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By M. Karmis, C. Haycocks

The evolution of longwall mining is briefly traced from its inception in England in the 1620's. In the beginning this method recovered 90% of coal with roof closure controlled by packs and walls. Mechanization began with kerf cutting, crude face conveyors, and improved face support. Full face mining was accompanied by the introduction of self- advancing hydraulic supports. U. S. longwalls evolved a retreating system to recover blocks of coal outlined by room and pillar panels. Computer control combined with the most modern technology have greatly increased productivity. Past trends are used to predict future technological directions.

Feb 24, 1997

By G. E. Vaninetti

During its modem era, the southern Powder River Basin (PRB) in Wyoming has grown from meager origins in the early 1970s to become one of the most important coal-producing regions in the United States. In 1993, production and sales of southern Powder River Basin coal exceeded 190 Mt (209 million st), or about 20% of the US coal industry. Despite the remote location of the PRB relative to its potential markets, most coal industry observers anticipate continued strong growth to meet utility compliance plans for Phases I and II of the Clean Air Act Amendments (CAAA). This article is an overview of supply and demand issues concerning the marketing of southern PRB coal. It reviews the events leading up to the recent run on spot coal and offers a forecast of demand and prices.

Jan 1, 1994

Several of the larger copper projects recently built have included a molybdenum byproduct circuit as part of the overall project due to the favorable molybdenum market conditions and overall economic contribution to the project. This paper provides a summary of moly plant flotation practices across a number of both recent projects and historical ones. Modern Molybdenum flotation flowsheets predominantly incorporate self-aspirated cells and forced air cells with nitrogen addition. The paper provides insight into the process considerations, capital and operating costs associated with both of the cell types. It also reviews metallurgical aspects and important safety aspects. Other aspects including instrumentation and degree of automation are also discussed along with overall plant design.

Feb 27, 2013

By Doug Harding

The Niagara Tunnel Project (NTP) is a 10.4-km- (6.5- mile-) long, 14.4-m (47.5-ft) bored tunnel that will run under the city of Niagara Falls from the Upper Niagara River to the Sir Adam Beck power station. The completed project will enhance the capacity of the Sir Adam Beck power station by adding 500 m3 /sec (17,657 cu ft/sec) of water through the tunnel. The project uses the world?s largest hard-rock tunnel boring machine (TBM) at 14.4 m (47.5 ft) in diameter to excavate the tunnel. Features of the project include the use of a high performance (HP) main beam TBM, state-of-the-art ground support and tunnel logistics systems. A continuous conveyor is used for muck transport from the TBM to the disposal area In June 2004, the Ontario government announced that Ontario Power Generation (OPG) had been given approval to proceed with the third tunnel under the city of Niagara Falls ? the first two tunnels were constructed in the 1950s using drill-and-blast techniques. The third tunnel, appropriately named the Niagara Tunnel Project (NTP), consists of a 10.4-km- (6.5-mile-) long TBM-bored, concrete-lined tunnel with a finished diameter of 12.5 m (41.1 ft). In August 2005, OPG the selected of Strabag of Austria, one of the largest construction companies in Europe, as the contractor to build the NTP at a price of C$600 million. In September 2005, Strabag selected The Robbins Co. of Solon, OH to design, manufacture and deliver a new 14.4- m- (47.5-ft-) diameter high performance, state-of-the-art main beam hard rock TBM to be used in the excavation of the tunnel. To meet the aggressive construction schedule as requested by OPG/Strabag, the TBM needed to be sup-plied as ready-to-bore within a 12-month period after the contract was awarded to Robbins.

Jan 1, 2008

By Dennis Ofiara

Several recent tunnel jobs have required special adaptations of hard rock TBMs. Some of the special job conditions are ?no blast? launch requirements, small shafts or launch pits, proximity to existing underground structures, and short tunnels where the TBM must be retrieved through the primary lining. This paper describes a few of these projects, and the machine adaptations that have made TBM excavation feasible.

Jan 1, 2008

By Douglas J. Lootens

Geologic mapping was undertaken in the Sierrita Mountains as part of a Doctoral program at the University of Arizona, Tucson. During the study, approximately 35 square miles was mapped in detail, with particular attention given to specific areas of great or significant structural complexity and their relation to mineralization in the vicinity. A combination, of field studies and photogeologic interpretation was used in order to define regional and local structural controls for disseminated copper-molybdenum mineralization in and adjacent to the study area. Gratitude is expressed to the faculty of the University of Arizona, Department of Geology for their assistance in this work and to Bear Creek Mining Company for making numerous reports and drill cores available for study.

