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By B. G. Cousins, B. O’Rourke, C. Spence

"Some non-flotation chemistries are added to flotation circuits directly and indirectly to control issues such as scaling and dust. Since the dosage levels are generally not very large, a standard laboratory float test may not be able to determine the effect a specific chemical has on the productivity of the flotation circuit. Hudbay and Ashland Water Technologies developed a laboratory testing protocol that uses kinetic float studies to test the effect of normal to extreme doses of antiscalant and dust chemistries (5 ppm to 500 ppm). Laboratory results indicate that this protocol helps to predict the potential interference that a particular chemistry will have on the flotation circuit.INTRODUCTIONFrom a chemical perspective, flotation is a very complex system involving more than the reagents used for flotation. Along with collectors, frothers, modifiers, suppressants and activators, there can be antiscalants for water treatment, dust suppressants used in the mining process, residual flocculants from recycled thickener overflows, grinding aids, and many other types of chemicals that are added upstream of a flotation circuit. Although these other chemicals are usually used at very low doses, it is important to know if they affect the flotation process detrimentally in the event of a spill or a build up from recycled water.Laboratory flotation testing of these chemicals characterizes their effects, but testing at expected doses in the float can mask the effects of the chemicals in the plant. Also, simple tests that do not measure the kinetics of flotation do not reveal the effects the other chemicals have on the flotation circuit. Thus, a new flotation protocol was needed to expose the full effects of chemical additives and to assist in choosing the chemical with the lowest potential for a negative effect.FLOTATION KINETICSMeasuring recovery kinetics in a laboratory flotation cell is a well-established procedure: analyzing concentrates taken in a timed sequence to determine the recovery rate of individual cells in a flotation circuit. The recovery from the early flotation cells are a true measurement of how well a flotation chemical is performing. The principles of kinetics can be mathematically determined by the following functions (Houston, 2006):"

Jan 1, 2013

By M. Kerr, Petra Lampinen, Jinming Zhang, Petra Brodin, C. Hull, Nils-Johan Bolin, R. Asmatulu

"According to Darcy’s equation, the rate of dewatering varies as inverse square of the surface area of the particles to be dewatered and is proportional to the pressure drop across a filter cake. Thus, the difficulty in dewatering fine mineral concentrates can be overcome by using high-pressure filters. When treating ultrafine particles, however, it is often necessary to further dewater the filter cake using a thermal dryer. In the present work, novel dewatering aids that can reduce the pressure requirement have been developed. The reagents are designed to reduce surface tension, increase particle hydrophobicity and increase capillary radius, all at the same time. They were tested for dewatering mineral and coal concentrates in both laboratory and pilot-scale tests. The results show that the use of the novel dewatering aids can substantially reduce cake moistures and, at the same time, increase throughput. In this communication, the case history of using the reagents commercially at the Garpenberg concentrator is given. The use of the novel dewatering aids allowed the operators to use a vacuum filter to obtain desired cake moistures and obviate the need to use a thermal dryer.INTRODUCTIONDewatering is an integral part of mineral and coal processing operations, as it is necessary to remove water from concentrates (or clean coal) to minimize shipping costs, meet contract specifications, and recycle the process water. In general, the cost of dewatering increases with decreasing particle size, which can be attributed to the difficulty in removing the water trapped in the pores (or capillaries) formed between the particles constituting a filter cake.The various parameters affecting the process of dewatering, including the effect of particle size, can be understood in view of Darcy’s equation (Darcy, 1856):"

