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By Jr. Smith

Silver-gold ratios were studied at the Tayoltita epithermal vein deposit using channel sample, channel sample line, stope, ore body and vein sample populations. The ratios are highly variable among individual channel samples (25:1 to greater than 500:1) with both high and low values randomly distributed within ore bodies and veins. Whole vein ratios for the fourteen most important ore producing structures range from 44:1 to 105:1, and show zonal distribution relative to two small granitic stocks, low values closest to the intrusives. The zoned nature of the deposit suggests that the stocks, apophyses of an underlying batholith of Late Eocene age, were the heat engines which powered the hydrothermal system responsible for ore deposition.

Jan 1, 1978

By Shiwei Wang, Ziwen Li, Chenhu Zhang, Peng Chen, Chengyong Wang

Accurate prediction of the partition coefficients in coal gravity separation is key to improving the preparation efficiency of coal and promoting its clean utilization. In China, the approximate formula method (AFM) has been applied to the calculation of coal gravity separation partition coefficients for decades, but its accuracy is limited. To improve the accuracy of the predicted partition coefficients, and thus the product yield of coal preparation plants, the present study proposes a modified hyperbolic tangent model to derive direct calculation formulas for the heavy medium and water medium separation partition coefficients. Four groups of coal samples were used to verify the accuracy of the direct formulas, and their predictions were compared with those of the AFM. The results showed that the partition coefficients and partition curves predicted by the direct formulas were closer to the actual values than those predicted by the AFM. Further, when the cleaned coal ash content was basically the same, the cleaned coal yield predicted by the direct formula was lower than that predicted by the AFM, and was also closer to the actual value. These results demonstrate that the direct formula produces more accurate results compared to the conventional AFM. As this formula has a reasonable theoretical basis, is simple to apply, and produces accurate results, it is expected to help improve the design and management level of coal preparation plants.

Oct 15, 2022

By J. A. Ober

"In 2016, the estimated value of total nonfuel mineral production in the United States was $74.6 billion, a slight increase from the revised total of $73.4 billion in 2015 (Table 1). Increased construction activity spurred increased production of industrial minerals, especially those used in infrastructure and residential construction. Although starting the year relatively low, prices for several metals, especially for some of the precious metals, began to trend upward. Decreased production of most metals produced in the United States, however, contributed to an overall decline in the value of metal production.Several U.S. metal mines and processing facilities were idled or closed permanently in 2016, including iron ore mines in Michigan and Minnesota; three primary aluminum smelters in Indiana, Missouri and Washington; one secondary zinc smelter in North Carolina; a titanium sponge facility in Utah and titanium mineral operations in Virginia. In addition, in May, the weekly average rig count for oil and gas drilling reached its lowest level since the 1940s when that measurement was first recorded. The reduced drilling activity resulted in decreased production of some industrial mineral products used in the drilling sector. Trends in mineral-related sectors of the domestic economy declined or held steady, except in the manufacturing of nonmetallic mineral products and nonferrous metals excluding aluminum, which increased. Overall, mining trended downward as the result of significant declines in coal mining, oil and gas extraction and metal mining (Table 2). Discussion of mine production is frequently segmented according to the type of materials produced within the broad categories of metals and industrial minerals (also known as nonmetallic minerals). Industrial minerals can be further subdivided as construction aggregates and other industrial minerals. Metals tend to have higher unit values but very low production quantities compared with those of industrial minerals, which have higher production quantities but are lower-valued materials, such as crushed stone or construction sand and gravel. Therefore, for discussion and analysis of the performance of the nonfuel minerals industry, the value of production is used rather than the tonnage produced. Tonnages of construction aggregates are orders of magnitude larger than those for most other mineral commodities thus making direct compar"

