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By Ronald P. Geitgey

Pumice and volcanic cinder are volcanic rocks characterized by a cellular structure. They are formed as gases (primarily water) dissolved in molten rock, or magma, exsolve to generate a froth that cools and solidifies into rigid foam. The cells or bubbles are referred to as vesicles and they range in size from a few thousandth of a millimeter to several centimeters. Due to their vesicular character, both pumice and cinder have lower density and higher porosity than most other rock types, and, as the vesicle walls are broken, sharp cutting edges are continually generated. These properties are the basis for their commercial value as lightweight aggregates, insulators, absorbents, and abrasives. There is a certain imprecision in the terminology applied to volcanic products, reflecting to varying degrees the diversity of volcanic rocks, the relative youth of volcanology as a distinct field of study, and customs and practices of commercial trade. In general terms, pumice is light colored (white, gray, pink, pale yellow, or brown) and highly vesicular, usually with vesicle walls that are visibly glassy. Many pumice fragments are light enough to float on water. Pumice is readily cut by steel tools and some can be crushed by hand. Individual pumice fragments may range from 1 or 2 m in one dimension to c1 mm. Commercially, finer fragments are called pumicite or volcanic ash. In volcanology the term ash refers to any fragment c2 mm in size regardless of its composition. Cinder, or scoria, is dark colored (black, red, brown) with thick vesicle walls that appear dull or stony and that may exhibit iridescence. Cinder typically is heavier than pumice and has a higher crushing strength. In volcanology the term scoria refers to dark vesicular material throughout a wide size range while it is common commercial practice to use scoria for larger fragments (usually greater than 2.5 cm) and cinder for smaller fragments. GEOLOGY Composition and Physical Characteristics Most pumice is silicic ranging from 60 to 70% SiO2, that is, dacitic to rhyolitic in composition. Pumice of less silicic composition, including basaltic, occurs but it is less common and does not have extensive commercial use. Scoria and cinder are typically basaltic to andesitic with approximately 50 to 60% SiO2. Pumice and cinder may contain phenocrysts of feldspars and various ferromagnesian minerals that crystallized in the magma prior to eruption. Fragments of rock through which the magma has passed may be entrained in the melt and wall rock may be fragmented and admixed during an explosive eruption. Some scoria particles have lithic fragment cores. Phenocrysts and lithic fragments are relatively unimportant in cinder end uses but their presence may be detrimental in certain pumice products. Pumice typically has vesicles <1 mm in size separated by thin walls. Vesicle shapes include irregular, spherical, elliptical, and elongate to the point of being tubular with a silky appearance (Fig. 1). In some pumices, the vesicles are interconnected making the fragments permeable and highly absorbent; in others the vesicles are isolated forming a highly porous but very impermeable pumice. Floating masses of pumice fragments from the eruption of Krakatoa in 1883 were reported in the Indian Ocean for up to two years after the eruption. Vesicles in cinder are larger and range from spherical to highly irregular in shape with much thicker walls and abundant interconnections. Scoria and cinder are typically heavier, porous, and do not float. Density and hardness of pumice must be expressed precisely to avoid confusion. Density may refer to the glass itself, the apparent density of the vesicular pumice particle, or the bulk density of pumice in a deposit or in a product. Pumice glass has a specific gravity of 2.5 or more depending on its composition. Pumice fragments typically have a specific gravity of 4.0 and so will float on water, at least until enough vesicles are saturated to cause them to sink. Expressed as density, pumice fragments typically weigh less than 1 g/cm3. Depending on moisture content, particle density, and particle size distribution, the bulk density of pumice typically ranges from 500 to 700 kg/m3. Typical bulk densities of cinder range from 700 to 900 kg/m3 for material used as lightweight aggregate while the bulk density of cinder used for highways and railroad ballast may be considerably higher. Hardness in pumice may refer to the glass vesicle walls, possibly including crystals or lithic fragments, or to the apparent hardness of the particle as a whole, which is more a measure of the strength of the vesicle structure. Pumice glass typically has a Mohs hardness of 5 to 5.5. A pumice particle may have a much lower apparent hardness and be easily cut with a knife or steel saw because the vesicle walls break readily. Pumice and cinder are primarily pyroclastic deposits formed as fragmental products of volcanic eruptions. Several classification - systems differing in various details have been proposed for pyroclasts and pyroclastic deposits based on particle size (Fisher, 1961, Schmid, 1981, Cas and Wright, 1988). Generally, particles >64 mm are referred to as blocks or bombs depending on their shape. Particles between 64 mm and 2 mm (4 mm in some schemes) are called lapilli and smaller particles are called ash. These names may be modified by compositional terms, for example pumice lapilli or scoria lapilli. Most commercial deposits are composed of fragments in the lapilli size range. In the United States, pumice fragments having one dimension of 5 cm or more are legally defined as block pumice. The procedures for acquiring pumice from federal land are determined in part by this definition and are described in a later section.

