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By K. V. Viswanathan, P. Sornasundaran, S. E. El-Mofty

Dolomite is found to undergo preferential dissolution in aqueous solutions and this is found to be strongly dependent on the solid to liquid ratio (SIL). Electrokinetic studies done under the sump conditions revealed that the mineral surface charge is also affected markedly by the solid content in the suspension. Conditioning of the dolomite at low SIL ratios for short time intervals showed preferential dissolution of calcium leading to a magnesium-enriched dolomite surface. At higher SIL ratios and longer conditioning times, calcium depletion from the solution and a calcium-enriched dolomite surface resulted. The results are discussed in terms of surface precipitation and/or bulk precipitation and surface conversion of dolomite to the calcium-enriched phase (calcium carbonate and/or magnesian calcites).

Jan 1, 1990

By J. F. Brune

"Re-occurring face ignitions in U.S. coal mines are concerning and require a closer look at air quality monitoring systems and practices employed in these mines. The explosion disaster at the Upper Big Branch mine in West Virginia in 2010 caused 29 fatal injuries and was largely caused by inadequate water sprays and inadequate ventilation monitoring. In this comparison, the author compares ventilation system monitoring in Australian, German and U.S. underground coal mines and makes recommendations for improvements and best practices. Mines in Germany and Australia are adhering to more stringent requirements for monitoring air quality and quantity and for monitoring water spray systems on cutters to prevent frictional ignitions. Air quality should to be monitored for sufficient oxygen, toxic gases, explosibility and for fire gases indicating a potential fire. Ventilation monitors must also confirm that sufficient quantities of air are available. Fully automated, continuously recording atmospheric monitoring and alarm systems are established practices in Germany and Australia and should be mandated for U.S. mines as well, in addition to the current, regular spot inspections of the ventilation system by certified mine examiners. BACKGROUND: METHANE EXPLOSIONS, FACE IGNITIONS AND NEED FOR AIR QUALITY MONITORING Accumulations of methane in face areas of underground coal mines frequently lead to ignitions that can cause burns, traumatic injuries and, in the case of the 2010 Upper Big Branch disaster, cause major explosions with multiple fatalities. Table 1 shows the number of reported face ignitions in U.S. coal mines between 2010 and 2014, based on statistical data published by MSHA (MSHA 2010 – 2014). Although there appears to be a downward trend in such ignition incidents over time, ignitions continue to occur with some regularity; and each ignition may cause a potentially catastrophic mine explosion.Per regulation, all U.S. coal mining machinery, continuous miners and longwall equipment, is outfitted with continuously monitoring methane sensors wired to cut power to the equipment as the methane level exceeds 1%. Face ignitions keep occurring because these sensors are usually not positioned in sufficiently close proximity to the coal cutting drums or to the freshly exposed coal face where the methane is most likely released. Therefore, methane may accumulate in explosive concentrations near the coal face and the cutting drums long before the gas concentration reaches the 1% level near the monitor and creates an alarm."

Jan 1, 2016

By A. P. Mehta

The role of microorganisms in the leaching of metal sulfides is well established (Torma, 1977; Murr, 1980). However, this established knowledge applies mostly to chemolithotropic microorganisms such as Thiobacillus ferrooxidans which function optimally in leaching catalysis between 25-35° C, and in a pH range of 2-2.5. Although leaching with thermophilic microorganisms capable of extending the range of catalytic viability beyond 35° C is also documented, there are few if any attempts to optimize or extend sulfide concentrate leaching with thermophilic microorganisms. When mixed metal sulfides or other materials having different rest potentials (referenced to the standard hydrogen electrode, SHE, in the electromotive series) make contact in a conducting, aqueous medium, the contacting members will act as an electrochemical cell, with the member having the higher rest potential assuming the role of an electrical cathode. In leaching reactions involving such galvanic couples, the cathode becomes passivated, while the anodic member reacts vigorously due to the electro- chemical reaction which occurs (Hiskey and Wads- worth, 1975). Serry, eta1 (1978) observed that when chalcopyrite and pyrite were in intimate contact in natural ores, the chalcopyrite reacted vigorously by galvanic conversion as a result of the higher rest potential (~ 0.63 V) as compared to the chalcopyrite (~ 0.53 V). In addition, it was postulated that because of the elemental sulfur which can form on the anodic chalcopyrite in this galvanic conversion process, reactions in acid-bacterial medium would be expected to have accelerated copper extraction because of the conversion of any sulfur product layer on the chalcopyrite anode to sulfuric acid according to the following general reactions: [MS?M2+ + S° + 2e- (1) and 2S° + 302 + 2H20 bacteria?-2H2SO 4 (2)] where M in reaction (1) designates the metal (or metals in the specific case of chalcopyrite) to be released to solution by galvanic conversion.