Jan 5, 2017

By U. S. Geological Survey Staff

"In 2017, the total estimated value of nonfuel mineral production in the United States increased by 6 percent from 2016 (Table 1). The value of metals produced domestically increased by 12 percent and the value of industrial minerals produced domestically increased by 3 percent. Some metal commodity values (cobalt, magnesium metal and palladium) increased by more than 35 percent in 2017 from 2016 owing to higher prices.Some U.S. metal mines and processing facilities remained idle in 2017, including three primary aluminum smelters in Indiana, Missouri and Washington; a titanium sponge facility in Utah and a byproduct vanadium production facility in Utah. In contrast, new gold mines opened in late 2016 and 2017 in Nevada and South Carolina, respectively, and iron ore mines in Michigan and Minnesota restarted or operated for the full year. In addition, increased oil and natural gas drilling activity led to increased production of some industrial mineral commodities that are used for oil and gas drilling. Production of some industrial minerals, especially those used in infrastructure and residential construction, remained essentially unchanged in 2017, a reflection of the limited growth in construction activity. The production of some metals, including iron and steel, aluminum and other nonferrous metals and nonmetallic mineral products increased. Overall, mining activity trended upward as the result of increases in coal mining, oil and gas extraction and metal mining (Table 2).Discussion of mine production is commonly segmented according to the type of materials produced within the broad categories of metals and industrial minerals (also known as nonmetallic minerals). Industrial minerals can be further subdivided as construction aggregates and other industrial minerals. Metals tend to have higher unit values but very low production quantities compared with those of industrial minerals, such as crushed stone or construction sand and gravel, which have higher production quantities but are lower-valued materials. Therefore, for discussion and analysis of the performance of the nonfuel minerals industry, the value of production is used rather than the tonnage produced. Tonnages of natural aggregates are orders of magnitude larger than those for most other mineral commodities, thus making direct comparisons based on weight meaningless (Fig. 1)."

Jan 5, 2018

By Caibin Wu, Bin Xie, Jiaqi Tong, Ningning Liao, Chong Zeng

Understanding the energy-size reduction relationship is vital to grinding process; therefore, this paper aims to show the energy-size reduction of magnetite-calcite binary mixture in a laboratory wet conical ball mill. Single magnetite, single calcite, and blended magnetite-calcite mixture at three weight ratios in four particle sizes were ground in a laboratory wet conical ball mill at four grinding time periods. The results showed that the particle size distribution of both fine particles and coarse particles of single and mixture ground product fitted well with the PSD computed by Rosin–Rammler-Benne function. The larger mass percentage of calcite is, the higher t10 of binary mixture ground product is. On the contrary, t10 in the mixture decreases as the percentage of magnetite in the mixture increases. The different breakage behaviors in blended samples are due to the hardness and particle size. The results of calculated ratio of energy absorption factor showed that the calcite consumed more energy in the breakage process of binary mixture than ground alone. The JK size-dependent breakage model based on the t10 method fits all the experiment data, be it generated from pure minerals, mixtures at different weight ratios, or each component separated from the mixture.

Jun 4, 2022

By G. V. Sullivan

The Federal Bureau of Mines examined tailings samples from 13 western copper operations to determine the potential for recovering rutile. Results showed that six of the samples contained sufficient liberated titania to be considered potential sources. One sample contained 0.75 percent Ti02 or 0.40 percent liberated rutile. Batch flotation studies developed a procedure that recovered 70 percent of the liberated rutile at a grade of 34.7 percent TiO2. Sulfuric acid leaching studies on 12 of the samples dissolved 100 to 2,200 grams Cu per ton of tailings; leaching of the slimes showed slightly more copper was dissolved, 1,800 to 3,300 grams Cu per ton of minus lo-micrometer material. Bulk sulfide flotation of nine of the samples resulted in concentrates that contained 0.38 to 2.0 percent Cu and 0.7 to 2.1 and 6.9 to 42.9 grams per ton Au and Ag, respectively.

Jan 1, 1981

By Sean Cassady, Jason Liu, Sanja Zlatanic, Taehyun Moon, Chris Devery

"For the Hollywood International Airport Runway Expansion Project at Fort Lauderdale, Florida, the structural fire durability analysis was completed for a series of tunnels formed by roadway and railroad cells located under the runway structure. A systematic design approach was developed to mitigate structural damage during a fire event and arrive at a practical method to structural fire engineering that is compliant to NFPA 502. To ensure the NFPA 502 requirements are satisfied, the performance based approach was implemented and the engineering analyses were performed for the adopted design fire event. The analyses considered the facility’s unique features including its fire safety systems to determine applicable design fire curves for structural durability analyses. The paper also outlines the process of defining the project specific fire curves for a specific design fire scenario and summarizes the results of heat transfer and structural fire durability analyses. This approach was aimed to assist the owner and Authority Having Jurisdiction to achieve practical decisions to the tunnel facility fireproofing.INTRODUCTIONFort Lauderdale–Hollywood International Airport (FLL) in Broward County, Florida is a major hub facility serving more than 23 million passengers annually. As part of the Airport Expansion Program, the South Runway (9R-27L) Expansion project aimed to meet ever increasing service demands via an increase to runway lengths. This necessitated the placement of one of the reconstructed runways on bridge structures over the existing U.S. Route 1 (US 1), a major north–south U.S. Highway that serves the East Coast of the United States, and the Florida East Coast (FEC) Railway, thus effectively creating multiple tunnel cells beneath the subject runway. For this project, HNTB suggested a tunnel fire damage mitigation system that would protect the runway major structural elements from the design fire event that may happen within the tunnel cells. This paper addresses the issues related to the fire event originating within the tunnel encompassing the US1 highway only, and deals with requirements of NFPA 502 [5] exclusively. Therefore, while approaching the structural fire protection issues for the specific tunnel cells beneath the runway structure, the requirements of the American National Standard NFPA 502 (Standard for Road Tunnels, Bridges, and Other Limited Access Highways, 2008 edition) were followed. Per this standard, regardless of tunnel length, all primary structural concrete and steel elements shall be protected in order to:"

