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The Pueblo Viejo Mine, a 7, 250 mtpd (8,000 stpd) gold-silver cyanidation plant built by Rosario Dominicana S. A., was described in Volume I of this monograph. At the time of writing that volume, Pueblo Viejo had not yet gone on-stream and operating data or costs could not be presented. Since that time this information has been obtained and several interesting modifications and an expansion have been made to the plant. Because Pueblo Viejo is the largest open-pit gold mine in the world and one of the world's leading gold-silver operations with production of approximately 31 kg (1,000 oz) gold and 125 to 155 kg (4,000 to 5, 000 oz) silver per day, the authors have updated the previous data and flow sheet. The Dominican Government, which held a 4670 interest in Rosario Dominicana S. A., completed purchase of the mine to gain full control in 1979. Rosario Resources will continue to manage the mine, at least until the end of 1980. Gold was produced at Pueblo Viejo almost 500 years ago with initial production in the year 1505. Rosario Resources became interested in the property in 1969 and found surface oxidation had rendered the upper portion of the ore body amenable to direct cyanide treatment. The treatment of the underlying gold-bearing sulfide zone is still undergoing metallurgical studies. The ore is considered to be a laterite; and because there appeared to be few boulders in the ore zone, only a 400 m (16 in. ) square grizzly was initially installed ahead of the mills when the plant went on-stream in late 1974 at a design capacity of 7,250 mtpd (8,000 stpd). Operation also proved the ore to be harder than was originally anticipated. During 1967 a 1. 25 m by 1. 5 m (48 in. by 60 in. ) jaw crusher was installed to -feed the 1, 000 mt (1, 100 st) mill bin. Minus 200 mm (8 in.) crushed ore is fed directly to two 5.5 m by 1. 8 m (18 ft by 6 ft) semi-autogenous mills re-powered with 750 km (1,000 hp) motors and 50 mm (2 in.) grates. Each mill product is screened at 13 mm (1 /2 in.) by a vibrating screen. Screen oversize from each mill is combined on a single return belt equipped with a magnetic head pulley for grinding ball removal. The non-magnetic oversize is then split into two fractions for return to the primary mills. Originally, a minus 6 mm (1/4 in ) product was made on each screen and fed to a 300 kw (400 hp) 2.6 m by 3. 7 m (8-1/2 ft by 12 ft) regrind mill. During a plant expansion in 1978, an intermediate mill of 746 kw (1,000 hp) was installed to operate in open circuit on the combined primary mill

Jan 1, 1981

By S. G. Hardcastle, C. K. Kocsis

In Canada’s metal mines, ventilation, which requires electricity to operate the fans and fossil fuel for heating, accounts for a significant portion of the overall mine’s underground power consumption. Mine ventilation systems are usually designed near the end of the mine design process and often designed for the ‘worst-case-scenario’ with respect to ventilation demand. In Canada’s metal mines this is commonly dictated by either diesel equipment usage or heat management considerations. Once designed, mine ventilation systems tend to operate at this peak level throughout the operating life of the mine. This is despite there being significant periods when this quantity is not required this is done mainly due to lack of appropriate ventilation controls. Consequently, such systems are inefficient and wasteful and this must be changed if mining operations are to remain competitive while meeting increasingly more stringent regulations of underground environmental conditions. The advances in computing power and modelling software now make it possible to design, model and schedule a mine from opening to closure. The tools used for this include several disparate types of software. A developing trend is to design and plan the mine using orebody modelling software, followed by using discrete event simulation to predict production and evaluate various operating scenarios. It seems that again ventilation design is not being integrated into this process. Although, several modelling packages exist for ventilation design, little work has been done on integrating ventilation modelling into the overall life cycle plan of the mine. This paper will present a discussion of the work where the authors are attempting to integrate discrete event simulation for mine planning with ventilation modelling to predict the ventilation requirements for the operating life of the mine.

