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By Douglas B. Silver

Study Parameters (Status as of February 1993) Time Period: 1989 -1991 151 North American Public Metal Mining Companies Fiscal not calendar year basis 85+% of Canadian and U.S. Metal Production Au, Ag, Cu, Pb, Zn, Mo, Ni, W Results are Preliminary and Research Continues Chicken Little is Alive and Well

Jan 1, 1993

By Diana Diaz, Rakshith Shetty, Vitaly Proschenko, Mike Mooney

Cohesive clay soil poses a significant risk to earth pressure balance tunnel boring machines (EPBM) due to unstable face pressure, clogging potential, high cutterhead torque, poor muck flow, low advance rate, etc. This paper details the performance measures desired when EPBM tunneling in clay soil, and the scientifically-supported conditioning methods to transform in-situ clay to a muck with such characteristics, giving particular attention to ground conditions. The paper then examines TBM data from multiple clay soil projects in the context of these performance measures to demonstrate the influence of cohesive soil conditioning on EPBM performance.

Jun 13, 2023

By Robert W. Lawson

INTRODUCTION Prior to 1705, underground mining was limited to mineral deposits located above or a very small distance below the water table. The development of the steamdriven mining pump was motivated by the need to extract minerals from deposits considerably lower than the water table. Today, the majority of mine pumps are driven by electric motors, although some small utility pumps are driven by compressed air. Of the numerous types of pumps that might be applied to mine service, the two types used most frequently underground are the centrifugal and plunger pumps. Each of these types has its proper application. In most instances, plunger pumps are best for handling low water volumes against high heads, while centrifugal pumps effectively handle either low or high water volumes against low heads or high water volumes against high heads. This chapter describes pumps applied to underground mine service, where the mine service consists of mine drainage (removing mine water as it accumulates), mine dewatering (removing water from a flooded mine), and pumping for special applications such as hydraulic mining and hydraulic hoisting. CENTRIFUGAL AND PLUNGER PUMPS Modern mine pumps are classified as either centrifugal (kinetic) or plunger (positive-displacement) pumps. The following paragraphs describe each of these classifications. Centrifugal Pumps Centrifugal pumps may be grouped into various types, depending upon their various features: Number of Stages: In a single-stage pump, the total head is developed by one impeller, while a multi¬stage pump utilizes two or more impellers acting in one casing to develop the total head. Fig. I shows a cutaway view of a single-stage horizontal split-case double -section centrifugal pump. Fig. 2 shows a cutaway view of a six-stage medium-pressure split-case diffuser-type centrifugal pump. Type of Casing: A volute pump has a casing in the form of a spiral or volute. A circular-casing pump has a casing of constant cross section concentric with the impeller. A diffuser pump is equipped with a diffuser that converts velocity head to pressure head. Shaft Position: A horizontal pump normally has the shaft in a horizontal position, while a vertical pump normally has the shaft in a vertical position. Fig. 3 illustrates a vertical turbine-type slurry pump. Suction: A single-suction pump equips the first stage with a single-suction impeller, with fluid entering the impeller on only one side. A double-suction pump equips

Jan 1, 1982

By Chas. F. Jackson

INTRODUCTION This paper is one of a series dealing with mining methods and costs, prepared and published under the sponsorship of the US Bureau of Mines (USBM) and made possible through the cooperation of many mining companies in the US and foreign countries. The data presented have been obtained from papers previously published by the Bureau dealing with indi¬vidual mines, from the technical press, and from infor¬mation furnished by the mining companies. DEFINITIONS Top Slicing The term top slicing is commonly applied to that method of mining in which the ore is extracted by a series of timbered slices, beginning at the capping; the slice is caved, bringing down the capping to the floor of the slice; the succeeding lower slices are mined up to the overlying mat or gob, consisting of an accumulation of timber from the upper slices and broken capping, which follows the mining progressively downward (Fig. 1). The term has also come to be applied to the mining of ore bodies only one slice thick, by a series of tim¬bered slices one beside the other. The timbers are blasted out, bringing the capping down to the floor, suc¬ceeding slices being driven alongside those already caved (Fig. 2). In USBM classifications of mining methods, top slic¬ing has been placed under the heading caved stopes. The method differs fundamentally, however, from the cav¬ing methods of mining in which the breaking of the ore itself is accomplished by caving action induced by undercutting. In top slicing the ore is broken by the ordinary methods of drilling and blasting, and only the capping is broken up by caving. Main Levels or Haulage Levels Main or haulage levels are the main extraction levels on which the ore is hauled to the shaft. These levels and the shaft constitute the preliminary development of the mine.

