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By R. S. C. Rogers

The present study examines the use of two vs. one stage of hydrocyclones in a pilot scale ball mill circuit. The approach used for doing this is based on computer simulation with mathematical models that explicitly account for the grinding mill/classification system interaction. Parameters for the ball mill model are obtained using a short-lived radioactive tracer method in open circuit tests of the study mill. The hydrocyclone model, based on the size selectivity concept, is developed and validated in standalone testing of the study hydrocyclones. Simulation procedures are validated through actual tests of the closed circuit grinding configurations of interest. Results of the evaluation indicate that two stages of hydrocyclones in the study circuit would improve classification, increase productivity and lead to more closely sized circuit products when compared to the conventional one stage hydrocyclone circuit. A computer simulation approach for comparing these circuit configurations in larger scale grinding circuits is also suggested.

Jan 1, 1981

By James Corcoran, Richard McLane, Matt Neuner, Joseph DeMello, Hugh Davies

The Los Angeles County Metropolitan Transportation Authority (LA Metro) Purple Line Extension Section 1 (PLE1) is a $3.12 billion USD design-build, underground heavy rail project, connecting an existing station at Wilshire Blvd. and Western Ave. and extending 3.92 miles under Wilshire Blvd, terminating approximately 550 feet west of Wilshire and La Cienega Blvds. The project alignment runs immediately adjacent to the La Brea Tar Pits, world renowned for Pleistocene fossils and continuous seepage of asphaltum (locally known as tar) and gas in an urban setting. This paper presents a successful case history of the planning, design, and construction efforts to safely construct the bored tunnels through Reach 3 of the alignment (between Wilshire/Fairfax Station, and Wilshire/La Cienega Station), in a designated Methane Zone in the City of Los Angeles. Historical context on decades of challenges and studies is summarized. Further, this paper outlines the pro-active partnership between the Owner: LA Metro, the Design Builder: Skanska-Traylor-Shea Joint Venture, and geotechnical design services provided by Golder Associates to safely manage pressurized face tunneling through a confined gas zone near the La Brea Tar Pits. Specifically, a program of in-situ oxidation and soil gas extraction was designed to test and analyze risks associated with pressurized face TBM tunneling through the complex subsurface geological conditions, then implemented during construction. In advance of tunneling, a network of wells was used to draw air into the gas zone to oxidize the 6,500 ppm hydrogen sulfide gas, as well as determine methane recharge rate. During TBM tunneling, the wells were converted to a gas extraction system to evacuate, filter (H2S) and burn (CH4) the gas as the Tunnel Boring Machine passed, providing a preferential pathway for the gas to migrate toward extraction wells, and preventing the migration to adjacent buildings. The team extracted and treated 3,857,000 cubic feet of mostly methane gas over 40 days as the TBMs passed through the zone. Gas behavior, pressures, and concentrations were monitored not only from the extraction system, but also in basements and utility vaults along this section of the alignment.

Jun 13, 2023

By H. R. Manouchehri

In flotation practices, as particles become finer, such as smaller than 20 μm, process efficiency declines markedly. Selective agglomeration of fine particles is a technique to enhance the recovery of fine valuable minerals in flotation circuits. Different agglomerating methods have been introduced and tested. One method that has recently received much attention is to make use of magnetic force to aggregate fine particles. A selective aggregation of fine paramagnetic particles, such as sulfide minerals, can be achieved in the high-intensity magnetic field prior to or during flotation. The method is simple, selective and effective for fine particles and has low operational cost, though a minimum magnetic susceptibility for fine grains is required to promote the process. In this paper, the implementation of the ProFlote magnetic conditioning device in Boliden’s Garpenberg old concentrator in Sweden, where a complex massive sulfide ore is treated, is presented and discussed based on Boliden’s Garpenberg plant. The results showed an increase in the flotation recovery of fine valuable minerals. Zinc (Zn) production was increased by between 1,100 and 1,500 t/a, while salable yearly silver (Ag) production was increased by 1,500 kg. The copper (Cu) grade in the final concentrate was increased by 1 percent, while reductions in its Zn and lead (Pb) grades were obtained. Moreover, considerable reduction in Zn deportment to the final tail was observed

