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By Rosana Rocha Cunha

Estudou-se as propriedades de filmes finos de TiO2 depositados em substratos de vidro.Os filmes foram obtidos pelos métodos Sol-gel e Evaporação por feixe de elétrons (e-beam) visando obter a propriedade autolimpante. Essa propriedade dos filmes de TiO2 está relacionada à hidrofilicidade fotoinduzida e pode viabilizar várias aplicações tecnológicas como a obtenção de vidros autolimpantes para módulos fotovoltaicos. O tetraisopropóxido de titânio foi utilizado como precursor no método sol-gel com deposição dip-coating. Na evaporação e-beam, partiu-se do TiO2 sólido. Os filmes passaram por diferentes tratamentos térmicos e as propriedades dos filmes obtidos pelas duas técnicas de deposição. A cristalinidade da fase anatásio foi identificada por DRX de baixo ângulo. A espessura foi medida por perfilometria e Microscopia de Força Atômica, obtendo-se valores próximos de 170 nm. Parâmetros como topografia, rugosidade e tamanho dos cristais de anatásio foram avaliados. A transmitância das placas de vidro com os filmes depositados foi medida por espectrofotometria UV-Vis. O caráter hidrofílico dos filmes finos foi comprovado por meio de medidas do ângulo de contato com água. Os filmes obtidos por ambas as técnicas apresentaram boa capacidade autolimpante devido ao efeito da hidrofilicidade fotoinduzida sob radiação UV.

Aug 16, 2017

With the employment of a system of ore pillars to support the hanging wall during the mining operations at the North Mine, it was found that, when the stopes were worked out and the pillars remained intact, the main footwall drives developed an undulating longitudinal section due to the shrinkage of the filling in the worked out stopes.These depressions collected water, which made the footwall drives very wet under foot, and everitually worked its way into the pillar workings and the levels below.Water was also finding its way into the shafts because of the silting-up of the level drainage systems and, as both the shafts are down-cast, this tended to increase the humidity of the air entering the mine.To overcome these troubles it was decided to try a system of siphons as a method of subsidiary drainage.SYSTEM AT PRESENT IN USE.All drainage water is collected as near to its source as possible, run into a sump in an adjacent low lying part of the level, and continuously removed from these sumps by a siphon system.Each level has its own system. Water is collected from the sumps by a 1-in. pipe and delivered to a pipe running the length of the level along the back of the footwall drive. At the shaft the pipe is increased to...

Jan 1, 1938

By E. K. Stanek

The field tests involved ten coal mines in which transients were initiated on the dc system from which the parameters of the dc mine electrical power system could be determined. The data processing involved the use of a Fourier Analyzer to filter noise and fit an exponential curve to the field waveforms. From this data analysis it was possible to find the dc system resistance, inductance and time constant. The survey of nationally recognized laboratories was conducted to establish that the recommended test criteria were practical. The development of test criteria for dc fuses used in mines was based on the measurement of parameters in the field, the survey of testing laboratories, literature searches, laboratory test, etc. A computer program was written to analytically predict the parameters measured in the field. This approach has limitations but reasonable agreement with field results was obtained. A brief laboratory testing program was carried out to verify the practicality of the recommended criteria and establish the accuracy of the conclusions concerning dc fuse performance.

Jan 1, 1984

By Mitchell L. Fong

The Bay Area Rapid Transit (BART) District will be extending BART service south along an 8.7-km (5.4-mile) -long corridor in the city of Fremont, California as part of the Warm Springs Extension (WSX). The WSX project will link the existing BART system to the future BART to San Jose extension. A segment of WSX is located in Fremont Central Park (referred to as the Fremont Central Park Subway Project). The Fremont Central Park Subway is considered the most complicated and geotechnically challenging portion of the project with an underground subway box being constructed near the active Hayward Fault which is capable of ground motions up to 0.75 g and is located in an aquifer which is used for water storage and supply. Soil-structure interaction analysis was used in the design of the subway box to resist deformations due to earthquake ground motions. A water-tight excavation support system has been designed to allow subway box construction while minimizing impacts to the aquifer.

