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By Gordon R. Haworth

Conditions affecting minerals investments are continuing to change at an increasing rate, and in this paper we will attempt to predict the course of mine financing in the future. We will first review the situation historically and then examine the problems and constraints that are now making the financing task more difficult. Suggested solutions are discussed, and a new method of financing a group of mining projects is hypothesized.

Jan 1, 1977

By J. A. Marts, R. C. Gilmore, Jr. Bogin, S. A. Saki, J. F. Brune, J. W. Grubb

"Colorado School of MinesResearchers at Colorado School of Mines (CSM) have developed computational fluid dynamic (CFD) models to study gas distributions and explosion and fire hazards in longwall gobs. In underground coal mines, methane continuously emitted from surrounding strata mixes with air from active mine workings and may form explosive gas zones (EGZs). Some western United States coal mines are also prone to spontaneous combustion (spon com). Insight into oxygen concentrations within the gob is crucial for assessing spon com hazards and mitigation strategies. Nitrogen injection used in conjunction with progressive gob sealing can reduce EGZs and spon com hazards by forming a dynamic seal that separates the methane in the gob from the air that ingresses from the face. This paper describes CFD modeling simulations studying the formation of such dynamic seals by optimizing the nitrogen injection locations. The impact of nitrogen on oxygen ingress and formation of EGZs is discussed. Optimum nitrogen injection quantities and injection locations were determined. Dynamic seal formation is most effective if the headgate nitrogen injection locations are split between the first crosscut inby the face and a second location about 300 m (1,000 ft) further inby. INTRODUCTION Underground longwall coal mine ventilation systems are designed to dilute hazardous gases and to provide breathable air to miners working in the area. Methane gas is liberated as the mining process extracts the coal and disturbs the surrounding strata. Methane mixes with the ventilation air and often produces explosive gas zones (EGZs) within longwall gobs (Brune 2013). Past CFD modeling research of underground coal mine ventilation systems has shown the effects of face air quantity on EGZs (Worrall 2012) and nitrogen injection to control spon com (Balusu et al. 2005; Ren et al. 2012; Ren et al. 2011; Smith and Yuan, 2008; Yuan and Smith, 2014). Other modeling approaches include network ventilation models of oxygen ingress (Dziurzynski and Wasilewski, 2012), and coupled Linear Network CFD algorithms (Wedding 2014). In a project sponsored by the National Institute for Occupational Safety and Health (NIOSH), CSM researchers are using Fluent®, a CFD software package by ANSYS, Inc., to model gas compositions and flows in underground longwall gobs. Figure 1 shows a progressively sealed gob with a U-type ventilation system in a three entry development. As the longwall advances, seals are constructed along the headgate in the crosscuts between the center entry and the gob. Additional gob isolation seals are built to block off the headgate entries inby the face. Nitrogen is injected through the seals in the first two crosscuts on the headgate side and at the first crosscut inby the face on the tailgate side, as shown in Figure 1."

Jan 1, 2015

By Adrian Brown

Groundwater inflow and impacts have become major aspects in the permitting and operation of many gold mines. First, the hydrothermal or placer genesis of many of the orebodies being investigated or produced today almost guarantees that mines will be "wet", involving groundwater control as part of operations. Second, the style of ore deposition a1 so often involves a1teration of the host rock, resulting in relatively weak, low permeabi1ity materials that require extensive groundwater pressure control for stable mining. Third, the location of many mines in arid areas guarantees that impacts on water resources will be matters of key focus during permitting and operation. However, groundwater control and protection is a technically difficult area and often involves managerial decisions and activities that do not fit comfortably into traditional mining. In an attempt to overcome some of these difficulties, this paper provides a guide to mine managers and hydrologists as to appropriate strategies for designing, setting up, operating, and evaluating groundwater programs at gold mines that get the job done and are cost effective.

Jan 1, 1988

By R. Karl Zipf, Z. T. Bieniawski

Based on the premise that understanding the fundamental mechanics of fine fragment formation in coal will lead to reducing coal dust problems in mines, a thorough study of the mechanics of crack propagation in coal was undertaken. Two approaches were considered in an attempt to understand and quantify the fracture process as it relates to fine fragment formation. In one approach, theoretical models are used which describe the size of the fracture process zone which may relate to the amount of structural damage and fine fragment formation on the new crack surface. The other approach is based on the relationship between crack tip stress intensity and new surface appearance for mixed mode crack propagation. Preliminary observations with a scanning electron microscope support the premise that fine fragment formation is related to fracture surface appearance and fracture initiation conditions. An experimental program designed to supply the input parameters for these approaches is presently underway. The experimentation features mixed mode fracture toughness testing, using a special mixed mode testing rig, and fracture velocity measurements with a crack propagation gage. The interpretation of this data via the approaches discussed will provide further under- standing of the mechanics of fine fragment formation in coal.