Jan 1, 2016

By John G. Holmes

The generation of low cost power is but one phase of the TVA program for regional development. During the 36 years since TVA began, growth in its generation of electric power has necessitated a shift from a predominantly hydroelectric power system to a combination steam and hydroelectric system. The addition of steam-electric power plants to TVA's generating system was necessitated by the rapid increase in the traditional and defense demands for electric power in the 80,000-square-mile area served by TVA, the need to firm up the hydroelectric power, and the fact that all available sites for sizeable hydroelectric projects had been developed. At present TVA owns and operates 40 power plants--29 hydroelectric and 11 steam-electric plants. The total generating capacity of the hydroelectric plants is 3,105,430 kw, and the capacity of the steam plants is 13,951,135 kw. This provides a total generating capacity of 17,056,565 kw for the plants operated by TVA. Individual capacity of the 112 hydroelectric units ranges from 10,000 to 67,500 kw, and the individual capacity of the steam-electric units now in operation ranges from 60,000 to 950,000 kw. In addition to this generating capacity, TVA distributes the power from 6 U. S. Army Corps of Engineers hydroelectric plants on the Cumberland River. These plants contribute an additional 725,000 kw. Also, under an agreement with the Aluminum Company of America, TVA directs the stream flows and generation of their 423,715-kw system on Tennessee River tributaries and shares with Alcoa in the increased generation resulting from this coordinated operation.

Jan 1, 1969

By A. Festa

Secondary crushing often gets good press for its increases in energy efficiency and SAG milling rates but for a project considering this option the proposed benefits soon get overshadowed by implementation concerns. Reverse engineering from the published case studies is risky unless the reader understands the drivers impacting stability and operability of the circuit. This paper discusses the features of secondary crushing for Greenfield and Brownfield SAG mill grinding circuits. It is the author?s view that secondary crushing rarely adds value to a Greenfield project and restricts future expansion. Its application is best retro fitted to Brownfield operations where the benefit gained for capital expended is excellent. Two case studies are presented to reaffirm these statements. The first case study shows that the implementation of partial and total secondary crushing increases SAG mill power efficiency and it offers substantial incremental increases in milling throughput with staged capital investments for the crushing and grinding circuits respectively. The paper provides a critical analysis of process conditions for secondary-crushed grinding circuits, with particular emphasis on Brownfield circuit retrofits. Furthermore, the second case study quantifies the economic impact of secondary crushing on circuit design for plant start up and it illustrates the limit imposed on plant expansion.

Feb 23, 2014

By R. R. Beebe

Marcona Corporation produces about 3.5 million long tons of iron ore pellets annually on its two travelling grate pelletizing machines at San Nicolas, Peru. During 1969, these pellets will be shipped to customers in four marketing areas--Japan, the United States, Europe, and South America. All of these sales are on the open market, and product quality is a major concern. Typical chemical, structural, and quality test results for Marcona pellets are given in Table 1. [ ]