By Jackson de Brito Simões

As ligas com memória de forma (LMF) apresentam características funcionais de recuperação de deformações plásticas aparentes e mudança de suas propriedades mecânicas quando submetidas a variações de temperatura, proporcionando um crescente interesse para aplicações de engenharia e originando uma nova maneira de projetar sistemas mecânicos. Nesse contexto, é importante desenvolver novos métodos de fabricação de componentes e dispositivos a partir de LMF. Infelizmente essa fabricação pode ser ainda extremamente complexa e dispendiosa, principalmente para LMF do sistema Níquel-Titânio (Ni-Ti). No final do século XX, a fundição de precisão se tornou uma alternativa eficaz para a conformação de componentes de titânio e suas ligas em aplicações de alta tecnologia. Entretanto, não existem informações da utilização desse processo para fabricação de componentes mecânicos de LMF. Assim, o objetivo deste trabalho foi avaliar o processo de fundição de precisão para o desenvolvimento de novos, produtos principalmente miniatuadores ativos de LMF Ni-Ti. Para isso, foi realizada a fabricação de diferentes formatos de miniatuadores de LMF Ni-Ti (de composição nominal em peso de 54,9Ni-45,1Ti) pelo processo de fundição de precisão com molde sólido, e ainda sua caracterização térmica e por ensaios não destrutivos. Foram obtidos quatro miniatuadores distintos, nos formatos de minitubo duplo, arruela Belleville, mola e parafuso, com bom acabamento superficial. A presença da transformação de fase característica das LMF foi avaliada por técnicas de calorimetria diferencial exploratória (DSC) e resistência elétrica em função da temperatura (RET) nos quatros tipos de miniatuadores. As técnicas não destrutivas de raios X e tomografia computadorizada foram empregadas para avaliar a qualidade dos miniatuadores produzidos, sendo importantes na detecção da presença de defeitos de processo. Ficou evidente a eficiência do novo processo proposto, porém ainda se faz necessário mais investigações principalmente com relação ao comportamento termomecânico dos miniatuadores obtidos por esse processo.

Aug 16, 2017

By W. Keith Buck

Introduction During World War II years, the magnetometer was used by various field parties of the Geological Survey of Canada, specifically in the search for chromite, a strategic war mineral. Throughout the summer of 1944, Professor J. W. Ambrose used the instrument experimentally on eight separate projects (1). Since then, several members of the Survey have come to consider its use to be of valuable assistance in the season's mapping. Dr. C. H. Stockwell, in particular, regards use of the magnetometer as a necessary part of detailed geological survey work. Throughout the field season of 1949, the magnetometer was used by Dr. Stockwell?s party as an aid to mapping in detail, to the scale one thousand feet to the inch, the south-west quarter of Dasserat township, Temiskaming county, Quebec. The principal geophysical project that was undertaken was the location of the Horne Creek fault and the Diabase fault in the area approximately midway between Arntfield and Kearns, on the Quebec side of the Interprovincial border. The location of these faults on either side of this central area was known. The Horne Creek fault is a subsidiary fault to the Cadillac 'break' which extends ?westward from Val d'Or through Cadillac to beyond Larder Lake. It lies to the north of that major fault zone and has a general southwesterly trend.

Jan 1, 1951

I would like to thank The Australasian Institute of Mining and Metallurgy for inviting us to share with you some of our experiences in the handling, storage, and transportation of industrial minerals in North America. Cometals, Inc. is a wholly-owned subsidiary of Commercial Metals Company, headquartered in Dallas, a public corporation whose shares are traded on the New York Stock Exchange. Sales exceed one billion dollars. Cometals, Inc. is located in New York and specializes in marketing of chemicals as well as raw materials used in the manufacture of steel, refractories, abrasives, glass and ceramics. This makes us one of the larger regular shippers of industrial minerals. Many people are aware that industrial minerals need to be viewed and judged on the merits of their chemical and physical characteristics. In addition you are surely aware that close attention must be paid to the economics of these minerals to determine the appropriate value and competitiveness of the minerals or products delivered at the doorsteps of the consuming work. You may, however, not be aware that the handling and transportation of the mineral is of crucial importance, in fact, the transportation and handling costs of industrial minerals frequently are a major component of the value of the ores marketed and, therefore, it is only natural that close attention should be paid to them. Many of the industrial minerals require special handling to assure that the material reaches the consumer without being contaminated and without getting wet. I invite you to accompany me through the various steps involved in "delivering the goods" to the consumer.