Jan 1, 1982

By F. Milton Lewis

In this paper an attempt has been made to review the cost trends in producing copper by conventional milling. smelting and hydro-metallurgical means during the last five years. The primary objectives of this cost analysis are to provide a base for future projections as well as to indicate which cost items are more volatile in their influence on overall cost of producing copper.

Jan 1, 1977

By G. L. Mowrey

In addition to developing various types of coal interface detection systems, the U.S. Bureau of Mines is actively involved in developing a coal rib thickness monitoring system for high wall mining applications. One particular system that appears to show promise uses a ground-penetrating radar system to detect the coal-air boundaries of coal ribs. Based on preliminary laboratory and field tests, results indicate that this method can be applied successfully in highwall mines to maintain a constant rib thickness. The coal seam should be relatively clean in the vicinity of the antenna (e.g., have minimal partings or dirt bands) for best results.

Jan 1, 1995

By Ossi V. I. Hintikka

There are several limestone deposits around the Lohja area in southern Finland. Raw material for cement rock is mined from some of them. The formations are geologically complicated, and therefore selective mining is used whenever possible. One of these mines is the Tytyri underground limestone mine, which is divided into two parts; Törmä and Solhem. In addition to the selective mining system hand sorting or picking must be used at the Tytyri mine to improve the overall grade of the blended limestone. Some means were needed in order to improve the quality and to increase the feed rate by the elimination of hand sorting. Sorting machines were considered and eventually a Sortex 811MW was pilot plant tested at the Ojamo mine near Tytyri. This machine now continues to be used on production.

Jan 1, 1971

In cold regions rinsing of spent cyanide leach heaps is stopped during winter and is resumed again after snow melts. The effect of this idle time on the overall cyanide removal process was studied in this work. Samples were collected for rinsing tests from one heap at the Ryan Lode Mine of Citigold Alaska, Inc., near Fairbanks. The material was tested for cyanide removal a large column, 1.22 m high by 20 cm square, and in a small column, 1.22 m high by 10 cm in diameter. The rinse water was analyzed at regular intervals to determine the rate of cyanide removal from the solids. It was found that diffusion plays a major role in the removal of cyanide from the ore particles. Calculations showed that the insulating effect of the snow cover on the heap provides an excellent moderates the interior temperature of the heap, and would be expected to help the progress of the diffusion reaction during winter. The result expected result wil1 be higher cyanide values reporting to the rinse water after snow-melt.

Jan 1, 1993

By Dipl. -Ing. Mertens

Gentlemen: I am pleased and regard it as a priviledge to give you a report on rapid roadheading with heading machines in the coal mining industry of Western Germany. Importance of Heading Operations in the West German Coal Mining Industry Every year about 770 km of headings are driven In the seams of the West German coal mines, most of them gate roads, the rest rise headings, to open new faces. In thick seams the heading operations are carried out entirely in the coal, in thin seams the country rock has to be ripped. The total length of 770 km corresponds to a rock volume of roughly 9.5 million m3; this figure underlines the importance of the heading operations in the coal mining industry of our country.

Jan 1, 1970

By F. B. Olender

Idler engineering, operation, and maintenance cannot be covered in depth in a short paper. Therefore, this will be a general look into the subject matter in light or the present-day technology. Depending on the source or reference used, belts for handling bulk material underground came into being between 1900 and 1920, while strip mining appeared in the thirties. The conveyor belt speeds in that era were in the 300 rpm to 500 rpm range. Belt speeds or 600-700 rpm were in vogue in the thirties, and the early sixties saw speeds or 800-900 rpm. Today, speeds or 1000 rpm are not looked at with dismay; in fact, speeds or 2000 rpm are being discussed. Among the driving forces moving the bulk materials handling industry to these greater heights have been the mining operators and engineers. Their appetite to increase output, yield, and reduced per-ton costs has constantly challenged the bulk material handling industry to develop products capable or handling these increased capacities. One or the products affected by this movement is the idler. Apart from the conveyor belt itself, it is one or the most significant parts or a conveyor system because or the sheer numbers needed in an installation.

Jan 1, 1971

By Summers D. A.

