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By Stuart Brashear, J. W. Reil

The manuscript of this paper was not available for publication when the Proceedings went to press. Should the authors elect, they may distribute copies at the time of the Symposium.

Jan 1, 1986

By Jan M. Mutmansky, David R. Kalasky

Computer simulation continues to be one of the most successful analytical applications of computers in the mining and mineral processing industries throughout the world. Through simulation, managers and engineers can explore the impact of new technologies, equipment designs, plans and operating strategies to improve their operations. It is not uncommon for a single simulation application to provide a quick payback of analysis expenses (within weeks or months) yielding long-term financial and operational dividends. The paper will present a summary of the types of software systems that are available for use on PCs and other computer systems. Support software for curve fitting, statistical analysis, and optimization of simulation models will also be presented. Methods of leveraging simulation efforts through networking and coupling of software systems will be discussed. Finally, the trends in simulation in the mineral industries will be analyzed. Areas of strength and weakness of simulation will be discussed along with the usefulness of commercial general-purpose and custom-writ- ten simulation packages. The future possibilities for simulation in the mineral industries will be outlined and predictions on trends for the future will be presented.

Jan 1, 1996

By Zhongxue Li, Baolu Zhou, Yiqing Zhao

"Rare earth elements (REEs) are a kind of new materials which have excellent optical, electrical and magnetic properties, and they play an important role in the development of high technology and green energy industries. With abundant reserves and a wide range of REE type, rare earth industry has a rapid development in China in recent years. However, environmental issues associated with REE exploitation have severely restricted the sustainable development of rare earth industry in China. At present, literatures on the externalities of REE exploitation are very limited, especially in China. This paper builds an evaluation model based on life cycle evaluation to estimate the external costs of REE exploitation at Bayan Obo. The results show that the external costs for producing one metric tonne of rare earth oxides (REO) in Bayan Obo was CNY 34739 in 2013, the external costs of waste gas, waste water, radioactive substance, REE resource depletion, and land occupation are CNY 14945, 12515, 1400, 3199, and 2680, respectively. Waste gas and water constitute about 79% of the total external costs. The internalization of the external costs would reduce the financial profit of Northern Rare Earth (Group) by 18%. This study has taken into account only those externalities whose market values can be estimated, and therefore the external costs of REE exploitation in Bayan Obo is likely to be underestimated. The results fill the gap in literature and provide further understanding on the external cost of REE exploitation.Introduction / Background Along with increasing concern about environmental pollution problems caused by the usage of fossil fuel and the shortage of fossil energy, a transition has occurred where development has moved toward green and renewable energy sources with less pollutant emissions (Stegen 2015). Rare earth elements (REE) are a group of important raw materials for these trends since they have unique magnetic, electronic and optical properties, and thus make them widely used in making high-performance magnets and energy saving lamps (U.S. DOE 2010). In addition, REE are crucial for manufacturing of widespread high-tech applications in medical, defense and electronic industries. Many countries have made medium-term and long-term plans for the development of their REE industries, and the annual growth rate of global REE demand is expected to increase by 6% by 2020, and reach about 170,000 metric tons of rare earth oxides (REO) by 2020 (Rollat et al 2016)."

Jan 1, 2017

By Oscar Auerbach, Marvin Kuschner, Rosemarie Mick, Geno Saccomanno, Stephen Wood, Victor E. Archer, Marlene Egger

