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By Robert Roggenthen

In 1994, ASARCO's Mission Complex Mine Planning Department designed a new stripping schedule to take advantage of reserve opportunities. Based upon the new stripping design, overburden removal exceeded available hauling capacity. This increased hauling capacity requirement required that ASARCO consider alternative technologies for material transport. In 1997, ASARCO Mission Complex completed the purchase and installation of a 3.5 km, 8,600-tph conveyor system to transport waste material. The conveyor system is composed of two apron feeder/sizer units manufactured by Mining Machine Development LTD. and a conveyor system manufactured by Krupp-Robbins. This paper will review the option of truck haulage versus conveyor transport for overburden removal by (1) describing engineering studies contributing to the solution, (2) researching proactive options to create alternative management decisions, and (3) revealing final results of the project.

Jan 1, 1998

By Carl D. Wood

Traditionally, when one considers the optimization of a flotation circuit, the scope of work focuses on a review of unit process equipment. This usually includes topics such as grinding ball typed, grind size, classifier efficiency, mill liner design, chemical reagent addition rates, alternative chemical reagents, on-line process analysis, and automated control strategy. However, since very few companies can afford the capital expenditure needed to completely automate the processes, the flotation operator remains as a critical link in optimization of the circuit. Therefore, upgrading of operator skills and knowledge through training must be considered as equally as important as unit process review. This paper will review some concepts and approaches to innovative operator training. INTRODUCTION Consider for a moment the fantastic changes that have occurred in process automation at many flotation plants during the last several years. Flowmeters, density gages, and on-stream analyzers now routinely measure process conditions and effect control strategy. These functions had until recently been entrusted to human flotation operators. Now with a little stretching of the imagination it is possible to envision a plant where very little human intervention would be required. However, when one begins to calculate the capital cost required to fully install automatic equipment, it quickly becomes apparent that many parts of flotation plants will continue to require skilled, knowledgeable operators to ensure successful operation. Additionally as these automatic systems are put into place, the operator's duties become increasingly complex. Therefore no flotation plant can be considered optimized without upgrading each operator's skill and knowledge to match the technology utilized. BACKGROUND At Henderson, one of the hardest steps towards the optimization of operators was to realize that present level of operator skill and knowledge was not sufficient. Since Henderson had a track record of producing the highest quality molybdenum concentrate in the world, it was difficult to accept the idea that change was needed, or even possible. This realization came about as Henderson began a program to modernize the cleaner plant circuit. Henderson utilizes a complex cleaner flotation circuit involving multiple stages of flotation, with a counter- current routing of flotation tailings. Since start-up in 1976 Henderson had relied upon next-day laboratory analysis techniques, that provided an after the fact measurement of process. Hour to hour process control was implemented by the operator, the basis for the operators' control decisions was primarily the individual operator's experience and "feel'. Bench marking of current flotation technology indicated that on-stream analysis was a proven state-of-the-art method for improving process control. An Outokumpu Courier 30 analyzer was purchased and installed to provide real-time analysis of critical cleaner plant flows. The analyzer quickly began to provide valuable assay information, allowing the metallurgists to develop specific target values for important flotation variables. However due to the complexity of the circuit, the analyzer information showed that a problem was usually caused when several targeted parameters went out of range simultaneously. This made it difficult for the operator to determine just where to implement the proper corrective action. It became apparent that to take full advantage of the new analyzer information each operator would have to become proficient at understanding the material balance of the entire circuit. TRAINING PLAN CONCEPTS With the goal of giving each operator a working knowledge of a circuit material balance the following concepts were applied to develop a training plan: - Most operators were high school graduates, but had fairly weak mathematical skills, and had very little experience at metallurgical calculations. - The training would have to address a wide range of topics from basic fundamentals to complex material balance. The basic sequence decided upon, was to present a fundamental topic to the entire group, break into small groups to work a “hands on'”case study example of that topic, and design the case study results so that they could be combined to highlight a major portion of the material balance concept.

