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By Ronald P. Geitgey

Pumice and volcanic cinder are volcanic rocks characterized by a cellular structure. They are formed as gases (primarily water) dissolved in molten rock, or magma, exsolve to generate a froth that cools and solidifies into rigid foam. The cells or bubbles are referred to as vesicles and they range in size from a few thousandth of a millimeter to several centimeters. Due to their vesicular character, both pumice and cinder have lower density and higher porosity than most other rock types, and, as the vesicle walls are broken, sharp cutting edges are continually generated. These properties are the basis for their commercial value as lightweight aggregates, insulators, absorbents, and abrasives. There is a certain imprecision in the terminology applied to volcanic products, reflecting to varying degrees the diversity of volcanic rocks, the relative youth of volcanology as a distinct field of study, and customs and practices of commercial trade. In general terms, pumice is light colored (white, gray, pink, pale yellow, or brown) and highly vesicular, usually with vesicle walls that are visibly glassy. Many pumice fragments are light enough to float on water. Pumice is readily cut by steel tools and some can be crushed by hand. Individual pumice fragments may range from 1 or 2 m in one dimension to c1 mm. Commercially, finer fragments are called pumicite or volcanic ash. In volcanology the term ash refers to any fragment c2 mm in size regardless of its composition. Cinder, or scoria, is dark colored (black, red, brown) with thick vesicle walls that appear dull or stony and that may exhibit iridescence. Cinder typically is heavier than pumice and has a higher crushing strength. In volcanology the term scoria refers to dark vesicular material throughout a wide size range while it is common commercial practice to use scoria for larger fragments (usually greater than 2.5 cm) and cinder for smaller fragments. GEOLOGY Composition and Physical Characteristics Most pumice is silicic ranging from 60 to 70% SiO2, that is, dacitic to rhyolitic in composition. Pumice of less silicic composition, including basaltic, occurs but it is less common and does not have extensive commercial use. Scoria and cinder are typically basaltic to andesitic with approximately 50 to 60% SiO2. Pumice and cinder may contain phenocrysts of feldspars and various ferromagnesian minerals that crystallized in the magma prior to eruption. Fragments of rock through which the magma has passed may be entrained in the melt and wall rock may be fragmented and admixed during an explosive eruption. Some scoria particles have lithic fragment cores. Phenocrysts and lithic fragments are relatively unimportant in cinder end uses but their presence may be detrimental in certain pumice products. Pumice typically has vesicles <1 mm in size separated by thin walls. Vesicle shapes include irregular, spherical, elliptical, and elongate to the point of being tubular with a silky appearance (Fig. 1). In some pumices, the vesicles are interconnected making the fragments permeable and highly absorbent; in others the vesicles are isolated forming a highly porous but very impermeable pumice. Floating masses of pumice fragments from the eruption of Krakatoa in 1883 were reported in the Indian Ocean for up to two years after the eruption. Vesicles in cinder are larger and range from spherical to highly irregular in shape with much thicker walls and abundant interconnections. Scoria and cinder are typically heavier, porous, and do not float. Density and hardness of pumice must be expressed precisely to avoid confusion. Density may refer to the glass itself, the apparent density of the vesicular pumice particle, or the bulk density of pumice in a deposit or in a product. Pumice glass has a specific gravity of 2.5 or more depending on its composition. Pumice fragments typically have a specific gravity of 4.0 and so will float on water, at least until enough vesicles are saturated to cause them to sink. Expressed as density, pumice fragments typically weigh less than 1 g/cm3. Depending on moisture content, particle density, and particle size distribution, the bulk density of pumice typically ranges from 500 to 700 kg/m3. Typical bulk densities of cinder range from 700 to 900 kg/m3 for material used as lightweight aggregate while the bulk density of cinder used for highways and railroad ballast may be considerably higher. Hardness in pumice may refer to the glass vesicle walls, possibly including crystals or lithic fragments, or to the apparent hardness of the particle as a whole, which is more a measure of the strength of the vesicle structure. Pumice glass typically has a Mohs hardness of 5 to 5.5. A pumice particle may have a much lower apparent hardness and be easily cut with a knife or steel saw because the vesicle walls break readily. Pumice and cinder are primarily pyroclastic deposits formed as fragmental products of volcanic eruptions. Several classification - systems differing in various details have been proposed for pyroclasts and pyroclastic deposits based on particle size (Fisher, 1961, Schmid, 1981, Cas and Wright, 1988). Generally, particles >64 mm are referred to as blocks or bombs depending on their shape. Particles between 64 mm and 2 mm (4 mm in some schemes) are called lapilli and smaller particles are called ash. These names may be modified by compositional terms, for example pumice lapilli or scoria lapilli. Most commercial deposits are composed of fragments in the lapilli size range. In the United States, pumice fragments having one dimension of 5 cm or more are legally defined as block pumice. The procedures for acquiring pumice from federal land are determined in part by this definition and are described in a later section.