INTRODUCTION Excess bronchogenic carcinoma has been demonstrated among underground uranium miners in the United States, Czechoslovakia, and Canada (Archer 1981). This excess cancer is attributed largely to radiation from the alpha particles delivered to the tracheobronchial epithelium by the decay of short-lived daughters of radon. Interaction between the radiation and cigarette smoking has been demonstrated in production of the excess cancer (Archer 1973). The distribution of histologic types of bronchogenic cancer among uranium miners was established as different from that in other men in 1964 when an analysis of the first 51 cases among United States uranium miners was published (Saccomanno 1964). It was confirmed five years later by Yugoslavian studies (Horacek 1969). A later analysis, using a relative frequency method, indicated that oat cell and other small cell undifferentiated carcinomas increased markedly with increasing exposure to radiation in uranium mines (Saccomanno 1971). A subsequent analysis used only cases from an epidemiological study so as to enable calculation of expected numbers. It showed that there was an elevation in incidence of epidermoid, adenocarcinomas, and possibly other types, as well as small cell undifferentiated carcinomas (Archer 1974). At that time, it was felt that the histological distribution of cancer among uranium miners was well established. However, one of the authors (GS) has noted that fewer oat cell carcinomas were appearing among uranium miners in recent years. In his material the fraction of oat cell carcinoma, in successive 5 year periods between 1960 and 1980 was 59, 46, 37, and 22 percent. The association with calendar years is almost certainly spurious, reflecting some other factor associated with time. From the standpoint of tumor biology such a change must be important. This is a preliminary report which attempts to determine the cause of that change. POSSIBLE REASONS FOR OBSERVED CHANGE IN CELL TYPES 1) It might reflect a decrease in radiationinduced carcinomas, so that most of the ones being seen now are cigarette-induced. This appears to be a possibility because radiation levels in mines had been markedly reduced in the early 1970s, and because most of the uranium miners now developing carcinoma had quit mining during the 1965-1975 period. 2) It might represent a change in interpretation by the pathologists involved. 3) It might represent a real change in distribution as a result of increased latency, an aging population, cessation of smoking, increasing pack years of cigarettes, or other factors which have changed with time. Each of these possibilities is being checked. Dr. Waxweiler, later in this conference, is presenting an updated mortality analysis of United States underground uranium miners. His data indicate that lung cancer incidence among the Study Group of uranium miners is still quite high, but the ratio of observed to expected is falling somewhat. It is apparent that decreasing exposures in uranium mines is not yet reflected in normal lung cancer mortality rates. Reason #1 is therefore very unlikely. Thirty-five percent of the histologic types of carcinomas in this study were classified by a panel of three pathologists, 45% were classified by one of the panel members, and 20% were classified by a number of

Jan 1, 1981

By Gregg J. Hodges

The Stillwater Mining Co. is a partnership of The Pittsburg & Midway Coal Mining Co. and Manville Corp. The Stillwater Mine, located near Nye, MT, is the Western Hemisphere’s only primary platinum-palladium deposit. The mine began production of flotation concentrates in March 1987. In the fall of 1987, an integrated pilot plant testing campaign of electric furnace smelting and oxygen-blown converting confirmed the feasibility of further upgrading to semi-refined matte, or “white metal.” In the summer of 1990, the production smelter was brought on line. The record of the discovery and development of the Stillwater deposit, mine and concentrator has been summarized in several articles (White, 1987; Kennedy, 1987; and Hodges and Clifford, 1988). Similarly, the pilot campaign to test the feasibility of treating the flotation concentrates in an integrated smelting plant has been described (Hodges and Clifford, 1988; Matousek, et al., 1989; and Matousek and Whellock, 1990).

