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By T. J. Haddon

For the mining industry in general and gold mining in particular the past few years have been difficult. Economic conditions coupled with growing regulatory restrictions have led to increasingly important reasons for managing assets wisely. From a public company perspective this makes sense because it ultimately provides for an increase in shareholder wealth and that's what we're in business to do. Regardless of whether a company is public or not, assets must be managed effectively to remain a player in today's competitive environment. So, as the CEO of a gold mining company, how do we manage our assets to ensure that we are satisfying our obligations to our customer --the Amax: Gold shareholder? Let me tell you. As I said earlier, the gold industry has been under siege. We have just completed our third year of average prices below $400 per ounce. When you add finding and/ or acquisition costs and development costs to operating costs, there isn't much of a profit margin left. What this environment provides, however, is opportunities for growth. In the gold business, you either grow or you die. Today, most North American gold producers have at most a 10 year mine life. We are all scrambling to add reserves so we don't become extinct. As prices remain low, opportunities for increasing diminishing reserves abound. This is the time for the opportunistic company to take advantages of market conditions and that's precisely what we, at Amax: Gold, have done!

Jan 1, 1992

By R. J. Reuss

The ore at this new underground operation is a massive sulfide breccia with high copper values. A major highway and electric transmission line pass directly over the near-surface orebodv. The mining method being used is undercut and fill. A continuous miner together with a single boom, hydraulic jumbo is used for the mining. Backfill is a weakly cemented sand-gravel mixture that is pneumatically placed. The ore is treated by conventional crushing, milling and flotation.

Jan 1, 1992

By J. C. Heter

The P.W. Gillibrand Company has been processing and stockpiling a suite of heavy minerals at its Soledad Canyon Mine as co-products with construction aggregates since 1984. The heavy minerals are composed of ilmenite, magnetitie, apatite and zircon. The source of the heavy minerals is the Precambrian San Gabriel Anorthosite Complex of the western San Gabriel Mountains. The valuable minerals are readily amenable to standard ore dressing techniques, such as, gravity, magnetic, flotation and electrostatic separation with good recovery and product quality. More than 20,000 short tons of coarse ilmenite were sold in 1990 to the export market for titanium pigment production.

Jan 1, 1992

By T. McDonald

Test work indicated and plant operation has since confirmed that SAG milling is a viable option for INCO's Sudbury Operation milling rationalization project only if pebble crushing is included in the SAG/ball mill circuit. Throughput increases more than fifty percent with pebble crushing incorporated into the comminution process. The finer product of high speed pebble crushing provides further energy savings. The unconventional approach of pumping the pebble crusher product, while simplifying plant layout, has produced challenging wear problems.

Jan 1, 1992

By R. G. Hite, R. G. Rowe

The Crandon deposit, located in northern Wisconsin, is a 65.8 million ton Precambrian volcanogenic massive sulfide deposit which averages 1.4% copper and 5.8% zinc. The deposit is classic in origin, mineralogy and shape. Comprehensive understanding of the geology of both the deposit and the project site has been fundamental to the credibility and success of project feasibility studies and regulatory permit preparation. Mine development in the current investment and regulatory climate requires thorough and timely application of geologic tools. From 1977-1980 geologic activities were focused on the typical objectives of orebody delineation, reserve estimation, depositional geology, and general site investigation. Results from these programs formed the basis for the project's preliminary feasibility studies. Since 1981 further geologic investigations have provided criteria for project design, site management, and operational permitting. Activities have included mine entry position definition drilling, devel reserve modeling, large diameter (150 mm) core drilling for mill pilot samples, rock mechanics testing, and evaluation of the glacial overburden/deposit geohydrology for computer simulation.