Jan 1, 1994

By Alfred Jr. Petrick, William A. Vogely

INTRODUCTION The scope of mineral finance extends beyond the economic aspects of property evaluation to all of those activities involving acquisition and utilization of funds with an objective to optimize the value of the firm. It must, therefore, en- compass consideration of the overall financial goals of the firm, decisions involving external versus internal growth and domestic versus foreign investments, management of working cap- ital, efforts to minimize the cost of capital, and decisions with regards to the instruments of long- term debt and equity financing. The scope of this section is limited to considerations of special interest to the mineral or petroleum engineer, which include the following aspects of mineral finance: (1) The technical aspects of mineral or coal property or oil and gas reservoir evaluation which provide the basis for estimation and forecasting of revenues and costs. (2) Estimation and forecasting of costs and prices in a inflationary economic environment. (3) Calculation of cash flows which model .. , the investment in minerals, coal or oil, and gas. Such models require assumptions as to the timing of cash flows, escalation of capital and operating costs, base prices, and escalation, the tax regime, royalties, division of profits and the economic aspects of loans. (4) The role of discount rate in the economic analysis of an investment which requires consideration of the opportunity costs of the firm, cost of capital, risk premiums. (5) Risk analysis including application of the concepts of conditional net present value, expected value, and risk preference as well as the application of the techniques of sensitivity and simulation. (6) Selection of application criteria for in- vestment decision making. (7) Capital structure with particular reference to the effect of debt financing. (8) Consideration of sources of funds utilized by the minerals industries. (9) Long-range planning including portfolio analysis. This section is limited to principles, methodologies, and trends in mineral investment, finance, and long-range planning in the United States with a perspective from the year 1984. Consideration of the key concepts is supplemented by case examples of investment risk analysis and financial structure. Important factors affecting mineral investment evaluation during the 1980s include volatile metals prices, cost inflation, and the introduction of techniques requiring the computer and its capacity for improved technical and economic analysis into the hands of those who know most about the industry. The personal computer is replacing the calculator on the desk of the individual analyst and is rapidly becoming a required tool for the study of engineering and economics. Examples of change brought about by the micro-computer include greatly improved techniques of cost estimation, wider application of the computer for project analysis, computer graphics, reserve estimation, geostatistical analysis, mine design and other techniques that capitalize on the ability of the computer to handle

Jan 1, 1985

By Richard L. Daley

Today&apos;s subject of discussion, "OSHA AND ITS PROBLEMS", must be covered in the time allotted with a slight tongue in cheek approach, for if one is to believe that the "problems of OSHA" can be covered in a twenty minute review, he, himself, has one of three problems: 1. He has residual combat fatigue left over from World War II. 2. He is an egomaniac. 3. He is afflicted with both of the above. Clearly, the difference between divinity and humanity lies in their work. All human endeavor is plagued by errors and omissions, and unless one would be so facetious as to equate bureaucracy with godliness, our government-sponsored ventures seem to receive more than their share of missive missles with which to combat the ills of our society. Coming from an industry known for its undertaking of gargantuan projects, I feel capable of looking at things from the big picture perspective. No one would deny that the massive influx of government, both in the monetary and supportive personnel roles, has accomplished much. But only we, as tunnel constructors, have moved countless mountains of muck, placed endless yards of concrete and engaged the public on numerous fronts and in spite of all, at times have even made a profit! Profit! What a dirty word in our society today. It makes one shrink back from the filthy overtones dripping with the cloying scent of decay. Never shall we judge the success of our government programs with such a slimy yardstick as profit. No, for that which has been conceived in the bowers of Camelot, the measure must be more elevating and inspiring. Something to bring a proud bearing to our efforts! Nothing has helped to alleviate the suffering of man as much as medicine. The eradication of typhoid, polio, and

