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By A. Iannacchione

Longwall mining began within the Pittsburgh coalbed of Pennsylvania (PA) in the early 1970?s. Originally, longwall mine layouts were designed to fit within existing room-and-pillar operations, where panels were limited to that of typical production panels, e.g. a few hundred feet wide by a few thousand feet long. In these early designs, the gate entries were comprised of chain pillars similar to those found along main entry systems or within pillar recovery sections. The modern longwall mine has little in common with their 1970?s predecessors. Today the entire mine layout is designed around the longwall mining method. The longwall panels have grown to well over one thousand feet in width with lengths now measured in miles. In addition, development pillar sizes and shapes are matched to specific performance requirements.

Feb 27, 2013

By P. J. Williams, A. R. Foster

Petrographic studies, assay records, and laser ablation-inductively coupled plasma-mass spectrometer (LA-ICP-MS) analyses of major sulfides suggest nearly all of the gold at the Ernest Henry Cu-Au deposit occurs in the form of native gold or electrum (95-65 wt.% Au); sylvanite and dissolved gold in cobaltite, chalcopyrite, and pyrite make only minor contributions. LA-ICP-MS analyses of the gold contents of chalcopyrite gave from 8 to 139 ppb (mean = 56 ppb), more than an order of magnitude lower than those experimentally determined in chalcopyrite in equilibrium with native gold at the estimated mineralization temperatures (350°-450°C). Gold content is more variable in pyrite (1-400 ppb, mean = 77 ppb) and highest in narrow growth zones of a subordinate type of complexly zoned pyrite wherein it is associated with elevated As, Ag, Sn, Sb, Te, and Bi. Deposition of gold-electrum was closely associated with, but preceded some of the chalcopyrite deposition, as indicated by microtextures and lower bulk Au:Cu ratios in late-stage chalcopyrite-rich veins. Gold grains have maximum dimensions from <1 to 50 micrometers, and are heterogeneously distributed with most occurring in microscale clusters. Fifty-five out of 76 grains recorded in polished sections are in contact with both chalcopyrite and pyrite, and many of the rest are in sites where such a relationship could exist in the third dimension. The dominant textural sites are intergrowths with chalcopyrite in microveinlets cutting pyrite, and on faces of pyrite grains in contact with chalcopyrite. Scanning electron microscopy, electron microprobe analysis, and proton induced X-ray emission studies show that pyrite associated with gold includes complexly zoned, weakly zoned, arsenian, and arsenic-poor types. The textures are compatible with the possibility that most gold was deposited electrochemically as native metal on pyrite surfaces. The textural distribution of gold has important metallurgical implications given that the ore processing circuits at Ernest Henry and most other sulfide copper mines are designed to exclude pyrite (and arsenic) from concentrates.

Jan 1, 2007

By Quentin Rhoton

To benefit two endangered fish species, waterfowl and other wildlife, and water quality in the lake and downstream, the decision was made to remove levees that had been in place since the 1950s. Because the levee material was mainly dredged up lake bottom peat, it was decided to pare down the sites chosen for breaching with dozers and trackhoes. This material was spread out onsite instead of expensive removal by dumping elsewhere. Because of the instability of the final pared down levees and the lake level being at a ten-year low, it was decided to use explosives to breach four of the sites. After over five months of earthmoving and two weeks of loading holes, the levees were detonated the day before Halloween, 2007. Somehow pumpkins showed up to be part of the explosive activities.

Jan 1, 2009

Study on Separation Technology for Copper-Molybdenum Collective Concentrate

Sep 13, 2010

By Rudiger Baltz

The sudden failure of bodies of rock is a serious problem commonly experienced in the international mining industry. These explosive releases of energy are referred-to as ?bumps?, ?outbursts? and ?rockbursts?. Rockbursts can occur at such a rapid speed that they present a direct threat to safety in large parts of the mine workings. The build-up of excess stress within the body of rock can be attributed to different causes. In shallow workings, for example, sudden and violent failure of the roof strata can be caused by leaving insufficient pillar width when practising room-and-pillar mining. At much greater working depths, as it is the case in the German coal industry, rockbursts are generally attributable to high levels of rock pressure. This can even result in coal outbursts when driving individual roadways. More than thirty years ago the German coal industry suffered from numerous rockburst incidents which caused many deaths and serious injuries. This led directly to the establishment of the Rockburst Prevention Centre, which was created at the instigation of the mining companies and the chief mines inspectorate. The consistent logging and analysis of all rockburst incidents has led to the development of a system that is still used as a basis for preventing underground rockbursts and minimising the risk of such phenomena occurring. Working closely with the mining authorities and mining companies the accredited experts of the Rockburst Prevention Centre have played a key role in helping to develop and implement a range of methods for the early detection and prevention of rockbursts.

