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By Nicholas J. Grant, William H. Ferguson, Bill C. Giessen

Ta-lr alloys have been examined over the complete range of compositions using metallographic and X-ray techniques. The terminal solid-solubility limits, solidus temperatures, and intermediate phases were determined. There are four inter-mediate phases: o, tetragonal, analogous to a (Fe-Cr); 0,. orthorhombic; az, tetragonal; and a TaZr,, cubic, AuCu, structure. Of these, o and a, melt peritecticaLly, a, decomposes peritectoidally, and a TaIrs has a congruent melting point. Three peri-tectic and one eutectic reactions occur. 1 HE Ta-Ir phase diagram has not been treated in the literature. Intermetallic phases and terminal solid solubilities have been described and estimated.'-4 The previous findings have been confirmed in this work. A complete diagram with additional phases and solidus curves is presented. EXPERIMENTAL METHODS Starting materials were tantalum powder of 99.8 pct purity, supplied by the National Research Corp., Cambridge, Mass., and iridium powder of 99.9 pct purity, supplied by the Bishop Co., Malvern, Pa. Both powders were -200 mesh. Table I lists the analyses as given by the suppliers. A standard procedure was employed in making the alloy buttons, which was described in detail in Refs. 5 and 6, and which included repeated arc-melting of powder compacts and determination of the composition by the weight-balance method. This is especially justifiable due to the similar vapor pressures of tantalum and iridium. In the critical parts of the diagram, a spacing of 1/2 at. pct was used, based on premelted master alloy material. The observed structures and X-ray spectra were consistent with the composition sequence of the alloys. Table II lists the final alloy atomic percentages with the calculated percent error of composition. Cross sections representative in grain size and composition were selected for the study, as described in Ref. 5. Based on prior experience, no contamination from the tungsten electrode was considered. Temperature measurements were obtained using a Leeds and Northrup optical pyrometer and have been described extensively in Refs. 5 and 6. All heat treatments were made in the high-vacuum tantalum tube furnace mentioned in Ref. 5. Samples annealed in tantalum containers cooled from 1800" to 1000"~ in 5 sec; those annealed in ceramic crucibles cooled over the same range in 15 to 30 sec. The thermal treatments are listed in Table 111. All specimens were homogenized at 1735°C for 24 hr. Tantalum-rich compositions were treated in tantalum buckets. Iridium-rich compositions were annealed in tantalum buckets below the eutectic temperature of 1950°C; up to 2200°C, tungsten-lined tantalum baskets were used; and above 2200°C thoria crucibles were used. It was found that refractory oxides (in early stages of the investigation alumina crucibles were used up to 1800°C and thoria crucibles were used to 2400"~) give off minute amounts of oxygen and thereby influence the microstructure considerably, or react directly with the alloys.

Jan 1, 1963

By Jerry Dolph

Hecla Mining's Lucky Friday Mine, located beneath the town of Mullan, ID, has been shaken since the 1960s by many deep underground rock bursts. The largest rock burst carried a magnitude of 3.5 on the Richter Scale. It occurred in 1969 when all of the stopes on a level approached an upper level at the same elevation. After that, a stair-step pattern was used to give the mine's levels more of an "arch." The article is an account of one of the more ferocious bursts to hit the miners of the Lucky Friday. I say "miners" instead of "mine" because I was there and it was a very personal experience for me. I had been working at the Lucky Friday for six years. During that time, I had heard and felt thousands of air blasts. In fact, in the early spring of 1986, the mine was experiencing as many as 1000 air blasts an hour, of different intensi¬ties, of course. Most of them sounded like popcorn popping. There were also a few bumps and occasionally a real boomer. That day did not seem any different

