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By Pradip

The development of highly selective mineral processing reagents, which are not merely metal-ion specific, but specific to the particular mineral surface structure, is essential for the exploitation of relatively more difficult-to-process ore deposits, in particular for the separation amongst minerals having the same constituent ion. Both the choice of the functional group as well as the molecular architecture of the reagent determine its selectivity. Several examples are presented in this paper to illustrate the concepts of structure specificity and molecular recognition at mineral surfaces - the concepts crucial to the advancement of the emerging science of reagents design. Recent advances made in the understanding of molecular interactions involved in the synthesis of biomineralized materials are discussed so as to delineate the utility of this approach in the design of selective reagents for mineral separation.

Jan 1, 1994

By F. N. Kissell, C. D. Litton

This study ranks the factors impacting survival during a coal mine fire. It has already been established that reducing time delays is the most important factor in saving lives. Consequently, every event during afire is measured in terms of its duration, and the effectiveness of any action taken to improve survival is measured in terms of the time it saves. By ranking actions according to time saved, these authors found that a combination of actions was most effective. This combination was: •installing lifelines, •moderately decreasing air leakage and •decreasing the fire growth rate. Changing ventilation leakage alone was much less effective, as was altering the CO (carbon monoxide), sensor alarm threshold. These results confirm an earlier fault-tree study on escape from mine fires. The fault-tree study had shown that, with the exception of delays, single-factor changes have minimal impact. Significant reductions in fire fatalities only take place with multiple factor changes.

Jan 1, 1994

By N. Edmonson

The demand for sulfur divides into two major categories: agricultural and industrial. Most of the agricultural demand is related to the production of phosphate fertilizer products. Industrial demand is derived from the demands for a large number of products and is related to a variety of industrial processes, no one of which characterizes it in a simple way.

Jan 1, 1994

By G. Sanders

Discussion by G. Sanders The studies reported on in this paper were initiated to draw attention to the severe contamination problem in the Section 30 drilling program at Chimney Creek. The lithologic-subset sampling study reached a different conclusion from that presented in your paper, and I wish to comment on your subsequent analysis of the data and your conclusions. Request for more complete data In the section on subsampling, you mention that the subordinate lithologies were separated and sampled, yet only the dominantlithology gold value is plotted in Fig. 4. In a contamination study, the reader is interested in the assay values for the individual subsets. Please include a table of the subsample assay data in your reply. Also, please indicate which analytical methods were used to arrive at the gold values in the subsampling study. Turning barren rock into low-grade ore Figure 5 is very revealing and typical of all of the cross sections in Section 30. Note the long strings of low-grade mineralization spread out for hundreds of feet below the ore zones. There were some very high gold values found in certain contaminated fractions during the subset sampling. The conclusion, here, was that the distinctive, strongly-mineralized dolomite layer was probably loose and crumbly and continued to disintegrate during drilling. This caused salting of the unmineralized rock samples below. Missing the high-grade part of the ore body In your statistical analysis, you directly compare the reverse circulation assays to the diamond drill assays in Section 30. Two points argue against a direct comparison and suggest the differences are greater than the 3 % that you report. First, any core loss in a gold zone most likely means that the true gold values are greater. The drillers lost significant amounts of the clay-rich, Section-30 gold mineralization. Also, the initiated salt-mud system, an attempt to improve the core recovery, met with little success. Second, the practice of not sampling core geologically, but instead sampling on even 5-foot intervals, adds a deliberate dilution to the core assay values by including a portion of nonmineralized rock in the first and last samples of each high- grade intercept. The result is often a pair of low-grade assay values on either side of a high-grade gold zone. In reality, a high-grade gold zone has a very sharp assay wall that is often bounded by barren rock. This sampling method may make the diamond-drill core assays more like the reverse circulation values and may help explain the statistical similarities you found. However, it does not represent the true gold values in the high-grade parts of the deposit. You cannot deny that, by careful geological sampling of the drill core, higher and sharper assay values will be obtained. The low core recovery and the diamond-drill-core sampling method used act together to lower the diamond-core assay values. The 3% difference you found between the reverse-circulation and diamond-core assay values could be much larger when you consider what the true diamond-drill core values would be with optimum core recovery and a geologic sampling method for the core. Should statistics have been applied here? The statement "... that reverse circulation holes have overestimated the values of some ore zones and underestimated the values of others" (p. 345) is not correct. The subsampling confirmed what the cross sections hinted at in Section 30. Namely, beneath the high-grade zones, the reverse circulation holes created, by contamination, large intercepts of low-grade ore in regions of barren rock. Because the low-grade material was not there to begin with, this is not a process of overestimating low-grade mineralization. The next statement that "the average result is similar to that of the diamond drill holes" may apply to the data set numerically, but it is not true when viewed spatially on cross sections. Adjacent reverse circulation and diamond drill holes are almost impossible to correlate, high-grade zone values vary widely and many low-grade intercepts make no geologic sense. The subset sampling and cross sections presented in the first part of the paper show that the reverse circulation portion of the data set has some serious problems, as highlighted above, and should not have been dealt with statistically at all. Conclusion Each ore body is different, and each drilling method presents unique sampling problems. In this case, the diamond drill is the

