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By S. Beitler

The availability of renewable energy does not meet the demands of consumption. Hence, fossil fuels will continue to be an important energy source, and coal promises to cover the requirements for the coming decades. Because of its high energy content, deep lying bituminous coal and anthracite are important for energy generation. One trend in the future of coal mining is thin seam mining, because thick seams more and more have been exploited. A well-known and approved longwall mining method for thin seams is plowing which has big advantages compared to a shearer because of its compact design. The extraction of those thinner coal seams will become more and more important in coal industry and therefore the plow will receive more attention in future. Most approaches in longwall automation are focused on the shearer and need a more or less intelligent exploitation machine. Therefore those approaches cannot be used for the plow technology. The authors introduce a shield-data-based horizon control (SDHC). The developed approach integrates the shield data provided by the roof support and process monitoring into the horizon control process to keep the plow in seam even if the seam trend changes. This control concept can be used for the shearer as well as for the plow. The basic idea of SDHC for plow application will be introduced in this paper and first simulation results will be shown.

Aug 1, 2013

By William A. Vogely

Mining employment in the United States declined from 986,000 employees in 1948 to about 600,000 employees today. This has occurred even though the Index of Physical Volume of Mineral Production (1957-59=100) has increased from 88 to 111 and the value of mineral production measured in constant(1957-59) dollars has increased from $14.7 billion to approximately $19.3 billion. Average unit mine value has increased 24% as compared with a 34% increase in prices in general. Apparent consumption has increased more than domestic production, indicating an increased dependence on imports. The mineral economy presents a complex pattern of development factors in the post-war period. This article presents a technique by which the various forces that have been acting on the market for a mineral commodity may be sorted out and by which the extent of the impact of technological change in use as well as the technological change in production can be measured. If one is interested in delineating fully and completely the impact of technological change upon the mining industries, it is not sufficient to describe the increase in productivity reflected by the above employment and production figures. What is reflected there is only the effect of technological change in the production function of the commodities under concern. These effects are obviously very substantial and have major implications for labor, capital and supplying industries. However, they are not the only effects of technological change and, in fact, may be relatively minor when the impact which arises because of changing technology in the using or consuming industries is considered.

Jan 4, 1965

By Fathi Habashi

"Crushing and grinding of ores and their beneficiation by washing away gangue minerals has been practiced since ancient times. Primitive crushing was done by hand pounding the ore with a hard stone then by using metallic hammers. The mortar and pestle was mechanized using a lever and when the size of operations increased in the middle ages, the stamp mill was introduced. The grindstone played an important role in grinding of ores. Panning for gold and hand sorting of minerals were two old methods of separation, now gave way to modern techniques. Flotation started in the middle of the nineteenth century by using oils to collect the mineral particles and float them on the surface of the aqueous slurry. It was only in the 1920s when it was discovered that organic compounds were affective floating agents. Textbooks written by distinguished engineers such as Rittinger, Rickard, Pryor, Taggart, Richards, Gaudin, and others contributed to the recognition of this field as a new discipline to be taught in Universities. INTRODUCTIONThe ancient Egyptians knew already that it would be easier to melt an earth rich in gold particles than another which is poor. As a result all efforts were made to enrich the gold by washing away the light gangue minerals (Figure 1). Another ancient method for enriching gold particles from a river stream was by means of fleece, hence the Greek myth of the “golden fleece”. The present day Georgia was known in ancient times as Colchis and was a center for gold working. It was known to the ancient Greek as the land of Golden Fleece. The use of special cloth to catch gold particles was also described by Agricola in his 1555 book De Re Metallica (Figure 2)."