Jan 1, 1992

By Dirk van Zyl

It can systematically assess if the control and management systems designed for protection of sensitive ecosystems are adequate. The results of the assessment can help to identify key elements in the project that pose higher risks due to uncertainties in design. These assessments can then be used to make recommendations to further manage and reduce risks as the project is developed. QUALITATIVE RISK ASSESSMENT The general principles of a risk assessment are well summarized by Kaplan and Garrick (1981): "In analyzing risk we are attempting to envision how the future will turn out if we undertake a certain course of action (or inaction)." Fundamentally, therefore a risk analysis consists of an answer to the following three questions: What can happen? (i.e. what can go wrong?) How likely is it that that will happen? If it does happen what are the consequences?" Risk assessments can be performed using various levels of sophistication depending on the amount and accuracy of data available. A qualitative risk assessment uses descriptors throughout to express the level of risk. The definitions of the descriptors are presented in terms of the magnitude or concentration of contaminants. The results of a qualitative risk assessment can be used to: a)Document the evaluation and decisionmaking process. Although differences of opinion may exist about the definitions of the descriptors, the process is well-documented; b)Express the relative risk associated with specific activities or design elements; and, c)Select those failure modes or release mechanisms that may result in significant risks. These mechanisms can then be further developed in quantitative risk assessments. A qualitative risk assessment can be performed in a systematic approach using four steps (Van Zyl, 1987): A qualitative environmental risk assessment can be used to describe the risks associated with the development of a new mine and to make an evaluation of the adequacy of its design for environmental protection. The relative magnitude of risk associated with selected failure modes and exposure/consequence scenario assessments is the final result of a qualitative risk assessment. These failure modes are based on site specific areas and components, and mining and construction phases. The four steps of a risk assessment (hazard assessment, exposure assessment, consequence assessment, and risk characterization) are used in the development of a qualitative risk assessment. Relative magnitudes (using a five point scale of negligible to high) for each step, can be quantified in a qualitative risk assessment. Development of the descriptors for the relative magnitudes in each step is a very important part of a qualitative risk assessment. The success of a qualitative risk assessment depends on the adequacy of the information base and the subjective judgements made in each step. The quality of the risk assessment is, therefore, dependent on the experience of the assessors. A mining project in a sensitive coastal environment is presented as an example to demonstrate the application of a qualitative risk assessment. INTRODUCTION Environmental impacts from mining operations have been a significant factor in the last century. This was especially the case prior to the development of a better understanding of environmental processes and the potential impacts of acid rock drainage (ARD), and associated heavy metals, or the uncontrolled disposal of tailings and waste rock (Smith, 1987). Much care has been exercised over the last two decades in designing and operating mines to limit the environmental impacts as far as possible. All new mines are specifically designed with mitigative methods to manage such potential environmental impacts. Attention is directed to ARD impacts, safe disposal of mine waste rock and tailings, transportation and storage of chemicals and fuels, and final reclamation. A qualitative risk assessment can be used to address all project systems and activities that may potentially pose a risk to the environment.

Jan 1, 1992

By Burton E. Gilpin, Dr. George W. Annadale

A two level risk analysis procedure which is specially designed for use in river environments, is presented. The first level risk assessment (Level I) is often adequate for purposes of most projects, and entails hazard assessment, exposure identification, consequence estimation, and risk characterization. Two unique features of the method are the Composite Hazard Rating system, which is used in hazard assessment, and a formalized decision model for risk characterization. The risk characterization procedure provides information on the acceptability of risks, can be used to distinguish between the relative severity of risks, and to evaluate whether more advanced risk assessment would be required.

Jan 1, 1992

By R. V. Ramani, R. Bhaskar

An airborne dust cloud is an ensemble of particles of varied size, density, shape and states of aggregation. An understanding and quantifying of the dispersion and deposition of the dust generated in mines is essential to the development of measures for reducing worker exposure to dust. In coal mining, the major portion of the dust is generated during the cutting of coal using a shearer or a continuous miner. The major phenomenon affecting ambient concentration is the deposition of dust. Particle deposition may take place due to the effect of gravitational, inertial, electrostatic, and thermal forces, and mechanisms such as Brownian and eddy diffusion and inertial impaction. The three major mechanisms of deposition in turbulent flow in mines are diffusion (Brownian and eddy), sedimentation and inertial impaction. The mechanisms determining particle deposition are size dependent. From a review of the literature, there appears to be a knowledge gap in the understanding of the deposition phenomena in mine airways. In order to obtain a better understanding of the deposition of dust for various particle sizes, and to develop a set of data for evaluating predictive mathematical models for dust-flow in mines, a series of dust flow experiments was performed under controlled conditions in mine airways. It appears that the deposition data generally follow the theoretical behavior of dust based on the combined effect of diffusional and gravitational deposition. In this paper, the findings of the study on the deposition of dust in mine airways and its dependence on size, velocity and concentration are discussed. A set of deposition equations that could be used to determine the approximate deposition at various points in a mine airway are presented.

Jan 1, 1992

A kinetic model for leaching of various metals with different lixiviants in a batch system has been developed. Material balances for reactants and products at the solid/liquid interface were formulated and solutions to these balances were obtained in view of practical conditions. Special emphasis has been given to examine mixed controlled reaction systems where both heterogenous reaction and mass transfer play important role on the overall rate expression. The resulting kinetic expressions for either powder or rotating disc are discussed in light of experimental findings for various metals. Examples of the metal dissolution systems considered in this study include cobalt, nickel, copper and gold in acid, cyanide or ammoniacal solutions.

