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By R. Romano

Some topics, which difficult the effective use of RMR for dam foundations, are reviewed and a new geomechanics classification system, DMR (Dam Mass Rating), is proposed -as an adaptation of RMR- giving guidelines for several practical aspects in dam engineering and appraisal of dam foundation. On revise quelques problems qui ont fait difficile l’application du RMR pour les fondations des barrages. On propose un nouveau classification système, DMR (Dam Mass Rating)-comme un désarroi du RMR-qui donne recommendations pour quelques problèmes pratiques dans le projet et construction des barrages, et de ses fondations. Es werden einige die praxisgerechte Nutzung des RMR (Rock mass Rating) erschwerende Themen betrachtet und ein neues Geomechanisches Einteilungssystem, das DMR (Dam Mass Rating), eine Anpassung des RMR, vorgeschlagen. Daraus resultieren neue Richtlinien für verschiedene praktische Aspekte beim Dammbau und bei der Beurteilung von Dammunterbauten

Jan 1, 2003

By María Guadalupe Sánchez-Loredo

Silver from nitrate aqueous solutions was extracted by commercial organophosphorous extractants (tri-n-butylphosphate, Cyanex 471x, Cyanex 301 and Cyanex 302). Quantitative silver extraction was obtained using the Cyanex reagents. After loading, aqueous solutions of several reducing reagents were used to prepare fine silver powders by reductive stripping. Only both extractants Cyanex 471x and tri-n-butylphosphate (TBP) could be reductive stripped and regenerated by aqueous solutions of ascorbic acid, and Cyanex 471x was decomposed to the corresponding phosphine oxide by using sodium borohydride as reducing agent. Silver was recovered as fine particles, which were characterised by means of scanning electron microscopy (SEM). Micrographs showed that the powder size and morphology were directly affected by the composition of the applied organic phases and aqueous reducing media.

Jan 1, 2003

By V. A. Luganav

The behavior of arsenopyrite under heating has been studied by many scientists. It has been already established that under heating at more than 650°c and without air access the arsenopyrite dissociates with the formation of one atom arsenic. Under vacuum the dissociation process begins at 5500C with the formation of elemental arsenic. The residue of dissociation process contains pyrrhotite and throilite. In the presence of pyrite, arsenopyrite dissociates under lower temperature and with a higher velocity than without it. The industrial realization of fool scale processing of arsenic bearing raw materials is possible only by the use of standard equipment and oxygen containing blast. In this view the paper presents the results of the study on the effect of oxygen in the gaseous phase and its addition into the charge of pyrite in the process of arsenopyrite decomposition. Thermodynamic analyses showed that under thermal processing of arsenopyrite in the presence of pyrite and limited quantities of oxygen in the gaseous phase the formation of arsenic sulfides is possible according to the following reactions:

Jan 1, 2003

By R. Hope, C. van Heerden

In any process or organization inefficiencies are costly. In times of abundance this reality often does not receive much attention. During such times the focus is rather on increasing capacity to increase production. However, there is a growing awareness in the world of tougher economic, social as well as environmental conditions, and enterprises find themselves facing greater demands for accountability towards shareholders, the environment and the public, as well as growing competition for market share and limited global resources. This reality is no different in ensuring a sustainable mineral sands operation. In order to achieve this, any operation needs to be stripped of all process as well as operational inefficiencies. In this context it has become essential for any Mineral Separation Plant (MSP) to have the necessary process monitoring and control systems in place to continually monitor and optimize the production of on-spec products and maximize operational efficiency and consistency. The MSP Grade Control Solution developed by Crusader Systems and running on top of the CSense platform contributes towards these goals by improving the consistent production of on-grade product. This allows the process to operate closer to the maximum allowable product grade constraint, which in turn maximizes production.

Jan 1, 2003

By Paul Downing

Anyone in business today knows how difficult and time consuming it is to keep abreast of new and revised federal regulations. Those in the explosives industry know that such a task can be next to impossible as the regulatory environment faced by those in the hazardous materials community continues to undergo a major overhaul following the events of September 11th, 2001. This paper will attempt to clarify today’s regulatory picture by identifying some of the regulatory “hotspots” and “pitfalls” that affect individuals and companies involved in the sale, transportation, distribution and use of explosives.