Jan 1, 1994

Aspects of the formation, decomposition and acid solubility of zinc ferrite were examined to find potential ways of increasing the recovery of zinc from a calcination process of mineral concentrates. Ferrite can begin to form within 2 hours at 450¦C. while complete reaction can occur after 35 minutes at 700¦C. The nature of the starting materials has a pronounced effect on the rate of formation and below 700¦C. ZnSO4 and Fe2O3 proved to be the least reactive of the materials investigated. It is possible that iron in a mineral admixed h sphalerite can be converted to a relatively inactive form, however, it does not seem possible to prevent zince f formation when iron is in the sphalerite lattice. At the two temperatures examined, 650¦C. and 700¦C, the presence of SO2 in the atmosphere accelerate .e formation of ferrite. Prolonged exposure to such atmospheres, however, caused the ferrite to decompose to ZnSO4 and Fe203. The optimum temperature for decomposition was 650¦C. and it was virtually complete within 2 hours in an atmosphere of 10% SO2 in air. Zinc ferrite was also decomposed by CO at low concentrations, and by heating with limestone at 1000¦C. for at least 2 hours. The solubility of zinc ferrite in acid was influenced by the starting materials used. As both the reaction temperature and the time at temperature increased the acid solubility decreased. The acid solubility was a minimum when the ___i_.. n - I -r~...................c -..... F, fe..i+e --A frn... A01- +^ Z(lo/

Jan 1, 1970

By Gordon M. Pugh, David G. Rasmussen

INTRODUCTION This method is a variation of cut-and-fill mining where either the wall rock or the vein is too unconsolidated to permit safe mining by conventional cut-and-fill methods. Basic development consists of driving a 2.4 x 2.7-m (8 x 9-ft) haulage heading laterally in the footwall side of the vein. Crosscuts are driven over to the vein at 91-m (300-ft) intervals. Then the vein, at each inter¬section, is mined out to a distance of about 9 m (30 ft ) above the track level. After the installation of an ore chute, scrams or intermediate drifts are driven in both directions along the vein. Mining then starts imme¬diately below the level bounding the upper limit of the stope. A cut varying between 3 and 4.2 m (10 and 14 ft) in depth and mined for a distance of 45.7 m (150 ft )along the strike is taken from the orepass in each direction (Fig. 1). In this mined-out void, the floor of the cut is equipped with 203 x 203-mm (8 x 8-in.) caps hitched into the wall with steel saddle hitches installed on 1.5-m (5-ft) centers. Double wood stringers, 152.4 x 152.4 mm (6 x 6 in.), are then installed on 1.2-m (4-ft) centers longitudinally down the length of the stope. Reinforc¬ing wire mesh is also placed, overlying each mat of timber. Directly above the stringers, stulls are installed from hanging wall to footwall to hold the timber in place during the sand-filling operation. Then a cement¬sand mixture in a ratio of about 1:10 weight is poured to a depth of about 2.4 m (8 ft). The entire cycle is then repeated down to the scram drift. Another variation of timbering is illustrated in Fig. 2. There is a vein width of approximately 5.5 m (18 ft) with the same unconsolidated ground conditions. The primary difference between handling this situation and the previously described undercut-and-fill method is that standard timbered sets are installed in each excavated stoping void rather than stulls. Once again the basic method is to work down the ore block from an upper timbered drift to a lower timbered drift. Cuts are taken from a timbered raise with a chute on the stope side. Each piece of ground excavated is essentially two sets high, 5.5 m (18 ft), by two sets wide, 5.5 m (18 ft), by the length of the cut along the strike of the vein. The timbered sets are 2.4 x 2.4 x 2.4 m (8 x 8 x 8 ft). The net result is, therefore, two sets of timber on a top floor separated by doubled-up 76-mm (3-in.) lagging from

Jan 1, 1982

By Bill M. Stewart

The Bureau of Mines conducted laboratory tests to determine the effects on the physical properties of coarse coal waste of adding large amounts of fine coal waste. Maximum laboratory dry density, optimum moisture content, shear strength, and permeability tests were conducted on samples that contained 18 to 60 pct minus No.4 (U.S. Standard sieve size) coal waste. For the nonslaky materials, maximum laboratory densities were highest and permeabilities lowest when the samples contained between 30 and 40 pct minus No.4. Shear strength increased rapidly when the proportion of minus No. 4 was increased from 20 to 40 pct, but then increased only slightly or leveled off when the minus No. 4 was increased to 60 pct. Optimum moisture content and permeability were the physical properties most affected by the addition of fines. Optimum moisture content increased as much as 3 pct, and permeabilities decreased up to three orders of magnitude. Slaky coal waste material had physical property reactions to the addition of fines substantially different from those of nonslaky material.