Jan 1, 1979

By J. Drelick

Among the wide variety of modern surface chemistry analytical techniques, contact angle measurements still remain attractive for wetting characterization of solid surfaces. The captive-bubble and sessile-drop techniques are the most popular methods for the examination of flotation systems. Systematic measurements of advancing and receding contact angles for several three-phase systems using the captive-bubble and sessile-drop techniques show that the contact angle measurements depend on the technique used and may differ significantly for some heterogeneous and rough solid surfaces. Importantly, it was found that these discrepancies in contact angle measurements depend on the bubble (drop) size. Contact angles as measured with the static captive-bubble technique are compared with those measured with the dynamic captive-bubble technique, in which the capture of a bubble at the solid surface results after buoyant transport and attachment The dynamic captive-bubble technique allows for the formation of much smaller bubbles than is possible with the static placement technique in which a bubble is placed at the solid surface with a microsyringe. Although this dynamic technique cannot be recommended for the systematic wetting characterization of solid surfaces, its significant advantage is the ability to examine the contact angle/bubble size relationship over a wide range of bubble sizes, from several micrometers to several millimeters in diameter.

Jan 1, 1995

By Mark A. Anderson

INTRODUCTION The accomplishment of a well engineered design, and the realization of efficient plant operation cannot be achieved without weaving a web of safety consciousness from the beginning of the project. When the plant becomes operational, and throughout its life, responsibility safety will rest with the client or operator. Recognition of this understanding does not reduce the importance of the engineering and construction contractor&apos;s role, but merely puts the responsibility where it belongs. A project which has had little or no operator input during the early stages of design is almost certain to have serious work place safety, health, and environmental problems in spite of the fact that all MSHA and OSHA design requirements were met and the engineering was performed using accepted practices. DEFINITIONS The author has a personal preference in safety definitions that begins and ends with simplicity. If the safety criteria, program, and rules are confusing or complex, the results will soon become obvious. Confusing and complex are the key elements in the avoidance of responsibility and if punitive is added to the list, a brew exists which breeds accidents, illness, and poor performance. A safely designed and operated plant is one that a worker can journey to each day; leaving that person and his or her family with the above average expectation that the person will return healthy, emotionally intact, and hopefully a little wealthier. If the objective or results of a planned or existing safety program don&apos;t fit the definition. then the reader is probably contemplating a very sophisticated

Jan 1, 1986

By Bernard Lippe

The successful construction project is one in which the component construction operations are completed within the scheduled time and cost parameters. Most construction projects, however, are subject to delays and/or disruptions which adversely affect the time (start, duration, and completion) and cost aspects of the project. DELAYS Delays fall into two categories: Compensable Delays for which the contractor is entitled to contract time extensions and additional money as compensation for the extra expenses generated by the delay or obstruction to job progress, and Non Compensable Delays, for which the contractor may or may not receive an extension of time but no additional compensation. Compensable Delays Compensable delays may take the form of holds or suspensions on all or certain segments of a project by the owner, failure of the owner or his Engineers to approve shop drawings, cuts or material samples within a reasonable period of time, failure of the Owner or his Engineer to properly coordinate the job, discovery of design deficiencies in the plans and specifications which prevent the continuation of construction until

Jan 1, 1974

By K. L. Browne

After a decade of high copper prices, major mining companies are renewing their interest in purchasing operating properties and/or developing ore bodies. An existing operation carries with it a history that can present unique opportunities, while a greenfield operation allows for the establishment of a defined culture. Capital investments are distinctly different. A comparison of BHP Copper&apos;s Robinson operation, a greenfield property, and BHP Copper&apos;s Tintaya operation, a government owned Peruvian property, will provide insights into mining, concentrating and cultural differences between North and South America operations. The Broken Hill Proprietary Co. Ltd. (BHP) is Australia&apos;s second-largest company. Fiscal year 1996 sales were US$16 billion, profits were more than US$1 billion and total market capitalization was about US25 billion. In 1885, BHP began mining silver, lead and zinc at Broken Hill, New South Wales, Australia. Throughout its 112-year history, BHP achieved an impressive record of performance and expansion. Today, BHP is one of the world&apos;s leading companies (66th on the Standard and Poors 500), having diversified into steel, petroleum and mining with more than 65,000 employees in 70 countries.