Jan 1, 1994

By Aldino Campos, Frederico Carvalho Dias, Pedro Madureira, Patrícia Conceição, José Gomes-Pereira, Inês Tojeira, Andreia Afonso, António Calado, Luísa Pinto Ribeiro

Since 2008, the Portuguese Task Group for the Extension of the Continental Shelf has been operating the ROV "Luso" (rated for 6000m depth) for geological sampling of the deep North Atlantic seabed, performing surveys on, e.g., seamounts and hydrothermal vent fields. Amongst other sensors, the ROV is equipped with a full HD video camera with which still images of the deep ocean floor are recorded. Fixed on the ROV’s frame are two underwater "line" lasers, each generating a sharp green line (532nm) over the seabed. The two lasers are paralleled and calibrated at a set distance. Provided that the camera’s angle of view is known, numerical values for seabed surface area may be calculated using direct measurements taken from the pictures containing the laser lines. We present the corresponding main mathematical formulas, which are derived from simple geometrical considerations, and discuss how to generalize these results for an arbitrary camera tilt or pan. We present an example of application of our method by estimating values for percent coverage of rock substrate versus sediment. Our results are also relevant for determining seabed polymetallic nodule abundances from still images obtained during ROV surveys.

Sep 1, 2014

By Ernest Y. Baafi

This paper describes the results of a series of comparative studies in which polygonal, IDS, and kriging were compared for their local estimation accuracy. The specific objective of this study was to determine the impact that the particular nature of the mineralization has on the results of such comparative studies. The study was performed on simulated coal deposits and the evaluation parameter chosen was the coal thickness. For this study, many conditionally simulated deposits having different degrees of seam thickness continuity were first developed. Each simulated deposit covered an area of 30,000 ft x 30,000 ft which was, in turn, subdivided into 100 mine planning blocks of 3,000 ft x 3,000 ft in size. Thickness estimation was made for these mine planning blocks using surrounding DDH assays. In all cases tested, e.g., from a perfect continuity to a complete lack of continuity in coal seam thickness, kriging gave the best estimates among the three, followed by IDS and polygonal methods. As expected, the relative efficiency (i.e., superiority) of kriging over other estimators was highly dependent on the nature of mineralization.

Jan 1, 1982

By Francisco J. Escandon V.

Numerous lead-zinc-barite-fluorite ore deposits, with simple mineralogy and roughly concordant with bedding, are found widely distributed all over the world, having been denominated and well described as "stratiform deposits" or "strata-bound ore bodies", not having any genetic relationship. During several years, its origin has been discussed, without getting to general agreement regarding the main mining districts of this type. Through studies made of large stratiform deposits in the United States, Europe and Russia, it has been found that there are, within this classification, syngenctic diagenetic and epigenetic ore bodies. During the Symposium about the genesis of the stratiform lead-zinc-fluorite-barite deposits, carried out in New York in 1966, Frank G. Snyder (1), presented an excellent analysis of the theories of the origin of these deposits and of the evaluation of the criteria regarding classification. As per his definitions (Table 1), "a deposit is syngenetic if formed by processes similar to and simultaneously with the enclosing rock, epigenetic if introduced into a pre-existing rock and a diagenetic origin implies deposition of metals with the host sediments but with recrystallization, rearrengement and limited migration".