Jan 1, 2009

By A. Dienenthal

"The casthouse floor has always been one of the most dangerous working places on a blast furnace or a ferro-alloy/nonferrous furnace. Apart from working in an atmosphere including toxic gases, fumes, and dust, the workers have to perform hard and heavy manual work close to runners and ladles filled with hot liquid metal and slag.Before the invention and installation of tapping equipment the tap-holes were opened and closed manually. Opening was done by means of steel bars and sledgehammers, whereas the tap-hole was closed by repeatedly ramming small amounts of clay or refractory material into the tap-hole, again with the help of long, heavy bars. In addition, on blast furnaces the blast had to be stopped, since it was impossible to close the tap-hole properly against the blast furnace pressure. This stoppage of the blast resulted in regular losses of production. Around 1900 a major change in technology occurred. Samuel W. Vaughen, superintendent of the blast furnace department of the Cambria Iron company at Johnstown, Pennsylvania (USA), invented the first clay gun in 1895 (Wiley, 1896) (Figure 1)."

Jan 1, 2014

By D. K. Sarkar, J. Perron, J. D. Brassard

"Nearly perfect spherical shaped water drops rolling-off from the surface of lotus leaf is one of the beauties of nature. This kind of surface is called superhydrophobic, since the water does not like it. Physically, a superhydrophobic surface provides a contact angle (CA) of water over 150°. The combinations of both mico-nanostructure topography as well as low surface energy are essential to have such high CA on a surface. Nano-micro structured superhydrophobic surfaces have been developed in different methods. (i) Monodispersed fluorinated silica nanoparticles have been synthetized via Stöber Sol-Gel process and deposited on various surfaces, such as aluminium or glass, to obtain transparent superhydrophobic thin films. (ii) Similarly, zinc stearate nanocomposite coating has been fabricated by spray process on the same substrates. These thin films are found mechanically robust with drag reduction of coefficient 16% lower than as-received surfaces. (iii) By electrodepositing pure zinc on steel surfaces and further coating it with diluted room-temperature vulcanized silicone rubber, the surface become superhydrophobic. This superhydrophobic surface protects the steel against corrosion by increasing the polarization resistance from 1.5 k? on steel to 44.4 k?. This coating also reduced the ice adhesion on the steel surface 6.3 times as compared to bare steel substrates. Globally, these superhydrophobic surfaces have tremendous applications against corrosion reductions, drag reductions and ice adhesion reductions.INTRODUCTIONSuperhydrophobic coatings are increasingly attractive to the industry and academia due to their unique self-cleaning properties as a result of their water repelling characteristics. Fabrication of superhydrophobic coating is an inspiration from nature as water is seen to repel on many natural surfaces such as those of the lotus leaves, butterfly wings, water striders’ legs, and so on (Gao & Jiang, 2004; J. Huang, Wang & Wang, 2006; Neinhuis & Barthlott, 1997; Zheng, Gao & Jiang, 2007). This non-wetting phenomenon is well understood on lotus leaves, shown on the Figure 1 (a), and it is considered as the basis of the studies of superhydrophobicity. The existence of this binary structure on the surface of the lotus leaves allows a large amount of air entrapment and consequently reduces the contact area of water on it and the presence of low surface energy waxy components with reduced affinity to water together leads to the superhydrophobic properties. The phenomenon is shown on Figure 1 (b). Cassie and Baxter (Cassie & Baxter, 1944) as well as Wenzel (Wenzel, 1936) proposed two mathematical models to explain the wetting phenomena on rough surfaces that leads to superhydrophobic properties. By definition, superhydrophobic surfaces are characterized by a water contact angle value = 150° with the rolling off of water drops from the surfaces (Sarkar & Saleema, 2010). Superhydrophobic surfaces find tremendous importance in the technological world where it can applied in domains such as anti-corrosion, anti-biofouling, electrowetting, icephobic and even in drag reductions (Bushnell & Moore, 1991; Cao, Jones, Sikka, Wu & Gao, 2009; Carlborg & van der Wijngaart, 2010; Carré & Mittal, 2009; Y. Huang, Sarkar & Chen, 2010a; R. Karmouch, Coude, Abel & Ross, 2009). However, the most important challenge faced by industries is their feasibility large scale in an effective an economical manner."

