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By F. F. Aplan

The material known as coal has a highly variable composition. As a consequence, coals show a great variation in their physical and chemical properties as a function of coal rank. The situation is further complicated because the preparation engineer must deal with raw coal, as mined. This is an assemblage of coal, upwards of 30% mineral matter and, typically, several percent pyrite. The kind and amount of the mineral constituents is also highly variable from source to source. A knowledge of coal rank and source location, and the kind and amount of associated impurities, is the first step in evaluating the response of a raw coal to preparation procedures. The raw coal must first be characterized before information from one source can be extrapolated to that of another.

Jan 1, 1988

By G. L. Myers

The Fortitude skarn near Battle Mountain, NV is currently one of the largest producing gold skarns in the world. It contains about 11 Mt (12 million st) of minable ore grading 5.14 g/t (0.149 oz per st) and is the distal portion of a continuous skarn system in the Copper Canyon area centered on the Eocene Copper Canyon granodiorite porphyry. Calcsilicate compositions, opaque mineralogy, and the high gold grades are atypical of other base metal skarns (iron, Fe; copper, Cu; lead-zinc, Pb-Zn; or tungsten, W). The Copper Canyon skarn is systematically zoned from a garnet (AD 70-100) dominant, pyroxene (HD 20-45) subordinate zone, with major Cu mineralization, adjacent to the intrusive (West ore body), to a pyroxene (HD20-100) dominant, garnet (AD90-100 cores. AD 30-60 rims)subordinate assemblage, with major Au, near the distal marble front (Fortitude ore body). An extensive biotite ± diopsidic pyroxene ± kspar alteration halo surrounds the pyroxene > garnet gold-bearing skarn and represents the early stages of metasomatic alteration. Retrograde alteration is limited in areal extent and intensity, and consists of actinolite, chlorite, quartz, and prehnite. Economic gold mineralization begins in the pyroxene > garnet zone and continues to the marble front, a distance of 1 to 1.5 km (0.6 to 0.9 miles), respectively, from the plutonic contact. The opaque mineralogy in this gold zone includes pyrrhotite, arsenopyrite, marcasite, minor chalcopyrite, galena, sphalerite, argentite, hessite, hedleyite, volnyskite, and native bismuth and gold. The pyrite-pyrrhotite geothermometer yields temperatures that range from 450° C to 300°C (842° F to 582° F) and the electrum-argentite-sphalerite geothermometer yields temperatures which range from 290°C (554° F) at the marble front to about 420°C (788° F) more proximal to the intrusive. Log fS2 calculations from the sulfide assemblages yield values near - 10 with log fO2 values of about -30, in a solution of near neutral pH (5-6). Calculations of metal solubility suggest that the metals were transported as chloride complexes in the proximal skarn but that bisulfide complexes were predominant within the distal gold skarn. Relatively low oxidation states buffered by the carbonaceous to argilliceous, calcareous protolith and subsequent ferrous iron-rich skarn assemblages appear to have increased the gold carrying capacity of this large hydrothermal system.

Jan 1, 1991

By Enrique Fernandez

The success of the excavation of a sewage tunnel in a very extreme geological conditions, from river deposits and sandy layers to hard dolomite, and several meters below the estuary under the sea water influence, shows that the choice of a right equipment together with the use of chemical products like foam and polymers enable to dig tunnels in unexpected areas and give solution to the environmental problems. The paper describes the excavation and support process as well as the adopted solutions in every material and during the cross through the intermediate shafts, also under sea influence.

