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By Peter Zhang, Todd Minoski, Gabriel Esterhuizen, Jack Trackemas, Berk Tulu, Morgan Sears

Longwall mining is a highly productive and efficient coal mining method used in the USA. During longwall retreating, the belt entry must be maintained stable, and any roof fall in the belt entry would jeopardize mine safety and substantially interrupt the continuous production of coal in the longwall face. Past experience of longwall mining has shown that belt entry stability was the greatest challenge in longwall ground control, and the occurrence of roof falls in belt entries was largely associated with high horizontal stress. To properly support the roof in the belt entry, it is important to understand how longwall-induced horizontal stress changes affect roof stability in belt entries and to strategically install supplementary support to prevent any potential roof falls. Researchers from the National Institute for Occupational Safety and Health (NIOSH) performed horizontal stress measurements in the immediate roof of the belt entries for two Pittsburgh seam longwall panels oriented unfavorably to high horizontal stress. Hollow inclusion cells (HICells) were installed in the immediate roof at the intersection in each of the belt entries, and stress changes were monitored as the longwall face was approaching and passing the intersection. Numerical models were set up to calculate the longwall-induced horizontal stress changes in the roof at the monitoring sites. With the verified model, investigations were made of how horizontal stress is concentrated and relieved in the belt entry roof near the face under different panel orientations. Both measurements and modeling results showed that high horizontal stress is concentrated in the roof in the belt entry within about 15 m outby the face when a longwall panel is unfavorably oriented to the major horizontal stress. The study demonstrated that longwall-induced differential horizontal stress can be used as an indication of the degree of horizontal stress concentration. Roof support strategies are discussed on how to maintain the stability of belt entry under high horizontal stress concentration.

Jun 14, 2022

By Bob Munz, Ry Stone

To facilitate the installation of the longwall equipment for each extraction panel, West Elk mine develops set-up room roadways that are between 26.5 and 30.5 feet wide. Historically at the mine, the set-up room roadways have been driven in a single 20-foot-wide pass, then incrementally widened to the required width during installation of the longwall shields. The first pass roof is supported with a generic roof support plan consisting of partially encapsulated roof bolts and point-anchored cables. This ground support plan was utilized regardless of the geotechnical conditions encountered in the roadways or consideration of the required stand-up time of the roadway before the longwall shields were installed. This "blanket" approach tends to result in over-conservative or inappropriate roof support designs, particularly in changing geotechnical environments. Guided by the desire to optimize the ground support plans and increase mining efficiency for future set-up rooms, the West Elk mine and Agapito Associates, Inc. have developed and implemented a strata management program. Strata management, as a formal and structured process, allows ground support and mining methods to be tailored to the anticipated and encountered geotechnical environment in a con- trolled manner (Thomas 2007). To arrive at adequate site-specific ground support plans for the set-up rooms at the mine, several struc- tured processes were utilized. Firstly, the geotechnical environment was characterized by examining the roof lithology and geomechanical properties from nearby rock core obtained from exploration boreholes. To increase both mining efficiency and continuity, and to achieve longer stand-up times before the longwall shields are installed, a multi-pass approach was implemented into the design. During mining, the geotechnical conditions of the roadway are mapped, and the roof is strategically surveyed with a borescope. This process was used to ensure that the encountered ground behavior was in alignment with the design standards used for the roof support design. To support this process with measured data, roof extensometers were strategically installed throughout the roadway. This data was used to monitor the magnitude of roof displacement at various horizons and record displacement rates up until the longwall shields were installed. Lastly, a Trigger Action Response Plan (TARP) was used during mining to cater for any unforeseen changes in ground conditions that would warrant additional con- trols such as increased monitoring or the installation of additional ground support. This paper presents two case histories at the mine where the above strata management approach was implemented to arrive at a site-specific ground support plan. The main changes to the mine's ground control plan included a multi-pass mining approach, the utilization of fully encapsulated roof bolts, and the transition to a stiffer roof support system. The geotechnical mapping, the roof borescope results, and the roof extensometer data will be presented to demonstrate the effectiveness of the ground support system up until the longwall shields were installed in both presented cases.

