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By Brian Gettinger, Jim Schlaman, Alston Noronha

"INTRODUCTION The public understanding of green solutions today is based on the definition of sustainability adopted by the Brundtland Commission (World Commission on Environment and Development) in 1987: “development that meets the needs of the present without compromising the ability of future generations to meet their own needs.” Over time this initial definition evolved to identify three distinct factors impacting sustainability that are often referred to as the “Triple Bottom Line”: Economic, Environmental and Social. The triple bottom line approach seeks to drive outcomes that create maximum value for all stakeholders. In the last ten years purveyors of water and wastewater tunnel solutions have found themselves on the wrong side of a politically polarizing issue in the crosshairs of politicians, environmental activists and community groups branding tunnels as expensive, “gray” and not-sustainable. Tunnels under design were stopped and large planned tunnel programs were delayed or canceled. Therefore being sustainable and “green” is not simply using natural vegetation, but creating an asset that meets current and future needs and will not become a future liability. As this paper will discuss, tunnel projects embody a sustainable triple bottom line project well, are equally sustainable as green infrastructure, and have begun to gain awareness for their sustainability. GREEN INFRASTRUCTURE CHANGES TUNNELING LANDSCAPE The green movement quickly swept across the nation in the mid to late 2000’s and was a hot topic in the media and at all the local, regional and national industry conferences. Politicians espoused the benefit of green infrastructure including job creation, urban renewal, aesthetics, property values economics and sustainability. The political microscope was focused the closest on stormwater and wastewater management, particularly in communities responding to combined sewer overflow (CSO) consent decrees from the Environmental Protection Agency (EPA). As communities with CSO problems evaluated their long term control program (LTCP), local government officials and planners began to balk at the huge price tag required for compliance and began looking for alternatives. “Green” infrastructure was proposed as lower cost solution that could be used to offset capital-intensive “gray” infrastructure like new sewers, storage tanks, tunnels, and treatment facilities. In addition, including green infrastructure in a previously negotiated LTCP required a reset on the entire planning process, additional studies and more planning which would push capital investment further off into the future, subsequently delaying unpopular user rate increases. As a result, tunnel projects as well as trenched conveyance and treatment plant projects that had not yet started construction were stopped, delayed or substantially changed."

Jan 1, 2016

By Francis F. Pitard

North America had an Important role in the early development of sampling theories. Unfortunately many progressive ideas were soon frozen into a series of guidelines based on the philosophy that "honest sampling only requires good judgment and practical experience". Such a philosophy appeared to be good enough In the early age of the mining Industry; however, it became quickly necessary to find new approaches. During the last thirty years, Pierre Gy's sampling theory provided tremendous breakthrough in the comprehension of this new science, nevertheless went unnoticed in North America. Sampling always generates complex problems and as the philosopher and mathematician Descartes suggested: "A complex problem can often be dissociated Into a series of several simpler problems, only then you try to solve those one by one". The only way to solve sampling problems is to consider each component of the overall sampling error: components of a continuous model such as long-range quality fluctuations, periodic quality fluctuations, weighting fluctuations; components of a discrete model such as materialization errors, delimitations errors, extraction errors, fundamental errors, grouping errors, and segregation errors. PAST AND CURRENT PRACTICES Many sampling methodologies have been developed, improved, and standardized during the first half of this century. Accordingly, sampling equipment has been proposed, selected, and used by standards committees. Today, there is a tremendous variety of sampling methodologies and corresponding tools offered to anyone with limited experience in sampling and it is very easy for a chemist, metallurgist, geologist or miner to spend considerable money in equipment transgressing the most basic rules of sampling correctness. Sampling stations that never worked properly in modern plants often cause engineers to abandon them and return to a primitive form of grab sampling.

Jan 1, 1986

By Harry Perry

A technology for producing liquid fuels from oil shale at prices competitive with crude oil prices is a necessary but not exclusive prerequisite for the development of a shale oil industry. Many other factors will affect the timing and the rate at which oil shale is commercially developed. Among the more important are: governmental policy concerning oil shale and oil resources (including the Outer Continental Shelf) that are under Federal control; oil import policy; Federal taxation of shale oil production including depletion allowances; regulatory practices; competition from other energy sources, both synthetic and natural; Federal treatment of factors affecting competing energy resources; and present legislation under which the public resources must be leased. Significant changes in any of the foregoing factors could have a controlling effect on the timing and rate of oil shale development. The effect of changes in each of these factors is evaluated.