Jan 1, 1965

By Steve Kral

In a lagging economy where profits are tight, businesses cut costs. No revelation there. The mining industry, though, has always looked for ways to reduce production costs — no matter the state of the economy or commodity prices. The fact is, when planning a new mine or the expansion of an existing one, mining companies gamble that commodity prices will be reasonably high when a project comes onstream. It takes millions of dollars and several years to bring a mine into operation. And a lot can happen economically between the time management gives the go-ahead for a new project and its completion.

Jan 1, 2002

By David E. Nicholas

Design of underground openings is becoming more critical as the mine deposits become lower in grade, initial investments increase, ore depth increases, additional safety regulations come into law, and increased ore recovery is required for conservation of minerals. Stability of these openings is dependent on the strength of the rock mass and the pre-mine stress field. The rock mass is composed of solid blocks of rock (rock sub- stance) and structural features (faults, joints, bedding, etc.). Methods of testing the rock mass strength are improving and be- coming more common, however it is difficult to justify the high cost of large scale testing for an initial mine design. An alternative to testing the rock mass is to measure the rock substance and the structural features separately, and then combine them to estimate the rock mass strength. The rock mass strength will vary depending on the orientation of the opening with respect to the structural features. The other factor affecting the stability of underground open- ings is the pre-mine stress field. Methods are available to measure "directly" the pre-mine stress in competent and relatively massive rock. These methods are costly to employ, therefore, they may not be justified in an initial study. The pre-mine stress field can be estimated based on the structural relationships formed from past tectonic events.

Jan 1, 1976

By David L. Veith

As the basis for the State of Minnesota's Regional Copper-Nickel Study environmental evaluation, hypothetical mine models were developed ranging in ore capacity from 5.35 to 20.00 x 106 mtpy. Open pit and underground mining operations were defined utilizing conventional methods of ore extraction. Processing of the copper-nickel sulfide material involved conventional bulk flotation of the valuable minerals, with maximum water recycle And tailing disposal. Flash smelting and electrolytic refining of the concentrate resulted in 0.10 x 106 mtpy copper plus nickel metal, plus associated cobalt and precious metals. Variations in model parameters allowed environmental trade-offs to be identified.

Jan 1, 1980

By Werner Burger

The last decade has witnessed a rapid development and application of slurry and EPB type tunnel boring machines. Both soft ground types are able to excavate tunnels in unstable ground conditions below the water table with positive face support. The most significant component of the excavation process is the cutterhead and tool con-figuration were the excavation and face support meets the geological challenge. The TBM downstream processes cannot take place unless the cutterhead and tools effectively do their job. This paper will review the current state of the art design for both slurry and EPB cutterheads and highlight both common as well as geological specific design features.

Jan 1, 2007

By Robert Vergie

Like most of you, I would rather work on a job than talk about it. But it is fruitful to spend some time taking stock of important developments in the heavy construction field. One of the strongest recent movements affecting the industry has been the push for safety. I regret that it is a recent development. Not that builders were against safety. Too often though, it was easier to continue with dangerous old work methods than to try something new. Too often, it was easier for equipment manufacturers to build production tools with little consideration for worker safety. And too often, accidents and gruesome disasters occurred. The ultimate result of on-the-job injuries in construction and other industries was the Federal Government's Occupational Safety and Health Act of 1970. Individual states were required either to accept OSHA or pass updated regulations at least as stringent as the Federal requirements. These new rules must be strictly obeyed -- not just because they carry civil and criminal sanctions -- but because they correct unsafe conditions and reduce hazardous acts. Though some OSHA measures have been criticized as superfluous, most of them do in fact save lives and limbs. Equally important, the tunneler who follows the new safety regulations can be fairly certain of an efficient, uninterrupted operation. Regulations do sometimes bring rewards.

Jan 1, 1974

By Giorgio De Tomi, Ricardo Tichauer

Mineral exploration is a critical step for success in mining. However, small-scale mining often ignores exploration best practices. This paper introduces the Tichauer-DeTomi Matrix, a tool for assessment of geological uncertainty in small-scale mining. This matrix, which measures the level of compliance of exploration programs in small deposits with industry best practices, has been applied to three small mining projects in Brazil: an artisanal gold mine in the Amazon, a small-scale manganese mining venture in the Northeast, and a small manganese deposit in the Southeast. The application of the matrix resulted in indexes that reflect the actual level of maturity of the mineral exploration program in each project. Therefore, the matrix has shown potential to be an effective tool for assessment of the geological uncertainty remaining in small-scale mineral projects, as well as to identify priority exploration activities for reduction of risks associated with the geological uncertainty. As a risk assessment tool, the TichauerDeTomi Matrix may be helpful in promoting investment and sustained development in and around small mines.