Jan 1, 1981

By E. S. Bumps

A series of macrographs are presented for the purpose of graphically recording the strain phenomenon that accompanies the energy transition in the Charpy impact testing of a mild steel that is susceptible to strain aging. STRAIN patterns in mild steel Charpy impact specimens were obtained in order to determine whether, on the first appearance of plastic strain during deformation, the initial fracture cracks appear in the region of plastic strain or in the elasti-cally deformed regions between. Although this attempt to locate the initiation of cleavage was not successful, the observed strain patterns illustrating various stress conditions in partially deformed Charpy specimens are presented along with a discussion of the possible dependence of transition energy on the yield phenomenon. Earlier work on the development of strain patterns in mild steel have been reported by Fry1 and later by Jevon.2 Harris, Rinebolt, and Raring3 observed characteristic strain markings on the surface of Charpy V-notch impact specimens fractured above and below the transition temperature which they presented schematically. It is intended that the strain figures presented here will add to the literature a graphic correlation of strain with transition energy in impact specimens. Samples of % in. round hot rolled, 0.20 pct C steel were machined to standard 0.394 in. sq, V-notch Charpy impact specimens. Preliminary testing involved determination of transition temperature, Fig. 1, using a Sontagg impact tester. These data were subsequently used to select temperatures above, within, and below the transition range at which specimens were partially deformed. Partial deformation was obtained by either varying the energy or the testing temperature, see Table I. Macroscopic strain figures shown in Figs. 2 to 19 were produced by several metallographic repolish-ing and etching steps. The macroetchant used was as follows:4 120 g HCl, concentrated; 100 ml water; and 90 g cupric chloride. Strain figures were obtained on the outer surface and on sections through the central portion of the impact specimens in order to determine an approximation of the volumetric strain pattern. In the tensile strain figures reported by Jevon, it was found that strain etching would not work immediately following strain unless the material was heated to 200°C. The impact strain patterns presented here were obtained without this heating, but the specimens were not etched until ten months after straining. This confirms a discussion of Jevon's paper, in which it was pointed out that strain figures can also be developed after aging for long periods of time at room temperature. Hardness of the strained and unstrained portions, revealed by the etched pattern, was explored using R, impressions converted to R, hardness values. Discussion of Results In the impact test, as in the tensile test, some parts of the specimen yield and deform plastically, while other regions are deformed only elastically. The plastic deformation bears a relation to the imposed stress pattern. In the strain figures presented here, the plastically deformed regions are the dark etching ones. The strain figures are always symmetrical because the stress state in the Charpy-type specimen under impact loading is symmetrical. The difficulties encountered to produce initial cracks are intimated in Figs. 2 and 4. At a temperature of —75ºF, the stress was not sufficient to pro-

Jan 1, 1953

By Matveyeva Tamara

The main deposits of gold-sulfide ores of Russia are characterized as refractory raw material with the non-uniform finely-interspersed sulfide mineralization, submicron gold, the low gold content (3-5 ppm) and non-uniform distribution of the gold associated with pyrite and arsenopyrite. These ores show low indicators of extraction of gold and silver at cyanidation. Flotation is one of the basic technological procedures of processing of gold sulfide ores however simultaneous presence of pyrite and arsenopyrite and lack of effective methods of their selection constrains application possibility of flotation schemes because of rigid requirements to flotation concentrates under the arsenic content and practically excludes smelting of pyrite concentrate. The main losses of precious metals at flotation technologically are concentrated in thin classes (up to 15 %) demonstrating an inefficiency of standard reagent modes. For an estimation of expediency and possibility of application of selective flotation of pyrite and arsenopyrite a scientific substantiation of the mechanism and criteria of selection of gold-bearing ferrous sulfides of various material structure is developed and for difficultly divided pairs of sulfides with close technological properties the new selective reagents providing effective extraction of gold from hard-to-beneficiate ores are designed. The original technique for modifying surface composition of natural sulfides by nano-sized Au is worked out and the mechanism of selective adsorption of new reagents ? oxypropyl ester of diethyl-dithiocarbamatic acid (OPDTC) and oak bark extract (OBE) on Au-bearing sulfide minerals is revealed. Formation of almost insoluble OPDTC-Au compounds is defined by methods of scanning electronic microscopy (SEM) and UV-spectroscopy. Application of developed reagent modes using new reagents have been tested in laboratory conditions at flotation gold-sulfide ores samples and collective concentrate probes providing high extraction of gold and improved quality of the concentrate (less than 2 % As). Keywords: pyrite, arsenopyrite, selective flotation, flotation reagents adsorption, complex-forming, gold recovery.