Jan 1, 1969

By Henry H. Roos

NTRODUCTION In the mining industry, a "drill jumbo" is a drilling unit equipped with one or more rock drills and mounted on a mechanical conveyance. Jumbos range from single¬drill ring drills mounted on simple steel skids to sophisti¬cated multiple-drill units mounted on diesel engine powered carriers and equipped with automatic controls and sound-abatement cabs. Individual types of jumbos usually are designed for specific tasks such as fan drilling in sublevel caving operations. Some units, such as development jumbos, can be utilized for several functions in addition to their normal applications, e.g., for production drilling in room-and-pillar operations, stoping in cut-and-fill mining, etc. Mine operators can purchase individual components from manufacturers, assembling these components into a jumbo suitable for specific conditions. However, this requires that mine personnel have good engineering and mechanical abilities. Although manufacturers of jumbos maintain facilities for designing machines to meet con¬ditions created by new mining methods and unusual ap¬plications, the cost of the engineering and experimental work for new types of jumbos should be evaluated in terms of both costs and benefits; it may be advantageous to plan the mining operation so that existing and proven units can be utilized. GENERAL SELECTION CRITERIA Since the operating conditions vary in underground mines, the design of a jumbo must be selected to cope with the individual characteristics of the mine. The necessary considerations include access space into the working areas, grades expected to be encountered, radii of the curves, ambient temperatures, the characteristics of the rock, the acidity or alkalinity (pH rating) of the mine water, etc. Access to Mine Workings The mine workings must be accessible to the selected jumbo. Frequently, a jumbo must be disassembled at least partially to pass through the mine shafts. There¬fore, a bolted construction allowing disassembly into pieces of suitable size and weight is desirable in most applications. Type of Undercarriage Generally, a crawler-type undercarriage should not be used in trackless mines having acidic mine water. The acidic water causes an electrolytic action between the individual crawler parts and causes rapid corrosion and early failures. Propulsion A two-wheel drive on a pneumatic-tired jumbo is marginal for grades exceeding 12%. A four-wheel drive unit with good weight distribution is capable of operat¬ing on grades of up to 35%. At least 30% of the gross vehicle weight (GVW) should be carried on the steering axle; otherwise, the steering tires may not have sufficient traction on loose road surfaces and may "plow" instead of steer. To assure stable operation in mines with steep grades, the height of the center of gravity of the jumbo should be considered. It should not make the unit prone to rolling over on the steep grades that may be encoun¬tered. Turning Ability In confined working areas, a skid-steering or crawler unit has the best maneuverability. An articulated carrier is preferable when base-rotated parallel booms are being utilized. A rigid-frame jumbo with automotive steering is compact and economical, having lower maintenance requirements than the other two types. However, the turning radius of a rigid-frame unit is wider than either the skid-steering or articulated units, and this wider turning radius may be detrimental in mines with narrow drifts. JUMBO COMPONENTS Rail Undercarriages A mine with a rail-transportation system generally utilizes drill jumbos that are mounted on rail-type under¬carriages. With a light load and good weight distribu¬tion, this carrier may consist of a simple two-axle four-wheel platform onto which the boom-mounting brackets are attached. As the depth of the round and the penetration rates increase, the weight of the equip¬ment installed on the chassis also increases. The greatest problem with a heavy overhung load is balancing the carrier; a three-boom unit may require a substantial amount of counterweighting to maintain an acceptable 70% to 30% axle-load balance. Although lengthening the wheelbase helps balance the unit, a long wheelbase increases the turning radius, often creating problems on curves and sometimes requiring a swivel truck-type chassis. A good rule of thumb for a simple four-wheel undercarriage is to maintain a wheelbase length to track gage-width ratio that does not exceed 2.5 to 1.0. For a larger ratio, a swivel truck should be utilized. Swing-out outriggers or roof jacks help keep a jumbo in place during the drilling cycle. Usually, a rail-mounted jumbo is not self-propelled. Instead, it is maneuvered into place by a locomotive. Occasionally, several headings are being advanced in close proximity, and a self-propelled jumbo is con¬venient. In electrified mines, such a jumbo utilizes conventional battery-powered traction gear; in dieselized mines, hydrostatic drive components offer good flexi¬bility. The tractive power requirements of a typical rail jumbo may be calculated from the formula: HP = [(RR + GR) X Sl/[33,000 X Em X Eh]

Jan 1, 1982

By R. Hogg

A standard procedure for determining size-specific gravity distributions of fine coal (including the -400 mesh fractions) by sieving and centrifugal sink-float separation is described. The significance of using a centrifugal sink-float technique and the effect of the magnitude of the centrifugal force on the separation of fine coal are confirmed in the present study. The relative merits of cumulative versus incremental sink-float are discussed. The procedure is evaluated quantitatively using data obtained for the products of froth flotation of -100 mesh coal.

Jan 1, 1994

By W. R. Bull

This paper examines water-only cyclone performance for the cleaning of fine coal, and the effects of changes in feed flow rate, feed pulp density, and vortex finder diameter. A model is presented for performance simulation which can be used to predict products obtained based on feed washability data.