Jan 1, 1986

By David M. Mchaina, Allan E. Hall, Siegfried Rohr, J. D. Botsford

Incidents associated with secondary dust ignitions in the mining of massive sulphide ore deposits are of major concern in Canadian underground metal mines. During stope or development blasting, a highly concentrated cloud of sulfide dust is created and may be ignited, resulting a secondary explosion which releases a considerable volume of sulphur dioxide and possibly other sulphur gases. The consequent pressure, heat and toxic gases can result in loss of life, significant damage to equipment and loss of production. These losses are expensive and should be prevented. Explosions of this type have occurred at the H-W mine of Westmin Resources mainly in the development headings and cut and fill stapes. This paper presents the results of a study conducted at the H-W mine to compare dust sampling methods for explosivity tests. The associated benefits and pitfalls of each sampling technique are examined. The investigative work conducted to develop and test preventive and control methods against sulphide dust ignitions is also discussed. The techniques which will minimize the risk of sulphide dust ignition in metalliferous mines are outlined. A review of current preventive and control measures practised at the H-W mine is also presented.

Jan 1, 1989

By J. Brent Hiskey

INTRODUCTION Metal electrodeposition processes are of fundamental technological importance to a number of fields. Electrorefining, electrowinning, electroplating, and electrogalvanizing have all been the subject of intense study for over a century. More recently, electrochem- ical deposition has played a critical role in advances in microelectronics and lately has been an enabling technology for the production of certain nanostructured materials. Electrometallurgists have most frequently been concerned with the structure and morphology of massive deposits. For example, in metal recovery steps such as electrorefining and electrowinning, deposits demonstrating adherent coarse-grained characteristics are most desirable. In the case of electroplating, a bright fine-grained, tenacious and strongly adherent deposit is required. The fabrication of microelectronic devices and the production of nanoscale structures such as nanoparticles, nanowires, and nanorods requires a keen understanding of early stage deposition effects. The initial stages of metal deposition, usually referred to as electroclystallization, are fundamentally linked to nucleation and growth phenomena. Early stage deposits are typically very ordered. Whereas, bulk metal deposition structures are much more ran- dom. In both cases, the discharge of a metal ion at an electrified interface is represented by simple cathodic reduction as follows: [ ] Me(H2O)xn[ ] is a hydrated metal ion residing in the bulk solution and Me is the metal atom occupying a crystallographic lattice position. A similar reduction reaction can be

Jan 1, 2005

By Robert Snow, Yingxue Yu, Howard Hanson, Patrick Zhang

One of the major current efforts by the Florida phosphate industry to reduce deep aquifer water consumption is to use 100% recycle water for flotation. This measure alone could save billions of gallons of deep well water annually. However, this also results in higher suspended solids (slimes) in flotation water, causing poor process performance particularly for amine flotation. Polymers could play a major role in allowing the industry to use high-turbidity recycle water for amine flotation without compromising its impact on the Florida economy. The enhancement of rougher flotation by polymers may also have potential. Most importantly, dramatic efficiency improvement may be realized by floating silica first. Adding polymer to flotation feed and/or water is perhaps the most economically viable way of reversing the Crago "double float" process, in order to reduce operating costs and increase phosphate recovery. This paper presents both laboratory and pilot flotation data showing the effect of different polymers on collector dosage and flotation recovery. There appeared to be an optimal range of polymer concentration beyond which the benefits do not offset the drop in phosphate recovery. The effect of poly mer is slime-level dependent. Pilot testing data show that the "Reverse Crago" process (floating silica first followed by phosphate flotation) can outperform the Crago process.

Jan 1, 1999

By D. L. Jones, S. Knoerr, J. Mansanti

The Buckhorn Mine in Nevada currently treats oxide ore using heap leach methods, but exploration has identified sulphide reserves which are refractory in nature. Preliminary testwork was conducted on the sulphide material to screen potential pre-cyanidation treatment methods. Processes evaluated included pressure oxidation, biological oxidation, nitric acid oxidation and roasting. An initial economic and process analysis of the results concluded that roasting was the only viable process, and only if the roaster off-gases were converted to soleable sulphuric acid. Further economic analysis indicated that roasting of the whole ore was more attractive than pre-concentrating by flotation, followed by roasting of the concentrate. These results were generalized to show that for high sulphur ore a roaster/acid plant combination is more attractive that either of the other options, ie. pressure leaching or bioleaching, provided the by-product acid is soleable.