Jan 1, 2003

By Heinrich Hutchison, Thomas von Moltke, Roelof F. Sandenbergh, Katarina P. Cerovic

Although the cyanidation process for gold leaching has been applied for more than a hundred years, some aspects of it, such as the passivation of the gold and the depassivating action of heavy metals, are still not well understood. In this work the anodic behaviour and surface composition of gold in alkaline aqueous cyanide with lead additions were investigated using polarization experiments and XPS. It was found that lead in the solution activated the gold at low concentrations, somewhat more positive than the reversible potential for gold, but that the activity again decreased at higher concentrations of lead. The potential range for the activation of the gold coincides with that where underpotential deposition of lead occurs, i.e. –200 to –600 mV(SCE), as indicated by the surface composition of the gold, shown in figure 1. Note that the concentration of lead on the surface of the gold only increased with time in the bulk plating potential range for lead, where gold is not activated by the presence of lead. It is also shown that up to 20 mg/L of lead added to the solution will activate the gold, provided that bulk plating of the lead is avoided. It is also important to avoid reducing conditions during leaching, where bulk plating of lead may occur, if the gold is to be activated by lead to achieve a high leaching rate, as the bulk plated lead screens the surface rather than activating it.

Jan 1, 2003

By M. Ghiani, P. Massacci, A. Manni, R. Peretti, Center for Mining and Mineralurgical Studies, S. Serranti

"The research study has been devoted to point out the better way to process a colemanite concentrate characterised by a high content of two kind of As sulphides (realgar and orpiment) finely disseminated in the matrix of the boron mineral.Scanning Electron Microscopy analyses have been carried out to determine all the mineralogical constituents and to evaluate their distribution, frequency and mutual relationships.There is a not neglectable part of realgar highly disseminated into the colemanite crystals.The orpiment recurs in small acicular crystals of 20÷30 µm in length and 5 µm in width, very difficult to liberate from the colemanite mineral particles.The colemanite concentrate, in fact, has been addressed to a chemical plant which products were boric acid and gypsum, the contaminated by As. It was unacceptable for further applications and very dangerous if rejected in the environment.Grinding tests under dry and wet conditions have been carried out in order to evaluate the liberation modality of the As sulphide minerals from the colemanite.Some difficulties have been overtaken in order to obtain a selective liberation of the As sulphides from the colemanite even if a certain decreasing in As grade in the higher size classes has been registered.All the comminution products have been analysed by SEM monitoring the liberation degree of the mineralogical constituents.Flotation tests have been carried out after different comminution flow sheet adopting different modulating conditions in order to evaluate the influence of the following parameters:• collector concentration versus contaminants concentration (As minerals) in the froths;• kind and quantity of the frothing agent to maximise the mineral recovery in the froths;• kind and quantity of the modulating agents to maximise the selectivity of the process;• conditioning modalities in order to obtain a suitable dispersion of fines and to avoid segregation of Asbearingparticles together with colemanite ones;• solid/liquid ratio of the pulp to minimise the water flow into the plant."

Jan 1, 2003

By Ragnhild Aune

In fire refining of copper, the affinities of various impurity elements on dissolved oxygen is of great significance. Further, in the design of oxygen probes in liquid copper, the influence of solute interactions on the activity of oxygen need to be considered in order to evaluate the oxygen concentration in molten copper. The present paper presents a series of measurements of the activities of oxygen in liquid Cu-M-o alloys (where M stands for Mn, Zn, As, Se or Te) carned out by the present group employing the solid electrolyte galvanic cell technique. Extreme care was taken to control the oxygen potentials in the inert gas atmosphere, and to keep the oxygen levels very low in the molten metal. The oxygen content was determined by analysis of the samples taken out from the melt. The results obtained showed that Mn has a strong negative influence on the activity coefficient of oxygen in liquid copper. A similar, but less prominent effect was observed in the case of Zn. Arsenic had no influence on the activity of oxygen in Cu (liq.). Se and Te had slight negative effect on oxygen activities in copper at XQ >10-5, while at lower oxygen levels the interaction coefficients were found to be positive. The results obtained were compared with empirical models for the calculation of interaction coefficients available in literature.

