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By Archie M. Richardson, Carl E. Brechtel, Tom R. Kelly, Frank Feero

Recent work to upgrade the ventilation system for the el Mochito lead/zinc mine in central Honduras is discussed. Network modeling and underground measurements were used to evaluate cost-effective alternatives for achieving satisfactory ventilation in a complex and expanding underground operation. Both interim and long-term solutions were implemented to make mining possible under difficult conditions. INTRODUCTION Mining operations at the el Mochito Mine, located in the central highlands of Honduras, Central America, have been virtually continuous since the opening of the mine in 1948. Initially a high-grade silver mine, the mine has expanded along a westward trend of pipe-like orebodies to a distance of roughly one mile from two centrally located shafts. Production of the relatively large San Juan orebody at the western most extension of the mine (Paddock, 1981) led to the introduction of diesel-powered equipment; however, the ventilation infrastructure was insufficient to meet the needs of mechanized mining. A succession of owners/operators in the 1980s allowed the existing ventilation infrastructure to decay to the point that ventilation in the production areas of the mine was very poor. Environmental conditions in some working areas were not conducive to efficient ore extraction because of high dry bulb temperature, high humidity, and diesel emissions. Upon acquiring the mine in 1990, Breakwater Resources of Tucson, Arizona began an aggressive program to refurbish the mine infrastructure to complete extraction of the San Juan orebody and to allow the extension of the mine another 2500 ft to the west for extraction of the Nacional orebody. The program included increasing the capacity of the main ventilation system. This article presents a case history of the process of upgrading the ventilation system in a mine where extensive old workings cause large air leakage. This process has been one of selecting solutions to difficult technical problems that are compatible with the existing mine infrastructure and economic constraints. The initial ventilation system is described in the background section, along with ventilation projections for the mine expansion. Field characterization of the ventilation system for design verification and fan specification is then discussed. The paper describes a series of interim changes to the system to improve ventilation pending completion of new ventilation boreholes. In addition, the temperature/ heat problems in the mine are described. BACKGROUND Initial Condition of Ventilation System The ventilation system is illustrated in Figure 1, which shows the extent of mining with the main ventilation paths superimposed. Early mining around the two shafts opened up vertical connections (stopes and raises) over the entire 2420 ft (737.6 m) of vertical extent, and mining progressed to the west primarily using compressed air and electric-powered equipment. Since ventilation was not a complex problem in the original mining system, the stopes and interconnecting raises were not sealed. The San Juan orebody was much larger than the silver ore zones mined previously, being primarily zinc and other base metals. Its geometry, size, and grade allowed the use of vertical crater retreat (VCR) stoping with diesel mucking and haulage equipment. Its depth, along with the existence of warm groundwater, resulted in a mine climate problem on the lower levels. To establish a complete ventilation circuit, two vertical boreholes (Bonanza Nos. 1 and 2) had been drilled by previous owners from the surface in the vicinity of the San Juan orebody. The system design called for air to be drawn down the intake shafts, across the lower mine levels to the San Juan workings, then up through the San Juan ramps and ore passes to these two exhaust boreholes (see Figure 1). In practice, however, only the Bonanza No. 1 borehole was drawing air through the desired path. Leakage across the old upper levels from the intake shafts, the Caliche tunnel, and from intervening abandoned stopes and raises supplied most of the air flowing to the base of the Bonanza No. 2 borehole. In effect, there were two ventilation circuits in semi-parallel through the mine, of which only one was delivering appreciable air to the San Juan workings.

Jan 1, 1993

By Yoginder P. Chugh, K. V. K. Prasad, R. Missavage

This paper presents results of field monitoring and finite element studies to analyze and improve a room-and-pillar retreat mining system. Fie1 d instrumentation was utilized to monitor pi11ar load changes, roof to floor convergence and differential roof strata movement as retreat mining progressed and to determine in-situ horizontal stresses. A two-dimensional finite element model depicting strata behavior at this mine was developed and used to analyze existing and alternate improved mining geometries. The results showed excellent correlation between fie1 d observed and model predicted behavior. Some of the recommended changes in mining geometry based on the study were incorporated in the mining system.