Jan 1, 1990

By William C. Larson

The number of uranium in situ leach operations has increased significantly since 1975. As of May, 1980, there were a total of 27 active projects, including 16 commercial scale operations (or under construction) and 11 pilot scale operations. The south Texas uranium district and Wyoming have been the most prominent areas in early field experiments as well as in commercial application of this new recovery technique, although in situ leach tests are now being conducted in Colorado and New Mexico. The growing number of commercial-scale operations is accepted as prima facie evidence that in situ mining now offers a third option along with open pit and underground mining for winning uranium from sandstone host rocks. It is estimated that in 1979 about 9 percent of the nation's total uranium production was from in situ mining. However in situ mining of uranium is not without its environmental controls. The primary emphasis of environmental controls falls into two catagories; namely, control of the leach solutions during mining and demonstration of ground water restoration. Finally this paper briefly reviews the Bureau of Mines research program in uranium in situ mining.

Jan 1, 1980

By Giin-Fa Fuh, Sally A. Shoop

An instrumentation program was developed based on the results of an analytical study of the geomechanical effects of longer longwall face lengths. Boundary element simulations showed that longer face lengths can cause in- creased face convergence and an increase in the shear stresses in the immediate roof. Empirical design methods predict that longer faces will cause little effect on abutment stresses as long as the roof caving is well behaved. On this basis, a longwall face instrumentation program was designed with emphasis on the interaction between face support and ground response for optimizing face conditions. At a 600-foot (183 m) face, five midface shields and two headgate shields were monitored with vary- ing hydraulic pump pressure. The instrumentation included six convergence rods with linear potentiometers to measure canopy-to-toe convergence; fourteen pressure transducers to monitor leg pressures; and two portable data loggers. Similar instrumentation will be in- stalled on a 750-foot (229 m) face for comparison. The results from the 600-foot (183 m) face indicate that a ground reaction curve, as determined from the relationship between the sup- port set pressure and the roof convergence, can be used to optimize the support pressure to control convergence, the key element to ground stability in the face area.

Jan 1, 1986

By Dae S. Young

The Disjunctive Kriging (DK) procedure was developed to estimate ore recovery figures within a deposit/ domain from limited diamond drill hole (DDH) core assay data taken at the exploration stage. Local recovery figures include minable ore tonnage and ore grades within relatively small areas such as stopes or small panels on a pit bench, for a given cut-off grade. The grade and tonnage should be computed based on the true selective mining units, that is, the average grade distribution of selective mining units within a panel. Local recovery figures are critical information for economic and engineering feasibility studies before mine development, as well as for short-term mine planning for operating mines. This kind of information can be provided only by non-linear geostatistical methods including DK and the Multivariate Gaussian Approach (MG) (Journel, 2, Parker, et al, 5).

Jan 1, 1982

By Joseph J. Wojcik

INTRODUCTION A great deal more is involved in a sampling effort directed at a placer deposit than physically capturing a quantity of representative material and extracting the desired component. The distribution and dimensions of the sample sites must be chosen after consideration has been given to the type of deposit and the concentrating mechanism. Interpretation of the sampling results is likewise an extremely important part of the sampling program. SAMPLE SPACING The interpretation begins with the selection and design of the sampling program. A decision regarding genesis of the deposits and their geometry must be made in order to select a suitable technique and sampling pattern. Deposits differing genetically will have differing distributions and degrees of concentration.

Jan 1, 1992

By Daryl R. Tweeton

The Bureau of Mines has developed PC-based tomographic computer programs for geophysical applications, and is making them available to potential users as part of a Bureau plan to facilitate the transfer of technology to industry. These programs were initially developed for predicting and monitoring the flow pattern of leach solution during in situ mining. Seismic crosshole tomography has located fractured zones of low seismic velocity and saturated zones of high seismic velocit above the natural water table. The Bureau has applied tomography also to assessing high-wall blast damage, and examining the integrity of mine-related geological structures. The tomographic programs include the straight ray pro ram BOMTOM (Bureau of Mines Tomography? and the program BOMCRATR (Bureau of Mines Curved Ray Tomographic Reconstruction) that can be run with either curved or straight rays. Both programs provide optional mathematical constraints to help counteract the nonuniqueness of reconstructions that occurs with crosshole data. They are available from the Bureau free of charge. With typical data sets, they can be run on a 386 microcomputer with 640 Kb RAM. BOMTOM was described in the Bureau Report of Investigations 9159, so this report emphasizes BOMCRATR. Curved and straight ray reconstructions using seismic field data collected while simulating injection of leach solution were compared. The curved and straight ray tomograms were quite similar even with velocity variations of more than 50 percent.