Jan 1, 1982

By Simon D. Strauss

The recession that began in late 1980 has proved to be not only prolonged and severe, but in certain ways unique in its effect on the mineral industries among the periods of economic slowdown experienced in the Western world since the end of World War II. This time almost all minerals have been affected. In previous business turndowns, by contrast, some mineral sectors have with-stood economic adversity well. They experienced little or no adverse effect-thanks either to a strong secular expansion in the markets for their particular product or to specific factors that caused demand to be well maintained. For example, aluminum, molybdenum, and nickel are three metals that enjoyed extraordinary growth in applications during the years 1946-1973. These metals were little affected during the recessions that occurred in that era. Similarly, coal did not suffer a pronounced drop in sales in the 1974-75 turndown because, with the price of oil rising sharply, a switch away from oil and back to coal was clearly indicated for some energy-intensive applications. Oil itself was largely impervious to the ups and downs of the business cycle until very recently. And the precious metals, gold and silver, have often been regarded as benefiting from reduced economic activity because labor becomes more available, productivity rises, and operating costs diminish. In the current recession, however, no major mineral has escaped the broad trend. The secular growth factors that were previously so evident for aluminum, molybdenum, and nickel have disappeared, at least temporarily. The stable pricing behavior that previously characterized all three of these commodities has been replaced by extreme price weakness and apparent inability of the major producers to continue their roles as market leaders. Coal and oil both have suffered from a sharp drop in energy requirements. There are those who now anticipate a collapse of the market control over oil prices so clearly exercised by OPEC since 1973. If oil prices are no longer effectively controlled by the governments of the exporting countries, then coal prices are also certain to be affected. And the combination of high interest rates, tight money, and a change in public perceptions of precious metals put the skid under gold and silver quotations in 1981 and early 1982. Although inflation has been viewed as the scourge of most Western countries ever since the oil crises of 1973-74, prices-in constant dollars-of most minerals have not risen. On the contrary, with the exception of the precious metals and oil, for most minerals the prices that prevailed at the end of 1982 were close to the levels of the Great Depression of the 1930s in constant dollar terms. Table 1 compares prices for copper, lead, zinc, and aluminum at the end of 1982 with the average prices in 1934, stated in constant 1967 dollars. This emphasis on prices for mineral commodities reflects the fact that profits of mining enterprises vary directly with the level of prices. Manufacturing and retailing enterprises march to a different tune. They establish sales prices based on costs. Their profits tend to vary with volume. Commodities are for all practical purposes fungible, that is the advantages of known brands in marketing manufactured goods have little application in a commodity market. Thus the individual seller of minerals is unable to establish his sales prices. Except where a monopoly is present, he must sell at the going market. His option is to abstain from selling if he finds the price unremunerative. In past recessions, some mineral producers chose to do precisely that-either accumulating a substantial share of their output in inventory or, in prolonged downturns, abstaining from production. During the current recession, however, private-sector mining companies did not have the option of accumulating inventories to any great extent. Capital costs for new mineral projects or for expansion of existing facilities have escalated at an alarming rate since the early 1970s. Added to this has been the heavy cost of installing pollution control or safety equipment to comply with the regulations adopted in most industrialized countries (and particularly the United States) since 1968. The consequence has been that the financial position of most major mineral enterprises in mid-1980 was already strained. To finance increased inventories meant incurring additional funded debt at high interest costs, thus impairing the concern's credit rating. Management Choices Private-sector managements have had to face up to the alternative of either continuing to produce at an unchanged rate and marketing output at unremunerative prices or reducing output. The latter has meant either operating at a curtailed rate, with con-

