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By R. K. Singhal

Canada is a world class producer and exporter of minerals and mineral products. It is also a major exporter of minerals. Canadian open pits are highly mechanized and use state of the art equipment and support technology. During the past few years significant productivity improvements have been achieved by taking advantage of larger equipment; in pit crushing and conveying; truck dispatch systems and electronic management tools. The most recent developments in Canadian Open-pit Mining are related to hydraulic transportation and the application of Global Positioning Systems. Mine planning is computerized; environmental issues are dealt with in all phases of planning; equipment modifications are pursued with vigor to keep them functioning in the hostile Canadian North.

Jan 1, 1999

To the members of The South African Institute of Mining and Metallurgy We have audited the annual financial statements set out on pages 269 to 276. These financial statements are the responsibility of the Institute?s Council. Our responsibility is to report on these financial statements. We have conducted our audit in accordance with generally accepted auditing standards. These standards require that we plan and perform the audit to obtain reasonable assurance that, in all material respects, fair presentation is achieved in the financial statements. The audit included an evaluation of the appropriateness of the accounting policies, an examination, on a test basis, of evidence that supports the amounts and disclosures included in the financial statements, an assessment of the reasonableness of significant estimates, and a consideration of the appropriateness of the overall financial statement presentation. We consider that our auditing procedures were appropriate in the circumstances to enable us to express our opinion presented here. In our opinion these financial statements fairly present the financial position of the Institute at 30th June, 1999, and the results of its operations for the year then ended in conformity with generally accepted accounting practice.

Jan 1, 1999

By K. Peri

The leaching behavior of gold in ammonical solutions with iodine as an oxidant has been investigated using cyclic voltammogram and Tafel polarization. The majority of experiments was carried out at 75°C and the results were compared with the equilibrium consideration on the iodine-ammonia system. The distribution of nine iodide containing species at various pH values in the absence and presence of ammonia was considered at three different temperatures. It was found that by introduction of ammonia into the system, the concentration of iodide (r), iodine (12) and triiodide (13') is increased substantially which in turn helps the rate of dissolution of gold. The apparent activation energy was found to be about 46 kJ/mole, indicating a chemical controlled mechanism.

Jan 1, 1999

By J. C. Harrison

Eldorado Gold Corporation of Vancouver, B.C. owns and operates three gold mines. The Sao Bento underground gold mine in Minas Gerais State, Brazil produced 105,907 ounces in 1997. The La Colorada and La Trinidad open pit, heap leach mines in Mexico produced over 83,000 ounces in 1997. With a deteriorating gold market plaguing the industry throughout 1997 Eldorado had to take critical measures at each mine to enhance gold production while lowering cash operating costs. Each mine had its own unique problems to confront. This case study will discuss three distinct courses of action taken at the three mine sites.

Jan 1, 1999

By M. Canty

An innovative biological treatment system designed to detoxify cyanide and nitrate and immobilize metals from cyanide leach operations is described. A pilot-plant demonstration was conducted to detoxify cyanide and immobilize several metals from a process stream at the McCoy/Cove Mine. Testing was performed under the EPA's Mine Waste Technology and Superfund Innovative Technology Evaluation Demonstration Programs. This technology was successful in detoxifying cyanide and effective in removing metals. The pH was consistently neutralized and nitrates were successfully removed. Results show that biological treatment can offer an innovative, cost-effective alternative for the treatment of mining wastewaters.

Jan 1, 1999

By D. R. Taylor

The use of clay granules as carriers for pesticides dates from the early 1940's and by the present day represents a business conservatively estimated at between 200 -300 thousand tons / year in the U.S. alone. Aside from economic and specific target pest efficacy advantages, the use of clay granules as pesticide carriers also delivers a number of environmental benefits which will be reviewed. Topics to be discussed will include: I) drift control (versus liquid sprays), 2) mobility (in the environment), 3) worker safety, and 4) transportation (spill) safety.

Jan 1, 1999

By P. A. Schmitz

The characteristics of gold leaching from carbonaceous matter by sodium cyanide, and sorption of gold cyanide to carbonaceous matter in autoclaved and non -autoclaved gold ore from Barrick Goldstrike Mines Inc. (BGMI), Nevada, was investigated. Much greater gold cyanide complex sorption was observed for the carbonaceous matter in high preg-robbing ores relative to the low preg-robbing ores. This observation corroborates previous reports that have attributed observed preg-robbing behavior to the carbon in the ore. Gold cyanide complex sorption was found to be reversible for carbonaceous matter from low preg-robbing ore, but was irreversible for carbonaceous matter from high preg-robbing ores. Autoclaving the ore appeared to enhance the sorptive behavior of the carbonaceous matter from both high and low preg-robbing ores.