Jan 1, 1986

By Robert A. Jankowski, Charles Babbit, Natesa I. Jayaraman

The Bureau of Mines, together with Foster Miller Inc., has developed a compact, high pressure scrubber system for continuous miners. Powered by water energy alone, it can move up to 1.4 m3/s (3,000 cfm) of air and scrub a significant amount of the dust in the air. Full- scale model and underground trials showed excellent performance. Operated at 8.3 x 10[3] kPa (1,200 psi) and 38 L/m (10 gpm), the scrubber has reduced operator and return dust concentrations by more than 50 pct. This paper describes the full-scale model development, system fabrication and underground evaluations of this novel and inexpensive scrubber.

Jan 1, 1989

By David S. Yantek, Paul Jurovcik, Eric R. Bauer

Workers in coal preparation plants, where vibrating screens are significant noise sources, are often exposed to sound levels exceeding 90 dB(A). The National Institute for Occupational Safety and Health, a major coal company, and a vibrating screen manufacturer conducted a cooperative study of vibrating screen noise. Rubber isolators reduced sound levels by 1 dB. Urethane screen panels did not reduce sound levels in this case. Drive noise was determined to be the dominant noise source on the screen. Damped side plates reduced vibration levels on the screen sides by 1 to 7 dB(A). Detailed results of the study are presented.

Jan 1, 2005

By R. N. Tempel, M. Lengke

Arsenic sulfide (orpiment, realgar, amorphous AsS and As2S3) oxidation rates were measured in mixed flow reactors at pH-2 and at temperatures of 25 ° to 30 °C. The measured oxidation rates for arsenic sulfide solids by dissolved oxygen are in the range of 10-11 to 10-10 mole m-2s-1 after being normalized to final surface area. The order of arsenic sulfide oxidation rates decreases at pH-2 from amorphous AsS > realgar > orpiment > amorphous As2S3. Compared to pyrite, arsenic sulfide oxidation rates are approximately 1.5 to 15 times slower than pyrite oxidation rates at pH-2.

Jan 1, 2003

By Leif A. Nordell, Philip E. Freeland

A paper discussing specification, methods, situations and results encountered in underground phase construction of the Rocky Mountain Pumped Storage Project near Rome, Georgia. The scope of work included excavation, rockbolt/shotcrete/wire mesh primary support and cast-in-place concrete lining of the (1) 216 m, top flared shaft, connecting 1.57 radian elbow, and 590 m tunnel to a 10.67 m finished diameter; (2) complex double bifurcation section; (3) excavation, support, installation and backfill concrete for three parallel, 135 m steel penstocks of 5.79 m finished diameter; (4) construction of a 43 m diameter reinforced concrete intake/discharge structure atop the shaft.

Jan 1, 1985

By Qiu Rongqing, Huang Kongxuan

This paper summarizes the results of treating arsenic­bearing refractory gold concentrates from six gold Mines of Chi­na by using bioleaching method and discusses the conditions of bioleaching processes. Results indicate that Thiobacillus fer­rooxidans T-3 Strain can intensely oxidize arsenopyrite, how­ever oxidation rate and degree differe considerably for different. During initial inoculation of 5 X 106 cell/ml. FeH contration generaly 4 -8 g/1. Sample size > 80 % - 3 20 mesh and pulp density 10 % ( w /v) and leaching time ,1 -- G clays, arsenic re­moval rate reached more than 80 % , Fe extraction ,10 - GO% desulfurization rate 30-45% after bacterial oxidation of 4-G days.