A mining machine has been designed and fabricated to mine coal from room and pillar operations combining high pressure waterjet cutting and mechanical fragmentation. Waterjets are used to slot the coal face with an advancing plow wedge then breaking out larger coal pieces. The machine has the following advantages: - simply built around a disassembled longwall chock and gathering arm loader apron; - few moving parts which are simply and inexpensively maintained; provides immediate roof support in the face working area; - coal produced is larger, with resulting lower preparation cost; - no dust is generated; - risk of spark generation is virtually eliminated.

Jan 1, 1992

By Sotiris Psomas, Colin M. Eddie

"Steel Fibre Reinforced Concrete (SFRC) Segmental Tunnel Linings have successfully been used for over 20 years in the UK and have been adopted in a number of high profile projects such as High Speed 1, Crossrail, Thames Tideway, as well as High Speed 2. Tunnel linings and especially SFRC design are not covered in the Eurocodes. This shortage of SFRC tunnel design rules seems to be partially addressed by several international publications. However, in the UK, the ‘design-assisted by testing’ (DAT) approach has also been adopted. The Paper discusses the UK’s best design practice and focuses on the DAT methodology as applied in the case of the 6.9km (4.3miles), 7.8m (25.6 feet) ID Lining for the £635million Lee Tunnel Project. The design approach, the full scale testing at the Building Research Establishment (BRE), and the construction innovations are presented. This experience will be transferred to the £4billion Thames Tideway Tunnel.INTRODUCTIONSteel Fibre Reinforced Concrete (SFRC) has been used for Tunnel segments for more than 20 years. The first application of SFRC in the UK was for the Heathrow Baggage tunnel (1994). Since then significant size tunnels have been designed and constructed, such as the Jubilee Line (1999) High Speed 1 (CTRL, 2006), Crossrail (2014), Lee Tunnel (2014) and the scheduled 25km Thames Tideway (‘Super Sewer’) and High Speed 2 rail tunnels. However one the main obstacles in achieving streamlined design and improving efficiency are the lack of appropriate design guidelines for SFRC tunnel segments. This issue will – to some extent – be addressed by a number of current documents on tunnel FRC design either being produced by BSi (PAS8810, expected 2016), ACI (544.R) and ITAtech (Design Guideline PCFRC, 2015) in an effort to advance the design of SFRC and take into consideration the recent developments in Steel and Macro-Synthetic FRC technology."

Jan 1, 2016

By T. A. Lloyd

The use of tank cells over the years has provided a means for low cost, space efficient, extra capacity in existing flotation circuits. In some cases, new plants have selected tank cells as the machine of choice. Typical tank cells use high efficiency impellers for mixing, which results in low power draw. Unfortunately, these mixers have poor aerating characteristics that compromise metallurgical performance. This has all changed with Outokumpu's new flotation concepts. Outokumpu has recently developed the HG or High Grade flotation cell that can provide higher recovery with better selectivity while maintaining the simple operation of conventional cells.

Jan 1, 1993

By Roger Holmberg

INTRODUCTION The driving of drifts is a very important aspect of underground mining. It is not unusual for the percent¬age of rock broken during development in a mine using sublevel caving, for example, to be as much as 25% of the total. If one also considers the amount broken for transport, ventilation, and exploration drifts, one can easily understand that the planning and excavation of drifts play a major part in the total economics of the mine (Fig. 1). Increasing mechanization in mining demands larger tunnel areas for transport and mining equipment. With modern machines the hard work involved in using hand¬held pushers is gone, and a better environment is achieved. More rational methods could be used, but much of the experience the working man acquired by working close to the rock face (such as utilizing the natural weak planes in the rock when he placed the drill¬ing holes) has unfortunately been lost. By having sepa¬rate shifts for drilling, loading, and hauling, more atten¬tion has to be placed upon a well-designed drilling pattern. Some reduction in the number of holes required can be achieved with mechanized drilling because of the larger holes that can be produced. On the other hand, it is probably not possible to achieve the same precision as with pneumatic pushers, and it is difficult to utilize the larger holes because these cause more damage to the re¬maining rock. Recently, however, the precision has be¬come very good with the parallel booms and automatic devices for setting the lookout angle (Fig. 2). A larger arch of the drift roof requires a more carefully executed blasting procedure than before in order to prevent rock fall and to insure a sufficiently long stand-up time. In this chapter, empirical relationships that can be used to design an economic and optimal drift blasting design will be presented. The principles of the calcula¬tion method are based upon the earlier work of Langefors and Kihlström (1963) and Gustafsson (1973). COMPARISON OF EXPLOSIVES To provide for the use of various explosives it is necessary to have a basis of comparison. Several meth¬ods have been developed to characterize the strength of an explosive. Some examples are comparison of values given by (1) calculated explosion energies; (2) the ballistic mortar test; (3) the Trauzl lead block test; (4) the brisance test; (5) the weight strength concept; and (6) the underwater test. However, most of these meth¬ods should be used carefully when stating the breaking