Jan 1, 1997

By T. Zoltai

Asbestos is a generic term for industrially useful fibers recovered from exploitable deposits of the asbestiform varieties of five silicate minerals: chrysotile, anthophyl-lite, actinolite-tremolite, cummingtorute-grunerite, and rie-beekite. Asbestos and asbestiform fibers of some other minerals are known to be carcinogenic. Minerals crystallized in the asbestiform habit-are characterized by unique properties (morphology, strength and flexibility, physical and chemical durability, and defect-free surface structures). The key to the unusual properties, and health effects, of asbestiform fibers appears to be in their unusual surface structure. In contrast, non-asbestiform crystals of the same minerals, including the five so called asbestos minerals, do not have these properties and are not carcinogenic.

Jan 1, 1989

By Daniel H. Stevenson

Safety and health are fundamental values at Barrick Goldstrike. An effective safety and health program protects employees, controls costs and increases productivity. Barrick Goldstrike believes that all occupational injuries and illnesses can be prevented and that safety must be the responsibility of every employee on the property. Safety and health must be thoroughly integrated with the company&apos;s efforts to maximize production at the lowest reasonable cost. The goals of safety and production are not mutually exclusive. They must work together to achieve safe production. Barrick Goldstrike began to mine the Betze deposit in 1987. From 1987 to 1992, Barrick employed a traditional safety system using safety specialists on each crew. These specialists were responsible for ensuring that the work areas were safe and that employees were properly protected and trained in safe work procedures. As the work force increased, it became apparent that this system was not the most effective method of ensuring safe production. In 1992, Barrick Goldstrike implemented a loss control program. It was modeled after the International Loss Control Institutes&apos;s (ILCI) International Mine Safety Rating System. This program was based on the philosophy that safety is a management responsibility. It can be managed in the same manner that production and cost issues are managed. Under the loss control system, safety needs are identified and evaluated. Programs with performance standards are developed and implemented and the activities and results are regularly monitored. Between 1992 and 1996, Barrick Goldstrike worked at developing and improving its safety management systems. These efforts had a positive return. The incident rates began to decline as these improved systems were implemented. Studies were undertaken in early 1996 to evaluate the effectiveness of the safety and loss control programs in reducing accidents. The studies showed a strong correlation between the implementation of the loss control programs and the resulting reduction in all accidents. Studies in the process division revealed that Barrick had experienced reductions in personal injury accidents from the projected number that could have been expected had no changes been instituted. These reductions ranged from 39% in 1993 to 59% in 1995. These reductions from the projected rates held true for all types of accidents; personal injury, property damage and Mine Safety and Health Administration (MSHA) reportable.

Jan 1, 1997

By R. Gray

"Experience from Australia has identified what is referred to as non-conventional surface subsidence behaviour. This occurs under irregular surface topography, resulting in valley closure, valley floor uplift or “upsidence”, and far-field horizontal movements – even occurring beyond conventional “angle of draw” limits. This paper discusses such behaviour recently observed in Pennsylvania and focuses on the 2005 case of Duke Lake Dam in Ryerson Station State Park. In July 2005, there was a significant increase in water leakage through a number of growing cracks in the dam leading to the dam being breached to avoid an uncontrolled failure. An underground longwall mine was located approximately 900ft to the north, mining at depths of 330 – 720ft. Investigations (including a subsequent ground movement monitoring program) found a range of evidence in the vicinity suggesting that valley closure and far-field horizontal movements may have occurred resulting from the adjacent mining. The paper discusses the phenomenon of non-conventional subsidence behaviour and the Ryerson State Park case study, including an assessment of mining, geology and subsidence impacts and suggested ground behavioural mechanisms. INTRODUCTION Non-Conventional Subsidence The conventional understanding of coal mine subsidence on which most current subsidence understanding and prediction techniques are based, includes the concept of angle of draw which effectively limits the lateral extent of subsidence effects and impacts. Within this zone – above and marginally beyond the boundary of mining – downward vertical subsidence is the dominant component, together with localised horizontal movements towards the mined region, with related tilts and strains. However, more recent experience from Australia over the last two or three decades has identified what is referred to as non-conventional surface subsidence behaviour. This is found to occur in areas of irregular surface topography or variable terrain, and is characterised by phenomena such as valley closure, valley floor uplift or upsidence, and far-field horizontal movements, all of which can occur beyond the conventional angle of draw limits. NSW Department of Planning (2008) defined the conditions for both conventional and non-conventional subsidence behaviour as follows: “The conventional or general model of surface subsidence, which finds worldwide acceptance, is based on assuming the following site conditions:"

