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By Richard E. Bischke

Computer assisted finite element model analysis, originally developed to study stress distributions in aircraft, has been modified into a versatile mining program, that can be used to assist the engineer with predictions of mine subsidence. International Exploration, Inc. has developed an in-house finite element model program which incorporates a multitude of factors influencing mine subsidence such as mine design, physical rock properties, structure, faults, joints and topography. Finite element analysis of a mine model can mathematically determine the magnitude and direction of the principal stresses within each of the elements forming the model. By comparing the calculated in-situ stresses to the actual rock strengths, high risk regions within a mine can be identified. These potentially unstable regions of the mine can be allowed to fail within the model and the resultant stress redistribution and element movement calculated. Thus, the effects of the mine collapse at the surface can be predicted for the purpose of determining the potential damage, if any, that could occur to surface structures from deep mine failure. Stabilization materials can also be mathematically inserted into the model to design and analyze the effectiveness of subsidence prevention programs. Two examples are presented of the finite element program being used to predict mine subsidence at substantially different geologic and mining provinces in Pennsylvania.

Jan 1, 1984

By R. R. Godard

The practice of dust abatement or control is not new to any operation of United States Steel Corporation. This report will review those activities, past and present, within the five operating districts of United States Steel-Coal Operations with specific reference to mechanical and continuous mining, and including both the health and safety aspects of the problem. Obviously, the first principle of dust control is to inhibit its formation If this is not practical, steps may be taken to prevent its becoming airborne. Airborne dust control can be realized by either collecting it at the point of generation, diluting it with large volumes of air to reduce concentration, settling it by various means, or with reference to ignition hazard only, render it incombustible by neutralization with an inert material. These basic principles have been verified by the work of many, including the Bureau of Mines, U. S. Department of Interior, Bituminous Coal Research, Inc., and the Mining Research Establishment of the National Coal Board of Great Britain. Their application to every day mining problems is best illustrated by the following examples.

Jan 1, 1967

By Walter W. Kaufman

This Bureau of Mines manual for design of surface mine haulage roads covers such aspects of haulage road design as road alinement (both vertical and horizontal), construction materials, cross slope, and drainage provisions. Traffic control and design of proper lane widths to promote safe vehicle movement are included, as are suggested criteria for road and vehicle maintenance and for runaway-vehicle safety provisions. The aim of this publication is to provide those involved with surface mine haulage road design with a complete manual of recommended practices that, if implemented, will promote safer, more efficient haulage routes.

Jan 1, 1977

By S Henderson

The Thames gold-silver deposits are part of the Hauraki goldfield, situated within the Miocene to Pliocene calc-alkaline Coromandel Volcanic Zone (CVZ). The Waitangi vein system is one of the mineralised ore shoots in the Thames district. The Thames gold deposits are characterised by shallow level epithermal vein mineralisation with phyllic to advanced argillic alteration assemblages and abundant sulphide minerals including pyrite, arsenopyrite, chalcopyrite, galena and sphalerite. Gold occurs as electrum in association with sulphide minerals. Microprobe analyses.of sphalerite grains from the Waitangi deposit mostly range from 0.8 to 1.5 mole % FeS, although one sample contains 9.5 mole % FeS. Arsenopyrite from Waitangi yields a range from 33.1 to 34.6 atomic As (%). There is no discernible correlation between the FeS content of sphalerite and gold grade in the Waitangi deposit suggesting that gold deposition is probably not controlled by changes in temperature and activity of sulphur aS2 that control the FeS content of sphalerite. The possible causes for gold deposition are thought to be boiling, mixing and changes in pH. Sulphur isotope analyses of mixed sphalerite-galena and sphalerite-galena-ehalcopyrite samples yield a narrow range of d34SCDT values (-1.0 to 0.9 ë;n=5), whereas late spongy pyrite gives unusually light sulphur isotope values (-16.7 to -27.9 ë; n=4). The sulphur isotopic values of base metal sulphides from Waitangi suggest that the sulphur was derived from a magmatic source. However, the source of light sulphur in the late pyrite grains is not known. Preliminary fluid inclusion+studies indicate homogenisation temperatures between 173¦ and 284¦C and salinities of 0.23.0 NaCI equiv. wt % (uncorrected for C02). Vein quartz at Waitangi yields d18OSMOW values from 6.8 to 12.7 ë (n=23). The calculated oxygen isotopic composition of ore fluids is between -2.1 to 3.8 ë at 250¦C and -0.1-5.8 ë at 300¦C. Oxygen isotope analyses have revealed significant variations in d18O values with elevation and gold grades. Zones of gold enrichment coincide with a zone of variable oxygen isotope values at the top of the vein system, where boiling and/or fluid mixing most likely occurred. Oxygen isotope values varying with gold grades within the Waitangi conduits suggest that d18O values may be useful in targeting bonanza grade gold mineralisation in epithermal vein systems.