Jan 1, 1994

By G. Bonifazi

In the present work the possibility to utilize the morphometrical and morphological characteristics of an articulate solids system in a slurry flow to monitorate and to control a continuous process is considered. This goal has been reached by mean of an optical system able to acquire, to handle and to process the pictorial information derived by a suitable hardware architecture designed to realize the best lighting, focusing and sampling conditions for the examined flow stream domain. The procedure has been tested using different flow stream slurries coming from different sections of a beneficiation plant. A suitable strategy and a consequent software architecture has been set up in order to assure to the system the necessary speed and the stability to achieve correct on-line measurements and control.

Jan 1, 1994

By P. K. Berger, G. T. Lineberry, H. P. Cole, J. V. Haley

Sixty-five simulation exercises were developed for teaching and testing problem solving and decision making skills to miners and mining engineers. The exercises focused on judgment and decision making for preventing and controlling mine emergencies. The structure and field testing of the exercises are described, and sample frames of individual exercises are presented. Empirical data are summarized about the effectiveness of these simulations based on the performance scores of a national sample of miners and mining engineers.

Jan 1, 1994

By L. R. Duncan, W. H. McCracken

Magnesium is the eighth most abundant element in the earth's crust and the third most plentiful element in seawater. It is found in more than sixty minerals and in brines and seawater as a magnesium salt. One of the more important magnesium minerals is magnesium carbonate, MgCO3, with a theoretical maximum magnesia, MgO, content of 47.6%; this carbonate form represents the world's largest source of magnesia. The next most used sources for magnesia are magnesia-rich brines and seawater, where it occurs as magnesium sulfate and magnesium chloride. Other commercially important magnesium-bearing minerals are dolomite, CaMg(CO3)2, which serves the aggregate industry as well as the chemical industry; brucite, Mg(OH)2, which is used in the production of both caustic and sintered magnesia; olivine, ([MgFe]2-SiO2), which serves the refractory and heat storage industries; talc, (H2Mg3(SiO3)4), which serves several industries as a filler and as an ingredient in cosmetics; and serpentine, (H4Mg3SiO9). All these minerals are of commercial value because of the desirable characteristics given to them by magnesia and by its placement in the crystal structure. These minerals are the starting raw materials for a wide range of products. These include the production of magnesium metal, and several grades of magnesia used for the production of both sintered magnesia for refractory manufacture and lighter fired caustic magnesia, the latter is used in fluxes, fillers, insulation, cements, decolorants, fertilizers, chemicals, in the treatment of waste water including pH control, and in the removal of sulfur compounds from exhaust stacks. Magnesite is one of several major minerals possessing a dual character, i.e., non-metallic industrial mineral because of its principal end use as a calcined/dead burned raw material in non-metallic end products and magnesium metal. A large percentage of the magnesia used to produce magnesium metal comes from seawater1 brines. The total primary metal production worldwide is about 350 ktpy. This report reviews magnesite solely as an industrial non- metallic raw material. Magnesite for most refractory purposes must have a content of sintered magnesia above 85%, with a preference for those sources that have the potential for 90 to 98% magnesia values. Dolomite, used in large tonnages because of its physical properties in the construction industry, also has a use in the chemical and the refractory industry. In its calcined form, dolomite is used as a slag addition in the making of steel, and it is used in a high-purity calcine to precipitate magnesium hydroxide from brines or seawater. The precipitated magnesium hydroxide is intermediate for the production of deadburned clinker for refractories and the production of magnesium metal. In many cases the high-purity magnesium hydroxide obtained by precipitation with calcined dolomite, or in some cases limestone, has supplanted much of the world's production of magnesia from the natural mineral magnesite. This is especially