Jan 1, 2003

By M. C. Roberts

Currently, mineral producers are suffering through a major downturn in prices for their products, even though it has only been a few years since they were enjoying high prices. From an historical perspective, the current situation is another of the cyclical down-turns that often reoccur every 5 to 7 years or so. This paper uses time trend decomposition techniques to identify the cycles and statistical methods to find the duration of these cycles for a variety of mineral prices. Given some idea of how long and severe these cycles typically are, the mining industry can better plan to weather the downturns and take advantage of the upturns. For example, timing investments in new projects to take advantage of the cyclical upturns can dramatically improve project profitability.

Jan 1, 2000

Sm-Co alloy is a kind of magnetic material with high power and has been applied in modern industry widely. In this study, the wet chemical co-precipitation was developed for synthesis of the Sm-Co alloy oxide precursor. The thermodynamic analysis of the studied system was done to clarify the solution behavior theoretically based on the thermodynamic equilibrium and simultaneous equilibrium. Then, the experiments were done to address the various effects on the wet chemical process, including solution pH, reactant concentration, dispersant, reaction temperature and time, etc. It is found that by precise control of the process, the Sm-Co alloy oxide precursor was synthesized with fine crystallization and special size & size distribution.

Jan 1, 2005

By E. Iasillo, R. R. Carneiro

Independent of the method chosen to forecast production, an accurate method to project metal extraction is needed in order to accommodate leach cycles that exceed leach data on hand and thus be able to accurately forecast production. Metal extraction data must be developed for each ore type identified in the deposit in order to apply the correct rate of leaching when a specific ore is being treated. Curve fitting is used to model the rate of disengagement of metal into the pregnant solution. This paper provides a description of a curve fitting algorithm developed by Mr. John T. Bartlett, inventor of the METSIM™ process simulation program. A methodology is provided by which the metallurgical data developed is evaluated to determine if accurate projections may be made from the data. A criteria has been developed to help determine when a column experiment may be terminated.

Jan 1, 2001

By Shular R. Scudamore

There was a time when heavy-duty apron feeders were built to last almost forever. The machines were heavy and built to maintain certain expected longevity and reliability. Increasing emphasis on return on capital leads to cost-effective designs. Costs can be increased or decreased, depending on customer specifications and the design philosophy of the feeder manufacturer. Specifiers can make important contributions to cost effectiveness. To do so, this article describes what should be known about planning with a supplier for heavy-duty apron feeders. There are several factors that should be considered, including capacity, characteristics of material carried, length, method of feeder loading, degree of lift, hopper opening, pan construction, and type of drive. Today's apron feeders are built in various sizes and with a variety of components to handle heavy, lumpy, or abrasive materials that can ruin lighter feeders. Careful feeder selection is important if it is to provide a controlled feed rate, absorb huge impacts, be used with long hopper openings, and have a relatively low power-perton capacity. Variations in systems and materials demand that each feeder be designed for its application, drawing on a wide range of components. Therefore, certain factors must be considered before final specifications are drawn. Capacity The design and application of an apron feeder is based on how material passes through a given system over the feeder into processing machinery. The processing machinery's capacity governs other equipment and productivity of the flow. From this basic information, related sizes of upstream equipment can be determined. Of these, the apron feeder acts as the "mouth and neck of the bottle." No more will pass than the mouth and neck will accommodate. Everything in the apron feeder design, from dimensions to power, is based on processing machinery. Material Considerations Are Vital Just as the nature of materials to be crushed or screened affects capacity and productivity of a crusher or a grinding mill, so does it affect capacity and performance of a feeder. Lump size must be identified closely so the pan width can be selected to accommodate the maximum lump with room to spare. For example, a lump size of 760 mm (30 in.) indicates a pan width of 1.5 m (60 in.) While two times the maximum lump is considered minimum width, if the maximum lump