Jan 1, 1993

By Nikhil Dhawan, Veeranjaneyulu Rayapudi

This study investigates upgrading of low-grade banded hematite quartzite iron ore (Fe ~31%). Conventional beneficiation was found to be futile. The susceptibility of iron phases to microwave exposure and their selective absorption assists in the liberation of iron values. Microwave exposure of coarse particles at 540 W for 10 min yielded a concentrate with Fe 56.30% and recovery of 50.68%. Conventional carbothermic reduction at 500 °C, 60 min and 9% charcoal yielded a concentrate with Fe 57.6% and iron recovery of 68%. The presence of sufficiently bonded silica leads to an easy formation of a fayalite phase. The microwave reduction design yielded FeG of 57.6%, FeR of 47% and a yield of 24% at an optimal condition of 540 W, 8 min and 6% charcoal. It was found that a small fraction of microwave-irradiated ore-charcoal mixture melted rapidly, and pure ferrite balls were observed within 8 min. An optical micrograph of a ferrite ball reveals the retained austenite and martensite phase.

By James L. Ash

This report contains the results of a technical and economic evaluation of conceptual systems for the underground mining, rubblization; and in situ retorting of deep oil shale deposits. Study efforts were first directed towards evaluation of the applicable geology, associated minerals, rock mechanics, in situ retorting, access mining, ventilation, rubblization, safety, and environmental impact factors. Conceptual systems were synthesized and then evaluated against these factors from both a technical and limited economic viewpoint. The results of these evaluations were then analyzed 'and, based upon this analysis, the following two systems were selected for further study: System II: Room and Pillar-Vertical Drill and Blast System IV: Tunnel Boring-Horizontal Ring Drill and Blast Due to the large number of variables to be considered, a computer program was developed and utilized to provide data for the cost trade-off studies and economic analysis. Results of the early computer runs indicated the value of the tool available in the computer program and led to an extension in the contract to determine the sensitivity of the systems to several of the more apparent significant variables. These results in turn led to a refinement in the design assumptions and a better understanding of the technical and economic options available to an owner-operator of a Vertical Modified In Situ Shale Oil Extraction System. This report is submitted in fulfillment of the requirements of Contract Number S0241073 by Fenix & Scisson, Inc. to the Denver Research Center, United States Department of the Interior, Bureau of Mines. Work was completed as of November, 1976.

Jan 1, 1976

By J. Whitford

The established crown pillar extraction method at Gold Fields Australia Ltd.’s Crusader Mine, leads to the significant dilution and poor recovery of ore due to caving of the overlying loose rockfill. The application of selectively injecting specifically developed ‘FB200’ ettringite (calcium sulphoaluminate hydrate) type cement grout into loose rockfill to form a stabilised rockfill material, enables an artificial crown pillar to stabilise the surrounding rock mass and prevent caving of the overlying loose rockfill during crown pillar extraction. Investigation of the geomechanical criteria for crown pillar extraction beneath stabilised rockfill has enabled the safe and efficient extraction of two crown pillars at the Crusader Mine. La méthode actuelle d'extraction des piliers horizontaux à la mine Crusader dont la propriétaire est le Goldfields Australia Ltd amène à une dilution sensible du minerai, à cause de l'effondrement du remblai peu compacté qui se trouve au-dessus. Par moyen d'injection sélective du coulis de ciment FB200 ettringite (sulfoaluminate de calcium hydraté) qui a été développé spécifiquement pour cette application, un pilier artificiel est crée et celui-ci empêche l'effondrement du remblai pendant l'extraction du pilier de minerai au-dessous. A la suite des études géotechniques de la méthode, deux piliers horizontaux à la mine Crusader ont été extraites, de manière efficace et sûr. Die feststehende Krone Pfeiler Extraktionsmethode beim Crusader Mine von Gold Fields Australien GmbH, führt wegen caving des overlying lockerer rockfill zur bedeutungsvollen Verdünnung und schlechtem Wiederfinden des Erzes. Der Antrag, ausdrücklich entwickelten 'FB200' ettringite selektiv zu spritzen, (Kalzium-sulphoaluminate-Hydrat) Art kittet Mörtelschlamm in lockeren rockfill, um ein stabilisiertes rockfill-Material zu bilden, ermöglicht einem künstlichen Kronenpfeiler, die umliegende Steinmasse zu stabilisieren und caving des overlying während des Kronenpfeilerherausziehens lockeren rockfill zu verhindern. Untersuchung der geomechanical-Kriterien für Kronenpfeilerherausziehen unter stabilisiertem rockfill hat dem sicheren und tüchtigen Herausziehen von zwei Kronenpfeilern beim Crusader Mine ermöglicht.

