Search Documents

By Tim O’Neil

The earthmover tire shortage has been a case of bust and boom for the tire industry. Tire producers were unwilling to invest ahead of the mining boom. In their defense, though, the metals sector of the mining industry tends to be cyclic, tire manufacturers are not prescient. Until two years ago, low tire demand depressed prices. The incentive to invest in new, big-tire capacity was almost nonexistent, according to Prashant Prabhu, president of Michelin Earthmover Tire worldwide. “There has been very poor anticipation or a miscaluation of the amplitude of the (tire) demand on the part of just about everybody,” said Prabhu. What a turnaround. The earthmover tire market has grown by 30 percent over the past two years. Now there are not enough earth-mover tires and likely won’t be for the next two years. Goodyear said it was offering customers bias-ply tires when it could not supply enough radial-ply tires. Komatsu said it lost equipment sales because it could not provide the tires that customers requested. Volvo and Caterpillar said they are delivering some vehicles without tires, either promising tires later or leaving the customers – mine operators – to find their own rubber.

Jan 1, 2006

By J. D. Miller, C. L. Lin

In the processing industries, it is well known that particle shape is an important factor which determines the behavior of particulate systems. For example, system properties of technological significance including rheology, suspension stability, agglomeration, packing, permeability…etc, are affected by particle shape. In this regard, characterization and analysis of particle shape is essential for more detailed understanding and improved development of particulate processes. In general, it is clear that the behavior of these systems depends on the statistical characteristics of particle shape. Remarkably few techniques exist to predict the mechanical and hydrodynamic behavior of an irregularly shaped particle or a population of irregularly shaped particles for that matter. The lack of models and correlations can be attributed to the wide variety and complexity of particle shapes, the difficulty of defining shape descriptors suitable for modeling, the limitations of measuring shape, and the lack of classifying techniques to characterize particle shape. In this paper, we present information on how 3D particle shape can be measured, characterized, and analyzed using cone-beam X-ray microtomography (XMT).

Jan 1, 2005

By D. Janicijevic

This paper describes the process of scraper winch pull force measurement and shows the results of the actual winch pull force in extreme stall situations as well as during the face and gulley cleaning. It was found that by slowing down the motor and causing it to slip, torque up to 3.5 times higher than the nominal can be developed, resulting in the same increase of winch pull force. On the other hand, measurements of the actual force needed for cleaning of the face and the gully have shown that the currently used winches are too powerful. The extra torque that can be developed by the already too powerful winch motor poses a significant danger and necessitates the implementation of measures that will eliminate this risk.

Jan 1, 2008

To George Orwell the year of 1984 was the inspiration for a book. To most New Zealanders it was the year that the fourth Labour Government was elected to power. It was also the year that the review of mining legislation commenced. While Orwell's book and the election of Labour are clearly events of some historic note, one could be excused for classifying the review of minerals legislation somewhat differently in terms of its present achievements! Since the review began it has led a tortuous path through a rapidly evolving policy environment to a point three years hence where no major policies have been determined.

Jan 1, 1987

By H. F. Silliman, Daniel R. Hull, Earl W. Palmer

THE brass-rolling industry has not had a great deal of experience with antimony in its product. There have been some recent excursions with antimony as a corrosion inhibitor in tubes, but in sheet brass it has been regarded with apprehension and generally avoided. This is not to say that [ ] contaminations have never occurred, and probably a great many brass mill men have had their own ideas on the effect of such contamination. Our own views were based upon certain experiences some years ago with strip castings that split lengthwise in the early stages of rolling. The nature of this splitting is shown in Fig. I, from a photograph taken in 1922 as a record of 20 bars of 65-35 common brass made with an antimonial brand of copper. These bars were cast 6 ¾ in. wide by 1 in. thick by 45 in. long. In the first pass through the rolls, 19 of the 20 split lengthwise throughout their length, while each half curved outward in a wide arc as it emerged from the rolls. [ ] In those days, if splitting was not a frequent occurrence, it was not unfamiliar. One can recall periods of short duration when large amounts of common brass would behave in this way. There was nothing imaginary about these spells. The affected metal would split lengthwise in the breaking rolls, and no maneuvering of mill practice made any difference. The condition would descend like a plague, demoralize the mill for several days, and disappear. It is doubtful if anyone knew the cause-however many explanations may have been current. In 1921 a quantity of split brass was traced to the use of fired small-arms