Jan 1, 1969

By Don Phelps, Christopher Tattersall, David McAllister

Located south of downtown Seattle, the Beacon Hill Station & Tunnels is the key section of the southern segment of Sound Transit’s proposed new LINK light rail system. This paper presents an overview of the design, which includes 4,300 ft of segmentally-lined bore twin tunnels and a deep mined station. With platforms located156 feet below grade, the station itself is only the second large-scale mined station in soil the US. Its complex geometry combined with variable soil conditions—sands, silt sand clays with slickensides—challenged the designer’s to come up with a SEM-based design that addresses the owner’s risk, cost and schedule concerns.

Jan 1, 2003

By G. R. Green

The centre of the mining operations of the International Nickel Company, Ontario Division is Sudbury, a city of 160,000 population located 240 miles northwest of Toronto (Fig. 1). Within thirty miles of this city and located around the rim of the geological formation known as the Sudbury Basin are the ten underground mines and one open pit operated by the Company (Fig. 2). There are also four developing mines, three in the Sudbury area and one at Shebandowan, near the city of Thunder Bay, Ontario and approximately 150 miles north east of Duluth, Minnesota. In 1971 the mines produced 22,800,000 tons, 20,600,000 tons from underground and the balance from open pits. Also located in the Sudbury District are facilities to extract and refine the metals contained in the ore. There is a nickel refinery located at Port Colborne on Lake Erie. An additional nickel refinery is under construction near Sudbury. Fifteen elements are recovered from the Sudbury ores, nickel, copper, iron, sulphur, gold, silver, cobalt, tellurium and the six platinum group metals, platinum, palladium, iridium, rhodium, ruthenium and osmium. In 1966 a major expansion program was undertaken to meet increasing market requirements. Coinciding as it did with a severe

Jan 1, 1972

By David A. Holmes

Zeolites are crystalline, hydrated aluminosilicates of the alkali and alkaline-earth metals. Their crystalline framework is based on a three dimensional network of SiO4 tetrahedra with all four oxygens shared by adjacent tetrahedra. The alkali and alkaline-earth cations are loosely bound within this framework structure and may be exchanged, to varying degrees, with other cations or molecular water. Most zeolites can be reversibly dehydrated. At present, close to 40 natural zeolite minerals have been identified and over 100 zeolites have been synthesized. Zeolites are a family of hydrous aluminosilicate minerals whose physical properties provide unique features for a wide variety of practical applications. Zeolites have been known for more than 200 years, but it was not until the middle of this century that their economic potential and widespread occurrence in sedimentary rocks were known. Since 1950, literally thousands of articles and patents have appeared in technical literature, and commercial pro¬duction of natural zeolites may now exceed 1 Mt worldwide an¬nually. In the past 40 years, the zeolite mineral group has changed from that of a museum curiosity to one of an established industrial mineral commodity. According to Breck (1974), zeolites are characterized by the following properties: 1) High degree of hydration, 2) Low density and large void volume when dehydrated, 3) Stability of the crystal structure of many zeolites when dehydrated, 4) Cation exchange properties, 5) Uniform molecular-sized channels in the dehydrated crys¬tals, 6) Ability to adsorb gases and vapors, 7) Catalytic properties. All zeolites are molecular sieves, but not all molecular sieves are zeolites. Activated carbon, activated clays, alumina powder, and silica gels are also molecular sieves. Molecular sieves are materials that can selectively adsorb molecules on the basis of their size, shape, or electrical charge (Clifton, 1987). Commercial application of zeolites is based on the following physical properties: molecular sieving, ion exchange, adsorption, and catalysis. Potential commercial utilization includes hundreds of possible applications. The principal uses at this time, however, are as fol¬lows: -Ammonium-ion removal in waste stream treatment, sewage treat¬ment, pet litter, and aquaculture, -Odor control, -Heavy metal ion removal from nuclear, mine and industrial wastes, -Agricultural use, such as soil conditioner and animal feed supplement. An estimated 800 kt to 1 Mt of natural zeolites were produced and consumed worldwide in 1991. Eight small operators reported collective production and consumption of an estimated 18 kt of natural zeolites in the United States during 1991, mostly for feed additives and for odor control, aquacultural, agricultural, catalytic, and ion exchange applications (Eyde, 1992).

