Search Documents

By J. R. Hunter

The present is rooted in the past. This is particularly true in the case of mining operations. Coal mining in the United Kingdom is considered an old Industry comprising today 246 Coal Mines many of which have worked coal reserves in their locality for over 100 years. More than half the current producing mines lie in the Yorkshire and Midlands coalfields. They are in the oldest age group and produce 70% of the Industry's output. Some 50% of the remaining U.K. workable reserves amounting to approximately 98,000 million tons are still available to these regions. Fig. 1 Over the past two decades a gradual erosion of demand for coal in the U.K. has virtually halved the Industry's capacity. The number of Mines has reduced by 53% during the past 10 years. Productivity has increased by some 42% mainly through improvements in the central coalfields which has enabled costs to remain broadly competitive with oil.

Jan 1, 1976

By R. N. Edwards

The Magnetometsic Resistivity (MMR) method is based on the measurement of the low-level, low-frequency magnetic fields associated with non-inductive current flow in the earth. The traditional resistivity method maps the electrical properties of the earth by measuring the electric field caused by galvanic current flow between a pair of current electrodes. The MMR method differs from it in that the potential electrodes are replaced by a sensitive coil or magnetometer and a component of the magnetic field due to the current flow is recorded. The presence of an inhomogeneity redistributes the current flow which results in a perturbation of the electric field and, usually, of the magnetic field. The electric field immediately above a relatively conductive inhomogeneity must, by Ohm's Law, be smaller than that expected for a uniform earth. The current density in this region is also reduced but the current density within the inhomogeneity itself is enhanced so that the horizontal component of the magnetic field measured above the inhomogeneity is usually larger than that expected for a uniform earth. A method of interpretation using the magnetic anomaly was patented by Jakoskyl in 1933 but it met with little success at that time. Part of the problem was undoubtedly with the instrumentation, and only recently have robust instruments of sufficient sensitivity been developed2 and field data of good quality obtained. There are many common configurations of the potential and current electrodes in the resistivity method. Similarly, in the MMR method one or both current electrodes may be moved with the magnetometer, either horizontally or vertically ( in a bore-hole), or the current electrodes may be maintained in fixed positions and the magnetometer alone moved. The MMR anomaly is defined as the difference between the

Jan 1, 1975

By J. D. Miller

The effects of operating variables on water transport to the over- flow, classification of hydrophilic particles and the recovery of copper and molybdenum from a low-grade porphyry ore are presented. Recoveries of copper and molybdenum exceeding 90 percent at a grade of 8 percent Cu and 0.2 percent Mo were realized for minus 100 mesh (1 49 µm) material at retention times of less than 500 milliseconds. The rapid rate of flotation and the effective separation of fine particles for an air sparged hydrocyclone appear to be due to directed interaction of particles in a high force field with numerous freshly formed small bubbles. This interaction occurs in the swirl flow developed by the system and is analyzed in terms of collision and induction time phenomena.

Jan 1, 1982

By Raymond K. Will

Computers are becoming increasingly valuable tools in the mining industry as a greater variety of appropriate hardware and software becomes available, combined with greater acceptance by management, Within a given time period an engineering staff can evaluate or design a project to much greater detail and higher accuracy by utilizing computers once suitable programs have been developed. We are all aware that throughout the world the decreasing grade of minerals coupled with increasing waste to ore ratios necessitate larger capacity, longer term mining operations and attendant higher capital costs. Computers can be of assistance in all stages of mineral exploitation, from geologic exploration through mine feasibility studies and design, to marketing and transportation. Because of the high speed with which data can be digested and manipulated by computers, preliminary information from any stage of investigation can be analyzed to assist in further guidance of that stage. By use of preliminary mine feasibility studies, financial forecasts and sensitivity analysis, even information from a far-removed phase such as marine transportation of the product, can help guide the exploration phase to a realistic target.