Jan 1, 2003

By Sara Jane Boles

In recent years the demand for products of greater refractoriness has placed an ever-increasing emphasis on ceramic materials, including the metallic oxides. Magnesia (MgO) is one of the most important of these oxides, exhibiting, as it does, high electrical resistivity, high slag resistance, and a melting point of 2,800° C. However, magnesia has a tendency to hydrate in the presence of water and to volatilize above 1,500° C. in certain kiln atmospheres and has a comparatively low resistance to thermal shock. Because of these disadvantages, the previously listed advantages inherent in this material have been largely overlooked, and research on magnesia has lagged behind that on oxides such as alumina and zirconia. This bibliography has been prepared in an effort to present to Government and industry a comprehensive picture of the prospects for greater utilization of magnesia as a refractory material in future research. To provide as selective and accurate a collection as possible, the references included cover magnesia in a pure state, not as an additive or in combination with other materials. However, several references discuss the effect of minor impurities (less than 5 percent of the total) on the properties of magnesia, as these papers are considered to be of special importance. A few references to articles on forming techniques are also included, as they are valuable additions to the overall treatment of the subject. The processes used in obtaining and refining the raw materials are adequately covered in earlier publications and are excluded. A number of references are omitted as being of questionable value in enhancing the cumulative study of pure magnesia as an ultra-high-temperature refractory material.

Jan 1, 1962

By Noel N. Moebs

Valley Camp No. 3 mine was the scene of an experimental shortwall introduced in 1973 in an attempt to improve the recovery from the Pittsburgh coalbed in the Ohio Valley area where adverse ground conditions have imposed partial extraction methods with only 40 to 55 percent recovery of the valuable resource. The Bureau of Mines, under a cooperative agreement with Valley Camp Coal Co., monitored ground pressures and caving in the shortwall section in an effort to determine whether the roof strata, notably the limestone main roof, will cave to the extent that roof pressures at the face are relieved and whether the powered roof supports can sustain the roof load. The Bureau's efforts included mapping of clay veins, instrumentation of chain pillars and shortwall panels with encapsulated pressure cells, recording hydraulic pressures in the legs of the shortwall chocks, and core drilling underground and from the :surface. The experimental shortwall was a qualified success. Recovery increased 5.4 percent compared with partial extraction. Pressures in chain pillars and the abutment zone were not excessive. Hydraulic pressures in the chock legs did not approach the yielding pressure. Apparently, the limestone strata caved and the roof pressure at the face was relieved.