Jan 1, 1974

By C. RAMADINI, F. NURJAMAN, A. SHOFI, B. SUHARNO

In this work, the selective reduction of lateritic nickel ore was carried out using sodium sulfate, sodium carbonate, and sodium chloride as additives. The 5 wt% of anthracite coal, which contains 60.35% of fixed carbon and 1.9% of sulfur, was used as a reductant. All raw materials were mixed homogenously prior to the pelletization process into 10–15 mm of diameter. The reduction process was carried out to 50 g of pellets at 950 °C, 1050 °C, and 1150 °C for 60 min in a muffle furnace at atmospheric pressure. It continued with a wet magnetic separation process to separate ferronickel (concentrates) and impurities (tailings). Iron and nickel grade analysis was performed using XRF, while phase transformation and microstructure were analyzed with XRD and SEM–EDS. The results showed that the sodium sulfate was superior, resulting in the highest nickel grade in concentrate, i.e., 15.06%. The sulfidation mechanism, which could inhibit the metallization of iron, effectively increased the nickel grade in concentrate than decomposition of carbonate and chloridization process. The sulfur content in the reductant also influenced the selective reduction process. It promotes more sulfidation of iron, thus increasing the nickel grade in concentrate.

Jul 7, 2021

By R. R. Fernández

The Newmont roasting plant in Carlin, Nevada, commenced operating in December 1994. Over the years, refractory ores and pyrite concentrates from different gold deposits constituted the feed to the facilities. Historical plant performance indicated that the roasting temperature was the main variable affecting the structural characteristics of the calcine, which in turn affected the recovery of gold by cyanidation. Gold recovery as a function of roaster temperature has been closely monitored since October 2000. The original design temperature was 550° C. Lower roaster temperatures of around 500° C resulted in a gold recovery increase of more than six percent. This increase was directly related to an increase of the surface area of the calcine. The implementation of an ?intelligent? process control system helped significantly in achieving steady low roasting temperatures, thus obtaining high gold recoveries of 92 to 93 percent. Under these conditions, several roasting campaigns with high-arsenic-containing ores were conducted, which resulted in a significant decrease in gold recovery. The reduced gold recovery was caused by the loss of surface area (e.g., porosity) of the calcine as the arsenic content of the roaster feed increased.

Jan 1, 2010

By Matthew E. Eisenmann, Gerald H. Luttrell

Performance data from phosphate plants are often untrustworthy because of difficulties associated with highly variable feeds and unstable equipment operation. In some cases, this problem is further compounded by improper sampling procedures and unreliable laboratory analyses. Questionable data often lead to misleading conclusions that result in lost productivity and profits. Data reliability may be checked using mass balances, but the mathematics associated with this procedure can be overwhelming when multiple data sets or complex circuits are evaluated. To overcome this problem, a simple spreadsheet-based mass balance program has been developed specifically for plant operators. To use this program, operators simply enter a description of their circuit and input the assay values (e.g., % BPL, % Insol, etc.) for each stream. The program then generates the best estimates of the assay values and flags values that may be unreliable. The spreadsheet is specifically designed to be easy to use and requires no knowledge of statistics or programming. This manuscript reviews the mass balance problem and describes how spreadsheet programs can be used to evaluate plant data. An example problem involving the analysis of data around a two-stage phosphate flotation circuit is presented.

Jan 1, 2002

By F. P. Schwarz, A. J. Erickson, S. M. Weber

The Mount Hope stockwork molybdenum exposit, Eureka County, Nevada, occurs in a small igneous cauldron complex 32 to 38 mybp in age. The deposit is characterized by alteration zones and mineralized shells symmetrically distributed around multiple intrusives. For samples from the 25 000 meters of 1981-82 drilling, an appraisal of error in in-house sample preparation and in commercial assaying has been made. After splitting, drill core is crushed and reduced in volume (8:1 at 10-mesh, 8:1 at 70-mesh, 6:1 at 200-mesh) to supply 25 grams of 200-mesh pulp for replicate analyses. A 0.5 g portion of the pulp is used for dissolution and atomic absorption analyses. Factors which initially generated unacceptable data variances have been minimized by planning, repeat analyses, introduction of standards, and routine monitoring. Assuming that error between replicate assays defines a Gaussian distribution with its average ideally equal to zero, precision (from preparation including core splitting and analysis of 8400 pairs of molybdenum samples) is on the order of + 25%. The error distribution is not biased. Accuracy is approximately 4% lower than absolute as determined by replicate assays of commercially prepared samples.

