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By W. J. Schlitt

Introduction A major uncertainty in assessing the potential for heap-and dump-leach projects is how to determine the extraction-rate curve for the recovery of the mineral values from coarse ore. Such material could either be run-of-mine (ROM) or primary crushed ore. The problem with field testing coarse ore, especially for new projects, is the large scale and extended leach times needed to accurately determine the final extraction-rate curve. At least 5 x 103 to 5 x 104 t of representative ROM ore are typically required for a copper test heap, and much more is often used. Kennecott, for example, recently constructed a 0.9 Mt (1 million st) ROM test heap at the Bingham Canyon Mine in Utah. In such coarse ore operations, the ultimate level of extraction will require a leach cycle that can extend from several months to a few years. Quite often, project development schedules do not provide the luxury of mining such large quantities of material or running such long tests. Instead, test data are usually limited to results from column leach studies on relatively fine ore, often with a top size that does not exceed 25 mm. Maximum leach times are also short, typically less than a year before an initial decision is needed on project viability. Proposed method One approach to estimating the recovery from a coarse ore leach is to assume that the leach solution will have some ultimate penetration distance into the rock. Then, the final level of mineral extraction in this "leached rim" will equal the ultimate level of extraction identified in various testing programs. Obviously, if the radius of a given rock fragment is less than the penetration distance, that fragment will be fully leached at the end of the operation. With larger rock sizes, the percent recovery will fall off as the size increases and the fraction of unpenetrated rock mass increases. Such an approach sounds simple but is likely to be complex when applied to a real project. For example, the penetration distance will be a function of both the rock characteristics and the effective length of the leach cycle. The important rock characteristics include rock porosity, the degree of internal fracturing and the mode of mineral occurrence. With regard to the latter, penetration is likely to be greater if the leachable mineralization occurs on fracture surfaces or in veinlets, as opposed to fine grains uniformly disseminated throughout the rock mass. An estimate of penetration distance may be derived from column or heap tests by noting the depth of solution penetration into the larger rock fragments after three, six and 12 months of leaching. While the penetration rate is ore specific, something on the order of 10 to 20 mm/y may be appropriate for competent, primary copper (chalcopyrite) ore. For gold in tight quartz, the rate may be about the same. Copper oxide ores and gold that is hosted in a more porous rock matrix are likely to have penetration rates that are at least two to three times higher, and an even higher rate should be appropriate for uranium hosted in sandstone. As noted above, the length of the effective leach cycle is likely to be measured in years. On this basis, the ultimate penetration distance (dp) would vary from less than 50 to several 100 mm when a particular ore is leached to exhaustion. Several sets of mathematical manipulations are necessary to convert a rock size distribution and corresponding value of dp into an estimated extraction-rate curve. The first step is to break the ROM size distribution down into intervals and then calculate the radius for the mean rock size in each interval. This is shown in Table 1 for rock sizes up to 1.75 m (about 6 ft) in diameter. The next step is to calculate the volume of unleached core and the fraction of rock that is leached. This is done for the following three values of dp: 25, 100 and 250 mm. Results are shown in Table 2. The third step is to select the ultimate level of recovery that will be achieved in the fraction of material that is effectively leached, i.e., the outer zone that is penetrated by the leach solution. This is clearly a site-specific factor that can only come from metallurgical test results on representative ore

Jan 1, 1998

By Joseph M. Zigich

The Anaconda Minerals Company operates a molybdenite and copper producing mine and mill facility near Tonopah, Nevada. Included with the milling facility is a ferric chloride leach plant for removal of copper mineralization from the molybdenite concentrates. Discussed are the engineering and construction schedules associated with the leach plant. The chemistry associated with the process along with a description of the process flow, equipment, and operating parameters are contained in the paper.