Jan 1, 1991

By Edie Trimmer

Utah statute defines sovereign lands as "those lands lying below the ordinary high water mark of navigable bodies of water at the date of statehood, and owned by the state by virtue of its sovereignty." The lands within the bed of Great Salt Lake (GSL) are, by this definition, sovereign lands, acquired at statehood in 1896 in accordance with the "equal footing" doctrine, granting each state control and ownership of navigable waters and the lands underneath those waters within its borders. Under public trust doctrine, the state, as trustee for the people, bears responsibility for preserving and protecting the right of the public to use of the waters for navigation, commerce, fishing, recreation, and wildlife habitat. Also by statute, sovereign lands are defined as "state lands," to be managed by "multiple use sustained-yield principles." The Division of Forestry, Fire and State Lands is given management authority for sovereign lands and, as manager, has responsibility to prepare comprehensive plans, initiate studies of the lake and its resources, implement comprehensive plans through state and local entities, and coordinate the activities of various divisions within the Department of Natural Resources (DNR). The Division of Forestry, Fire and State Lands also has responsibility for management of mineral leasing on sovereign lands. The many resources on the lake--water, minerals, wildlife, recreation, archeological and historical values--are managed by as many state agencies which occasionally creates conflicts. The brines of GSL contain several ions that crystalize into valuable minerals during evaporation. The major ions in the lake are, in order of relative abundance, chloride, sodium, sulfate, magnesium, and potassium. Mineral products which are currently extracted from lake brines are sodium chloride, magnesium chloride brine which can be sold as flake magnesium chloride or further processed into magnesium and chlorine gas, and potassium sulfate. Mineral products which have potential for extraction include gypsum, sodium sulfate, and trace amounts of lithium, boron, and bromine. The GSL contained an estimated 4.3 billion short tons (st) (3.9 billion metric tons [mt]) of dissolved salts in 1998. Utah Geological Survey (UGS) estimates of the dissolved salt content in GSL have fluctuated from 4.0 to 5.5 billion st (3.6 to 5.0 billion mt) due to the dynamic conditions in the lake as salts are precipitated and redissolved, and due to the diversion of brines from GSL, such as the West Desert Pumping Project. The lake has four areas of varying salinity, separated by dikes or other man-made structures: north arm and Stansbury Bay brines at near saturation (25 to 27 percent total dissolved solids [TDS]); the main body of the south arm with concentrations ranging from 7 to 15 percent TDS as lake elevations fluctuate; the waters in Farmington Bay at approximately 3 to 5 percent TDS; and Bear River Bay at <1 to 7 percent TDS. The percent TDS in Bear River Bay fluctuates with lake level, and changes in Bear River inflow. The transfer of salts from the south arm to the north arm has raised questions about the viability of the mineral and brine shrimp industries. The UGS and the U.S. Geological Survey (USGS) continue to monitor salinities at designated sites on the lake to document changing lake salinity. A recurrent theme is that placement of dikes and diversions can have significant and rapid impacts on various conditions in the lake. Hydrocarbon resources on the lake are significant, but presently undeveloped. The hydrocarbons are low gravity (4 to 9 degree API) and tar-like, contain high nitrogen concentrations, and up to 12 percent sulfur. The unusual characteristics of the oil have been the subject of studies by chemists at Weber State University and University Louis Pasteur de Strasbourg. However, these resources are difficult, and at present, uneconomic to extract using current technology because of the nature of the hydrocarbons, and production in "an offshore, highly saline environment." Oolitic sand deposits make up many of the beaches and shorelines around the lake. Because of their high calcium carbonate content, oolites have been used by Magnesium Corporation of America (MagCorp) and its predecessors for acid neutralization and dike construction. Oolites are also used in very minor amounts in flower drying. The Utah Division of Oil, Gas and Mining reports up to 130,000 st (118,000 mt) mined annually by MagCorp from U.S. Bureau of Land Management (BLM) lands adjacent to GSL. Currently, there are twelve producing mineral leases which generated slightly more than $1,000,000 in royalties during calendar year 1998. IMC Kalium Ogden Corp. (IMC Kalium) produces potassium sulfate and magnesium chloride from brines concentrated through solar evaporation in Bear River Bay and Clyman Bay. By-product sodium chloride is transferred to IMC Salt, which packages and sells the salt. MagCorp produces magnesium metal from brines concentrated in Stansbury Bay. Cargill Salt produces sodium chloride from brines provided by MagCorp under a lease agreement. Morton Salt produces salt at the southeast end of Stansbury Island. Lastly, North Shore Limited produces cocentrated brines for use in dietary and mineral/vitamin supplements near Spring Bay in the north arm of the lake. Producers of magnesium, potash, and salt from GSL contribute significantly to the value of metals and industrial minerals in Utah. Together these companies contribute approximately $240 million in gross value, or 18 percent of the value of the state&apos;s nonfuel mineral production. Most of this production is exported.

Jan 1, 2001

By K. R. Gardner, P. B. Altringer, R. H. Lien

The Bureau of Mines, U. S. Department of the Interior, is investigating biological and chemical reduction of selenate and selenite from waste waters. A mixed bacterial culture, isolated from agricultural waters, removed selenium from four oxidized cyanide solutions from precious metals operations containing 0.6 to 30 ppm Se and 13 ppm CN. Up to 85% selenium removal was attained using bacteria under controlled batch conditions in a 3-L stirred tank reactor and in small-scale continuous tests conducted in a rotating biological contactor (RBC). Fe(OH), reduction of the selenium reduced the effluent concentration to 0.02 ppm Se; however, the reagent costs were prohibitive. A final processing scheme may involve a combination of biological and chemical treatments.