Jan 1, 1992

By R. Fernández, E. Marczak, A. Collins

Newmont roasting plant in Carlin, Nevada commenced operating in December 1994. Over the years, refractory ores and pyrite concentrates from different gold deposits constituted the feed to the facilities. Historical plant performance indicated that the roasting temperature was the main variable that affected the structural characteristics of the calcine which, in turn, affected the recovery of gold by cyanidation. Gold recovery as a function of roaster temperature was closely monitored since October 2000. Original design temperature was 550oC. Lower roaster temperatures of around 500oC resulted in gold recovery increase by more than 6 percent. This increase was directly related to an increase of the surface area of the calcine. The implementation of an “intelligent” process control system helped significantly in achieving steady low roasting temperatures thus achieving high gold recoveries between 92 and 93 percent. Under those conditions, several roasting campaigns with high-arsenic-containing ores were conducted, which resulted in a significant decrease of gold recovery. The reduced gold recovery was caused by the loss of surface area (e.g. porosity) of the calcine as the arsenic content of the roaster feed increased.

Jan 1, 2007

By R. K. Mensah-Biney, M. T. Hepworth, K. J. Reid

The loading characteristics of gold-bromide species onto activated carbon were evaluated using a batch system. The overall loading of gold onto activated carbon was rapid for the first few hours, but it continued without cessation as a result of the reduction of gold. Therefore, conventional equilibrium considerations were not applicable. Although loading continued slowly after several days, an abnormally high, loading capacity value of 10-12 meq/g carbon (650-800 kg Au/t) could be attained in 72 hours. The loading of gold-bromo species by activated carbon was by the mass transfer of (AuBr4)- species to the external surface to be reduced to metallic gold by carbon. Elution of gold from loaded carbon was feasible provided the carbon had not been loaded to high capacity values. If loading is carried to high levels, complete elution becomes impractical, and the gold may be recovered by ashing the carbon. For the high loading capacities observed, this option would appear to be cost effective. The effect of several variables on the loading capacity of the activated carbon for gold-bromo species is discussed.

Jan 1, 1994

By K. Chief

American Indian lands contain a vast amount of renewable and non-renewable resources that have consequently been mined (Smith and Frehner). Therefore, it is understandable that tribes are concerned about environmental impacts from mining and their ability to minimize and mitigate these impacts. This has created a need to better understand mining and its environmental impacts. The University of Arizona Superfund Research Program Mining educational modules developed educational modules for tribal colleges focusing on environmental impacts of mining, remediation of mining wastes, and sociocultural impacts of mining. Educational modules are independently packaged units of study designed to enhance the learning process and can be modified and adapted to different learning scenarios and objectives. In addition to providing specialized knowledge, the modules feature hands-on activities, incorporation of technology, student involvement, discussion, and exchange of ideas. Modules will aim incorporate traditional ecological knowledge and approaches that promote effective science learning for native students. Modules are designed to augment existing associates of science programs (e.g. biology, chemistry) currently offered at tribal colleges and can be modified for use in K-12 education and for non-tribal audiences.

Feb 23, 2014

By D. Tao

The presence of insoluble slimes in potash ore poses a serious processing problem to the potash industry. These insolubles must be removed prior to potash flotation because of their high adsorptive capacity for amines which are generally used as collectors in the subsequent sylvite flotation. This is usually accomplished by scrubbing of the ore in brine followed by hydrocyclone classification to separate slimes from the salt particles. Insoluble slimes that remain in the ore after the desliming procedure are depressed by reagents such as guar gum or starch during sylvite flotation. In this research, the feasibility of using GP clay binders to replace guar gum for potash flotation was investigated. Batch mechanical flotation tests were conducted with the potash samples provided by a leading potash company. It has been found that GP clay binders increased potash concentrate yield and recovery at the same product grade. Effects on potash flotation efficiency of flotation process parameters such as impeller rotation speed, slurry temperature, binder type, dosage and conditioning time have been investigated to establish the optimum conditions for flotation. Binder GP374G33 has been identified as the optimum substitute for guar gum as slime depressant in potash flotation.