Jan 1, 1992

By R. K. Mehta, C. W. Schultz, J. B. Bates

Introduction The Mineral Resources Institute, The University of Alabama, has for the past three years been engaged in a program to develop a beneficiation system for eastern (Devonian) oil shales. One objective of that program was to evaluate advanced technologies for effecting a kerogen-mineral matter separation. Column flotation was among the advanced technologies selected for evaluation. Early in the program it was shown that column flotation was superior to conventional (mechanical) flotation and to the other advanced technologies being evaluated. The investigation then proceeded toward the further objective of defining the optimum operating conditions for column flotation. One observation made in the course of optimization testing was that introducing the feed into the froth (above the pulp-froth interface) resulted in an improved combination of concentrate grade and kerogen recovery. This observation was reported in a previous paper (Schultz and Bates, 1989). Because the practice of maintaining the pulp froth interface below the feed point is contrary to "conventional" practice, it was decided to subject the observation to a systematic series of tests. This paper describes a recent series of tests and the results that were obtained. Experimental equipment and procedure The arrangement of the column cell and auxiliary equipment for continuous flow testing is shown schematically in Fig. 1. The feed sump [O] is filled with a sufficient volume of prepared sample to permit a large number of tests to be performed (typically 12). Past experience has shown this is necessary to control sample variability and variability in the size distribution resulting from ultra fine grinding. The feed slurry is maintained at about 20% solids and is constantly recirculated and stirred. The sample is metered from the circulating pipe by a peristaltic pump [O]. The feed slurry is diluted with reagentized water [O] by a second peristaltic pump [O]. Wash water [O], also reagentized, is supplied through a third peristaltic pump [O]. While this feed system may seem unduly complex, it does permit users to independently vary either the wash water rate or the net solids content of the cell. In the tests reported here, the feed rate and net percent solids were constant at 12.5 gms/min. and 3.3%, respectively. Diluted feed enters the column through 6.35 mm-diam (0.25 in.-diam) copper tubing and is discharged upwardly at the center of the column. Tailings are discharged through flexible tubing that can be adjusted so as to control the position of the pulp-froth interface. The column is 76.2 mm-internal-diam (3 in.-internal-diam) and 1090 mm (43 in.) high. It is made from lucite tubing and is fitted with a 51-mm-diam (2-in.-diam) fritted glass air sparger having an average pore diameter of 50 µm. In performing a series of tests, the concentrate and tailing are allowed to discharge continuously. The system is allowed to equilibrate for 30 minutes after the pulp and froth reach operating levels. Concentrate and tailing samples are taken simultaneously for timed intervals (five to 15 minutes, depending on the volume of sample desired). After sampling, a change in operating conditions is made and the system is again allowed to equilibrate. The tests to determine the effect of the pulp-froth interface level were part of a larger series of tests in which the objective was to optimize the conditions for a rougher flotation stage in a two stage circuit. The sample used in this series of tests was an Alabama shale ground to d90 = 23.1 µm and d50 = 7.9 µm. The operating conditions remaining constant in this series of tests were as follows: Column height - 1600 mm (63 in.) Air sparser - 50 µm (average pore diameter) Spray water - 130 cc/min. Feed rate - 12.5 gm/min (0.4 oz per min) (dry solids) Percent solids - 3.3% Frother (Dowfroth 250) - 45 ppm The variable test conditions are tabulated in Table 1. Positions of the pulp level (pulp froth interface) and feed entry are presented as a percentage of column height (as measured from the face of the air sparser). These test conditions are presented Fig. 2. At each of these test conditions, individual tests were performed at varying air

Jan 1, 1992

By Andreas G. Mueller

Gold-silver and copper-gold deposits with high-temperature wallrock alteration of Ca-Mg-Fe-Al silicates occur in ca. 3.0 Ga old greenstone belts of the Yilgarn Block, Western Australia. The deposits are hosted by amphibolite-facies komatiites, basalts and BIF, controlled by ductile shear zones and located within the contact-metamorphic aureoles of composite granodiorite-granite batholiths. Disseminated sulfides and free gold form foliation-parallel ore zones in a gangue of anhydrous silicates (garnet, clinopyroxene, olivine), hydrous silicates (amphibole, biotite) and calcite. The deposits may be classified on the basis of their dominant economic metals as: 1(1) Gold skarns with substantial silver as by-product, represented by the Marvel Loch mine (production: 2,200,000 t at 3.5 g/t Au), and characterized by the mineral association pyrrhotite, loellingite, arsenopyrite, galena, gold and magnetite. (2) Gold skarns with low silver contents, represented by the Nevoria mine (production:1,850,000 t at 3.4 g/t Au), and characterized by the mineral association pyrrhotite, chalcopyrite, arsenopyrite, gold, Bi-tellurides and magnetite. (3) Copper-gold skarns, represented by the Elverdton mine (production: 850,000 t at .7 5 Cu, 0.81 g/t Au), and characterized by the mineral association magnetite, chalcopyrite, pyrrhotite, pyrite, gold and Ag-Bi tellurides.