Jan 12, 1983

By G. L. Myers

The Fortitude skarn near Battle Mountain, NV is currently one of the largest producing gold skarns in the world. It contains about 11 Mt (12 million st) of minable ore grading 5.14 g/t (0.149 oz per st) and is the distal portion of a continuous skarn system in the Copper Canyon area centered on the Eocene Copper Canyon granodiorite porphyry. Calcsilicate compositions, opaque mineralogy, and the high gold grades are atypical of other base metal skarns (iron, Fe; copper, Cu; lead-zinc, Pb-Zn; or tungsten, W). The Copper Canyon skarn is systematically zoned from a garnet (AD 70-100) dominant, pyroxene (HD 20-45) subordinate zone, with major Cu mineralization, adjacent to the intrusive (West ore body), to a pyroxene (HD20-100) dominant, garnet (AD90-100 cores. AD 30-60 rims)subordinate assemblage, with major Au, near the distal marble front (Fortitude ore body). An extensive biotite ± diopsidic pyroxene ± kspar alteration halo surrounds the pyroxene > garnet gold-bearing skarn and represents the early stages of metasomatic alteration. Retrograde alteration is limited in areal extent and intensity, and consists of actinolite, chlorite, quartz, and prehnite. Economic gold mineralization begins in the pyroxene > garnet zone and continues to the marble front, a distance of 1 to 1.5 km (0.6 to 0.9 miles), respectively, from the plutonic contact. The opaque mineralogy in this gold zone includes pyrrhotite, arsenopyrite, marcasite, minor chalcopyrite, galena, sphalerite, argentite, hessite, hedleyite, volnyskite, and native bismuth and gold. The pyrite-pyrrhotite geothermometer yields temperatures that range from 450° C to 300°C (842° F to 582° F) and the electrum-argentite-sphalerite geothermometer yields temperatures which range from 290°C (554° F) at the marble front to about 420°C (788° F) more proximal to the intrusive. Log fS2 calculations from the sulfide assemblages yield values near - 10 with log fO2 values of about -30, in a solution of near neutral pH (5-6). Calculations of metal solubility suggest that the metals were transported as chloride complexes in the proximal skarn but that bisulfide complexes were predominant within the distal gold skarn. Relatively low oxidation states buffered by the carbonaceous to argilliceous, calcareous protolith and subsequent ferrous iron-rich skarn assemblages appear to have increased the gold carrying capacity of this large hydrothermal system.

Jan 1, 1991

By K. Awuah-Offei

An aggregate plant may have difficulty balancing product stockpile inventories if hot mix asphalt (HMA) design engineers do not account for aggregate inventory during mix design. Yet HMA design engineers do not, often, take this into consideration during asphalt mix design. This is due to the lack of tools that enable the lab technician or engineer to optimize the mix for good performance while helping the aggregate plant manage its stockpile inventory levels and reducing the aggregate cost. This work presents a linear programming model of the asphalt mix design problem that helps aggregate plants manage their inventory levels while meeting HMA customer demands. The algorithm is implemented in MATLAB as an Asphalt Mix Design Optimization (AMIDO) program. The program is successfully validated with real-life data. The results show that AMIDO can be used to successfully produce any mix design while reducing the cost of aggregates by using the cheapest stockpile materials. The application of AMIDO will increase aggregate plant profitability when serving HMA customers and could potentially be modified for concrete aggregate customers too.

Jan 1, 2009

By R. W. Lawrence

"Biological leaching can be used to enhance the recovery of gold and silver from refractory ores, concentrates and tailings. The method liberates precious metals associated with sulphide minerals such as pyrite and arsenopyrite making them amenable to cyanidation. The chemistry and features of biological preoxidation leaching is discussed. A summary of the results obtained on various ores, concentrates and tailings is presented.INTRODUCTIONRefractory precious metal ores in which gold and silver are finely disseminated in sulphide minerals such as pyrite and arsenopyrite are becoming more important to the mining industry. This is due both to a depletion of simpler, free-milling ores and to a significant increase in the price of gold in recent years. Whereas many ores can be directly cyanided with gold solubilizations over 90% obtained, the refractory ores respond poorly to direct cyanidation and require decomposition of the precious metal-bearing sulphide minerals to increase recoveries.Decomposition of sulphides by oxidation prior to cyanidation can be carried out by several means. The oldest method is roasting which removes unwanted ore constituents by high temperature oxidation and volatilization. In Canada, for example, roasting is used at Giant Yellowknife (Connell and Cross, 1981). Another method gaining increasing acceptance is pressure hydrometallurgy which uses aqueous oxidation conducted at high temperature and pressure. Homestake Mining Company have recently completed construction of a plant incorporating pressure oxidation at their Mclaughlin property in California (Guinivire, 1984)."