Jan 1, 1976

By C. Erichsen

ABSTRACT: The Berg Bock Freeway Tunnel represents the southernmost link of the "Thuringian tunnel chain" of the new freeway A71 located in the eastern part of Germany. It comprises two tubes each 2700 m in length. From north to south, it passes through the Suhl granite, the base sediments and the porphyrite of the New Red as well as the layers of the Middle Bunter. The two tunnel tubes were driven by the shotcrete method within appr. 10 months. With four tunnel faces, maximum performances totalling appr. 30 m/d were attained. Additional, supplementary demands on the safety conception, resulting from the findings from and the analysis of fire accidents in tunnels in recent years, had to be fulfilled in the execution planning at short notice. The inner lining is largely constructed using non-reinforced concrete. Reinforcement is only installed in the portal zones, in tunnel sections in less stable rock and in areas with a special cross-section as for instance cross connections and niches. ZUSAMMENFASSUNG: Der Autobahntunnel Berg Bock stellt das südlichste Glied der "Thüringer Tunnelkette" auf der Autobahn A71 dar, die im Osten von Deutschland liegt. Er besteht aus zwei Röhren von je 2700 m Länge. Vom Norden nach Süden durchörtert er den Suhler Granit, die Basissedimente und den Porphyrit des Rotliegenden, sowie die Schichten des Mittleren Buntsandsteins. Die beiden Tunnelröhren wurden in Spritzbetonbauweise in einer Bauzeit von etwa zehn Monaten aufgefahren. An vier Vortriebsorten wurden Spitzenleistungen von insgesamt etwa 30 m/d erzielt. Ergänzende Anforderungen an das Sicherheitskonzept, die sich auf der Grundlage der Auswertung der in den letzten Jahren aufgetretenen Brandunfälle in Tunneln ergeben haben, wurden im Rahmen der Ausführungsplanung kurzfristig berücksichtigt. Die Tunnelinnenschale wurde weitgehend aus nicht bewehrtem Beton hergestellt. Nur in den Portalzonen, in Tunnelabschnitten mit weniger standsicherem Fels und in Bereichen mit speziellen Querschnitten, wie beispielsweise im Bereich von Querstollen und Nischen, wurde bewehrter Beton ausgeführt. RÉSUMÉ: Le tunnel d'autoroute de Berg Bock représente le plus méridional maillon de la "chaîne thuringienne de tunnels" sur l'autoroute A71 dans l'est de l'Allemagne. Il se compose de deux tubes d'une longueur de 2700 m chacun. Du nord vers le sud, il traverse le granit de Suhl, les sédiments de base et le porphyrite du Rotliegendes, aussi que les strates du grès bigarré intermédiaire. Les deux tubes étaient creusés en méthode de construction de béton projeté dans une période de construction d'environ dix mois. À quatre fronts de taille rendements maximaux collectifs d'environ 30 m par jour étaient obtenus. On a eu égard à court terme dans la conception d'exécution à des demandes supplémentaires vers la conception de sécurité, qui ont résulté sur la base de l'interprétation des accidents d'incendie dans des tunnels dans les années dernières. La paroi intérieure était construite largement de béton non armé.

Jan 1, 2003

This report summarizes the results of several field tests conducted by Collins for the Bureau of Mines under contract S0122076 and contract H0232056. The field projects represent a part of Collins continuing effort on a broad study of coal mine communications. These experiments analyze the propagation characteristics of radio signals in a working coal mine environment. The intent of the program is to provide basic propagation loss characteristics by which we may evaluate various approaches to an integrated mine communications system. The goal of such a system is to satisfy both operational and emergency communications needs in the mine.

Jan 1, 1974

By Larry Joe Linley

The Department of the Interior, Bureau of Mines is reviewing explosion protection methods for use in gassy coal mines. This performance criteria guideline is an evaluation of three explosion protection methods of machines electrically powered with voltages up to 15 000 volts AC. A sufficient amount of basic research has been accomplished to verify that the explosion-proof and pressurized enclosure methods can provide adequate explosion protection with the present state of the art up to 15 000 volts AC. The routine application of the potted enclosure as a stand alone protection method requires further investigation or development in order to clarify performance criteria and verification-certification requirements. An extensive literature search, a series of high voltage tests, and a design evaluation of the three explosion protection methods performed at White Sands Test Facility indicates that the explosion-proof, pressurized, and potted enclosures can all be used to enclose up to 15 000 volts AC, if the performance criteria and verification-certification requirements recommended in this guideline are implemented.

Jan 1, 1982

By Steven R. McCutcheon

ABSTRACT - The Bathurst-Newcastle district, a subcircular area approximately 50 km in diameter, contains 37 massive-sulfide Zn-Pb-Cu deposits that have defined tonnages, and has 58 additional significant occurrences. The largest deposit is Brunswick No . 12, with total reserves (including past production) of 148 million tonnes grading about 12.50% combined Pb-Zn. The deposits/ occurrences are spatially associated with a felsic volcanic pile that contains a significant sedimentary component. In the vicinity of the Brunswick deposits the pile is divisible into lower and upper sequences. The lower is characterized by megacrystic rhyolite (QFAS) and coarse- to fine-grained quartz ( ± feldspar) wackes and/or tuffites (QAS); the upper sequence is characterized by aphyric to sparsely porphyritic rhyolites (HWR), micro-breccias, and acid hyaloclastites with interbedded dark gray sedimentary rocks. A greenish gray to dark gray siltstone (GGS) separates the two sequences and hosts the sulfide deposits. Lithogeochemistry of !east altered samples shows that the QFAS and HWR have an igneous character, whereas the QAS and GGS have a sedimentary sig­ nature. The two types can be distinguished on the basis of total alkalies (Na2O + K2O) versus SiO2/Al2O3, and Ti02 versus Fe/(Fe+ Mg). Some trace elements, such as Sr and Y, also help differentiate the two types. The QFAS differs from HWR by having higher La/Yb ratios but lower Zr and Th. The Bathurst deposits do not show a close spatial association with rhyolites but rather are stratiform bodies (lacking clastic textures) within fine-grained sedimentary rocks. The scarcity of barite and other sulfates indicates that there was little mixing between the metal­ bearing fluids and cold seawater. High Fe/(Fe+ Mg) ratios in chlorites also indicate the fluids did not contain a significant seawater component. These features and the large size of many deposits suggest that the deposits formed from metal-rich pore waters that were released catastrophically from an acquifer in the footwall stratigraphy.