Jan 1, 1992

By A. S. Ericson, J. H. Corrigan, E. J. Jahnsen

Calcine is transported from the Reduction Plant at 850°C in insulated hopper cars and charged into three rectangular electric melting furnaces each equipped with three - 18.5 MVA transformers. The electrical energy is applied through six in line prebaked carbon electrodes, and slag and metal are tapped at opposite ends of the furnaces on an intermittent basis. The slag, 5000 tonnes per day, is disposed of by a pot train directly to the dump. The ferronickel, 250 tonnes per day, is tapped into 40 tonne capacity ladles in which it is refined in two ASEA-SKF ladle furnace stations. Casting is done over lip at 1520°C in a pig casting machine with stepless speed control at up to 55 tonnes per hour. The ingots are stacked into self palletizing bundles weighing about 1500 kilograms and are strapped and tagged and transported to the seaport, from which the final shipment is made to the world market. The paper describes constructional details and gives information of both normal operation and start-up and shut-down procedures. Consumption figures for refractory, electrodes, electric energy and refining additions are given and metal chemistry is given before and after refining.

Jan 1, 1979

By S. P. Banerjee

By international standards, Indian coal seams are not very gassy. In some of the major coalfields such as Singareni, Wardha, Pench, Chirimiri, Rewa and Talcher Coalfields practically no methane is emitted from the coal seams. Even in the coalfields of Ranigang, Jharia, Bokaro and Karanpura, all of which are situated in the basin of the Damodar river, only a few mines are faced with excessive gas emission problems. But the number of such mines is increasing as deeper reserves are being worked and already the exploitation of some of the best quality coal reserves in the country is held up pending measures for control of methane emission in these mines. Even in mines having no previous history of gas emission, methane has been met near dykes and faults. This was dramatically revealed by an explosion in Dhori colliery in 1965 wherein 268 persons got killed. Until that time, Dhori colliery was considered as a non-gassy mine but on that fateful day gas came to the workings through a freshly exposed fault plane. Similar incidences of ignition of firedamp in so-called non-gassy mines have also occured in the past, for example, in Chapui Khas and Samla Dalurband collieries, but the casualty figures were not as high. After the Dhori explosion, all Indian coal seams have been declared to be gassy, whether presence of methane is detected in the workings or not.

Jan 1, 1980

By G. A. Rowell, T. M. Barczak, J. C. Zelanko

The US Bureau of Mines conducted a multifaceted geomechanics research project at a bump-prone longwall coal mine in eastern Kentucky. This mine presented a unique opportunity to study coal mine bumps because the problem appeared to be confined to areas beneath a sandstone channel of limited areal extent. The Bureau's research plan sought to exploit the uniqueness of the site by monitoring strata behavior and longwall support reactions as the longwall face approached and passed beneath a sandstone channel. The study incorporated static pillar stress and strata deformation measurements, shield support leg pressure measurements and microseismic monitoring, as well as geologic mapping and the collection of observational data. Data collection was underway when a major coal bump occurred on the longwall face at the mine. Pillar behavior (load and deformation), shield loading and microseismic activity were monitored prior to, during and after the bump. Observations in the tailgate indicated that these pillars were failing prior to and following the face bump. Shield load data, evaluated in an effort to identify trends that could be used to forecast coal bumps, appear to provide a measure of the effectiveness of destressing operations conducted on the face (e.g. shot firing). Analyses of microseismic data revealed anomalous values associated with microseismic "energy" prior to the face bump. In addition, microseismic source-location data and underground observations provided some insight as to the sequence of pillar and face bumps.

Jan 1, 1992

By A. S. Malicsi, Vathsala Rajagopal, I. Iwasaki

Corrosion and abrasion properties of a series of chromium-containing, cast-iron balls, with Cr contents ranging from 0% to 29%, were evaluated and compared with austenitic stainless-steel and mild-steel balls. Marked ball wear tests were performed on artificial ore samples consisting of 95% quartzite, with either 5% pyrrhotite or 5% chalcopyrite, under a nitrogen or oxygen atmosphere. The electrochemical mechanism was investigated by correlating the corrosive wear with the corrosion currents obtained from potentiodynantic polarization curves under abrasion. Flotation recoveries were determined on a 95% quartzite + 5% pyrrhotite sample ground with various cast-iron ball materials under an oxygen or nitrogen atmosphere. Electrochemical results are found to be in good agreement with flotation results and with corrosive wear data obtained from marked ball wear tests.