Jan 1, 1993

By R. L. Grayson, T. L. Dickinson, C. G. Anderson

Sponsored by the EPA, USGS, DOE, and NSF through the Committee on Earth Resources, the National Research Council’s Committee on Material Flows Accounting of Natural Resources, Products, and Residuals, created in August 2002, studied the value that material flows accounting, which can track the flow of a material from the time it is extracted to its ultimate disposal, may provide for making better integrated economic, social, and environmental policy decisions. This could be a crucial technology for the mining industry to incorporate. This paper will recount the statement of tasks, the study process, and the science-based conclusions and recommendations reached.

Jan 1, 2004

THE PENNSYLVANIA STATE UNIVERSITY, 101 MINERAL SCIENCES BUILDING UNIVERSITY PARK. PENNSYLVANIA 16803 To the Editor: With respect to the Fenvessy and Schwab article, I offer the following: As thorough as the study may be, it still has a glaring weakness. The presumption of constant supply in face of falling demand - their "low growth" case - is just wrong. It does not allow for the rapid migration, by transfer and change of major, from former high-demand programs, such as mining, to programs that have more recently obtained the cachet of job security. The figures that are shown for rapid growth in mining engineering enrollments in the period 1970-1981 are, no doubt, correct and reflect a rapid inmigration of students into mining. A similar out-migration, which began in 1982, from mining to other engineering and science disciplines is not factored into their study. Given 1983-84 enrollments, which can already be documented, it is clear that the low-growth case will, by 1985, be 50% or less of 1981. I wish students would pick their majors on the basis of their own individual abilities and interests rather than rushing lemming-like to programs that are reputed to have jobs. In the end, students will have better jobs and careers if their college majors match their talents and we, in the academic side of things, will have a livelier and more dedicated student. Lee W. Saperstein Professor and Chairman of Mining Engineering UNIVERSITY OF MISSOURI-ROLLA To the Editor: I write concerning the recent article on future demand for graduates in the mining industry. The article is, unfortunately, inaccurate because of the erroneous assumptions it makes in its basic premises. To cite but two of these, class sizes will not continue at their current level, but will, in fact, alter dramatically as a function of the perceived immediate job market rather than the future trend, so that enrollments are already below those predicted. Secondly, it is patently wrong to assume that everyone who gets a degree in the mining field will continue until retirement to work in that field. People who do not have a job in the industry will get work elsewhere and often do not come back. Others will later move to different areas. My major argument, however, deals with the underlying assumptions and methodology of the survey itself, with the concomitant challenge to the subsequent conclusions. It is no great secret that the technological world is undergoing a dramatic revolution. Computer use is rapidly spreading to the point where the microcomputer will be an integral part of every mine engineer's desk. Such a tool, which for optimal benefit must be operated by knowledgeable mining engineers, will make mining much more of a science than the current level. To remain competitive, mines will increasingly rely on higher level deci-

Jan 1, 1984

By Lynn E. Bowman

Efficient filtration of fine kaolin particles plays a crucial role in the processing of raw kaolin to a marketable product. Filtration can often be the rate-controlling step of the whole process. Consequently, plant production depends on the rates being achieved in filtration. To alleviate the bottleneck in production, Nalco Chemical Co. initiated a reagent development program to chemically enhance the performance of the filtration units. Filter aids of different classes were assembled and evaluated in bench simulations. These included reagents whose primary mode of functionality were coagulation, flocculation, thickening and combinations of each. This article discusses the development and application of a new reagent that improves the filter production rate with minimal impact on filter cake percent solids. Plant data indicate that this reagent can increase production rates by as much as 35% on clays of varying particle size, as well as clays that are calcined. The reagent's impact on solids content, re-slurrying characteristics, Brookfield and Hercules viscosity and drying is within the standards set by plants that evaluated and now use this product.