Jun 25, 2024

By Anup Tiwari, Khanindra Pathak, BIBHUTI BHUSAN MANDAL

Failure of in-pit overburden dumps in open-pit coal mines causes debris to flow toward the active working face, threatening the safety of people and equipment. The evaluation of the potential mobility of failing mass will aid in hazard mitigation associated with unwarranted dump failure. The potential mobility is shown by mobility ratio (ratio of total drop between debris flow's initial and final deposition points to total travel distance) and runout characteristics. In light of above, a laboratoryscale debris flow flume was developed to investigate the effect of material gradation and slope angle on runout characteristics and mobility ratio. The total mass of experimental debris mix (Q) is fixed at 30 kg with 20% water content. Experiments at three different slope angles (30°, 35°, and 40°) demonstrate that increasing the proportion of fines in the experimental mix increases runout characteristics while decreasing the mobility ratio. The length and area of the runout decrease as the slope angle increases, while the mobility ratio increases. There is a positive correlation between d50 and runout characteristics at a fines content of 0.1Q, but a negative correlation at a fines content of 0.2Q and 0.3Q. Conversely, there is a negative correlation between d50 and mobility ratio for fines content of 0.1Q, but a positive correlation exists for fines content of 0.2Q and 0.3Q. A new index called the fine-to-coarse (F/C) ratio is used to identify the critical value of fines and coarse proportion that causes a transition from dry granular flow to fluidized debris flow.

May 29, 2023

By Erik Klohn

The El Soldado copper deposit occurs in volcanic rocks of alkaline affinity of Lower Cretaceous age. The orebodies are discordant and show strong structural and lithological control. The mineralizing event was accompanied by hydro- thermal alteration expressed as carbonatization, silicification, and chloritization. Individual orebodies contain bornite-chalcopyrite cores which are surrounded by haloes dominated by chalcopyrite and pyrite respectively. The sulfur isotope composition of copper sulfides strongly suggests the sulfur is of magmatic origin. Fluid inclusion studies show the mineralizing fluid to be a highly saline NaC1-CaC12, brine. No evidence of boiling was found. The deposit is most likely of epigenetic origin. Hydrothermal fluids were produced during crystallization of a sodium rich trachytic magma during the waning stages of an episode of alkaline magmatic activity. Similar copper deposits along the Chilean Coastal Range may also be associated with alkaline host rocks.

Jan 1, 1986

By Yousef Ghorbani, Abolfazl Danesh, Fatemeh Kazemi, Ataallah Bahrami, Morteza Abdollahi

The abstract highlights the impact of flocculants used in the middle thickener of a copper-molybdenum plant on both process water quality and molybdenite floatability. The study investigates the effect of a starch-based flocculant (wheat starch) on the efficiency of the middle thickener and molybdenite flotation. The findings indicate that the presence of starch influences the settling behavior of particles with different shapes, and the dosage of starch affects both molybdenum recovery and the presence of copper minerals in the molybdenum concentrate.

