Search Documents

All large open pits in Australia have been mined, or are planned to be mined well below the local water table. This raises several issues that impact on mine safety, mining costs and regulatory approvals. Some pits will be æwetÆ, where they are mined through permeable horizons and where there will be measurable groundwater inflows. These will require some form of dewatering. There may also be some difficulties in the disposal of excess water. Other pits, may be ædryÆ, where they are mined through impermeable material and there are no measurable groundwater inflows but where there are stability issues related to hydrostatic pressures within the pit walls. These may require some form of depressurisation. Some pits are a combination of both. Effective management of groundwater inflows and groundwater related stability issues and the development of cost effective and environmentally acceptable dewatering and depressurisation systems requires an understanding of site specific hydrogeological conditions and practical experience in what works best for different conditions. The presentation will include an outline of the key hydrogeological factors that impact on large pits, practical methodologies for achieving dewatering/ depressurisation, and some case studies from the Goldfields, Pilbara and North Queensland.

Jan 1, 2003

By Del Brock, Dan Wooton

The design/build of two adjacent vertical mine shafts in difficult ground conditions at a mining complex in the midwestern United States required innovative construction techniques. Construction of the 267-m-deep Service Shaft required full depth dewatering wells and ground freezing. Blind drilling was utilized to excavate the 257-m-deep Production Shaft and it was finished with a steel/concrete composite liner that was floated into place. An equally unique component of the installation included supplying a high capacity vertical conveyor system, featuring a 273-m-lift. Other components of the project include the mine level development, as well as the design and installation of three hoisting systems, including a 45-ton capacity men/materials hoisting system.

Jan 1, 2003

"Adopted in 2003, theses guidelines are intended to assist the Qualified Person(s) in the planning, supervision, preparation and reporting of mineral resources and mineral reserve estimates. The report is divided into two broad sections “General Guidelines” appropriate for most metals and “Guidelines Specific to Particular Commodities” for potash, industrial minerals, uranium and coal. “These guidelines are reference in the Companion Policy of NI 43-101 with a statement that a qualified person classifying a mineral deposit as a mineral resource or mineral reserve should follow them.”Executive SummaryThe following is a summary, in table format, of the main elements of the Estimation Best Practice Committee's report ""Estimation of Mineral Resource and Mineral Reserve Best Practice Guidelines"". While the summary table is provided for convenience, the Committee recommends that the report be read in its entirety and the table summary not be used as a stand alone document. These guidelines are not intended to be either prescriptive or exhaustive. They do not preclude innovation. Preamble: These guidelines have been prepared by the Canadian Institute of Mining and Metallurgy and Petroleum (CIM) led Estimation Best Practices Committee. They are intended to assist the Qualified Person(s) (QP) in the planning, supervision, preparation and reporting of Mineral Resource and Mineral Reserve (MRMR) estimates. All MRMR estimation work from which public reporting will ensue must be designed and carried out under the direction of a QP in accordance with National Instrument 43-101 (NI 43-101) and related forms. A QP is defined in NI 43-101 as ""an individual who is an engineer or geoscientist with at least five (5) years of experience in mineral exploration, mine development, mine operation, project assessment or any combination of these; has experience relevant to the subject matter of the mineral project and technical report; and is a member in good standing of a professional association"". Disclosure of MRMR estimates is to be made in accordance with industry standard definitions approved by the CIM (the CIM Standards adopted by the CIM Council in August 2002) which have been incorporated by reference into NI 43-101."

Jan 1, 2003

By F D. I Hodgson

Twenty-seven observation test pits were excavated at four different spoils dumps at three collieries in the Witbank Coalfield. The holes were dug into the upper three metres of the spoils to ascertain if any weathering profiles, variation with age or influence of topsoil covering could be gauged. Samples from these holes were also subjected to laboratory testing (ABA, humidity cells and mineralogy on several selected samples). The test pits showed that there was a good correlation between in situ paste pH-values and ABA results for samples taken from the pits. At all the collieries, no correlation between age of spoils and in situ acidity could conclusively be drawn. The depth of soil cover also appears to be a minor consideration in determining the eventual acidity of the spoil. In the pits where acidity was found, the weathering was evident when contrasted to areas still buffered. It is unclear if the weathering leads to the acidity or vice versa, as the soil covering appeared to be similar. The spoils proved to be extremely variable with regard to particle size and material on a micro and macro scale. Evidence from most of the holes suggested that there was enough water contained in the fine material in the spoils to support the initiation of acid generation. Conclusions from this investigation are that the mineralogy of the spoils is the most important factor in determining the eventual occurrence of acidic hotspots, and that prior characterisation and selective handling will provide the best management practice for these spoils.