Sep 1, 2012

By S. J. Aresco, A. A. Orning

This paper presents a scheme for determination of precision for the various steps in coal sampling, sample preparation, and analysis. It also gives resulting data on 100 American coals from various coal fields covering all ranks from lignite to low-volatile bituminous. The variances of the various steps of the process are studied as a function of the coal preparation, the top size of coal as sampled, and the ash content. To understand the variables that control the overall precision of coal sampling, sample reduction and analysis, there is need for measurement of the variances due to successive steps of the process. The purpose of the present paper is to study these variances as a function of the coal preparation, the top size of the coal as sampled, and the ash content. The sampling data included are from 100 individual preparation plants from various coal fields in the United States and cover all ranks of coal from lignite to low-volatile bituminous; various types of preparation; deep, strip and auger mines; and, in many instances, mixtures from two or more coal beds or types of mines. The collection of data is continuing, but sufficient work has been done to draw some important conclusions. Since the work was done in conjunction with the Bureau of Mines sampling of coal, the time that could be spent at any one preparation plant was limited. This, in turn, limited the number of samples that could be taken for each coal. For this reason, the results from various plants were pooled in blocks. Two major blocking categories were "raw" and "washed!' The raw coals had no preparation other than crushing and/or screening. The washed coals were prepared further by some combination of wet or dry mechanical cleaning. The categories were further divided ac-

Jan 1, 1965

By Vladko Panayotov, Marinela Panayotova

"Recently, in order to extract metals, the industry is trying to process old metallurgical slag. The material requires very fine grinding that results in enhanced slime-formation. This in turn leads to problems in the course of the flotation process and to a loss of metal. In addition, it causes difficulties in the wastewater treatment aimed at water reuse. The aggregation and separation of the fine particles and their further subjecting to mineral processing would result in more efficient use of raw materials. Closing the water cycle also would be facilitated. The paper presents results from studying sixteen flocculation reagents, commercially available for treating municipal wastewater, including products based on nanotechnology, for their ability to rend the production wastewater in suitable for reuse in the flotation. It turned out that, from all studied reagents, the cationic C-587 is suitable for the purpose. Some of reagents were studied for their ability to flocculate selectively, in presence of coke fines, rich in copper fines which are produced at grinding of a slag from lead-zinc metallurgy. Most promising reagents are chosen, based on the chemical analysis of the flocculated materials. Open-cycle rough copper flotation experiments with the flocculated fines and recycled wastewater gave encouraging results."

Jan 1, 2014

By E. J. KENNEDY

THE 142D MEETING of the Institute is rapidly shaping up with splendid prospects of a strong technical program and the lighter side of this annual occasion amply provided for. The date is February 20 to 23. The technical sessions will be held in the Engineering Societies building; the smoker-dinner, the informal dance, and the annual reception and dinner, at the Commodore Hotel, Monday, Tuesday and Wednesday respectively. The news to date on the technical side is as follows: Mining Methods-Subsidence The Mining Methods Committee has prepared an interesting program which will be divided into two sessions to be held early in the week. At the first there will be papers on mining methods and development, including a description of the "Sinking and Equipment of No. 2 Shaft at Minas de Matahambre," by Dudley D. Homer and R. H. Cromwell. They describe in considerable detail the equipment used and the practice followed in sinking this important shaft, giving detailed costs and performance figures. Hoist¬ing ?arrangements and mining practice at the "Red Ore Mines of the Woodward Iron Co. at Bessemer, Ala.," are described by Tenny C. DeSollar, superintendent of mines, in a second paper. At this session of the Mining Methods Committee, H. M. Roche and R. E. Crockett, of the Committee on Eastern Magnetite Mining and Milling Methods, will present their paper, "Iron Ore Mining at the Scrub Oak Mine." This mine is in the highlands of New Jersey about 40 miles west of New York City. Prof. Robert K. Warner of Yale University will present a paper on "The Selection of a Mining System," which should have an interesting discussion. Pierre R. Hines, of Portland, Ore., will present, with stereopticon slides, his paper on "The Owyhee Tunnels, U. S. Reclamation Project, Owyhee, Oregon," describing one of the recent irrigation undertakings.