Jan 1, 2003

By Daniel Su

This paper describes recent ground control challenges encountered at the longwall recovery areas of one of Bailey Mine?s two longwall faces and the proactive measures taken by CONSOL management and engineering to mitigate them. The challenges derived primarily from the following causes: (1) irregular roof coal and draw slate thickness, (2) presence of thick sandstone at the recovery area and extremely weak rocks below the sandstone, (3) close proximity to a regional anticline, (4) low shield set pressure and tip load, and (5) ineffective primary roof support that led to progressive failure of the headgate roof. The presence of the anticline contributed to extensive fracturing of the sandstone. Excessive pot-out in advance of the shields frequently occurred near mid-face due to the presence of thick draw slate and irregular roof coal near the recovery area. This, in turn, resulted in face heights that exceeded the maximum reach of the shields. Subsequently, during longwall meshing, when the advance rate slowed considerably, fractured sandstone would often break loose, causing the shields to yield, thereby reducing the height and inhibiting shearer movement. To improve the headgate and face conditions within the longwall recovery area, several actions were taken, including: (1) assessing site-specific roof geology by conducting in-mine roof coring around the recovery areas and by mapping immediate draw slate and roof coal thicknesses within surrounding entries, (2) increasing pump pressure and thus shield set pressures (3) diligently monitoring shield set pressures and longwall extraction horizon, (4) installing additional cable bolts and roof screening to prevent progressive failure of the immediate headgate roof, (5) fully-grouting supplemental cable bolts to improve headgate support stiffness, and (6) gluing the headgate roof within the recovery areas with polyurethane. As a result of these collective efforts, longwall recovery delays at Bailey Mine were reduced from 21 days in 2006 to nearly zero in 2009.

Jan 1, 2009

By Sheldon Shepherd

Fifty years ago, belt scales were mechanical devices based on a complex weight balancing design. Today's systems use load cells to assess material weight, belt speed sensors and microprocessor-based integrators to continuously compute the rate of material transferred along a conveyor. Belt scales have become important assets to a plant. They help maximize the use of raw materials, control inventories and aid in the manufacture of a consistent product. Choosing and installing a belt scale system may seem complicated but it can be simplified by following a few guidelines.

Jan 1, 1999

By Y. C. Kim

M.S. Azun The article unfortunately has some serious flaws negating the usefulness of the paper. The authors claim that kriging (linear kriging) is superior to other methods such as polygon. This is not the case. The deterministic methods (referring to polygon, ID, IDS, etc.) should not be compared with the statistical methods (linear kriging, disjunctive kriging, etc.) because they differ not only in their assumptions, but also their tools used in estimation. Thus, they give different results. By comparing the results of deterministic methods and linear kriging, the authors conclude that polygon, IDS, and linear kriging give an average thickness close to the value obtained from realizations. Besides, they argue that linear kriging gives less variance than the others (Fig. 2). The first conclusion is expected, due to the well-known central limit theorem. The second is the result of the statistical properties of different estimators. Thus, the comparison presented in the paper is rather meaningless because the authors have failed to follow basic statistical procedures. The numerical results of different approaches to an estimation problem cannot be generalized. In conclusion, the paper is not a meaningful contribution, and sadly, quite erroneous. Reply by E.Y. Baafi and Y.C. Kim The two key contentions made by M.S. Azun regarding the paper are: deterministic methods should not be compared with statistical methods and, hence, the results are erroneous; and the paper does not make a meaningful contribution. The first contention is an academic one. Most practitioners in ore reserve estimation could care less whether the tool they are using falls under a deterministic or a probabilistic method, so long as it gives the desired answers. It is probably for this reason that, whenever any new tool such as linear kriging is introduced to practioners in the mining industry, they would like to see a comparison test performed between the existing and the more familiar tools with a new and "strange" tool. Only when a new tool passes such a test, the generally conservative mining community would begin to utilize the new tool to its advantage. The second contention, is a subjective one. The final judgment should be left up to the readers within the mining community. If kriging is accepted more among practitioners, partly due to the paper, then the paper makes a practical contribution to the state-of-the art in ore reserve estimation. Finally, M.S. Azun entirely missed two main points in the paper. The first is that any comparative study of kriging vs. Polygonal or IDS should be performed for local estimation and not for global estimation. In the past, kriging was frequently compared with other existing tools in its performance on global estimation. Such results were nearly identical due to the central limit theorem effect, which further prevented the acceptance of kriging by practitioners. The second point is that a single case study using an existing property, as it was frequently performed in the past, is not sufficient because results depend not only on the tool itself, but also on the nature of the mineralization.