Jan 1, 1991

By J. Kemeny, B. Norton, T. W. BoBo

Digital image analysis systems to quantify particle size of crushed materials have successfully been applied in large-scale mining operations throughout the world. Particle size measurement at various crushing and sieving stages, especially in aggregate production, will facilitate the industry’s desire and need to achieve higher levels of process control and automation. This paper will 1) summarize applications of digital image analysis in the industrial minerals industries and introduce the Split-Online technology; 2) detail an actual recent test application of digital image analysis that ultimately lead to the installation of an automatic, non-invasive particle size distribution monitoring system; 3) document how this information is being applied: and 4) summarize the new Split-Online Aggregates Module now available.

Jan 1, 2004

With the advent of the environmental "green" movement of the 1960s, eventually leading to Earth Day 1970, Congress responded by passage of the National Environmental Policy Act (NEPA), 1970. NEPA gave impetus to a flood of federal acts and laws in the subsequent three decades. Many of those protecting man&apos;s environment, health, and well-being also affect mining. For purposes of this chapter, a current mineral law summarization lends itself to a division into two parts: viz., Part I, General Mining Law, and Part II, Enviromining Law. The word enviromining has been coined by the author and is defined and used herein as those federal and state statutes and regulations that were created to provide protection and preservation of man&apos;s environment, health, safety, and welfare, and they have particular application to and affect on mining activities. They are listed and treated under Enviromining Laws in Part II. Mining, as a basic industry to provide the essential minerals for mankind&apos;s necessities and well-being, truly reflects the mining industry&apos;s slogan, "If it can&apos;t be grown, it must be mined." Without the basic minerals and rocks won from the earth by mining and mineral processing for their valuable physical properties or chemical constituents, man would soon be forced to revert to the cave-dwelling age. Unfortunately, for man to survive in the "manner of life to which he has become accustomed," he is caught between the demands of cleaning up his deteriorating environment and a continued supply of his basic requirements and amenities for daily living supplied by mining of the earth&apos;s minerals. He must have "clean living" at the same time with "good living;" neither is expendable. A very high pricetag accompanies this essential and critical choice which must be paid by society. The United States is internationally recognized as the world leader in environmental matters. Many countries are following suit, principally the other Anglo nations. Because US law is founded and based on English law, on occasion, Anglo-American law is referred to and cited as authority in litigation anywhere in the Anglo-American world of jurisprudence. For this reason, and because mining and the industry is international in nature and operations, some British Commonwealth cases will appear in various topics. If the case is of interest to the reader, further inquiry at a law library may be made through use of the case&apos;s style and citation given. "Style" refers to the name of the litigating parties. "Citation" refers to the law publication in which the case and decision may be found, as well as the jurisdiction and court of decision. Citation of cases from the United States and British Commonwealth nations is explained under Case Citation Explanation. Space and time limit exhaustive treatment of subjects and covering all geographic and jurisdictional areas. This chapter is intended as a broad outline and is based on the author&apos;s master&apos;s thesis at the University of Missouri-Rolla, 1992. The following Case Citation Explanation provides guidance on formatting of citations.