Jan 1, 1933

By Giancarlo Alfonso Lovón Canchumani

A indústria da mineração do ferro brasileira ocupa posição relevante no cenário mundial, exportando para os principais mercados consumidores os produtos beneficiados. Esta indústria de beneficiamento tem consumo elevado de recursos e de energia, o que consequentemente gera grandes quantidades de emissões gasosas, líquidas e sólidas, contaminantes do meio ambiente. Nesse contexto o presente artigo tem por objetivo avaliar o ciclo de vida da produção de pelotas de minério de ferro, através da identificação dos impactos ambientais gerados nas etapas de lavra, beneficiamento, transporte e pelotização, com o intuito de dar subsídios a medidas mitigadoras. Foi realizado um estudo de caso em uma empresa de produção de pelotas de minério de ferro e utilizando a metodologia de Avaliação do Ciclo de Vida, baseado na norma ISO 14040. De acordo com os resultados obtidos os impactos ambientais mais importantes em relação ao ciclo de vida da produção de pelota, são referentes à categoria de depleção dos recursos minerais com 64,4% do total ponderado e a emissão de particulados no processo de lavra, que monta a 28,6% do mesmo total. Enquanto a fase com maior contribuição para o impacto total para a produção da pelota é a de beneficiamento.

Aug 16, 2017

By T. J. Nowak

The heat flow processes determining the injection and shut-in temperature logs in a water injection well have been analyzed and the theoretical basis for determining the water injectivity profiles from the temperature logs has been presented. Both the injection and the subsequent shut-in logs are necessary to resolve the injection interval into relative water intake strata; the former, to provide an accurate estimation of the thicknesses of the strata, and the latter to indicate the major and minor intake rates into the strata. A procedure is described for estimating the injectivity profile from the temperature logs and is applied to several temperature logs. For a water injection well, a comparison is made of the injectivity profiles obtained from the core analysis, the spinner survey, and the temperature logs. INTRODUCTION In secondary recovery of oil by water flooding, the injectivity profile is needed to obtain diagnostic evaluation of water intake distribution over the injection interval. If the distribution is unfavorable among the various strata, corrective measures can be taken to provide better control. Numerous methods have been developed for determining the injectivity profile from water velocity measurements in well bores. Often, dependence is placed upon core analyses and/or electric logs for estimating the relative water intakes over the injection interval. In many cases, the temperature log method described herein will give results more diagnostic than those obtained through use of the other available methods inasmuch as it is based upon the study of temperature disturbances in and around the well bore as a function of water flow in the well bore and in the formation. This method is the result of analyses of a number of temperature surveys made in water injection wells to determine the point of entry of the water into the formation. The material in this paper is presented in two sections: the first deals with the theoretical study of temperature survey data, and the second deals with the field application. PART I — THEORETICAL TREATMENT OF TEMPERATURE LOG DATA Before discussing the various aspects of heat flow relative to temperature log data, the phenomena that give rise to well bore temperatures — namely, the indigenous formation temperature and the associated rates of heat flow — will be considered. Geothermal Gradient The geothermal gradient is defined as the increment of depth at which the indigenous subsurface temperature increases by l°. It is caused by the continuous flow of heat outward from the interior of the earth. The flow of heat is an equilibrium process between the heat sources, the thermal conductivities of the formations, and the mean surface temperature. Therefore, there is no accumulation of heat energy in the path of heat transmission, and the geothermal gradient for a given formation will depend upon its thermal conductivity.