Jan 3, 1983

By A. M. Al Taweel, S. M. El Mofty, T. A. Hassan, M. R. Moharam, A. M. Ramadan

The axial mixing characteristics of a pilot-scale flotation column were investigated with the objective of identifying means to mitigate the extent of axial mixing that adversely affects its grade/recovery performance. A wide range of design and operating conditions was investigated and the experimental results, obtained using the dynamic response method, were analyzed using three axial mixing models. The dynamic response of the column can best be described using the axial dispersion model. The results obtained suggest that the value of the axial dispersion coefficient, EL. can be signi6cantly reduced by judicial selection of hydrodynamic conditions and/or the use of column inserts that suppress the onset of hydrodynamic instabilities inherent to the operation of conventional flotation columns. Up to 40% reduction in the value of EL was thus obtained by using spargers that produce more uniform bubble sizes, while up to 30% reductions were obtained by controlling the residual frother concentration.

Jan 1, 1995

By Connor Meinke, Shaihroz Khan, Kevin Erwin, Rajiv Chandramohan, Muhammad Usman Siddiqui

High-quality sample selection for metallurgical test work is essential to a geometallurgy study, but the large multidimensional dataset makes sample selection a daunting task, as classifying the dataset while respecting its heterogeneity is difficult. This paper presents a streamlined approach for sample selection, utilizing custom-built tools in Python to standardize the methodology, saving time and costs. This approach uses the cumulative sum method, principal component analysis, and k-means clustering method to elegantly cluster the data and select representative samples. A case study is used to demonstrate the effectiveness of the methodology by selecting 40 samples for flotation test work.

Feb 1, 2024

By G. W. Toth

The coal mining cost models described in this paper represent a computerized estimating procedure for analyzing mining costs and requirements of proposed coal mining projects. Both surface and underground mining analyses can be conducted through the use of these models. These models were developed by the NUS Corporation for the Electric Power Research Institute (EPRI). The methodology design of the cost models follows a process engineering approach for determining mining requirements and costs similar to the logic typically employed in preliminary mine feasibility studies. All capital and operating costs associated with a new coal mining project are thereby estimated. The results of these analyses are then entered into a financial analysis framework which computes annual cash flow summaries, utilizing a profit and loss statement approach, to solve for either the coal value/ton (minimum required selling price) or the rate of return on equity for the project. The coal value/ton is also referred to as the economic cost of production (F .O . B. mine, including preparation).

Jan 1, 1980

By Lawson. Heather

"The purpose of this study is to explore how the geochemical and petrographic components of coal may impact its physical properties, as well as how these components correlate with a history of reportable dynamic failure in coal mines. Dynamic failure events, also termed bumps, bounces, or bursts, are the explosive failures of rock in a mining environment. These events occur suddenly and often with no warning, resulting in worker injury up to and including fatality in greater than 60% of MSHA reportable cases. A database of variables was compiled using publicly available datasets, which included compositional geographic, strength, and Hardgrove Grindability Index (HGI) data (ACARP, 1998). Results indicate that bumping coals are less mature, lower in carbon, higher in oxygen, softer, and less well cleated than coals that do not bump. High liptinite content was found to correlate with higher average UCS values. However, no clear, direct correlation between UCS and dynamic failure status was observed. The findings of this study establish that differences exist between coals that have experienced reportable dynamic failure accidents versus those that have not. These differences are inherent to the coal itself, independent of mining-induced risk factors. Results further illuminate how compositional attributes of coal influence physical properties and begin to clarify potential links between geochemistry and dynamic failure status. Only through the better understanding of risk can more effective mitigating strategies be enacted.INTRODUCTIONDynamic failure events, also termed bumps, bounces, or bursts, are the sudden failures of rock in a mining or quarrying environment. Failure occurs when the rock’s critical bearing capacity has been exceeded and the rock fails energetically through the outward expulsion of rubblized material (Peng, 2008). These events occur suddenly and often with no warning, resulting in worker injury up to and including fatality in greater than 60% of reported cases through the Mine Safety and Health Administration (MSHA). Much research has been devoted to the prevention of these events. The effects of overburden depth and stiffness, mine design, mining practices, and in situ stresses are well documented (Agapito and Goodrich, 2000; Brauner, 1994; Campoli and Kertis, 1987; Holland and Thomas, 1954; Iannacchione and Zelanko, 1995; Lawson et al., 2016b; Mark, 2016; Newman, 2002; Peng, 2008; Whyatt, 2008). Despite these significant advancements in coal mine ground control, however, events continue to occur. Proactive risk mitigation remains an important research area. This is particularly true in underground coal settings, where the rockmass is layered, lithologically diverse, and does not exhibit consistent material properties across deposits.Many conditions have been associated with the occurrence of dynamic failure phenomena, including:"