Jan 1, 2016

By M I. Pownceby, M A. Rhamdhani, D M. Fellicia, S Palanisamy, R Z. Mukhlis

The trend of global copper production has prospectively increased over time. Based on typical mined ore grades, 1 t of copper ore generates approximately 6–10 kg of copper, which requires much energy, usually in the form of metallurgical coke. Copper production using carbon as a fuel and reductant contributes up to 0.3 per cent to global greenhouse gas (GHG) emissions. As a result, research into decarbonisation processes applicable to reducing low-grade copper sulfide ores, copper oxides, electronic wastes and other alternative complex Cu-rich materials has increased. Alternative fuels for reducing carbon-rich emissions in pyrometallurgical copper processing include methane, ammonia, biomass, solar and wind power, but in recent times increased focus has been on hydrogen as a potential fuel and reducing agent for materials such as oxidised copper scrap, Cu2O/CuO and Cu-rich slags/e-wastes. From a thermodynamic perspective, hydrogen exhibits a significantly more negative standard Gibbs free energy (ΔG°) than copper oxide making it a suitable reductant and the exothermic thermal effect from reaction between hydrogen and Cu2O/CuO may be used to control process parameters. These characteristics renders hydrogen an ideal gas for reducing copper oxides and copper-containing slags/e-wastes. This review article assesses previous research on utilising hydrogen for producing and refining copper from primary and secondary feed materials.

Jun 19, 2024

By E. H. Crabtree, Neil S. Parker

THE custom milling plant of the Eagle-Picher Mining and Smelting Co. is at Sahuarita, Arizona, approximately 20 miles south of Tucson. It is connected by a 2-mile railroad spur to the main line of the Southern Pacific Railroad between Tucson and Nogales. The capacity of the plant is 500 tons per day. The mill is conventional except perhaps in the rather wide variety of ores treated. These vary from straight copper ores, from which only one concentrate is produced, and lead-zinc or copper-zinc ores from which two concentrates are produced, to complex gold-silver-copper-lead-zinc ores, which require the simultaneous production of three or four concentrates. Custom ores are received in lots varying in size from a few truckloads to several carloads. Similar ores, after crushing and sampling, may be commingled, or individual lots may be milled individually. The ores are first dumped either into one of two 200-ton railroad bins, or into one of the two 75-ton truck bins. From these bins the lot of ore is individually crushed in a 24 by 16-in. jaw crusher to 3-in. size, and then to 1/2-in. size in a 3-ft Symons shorthead crusher. After crushing to 1/2-in., the ore is conveyed to the automatic sampling plant. This consists of three Vezin samplers in series, each successively cutting out 10 pct, to pct and 5 pct of its feed. After No. 1 sampler, the material passes through a mixing barrel and is then crushed to 1/4-in. in a set of rolls before passing to No. 2 sampler. Between No. 2 and No. 3 samplers, the ore is again mixed in a mixing barrel. The final sample, consisting of one pound per ton of ore, is taken to the laboratory, where it is further crushed to 1/8-in. in a coffeemill, and then riffled down to the size required for grinding in a pulverizer. The capacity of the crushing and sampling plant is up to too tons per hour, depending upon the character of the ore. After sampling, the ore is stored in five ore-storage bins, consisting of four 200-ton bins and one 175-ton bin. Each of these bins is discharged by means of belt feeders and conveyor to the ball mills, so that ores may be composited for milling in any required ratio, or milled separately by themselves. Fine grinding is done in one 6 by 4-ft Allis-Chalmers ball mill and one 8-ft by 36-in. Hardinge mill. These two mills both discharge to one 54-in. Akins Simplex Highweir classifier. The classifier sands can be returned to either or both mills, so that flexibility in grinding for different ores is easily obtained. Flotation equipment consists of four 66-in. Fagergren machines for copper-lead roughing and six similar machines for zinc roughing. Lead-copper bulk concentrate is cleaned and recleaned in eight No. 18-S Denver machines, and zinc concentrate is cleaned in three 66-in. Fagergrens. Copper-lead differential separation

Jan 1, 1947

By M. P. Oommen

This paper provides a brief look at a proposed short-longwall for coal, development. The proposed method is an attempt to realize the advantages of longwall mining in deposits that, historically, would only be minable by continuous mining methods. An overview of the proposed layout, development requirements, production rate, ventilation scheme and other associated features is provided. This mining method could help operators in above-drainage seams where minable areas are smaller. It may also have application in areas that are peppered with gas wells and in environmentally sensitive areas which preclude the use of conventional longwalls.