Jan 1, 1953

By N. S. Dalal, B. Jafari, F. H. Y. Green, M. M. Suryan, V. Vallyathan

"Freshly ground and aged anthracite and bituminous coal samples were investigated by electron spin resonance (ESR) spectroscopy to detect the presence, concentration and reactivity of free radicals. Freshly ground anthracite coal produced greater concentration of free radicals than the bituminous coal, and the radical reactivity was also greater for the anthracite. The reactivity of the newly produced free radicals in the anthracite dust correlated with the dust's toxicity. Furthermore similar coal-based free radicals were detected in the lung tissue of autopsied coal miners, suggestive of persistent reactivity by the embedded coal dust leading to the progressive disease process. Results of the studies on the severity of coal workers' pneumoconiosis (CWP) and free radical concentration m lung tissue support this hypothesis.INTRODUCTIONCOAL WORKERS' PNEUMOCONIOSIS (CWP) has been an important topic of concern to miners, mining engineers, epidemiologists and medical researchers for decades. It is well known that the prevalence and severity of CWP differ markedly between different regions and mines despite comparable exposures to respirable dust (REISNER and RoBOCK, 1977; HURLEY et al., 1979). These variations in pathogenicity of coal mine dusts can only partially be explained by differences in the mineral composition and by rank of coal (CHRISTIAN and NELSON, 1978; CHRISTIAN et al., 1979; HATCH et al., 1980). Cytotoxity studies on mammalian cells do not correspond well with the human disease pattern (CHRISTIAN and NELSON, 1978; CHRISTIAN et al., 1979; HATCH et al.,1980; VALL YA THAN et al., 1988). For example, while epidemiological studies of coal miners (REISNER and ROBECK, 1977; HURLEY et al., 1979) indicate that the prevalence of CWP correlates roughly with the rank of coal, such correlation has not yet been established in biological studies, despite considerable effort (CHRISTIAN and NELSON, 1978; CHRISTIAN et al., 1979; HATCH et al., 1980). In order to help resolve this apparent paradox we have undertaken a systematic study to evaluate whether any correlation exists between the concentration of free radicals present in fresh or aged coal dusts from two well-characterized U.S. coals. This study was also prompted in part by observations reported in the literature that organic free radicals can be formed on the surface of freshly fractured coals (LEBEDEV et al., 1978; DULIBA and CLARKSON, 1984). In particular, ARTEMOV and REZNIK (1980) noted that the decay lifetimes and, hence, the reactivity of the organic free radicals formed on crushing Russian coals, .depended"

Jan 1, 1989

By Oliver Bowles

Limestone is the most widely used of all racks and is essential to a great many industries, including tae building trades, highway construction, metallurgy, agriculture, end many chemical and manufacturing enterprises. It occurs in some form in every State and is produced in thousands of quarries. Production in 1930 exceeded 134,000,000 tons. It has more numerous and more diversified uses than any other rock. This paper is designed to furnish general information on the various branches of limestone quarrying and their economic importance. Brief reference is made to dimension stone, and a more complete discussion follows of the uses, requisite qualities, quarry methods, grid processes of preparation of crushed and broken limestone. Footnote references serve to guide the reader to more detailed information.

Jan 1, 1933

By A. Wahab Khair

"This paper presents an analysis of fracture mechanisms in coal subjected to bi-axial state of stresses, indentation of laterally confined coal specimen. Coal specimens were loaded to failure by the straight wedge indenters at various lateral confinement pressures. Strain distribution and acoustic emission characteristics of coal specimens under stress were recorded. The influence lines of vertical forces acting on the horizontal straight boundary of the coal specimen for each type of wedge indenter have been established using holographic interferometry technique. The effects of wedge indenter angle, confinement pressure, and coal anisotropy on fracture types, failure modes, and post-failure conditions were studied. The results indicated that combined application of holographic interferometry and acoustic emission monitoring techniques is not only suitable ·for studying deformability of heterogeneous and microscopically discontinuous material under stress but it also enhances the mode of fracture during the post failure stage. INTRODUCTIONOne of the relevant processes in the coal cutting technology is the application of indentation theories. Since most cutting tools in the coal industry are wedge shaped most of the indentation research is found for a wedge shaped tool.A wide range of behavior is found in different rocks subjected to the wedge penetration. A rock which is elastic brittle at standard pressure might become elastic plastic at high confining pressure (Gnirk and Cheatham, 1963). It was also observed that some rocks will merely be crushed and indented by a wedge whereas others will crack and form chips, furthermore the existence or non-existence of chips depends mostly on the geometry of the indenter, type of rock and the depth of penetration (Evans and Murrel, 1958). However, coal cutting technology is mostly explained by models which use rigid wedge to penetrate into a brittle material in which both crushing and chipping will occur (Evans and Murrel, 1958, 1962)."