Jan 1, 2019

By G. T. Adel

The selective recovery of fine particles by flotation has been a long-standing problem in the mineral processing industry. Fundamental studies carried out at Virginia Tech since 1980 have suggested that many of the problems encountered in separating fine particles can be alleviated by using significantly smaller air bubbles than those used in conventional flotation processes. The main advantage of using smaller bubbles is found in an increased recovery rate, which can be attributed to an improved bubble-particle collision efficiency. This concept has been applied in column flotation as a means of improving flotation kinetics. A computer simulator has been developed to better study the effects of various parameters on flotation column performance. The simulation results suggest that the use of small bubbles and tall columns improves the recovery of fine particles while a judicious use of wash water greatly improves product quality. Information collected as a result of this analysis has been applied in developing scale-up relationships for column flotation.

Jan 1, 1989

By X. Cheng

A series of batch flotation tests was performed on chalcopyrite-quartzite, pyrrhotite-quartzite, and on chalcopyrite-pyrrhotite-quartzite mixtures. Pulp potential measurements in the flotation tests of single sulfide minerals indicated that each sulfide mineral had its own optimum potential range for flotation. When these results were used to select the potential ranges for the separation of the two minerals from their mixture, their flotation responses changed and the selectivity of separation was adversely affected. A possible mechanism involving surface alteration through galvanic interaction is discussed. A method to improve the selectivity of flotation separation was proposed.

Jan 1, 1992

By T. Weatherwax

As part of a strategic research initiative at UBC to design and evaluate integrated underground mining and mineral processing systems, work has been done to determine how to utilize the coarse rejects of pre-concentration in the underground environment. An amenability study for nine orebodies from four of Xstrata Nickel?s Ontario operations evaluated both processing and waste disposal methods. The utilization of the rejects as a high quality backfill with minimal binder requirements has been identified as the preferred disposal method. Fill mixes utilizing the rejects in combination with classified tailings, full tailings, and cement were developed based on the geotechnical properties of the rejects. The mix designs were examined for both strength and rheological properties. The paper will present the results of the pre-concentration testwork, the design and strength testing of various mix designs for rejects from the nine ores and presents a conceptual design for an underground pre-concentration system based on this test work.

Jan 1, 2008

By William P. Shell

An important part of process control engineering is the implementation of the basic control system design through commissioning to routine operation. This is a period when basic concepts can be reviewed and improvements either implemented or recorded for application in future systems. The experience of commissioning the process control systems in the Homer City coal cleaning plant are described and discussed. The current level of operating control performance in individual sections and the overall system are also reported and discussed.

Jan 1, 1983

By B. Radwanek-Bak

The assurance of future raw materials supply to the EU mineral industry has become, in recent years, one of the most important tasks of the EU Commission. It is focused on creation a new mineral policy within the EU zone. One of the starting points for this activity was identification of the mineral commodities that are critical for the sustainable development and technological progress. The paper presents the glance to this problem from the National Member level. Domestic mineral reserve base as a possible source of critical raw materials for the EU was shown. Poland cannot be considered as its resource base. The source of these raw materials are not only scarce in Poland, but also they are not produced, and their demand is now - and according to forecasts is going to be in the future - met by imports. The raw materials in question are not considered exactly critical for Polish economy, but they are of limited economic importance. On the other hand, their growth is a best opportunity and at once the need to the future sustainable development.