true of the United States and in major industrialized areas of Europe and Japan. The best known of the minerals directly and widely exploited for its magnesia content is magnesite (MgCO3), one of the calcite group of rhombohedra1 carbonates, which includes calcite (CaCO3), siderite (Fe2CO3), and rhodocrosite (MnCO3), among others. The members of this group enter into a wide range of substitutional solid solutions when the positive ions have similar radii. The radii of magnesium and iron ions are within 6% of each other; hence magnesite and siderite form a complete series, of which the mineral breunnerite (ferroan magnesite) is a well known end member. The radii of calcium ion is 36% larger than that of magnesium ion and only limited substitution exists at each end of the MgC03-CaCO3 series. Dolomite is not a member of the calcite group, but it occurs when calcium and magnesium ions alternate in equal number in an ordered structure among carbonate ions. The result of this relationship is that calcite and dolomite are commonly found intermixed with magnesite. They occur, commonly, as identifiable crystal entities, which can be separated to a varying degree from the magnesite by benefication techniques. Magnesite, when pure, contains 47.8% MgO and 52.2% CO,. The pure mineral is found occasionally as transparent crystals resembling calcite. Magnesite principally contains variable amounts of the carbonates, oxides, and the silicates of iron, calcium, manganese, and aluminum. Although the genesis of natural magnesite deposits can be complex, it is distinguished in nature in two distinct physical forms, namely crystalline, (with a wide range of visible crystal sizes) and cryptocrystalline, sometimes referred to as amorphous, where the crystal size is not detectable to the eye and will range from 1 to 10 pm. The two types not only differ in crystal structure but in the sizes of the deposits and in modes of formations. The crystalline form has a Mohs hardness of 3.5 to 4.0. The color range is from white to black with shades of yellow, blue, red, or gray. The color is not a significant indicator of purity but in a given deposit an experienced person can often roughly grade the magnesite by observing color and crystallinity. Macrocrystalline deposits occur in relatively few, but generally large, deposits on the order of several million tons. The ore shows a marble-like crystal structure and belongs to the sedimentary or metasomatic groups of origin. The cryptocrystalline variety of magnesite frequently occurs in many small deposits, although there are exceptions. Cryptocrystalline magnesite is typically massive with no cleavage and is sometimes descriptively called bone magnesite. The fracture is usually conchoidal, with a hardness of 3.5 to 5.0. The color is mainly white, but it can have tints of yellow, orange, or buff. Accessory silaceous minerals such as serpentine, quartz, or chalcedony are usually present. Calcium minerals are normally absent or in low concentration, this contrasting with the macrocrystalline form where calcium minerals are almost invariably present and some- times in high concentration. The specific gravity of cryptocrystalline magnesite ranges between 2.90 and 3.00, whereas the value of pure crystalline magnesite is 3.02. In actuality, the normal specific

Jan 1, 1994

By B. J. Arnold

Coal blending inherently means homogenizing a mixture of coals so that the properties of the blend meet some specifications for maintaining power plant performance and emission requirements. In practice, however, coal blending is, at best, coal mixing. The degree of blending sophistication required depends on the reason for coal blending in the first place. If it is to maintain fuel characteristics that will diminish the chance of slagging and fouling, then some swings in variability may be tolerated at some power stations. However, if emissions limits are the issue, then more sophistication may be needed. Emissions limits are becoming stricter with requirements to meet averages for shorter time frames (hours and days instead of weeks and months). These restrictions require closer control over the quality of the blend being fed into the bunkers at the station. Even scrubbed units should have a consistent quality of fuel as feed so that sorbent additions can be minimized. To meet these challenges, engineers must consider available equipment and control techniques and the properties of the parent coals when evaluating new blending systems.

