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By E. D. Attanasi, M. W. Bultman, J. H. DeYoung

The 1987 recovery in the US mining industry permitted modest increases in exploration expenditures that year (Fig. 1). Favorable market conditions apparently allowed the gains to be sus¬tained in 1988. There was great uncer¬tainty early in the year as to whether world and US economic growth would be a casualty of the October 1987 worldwide stock market crash. By nearly all measures, the performance of the US minerals industry was strong¬. A weak US dollar and the strong growth of worldwide capital spending resulted in in¬creased US exports of con¬sumer and producer durable items as well as strong domes¬tic demand for metals. In fact, 1988 US steel industry exports reached levels not attained since the mid-1970s. It was re¬ported that steel industry labor productivity is now roughly twice the 1981 level. Among metals with signifi¬cant average nominal price increases in 1988 over 1987 levels were copper (43%), alu¬minum (52%0), and zinc (44%). Even though domestic copper production has grown since 1984 by 30% in mining and 24% in refining, em¬ployment in mining and milling is 4% below the 1984 level. Domestic unit costs are reported in the range of $1.10 to $1.33/kg (50 to 60 cents per lb). The US base metals industry is proba¬bly in its best cash position in many years. However, there has not been a large increase in exploration expendi¬tures. This is due mostly to the percep¬tion that worldwide capacity can easily be increased. Industry reports do show that "low cost" copper producers have been buying reserves from weaker com¬panies. The 1987 Society of Economic Ge¬ologists (SEG) survey of exploration activity indicated that 95 cents out of every exploration dollar spent by US and Canadian firms was for base and precious metals (Economic Geology, January 1989). Press reports, though, make it clear that most of that spending was targeted for precious metals. US claim staking data (Fig. 2) rein¬forces this suspicion. The apparent lag in new claim filings in Alaska and phe¬nomenal growth in filings in the lower 48 states suggests that exploration is directed at relatively low risk targets. In the conterminous 48, more than 40% of the new claims were made in Nevada, indicating an emphasis on gold (although even Nevada had some base metals exploration). Even with a price decline during 1988, the difference between the gold price and average global "cash" production cost of $7.30/g ($227 per oz) still leaves room for an attractive return (Northern Miner, 1988). Exploration plans and results Metals Economics Group (Halifax) indicated in its 1988 exploration survey that exploration expenditures by US and South African firms would be at about 1987 levels. It also reported that Canadian and Australian firms were ex¬pected to reduce their exploration spend¬ing significantly. Firms in both coun¬tries were caught in changes in tax laws. In Canada, the Mining Ex¬ploration Depletion Allow¬ance (MEDA) once permitted generous tax write-offs to in¬dividuals investing in miner¬als exploration. It was to be replaced in January 1989 with the Canadian Exploration In¬centives Program (CEIP). Although structured and ad¬ministered differently than MEDA, CEIP can provide an equivalent or possibly greater financial incentive for min¬eral exploration, for junior mining companies. In 1987, it is estimated that junior com¬panies accounted for two¬-thirds of the off-property (or grass roots) exploration ex¬penditures in Canada. Australia will revoke the tax exemption for gold in 1990. Australian operators, therfore, were expected to concentrate efforts on speeding up pro¬duction during 1988 and 1989. In 1988, Chile and Mali announced special efforts to attract gold explora¬tion by foreign companies. The Cana¬dian government continues to express concern about the write-off (and drawdown) of base metal reserves. Falconbridge did announce a new initiative to identify additional base metal reserves in the Sudbury district. Discoveries Gold deposits dominated discoveries

Jan 1, 1989

By K. A. Natarajan, Namita Deo

The interaction of Bacillus polymyxa and minerals such as hematite, corundum and quartz resulted in significant surface chemical changes, both on the cell surfaces and on the interacted oxide minerals. After such treatment, quartz was rendered relatively more hydrophobic, while hematite and corundum were rendered more hydrophilic. Biopretreatment was observed to be beneficial in the separation of silica from hematite and alumina by both selective flocculation and flotation. The possible role of bacterial adhesion and metabilites in the biobeneficiation process is illustrated.