Jan 1, 2008

By Joner O. Alves

The disposal of scrap tires has been a serious environmental problem. The treatment of this waste by pyrolysis and combustion has advantages since the landfill space is dwindling and the production of fuel becomes of technological interest. However, that processes needs a rigid control of emissions. This work presents a study of the light hydrocarbon gases (HC) generated during the burn of waste tire chips in a two-stage laminar-flow horizontal furnace. Different temperatures in the primary and secondary stage of the furnace were tested, and the oxygen/nitrogen percentage was also varied during the combustion process. A gas chromatograph was used to identify and quantify the components of the gaseous products of combustion and pyrolysis. The results showed the behavior of the gases during the burn of tires, providing valuable information to the control of hydrocarbon emissions.

Jan 1, 2010

By Rufus Flinchum

Two of the most critical concerns a blaster faces today are airblast and flyrock. Airblast, sometimes called noise or overpressure, can cause damage to neighboring structures, especially windows. It also is the cause for many vibration complaints. The human sense of hearing is often more acute to identifying source than the sense of touch. When a blast occurs, the airblast is what identifies the event. The vibration that may be felt is then associated with the airblast. Vibrations of greater magnitude, such as passing trucks or construction work on the house, go unnoticed because their sounds are familiar or expected. Flyrock is the number one killer and cause of damage. Elasting laws provide limits for these two concerns. Failure to comply may result in fines, closing of the operation, and even prison. Airblast and flyrock originate from two distinct areas, the open face and the bench surface. Each of these areas is addressed in the detailed proven procedures that follow, and if used by the blaster in conjunction with his own blasting knowledge, a sound blasting plan can be developed to minimize the occurrence of airblast and flyrock.

Jan 1, 1992

The La Colosa, Colombia porphyry gold deposit is currently in the pre-feasibility stage. This large deposit has many types of gold mineralization: native gold, electrum, and tellurides. These variations in the gold mineralization lead to variability in the gold recovery. The final process flowsheet may include gravity concentration with cyanide leaching. Metallurgical testwork is utilized to identify the zones of ore that may be problematic to recover. To help select the samples that represent the fluctuating variability zones, geometallurgical models are constructed using mineralogy and geology data. These zones are then wireframed and compared to the geological and structural models for spatial correlation. Samples for the variability testwork will be selected from these different zones to identify and analyse the effect the different gold mineralization types have on the recovery. By using geometallurgy to aid in the sample selection for metallurgical testwork, the variability in the ore body can be understood and constrained to aid in process optimization.

Feb 27, 2013

By Hugo E. Camargo

Noise Induced Hearing Loss is the most common occupational disease in the U.S. and of paramount importance in the mining industry. According to data for 2006 from the Mine Safety and Health Administration (MSHA), Continuous Miner operators accounted for 30.2% of underground mining equipment operators with noise doses exceeding the Permissible Exposure Limit (PEL). This figure becomes more significant considering that 49% of the 2006 national underground coal production was extracted using continuous mining methods. Thus, there is a clear need to reduce the sound radiated by Continuous Mining Machines. The first step towards efficient noise control of a Continuous Mining Machine requires identification of the various noise sources under controlled operating conditions. To this end, a 42-microphone phased array was used in conjunction with 4 reference microphones to sample the acoustic field of a machine in the Hemi-anechoic chamber of the Pittsburgh Research Laboratory. These data were processed using a frequency-domain beamforming algorithm to obtain acoustic maps of 5 sides of the machine. The focus of the test was on the conveyor noise since previous studies showed that operation of the conveyor is the most important contributor to the sound radiated by the machine. From the acoustic maps, the following potential areas for noise control were identified, and included: chain-tail-roller interaction, chain flight tip-side board interaction, and chain-upper deck interaction.

Jan 1, 2008

By James F. Kvitkovich, George V. Weisdack

Longwall mining techniques were introduced into U.S. bituminous coal mining operations in the early 1960s. These techniques were gradually adopted by many mines during the 1970s. By 1983, considered to be the peak of the longwall mine census, there were 118 active longwall faces in 79 coal mines throughout the United States. Beginning in 1984, longwall faces began a decline in numbers that has continued to the present day (Fig. 1). The geographic distribution of longwall faces today is shown in Fig.2 according to region. A breakdown of recent longwall mine production by region is shown in Table 1. An approximate breakdown of present longwall face installations by product (metallurgical and steam) is shown in Table 2.