Jan 1, 1994

By J. A. Marts, R. C. Gilmore, Jr. Bogin, S. A. Saki, J. F. Brune, J. W. Grubb

"Most, if not all longwall gobs contain explosive gas zones (EGZs), i.e., zones of explosive methane-air mixtures that can cause – and have caused – mine fires and explosions. If the coal is prone to spontaneous combustion, oxygen penetration into the gob must be avoided. This paper summarizes the significant research findings from five years of computational fluid dynamics (CFD) modeling research conducted at the Colorado School of Mines (CSM) under funding from the National Institute for Occupational Safety and Health (NIOSH). CSM Researchers have developed CFD modeling techniques to identify where and under what circumstances EGZs can form in longwall gobs and how EGZ formation and oxygen penetration depend on the ventilation method, face and bleeder ventilation parameters, injection of inert gases and the operation of gob ventilation boreholes. Recognizing these explosion and fire hazards is an important first step in improving the safety of longwall coal mines. CSM modeling research has shown that EGZ formation can be effectively controlled by adjusting ventilation parameters, choosing the proper ventilation pattern and injecting inert gases where necessary. INTRODUCTION In a project sponsored by the NIOSH Office of Mine Safety and Health Research, researchers at the Colorado School of Mines have examined gas compositions and flows in longwall gobs in order to assess explosion and fire hazards. Since gob areas are inaccessible, researchers developed a series of computational fluid dynamics (CFD) numerical modeling tools to characterize these hazards. A variety of CFD models were developed to cover progressively sealed as well as bleeder ventilated gobs for both coal and trona mines. The explosion and fire hazards posed by EGZs in longwall gobs can be summarized as follows.• If the EGZ lies closely behind the longwall face, flames and pressures from an explosion can penetrate the shield supports and reach the active face area, creating blast trauma, burn hazards and toxic, unbreathable atmospheres. • EGZs can be pushed around inside the gob by roof collapses and cave-ins. If they get pushed out into the face area, sudden methane inundations and explosion hazards in face areas can result. • Fresh air flowing into the gob can create an explosion hazard as the gas composition in the gob moves from fuel-rich inert to explosive, creating EGZs. • Ignition sources inside the gob can be frictional ignitions or spontaneous combustion. • Bleeder ventilated gobs are surrounded on all sides by an EGZ that forms along the fringe areas between the fresh-air ventilated bleeder entries and the methane-rich interior of the gob. It is suspected that diffusion flames can propagate rapidly along these EGZ fringes if an ignition occurs"

Jan 1, 2015

By Steven M. Puricelli

In recent times, smelter off gases treatment plants have become more efficient and environmentally friendly. Where in the past it was acceptable to process only high strength, treatable furnace gases, new smelters must now treat primary gases and abate dust and SO2 from secondary gases: Processing smelter gases can present some interesting challenges. Some equipment can see varying concentrations of sulfuric acid, up to the boiling point, with a periodic table of contaminates thrown in for good measure. Treating weaker secondary gases have, in the past, been cost prohibitive. Nowadays, new technology, like physical absorption or catalytic carbon, show promise for economically treating low strength secondary gases. Modem smelters do a much better job of treating the SO2 laden gases generated by the smelting process but significant challenges remain.

Jan 1, 1998

By D. R. Wilburn

This summary of international mineral exploration activities for 2012 draws upon information from industry sources, published literature and U.S. Geological Survey (USGS) specialists. The summary provides data on exploration budgets by region and mineral commodity, identifies significant mineral discoveries and areas of mineral exploration, discusses government programs affecting the mineral exploration industry and presents analyses of exploration activities performed by the mineral industry. Three sources of information are reported and analyzed in this annual review of international exploration for 2012: 1) budgetary statistics expressed in U.S. nominal dollars provided by SNL Metals Economics Group (MEG) of Halifax, Nova Scotia; 2) regional and site-specific exploration activities that took place in 2012 as compiled by the USGS and 3) regional events including economic, social and political conditions that affected exploration activities, which were derived from published sources and unpublished discussions with USGS and industry specialists.