Jan 1, 1992

By J. R. Gaw

Recent events pertaining to U. S. energy needs and development of alternative energy fuel resources have made the American public more aware of past and present coal mining operations, and their impacts on the nation's economy and environment. This awareness has developed rapidly due to increased government involvement and consequent media coverage. This is true particularly in the Western states and in Texas. One of the consequences of this increased public awareness is public concern over the perceived and real consequences of mining operations. Emphasis has been placed on potential releases of toxic and hazardous substances, and possible carcinogens. The result of this public concern is a mounting effort at both state and Federal levels to promote stricter laws regulating the mining industry.

Jan 1, 1992

By I. Cameron-Clarke

This paper describes the design of a wellfield to provide a water supply for a new mine in southern Africa. A hydrogeological investigation was conducted that included the drilling and test pumping of eight wells located within a highly jointed pyroxenite aquifer. The wellfield was designed using a simple probabilistic analysis. This approach allowed the variability of the aquifer parameters to be taken into account. A risk assessment analysis was then carried out to evaluate the level of assurance that a reliable water supply could be provided by the wellfield. The analysis was also used to assess the effects of supplementing the water supply by pumping from nearby flooded workings.

Jan 1, 1992

By D. E. Ranta, William B. Ryan, Ronald W. May

The Lower Cretaceous McMurray Formation in northern Alberta contains bituminous sands interbedded with other sediments which form the reject encountered during mining operations. Grade prediction is based on a combination of geological interpretation, computer modelling and past mining experience. In addition to estimates for ore, an accurate estimate of "waste" or "reject," are required for Mine Planning. This study investigates the ability of point-kriging using geostatistics, to augment the existing data base of drill-holes in a study area on Syncrude's leases. This approach enables the assessment of potential "worst" case - "best" case scenarios within the context of Mine Planning.

Jan 1, 1992

By W. Allen Dupree, Charles D. Campbell

A field investigation was conducted by the Ventilation Division, Pittsburgh Health Technology Center (PHTC), Mine Safety and Health Administration (MSHA) to evaluate the effectiveness of a blowing face ventilation system utilizing a water sprayfan system and a single inlet flooded bed dust collector (scrubber) in controlling methane liberation in the face area while mining at brattice distances up to 12.2 meters (40 feet) from the face. The rated capacity of the scrubber was 117 m3/s (4,145 cfm) of air. Results from the investigation indicated a methane dilution capacity of 0.57 m3/s (20 cfm) with the air quantity behind the line brattice averaging 138.7 m3/s (4,900 cfm).

Jan 1, 1991

By T. B. Whitmoyer, J. E. Sneckenberger, M. A. Jerabek, C. F. Stanley

The measurement of acoustic impedance at frequencies up to 6,400 Hz has been proposed as a diagnostic tool to yield more detailed information about lung condition. A three generation branching system of plastic Y-tubes has been constructed. The impedance of the branched system is measured by an impedance tube using the two-microphone technique. The impedance spectrum is used to calculate the reflection coefficient spectrum, which is converted to an impulse response by an inverse FFT. The area function is extracted from the impulse response by the Ware-Aki algorithm. Measurements of acoustic impedance of the branched system were made for several different end conditions of the eight terminal outlets. The outlets were either blocked with modeling clay, plastic packing material, or aluminum blocks or were unblocked. Six measurements were made of each configuration. In general, the more outlets blocked, the larger the shift to the right of the impedance magnitude peaks for frequencies above 3000 Hz. The impedance magnitude peaks for the plastic packing material were shifted in frequency to the right relative to the peaks of the other system terminations. The impedance magnitude peaks for the clay and aluminum system terminations were significantly different in magnitude but not shifted in frequency. The area functions at the end of the branched system were significantly different (a > 99%) for most of the end conditions. Area functions for the modeled branched lung systems between the end of the impedance tube and the termination outlets of the branched system were similar but distinctively different for the various end conditions. These results indicate that the two-microphone technique can sense small changes in the terminating end conditions of a rigid system of branched tubes and thus may sense impedance changes due to lung disease in the conducting airways. Keywords: acoustic impedance, lung model, area function.

Jan 1, 1991

By Raj K. Rajamani

In ball milling the rates of breakage vary primarily with the size distribution of powder in the mill. In wet grinding viscosity of the slurry varies continually as size distribution changes and hence the breakage rates change. In this study a simpler estimation scheme is used to determine breakage rates in batch grinding. Using an approximate solution to the batch grinding equation, acceleration and deceleration of breakage rates of all individual size classes is determined when the grinding environment is varied. Experimental results with limestone and copper ore show time-dependent breakage rates under both dry and wet grinding conditions. In general the breakage rates increase for coarse sizes and decrease for fine sizes with increase in the fines present in the mill. Such variations have strong implications in closed-circuit grinding.