Jan 1, 1985

By Federico Schwalb

Actualmente la minera Yanacocha opera cuatro mineras a tajo abierto que abastecen a tres operaciones de lixiviación de oro. Paralelamente a estas, la minera planea otro yacimiento a fin de asegurar su nivel de producción. En este sentido, el presente trabajo señala el nuevo yacimiento denominado Quinua, que está ubicado al suroeste de las operaciones actuales. Esta nueva área incluye la construcción de instalaciones de lixiviación, planta de aglomeración, sistemas de recolección, transferencia y manipulación de solución y el tratamiento de soluciones en una planta de procesamiento Merrill Crowe ubicada en el área de Yanacocha Norte.

Sep 13, 2001

By Carlos Alberto Silva

A aplicação de lubrificação de tiras é um desafio para a maioria das empresas. Aplicações irregulares, não uniformes e excesso de óleo são problemas típicos encontrados quando se utiliza rolos de transferência ou tubos furados. Outros problemas como névoa, baixa eficiência de transferência e um ambiente de trabalho perigoso e insalubre são problemas comuns encontrados com equipamentos que utilizam a pulverização atomizada. O atual trabalho busca comparar os resultados da lubrificação de tiras obtidos com um equipamento de pulverização hidráulica da Spraying Systems frente ao antigo equipamento utilizado, atomizado.

Aug 16, 2017

By R. E. H. Pomeroy

Early in 1917, it became evident, owing to existing and pending market conditions, that a substitute for crude petroleum must be found for firing the smelter furnaces. After a review of the plants then existing, it was deemed advisable to depart from their practice and to adopt the following described system of distributing pulverized coal to the furnaces. The principal advantages of the proposed system, which influenced this decision, were: (I) Equal safety; no pulverized coal is stored at the furnaces; (2) greater ease of operation, furnace fires being controlled by regulating valves in burner branches, as in gas firing; (3) better organization; all machinery, including pulverized coal feed, is under one roof, and the organization is separate from the furnace department; (4) greater cleanliness; all machinery is under vacuum; (5) greater flexibility of application, the coal and air mixture can be piped where needcd. The design of the plant is the result of the combined efforts of the local engineering staff and of the machinery manufacturers. Many new features were embodied in this design to insure greater safety, cleanliness, and efficiency of handling. After 14 months of continuous operation, the plant has proved entirely satisfactory. The building is of structural steel, covered with corrugated steel, with many windows and is painted light gray inside and out. The building floor is of concrete with ample drains to the sewer, and the building is equipped with fire and service water piping. Fig. 1 shows the east side of the building and the incline conveyor from the raw-coal bins. The plant is operated entirely by electric power. All alternating current is 550 volts, 3-phase, 60 cycles. The pulverized-coal feeding niotors and control mechanism are operated by 220-volt direct current supplied by motor-generator sets in the building. Autamatic push-

Jan 1, 1921

By C. A. F. Sweet

The inter-relationship between these parties and the effect on the outcome of the project is often grossly underestimated. There are numerous success stories where the parties have worked as complementary teams aiming at the best outcome for the client company and achieving significant success. While there are a good number of occurrences where either the roles of the parties were unclear or perceived to be different from what others in the team believed or required them to be and the results were less than desired. This usually resulted in ongoing conflict, incorrect focus, working to different agendas and the result being a less than optimum result to Client Company. Mining, by its very nature of exploring where you cannot see, be it a shaft being sunk, tunnel being developed or other excavation that needs to be made, requires a very special working relationship between the parties. To understand this, and it applies equally well to mine and plant construction and other multiple function projects, one needs to start by describing the relationship of the parties. Often people believe that because they manage ongoing complex operations and large numbers of people that they can manage projects and as such the participants will ?fall into line.? At the outset it needs to be stressed that ?Project Management? is a specific type of management and needs to be understood as such. There are enough Colleges and Universities that teach project management, not only as a subject but also as a Master Degree. As you start up your project the relationship you establish between the client, project team (C.P.T) and the Engineering, Procurement, Construction and Management team (EPCM) will largely determine how successful your project will be. It is essential that from the outset a spirit of co-operation, support and respect be nurtured, and that it be actively carried through the project life cycle. There are several methods to facilitate this including team building exercises right at the start. This time and money will be well spent and recouped many times over during the project life cycle.