Jan 1, 1943

By Travis Q. Lyday

During 1983, Ecuador's gross domestic product (GDP) decreased by a reported 3.3% in real terms, the second consecutive decline in the economy after more than a decade of growth generated mainly by petroleum export revenues. The slowdown was due, in part, to the effects of the world recession, lower foreign demand for oil, depressed world oil prices, and reduced demand and prices for Ecuador's traditional agricultural exports. Inflation accelerated to an estimated 55% annual rate. The sucre was devalued in March, for the second time in less than a 12-month period, by 27% after remaining unchanged during the previous decade. In addition, continuous adjustments were made every weekday, effectively devaluing the sucre another 30% by yearend. Ecuador's production of crude petroleum increased almost 12% in 1983 compared with that of 1982. Average daily production was 237,100 barrels per day (bbl/d), up from 211,300 bbl/d in 1982.

Jan 1, 1985

By M. Tarvainen, J. Kallioinen

"Depressed metal prices coupled with increasing production costs have presented a great challenge for operators to control and reduce the costs of production to maintain profitability. Depleting ore reserves, added to the above has forced Outokumpu to take a hard look at its operations, to develop new methods to profitably extend the life of its mines. One of the areas investigated and approved for further development has been the use of larger and more energy efficient equipment. As a result, large flotation machines were developed and today 38 and 60m3 flotation machines are in use.Secondly, ore preconcentration has been developed to avoid processing the part of the ore that has little or no mineral values.Another quite recent development and the topic of this paper, has been the use of coarse flotation before conventional flotation. The main idea is that part of the valuable mineral is separated as early as practical by floating it with specially designed flotation equipment, installed in the grinding classification circuit. The new flotation cell is specially designed for this application and differs from the conventional cells in the tank design, feed arrangement and modified mechanisms in some cases."

Jan 1, 1984

"Geoscan is used for multi-elemental analysis of conveyed bulk materials in the minerals industry with proven performance and demonstrated paybacks of weeks or months in iron ore, manganese, copper, zinc-lead and phosphate industries. Geoscan-M measures continuously through the full bed depth and is unaffected by belt speed, particle size, layering, mineralogy and dust levels. Increments of typically two minutes are accurately measured and provide the plant operators with tonnage weighted results of contained elements. Measurement of the composition in real time enables prompt feedback to the mining operators and also feed forward to the process operators. Crushed ore increments can be diverted based on composition, such as diverting waste for disposal or marginal material to a stockpile for separate processing. Bulk sorting allows material to be placed into relevant stockpiles for subsequent blending to achieve consistency for process feed. Parameters used for decisions may be primary metal content, deleterious component content, other process parameter, or a combination of these. Process parameter may be the elemental ratio between critical components, e.g. Cu:S ratio, basicity, or the content of an “indicator” element (such as Si indicating material hardness). Benefits will be discussed based on case studies in copper and iron ore.IntroductionAs operators of process plants strive to remain competitive as capital and operating costs increase and commodity prices fluctuate, more focus has been directed at incremental performance improvements at incremental cost rather than major expansions to increase output. The philosophy of working smarter allows plants to adopt technologies proven in other industry sectors to minimise risk. This paper discusses one such technology that the minerals sector is adopting and has found to be safe, reliable and accurate with paybacks of weeks in most applications. New applications continue to be found and major benefits realised at various stages in the processing and handling of ores and products."

Jan 1, 2016

By Nathaniel Herz, R. J. Adamson, C. M. Romanowitz, Frank W. Jr. McQuiston, C. D. Hoyt, Robert S. Shoemaker, P. H. O’Neil