Jan 1, 2005

By Aline Maria dos Santos Teixeira

Serpentinite is an ultra basic and metamorphic rock consisting mainly of magnesium, calcium and silicon oxides. The rock under study is a host rock of chromite mine located in Andorinha, BA. The objective of this paper is to evaluate the rock&apos;s physical and chemical characteristics to be used as an additional fertilizer of acid soils. After comminution, rock samples were submitted to chemical analysis, XRD, SEM-EDS and TGA. Afterwards, particle size distribution was determined. Result analysis confirms that our rock consists mainly of dolomite, calcite and diopside. According to the result obtained, it can be said that the serpentinite rock has promising applications in agriculture for the correction and additional fertilization of acid soils. However, it is necessary to study the characteristics of the rock such as its dangers and toxicity as well as evaluate them according to the legislation for corrective acidity.

Jan 1, 2010

By James A. Pendleton

In response to Public Law 95-87 (SMCRA), Colorado promulgated regulations governing the mining of Coal. These regulations require the prediction, monitoring and mitigation of "material damage" caused by subsidence. All permitted underground coal mines within Colorado have approved subsidence programs. Preliminary monitoring results indicate the subsidence mechanical predictions have been sufficiently accurate to preclude material subsidence damage. The State of Colorado has developed a practical approach to regulating subsidence, which stresses monitoring verification of predicted subsidence phenomena. However, shortcomings exist in our ability to precisely predict the secondary consequences of subsidence, including effects to structures, the hydrologic balance and the environment. Lack of accuracy in predicting these secondary consequences results in uncertainty, necessitating conservatism in permitting. To avoid increasingly stringent permit restrictions, future research should emphasize the secondary consequences of subsidence.

Jan 1, 1986

By Tim O’Neil

“America’s mining industry brings good jobs to communities across America and provides the energy, minerals and equipment that are vital to our economic security and our way of life.” That was the surprise videotaped greeting from President George Bush at the official opening ceremony of MINExpo 2004in the Las Vegas, NV Convention Center. Jack Gerard reinforced the upbeat mood at MIN-Expo. He praised Nevada Gov. Kenny Guinn for his support of the mining industry, the state’s largest manufacturing sector. Gerard is the president and chief executive officer of the National Mining Association, the sponsor of MINExpo 2004.

Jan 1, 2004

By William Billiet

"The Dulles Silver Line Phase II is an 11.4 mile extension of the Washington Area Metro Transit Authority’s Silver line in northern Virginia. There are three miles of elevated guideway, which are supported on 188 large diameter mono-shafts founded within the Triassic Geologic Aged Culpeper Fault Basin. Three lateral load tests were performed on fully instrumented test shafts. The challenge in developing the load testing program was how to reproduce the effects of the extremely high design loads along the test shafts, considering the limitations of the load test equipment. Development, execution, and analysis of the lateral load test program is discussed.INTRODUCTIONPlans for Dulles Silver Line Phase II include two Aerial Guideway sections on elevated track, the Main Line and Yard Leads. The Aerial Guideways are supported on mono-shafts (single, largediameter drilled shafts) socketed into rock. Lateral loads are resisted primarily through the stiffness of the shaft and the geotechnical resistance of the rock socket. The monoshafts were designed in accordance with AASHTO LRFD 2014. Based on our preliminary analyses, the production mono shafts were expected to consist of 6.5, 7.5, and 8.5 foot diameter drilled shafts with rock socket lengths varying between 8 and 34 feet (averaging 14 feet). Table 1 summarizes the maximum service load combinations for each size production shaft along the aerial guideway alignment.GEOLOGYThe project is located within the Piedmont Province, a major physiographic province on the east coast of the USA extending from Alabama to Pennsylvania. Within the Piedmont, a number of Mesozoic basins formed in rift valleys. Dulles Airport is located in the Culpeper Basin, characterized by a relatively shallow siltstone rock surface compared to the adjacent areas underlain by Piedmont crystalline rocks. The geologic stratigraphy at the load test sites generally consist of residual soils and intermediate geo-material (IGM) overlying siltstone rock. IGM is a term used by Virginia Department of Transportation (VDOT) to describe residual material as it transitions between soil and rock. For the purposes of the load test, the siltstone rock is classified as fractured rock (RQD<50), and competent rock (RQD=50). Table 2 summarizes the stratigraphy encountered at each test site."