Jan 1, 1992

By J. Korak

Belt conveyor systems, long the standard transportation technique in soft-rock open-pit applications, are encountering growing interest in the hard-rock open-pit sector as economic factors force companies to seek an alternative to costly truck haulage. A general review of mine conveyor systems is followed by detailed analysis of the mobile and semi-mobile in-pit crushing plant essential to successful use of mine conveyors. A final section presents case studies of three crusher-conveyor systems handling overburden, copper ore and granite.

Jan 1, 1985

By J. R. Thoenen, J. L. Vallely, M. C. Malamphy

"SUMMARYMagnetic and gravimetric surveys wore conducted over an area of ap¬proximately 1,400 square miles in the bauxite district of central Arkansas. The primary purpose of these surveys was to discover any possible buried and hitherto unknown syenite masses favorable for the occurrence of bauxite and to determine the approximate position of the buried flanks of the known syenite masses which might offer conditions favorable for the discovery of new ore bodies.Those surveys indicated that the various syenite outcrops were domes or bosses on a large batholith and that ether similar domes occurred on the batholith but did net outcrop.Drilling on the local geophysical anomalies proved the presence of 10 buried domes, but only 2 of them were found to project above the upper surface of the Midway clays, a requisite of conditions favorable for the occurrence of bauxite ore bodies. The geophysical data indicated the approximate configuration of the buried flanks of the known syenite coutcrops, and the portions of these flanks that project above the Midway have now been outlined more accurately by drilling.The geophysical surveys have produced evidence permitting the elimi¬nation of a large area as unfavorable for the occurrence of bauxite.Magnetic surveys extending along the Midway-Wilcox contact from Gurdon, in Clark County, on the southwest to Searcy, in White County, on the northwest have proved the improbability of the existence of other syenite masses similar to those found in Pulaski and Saline Counties. A detailed magnetic survey of the Magnet Cove area in Hot Spring County has proved that the syenite mass exposed in that locality is an isolated intrusion and entirely unrelated to those of Pulaski and Saline Counties. This syenite mass does not occur under conditions believed to be favorable for the occurrence of bauxite."

Feb 1, 1945

By M. Rahmanpour

"Mine planning is a multidisciplinary procedure that aims to guarantee the profitability of a mining operation in changing and uncertain conditions. Mine plans are normally classified as long-term, intermediate-term, and short-term plans, and many factors affect the preciseness of these plans and cause deviations in reaching the objectives. Commodity price is the heart of mine planning, but it has a changing and uncertain nature. Therefore, the determination of mine plans in the presence of uncertain mineral price is a challenge. A robust mine plan reduces the risk of early mine closure. A procedure is presented to determine the value at risk (VaR) in any possible mine planning alternative. VaR is considered together with downside risk and upside potential in order to select the most profitable and least risky plan. The model is tested on a small iron ore deposit. IntroductionMining projects are normally evaluated with the objective of maximizing economic value, as measured by the net present value (NPV). The aim of mine planning is to develop a yearly extraction plan that guides the mining operation to the highest NPV (Dagdelen, 2007; Yarmuch and Ortiz, 2011). This plan considers the technical constraints such as blending requirements, block sequencing, and pit slope (Caccetta and Hill 2003). Thus, the mine plan affects the economics and the payback period of mining operations.Mine planning is a procedure based on which the profitability of the mining operation is guaranteed in changing and uncertain conditions (McCarter, 1992). However, conventional mine planning ignores the volatility and uncertainty of future commodity prices and does not allow for managerial flexibility. It is common practice to assume a deterministic and constant commodity price through the mine life. The problem with this approach is that the commodity price is the heart of the mine planning procedure and governs the profitability and feasibility of the operation; thus ignoring price volatility will result in a sub-optimal mine plan."