Jan 1, 2008

By L. Borsch

Geochemical laboratories are commonly criticized by geologists about poor analytical reproducibility and erratic anomaly patterns, especially when gold and trace metals from resistant minerals are reported. Geochemical analysis in mineral exploration is a compromise between high productivity on the one hand, imposed by large numbers of samples, and analytical precision and accuracy on the other. However, the physical properties of resistant minerals, such as cassiterite, gold, beryl, chromite, zircon and others, interfere with both of these requirements. Therefore, the degree of sample homogeneity that can reasonably be achieved in sampling and sample preparation must be considered. Subsequently, the understanding of its effects on analytical data quality and the consequences on data interpretation will provide a basis for understanding the problems common to exploration as an interdisciplinary science. Complaints about poor and inadequate analytical performance are not confined to exploration geochemistry. They are a common feature in mining and metallurgy and wherever sampling and analysis of "grains" are concerned - the "nugget" or "grain size effect." The "grain size" effect Poor analytical reproducibility is normal for gold and a well-defined group of other elements usually found in resistant placer minerals. Those who use and interpret geochemical data must realize and appreciate the chemical, the physicochemical, the physical and the mineralogical properties of the elements and their minerals. Especially for the "placer" minerals and their elements, such comprehensive interpretation is crucial. The most important factor to consider is the behavior of a mineral and its metal component(s) during weathering and their integration into the sampled medium, in exploration mostly sediments and soils. (Data interpretation for samples of water, gas, to a certain extent rock, follows different patterns.) A mineral may be chemically and physically stable or it may easily disintegrate physically or decompose chemically, or any combination of such processes, at varying degrees. The breakdown products, in turn, may or may not, interreact with the environment. If the nature of an element or a mineral predestines it for a heterogenous distribution in the sample medium, then nature, size and number of grains likely to occur should be considered in relation to the sample portion taken for analysis. This allows the estimation of their effect on analytical precision and accuracy. Elaborate and sophisticated statistical calculations exist on this subject. But these approaches do not cope with the complexity of the natural surface environment. The miner alogical, chemical and environmental behavior of elements and minerals can be estimated but not calculated. However, the mineral grain sizes and their influence on analytical precision can be precisely calculated if certain conditions, assumptions and idealizations are made. If the geochemical and mineralogical characteristics of minerals and elements are understood, such calculations demonstrate the grain (or nugget) effects that mineral properties and (geo)chemical behavior of minerals and elements cause on the precision and accuracy of geochemical analysis through their influence on sample homogeneity. Two other factors that influence the sample homogeneity and the nugget effect are the efficiency of sample preparation and the sample portion taken for analysis. In this way, certain element- or mineral-specific parameters can be established as a guide for the sampling program. The information, for example, may assist in determining sampling procedures in the field, especially the sample weight to be taken for "representative samples." Also, it may help assess whether analytical data, as provided by the laboratory, are acceptable. Finally, it may help determine the approach in data interpretation. However, all such simplified calculations are based on idealized, that is, unreal assumptions and conditions. As such, they represent one extreme end on the scale of probabilities. The reality is found somewhere away from this extreme, towards homogeneity. An example from a study of an eluvial gold prospect may be given for illustration: •Original sample weight: 20 kg (44 lbs) of rock gravel, crushed and ground to -0.18 mm (-80 mesh). •Au content: 20 grains of Au, average size of about 0.5 mm3 (0.03 cu in.) each = 7.5 mg each, making a total of about 150 mg Au in the sample = 7.5 ppm Au. Assumptions •Au occurs in the sample as free, discrete grains only. •Not more than one grain, if any, goes into each sample split (analyte) portion (20 grains of 7.5 mg Au each). •Analysis of original rock sample: 100 g sample for analysis, 20 kg/100 g = 200 samples 20 samples with 1 grain each: result, - 75 ppm Au. 180 samples with no grain: result, 0 ppm Au chances 1:9 •10 g sample for analysis:

