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By Bryson D. Trexler

Man's activity in developing, operating, and abandoning a mine often affects the quality of the ground water and surface water. Acid water drainage from mines is an example of an impact from mining that results in degradation of ground and surface water. New flow systems are created by the mining activity. The mining made possible complex chemical reactions that, with water movement, create a discharge of low pH, poor quality water. Remedies for these problems fall into two general solutions: 1) treatment of the end product and 2) reversal of some aspect of man's disturbance of the natural system. The relative reversibility of various aspects of man's impact from mining activities ranges from relatively easy to very difficult, from economically feasible to economically infeasible, and from technically possible to essentially impossible with present knowledge. The relative reversibility of a mine-related problem cannot be assessed without first understanding the detailed physical interactions that combine to form the problem. Acid water drainage is a combination of the availability of several chemical factors with the availability of water for a transport mechanism.

Jan 1, 1982

By A. L. Mular

Si define la simulación digital y las técnicas de simulación son revisadas. La metodologia tipica conlleva la selección de modelos, el ajuste o reajuste de los datos primarios, la selección de una estrategia de acoplamiento, la valoración de la precisión del modelo en un sentido estadistico, y el desarrollo de estructura de simulación ejecutiva. La simulación sirve de ayuda para los ingenieros de procesos para evaluar la viabilidad de un esquema de flujo propuesto y el efecto de la modificación de un flujograma ya existente. Por otro lado, la simulación juega un papel importante en la optimación "off-line" y en la evaluación de estrategias de control de circuitos alternativos. Son presentados varios ejemplos para ilustrar estas utilizaciones para la simulación, incluyendo aplicaciones en los circuitos de trituración, circuitos de molienda y circuitos de flotación. Es de opinión de los autores que, dentro de la próxima década, las plantas de proceso de minerales serán estudiadas rutinariamente a través de una simulación digital durante las etapas preliminares de diseño. La simulación constituirá un importante componente en la toma de decisiones de un proceso.

Jan 1, 1982

By Francis S. Kendorski

INTRODUCTION Drift design problems in caving operations are a re¬sult of the geologic factors contributing to the overall success of the system, of the engineering factors dictated by economic and technical considerations, and of ore production practices. Combining these factors, a rational underground sup¬port system of rock reinforcement, light steel channel section or welded wire fabric, and shotcrete can be de¬signed based on rock fracturing, rock load, abutment loadings, ground movement, expected repair and desired flexibility. The design concept uses the effect achieved by restraining, reinforcing, and maintaining some of the intrinsic strength of the fractured rock mass composed of interlocked blocks of intact rock and rock fractures. Three different examples of drift support design in hypo¬thetical mines using the caving system are given. Caving is a system of underground mining where ore is extracted by means of gravity after the ore body is allowed to fail by removing support from underneath. The rock mass of the ore body fractures and flows ver¬tically downward to let gravity do as much work as pos¬sible. Caving differs from many other mining systems in that blasting is used only to initiate the rock mass failure by removing the rock supporting the ore but not to break the ore itself. The initial movement of the rock mass dur¬ing failure and the consequent crushing and grinding during the continued movement serve to reduce the ore to particles of a manageable size, with only limited sec¬ondary blasting necessary. The broken ore is extracted from the bottom of the failed rock mass through funnels of some sort pre-excavated in the rock. Ore extraction must continue or the swell of the broken rock will even¬tually fill the cavity and stop further rock mass failure and movement. The excellent general discussion on block caving in the SME Mining Engineering Handbook (Julin and Tobie, 1973) adequately covers the principles and application of this type of underground mining. Many rock mechanics aspects of block caving have been covered by others (McMahon and Kendrick, 1969; Swaisgood, et al., 1972; Mahtab and Dixon, 1975; King, 1946) and will not be reviewed further. Maintaining the stability of production drifts is one of the most troublesome problems plaguing the mine manager in a caving operation. Many factors contrib¬ute to drift support problems, and identifying the causes of instability and producing a reasonable support design are two steps toward achieving stability consistent with the mine plan. This chapter sets forth a technique for the design of support systems for production drifts in caving opera¬tions. The basic support system elements employed are rock reinforcement, welded wire fabric, and shotcrete. Recognized as contributing to the design are the factors of rock load, additional load from mining activity, rock fracture characteristics, repair expected, and flexibility. It must be emphasized that the drift must first be stabilized as for a tunnel, and the additional strengthen¬ing for mining-induced loads cannot contribute to the initial premining stabilization, or the reserve of strength is used up. MINE PLANNING The efficient mine planning engineer not only must satisfy the economic, human, and environmental aspects of his task but must also consider the mechanical con¬sequences of his plan. The problems created for the mine by placing parallel drifts too close, by crossing drifts on different levels with inadequate, if any, separa¬tion, and by installing connections and crossovers in the haulage plan without regard for the effective spans cre¬ated, are only a few of the problems a mine planning engineer can create for himself and the mine. The effect on immediately adjacent mine areas when an area is caved is important to drift design because the removal of vertical support from a rock mass causes the weight of that rock mass to be shifted elsewhere. The adjacent rock mass will carry this load and reach a new equilibrium with the applied stress. The advancing front of stress increase that results from caving (and many other mining systems) is generally called the abutment load and is the increase in stress over the gravity or tec¬tonic stress that already exists, as shown in Fig. 1. In general, the abutment load will be similar in nature to the stress change found around an opening in rock and will be taken as causing an increase in the vertical prin¬cipal stress, due to an approaching caving boundary, so that