Jan 1, 1989

By J. Dean Warner

From 1984 through 1987, the Bureau of Mines investigated numerous prospects and new discoveries of columbium, rare-earth elements (REE), uranium, zirconium, and other metals associated with the multi-phased peralkaline granite at Bokan Mountain, southeastern Alaska. This report summarizes the mineral evaluations and estimates indicated and inferred resources for those prospects containing significant tonnage and grade. A total of approximately 96.2 MM lb Cb205 (43 pct of the tonnage at a grade exceeding 0.125 pct Cb205), and 11.8 MM lb U308, 27.9 MM lb Th02, 133.0 MM lb Y203, 637.6 MM lb ZrO2, and 241 MM lb REO are estimated to be contained within nine deposits totalling 37.8 million tons (at least 80 pct of resource tonnage also exceeds 0.5 pct Y203 + REO). Generally, half of the REO content is composed of the heavy yttrium subgroup. Several deposits also contain beryllium and tantalum; 2.1 MM lb of Ta205 and 8.9 MM lbs of BeO were estimated. These estimates would likely be substantially increased with additional exploration. Four deposit types were investigated; shear zones and fracture-related deposits, pegmatites, mineralized dikes, and placers. Mineralized dikes contain most of the beryllium, columbium, tantalum, yttrium, zirconium, and REE resources, whereas shear zones and fracture-related deposits (Ross-Adams mine) contain the principal of the uranium resource. Pegmatites are similarly mineralized as are dike deposits, and contain low levels of gold. Placer potential is suggested, but no deposits were found.

Jan 1, 2011

By E. J. Gleim

The importance of "good voltage,? especially for direct-current systems in coal mines, is not always fully appreciated. From the practical 4 aspect there are three viewpoints from which low voltage may be considered, namely: (a) its effect upon operation of electrical equipment, (b) its effect upon cost of maintenance and power, and (c) its effect upon safety in the mine. The design of electrical motor-driven equipment usually is based upon a given or assumed constant value for the voltage of the system; consequently, when there is an appreciable drop below this value, unsatisfactory operation is likely to follow. In the case of shaker conveyors, for example, one manufacturer has pointed out that these conveyors must be operated at a certain definite speed if maximum output is to be secured. As shunt motors are used in the conveyor drives, either a rise or fall in voltage will produce corresponding changes in speed and thus seriously affect the efficiency of the conveyor. The introduction of automatic control for mine equipment has been greatly retarded because the relays, contactors, and other special devices required have failed to function properly when attempt was made to operate them on systems subject to variable and low-voltage conditions.

Jan 1, 1937

By G. Krogman, C. Walla, B. Wood

The Gebo Mining District (District) is located in the Bighorn Basin of Wyoming. Commercial underground coal mining began in 1906 with the arrival of the railroad in Thermopolis, which is located approximately 11 miles to the south. Mining in the District ceased by the early 1970’s. In Fall of 1999, Lidstone and Associates, Inc. (LA) and their subcontractors were retained by the Wyoming Abandoned Mine Land Division (WyAML) to perform an inventory of over 500 abandoned mine sites across Wyoming. During the summer of 2000 field inventory, a 30-foot deep headcut (Figure 1) and sink-hole were noted in the West Fork of Sand Draw (WFSD), immediately west of the Town of Gebo. The headcut and sink-hole were located at the culvert outfall associated with a stream crossing of a relatively well traveled county road. Upon further investigation, it appeared that underground mine workings had been exposed at this location. This resulted in a condition whereby water would be conveyed directly into the mine workings during a runoff event. The exposed mine workings as well as stream capture created a very hazardous condition. The WyAML implemented mitigation measures in the summer of 2000 by constructing a temporary stream crossing upstream of the existing failed crossing. To address this hazardous situation as well as a number of other hazards identified in the District during the field inventory, the WyAML retained PHC Reclamation, Inc. (PHC). PHC was directed to perform a field investigation and develop a Reclamation Plan to address all existing abandoned mine hazards in the District. Federal, state, and private parties own lands within the District. Hazards identified during the investigation included an underground mine fire, open adits, open shafts, subsidence, drainage problems, and coal slack. A Report of Investigation (ROI) was submitted to various regulatory agencies that documented the existing conditions and conceptual reclamation plans to remediate the hazardous conditions. After review of the ROI by the US Department of Interior - Bureau of Land Management (BLM) an on-site meeting was conducted. BLM Cultural Resource personnel declined to approve a District reclamation project until a historical overview of the entire District was prepared. Due to the hazardous situation associated with the WFSD stream crossing, Hot Springs County Road and Bridge Department convinced various state and federal regulatory agencies to allow reclamation of the stream crossing to occur. A decision was made to allow reclamation on privately owned lands within the WFSD drainage. This decision limited the amount of channel that could be subjected to reclamation upstream of the crossing to privately owned lands. PHC contracted LA to perform a geologic, geomorphic, hydrologic, and hydraulic investigation of the drainage to assist in the development of a WFSD reclamation plan. LA’s investigation consisted of four parts: Delineate the extent of mine workings in the area; Identify all drainage structures that required mitigation; Survey a series of channel cross-sections and a longitudinal profile of the impacted channel; and, Develop basin hydrology to assist in the design of a stable reclaimed stream channel.