Jan 1, 1998

By A. T. Yu

Two key components make up the core of a rapid excavation operation. They are: the breaking up of the rock and its removal. Owing to the complexity inherent in mechanical rock-breaking and the relative infancy of the art, for a number of years the first of these two components has received virtually undivided attention from the industry. Only recently has some concern been expressed about the technology and the economics of the much ignored second component: muck removal. As the continuous boring machine's percentage downtime continues to trend lower in the future, the need for adequate and more effective materials handling systems in rapid excavation will become increasingly more acute. (1) Recognition of the need for a broader and more far-sighted approach to our problem has been eloquently underscored in the conclusions of the Committee on Rapid Excavation sponsored by the National Research Council: "Ultimate attainment of the desired cost and speed improvements is significantly dependent on recognition of the excavation process as a system whose subsystems are critically inter-related. Substantial amounts of full-scale field testing of integrated driving, muck removal, and support subsystems are required." (2)

Jan 1, 1997

By Neville G. W. Cook, John Kemeny

Utilizing the principles of elastic-brittle fracture mechanics, stress-displacement relationships are derived for an elastic solid containing a slip plane consisting of various configurations of collinear arrays of cracks. These models take into account the heterogeneous nature of slip planes as observed in the lab and in the field, and are relevant to the behavior of rock containing faults, joints, bedding planes, and fractures. All of our models exhibit slip weakening behavior, and show regimes of both stable (aseismic) and unstable (seismic) deformation. For given configurations of cracks and applied boundary conditions, our results show explicit ly the energy released through unstable crack growth. For instance, it is found that two equal length cracks growing together release more seismic energy than, say, a large crack growing into a small crack. Also, by allowing cracks to coalesce, our models show multiple stick-slip events without crack healing or other geochemical means.

Jan 1, 1986

By C. Y. Kao, Roger Y. Cheng, C. S. Hsieh

The mushroom-shaped Minghu power cavern located in central Taiwan is 21.2 m (W) by 40.5 m (H) by 127.2 m (L) and is designed to house 4 units of power generating-pumping equipment with a total capacity of 1,000 MW. This paper presents an introduction to the geological conditions at the cavern site; the rock mechanical tests undertaken; the design approach adopted; the construction method and sequence followed; and the instrumentation provided in the roof arch to monitor the behavior of the surrounding rocks. The measured data collected from the embedded instruments will be compared with those obtained from theoretical analyses and presented in this paper. Several technical problems encountered during the construction stage are covered and the solutions of these problems are also described therein.

Jan 1, 1983

By Emily Wortman-Wunder

Attendees at December?s Arizona SME Section Conference at the Hilton El Conquistador Resort outside of Tucson, AZ were feeling optimistic and ready to get to work after a year of steady growth and recovery in the mining industry. During the two-day event (Dec. 5-6, 2010) and the preceding American Mining Hall of Fame banquet and awards ceremony, the focus was on copper, worldwide population growth and regulatory pressures, with several smart new projects featured alongside updates to traditional large-scale copper development projects. Keynote speaker Timothy Snider, chair of the University of Arizona?s Lowell Institute for Mineral Resources, hit the mood of cautious optimism when he analyzed the global demand for resources, using the case example of copper. Over the next 20 years, he said, the world?s population is expected to grow to 9.2 billion and the average annual per capita copper use is expected to rise from 2.2 to 4.5 kg (5 to 10 lb). The increase in demand will provide tremendous opportunity for mining companies, he said, but cautioned that the opportunities are balanced by negative influences on demand and pressures on supply. While demand for copper is currently growing, Snider noted that there were significant downward pressures on demand as well. These included a western world that is overbuilt, in-creasing use of substitute materials in new construction and the rise of wireless devices. He also noted new regulatory pressures, and pointed out that resource development now had to occur within a context of sustainability on several levels.

Jan 1, 2011

By Carl G. Bock

INTRODUCTION Rapid transit systems involving near surface tunneling in hard rock are becoming more numerous, especially along the northeast corridor of the East Coast. Tunneled systems are under construction in Washington, D.C. and are being planned for Atlanta, Buffalo and Baltimore. Near surface tunneling is defined for this paper as being that in which the crown is 100 feet or less below ground surface. For Rosslyn Station, the total cover ranged from 52 to 70 feet. The rock cover, however, ranged from 40 to 50 feet which is slightly less than the station height and about two-thirds of its width. Rosslyn Station (Fig. 1) is the only station excavated completely in hard rock in the Virginia portion of the 98.5 mile Washington Metropolitan Area Transit Authority's (WMATA) rapid transit system. The station site, oriented in a north-south direction beneath a main thoroughfare and flanked by multistory office buildings, was fixed by the need to serve a dense population center at a specific location and geologic conditions were a secondary consideration in siting. There was no previous underground rock excavation in the Washington Metropolitan Area of the size and scope of Rosslyn Station that offered a practical case history guide to the geologic conditions and excavation problems to be encountered. GEOLOGY The regional geology of the Washington Metropolitan Area is divided into two physiographic provinces by the northeast trending Fall Line (Fig. 2). Northwest of this boundary is the Piedmont Province