Jan 1, 1993

By E. Bakhtavar

In this paper, problem of short-term production planning for dimension stone quarries was mathematically modeled using a binary integer programming. The model includes an objective function, which was founded as the minimization of the costs due to the total cutting planes of the blocks. This objective may cause to maximization of the net present value (NPV) in dimension stone quarries. During the mathematical modeling the essential constraints are dimension stone quarry capacities and the market demand, block accessibility for the equipment and the reserve constraints. As a base, an optimal size and shape of extractable blocks should be first assigned according to the available extraction technique and the market demand, in order to create a geological block model. Then an economical block model is provided by assignment of a value of ?one? for ore blocks and ?zero? for waste. Maximum profitability and minimum amount of the ore wastage can be gained using this plan and modeling.

Jan 1, 2012

By C. Clark, R. Pakalnis, B. Seymour, L. Martin, R. Jacksha, M. Stepan, M. Roworth, C. Caceres

The National Institute for Occupational Safety and Health (NIOSH) is conducting research to develop safe practices for the use of shotcrete as ground support in underground mines, particularly mines operating in weak host rock. As part of this research, a rugged, portable direct tensile test system was developed for measuring shotcrete adhesion strength in underground mines. During the development of this test system, more than 185 direct tensile tests were conducted with a common, commercially available macro-synthetic fiber-reinforced shotcrete that was applied to concrete test panels using a dry mix process and machinery. The average bond strength of the shotcrete to the concrete substrate typically increased as a function of the shotcrete’s curing age, ranging from 0.44 MPa (64 psi) after one day of curing to 1.58 MPa (229 psi) after 90 days of curing. Adhesion strength increased markedly between one and three days of curing, reflecting a similar trend of increasing shotcrete tensile strength with curing time. This robust direct tensile test system can improve mine safety by providing a reliable means of measuring shotcrete adhesion strength and also supplying important information about the quality of the applied shotcrete and the competency of the underlying rock.

Jan 1, 2010

By A D. Campbell

Conversion of Mineral Resources to Ore Reserves requires a multidisciplinary approach and application of a number of Modifying Factors. The Modifying Factors for mining, particularly dilution and recovery in a caving mine are complex and can be difficult to determine. Cave flow modelling software is widely used for mine planning, scheduling and forecasting metal production. However, the conversion of Mineral Resources to Ore Reserves remains a difficult and subjective process and a consistent approach to convert Mineral Resources to Ore Reserves as part of the cave flow modelling process is not published in the literature. This is due to the difficulty in estimating the Ore Reserve that remains as cave stocks at a particular point in the mine schedule, the recovered tonnage and grade of the diluting material at various stages in the mine life, as well as the Mineral Resource classification of both the recovered and diluting material that forms the Ore Reserve. The key principle of this paper is the tracking of the Mineral Resource classification in the flow model used to estimate the Ore Reserves. This is critical to defining the Ore Reserve as Proved or Probable and enabling transparency in the reporting process. An approach for dealing with mineralised external dilution in the Ore Reserve estimation process is also provided.This paper outlines the approach to convert Mineral Resources into Ore Reserves developed at the Ernest Henry mine sublevel cave (EHM SLC). The same method could be used in any cave mine and applied at any stage of the mine life. The process replaces broad-brush assumptions for the mining Modifying Factors, such as dilution and recovery, as these are determined numerically as part of the model computation. This paper explains the Ore Reserve estimation method with a worked example to enable the reader to adopt the process at any caving mine. Mineral Resource classification within the block model is embedded in the cave flow model and the flow model results used to attribute tonnes, grade and the mixed proportions of the Mineral Resource classification for material extracted from each drawpoint. This information is then used to convert planned mine production into the appropriate Ore Reserve classification. Since the flow model simulation follows the mine schedule, it can be used to predict depletion and cave stocks at any stage of the mine life, and can calculate a residual block model at the end of the mine life. The accuracy of the flow model is checked by validating the forecast ore grade and metal tonne with reconciliation data from the concentrator which is also used to calibrate the flow model.CITATION:Campbell, A D, 2017. A simple and accurate method for Ore Reserve estimation and Mineral Resource depletion in caving mines, in Proceedings 13th AusIMM Underground Operators’ Conference 2017, pp 253–260 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Oct 16, 2017