Jan 1, 1982

By Simon W. Houlding

This paper summarizes recent developments in computer modelling and estimation technology. Significant improvements in computational and modelling efficiencies have advanced technical computing to the stage where, for the first time, it can be realistically applied to short-term mine planning and production control. Real-time interactive grade estimation of complex shapes, volumes and grade distributions, based on immediate turn-around of production sample grades, is now possible. An added benefit is the ability to produce complete geostatistical estimates which include confidence limits. These can be incorporated into the decision making and risk assessment processes of production control. Why the need for new technology? What is wrong with the conventional methods which have sufficed for the last thirty years? The response is manyfold. They suffer from inefficient computational processes and conflicts with geostatistical theory. They are responsible for constricting the flow of information between the disciplines involved in the mine production process. Finally, it is illogical to approximate irregular geological and mining volumes with orthogonal sets of rectangular blocks. Geological materials do not occur in block formation; and mining methods which excavate rectangular blocks have yet to be developed. Other computer based technologies have evolved out of the dark ages of rectangular approximations and have successfully dealt with irregular three-dimensional geometries. It is time for computing in the mining industry to follow this example and take full advantage of available technology. To provide the necessary background, consider the basic requirements for successful implementation of technical computing within the mine production process.

Jan 1, 1992

By Edmond F. Lawrence

The Calico area lies within the Walker Lane fault zone, six miles north of Schurz, Nevada. The mineralized area is overlain by a thick section of Tertiary tuffs and ash-flows, that have been intruded by a series of andesite plug, dikes, and sills. The pre-Tertiary rocks outcrops only in two areas at one to two miles distance from the drilling areas. Underlying the volcanics are sediments ranging from siltstones, sandstone, calcareous shales, to carbonates of the Luning sequence. These have been intruded by one or more phaneritic intrusives ranging in composition from quartz diorite to quartz monzonite, with the development of a skarn zone on the south flank that contains extensive mineralization consisting of magnetite, pyrrhotite, pyrite, and chalcopytite, with traces of sphalerite, galena, and molybdenite. The magnetite, pyrrhotite, and part of the pyrite appears to be contemporaneous with the skarn, while, part of the chalcopyrite, galena, sphalerite, molybdenite, quartz, and calcite, occurs as minute veinlets cutting the other minerals. This later mineralization may be associated with a late stage of the same sequence, or possibly associated with another intrusive to the southwest. Geophysical work has consisted of aerial magnetics, ground magnetics, gravity, seismic, and induced polarization surveys. Preliminary induced polarization surveys indicated anomalies at depth, both over the magnetic anomaly and to the northwest. Subsequent IP work confirmed this earlier anomaly, and drilling disclosed extensive mineralization at depths of 400 feet on the northwest end and over 1,000 feet to the southeast.

Jan 1, 1967

By P. A. S. Manning

Eastern Jamaica consists predominantly of non-carbonate rocks reaching elevations of over 2200 m. The area is drained by a well established river network which supplies close to 30% of the sand and gravel used by the building and construction sector. Present high extraction rates and slow rates of replenishment will result in early exhaustion of this source of aggregate. A number of volcanic and carbonate rocks are being examined as a possible source of high quality aggregate which meet the requirements for all types of construction. Preliminary evaluations show a dacitic deposit to be the most suitable source for aggregate use.

Jan 1, 1998

By Don C. White

Santa Rosa is a mid-Tertiary, volcanic-hosted, bulk-mineable, open-pitable, heap-leachable, gold-silver deposit. It is the product of hydrothermal mineralization along an arcuate segment of a caldera collapse ring fault in a probable maar volcanic setting. This segment was later broken by radial faults. Gold occurs principally as electrum finely disseminated through intermediate tuffs, and associated with pyrite, at Santa Rosa. The nearby Alto de la Mina deposit displays stockwork silica-pyrite-gold in a tectonically and hydrothermally shattered andesite flow. Miocene epithermal mineralization was accompanied by central silicification and pyritization and more distal argillization. An andesite flow cap rock at Santa Rosa played a pivotal role as an upward permeability barrier. Highest gold grades and most intense alteration occur closest to the ring faults and immediately beneath the andesite flow. Supergene alteration effects on the gold distribution are minimal.