Jan 1, 1999

By K. H. McDaniel

The Waste Isolation Pilot Plant (WIPP) is adding a third fan to operate in parallel with, and supplement, its two existing main fans. An engineering analysis conducted in 1995 identified the need for improved system availability and efficiency. The WIPP, located near Carlsbad, New Mexico, is a U.S. Department of Energy (DOE) Carlsbad Area Office facility designed to permanently dispose of U.S. defense-generated transuranic waste in a deep bedded salt deposit. Engineers at the WIPP performed a feasibility analysis for either modi tying, supplementing, or replacing its two main mine fans. Since the centrifugal fans were installed in 1988, multiple operational and performance concerns have been identified. A comprehensive engineering study was conducted (McDaniel, et al., 1997) to: identity and quantity operational concerns, evaluate possible alternatives, and recommend an optimum solution. The study indicated that adding a third single-duty centrifugal fan similar to the two existing fans, and equipping that fan with Inlet Van Controls (IVCs) was the best choice. This alternative provided the most desirable combination of operational readiness, and improving system performance. The fan installation project accommodates several operational and scheduling constraints. WIPP is scheduled to receive waste in May 1998. This milestone is proceeded by an operational readiness review. Fan installation could not be allowed to compromise the WIPP's ability to declare facility readiness and had to minimize operational disruptions during the system tie-in. All engineering for the project is completed and physical modifications started in July 1997. The project was completed in 1998.

Jan 1, 1999

By John William Carlson

The Y2K or "Millenium" bug is a tiny critter, comprising no more than two digits in a date field. This bug, like its' more lethal cousins of biological and computer virus fame, has the potential to derail the economy of the U.S. and the rest of world. Whatever the reader's perception, rest assured that you will be affected by Y2K along with every person in the civilized world. How did we get to this position? It is really quite simple. The Y2K problem is a creation of computer programmers who, in an effort to conserve valuable memory in the early days of computer development, used two digits as shorthand- to define the year in date sensitive applications. Instead of typing in "1982," our experts employed "82." They believed-correctly­that the problem of limited memory would be solved by technology and assumed (nasty word) that software would be modified to take care of any problems associated with a date rollover in the year 2000. Their assumption resulted in the problem facing us today.

Jan 1, 1999

By Ivan C. Machado

In full autogenous grinding (FAG Mills) the ore itself determines almost exclusively the product size that will be produced, as opposed to conventional steel-media grinding where the product size can be "engineered" by changing media size, feed size, feed rate, classifier cutpoint size, etc. SAG Mills are in the middle of the way, since they offer some room to engineer their product size by properly defining some critical process variables, such as feed size, ball charge and size, mill charge and speed. SAG Mill product P80 values are typically in the range of 500 µm (35 US mesh) to 2000 µm (10 US mesh.) Whenever it is possible to determine an optimum value for the SAG Mill product P80 value (which will be the Ball Mill fresh feed F80 value), the Engineer should define the process variables that will yield a SAG product size as close as possible to the optimum calculated P80 value. In general, a coarser SAG product will draw less power from the SAG Mill and more power from the Ball Mill, and conversely, a finer SAG product will draw more power from the SAG Mill and less power from the Ball Mill. Metal consumption analyses also have to be taken into consideration, for they typically account for 30% to 45% of the total grinding cost. This presentation addresses the issue of defining an optimum SAG Mill product size (X=P80), during the design phase of the SAG and Ball milling circuits, from a general perspective, i.e., the SAG product size that will lead to an overall SAG Mill - Ball Mill optimum performance. Bond's Third Law approach is used, as well as the SPI (SAG Power Index), and also the generally accepted equations and Engineering Practice currently utilized to design SAG Mill

Jan 1, 1999

By Michael Brittan

For every million ounces/year of gold produced by mining and process operations, each 1 % loss to tails represents 10,000 oz/year of production sacrifice. Recovering this lost gold would generate aditional revenue of $3 million/year at $300/oz. Similarly, if the average recovered grade is say 0.15 oz/st, every $0.45/st reduction in operating costs will result in equivalent annual savings of $3 million. This paper describes the application of a technique to realize such cash flow benefits for milling operations.