Jan 1, 2006

By Benoit Bissonnette, David Gelderland

"The Campbell Mine Constructed Wetlands has been in full operation, processing effluent from the water treatment plant of the mill circuit for the last two years.The overall results are extremely positive with dramatic improvements for the originally targeted parameters – Ammonia, Copper and toxicity.• Ammonia concentrations were reduced from an average of 5 mg/L to an average of 0.43 mg/L which translates to an average reduction of 91%.• Copper concentrations were reduced from an average concentration of 0.054 mg/L to an average of 0.019 mg/L, which translates to an average reduction of 65%.• LC50 Acute toxicity testing revealed no impact.• IC25 Chronic toxicity tests revealed no impairment to growth or reproduction.As a result of the improvements in discharge water quality from the wetland, 100 percent compliance with respect to all Certificate of Approval, MISA and MMER regulations for effluent will be consistently achieved.The system has proven to be very easy to operate and maintain, with a minimum of care. Given some basic rules are followed, the construction of the wetlands was straightforward and relatively inexpensive compared to other treatment methods.The ecological benefits of the operation of the wetland are also quite substantial, as is the positive image of the corporation in environmental stewardship.INTRODUCTIONOver the last four years, Campbell Mine has adopted an aggressive schedule for the development of wetlands for use as the final stage of effluent treatment within the tailings management facility. The focus of this work has been to utilize natural biological systems to provide Campbell Mine with a 100 percent compliant water quality with respect to all MISA, MMER and COA discharge criteria at all times throughout the effluent discharge period."

Jan 1, 2003

By Erin Legault Seguin, Mike Rylatt, Curtis Mohns

"With energy costs increasing and ore grades diminishing, the role of pre-concentration in hard rock mining operations has been gaining greater interest. To maximize energy conservation, the pre-concentration process should be conducted at as coarse a crush size as possible while minimizing losses of pay metals. Dense medium separation (DMS) is a robust process that can be conducted at particle sizes as coarse as 300 mm and as fine as 500 µm with high separation efficiency, depending on liberation characteristics of the value minerals. The DMS process involves three steps: feed preparation, dense medium separation, and ferrous-based media recovery. This paper discusses each of these processing steps, but focus will be given to the dense medium separation stage. Various types of DMS equipment are reviewed. Pilot plant campaign case studies conducted at the SGS Lakefield site are presented, which have included a variety of mineral systems such as spodumene, sulphide-bearing gold ores, and complex sulphide ores. These case studies demonstrate that for amenable ores, mass rejection of 20-60% is possible while maintaining recoveries of greater than 90% in most cases.IntroductionPre-concentration is a process of rejecting mass of gangue while ensuring recovery of valuable minerals prior to more intensive, downstream processing. Pre-concentration has been practiced in industry for many years, and is gaining greater interest as the industry copes with processing lower grade, more difficult ores, typically requiring finer grind sizes and higher energy costs."