By S. C. Sethi

The WIPP (Waste Isolation Pilot Plant) Project near Carlsbad, New Mexico, is a research and development project sponsored by U.S. Department of Energy, designed to demonstrate the safe containment for disposal of radioactive waste. A mine (repository) is currently being developed 2150 feet below the surface, in a thick salt bed which will serve as the disposal medium. Provision of a proper ventilation system at the WIPP Project is a major priority of those responsible for its design, management, and operations. As an ongoing effort towards this goal, it was decided to simulate the mine's ventilation system using Dravo's MINEVENT computer program. Specifically, the work included the development of the following simulation models: 1. Simulation of the current ventilation system 2. Simulation of the designed ventilation system for the following modes: o Mine Construction mode/shift o Waste storage mode/shift o Fire or exhaust filtration mode These computer models are useful in solving complex ventilation problems likely to be encountered in an R&D project, like WIPP. They are particularly helpful for the development of contingency plans to incorporate during emergency situations, such as fires, fan stop- pages, radiation leaks, etc. Also, they can be utilized when considering expanding certain underground areas to ensure the availability of adequate ventilation.

Jan 1, 1986

By M. Dayne Aldridge

A description is given of an experimental ventilation control system designed, built, and tested by WVU under United States Bureau of Mines sponsorship. A description is given of the control, system used and the mine-wide microcomputer-based ventilation monitoring system used with it. Test results of experiments conducted with this system at Eastern Associated Coal Corporation's Federal No. 2 underground coal mine are presented. In addition, a brief description is given of a new microprocessor based system presently being tested.

Jan 1, 1980

By L. Harris

The gold mining and ore processing operations of Minera Yanacocha S.A. are 10cated in an area 4,000 meters above sea level in the Peruvian Andes same 600 km north of Lima and 20 km north of Cajamarca. The joint venture partners are Newmont Second Capital (USA); Compania Minera Condesa (Peril); Mine Or (France) and the IFC. Newmont manages the operation. The Yanacocha district comprises several areas with mineralization evidence. The first ore with minable reserves of 28 million tonnes of ore assaying about 1.4 gpt Au is called Carachugo and is being mined and treated at the rate of 14,000 tonnes of ore per day by open pit mining methods. ROM ore is dump leached and the gold recovered in a Merrill Crowe plant. The plant design incorporates some unusual considerations to overcome the problems of the high rainfall in this area and assure the protection of the environment.

Jan 1, 1994

By Omar. M. Arafat, Edgar Pérez, Kyle. M. Bartholomew, Robert. E. McIvor

The “circulating load” confounds understanding of ball milling circuits. Conflicting opinions exist as to its role. Should it be high, or low? Why does it even exist? It is commonly accepted in the plant as a given, the outcome of largely unknown factors. As such, it may often go unmeasured or even ignored. This paper describes the importance of the circulating load in wet ball milling circuits. It is characterized not only in terms of solids mass flow (or ratio of mass flows), but also by its other key physical characteristic, its size distribution. Its effect on grinding circuit performance is explained. The equipment application design steps to achieve a desired circulating load, in terms of both its mass flow and size distribution, are described. Finally, its pivotal role in grind control is specified. Our goal is for the reader to come away with a fresh understanding of the role of the circulating load in wet ball milling circuits, including how and why it should be measured and managed.

Feb 22, 2026

By Jean-Pierre Nossereau, Allen J. Hulshizer

The main thrust of this paper covers the design, installation techniques and experience associated with the installation of eleven 1.5 m (4'-11") and three 2.87 m (9'-5") diameter shafts in 15 to 23 meters (50 to 75 ft) of water over 1.6 Km (a mile) out in the Atlantic Ocean. The approach implemented, permits the use of pre-fabricated shaft linings and incorporates a safe dry-tap method for connecting the offshore shafts to tunnels driven blind from deep land shafts over 4.8 Km (3 miles) away. This tunnel-shaft system is a unique venture employed at the Seabrook Nuclear Power Station to meet plant cooling water requirements.

Jan 1, 1981

By Northcutt Ely

My topic today is our Nation's interest in the minerals beneath the oceans. I will state what I think should be our objectives, the means available to attain these objectives, and the obstacles to their accomplishment. It is possible that as early as this year of 1969 our country must make policy decisions on this subject, and that these, once made, will be almost irreversible. Two factors are hastening an. early decision. First, the 1958 Convention on the Continental Shelf becomes eligible for amendment after June 10, 1969, if the Assembly of the United Nations so decides. Second, the United Nations has created a permanent committee of 42 nations, which was preceded by an ad hoc committee of 35 nations, to study the question of the peaceful uses of the seabed "beyond the limits of national jurisdiction. While these measures purport to deal with the creation of a regime to govern mineral development on the deep sea floor beyond the limits of the jurisdiction of the coastal nations, it has become clear that the urgent issue is the extent to which this future regime shall acquire jurisdiction over the mineral resources of the continental margin, and receive royalties therefrom. This brings the proposal into potential collision with the interests of the coastal nations under the 1958 Convention on the Continental Shelf, including, of course, the United States.