Jan 1, 1996

By T. Resende, J. Sismour

"Signs in underground mines are subject to variable airflow, which carries dust and moisture. Dust buildup reduces their visibility, hampering production efficiency and safety. Underground workers commonly must stop to clean signs in order to gauge their location, or find critical supplies or services. There are currently a variety of coating products, including dust and water repellants, available on the market that have the potential to reduce dust accumulation on sign surfaces. This paper describes a preliminary study to determine their effectiveness. The study involved a practical testing protocol using a trickle rock duster and samples cut from a clean, used road sign. Product effectiveness, under both dry and wet conditions, was evaluated based on photographic evidence by comparing changes in sign luminosity after a period of rock dust application. By analyzing the frequency of different pixel luminosities on the dust-covered samples, both uniformity of dust coverage and the total amount of accumulation was assessed. Results indicate that at least one product may reduce the amount of dust buildup on sign surfaces and increase visibility. INTRODUCTION In all underground mines, visibility of signage is critical. Signs inform miners of their location, direction toward escape routes, and location of supplies. Over time, sign surfaces can collect dust and can eventually become unreadable. The rate of dust accumulation on surfaces is often particularly high in coal mines, where both mining (e.g., cutting and drilling) and rock dusting activities can contribute significant amounts of dust to the airways. Several factors may contribute to dust buildup on sign surfaces. First, basic principles of fluid and particle flow are at play. When a fluid travels past a stationary surface, the velocity of the fluid at the surface boundary is zero. If a very small dust particle moving with air collides with a surface, it does not immediately fall off since the air velocity is zero at the sign surface. (This is the same reason that dust can collect on a rotating ceiling fan.) Further, once the collision occurs, other mechanisms may help keep the particle there – including friction that resists particle falling due to gravity, and adhesive forces due to humidity and/or static charges the particle and others already on the surface. Currently, the most common way to deal with reduced sign visibility due to dust buildup is for mine personnel (e.g., a compliance foreman, supply worker) to periodically clean sign surfaces – usually just by wiping them with a cloth. As a regular activity, this solution is inefficient; in cases of emergencies, it can also pose unnecessary risks. Application of an off-the-shelf coating to sign surfaces may represent a simple yet effective way to reduce the rate of dust accumulation. There are currently a variety of products on the market that may be suitable for this purpose, including dust and water repellants."

Jan 1, 2017

By . A. Drouin, J. -M. Lalancette, D. Lemieux, C. Chouinard

"A gold bearing pyrite concentrate was treated at the demonstration scale (15 t/d) for the extraction of gold using a cyanide-free process. The pyrite was depressed in the flotation circuit in order to promote the flotation of copper and to achieve a sufficient copper grade to meet the copper smelter criteria. However, the recoveries of copper were 80% and only about 50% for the gold was found in the copper concentrate. The balance of the gold (50%) and copper (20%) contained in the pyrite concentrate as a reject from an overall flotation circuit. The gold grade in the pyrite concentrate is 5.40 g Au/t and copper about 0.77%. About 170 tons of pyrite concentrate were processed in the DST demonstration plant. The concentrate was first oxidized using a fluid bed to produce a calcine. Copper was then extracted as copper sulphate using diluted sulphuric acid. The residual solid was submitted to the DST chlorination process for gold extraction. Thereafter, the gold was recovered from the pregnant brine by precipitation over silica using DST proprietary process. The maximum gold recovery by chlorination was 90%. The average gold recovery by cyanidation of these calcines was 71%. INTRODUCTION Dundee Sustainable Technologies (“DST”) has developed a chlorination process as an alternative to the conventional cyanidation process for the extraction of precious metals from ores or concentrates. The technology offers viable and efficient gold recoveries and the ability to handle refractory ores and contaminated material (As, Hg, etc..). The process was successfully demonstrated on hundreds of samples provided by various mines, exploration and development projects and has evolved from laboratory experiment to demonstration at an industrial scale. DST’s chlorination process operates in a closed loop circuit, which implies that no liquid effluents are generated. The chemistry and process design allows precious metal deposits containing base metals to be treated viably. The tailings from the process are inert and non-toxic, sulphide depleted and thus non-acid generating. The efficiency of the process has demonstrated excellent gold recoveries within a fraction of the time needed for cyanidation to obtain similar results. The company completed in 2015 the construction of the first industrial demonstration plant operating with the DST technology. The plant has a capacity of 15 tons per day of mineral concentrate, and the ability to extract gold and silver utilizing DST chlorination technology. DST has tested its chlorination technology at demonstration scale on the refractory pyrite concentrate containing 5.40 g Au/t and 0.8 %copper. This auriferous pyrite concentrate, was by-product of copper concentrate respecting the copper smelter norms, is produced in a country where cyanide is prohibited and refractory to cyanidation. The pyrite concentrate was initially processed successfully (gold recoveries: > 90%) by the DST technology at laboratory (2011: 20 kg) and pilot (2014: 5 tons) scales to extract gold. About 170 tons of this pyrite concentrate were processed in the DST demonstration plant located in Thetford Mines."