Jan 1, 1993

By E. J. Garrison

Discussion by E.J. Garrison A.C. Noble presents a clear and concise summary of the factors pertinent to a competent reserve evaluation of a mineral occurrence. However, I believe that he confuses the difference between a resource and a reserve. By definition, a reserve estimate includes all known economic, legal, mining, metallurgical and environmental factors impacting the recovery of the product(s) found in the deposit. A resource estimate, however, is an estimate of what is there - what is available for exploitation and should not include economic and other considerations. Only after defining the resource, its extent, location, physical and chemical properties, can an intelligent selection process begin of the extraction and processing technologies most appropriate to the circumstances encountered. The early and almost certainly inappropriate application of these often cookbook choices has probably lead many companies to walk away from good properties. (How many mines have been found in others rejects?) An example of the process is the early selection of metallurgical samples, after encouraging values are found in a few holes or surface samples, in an attempt to determine the economics of the prospect. Unfortunately, the sampler does not know how representative of the occurrence the sample is because he does not know what the deposit looks like. As a consequence, the property becomes saddled with a bad metallurgical sample that is often inappropriately used in evaluating the deposit which it does not represent. Reply by A.C. Noble E.J. Garrison asserts that I confuse the difference between a resource and an ore reserve. In fact, this paper was motivated by the observation that resources and reserves are almost universally confused throughout the industry. While Garrison is concerned that too-early consideration of engineering, metallurgical and economic factors will result in dropping properties too soon, some issues that must be considered include: •The purpose of exploration is to discover ore reserves, not to discover resources. •Ore reserves are always smaller than resources. • Decisions on exploration expenditures must be made based on the expectation of the quantity of ore reserves that will ultimately be defined. Noble's Fig. 2 can be used to give guidance as to when it is appropriate to begin reserve calculations. When exploration enters the "flat" portion of the curve, representative samples can be selected for metallurgical studies and appropriate mining methods chosen. It is at this stage that we know enough about the deposit to make intelligent choices of representative samples and recognize constraints on mining caused by the deposits shape, environment and physical properties. Once the appropriate technologies have been chosen, then their cost can be estimated with reasonable accuracy. Early entry of economic and process factors gives the false appearance of reserve status to the resource estimation. It would be more informative and less subject to abuse and misunderstanding if resource calculations were made at a number of cutoff grades. The cutoff grades should be chosen to cover the range of grades found in practice in existing operations of similar type. This would emphasize the open nature of resource estimates and encourage creative evaluation of mining and process technologies. It does not preclude the use of economic, environmental and recovery technology factors in deciding the advisability of continuing exploration expenditures, but would highlight their speculative nature. It is thus hoped that decisions on the future of the deposit would not be made on the presumed suitability of a given technology but on the actually known reality. I agree that resource estimates should be reported as a range of cutoff grades. Since reporting at a cutoff implies application of underlying economics (even by analogy to similar properties), however, it should be clearly stated that resources do not consider economic, mining or cost factors, and that ore reserves will be substantially less. The dilemma of the explorationist is that until the continuity and limits of ore-grade mineralization have been established, it is difficult to make quantitative estimates of either resources or ore reserves. Further industry discussion is needed regarding standards for disclosing early exploration information in such a way as to fairly represent the potential of an exploration property.

Jan 1, 1995

By Charles E. Barker

Striking similarities exist between the sediment features and facies formed in some modern heliothermal lakes and the characteristics of some ancient borate depositional environments. Heliothermal lakes are density-stratified with shallow submerged margins surrounding areally restricted deep pool(s) containing a dense brine overlain by a much less dense brine. The reflective brine interface allows solar energy to be trapped in the dense brine which may warn to over 900C. carbonate precipitated from the dense brine is the typical sediment produced in warm deep pool. The strong density stratification reduces turbulence in the lake so clastic sediment is deposited under most of the lake as finely-stratified mudstone-limestone couplets (varves). This depositional process results in clastic lake sediment interfingering with and enclosing a thick evaporite pod(s). Because deep pools can exist at the same time or through geologic time, the evaporite pod(s) may occur sporadically throughout the lacustrine beds.