Jan 1, 2015

By H. L. Ehrlich

Processes involving biological solubilization of metal values from ores, or removal of mineral constituents that interfere with metal value recovery from ores by abiological means, published mostly in the last 10 years, are reviewed. Many of them, though promising, have yet to be tested on a pilot scale or applied industrially.

Jan 1, 1987

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

A model describing size reduction and mineral liberation during grinding has been extended to include multiple classes of composite particles. The majority of the model parameters have been directly determined using computerized image processing equipment to analyze the products from batch grinding tests. A coarse-grained sphalerite ore from Tennessee, representing a nearly ideal binary mixture of sphulerite and dolomite, has been used to experimentally validate the model for the case of dry batch grinding. In all cases, excellent agreement has been observed between the model predictions and the experimental results.

Jan 1, 1988

By T. R. von Ow

The method of powering mills such as AG, SAG and Ball has a long and technically interesting history. It can be said that almost every decade in the last half century had its own trend. The trends were dominated by the market demand, the advanced process development and requirement of the mechanical and the electrical technology but mostly by the price of the applied technology. The increasing size of the ring geared mills in the last years requires more awareness on the drive train solution. Special attention must be paid to the mechanics and the requirements of the power grid. Operational challenges such as soft starting and controlled operation as well as the protection of the equipment have gained importance. Frequency converter drive solutions dedicated to single or dual pinion ring-geared mills offer significant advantages over conventional drives due to their application specific features and controls. Solutions with low speed motors as well as high speed motors cover all possible configurations available for ring geared mills.

Jan 1, 2010

By Arnolfo A. Valdivia

Prior to 1971, there were several clinical trials to evaluate programs for early detection of lung cancer. Among these, the Philadelphia Pulmonary Neoplasm Research Project,(3) the Veterans Administration Study published by Lilienfeld,(7) and the controlled trial of the Kaiser Foundation Health Plan showed an overall five year survival rate of 8% for newly detected cases (the same as the national statistic for unscreened patients). In 1971, the National Cancer Institute initiated three randomized, controlled mortality studies using lung cancer screening of persons at high risk (male smokers over 45 years old). The studies are being conducted at the Johns Hopkins University Hospital, the Mayo Clinic, and the Memorial Sloan-Kettering Cancer Center. The studies have slightly different designs in the combination of sputum cytology and chest x-rays. At the Mayo Clinic the study group is offered screening with sputum cytology and chest x-rays every four months, whereas the control group is advised to have an x-ray and cytology every year. No reminders are sent, and it is believed that only about 20% of the control group is screened. At Johns Hopkins and Memorial, both experimental and control groups are offered annual chest x-rays. The experimental group is additionally offered sputum cytology every four months.(5) At present all of the programs show that screening can detect cancers that are undetectible by other means. However, at this time mortality rates in the control and experimental groups are not significantly different in any of the three studies. OUR PROGRAM Our clinic is located in Grants, New Mexico and we provide most of the pre-employment physical examinations for the mines operating in the Grants area (Kerr McGee Nuclear, Homestake Mining, United Nuclear, Western Nuclear, and Ranchers). In the examinations, we obtain the previous mining history of the worker, a chest x-ray, a sample of sputum for cytological examination, and a blood sample. We also provide routine annual physical examinations of the workers, with special interest in the detection of bronchogenic carcinoma. In the early seventies, we did not have a definite surveillance program. We did not know whether we should have a program like the one started at Memorial or like the one started at the Mayo Clinic. After long consideration, we decided to have a program that does not demand a sputum cytology and chest x-ray every four months, but that allows as many chest x-rays and sputum cytologies as needed to diagnose lung cancer as early as possible. We believe that, if a screening method for cancer is to be optimally effective, it must detect the process at stages early enough for curative therapy. We order a test depending on the age of the miner, the race, the mining history, the smoking history, the radiation exposure levels, and the results of the previous chest x-ray and sputum cytology. With the help of the computer, we have a list of all the miners who should be watched closely because of age, race, mining history, smoking history, radiation exposure, etc. Examination of the miners is performed at our clinic, where all the records are kept. The sputum is collected there but examined in Grand Junction, Colorado, by Dr. Geno Saccomanno. There are two ways to collect sputum. The best way is to collect three consecutive morning samples. For this, we need the cooperation of the miners. They have to follow these instructions and mail the bottle containing the sample to Grand Junction. "Instructions for obtaining a good cough specimen" The enclosed plastic bottle contains a preservative solution, so do not empty out the liquid in it. When you go to bed, place the plastic bottle at your bedside where it will be handy in the morning. When you first get up in the morning (before breakfast) try to cough up some "phlegm" from deep in your chest, and spit it into the liquid in the bottle. Try coughing several times. If you have difficulty coughing, try inhaling deeply the steam from a teakettle (or home-type inhalator). Keep the amount of saliva (ordinary spit) that you put into the bottle along with the cough specimen as small as possible. Do not collect the "phlegm" or mucous that comes from the back of your nose. Put the cap back on the bottle, and shake it vigorously for two minutes. If the amount of material you have coughed up is quite small, then keep the bottle at your bedside for three or four days, and each morning try to add another cough specimen. After obtaining your cough specimen, repack the bottle in the mailing container, and attach the enclosed mailing label. It does not require any postage stamps. Unfortunately, some miners "forget" to mail the sample and end up with an incomplete physical examination. To avoid this some companies, like Homestake, request that we obtain the sample in our clinic by forcing cough and expectorant with a nebulizer machine. This method does not give as good a sputum sample as the previous one, but we do get a sputum sample for every miner. The policies of different companies, in regard to annual physical examinations are different. All