May 1, 2013

By P. T. Bissert, J. P. Ducarme, J. L. Carr, A. K. Smith

"The continuous mining machine is a key piece of equipment used in underground coal mining operations. Over the past several decades these machines have been involved in a number of mine worker fatalities. Proximity detection systems have been developed to avert hazards associated with operating continuous mining machines. Incorporating intelligent design into proximity detection systems allows workers greater freedom to position themselves to see visual cues or avoid other hazards such as haulage equipment or unsupported roof or ribs. However, intelligent systems must be as safe as conventional proximity detection systems. An evaluation of the 39 fatal accidents for which the Mine Safety and Health Administration has published fatality investigation reports was conducted to determine whether the accident may have been prevented by conventional or intelligent proximity. Multiple zone configurations for the intelligent systems were studied to determine how system performance might be affected by the zone configuration. Researchers found that 32 of the 39 fatalities (82%) may have been prevented by both conventional and intelligent proximity systems. These results indicate that, by properly configuring the zones of an intelligent proximity detection system, equivalent protection to a conventional system is possible. INTRODUCTION Underground coal miners are exposed to a variety of hazards on a daily basis. Among coal and rock dust exposure, high noise levels, roof and rib falls, and the potential for fires and explosions, operating and working with heavy machinery poses a significant risk to miner safety. One of the most hazardous jobs is operating or working nearby a continuous mining machine (CMM). According to Mine Safety and Health Administration (MSHA) statistics, 39 miners have been fatally struck or pinned by a CMM since 1984. In an effort to prevent future striking and pinning fatalities from occurring, proximity detection systems have been developed and are now required on all operating CMMs in underground coal mines with the exception of full-face CMMs [1]. Commercially available proximity detection (cPD) systems are based on the principle of magnetic flux density (B-field). Typically, four magnetic field generators are positioned on a CMM, and personal alarm devices (PADs) are worn by the miners that detect magnetic flux density difference. As a miner wearing a PAD gets closer to the machine, the flux density increases. Zones can be constructed around the machine so that an alarm will trigger on the PAD based on the flux density."

Jan 1, 2016

By S. Murdock, R. L. Fleischer, H. W. Alter, J. E. Gingrich

The use of solid state track deters allows totally passive, integrating measurements of 222Rn (radon) or of 220Rn (thoron) plus radon. A track-detecting solid is placed in a holder that is closed by a selective membrane and exposed to the atmosphere of interest to produce an accurately time-averaged record over times of interest that range typically from a week to a year. By selection of the proper membranes, dosimetry can be done for radon or for the sum of radon and thoron. A different membrane is appropriate for measuring radon under humid conditions such as are found in the ground. Large numbers of measurements have been made with these systems both in the ground, where radon levels are high, and in indoor environments, where levels are orders of magnitude less. Calibrations have been carried out at both high and low concentrations of radon. New results in the air at the site of the Shirley Basin mine and mill give reproducible results with month-long integrating periods. The off-site background levels are in the range 0.7 to 1.0 pCi/l (26-37 Bq/m3). The average yearlong on-site level is 1.5 pCi/l (56 Bq/m3); at the mill it is 2.6 pCi/l (96 Bq/m3); and the level measured at the backhoe in the open pit mine is 3.9 pCi/l (144 Bq/m3). The region of significantly elevated radon levels is confined to a radius of 1.6 km of the mine and mill. All of the on-site radon concentrations are less than but comparable to the typical values found in the living areas of modern energy-efficient homes.

Jan 1, 1981

By V. Galla

In the present paper, two large diameter columns 2 m tall and 1.3 m diameter filled with crushed (finer) and run off mine (coarser) heap leach materials respectively were used to perform unsaturated flow studies. Instruments measuring moisture content and matric suction were placed in the columns at different depths as water was applied at calibrated flow rates from the top of the columns. The outflows from the columns were recorded using tipping bucket rain gauge placed at the bottom of the columns. Unsaturated hydraulic parameters were also obtained for the heap leach materials, scalped (passing 4.75 mm sieve size) and whole (passing 37.5 mm sieve size) sample. The measurements obtained from the columns were later compared with unsaturated flow modeling results. The comparison indicated sensitivity towards the sample size selection for unsaturated hydraulic parameters, and initial conditions considered in the model.

Jan 1, 2009

By Dan Swidrak, Bill Zietlow

Halfway through a 17,770-ft long stormwater tunnel, an 11-ft diameter TBM encountered a karst void below the Mississippi River in Missouri, resulting in significant inflow. It was decided that the TBM could not safely advance without external intervention. Low-mobility grout was pumped from the surface. A rescue shaft was constructed and a conventional tunnel with spiling support was mined back to the machine. The TBM was removed and a 14-ft diameter TBM equipped with probing drills was relaunched. Probing from the new TBM encountered one additional karst feature but the machine advanced after grouting and successfully completed the tunnel.