Jan 1, 2003

By David Corkum, David Hatem

Subsurface construction projects are risky ventures and the decision to deliver a project using the Design-Build model does not eliminate those risks. Differing site conditions, inadequate design, and delays will continue to plague some projects. The Design-Build procurement model, however, presents a broad opportunity to allocate those risks much differently than in the familiar Design-Bid-Build model. Starting with a philosophical approach to risk and reward, this paper discusses the continuum of possible risk allocation strategies. It concludes with a proposed optimum strategy in terms of the project’s overall economic efficiency, and points to the dispositive contractual provisions that serve to contour the risks.

Jan 1, 2003

By Bruce Hebblewhite

An ACARP-funded industry research project in Australia recently investigated the problem of premature rock bolt failures in underground coal mines. The project carried out limited sampling from 9 different collieries in NSW and Queensland, followed by a more comprehensive, controlled sampling from one colliery. Over 50 broken bolts were collected and subjected to metallurgical analysis at UNSW to determine both the steel composition and to analyse the fracture surfaces. Prior to this study, there had been anecdotal evidence of similar bolt failures from a number of sites within the industry. The sampling and analysis conducted by this project - whilst being below a statistically representative sample of the entire industry bolt population - highlighted the fact that bolt failures were continuing to occur at a number of sites, in both older and recently installed bolts. The failures were almost entirely attributable to stress corrosion cracking (SCC). It appears that a combination of factors - including steel composition, bolt manufacturing process, loading environment, geological and hydrological environment, bacterial corrosion - can all contribute to this problem. There is no simple solution, however, as with similar research findings from the UK, it appears that steels with higher values of fracture toughness, or Charpy Index, are less susceptible to SCC. Testing to date has been limited to bolt failures below the resin encapsulation horizon. A real concern is the potential extent of the problem at higher horizons, within the encapsulation. These may require some form of non-destructive testing (NDT) for detection. Initial trials in Australia of the ultrasonic device developed by DMT in Germany have proved encouraging. Further testing using this device is anticipated in future research. This paper describes the outcomes of the project, completed in 2002.

Jan 1, 2003

By Brajendra Mishra

Molten Salt electrolytic processes offer unique opportunities to extract and refine metals where gaseous or metallothemlic reduction, hydrometallurgical extraction and aqueous electrolytic methods are thermodynamically constrained. Production of aluminum and magnesium by molten salt electrolysis are well known commercial processes. Several other reactive metals, such as lanthanides and actinides, as well as beryllium and calcium, make use of molten salt processing for extraction and refining. This presentation describes the science of molten salt chemistry and electrochemistry for winning and refining of several metals. In addition, recovery of metals from waste process salts by molten salt reduction as well as oxidation have been discussed. Material issues in design of molten salt reactors have been included. Various applications have been presented through case studies. Experimental data have been included to justify the suitability as well as limitations of these specific processes.

Jan 1, 2003

By H Plewes, A Bur, L Murray, J Pottie

Water recovery from tailings for reuse in mineral processing is essential to operation of mines in the Atacama Desert of Chile. With annual rainfall of 5 mm, the prudent and efficient use of available water resources is a major issue for the Escondida Mine and other mines in the area. The Escondida Mine is located at an altitude of 3100 m, in a very arid, seismically active part of the Atacama Desert of northern Chile. The site is located about 170 km from the coastal city of Antofagasta. From 1994 to 2002, tailings were discharged into the Hamburgo Tailings Facility, which comprises a series of æpaddiesÆ located near the open pit and mill. Because water in the region is only obtainable from groundwater sources, the paddy system incorporated a number of design features with the aim to maximise water recovery from the tailings. As part of the recent mill expansion to 237 500 metric tonnes per day, a new tailings facility, the Laguna Seca Tailings Facility, projected to be one of the largest tailings facilities in the world, was commissioned in 2002. Extensive studies were conducted for the design of the new facility to predict water recovery from the conventional wet disposal of tailings. The predictions were calibrated against the performance of the Hamburgo Tailings Facility and subsequently re-calibrated against actual performance during the first year of operation at the Laguna Seca Tailings Facility. Initial operation of the Laguna Seca Facility was marked by a coincidental change in tailings characteristics from design, which highlighted the need for thoroughly understanding tailings behaviour during deposition, and the parameters and deposition techniques that could enhance water recovery. Systems have been put in place to manage the tailings deposition and respond to changes in key parameters such that water recovery targets can be reliably achieved. This paper describes the background studies that were conducted to evaluate evaporation and tailings behaviour, summarises the water balance and then presents some observations from the commissioning and start-up of the facility.