Jan 1, 1999

By Ali Sogue, Steven Schurman, R. Jensen

This paper presents the results of the remediation of the Gregory Gulch #1 Superfund site, an EPA Clear Creek Superfund project located in central Colorado. The Gregory Gulch #1 site was an historic gold mine and mill located within the city limits of Central City, Colorado. Remediation efforts included the use of the Envirobond™ additive to chemically bind the metals in 3,000 tons of acid generating mine waste that contained high levels of arsenic, lead, zinc and mercury. The toxicity of the mine waste amended with Envirobond™ was not only reduced to RCRA TCLP standards but also to the more stringent UTS standards. The final cost of the treatment was much less than standard industry solidification processes and significantly less than offsite disposal options.

Jan 1, 1999

By R. D. Bartlett

Large open pit mines in desert climates, such as the Phelps Dodge Morenci copper mine in Arizona, can create groundwater cones-of-depression of considerable size and :ability. The hydraulic containment provided by the groundwater depression prevents migration of process solutions into the surrounding regional aquifer. Copper leach operations that fall within the groundwater depression may not require costly lining if passive containment can be demonstrated. An approach is presented in this paper that was successfully used to demonstrate passive containment. The approach includes a combination of groundwater modeling and a water balance analysis of leaching operations failing within or immediately near the open pit.

Jan 1, 1999

By F. B. Henderson III

Since the "end" of the Cold War, revolutionary new research and commercial remote sensing capabilities are being developed that will dramatically change the way we map the earth and address its environmental problems. The technology challenge is not the growth of new environmental remote sensing technologies themselves. It is, rather, how these new innovative observing systems can be accepted and used to the benefit of both the regulatory and the mining communities in the light of present concerns about unknown risks of discovery and liability. The basis for this paper is an unpublished technology primer prepared for the industry-government Workshop on Advanced Measurement and Site Characterization for Mining Impacts held at Colorado School of Mines, Golden, Colorado, July 14-17, 1997

Jan 1, 1999

By M. Karmis, C. Haycocks

Geographic Information Systems (GIS) are becoming a more commonly used tool for resource estimation as they provide not only a database management platform, but also the graphical capabilities to visualize resource characteristics. Interpolation methods used commonly in these resource studies do not typically provide a quantitative answer to the question: "How accurate is the estimate?" By comparing localized measurements at several locations to the interpolated thickness distribution used in a resource estimate, a quantitative analysis of accuracy can be obtained. The technique is demonstrated with a case study from Central Appalachia.

Jan 1, 1999

By S. A. Pierce

Heightened environmental consciousness has resulted in the development of various international accords dealing with natural resource management. This international awareness is now being translated into regional and local initiatives that proactively implement collaborative environmental management programs. One such program was recently initiated in northern Chile in recognition of the interconnection of Andean salars. Cooperative efforts between industry, governmental agencies and academic professionals have resulted in the implementation of simultaneous environmental monitoring of flora and fauna in the salars of northern Chile. This coordinated effort is leading to an improved understanding of the migratory patterns of South American fauna, as well as improved access to an expanded database for the multiple user groups associated with the Andean salars. The El Abra Mine is actively participating in these coordinated monitoring efforts.

Jan 1, 1999

By R. Mensah-Biney

The aqueous biphase separation process (ABS) has been used to separate ultrafine industrial minerals. The partition behavior of TiO2, Al2O3, Fe2O3 and kaolin was not pH dependent. The partition behavior of SiO2 was, however, pH dependent. The partition coefficient of kaolin in PEG 3400/ Na2CO3 biphase system was = 150 and that of the silica in the same system was = 0.02, resulting in a separation factor of = 8500 between kaolin and silica. The aqueous biphase separation system was used to separate free silica from kaolin in a raw clay sample from Mexico. The partition behavior of mica, feldspar and clay from North Carolina was also evaluated.