Jan 1, 1988

By B. Mather

I was very glad to see an article on alkali-silica reactivity of concrete aggregate in Mining Engineering. It is a topic that should be reexamined every 45 or 50 years. The last paper (that I am aware of) that examined this topic in Mining Engineering was Rexford (1950), who, at the time, was chief of the Petrography Section, South Pacific Division Laboratory, Corps of Engineers, Los Angeles, CA. The paper was presented at the AIME meeting in Los Angeles in October 1948. Professor Leming's discussion generally reflects the current state-of-the-art; but it provides no references for more detailed information. I wrote a paper titled "How to avoid excessive expansion of concrete due to alkali-aggregate reaction," which was included in the Proceedings of the Second International Conference on Alkali-Aggregate Reactions in Hydroelectric Plants and Dams (Mather, 1995). In it, I emphasized that it was the hydroxide ion (not the alkali ion) that caused the pore fluid in the concrete to dissolve reactive silica, producing alkali-silica gel capable of taking up water, thereby, causing swelling and rupturing of the concrete. Excessive expansion will not occur unless there is a sufficient amount of potentially expansive alkali-silica reaction product and water. However, this will not occur unless there is a sufficient quantity of reactive aggregate and unless there is a mechanism by which the pH of the pore fluid can get well above the normal value of about 12.6. In many cases it is sufficient that the cementitious medium not only contains portland cement but also contains ground granulated blast-furnace slag (GGBFS) or a pozzolan such as fly ash, silica fume, metakaolin, volcanic glass or calcined shale - any of which may have been included for economic reasons. If, however, the person selecting the ingredients for concrete knows that the aggregate is reactive (with no alternate nonreactive aggregate available) and if the person knows that the only available portland cement has a high alkali content (i.e., more than 0.6% Na2O.; Na2e = % Na20 + 0.658 x % K20), then it becomes irresponsible not to establish what reasonable precaution one should take. Professor Leming suggests using one of the following: 30% Class F fly ash, 50% GGBFS or 7% to 10% silica fume. My view is that one should prepare test specimens with the cement and aggregate to be used and then expose these both with and without at least two dosages of each of the various alternative materials (slag, pozzolan and lithium salts), so that the required dosage. to control the expansion is established. Then, economic considerations can dictate the final selection. I would point out to the author that GGBFS is not a pozzolan and is not an admixture, but, rather, it is a latent hydraulic cement. An admixture is, by definition, a material other than hydraulic cement. I commend him for suggesting that aggregate producers should become more active in knowing about the reactivity of their products and the precautions needed to permit those products to be safely used in concrete.

Jan 1, 1997

By M. Galetakis, C. Roumpos

A sustainable coal industry needs to achieve a number objectives concerning mainly with superior utilisation of deposits and improved environmental performance. Modern quality control systems, which are greatly based on the on-line analysers, play an important role in achieving sustainability targets. This paper discusses the testing and application of on-line ash analysers installed in the Ptolemais and Megalopolis lignite mines in Greece and examines the possibility of using this type of analyser to control blending and homogenisation operations. The effect of the accuracy of on-line analyser to control process, when used for the characterization of low rank coals with complex and variable composition, such as greek lignites, is examined.

Jan 1, 2005

By H. Peter Knudsen

Karst hosted lignite deposits are characterized by variable thickness of lignite that was deposited in depressions in the karst topography and by the variable extent and shape of the lignite pods. Since the lignite to be mined will feed a mine mouth generating plant, an extremely important criteria in the mine plan is to assure continuous feed to the plant. The variability in both the extent of the pods and the thickness of the lignite within the pods must be taken into account in any mine design in order to quantify the risk that an area being developed will have enough lignite to feed the plant for the specified period. Indicator kriging was used to create a model of lignite thickness of the deposit. Pod boundaries were determined from the indicator kriging model by two methods. First, contour maps showing the probability that the lignite is above a minimum mining thickness were prepared. Using these maps the mine planning engineer can determine either conservative or optimistic boundaries. The second method recognized that the most costly error that can be made in the mine plan is to run out of lignite. Thus, a loss function was determined from the costs of overestimation and underestimation. Using this function, the probability that minimizes the risks of overestimation versus underestimation was calculated.