Jan 1, 1982

By John C. Brower

The purpose of this paper is to examine the Gays in which- the policies of the U.S. government, mining companies and third world countries affect each other with regard to the availability of minerals. The interaction involves U.S. policy towards the mining industry, the policies of the companies themselves, and the policies of third world countries towards the U.S. and multinational companies. It is assumed in this discussion that U.S. policy will continue to be to seek certain minerals from abroad rather than attempt to develop domestic sources for all its requirements. This would seem to make sense both from the standpoint of cost, and for preserving what domestic resources there are so as to maintain some degree of market leverage. In today's jargon, this means greater dependency on the "third world", which, for this discussion, includes virtually all the nations in Africa, South America and Asia. Concern for availability raises the important distinction between dependency and vulnerability, and as the Director of the Bureau of Mines has pointed out, the two are not the same. Dependency is not neccessarily a bad thing; it is vulnerability that counts (Norman, 1980)

Jan 1, 1982

By Keith E. Dyas, John Nelson, Ronald T. Johnson

GENERAL DESCRIPTION The Bruce mine of Cyprus Mines Corp. is located in Bagdad, AZ. The mining method used is open cut-and-fill. Of the annual production of 81 647 t (90,000 st), approximately 83% is taken from load-haul-dump (LHD) stopes and the balance from slusher stopes. All ore is produced from the area between the 1250 level and the 2300 level. The average travel time from the shaft pocket to the stope is approximately 5 min. GENERAL ORE BODY REQUIREMENTS AND LIMITATIONS Size, Shape, and Dip The Bruce ore body occurs in quartz-sericite schist with Dick rhyolite on the footwall and andesite on the hanging wall. Diabase dikes are found in the hanging wall; there is also a dike coming off the footwall and crosscutting the ore body. All of the rock types are of the Precambrian Yavapai series and have been subjected to regional metamorphism. A composite of the ore body is given in Fig. 1. The deposit is of massive sulfides occurring as a steeply dipping replacement body. On the upper levels the ore is veinlike with widths from 0.6 to 4.6 m (2 to 15 ft), dipping at 1.4 to 1.5 rad (80° to 85°). On the lower levels the ore is dipping from I to 1.2 rad (60° to 70°) with widths from 3 to 16.8 m (10 to 55 ft). The strike length varies between 107 to 183 m (350 to 600 ft). The rhyolite footwall generally has a knife-edge contact with the massive sulfides. The exceptions to this are the upper levels where there is a 1.5 to 3 m (5 to 10 ft) band of silicified sericite schist between the sulfides and the rhyolite. In the southern part of the ore body the hanging wall is tuffaceous andesite and andesite. In this area the contact is generally sharp and easy to follow. However, to the north there is a large chlorite schist zone that crosscuts the bedding and comes in contact with the massive sulfides. This is apparently due to hydrothermal alteration of the andesite. The chlorite schist is highly mineralized with chalcopyrite and pyrite and quite often forms economic pockets of ore. In the massive sulfides the chief ore minerals are sphalerite and chalcopyrite. Pyrite is the predominant sulfide with considerable pyrrhotite throughout. Bright arsenopyrite ouhedrons in fine grain massive sulfides are quite common. Occasionally