old on-site mill. Degerstrom uses the tailings to protect the liner from tears when the ore is dumped. The ore is leveled and built up in 9 m (30 ft) lifts by the D9H. The tractor rips the top layer. Then, a network of plastic irrigation pipe is put in place to distribute a cyanide solution over the surface. The leaching solution percolates through the ore and dissolves the gold. The solution drains from the pads and is pumped to a 22.7-ML (6-million gal) pregnant solution holding pond. The liquid then goes through two separate filtration units. One unit removes entrained solids and the other side adds a zinc dust to precipitate the gold. This is collected on filters. The affluent then returns to a solution holding pond for redistribution through the pipeline network. Typically, 80% of the pad's potential recovery takes place in the first 30 days of leaching. The process stops when the ambient temperature falls below the cyanide's freezing level. And each pad has a leach cycle of four to five years before recovery values decline to a point where further leaching becomes uneconomical. At Zortman, it takes 9 t (10 st) of ore to produce 31 g (1 oz) of gold. It is therefore critical to keep total production costs down and efficiency high.

Jan 1, 1986