Jan 1, 1989

By F. W. Brackebusch

In the paper presented by F.W. Brackebusch on the "Basics of paste backfill systems," paste fill was presented as a backfill process that offers many advantages over other alternatives such as hydraulic fill and rock fill. It was observed, however, that the mechanics of paste-fill transportation in pipelines is not fully understood and that the success of its implementation in practice depends on the precise control of the proportions of fines, aggregates and water in the mixture. The author emphasized the necessity for laboratory and full-scale testing to determine the suitability of a material to be used as paste fill. Although experimental testing is definitely an important operation in the design of a reliable paste fill, advances in the understanding of the fundamental laws that govern paste flow in pipelines are equally relevant. Ideally, the results of such efforts would provide predictive models for the rheology of the paste and the corresponding pumping-energy requirements. In an attempt to achieve this objective, an ongoing research program has been active at McGill University's Department of Mining and Metallurgical Engineering. Preliminary results showed that the underlying mechanics of paste-fill flow in pipelines may be described in terms of what is known as "plug flow," as depicted in Fig. 1. Although this flow mechanism has been known qualitatively for many years, few attempts managed to offer a comprehensive model (Gandhi, 1987; Duckworth, 1986). In our model, it is assumed that coarse aggregates present in the mixture form a porous core, which is filled with paste (fines and water) and is surrounded by an annular non-Newtonian (Bingham-plastic) lubrication layer, which enables the mixture to flow with pressure losses that are easily overcome by common positive-displacement pumps. In summary, our model predicts the thickness of the annular lubricating layer, which controls the magnitude of the pressure losses. This is done either by collecting data on the apparent viscosity of the Theologically-active fine fraction and using an analytical equation (Bouzaiene, 1994), or is done by measuring the void content of the coarse aggregates and deducing the thickness as a function of the fine- to coarse (weight or volume) fraction ratio in the mixture for a given pipe diameter and solids concentration. Our model predictions showed good agreement with data from Duckworth et al. (1986), as shown in Fig. 2.? References Bouzaiene, R., 1994, "Hydraulic transportation in mining," Ph.D. dissertation in progress, McGill University, Dept. of Mining and Metallurgical Engineering, Montreal, P0, Canada Duckworth, A., Addie, G.R., and Maffei, J.R.,1986, "Mine waste disposal by pipeline using a fine slurry carrier," Proceedings of the 11th International Conference on Slurry Transportation, Slurry Transport Association, Washington DC. Gandhi, R.L., 1987, "Effect of rheological properties of fines fraction on slurry hydraulics," Proceedings of the 12th International Conference on Slurry Technology, New Orleans, LA.

Jan 1, 1996

In late 1993, Inco Ltd. completed a $600-million environmental improvement project at its Sudbury, Ontario operations -the largest single environmental project ever undertaken by a Canadian corporation. Efficient new facilities and innovative technologies installed during the course of the project have also significantly improved Inco's productivity and competitiveness. In early May 1994, a panel of 18 Inco authors contributed to a Technical Forum, "Environmental Programs at Sudbury," presented at the 96th Annual General Meeting of the Canadian Institute of Mining, Metallurgy and Petroleum (CIM) in Toronto. Their papers have been published in CIM's Toronto `94 Proceedings Volume, pp. 62-77. The following report draws primarily on discussions of Inco's milling and smelting operations published in the Proceedings Volume. The Proceedings Volume also includes papers on the acid and oxygen plants and on engineering, construction and commissioning of the project. The 222-page Proceedings Volume is available from CIM, $C27 plus shipping. To order, contact: V. Ward, CIM, Xerox Tower, 1210-3400 de Maisonneuve Blvd W, Montreal, Quebec, Canada H3Z 3B8; phone 514-939-2710, fax 514-939-2714. Lane White, Publisher.