Jan 1, 2003

By A. D. Davis, C. J. Webb

Brohm Mining Co.'s Gilt Edge Mine in the northern Black Hills was a surface heap-leach operation that was active from the 1980s until 1999. Financing problems and acid drainage concerns at the mine were reported in the late 1990s. In February 1999 the Governor of South Dakota announced plans to request the US Environmental Protection Agency to help clean up acidic water at the mine and reclaim the site. In July 1999 the parent company of Brohm, Dakota Mining, filed for bankruptcy in Canada. Because of the bankruptcy and environmental problems, the State of South Dakota intervened and began water treatment. The mine was declared a Superfund site in 2000. Hydrologic issues include the potential for acidic drainage from the site. The mine is at the headwaters of Strawberry Creek, which drains into Bear Butte Creek. About four miles downstream, Bear Butte Creek loses its discharge to swallow holes in the karstic Madison Limestone aquifer, a regionally extensive and valuable groundwater reservoir. Other concerns at the site include treatment of acidic water in mine pits and a waste rock dump.

Jan 1, 2003

Slake durability of rocks is an important property of rock-mass and rock-materials in geotechnical practice. The slake durability of rocks is closely related to their mechanical properties. In this paper, mechanical properties and slake durability tests for weak and clay-bearing rocks from Beypazari Trona Bed in Ankara, were performed in order to assess the slake durability and mechanical properties (especially rock strength) of these rocks as well as to understand the relationship between mechanical properties and slake durability. In performing this relationship, statistical based correlation has been applied.

Jan 1, 2003

Simulator technology has advanced to the point where the cost of mining equipment simulators is beginning to make commercial sense. Simulator-based evaluation allows operators or potential employees to be assessed in a pseudo-real environment under surface and underground mining conditions. Simulator training also allows operators to be exposed to emergency and advanced situations such as brake or steering failure or a tireblowout. ThoroughTec, of South Africa, provides simulator equipment to the mining industry. The company’s various packages of simulator products provide an unbiased evaluation score that removes human error from the assessment process. This same evaluation score is also presented at the end of normal training or refresher training sessions. In this way, the simulator helps eliminate bad habits and improve efficiencies.

Jan 1, 2003

By A. I. A. Salama

The CANMET Western Research Centre (CWRC) has developed a hydrocyclone model simulation of dewatering and fine particle separation circuits. The simulation is based on an existing empirical model. Utilizing a cyclone manufacturer’s published data, some modifications have been developed and integrated into the model. Feed stream characteristics, cyclone mechanical dimensions, and operating conditions are used in the CWRC modelling simulation. The computer results are presented in 3D graphs and corresponding 2D maps showing the cyclone mass recovery, percent solids by mass in underflow and overflow, and cut size as functions of the cyclone apex diameter and cyclone throughput (i.e., inlet pressure or pressure drop). Results of the computer simulation have been used in the economic feasibility and design of several dewatering circuits in oil sand plants.

Jan 1, 2003

By Osvaldo A. Bascur, J. Pat Kennedy

"The profitability of mining and metallurgical operations continues to lag behind that of other industries despite the technical advances that have occurred in recent years. A primary reason for poor performing in this economic sector is the lack of integration of mining and metallurgical information. The mine cut-off grade can be optimized if mining and metallurgical engineers have the data to optimize milling for the type of ore in hand.Integration of mine transactions, stockpile inventories, process flows and assays is the key to determining the economics for each blast strategy in a mining site. Real-time information from manufacturing assets greatly affects the profitability and flexibility of a company, but gross errors from faulty sensors, inaccurate instrument calibration, or incorrect process models may corrupt actionable information. New software tools can model the process, sift through available data to identify and eliminate gross errors, and use statistical data reconciliation to create materially balanced and consistent readings. The reconciled data is unified for use by both monitoring and decision making processes.Creating a real-time information environment where upgrade and change are allowed is becoming an accepted methodology to accelerate and simplify the integration of applications such as production monitoring, equipment performance management and yield and inventory management.This paper describes the data integration requirements in a mine, concentrator and port for unification of the redundant data. The capture of the mining events, stock pile management and the metallurgical information is the base requirements for a dynamic environment to reduce the overwhelming amount of information to unified set of information. Part of any decision support program should entail these results to continuously improve the measurement system to address the costs in mine and milling the ore."