Jan 1, 2017

By R Blair

The Domain and Burnley Tunnels, which are major features of the Melbourne City Link Project, are MelbourneÆs first road tunnels. They are 1.6 km and 3.5 km in length respectively and are being constructed through a variety of ground conditions. Deeper sections of the tunnels have been driven through the Silurian mudstone which underlies Melbourne. Other shallower sections of the tunnels pass through a variety of ground conditions including silts, sands, clay and rock and have been constructed using both top-down and bottom-up cut and cover construction techniques. The Yarra River Crossing is a 140 m length of the Domain Tunnel which crosses under the Yarra River on a relatively shallow alignment. The crossing of the river using cut and cover techniques was identified in the early stages of design development as being one of the most challenging stages of the works on the Southern Link. The prevalence of varying geological conditions combined with the need for maintained traffic and stream flow conditions provided a demanding and often conflicting set of criteria for which there appeared to be no one clear solution. A team of designers, constructors, estimators and specialist contractors were involved in a concept evaluation and risk analysis study spanning a period of approximately 12 months. During this study, four concepts were considered as likely contenders. This paper provides a brief outline of the four concepts addressing their relative merits, disadvantages and risks followed by a detailed description of the adopted solution, namely top-down construction using secant pile walling (east bank) and bottom-up in situ construction (west bank).

Jan 1, 1999

By M. Radwan, S. Shimada, S. Z. El-Tawil, K. A. El-Barawy, Y. Miyamoto

This study presents the results of synthesizing monolithic siliconoxynitride, Si2N2O, ceramic from a mixture composed of reclaimed silicon and natural desert sand by using the nitriding combustion synthesis method. Single-phase Si2N2O powder was prepared by the combustion of a mixture composed of silicon and pulverized sand in 3 MPa nitrogen gas. The combustion reaction completed in 2 min and the combustion temperature reached 1577°C.The as-synthesized Si2N2O powder is agglomerate of fine particles with sizes < 5 µm and has various morphologies; rod-like and irregular crystals, irregular kinking, hollow crystals and grown pseudo-hexagonal prismatic crystals. Porous Si2N2O compacts (24.5–47.1% porosities) were fabricated from the synthesized Si2N2O powder at different calcia-alumina additives (5–20 wt%) by normal sintering at 1500°C for 1 hr in N2atmosphere.They showed superior oxidation-resistance at high temperatures up to 1500°C in an oxidizing atmosphere of Ar/O2/H2O(70/20/10 kPa).Near-full dense Si2N2O compacts were also successfully fabricated from the synthesized Si2N2O powder with 5 wt% oxide additives by using the spark plasma sintering at 1600°C.DenseSi2N2O had good mechanical properties (18.7 GPa Vickers hardness, 3.3 MPa.m1/2fracture toughness and 363 MPa strength) and excellent chemical and oxidation resistance.

Jan 1, 2004

By Ken Andromalos

Continued population growth combined with limited water resources in the Denver area has resulted in the conversion of a number of mined out gravel pits in the area into municipal water storage facilities. The use of slurry walls provides a cost effective means of isolating groundwater to convert these pits into efficient water storage facilities. Design considerations include: stability, underlying bedrock conditions, backfill mix design and earthwork requirements. Installation issues during construction include: trench stability considerations when excavating through relatively clean sand and gravel deposits in potentially high groundwater conditions; keying into three to ten feet of fractured claystone, siltstone or sandstone that makes up part of the Denver formation, and quality assurance procedures to assure a proper groundwater barrier is constructed. The paper concludes with two brief case histories to illustrate how these considerations are applied

Jan 1, 2007

By O. F. Oxtoby, J. E. Olsen, M. W. Erwee, Q. G. Reynolds

"The extraction of molten products and wastes through smelting furnace tap-holes during the tapping process is a complex procedure involving many coupled thermophysical effects. Insight into the fluid flow behaviour in such systems can be gained by using computational mechanics tools to build highfidelity models of the fluid flow and other relevant physics. Previous work using such models indicates that the nature of the flow in the tap-hole, as well as operational parameters such as the tapping flow rate, depends strongly on the properties of the material being tapped and the geometry of the tap-hole channel. Additional complications arise when multiple fluid phases (for example, slag and metal) are present simultaneously, when porous coke beds hinder flow to the tap-hole entrance, and when the geometry of the tap-hole changes over time due to cycles of wear and repair. In the present work, challenges with the coupling of phenomena such as multiphase flow and porosity into computational fluid dynamics methods for tap-hole modelling are discussed in the context of electric furnaces used for ferromanganese production. Qualitative and quantitative results of computational models of flow through tap-holes are presented and compared as a function of material parameters to determine sensitivity effects, and in response to operational parameters to determine typical process behaviour over the duration of a tap. IntroductionPyrometallurgical production using electric furnaces accounts for substantial portion of the world supply of ferroalloys and other strategic materials (Degel et al., 2015). A range of different furnace designs may be used depending on the metallurgical process, with circular three-electrode submerged arc furnaces (SAFs) powered by alternating current being the most common for commodities such as ferromanganese and silicomanganese (Olsen, Tangstad, and Lindstad, 2007).As shown in Figure 1, manganese furnaces typically operate with a deep charge consisting of an upper layer of loose burden (onto the upper surface of which is fed solid raw material), a molten slag layer partially or completely filled with unreacted carbonaceous reductant (generally metallurgical coke), and a molten metal layer which settles to the bottom of the furnace due to its high density. The solid particles present in the slag and burden layers form porous beds which hinder the fluid flow of molten process material and gases inside the furnace (Olsen, Tangstad, and Lindstad, 2007).In order to remove material from the furnace during normal operations, a single tap-hole is built into the sidewall of the vessel near to the level of the hearth. Tapping involves removing both slag and metal phases through the same tap-hole channel, which makes tap-hole design, operation, and maintenance particularly complex. In the case of processes such as ferromanganese, which operate with no external gas injection or open arcs present at the furnace electrodes, flow of material out of the tap-hole is driven primarily by the hydrostatic pressure generated by the weight of the solid and liquid phases above the tap-hole."