Jan 1, 1981

By Walter R. Jr. Hibbard, William A. Vogely

INTRODUCTION Volatile markets and pricing, increasing imports, constraining but effective laws related to the environment, health and safety and price controls lead to concerns which generated pious laws stating non-fuel policy and authorizing studies but resulting in ineffective implementation. Several commissions, reports by the Secretary of Interior and even the President have led to many recommendations but little or no action. No single comprehensive policy could solve problems which are diverse, commodity specific and not categorizable (Landsberg 1982, 1983). Thirteen laws administered by 27 agencies regulate or affect minerals and materials. Political instability created by communist regimes in Southern and Central Africa jeopardized sources of critical imported materials. This situation led to a Resource War mentality. It was feared that the U.S.S.R. was seeking to control this area and exclude the United States from resources (Vogely, 1980). The success of the Organization of Petroleum Exporting Countries with a petroleum cartel led to fears of an Organization of Minerals Exporting Countries which might create more cartels and/or make the existing ones more effective. Economic needs of developing countries required export to maintain employment and balance of payments have led to world surpluses, weak markets, low prices, and large loans from the World Bank which have under- mined U.S. industry (Landsberg, 1982a). Un- cooperative environmental laws, obsolete facilities and non-competitive costs have led to shipping U .S. ores to other countries for processing into ingot and bars which are imported back to the United States. Yet massive internal turmoil has interrupted supplies, and led to un- certain availability and higher prices. This situation could happen again. Included in this category of critical materials with uncertain sources are metals required in the manufacture of military aircraft, which has led to concern regarding the defense industry base (Morgan 1983). Remedies have been proposed which include: updated stock piles, material substitution, international cooperation and coordination, foreign policy aimed at resolving racial and national stresses in South and Central Africa, relaxing U.S. environmental and public land regulations and action under the Defense Production Act (Goth 1982). The President&apos;s report (1983) to Congress has stated a national materials policy which recognizes: that materials play a critical role in our economy, defense, and standard of living; that public lands contain a vast untapped mineral wealth; that the role of government is to identify mineral issues and act on them; and that there is a need for long term high potential pay off research (Bureau of Mines 1983). There is a serious question as to whether or not a comprehensive national mining, minerals, and materials policy is feasible let alone necessary. One solution is to abandon the attempt at comprehensiveness and to target specific is- sues with realistic policies (Comptroller General 1979). In the following sections, the major studies of the 1970s will be reviewed, major issues yet to be faced will be identified, the principles involved in these resolutions will be reviewed,