Jan 1, 1990

By Ruifeng Li, Yanghui Ren, Hua Gao

"Since entering the new century, China’s coal industry has witnessed the rapid development, and provided a reliable energy supply for the national economic and social development. But after the “golden decade” of rapid development, the coal industry now is facing overcapacity, low industrial concentration and production efficiency, high pressure of production safety and environmental protection and other prominent issues. Based on defining the connotation of highly-efficient recovery of coal resources, this paper established the relevant 8 indicators to reflect the highly-efficient recovery level of coal resources, summarized the present situation of China's coal resources recovery and the main problems, analyzed the development environment of China's coal industry under the new situation, and finally put forward the strategic measures to promote highly-efficient recovery of coal resources in China.1. Background Coal is the main energy in China. Since entering the new century, China's coal industry has made significant progress, and the level of production safety, resource recovery rate and mining mechanization increased significantly, which provided a reliable energy supply for the rapid development of the national economy. However, due to the changes of China's economic environment, slow growth of energy demand and other factors, some prominent contradictions in the coal industry have significantly restricted the healthy development of the industry. The first problem is serious overcapacity. In the past few years, 16 industries including coal, electric power, chemical and others have invested in coal mines. It is reported (Han 2016) that only during the nine years from 2005 to 2014, the fixed assets of coal industry increased totally more than 3.3 trillion RMB, which brought a large number of production capacity. Affected by the slowdown of economic growth and energy structure adjustment, Chinese coal demand has reached the peak platform and caused the overcapacity of coal supply, so shutting down the backward capacity is the most important task in the future. The second problem is the low efficiency of coal production. There are about 4.3 million coal mine workers in China, and the annual coal production per capita is less than 900 tons, while it was reported (EIA 2016) that the annual production per capita in the United States is more than 10 thousand tons. The third problem is that the green coal resources are not rich. Among the 1.53 trillion tons proven reserves, only about one third are green coal resources in accordance with the principle of ""safety, technology, environment and economy"". The coal resources with high quality and easily mining conditions are not abundant."

Jan 1, 2017

By M. Girardeau, J. Blondin, M. Nomine

It is well known that surface moisture and fine content have a strong influence on coal handle- ability. It is known as well that these two criteria are not sufficient to classify coals. It seems that certain types of coals are intrinsically difficult to handle, the reason being still not well understood. For these coals, moisture and fine content are aggravating factors and have to be strictly controlled in order to avoid handling problems (sticking, arching in hoppers.. .). CERCHAR has undertaken research aimed at identifying the role of intrinsic characteristics of coal with regard to handling properties. Two of them have been identified as particularly relevant : the clay content and the "colloidal particle" content. Two simple tests commonly used for soils characterisation, but never used so far for coal, have been applied to characterise a wide range of coals. The derived classification has been compared with an empirical classification based on dry screening tests. DRY SCREENING EXPERIMENTS Dry screening at a relatively low screen aperture (e.g. 6 mm) may be considered as a good tool for assessing the handleability of wet fine coals. Difficult to handle coals always lead to rapid plugging of the screen whilst easy to handle coals can be screened without difficulties. A wide range of coals has been selected with various ash, moisture and fine content. Their characteristics are given in table 1. The experimental set-up consists of a 2 t.p.h vibrating screen equipped with two automatic re- cording balances collecting respectively oversize and undersize material. Provided that the feeding rate is accurately controlled, good reproducibility in the percentage passing as a function of time is obtained. Figure 1 gives examples of different types of relations that were obtained. - LMC coal exhibits a behaviour that is characteristic of easy to handle coals : % passing remains constant in the course of the screening operation. - B coal behaves slightly differently. One observe first a rapid decrease in the flow passing through the screen and then a stabilization. Hand- ling properties can be considered as intermediately - The curve relative to LHB coal is characteristic of a very difficult to handle coal that blinds the screen almost immediately. It is necessary to point out the fact that the classification derived from screening experiments is a global one, including not only intrinsic factors but also external factors such as fines and moisture content. The role of surface moisture is in particular very important and variations in this parameter may upset the empirical classification