Jan 1, 2016

By Caroline B. Chapleau, Mélanie Proulx, Claude Bazin, Gaétan Lavoie

"Quebec Cartier Mining operates a pelletizing plant in Port-Cartier, QC. Grinding, agglomeration and pellets induration are the three main steps in the preparation of iron oxide pellets. In 1998, following different recommendations, the company increased the speed of one of its ball mill in order to increase the grinding efficiency of the machine. As expected, the increased speed lead to an increase of the power draught, which did not produce the expected increase of fineness of grind, neither its allows to increase the mill throughput. The change of behaviour of the mill could hardly be understood by comparison of discharge size distribution at initial and modified mill rotation speed. On the other hand, the use of the selection function from a population balance model provides an insight of the changes that occurred in the mill. This paper reviews the various steps required for the estimation of a grinding mill selection function. Results of the calibration to Quebec Cartier grinding mills show that the increase in the mill speed leads to higher rate of breakage of coarse particles, at the expenses of less efficient breakage of medium and fine size particles. In the case of the studied mill, breakage of coarse particles was probably not the critical step of the mill operation. INTRODUCTIONOre size reduction is the major energy consumption step in any mineral processing operations (Austin et al., 1984). Size reduction is required to either liberate valuable minerals from the gangue minerals in which they are imbedded, or to increase the specific surface of the ground material. Plant engineers continuously face the challenge to find grinding machines, operating conditions or grinding circuit flowsheet configurations that could improve the size reduction process at lower energy or m6dia consumption."

Jan 1, 2000

By Charles L. Allie

Since Reserve Mining Co. began commercial operations at Silver Bay, MN, some 25 years ago, major improvements in taconite processing technology have become available. In addition, significant new government standards have been imposed on industrial operations. By implementing a $370-million modernization program, Reserve was able to accomplish two major company objectives: the quality of concentrates produced from the Peter Mitchell mine has improved, and the operation meets both present and foreseeable environmental standards. Process modifications at Reserve were designed to: •Reduce the pellet silica content from 9% to 5%; •Increase the pellet iron content from 62.5% to 65.8%; •Implement a tailings disposal system utilizing "best available technology" water quality controls; and •Reduce air emissions by installing "best available technology" air emission controls. By adding dry cobbing, fine screening, and flotation to the concentrating process, pellet silica content has been reduced; the process reclaims and reuses all process waters; all tailings are stored in a zero discharge tailings basin; and all air emission standards are being met. Initial Beneficiation at Silver Bay Reserve's Peter Mitchell mine at Babbitt, MN, is on the eastern end of the Biwabik iron formation. The open-pit mine is approximately 16 km long, 0.8 km wide, and presently has a maximum depth of about 50 m. Principal constituents of the ore body are magnetite, quartz, and iron-magnesium silicates. The company's large commercial plant began operating at Silver Bay, 75 rail km from the mine, in 1955. Facilities have historically had the capacity to process 31.5 Mt/a of taconite, containing an average 24% magnetic iron, into 11 Mt/a of iron ore pellets. Reserve's initial beneficiation process-which existed up to early 1979-consisted of two crushing stages at the Babbitt mine site, two additional crushing and screening stages at Silver Bay, grinding in a conventional rod-ball¬regrind mill circuit, size classification with cyclones, and concentration with magnetic and hydraulic separators. Concentrate produced by that circuit assayed 65% iron and 8.5% silica, with a screen analysis of 94% -44 µm, and a surface area of 9300 cm2/cm3. Pellets produced from this concentrate assayed 62.5% iron and 9% silica (dry basis). Construction began in 1977 to modify Reserve's operation. Process modifications were designed from pilot scale operations that had been operated and researched by Reserve for more than 10 years. There were two design restraints imposed on the process: economic constraints that Reserve continue to use much of the existing processes and structures in the new operation; and a substantial number of government-imposed permit constraints. In effect, the tailings process was designed first and then a concentrating process was developed that would "fit" the tailings disposal system. Operation of the modified process began in June 1980. Crushing Remains Unchanged No changes in process flow were made at either the Babbitt mine and crushing plant or at the Silver Bay fine crusher. Gyratory crushers reduce run-of-mine taconite to -90 mm-diam at the mine. Taconite is then transported to Silver Bay by intra-plant railroad. There are 10 fine crushing lines. Each consists of a double deck screen, followed by a heavy duty short head crusher, a second double deck screen, and second short head crusher. All screen undersize material bypasses the crushing lines, resulting in an open circuit crushing process. Fine crusher product is approximately 98% - 20 mm, 80% -12 mm, and 50% -10 mm in diameter. Each fine crusher line processes about 400 t/h of crude taconite. Cobbing Provides Aggregate for Tailings Dams The first major process change was the addition of dry cobbing, a dry magnetic separation step between the fine crusher and concentrator. Dry cobbing serves two major purposes in the new process. Its principal function is to provide large volumes of dry coarse aggregate for use in construction of tailings dams. This process rejects about 20% of the fine crusher product as tailings with a size analysis of 98% -20 mm and 50% - 10 mm. These tailings are free draining and have high frictional shear strengths-two key requirements for dam building aggregates. Fine crusher product is conveyed to a new dry cobbing building. Here crushed ore is discharged into one of two 30-minute capacity surge bins. Crushed ore is withdrawn by 12 constant speed conveyor belts; each discharges 500 t of crushed taconite into a dry cobbing machine. Each machine consists of a 3-m-long riffle splitter and two vari-