Jan 1, 1973

By J. P. Ferro, W. H. Stewart

Wet ground and dry muscovite mica continued to be the most commercially significant types of mica in the US. Canada's phlogopite mica and some US deposits of sericite mica have also contributed to the overall application of mica in a variety of industries. Mica's major end uses are paint, rubber, and construction material. Its value was about $30 million last year. The southern Appalachian Mountains weathered granitic bodies and pegmatites continued to be the primary US muscovite mica source. North Carolina production of mica as a coproduct of feldspar, kaolin, and lithium processing accounted for more than 60% of the total output. New Mexico, South Carolina, South Dakota, Georgia, and Connecticut accounted for the rest. Flake mica was also produced from mica schists in North Carolina and South Dakota. It is also being investigated in Ontario, Canada. Wet ground mica Wet ground mica was produced by four companies: KMG Minerals, Franklin Mineral Products, J.M. Huber Corp., and Concord Mica. KMG and Franklin Mineral Products accounted for more than 80% of the production. Wet ground mica is a highly delaminated platey powder used to reinforce solvent and aqueous system paints for increased weatherability, durability, and greater resistance to moisture and corrosive atmospheres. In plastics, it is an excellent filler and reinforcing agent, providing better dielectric properties, heat resistance, and added tensile and flexural strength. In the rubber industry, wet ground mica is used as a mold lubricant to manufacture molded rubber products, such as tires. It also acts as an inert filler that reduces gas permeability. Miscellaneous uses include additives to caulking compounds, foundry applications, lubricants, greases, silicone release agents, and dry powder fire extinguishers. Wet ground mica prices range from $353 to $496/t ($320 to $450 per st) fob plant. Specialty products may be higher, depending on customer requirements. Dry ground muscovite mica Dry ground mica was produced by nine companies: KMG Minerals, Unimin, US Gypsum, Mineral Industrial Commodities of America, Spartan Minerals Corp., Asheville Mica Corp., Deneen Mica Co., Pacer Corp., and J.M. Huber Corp. Dry ground mica's primary market is wallboard joint compound. Here, it is a functional extender that improves the physical properties and finishing characteristics of the mud. It is also used in various grades as a filler in asphalt products, enamels, mastics, cements, plastics, adhesives, texture paints, and plaster. Dry ground mica became popular as an additive in oil well drilling fluids, where the mica flakes platey nature helps seal the well bore, preventing circulating fluid loss. But oil's dramatic price drop and consequent curtailing of well drilling brought this once booming market to a virtual halt. Forecasters predict that this business will gradually pick up during the next few years and most current dry ground mica producers will again produce the oil well drilling material. Dry ground mica prices range from $110 to $420/t ($100 to $380 per st) fob plant. High quality sericite mica, sometimes referred to as an altered muscovite, was mainly produced by two US companies. Mineral Industrial Commodities of America and Mineral Mining Corp. have equivalent capacities of about 27 kt/a (30,000 stpy). The majority of the material produced was consumed by the joint compound industry. Minor uses are in paint and oil well drilling. The lack of ground sericite penetration into the traditional ground muscovite markets is attributed to high silica content, typically in excess of 20%, and a bulk density. Prices range from $88 to $187/t ($80 to $170 per st) fob plant. Phlogopite mica is a dark colored, magnesium bearing mica rarely found in the US. Suzorite Mica Corp., a division of Lacana Petroleum, mines a deposit in Quebec that is 80% to 90% phlogopite. The dark color has prevented the material's entry into the traditional paint markets. But the physical properties and high purity make it useful as a low-cost reinforcing filler in many plastics and several asphalt applications. Phlogopite mica is ground to several grades and may be treated with various surface coatings for use in plastics or coated with nickel for EMI/RFI shielding applications. Prices for phlogopite products range from $144 to $580/t ($104 to $580 per st) fob plant. As in recent years, production of domestic muscovite sheet - block, film, and splittings - remained insignificant. These resources are limited and uneconomic due to the high cost of hand labor required to process sheet mica in the US. Imports from India and Brazil were the primary sources of the estimated 1 kt (2.4 million lbs) valued at $2.5 million consumed by US electronic and electrical equipment manufacturers in 1986. Reserves As a feldspar, kaolin, and lithium industry coproduct, flake mica will continue to provide a large percentage of mica re- This summary of 1986 mica activity was received too late to be used in the June issue.