Jan 1, 2005

PRESIDENT LITTLEJOHN: We have with us a gentleman from Utah, who is familiarly known -as the "Mudite King," Mr. Reid, of the Lion Coal Company. Here is a letter I would like to read, and probably Mr. Reid will give us an idea of his Mudite machine, or the results he is obtaining. This question was brought up in Rock Springs, Wyoming, but Mr. Reid was not there personally during the discussion, but Mr. Burnell, who is general superintendent of the Lion Coal Com¬pany, as much as he possibly could, described the system and its effects. I believe Mr. Reid will probably be able to give a somewhat clearer statement this afternoon. This letter is from the Coal Mining Inspector of the State of Utah, John Crawford. "February 10, 1925. "The Industrial Commission of Utah, Building. "Statement of John Crawford, Coal Mine Inspector, in regard to Muditing in Coal Mines: "That Muditing used in connection with our present sprinkling system in coal mines is the missing link to the system we have had heretofore, because the water applied by the former system began to dry out, in heavy air currents, the moment it was put on. Consequently the dust that had been humidified by sprinkling, came back to its natural condition, and if anything, the combustible parts of it, in my opinion, were more intensified than previous to being wetted down. "The advantages that Muditing has over the old system of sprinkling are: "1st. The dust that is on the roof, timbers and sides of the entry is washed completely off and rolled up in the Mudite solution which entirely destroys the wings, crudely speaking, of the fine coal dust. "2nd. Sprinkling with the Mudite system, the water and mud is of greater extent than could be applied with a hand hose by a sprinkler. This sprinkling can be done while the mine is in operation, just the same as if water alone was being used. "3rd. The Mudite solution, when dried out, leaves a coating which serves as an armour to the coal, so that in the event of a local explosion, the inflammable matter on the coal is non-combustible; whereas, if that same coal had been sprinkled with water only, and made free of dust, the heat would have the same effect on the coal as it has on a stove when coal is thrown into it-instantaneous combustion. "Therefore, it is my opinion that the Mudite system is the missing link to the perfecting of our sprinkling system here in Utah. "(Signed) JOHN CRAWFORD." Mr. Reid has with him a few sam¬ples of his Mudite, after it has become solidified, taken from the floor, as I understand it. It is interesting. We have a few minutes to spare to good advantage, were we to ask Mr. Reid to give us an idea of his machine, as briefly as he possibly can, and also what he thinks the effect of the Mudite is compared to dry rock dust. Mr. Reid. (Applause.) MR. W. J. REID (Lion Coal Company) : I came down here with no intention of making any talk on Mudite. However, there being so many people that have seen Mudite at Wattis

Jan 1, 1925

By M. ROWE, H. E. Gilliland, L. BARNES

The authors of this paper are to be commended for a clear exposition of a timely subject. However, some important conclusions, in addition to those presented in the paper, can be drawn from the results of their elaborate and rather complete numerical computations. First of all, the major part of the calculations presented in the paper are for semi-infinite slabs of oil shale (the authors designate this as Model I) and a question must be posed — Are these elaborate computations needed to arrive at realistic estimates of the shale oil displaced. Consider the model of Lauwerier* that corresponds to the authors Model I if thermal conduction parallel to the fracture be neglected. If one also neglects the finite (but relatively small) heat capacity of the material in the fracture, it is easily shown from Lauwerier's solution that the cumulative oil production would be:

Jan 1, 1969

Visit to the Modderfontein factory of A. E. & C. I. Ltd 23rd November, 1972 A full programme was arranged to suit both the mining and metallurgical sections of the Institute. After refreshments were taken and visitors welcomed by the factory management we were split into two groups, viz metallurgical and mining. Book review Stress-relief Heat Treatment of Vanadium Steels by Or G. O. Joy and Or A. M. Sage (21 pp, 77 references).