Jan 1, 2003

By M Wen, J Gerit, C A. Pelletier, D Muggli

On-land waste rock dumps at BHP Billiton Base MetalsÆ Island Copper Mine (ICM) near the northern end of Vancouver Island, B.C. continue to discharge ARD. These waters, which amount to approximately five million cubic metres each year, are injected into a three-layer, meromictic pit lake for treatment. The top layer is brackish water, replenished by each yearÆs rainfall (amounting to nearly 2 m/year). This top layer of water must meet effluent permit limits for heavy metals. This water eventually exfiltrates through a æbeachÆ waste rock dump, which is 93 per cent submerged along the north shore of Rupert Inlet. The middle and bottom layers of the Pit Lake are saline and currently oxic (2 mg/L dissolved oxygen) and anoxic (0.03 mg/L dissolved oxygen), respectively. Spreading of a liquid fertilizer every ten days throughout the top layer results in plankton and bacterial blooms that scavenge zinc, copper and cadmium out of this layer eventually to become mineral sediment in the bottom of the pit lake. Adsorption on planktonic skeletons and mineral precipitates also scavenges these dissolved metals from the middle and bottom layers to form bottom sediment. Sulfate reduction has recently begun in the bottom sediments. Diagenetic processes in the bottom sediments will eventually transform most of the dissolved heavy metals into insoluble sulfides. Cycling of ferric iron between the sediment and the water column and back seems to contribute dramatically to the biogeochemical metal removal processes. This biogeochemical system serves to maintain the top-layer water well within permit limits for discharge to the environment.

Jan 1, 2003

By R L. Verburg, R Johnstone

DeBeers Canada Mining Inc (DeBeers) recently submitted an Environmental Assessment (EA) for its proposed Snap Lake Diamond Mine located in Northwest Territories, Canada. As part of the EA process, a site water quality management plan must be developed. Plan development requires an integrated approach such that the key factors influencing water quality can be identified and managed to minimise potential impact. A system model was therefore developed to simulate the site-wide water quality conditions and mass loadings to the principal environmental receptor of concern, Snap Lake, during operations and post-closure. Requirements of the simulation included integrating hydrology, geochemistry, hydrogeology and site management practices in a dynamic way. A unique feature of the site was the need to accommodate a complex flow system that included a feedback loop between lake water and mine water. A system model was constructed using the GoldSim software package that integrated on-site water quality and flow measurements, as well as results from independent groundwater flow and geochemical modelling efforts. The GoldSim model simulated concurrently the movement of 39 solutes through the subsurface mine and surface facilities. Solute sources considered included four different waste rock and tailings types, explosives use in the mine, treatment plant discharge, and recycled process water for dust suppression. Separate solubility constraints were identified for different regions of the flow system (eg underground mine; treatment facility; surface water bodies). Kinetic test data were used to derive temperature-dependent rate constants for use in calculating mass inputs from surface sources such as waste rock piles. The model generated water quality estimates over time for a variety of management scenarios at several potential discharge locations. The integrated approach used by the model was effective in identifying the significance of key factors influencing overall water quality such as explosives use, mine water inflow rates, waste rock reaction rates, site/mine management options, and effectiveness of treatment. The model provides an example of an effective tool for comprehensive, integrated system evaluation and management.