Jan 1, 2011

By Rolf Pollak, Jan Tegtrneier, Gerhard Keller, Horst Gerhardt, Wolfgang Müller, Dieter Tetzner

INTRODUCTION Under certain geological and mining conditions mining near the surface results in an intensive destruction of the overlying rock strata. If the system of mine openings remains filled with air after having completed all mining activities because the flooding of the mines depending on the morphology of the mining area does not exceed a certain level, this circumstance might result in dangers for the public. This is particularly true where uncontrollable air- ways occur within the destroyed rock or if former uranium mining areas are concerned. In these areas radon emanation resulting in undue radon concentration should be taken into account. This circumstance can be counteracted by suitable measures of ventilation. In the following the example of a uranium deposit in the Erzgebirge Mountains (Saxon Ore Mountains) is used to illustrate how statements about the ground flow through overlying rock can be made on the basis of systematic investigations. Finally comparisons with experience gained in coal mining yield orientation data which are used as input quantities in ventilation network calculations and in project preparation of mine fans. Last not least it is proved that endangering the population by radon can be excluded by installing an appropriate fan. INITIAL SITUATION From 1946 to 1989 the uranium deposit of Schlemal-Alberode was mined starting from superficial zones down to depths of 1,800 m. The total output amounted to 80,000 t of uranium, i.e. Schlemal Alberode is one of the largest uranium deposits in the world. The mine openings comprise a cavity of 40 million m3. Al- though thin seams (0.2 to 0.3 m) and steep to semi-steep veins (60 - 70 degrees on average) were extracted using the method of overhand cut-and-fill there were also deposit sections with larger thicknesses and poor ore zones, respectively, where especially after the war until about 1955 large openings were formed due to missing filling. Due to this uncontrolled, relatively "wild" mining considerable subsidence of the surface and fractures in the border zone of the subsidence area occurred. The town of Oberschlema was destroyed and an area of 0.14 km2 was damaged by mining involving a maximum subsidence of 6 m in the centre - called deformation area. The rehabilitation work for the deposit area of Schlemal Alberode involves the flooding of the openings up to a level of the Markus-Semmler-Sohle as long-term preventive measure. Fig. 1 shows the flooding level of October 1996. The level of the -540 m drift will probably be reached in June 1997. From that point of time a general rearrangement of the ventilation has to be made because the central return air ventilation via shaft 373 will no longer be possible. This shaft has no connection with the superficia1 system of mine openings. A new return air ventilation system based on shaft 382 as return air shaft will be designed (Fig. 1). The capacity of the future mine fan system will e.g. be determined by the flow conditions in the deformation area mentioned above. For this reason investigations were carried out in a test drift 13a on the level of the Markus-Semmler-Sohle in the stretching zone of the subsidence trough for several days (Fig. 2 and 3). INFLUENCE OF THE OPERATING CONDITIONS OF THE MAIN MINE FAN ON THE RADIATION SITUATION ON SURFACE The beginning of flooding in 1991 was also the beginning of the investigations into the options of future ventilation due to the reduction of the mining area. The first analyses of radon emanation made in May 1991 showed that only about 20 % of the total radon emanation result from systematically ventilated mine workings. This means that despite of existing dams the air streams through the majority of mine openings of the deposit. The analysis of the individual radon inflows illustrates the special problematic nature of the deposit involving all possible effects on the surface. The shutdown of the main mine fan over the long period between 2.10. and 6.10.1991 showed the essential influence of the operating conditions of the fans on the whole radiation situation on surface. Fig. 4 shows the comparison of the radon concentration level and its daughters during a 'normal" weekend with the level during long-term shutdown in the old 'Casino" of the papermill of Niederschlema. This papermill as well as the 'Casino" are situated in the outcropping zone of the deposit section of Niederschlema. The -60 m level was driven as the upper level in this area, from which the panels were driven to about 20 m below the surface. Also below the "Casino" there is such a panel in the vein 'Glirck", whose roof is directly situated below the building in a depth of 39 m. Directly next to it there is the raise 2 of the panel 'Namenlos" in a depth of 27 m. The graphics clearly shows the immediate increase in radon concentration as well as in the daughter concentration after the shutdown of the fans. The elimination of the artificially generated negative pressure results in the reversal of the convection direction due to the natural ventilating pressure. The interface structure allows the mine airto pass through aero- dynamic connections to the surface. Neglecting the meteorological parameters the concentrations of radon and its daughters in- creased by about 350 % as compared to a 'normal" weekend during longterm shutdown (i.e. in 4 days). Furthermore it could be noticed that a stationary state between the radon and its daughters has not been established in the period