Jan 1, 1983

By John R. Buzek

Thickeners are simply large tanks, usually circular in shape, which are designed to allow settling of solids and to operate with continuous overflow of clear water and underflow of thick pulp. The dimensions of the thickener are usually such that dewatering of very fine pulps may be accomplished while still 1 overflowing clear water. Some thickeners such as the Genter, Hardinge and Hydrotator types combine thickening with filtering2 while others such as the Dorr type are pure thickenersl,2,3. A schematic diagram of the traction type Dorr thickener is shown in Figure 1. This type is appropriate for tanks over 15 m (50 ft) in diameter. This tank employs a rotating raking mechanism which moves the settled material toward the central discharge. For this and other thickeners, it is common to have a shallow conical tank bottom in order to conform to the geometry of the raking mechanism, and it is often desirable to elevate the tank for ease of access to the product. When the tank does not rest on the ground, the forces resisted by the cone are large, and thick plates must be employed. The fabrication of these tanks requires temporary supports in order to erect the cone. A flat-bottomed tank could also be used because the settled material would soon form a hardened conical surface. However, because of the presence of large bending forces, even larger plate thicknesses are required than for the conical bottom. Significant cost savings often can be realized by the use of a scalloped-bottomed tank such as the one partially shown in Figure 2. The particular scalloped bottom discussed in this paper (and shown in the Figure) employs radial beams forming the outline of the cone-shaped bottom. These beams are supported directly by columns. Cone segments are hung between adjacent beams. The exact geometry of these segments depends upon the cone angle and radius, the number of radial beams, and their inclination. The geometry is chosen to satisfy certain clearance restraints and to utilize the material as efficiently as possible. The resulting thickness of these segments is significantly less than that of the

Jan 1, 1977

By G. Davis

It is well known that anticipated mineral prices can have an overwhelming effect on a property's expected value. However, price movements throughout the life of a project also affect value. Thus, it is necessary to not only estimate the expected commodity price at the start of a project but also the manner in which that price is likely to fluctuate throughout the project's life. This paper provides a simple method of incorporating mineral price movements into mineral project valuations.

Jan 1, 1997

By G. R. Struble, J. R. Marks, A. B. Brown

The center of mining at the Homestake gold mine in Lead, SD, is moving deeper every year. As a result, it has become necessary to upgrade the ventilation system. This paper describes the first phase of a scheduled two-phase upgrade - installation of a 2.2-MW (3000-hp) centrifugal fan. The higher pressure fan is required to route larger airflows into the deeper production levels. Selection of the fan began by specifying the necessary operating point to provide these larger airflows. Special site work had to be done on the surface to accommodate the new fan structure as well as underground to reroute airflows.

Jan 1, 1987

By C. A. Pickles, D. Mallette

Silicon nitride (Si3N4 ) is an advanced structural ceramic materia1 which is presently being considered for a number of potential engineering applications, particularly in heat engines, gas turbines, and electronics. With respect to other structural ceramics, silicon nitride has relatively low thermal conductivity and thermal expansion coefficients and a moderate elastic modulus. Thus, during thermal cycling the stresses developed in this material are lower than in other structural ceramics. At the present time silicon nitride is produced via three main processes: thermal decomposition of silicon imide or amide, treatment of silicon tetrachloride or silane vapour with ammonia and nitriding of silicon powder. These three methods of production are discussed with particular attention to the effect of morphology and phase content on the properties of the final product. In this work carbothermal production of silicon nitride has been studied in a high temperature resistance furnace. Compacted briquettes of silica and carbon were produced which were reacted in a nitrogen atmosphere. The optimum reaction temperature and the carbon to silica ratio were found to be 1425OC and ten to one, respectively. The presence of large amounts of ash in the reductant promoted the formation of silicon nitride. The specific surface area of the briquettes did not have a large effect over the range studied in the present work. Briquette seeding with small amounts of Si3N4 was effective in increasing the reaction rates.

Jan 1, 1990

By C. J. Webb, C. J. Paterson, A. Davis

This work focused on identifying, examining and ranking the physical and environmental hazards at inactive and abandoned mine sites in the Black Hills of South Dakota. Earlier inventory projects in the Black Hills concentrated on federal lands, while more recent efforts have examined abandoned mines on state and private lands. The more recent efforts are a result of passage of legislation by the State of South Dakota requiring a comprehensive inventory. The inventory information provides criteria for identifying those sites that require further investigation or characterization of the physical safety or environmental hazards. For most AML sites in the Black Hills, location information is all that is typically needed, because the majority of sites pose little environmental or physical hazard.

Jan 1, 1999

By John F. Shea

When Dick Robbins asked me to give a keynote address, I felt it might be in order to review some of the practices and techniques used in tunneling and work up to some of the concepts now used to mine and construct tunnels. Needless to say, there have been many changes in tunneling technology and also many changes in the Safety Codes controling them. An example of this latter change was the fact that in 1931, my father excavated the Owyhee Tunnel No.5 with gas locomotives. He was able to do it because there was no natural gas in the rock and the ventilation system was designed to free the tunnel atmosphere from powder and exhaust fumes. Today OSHA rules would never permit gas locomotives underground, although there were no incidents on this particular project. One of my first tunnels, as Project Manager, was the Clear Creek Tunnel for the Bureau of Reclamation. Our method of handling muck was the Conway Muckers. This unit was a valuable improvement to the hand mucking of previous generations. The Conway was also used in our Navajo Project, in New Mexico. Unlike the Clear Creek project, where water was one of our main problems - up to 7,200 gallons per minute, at a pressure of 395 pounds per square inch - in the Navajo Tunnel, we had a mixed face which caused a major problem with our support system. In one of the Navajo Tunnels, there was a major cave-in, when the squeezing shale came in during an attempt to strengthen the support system. Although moving shale was not a constant problem, there were areas where the shale was five to six feet above the spring line.