Jan 1, 2003

By Michael Karmis

The International Conference on Sustainable Development Indicators in the Mineral Industries(SDIMI 2003) was held May 21-23, 2003 on the island of Milos, Greece. The objective of this international conference was to assist the mining and minerals industries in their global transition to sustainable development. The main theme of the conference was the development, monitoring and assessment of sustainable development criteria for mineral operations. Emerging technologies were also presented that can assist in the development of criteria and performance indicators.

Jan 1, 2003

By Gordon T. Clark, Stephen H. Gleaton

This paper discusses the conceptual design of cut-and-cover tunnels currently being considered as one of the replacement options for the earthquake damaged, elevated double-deck highway and seawall built in downtown Seattle 50 years ago. The 4.8 km (3 mile) long, 6-lane improvement consists of 1.6 km (1 mile) of at-grade roadway with aerial interchanges, 1.6 km (1 mile) of large two-level cut-and-cover tunnels along the Elliott Bay waterfront, and retrofit of the 50-year old, 1.6 km (1 mile)long Battery Street tunnel and north transition to grade. Construction of deep cut-and-cover tunnels, in complex glacial geology overlain by hydraulically placed fill immediately adjacent the existing sea wall, will require extensive use of concrete diaphragm walls, ground improvement and dewatering. The potential liquefaction and lateral spreading of the fill materials in this active seismic region pose significant design challenges and risk.

Jan 1, 2003

By Manuel Arnáiz, Pedro R. Sola, Rogelio Baudot, Manuel Herrera, Carlos S. Oteo

The aim of this paper is to describe and analyze the ground treatment performed between January and May 2002 in order to increase safety during excavation and reduce instability problems along 180 m of tunnel, during the construction works associated with line 10 extension to the Madrid Metro. The tunnel was excavated using the traditional Madrid Method and in the section considered in this paper layers of sand were detected around the tunnel crown area with a significant presence of water, the in?ow of which needed to be controlled with a minimum impact on the surrounding environment.

Jan 1, 2003

By S. N. Groudev

Intensive uranium mining activities at the Curilo deposit in Bulgaria has caused widespread contamination over a wide area. A number of receptors including soils and watercourses as well as the ecosystems in the area have been severely affected. Even today, 10 years after the cease of activities, acidic waters generated from the abandoned mining works, the low-grade ore and waste dumps contaminate soil, surface- and groundwater. The present paper describes in general the environmental status of the wider Curilo area and examines the potential of preventive and remedial measures that can be applied in situ to rehabilitate the site and restore the ecosystem. The main rehabilitation technologies examined include modification of the acid generation potential of the pollution sources, treatment of the acidic drainage by means of a natural wetland and in situ bioremediation the of contaminated soils. Finally, a number of efficient indicators are proposed so that the rehabilitation potential at Curilo and similar heavily contaminated sites is assessed.

Jan 1, 2003

By Keith Heasley

An eastern longwall mine was required to mine through a set of three entries located midway down the length of a panel. Of course, the mine desired to design a successful support system for the mine-through area at the least cost. To further complicate the design process, the mine-through entries were located directly under the end of a previously mined, overlying longwall panel and the entries were close enough to be subject to stress interactions from the overlying seam. In order to accurately evaluate the multiple-seam stresses and modify the mine-through support system appropriately, the boundary element program LaModel was used to model the stress and displacements in the two mines. Using the results of the model's stress analysis, the support density was systematically varied throughout the mine- through entries for optimum sup@ efficiency and economics. During the actual mining of the cross panel entries, the longwall experienced few, if any, additional delays, and overall, the support and mine through of the cross-panel en- tries at Harris #1 was very successful, saving the mine confineable time and money.

Jan 1, 2003

By Charlie Yates, Max Ramey, Kurt Nielsen, Michael Hardy

The Yankee Gulch sodium minerals project (YGP) is a solution mining project operated by American Soda. The mine operates on a federal lease administered by the U.S. Bureau of Land Management (BLM). Commercial operations began in November2000. In 1964, Irv Nielsen discovered nahcolite mineralization where the YGP pilot plant is now located near the Piceance Creek in Rio Blanco County, Colorado (Nielsen, 1969).Development of the project accelerated after Williams Corp., of Tulsa, OK, joined with American Alkali in1996 to form American Soda. Pilot testing by American Soda led to commercial permitting, plant design, construction and startup. Figure 1 shows the location of the Yankee Gulch leases and the location of the upper and lower plant sites.