By Lee W. Abramson, William H. Hansmire

The H-3 Project is planning, design, and construction of a 10-mile (16 km)-long final segment of new highway that traverses the Koolau mountain range in Oahu. Interstate H-3 traverses North Halawa Valley on one side of the Koolau Mountains and Haiku Valley on the other side. The project includes a tunnel through the mountain range. The one-mile (1.6 km)-long twin-bore Trans-Koolau Tunnel will have two lanes in each direction. The total roadway width including shoulders in each bore will be 38 ft (11.6 m). The geologic and geohydrologic conditions along the alignment present a variety of tunneling problems. Geologic conditions consist of volcanic materials deposited generally in fairly thin basaltic layers. These volcanic materials generally weather down to "MH" soils which are compressible but relatively strong. Perched ground water that is recharged by heavy rainfall is present in the mountains. The paper presents results of initial geologic surveys and exploratory boring, and plans for exploratory tunneling and testing programs. A site specific classification method developed to characterize the weathered profile is presented.

Jan 1, 1989

By Bradford F. Townsend, Colin R. Speers

INTRODUCTION This is the first in a series of papers addressing practical tunnel lining design. The format for this and future papers is to present a particular topic and support the presentation of the guidelines by the practical application of a case history. The primary intent is to provide guidelines for the geotechnical and structural design of tunnels where the tunnel size and/or ground conditions dictates that systematic support of the excavation is required following each increment of excavation. This method of tunneling is commonly referred to as Sequential Excavation and Support(SES) and is also commonly termed the New Austrian Tunneling Method (NATM) The authors developed the design guidelines from experience gained over the past two decades during the design and construction of several major railway, highway and water-transfer tunnel projects in Africa and Asia. During this time it has been possible to compare the performance of the as-constructed structures to the predicted performance as given by the design process. Excavation was typically carried out in widely varying ground conditions (weak-bedded rock, jointed hard rock, and soil-like poorly cemented rock with groundwater). It is therefore intended that the design guidelines could be applied, in general terms at least, to any tunnel excavated in any ground mass condition with any ground material type (hard rock, soft rock, bedded rock, soft ground, and soil) with or without ground water. This first paper is an introductory paper that defines the scope and a brief outline of the design issues that may be presented in detail in later papers. What is design? It may be thought of as any rational/verifiable/justifiable process whereby a concept is transformed into information that can be used to bring the concept to reality. In the case of a civil structure, design may be defined as that process, which is documented and can be audited, that determines information such as the shape (form) of the structure, the dimensions (size) of the structure, the thickness and strength of structural members that comprise the structure, etc. This information can be used to compute the time, money and resources required for

Jan 1, 2005

By Steve Kral

After years of cutbacks, closures and layoffs, the mining industry is beginning to expand again. Metals prices are up and so is investor interest and confidence in the industry. Gold prices began to slowly move up in January2003 and finally cracked the $12.86/g ($400/oz) mark in early December. Silver, too, is up, as is copper. So the mining industry is feeling good about itself again and many companies are expanding existing mines and developing new ones. One side benefit to mining’s improved outlook is that companies are beginning to send more of their employees to industry conferences. Such was the case at the109th Northwest Mining Association meeting in Spokane, WA. The meeting was held in early December and attracted 1,100 attendees and 84 exhibiting companies. That is up from 2002’s attendance of about 900 people and 65 exhibitors. The theme was “A Partnership into the Future.”

Jan 1, 2004

By L. Echeverri

Research studies have shown that the flow within feedwells displays a vortical structure and high velocities at the locations where standard tangential inlets force its way into the feedwell swirling flow, producing high local shear rates and flow non-uniformities. These hydraulic deficiencies can be attributed to the discrete feeding through a few entrances, usually one or no more than a few tangential feedpipes, which practically project jets into the vortex within the feedwell. The main consequences are unequal flocculation with aggregates subjected to different amounts of shear and a non-uniform discharge from the feedwell. This paper presents results on the application of CFD and small-scale models to develop a new design that overcomes these problems by using an involute shaped inlet that converges around the feedwell. The result is a new feedwell with enhanced hydraulics that perfectly couples with the FLSmidth E-Duc® Feed Dilution system by protecting the flocculated aggregates that have been carefully produced upstream, and that favors uniform sedimentation conditions within the thickener thanks to a uniform discharge, while maintaining a practical and trouble-free geometry with excellent turndown.