Jan 1, 1976

By Steve Kral

One of the world’s most successful mining shovel manufacturers believes its name is not very well known in North America, particularly in the United States. And there are plans under way to improve on that. Never mind that it is one of the largest mining shovel manufacturers in the world. Or that the mining division has 800 machines in operation worldwide, 100 of them in the United States. And the company currently holds 30% of market share worldwide and 10% in the United States. Forget about the fact that it has already sold more machines world-wide this year than it did during 1995. None of that is good enough. O&K Mining GmbH Dortmund is the mining division of Germany’s giant O&K Orenstein and Koppel. It is one of three divisions of O&K Orenstein and Koppel AG, a US$1.2-billion company. The other two divisions are construction equipment and escalators. The mining division, though, is one of the company’s most successful.

Jan 1, 1996

By John R. Wright

This paper reviews the increased use of mechanization in order to develop lateral headings efficiently and economically. Particular emphasis is placed on the role of the Electric-Hydraulic Drill Jumbo in achieving this goal. Also, the use of modified mining equipment to suit various operating conditions is discussed.

Jan 1, 1981

By R. Srikanth

Dust control in high production longwalls is a major problem requiring, among other things, careful attention to the design of operating practices, and ventilation schemes. Several studies have shown that the shearer is the major source of dust on a longwall face. Support movement has not been regarded as a major source of dust in U.S. longwalls; yet under certain conditions, 31 percent of the shearer operator's dust exposure can be due to support movement. Several methods have been developed for the control of shield-generated dust. Yet the need for better methods is apparent. In this paper, the amount of airborne respirable dust generated per shield move is estimated from specially designed experiments on longwall faces. A total of ten experiments were conducted in five longwall faces in four different mines. Each experiment involved one face visit and lasted three to six hours. The contribution of shield movement to the airborne respirable dust concentration immediately downwind of the shield moved, varied between 0.12 and 1. 75 mg/m3 in the five longwall faces. The mass of airborne respirable dust generated by shield movement was found to vary between 39 and 386 milligrams per shield move. The results from this study reveal that control of dust from longwall shields requires a combination of approaches involving alternative operating practices, reducing shield dust generation rate, increasing face air flow, and decreasing personnel exposure.

Jan 1, 1994

The National Mining Hall of Fame and Museum (NMHF&M) will induct its the 2014 National Mining Hall of Fame Class on Sept. 13, 2014 during its 27th Annual Induction Banquet and Ceremony at the Westin Hotel in Denver, CO. Representing the domestic and worldwide metal production, education, and health and safety sectors of the industry, this year?s four inductees cover a diverse cross-section of the mining industry. Harry M. Conger III, Günther Franz (Frank) Joklik, Ellen Swallow Richards and Dr. Alfred Weiss will join 223 other mining industry pioneers when they are formally inducted into the National Mining Hall of Fame. They were selected for being visionaries, leaders and ambassadors, both within their own sectors and across the industry at large. Conger was a great role model and strong advocate within Homestake Mining Co. and among his industry peers on behalf of environmentally responsible, safe, profitable and high-performance operations. As chairman and chief executive officer, Conger was instrumental in revitalizing and rebuilding Homestake into an industry leader in technological advances and environmental protection. Through his contributions in exploration, project development and operations management as Kennecott president and chief executive, Joklik did much to strengthen Kennecott as a company and assisted in restoring the competitiveness of the U.S. mining industry. Richards is generally recognized as the founder of ecology. She was the very definition of a pioneer in such diverse fields as chemistry, geology and mineralogy, mining and metallurgy, environmental science, public health, home economics and education. Weiss was a true visionary in using quantitative methods and digital computers to aid mineral exploration, plan and design mines, operate mineral production facilities and integrate the disparate information resources throughout a mining company into a modern management information system. NMHF&M Board of Directors Chairman, Paul C. Jones, said, ?Again this year we are honored to be able to induct an outstanding group of deserving individuals who have made exceptional contributions to the mining industry in the United States. Included are two living inductees who have made significant contributions to management in the industry. One inductee was the first female graduate from the Massachusetts Institute of Technology, its first female faculty member and the first female member of AIME who had an outstanding career as a mineral investigator in the United States. Another inductee was a lifetime innovator in bringing digital technology into common use in our industry. Each of our 2014 inductees made significant and lasting contributions to our industry and are well deserving of becoming a member of the National Mining Hall of Fame.? The Hall of Fame Induction Banquet and Ceremony is a marquee event for the National Mining Hall of Fame and Museum each year. The 27th Annual Induction Ceremony and Banquet will be held at the Westin Hotel in Denver, CO on Saturday, Sept. 13, 2014. For banquet reservations, contact the NMHF&M office at 719-486-1229. More information is available on the NMHF&M website at www.mininghalloffame.org.