Jan 1, 2003

By Florian Kongoli

The production of a homogeneous self-fluxing sinter is an important step in iron making processes. A good sinler should have good permeability and reducibility and has to keep those characteristics for a certain time. An early melt down of the sinter in the blast furnace, where its solid state reduction is essential, would cause many problems such as low permeability and reductibility. Nevertheless, the important factors that influence these characteristics, such as the chemistry of the sinter and the fluxing effect during sintering and sinter reduction conditions have not yet been clarified, In today's new reality where many new minor components such as Al2O3 and MgO enter to the sinter through raw materials, the quantification of the fluxing effects during sintering becomes even more important. In this work, the liquidus surface and phase relations of the sinter primary melts in the CaO-FeO-Fe203-Si02 system at sintering conditions have been quantified. The fluxing effect of oxygen potential, Al2O3 and MgO has also been quantified by the means of some practical diagrams that can directly help the optimization of the sintering processes.

Jan 1, 2003

By A. K. Singh, R. Singh, P. K. Mandal

On the basis of in situ study of pillar loading at different sites, an attempt is made in this paper to visualize the development of mining induced stress under varying geo-mining conditions. Field study demonstrated interesting interaction between size of pillar and nature of roof rock mass under the influence of increasing dimension of the excavation. Stiffness of pillars/overburden, extraction ratio and depth cover are observed to be the important parameters for the estimation of mining induced stress over the pillar. These parameters influence, both, the value of ultimate induced stress (vertical) and its range of influence ahead of the face line. Further, it is observed that the change in width/height (w/h) ratio of a pillar has got considerable influence over the nature of mining induced stress over it. Impact of highly dynamic nature of mining induced stress over the natural supports is observed to be the most serious factor for the safety of working under a hard and massive roof rock mass. On the basis of these observations, a conceptual model of interaction between the natural support and overlying strata is discussed in the paper. ZUSAMMENFASSUNG: Aufgrund ist in situ Studium von Säule Beladung an verschiedenen Stellen, ein Versuch in diesem Papier gemacht, die Entwicklung des Bergbaus vostellen sich, Spannung unter Änderung von Geo Bergbau von Bedingungen hat veranlaßt. Feld Studium hat interessante Wechselwirkung zwischen Größe von Säule und Natur von Dach Felsen Masse unter dem Einfluß von Vermehrung Dimension des excavation vorgeführt. Steifheit des Säulen Overburden, Herausziehung Verhältnisses und Tiefe sind beobachtet bedeckt, die wichtigen Parameter für die Schätzung des Bergbaus zu sein, Spannung über der Säule hat veranlaßt. Diese Parameter beeinflussen, beide, der Wert allerletzter veranlaßter Spannung (senkrecht) und sein Bereich des Einflusses voraus von der Gesicht Linie. Weiter ist, es beobachtet, daß die Änderung in Breite Höhe (W H) Verhältnis einer Säule beträchtlichen Einfluß über der Natur des Bergbaus erhalten hat, Spannung hat darüber veranlaßt. Schlag sehr dynamischer Natur des Bergbaus ist Spannung über den natürlichen Stützen beobachtet hat veranlaßt, der ernsteste Faktor für die Sicherheit des Arbeitens unter einer harten und massiven Dach Felsen Masse zu sein. Aufgrund dieser Beobachtungen, ein begriffliches Modell der Wechselwirkung zwischen der natürlichen Stütze und der überlagernde strata ist im Papier diskutiert. RESUME: En se basant sur dans l'étude de situ de chargement de pilier aux sites différents, une tentative est faite dans ce papier pour envisager le développement de creuse la tension persuadée sous varier de conditions de geo creuse. L'étude de champs a démontré l'interaction intéressante entre la taille de pilier et la nature de masse de rocher de toit sous l'influence d'augmenter de dimension de l'excavation. La raideur de piliers overburden, la proportion d'extraction et la couverture de profondeur est observée pour être les paramètres importants pour le jugement de creuse la tension persuadée par-dessus le pilier. Ces paramètres influencent, les deux, la valeur de tension persuadée ultime (vertical) et sa gamme d'influence en avant de la ligne de face. Plus, il est observé que le changement dans la largeur hauteur (le w h) la proportion d'un pilier a reçu l'influence considérable par-dessus la nature de creuse la tension persuadée par-dessus il. L'impact de nature extrêmement dynamique de creuse la tension persuadée par-dessus les soutiens naturels est observé pour être le facteur le plus sérieux pour la sûreté de fonctionnement sous une masse de rocher de toit dure et massive. En se basant sur ces observations, un modèle conceptuel d'interaction entre le soutien naturel et les couches recouvrant est discuté dans le papier.