small amounts of galena are seen, usually near the foot or hanging wall contacts. On rare occasions tennanite is associated with massive arsenopyrite. Minor amounts of quartz, calcite, and un¬replaced remnants of sericite schist occur, but essentially pyrite is the gangue in which the ore minerals occur. The ore values are in excess of 3.5% copper and 12.5% zinc with some silver and rare gold as byproducts. Ground Conditions The massive sulfides are generally self-supporting. One exception is in the 1850 stope where the ore body is 9 to 11 m (30 to 55 ft) wide and 152 m (500 ft) long. There are flat to shallow dipping slips and seams in the ore, creating extremely blocky ground. For support, old 25.4-mm (1-in.) hoist ropes were installed tensioned to 27 t (30 st), and then cement grouted over the entire length in longholes [14 to 15 in (40 to 50 ft) in length) drilled on 3-m (10-ft) centers from the level above. This has tied the formation together very successfully and virtually eliminated the blocky ground condition. Both the hanging wall and footwall are quite shaley in some areas. Reasons for Adopting Trackless Open Cut-and-Fill Methods First, any method other than open cut-and-fill would have caused too much dilution. The use of rubber-tired mining equipment in the pro¬duction stopes requires a footwall ramp. The inclines in ore will be mined out, so this ramp in the footwall will provide access to and from the stopes (Fig. 2). This incline is very expensive, but necessary to convert existing stopes to LHD mining. 'The final cost of ore mined by the LHD machines has not been determined. As of 1972, tons per manshift in the 2150 stope-the only one to complete a full cut-had increased from 7.58 t (8.36 st) to 12.83 t (14.14

Jan 1, 1982

By Cyrus W. Field

Metalliferous sediments constitute an important component of the sedimentary veneer that overlies basaltic oceanic crust of the Nazca Plate and elsewhere. Although first collected more than one century ago near the East Pacific Rise during the Challenger Expedition and recognized for their anomalously high content of Fe and Mn, occurring as very fine-grained, yellow-orange, oxides, hydroxides, and oxyhydroxides, it was not until the more detailed studies of Bostrom and Peterson (1966) that their geologic significance and concentrations of other transition metals were fully appreciated. The Nazca Plate is a dynamic lithospheric unit bordered by the Peru-Chile trench and the East Pacific Rise to the east and west, and by the Galapagos Rift and the Chile Rise to the north and south (Fig. 1). Samples employed in this study were taken from piston core recovered from the Nazca Plate (Fig. 2), D. S. D. P. drill core from the northeast Pacific (Dymond and others, 1973), ferromanganese nodules from dredge-haul s at several locations, and from hydrothermal mineral deposits of the Andes. Our efforts have been largely sponsored by the National Science Foundation through its International Decade of Ocean Exploration Pro- gram. The metalliferous fraction of these sediments is widespread, but generally small. Sedimentation is dominated by biogenic silica in the equatorial latitudes, terrigenous debris adjacent to the South American Continent, and by biogenic carbonate elsewhere, except at depths below 3500 m in the central and northwest parts of the Nazca Plate near the East Pacific Rise. Contributions of these distinctive sediment types are shown by the distributions of Si02, A1203, and CaC03 given in Figure 3.