By Glenn E. Craig

The practical and effective pulp distributor here presented is believed to be of a completely new and innovative design. It was developed at the San Nicolas Plant of the Marcona Mining Company in Peru, where it has been thoroughly plant tested using iron ore slurries of a particularly abrasive nature. It has proven to be superior to the apparatus originally installed, or to any observed in operation elsewhere. In plant practice the capacity and efficiency of many process units such as screens, magnetic separators, and jigs are strongly affected by the loading pattern, and for better results the flow of pulp must be proportioned across the receiving lip in equal quantities per unit width. The distributors originally installed on the drum magnetic separators in San Nicolas proved to be unsatisfactory, and several trial modifications failed to show any improvement. As is usually the case, feed rates were being steadily increased, and appreciable losses to tailings resulted. A check of the distributors on the market discloses no reasonable substitute, so efforts were directed toward devising an entirely new type. Required was a positive type of action which would guarantee that the pulp flow be spread equally along the length of the drum. Discussion As indicated, the motivation for development was simple necessity. The plant in San Nicolas crushes, grinds, and concentrates magnetic iron ores of a particularly abrasive nature, and depends largely on magnetic separation to obtain a marketable product. Feed to the numerous drum magnetic cobbers and finishers varies from rod mill discharge at a nominal minus ten mesh to a ball mill fine grind of seventy percent minus three hundred and twenty-five mesh. Operational factors affecting the magnetic separators were well controlled,

Jan 1, 1971

By Bertrand Quiniou, Pierre Amadieu

Ion exchange technologies and processes are proven and established technologies widely used in numerous industries including hydrometallurgy for metal separation and recovery from metal bearing solutions. They have evolved through innovation which includes the development of countercurrent multistage (or multivessel) ion-exchange contactor systems with the benefit, for industrial operations, of greatly reduced footprints and ion-exchange media inventories, as compared to more traditional fixed bed contactor systems. Information on procedures for design and sizing of countercurrent multistage ion-exchange contactor systems is not readily available since it is most often proprietary know-how. The purpose of the present work is to develop a simple and innovative approach for the sizing and modeling of industrial countercurrent multistage ion-exchange contactor systems. The suggested approach builds upon published results and upon the following observation: in an industrial setting, knowledge of how component concentration or load on a contactor output streams vary with time t within a cycle duration (0 < t < T) is generally of little interest, only knowledge of time average of such concentration or load over a cycle duration T is sought for. The presented approach will be tested against current or past performances of industrial countercurrent multistage contactors of Orano Mining operations such as SNK‑3M moving packed bed contactors in Kazakhstan and NIMCIX fluidized bed contactors in Namibia.

Jan 1, 2020

By B Mack

The cost of water treatment is now more than ever a major consideration for maintaining an environmentally and economically sustainable mining operation. As an industry, we often have to consider water sources that are highly impure and difficult to treat. We are also discovering the value of our waste waters in this regard and using new and improved methods and technology to reclaim and reuse water. In many instances, the water or waste water to be treated is highly acidic and saturated in sparingly soluble salts. Conventional systems used to liberate this type of water typically involve high doses of lime with large volumes of waste sludge produced, and are comparatively complex to operate, to pretreat the water in order to reduce scaling tendency on the reverse osmosis stage. However, if the water is considered valuable for reuse, then why not avoid difficult and cumbersome pretreatment processes and treat the water at low pH to keep the sparingly soluble salts, metals and other dissolved species in solution. This paper describes a patented technology that uses and successfully proves this concept as a cost effective option for certain situations. Results from a treatability study on an Australian groundwater are discussed, along with an economic comparison to a conventional method and discussion on full-scale potential.