Jan 1, 1969

By Dominc C. Torre

INTRODUCTION Rapidly increasing capacities of equipment used to load and handle material at the face require improved haulage equipment and better methods of transporting the mined materials or "muck" to the shaft or slope and out of the mine to the processing plant on the surface. Increasingly, those transportation demands are being satisfied with underground belt conveyors. Such con¬veyors provide the most readily available, most efficient, and most reliable method of carrying materials in a continuous and rapid flow from the face loading equip¬ment to the surface plant. Almost universally, belt con¬veyors are used in coal mines and those nonmetallic and metallic mines operating in relatively flat bedded deposits. Belt conveyors are available in a wide range of capacities, mainly limited by belt width, belt speed, and weight of the material to be transported. They can be used on the level, on grades, on the surface, or under¬ground. They provide a rapid and constant flow of material, transporting the material as quickly as it is mined. Length of belt conveyors is almost unlimited. Where the haulage distance exceeds the practical capacity of a single conveyor unit, two or more conveyors can be used in series. Single conveyors more than 1.6 km (1.0 mile) long are common; multiple-unit conveyors in series operation are transporting materials over distances exceeding 16.1 km (10 miles). Depending upon mate¬rials being transported, job conditions, cost of the terrain being spanned, and alternative haulage methods avail¬able, conveyors can be conceivably economical for even greater distances. Table 1 lists maximum belt speeds recommended for most materials, relating belt speeds to belt widths. Table 2 lists capacities of typical conveyors of various widths and speeds, transporting commonly mined mate¬rials of various weights. ADVANTAGES OF CONVEYOR SYSTEMS For several years after their initial introduction, belt conveyors were available only with rigid side frames or a supporting structure of steel and concrete. That con¬struction limited underground applications, due to the cost and relative inconvenience of extending or retract¬ing the belt conveyor in the confined underground environment. However, during the last 20 years, wire-¬rope side-frame belt conveyors, as shown in Fig. 1, have become widely used in underground applications. Even wider use can be anticipated with their application to the fast movement of materials in surface mining operations. Advantages of the wire-rope side-frame belt con¬veyors were realized first in panel or section belt haulage in coal mines. Soon afterward, use of those conveyors was extended to gathering and main-line haulage. The mobility of the wire-rope side-frame conveyor is the principal reason for its success. The conveyor can be extended, retracted, dismantled, moved, and reassembled easily, even in relatively confined under¬ground spaces. The intermediate structure consists of rope support stands, wire-rope side frames, wire-rope tie-off stands, and the necessary carrying idlers and return idlers. An important and very attractive feature is the ability to suspend the conveyor from the roof in an underground mine, as shown in Fig. 2, leaving more room for improved housekeeping and allowing passage of face-service equipment, haulage vehicles, and other mining equipment. The conveyor's open construction allows quick and easy visual inspection of its com¬ponents for failures or malfunctions; it also facilitates checking and correcting conveyor-belt alignment. Other advantages contributing to the attractiveness and widespread application of wire-rope side-frame conveyors in main-line, slope, and surface installations include: lower capital costs, lower installation costs, lower maintenance costs, reduced impact on idlers and belting, reduced spillage and minimal cleanup, improved conformation to undulating terrain or mine bottoms, and the ability to span most obstacles without heavy structural support. CONVEYOR CLASSIFICATIONS Underground belt conveyors are classified normally according to their function. Generally, conveyors are classified into one of four main categories: 1) Panel or section conveyors normally receive the material to be transported directly from the face-haulage equipment. 2) Gathering conveyors are secondary haulage units that usually receive material from two or more panel conveyors. 3) Main-line conveyors transport all the material mined in the underground operations to the slope or shaft. Normally, they receive the material from two or more gathering conveyors. 4) Slope conveyors generally operate in tandem with the main-line conveyor, providing continuous Table 1. Maximum Belt Speeds Recommended for General Use Run-of-Mine Hard Ores and Belt Width, Coal and Earth, Primary Crushed mm (in.) m/s (fpm) Stone, m/s (fpm) 356(14) 1.52 (300) 1.52 (300) 406(16) 1.52 (300) 1.52 (300) 457(18) 2.03 (400) 1.78 (350) 508(20) 2.03 (400) 1.78 (350) 610(24) 2.54 (500) 2.29 (450) 660(26) 2.54 (500) 2.29 (450) 762(30) 3.05 (600) 2.79 (550) 914(36) 3.30 (650) 3.05 (600) 1067 (42) 3.56 (700) 3.05 (600) 1219 (48) 3.56 (700) 3.30 (650) 1372 (54) 3.56 (700) 3.30 (650) 1524 (60) 3.56 (700) 3.30 (650) 1676 (66) 4.06 (800) 3.81 (750) 1829 (72) 4.06 (800) 3.