Jan 1, 1982

By Edward C. Heistermann

The Falkirk Mining Company, a wholly owned subsidiary of The North American Coal Corporation, is located 80 kilometers (50 miles) north of Bismarck, North Dakota. Falkirk is under contract to provide 5.08 mil- lion tonnes (5.6 million short tons) annually to the Coal Creek Generating Station, an 1100 mega- watt electric plant owned by the Cooperative and United Power Associations of Minnesota. Coal Creek is located 2.4 kilometers (1 ½ miles) south of the Mine. Electricity from the plant is transmitted to rural electric customers in Minnesota via a 400-kilovolt D.C. power line.

Jan 1, 1982

By Arthur R. MacPherson

Este capítulo revisa las etapas que deben seguirse desde el momento de considerar la molienda autógena en el desarrollo de un nuevo depósito de mineral o en la expansión de una planta existente, hasta la compra de un molino autógeno. En este caso el término autógeno incluye: semi-autógeno, molinos de pebbles secundarios y molino de bolos (trozos), así como los sistemas de molienda autógena total. También se han incluido las alternativas por vía húmeda y seca. Antes de programar el ensayo debe decidirse cuantas muestras brutas son requeridas para calcular propiamente las posibilidades de molienda autógena del depósito. También ha de tomarse la decisión, de como y donde deben tomarse las muestras, por ejemplo: planta piloto situada en el sitio de localización de la planta o en otro lugar establecido; molienda en húmedo y/o en seco....etc. En el mismo programa del ensayo se obtendrán ciertos datos fundamentales. Los ensayos deberán incluir un trabajo suficiente. para determinar cuál de las moliendas, totalmente autógena o semi-autógena, debe utilizarse; y qué tipo produce la máxima eficacia en la potencia consumida. También, los otros datos pertinentes deben ser recolectados, como por ejemplo: potencias, tonelajes, alimentación, carga, tamaño del producto, carga circulante, etc. Si es necesaria una molienda secundaria para obtener el tamano final, la decisión de qué molienda debe emplearse (molino de pebbles o molino de bolas) puede requerirse un ensayo de trabajo adicional. Finalmente, la concentración del mineral puede jugar un papel importante en la selección del circuito y debería ser una parte del ensayo final una vez que se ha establecido la molienda. Para determinar qué tipo de molinos pueden satisfacer los requerimientos establecidos por la planta piloto, debe tomarse una escala para ciertos datos como: potencia del molino, consumo de acero, simple o doble etapa de molienda, tipo de molino secundario. Para asegurar un posterior entendimiento del depósito de mineral y sus características de molienda, deberán efectuarse algunos trabajos adicionales a pequena escala utilizando pequeñas muestras y molinos para producir unos datos comparables de molienda. También, algunos ensayos tales como medio de molienda óptimo, e índice de trabajo, deberán ser completados.

Jan 1, 1982

By Howard M. Wells

Investment in minerals development usually entails big financial outlays. which will remain at risk for a long time before the venture can begin to generate a return cash flow. Before 'committing himself to such a venture the investor would be wise to carefully examine the possible consequences of his exposure to risk. In this context risk is defined in multiple terms, which relate the magnitude of possible loss with the probability that such loss may occur--normally the probability will decrease as the amount of possible loss increases. The analysis of risk is an essential component of the decision making process, especially so in the case of low grade high tonnage mining ventures where a very real possibility exists that future unfavorable circumstances may lead to losses that could cripple or ruin even the richest corporation. Wells (1979) postulates a rationale for making the investment decision under uncertainty based on the comparison of two independent risk criteria: 1) the risk inherent in the venture represented by the negative portion of the cumulative distribution of the net present value (NPV), as derived by a stochastic evaluation procedure, 2) the limits of risk the decision maker is willing to accept, taking account of the financial capacity-of the 'firm to absorb various levels of future cash shortfall should the venture prove disappointing. The chance the investor would be prepared to accept can be expected to decrease as the amount of the possible shortfall increases. The limits of acceptable risk are-defined by a curve called the "LL-curve" which can be directly compared with the cumu¬lative NPV curve. A positive investment decision is implied if the limits of acceptable risk are not exceeded.