Mar 7, 2022

By L. W. Saperstein

Surface mining of coal is undoubtedly one of the more controversial aspects of the mineral industries today. There is a constant tug between the need for readily available and inexpensive energy supplies and the desire to minimize disturbance to the land. Without a doubt, surface mining severely disturbs the land surface. The duration of this disturbance, from a minimum of a few months to a maximum of infinity, however, is strictly dependent upon the mine operator's willingness to reclaim. Surface mining critics claim that it is impossible to ameliorate the detrimental effects of this mining to insignificance. The more vocal critics, indeed, are calling for complete abolition of surface mining for coal. Thus, they do not believe that it is possible to restore surface- mined land to pre-mining conditions. As a consequence of this position, an adversary relationship has developed between the operators and their critics who, simultaneously, believe they are doing their best for the United States. In a forum of mining experts, there is little need to recount the kind and amount of devastation that can result from poorly reclaimed land. This has been done numerous times, including once 1 by the author. Of particular interest to this paper, though, are the environmental hazards associated with contour strip mining. In addition to the problems of area mining: denudation of vegetation; exposure of toxic spoil; increase of erosion runoff; etc.--contour mining has the very real problem of landslide due to the outslope stacking of overburden. Contour mining is understood to be the extraction of coal from a hillside outcrop such that the resultant pit follows, or nearly follows, an elevation contour. The problem with contour mining as usually practiced is that the spoil from the cut, or the first cut if multiple cuts are made, is placed on the outslope. If this slope is steep, the resulting pile is difficult to stabilize, generally erodes swiftly, and may fail disastrously.

Jan 1, 1973

By Fouad Faraj

For every blast pattern, zones of unique material types need to be classified before mining. Most material types can be summarized into different kinds of ore and waste. Blocks generated from blasthole assays are too small to be selectively mined so areas with a single material classification meeting the mine’s selective mining unit must be defined. Current industry standard practices are to manually draw ore/waste dig limits but this process is subjective and results in quantities of dilution and ore loss which can be improved upon to enhance the profitability of mining operations. Two weeks production data from a homogeneous Cu porphyry and heterogeneous Manto-type Cu deposit are used to assess the variability in the hand-drawn dig limits for 20 geologists, mining engineers, or ore control specialists and are compared with the optimal ore/waste delineation. The profit for 20 distinct hand-drawn dig limits for the homogeneous mine ranged by 3.7% from $10.5 million to $10.9 million averaging at $10.8 million. The percent range nearly doubled for the more heterogeneous mine at 5.9% from $17.9 million to $19.0 million averaging at $18.6 million. Using the optimal ore waste delineation, the profit increased to $11.0 million (1.9% increase) and $19.3 million (7.0% increase) for the homogeneous and heterogeneous deposits respectively. The natural variability, diggability requirement, and selectivity are identified as the main drivers of ore loss and dilution. Recommendations are provided for reducing the subjectivity in manual hand-drawn dig limits by integrating dig limit optimization algorithms as a tool to assist practitioners.

Feb 23, 2024

By D. Boreck

The Bureau of Mines is conducting research on the feasibility of incorporating in situ stope leaching into active underground metal mines. Stope leaching, a modified in situ leaching technique, proposes to recover metals by leaching fragmented ore in existing underground openings and collecting and processing the metal-bearing solution to recover the valuable metals. If leaching solutions escape from the stope, either through geologic discontinuities or highly permeable zones in the rock, valuable metals dissolved in the solution may be lost. Escaping solutions may also contaminate ground waters. Consequently, in fractured rock, the characteristics of the fractures in the vicinity of the leaching stope must be understood before introducing actual leach solutions into the stope. Effectively characterizing a rock mass requires the integration of several disciplines including structural geology, borehole geophysics, hydrology, geochemistry, and mining engineering. This paper will focus on the general geologic and geophysical techniques that can be used to characterize the rock mass at an underground simulated stope leaching site. The results of several geophysical logging methods, tested at the site, are compared to the geologic core descriptions. Then, the? effectiveness of the different geophysical techniques in delineating fracture zones will be assessed. Knowledge gained through the geologic and geophysical analyses can be used to supplement results from hydrologic testing. This information can also be utilized in designing blast patterns and developing strategies for controlling or blocking movement of escaping leach solutions.