Jan 1, 1987

By R. K. Mehta

Stirred ball mill feed used for ultra-fine grinding application requires fine size separation step in order to avoid over-grinding. This paper presents the selectivity curves obtained for oil shale and complex sulfide are using 460 mesh (30 micron) Derrick vibrating screen. Interestingly, the selectivity curves generated from the experimental data were monotonic increasing selectivity for oil shale but not monotonic increasing for sulfide ore. These non-monotonic increasing selectivity curves were similar to the mechanical air separator fishhook selectivity curves described by Luckie and Austin. A 2 stage classification in series model describing the fishhook selectivity curve has been used in proposing the classification mechanism for fine vibrating screens when heterogeneous multicomponent sulfide are undergoes size separation.

Jan 1, 1992

By Dale R. Ralston, Roy E. Williams, Gerry V. Winter, George L. Bloomsburg

The literature on four different topics is re¬viewed herein for purposes of mathematical mod¬eling of mine water inflow. The first of the topics reviewed is modeling of fissured or fractured ma¬terials; the second is general Darcy based flow models; the third is field methods for determining fracture flow properties; and the fourth is methods used presently for determining mine water inflows. The four topics are considered in the foregoing order. FRACTURE FLOW MODEL Two basic types of fracture flow models have been developed. The first type uses various tech¬niques for space averaging to obtain the equations. Systems are considered in which the porous media properties vary smoothly enough and the fracturing is sufficiently profuse and well distributed that the locally averaged properties are meaningful when viewed on the macroscopic scale. The final result is that a coefficient is used which is similar to saturated hydraulic conductivity and in many cases, simply is hydraulic conductivity. In other cases, the coefficient is apparent hydraulic conductivity be¬cause the response from flow in the fractures is more rapid than flow in the pore spaces. Faust and Mercer (1980) refers to this method as the contin¬uum approach. Some of the papers on this type of problem are by Duguid (1973), Verner et al. (1974), Owili-Eger (1975), Duguid and Abel (1974), duPrey and Weill (1974), and O'Neill (1978). Duguid and Lee (1977) also considered heat flow in the fluid and the porous medium. These papers all result in various types of computer programs. Some papers on this topic that do not result in computer programs are by Snow (1968, 1969) and Streltsova (1976). Some of the foregoing articles consider con¬solidation of the porous media and the resulting effect on hydraulic conductivity. Barenblatt et al. (1960) developed an analytical solution for fracture flow and discussed the time that is involved in the drainage process and the effect that fracture flow has on the drainage time. The second type of fracture flow model con¬siders the width of the fractures as a function of the pressure in the field. Faust and Mercer (1980) refers to this method as the discontinuum approach. This approach often requires two finite element programs that consider the stress in the material and the flow in the fractures separately. The pro¬grams are then linked to arrive at the final solution. Some of the articles that consider the interrela¬tionship between pressure and the size of the frac¬ture but do not use computer solutions are Gringarten et al. (1975), Narasimhan and Palen (1979), and Witherspoon et al. (1979). Papers that use a linked computer program between stress and flow are by Ayatollahi (1978), Gale et al. (1974), and Noorishad et al. (1971). Ayatollahi's program is primarily for the petroleum industry because it does not consider the effect of gravity. Ayatollahi assumes that pressure effects are very large in com¬parison to gravity effects. This assumption would apply only to very deep aquifers. Articles that consider fracture flow on a more applied basis are by Wittke et al. (1972), who con¬siders that the flow is entirely through fissures and negligible through the pores of the rock. Gringarten and Witherspoon (1972) developed type curves that may be used for analysis of fracture flow systems; the curves are based on the assumption that it is possible to distinguish between aquifers with hor¬izontal and vertical fractures and that it is possible to analyze the system as an equivalent anisotropic homogeneous porous medium with a single fracture with much higher permeability. DARCY FLOW MODELS The Darcy flow models of greatest interest to mine water inflow prediction are those which allow

Jan 1, 1986

By M. Morrongiello

The Kalgoorlie Consolidated Gold Mines Fimiston Open Pit is mining through a dense network of disused level workings and stopes of varied sizes and orientations. This study investigated the interaction between underground workings and the pit slope stability, in particular for the ultimate pit depth of over 600 metres. Parametric analyses were conducted on the structural and rock mass properties in order to provide realistic input. Several cases in both 2D and pseudo 3D using UDEC were modeled and analyzed to investigate the performance of the rock mass at various mining stages. The concept of equivalent property factor was also introduced to model the 3D behavior using 2D models. Based on the modelling results, the possible failure mechanisms and deformation of the pit walls were assessed. Factors of safety have been derived for the pit slope at different mining stages using the strength reduction technique. The modelling results agree well with pit performance monitoring results to date. The concept and results presented in this paper could be a useful reference for operations with similar circumstances and stress regimes.