Jan 1, 2009

Using a cylindrical hydrocyclone with a long vortex finder as the separator, a batch sizer was developed for the fast comparative sizing of the coarse solids normally encountered in mineral pulps.Operating times as short as 2 or 3 min gave separations ranging from 16 mesh down to the subsieve sizes.Reproducibility was good and sensitivity was adequate for most applications.

Jan 1, 1968

By A. G. Doll

"Multi-stage crushing plants, including high pressure grinding roll (HPGR) circuits, require more materials handling equipment than SAG and ball mill circuits. A temptation exists to neglect the energy consumption of materials handling when doing desktop comparisons of HPGR versus SAG milling circuits because estimation of materials handling power requirements can demand significant general arrangement drafting that is not available when performing preliminary scoping or ""desktop"" studies.The largest component of materials handling power is consumed by conveyors when lifting material between stages of crushing, meaning that a simple potential energy model can be used to evaluate conveying specific power consumption. This potential energy consumption for conveying can then be factored to provide overall materials handling specific energy consumption suitable for desktop studies of HPGR and other multi-stage crushing circuits. The technique also permits different crushing circuit flowsheets to be evaluated, at a preliminary level, by simply counting the number of times a conveyor must ""lift"" ore from ground level up to a bin or other equipment mounted up high.INTRODUCTIONTrade-off studies of multi-stage crushing plants involving high pressure grinding rolls (HPGRs) versus semi-autogenous grinding (SAG) mill circuits typically focus on the operating cost savings of crushing plants versus the capital cost savings of SAG mill plants. Very high-level (or desktop) studies of this type do not include a great deal of engineering work, meaning that the details (and costs) of ancillary systems are often not captured when doing the comparisons. The more complicated nature of the multistage crushing plants means there are more ancillary systems than a SAG mill plant, risking a skewed analysis of the operating costs, benefiting the HPGR option.One of the ancillary systems that may be overlooked is the more complicated conveying systems inherent in multi-stage crushing plants. Due to the mass of material being handled in large mining operations, these conveyors become a significant portion of the operating costs. A simple way to estimate the specific energy consumption of conveying systems without requiring engineering drawings and a site layout would allow high-level studies to capture this operating cost."

Jan 1, 2015

By D. Kolymbas

A simple formula is introduced which allows the evaluation of dynamic pile tests. The following case is considered: The pile top is dynamically loaded by an impact. The velocity v of the pile top is recorded over the time. Let v1 and v2 be the first and the second maximum of this curve. Then, the pile bearing capacity (resulting from ideally plastic resistance at the pile wall and at the tip) can be set approximately equal to Z(v1- ½ v2), where Z is the impedance of the pile cross section. Due to the assumption of ideal plastic resistances, radiation damping needs not be taken into account. Material damping may be important in rate sensitive soils (such as clay, even if it is highly overconsolidated). A simple correction procedure for material damping is proposed.

Jan 1, 1989

By J. Rabe

Tasked with developing a flow sheet for a new resource, one typically turns the experts for help. The advice of an expert can be invaluable in reducing the time and costs associated with characterizing an ore (not to mention extracting maximum information from limited samples). While guiding and optimizing a metallurgical concept study requires a certain skill set, selling a project is something different. The metallurgical specialist is usually not responsible for sharing the results of investigations with potential investors. However, the person responsible for selling the project can ensure that a metallurgical concept study is conducted thoroughly and responsibly without having the ability to do the work, while being sufficiently familiar with the metallurgical aspects to authoritatively sell the project. The process of identifying suitable process routes through to constructing a concept flow sheet and mass balance is discussed as a basic example. From basic mineralogical information and a thorough literature survey, the most likely beneficiation routes can be identified and targeted testing conducted. The final top size will depend on the required product properties (mainly grade), the selected beneficiation technology, and the ore?s liberation properties. Once the required top size has been identified, comminution options can be evaluated. Once again, literature surveys can be used to supplement concept-level comminution property information, and select possible equipment and circuit configurations. Marketing, material handling, and logistics-related information can be used to determine required dewatering technologies. At this stage, enough information is available to develop a concept mass balance and conduct basic equipment sizing..