Jan 1, 2005

By S. Yalcin, S. Chang, M. Oliazadeh

"Present day ferrochrome demand is on the rise, as more steel products require this material as an alloying element. It is projected that the stainless steel demands will grow by about 6% per year to 2020; as such, the supply and demand for ferrochrome appears promising. Chromite is the only economical source of chromium, which is commonly upgraded by gravity techniques and used to produce ferrochrome. The gravity separation methods are not able to treat particles finer than 0.1 mm efficiently. Therefore, in processing chromite ore, a large quantity of fine tailings; some 25% of the mineral values have been reported as lost in slimes during processing. The chromite content of these tailings is typically 10-20% Cr2O3 and accumulates into a large stockpile/pond. A chromite concentrator project in Canada, considers a cut-off grade of 20% Cr2O3. This indicates further processing might be required to recover chromite from low-grade stockpile when the high-grade deposits are depleted. Low-grade ores normally indicates disseminated chromite ores with low liberation and consequently fine comminution. This paper reviews the techniques for treating chromite from fine material and provides some examples of successful operations in fine chromite recovery. Beneficiation techniques for fine particles include gravity separation, magnetic separation, and flotation. Several case studies are presented here that used one of the aforementioned methods or a combination of them.INTRODUCTIONChromium is one of the essential element and important material for production of ferrochrome alloys and special steel. Chromium occurs as chromium spinel, a complex mineral with chemical composition of (Fe, Mg) O (Cr, Al, Fe)2 . Chromite ore is exclusively found in ultramafic igneous rocks. Major associated gangue minerals are talc, quartz, serpentine and iron oxides.Chromite is a heavy mineral, with a specific gravity in the range of 4-5, relative to associated gangue minerals in a chromite ore, which makes gravity concentration a suitable process. This is generally true for coarse particles, ranging from 1 mm to 100 mm. Typically, the ore is prepared by crushing (and grinding if necessary) to a suitable size and the material is sized for the appropriate beneficiation techniques. It is common to use heavy medium separation (e.g. dense media drums, dense media cyclones, or Dyna Whirlpool) to treat coarse size and intermediate size particles (1 – 100 mm). Intermediate and fine particles (20 – 0.1 mm) could be treated by jigs. Spirals, shaking table, sluices, and Reichert cones can upgrade fine particles. Figure 1 shows a typical chromite beneficiation process flowsheet. As can be seen, it consists of three major sections: feed preparation (crushing, screening), de-sliming, and concentration. Beneficiation recoveries range from 80 to 85%, although the ratio of upgrading is only 2 to 3."

Jan 1, 2013

By H. U. Ross

"INTRODUCTION Extensive studies have been carried on pure gold to determine the various factors that affect its dissolution in alkaline cyanide solutions. With the extension of milling to refractory ores more intensive investigations on the effect of impurities in the ore on the dissolution kinetics are needed. The present work describes experiments carried on refractory flotation tailings with the object to determine how the recovery of gold could be increased. The effect of arsenic and antimony in the ore and the excessive use of lime are discussed. Control of cyanide losses is also dealt with.MECHANISM OF THE GOLD DISSOLUTION REACTION In aqueous cyanide solutions, gold is believed to be dissolved by one of the following reactions:4Au + 8NaCN + O2 + 2H20 = 4NaAu (CN)2 + 4NaOH (1)2Au + 4NaCN + 2 + 2H20 = 2NaAu (CN)2 + 2NaOH + H202 (2)2Au + 4NaCN + H202 = 2NaAu (CN)2 + 2NaOH (3) The first of these, known as the Elsner Equation is supported by )4 3,2,1(several authors while others(5,6) support reactions 2 and 3 known as the Bodlander Equations. According to Habashi(7), the overall reaction for the dissolution process is as shown in equation 2. Most of the workers agree that hydrogen peroxide is produced in the course of the reaction."

Jan 1, 1973

By Gerardo Vargas

Without an adequate data sample there can be no Reliability Analysis (RA). Without analysis there can be no systematic, verifiable improvement in reliability or in operational economy. A sample is a collection of life cycles. A beginning and ending event define a failure mode life cycle. Well known obstacles impede the reliability engineer in his role to analyze maintenance data. The main problem lies in the difficulty to obtain analyzable data samples. Although modern Computerized Maintenance Management Systems (CMMSs) should provide the needed information they rarely deliver samples of adequate quality. Cerrejon, an integrated mining operation in Colombia, South America solved the information management problem by applying a "Living Reliability Centered Maintenance (LRCM)" process to its fleets of Trucks, Graders, Dozers, Loaders, and Shovels. This paper describes a method wherein completed work orders capture reliability analysis enabling information. The 'right' maintenance observations reference significant failure modes. Work orders link to records in a continuously growing Reliability Centered Maintenance (RCM) structured knowledge base. Grouped and filtered knowledge-to-work order links, being instances of failure modes, provide the samples required by reliability analysis software tools and methods. LRCM software and related procedures facilitate the growth of knowledge, manage the work order-to-RCM relationship, and generate samples for subsequent reliability analysis.