Jan 7, 1987

By J. H. Tu

The technical paper correctly points out that the kriging variance is not a good measure of the uncertainty of the estimated (i.e., kriged) value of individual blocks. The authors claim that their proposed jack-knife method, which is a rekriging of each block by eliminating, in turn, one sample from m the original sample set and then taking the average of the rekriged estimates, not only gives good block estimates, but the resulting jackknife kriging standard deviation is a useful indicator of the "true uncertainty associated with block estimates." However, they immediately abandon the idea of using the block-by-block standard deviations, reasoning that these standard deviations are not independent and that there is no easy way to utilize them. There may be another reason for not using them. The jackknife standard deviations for individual blocks given in their example are mostly in the range of 0.004 to 0.005 oz/st (0.14 to 0.17 g/t) with only one block having a high value of 0.012 oz/st (0.41 g/ t). These individual block standard deviations are as low as the jackknife standard deviation for the mean grade of the entire shape, i.e., 0.0041 oz/st (0.14 g/t). Do they represent the "true uncertainty" .of the individual block estimates? Could the authors explain this? In a global shape consisting of a large number of blocks, any given sample will affect the kriged estimate of only those few blocks within its vicinity. This is the rationale for the authors' selective rekriging, making the jackknife algorithm more efficient. On second thought, why not do away with jackknifing altogether? Just cumulate and normalize, if necessary, the kriging weights of each sample used during the ordinary block kriging process, and then compute the global variance from these kriging weights and their respective sample grades? After all, isn't the global mean grade nothing but the weighted average of the samples used in the estimation? Reply by G.S. Adisoma and M.G. Hester The jackknife is one of the many tools in a practitioner's toolbox to solve estimation problems. The strengths of the technique lies in its simplicity, i.e., it uses the concept of mean and standard deviation and the fact that it can be easily combined with other tools, in this case kriging. Because the jackknife kriging (JK) estimate is also the mean of the pseudovalues, the JK standard deviation is attractive just as the standard deviation of the mean explains the variability of the data. The difference is that the pseudovalue calculation in jackknife kriging uses the ordinary kriging (OK) weighting scheme instead of simple arithmetic averaging. The data used to illustrate the jackknife technique in the paper con¬sist of high values that are roughly three times the low values. The resulting JK estimate of the block grades show that the highest estimate is roughly twice the grade of the lowest estimate. The contrast between the low and the high estimate is more evident in the JK estimate than in the OK estimate, even though the mean grades of the blocks for the two estimates are very similar. Nonetheless, in this paper, we are concentrating more on the need for a more realistic measure of uncertainty, or precision, for the estimate. Unlike its OK counterpart, the JK standard deviation of the blocks clearly reflects the original data variation. The highest JK standard deviation of the blocks is three times its lowest value. This follows our intuition that, when the samples used to estimate a block is more variable, the resulting estimation variance (or standard deviation) should be higher than the case where the samples are more uniformly valued. However, block-by-block standard deviation or variance is of little practical value in reserve estimation and classification, as well as in mine planning. One is usually more interested in quantifying not the variance of the individual block estimate, but the uncertainties associated with a much larger dimension, such as the minable reserve. Thus, the thrust of the paper is to find a simple way to obtain a single estimation variance or standard deviation associated with the reserve grade estimate. The discussion by J.H. Tu did not mention how one would obtain the global variance from the OK weights and the sample grades. As a technique that offers a data value-based measure of uncertainty for its estimate, the "leave-one-out" jackknife fills this need nicely through the block kriging shortcut approach described in the paper. Note: The first column and the last two columns of Table 3 in the paper should have contained a single number each, namely, an OK estimate of 0.0317, a JK estimate of 0.0333 and a JK standard deviation of 0.0041 oz/st, respectively, for the shape, as are obvious from the text.