Jan 1, 2017

By E. J. Jacques

A typical problem in ventilation networks with multiple fan systems is the possibility of them interacting. Multiple fan systems are no exceptions in complex tunnels, and may also be met in mines where underground fans are installed. When aiming at controlling a multiple fan system in a ventilation network, e.g. with a view to maintaining an acceptable air quality level, yet at minimum power consumption, transient flow conditions frequently occur. Although in most applications these transients are short compared to the time needed to achieve the planned actions on the ventilation, one should, however, keep in mind that it is important to avoid any bouncing effect between different (adjacent or distant) fan systems. Therefore a simulation of the unsteady-state flows could allow us to learn more about the propagation of transients within the network, and their possible secondary effects Among others, one question that often is raised, is to find out in which sequence and at what time schedule each of the fans in a network should e.g. be started up? Another typical problem, into which an unsteady-state simulation could provide some insight is the following: how should the facilities of variable pitch angle and/or changeable RPM of several fans operating in parallel be handled and combined in order to obtain a flow rate that changes gradually from zero to its maximum value i.e. the sum of the individual throughput flows of all the fans. The literature is not very abundant on the topic of simulating transient flows in networks. There is no doubt that numerical models have been developed (Pollak, Christensen, 1987), most of the time for particular applications (Wala, Kim, 1985), (Tanaskovic et al., 1984), (Schultz, Sockel, 1991), etc. The aim of this paper is to present a model that also simulates one-dimensional compressible flows in unsteady-state conditions with, however, the specific intent to handle networks with more than one fan. PROBLEM STATEMENT The mathematical model chosen to describe the unsteady flows in a ventilation network is based on the dynamic and continuity equations applied to each of its airways. The following basic assumptions are made : - the flow in the airway is considered to be one- dimensional, - - the flow is assumed to be fully turbulent, and hence the ATKINSON equation for calculating the friction losses will be applied. Whether this equation remains valid for transient state flows remains an open question. However, this may reasonably be assumed since the interesting flow frequencies are low. A discussion may be found in (Kämpf, 1987) ; - the airways are assumed to have a constant cross- sectional area along their length. If obviously this would not be the case, it is always possible to subdivide the concerned airway into sections for which the previous assumption holds. Applying the basic equations of mass and energy conservation, the flow in each branch may be described by the Euler equation for Newtonian flows.

Jan 1, 1995

By Dennis P. Bryan

Nevada is especially well endowed with industrial minerals, both in the number of ore deposits and the diversity of commodities. More than 600 significant industrial mineral deposits, containing 22 principal commodities, are present, in the State. The materials produced in Nevada in 1978 had a value of approximately 113 million dollars, and additional processing of some of them (e.g. gypsum into wallboard, limestone and clay into cement) added considerable more value. Table 1 shows the value of Nevada&apos;s industrial mineral production in 1978. Nevada currently supplies 85 percent of the country&apos;s barite producing 1.6 million tonnes (1.8 million short tons) valued at 30 million dollars in 1978. Nevada is second in diatomite production and contributes one-third of total lithium produced. Other industrial minerals being produced include clays, fluorspar, gypsum, lightweight aggregates, limestone and dolomite, magnesite and brucite, perlite, salt, sand and gravel, and silica. In general, Nevada produces high-value industrial minerals which are not consumed within the State, but rather, are shipped out of State. In contrast, most more populous states produce larger tonnages of lower value industrial minerals which are consumed chiefly within that state.

Jan 1, 1980

By Virginia T. McLemore, Abena S. Acheampong-Mensah

Critical mineral endowment of mine wastes in two mining districts in New Mexico (Copper Flat at Hillsboro and Carlisle-Center mines in the Steeple Rock district) will be characterized and estimated. “Beta-testing” of USGS procedures was performed. Potential critical minerals at these deposits include As, Bi, Te, Zn, Co, Ni, Mg, Mn, and fluorite. pH and particle size of samples were analyzed to determine weathering and migration potential of heavy metals. Soil pH was also measured to determine the potential for Acid Rock Drainage. The pH of the waste rock piles ranged from 3.66 to 5.67 which indicates fine- grained pyrite or sulfide oxidation. The samples collected from the tailings however, showed a different range of pH, from 6.30 to 8.62, probably due to the presence of carbonates. Difference in particle size fractions and its distribution along the slope are generally influenced by natural occurrences (e.g., gravity and pre-mining hydrothermal alteration) and operational activities such as material piling or dumping. Future work includes analyses of mineralogy and particle size correlation and estimation of critical mineral endowment of these mine wastes at New Mexico.