Jan 1, 1994

By J. W. Hawkins

Understanding aquifer properties in surface mine backfill is essential for managing the groundwater flow system as well as controlling the formation and discharge of acid urine drainage. Slug tests (injection and withdrawal) performed on wells in mine spoil may yield two distinctly different response characteristics. One type of response is indicative of a porous media system. The second type of response indicates the presence of a pseudokarst system. The presence of voids or conduits in the backfill is indicated by an almost instantaneous partial recovery of the water level displacement. This rapid recovery is turbulent flow and cannot be analyzed by conventional (Darcian) methods. The turbulent flow may cause the calculated hydraulic conductivity to be less than the actual values. The slug dissipation surface area created by the voids contiguous to the test well add to the known dissipation surface area of the screened interval. This can cause the calculated hydraulic conductivity to be greater than the actual hydraulic conductivity or the aquifer to appear more permeable. Whenever analyzing data from aquifer tests in mine spoil, these potential problems must be kept in mind. In spite of the problems encountered during slug testing of spoil, the aquifer hydraulic parameters derived and the slug responses observed remain useful in the hydrologic characterization of a mine site.

Jan 1, 1994

By R. Mensah-Biney

The kinetics of loading of gold from bromide solution onto an anion exchange resin, PAZ-4, were investigated in a batch stirred reactor. The initial loading rate was described mathematically by a first-order reaction rate equation. The effect of agitation speed, temperature, resin particle size, resin concentration, initial concentration of gold and bromine in solution on the rate was investigated. The model described fairly accurately the loading process in terms of the variables investigated. The rate constant for the initial loading ranged from 0.5 to 1.3 x10-3 sec-1 and the half-time was 9.3 to 56 minutes. The initial rate constant increased with increasing temperature with an activation energy of 15.7 kJ/mole (3.8 kcal/mole). The rate constant was directly proportional to the concentration of the resin in solution. The subsequent reduction reaction was also modeled by the first-order rate equation and the apparent rate constant was estimated to be 3.0 x 10-6 sec-1 with a half-time of about 44 hours.

Jan 1, 1994

By R. W. Smith, A. M. Raichur, M. Misra

Mycobacterium phlei has very good potential as a hematite flotation collector. The flotation recovery of hematite is dependent upon the solution pH and concentration of the microorganism. The critical pH for maximum recovery of hematite is around three, which corresponds to the point of zero charge of the microorganism. An excellent correlation between the flotation recovery and bacterial adhesion on hematite is observed. The adhesion of Mycobacterium phlei on hematite can be described by the potential energy of interaction calculations using an extended DLVO theory.

Jan 1, 1994

By Palmer C. Sweet

Kyanite. andalusite, and sillimanite are anhydrous aluminum silicate minerals, and they have the same chemical formula, Al2SiO3. Dumortierite and topaz are also classified as aluminum silicates although they contain boron and fluorine respectively. Mullite (a rare mineral named for its discovery site, the Scottish island of Mull) is produced when kyanite, andalusite, or sillimanite are heated. Synthetic mullite, also classified as an aluminum silicate, is formed by melting alumina and silica, bauxite, and kaolin or alumina, kaolin, and kyanite, depending on the type of synthetic mullite desired. These materials are either sintered in rotary, periodic, or tunnel kilns, or fused in an electric arc furnace. The world's largest producer of kyanite is the United States. Domestic kyanite is presently produced from one company at two sites in Virginia; Kyanite Mining Corporation mines kyanite from Willis Mountain and adjacent East Ridge in Buckingham County in the central Piedmont province of Virginia. Internationally, kymite is produced in Australia, Brazil, India, Kenya, Sweden, and Zimbabwe; the former USSR also produces kyanite (Fig. 1). Andalusite is produced by Piedmont Minerals Company, Inc. in the Piedmont province near Hillsborough, NC. Andalusite is also produced in France, India, the Republic of South Africa, and Spain (Fig. 1). Sillimanite is produced in Australia, Brazil, India, Spain, and the Republic of South Africa; the former USSR is also thought to be a major producer (Fig. 1). Some of the countries produce only for domestic use. Synthetic mullite, made by sintering and by electric arc fusion, is produced by Mulcoa (Mullite Company of America) in Andersonville, GA, and by Washington Mills Electro Minerals Corporation in Niagara Falls, NY. Annual world production of kyanite, andalusite, sillimanite, and synthetic mullite is approximately 672 727 tons (Potter, 1988). GEOLOGY Mineralogy Kyanite is a blue to light-green, triclinic mineral that occurs in long, thin-bladed crystals and crystalline aggregates in gneiss, schist, and pegmatites. The mineral has a hardness of 5 parallel to the long axis of the crystal and a hardness of 7 across the crystal. Andalusite is a yellow, brown, green, or red orthorhombic mineral that occurs in thick, almost square prisms in schist, gneiss, and hornfels. Gem quality andalusite exhibits a strong pleochroism; brownish-green in one direction and brownish-red perpendicular to it. Andalusite also occurs in placer concentrations where it has weathered out of rock. Sillimanite is a brown, pale-green, gray, or white orthorhombic mineral that occurs in long, slender, needlelike crystals in schist and gneiss. Chemical and Physical Properties Chemical and physical properties of kyanite, andalusite, and sillimanite are noted in Table 1. Kyanite is the only mineral that irreversibly expands when heated (calcined to produce mullite) and may offset the shrinkage of most ceramic or refractory ingredients when heated.