Jan 1, 1997

By J. H. Tu

The technical paper correctly points out that the kriging variance is not a good measure of the uncertainty of the estimated (i.e., kriged) value of individual blocks. The au thors claim that their proposed jackknife method, which is a rekriging of each block by eliminating, in turn, one sample from the original sample set and then taking the average of the rekriged estimates, not only gives good block estimates, but the resulting jackknife kriging standard deviation is a useful indicator of the "true uncertainty associated with block estimates." However, they immediately abandon the idea of using the block-by-block standard deviations, reasoning that these standard deviations are not independent and that there is no easy way to utilize them. There may be another reason for not using them. The jackknife standard deviations for individual blocks given in their example are mostly in the range of 0.004 to 0.005 oz/st (0.14 to 0.17 g/t) with only one block having a high value of 0.012 oz/st (0.41 g/ t). These individual block standard deviations are as low as the jackknife standard deviation for the mean grade of the entire shape, i.e., 0.0041 oz/st (0.14 g/t). Do they represent the "true uncertainty" of the individual block estimates? Could the authors explain this? In a global shape consisting of a large number of blocks, any given sample will affect the kriged estimate of only those few blocks within its vicinity. This is the rationale for the authors' selective rekriging, making the jackknife algorithm more efficient. On second thought, why not do away with jackknifing altogether? Just cumulate and normalize, if necessary, the kriging weights of each sample used during the ordinary block kriging process, and then compute the global variance from these kriging weights and their respective sample grades? After all, isn't the global mean grade nothing but the weighted average of the samples used in the estimation? Reply by G.S. Adisoma and M.G. Hester The jackknife is one of the many tools in a practitioner's toolbox to solve estimation problems. The strengths of the technique lies in its simplicity, i.e., it uses the concept of mean and standard deviation and the fact that it can be easily combined with other tools, in this case kriging. Because the jackknife kriging (JK) estimate is also the mean of the pseudovalues, the JK standard deviation is attractive just as the standard deviation of the mean explains the variability of the data. The difference is that the pseudovalue calculation in jackknife kriging uses the ordinary kriging (OK) weighting scheme instead of simple arithmetic averaging. The data used to illustrate the jackknife technique in the paper consist of high values that are roughly three times the low values. The resulting JK estimate of the block grades show that the highest estimate is roughly twice the grade of the lowest estimate. The contrast between the low and the high estimate is more evident in the JK estimate than in the OK estimate, even though the mean grades of the blocks for the two estimates are very similar. Nonetheless, in this paper, we are concentrating more on the need for a more realistic measure of uncertainty, or precision, for the estimate. Unlike its OK counterpart, the JK standard deviation of the blocks clearly reflects the original data variation. The highest JK standard deviation of the blocks is three times its lowest value. This follows our intuition that, when the samples used to estimate a block is more variable, the resulting estimation variance (or standard deviation) should be higher than the case where the samples are more uniformly valued. However, block-by-block standard deviation or variance is of little practical value in reserve estimation and classification, as well as in mine planning. One is usually more interested in quantifying not the variance of the individual block estimate, but the uncertainties associated with a much larger dimension, such as the minable reserve. Thus, the thrust of the paper is to find a simple way to obtain a single estimation variance or standard deviation associated with the reserve grade estimate. The discussion by J.H. Tu did not mention how one would obtain the global variance from the OK weights and the sample grades. As a technique that offers a data valuebased measure of uncertainty for its estimate, the "leave-one-out" jackknife fills this need nicely through the block kriging shortcut approach described in the paper. Note: The first column and the last two columns of Table 3 in the paper should have contained a single number each, namely, an OK estimate of 0.0317, a JK estimate of 0.0333 and a JK standard deviation of 0.0041 oz/st, respectively, for the shape, as are obvious from the text. ?

Jan 1, 1998

By Paul E. Scheerer

Synthetically produced magnesium hydroxide serves as the precursor for much of the magnesium oxide produced in the world today. Magnesium oxide, in a variety of physical and chemically reactive forms, is a very important commodity. It is used as the main component in refractories employed in steelmaking furnaces and in many base metal refining furnaces. In the chemical industry, it serves as a raw material in the production of epsom salts, rayon acetate, oxychloride and oxysulfate cements and magnesium sulfonates. It is a minor component in fertilizers and animal feeds. It serves as the starting material for producing fused magnesia, used as an electrical insulator in electric heating elements. It is employed in the magnesium sulfite process for pulp digestion in the paper industry. Additional uses are in SO2 scrubbers, as a neutralizing agent in the tanning industry and as a component in rubber compounding. Magnesium oxide is produced not only from synthetically produced magnesium hydroxide. It is produced from natural magnesites, natural brucites, and natural and synthetic hydro-magnesites. Synthetic magnesium hydroxide, as a starting material provides more control of the chemical purity and chemical reactivity of resulting magnesium oxide products because of the uniform nature, chemical and physical, of the hydroxide that can be produced. Synthetic magnesium hydroxide is produced by precipitation of Mg (OH)2 from magnesium chloride bearing seawater or natural brines through the use of a base such as Ca(OH)2 or NaOH.