Jan 1, 1988

By Herbert P. Haschke

I. Changes made by the Economic Recovery Tax Act of 1981 (ERTA) which have an effect on investing in tax shelter investments A. Maximum ordinary income tax rate on individuals is now 50%. B. Maximum tax rate on long-term capital gains for individuals is now 20%. C. Maximum tax rate on alternative minimum taxable income for individuals is now 20%. D. Although not changed, the "add-on" 15% minimum tax on tax preference items and the possibility of paying the alternative minimum tax cause individual U.S. income tax planning to continue to be very complex. II. Real Estate A. The new Accelerated Cost Recovery System of depreciation (ACRS). 1. Mandatory for assets placed in service after 1980. ACRS will eliminate most if not all controversies with the IRS over depreciation. 2. Real property now depreciated over 15 years. Component depreciation is not available. 3. Accelerated depreciation is available - a 175% declining balance method with an automatic shift to straight line method at the optimum point in the asset's life. Alternatively, a taxpayer can elect to use the straight line method.

Jan 1, 1982

By Monica Pavlik, Thomas Wildeman

Water from the Forest Queen mine adit near Silverton, Colorado drains into a natural wetland. Because the pH of the water averages 5 and the iron concentration averages 18 mg/L, it was thought that the wetland might naturally treat the water. Of most concern with respect to the aquatic environment is zinc whose concentration averages 0.60 mg/L. Starting in October 1997, the surface waters, ground waters in the peat substrate, and the sediments in the wetland were sampled and analyzed four times over the course of four months. The adit water primarily remains as surface water where Fe, minor amounts of Al, and no Zn are removed. After the adit water enters the peat, then it is found that the pH rises to 5.8-6.5 and sulfate is reduced. The removal of Zn and A1 is caused by these two changes. However, Fe in its reduced state is quite soluble and may be remobilized in the reduced environment of the peat.

Jan 1, 2000

By James J. Scott

Introduction Friction Rock Stabilizers, trade name Split Sets, are presently under research and development by Ingersoll-Rand Company and Dr. James J. Scott, inventor. Conceived in 1953, the system is a patented process undergoing extensive field and laboratory testing. The author has published papers on the Split Set System earlier (References 4, 5, 6) The Split Set System holds promise to be a revolutionary development in the field of ground control. The system produces an interior reinforcement to a rock mass which: 1. Is simple in its concept. 2. Adjusts to the degree of restraint needed to match rock properties. 3. Provides a yieldable support and, later, a more rigid support as it is needed. 4. Pre-loads the rock in compression to increase stability. 5. Is a full-contact, fully tensioned device to resist rock loads. 6. Minimizes the stress concentration effects inherent in many interior support devices. 7. Improves safety for the miner. 8. Is cheaper than a grouted system. 9. Offers the rock mechanics engineer an opportunity to design in a fashion not before possible.

Jan 1, 1977

By Greg Barfoot, Kurt Keskimaki

The Henderson Mine is located approximately 50 miles west of Denver, Colorado. A project is underway to replace the existing rail system which transports molybdenum ore 15 miles from the mine to the mill using three flight conveyor system. The first conveyor is a 1 mile, high lift conveyor which transports the ore from an underground crushing station to the end of the existing rail tunnel. The second conveyor is 10 miles in length and utilizes the existing rail tunnel to transport the ore from the mine, which is on the east side of the Continental Divide, to the mill located on the west side. The third conveyor takes ore from the tunnel portal to the mill through a series of 7 horizontal curves and inclines up to 15 degrees. The project applies advanced conveyor design to tackle the installation of the system in an operating mine and achieve the highest possible level of reliability. This paper outlines the design process for this system, discusses the options which were evaluated and how the current design evolved.