Jan 1, 1999

By I A. Lamb

The Melbourne City Link Project has two tunnels, the Domain and Burnley Tunnels, which have been constructed by Transfield Obayashi Joint Venture (TOJV) under a design and construct contract. The two tunnels are located essentially under the Kings Domain, the Yarra River and, in the case of the longer Burnley Tunnel, under the inner suburb of Richmond. The Burnley Tunnel is 3.5 km long and reaches a depth of 65 m at the central Swan Street Shaft, the invert being at RL -60 m. The Domain Tunnel is 1.6 km long, with the invert reaching RL -20. The tunnels were driven, for the most part, in the siltstone and sandstone of the Silurian Age Melbourne Formation. Construction aspects of the driven tunnels as related to the engineering geology have been described by Hutchison et al (1998). The Silurian bedrock is a fractured rock aquifer that is connected to overlying alluvial aquifers. Excavation of the tunnels allowed temporary groundwater inflows which substantially de-pressurised portions of the various aquifers. This de-pressurisation provided the potential to accelerate on-going secondary consolidation rates of the Holocene Aged Coode Island Silt (CIS) and the older Quaternary Fishermens Bend Silt (FBS) deposits, in areas where these materials directly overly the aquifers. As a large portion of the urban area of South Melbourne and the old river course of the Yarra River contain extensive CIS deposits, and were within the drawdown influence of the tunnels, the management of the hydrogeological regime was very important. The permanent design of the tunnels comprised drained and undrained sections (a partially tanked design) which, along with some permanent recharge, provide long-term protection against the possibility of accelerated settlement rates. During construction TOJV implemented a comprehensive groundwater management plan to deal with issues related to the temporary drawdown of the aquifers and the temporary acceleration of settlement. This paper describes the hydrogeological regime, the effects of the tunnelling, the monitoring programs, the extensive temporary recharge system, and the consultation program that TOJV utilised to manage the hydrogeological issues.

Jan 1, 1999

By F. Warnaars

Historically, this area produced gold and silver from many well-known vein deposits, like Tayoltita, Topia, and San Jose de Gracia. Modern exploration identified three categories of deposits: 1) low grade porphyry golds in shallow level dacite porphyries; 2) batholith-related deposits; and 3) those formed in volcanic sequences of Late Cretaceous to Late Tertiary. At least four porphyry golds have been identified, of which Metates is best known. These are formed by and within dacite porphyries, associated hydrothermal breccias and sometimes within surrounding metasediments. Their ages are from mid-Cretaceous to Early Tertiary. Precious metal deposits associated with batholiths occur as veins, contact haloes in metasediments or volcanics, skarns, tectonic breccias, hydrothermal tourmaline breccias, dacite dikes or as disseminated or stockwork deposits such as La Fortuna. Several new gold discoveries were made in older Early Tertiary Volcanic Sequences and in the younger Tertiary volcanics within prominent structures exceeding 3 to 5 km in lengths. Some of these are open-pittable but most have to be mined by underground methods.

Jan 1, 1999

By R Crookes

Mine to mill optimisation is not a recently developed concept. It is one which is finally gaining greater acceptance in the Australian mining industry, possibly as a consequence of the downturn in markets and certainly made possible by the development of tools and techniques to measure and predict performance of mining equipment and milling plants. Fragment size after blasting has a major bearing on the performance of all aspects of mining and a major influence on the economics of the mine and mill. The process to optimise fragmentation consists of identifying the key factors, measuring their sensitivity through a modelling and trialing program and conducting economic evaluations on the changes on both the mine and mill. Management of the Ernest Henry copper-gold mine in Northern Queensland, Australia, has espoused the mine-to-mill concept and is actively pursuing excellence in blasting to drive down the total cost of mining. Ernest Henry has extremely hard, wet and heavily jointed geological conditions, and had high powder factors and a large percentage of oversize material reporting to the crusher or ROM stockpile. A blasting improvement program was undertaken between Ernest Henry Mining, Thiess Contractors and Orica Explosives to optimise the ore size distribution, particularly the oversize component, as a step to reducing production costs. Measures of success included bringing the rock breaker back from double shifts to part-time operation and increasing direct dumping into the crusher from 70 per cent to 92 per cent. Tools and technologies to predict and measure the performance of individual blasts are needed before it is possible to optimise fragmentation or the downstream processes. These include such specialised Orica Explosives tools as SABREX, POWERSIEVE, and POWERLINE and commercially available drill monitors. As important are the more common still and video camera, borehole loggers, measuring tapes, surveying equipment such as face profilers, and a high speed camera if possible. There are many tools which can be applied however it is rarely necessary or possible to use all of them due to time constraints and a point of diminishing returns. The critical point is knowing what the true parameters of the blast were compared to design -only then can the predictive tools be effectively utilised. Stage one of the program has seen gradual improvement as the understanding grew and practices have been implemented resulting in reduced bridging in the crusher, geological mapping with respective blast designs and the oversize component under control. This paper is about a process approach which links tools and technology to understand the fragmentation drivers and then to optimising the size distribution. The continuous improvement program continues . . .

Jan 1, 1999