Jan 1, 1974

By Thomas E. Bruner

Today many small diameter tunnels are being constructed in Metropolitan areas and towns as transmission holes for utilities such as water, electricity, natural gas and sewage, to name a few. These tunnels function as utilities beneath the streets, highways, railways, and other structures where open-cut techniques are impractical for any one of a number of reasons. Many such bores range in diameter from 15 to 72 inches and in lengths from 100 to 500 feet. Auger drills with auger type heads have long been used to bore these "road crossings" as they are usually termed; however, many such crossings must be bored in rock with rock-boring heads. Rock with a compressive strength of 15,000 p.s.i. and higher seems to present the greatest challenge for the contractor. These rocks include most igneous and metamorphic rocks and some sedimentary rocks. In general, this grasps most granites, basalts, gneisses, slates, schists, quartzites, limestones, and cherts. In the past ten years boring machines have been developed and used to excavate road crossings through hard rock. Many crossings have been successfully excavated using these machines, and the degree of success has increased substantially in the last few years. A variety of machines have been built and manufactured to bore most rock in a range of diameters up to 72 inches. The machines vary in capabilities, size ranges, and designs but all perform the same basic task and function of boring horizontally. Incidently, here the term horizontal implies horizontal or within five degrees of horizontal. In addition, there is a wide variety of designs, sizes, and types of drill stems, joints, and pipe to meet the various conditions and

Jan 1, 1974

By F. A. Aplan, Richard R. Klimpel

This article discusses the role of mathematical optimization techniques as applied to the design and analysis of particulate processing plants. The emphasis will be placed on the macro engineering view of integrated multiple operation plants such as those that typically involve stages of size reduction, sol id-sol id separation, solids storage, chemical reactions involving sol ids, sol ids disposal, etc. The macro engineering view is chiefly concerned with balancing and optimizing the bigger picture of how various unit operations interact technical and economically with each other in an approximate sense rather than how a specific unit operation can be technically described and optimized in detail (micro engineering.)

Jan 1, 1991

By E. S. Erickson, R. L. Stone

Introduction Evidence from blast furnace operations has indicated that using pellets with a higher ISO low temperature reducibility, a lower SiO2 content, and better resistance to low temperature degradation results in considerable coke savings and improved furnace operation. Although these benefits could not be directly related to reducibility differences alone, we believed there was sufficient evidence of the advantages in improved pellet reducibility to warrant laboratory investigation of ways and means to effect such improvements. It is well known that pellet reducibility can be significantly altered by changes in the basicity and the amount of non-iron oxide constituents. Past work (Friel and Erickson, 1980, 1982; Saeki et al., 1977; Thanning, 1974) has shown that with increased MgO contents, and at optimum CaO/S1O2 ratios, significant improvement in low temperature reducibility can be attained. The improved properties of such fluxed pellets have reportedly led to increased blast furnace efficiency and productivity (Saeki et al., 1977; Ilmoni, 1975). Less well known, however, is exactly what factors control reducibility in acid pellets. Because of this gap in knowledge, studies were undertaken of the factors affecting reducibility in acid pellets and to estimate their relative significances in modifying reduction behavior. This paper describes that part of our work done to determine the effect of bentonite on reduction behavior. Our approach was to first examine the effect of bentonite's presence on as pure an iron oxide as possible (i.e., a magnetite "superconcentrate" containing about 0.2% SiO2) so as to eliminate any gangue-binder interaction. The next step was to look at bentonite effects on concentrates with only limited amounts of gangue (containing about 1% SiO2), but of two different types, simple and complex silicates. Last, we

Jan 1, 1988

By W. J. Maloney, H. E. Tuneblom, A. J. Smith

The development of a large regional water supply in Southern West Virginia faced several hurdles. This paper deals with the design and construction of the intake shaft where a combination of cutting edge mechanical excavation technologies were utilized to produce a world class project.

Jan 1, 1999

By Sarah Vest, Richard Sherman, Leo Martin

In 1988 a major exploration program was undertaken to determine the characteristics of the rock and soil for a 7.6 m diameter sea outfall tunnel beneath Boston Harbor out into Massachusetts Bay. The diffuser discharge location had been mandated by the EPA to a 10 sq. km area of seafloor connected to the proposed Deer Island Treatment Facility by a 14.5 km tunnel corridor. Geophysical surveys, deep rock borings, and laboratory testing, provided the information for the conceptual design. The program identified the range in material types and parameters to prove feasibility of a TBM driven tunnel and to locate the optimum alignment and depth.