May 1, 2011

By H. Ewaschuk

"INTRODUCTIONRio Algom's involvement with the Enviro-Clear thickener began in May 1975, when tests on a laboratory waif were carried out by our Research and Development group. Commencing in June, further tests were carried out using a 3 foot diameter pilot unit. By December, a 30 foot full-scale thickener had been installed. In the near future, 3 more Enviro-Clear thickeners will be commissioned. With in the space of a year, almost $2.5 million had been committed to liquid/ solid separation facilities using the Enviro-Clear thickener. This paper briefly traces the extent and development of this commitment.BRIEF HISTORY OF QUIRKEQuirke Mine started operating in September 1956 at a rated capacity of 3,000 TOD. Because of market conditions, Quirke was shut down in December 1960. The facilities were re-opened at an increased capacity of 4,000 TPD in July 1968, by which time the demand for uranium had returned. Also, a second shaft was sunk, and by 1970, all of the ore treated in the concentrator was coming from the new Quirke II mine. The Quirke I stopes were allowed to fill with natural seepage. As well, acidic barren solution from the concentrator was pumped underground.With increasing demand for uranium, the capacity of Quirke will be further expanded to 7,000 TPD by 1978. Studies of how this expansion could best he carried out led to the consideration of a fairly new piece of equipment, the Enviro-Clear thickener, for certain operations in the concentrator. These operations are as follows:"

Jan 1, 1977

By Roe-Hoan Yoon

"Industrial flotation columns often suffer from low recoveries and high maintenance requirements because of poorly-designed air spargers. The MicrocelTM bubble generators were developed at Virginia Tech to overcome these problems. In this system, small air bubbles are generated by circulating a portion of the flotation pulp through a set of static in-line mixers. The small bubbles improve flotation kinetics and allow a higher recovery (or capacity) to be achieved. Other advantages of the system include reduced air consumption, plug-free operation and on-line maintenance. This article discusses the advantages of the MicrocelTM bubble generators and presents examples of successful in-plant demonstrations.IntroductionColumn cells are widely accepted in industry for cleaner operations because they are more selective than mechanically-agitated conventional cells. The improved selectivity can be attributed to the use of wash water which minimizes the entrainment of fine gangue particles into the froth product. Columns may also produce higher recoveries if the air sparging system is properly designed and steps are taken to minimize back-mixing. Furthermore, the quiescent conditions afforded by column cells may be beneficial for recovering coarse particles that are readily detached from bubbles under more turbulent conditions. Also, properly-designed columns offer advantages in terms of savings in floor space, reduced operating and capital costs, and simplified circuitry.It is unfortunate, however, that some of the advantages of columns are not fully realized in industrial practice. Some column circuits are unable to achieve their design capacity, while others require extensive maintenance programs. These shortcomings can usually be attributed to deficiencies associated with the design, scale-up and operation of the air-sparging system. In this article, some of the basic problems associated with commercial air sparging systems are discussed and alternatives are suggested."

Jan 1, 1994

By B. Dubé, R. Friedman, J. Oliver, R. Aubertin, M. Burson, G. Panneton, M. Hamilton, J. Ayer

"Abstract — The Detour Lake gold deposit is located within the northwestern limit of the Archean Abitibi Subprovince of the Superior Province. Mineralized zones are hosted by a sequence of pillowed and massive flows, hyaloclastite units, and altered ultramafic rocks, and are commonly oriented parallel to a series of high-strain zones that are co-planar to the regional-scale Sunday Lake Deformation Zone. Early in its kinematic history, the Sunday Lake Deformation Zone placed older (2.72 Ga) volcanic rocks of the Detour Lake Formation over younger (2.70 Ga) sedimentary rocks of the Caopatina assemblage. Gold mineralization is also parallel to the position of a laterally persistent siliceous rock unit, the 2.725 Ga ‘Chert Marker Horizon.’ The Chert Marker Horizon coincides with the boundary between the mafic-dominated upper Detour Lake Formation and the ultramafic-dominated lower Detour Lake Formation. Stratigraphic and geochronological data suggest that the Chert Marker Horizon is a deformed felsic volcaniclastic unit. At a cut-off of 0.6 g/t Au, the Detour Lake deposit contains 17.26 million ounces of Au within 445.9 million tonnes of rock grading 1.20 g/t Au. Gold occurs in shear-hosted and extensional vein arrays within rocks of the upper and lower Detour Lake Formation and within the Chert Marker Horizon. The Detour Lake deposit has many of the characteristics of a greenstone-hosted, quartz-carbonate vein deposit; its very large size may be attributed to large-scale rheological controls resulting in the formation of dilatant sites in permissive rock units. © 2012 Canadian Institute of Mining, Metallurgy and Petroleum. All rights reserved."