Jan 1, 1993

By J. W. Stevenson

At this 5th U.S. Mine Ventilation Symposium I would like to focus your attention on safety and the contribution of the ventilation engineer over the past 50 years. This conference affords us the opportunity to express, to listen, and to learn. As ventilation engineers it is indeed an exciting time--a time that not only stimulates our imagination but also pin points our aims in our quest to obtain zero fatalities by the year 2000, the goal expressed by William J. Tattersall, Assistant Secretary of Labor, Mine Safety and Health Administration. In the past, coal mine ventilation has often been unfortunately synonymous with explosions and resulting fires. Those not familiar with us do not recognize the painful evolution of the coal mining industry and particularly the evolution of mine ventilation. To put my presentation into perspective, I recently reviewed a U.S. Bureau of Mines Bulletin No. 586 - "Historical Summary of Coal-Mine Explosions in the United States 1810 - 1958 prepared by H. B. Humphrey Mining Health and Safety Engineer. This bulletin was published in 1960. Mr. Humphrey stated "In 1946, factors contributing to the explosions occurring from 1941 to 1945 were: (1) The rapid increase in the use of electrical equipment at face regions where gas and dust are most likely to be found; (2) the increased demand for coal with the desire to obtain maximum tonnage per machine at minimum cost, which in many mines has resulted in neglect of even rudimentary precautionary measures; (3) multiple-shift operation without provision of time for adequate maintenance of equipment, effective rock dusting, and testing for gas; (4) decrease in supervision owing to demands on supervisors for maximum tonnage and loss of competent supervisors to other employment; (5) lack of effective supervision, owing to numerous new conditions, some of them war-connected; (6) inability to obtain adequate equipment repair and replacement parts; (7) shortage of labor and inadequate training of coal-mine workers; and (8) failure of both miners and mining officials to show regard for safety in changing from hand-loading to mechanized methods". Most of the eight factors listed by Mr. Humphrey continue to affect our work lives as mining engineers. The increased demand for coal with the desire to obtain maximum tonnage per machine at minimum cost has never changed. The local and regionalized coal industry of the 40's is today competing against the world coal market. Our mines work or shut down based on cost. This has always been the case. During the five year time-frame Mr. Humphrey was documenting, 345 miners were killed in major explosions. A major explosion was one in which five or more miners were killed in a single accident. In addition, 105 more miners were killed in minor explosions for a total of 450. What a wanton waste of life. What fears, anxieties, miseries, and sufferings were created by these accidents. However, we must remember and keep in mind that the coal mining company officials, engineers, and foremen, the governmental agencies- federal, state, and local - were using the technical tools and knowledge available to operate the mines as safely as they could. Obviously mine ventilation engineering technology was woefully inadequate.

Jan 1, 1991

By F. Warnaars

Historically, this area produced gold and silver from many well-known vein deposits, like Tayoltita, Topia, and San Jose de Gracia. Modern exploration identified three categories of deposits: 1) low grade porphyry golds in shallow level dacite porphyries; 2) batholith-related deposits; and 3) those formed in volcanic sequences of Late Cretaceous to Late Tertiary. At least four porphyry golds have been identified, of which Metates is best known. These are formed by and within dacite porphyries, associated hydrothermal breccias and sometimes within surrounding metasediments. Their ages are from mid-Cretaceous to Early Tertiary. Precious metal deposits associated with batholiths occur as veins, contact haloes in metasediments or volcanics, skarns, tectonic breccias, hydrothermal tourmaline breccias, dacite dikes or as disseminated or stockwork deposits such as La Fortuna. Several new gold discoveries were made in older Early Tertiary Volcanic Sequences and in the younger Tertiary volcanics within prominent structures exceeding 3 to 5 km in lengths. Some of these are open-pittable but most have to be mined by underground methods.

Jan 1, 1999

By C. W. Chiaretta

Utah Power and Light Company's Deer Creek Mine had been developed to a point where mine ventilation efficiency had declined to an unacceptable level. Problems identified were ventilation of inactive areas, excessive leakage, and restrictions in the return and intake air ways. Mine management implemented an intensive mine ventilation improvement program to alleviate future problems with respirable dust in the working sections and diesel equipment emissions. Program objectives included sealing of inactive areas of the mine, rehabilitation of high resistance areas, and construction of additional intake and return aircourses. Applications of computer modeling techniques are used to predict the effects of ventilation changes and improvements. Improvements are then prioritized to achieve the largest efficiency increases first. Actual real time assessment of the mine environment and ventilation changes are accomplished with a mine wide monitoring computer system. The Deer Creek ventilation improvement program has more than doubled the ventilating efficiency of the mine.

Jan 1, 1990