Jan 1, 1991

By Bernard Scheiner

A number of wells were drilled at two phosphogypsum stacks, one at P-21 owned by IMC and the other at Agrico's South Pierce Stack. Each well was sampled, and composites representing 5-ft increments were leached with synthetic rainwater to determine the extent of metal and nonmetal migration. To simulate what was occurring in the stack, composite samples were placed in a column, so that the column represented the stack in miniature form. Leaching experiments showed that both metals and nonmetals moved down the column when water was added to the top of the column. Data obtained from P-21 showed that with time the concentration of metals and nonmetals reached equilibrium values. The concentration of Ca, SO4, F, Si, and PO4 were -600 ppm,~1,500 ppm, 32 ppm, 14 ppm, and 22 ppm, respectively. Column leaching of South Pierce material, representing 0 to 55 ft of stack, showed that after 355 in. of water, the stack was near equilibrium values down to the 33-ft level. With continued addition of water, the portion of the stack at equilibrium would continue to increase and eventually reach the values observed for P-21. The test showed that the sulfate concentration of the effluent from the stack would never reach the USEPA standard value of 250 ppm. During the leaching test, it was determined that the permeability of the phosphogypsum in the columns was 0.000103 cm/sec. This number was used in the modeling. The data obtained from the leaching experiments cast some doubt on the practice of entombment now being practiced for closure of phosphogypsum stacks. The data clearly shows that with time, the amount of material leaching from the stack is low in concentration, with only the calcium and sulfate at higher levels. When a stack is closed at an existing operating plant, allowing rainwater to fall on the stack and capturing the solution in the existing pond system would eliminate the need for covering the stack, since with time the closed stack would continue to leach and at some point reach the equilibrium values of the P-21 stack. Entombment means that the leachable material in the stack will always be there and will require monitoring forever. Allowing rainwater to decontaminate the stack may be the best environmental solution to the problem.

Jan 1, 1999

By Jacques Mongrain, Serge Barbeau, Gary Brierley

The Communaute Urbaine de Montreal is currently involved in construction of the South Interceptor which consists of 53 kilometers (33 miles) of 1,800 mm (6.0 ft) to 5,400 mm (18.0 ft) diameter tunnels for the purpose of collecting, storing, and delivering sanitary and combined sewage to the treatment plant. Work is divided into ten separate contracts; nine of which have already been bid. The purpose of this paper is to describe construction activities that have been performed through the end of 1986 with emphasis on a general layout of facilities, a summary of subsurface conditions, and brief descriptions of actual construction activities for the six contracts where tunneling has been performed. All projects are being excavated with tunnel boring machines.

Jan 1, 1987

By William C. Larson

The number of uranium in situ leach operations has increased significantly since 1975. As of May, 1980, there were a total of 27 active projects, including 16 commercial scale operations (or under construction) and 11 pilot scale operations. The south Texas uranium district and Wyoming have been the most prominent areas in early field experiments as well as in commercial application of this new recovery technique, although in situ leach tests are now being conducted in Colorado and New Mexico. The growing number of commercial-scale operations is accepted as prima facie evidence that in situ mining now offers a third option along with open pit and underground mining for winning uranium from sandstone host rocks. It is estimated that in 1979 about 9 percent of the nation's total uranium production was from in situ mining. However in situ mining of uranium is not without its environmental controls. The primary emphasis of environmental controls falls into two catagories; namely, control of the leach solutions during mining and demonstration of ground water restoration. Finally this paper briefly reviews the Bureau of Mines research program in uranium in situ mining.

Jan 1, 1980

By Hassan El-Shall, Rosana M. Macedo Borges, Ponisseril Somasundaran, Regis Stana, José Renato B. Lima, Patrick Zhang

The phosphate fertilizer industry is a large activity in Brazil because the soil has a phosphorous deficiency. The phosphoric acid that is produced is extensively used in the production of fertilizer. It is produced by reacting phosphate carbonaceous rock with sulfuric acid, generating phosphogypsum as a by-product. In 1991, there were about 29 million tons of phosphogypsum stored in Brazil. This has increased to an estimated 280 million tons in 2001. While the phosphogypsum is used in the cement industry and also in agriculture, the quantity used is much less than the production rate, and the stockpiles are still increasing. The radioactivity of this waste may not allow its continued use as a construction material and some other uses. However, Brazilian phosphogypsum contains a smaller quantity of radioactive materials than is reported for phosphate rocks from other countries. One important reason is the geological origin of the Brazilian apatite. All the large deposits being currently mined are igneous, not sedimentary, as is the majority of the phosphate rock produced around the world. An extensive study is being conducted to characterize the phosphogypsum generated in two production facilities in Sao Paulo state to develop safe uses for this waste and determine the environmental impact caused by the present method of phosphogypsum disposal.