Jan 1, 1991

By James W. Echerd

Anthracite preparation developments, particularly in the early days of the anthracite industry, formed the basis for the modern coal preparation plants that have become so essential to the coal industry today. The anthracite industry, from early in the 19th century until relatively recently, was a leader in mining, preparation and marketing of coal, and played a leading role in the development of the industrial America we know today. Anthracite was discovered in America in about 1760--the story of Necho Allen is well known--but the rediscoveries leading to mining operations took place about 50 years later. The Wurtz brothers in 1815 at Scranton, the Smith brothers at Wilkes-Barre in 1807, Beach in Hazleton in about 1814, and Boyd in 1816 at Shamokin were all instrumental in promoting early mining and marketing of anthracite (J3. The early canals and railroads were built for the specific purpose of moving anthracite to the market areas. Eventually, the industry grew until, in 1917, it reached a production zenith of a little over 100,000,000 tons, representing about 20 percent of the total coal output in the United States. Almost half of the anthracite produced that year was consumed for domestic heating, a utilization that had dominated the industry for almost 100 years. Initially, anthracite had to be used by gunsmiths and blacksmiths, after which had followed the consumption of extensive quantities for railroads, blast furnaces and foundries, and electric power generation. Most of the markets have been lost to coke, oil, and natural gas. Near the anthracite regions, however, significant quantities are still used for domestic heating, power generation, carbon black manufacture, blending with bituminous coal to make metallurgical coke and fuel, and for other industrial purposes. Thus, anthracite production has not been entirely committed to history, but remains an active industry that follows modern practices in the mining, preparation, shipping, and utilization of a fuel that is still a valuable adjunct to the national economy. In fact, its inherent low sulfur content may make it an important fuel of the future. Estimates indicate there are reserves of anthracite to last for 300 years at a consumption rate of 50,000,000 tons/year. Anthracite Preparation Yesterday A 170-year history of the anthracite industry obviously is not the purpose of this discussion. A complete history of anthracite preparation, the rather unglamorous step in the processing of "mine run" hard coal to make it suitable for the user, is also not practical. Hence, the purpose of this report is to trace the development of some of the most important processes used through the years to meet a part of the demand for energy developed by our modern society. Anthracite preparation in the early days of the industry consisted solely of separating slate from the coal, by hand, underground (Z). This method prevailed for almost 20 years until wrought iron hand rakes were introduced to separate the large and small sizes. Shortly thereafter, the first attempts were made to size and clean the coal aboveground. The coal was dumped on a perforated cast iron plate, and men used sledge hammers to break the larger pieces into smaller sizes suitable for the market. The smallest sizes--that is, the material that went through the plate--were thrown away because they had no value at that time--a concept that existed for many years and actually was the basis for the subsequent "river" coal production and the many silt banks which are landmarks in the anthracite region. The larger sizes, at that time, sold for 50 cents per ton. The Batten breaker, or roll crusher, was invented in 1844, followed soon thereafter by the Snell-Diehm breaker (A). The latter had disadvantages, including excessive waste and fixed product size, but it later was improved in these respects. A breaker was also developed at Minersville, Pa., at about the same time that processed 200 tons of coal per day, using roll crushers and circular screens (1). Handpicking, from the beginning of anthracite preparation, was an important part of the cleaning process and was still being practiced as late as 1950. It was this process that involved the "breaker" boys of coal region lore. How much good handpicking accomplished depended on how much impurity was present in the coal--the more the impurities, the greater the reduction in ash. Thus, high-impurity streams were significantly improved, whereas picking of relatively clean coal was mainly to show an effort to make a quality product. As indicated, picking is largely a visual operation. It was and is wasteful of coal in the larger sizes since some good coal is always associated with the bad. However, it was probably much more effective' in the larger than the smaller sizes.

Jan 1, 1971

By John Rajala

The Otjikoto Gold Mine in the Republic of Namibia is located approximately 300 kilometers north of the capital city of Windhoek. The project features surface mining with a modern gravity/carbon-in-pulp mill for ore treatment and recovery of gold. Initial mill design capacity was 2.5 million tonne per annum but then expanded after 9 months of operation to 3.1 million tonne per annum. The technical steps to establish the Otjikoto mill design from process selection in the due diligence stage, through flowsheet development in the feasibility study followed by detailed engineering design are reviewed in this paper along with mill performance during start-up and in 2019.