By Ruoming Gong, Arindam Samanta, Ragula Bhaskar

Three studies conducted at the University of Utah relating to the effect of scrubbers on face airflow patterns, the resulting dust exposure of operators and the development of a throat scrubber for continuous miners are summarized in this paper. The first study involved full-scale laboratory tests to determine the potential dispersion patterns and transport of dust at a continuous miner face, using different ventilation configurations and a scrubber. Concentration maps were developed and potential exposures at operator positions were examined. The second study involved the development of a 3-D numerical model to predict airflow patterns generated by a scrubber at a continuous miner face. The model was designed to evaluate the role of various face parameters on airflow patterns at a miner face and to complement the full-scale testing. The third study involved the design and fabrication of a low profile hydraulically powered continuous miner throat scrubber. The scrubber uses three hydraulic motors and small diameter fans to draw about 3000 cfm (1.42 m3/s) of air and uses a flooded bed scrubber to filter dust particles.

Jan 1, 1993

By William J. Attwooll

The development of gold heap leach projects in the Cripple Creek, Colorado, mining district has required utilization of heap leach pad sites other than relatively level natural ground. This paper describes the construction of a heap leach pad adequate to accommodate 907,000 tonnes (1,000,000 st) of ore over the surface of a tailings pond constructed during previous milling activities at the site. Based on the design parameters and the observed behavior to date, it has been found feasible to construct a major heap leach pile on the surface of a conventional tailings pond.

Jan 1, 1987

By A. John R. Hart

INTRODUCTION In each given set of operational criteria for tunnel design, ground conditions dictate the selection of the most appropriate construction method and tunnel lining. The designer has the responsibility to choose or restrict the choice of the tunnel lining to insure that the final solution provides a cost-effective permanent construction which will require the minimum of maintenance and endure to the benefit of future generations. This Paper deals with some of the aspects of precast concrete tunnel linings, their history and development through the years. It does not purport to be a comprehensive review of all that has ever been tried or developed but, hopefully, a starting point to encourage discussion and development for the future. BOLTED LINERS As a result of anticipating a shortage of cast iron tunnel lining in 1936 when work was proceeding on London Transport's Central Line Metro, a design for the precast reinforced concrete bolted lining was born. The design took the form of the traditional cast-iron lining but with substantial concrete stiffeners to take the shield ram forces. This new lining was used to construct some 14,000 feet of running tunnel using a ring width of 1'8" which was the standard cast-iron width of the time. (Groves, G.L., 1943)

Jan 1, 1987

By P. Coleman, J. C. Kerkering, S. Iverson

Fault tree analysis is a systematic safety analysis tool that proceeds deductively from the occurrence of an undesired event (accident) to the identification of the root causes of that event. One recurring mine safety problem-a dozer falling into a void over a drawpoint on a coal surge pile-was analyzed using available, inexpensive fault tree programs on a personal computer. The analysis identified basic and intermediate events that led to the burial of the dozer and graphically depicted the interrelationship between these various subordinate events as well as the various chain of events leading up to the primary event. A sensitivity analysis on these probabilities showed which events had the greatest influence on dozer burial in a coal surge pile.

Jan 1, 2001

By L. R. Nelson

Cyprus Pima is a medium-sized open-pit copper mine located 35 km (22 miles) south of Tucson, AZ. The ore body was discovered using geophysical prospecting methods in 1953 and was originally worked as a small underground mine followed by small open-pit operations. As mining equipment grew larger and the economic ore grade dropped, the operation grew in size, through four expansions, to the present 50 500 tpd (56 500 stpd) milling rate. The remaining stripping ratio is about 2.5 to 1. Mining equipment includes 11 electric shovels ranging in size from 6 to 15 m3 (8 to 20 cu yd) and 42 diesel-electric haulage trucks ranging in size from 89 to 223 t (100 to 250 st). Mine planning is performed at Cyprus Pima to serve several functions. The most important is to plan ahead, one year at a time, to predict the ore grade and stripping requirements on a month-by-month schedule. This yearly plan is necessary for budget preparation and is revised once each quarter to incorporate variations in actual production experienced during the preceding quarter.

