Search Documents

By William Lyman

GENERAL DESCRIPTION Shrinkage or shrinkage stoping refers to any mining method in which broken ore is temporarily retained in the stope to provide a working platform and/or to offer temporary support to the stope walls during active mining. Since ore "swells" when broken, it is necessary to shrink the muck pile a corresponding amount by draw¬ing some of the broken ore out as the stope is advanced-hence the name. Broken ore retained during stoping is drawn out after the stope has reached its limits. The stope may be left empty or may be filled with waste contemporaneous with, or subsequent to, the final draw. Traditionally the method implies conventional overhand stoping methods with miners working between the muck pile and the stope back, in a space which advances updip with mining and is maintained by balanc¬ing "swell" with "shrink." The shrinkage classification is also applicable to so-called "semishrinkage" methods in open pillar-supported stopes where broken ore is temporarily retained as a working platform but offers no wall support; and to various blasthole shrinkage methods which utilize broken ore temporarily retained in the stope for wall support, but which do not require miners to work from muck pile in the stope. The method is generally applied to steeply dipping veins of strong ore between strong walls. APPLICATION Geometry The geometry of a shrinkable vein is described in terms of dip, width, and regularity along dip. Overall strike and dip dimensions and irregularities along the strike generally impose no restrictions on the method. Dip is ideally 1.2 to 1.5 rad (70 to 90°). As dip falls below 1.2 rad (70°), the shrinkage draw begins to strongly favor the hanging wall side, thus leaving a poor working platform for conventional overhand work. This is particularly true in relatively wide stopes. The sup¬port afforded to the hanging wall also diminishes with decreasing dip, reaching nil as the dip approaches the repose angle of broken ore. Dips below 0.78 to 0.87 rad (45 to 50°) are not generally shrinkable except by open stope "seinishrinkage" methods. Minimum mining width is fixed by working space requirements in the stope-generally about 1 m. Shrink¬age in narrower veins requires that waste rock from one or both walls be broken with the ore and the attendant dilution accepted to achieve the minimum width. Nar¬row stopes are less suitable, encouraging hang-ups and bridging of broken ore, with the attendant problems of erratic draw and incomplete recovery of broken ore. Maximum practical width may be 3 m or less to over 30 m, depending upon the competency of the ore and its ability to stand unsupported across the stope back. This is a vital safety consideration in conventional over¬hand stopes, but is much less of a factor in blasthole shrinkage methods. Very wide veins and massive ore bodies have been mined by transverse vertical shrinkage panels separated by transverse vertical pillars which are either abandoned or recovered later by other methods. Regularity along the dip is a prerequisite of shrink¬age as there must be no serious obstruction to the flow of broken ore downward through the stope to the sill level. Gentle rolls along the dip are acceptable if the local footwall dip everywhere exceeds 0.78 to 0.87 rad (45 to 50°). Off-dip hanging wall and/or footwall splits can generally be mined selectively from a conventional shrink stope as they are encountered without ad¬versely affecting subsequent continuation of shrinkage mining updip on the main vein. Vertical offsets or major rolls along the dip which cannot be "smoothed over" generally require that a sublevel be established with new draw control development. Blasthole shrinkage methods are much less flexible (and thus less selective) in their ability to accommodate any of these irregularities. Ground Conditions The wall rock must be strong enough to stand with the minimal support afforded by the dynamic mass of broken ore in the stope. During active mining, local sloughing from the walls is restrained, but the broken ore affords little, if any, useful resistance to closure of the stope walls. Such squeezing, if present, may bind up the stope and cause the loss of much ore. Pillars left between and/or within stopes are effective in preventing closure but reduce overall recovery. Walls may be re¬inforced by bolting after each stope cut in conventional shrinkage but not in blasthole shrinkage. Ore in place must be strong enough to stand with no natural support across the stope width, although tem¬porary artificial support or reinforcement may be used locally in conventional stopes. Some spalling or sloughing is permissible in blasthole shrinkage as men are never present in the stope. Physical and/or mineralogical characteristics of the broken ore may impose restrictions on stope design and/or operational plan¬ning, and may even preclude the use of shrinkage al¬together. Examples include: ores which, when broken, are cohesive or which tend to pack or cement together under the influence of ground water, wall pressure, and/ or chemical reaction. Such conditions precipitate er¬ratic draw during mining and often result in difficult and/or incomplete final draw; pyritic ores which oxidize very rapidly in the stopes and may generate heat, imposing a fire hazard by spontaneous combustion; sulfide ores which oxidize sufficiently in the stopes to adversely affect mill recovery by flotation; and ores (es¬pecially those containing uranium minerals) which ex¬ude radon gas and thereby impose ventilation constraints on stope design. In most cases these problems can be minimized by limiting the size of stopes, by minimizing the duration of mining activity in each stope, and by promptly drawing each stope empty following comple¬tion of mining.