Jan 1, 2012

By Zhigao Xu, Ming Wu, Jun Qu, Rong Zhang, Wenrui Nie, Ruan Chi, Zhenyue Zhang, Zhengyan He

The leaching processes and mechanisms of weathered crust elution-deposited rare earth (RE) ores with ammonium sulfate were investigated for their high efficiency and low consumption exploitation. The leaching process is a typical reversible heterogeneous ion exchange reaction in liquid–solid systems. The raw ore and leached tailings were analyzed by SEM and FTIR. Results indicated that no dissolution or structural changes of the ores occurred during the leaching process. The migrations of RE3+, Al3+, and NHþ 4 in the leaching process were studied under various liquid–solid ratios. With increasing liquid–solid ratio, the content of NHþ 4 adsorbed on clay mineral by physical effect decreased, NHþ 4 adsorbed by ion-exchange increased, and the content of exchanged RE and Al increased until reaching equilibrium. The adsorption capacity of the RE ores for NHþ 4 remained about 0.61–0.63 mg/g. It was difficult to desorb NHþ 4 from RE ores with washing water alone. The leaching mechanism of Al was the same as RE, but the leaching of Al slightly lagged behind RE. At the optimal liquid–solid ratio of 0.4:1, the leaching efficiencies of RE and Al were 95.51% and 90.99%, respectively, and 56.65% of NHþ 4 remained in the leachate. After impurity removal and RE precipitation, the leachate can be reused by replenishing fresh leaching agent. The aim of this study is to enhance the leaching process of RE, restrain the leaching of impurities, and decrease the consumption of leaching agents.

By Zhigao Xu, Ming Wu, Jun Qu, Rong Zhang, Wenrui Nie, Ruan Chi, Zhenyue Zhang, Zhengyan He

The leaching processes and mechanisms of weathered crust elution-deposited rare earth (RE) ores with ammonium sulfate were investigated for their high efficiency and low consumption exploitation. The leaching process is a typical reversible heterogeneous ion exchange reaction in liquid–solid systems. The raw ore and leached tailings were analyzed by SEM and FTIR. Results indicated that no dissolution or structural changes of the ores occurred during the leaching process. The migrations of RE3+, Al3+, and NHþ 4 in the leaching process were studied under various liquid–solid ratios. With increasing liquid–solid ratio, the content of NHþ 4 adsorbed on clay mineral by physical effect decreased, NHþ 4 adsorbed by ion-exchange increased, and the content of exchanged RE and Al increased until reaching equilibrium. The adsorption capacity of the RE ores for NHþ 4 remained about 0.61–0.63 mg/g. It was difficult to desorb NHþ 4 from RE ores with washing water alone. The leaching mechanism of Al was the same as RE, but the leaching of Al slightly lagged behind RE. At the optimal liquid–solid ratio of 0.4:1, the leaching efficiencies of RE and Al were 95.51% and 90.99%, respectively, and 56.65% of NHþ 4 remained in the leachate. After impurity removal and RE precipitation, the leachate can be reused by replenishing fresh leaching agent. The aim of this study is to enhance the leaching process of RE, restrain the leaching of impurities, and decrease the consumption of leaching agents.

By P. A. Dimas

A new family of sulfide flotation collectors has been developed in our laboratory. These formulations are comprised of novel renewable materials combined with conventional reagents. The resulting diversity permits tunability of collector chemistry to meet a range of flotation problems. Several attributes of the new collectors are presented.

Jan 1, 2012

By Brian Fulcher

The Arrowhead Tunnels Project represents the final portion of a 70 km (44-mile) long water conveyance facility that will bring up to 28 m3/sec (1,000 ft 3/sec) of water into Southern California. The 13 km (8-mile) tunnelling project is well underway and consists of two, 5.8 m (19-ft) diameter TBM bores through extremely variable geological conditions. An extensive and essential pre-excavation drilling and grouting program was performed in all reaches of the Arrowhead Tunnels Project, located north of San Bernardino, CA. This program supported the advance of two hybrid hard rock TBMs though extremely challenging ground conditions under substantial ground cover and up to 27 bar (900 ft) of ground water pressure. The well known San Andreas Fault lies nearby and has greatly influenced the local geological conditions. This paper will describe the means, methods and materials used throughout the numerous phases of the pre-excavation grouting program. It will also describe many versatile, flexible and innovative drilling and grouting methods and equipment systems utilized to improve performance, save time and costs in constantly changing geological conditions. Considerable lessons learned have been learned while overcoming some extremely formidable ground conditions and safely advancing the tunnels.

Jan 1, 2008