Jan 1, 1997

By Erhard M. Winkler

The rapid decay and disfiguring of stone monuments in urban and desert rural areas has challenged conservators to protect stone surfaces from premature decay. They attempt to halt the natural process of stone decay and possibly to restore the original strength lost mostly by chemical weathering and the loss of binding cement. Ageneral solution is not possible because the physical and chemical characteristics must be considered for different stone types. The failures of stone preservation and restoration are greater in number than the cures. The need for repair of stone decay goes back to evidence of Roman replacement of decaying stone. The presence of excess water in buildings has long been recognized. Moisture tends to enter masonry from air in humid climates, a most important but often underrated factor (Fig. 1) suggesting that sealing should be the answer. Undesirable staining and efflorescence result in accelerated scaling. Today, the great variety of chemicals available to the modem conservator for sealing. consolidating, or hardening stone fall into two very different categories: surface sealers and penetrating stone consolidants, or a combination of both. SEALERS Sealers develop a tight, impervious skin which prevents access of moisture. Surface sealing has saved monuments from decay by eliminating the access of atmospheric humidity. Pressure tends to develop behind the stone surface by moisture escape. Efflorescence, crystal growth action, and freezing can cause considerable spalling (Anderegg, 1949). Flaking results when moisture is trapped behind the sealed surface. Yellowing and blotchiness are also frequently observed. The following sealants are in common use today: linseed oil, paraffin, silicone, urethane, acrylate, and animal blood on stone and adobe. Extensive cracking and yellowing has resulted soon after application. In the past many such treatments have created more problems than cures: 1. Linseed oil and paraffin have been in use for centuries. Embrittlement and yellowing occur rapidly because these are readily attacked by solar ultraviolet radiation. 2. Animal blood as paint has temporarily waterproofed adobe mud and stone masonry. The origin of blood paint has a religious background rooted in the Phoenician and Hebrew cultures. Instant water soluble dried blood can substitute for fresh blood. Winkler (1956) described the history and technique of the use of blood. 3. Silicones have proven very effective and are long lasting. In contrast, acrylates, urethane, and styrene are generally rapidly attacked by UV radiation (Clark et al., 1975). Sealing of Different Rock Types Granitic rocks have a natural porosity traced to 4.5% contraction of quartz, during cooling of the parent magma, compared with only 2% contraction of all other minerals; protection against the hygric forces may require waterproofing of granite in some in- stances. The Egyptian granite obelisk in London is an example. Soon after its relocation from Egypt to London, Cleopatra's Needle was treated, in 1879, with a mixture of Damar resin and wax dissolved in clear petroleum spirit; surface scaling became evident after half a year of exposure to the humid London atmosphere. The treatment of the ancient granite monument from Egypt has denied access of high relative humidity (RH) in London to the trapped salts inherited from the Egyptian desert and has protected the monument from decay (Burgess and Schaffer, 1952). The sister obelisk set up in Central Park, New York City, has fared less favorably because similar treatment was done too late, only after the salts hydrated and hundreds of kilograms of scalings disfigured the obelisk surface (Winkler, 1980). Surface coating of other common stones may be needed. Crystalline marble absorbs moisture from high RH atmospheres: dilation may ensue when curtain panels bow as the moisture starts to expand during daily heating-cooling cycles. A good sealer may prevent the moisture influx provided that no moisture can enter from the inside of the building. Limestones, dolomites and all carbonate rocks are subject to dissolution attack by rainwater, especially in areas where acid rain prevails (Fig. 2). The interaction of sulfates in the atmosphere with the stone can be halted by waterproofing to avoid the formation of soft and more soluble gypsum. The stone surface attack can be diminished if nearly insoluble Ca-sulfite crusts can form, instead of Ca-sulfate. Replacement of fluorite or barium compounds at the stone surface acts as a hardener, rather than a sealant. Sandstones have generally high porosity and rapid water travel can occur along unexpected routes and from any direction. Any surface sealing may do more damage by scaling and bursting than if the stone is left without treatment. Sealing of sandstones is therefore not advised at any time. Testing the efficiency of sealants: Several authors discuss waterproofing materials, silicones, urethanes, acrylates and stearates, as to their water absorption, spreading rates of water on the treated surface, water vapor transmission, resistance to efflorescence, and general appearance (Clark et al., 1975). De Castro (1983) measured the angle of contact of a microdrop (0.004 cm3) on a stone surface as characteristic of the wettability. Laboratory tests and limited field performance are described by Heiman (1981). The crest of a Gothic sandstone arch, which was sealed with silicone,