Jan 1, 2003

By R. Ribacchi, P. Tommasi, C. Consorti, P. Campedel

The runout of dry blocky rock avalanches produced by planar rockslides affecting a limestone formation with clayey interbeds is analysed by means of distinct element modelling. Numerical analyses are validated by means of the back analysis of a historical rockslide occurred in the investigated area and physical aspects of the phenomenon evidenced by modelling are discussed. On analyse par la méthode aux élements distincts la distance de parcours des avalanches rocheuses sèches produites par des glissements plan interessant une formation de calcaire à intercalaires argilleux. Les analyses numeriques sont validées à l’aide de la back-analysis d’un glissement historique survenue dans le site en examen. On décrit les aspects physiques su phénomène mis en évidence par la modélisation efféctuée. In diesem Beitrag wird die Reichweite von Steinlawinen besthend aus trockenem blockhaftem Fels mittels der Distinct Element Methode untersucht. Die Steinlawinen werden erzeugt von Rutschungen in einer Kalkstein-Formation mit tonhaltige Schichten betreffen. Die numerischen Berechnungen wurden anhand einer Simulation einer historischen Bergsturzen verifiziert, der sich auf den untersuchten Gebiet ereignete. Auf der Basis der erhaltenen Ergebnisse wurden die physikalischen Aspekte der untersuchten Steinlawinen analysiert.

Jan 1, 2003

By A. W. Stradling, M. J. Fairweather

"The selective flotation of lead, zinc and iron sulphide minerals is key to the economic performance of concentrators treating zinc-lead ores. Diagnostic metallurgy is a tool to quantify mineral behaviour as a function of particle size and liberation. The result of such analysis may be used to select preferred strategies to improve metallurgical performance. The zinc flotation circuits at three Teck Cominco operations: Sullivan, Polaris and Red Dog are compared here. This paper analyses operating data from each of these circuits. The effects of mineralogy and performance by particle size are emphasized. Metallurgical performance at these three concentrators varies substantially. Liberation size is the major factor in determining metallurgical performance. Complex mineralogy requires a fine grind to achieve effective liberation. Fine grinding results in offsetting decreases in concentrate grade through entrainment. The economic treatment of complex fine-grained deposits requires optimisation of regrind size for liberation without unduly compromising concentrate grade through gangue entrainment.INTRODUCTIONUntil recently Teck Cominco Metals Ltd. operated three mines treating zinc-lead ore. In order of increasing mineralogical complexity they are: the Polaris Mine on Little Cornwallis Island in Nunavut in the eastern Arctic, the Sullivan Mine in southeastern British Columbia and the Red Dog Mine in northwestern Alaska. Both the Polaris and Sullivan Mines have recently ceased to operate due to depletion of ore reserves.The ore type and associated gangue, mineralogy and iron solid solution vary significantly between these deposits. Table 1 summarizes some of the important differences"

Jan 1, 2003

By Anders Salwén

In 1975 T. Nishizawa and A. Chiba reported on observed deviations from the ferrite-austenite local equilibrium in several diffusion couples based on the Fe-Cr system. In order to try to verify these results the austenite-to-ferrite transfonnation in a Fe-20 %Cr-Invalid Code [Fe-]-%Cr diffusion couple held at 1100 for 100 hours has been simulated. The simulation model is based on the postulated principle of maximum dissipation rate of Gibbs energy during transformation, which allows non-equilibrium interface conditions. Keynotes: Computer Simulation, Austenite-to-Ferrite Transfonnation, Diffusion Couple