Jan 1, 1991

By Hugh R. Wilson

Echo Bay's Waste Management Program for its Lupin Mine was developed in response to the terms and conditions of the water license issued to the mine in 1981 by the Northwest Territories Water Board. The gold mine, located about 80 km (50 miles) south of the Arctic Circle, commenced production in 1982. The Waste Management Program was based originally on the total containment concept, contingent on future treatability testwork results indicating the best treatment method to ensure pond discharges would be in compliance with stated Northwest Territories Water Board discharge criteria. To assess the various treatment technologies, an investigative program was established to determine the most effective means for treating the tailings pond water. In the course of milling, about 850,000 m3 (11 million cu yd) of tailings are produced annually that require appropriate management to protect the environment. This annual tailings stream consists of about 175,000 m3 (229,000 cu yd) of solids and 675,000 m3 (883,500 cu yd) of water. Following the completion of the required waste management studies, a two-ponds-in-series concept of tailings impoundment was developed. To attain this concept, the tailings impoundment area would require modification and construction to enable the use of such a system.

Jan 1, 1991

By H. Barry Holt, Charles A. Bischoff

On November 15, 1990, President Bush signed the Clean Air Act Amendments of 1990. The new legislation is sweeping in its demands for cuts in smog, acid deposition, toxic air pollutants and ozone-depleting chemicals. The Amendments will siqnificantly alter air quality permitting and compliance and are estimted to cost billions of dollars to implement. This article provides an overview and summary of each of the eleven titles of the Amendments. It also addresses how the Amendments will be implemented.

Jan 1, 1991

By J. E. Stephens

US Borax began exploration in southeast Alaska in the summer of 1971 with a staff of two, Barry Watson and Jackie Stephens, based in Spokane, WA. After several years of prospect examinations in the islands west of Ketchikan, AK, and with the able assistance of prospector-pilot Kenny Eichner, Jackie Stephens proposed and organized a boat-based, helicopter-supported, stream sediment sampling program to explore the western contact of the Coast Range intrusive complex on the mainland. The rationale for this included: the extension of known mineral trends from Canada into southeastern Alaska along favorable geologic zones; the western contact area of the Coast Range intrusives with metasediments and metavolcanics was a favorable target for metals exploration as shown by numerous small prospects. Knowledge gained from mineral exploration of the island areas indicated that they were well mineralized, but already well explored, and that the known mineral potential was probably present in subeconomic quantities (Brooks, et al.). Publications of the US Bureau of Mines and other scientific agencies were gathered and every prospect within the southem southeastern Alaska area was plotted. This in itself lent a tremendous amount of knowledge to the total exploration program. US Borax's McLean Arm copper property on Prince of Wales Island was drilled and dropped while this compilation of data was proceeding. We found that many companies had followed one another around the island areas, but little or no exploration had been done on the west side of the Coast Range, and that many explorationists flatly stated that the west side of the Coast Range was barren of mineralization. In summary, although some of the shoreline and near shoreline areas of the mainland had been explored, no organized boat-helicopter exploration program had been done along the favorable western zone of the Coast Range Intrusive complex. We decided to use a boat as a floating hotel for the crews that were to be helicoptered into the back country from tidewater for our initial stream-sediment sampling program.

Jan 1, 1991

By Suresh K. Bhatt

A mathematically simulated modeling technique is used in this U.S. Bureau of Mines paper to represent a hypothetical mining operation with existing mining technology and prevalent mining costs. Mining scenarios are prepared and evaluated for potential benefits and costs available through computer-assisted mining. Base criteria, parameters, and methodology are described.

Jan 1, 1991

By Michael S. Kucker, Robert A. Robinson, Harvey W. Parker

Ground deformations are of major concern during tunneling, especially in downtown environments, since they have a significant impact on the costs and practicality of tunneling. This case history describes soil and groundwater conditions and ground behavior during the construction of twin transit tunnels for the Downtown Seattle Transit Project (DSTP). The tunnels were excavated through complex glacial soils ranging from hard glaciomarine drift to flowing sand. The tunneling process was greatly facilitated by the prediction of soil layer positions to an accuracy of ±0.6 m (2 ft). Tunneling was complicated by the presence of over 500 temporary tiebacks and by disturbed ground overlying an operating railroad tunnel. A variety of ground improvement techniques were used to successfully minimize settlements, which ranged from 1 cm (0.4 in.) in glaciomarine drift to 6 cm (2.4 in.) in flowing sands. Ground improvement techniques included compaction grouting, chemical grouting, jet grouting, and eductor well systems.

Jan 1, 1991