Jan 1, 2002

By John Brouwer

Through the use of good preventive maintenance procedures in which the work of both production and maintenance personnel is well-coordinated, production downtime can be drastically minimized, and costly repairs and interruptions in planned maintenance and production schedules can be eliminated. There had been some conflict in the past between production and maintenance people over the proper method of achieving maximum machine performance. The usual practice was to operate production equipment at maximum capacity for the longest possible time until breakdown occurred, and then make hurried repairs to get back into production. In most cases, these repairs involved unscheduled work and were thus performed inefficiently. Both production and maintenance have the same objective: to produce a quality product at maximum efficiency and at minimum cost. Preventive maintenance is a common tool available for both production and maintenance personnel to achieve this objective. Actually, one of the main objectives of preventive maintenance is to find any abnormal machine condition that may cause machine failure before a breakdown occurs. This makes it possible to plan and schedule maintenance work with the least amount of interruption and plan production volume with a higher rate of accuracy. Maintenance people prefer to perform this work on a scheduled basis and get away from the "crash" situation that accompanies breakdowns. They thereby increase the utilization of available manpower and machine time, prolong equipment life, and improve maintenance costs.

Jan 1, 1979

By William R. Groseclose, Cecil E. Tackett

Since 1965 when the first mole was used on Bureau work, the Bureau of Reclamation has completed 17 tunnels of over 5,000 feet in length. The longest was 12.8 miles. Total length of the 17 tunnels was 376,207 feet, or over 71 miles. The finished diameter varied from 7 feet 0 inch to 18 feet 0 inch with 82 percent (58 miles) being less than 12 feet 0 inch in diameter when lined. All of these tunnels except one are gravity flow, water conveyance tunnels with relatively flat gradient. One is a low-head pressure tunnel. All were constructed by contracts resulting from fixed-price bids. Starting in 1964 the Bureau of Reclamation initiated the practice of giving several options in the specifications on methods of tunnel excavation. Since that time, construction work has been completed on 17 tunnels. Of this number, 11 were mole excavated and 6 were excavated by conventional drill and blast methods. In general, there has been 2 feet of mole excavation for every 1 foot of drill and blast. Cost comparisons are based on only 13 tunnels because the Bureau has 4 recently completed tunnels that have pending claims; therefore, final cost data are not available. Some definite trends show from the data available; however, the number of completed tunnels in some categories is so small the results cannot really be considered a trend. As more data become available, the indications will become more reliable. The information is presented to indicate general trends and comparisons and cannot be meaningfully used for a one-on-one comparison because of individual tunnel differences not considered.

Jan 1, 1974

By G. Bryant, P. Ziemkiewicz

Acid mine drainage (AMD) from both abandoned surface and underground mines is a serious problem. The flow of water and changes in quality over time from abandoned mines is important in determining remediation strategies. Acid mine drainage from surface mines is estimated to last for 10-20 years, while estimates of acid drainage from underground mines vary from 10- 100s of years. Fifteen underground mine discharges in West Virginia were studied to compare water quality changes between 1968 and 1999 to see if our data are consistent with other studies. Each of the discharges were categorized into one of three groups: undisturbed since 1968, affected by surface mining since 1968, and reclaimed. Comparing water quality between 1968 and 1999, the discharges in the undisturbed category showed a 35 to 95% improvement in acid concentration and a 40 to 99% reduction in iron concentration. The discharges affected by surface mining showed the most dramatic improvement. For acidity, iron, and aluminum, the percent improvements were all above 44%, and in most cases in the 70 to 99% range. In the reclaimed category, one of the four discharges declined in water quality. Discharge 82 showed a 76% increase in acidity, and iron and aluminum concentrations worsened by 58 and 96%. However, discharges 15 and 74 improved in water quality with a 94% acid load improvement and a 95% iron load improvement at both sites.

Jan 1, 2000

By David E. Thompson, Wesley E. Stimpson

The Massachusetts Bay Transportation Authority (MBTA) Red Line Extension Northwest is currently in the early stages of construction. The 3.1 mile extension of the Red Line from the existing Harvard Square Station in Cambridge, Massachusetts to Alewife Brook Parkway in Cambridge, Massachusetts will include a large, near surface hard rock, rapid transit station chamber at Porter Square in Cambridge (Figure 1). [ ]

Jan 1, 1979