Jan 1, 1982

By Kevin D. Lofftus

This paper presents a dynamic model for column flotation. The model equations are normalized and the dimensionless groups that are directly responsible in determining the column flotation behavior are identified. The resulting model equations are incorporated for computer simulation. Numerical results from computer simulations are analyzed to gather information about design and operation of column flotation devices.

Jan 1, 1988

By Kenneth S. Johnson

High-purity gypsum of Permian age crops out in three major gypsum districts of western Oklahoma. The northwest and southwest districts have important reserves in the Blaine Formation, whereas reserves of the west-central district are in the Cloud Chief Formation. Gypsum beds of the Blaine Formation typically are 10 to 30 feet thick, 95 to 99 percent pure, and interbedded with shales that are 2 to 30 feet thick. The base of the Cloud Chief Formation consists of a massive bed of gypsum that typically is 20 to 100 feet thick and is 92 to 97 percent pure. Anhydrite is present in the sulfate beds, beneath 20 to 100 feet of overburden, at a number of places in all three districts. Total gypsum reserves in the three districts are estimated at 48 billion short tons. These reserves are well suited for open-pit mining or quarrying, because gypsum typically forms hills in the semiarid climate of western Oklahoma, and the gypsum layers are nearly flat lying, without folds or faults. Seven companies currently mine a total of 1.0 to 1.4 million tons of Oklahoma gypsum each year for wallboard, for plaster, as a retarder in portland cement, and as a soil conditioner.

Jan 1, 1978

By P. K. Chatterjee

Before coal can be extracted from surface or underground mines, approval must be obtained from state and federal authorities. Permitting is the application process through which such approval is sought. The application includes en environmental impact statement Which focuses on Such topics as subsidence, toxicity of acid mine drainage, pollution levels of rivers and streams, post mining reclamation, and the effect on the hydrological balance of the area. The permitting procedure is extremely time and labor intensive, and requires extensive interdisciplinary knowledge. This paper examines a LISP based permitting procedure which will help to reduce the time taken to prepare and review a permit application.

Jan 1, 1986

By Chun K. Ip, Simon T. Johnson, Robert J. Fowell

Laboratory conducted cutting tests at traverse speeds up to 1 m/s have been undertaken with high pressure water jets assisting the cutting action of drag tools. Four sandstones and one limestone have been investigated, which represents a wide range of compressive strength. Variables investigated include water jet pressure, nozzle diameter, depth of cut, traverse speed, jet position, and tool bluntness. The test programme has allowed a model to be developed which describes the action of water jet assistance for three conditions dependent on the ability of the jet to penetrate the rock: where no significant penetration occurs, where penetration is greater than 50% of the tool depth, and an optimum condition around 30% of tool depth.

Jan 1, 1986

By G. Pierson

Explanations of commodity price levels, or movements, commonly focus on the supply and demand fundamentals of the particular commodity, or else are assigned to speculative activity. Comparisons of metal price histories with monetary and other economic data support the argument that the supply of and demand for money are no less important in price determination than are the supply and demand of the commodity itself. That these relationships should exist is evident in the price identity and are consistent with monetary theory. The patterns developed have limited usefulness as predictors, but their recognition is essential for the construction of price scenarios for planning purposes.