Jun 1, 2019

By A. T. Miesch, L. B. Riley

Distribution of minor elements in sandstone-type uranium deposits of the Colorado Plateau is being studied by the USGS on behalf of the A EC. A primary objective has been to provide basic data which could be useful in geo-chemical exploration for new deposits. The basic statistical measures — similar to those used in sedimentary petrology—are described. The underlying principle is that the frequency distributions fit or approach the log-normal form. Since 1952 the U. S. Geological Survey on behalf of the U. S. Atomic Energy Commission has conducted a study of the distribution of minor elements in sands tone-type uranium deposits of the Colorado Plateau. A primary objective in this study has been to provide basic data which could be useful in geo-chemical exploration for new deposits. Among the basic data considered important are estimates of the abundance and habit of each element in the ore and in the host rocks. It has been found that a few basic statistical techniques, and variations of these techniques, are useful in this type of study. Some of the basic techniques have been used to advantage by researchers in geochemistry and in other fields of geology, especially sedimentary petrology; others have been used to only a limited extent. Among the latter is the linear correlation coefficient, which has proved useful in assessing the element associations in a particular rock type without analysing individual mineral separates. In computing the basic statistical measures a scale has been used which is, in some ways, similar to the phi ($) scale used by sedimentary petrol-ogists in grain-size studies.&apos; FREQUENCY DISTRIBUTIONS It has been recognized for some time that the results of analyses for a given minor element in a suite of samples of rocks or ores yield frequency distribution curves which are approximately normal when the curves are plotted on logarithmic or geometric scales. In other words, the analytical results give an approximate lognormal frequency distribution. A classical example is given by D. G. Krige2 in the study of the distribution of gold values from a mine on the Witwatersrand. Another example is shown in Fig. 1, the distribution of barium concentrations in samples of uranium ore from the Chinle formation. The geochemical data are analogous to grain-size data gathered by the sedimentary petrologist. Both types of data, after simple logarithmic transformations, may be treated by conventional statistical methods based on the normal distribution. This is not to say that other types of transformations may not serve equally well or better for particular element distributions.3 Spectrographers and other analysts are quite aware of the dependence of their precision on the concentration of the element present.4 For example, in the part per million range the variation may

Jan 1, 1961

By Jack R. Woodyard

Scientists at the U.S. Bureau of Mines are studying iron aluminides as possible substitutes for stainless steels to reduce the Nation&apos;s dependence on imported strategic and critical materials. In a Bureau investigation on the mechanical properties of Fe-28Al, it was found that the material&apos;s machining properties were significantly improved at slow tool and feed speeds. Machining techniques normally used for brittle materials failed or were costly. Further experiments using a 5-in (12.7-cm) mill cutter with carbide inserts, operating dry at minimum machining speeds, produced visually smooth sample surfaces with no tool damage. As a result of these experiments and a review of published data on hydrogen embrittlement of iron aluminide under tension, non-water-based (e.g., sulfur-based) lubricants were chosen for production machining. Four-flute, 3/4-in (19-mm) carbide end mills were used at slow speed under lubrication. This latter procedure reduced tool wear and breakage by a factor of 2. Machined surfaces and specimen cross sections were analyzed by scanning electron microscopy to detect microcracking. Tensile tests gave the expected yield and ultimate strengths, indicating that no degradation by low-speed machining occurred. This study extends this work to show that the alloy can be machined at higher speeds using high-speed steel end mills, and that water-soluble cutting oil is a suitable lubricant and coolant.

Jan 1, 2010