Jun 23, 2024

By Duluth Engineers' Club, Engineers' Club of Northern Minnesota

"The history of Duluth commences with Daniel de Greysolon du Lhut, one of the explorers of the Upper Mississippi who came to the head of the lakes in the summer of 1679. Radisson and Groseillier, and Claude Allouez, a Jesuit priest, are supposed to have visited the head of the lakes, -but there is no authentic record previous to that of du Lhut.In 1792, the fur traders established a fort at Fond du Lac, fifteen miles up the St. Louis River from Lake Superior, but within the limits of the present city •of Duluth. In the early 50's, there were a few scattering settlers at Oneota and around the George Stuntz trading post on Minnesota point. In 1855-6, the settlement on Minnesota point was called Duluth, commemorating the name du Lhut, and organized as a town in 1857. The first board of trustees and town council consisted of -William Nettleton, J. B. Culver; Robert E. Jefferson, Grin W. Rice and William Old: In 1870, the city of Duluth was incorporated, and five years later a portion of the same territory was incorporated as the village of Duluth, and the two municipal corporations were still in existence on March 1, 1887, when the city and the village of Duluth were incorporated as the present city.The first saw mill in Duluth was erected in 1856-57, on the present site of the ship canal. It cut logs from a virgin forest at the upper end of Minnesota point.The first railroad was built to the head of the lakes in 1870. The charter for this road had been granted in 1861 to the Lake Superior and Mississippi Railroad Company, afterward called the St. Paul and Duluth, and which is now a part of the Northern Pacific Railroad."

Jan 1, 1920

By C. Roos

Tradicionalmente en la industria minera, el flujo principal del proceso funcional para la evaluación de recursos y reservas procede de geólogos que elaboran el modelo geológico, de allí a los geólogos que hacen la estimación de los recursos (los modeladores) quienes estiman los grados, y a los ingenieros de mina que desarrollan el diseño de la mina y su calendario. La interfaz entre estas tres disciplinas no está siempre exenta de baches. Las presunciones hechas durante una etapa del proceso no siempre son comunicadas a los demás, a pesar que la mayoría de las empresas mineras tienen procedimientos y protocolos establecidos para promover la comunicación a lo largo de las distintas disciplinas. Estos procedimientos no siempre logran su propósito debido a una variedad de razones que incluyen restricciones de tiempo, no tener disponible a las personas apropiadas, o a una falta de entendimiento de lo que las otras disciplinas requieren, y el proceso de traspaso puede degenerar en el envío de archivos a la siguiente disciplina en el flujo de proceso. Este artículo se ocupa de la interfaz entre la estimación del recurso y las disciplinas de la ingeniería de minas y el esquema de algunas de las presunciones comunes hechas al generar un modelo del recurso y los riesgos que los ingenieros podrían correr al elevar los grados de corte, optimizar calendarios o realizar predicciones. Los casos de estudio presentados se centran en depósitos de oro a cielo abierto, pero los conceptos deben ser aplicables a toda la industria. Aquí también proveemos un resumen de preguntas clave y recomendaciones.

Jan 1, 2014

By Courtney Black, Paul F. Ziemkiewicz, Eberhard Werner, Matthew Daly, Joseph J. Donovan, Jeff Frazier

Injection of alkaline waste-lime slurry was performed at a West Virginia surface coal mine site, to attempt neutralization of acid springs by an alkaline recharge method. Deep trenching (>5 m) using an excavator yielded the most effective injection into the aquifer. Water from two springs, 90 m from the deep trench, showed 70%-80% reduction in acidity in response to injection. Neutralization persisted >170 days after treatment, with pH between 5.1-5.7 and metal acidity from 25-60 mg/L. A minor fraction of lime introduced was consumed. The sustained neutralization is attributed to reaction of acid water with subsurface lime, entrained below the wafer table by macropore infiltration. Characteristics of groundwater transport are critical in determining recharge structure location.

Jan 1, 2000

By T. G. Melkus

A Setaram C-80 heat flux micro- calorimeter was used to study the surface and interfacial properties of fine coal particles in water containing flotation agents via heat of immersion measurements. Heat of immersion (?Himm) is usually a small exothermic quantity and can be used' to characterize a solid in terms of its relative hydrophobicity or hydrophilicity. The effects of coal type, surface oxidation, mineral matter content, kerosene concentration, and pH on the wetting characteristics were investigated. Results obtained from the calorimetry experiments correlated well with results from independent flotation experiments.