Jan 1, 1985

By R. D. Beard

Puerto Rico lies within the remnants of a deformed Cretaceous island arc system in the northeastern Caribbean. The Island can be divided into three broad geologic provinces: the Central Volcanic-Plutonic Province (Lower Cretaceous to middle Eocene), and the Northern and Southern Limestone Provinces (early Oligocene to middle Miocene). Known precious metal deposits are generally small and occur in veins and shear zones within Lower and Upper Cretaceous volcanic and plutonic rocks. Some Tertiary igneous rocks are also mineralized. Selected indications of disseminated lithology-controlled mineralization could represent larger deposits. Associated metals in some deposits include copper, zinc, and lead. At present, tax policies, population density, political outlook, and lack of proven significant precious metal deposits discourage the establishment of a metal mining industry.

Jan 1, 1993

By Linda Frederick

In July 1997, Krupp Canada obtained the contract to design and supply the conveyor system for Chile&apos;s Los Pelambres copper mine expansion project. Progress on the overland conveyor system is currently on schedule. It is a challenging task to convey copper ore from an open-pit mine located on a mountain site 3,000 m (9,840 ft) above sea level down 1,300 m (4,265 ft) to the processing plant at the valley floor below. The Los Pelambres conveyor system moves copper ore at a rate of 8.7 ktlh (9,600 stph) and at a speed of 6 ml sec (1,180 ftlmin) for 12,750 m (41,830 ft). The distance is divided in three conveyors, each 1,800 mm (71 in.) wide. The largest conveyor is 6 km (3.7 miles) long. To protect against avalanches and rockslides, the conveyors run through a 12-km- (7.4-mile-) long tunnel system. The lowest of the three conveyors is equipped with a shuttling head end. With this, the conveyor discharge point can be moved back and forth by 100 m (330 ft), allowing it to build up a longitudinal stockpile at its end. To meet the extreme design parameters, the limits of conveyor design had to be pushed to record-setting marks. For instance, the ST-7800 steel cord conveyor belt is the strongest belt ever installed in a conveyor system. A total drive power of 25 MW (33,535 hp), consisting of 10 2.5-MW (3,352-hp) drives, is included in the design plans. In loaded condition, the electric motors act as generators and feed electric energy back into the power grid. The motors are controlled by variable frequency inverters that provide an infinite adjustment of motor speed. This technology allows starting and stop- ping the conveyors precisely along predetermined acceleration and deceleration ramps. This is done so harmful belt jerking and stress waves can be avoided.