Jan 1, 2016

By H. Thomas, I. N. M. Nday

"*Paper written on project work carried out in partial fulfilment of BSc.Eng (Mining Engineering) degreeThe optimization of the cycle time to increase productivity at Ruashi Mining was an on-site project investigation conducted from December 2017 to January 2018. The main objective of the investigation was to determine the actual cycle time components. These comprise the queuing time, loading time, hauling time, and dumping time of ADTs (articulated dump trucks). Data was also collected on two hydraulic shovels to identify where these could be optimized. The actual cycle time obtained was compared to the theoretical cycle time to ascertain the constraints, which affect productivity. By applying Systems Thinking to the cycle time, man-made constraints of the actual cycle time were identified and recommendations to mitigate them suggested to optimize the cycle time. However, rainfall is a natural constraint that adversely affects the actual cycle time, and which cannot be mitigated.In addition, both the theoretical and actual cycle time were analysed, as well as the theoretical and actual productivity for the year 2017. Based on the findings, conclusions and recommendations were made to optimize the cycle time. IntroductionThe aim of the project was to increase Ruashi Mining’s productivity by 39%, from about 7.537 Mt of broken material mined to 12..367 Mt targeted in 2017.BackgroundRuashi Mining is a copper (main commodity), cobalt (by-product), and acid producer located in the Democratic Republic of Congo (DRC), 10 km from the city of Lubumbashi. Figure 1 shows the location of the Ruashi Mining open pit.Ruashi Mining started production in 1911 and in 2005 the mine was registered as a DRC company owned by Metorex Group Limited. In November 2013, the Chinese company Jinchua Group International Resources Co. Ltd. bought a majority stake in the business. Ruashi Mining currently produces 38 000 t of copper and 4400 t of cobalt per annum. The company has contracted NB Mining (a contract mining company) to transport its ore. To optimize the productivity of the mine, considering ore flow delivery at Ruashi Mining, the cycle time is the indicator used in this project. The cycle time components were recorded on site using a stopwatch."

Jul 1, 2019

By Cláudio S. S. Pinto

Em face do agravamento da situação da energia elétrica no Brasil, com disponibilidade cada vez mais restrita e custo cada vez maior, torna-se urgente reduzir o seu consumo onde possível. Ventiladores centrífugos de processo de médio e grande porte são grandes consumidores de energia elétrica e podem ter um elevado potencial para a redução do seu consumo. Este texto mostra como identificar a possibilidade de economizar o uso da energia elétrica em um determinado ventilador e que modificações ele necessita para cumprir este objetivo.

Sep 25, 2017

By G. C. Lammers

The object of this study was to determine the economic feasibility of hydraulically transporting Sandow (Tex.) lignite 100 miles and dewatering and thermally drying the transported lignite to a surface-dry condition. The most important factors involved in the feasibility of hydraulic transport, are the degradation incurred during transit, the length of the line, and the cost of alternative methods of shipment. In pipeline tests in which roughly 75 miles of hydraulic transport was simulated the percentage of minus-325-mesh solids increased from about 1 to 41 percent for both lignite and bituminous coal; in the micron sizes the coal fared considerably better than the lignite. Such degradation, even though it enhances flow through the pipe-line, severely aggravates the dewatering problem on lignite. Cost studies indicated that continuous vacuum filters offer the most economical means of dewatering minus-1/8-inch material. Surface moisture, if high, must be removed by relatively expensive thermal drying.

Jan 1, 1958

By Y. X. Zhao

This paper briefly describes the characteristics and induced factors of coal mining bumps based on the investigation of recent bumps accidents occurred in China. According to the theory of non-equilibrium thermodynamic and dissipate structure, the process of strain energy accumulation and dissipation in the ?Coal-Surrounding Rock? system (CSRS) is discussed during the preparation of coal bumps. In addition, a series of experiments are conducted to analyze the relationship between bump-prone property and micro-structural characteristics of coal. The process of coal bumps induced by propagation of fractures and deterioration of coal mass properties are also analyzed systematically.