1. INTRODUCTION In this section, precious metals are defined as gold, silver, and the platinum group metals comprised of platinum, palladium, iridium, osmium, and rhodium. If the first three years of the 1970's are the criteria, gold, silver, and platinum seem destined for a bright future. Gold advanced in price from the historic figure of $35 established in 1934 to over $100 per oz (1973). For the five years 1966 to 1970, silver consumption exceeded production by about 50%. The silver price appears to be definitely on the uptrend, and a price of over $3 per oz seems probable. On this basis (at 1964 costs) the United States has an estimated 5 billion oz of unmined silver. The fresh burst of interest in platinum with a surge of renewed price strength (end of 1972) is due to the activity in the automobile emission control area, where platinum re¬mains the front runner in the catalyst area. Some international financial experts believe that governments will not rush into reform of the monetary system, and "Special Drawing Rights" (SDR's) will gain increased standing as international mone¬tary reserve assets. Gold will continue to be reviewed as the ultimate store of value and will remain the global monetary base. Devaluation of the U.S. dollar caused by imbalance of import payments over ex¬ports is the basic reason that the price of gold will likely remain above the $90 per oz figure for the balance of the 1970's. Gold and silver usually occur intimately associated, and recovery methods are often closely related; however, they were assigned sepa¬rate chapters, because the major production of each metal is from ore deposits classified as either gold or silver. For example, the gold ore occurrences in South Africa, the world's leading gold producer, have a ratio of gold to silver of approximately 10 to 1. The ores at the Homestake Mine, Lead, S.D., the largest U.S. gold producer, are predominantly gold with a ratio to silver of approximately 5 to 1. Silver in each example is a byproduct. By this same classification, the largest U.S. silver producers are the silver ores of the Sunshine, Galena, and Lucky Friday mines in the Coeur d'Alene district, Idaho. However, the largest single-mine silver producer in the Free World is the Kidd Creek Mine at Timmins, Ont., where the occurrence is with sulfides of copper, lead, and zinc. Thus, the major gold production of the world is derived from those ores classified as gold ores; whereas, less than one-half of the silver production is from silver ores, and only a small percentage of the silver production is from gold ores. 2. GOLD Gold, the noblest of metals, has been mined for thousands of years. Its chemical symbol, Au, is derived from the Latin "aurum," meaning "shining dawn." A precious substance because it is one of the rarest metals, it has unique physical properties: it does not tarnish; it exceeds all other metals or alloys in malleability and ductility; it is a good conductor of electricity and is one of the most nonreactive metals. Its greatest strength is its indestructibility. It is the only metal mined at depths exceeding 10,000 ft. Since the early 1800s, its chief role has been as a medium of exchange, providing the basis for interna¬tional trade. In the past 15 years, however, gold has emerged as a useful industrial commodity. This role has been fortified by the estab¬lishment of a two-tier pricing system which maintains monetary gold prices at an established U.S. Government price, with industrial gold being priced higher by the free-market system. Occurrences and Production Native gold furnishes most of the world's production, since gold forms stable natural compounds with few other elements. Neverthe¬less, the metal is widespread with traces of it found in seawater and in the ashes of plants and animal material. Next to the native metal, the tellurides have been the most important gold-bearing minerals; these include calaverite, krennerite, slyvanite, hessite, and nagyagite. Native gold is invariably alloyed with more or less silver, but it is exceptional to find any other metal in the alloy. It is found in veins associated with quartz, calcite, alunite, other gangue minerals, and with various sulfides. Sulfide minerals in order of frequent associa¬tion are: pyrite, galena, chalcopyrite, sphalerite, arsenopyrite, tetrahe¬drite, and pyrrhotite. Small amounts of metallic gold are commonly disseminated through such sulfides. When considerable amounts of silver occur in gold, the mineral electrum is formed. In a few deposits, gold and mercury form natural amalgam. Native mercury is formed by weathering from cinnabar and other mercury minerals. Among the minerals sometimes mistaken for gold, pyrite, marcasite, and especially chalcopyrite may be men¬tioned. The flakes of biotite and other micas, especially when partially oxidized, also may imitate it closely. World gold reserves never have been estimated carefully. Esti¬mates indicate that present world reserves approximate I billion oz, of which about 60% occurs in South Africa and 20% in the USSR. World gold output is dominated by South Africa which produces two-thirds of the world's production from reserves that are adequate to maintain existing output levels. South African gold output comes from approximately 50 large underground operations that mine and mill 70 to 80 million tons of ore annually to recover 30 to 32 million oz of gold. The USSR is the second largest gold producer, followed by Canada and the United States (see Table 1). Gold production in the United States and Canada rose to high levels in the 1930's, following the increase in price from $20.67 to $35 per oz and with an abundance of good labor due to depression in other industries. Production of over 10 million oz in 1940 was behind only that of South Africa. World War II caused a precipitous drop in gold output due to the imposition of War Production Board Limitation Order L-208 issued in October 1942, which caused over 9,000 gold mines in the United States to shut down, most of which never reopened. The U.S. Treasury, which suspended purchases of newly mined gold in 1968, had been the sole buyer of U.S. produced gold since 1934. This created the two-tier pricing system, and in March 1972 the President signed into law a bill authorizing a $3 increase in the official price of gold to $38 per oz. In February 1973 the President ordered a second devaluation of the dollar, amounting to about 10% which raised the official price to $42.22 per oz. The erratic development of the gold market, which has seen the