Jan 1, 1994

By D. Gove

All mining operations using trucks have a common need to properly match the number and size of hauling units (trucks. wagons. scrapers. etc.) to a loading unit (wheel loader. hydraulic shovel/excavator, cable shovel. push tractor. etc.) to provide the best possible fleet match. Optimizing fleet match minimizes the cost per unit of material moved by that fleet. As haul conditions change (haul length. grade. or rolling resistance), there may be need to adjust the number of trucks to maintain the optimum fleet match. Fleet Production and Cost is a tool which, among other things, can be used to optimize the truck-loader match.

Jan 1, 1994

By H. Lyn Bourne

Daily everyone depends on the great variety of glass products, so much so that glass is often taken for granted. In fact most people do not realize how versatile glass has become. Consider the various uses and then try to imagine a day in which we are not influenced by glass. Common uses include container ware, table ware, window glass, lead crystal, automobile glass, and fiber glass. Several less common, but important, uses include laboratory ware, pharmaceutical, TV bulbs, light bulbs, glass ceramics, optical glass, fiber optics, and laser glass. Corning, Inc., a leader in specialty products, uses nearly 1 000 different compositions to manufacture about 60 000 different products (Edwards and Copley, 1977). Glass is such a complex product that-definitions vary and exceptions can be found for most definitions. Glass is an inorganic amorphous (non-crystalline) solid. Most glasses are produced by melting of a mixture of oxide raw materials, and then cooled to room temperature. Soda-lime-silica composition.s account for about 90% of all glasses melted (Anon, 1973). The properties of the glass product come mainly from its chemical composition. All of the different glasses require melting a combination of raw materials and forming the molten material into the desired shape. Both the melting and the forming processes use sophisticated technology and these technologies require experts to manage these production systems. The manufacturing process is continuous and takes place in tonnage quantities, so adjustments in the batch to achieve the desired finished product requires a great deal of expertise. Raw materials are fed to the batch mixing area in very large quantities (tons in most cases). As a result, impurities in the range of 0.1% result in addition of that impurity within the molten glass in kilogram amounts. More than twenty different industrial minerals are consumed in the manufacture of various kinds of glass (O'Driscoll, 1990). This chapter describes the major and minor ingredients of the various glass batches. It discusses the roles of the various oxides in the glass batch and most importantly considers the mineral raw materials which supply the glass industry. Each of the raw materials is described in detail in other chapters so the geology and mineralogy sections are kept brief here. Container glass, by far, accounts for the most production; followed by flat glass, fiber glass, and specialty glass of which table ware accounts for the greatest tonnage. [Table 1] shows the general production data for 1987 through 1990. Statistics for many of the uses do not appear because production volumes are small compared to the major uses. The glass industry is organized in four categories: containers, flat glass, fiber glass and specialty glass. The US Department of Commerce, Bureau of Census, publishes production data about the glass industry in three different categories: 1) glass containers, 2) consumer, scientific, technical and industrial glassware, and 3) flat glass. The Bureau has very complete statistics about the glass industry in these three categories but they report production data in different units according to industry standards. Therefore, [Table 1] gives the production data in dissimilar units. The production of most glass articles follows similar steps. The raw materials are mixed and the resulting batch is fed into the furnace. In soda-lime-silica glasses melting begins between 600 and 900°C. At these temperatures CO, and other gasses are released which create bubbles in the molten glass. To remove the bubbles and insure complete melting the temperature is raised to between 1 500 and 1 600°C. This is the melting-refining stage during which the refining agents in the glass batch serve to aid in the release of gas bubbles, homogenize the melt, and prevent the formation of scum on the surface of the molten liquid. At the conclusion of the melting-refining stage the glass is too fluid for working and the melt is cooled to about 1 100°C to attain the proper viscosity for working and forming to begin. After the glass article has been made, it must undergo annealing (slowly and uniformly reheated and cooled) to remove thermal stresses that were created during the forming process.