Jan 1, 1994

By S. Z. Galiyev

In this paper the basic approach to the present planning and quality management of open-pit ore streams is presented. This is accomplished within the framework of a unified system of information management for the administration of a geotechnological complex on open-pit development of mineral deposits.

Jan 1, 2003

By Robert L. Akright

The Sumich (Victorine) gold mine is located in the Toiyabe Mountain Range on the east side of Victorine Canyon, a north-trending branch off Kingston Canyon in the northwest quarter of Section 27 and southwest quarter of Section 22, T16N, R43E, in the southern end of Lander County, Nevada (Fig. 1). HISTORY Discovered in 1862, the Victorine reached a peak of development between 1872 and 1887. The "Victorine" and "Morning Star" lode mining claims, located on the outcrop of a prominent auriferous quartz vein, were patented in 1869 and 1891, respectively. 1, respectively. Gold ore was mined underground in adits driven, on the level, directly into the side of the mountain. Ore brought to the surface was trammed about 457 m (1500 ft) south on a track constructed along the contour to ore bins. From this transfer point, the ore was moved by aerial tram to the bottom of the canyon then hauled by horse-drawn wagon to the mill located about 3.2 km (2 miles) east down Kingston Canyon. Exact details of the milling process used on the Victorine are lacking, but old reports mention water-driven stamp mills, amalgamation, chlorination, and cyanidation. Gold and silver mill products are reported to have been sent to England for final refining. High-grade gold values of 103 g/t (3 oz per ton) remaining in mine walls and on outcrops, attest to the lack of success in treating the Victorine ore in the early mills. The Victorine mine may have been worked sporadically after 1887 with little success. In 1934, control of the property was acquired by William P. Moloney, an attorney from Marion, OH, who also control- 1 led an interest in the successful Goldacres mine in Lander County, NV. This property was studied, sampled, and metallurgical tests were done in 1934, but no development resulted from this work.

Jan 1, 1990

By Raymond E. Krauss

The McLaughlin Mine is based on a world class epithermal gold deposit located in the coastal thrust fault of northern California, about 1 12 air km (70 air miles) north of San Francisco. Owned and operated by Homestake Mining Co., the McLaughlin deposit contains about 18 Mt (20 million st) of gold ore at an average grade of 5.2 g/t (0.152 oz per st), or about 93 t (3 million oz). The area was identified as a gold target by Homestake in early 1978. Drilling confirmed it to be a commercial deposit by 1980. The mine was then planned, engineered, built and brought into production by March of 1985. The deposit was historically a part of the Knoxville District. It was mined for cinnabar, which was used to produce mercury for use in recovering gold and silver in the Mother Lode and Comstock districts. At that time, the mine was called the Manhatten and later the One Shot Mine. It was worked for more than 100 years, producing about 76,000 flasks of mercury without any awareness of the presence of economic concentrations of gold. By 1978, the site was largely disturbed and entirely unreclaimed.

Jan 1, 1990

By J. D. Miller

X-ray computed tomography (CT) techniques have been developed for the medical services field in order to provide accurate internal images of the human body.(l-7) Now, a decade later, CT techniques are starting to be used in non-medical applications such as, non-destructive testing(8), flow pattern analysis(9), drill core examination (10,11), and coal characterization(12,13). In these fields of application, CT techniques offer the potential to extend our knowledge and understanding beyond that provided by more traditional methods of analysis. Although, CT systems involve very specialized and expensive equipment, the advantage of x-ray CT in revealing the detailed internal structure of an opaque material non-destructively should make it an important tool to provide a more complete analysis of mineral processing phenomena. X-ray CT systems generally consist of an x-ray source/collimation unit and a detector/data acquisition unit. The object to be examined is placed between the two functional units as shown in Figure 1. With this system the density array of selected cross sections of a chosen opaque object can be obtained in two dimensions. There are numerous areas in mineral processing to which x-ray CT technology can be applied and it is the aim of this article to identify these potential areas noting the advantages and limitations of the technology. Particular emphasis is placed on particle composition distribution and multiphase fluid flow measurements. In the case of particle composition distribution, liberation analysis and coal washability are considered. While in the case of multiphase fluid flow, swirl flow in the air-sparged hydrocyclone is given by way of example.