Jan 1, 2012

By J. Lobel, M. Bourassa, J. A. Kozinski, B. Peng

Non-isothermal kinetics studies of the reduction phenomenon of electric arc furnace (EAF) dust generated in stainless steelmaking have been carried out. The dust was mixed with carbon as a reducing agent and dolomite as a binder to form pellets. A Thermo-Gravimetric Analyzer (TGA) was used to determine the weight loss of pellets heated at an average rate of 40 K/min. up to a temperature of 1500°C. The degree of metal reduction was calculated by considering the pellet weight loss, and evaporation of moisture, dust, zinc and lead at high temperature. The reduction process was divided into three different steps. The first covers the 300°C to 760°C temperature range (from 7 to 18 min.), the second step ranges between 760°C and 980°C (18 to 24 min.), and the third covers temperatures above 980°C. Each step is characterized by different chemical reactions. Non-isothermal reduction kinetics equations were set up to describe each step. The kinetics parameters such as apparent activation energies and frequency factors were established. It was found that the first step was chemically controlled, while the second step was diffusion-controlled. Reduction behaviour in the third step was strongly dependent on the initial carbon content in the pellet. Chromium oxide (CrO) could only be reduced in this last step. High temperatures and higher initial carbon content favoured the reduction of CrO.

Jan 1, 2001

By Bjarne Ekberg

"The most economical way of dewatering mineral concentrates is to reduce the moisture content in the material mechanically using thickeners and filtration avoiding thermal drying whenever possible. In addition to this, the dewatering process should produce low moisture cake, high quality liquid, consume little energy. As a part of the dewatering process The CERAMEC® capillary filter has been proven to meet these requirements in over 150 installations. The filtration is done by using ceramic filter plates with small pore size. The capillary action in the filter medium secures gas free filtration at good vacuum, and due to the small pore size, filtrate is crystal clean and particle free. The energy consumption is minimal. This paper will discuss results from filters installed at Pyhäsalmi Mine Oy in Finland where the technology was has been used since the late eighties. Results from more recent installations like Los Pelambres in Chile and LKAB in Sweden will also be discussed.INTRODUCTIONThe idea of using capillary action to make dewatering more efficient was invented two decades ago. Ten years later whole filter plants utilizing the new method were delivered to mine concentrators for dewatering of mineral concentrates. Further development of ceramic membrane plates made it possible to meet the requirements in iron ore dewatering. In addition to low cake moisture, high capacity and low energy consumption, there are a lot of environmental advantages in using capillary filtration. One of them is clear filtrate.CAPILLARY FILTRATIONA micro-porous filter material behaves like a large number of narrow capillaries forming a network. When a pressure difference ?P is applied over the wetted, hydrophilic pore with the radius r, the force striving to push the water out of the pore will be ?Ppr2. The force striving to hold the water in the pore will be the vector force 2pr? cosa of the surface tension ? and the cosine contact angle a. Equalling those forces and solving the equation for ?P we get"

Jan 1, 2003

By B. Simser

Noranda?s Brunswick mine is a 10 000 t/d producer of lead-zinc-copper-silver ore that has been in operation since 1964. Mining of this multiple lens deposit is primarily by blasthole stoping techniques between 400 m and 1200 m below surface. The combination of a high overall extraction ratio, an overall steeply dipping tabular shape, and high horizontal stresses (twice the vertical) have elevated the induced stress regime to levels comparable to much deeper operations. Improved mine design, and a better understanding of how the rock mass responds to mining in high-stress environments is essential to improve overall recoveries and maintain safety. Seismic monitoring has proven to be an essential tool at Brunswick, for both short-term safety of workers, and long-term strategic planning. Practical case studies illustrate how seismic data, particularly source parameter information, can be used to measure the rockmass response to mining and improve mining layouts in difficult regions. As the global trend continues toward mining in deeper, higher stress environments (e.g., South African Witswatersrand Basin, Sudbury Basin) and as local extraction and thus ground stresses continue to increase in existing deposits, seismic monitoring will play a critical role in mining safely and economically.