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 A. R. Laplante

A novel methodology to estimate gold recovery by gravity is presented. The methodology makes use of a population balance model which represents gold liberation, breakage and classification behaviour and applies pre-concentration and recovery performance curves to gravity-recoverable gold to predict overall recovery. Derivation of the necessary parameters is explained and demonstrated using data from an actual gravity circuit and one projected application. The methodology makes it possible to estimate the performance of circuits with large gold circulating loads and relatively low unit recoveries (e.g. jigs), or with high recoveries on a bleed of the circulating load (e.g. Knelson concentrators).

Jan 1, 1994

By K. F. Unrug

Fractures of sedimentary rocks in the vicinity of the outcrop are commonly encountered around the world. Mine highwalls and numerous highway cuts give excellent views for detailed study of surface fractures. This paper gives an explanation of the origin of fractures as well as characterization of the distribution and extent of joint system with reference to lithologic composition of the rocks. Practical implications of the joint system affecting mine operations are described. Among the subjects discussed are: discontinuous deformation as an effect of surface subsidence, stability of mine portals and near outcrop underground operations, and stability of highwalls, when using highwall miners and strip operations. Some design procedures are recommended that can minimize the problems encountered in mining areas with intense joint systems.

Jan 1, 1994

By B. E. Penrod

The main constituents of flat glass are the eight commonest elements of the earth's crust. Five of these, silicon, sodium, calcium, magnesium and oxygen are essential. Two more, Aluminum and potassium have beneficial properties. For colorless glasses iron is undesirable, in standard clear glasses a small amount of iron is tolerable, while for most tinted glasses iron is essential. These elements are present in glass as oxides and because they are so common there is no foreseeable resource shortage. The availability of supplies of materials at particular sites at prices which enable a glass manufacturer to be competitive may be another matter. In this paper it is intended to provide a historical perspective to the current situation, to contrast some of the traditional North American and European practices, and to progressively review some of the driving forces for future change and to attempt to assess their effects upon both raw material supplier and consumer.

Jan 1, 1994

By H. Lyn Bourne

The is the 13th year for this column and the 12th in which the royalty data have been tabulated. There still exist some holes in the list of royalties that readers hopefully will fill. The most common mineral commodity is construction aggregates - either sand and gravel or crushed stone. In spite of their pervasive use nationwide, there are states from which the author has no information about royalties for either of these commodities. The reader can help - share information about these missing states and next year there will be fewer states without information. Severn Brown again sends helpful information from the Prospectors and Developers Association of Canada (PDAC). The PDAC Digest contained an article that distinguished between ‘net smelter return royalty' and ‘net profits royalty’ (Haase). The article also lists clauses and details that Brown suggests should be included in a net profits royalty contract.

Jan 1, 1994

By Staff

Assembling consistent data for a 40-year time series is a challenge because of the many changes that have occurred in this period. In many cases, because of process improvements and consumer requirements, grades of materials change in a 40-year span. This can lead to a wide fluctuation in price data simply because of increased costs for premium grades. Sources for obtaining price data can also change during a 40-year period. Changing the data source also introduces anomalies in a time series. In some cases, published price data are not representative of the real value of the material and provide little basis for further analysis. For some industrial mineral commodities, there are only a few producers, and value and production data are considered proprietary. In the data presented in this chapter, every attempt was made to ensure that the data were as consistent and representative of the industry as possible. However, the factors mentioned above may have introduced inconsistencies in some of the data series. Many different factors influence trends for industrial minerals because of the diversity of end uses for these commodities. Trends in production and prices for most of the industrial minerals can be related to one or more of the following: changing demand or technologies in end-use industries, development of new end uses, the effect of environmental regulations, production and processing technology changes, energy costs, foreign competition and substitution by other materials, and production as a byproduct of other minerals. World economic conditions, such as recessions and inflation rates, also play a part in some production and price trends. Data for 40 years of production for industrial minerals in the United States are presented in [Table 1] in 10-year increments. Unit values for the industrial minerals, in actual and constant 1990 dollars, are shown in [Tables 2 and 3].

Jan 1, 1994