Jan 3, 1984

By Steven M. Bishoff

The reclamation of surface land areas disturbed during the course of coal recovery became a major, universal consideration upon the implementation of the Surface Mining Control and Reclamation Act of 1977. This legislation not only established reclamation as an absolute requirement, but also presented guidelines for reclamation standards and required bond-posting procedures to assure completion of the reclamation process. The Office of Surface Mining was established to enforce the provisions of the Congressional mandate by promulgating specifically detailed regulations and supervising the State participation in this regulatory process. The major operational consequences of the reclamation-related provisions of the Act and the OSM regulations are the increased costs and complex procedures necessary to accommodate the regulatory authorities. It is anticipated that many of these costs and procedures have not been adequately evaluated by either the coal operators or the regulatory bodies. It is, therefore, necessary to proceed with an examination of the general reclamation processes, the effect of these processes on product costs, and the methods, if any, which may be utilized to minimize their impact on the overall operation.

Jan 1, 1981

By Jörg Weidemann, Peter W. Kuchar, Paul Burgwinkel

The West German Ruhrkohle AG and the engineering company BEDIA have developed an emission control system for diesel engines that is suitable for use in underground coal mining, consisting of a granular catalytic converter and a dry cooling system. Its first ever application was to a diesel mining locomotive. In the catalytic converter the exhaust gases pass over porous, platinum-covered ceramic balls in a double tube, oxidizing CO to CO2. Simultaneously, soot particles in the gases are subjected to afterburning. Laboratory tests carried out by BEDIA and at Aachen University of Technology showed that there was a reduction of over 80% in the CO content of the exhaust gases and over 30% in soot emission. The dry cooling system fulfills all the requirements demanded of exhaust cooling underground and does not have the disadvantages of conventional systems. It needs little maintenance, and it is light and compact. The most important components are a waterjacketed exhaust manifold, a tube and shell heat exchanger, a new type of flame arrestor in a stacked crimped ribbon design and a Venturi diluter. The system has its own thermostatically-controlled cooling circuit to keep the exhaust temperature between 120° C and 150° C, thus effectively preventing the tubes becoming blocked up.

Jan 1, 1989

By William P. Shinn

The site of Pittsburg from the first knowledge by white men of its location has been regarded as a position of great strategic importance.

By J. E. Litz

The hydrometallurgy review did not arrive in time for publication in the May issue. 1992 was not a banner year for hydrometallurgical installations or new hydrometallurgical developments. Installation of copper solvent extraction/electrowinning circuits were under construction or began operation in Nevada (Yerrington ), Arizona (SilverBell), Chile (Copiapo and Escondida), Peru (Toquepala and Cuayone) and Australia (Girilambone). These installations will produce more than 100 kt/a (110,000 stpy) of cathode copper. Several new heap leach gold facilities using conventional technologies were announced or were put into operation. New technologies undergoing widespread testing include biological oxidation of low-grade ores in a heap leach mode and evaluation of new agglomerating agents.

Jan 1, 1993

By Helen Joyce, Larry Twidwell, Jay McCloskey, Eric Dahlgren, Andy Hadden

The reduction of dissolved selenium oxyanions from mine wastewater utilizing an elemental iron cementation technology on been studied on a laboratory scale at Montana Tech of The University of Montana and on a pilot scale at MSE-Technology Applications as a water treatment process potentially capable of removing dissolved selenium to GO WL. Laboratory and pilot scale studies using elemental iron have demonstrated effective removal of dissolved selenium. Enhanced selenium reduction rates have been demonstrated when galvanically coupled iron/copper and iron/ nickel are utilized. The laboratory and pilot scale results are presented and discussed.