Jan 1, 1985

By Ioannis K. Kapageridis

The lignite deposits of the Kozani-Ptolemais-Amyntaio basin in western Macedonia (North-West Greece) present a difficult modelling problem. Each deposit consists of several thin lignite layers ranging from a few centimetres to a few tens of centimeters in thickness, and thin intercalated sterile layers of marly limestones, marls, clays, and sands. These layers are practically impossible to model individually due to fast lateral transition of lignite layers to humus clay and vice versa and the lack of reliable and detailed stratigraphic correlation, leading to compositing methods being applied prior to any interpolation and modelling. The complexity of the deposit is further increased by the presence of a number of faults. This paper presents the modelling and estimation procedures applied during the most recent study of the South Western Field ? a new deposit that is considered for development and lignite production over the next years and will support the operation of a new power station in the area. Special focus is given to drillhole database structuring, fault modelling, stratigraphic correlation, mineable lignite intervals compositing, and resource estimation. The use of specialised mine planning software in all stages of modelling and estimation is thoroughly explained.

Oct 1, 2009

By Z. T. Bieniawski, Benjamín Celada

After emphasizing the importance of quantitative rock mass classifications in mining, originally directed to selection of rock support measures, but subsequently to estimates of rock mass properties such as rock mass strength and rock mass modulus of deformation, current attention calls for a classification specifically for rock mass excavability by tunnel boring machines (TBMs), which are used extensively in tunneling as well as in the mining industry. This paper introduces the Rock Mass Excavability (RME) index for predicting excavability of rock masses by TBMs using a quantification of machine performance and rock mass conditions. The RME index is based on five input parameters aimed at relating rock mass behavior and machine characteristics: (1) uniaxial compressive strength of the rock material, (2) drillability/abrasivity, (3) rock mass jointing at mine drift face, (4) standup time of the excavation, and (5) groundwater inflow. Development of the RME index entailed the collection of extensive data from more than 28 km of tunnels and some 400 case records from projects in Spain involving double-shield TBMs. In the process, a number of statistical correlations have been established between RME and such output parameters as degree of machine utilization, advance and penetration rates, thrust and torque of the cutterhead, and the specific energy of excavation. It was found that the RME index provides a particularly significant correlation for predicting the average rate of advance (m/day). In essence, the RME index is a classification system that features interaction of rock mass conditions with boring machine characteristics for use in the early stages of a project. It should be noted that the RME index does not replace the Rock Mass Rating (RMR) or Q-systems as used in mining and tunneling; indeed, one of the RME input parameters, standup time, is determined from the RMR. However, the approach presented introduces a specialized tool relevant to excavating tunnels and drifts. Possible applications to hard-rock mining are explored.

Jan 5, 2007

By Walter L. Finlay

The Bureau of Mines has developed prototype instruments promising to improve the ability to warn of imminent roof falls. An unusually good opportunity to test these comparatively under natural caving conditions was afforded by the forecasted caving in August 1977 of a mined-out region of the White Pine Mine. The latter's rock strata closely resemble those in many coal mines. The anticipated cave was of the competent-roof/weak-pillar type. It occurred as, and when, predicted. Automated convergence and bed separation gages agreed well with the standard manual convergence gage measurements. A micro seismic gage was found to be insensitive to the fall and may require different test conditions for effectiveness. A roof resistivity unit was tested under a separate Bureau of Mines contract. (No. H02720J7). An unplanned addition showed interesting potential.