Jan 1, 1982

By G. Capello

Carboniferous mining basins are today a non-negligible source of energy. So important in fact that returns now justify high investments and costs even for those deposits that were un-economical in the past. Nowadays, if properly explored and exploited, basins previously considered non-minable due to complex structural and stratigraphical situations may be economically interesting. It is while studying a faulted basin with such features that the Authors developed the described computer-aided methodology capable of constructing a model of the physical structure of coal deposits on the basis of stratigraphical data from drillings. The aim of the procedure is to define coal reserves, the exploitation of a deposit being conditioned by the possibility of identifying zones that are technically minable. This objective is pursued by making as detailed a reconstruction as possible of the geometrical, stratigraphical and tectonic features of the coal-bearing seams of a deposit.

Jan 1, 1982

By Joseph R. Hatch

During the past ten years detailed elemental analyses of approximately 8,000 well-documented samples of coils in the United States (including Alaska) have been produced by the U.S. Geological Survey and the various State geological surveys. Examples of data listings include Swanson and others (1976) Gluskoter and others (1977) Hatch, Affolter, and Davis (1979), and Wedge and Hatch (1980). These analyses serve as a basis for evaluating elemental abundances in coals from the various coal province, regions, and fields. When combined with additional geological and geochemical data, some of these analyses give insight into when certain elements were introduced into coals, and which physical and geochemical parameters are most important in determining coal elemental composition.

Jan 1, 1982

By H. Saito

To Japan, which is scarce in natural resources, limestone is the only mineral resource comparatively rich in ore reserves and having broadly recognized outstanding quality. Distribution of the limestone deposits extends from Hokkaido in the north to Kyushu and Okinawa in the south, and the deposits are located in a manner of framework formation of the Islands of Japan. Studies of the geological ages of these ore deposits reveals that almost all of the main ore deposits west of Kanto Area belong to the Carboniferous Period - Permian Period of the Paleozoic Era. Also in the east of Kanto Area, deposits belonging to the Paleozoic Era constitute the main part, although recently there are increasing examples of reclassifying the geological age of the deposits heretofore considered as Paleozoic Era to the Triassic Period of the Mesozoic Era by the recent discoveries of the fossils of conodont, etc. Large ore deposits and main ore deposit groups are given in the Figure 1, which shows that the deposits are roughly found well distributed throughout the country.