Jan 1, 1978

By Leonid P. Ni, Askar M. Kunayev

It is well known that processing of the high-silicon bauxites for obtaining alumina by the hydrochemical Bayer process is irrational due to the significant losses of alumina and alkali with red mud. The main source of losses of the mentioned compounds under the conditions of leaching by the Bayer process is the formation of difficultly soluble sodium alumosilicate of the composition Na20 .Al203, 2Si02 . n H20. A conventional method of an extra recovery of alumina as well as of regeneration of alkali out of red mud is the high-temperature sintering of the latter with soda and limestone with the subsequent leaching of sodium aluminate from the sinter by water or soda solution. A sequential version of the Bayer-sintering flow chart recommended for the prosessing of bauxites with an increased content of silica is based on this method. However, the sintering method is not the only alkaline method allowing to make an extra recovery of alumina likewise of alkali from red mud. Our investigations showed/I/, that the components mentioned can be recovered by a pure hydrochemical method of treating red mud with concentrated alkaline solutions, with lime (Ca0) being present, that was earlier succesfully used in the development of the hydrochemical method of processing nepheline rocks/2/. The possibility of extracting alumina and alkali from red mud is based on the reactions which can be schematically represented in the following way:

Jan 1, 1984

By V. A. L. Breguncci, A. H. Martins, C. P. Ribeiro Jr.

This work presents experimental results for the recovery of gold present in alkaline cyanide solutions by using the electroelution technique of strong-base anionic polymeric resins IRA 402-CL from Rhom and Haas-Brazil Ltd. loaded with gold. This technique of electroelution of anionic polymeric resins is based on the removal of metal ions adsorbed to the resin, resulting from a potential difference applied between the cathode and anode in an electrolytic cell. The electrolytic cell was composed of an aqueous solution with suitable chemical characteristics and an anionic polymeric resin bed loaded with gold. The resin used in the experiments was loaded using synthetic alkaline gold cyanide solution with 1.0 g/L of gold. The variables studied were electroelution time, cathode current density, distance between cathode and anode and the electrolyte chemical composition. Statistical methods made it possible to establish the optimum conditions that would achieve satisfactory gold recoveries by the electroelution technique. The statistically predicted response for the resin loaded with gold by percolation was 16.5% gold recovery, 2.0 A/m2 cathode current density, 20-mm distance between electrodes and 6.0 hrs electroelution time. For the centrifuging system, the statistically predicted response was 7.41% gold recovery under the following conditions: 0.25 A/m2 cathode current density, 1-mm distance between electrodes, 3.5 hrs electroelution time and 10.9% NaOH in the electrolyte chemical composition.

Jan 1, 2002

By G. T. Swanby

Members of AIME, I read to you now a portion of a very fine business letter which we received several years ago. This letter originated in Rangoon, Burma, and reads in part: "Rest assured, if your goodselves see with us eye to eye, sure as certain we should get the business". I don't plan to give anybody "the business" today, but you can rest assured that if some of "you goodselves see with me eye to eye" on what I am about to discuss, I would be most pleased. My talk with you today will discuss the Federal Corporate income tax and its effect on our lives as engineers. In the-engineering-construction business we are faced with all the usual form of taxation which includes such items as sales tax, use tax, school tax, contractor; gross receipt tax, import duties and excise taxes, severance taxes, etc, adinfinutum.

Jan 1, 1965

By K. Hanumantha Rao, K. S. E. Forssberg, B. -M. Antti

Selective flotation of muscovite from a material containing muscovite (15.4%), biotite (13%), and siliceous gangue (quartz and feldspar), using a mixed collector system of sodium oleate and dodecylamine acetate has been described. Muscovite is found to float in preference to biotite, when the pulp is initially conditioned with oleate followed by amine at basic pH values. The results indicate that a product containing 63% muscovite with a recovery of 93% can be obtained, while using 75-150glt of oleate and 96 g/t of amine. The biotite grade and recovery are found to be around 30% and 20%, respectively. A good selectivity between muscovite and siliceous gangue is obtained. A final product containing 95% muscovite with an overall recovery of 75% is obtained when the flotation concentrate is subjected to magnetic separation. These studies indicate the possibility of separating muscovite from biotite by using a mixture of collectors.