May 1, 2004

By Magella Pelletier

"IntroductionDepuis une vingtaine d'année, les nombreux travaux de géochimie effectués par l'industrie privée et les milieux gouvemementaux ont permis:• de découvrir de nombreuses zones minéralisées a valeur économique;• d'identifier et de vérifier certains patrons de dispersion géochimique au-dessu s de secteurs minéralises déjà connus;• de favoriser le développernent des techniques analytiques;• de forcer le développement d'une mise en carte des résultats d'analyse, qui soit plus adéquat afin de permettre une meilleure interprétation géochimique.L'une de ces cartes géochimiques qui permet le mieux de mettre en valeur les données analytiques et qui fut instaurée au debut des années 80, est la carte d'interprétation géochimique par pondération.Cette carte numérique semi-quantitative, qui est construite à partir des données de base et de l'importance des éléments indicateurs pour une substance donnée, permet d'identifier et de définir des zones possédants de fortes probabilités pour la recherché de sources minéralisées."

Jan 1, 1987

By Fathi Habashi

"A process is proposed for the treatment of phosphate rock for the recovery of uranium and the lanthanides. The process assures the production of phosphatic fertilizers without polluting the environment with radioactive material.IntroductionWhile many processes for uranium recovery from phosphoric acid produced by the H2S04 route are known and utilised commercially, little is known about uranium recovery from phosphoric acid produced by the HN03 route1. Advantages of the latter route are both the elimination of the gypsum disposal problem, and the possibility of radium disposal in a controlled way2. Further, the lanthanides originally present in the rock can be recovered if the nitric acid route is used; they will be mostly lost in the gypsum produced by the sulphuric acid route3. In the present work a scheme for the recovery of uranium and the lanthanides from phosphate rock without interfering with the normal route for fertiliser production is proposed using HN03 as a leaching agent. Attention was also given to uranium decay products and their separation so that they might not contaminate the fertiliser4. Further, an attempt was made to defluorinate the leach solution in order to upgrade the fertiliser and at the same time recover the fluorine5. Rapid analytical methods for the determination of uranium, radium, and lanthanides in phosphate rock were developed6,7."

Jan 1, 1997

By A. J. Magerowski

Energy consumption is a main component of operational costs for the comminution of mineral bearing ores. Reduction of energy consumption has continually been addressed by mill operators and equipment manufacturers. Our testing over the last few years strongly indicates that the overall energy needed to comminute a mineral bearing ore can be brought down significantly, if more work is done in the crushing stages of the comminution circuit.This calls for uprating of the conventional crushing equipment into a new generation of crushing equipment to produce finer products. This will result in the emergence of new ideas in the design and application of equipment and corrnninution circuits.

Jan 1, 1986

By V. C. Pandolfelli, L. Paulino, C. E. Zangiacomi

The continuous improvement in aluminum industry over the last years has increased metal output at lower cost. The potlining plays an important role in this regard due to high cost involved and more recently in its environmental aspects. In order to increase potlife and thus minimize the aluminum cash cost, a systemic approach is needed, through investigating the main cathode failure mechanisms by using a pot autopsy as a powerful tool, and then making the necessary chances to achieve extended potlife. In addition, preheating and pot start-up may also damage the cathode if not performed with an appropriate technique or even if the lining materials are not specified correctly, among other factors. All these aspects will be presented and discussed in this paper. Increased potlife, especially now that the current is reaching values up to 300kA, will allow aluminum plants to match their goals more efficiently at lower costs.