Jan 1, 1994

By J. Trimble, B. M. Davis, D. McClure

During initial mining operations at the Colosseum gold mine, discrepancies between the average blasthole grades and mill-head grades were quite large. In December 1987, mill-head grades averaged 39% lower than corre¬sponding estimates from the blastholes. The correlation between average blasthole grade and mill-head grade had an r-value of 0.015. The magnitude of the discrepancy and the lack of correspondence between estimated and actual grades led to a series of investigations of the sampling system, the effect of blast movement of the ore, and the estimation methodology. The discrepancy between blasthole grades and mill-head grades had been reduced by about half on a percentage basis at the conclusion of these studies. Ongoing studies have produced changes that reduced this discrepancy to its present level of less than 10%. Geology The Colosseum mine is within the Clark Mountain mining district about 68 km (42 miles) southwest of Las Vegas, NV in San Bernardino County, CA. Gold mineralization at the deposit is hosted in two 152 m x 213 m (500 ft x 700 ft) interconnected, rhyolitic intrusive breccia pipes that intruded Pre¬cambrian crystalline basement rocks and overlying Paleozoic marine sedimentary rocks. Subsequent erosion (deroofing) of all of the Paleozoic section and a portion of the Precambrian section has exposed the pipes to the present level (probably a significant depth in the original breccia pipe system). Lithologies exhibited within the breccia pipe complexes include rhyolitic felsite, and breccias of felsite and wall/ country rock. Breccia types grade from felsite plus Precambrian granite-gneiss fragments in an aphanitic felsite matrix to crosscutting breccias of felsite, Precambrian granite-gneiss, and Paleozoic sedimentary rocks in a matrix of finely comminuted material of the same composition. All the lithologies in and around the breccia pipes exhibit moderate to intense quartz-sericite-pyrite alteration, with sericite and pyrite the dominant visual alteration minerals. Gold at the Colosseum mine is generally submicroscopic and associated with sulfide mineralization, chiefly pyrite. It occurs as free gold, with minor alloyed silver. It is primarily in contact with pyrite in fractures or along pyrite grain edges. Secondarily, it appears as isolated particles in quartz and other gangue minerals but spatially always close to pyrite, and rarely as particles encased in euhedral pyrite. The pyrite mineralization and minor base metal sulfides occur in three distinct styles: as disseminations, as open space or vein/fracture filling, and in breccia clasts replacing dolomite. The pyrite megascopically ranges from absent to 30% of rock volume within the breccia pipes. Although the gold at Colosseum is apparently spatially and geochemically associated with pyrite, there is only a general proportional relationship between pyrite content and gold content. Sometimes, a high volume percentage of pyrite has only geochemically anomalous gold. This makes visual pyrite only a general grade control tool and not a specific tool. This further makes the ore control process at Colosseum all the more difficult. Initial grade control procedure Initial grade control was based on blasthole samples collected in two stages by an "automatic" sample collection device (rocket sampler). A sample was collected for the top 3 m (10 ft) in a hole. The bag was then changed so that a sample was collected for the lower 3 m (10 ft). Each sample was prepared and fire assayed to determine the grade. Large discrepancies were sometimes noted in the assays of top and bottom samples. The samples were averaged together and a plot was made showing the blasthole locations and their associated grades. Discrimination between ore and waste was based on as-