Jan 1, 1991

By Quansheng Li

Large-scale coal mining will cause environmental problems such as aquifer damage, land excavation and occupation, soil erosion, vegetation damage, and regional landscape damage. The existing coal mine environmental restoration technology is relatively simple, and there is a lack of systematic research on environmental total factors. Based on the mechanism of coal mining damage and the laws of environmental natural succession, the concept of “coal environmental protection mining” is proposed, which combines damage reduction mining and environmental element system restoration. In accordance with the environmental protection principle of “source protection, process damage reduction, and systematic restoration,” a technical system of “coal environmental protection mining” is constructed for the two types of mining damage scenarios: underground mining and open-pit mining. In view of the damage characteristics of underground mining, source environmental protection technology based on optimization of mining process parameters, stability maintenance and damage reduction technology for overlying rock bearing arch shell structure, zoning and time-sharing treatment of surface cracks, and direct drainage irrigation technology for mine water have developed. In accordance with the damage characteristics caused by open-pit mining, land-saving and source reduction damage technology, near-natural stratigraphic reconstruction, topsoil improvement, and environmental storage and utilization technologies for seasonal precipitation have developed. By applying the technology in this paper, the maximum surface settlement value of 12401 working face in Shangwan coal mine was relatively reduced by 25%, the surface cracks have been adjusted from step-type cracks to dynamic small cracks, and since the technical implementation of the Shendong mining area in 2010, the vegetation coverage has increased loss and crushing decreased by 0.06 km2 every year, the environmental restoration period of the dump site was advanced by more than one year, and the vegetation coverage rate increased by 41.78% compared with the background value in the semi-arid area of the victory open-pit coal mine demonstration area. A surface reservoir with a water storage capacity of 400,000 cubic meters has been built, and the seasonal and graded utilization of mine water has been realized. An underground reservoir with a water storage capacity of 1.22 million square meters has been built in the Baorixiler open-pit coal mine.

Jun 25, 2024

By Thomas E. Finch

Coal produced from surface mines in the Western United States is becoming a more important part of this nation's economy as other types of fuels become scarce. This paper reports the investigation of alternative methods of handling the parting between two coal seams. The results of this investigation are presented as the engineering-economic aspects of alternative parting handling methods involving stowing or back filling techniques. The coal and parting characteristics were selected as being representative of those under consideration or actively mined in the West. The basic philosophy of evaluation is to establish a mine-within-a-mine where equipment selected for minimal capital investment can remove the parting and second seam nearly independent of the ongoing, present production. With proper consideration of design, this parting-coal removal is evaluated as a second operation within the first and has its own profitability measure. The Fort Union Area of Montana, Wyoming, and the Dakotas contains large reserves of low sulfur sub-bituminous coal. In many locations, several coal seams are close to the surface and are separated by relatively thin layers of parting. The removal of overburden and the mining of the upper seam is accomplished effectively with conventional mining methods and equipment. Mining a second seam of coal and handling the parting in accord with economic and environmental controls presents a number of problems. Typically, mining companies have adapted the conventional strip mining techniques used in the East. However, the extreme thickness of the western coal seams offers alternative mining method possibilities for parting and second seam removal.

Jan 1, 1976

By R. W. Salmi

The authors discuss the cooperative efforts by Minnesota Ore. Operations and Research; from the earlier development, testing and installation of fine shear screens in the Minntac Step III concentrator to the most recent testing and operating data that has resulted in the installation of Derrick Multifeed sandwich deck screens in Minntac Steps I and II. Pilot-plant test results that were obtained at the Coleraine, Minnesota Research Laboratory are also reported and demonstrate the effects of feed rate and feed percent solids on sandwich screen performance with two sizes of Minntac fine screen feed.

Jan 1, 1984

By Norbert Patzelt, Johann Knecht

Future ore reserves of major gold producers in North America and elsewhere will consist of refractory gold ores. About 60 % of the current U.S. gold production is mined in Nevada. Several of the large gold operations in this state indicate that 40 to 90 % of their future ore feeds will contain refractory gold. To com­pound problems, average head grades for refractory U.S. gold ores had fallen from 8 - 9 g/mt to about 4 g/mt by 1991. In Latin America, 52 % of the gold operations will require milling for optimal recovery. Deeper reserves are, like in North America, refractory. Therefore a special treatment process is needed in order to allow for the gold ore to be leached downstream in a conven­tional cyanidation process for a high gold recovery. There are several options available for this oxidation process like treat­ment of the gold bearing ore in pressure oxidation, in a biooxi­dation or in a roasting plant depending on the reason for the refractoriness. If organic carbonaceous matters and sulfides are the prima­ry reasons for the refractoriness, whole ore roasting is a pre­ferred method for the treatment of this type of ore. Since dry ore is to feed to the roaster, a dry grinding mill is advantageous. For the dry grinding system, the moisture content and the ore char­acteristic is of importance. Those parameters decide the mode of the grinding system. For autoclave systems common wet grind­ing systems can be applied. This paper deals with technical aspects for dry grinding plants and gives an outlook on and pos­sibilities for new grinding systems.