Jan 12, 1980

By Eugene O. Binyon

"Belt and shaker conveyors, used singly or as combined units, have for many years been an integral part of many coal-mine haulage systems. The belt conveyor has also been used extensively as a main haulage unit in open-pit iron-ore mines of the Lake Superior district, particularly on the Mesabi Range. Few underground metal mines, however, either in the ferrous or non-ferrous branches of the mining industry, use the conveyors exclusively or even extensively for underground haulage. At present, only five iron-ore mines in the entire Lake Superior district have belt- or shaker-conveyor installations of any significant size. Of these mines, three are in the Crystal Falls-Iron River district of Michigan on the Menominee Range, one is on the Marquette Range near Ishpeming, Mich., and one is on the Mesabi Range near Keewatin, Minn.Results of the studies of tackless haulage in the Lake Superior district will not permit the establishment of any formula to prove or disprove the advantages of belt or shaker systems at all underground mines. The studies do show that trackless haulage can be used to advantage where the proper conditions exist. Advantages are particularly apparent when development can be planned sufficiently in advance of exploitation to permit installation of belts or shakers as part of the development program and where the systems are extended to include haulage in stopes as well as main entries.During the winter of 1947-48, the Bureau undertook a study of all of the underground ore conveying systems known to be in operation in the Lake Superior district for the purpose of making available to the entire mining industry the technologic data developed in the area. Because conditions that led to the installation of the belt and shaker conveying systems were often a function of the character of the deposit or the method of mining, a brief description of those conditions is included in this report.After a preliminary investigation into the extent to which trackless conveyors were employed in the district, it was found that a detailed study at five bites would result in fair appraisal of that method of haulage in the underground iron-ore mines.Each of the five significant installations is described separately in this report. In one instance, however, company policy does not permit identification of the mine wherein the conveying is done. In that instance the operation is designated as mine ""A"".Unless otherwise specified, all tonnage figures quoted herein are gross.The cooperation of officials of all of the companies operating underground mines in the Lake Superior district permitted successful completion of preliminary studies of mining practices and conveying systems.Special acknowledgment is made to R. D. Satterley, general superintendent, and to operating staffs of the Sherwood and Morris mines of the Inland Steel Co. The assistance given by W. D. Whitman, assistant superintendent, and Douglas Tippett, mine captain at the Morris mine, and P. D. Pearson, superintendent, R. O. Marsten, engineer, and W. Johnson, mine captain, at the Sherwood mine, is acknowledged."

Oct 1, 1949

By G. Roberts, S. S. Klima, W. R. Reed, J. Deluzio, G. Ross, A. Mazzella

The abstract discusses the problem of silicosis among roof bolter operators in coal mines due to respirable quartz dust (RCS) exposure. It presents a study comparing a new wet box collection system to the traditional dry box system. The wet box system uses water to saturate collected material, reducing RCS exposure during cleaning. The study found that the wet box system significantly reduced RCS exposures and quartz content in samples compared to the dry box system.

May 11, 2022