Jan 1, 1996

By Richard J. Adams

Coal jigs have played a predominant role in U. S. coal preparation for fifty years. Recently, an improved fine coal jig has been used to prepare the middle size range coal. These efficient machines are changing the historical thinking about jigs and is consistent with trends in coal preparation throughout the world. The performance achieved and operating cost savings are causing a change in fine coal cleaning strategy. With the exception of a handful of operators, fine coal jigs are generally not well understood by the industry. The objective of this paper is to provide some insight into the past use of fine coal jigs and their potential in the future. Improved Fine Coal Jig Since the mid 701s, an improved fine coal jig has been employed to an important niche in preparation, the 19 mm x 100 M range of cleaning. Several factors due to mining and liberation considerations have caused an expansion of this middle range of coal resulting in a host of challenges for coal preparation engineers. Fine coal jigs have been commissioned in several installations in North America to handle these important applications as shown in Table No. 1.

Jan 1, 1988

By B. C. Cornilsen, X. Shan, D. H. Carlson, J. H. Johnson

Airborne respirable Diesel Particulate (DP) presents an additional health hazard in that it has been shown to be mutagenic. This problem is of increasing concern as more coal mines introduce diesel vehicles. If the DP present in coal mine air is to be controlled it must first be measured. This paper describes development of the laser Raman spectroscopic measurement of the amount of DP in DP/coal mixtures collected on filters in the laboratory and in coal mines. The Raman technique provides a chemical measure of the carbonaceous material in each component, and is not dependent upon particle size. When this work was begun there were no known analytical methods for this measurement. Side-by-side in-mine comparisons of the results obtained from Raman, neutron activation analysis, and size selective analyses (MOUDI and personal samplers) are presented. The neutron activation and size selective analyses were obtained by the USBM Twin Cities Research Center and University of Minnesota. Good agreement has been found among these three methods.

Jan 1, 1991

By S. K. Kawatra, K. A. O, DeLa&apos

On-line sensors and process controls are important for efficient operation of coal preparation plants. The objective of this paper is to describe the current practice in on-line measurement of composition, density, moisture, level, flow and weight. This paper also discusses how on-line sensors can be implemented in process control, and how sensors which are currently being developed can be utilized.

Jan 1, 1988

By S. C. Howell

The mining of taconite, to provide feed for a processing plant, requires that the flow of material continue uninterrupted. This means first, that the crude must be of a size acceptable to the primary crusher in order to reduce the delays caused by plugging the crusher with chunks. Secondly, elimination of oversize in the pit will reduce costs of all wear parts used in the mining and processing of taconite. Savings in wear parts is readily recognized in dipper teeth, bases, buckets, truck boxes, and crusher parts, both primary and secondary. During the early days of taconite mining, it was soon recognized at reserve mining company's Babbitt operations that experience in mining other ores was not always (or ?necessarily??) Applicable to excavating taconite. This was especially true in drilling and blasting. Blasting of small tonnages in single or double rows simply filled the pit with scattered chunks and provided very shallow banks for shovel loading. It also created problems for the jet piercers, since all drilling had to be performed in fractured areas. Drilling efficiency suffered and costs were extremely high. Shovel and truck efficiencies were also low and again costs were high. A high percentage of secondary breakage was required. This necessitated the use of numerous man hours to jackhammer holes in chunks, preparatory to loading and blasting. After the chunks were reduced, bull- dozer and grader hours were needed to pile the taconite for acceptable shovel loading.

Jan 1, 1968

By Krzysztof Filek, Anindya Sinha, Bernard Nowak

Taking into account the possibilities of condensation of water vapour contained in air during its flow through a series of spot coolers as well as formation of eventual fog, a mathematical model of dynamic temperature, specific humidity and degree of fogging of cooled air in underground mining galleries with direct ventilation is developed. In the gallery, there situated various heat and moisture sources both of distributive and of concentrated types. The model is represented by three partial differential equations of first order. The cases of cooling with full as well as with partial air stream flowing through the gallery are distinguished. Owing to the fact that in practical designing, more important is the knowledge of the variation process of temperature, specific humidity and fogging of cooled mine air at steady state conditions, the model is modified to a set of three nonlinear ordinary differential equations. Based on the presented algorithm, the obtained set of ordinary differential equations is numerically solved which enables to: • specify the distribution of temperature, specific humidity, relative humidity and degree of fogging of cooled air in mining galleries; • determine the cooling powers of air coolers for their known locations; • indicate the locations of the coolers of known cooling powers. Exemplary calculations of temperature and relative humidity of cooled air are presented graphically in a number of diagrams.