Jan 1, 2014

By Jason Clarke, André R. Laplante

"The gravity-recoverable gold (GRG) ore characterization test was developed 15 years ago and has been applied to hundreds of ore samples. The test accurately determines the size distribution of GRG, at which grind it is recoverable, and the extent of its liberation above 150 µm. This contribution shows how the test can be simplified, what are the likely problems to occur, and what information is then lost. Two simplified versions of the test are presented, of which the simplest, grinding a 20-kg sample to a P80 of 75 µm, is retained as the best one. A database of 18 comparative tests is presented. The choice of the full GRG test vs. the simple test is discussed, as is the deportment of the GRG recovered in the standard test but not in the simplest test.INTRODUCTIONThe GRG test was developed in 1990 to characterize the progressive liberation of gold in representative samples of ores, with the primary objective of generating data for a gold gravity recovery model (Woodcock and Laplante, 1993; Laplante et al., 2000). Characterization includes the size distribution of GRG as well as the grind size at which it becomes recoverable. This is achieved in a 3-stage protocol of liberation and recovery using a laboratory centrifuge unit, a Laboratory Knelson Concentrator 3 inches in diameter (KC MD3). This protocol is shown in Figure 1. The first stage takes place at a F100 of 850 ?m (F80 of ~550 ?m), the second at F80 of 180 ?m, and the third at a P80 of 75 ?m. The rationale for the three cycles is the desire to preserve the original size distribution of the gold grains in the ore and to obtain a recovery grind size curve. The feed is a representative sample of ore that can be extracted from ore samples (e.g. drill core reject) or stream products of the grinding circuit other than circulating loads or product having undergone hydraulic classification (e.g. rod mill discharge or SAG screen undersize). Ideally the samples should weigh between 60 and 100 kg, depending on feed grade and gold top size. It is beyond the scope of this paper to fully discuss measures of representativity in the ore sample, for example Gy’s minimum sample mass model (Gy, 1979). However, further work in this regard may be an opportunity. The large initial weight facilitates representativity and minimizes weight and sulphide recovery to the concentrate (since concentrate weight is relatively constant at ~100 g), which limits the recovery of gold in nonsulphide gangue or gold carriers (i.e. sulphides). Thus, the 100 g concentrate carries principally discrete gold species, such as electrum, and native gold. The concentrate and a 600-g representative sample of gangue of each stage are screened down to 20 ?m and each size class is fire assayed (the concentrates to extinction, the tails up to 30 g per size class). The five coarsest size fractions of stage-1 concentrate are individually upgraded using a hydrosizer and the concentrates examined with an optical microscope to assess the degree of liberation of the gold phase. Scanning electron microscope work has established that the GRG has an excellent degree of liberation below 150 ?m in stage 1 and generally a good degree of liberation in stages 2 and 3 (Guerney et al., 2003); as a result the size distribution of the GRG has been found to approach closely that of gold grains (Nesset et al. 2005)."

Jan 1, 2006

By Louis Moyd

In the preparation of illustrations to accompany reports of investigations concerning particle shapes of various natural and manufactured materials proposed for use as fine aggretates in concrete structures, it was found that stereoscopic views of such materials presented the information much more effectively than the usual two-dimensional photographs. With the whole-hearted cooperation of the Photographic Section, a technique was developed in the petrographic laboratory of the Concrete Research Division, U.S. Corps of Engineers, at Clinton, Miss., for simple and rapid preparation of paired stereoscopic photographs and micrographs. The method requires only equipment which is usually part of the general stock of any laboratory, and it is adaptable for all purposes in which three-dimensional views would be found superior to ordinary photographs.

Jan 1, 1949