Oct 30, 2020

By Derek J. Barratt

The existence of a critical size buildup in an autogenous or SAG mill can be predicted from proper examination of drill core and ore samples. Methods of dealing with such critical size in a primary mill are reviewed in the context of ore properties, whether or not pilot plant-scale testwork has been conducted, and also with respect to the design of new plants or the retrofitting of existing operations. The implications of not planning for pebble crushing in situations where it is appropriate are discussed.

Jan 1, 1992

By R. Y. K. Yang, O. Olajide, E. H. Cho

"This study focuses on partial leaching of coal pyrite with sodium sulfite in order to increase its degree of liberation from the coal matrix, which might help to increase the removal of coal pyrite, together with trace elements of arsenic (As), selenium (Se) and mercury (Hg) by froth flotation. The U.S. Bureau of Mines’ two-stage reverse flotation process was applied to further reject coal pyrite in the second stage, where pyrite was floated while coal was depressed. The results show that the leached coal flotation with sodium sulfite produced lower pyritic sulfur content in the clean coal by approximately 25% compared to the flotation of unleached coal. The synergism mechanism between the leaching and the two-stage flotation is delineated. The rejection of trace elements (As, Hg and Se) after the two-stage flotation process with unleached coal followed approximately that of pyritic sulfur (64.6%). However, after the two-stage flotation with leached coal, the rejection of Se was as high as that of pyritic sulfur (77.9%), while the rejections of As and Hg were 20% lower than that of pyritic sulfur, or followed approximately the same rejections obtained through the two-stage flotation with unleached coal.IntroductionSO2 is a reducing reagent, but when it is combined with oxygen in an acidic solution, it will become a strong oxidizing reagent for leaching coal pyrite. Sundaram et al. (2001) found that the reagent could leach coal pyrite to produce ferric iron, which, in turn, catalyzed the oxidation of SO2. Similarly, Cho et al. (2009) found that the reagent could leach pyrite as well as mercury from coal. In the present study, coal was preconditioned by partially leaching coal pyrite in water-coal slurry with sodium sulfite at 48° C. The partial leaching of coal pyrite may enhance its degree of liberation from the coal matrix and give a chance to be rejected more effectively during the flotation.The two-stage U.S. Bureau of Mines’ reverse flotation process (Miller, 1975) was used in this study. The first stage is conventional flotation, in which coal is floated while material with higher ash and pyrite content remains in the cell. Kerosene is used as a promoter to float the coal and MIBC (methyl isobutyl carbinol) is used as a frother. In the second stage, the floated coal from the first stage is depressed using a starch-based reagent, while coal pyrite is floated using potassium amyl xanthate. In this second stage, the liberation of coal pyrite from the coal matrix seems to be an important factor for successful rejection of coal pyrite."