May 1, 2009

By C. Pritchard

John Marks said in his acceptance of the Hartman Award in 2008 ? ?I guess that without the occasional complaint, your mine is probably over-ventilated? (Marks, 2008). Miners are seldom in this situation and often spend much of the time trying to find enough air to keep the operation running. With examination there are some things that can be done to make the best use of ventilation systems. Should there be surplus air, in which some of these options may result - financial and other benefits can be obtained. Some of the issues mine operators have needed to address recently are increased airflow requirements to dilute diesel particulates in metal and non-metal mines. Also, operations are faced with demands from reserves that are deeper, hotter and further away from fans and shafts, not to mention increased production demands. Mine ventilation air is a costly commodity, especially by the time it has been heated or cooled and moved to the bottom of the shaft and through the mine airways. Most of the options presented in this paper are useful for metal non-metal operations but some may be applicable to coal too. OPTIONS FOR IMPROVEMENT Some of the areas to be addressed are shop ventilation methods, auxiliary equipment areas, dedicated intakes and returns, optimizing development, examination of mine airway utilization and alternative ventilation methods. UNDERGROUND SHOPS First, examine what is being done with the underground shop air. If it is being coursed directly to the returns there may be some potential to better utilize this, in most cases, relatively contaminant free air. Research the legal options for ventilating mine shops. MSHA regulations in 30CFR 57.4761 (1) allow the following options: To confine or prevent the spread of toxic gases from a fire originating in an underground shop where maintenance work is routinely done on mobile equipment, one of the following measures shall be taken: use of control doors or bulkheads, routing of the mine shop air directly to an exhaust system, reversal of mechanical ventilation, or use of an automatic fire suppression system in conjunction with an alternate escape route. The alternative used shall at all times provide at least the same degree of safety as control doors or bulkheads. Discussion This regulation gives some operators flexibility in ventilating underground shop facilities. If shop air is to be coursed through the work area, and then directly to the mine return, the question should be asked ? is the quality of air good enough to be reused in the mine, and if so, what are the risks? Can the risks be accommodated and managed to accomplish the change? If so, a considerable increase in mine level airflow could be attained by reusing shop air. Clearly, regulations are a minimum standard, and can be exceeded. Metal non-metal mine regulations are not as specific as coal due to the multitude of different mining methods and conditions utilized. Risks must be thoroughly examined and addressed to assure a safe environment. Issues Determine what contaminants are being produced in the work area ? welding fumes, diesel exhaust, paint fumes, chemicals and solvents, etc. Survey the area and determine exposures. MSHA requires exposure monitoring in 30 CFR 57.5002 (1) of dust, gasses mists and fumes to assure air quality is being met. Perform surveys and examine existing data to quantify personal and area concentrations of contaminants. Often there is adequate circulation such that exposure levels in shop work areas are low. After sending shop air back into the system any contaminants would be further lowered by dilution with other mine intake air downstream. Look at the shop work schedule. If only on day shift, the other two shifts and possibly weekends have no activity or source of contamination to affect the ventilation system. The worst case planning scenario would be a shop fire. Study and simulate how this would affect the mine and shop area. MSHA regulations require an escape route and a fire suppression system be installed and maintained as follows in 30 CFR 57.4671 (1): (d) Automatic fire suppression system and escape route. If used as an alternative, the automatic fire suppression system and alternate escape route shall meet the following requirements: (1) The suppression system shall be? (d)(1)(i) Located in the shop area; (d)(1)(ii) The appropriate size and type for the particular fire hazards involved; and (d)(1)(iii) Inspected at weekly intervals and properly maintained. (2) The escape route shall bypass the shop area so that the route will not be affected by a fire in the shop area. Case Study In an underground room and pillar mine, active mine workings were advancing further away from the mine shaft with deteriorated returns and leakage having a negative effect on ventilation airflows to the face. Mine level airflows were 236 m3/s (500,000 cfm) and shop airflows were 24 m3/s (50,000 cfm) (see Figure 1A). No additional capacity was available at the main surface fan. A solution was to utilize the shop air then send it to the mine areas instead of directly to the return. Considerable information on shop air quality and exposures from many years of operation was examined and no negative data was discovered. A risk analysis determined that moving forward with a shop air reuse program was desirable. A plan was developed, analyzed and decision to proceed approved by mine management. The change was simulated on the computer with the USBM/MTU MFire program before being implemented. This included utilizing fire scenarios to examine potential exposures to inby mining sections and plan escape routes. A monitoring system was designed and installed in cooperation with the US Bureau of Mines to monitor carbon monoxide