Jan 1, 1996

By Eberhard Stolarski, Michael Tacke

When the oxidized surface gold deposits are mined out, the underlying refractory gold ores become the challenge of treat­ment systems. The size and value ofrefractory gold ore reserves are a function of recovery efficiency and operating cost. The start-up of LURGI's gold roasters at NEWMONT's Carlin site has established whole ore gold roasters as a key to high gold recoveries. The ores from several deposits of the Carlin trend are roast­ed utilizing LURGI / NEWMONT technology, which has achieved gold recoveries approaching 95%. This is in dramatic contrast to the traditional perception that roasting is limited to gold recoveries in the mid 80's. Extensive investigation in pilot scale is required to achieve stable high gold recoveries for most variables in the ore body. The key question for all pilot tests is the classic question of (ROM) run of mine ore roasting or concentrate roasting. All variables are dominated by the leaching/ recovery char­acteristics of the natural ores. The degree ofrecovery improve­ment by roasting / calcining establishes the frame of the eco­nomical conditions. The full range of flexibility is required for the design of the plant to allow for ore variations in heat values, combustible con­tents, agglomeration behavior and off-gas composition. The variables in the ore body influence, therefore, the price of the plant proportionally to its flexibility. Concentrates are usually fairly stable in composition, com­bustion behavior, heat values and particle size since they are a product of the very selective flotation process. Flotation is not the successful process step when the tailings remain high in refractory gold contents.

Jan 1, 1996

By Dmitriy A. Malovichko

The general theory for the description of seismic sources is briefly discussed. The effect of excavations on seismic radiation is considered. Expressions for seismic source mechanisms in terms of the geometrical and mechanical parameters of source processes are provided for the following cases: fault slip and shear failure in a confined environment, dynamic stress fracturing around a tunnel, rock fall, landslide and sudden subsidence. A classification of seismic events in mines based on source mechanisms is introduced. The classification separates blast-, slip- and crush-type events. Various approaches of analysis of source mechanisms involving forward modelling and inversion are discussed. The following examples demonstrating the utility of source mechanisms in mining are presented: forensic analysis of damaging seismic events, assessment of the increase in the depth of failure for dynamic stress fracturing around tunnels and its duration, examination of the rockmass deformation regime, assessment of deformation around tunnels using crush-type events, identification and parameterisation of weak geological structures, stress inversion from slip-type events. Finally, the requirements for seismic data to ensure high quality source mechanism solutions are briefly reviewed and future challenges in the interpretation and utilisation of seismic source mechanisms in mines are speculated on.

Apr 26, 2022

By A Pettersson

LKAB owns and operates two of the largest underground mines in the world in Northern Sweden. In Malmberget, with a production capacity of about 30,000 t/day of iron ore, the current main 815 m haulage level is rapidly approaching the end of Its life and plans are being made for its replacement on the 1000 m level. Due to the separation of the orebodies, trucks have been chosen for transporting the ore from the orepasses to the crushers. The trucks currently in use have a capacity of 120 tons. To increase the efficiency of the loaded haul, the new main level will have a favorable slope from the drawpoint locations to the crushers. From the new level the crushed ore will be transported by conveyor to the 815 m level for hoisting to the surface. The paper discusses the planned mining and transportation system.

Jan 1, 1998

By Robert W. Bartlett

Pretreatment of sulfidic refractory gold ore by biooxidation in coarse-crushed ore heaps is a promising new technology, especially for low-grade ores that cannot afford pressure leaching or roasting. An algebraic equation for determining the economically optimum biooxidation of the sulfide minerals in the ore is provided that is based on the empirical biooxidation rate constant for the ore, the project's financial discount rate, the ore grades of both refractory and non-refractory gold, and the gold price. Then, the economically optimum duration of bioheap pretreatment, t$, is determined from its logarithmic relation to the optimum fractional extent of ore biooxidation, F$, through the ore's biooxidation rate constant. In doing so, it is assumed that the ore is adequately crushed and amenable to bioheap pretreatment and that the cumulative oxidation of the ore with time is known from ore testing so that the rate constant can be determined.

Jan 1, 1995