Jan 1, 2015

By M. Javier

"Mining makes civilization possible. It also creates socio-environmental liabilities forcing us to ask how much more of this mining can our planet support. It is clear that the future of mining differs from mining in the future. The laws of nature are being compromised by mining. This paper studies the problems at the core of the mining business which need to be addressed. What kind of mining will serve our existence with nature on this planet? What kind of mining perspectives are we able to formulate without having negative effects for future generations? Is mining technologically sustainable? The values of predictions, imagination, and creativity must be integrated to define what mining should be. Those values should be in the technologies necessary to restoring equilibrium of nature (Geomimic) as well as in complete extraction of metals, better utilization of the mineral reserves, and design the usage of metals to recycle. The purpose of this research is to examine many views and perspectives for future generations and to accelerate the pace of innovation of having mining without socio-environmental liabilities by design and by understanding nature. KEYWORDS: Geomimic, Sustainability, Waste mine Design, Management by Loss. INTRODUCTION The future of mining is being stifled by many antiquated and stagnant attitudes and policies by the industry and society as a whole. The time is now or never for real action and education against these attitudes and to upgrade them to meet the current needs of this planet if we are to survive. Doing this will prove that we understand and respect nature for us and our posterity. It will also show a positive assessment that the mining process can be reversed before the point of no return. And that is to say, only if reversibility is still an option. It may not be anymore but it’s worth a try. We need to use our imagination and engineering know-how to come up with new proposals to change the core of mining. It would entail re-engineering. There is a profound difference between the future of mining and mining in the future. The future of mining is the continuation and persistence of past practices in the industry and expecting new results. Mining in the future requires a paradigm shift for extraction through modern thinking about mining as it pertains nature. The new paradigm for mining in the future would restore equilibrium with nature. Always keep in mind the connection of mining to nature. What is the future of nature? To predict mining in the future we need to use past experiences in mining and our knowledge of modern science and engineering to formulate a prototype that will enhance mining while maintaining equilibrium with nature. Mining and protecting nature are not mutually exclusive. This new prototype has nothing to do with the level of bonding or insurance that the mining industry can legally provide. The goal of this paper is to contribute some new ideas to help transform the mining industry based on the laws of nature and its limitations. Using this new prototype we will develop the following 1. Extraction of minerals Reserves-Dimensions-Technologies 2. Usage of mineral resources-Manufacture’s products designed to be reused and recycled 3. Nature- Equilibrium (physical, chemical and biological)"

Jan 1, 2016

By A. I. Johnson

This paper describes," the application, of a modular or building block approach to the analysis, design, and control of complex mineral treating processes. The main purpose of the paper is tutorial, to show the reader how such processes can be modeled using a modern digital computer" and, not to discuss in any detail the results that may be achieved in such studies. It is proposed that, the main techniques be illustrated by reference mainly to the Bayer process for alumina extraction and purification; in cooperation with the Aluminum Company of Canada Ltd. the author and his Colleagues at McMaster University and their students have studied this, process as a means of applying new computer techniques to extractive metallurgical processes. The plant described was studied by the author and his colleagues as a senior undergraduate project in cooperation with the Aluminum Company of Canada. It is one of several studies that have been carried out with Canadian industry. (1)

Jan 1, 1972

By D J. Bradshaw

It is well known that the chemical environment determines the success of the flotation process, however its characterization and control is difficult to achieve. This work evaluates the use of various measurements, including mineral potential measurements, in gaining an understanding of the influence of varying parameters such as the milling media and the reagent suite composition on the flotation performance of a platinum group metal (PGM) bearing ore. The results showed differences in the response of the various mineral electrodes to the different conditions, however the changes in flotation performance of the different minerals in the ore could not be wholly described by the electrochemical changes, demonstrating the limitations of these measurements.

Jan 1, 1999

By E. W. Greig

This paper is an account of exploration for bauxite in the Amazon Basin, Brazil, and particularly of the discovery, exploration and development by Alcan of the Trombetas deposit so a general account of the Trombetas Project has already been published in E/MJ (Anon. 1975) to which the reader is referred for details on owner-ship, infrastructure and construction as well as the proposal for mining and treating the bauxite. It is impossible to consider the Trombetas deposits in isolation. A regional account of bauxite in and around the Guyana Shield and the northern portion of the Brazilian Shield is included and it is suggested that these deposits all formed during Tertiary time under similar conditions.