Jan 1, 2003

By B. P. Simser, R. K. Brummer, A. Mortazavi, P. P. Andrieux

"A large-scale panel destress blast was fired at Brunswick mine in the fall of 1999 in order to reduce the ground stresses in a critically important neighbouring mining region. This work, sponsored by the Mining Division of CAMIRO and Brunswick mine, consisted in heavily choke-blasting — and subsequently leaving in place — a massive waste sulphide pillar in the southwest end of the 1000 m level. This paper describes the approach and design methodology used to try to maximize breakage in the rock mass in the area to destress, while minimizing damage to critical infrastructures in the vicinity. The loading operations, as well as the results of the blast — in terms of its field performances, as recorded by near-field blast vibration monitoring equipment, visual postblast assessments and measured impact on the regional stress field — are discussed as well. A brief comparison between the measured stress changes and inelastic numerical modelling of the test site is also presented.Un tir à grande échelle de relâchement des contraintes dans un pilier a été effectué à la mine Brunswick à la fin de l’automne 1999 dans le but de diminuer les contraintes de terrain dans une très importante zone de production adjascente. Ces travaux, financés par la division minière de CAMIRO et la mine Brunswick, consistaient à tirer violemment sans aucune face libre, et à laisser en place, un pilier de sulphures massifs au sud-ouest du niveau 1000 m. Cet article décrit l’approche et la démarche conceptuelle utilisées pour tenter de maximiser les fractures dans le pilier visé, tout en minimisant les dommages collatéraux à des infrastructures critiques se trouvant dans les environs immédiats. Les opérations de chargement des explosifs et les résultats du tir — en termes de ses performances, telles qu’évaluées par de l’équipement de monitoring rapproché des vibrations de tir, d’observations visuelles, et de son impact sur les contraintes de terrain locales — sont également discutés."

Jan 1, 2003

By L Smith, R Beckie

Controls on environmental loading from acid rock drainage (ARD) are not well understood in waste rock material. In particular, relationships between subsurface flow and the timing, duration, and intensity of leaching of metals and acidity from waste rock dumps remain ill defined. This study investigates field-scale relationships between subsurface flow processes and geochemical processes in unsaturated waste rock. A 12-metre tall, unsaturated waste rock pile, constructed in 1994, was deconstructed and sampled at Key Lake, Saskatchewan, Canada, during the summer of 2000. A detailed sampling methodology was developed to characterise physical and chemical properties of waste rock material within the waste rock pile. Physical properties were characterised by measuring soil-water suction, volumetric water content, and grain-size distribution at 60 random locations within the pile and grain-size distribution at 20 grid locations within the pile. Attempts to develop a field-based soil water characteristic curve from physical field-data failed due to spatial variability and hysteresis of waste rock properties. As a result, grain-size distribution was used as a relative measure of subsurface flow. Paste pH, pore-water geochemistry, mineralogy, and water-soluble extraction results were used to characterise geochemical processes and sulfide oxidation at each of the 20 grid locations. Geochemical characterisation results demonstrated the preferential weathering of marcasite relative to pyrite and chalcopyrite. Dolomite was the main buffering carbonate mineral. Gyspum, jarosite and iron oxyhydroxides were the main secondary minerals. Pore-waters contained up to 800, 11.7, and 6 mMolar (78 000, 690, 1400 mg/L, respectively) of sulfate, nickel, and uranium, respectively, suggesting significant weathering has occurred. Measures of weathering indicators show no discernable correlation with grain-size distribution nor do they show any spatial relationship within the sampled grid. Reasons for this may include limited duration of waste rock exposure to weathering and development of fluid flow-paths, and limitations of characterisation methods used. Indeed, six years may not be long enough for weathering patterns to develop due to fluid flow-paths in this unsaturated waste rock pile.

Jan 1, 2003