Jan 1, 2005

By Lars Söderberg, Eric Sandström, Per G. Broman

INTRODUCTION Boliden Mineral AB currently mines sulfide ores in 18 mines and processes them in eight concentrators. Most ores are typically complex. Gold consti¬tutes a considerable part of the value of the ore reserves. The value of total production in 1984, distributed by different metals is shown in the pie chart below. Traditionally, gold has been recovered as a byproduct, or coproduct, along with silver in floated copper and lead concen¬trates. Gold-price trends over the past decade have prompted comprehensive efforts by Boliden to increase the recovery of gold in concentration processes. Gravimetric recovery of gold in the grinding circuit is one method that has led to quick results. This method supplements tradi¬tional recovery processes based on flotation. The development of a feasible circuit, and the results obtained by its application in the central concentrator at Boliden, in the northern Swedish province of Västerbotten, are reported below. GOLD MINERALOGY IN BOLIDEN ORES The gold content in Boliden Mineral's ores is primarily in the form of alloys with the elements silver and mercury. A minor quantity appears in an unalloyed form.

Jan 1, 1986

By Firoze E. Katrak, John R. H. Black, Paul R. Ammann, Michael J. Loreth, Servi. Italo S.

Germanium is produced primarily as a by product from zinc concentrates. The important sources of gallium are alumina ores (bauxites) and zinc concentrates and residues from zinc processing. In addition, gallium as well as germanium may soon be recovered from a depleted copper mine near St. George, Utah. The major uses for germanium are in semiconductors, lenses in infrared optical systems, catalysts, and gamma radiation detectors. The major markets for gallium are in light-emitting diodes, solar cells, laser diodes, integrated circuits, microwave devices, and magnetic bubble memories. CRA projects a healthy growth in the demand for both metals. However, the role of scrap metal will continue to be important over the next decade, thus decreasing the overall demand for primary gallium and primary germanium. This paper summarizes the key elements and the economics of the markets for germanium and gallium. Much of the information, such as plant-by-plant costs of production and estimates of consumption by end use for various countries is from proprietary databases of Charles River Associates.

Jan 1, 1986

By P. R. G. Bak

The integration of interactive computer graphics technology with data analysis tools can assist in the evaluation of deposit models: the super- imposition of mine openings on complex geology can be quickly perceived using dynamic visualisation, colour-coding and transparency control while analysis functions assist in quantifying displayed information. To illustrate the functionality of such integration a research prototype system is presented which allows the interactive visualisation and evaluation of deposit models comprising both structural boundaries and the distribution of continuous properties.

Jan 1, 1992

My first regular job nearly fell through. My parents were spending the summer in California and I joined them at Lake Tahoe where we were guests at the lovely summer home of the Reids of Belmont. The time went quickly but I was eager to start work so I left for Bisbee a few days earlier than I had arranged. This was lucky, as just after I left a letter came from Gene Whitely, chief engineer of Calumet and Arizona, saying that because of the depressed copper industry there would be no job. I reached Bisbee on a Saturday morning, a day or two before my 23rd birthday, July 27, 1907. The brown plastei four-story Copper Queen Hotel was only a few steps from the station where the branch railway ended. I rented the cheapest room on the top floor and, of course, there was no elevator. I soon learned how to walk up the mile of switching tracks to the Calumet and Arizona office at the Irish Mag mine. I was horrified when Whitely told me about his letter telling me not to come, but since I had not received it he relented and said I could work for a short time anyhow. I was to start at 7:30 the next Monday morning, "holding the ignorant end of the tape”-in other words being surveyor's assistant, at $100 a month. Hours were from 7:30 to 5: 00, seven days a week. I spent Sunday walking around the town. I rented a room at the Royal Lodging House, which was cheaper than the hotel. It smelled strongly of carbolic acid but that meant no bugs. Compared with Cobalt or Cripple Creek, Bisbee didn't seem unattractive. The main street, with one or two-storied stores and saloons, followed the bottom of the canyon with high steep hills on both sides. My lodging house was on a rock in a narrow spot in the canyon, discouragingly called Tombstone Canyon. Chihuahua Hill, opposite the

Jan 1, 1976

By F. M. Doyle, P. E. Richardson, E. Peters

A number of studies have attempted to correlate the semiconducting properties of mineral sulfides with their chemical reactivity. Frequently such studies are conducted on polished or abraded electrodes. Defects produced by abrasion may mask the influence of the semiconducting properties of electrodes, e.g., by pinning the Fermi level at the surface or by reducing the lifetimes of photogenerated charge carriers. It is shown that pyrite and galena electrodes have photocurrents that are extremely sensitive to abrasion of the electrodes. On freshly fractured galena surfaces, the space charge layer is readily polarized. Wet-abrasion is shown to produce a relatively thick ptype layer on galena electrodes and this p-type layer has a pronounced effect on the photoresponse. On freshly fractured pyrite surfaces, the Fermi level at the surface is pinned by a surface state. Wet-polishing reduces the magnitude of the photocurrent by over an order of magnitude.