Jan 1, 1997

By Klaus Schönert

Experimental investigations of single particle and interparticle breakage show that the microprocess in mills demands an energy input between 1 J/g and 10 J/g, if particles below 100 pm have to be comminuted. A system analysis of grinding media and roller mills is given in respect to the energy supply to the microprocess and the influence of the back stream caused by the compression of the material inside the active volume. The back stream diminishes the probability for capturing the particles in very fine grinding processes. Some possibilities are discussed how to solve this problem.

Jan 1, 1989

By F. Djahanguiri

The US Bureau of Mines con¬ducted research on underground stope leaching of metalliferous ores. Leaching underground would minimize the environmental impact of ore processing on the surface and would maximize minable reserves. An important aspect of this process is the minimization of pregnant solution losses and groundwater contamination by leach solutions. Bulkhead design and construction are important issues for solution control and stope-leaching economics. A reinforced-concrete bulkhead was designed, constructed and tested for solution control in an underground mine near Idaho Springs, CO. This paper presents the bulkhead-design methodology and construction procedure.

Jan 1, 1997

By R. E. Weeks, D. J. Millenacker

Utilization of true in situ technologies for mining copper in Arizona will involve a complex environmental permitting process. This process is a key factor in determining the feasibility, costs, and implementing time- frames required for development of this innovative mining method. The regulatory structure in Arizona is presently changing due to enactment of the Environmental Quality Act (EQA) of 1986 and development of new aquifer protection rules and regulations. The US Bureau of Mines has reviewed the comprehensive hydrogeologic characterization, ground water monitoring, mechanical integrity testing, well construction, contingency planning, and other regulatory elements that will serve as mechanisms to assure protection of ground water resources. The purpose of this paper is to inform the domestic copper industry of the significance of the new Arizona regulatory structure and its implications for prospective in situ operators.

Jan 1, 1987

By W. K. Collins, C. L. Dahlin, D. C. Dahlin, W. K. O’Connor, G. E. Rush

Direct mineral carbonation was investigated as a process to convert gaseous CO2, into a geologically stable final form. The process utilizes a slurry of water, with bicarbonate and salt additions, mixed with a mineral reactant, such as olivine (Mg2SiO4) or serpentine [Mg3Si2O5(OH)4]. Carbon dioxide is dissolved into this slurry, resulting in dissolution of the mineral and precipitation of magnesium carbonate (MgCO3). Optimum results were achieved using heat-pretreated serpentine feed material and a high partial pressure of CO2 (Pc02). Specific conditions include 155°C, PC02 = 185 atm and 15% solids. Under these conditions, a 78% conversion of the silicate to the carbonate was achieved in 30 minutes. Process mineralogy was utilized to investigate the appropriate feed characteristics, identify the process products and interpret the mineral dissolution and carbonate precipitation reaction paths. Key words: Mineral carbonation, Carbon dioxide sequestration, Carbonates

Jan 1, 2003

By Alice Blount, F. Patrick Carr

The quantitative evaluation,of quartz and other minerals in acid-insoluble residues from carbonate rocks and other industrial mineral products derived from sedimentary and low-grade metamorphic rocks is difficult. Commonly there are a dozen or more minerals present, and the suites vary from sample to sample. Because of these factors, either the absorption coefficient must be determined on a sample to sample basis or an internal standard must be used. Internal standards in general use are unsatisfactory. For example, [A1203] is often present in product samples because of ceramic grinding elements used in their production; CaF and LiF have peaks which overlap or nearly overlap mineral peaks in the samples. A careful evaluation has shown that magnesium aluminate (synthetic spinel) works particularly well as an internal standard for these types of samples. Not only does it have few, strong diffraction peaks which do not overlap, the peaks are in the same 28 region as the minerals, usually quartz and silicates, for which quantification is desired. Spinel also consists of equidimensional particles without prominent cleavages; this promotes a random orientation of the minerals in X-ray diffraction mounts. In addition, spinel can be used to correct for loss of diffracted-beam intensity due to thin sample preparations which are often unavoidable.