Jan 1, 1982

By Fred Leighton

INTRODUCTION Dynamic (seismic or microseismic) methods of determining the stability of structures in rock are based on detecting and analyzing the characteristics of seismic energy that has originated from or traveled through the rock mass. This seismic energy can be in the form of naturally occurring rock noise energy resulting from structural adjustments within the rock or can be introduced into the structure by physical means, such as by blasting or impact. In either case, the seismic energy radiating through the rock mass can be detected using standard equipment and can be analyzed by established techniques to reveal a wide variety of information concerning the condition and stability of the rock mass through which the energy has traveled. In the following sections, the basic instrumentation required for seismic and microseismic studies is described, and some of the presently used applications of these methods are discussed to exemplify the state of the art. INSTRUMENTATION Seismic disturbances in a rock structure generate two types of seismic wave radiation, body waves and sometimes surface waves, which radiate outward in all direc¬tions from the source of the disturbance. Underground mining applications are generally concerned only with discerning the characteristics of the resulting body waves, i.e., the compressional (p-wave) and the shear (s-wave) energy. As these two forms of energy travel through the rock structure, the particles of the rock mass are caused to vibrate, and the vibration character¬istics resulting from each of the two types of wave are distinct. Some important differences are: 1) Compressional and shear waves travel at different velocities through the rock structure. 2) The frequency at which each wave causes particles to vibrate is different, and may range from about 50 to 100 000 Hz. 3) The amplitude or energy level of each wave is different, with the shear energy usually being the greatest. These differences form the basis for equipment se¬lection for individual studies and for modern data analysis techniques. The following sections describe the basic equipment necessary to detect and record seismic wave energy data and show several examples of analysis procedures and how these procedures have been used. In principle, seismic equipment is very simple. It consists of a geophone (or geophones) to detect the seismic energy vibration and convert that vibration to an electric signal, an amplification system to increase the level of that signal, and a means of monitoring and/or recording the signals detected. Fig. 1 is a block diagram of a typical system. The following sections offer a very brief discussion of system components and their individual functions. A more complete discussion is given by Blake, Leighton, and Duvall (1974). Geophones The function of the geophone is to detect the vibrations caused by the passing of the seismic wave energy and to convert that vibration into an electrical signal that displays both the amplitude and frequency characteristics of the vibration. Particle motion or vibration can be quantified and measured by measuring displacement, velocity, or acceleration of the particles. Thus, there are three types of geophones: displacement gages, velocity gages, and accelerometers. The choice of gage depends on the characteristic frequencies of the seismic energy to be monitored and the sensitivities of each type of geophone. In general, displacement gages are used for low-frequency monitoring (periods to 1.0 Hz), velocity gages for medium-frequency monitoring (1.0 to 250 Hz), and accelerometers for high-frequency monitoring (250 to 10 000+ Hz). Experience has shown that in underground studies, the choice of which gage to use lies between velocity gages and accelerometers. An easy, accurate method for selection of gage type is discussed by Blake, Leighton, and Duvall (1974). Once the type of geophone has been selected for use, it must be properly installed, and in the installation procedure the most important step is insuring that the gage is firmly attached to a competent portion of the rock structure. Poorly mounted geophones may entirely fail to recognize low-level seismic signals and will distort the information from signals they do see. Amplifiers Seismic events associated with mine structures occur over a very broad range of energy which results in a broad range of geophone output levels. In general, geophone output levels occur in the microvolt to low milli-volt range, and it is necessary to amplify these signals in order to drive recording or monitoring equipment. Because either an accelerometer or a velocity gage might be used as the geophone, the amplification system must

Jan 1, 1982

By Vaughn E. Livingston

Washington State has a variety of industrial minerals and although not many are produced currently (1982) most have a history of production (table 1). The value of industrial minerals produced in the state exceeds by several times the production value of metallic minerals. In 1981, 15 minerals - cement, limestone, clay, gemstone, pumice, sand and gravel, stone, diatomite, gypsum, olivine, peat, talc, garnet, silica, and dolomite - were produced. Combined value of nonmetallic production for 1981 is estimated at $218,999,000. Cement had the largest estimated value at $102 million, followed by sand and gravel at $47 million, and crushed stone at $29 million. These figures are from the US. Bureau of Mines preliminary production figures for 1981.

Jan 1, 1982

By T. L. Dobecki

Numerous seismic techniques have proven to be important and cost effective aids to both coal exploration and nine planning. Projects conducted by Sandia in recent years have sham seismic refraction is a valuable tool for determining overburden properties while high resolution, 2-0 and 3-D seismic reflection surveys are the primary means of napping coal seam distribution, structure, and continuity. Further, seismic methods utilizing existing boreholes (e.g. downhole, crosshole and guided wave) provide detailed measures of overburden/interburden modulus variation, seam continuity, and calibration for other seismic surveys. Examples include mapping faults of 2-10 m threw in seams 3-15 m thick at depths of 80-300m.