Jan 1, 1989

By A. Athousaki

The Ecological Footprint is a resource accounting tool used to address underlying sustainability questions. Aggregates consist of natural, artificial or recycled materials. The production of aggregates is the fastest growing activity worldwide since huge quantities are required by the construction industry. This paper presents a parametric investigation of the ecological footprint of transporting aggregates for urban use as a function of tonnage and distance.

Jan 1, 2008

By P. R. McOllough

The Colorado Department of Highways awarded a contract to construct the Second Bore of the Eisenhower Tunnel in August, 1975. The contract was completed June 29, 1979, nine days ahead of schedule, with¬out major claims or delays. The tunneling involved complex construction through difficult ground conditions. The contract, plans and specifications were specifically planned to more equitably share the risks involved and to minimize adversary relationships. The Department produced a detailed tunnel design and maintained responsibility for the design. The contract employed some new provisions; e.g., a review board for settlement of claims and disputes; escrow documents (contractor's bid documents) to determine the contractor's basis of bid when determining adjustments. The tunnel contract, plans and administrative efforts employed by the owner and contractor were very successful in this project.

Jan 1, 1981

By Carl R. Peterson, John Herrick

INTRODUCTION The need for substantial advances in underground excavation technology has produced considerable research activity on a wide variety of concepts under a variety of Government funded programs. One goal of this "Rapid Excavation" effort has been the development of a means to apply the well-known virtues, both technical and economic, of the drill and blast method in a continuous process. The spiral blast concept, aimed at this specific goal, has been funded for initial studies (1) by the ARPA Rapid Excavation Program and, for the experimental work reported herein, by the Department of Transportation (2). The economy enjoyed by the drill and blast method stems from two factors: explosive energy is relatively cheap; and this energy is released so as to cause rock fragmentation largely through tensile failures. The relative ease and efficiency of tensile rock failures have long been recognized. The drill and blast process of course cannot be truly continuous since drilling and blasting (and other necessary functions) simply are separate, distinct operations. Although some surface explosive work has been done to avoid the need for drilled blast holes (3) it does appear that the high performance associated with explosive excavation requires placement of the explosive beneath the rock surface. This paper describes studies of blasting pattern which, in simplest terms, replaces the occasional heavy blast of conventional practice with frequent, much smaller blasts. The objective, of course, is to reduce the size of individual blasts

Jan 1, 1974

By Patrick J. Coughlin

Shortly after Asarco Inc. purchased the Ray Mines Division from Kennecott in 1986, the company began an expansion program to increase copper production. The Bechtel Corp. oversaw engineering procurement and construction management for a new in-pit crusher, overland conveyor system and concentrator facility. Construction started in May 1990 on these facets of the expansion project. The concentrator was commissioned in February 1992. The Ray concentrator uses a single-line, semiautogenous grinding circuit (SAG) with a design through¬put of 27 kt/d (30,000 stpd). In the early 1960s, Kennecott conducted pilot plant grind tests of Ray mine ores to determine their amenability to SAG and autogenous grinding methods. Those tests, though, were not followed up. During 1973 and 1982, Kennecott conducted additional pilot testing on some of the softer ore types. In 1989, Asarco ran a final series of SAG pilot grinding tests at Lakefield Research, which became the basis of the new Ray concentrator grinding circuit. Even though pilot test work demonstrated that some of the Ray ores gave satisfactory results during the autogenous grinding tests, the SAG option was selected for the primary comminution device. Due to the wide range of mineralogies encountered in the Ray ore body, selective mining and blending of these ores would be required to achieve the necessary production efficiencies and throughput rates using an autogenous grinding circuit.

Jan 1, 1994