Jan 1, 1987

By Emmet K. Oslen

Kaiser Steel Corporation, the pioneer steelmaker on the Pacific Coast, was founded by the late Henry J. Kaiser. In 1944 the Company purchased from the Southern Pacific Railroad an iron ore property 200 miles east of Los Angeles known as Eagle Mountain. Today the domestic operation of Kaiser Steel Corporation consists of the iron mine at Eagle Mountain; two coal mines, one each in Utah and New Mexico; an integrated steelmaking complex at Fontana, California; and several steel fabrication and erection facilities along the west coast. Kaiser Steel also has interest in Hamersley Iron, Ltd., Australia, and Kaiser Resources, Ltd., British Columbia. Eagle Mountain Mine is located about 80 miles east of Palm Springs and adjacent to the southeast corner of Joshua Tree National Monument. The area is one of the most arid in the world averaging only two inches of rain annually. Geologically, the mine is at the western edge of the Basin and Range Province which covers about one-half million square miles of the western United States. The Province is typified by north to northwesterly trending fault block mountain ranges separated by sediment filled valleys, Production has totaled over 82 million tons of finished products since the first shipment in June, 1947. Over 500 million tons of material have been mined from the deposit to date. Eagle Mountain Mine is noted for the pioneering use of the largest and most up to date equipment to mine and process its ore. In 1961 Eagle Mountain received the first fleet of 100-ton haulage trucks in the mining industry. There were thirteen semi-trailer units in the fleet. The first 12 to 17-yard size shovel in the mining industry was placed in operation at Eagle Mountain during 1962. Rotary drilling was introduced at Eagle Mountain in 1954 to replace churn drilling. Eagle Mountain was the first major mine to use metallized slurry when three aluminum slurries were introduced for primary blasting in 1962.

Jan 1, 1972

By A. A. El-Midany, R. M. Farag, A. M. Salem, S. E. El-Mofty

Bentonite represents one of the main players in the stability of the drilling mud. Its particle size and particle size distribution affect the physical properties of the drilling mud especially the rheological properties. Therefore, a specific particle size distribution was recommended by American Petroleum Institute (API) for use in drilling mud. To clarify the effect of individual size and size distribution, in this study, the bentonite sample was classified into different size fractions. Each size fraction was tested separately in terms of controlling properties such as filtration loss, plastic viscosity, gel strength, cake thickness, and packing density. The effect of each size fraction on the rheological properties of the suspension was correlated to the behavior of the whole particle size distribution in the bentonite sample. The results indicate that the coarser the particles, the higher the rheological properties; in this case, the API mixture is the highest. The filtration loss and cake thickness for the API mixture are lower than that of the individual size fractions due to its wider size distribution due to the filling of voids between larger particles with smaller ones, which lead to bed compaction and consequently lower fluid loss and cake thickness.

By John Bley

White Pine Copper Company operates a mine in the Upper Peninsula of Michigan using a modified room-and-pillar system for extracting ore.1 Mine production averages 15, 500 tons per day. The terrain is predominantly level and the depth of cover varies from 500 to 800 feet over the present workings with depth increasing as mining progresses down the dip. The deposit is situated on a low angle plunging, anticlinal structure composed of sedimentary beds. Local terminology for the stratigraphic units which contain the ore horizons, named in ascending order, is as follows: lower sandstone, parting shale, upper sandstone and upper shale. The ore zones of copper enrichment are, contained in the parting and upper shales. The parting shale will vary; from 6. 5 to 9.0 feet thick; the upper sandstone from 2 to 10 feet; and the upper shale from 1. 5 to 6. 5 feet. Two variation of the room-and-pillar system are used to extract the ore depending on grade and local ground conditions. One system is called the parting shale method and recovers the parting shale only. This system requires a mining height of 8 1/2 feet to accommodate large-scale, high-capacity equipment and this working height is obtained by removing approximately 1 to 2 feet of the barren lower sandstone with the ore. Under the second system, locally termed full column, the mining height is about 14-1/2 feet and this system removes the parting shale, the upper sandstone and the lower mineralized zone, approximately 1-1/2 feet, of the upper shale at which point it is possible to maintain a competent back (Fig. 1).1

Jan 1, 1964