Jan 1, 1993

By T. Hall, R. Ferris

Waterjets and diamond wire saws have raised the productivity and lowered the cost in dimensional granite quarries. While the cost of diamond wire sawing is substantially lower than waterjet, the judicial use of the waterjet can simplify and improve the overall operating efficiency and predictability. Granite is the hardest commercial stone and only the gem-stones garnet and diamonds are harder. The introduction of industrial diamonds has made it possible to quarry and process granite at costs equal to or less than other natural stones – making granite, with its superior properties, the best value available.

Jan 1, 2004

By Charles E. Weaver

A core from the La Camelia attapulgite mine in north Florida was studied in detail to determine the detailed vertical variability and the relations of the various parameters. The structural, textural, mineralogical and chemical data indicate there are two major depositional cycles represented within the minable interval. The sediments deposited during the two cycle differ in detail but in general are similar. The environments of deposition grade from shallow marine to lagoonal to tidal flat to marsh. The sedimentary structure (lamination, burrows, pebble conglomerate), mineralogy (attapulgite, montmorillonite, sepiolite, dolomite, calcite) chemistry (Al, Mg, Fe) are closely related to each other and their nature is determined by the depositional environments. Most of the clay minerals and carbonate minerals are authigenic and are therefore particularly sensitive to environmental differences. The variability and environmental features seen in this core are characteristic of the sediments in the general attapulgite mining area. A detailed understanding of the relationships discussed should be of value in prospecting, mining and processing.

Jan 1, 1972

By A. L. Mular

Optimization has been defined as the procedure of locating the best of something or the best way of doing something (Mular, 1971). Several texts (Himmelblau, 1972; Ray and Szekeley, 1973; Box and Draper, 1969; and Lee, Adams, and Gaines, 1968) on the subject are available. Such techniques have been placed in two categories, namely, off-line optimization and on-line optimization. For the former, an optimization model is employed; for the latter, a black box approach is involved. The essence of an optimization problem becomes obvious, when a response surface is considered. Suppose that a response (in this case, a criterion of improvement such as profit per day; grade of concentrate per day) denoted by Y, depends only on two variables, X1 and X2, which can be manipulated and controlled. The relationship between Y, X1 and X2 may be represented graphically as shown in Fig. 1. The diagram is called a response surface and its height, Y, is determined by X1 and X2. Points associated with equal responses constitute response contours. The shape is that of a hill, and optimization is the procedure of ascending the hill to reach the top (maximum). In practice, a response surface is subject to disturbances which distort its shape and shift its location from time to time, so that the exact location of a maximum is imprecise. Generally, constraints (restrictions of some sort) on responses and manipulable variables serve to define a region of permissible operation.

Jan 1, 1979

By M. E. Breitrick

Newmont Gold operates the Carlin East underground, one of four underground gold mines the company operates in northeastern Nevada. Carlin East began full production in early 1995. The mine's current rate is 900 t/d (1,000 stpd), producing about 4.6 t/a (150,000 oz/year). About 125 hourly and salaried personnel are employed at the project for its estimated six-year mine life. Two mining methods are currently used at the Carlin East Mine. Longhole stoping with cemented backfill accounts for 70% of the total mine production. Conventional underhand drift and cemented fill accounts for the balance of the daily tonnage. In December 1996. Newmont purchased an AC-Eickhoff ET-210 roadheader. The machine went into service in mid-June 1997. It is used in longhole Stope topcut development and cut-and-fill production at a rate of 225 t/d (250 stpd)

Jan 1, 1998