Jan 1, 1982

By N. B. Prenn

Many recent projects have been developed and mined based upon imaginary reserves. Imaginary or "geo-fantasy" reserves have cost many companies millions of dollars. The significant and varied technological advances in the mining arena have done little to curb reserve calculation problems. These advances may have served to increase the prevalence of reserve problems by putting more tools in the hands of personnel not properly trained or experienced in reserve estimation. This paper will discuss potential problems related to calculating reserves, which include: SAMPLING ERRORS -obtaining a representative sample. -Decay analysis of wet RC drilling -Bias introduced by sample preparation. -Assay bias; Coarse gold. -Specific gravity samples. GEOLOGICAL ERRORS -structural boundary definition. -Separation of high grade and low grade zones. -Incorrect continuity assumptions MODELING ERRORS -Too much influence of high grade samples. -Improper method of calculation. -Assumed range of influence. -Errors in the data. ENGINEERING ERRORS -Inaccurate assumptions. -Inadequate metallurgical testing. -Designed bottlenecks.

Jan 1, 1992

By Jeff Salai

The CP-3A contract is the final segment of the MWWST’s 28.3 km (17.6 mile)pressurized water supply tunnel for the metropolitan Boston area. The 1,288 m (4,226 feet) of U-shaped tunnel alignment passed through five rock zones employing four different primary support systems. The short tunnel began in Weston, Massachusetts, at Shaft 5A in soft, completely weathered argillite, passed through a fault zone, and ended in Dedham granite. An 18-foot diameter horseshoe starter tunnel was built to accommodate a 4.94 m (16-foot 2 1 / 2 inch) diameter Robbins TBM. Heavy water inflows were anticipated and subsequently encountered during probe drilling. Pre-excavation grouting was implemented at high pressures to displace high water inflows in the starter tunnel and consolidate the fault zone. This paper will provide an overview of the tunnel construction with an emphasis on ground control, grouting and survey control.

Jan 1, 2001

By R. O. Harma

Wet autogenous grinding is utilized in three iron ore concentrating plants operated by The Cleveland-Cliffs Iron Company (CCI). This paper will trace some of the development in converting from the use of metal grinding mill liners to the use of rubber and will update the current performance of rubber liners in these applications. The Cleveland-Cliffs Iron Company is a natural resources firm with major interests in iron ore mining and processing and oil and gas contract drilling. The company also has interests in oil shale, uranium, forest products, and Great Lakes shipping.

Jan 1, 1982

By J. L. Roll

The Surface Mining Control and Reclamation Act of 1977 (SMCRA) and the regulations promulgated for that "Act" have resulted in changes to surface mining operations in order to comply with the stringent federally enforced reclamation requirements for prime farmland. In many instances the operator has modified surface mining operations to meet the prime farmland requirements through changes to mining equipment operation, addition of new equipment targeted for reclamation or the use of totally different mining techniques. The major challenge to mine operators has been how to use existing mining equipment to meet the requirements of the "Act." Freeman United Coal Mining Company opened the first new large surface coal mine in Illinois following passage of the "Act." The Industry Mine, located near Macomb, Illinois started mining operations during March of 1982 and was required therefore, to meet all of the requirements of the "Act" including prime farmland restoration. At the Industry Mine a shovel and a cross-pit bucket wheel excavator (wheel) are used for overburden removal and the wheel is addition- ally utilized to assist in reclamation operations. The wheel mines the subsoil thereby elliminating scraper placement of that subsoil and the attendant compaction problems with scraper placed subsoil. The wheel is used to convey topsoil stock- piles from the highwall to the mined overburden in order to lessen scraper traffic and possible compaction on the graded overburden during top- soil removal and replacement. Close control of the operation of the wheel yields more uniform wheel spoil ridges which then require less grading prior to topsoil replacement.