Jan 1, 2003

By J N. Moncrieff

The resource estimation process for the underground Mount Isa Copper Mine has undergone significant change. Block models are now created using a commercial software package as opposed to the in-house software that was previously used. With mineralisation occurring over a strike length of more than 4 km, Mineral Resources for all categories totalled 190 Mt at 2.7 per cent Cu at 31 December 2002. Estimation is by ordinary kriging with two separate models generated to cover the X41 and Enterprise orebodies respectively. The underlying Upper Basement Contact and the silica-dolomite alteration envelope are both used as hard boundaries to constrain the modelling. From a validated block model, grade shells are generated at the appropriate cut-off grade for a given area. The grade shells are depleted for mined voids and subdivided into 30 metre strike length blocks. Application of a SMU criteria and crown and pillar constraints results in failed blocks being culled from the resource inventory. Mineral Resource blocks are further subdivided into resource categories (Measured, Indicated, Inferred) by the Competent Person on the basis of geological confidence, taking account of geological and grade continuity, drillhole spacing and structural complexity (JORC, 1999). A geostatistical æconfidenceÆ category is incorporated into the block model as an additional tool for the categorisation process. The shapes are assessed in concert with a mining engineer to determine whether a reasonable expectation of mining potential exists and if not they are removed from the resource. The final categorised blocks constitute the Mineral Resource inventory and form the basis for conversion to Ore Reserves. The resultant Mineral Resources and Ore Reserves are reported on an æinclusive ofÆ basis.

Jan 1, 2003

By Gift Makusha

The Witbank Coalfield in South Africa contains up to five economically viable coal seams. These seams have been mined continuously for over 100 years and the reserve in now becoming depleted. The normal mining method has been bord and pillar with examples of stooping. The situation now occurs where the formed pillars, left to maintain stability, have a higher quality than the coal that is left in the unmined reserves. Where the reserves are less than 70m deep and continuous over several kilometers, opencast mining is being successfully applied. After several years of investigation, Anglo Coal has identified blocks of coal that warrant investigation with regard to pillar extraction by underground methods The proposed method is pillar extraction using Mobile Roof Supports (MRS) It is proposed to mine three panels at a depth of 120m, by keeping the panels narrow and sub-critical. The sub-critical layout does not allow caving to surface and more stress is thrown onto the barrier pillar rather than the face pillars. The sub-critical span is anticipated to be 100m. The paper describes the full geotechnical investigation, including numerical modelling, instrumentation and drawing on the local South African experience of shortwall mining. The project will be unique in that pillars were not designed for pillar extraction and have low factors of safety (l.4 - 1.8) and width to height ratios of less than 4. The mining height will be approximately 4-4 5m, and this represents "new" operating heights for Mining Roof Supports. The required equipment was ordered in late 2002 and pillar extraction is anticipated to begin in June 2003.

Jan 1, 2003

By P. G. Gresse

The Orange-Vaal River system is known to be the primary secondary source for alluvial diamond deposits in the northern Cape and along the west coast of Namaqualand. The higher order sources for diamonds contained within this system are still not defined entirely to satisfaction, but certainly include kimberlite pipes exposed in the catchment regions of these rivers. The focus of alluvial diamond mining along the Orange-Vaal system recently changed from the traditional areas in the upper catchment regions?the Barkly West, Christiana, Bloemhof, Wolmaranstad, Schweizer-Reineke region, and the lower regions near the mouth of the Orange River at Baken, Alexander Bay and Oranjemund, to the area between Douglas and Prieska?the so-called mid-Orange region (Figure 1).

Jan 1, 2003

Experimental results are presented that test the hypothesis that the descaling behaviour of stainless steel slabs following reheating is controlled by interfacial roughening at the scale-steel interface. In this investigation, two stainless steels were considered: type 304 (austenitic, with 18% Cr and 8% Ni) and type 412 (ferritic/martensitic, with 11.6% Cr). It was found that the entanglement that arises at the scale-steel interface was in fact effective in maintaining scale-steel adhesion, under the mechanical descaling conditions used. In the case of type 304, descaling proceeded by fracture along chromite layers, which formed (by internal oxidation) on the austenite grain boundaries; for this steel, the extent of descaling depends most strongly on austenite grain structure, and not primarily on the conditions in the reheating furnace. In contrast, type 412 samples descaled only at the edge of the entangled zone, and showed a greater sensitivity to the reheating conditions; specifically, higher free oxygen in the reheating gas and longer reheating times were found to increase the residual scale thickness. Key words: stainless steel, reheating, scale, entanglement, descaling, fayalite, internal oxidation, grain structure, free oxygen.

Jan 1, 2003