Jan 1, 1998

By Hasan Sevim

A computerized heuristic model for an efficient and economic design of belt haulage networks in underground coal mines is discussed. The model is versatile, easy to use, and is valid for all mining methods singly or in combination. It may be used to design new networks or to analyze existing networks. The input data required are 1. maximum production rates from a section, 2. probabilities of production rates, 3. equipment costs, and 4. data necessary for network coding to represent different cases. The objective function is the "expected minimum cost per ton of coal hauled" while meeting production requirements. The output includes belt width, motor horsepower, bin size etc. and also values of operating parameters for each belt such as belt speed, effective tension, power consumption etc. A detailed account of the cost involved is also provided for each unit as well as for the entire network. Description of the model and an example of the design of a belt network in a mine with two longwall and four development sections are presented.

Jan 1, 1986

By M. J. Shulman

The exploration geologist is frequently confronted with the problem of allocating his resources, i.e., exploration effort, among various areas. Although geologic, financial and logistic considerations influence the allocations, no objective criterion is usually given which determines the optimal allocation. Maximizing the gain in information, subject to the constraint of a limited exploration budget, is used as the objective criterion to allocate reconnaissance effort. The information function, I(x), quantifies the expected gain in information, where x is the scale of exploration. To calculate the information function the following data are necessary: 1. The probability that an area contains a target must be estimated. 2. For each scale of exploration, four probabilities must be estimated: the probability that an anomaly is produced by the target; the probability that an anomaly is not produced by the target; the probability that an anomaly is produced by a barren area (false signal); and the probability that an anomaly is not produced by a barren area. Alternatively, the barren area can be replaced by other targets. To illustrate the allocation model, the optimal number of line kilometers/line spacing per area is determined for an aeromagnetic survey for iron in Egypt.

Jan 1, 1985

By D. Diggins

Experimental apparatus for the determination of powder wettability is described. The principle of the technique is based on the measurement of the equilibrium capillary pressure in a packed bed of particles. Both the macroscopic solid-solution-vapour contact angle, e, and the specific surface area, A(m2g-1), of the powder, can be obtained. Experiments on angular quartz particles have been performed. A wide range of situations have been covered: hydrophobic and hydrophobic particles wetted with water, a variety of organic liquids and solutions of surfactants. The results show that reliable and reproducible values for 0 and A for angular and relatively coarse powders can be obtained with the proposed equipment for advancing liquid fronts in the absence of soluble surfactants. In the latter case and for receding liquid fronts in general, only qualitative trends have been obtained.

Jan 1, 1992

By R. Stocker

Flotation recovery of molybdenite particles finer than 15 micrones sharpy decreases with decreasing size. A totally hydrophobic latex agglomerant (UBC-1), which was previously reported to be very efficient in agglomerating hydrophobic fine coal, has been found to agglomerate fine molybdenite particles. The agglomeration takes place only in the presence of MIBC which is commonly used as a frother in molybdenite flotation. Adsorption tests confirmed that MIBC is adsorbed onto molybdenite. The effect of the agglomeration on flotation has been studied by floating fine molybdenite from mixtures with quartz using the UBC-l agglomerant and the MIBC frother. A significant improvement in the flotation of fine molybdenite has been observed in the presence of the UBC-l agglomerant. The best results have been obtained around pH 5.5 which corresponds to the iso-electric-point of molybdenite.

Jan 1, 1997

By Kenneth S. Johnson

Western Oklahoma, with an estimated 48 billion tons of minable gypsum, has one of the largest reserves of high-purity stone in the United States (Figure 1). Gypsum beds of the Permian Blaine Forma¬tion are 10 to 30 feet thick in the southwest and northwest regions, and the Permian Cloud Chief Gypsum is 20 to 90 feet thick in the west-central region (Ham, 1962; Ham and Curtis, 1958; Scott and Ham, 1957). Republic Gypsum Company, in the southwest part of the State, is Oklahoma's second-largest gypsum producer. Since opening its plant in 1964, the company has steadily increased production and now accounts for about 15 percent of the State's annual output. The plant and quarry are 15 miles west of Altus at Duke, a small commu¬nity on the Hollis and Eastern Railroad in northwestern Jackson County.

Jan 1, 1970