Jan 1, 1991

By Wolfgang Pietsch

Roller presses were first invented in the middle of the 19th century, for the economical size enlargement of coal fines as fuels. Coal briquettes became quickly accepted for industrial and domestic use giving rise to a large and sucessful industry, particularly in Europe, Japan, and North America. When, towards the middle of the 20th century, coal was more and more replaced by other energy sources, such as electricity, gas, and oil, roller press manufacturers searched for alternate applications of this equipment. In addition to contemporary coal briquetting, in fields such as smokeless fuel and form-coke, it was found that redesigned and modernized roller presses, which are now capable of exerting high forces, are versatile machines for many tasks in mineral processing. Today they are used for: - the "classic" pressure agglomeration and - the "new" high pressure comminution. In pressure agglomeration, the characteristics of fine minerals are improved by forming briquettes or granulated products from compacts. During size enlargement with roller presses briquettes are directly obtained while granular materials are produced by crushing and sizing of compacted sheets. The processes are carried-out essentially dry and often do not require binders other than those inherently contained in the feed and "activated" by the high forces and/or elevated feed temperatures (e.g. hot briquetting). Therefore, no foreign materials (impurities) are added. Another advantage of the technology is, that wide particle size distributions are acceptable or desirable as feed materials, including millimeter or even centimeter sized particles. Plastic particles deform and brittle materials are crushed during pressure agglomeration. A relatively new application of roller presses in mineral processing is the utilization of the crushing effect when brittle materials pass the nip area between the rollers. It was found that this crushing mechanism is very efficient thus saving energy, particularly in grinding circuits handling large capacities. The paper introduces the fundamentals of the process and describes the design as well as applications of modern roller presses in mineral processing.

Jan 1, 1995

By W. J. Stone

In response to concerns over the impact of mining on the hydrologic balance at the Navajo Mine in northwestern New Mexico, a recharge study was conducted using a chloride mass- balance approach. Impact of mining on annual recharge volume was assessed by comparing pre- and post-mining recharge values. The mean regional recharge rate for reclaimed ground (weighted by acreage) is 1.02 mm/a (0.04 in. per year) or twice that for undisturbed ground, 05 mm/a (0.02 in. per year). Comparison of regional recharge volumes for identical areas shows mining increases recharge 92%. The increase is only 80% if no closed depressions are constructed during reclamation. However, the increased rates are so low that there should be no detrimental impact on regional water resources. The chloride method proved useful at Navajo Mine and should succeed at others surface coal mines as well.

Jan 1, 1991

By F. Mauviel, J. Bernard, G. Herrouin, J. P. Lenoble, C. Charles, B. Taine

Manganese nodule projects were quite fashionable during the 1970s. At the beginning of the 1980s, low metal prices led to an almost complete reduction of such activities; however, the Law of the Sea incited the countries that signed it to build a strategy for this ocean resource. Gemonod was created in France in 1984 with a four-year mission. This paper presents the results of its program devoted to the technical and economic studies of nodule exploitation. A commercial mining system is presented. The nodules would be collected by a self-propelled miner and lifted hydraulically through a rigid pipestring. A complete optimized scenario has been built taking into account offshore mining, ore transfer at sea, transportation and processing to analyze the profitability of the project. Considering an average conservative basis for metal prices, after a deep analysis of the market, the return rate of investment of the project appears fairly interesting. These results are new and are explained in comparison with previous foreign studies. These results must not hide the innovative nature of the project nor the associated risks. This is why a mining pilot is required and has been specified by Gemonod.

Jan 1, 1991

By G. T. Adel, W. Z. Choi

In previous work at Virginia Tech, a population balance-model describing the simultaneous processes of size reduction and mineral liberation has been developed. Experimental verification of this model, however, has been limited to a binary mineral system containing only one composite particle class. When considering multiple classes of composite particles, estimation of model parameters becomes much more difficult. In the present work, a procedure for estimating model parameters for a multiple-composite- class model has been developed. Emphasis is placed on direct experimental determination of these parameters. The physical significance of the breakage rate function and the liberation function in characterizing the liberation process is also discussed.

Jan 1, 1987