Jan 1, 1994

By Z. Kowalski

In the defunct Gorka quarry, there are situated both a waste disposal site of an area of 6.7 ha and containing approximately 1 million ton of high aluminium wastes and a pond of an area of roughly 3 ha, up to 15 m deep, with about 400000 m3 of polluted water. The reservoir is fed with the filtrates arriving from the disposal site mentioned, at a rate ~130 m3/day. An alarming phenomenon is the subsidence of the pond bottom and the infiltration of solutions into the Triassic and Jurassic water resources, assessed at ~40 m3/ day. The basic problem related to the effluents in the Gorka pond is their high alkalinity (pH 12-13.4) and variable pollutants whose level increases appreciably with the pond?s depth. The solution offered provides pumping out and treatment of about 500000m3 of effluents retained in the Gorka reservoir in an about yearly time. Effluents would be treated in a reverse osmosis plant, according to a process so far verified on a quarter-commercial scale. The treatment process by-product would be discharged into the Ropa stream. The brine solution (containing about 25% NaCl), whose amount may reach up to100000m3, might be supplied to the Debiensko Mine which produces technological salt from salt-bearing mine waters. Similarly, there would be provided an intake of underflows of infiltrates (by means of deep wells, and possibly girdling ditches) arriving from the high aluminum site, and such effluents would be subject to ongoing dilution in water courses. It would be possible to test the system of underflows reaching the Gorka reservoir by means of geochemical identification, previously performed. The next stage following the pumping, would be the utilization of approx. 50 000m3 of bottom slurry. Highly alkaline slurries would be utilized in the production of self-solidifying mixtures. Slurries would be pumped out and temporarily dumped on drying beds, located nearby the Gorka reservoir, and later on used successively for making self-solidifying mixtures in a plant similar to a concrete making seat. Those mixtures would be applied for sealing the bottom of the Gorka reservoir and the necessary part of the edges of the defunct quarry. An alternative solution is the utilization of slurries in the facilities of the Trzebionka Mining Works and the application of self-solidifying mixtures, made in the Trzebionka Works, for sealing the reservoir bottom.

Jan 1, 2006

By Gary A. Perry

Cyprus Sierrita produces copper and molybdenum from its Sierrita and Twin Buttes open pit mines south of Tucson, AZ. Both pits were started in the late 1960s and are more than 460 m (1500 ft) deep. Sierrita has used a Caterpillar 992C Remote Controlled Loader since January 1993. The loader was justified to increase safety and profits at Sierrita. It has exceeded all expectations. As of June 1993, the 992C had produced additional profits of more than $1.5 million. Safety and Geotechnical The safety of Cyprus personnel and equipment is always of prime concern. The remote controlled loader removes personnel from the active raveling area. But it requires prudent operation. The remote controlled loader discussed here is always intended to be used in a safe manner under a managed slope. Any increase in slope angle or use of any equipment under a critical slope is taken only after careful analysis of the specific

Jan 1, 1994

By John Wiebmer

Several industry trends are putting new demands on surface mining equipment. This is true both on the “hard” side of the equipment business - the research and product development programs, and on the “soft” side - the business processes, human resources and competitive strategies. This article describes seven key industry trends and the impact each is having on surface mining equipment suppliers. 1. Globalization Earth-spanning technologies are shrinking the world into an economic village, causing corporations to think and plan on a global scale. This “globalization” is one of the great buzzwords of the 1990s, meaning precisely whatever the user says it means. In this case, let us take it to mean that political boundaries arc less restrictive than in the past, permitting mining companies new freedom to roam the globe for ore bodies. Evolving out of this are global mining houses that have ownership and management interests in labyrinthian webs of mines spanning the world. There are several impacts on surface mining equipment suppliers.

Jan 1, 1994

By T. Skodack

This presentation will compare actual work site results for the loading and transport of shot rock for two major tunneling projects in North America. "SCARMAR" (the Canadian subsidiary of S & M Construction) is operating a rail bound Hagglund continuous gathering arm loader in combination with a Hagglund nine car shuttletrain system at the West End of Table Mountain on the B.C. Railway project near Tumbler Ridge, Canada. Al Johnson Construction is operating a Hagglund rubber tired continuous gathering arm loader in combination with haul trucks at the Rocky Mountain Pump Storage Project near Rome, GA. This paper will compare: 1) tunnel and ground conditions, 2) the total work cycle as it relates to mucking and haulage 3) efficiencies and related problems with the two systems 4) mucking and haulage rates 5) operating costs, and 6) recommendations for future large tunnel excavations. Manuscript not received in time for publication.

Jan 1, 1983

By Peter L. Hofmann

Significant quantities of nuclear wastes were first generated in 1944 as a byproduct of the national defense program. To establish the current inventories and future projections of nuclear waste products is not a simple task. The Oak Ridge National Laboratory recently issued a report which now constitutes the official basis for nuclear waste inventories and projections. Radioactive wastes originate from five major sources (U .S. Department of Energy, 1980b) : (1) From the commercial nuclear fuel cycle related to the production of electricity , (2) From defense related activities, (3) From institutions such as hospitals, universities, and research foundations, (4) From industrial uses of radioisotopes, and (5) From mining and milling of uranium ores.