Jan 1, 2006

By R. E. Michelutti

"The Sudbury area environment became drastically altered commencing in 1871 with lumbering, repeated fires and early open roasting operations from 1887 to 1929. These combined factors had such a pronounced effect that approximately 24 square miles were totally denuded of any vegetation and 87 square miles were semi-barren to somewhat stressed.The two nickel producing companies in the area have reduced the sulphur dioxide emissions considerably over the years. Falconbridge Limited, alone, reduced sulphur dioxide emissions by 77% from 1971 to 1984.These reductions have resulted in improvements to the air, soil, lake and vegetation quality in the Sudbury area.INTRODUCTIONThe Sudbury area environment became drastically altered commencing in the 1870's with lumbering, repeated fires and early open roasting operations from 1888 to 1929. These combined factors had such a pronounced effect on the Sudbury environment that approximately 24 square miles (64 sq. km.) were totally denuded of any vegetation and 87 square miles (225 sq. km.) were semi-barren.Over the years, the Sudbury area environment has improved considerably. This has been due to emission cutbacks by both Inco Metals and Falconbridge Limited, coupled with industry, government and community reclamation programs. Before the improvements are discussed, a better understanding of the historical degradation is required."

Jan 1, 1986

By S. Banisi, M. Poorkani

The Sarcheshmeh copper deposit contains 1 billion tones of ore averaging 0.7% copper and 0.025% molybdenum. It is located southeast of Iran and currently processes 41,000t/d. Molybdenite as a by-product is recovered in two separate stages. First, a bulk coppermolybdenum concentrate is produced and in the second stage these two are separated. The recovery of molybdenite in the first and second stages is 65% and 85-90%, respectively. The yearly production of molybdenite concentrate varies between 3500 and 4000 t. Sodium sulphide is used as the depressant of the copper and iron bearing minerals which due to a rather high consumption (17.7 kg/t) constitutes one of the major cost items of the plant (i.e., 58% of total reagents cost). A detailed laboratory scale study showed that replacing air with nitrogen could reduce the consumption of sodium sulphide (i.e., H2S or mineral origin). Nitrogen for the plant was supplied from an oxygen plant used for the smelter through a 1400 m long pipeline. The existence of the oxygen plant at the Sarcheshmeh complex was a key factor in the implementation and success of this project. After using nitrogen in the plant for a period of twenty one months, the consumption of sodium sulphide was reduced from 17.7 to 14.2 kg/t at constant metallurgy. The reduction was lower than expected which was mainly due to the type of sodium sulphide used and the lack of any automatic instrument to control the depressant (sodium sulphide) dosage. The latter in turn caused the operators to overuse sodium sulphide in order to reach and maintain the target metallurgy (i.e., higher molybdenite recovery along with lower copper content of the concentrate).

Jan 1, 2005

By C. M. Clapperton, K. E. Darke, A. J. Boyce, C. M. Rice, S. D. Redwood

"Abstract - The Kori Kollo gold deposit is hosted by a c.15 Ma sericitized dacite stock in the La Joya district on the Bolivian Altiplano. The mineralization is of the Bolivian polymetallic vein (BPV) type, with a significant amount of the gold reserves contained in the oxide cap. Field and microscopic studies, K-Ar dating, ??34S values of pyrite, alunite and jarosite, and ??18O values of alunite and jarosite demonstrate that some of this gold is supergene. Two types of supergene gold are present: minute gold grains, 1 to 10 microns across, of high fineness and associated with jarosite and iron oxy-hydroxides; and ‘invisible’ gold, which is probably sorbed onto minerals such as jarosite and iron oxy-hydroxides.Pyrite ??34S values fall in the limited range -3.5 ± 0.6‰, consistent with a magmatic origin. Sulfate ??34S values are homogeneous and overlap closely with those of pyrite (-1.2 ± 2.1‰), which supports petrographic evidence that sulfates replaced pyrite. By contrast, sulfate ??18O values are inhomogeneous with a large range (alunite +2 to 26‰, jarosite -5 to +18‰). These data are interpreted as reflecting kinetically controlled reactions involving various proportions of atmospheric oxygen and local meteoric water. This is typical of supergene alteration and is due to the seasonally dry climate of the Altiplano.The oxide-zone mineralogy is dominated by sulfates and iron oxy-hydroxide minerals with some phosphates and halides, which indicates that the groundwaters were acidic, oxidizing and relatively saline. Under these conditions the most likely complexes responsible for gold mobilization are halides.Geological data and K-Ar ages indicate that oxidation of the BPV deposits began at least around 11 Ma and possibly up to 15 Ma ago, and that supergene alteration lasted until around 4 Ma. During this period, erosion was minimal. Although supergene processes have been active on the Bolivian Altiplano since the Middle Miocene, in contrast to Northern Chile, enrichment of gold has not occurred."