Jan 1, 1982

By David L. Kuck

Siderophyle platinum-group metals and sane gold are a thousand times more abundant in metal and chondritic meteorites than in terrestrial or lunar rocks. Type I and II carbonaceous chondrites contain granules of the high boiling point metals W, Re, Mo, Ir and Os. Metal meteorites and the metal fractions of other chondrites contain siderophyle Pt, Pd, Ru, Rh, Os, Ir and Au. Spectra of sunlight reflected from asteroids, when compared with those of meteorites and specific minerals, provide a rough classification and guide to sources of precious platin-group metals.

Jan 1, 1982

By M. T. Atwood

For more than sixty years the rich oil shale formations of Colorado, Utah and Wyoming have been evaluated as a future source of petroleum. After many false starts the commercial production of shale oil is near. Union Oil and Colony (Exxon and Tosco) have begun construction of commercial plants. Occidental and Rio Blanco (Gulf and Standard of Indiana) are well along in the development of modified in situ (underground) processes. A number of other companies and groups are in advanced stages of development. This paper will review some of the major elements involved in the production of shale oil with emphasis on means available to express the efficiency of production of pyrolysis liquids and gases from oil shale rock.

Jan 1, 1982

By Doug Halbe

A number of CIP plants have been built in Western Australia in the past two years. The authors have surveyed several of these new plants and present drawings, data and discussion of operating and design innovations and areas of interest.

Jan 1, 1982

By B. Alegria

The depressing effects of different inorganic chemicals on the flotation of pyrite have been investigated in this study. The results of the flotation tests indicate that pyrite can be depressed by oxidizing as well as reducing agents under controlled conditions of pH and reagent dosage. Oxidizing reagents such as potassium chromate and potassium dichromate were found to cause complete depression of pyrite in the acidic pH range. These effects are similar to those obtained in the pyrite-cyanide system. A less stable oxidant, potassium permanganate, inhibited the flotation of pyrite at a concentration as low as 0.1 mol/L at all pH values, Addition of reducing chemicals such as ferrous chloride or manganous sulphate to the flotation of pyrite were found to produce depressing effects depending on the additive concentration and pH of the solution.

Jan 1, 1982

By Joel K. Waterland

GENERAL DESCRIPTION Homestake Mining Co.'s operations are at Lead, SD. Production from the various methods used are: 1 155 753 t/a (1,274,000 stpy) by open cut-and-fill, 68 039 t/a (75,000 stpy) by square set cut-and-fill, 144242 t/a (159,000 stpy) by shrinkage stoping, 107 048 t/ a (118,000 stpy) by blasthole stoping, and 67 132 t/a (74,000 stpy) in development work for a total of 1 542 214 t/a (1,700,000 stpy). Mining takes place from the 616-m (2000-ft) level to the 2073-m (6800 ft) level (Fig. 1). The average travel time to the stope is 45 min. GENERAL ORE BODY REQUIREMENTS AND LIMITATIONS Size, Shape, and Dip of Ore Body Six major ledges varying from 914 m (3000 ft) long by 228.6 m (750 ft) wide to 305 m (1000 ft) long by 122 m (400 ft) wide are mined. Within these ledges are irregular-shaped areas of varying sizes. These ledges dip at approximately 1.2 rad (70°) to the east and plunge to the south from 0.26 to 1.57 rad (15° to 90°). Ground Conditions The ore is cummingtonite (chlorite schist) which is very competent except for major bedding planes and fracture patterns. The footwall is a slate but because of the dip presents very few problems. The hanging wall is also a slate which because of the dip and bedding is very weak and requires considerable rockbolting. No problem has been encountered with rock bursts to a depth of 2438 m (8000 ft). Ore Value The ore values vary somewhat from ledge to ledge, but the average ore delivered to the mill is approxi¬mately 6.2 g (0.2 oz) of gold per ton. A small amount of silver is the only byproduct of this operation. Annual production of gold is approximately 10 575 183 g (340,000 troy oz). Production Requirements The mine has a mill capacity of approximately 1 723 651 t (1,900,000 st) but because of several fac¬tors (manpower, depth, etc.) this mill capacity has not been attainable for the past several years.

Jan 1, 1982