Jan 1, 1986

By H. A. Taylor

Bismuth, one of the heavier chemical elements, is a pinkish metalloid that is chemically related to antimony. It is a byproduct of lead and tungsten extraction and, to a lesser extent, of copper and tin extraction. Antimony is a metalloid and less heavy chemical element, an extraction coproduct of metals such as lead, silver and gold. While both bismuth and antimony are metalloids, their major uses are as chemical compounds. The most frequently updated resources that always cover bismuth and antimony are the Bismuth Advocate News (BAN) and link at www.basicsmines/bismuth and the frequently updated Basics Mines Update blog at http://basicsmines-update.blogspot.com. The Bismuth wiki on Wikipedia also can be very helpful.

Jan 1, 2010

By D. Robert Weir, Verner B. Sefton

The reduction roast-ammonium carbonate leach-hydrogen reduction process for laterites has been under development by Sherritt Gordon for the past 20 years. The process can treat high iron or low iron laterites, with some process modification, and gives extractions of 88-93% Ni or 82-88% Ni, respectively. Five campaigns on a 1 tonne per day Pilot Plant and four campaigns on a 35 t/d Demonstration Plant have been carried out on laterite from three different deposits, and many other laterites have been investigated in the laboratory. The Marinduque Surigao Nickel Refinery in the Philippines was designed on the basis of this work. The process comprises roasting to selectively reduce the nickel and cobalt in the laterite, leaching the calcine in ammonium carbonate to dissolve the metals, recovery of cobalt by precipitation of a mixed metal sulphide, concentration of nickel from the carbonate solution by basic nickel carbonate precipitation and recovery of high purity nickel by hydrogen reduction of nickel from ammonium sulphate solution. Ion exchange has been developed as an alternative to BNC and for recovery of trace nickel from BNC barren liquor. Details of the development of some of the process steps through the laboratory to commercial plant are discussed. The process metallurgy has been confirmed in the commercial plant.

Jan 1, 1979

By A. G. Provost

On April 3, 1981, Harrison Western Corporation was awarded a contract by Amax Alloy - A Division of Amax Inc., to sink the Henderson #5 ventilation shaft. The project was located on the Henderson Mine site 88 kilometers west of Denver near the town of Empire, Colorado (Figure I). The Henderson No. 5 Shaft, located in an Alpine environment at an elevation of 3145 meters, was a 9.8 meter diameter concrete lined shaft with a total depth of 793 meters. Work started and continued with Harrison Western employees until January 15, 1982. At that time, Amax made the decision to continue the shaft-sinking with their own labor, and with Harrison Western providing supervision under a management service contract. Shaft sinking continued under this arrangement to October 1, 1982, at which time Amax put the Henderson No. 5 project on standby status until further notice.

Jan 1, 1986

By R. W. Bartlett

I first met Milton Wadsworth in 1951 as an eighteen year old junior taking his mineral processing course at the University of Utah. He guided my senior thesis, evaluating the then new polymer flocculants on settling uranium leached ore pulps. This was before ion exchange and solvent extraction. After my military service and a brief working stint at Kennecott he supervised my PhD work. He encouraged me to be active in AIME and its constituent societies, where both of us have been directors of AIME and presidents of TMS. He has been a consultant for research groups that I have managed. Above all, he has been my mentor and friend for nearly 45 years. Thus, I am honored and particularly pleased to receive 5MB's Wadsworth Award.

Jan 1, 1996

By W. D. Elston, A. E. McLaughlin, G. B. Hampton, W. L. Barham, J. F. Murphy, W. H. Cundiff, J. W. Mulloy, R. G. Breuer, J. W. Shaffer