Jan 1, 1997

By C. M. Clapperton, K. E. Darke, A. J. Boyce, C. M. Rice, S. D. Redwood

"The Kori Kollo gold deposit is hosted by a c.15 Ma sericitized dacite stock in the LaJoya district on the Bolivian Altiplano. The mineralization is of the Bolivian polymetallic vein(BPV) type, with a signi?cant amount of the gold reserves contained in the oxide cap.Field and microscopic studies, K-Ar dating, ??34S values of pyrite, alunite and jarosite, and ??18O values of alunite and jarosite demonstrate that some of this gold is supergene. Two types of supergene gold are present: minute gold grains, 1 to 10 microns across, of high fineness and associated with jarosite and iron oxy-hydroxides; and ‘invisible’ gold, which is probably sorbed onto minerals such as jarosite and iron oxy-hydroxides.Pyrite ??34S values fall in the limited range -3.5 ± 0.6‰, consistent with a magmatic origin. Sulfate ??34S values are homogeneous and overlap closely with those of pyrite (-1.2 ± 2.1‰), which supports petrographic evidence that sulfates replaced pyrite. By contrast, sulfate ??18O values are inhomogeneous with a large range (alunite +2 to 26‰, jarosite -5 to +18‰). These data are interpreted as reflecting kinetically controlled reactions involving various proportions of atmospheric oxygen and local meteoric water. This is typical of supergene alteration and is due to the seasonally dry climate of the Altiplano.The oxide-zone mineralogy is dominated by sulfates and iron oxy-hydroxide minerals with some phosphates and halides, which indicates that the groundwaters were acidic, oxidizing and relatively saline. Under these conditions the most likely complexes responsible for gold mobilization are halides.Geological data and K-Ar ages indicate that oxidation of the BPV deposits began at least around 11 Ma and possibly up to 15 Ma ago, and that supergene alteration lasted until around 4 Ma. During this period, erosion was minimal. Although supergene processes have been active on the Bolivian Altiplano since the Middle Miocene, in contrast to Northern Chile, enrichment of gold has not occurred."

Jan 1, 1997

By Christoph Miller

About 80 years ago the mining industry saw an advertisement of a machine manufacturer: ?One man ? one machine?, meaning the productivity gain by using a pneumatic rock drill instead of manual tools. Mechanization in mining had started. In the 1950's and 1960's when mechanization progressed the word could be transformed into the meaning of ?one man ? one drill rig?. During the 80's automatic functions were added to the machines. Automation started. In the 90's, the first autonomous machines were seen, transforming the advertisement from the 1920's into ?one man ? multiple machines? operated from a remote control room. Soon, the productivity gain achieved by pure automation will also be flating out meaning that the margin cost of further productivity gain will be inefficiently high. What next? In mining operations there is still a high potential of unused productivity lost by ?trivial? things like organization, logistics and operational management. Changing the focus from mechanization and automation towards optimizing the overall mining process will unleash another big potential for cost cuttings and for enhancing efficiency of production. Optimizing an overall process is a task of much higher total complexity compared to an isolated machine automation focus. And a successful process integration requires the collaboration of machine vendors, infrastructure suppliers, IT services and the mine itself. It requires a number of of important preconditions to be fulfilled: ? Integrated IT systems with seamless interfaces between all components and peripherals involved ? Real time information access in all locations ? Real time overview of all operational aspects A crucial aspect for all of these issues is a seamless communication both above and also under ground and IT interfaces which are easy and price efficient to implement. This paper highlights ways to achieve productivity gains by process optimization. It also discusses needs for industry wide activities in order to enable cost efficient performance of mine process optimization projects.

Oct 1, 2009