Jan 1, 1993

By Myron W. Mellor

Much has been published concerning the subject of coal preparation as related to electric power generation however it is always a most vital topic for both utilities and coal producers, It also constitutes a field of study that is never finished since new concepts and changing demands continually require altered perspectives. One graphic illustration that has been used to emphasize the rapidity with which times are changing is the fact that during World War I, a station that consumed 1000 tons per day was looked upon as a large central station, while today some single generators require 1500 tons during the same period, For further emphasis, at that time a 20,000 horsepower turbo-generator was a mighty large machine; today, a unit of this size is planned for driving the boiler water feed pump required for a single large main unit. During the past ten years alone, electric utilities have more than doubled their percentage of coal consumed as compared to the total market. They now account for approximately 40% of the United States consumption and one-third of all production including export, Conversely, approximately 70% of all U. S. steam electric generation is by coal and this percentage is expected to increase. It is further predicted that utility consumption will increase from the current 160,000,000 tons per year to between 400 and 500 million tons in 1975 which is approximately equal to todays total production

Jan 1, 1959

By L. Xu, R. Bhaskar

The trends in dust exposure levels and longwall production over the last 20 years were examined. The study was conducted for nine major underground coal mining states: Alabama, Colorado, Illinois, Kentucky, Ohio. Pennsylvania, Utah, Virginia and West Virginia. The dust exposure and shift production data were obtained from the Mine Safety and Health Administration (MSHA). Trends were identified and analyzed for the headgate, tailgate, jack setter and shearer operator positions. The relationships between average scam height and dust exposure levels as well as the percentage of dust samples exceeding the dust standard for the four occupations were examined. The concentration to production ratio, a better indicator of the success of dust control measures, was calculated for the 20-Year period. The data show that, in general, dust exposures over the last two decades hare decreased. However, it appears that much of the decrease was in states that had significantly high dust exposure levels (such as Alabama and Utah), while for states such as Virginia, West Virginia and Pennsylvania, the decrease was not as dramatic. Major reductions were made in the period starting in 1982, when a host of longwall dust control techniques was introduced. However, nearly 35% of jack setter and shearer operator dust exposures were still above 2 mg/m3 in 1990, with nearly 20% of tailgate operator exposures and 8% of headgate operator exposures being above the federal standard. The concentration/production ratio has shown a remarkable decrease since 1981. This indicates that long wall operators have been able to meet increased production as well as, to a large extent, control chest production at the face. An analysis of the relationship between average seam height and dust concentration for the years 1984 and 1990 shows that while in 1984, the dust concentration could be correlated to seam height, in 1990 the relationship was less definitive. This indicates that technological factors may be more important than seam height.

Jan 1, 1994

By Frank E. McCall, Michael A. Trevits, Fred Garcia

The U.S. Bureau of Mines investigated the influence of atmospheric pressure changes on methane gas migration through mine seals at a mine site located in the Pittsburgh Coalbed. The mine gained access to a coal reserve through part of an abandoned mine and constructed nine seals to isolate the extensive old workings from the active mine area. Underground problems were experienced when atmospheric pressure fell, causing methane gas to migrate around the seals and into the active workings. During mining operations, methane gas levels exceeded legal limits and coal production was halted until the ventilation system could be improved. When mining resumed with increased air flow, methane gas concentrations occasionally exceeded the legal limits and production had to be halted until the methane level fell within the mandated limit. To assist the ventilation system, a pressure relief borehole located in the abandoned workings near the mine seals was proposed. Preliminary estimates by a gob gas simulator (computer model) suggested that a 0.76 m (2.5 ft) diameter pressure relief borehole with an exhaust fan would be necessary to remove enough methane from the abandoned area so that the ventilation system could dilute the gas in the active workings. However, by monitoring methane gas emissions and seal pressure, during periods of low atmospheric pressure, the amount of methane gas that migrated into the active mine workings was calculated. Researchers then determined that a relief borehole, 20.3 cm (8-in) with an exhaust fan could remove at least twice the maximum measured volume of migrating methane gas. Because gas concentrations in the abandoned workings could potentially reach explosive limits, it was proposed that the mine eliminate the exhaust fan. Installation of the recommended borehole and enlarging two other ventilation boreholes located in the abandoned area reduced methane gas leakage through the seals by at least 63%.

Jan 1, 1995