By M. S. Burton, H. H. Kranzlein, G. V. Smith

The influence of up to 2 at. pct of Ni and Pt on the yield strength of mono- and polycrystalline high-purity iron has been evaluated at temperatures from + 25° to -196°C. Current theories of solid -solution strengthening fail to explain the experimental observations. The temperature dependence of yield stress was found to be less in the alloys than that in high-purity iron. The room-temperature yield stress increased with alloy content, but at —78°C the yield strength first decreased with increasing a1loy content. AS a result of many studies, a number of theories have been proposed for solid-solution strengthening. The purpose of the present study was to evaluate these theories, as applied to the solid-solution strengthening observed in Fe-Ni and Fe-Pt alloys. Of various theories of solid-solution strengthening, those of Cottrell,1,2 Fisher,3 Suzuki,4 and Mott and Nabarro5 are most prominent, and have been discussed widely in the literature.'-' Of the recent concepts of solid-solution hardening the work of Fleischer9 is notable. Each of these models has been applied to particular alloy systems with some success, but in general none has proved generally applicable. In many of the previous studies to assess the effects of alloy additions in ferrous systems, lack of adequate control of the purity and grain size of the materials has obscured strengthening effects, so that few comprehensive data relating composition, temperature, and change of lattice parameter have been determined. In the present investigation an attempt was made to obtain data which would be meaningful in evaluating the theories of strengthening. Materials of high purity were used to minimize extraneous impurity effects, and both single crystals and polycrystalline materials were studied to evaluate the effect of grain boundaries. Nickel and platinum were chosen as alloy additions, because both belong to the same chemical group and have the same crystal structure and valence, with markedly different atomic diameters. It appeared that some conclusions regarding atomic size effect on strengthening might be made. MATERIALS AND PROCEDURES Fe-Ni and Fe-Pt alloys containing 0.5, 1.0, 1.5, and 2.0 at. pct alloy additions were prepared from high-purity materials. The iron was supplied by the American Iron and Steel Institute from a stock of 99.98 pct zone-refined iron prepared by Battelle Memorial Institute. The minimum purity of the nickel and platinum used for alloying was 99.98 and 99.999 pct, respectively. Alloys were prepared by levitation melting, cast into cylindrical copper molds, and cooled, all under a partial pressure (0.3 atm) of purified helium. Samples were 0.375 in. in diameter and weighed 20 to 25 g. Chemical analyses of the alloys are given in Table I. A sample of unalloyed iron also was cast as a control specimen.

Jan 1, 1965

By Franz Albert Nonnen

Backfill systems have been used for as long as mining activities have existed. Various backfill methods have been developed over the centuries with consideration for geological necessities, the technical means available, security requirements, and available finances. In the past, backfill systems were introduced and upgraded geographically in accordance with local experiences. In modern times, mining engineers participate in international forums for the exchange of knowledge so that backfill techniques and experiences are shared concurrently in mining areas all over the world. Mine backfilling increases the cost of mining so that great attention must be paid to choose a low-cost, reliable, and low maintenance backfill system. Some methods are described in this paper.

Jan 1, 2001

By Sean Gallagher, William S. Marras, Alan S. Litsky, Velimir Matkovic, Deborah Burr, John Landoll