Jan 1, 2009

Knowledge of true block grades is obtained from a mathematical model of an orebody, simulated with sample grades normally distributed and spatially correlated according io a spherical semi-variogram model.The superiority of kriging to the polygonal method of estimation is demonstrated on this modelled deposit by comparing the true values with the kriged and polygonal estimates obtained from sampling the deposit. Finally, selection of blocks of the deposit on the basis of the estimated values, shows that if kriging is used, what is predicted is largely mined, whilst if the polygonal method is used large biases can occur depending on the position of the cut-off grade.

Jan 1, 1978

By Paul Russell, M. M. Kimberley, Erick F. Welland, Louis Cope, C. C. Mosher, William M. Shepard, William C. Larson, Graham Closs

Exploration activities in 1980 felt the effects of unstable economic conditions and oscillating metal prices. In the cyclical, boom-or-bust precious metals and uranium markets, precious metals activity flourished and uranium was definitely in a slump. By November last year, the price for vellowcake was down nearly $20 from two years earlier. Many mining and milling operations closed, particularly in Wyoming, New Mexico, and Colorado. Decreasing emphasis on nuclear power continued to impact the market, as did the Three Mile Island accident of 1979. Earlier forecasts estimated that 10 to 12 reactors would be ordered per year by US utilities throughout the 1980s, but current forecasts suggest that it may be 1983 or 1984, or even later, before any new US plants are ordered, according to Thomas A. Boyden, vice president of Nuclear Exchange Corp. "Without those new plants, the consumption loss to industry is 4 to 5 million pounds (1.8-2.3 kt) of uranium per year. The cumulative loss to the industry is currently estimated at 25 to 30 million pounds (11.3-13.6 kt)," Boyden said in a May 1980 presenta¬tion. Despite the plunging market, there were a few notable uranium explora¬tion programs: •Exxon expanded uranium exploration in New Mexico, where the company reportedly took preliminary steps toward acquiring mineral rights to a 22-km2 prospect, 19 km south of Santa Fe. • Mountain States Resources began the second phase of an exploratory drilling program on its Sinbad/ Solo prospect in Utah. • Also in Utah, Cotter Corp. drilled its first exploratory hole in the Dirty Devil River district. Exploration for precious metals in 1980, however, appeared to tend toward the opposite extreme. High prices sparked near feverish searches in Alaska, California, Colorado, and Nevada. Numerous mines abandoned years ago were revived with some signs of success. Significant gold finds were reported in California and Nevada: • Homestake Mining Co. announced a gold discovery in California estimated to contain over 5 Mt with an average grade of about 5.8 g/t. Because the deposit consists of finely disseminated particles not visible to the eye, many speculate that prospectors bypassed the area during the 1849 California gold rush. • Newmont Mining Corp. discovered two gold ore bodies-Maggie Creek and Gold Quarry. Maggie Creek reportedly contains an estimated 13.7 t of gold in 4.3 Mt of ore, and Gold Quarry contains about 31.1 t of gold in 9 Mt of low grade ore and 2.3 Mt of higher grade ore. Highlights of this year's exploration review include articles on the modest growth recorded in geophysical activity, technical developments in exploration geochemistry, the variety of new instruments being tested or made available for exploration, and a state-by-state exploration review for the year.

Jan 5, 1981

This chapter summarizes data on crude nonfuel mineral production for the United States, its island possessions, and the Commonwealth of Puerto Rico. Also included are tables that show the principal nonfuel mineral commodities exported from and imported into the United States and that compare world and U.S. mineral production. The detailed data from which these tables were derived are contained in the individual commodity chapters of Volume I and in the State chapters of Volume II of this edition of the Minerals Yearbook. Although crude mineral production may be measured at any of several stages of extraction and processing, the stage of measurement used in this chapter is what is normally termed "mine output." It usually refers to minerals or ores in the form in which they are first extracted from the ground, but customarily includes the output from auxiliary processing at or near the mines.

Jan 1, 1988