Feb 1, 2024

By R. F. Kovar, R. N. Torbin, R. E. Gundersen

I have to express my .surprise and must send a note of warning concerning the use of polyurethane foam as described in a paper by R.N. Torbin and R.F. Kovar, entitled "Innovative Shaft Lining Method," published in your February 1989 edition. In September, 1986, 177 miners lost their lives when they were exposed to fumes downwind from a fire in a tunnel lined with polyurethane foam. Whilst polyurethane exhibits reasonable fire retardent properties in small-scale tests, mass use in a tubular configuration, exacerbated by the furnace effect of cross-radiation, can lead to a rapid, uncontrollable conflagration. I do not wish these comments to detract from the engineering achievements of the authors but rather to sound a loud warning as to the application of the system. Any shaft designed for human access- be it for transport or shaft work - and any intake airway, should not consider the use of polyurethane foam. It only needs a slip with a cutting torch or an electric fault to initiate a disaster. Many countries have banned or restricted the use of polyurethane foam in the workings of a mine and maybe alternative foams (e.g. phenolics) can be used or developed

Jan 1, 1991

All aspects of precious metals processing were featured at a symposium held Oct. 3-6, 2007, at Loews Ventana Canyon Resort in Tucson, AZ. Although billed as "Precious Metals Processing: Advances in Primary and Secondary Operations," the symposium also looked at economic, regulatory and environmental issues affecting the precious metals industry. The symposium was sponsored by SME; The Minerals, Metals & Materials Society (TMS); and the International Precious Metals Institute (IPMI). It included workshops, technical presentations, guest speakers and social activities. Mining industry management, process engineers, equipment manufacturers, consultants, metals marketers, academics and others involved in the precious metals industry attended the conference. Needless to say, with gold nearing $25.721g ($800/oz) and platinum pushing $41.801g ($1,300/oz) at the time of the meeting, the mood among the attendees could not have been more positive. The symposium was privileged to have Father Ernest S. Sweeney, professor of Latin American History at Loyola Marymount University, as a guest speaker. Sweeney, a Jesuit priest, provided a colorful account of the history of mining in Arizona and the surrounding region of North America (Fig. 1). He described the importance of the mining industry and said, "To go down into the bowels of the earth to extract its riches for the benefit of all of us is an awesome task deserving our sincere respect and gratitude." However, he warned the industry that: "The ever increasing de¬mands on the mining community for the protection of the environment calls for endless efforts to maintain ethical standards in a business filled with risk, uncertainty and frustrations." Sweeney noted that the Spanish conquest of the Americas was driven by the three fundamental motives of "God, glory and gold." He noted that gold was the basic, most powerful driving force of the conquest and occupation of the Spanish empire. The first European to explore Arizona was the Franciscan missionary Marcos de Niza. He came to Arizona in 1539 in search of the fabled Seven Golden Cities of Cíbola. Sweeny noted that Spanish explorers were consumed, as Cortes himself described it, "with a burning fever that only gold could cure." Sweeney told the story of some of these early explorers, including Francisco Vázquez de Coronado who "mounted an expedition in pursuit of gold and rich empires to conquer." Coronado passed through Arizona and discovered the Grand Canyon. "Coronado returned to Mexico exhausted, bankrupt and disillusioned, but with a wealth of new knowledge of the borderlands of the Spanish empire," said Sweeney. He then described the colorful history of early gold, silver and copper exploration and mining in Arizona, including the famous tale of the Lost Dutchman&apos;s Mine. In a luncheon address, David Kanagy, SME&apos;s executive director, introduced the attendees to the upcoming OneMine. org Web site. Kanagy told the audience" One-Mine.org will be a collaborative digital library that will

Jan 1, 2008