Jan 1, 1978

By T Baumgartl, D R. Mulligan, D Doley, A Schneider

In arid and semi-arid areas evapotranspiration (ET) cover systems are often used to mitigate contaminated seepage from hazardous mine waste into the adjacent environment. The theory of ET covers is based on the water balance equation with the aim of minimising seepage. While cover systems are commonly trialled, the influences of variability in climate and cover structure on water balance equation parameters are seldom investigated.Water balance equation parameters and their variability were analysed for two ET cover trials constructed from benign waste rock in semi-arid Australia. Seasonal and inter-annual variations in rainfall critically influence cover performance. For successful cover system operation, the average return periods for higher than average rainfall should be taken into account. In addition, failure of ET covers has a higher probability in areas with marked rainfall seasonality. Water holding capacity and plant available water content are low in covers constructed from waste rock. Changes in water holding capacity due to variation in particle size distribution are likely and critically influence cover performance. The application of topsoil can be beneficial for water ingress control through run-off, but a balance has to be struck between run-off, erosion and plant available water. Changes in vegetation composition only influence evapotranspiration water losses at plant coverage exceeding 50 per cent, which is unrealistic in semi-arid areas. This study showed that the capacity of ET cover systems to hold and dispose of received rainfall is often lower than assumed by industry practitioners. Furthermore, in order to improve reliability of long term cover performance, the variability of rainfall and water holding capacity of the cover has to be included in water balance models.CITATION:Schneider, A, Baumgartl, T, Doley, D and Mulligan, D R, 2012. Variability in parameters of the water balance equation and their influence on evapotranspiration cover performance, in Proceedings Life-of-Mine 2012 , pp 293-300 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 10, 2012

By Orlando Gallardo

El presente texto describe la implementación del software ADS (Sistema de Despliegue Activo) a los sistemas de control supervisor de los diferentes procesos del complejo metalúrgico a nivel administrativo -en tanto replica los archivos gráficos y de base de datos. Este servidor además de concentrar en su red de campo redundante data de controladores e instrumentos de campo, puede compartir información con clientes usuarios y clientes de visualización dentro de la planta. En ese sentido, el objetivo es simplificar la producción y uso de datos únicos y garantizar la fiabilidad de estos a tiempo real para todos los niveles de supervisión a nivel administrativo, al tiempo que se planea y optimiza los recursos con la toma de decisiones apropiada.

Sep 24, 2008

By Minna Karstunen, Patrick Becker

"Abstract The deformation behaviour of a foundation on deep mixed columns in a natural soft soil is a three-dimensional problem, which has to be considered adequately in numerical modelling. However, simplifications are often made due to the computational costs of fully coupled 3D analyses by either modifying geometry of the problem or material parameters in 2D for plain strain analyses or by modelling the problem as 2D axisymmetric case. The volume averaging technique (VAT) is an enhanced 2D FE technique that enables mapping the 3D problem in two-dimensions, yet modelling the two constituents (column and soft soil) with appropriate different constitutive models within a homogenized material. The performance of the volume averaging technique is demonstrated by considering unit cell simulations of floating and end bearing columns in soft soil. The results with VAT are compared and validated against conventional 2D axisymmetric and fully coupled 3D finite element analyses.IntroductionThe properties of very soft clays, silts and organic soils can be improved by stabilizing agents, such as lime and/or cement that are mixed into the soil in situ by using auger-type mixing tools in situ. Deep mixed columns are extensively used to reduce deformations and to improve the overall stability of embankments and foundations on soft soils. Whilst the most typical applications are embankments, increasingly the method is used under foundations. The first category of applications is very common in Scandinavian countries, whilst the latter application has been pioneered in Poland, as an environmentally friendly (low CO2) and cost effective alternative for piling. Due to economic and environmental reasons there is an increasing interest in the technique elsewhere in Europe. With deep mixing, the strength and deformation properties of the soft soil can be improved, and the risk of unwanted deformations is substantially reduced.Numerical methods, such as finite element (FE) analysis, can be used as an alternative to conventional design methods. They are particularly suitable when considering serviceability limit state, i.e. deformation analyses under working loads. FE analyses allow using advanced constitutive models that take account of the complex stress-strain behaviour of natural soil and stabilized columns, respectively. The problems that involve a grid of circular columns under an embankment or a strip footing are fully three-dimensional problems. As 3D analyses are very laborious and expensive, an enhanced 2D technique using the so-called volume averaging technique (VAT) is utilised. The basic idea is to describe the column-improved ground as a homogenized composite material, and using clever mathematics to map the true 3D problem into 2D. Once the constitutive relations of both composites are defined, the response of the column-improved ground can be simulated in 2D subject to arbitrary loading and boundary conditions."