Jan 1, 1988

By Clark R. Neuharth

To assess the supply status of ultra-high-purity silicon for national defense needs, the U.S. Bureau of Mines conducted a general study of the availability of materials and processing technology for silicon used in the manufacture of infrared (IR) detectors from raw materials to the highly advanced device state. The United States possesses all of the raw materials and processing technology for IR detector-grade silicon production, but does not produce at all of the processing stages on a regular basis. Consequently, the United States continues to rely on foreign sources for some of these critical materials.

Jan 1, 1989

By Edgardo Caro Orellana

El yacimiento Coroccohuayco fue descubierto durante el transcurso del segundo año de exploración (1971-1973) a través de un programa de Levantamiento Geológico del cuadriángulo Velli-Yauri, Cusco, considerándose como un ejemplo de prospección científica. En esta perspectiva, el objetivo del texto señala cuáles son los métodos de exploración empleados para dicho yacimiento. Entre los métodos del estudio regional tenemos la fotogeología, aeromagnetría y gravimetría y entre los métodos del estudio local están la geoquimiica, geofísica y perforación diamantina. Asimismo se menciona la prospección geofísica por el método de polarización inducida y la perforación diamantina.

Nov 20, 1978

By G K. Robinson

The existence of bias in samples taken by cross-stream sample cutters has been investigated using three-dimensional discrete element method (DEM) modelling. Detailed quantitative information on overall extraction ratios, size specific extraction ratios, missed and extra sample components can be made by comparing a reference sample to the actual sample. A key advantage of using this modelling approach over physical experimentation is that the reference sample can be measured on precisely the same portion of the stream of material as the actual sample, thereby allowing the elimination of a significant fraction of the variability and allowing statistically significant results to be obtained using many fewer replicates. Quantitative analysis of results broadly supports the commonly-used rule that the cutter aperture should be at least three times the nominal top-size of the material being sampled, but does not support the commonly-used rule requiring increase in cutter aperture if the cutter speed exceeds 0.6 m/s. Sampler performance can be understood in terms of the balance of forces in the congested region of material formed by the slowing of the particle stream due to collisional interactions around the mouth of the cutter.

Jan 1, 2008

By R. S. Hooper

In attempting to describe recent mining developments at the Bunker Hill mine, it may be well to recall first the old days of hand mining when holes were laboriously drilled by hand to a maximum depth of three feet, and were shot one or two at a time, in order that the miner could take advantage of every slip, crack or bedding plane, and so save as much drilling as possible. Broken muck, of course, was loaded by hand shoveling into wheelbarrows or small cars, and heading advances or stope tonnages were governed by the number of men that could find room to work in any given place. The first big improvement over these old methods was the introduction of the reciprocating type of air-powered rock drill. This innovation, crude as it was, enabled the miners to set up a machine and drill a complete round of holes in one shift; but broken muck was still loaded by hand, and the size and rate of advance in headings were limited by time required to remove the broken rock. The next improvement of consequence was the appearance of the hammer-type rock drill, which greatly increased drilling speed over the reciprocating type, and made possible the completion of a full cycle in one shift, by the use of crossbars in headings, and permitted drilling and mucking to be carried on at the same time. Rock drills continued to improve as time passed, and finally the smaller and more efficient mucking machines appeared on the scene, and it became possible to muck out a round of broken rock and have a clean setup for one or more drill columns and machines. A complete cycle of mucking, drilling, and blasting was completed in one shift with an average advance of five feet. These conditions prevailed for several years, but as the mine grew deeper, the distances to transport the workers grew longer, and this fact together with the shortening of the working day, soon presented the problem of attempting to complete a cycle of operations in a shift of only six hours at the working faces. Anticipating this condition, the operating heads at the Bunker Hill had started an intensive study of more and better mechanization, and over a period of comparatively few years have adopted and placed in service methods and machines that make it possible for a three-man crew to consistently advance headings seven by nine feet in cross section, at the rate of eight feet, and more, per shift, doing all the mucking, switching, drilling and loading. These improvements consist of the following major items: I. The development of a light, flexible, easily transported jumbo equipped with pneumatic columns (Fig I), that has decreased the "setting up" and "tearing down" time an average of 11/2 hr per shift, Or 25 PCt of the available working time. These jumbos were developed at the Bunker Hill mine by members of the staff and consist of two pneumatic columns attached to a suitable carriage. They fold

Jan 1, 1949

Treatment of the Siirt-Madenk÷y Ores by Flotation

Sep 13, 2010