Jan 1, 1977

By I. Ward, E. Milosavljevic, M. Botz

"The silver nitrate titration method is a rapid and acceptably accurate means of analyzing for cyanide in leach solutions that contain primarily free cyanide. However, in leach solutions containing elevated levels of copper, the titrimetric method overestimates the concentration of free cyanide and underestimates the concentration of weak and dissociable (WAD) cyanide. The authors have developed a modified potentiometric (MP) titration method for determining WAD cyanide that overcomes issues associated with high copper levels in solution. The new MP-WAD method involves addition of a chemical ligand to the sample prior to silver nitrate titration to release cyanide bound to copper. Once released from copper, cyanide in solution is no longer affected by the presence of copper, and titration results are quantitative rather than empirical. In multiple laboratory trials with synthetic solutions and complex actual leach solutions, analytical results obtained with the new MP-WAD method were found to be within about ±5% of analyses obtained with the USEPA OIA-1677 WAD cyanide analytical method.IntroductionThe silver nitrate titration method is widely used to estimate the concentration of cyanide in leach solution for purposes of cyanidation process control. Cyanide determined by silver nitrate titration is commonly referred to as “free” cyanide, but frequently should be referred to as “titratable” cyanide. By definition, free cyanide is the sum of the concentrations of aqueous hydrogen cyanide HCN(aq) and the cyanide anion CN- (ASTM, 2010). Titration will only yield a reasonably accurate measurement of free cyanide when metal-cyanide complex concentrations (e.g., cadmium, copper, mercury, nickel, silver and zinc) in solution are low. In other words, titration will only yield a reasonably accurate measurement of free cyanide if the solution primarily contains free cyanide."

Jan 1, 2015

By John C. Kleiber

From time to time since the initial installation of an experimental flotation section in 1940 (reference A), Permanente Cement Company has made efforts to beneficiate the low-grade limestone fraction which occurs in its deposit at Permanente, California, The encouraging results outlined in this paper are the result of Permanente's latest effort. This paper discusses the factors governing the selection of the flowsheet with particular reference to marketability of the sand tailing by-product. The process flow is outlined in detail, and operating statistics of the plant are presented. Finally, the problems encountered in the operation of Permanente's beneficiation plant are discussed as well as solutions sought and found.

Jan 1, 1964

By M. Wasel

The Gross Rosebel gold deposits are located in the Guiana Shield of north central Suriname. Initial discovery of surficial gold in 1880 by local artisanal miners preceded small-scale mechanized mining from 1885 to 1939. The first systematic exploration program was carried out by Placer Development from 1974 to 1977. In May 1992 Golden Star Resources optioned the property. Initial shallow reconnaissance diamond drilling of the extensive surface geochemical anomalies intersected sporadic gold mineralization with no apparent continuity between drill sections. Successive deep augering, trenching and systematic grid drilling based on information from surface mapping allowed development of a preliminary geological model. Further drilling of specific structural-lithologic targets and more complete synthesis of geological data from the trenching and deep auger sampling added to the geological model and defined the multiple controls of gold mineralization. Carefully planned infill drilling on a tighter grid spacing resulted in progressive definition of reserves within six discrete gold deposits. In a complex geological setting, the key to success at Gross Rosebel was persistent, systematic exploration, detailed mapping, careful core logging and perceptive geological interpretation. Reserves now stand at 48.6 Mt at 1.6 glt Au, or 2.4 million ounces of gold. The purpose of this paper is to describe the progression of exploration activity that led to the definition of substantial gold reserves and to summarize the geology of the deposits.

Jan 1, 1998

By Ryan C. Stephan, Zach Agioutantis, Christopher Mark

During the past 15 years, roof fall rates have fallen dramatically in US coal mines, particularly in regions where the roof is weakest. The remarkable reduction in the number of roof falls has been accomplished with more effective roof support systems. The purpose of this paper is to present a design methodology that builds on and quantifies the basic roof support concepts that have been successful in the USA. The methodology starts by defining three modes of roof support, based on the roof strength relative to the stress level: (1) suspension, where roof bolts mainly provide skin control for strong roof; (2) beam building, where moderate strength roof can be supported by roof bolts alone; and (3) supplemental support for weak roof. Next, a large database of roof fall histories at a number of mines is used to define the approximate boundaries of these three regimes based on the coal mine roof rating and the depth of cover. Finally, guidelines are presented for site-specific design of support systems within each regime. The new computer package, analysis of mine roof support (AMRS), implements the design methodology.

Sep 29, 2020