Jan 1, 1981

By Steve Kral

The Fourth International Symposium on Hydrometallurgy was organized to give those in the minerals processing field an opportunity to discuss current topics of interest in the broad field of hydrometallurgy. Held in Salt Lake City, UT Aug. 1-5, 1993, this fourth symposium also paid tribute to Milton E. Wadsworth for his many contributions in this area over the past 40 years. The science of hydrometallurgy has made great strides since the last symposium was held 10 years ago. The use of electrochemical principles and techniques has produced encouraging results. For example, the application of in situ electrode spectroscopy has helped to understand the mechanisms operating in hydrometallurgical processes. Sophisticated computer models have been developed to handle the thermodynamic properties of concentrated electrolytes. However, it is up to the hydrometallurgist to continuing working on bridging the gap between theory and practice. The successful application of solvent extraction-electrowinning (SXEW) is one illustration of the successful transfer of technology. Its widespread use in the United States during the 1980s played a significant role in the revival of the domestic copper industry. Currently, electrowon copper accounts for about 30% of total US production. Impressive developments in precious metals recovery have also occurred. Since the last symposium, carbon-in-pulp (CIP) and heap leaching have become widely used in gold recovery. And recovery of refractory precious metals ores and concentrates by pres¬sure oxidation and bio-oxidation have made significant advances. In all these examples, hydrometallurgy has played a significant role in the recovery of minerals and metals from primary sources. In addition, considerable attention has been focused on the treatment and recovery of values from secondary sources.

Jan 1, 1994

By D. Maxton

INTRODUCTION This paper traces the application of High Pressure Grinding Rolls (HPGR) at industrial and pilot scale in Australia. The Argyle Diamond Mine installed the first of two smooth segmented HPGRs during 1990 in an open-circuit secondary-tertiary crushing application to increase throughput. In 2002 a third HPGR was added to improve liberation and so increase the recovery of smaller diamonds. The latest improvements in wear technology (tyre with tungsten carbide studs) were incorporated in the design of this machine. Extensive HPGR pilot-plant trials were undertaken during the 1990s at both the Kalgoorlie Consolidate Gold Mine and the Boddington Gold Mine. The purpose of these trials was to evaluate HPGR as a method to increase throughput, as an alternative to SAG milling, and also to ascertain if downstream benefits existed. One of the challenges for HPGR circuit designers is to translate what occurs at small laboratory and pilot scale into what is likely to happen in a full-scale circuit. Scale-up from pilot machine results is normally recommended by manufacturers. However, such tests need relatively large quantities of material, particularly if meaningful data on wear are to be obtained. Laboratory tests are preferable, as they need relatively small quantities of ore, but may be questioned in terms of how they relate to full-scale operation. Modelling and simulation have played a particularly important role in this respect in Australia. Models are available which have proven to be very accurate at being able to scale throughput and specific energy response from laboratory to industrial machines. More recently, work in Australia has also been done in developing a model which has the potential to scale laboratory wear data as well.

Jan 1, 2004

By D. D. Harbuck, G. K. Green

The Bokan Mountain area on Prince of Wales Island, AK, contains vast quantities of heavy rare earth minerals. To lessen the US dependence on foreign sources, the US Bureau of Mines (USBM) investigated yttrium recovery from this ore. By sulfating the ore at 250 ° C for 1 hr at an H2S04:ore ratio of 1:1 and then water leaching the sulfated material for 1 hr at 20% solids and 25ºC, over 74% of the yttrium, cerium, and lanthanum were solubilized. Solvent extraction (SX), using a synergistic combination of OPAP and DEHPA, selectively loaded 100% of the yttrium. Yttrium was stripped directly as a solid using a 2M, 35 ° C NaOH liquor. When the OPAP/DEHPA mixture was tested in a continuous SX circuit, yttrium loading and stripping were 100% and 96%, respectively. The organic showed excellent recyclability properties with minimal solvent loss.