Jan 1, 2014

By M. Mead, J. Dumouchel, W. Yule, J. Giroux

The QMM mineral sands of South East Madagascar contain approximately 1,900 million tonnes of mineable sand with a total heavy mineral (THM) content of roughly 4.5wt%. The QMM deposits are the world’s largest known reserves of 60% TiO2 ilmenite and also contain a small volume of zircon. The deposits are semi-continuous and homogenous and the mineralized sands are free flowing with minimal overburden, induration & slimes. These characteristics are favourable to dredge mining and allow the application of conventional wet gravity, electrostatic & magnetic separation to final products. A mature THM mineral suite of high valuable heavy minerals (VHM) content has enabled the development of a relatively simple separation process.

Jan 1, 2005

By A. D. Pelton, Y. -B. Kang, S. A. Decterov

Computerized thermodynamic databases for solid and liquid metal, slag and solid oxide phases in the Al2O3-CaO-CoO-CrO-Cr2O3-FeO-Fe2O3-MgO-MnO-NiO-SiO2-S system have been developed by critical evaluation/optimization of all available phase equilibrium and thermodynamic data. The databases contain parameters of models specifically developed for molten slags, liquid steel and solid oxide solutions such as spinels, pyroxenes, olivine, monoxide (wustite, periclase, lime), corundum, etc. By means of the optimization process, model parameters are found which reproduce all thermodynamic and phase equilibrium data within experimental error limits. Furthermore, the models permit extrapolation into regions of temperature and composition where data are not available. The databases are automatically accessed by user-friendly software that calculates complex equilibria involving simultaneously slag, metal, refractories and gases, for systems with many components, over wide ranges of temperature, oxygen potential and pressure. A short review of the available databases is presented. The critical evaluation/optimization procedure is outlined using the Al2O3-CaO-FeO-Fe2O3-SiO2and Al2O3-CaO-MnO-SiO2systemsas examples. Several applications of the databases to deoxidation of iron and to inclusion control in steel are discussed. Keywords: thermodynamics, phase equilibrium, phase diagrams, databases, ferrous metallurgy, steelmaking, inclusion control, slags, oxide systems.

Jan 1, 2004

By Hua-Zhong Yu

Gold is one of the most widely used substrate materials for self-assembly. Self-assembled monolayers (SAMs) prepared from alkanethiols and their derivatives on gold are the most reliable and well-studied systems to date, which have attracted much attention because of interest in two-dimensional molecular assemblies, and of their potential applications in molecular devices, sensors, and functionalized interfaces. Gold electrodes are also very important in microelectronics and electroanalytical chemistry. This work reports the characterization of a new type of gold substrates for self-assembly. The gold substrates are constructed from recordable compact disks (R-CDs) with simple and straightforward wet-chemical treatment, and can be made at desired sizes and shapes that satisfy different experimental needs. In particular, an easy, inexpensive, and reproducible method to prepare self-assembled monolayers (SAMs) on CD-R gold substrates after removing the protective polymer films with concentrated nitric acid was described.

Oct 1, 2003

By John E. McCullough

The purpose of this development program is to design and develop a known volume air sampling pump for use in measuring the amount of radio-active material in the atmosphere of an underground uranium mine. The principle nuclear radiation hazard to underground uranium mines comes from the mine atmosphere. Daughter products of 222-radon, namely 214-polonium, 214-lead, 214-bismuth and 214-polonium, are inhaled by the miner, resulting in a relatively high lung cancer rate among these workers.

Jan 1, 1976

By S F. Simmons

The Ohaaki Rhyolite and the Rautiwiri Breccia are two volcanic units occurring in the shallow and deep parts of the Broadlands-Ohaaki geothermal system. Alteration of these units by chloride waters results in distinct mineral assemblages that also have distinct whole rock compositions. The Ohaaki rhyolite is altered to an assemblage dominated by quartz, adularia, illite and pyrite as a consequence of silica, potassium and sulfur metasomatism. Locally, these rocks contain up to 0.5 ppm Au. The Rautiwiri Breccia by contrast is altered to an assemblage dominated by albite, adularia, quartz, illite, chlorite and pyrite in association with modest sodium metasomatism. Whole rock oxygen isotope compositions of altered rocks range between 3.3 and 7.5 ë, and are generally lower compared to their fresh rock equivalents having values of 9.5 to 10.6 ë; the result is broad pattern of lower values with increasing alteration intensity.

Jan 1, 2002