Jan 1, 1999

By W. A. Haley

The use of diesel engines in underground hard-rock mines dates back to the late 1940s. For the first several years, they were used only occasionally, being limited to a few metal mines that experimented with crawler¬mounted front-end loaders, tractor-trailer hauling units, a few tractors for drill-compressor mounts, and utility cleanup machines. By the mid-1950s, track loaders had become commonplace in limestone mines and uranium mines on the Colorado Plateau in the United States, as well as in Canada. Use of crawler-mounted tractors as drill and compressor mounts also increased. By the end of the 1950s, rubber-tired loaders and some haulers began to replace the track-type machines and rail-mounted cars that had been in use. About 1960, the rubber-tired machines brought about a new era of underground mining mobility and flexibility, centered on a method commonly known as "trackless mining." Ultimately, many of the underground rail-type systems for loading and hauling were replaced by the trackless mining technique. ECONOMIC CONSIDERATIONS The size and nature of mineral deposits, plus ground control techniques, historically had dictated small open¬ings to the surface from many underground mines. The small mine openings led to the development of special rubber-tired loaders and haulers designed specifically for access through the small openings. However, some mines, particularly those in massive mineral deposits, are able to excavate and maintain very large openings, and some use modified room-and-pillar systems. With the large mine openings, the use of larger, more produc¬tive equipment such as that commonly found in surface mining becomes economical. In fact, productivity gen¬erally increases at a more pronounced rate than machine size increases because many of the larger machines were designed for heavy-duty shot-rock applications in surface mines and construction sites where the handling of blasted rock is common. Table 1 can be used as a very Table 1. General Productivity Comparison for Conventional Machines In Underground Use (Shot-Rock Conditions) 2.3 m3 (3 cu yd) 4.6 m3 (6 cu yd) Loader Loader Expected Surface 230 t/h 540 t/h Production (250 stph) (600 stph) Expected Underground 90 t/h 270 t/h Production (100 stph) (300 stph) Expected Total Efficiency: Surface 40%-60% 50%75% Underground 25%.-40% 30%50% Expected Useful Machine 8000 hr 12,000 hr Life Before Replacement general comparison of the production and efficiency between small and large machines. Combining greater productivity often inherent in larger machines, with reduced downtime resulting from using fully developed machines with fast parts and service backup, some mine operators have been able to reduce material handling costs appreciably while reduc¬ing manpower requirements for operators and main¬tenance men. Large mine openings increase the amount of rock that must be handled in the development work, and they sometimes increase the dilution in stopes or rooms, de¬pending upon the dimensions of the ore zone. Providing adequate space for the unrestricted operation of large surface mining machines could, therefore, lead to more waste segregation and handling costs. It could also cause greater ore dilution that would result in a lower grade of ore being delivered to the processing plant. The tradeoffs between opposing cost factors must be reconciled and balanced to achieve the best overall cost of the crude ore, concentrates, or product. EQUIPMENT MODIFICATIONS Loaders and haulers designed for surface mining are seldom used underground in their standard con¬figurations without some modifications. If done, the modifications generally are made by the equipment dealer and/or the user, and the modifications usually include one or more of the following items: 1) The exhaust stack is lowered, and its direction is changed. Usually, it is repositioned horizontally to the rear, or it is fed into the engine fan to diffuse the exhaust gases. 2) The operator&apos;s position is lowered by either lowering the seat or changing the seat to a side mount. 3) The operator controls are adjusted to fit the new operator position. 4) Other components, such as the radiator and loader tower, are lowered. 5) Special bumper guards are mounted at the base of the radiator area. 6) An exhaust conditioner is mounted and con¬nected, using either a catalytic or a water-type condi¬tioner, or both. This usually is controlled by the safety and health regulatory authority having jurisdiction. 7) The positions of other components are rearranged

Jan 1, 1982

By Edward S. Plotkin

The tunneling construction industry faces a new challenge in endeavoring to comply with the multitude of regulations and standards of the Occupational Safety and Health Administration and to work following accepted and experienced tunneling practices. Tunnel inspections appear to be gaining in priority. The national OSHA inspection activities reported for the year 1976 in the construction industry are as follows: 989 Inspections 45 As result of Accidents 186 As result of Complaints 605 General 153 Follow Up 34% Were found to be in compliance 714 Citations were Issued 1,825 Violations were found (201 of which were serious; 1573 were non-serious; 51 were imminent danger. There were no recorded failures to abate a violation in our industry.) The five general priorities by which a company would be scheduled for an inspection in descending order are: imminent danger situations, reports of fatal accidents or catastrophies, inspections in response to valid employee C( taints, inspections of work places covered by National Emphasis Program NEP, (OSHA&apos;s NEP has been designed to impact on any industry having a very high injury or illness rate) and finally random inspections of work places covered by OSHA. The following criteria in selecting companies for random inspections is used by OSHA.

Jan 1, 1979

By Y. C. Kim

An alternate development drilling strategy to the one currently in use at the nine was investigated using geostatistics for a portion of the pit. The study area consisted of 4,000&apos; x 5,000&apos; in plan and 1,080&apos; in elevation. The massive orebody, the three-dimensional nature of the problem, and the location of ultimate pit limit in the study area all created some unique problems in devising the development drilling strategy, as compared to the two-dimensional tabular deposits such as coal deposits. Rather than using the confidence interval of the global reserve estimate as the main criterion for development drilling, the confidence interval of short and medium range mine planning blocks was used as the objective. Based on somewhat arbitrarily selected level of confidence, the results from this study showed that a total of 50 DDHs rather than the planned 62 DDHs is sufficient in the study area, if the selected confidence levels are acceptable to the management. This paper also emphasizes the importance of the particular objectives being used in development drilling and how they influence the "optimai" place- ment of the development drill holes.

Jan 1, 1981