Introduction Alumina (aluminum oxide) is the material from which all the world's aluminum is produced. In the Western World, all the alumina is made from bauxite by the Bayer process. In the nearly 150 years since aluminum was first isolated by Oersted, the metal has grown from a laboratory curiosity to a position of major importance in the world's commerce. In terms of annual production rates aluminum is first among nonferrous metals. Oersted's discovery-reduction of aluminum chloride with potas¬sium amalgam-was improved on by Ste. Claire Deville, whose so¬dium amalgam reduction of aluminum chloride led to the commercial production of aluminum in France in 1855. Ste. Claire Deville's method prevailed until 1886 when Charles Martin Hall and Paul T. Heroult each invented a process for the production of aluminum by the electrolysis of alumina dissolved in molten cryolite. The inven¬tion by Karl Josef Bayer in 1888 of an economical process for making very pure aluminum oxide (alumina) from bauxite established the necessary link between known ores and the Hall-Heroult reduction process. Bayer's work completed the scientific base-the ore bauxite refined to alumina by the Bayer process (U.S. Patent No. 515,895), the alumina reduced to aluminum in the Hall-Heroult cell (U.S. Patent No. 400,766--upon which today's aluminum industry is founded. Small-scale production of aluminum in the U.S. began in 1888 utilizing the Hall cell. By 1903, bauxite properties and a Bayer process refining step had been incorporated into the production activities. On this base the aluminum industry in the U.S. has grown at an annual compounded rate of 15%. Since 1946 the annual growth rate has been 10%.1 The rapid growth of the industry is the result of many factors among which are the existence of widespread bauxite ore deposits; a sound and economic production technology; and the properties of the metal-lightness, strength, ductility, good electrical and heat con¬ductivity, and pleasing appearance, which lead to ever greater de¬mands for aluminum in an industrializing society. At the inception of the industry, the only market that could be found for aluminum was in the production of cooking utensils. How¬ ever, the rapidly accelerating industrial and technological development of the Western World soon created new needs for aluminum, and today aluminum is marketed in a broad range of industrial, commer¬cial, and consumer applications. The principal uses for aluminum are:' building and construction, 22%; transportation, 18%; electrical, 13%; packaging, 11%; consumer durables, 10%; machinery and equipment, 7%; other, 19%. The 1974 production of primary alumi¬num in the world was 14.5 million short tons, which at an approximate ingot price of 40¢ per lb puts a value of $11.6 billion on the industry product prior to fabrication. While aluminum is widely distributed in the earth's crust and is a major constituent of many rocks and soils, to date no method of extraction of aluminum from such nonbauxite material has been brought to commercial practice in the Western World. In the USSR alumina is produced by the complex processing of nepheline syenite, but elsewhere all commercial production of alumina is from bauxite. A brief discussion of recent developments and other processes for alumina is included in the subsection "Other Processes for Alumina," page 19-15. In early 1973, a major U.S. aluminum producer announced the successful development of processes for the production of aluminum from aluminum chloride. This achievement promises to exert a major influence on the future of the aluminum industry. In the initial com¬mercial application of this new technology, Bayer alumina will be chlorinated, and the aluminum chloride then reduced by electrolysis. Important claims for the new processes are lower energy requirements (one-third less than obtainable in Hall cells) and reduced labor costs. Capital costs are said to be no greater than for conventional plants. While the announced intention is to produce the aluminum chlo¬ride from Bayer process alumina, the new chloride reduction process will eliminate the other raw materials, carbon and fluorides, required by the conventional Hall cells. The electrodes in the chloride cell will not be consumed on the reduction process and the electrolyte will have, as the name indicates, a chloride rather than a fluoride base. 2. Bauxite Definition and Origin. Bauxite is a naturally occurring raw material composed principally of a mixture of one or more of the hy¬drated aluminum oxide minerals gibbsite (Al2O2 3H2O), boehmite (Al2O3 H2O), and diaspore (Al2O, - H2O), and impurities of silica, iron oxide, titania, and other various elements in trace amounts. It is an end or near-end product of chemical weathering. Depending on the amount of iron impurities, the color of bauxite varies from dark red and brown to pink to white. Some bauxite is finely divided, free digging earthy material, while other forms are dense and rocky, requiring explosives in mining. Many gradational forms exist. It is one of the most variable of mineral raw materials in chemical composition and physical appearance. It is generally believed that bauxite deposits resulted from intense chemical weathering of aluminum-bearing rocks or formations under tropical or subtropical conditions with alternating wet and dry sea¬sons. Topographic conditions were favorable for drainage and the in-situ accumulation of aluminum, iron, and titanium oxides. There was low to moderate topographic relief with a minimum of erosion during long quiet periods in earth history.2 The occurrence of bauxite is widespread and it has been found on all continents except Antarctica. Production was reported from 27 countries in 1974, at which time total world production was over 79 million metric tons. Of this production 76% was from seven coun¬tries-Australia, Jamaica, Surinam, Guinea, USSR, Guyana, and Greece-which ranked in that order of production. In Table 1 are shown typical compositions of bauxite from some

Jan 1, 1985

By J. L. Vanderbeek

The SAG milling of ores with markedly variable grinding rates presents definite process control challenges. Decisions must be made regarding the selection of the most appropriate combination of mill volumetric load level, percent solids, and mill speed for the combination of ore types being processed at the moment. An investigation was performed concerning the effects of these parameters. General results are presented.

Jan 1, 1985