Study Design. Survival analysis techniques were used to compare the fatigue failure responses of elderly motion segments to a middle-aged sample. Objectives. To compare fatigue life of a middle-aged sample of lumbosacral motion segments to a previously tested elderly cohort. An additional objective was to evaluate the influence of bone mineral content on cycles to failure. Summary of Background Data. A previous investiga¬tion evaluated fatigue failure responses of 36 elderly lumbosacral motion segments (average age, 81 ± 8 years) subjected to spinal loads estimated when lifting a 9-kg load in 3 torso flexion angles (0°, 22.5°, and 45°). Results demonstrated rapid fatigue failure with increased torso flexion; however, a key limitation of this study was the old age of the specimens. Methods. Each lumbosacral spine was dissected into 3 motion segments (L1-L2, L3-L4, and L5-S1). Motion segments within each spine were randomly assigned to a spinal loading condition corresponding to lifting 9 kg in 3 torso flexion angles (0°, 22.5°, or 45°). Motion segments were statically loaded and allowed to creep for 15 minutes, then cyclically loaded at 0.33 Hz. Fatigue life was taken as the number of cycles to failure (10 mm displacement after creep loading). Results. Compared with the older sample of spines, the middle-aged sample exhibited increased fatigue life (cycles to failure) in all the torso flexion conditions. Increased fatigue life of the middle-aged specimens was associated with the increased bone mineral content (BMC) in younger motion segments (mean ± SD, 30.7 11.1 g per motion segment vs. 27.8 ± 9.4 g). Increasing bone mineral content had a protective influence with each additional gram increasing survival times by approximately 12%. Conclusion. Younger motion segments survive considerably longer when exposed to similar spine loading conditions that simulate repetitive lifting in neutral and flexed torso postures, primarily associated with the increased bone mineral content possessed by younger motion segments. Cycles to failure of young specimens at 22.5° flexion were similar to that of older specimens at 0° flexion, and survivorship of young specimens at 45° flexion was similar to the older cohort at 22.5°. Key words: biomechanics, low back disorders, fatigue failure, age, motion segments, vertebral endplate fractures, torso flexion, lifting, bone mass. Low back disorders (LBDs) are a major cause of both short- and long-term occupational disability in the United States, and it is clear that workers in certain occupations are more susceptible to LBD.2-5 Specifically, epidemiologic studies have shown that jobs involving heavy physical demands such as construction,2,3 mining,2,4 and farming,5 engender increased risk of back pain. These occupations are thought to experience high LBD rates as a result of their extreme postural and manual lifting demands. Studies have shown that jobs involving significant lifting 6-9 and jobs that involve frequent bending10-12 are associated with increased LBD risk. Workers in the mining industry, in particular, often have to lift heavy materials in restricted workspaces that compel torso flexion. An understanding of the impact of repeated loading of the spine in flexion on fatigue failure of spinal tissues is thus a critical issue for our research agency, which is concerned with reducing the pain and disability associated with LBD in the mining industry. It is well accepted that loads experienced by the spine during manual lifting tasks are sufficient to cause fractures in the endplates of lumbar vertebrae, particularly on repeated loading. 13-15 Endplate fractures may not be painful in and of themselves 16; however, evidence suggests that the process of internal disc disruption and disc degeneration may be initiated via endplate fractures. 16,17 It has been shown that endplate damage will alter the distribution of stress in the disc, resulting in buckling of the lamellas of the internal anulus.17 Once this process has been initiated, repeated spine loading will cause additional disruption of the anular fibers, resulting in formation of significant fissures or tears. 11-21 If these tears occur near or extend close to the outer portions of the anulus, a wound healing process is initiated, which involves infiltration of mast cells, macrophages, and re¬lease of cytokines and growth factors. 21 The presence of these infiltrates has been strongly linked to discogenic low back pain. 21,22 Indeed, for patients experiencing chronic low back pain, the prevalence of internal disc disruption is at least 39%,19 which represents the most

By Mark Ward

The Rincon del Tigre (RdT) complex is one of South America’s largest and best-developed mafic-ultramafic layered intrusions. It is set in the SE Bolivian lowlands, about 50 km from the Brazilian border.The BGS (British Geological Survey) and GEOBOL (Servicio Geologico de Bolivia) carried out an initial investigation of the RdT complex from 1976 to 1986. In this sense, the paper point out the geology background of The Rincon del Tigre, economical potential, typical ore secuence in laterite nickle deposit and pega pega erosional surface (Oligocene).

Apr 24, 2001