Jan 1, 1979

By S. J. Knoll, D. F. Scott, T. J. Williams

Highly stressed rock in stopes continues to be a primary safety risk for miners in underground mines because it can result in failures of ground that lead to both injuries and death. Spokane Research Laboratory personnel investigated electromagnetic (EM) emissions in a deep under-ground mine in an effort to determine if these emissions could be used as indicators of impending catastrophic ground failure. Results suggest that (1) there is no increase in the number of EM emissions prior to recorded seismic activity, (2) some EM signals are generated during blasting, (3) interference from mine electrical sources mask seismic-generated EM signals, (4) EM emissions do not give enough warning (compared to seismic monitoring) to permit miners to leave a stope, (5) the distance an EM signal can travel in the rock is between 17.7 and 39.6 m (58 and 130 ft), and (6) current data acquisition systems do not differentiate between EM signals generated from seismic activity and random mine electrical noise. These results preclude monitoring EM emissions as precursors of impending catastrophic ground failure.

Jan 1, 2004

By J. Lorengo, C. H. Bucknam

"Standardization of the Inductively Coupled Plasma Mass Spectrometry (ICPMS) method for gold in cyanide solutions was undertaken to provide a more sensitive method to quantify the gold content than the atomic absorption method standardized in 1994 (E1600). The gold concentration range covered is from 0.001 mg/L Au - 0.3 mg/L Au (0.00005 toz/t Au – 0.009 toz/t Au). Interlaboratory testing was carried out with the assistance of the American Society of Testing and Materials (ASTM) International on two committees to determine the within laboratory and between laboratory reproducibility. Three barren solutions from metallurgical operations were measured in triplicate to satisfy statistical requirements for Committee E1 on Analytical Chemistry of Metals, Ores and Related Materials. A synthetically prepared matrix representing the metallurgical processing solutions was used to prepare Youden pairs to satisfy the requirements of Committee D19 on Water. Results of the standardization program are presented. INTRODUCTION Analysis of process solutions for gold concentration requires accurate and sensitive analytical methods in order to manage process control and metallurgical accounting. Flame atomic absorption spectrophotometry (FAAS) has been the work horse of the assay lab for this duty for decades. In 1994 the FAAS standard method was approved by the American Society for Testing and Materials (ASTM) (1). Six process solutions were collected and preserved by measuring the pH and adjusting to greater than pH 10, if necessary. Duplicate solutions were provided to eight laboratories in random order for analysis by FAAS covering the gold concentration range of 0.19 µg/mL (0.006 toz/t.) to 10.7 µg/mL (0.312 toz/t). A high precision method was used, which involved bracketing the sample with the higher and lower standards nearest to its concentration repeating readings three times and averaging the results. The optimum precision for the FAAS gold method was found to be at the 1.00 µg/mL (0.029 toz/t) and lower scope limit 0.3 µg/mL (0.009 toz/t) gold concentration. Since tailings solutions typically have concentrations below the lower scope limit, use of ICPMS was developed at Newmont USA Limited (Newmont) to assay the lower range solutions."

Jan 1, 2016

By John R. Keith

Keith, John R. 1968. Relationships of lead and zinc contents of trees and soils, Upper Mississippi Valley District. Preprint, Fall 1968 Meeting, Soc. Mining Engineers of AIME. Lead and zinc contents of elm, maple, and oak trees and of soils in which the trees grew were determined in samples from the Upper Mississippi Valley mining district, and from an area outside but contiguous to the district. The lead and zinc analyses of plant materials served to differentiate the mineralized and non-mineralized areas. Stems contained about two times as much lead and about 2-5 times as much zinc as did leaves taken from the same stems. Lead and zinc analyses of all soil horizons could be used to differentiate between the two areas. Soils at most sample sites in the mineralized district seemed to be more reliable than plants for geochemical prospecting and are a more practical sampling medium. Soil samples from areas with thick loess cover, however, failed to indicate the presence of mineralized bodies whereas tree samples from the same sites contained anomalous amounts of lead and zinc. It is suggested that in areas of thick loess cover plant samples could be used in prospecting for lead and zinc.

Jan 1, 1968