Jan 1, 2005

By G. Bonifazi

Certain deposits of incoherent materials which are near the surface and exploitable by open-pit mining may be characterized in real time before they are mined through an analysis of ground-surface imagery. If the slice to be stripped is not overly thick, in fact, surface texture and color properties may be extrapolated to its entire thickness. Image analysis techniques to process ground surface images acquired in situ (or in the laboratory shortly after their acquisition) which yield pattern vectors representative of RGB color component distributions and HSB texture parameters have been developed. The techniques were applied to a mineral sandy ore deposit containing three different lithotypes. Geostatistical analyses showed that the data used to characterize the lithotypes were reliable. The correct recognition of the lithotypes was carried out using a multi-barycenter classification algorithm. Such in situ image-analysis procedures open the way to the proper selection of the ore to be mined, or the proper way for run of mine (r.o.m). processing, or the appropriate blend to be processed before or at the same time as the mining process itself is enacted.

Jan 1, 1999

By F. A. Schinner

The present study has investigated the leachability of cadmium sulfide minerals by Thiobacillus ferrooxidans and the electrochemical reactions involved in the process. Using a cyclic voltammetric technic and carbon-paste-CdS electrodes, it was found that the bio-oxidation of semiconductor cadmium sulfide minerals consisted of a number of intermediate electrochemical reactions. The overall reaction was found to be controlled by solid state diffusion as suggested by the chrono-amperometric and chrono-potentiometric measurements. The activation energy of solid state diffusion was determined by the Sand's method to be AE=24.3 kJ. A generalized mechanism was proposed for the bacterial oxidation of cadmium sulfide by T. ferrooxidan and an explanation given for the importance of high redox potential of leach solution versus the decomposition potential of the sulfide mineral. Furthermore, the effects of n-type or p-type character of CdS substrates relative to their bioleachability was discussed.

Jan 1, 1993

By F. F. Peng

For a given flotation system, the rate-controlling step in fine coal flotation can be the attachment of bubble to the fine coal particles. The probability of attachment depends upon the surface characteristics and the collector adsorption on the coal particle surfaces. Thus, to further improve the flotation rate and selectivity is to alter the distribution of hydrophobicity on coal particles efficiently by applying the effective means of collector dispersion. In order to enhance the combustible recovery and selectivity of fine coal flotation, and lower the amount of collector used in the fine coal flotation processes, four modes collector dispersion/addition techniques are tested. They are direct liquid addition in pulp (mechanical agitation), ultrasonic energy dispersed collector into pulp, atomized collector into pulp and gasified collector transported by air and formation of collector-air bubbles in pulp. The effect of four collector dispersion/addition methods on the floatability of -600 µ m (-30 mesh US sieve) coal samples from four ranks of coals were studied. The ultrasonic energy dispersed collector and atomized collector flotation processes enhance flotation yield and most significantly improve the kinetics of fine coal flotation. The gasified flotation process can increase the selectivity of separation and decrease the collector consumption due to starvation flotation is achieved in this process. The flotation efficiency of gasified collector process is as high as that of conventional flotation. It is because that the effect of the decrease in the combustible recovery is offset by the increase of selectivity. In addition to flotation experiments, induction times of bubble attachment to the bed of fine coal particles for four ranks of coals are measured.

Jan 1, 1992

By Staff

In 2012, the estimated value of mineral production increased in the United States for the third consecutive year. Production and prices increased for most industrial mineral commodities mined in the United States. While production for most metals remained relatively unchanged, with the notable exception of gold, the prices for most metals declined. Minerals remained fundamental to the U.S. economy, contributing to the real gross domestic product (GDP) at several levels, including mining, processing and manufacturing finished products. Minerals? contribution to the GDP increased for the second consecutive year. Trends in other sectors of the domestic economy were similar to those in mineral production and consumption rates (Table 1). After continued decline following the 2008-2009 recession, the construction industry began to show signs of improvement late in 2011 and throughout 2012, with increased production and consumption of cement, construction sand and gravel, crushed stone and gypsum, mineral commodities that are used almost exclusively in construction.

May 1, 2013