Jan 1, 1996

By H. Sevim

A new method of designing haulage systems, consisting of belt conveyors and hoists for underground mines is discussed in this paper. Efficient and economic design of such systems will prevent operational bottlenecks and provide savings. The developed model uses a heuristic algorithm to optimize the design parameters and to select the proper equipment specifications. It is a probabilistic model because it considers the probabilistic aspects of face operations. It is versatile because it can accommodate belt conveyor networks of any configuration and hoisting systems that can be either drum or friction hoists for single or multiple-level operations. The model also has the option to internally determine the required capacities of the bunker(s) and shaft- bottom bin. The objective of the optimization process is to minimize the "expected cost per ton of ore hauled" from the working faces to the surface. A numerical example is included to illustrate the capabilities of the model.

Jan 1, 1987

By D. G. Krige

Discussion by D.G. Krige I read the paper "The jackknife approach" with interest. There appears to be a widespread misunderstanding of the kriging variance as a measure of the error variance of the kriged grade estimate of an ore block. Virtually all mineral deposits display skew frequency distributions and are subject to the well-known proportional effect. Thus, it is usual to find in an ore body, when subdivided a really into subpopulations, that the variances of the grades (or the total sills of the variograms) for the subpopulations will be correlated with the corresponding mean grades (usually linearly with the squares of the mean grades). Thus, the variogram will be station. When this feature is evident, the relative variograms for the subpopulations (i.e., with variogram values divided by the relevant mean squared) will be similar, or they could even be accepted at an averaged model for the whole ore body with stationarity. Using this approach, the kriging variance will reflect the relative error variance that is to be multiplied by the kriged block grade estimate squared to yield the usual kriging variance for purposes of confidential limits. The objection that the kriging variance does not take into account the local grades used for a block valuation then falls away. In the example given by the authors, the global mean grade is not recorded. But the global variance, taken at the value of the total sill, is 0.005, whereas the variance of the 11 values used in the example is 0.000152. The two variances differ by a factor of nearly six. If the relative variogram approach is applicable in this case, the need for a jackknife technique will fall away. Also note that, for skew distributions, the confidence limits for ore-block estimates will be skew as well, and symmetrical normal limits will not apply. RepIy by G.S. Adisoma and M.G. Hester There are a few interesting ways to utilize the block-by-block kriging variance that the authors have encountered. One of them is to classify a particular block into a proven-probable reserve or a possible-resource category, using a somewhat subjectively determined kriging variance value. Here, the kriging variance still represents the drilling density, i.e., data configuration more than the data values. Professor Krige mentions another ingenious approach through the use of relative variograms. This will yield a block kriging variance that takes into account local (block) grade, as he correctly points out, for purposes of confidence limits. However, we are more interested in quantifying the uncertainties associated with grade estimation in a much larger scale than a block. e.g., for a mining phase or the minable reserve. The jackknife, through the block kriging shortcut, provides a simple solution to obtain a single estimation variance for a general shape. The authors&apos; main reference discusses different ways to handle skewed distributions typical in mineral resource estimation, e.g., the weighted jackknife approach or data transformation. Also, as with any technique, we can always improve our estimate by subdividing into smaller populations that are geologically and statistically separate domains. As we have mentioned; the jackknife is but a tool in our collection of tools to solve estimation problems. The jackknife&apos;s appeals are its simplicity and versatility. It is handy when no other solution is available, or when the available solution is not practical. It is used with other methods, not to replace them altogether. ?

Jan 1, 1997

Development of process control in the metallurgical industry over the past ten years has been highly influenced by technical advances centered on use of computers as well as on measurement and associated equipment. The discussion in this section reviews advances in computer technology, measurement devices, data input-output techniques, and their use in mineral processing for the objective of guiding application of process control principles. Advances in the next ten-year period through the 1980&apos;s can be foreseen in the cost and application of data handling facilities in the coincident fields of data processing equipment, interface and control devices, and computer programming systems. These will lead to greater acceptance in a widely expanding range of mineral processing fields. It can be predicted that process control methods now known to be effective will become more re- fined. Costs of on-stream analyzers for assays and particle data will be reduced. Continued innovation can be anticipated in measurement devices required for effecting control. Control techniques developed over the last decade in key process operations such as crushing, grinding, flotation, smelting, and hydrometallurgical processes are described in the following chapters. The general forms taken by computer process control are first outlined briefly.

Jan 1, 1979