Jan 1, 1989

The central question concerning the health risks associated with mining and processing of taconite ores in the Eastern Mesabi Range is ??does asbestos, of any variety, occur within the gangue mineral population?? Free silica in the form of quartz does exist in the taconite, but silicosis has been relegated to a secondary issue. The focus has shifted to the asbestos minerals and the malignancies that might occur following low-level exposure to dust. Although mineral fibers do exist in the Mesabi taconite ores, Ross, Nolan and Nord conclude ??no asbestos?, as explained in their contribution ??The Search for Asbestos within the Peter Mitchell Taconite Iron Ore Mine, near Babbitt, Minnesota?. Their area of study is located in the eastern Mesabi Range. It is here that the tectonic and metamorphic effects associated with the intrusion of the Duluth Gabbro have been profound. A variety of amphibole minerals have developed as a result of these geological events, some with names recognized within the US Asbestos Standard. The issue tackled by the authors is whether or not these amphiboles are present in the mine and if so whether or not they are asbestiform in habit.

Jan 1, 2008

By Amir Karami, Scott Munro

This paper focuses on remediation of a 3.6 km long water conveyance tunnel that suffered two large falls of ground (FoGs), one of which subsequently progressed to the ground surface, resulting in full collapse of the tunnel. The tunnel is part of a network of water conveyance tunnels and open channels that direct water into two turbines located in an underground powerhouse, originally constructed in the 1970s. At the time of construction, the tunnel was partially supported with shotcrete or rock bolts, with no further ground support added since construction. Two sonar surveys in 019 and 01 identied two adacent large FoGs in the tunnel, approimately 1.2 km from the tunnel outlet. Historical geological and geotechnical information indicated that the FoGs occurred within a 60 m wide fault zone. Remediation plans were developed, which included stabilization of the outlet channel, the portal, the tunnel leading up to the FoG areas (1.2 km length) and the FoG areas. Several remediation options were considered to restore the tunnel, including construction of a diversion tunnel to bypass the FoGs or remediation of the FoG areas with steel ribs and backlling the void above the FoGs to surface.

Jun 23, 2024

By Dale R. Ralston, Roy E. Williams, Gerry V. Winter, George L. Bloomsburg

The term unsaturated flow refers to the conditions in which soil pores are filled partially with water and partially with air. This situation constitutes a porous material filled with immiscible fluids. Immiscible fluids by definition exhibit a distinct interface when in contact with each other resulting in a pressure discontinuity across the interface due to surface tension. The fluid that tends to wet the solid particles is called the wetting fluid and the other is the nonwetting fluid. In the air-water sys- tem, air is the nonwetting fluid and water is the wetting fluid. A somewhat analogous fluid system is that in a petroleum reservoir in which there may be up to three immiscible fluids-oil, salt water, and natural gas. The degree of wettability of the fluids is salt water + oil + gas. That is, salt water is the wetting fluid at any interface and oil is the wetting fluid at an oil-gas interface but is the nonwetting fluid at a water-oil interface. Since the oil-water and air- water systems are similar, much of the theory and methods of analyses for the air-water system or unsaturated flow have evolved through the petroleum literature. In the two-fluid system the pressure difference across an interface depends on the size of the pore space in which the interface occurs. The equation commonly used to represent this dependence is

Jan 1, 1986