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By C. J. A. Mcewan, C. M. Rice

The Rosita Hills contain rich, vein- and breccia pipe-hosted precious metal deposits. Volcanic activity occurred in two cycles - an early, mainly andesitic cone-building phase that terminated in the formation of a caldera and breccia pipes and a later phase characterised by trachytic lavas and dykes, rhyolite domes and lamprophyre dykes. Alteration consists of weak propylitic and argillic and, locally, intense advanced argillic, K-feldspar sericitic and silicic types. Marked trace-element depletions (Rb, Sr, Zn, Mn) are associated with K-feldspar-sericitic alteration and with advanced argillic alterations, whereas enrichments (Pb, Ag) are associated with K-feldspar-sericitic alteration. Gold distribution is highly localised and is controlled by breccia pipes and a caldera ring fault; it is not related to district scale alteration. In general, the geochemical and alteration patterns are complex, but they are clearly influenced by linear structures, the caldera ring fault and breccia pipes. Pipe-hosted Au-Ag and vein-hosted Ag mineralisation are associated, respectively, with early andesitic and late, post-caldera rhyolitic activity. The pipe-hosted and, especially, the vein-hosted mineralisation show affinities with adularia-sericite-type epithermal deposits

Jan 1, 1991

By R. J. E. Stewart

Another very successful evening meeting was organized by the Johannesburg Branch of The South African Institute of Mining and Metallurgy on 20th November, 1990, when Mr R.D. MacPherson, General Manager of Richards Bay Minerals, gave a presentation on the Richards Bay operations. The function was held in the Ballroom of the Johannesburg Country Club, and the very high attendance (some 250 people) was indeed a reflection of the high profile of the subject mater. It was also a fitting reward for the efforts of Mr MacPherson and his team, who spent a considerable amount of time and effort traveling the country to present 'the other side of the story'.

Jan 1, 1991

By O. Dojcar

The results of a laboratory investigation of rock fragmentation conducted with a model material were partially verified under field conditions. The object of the investigation was to study the qualitative and quantitative relations between the parameters of the primary blast and fragmentation to enable the planning of an economically efficient degree of disintegration with optimum utilisation of the blast energy. The three blast parameters that were considered were burden, specific charge and the ratio of spacing to burden

Jan 1, 1991

By Salehi M. R

Although inherent mineral matter appears to have no effect of the reflectivity of inertinite in the reflecting light microscope, it has a marked effect on the grey levels resulting from the backscattered electron response in the scanning electron microscope. Inertinite with a high inherent mineral matter content has a high grey level response but not as high as that of mineral matter. The highest grey level response is with inertodetrinite which at times could be mistaken for mineral matter. Fusinite has a higher grey level response than semi-fusinite. The backscattered electron grey level response corresponds to average atomic number and hence approximately to density. If a porous structure develops and becomes filled with mineral matter such as S, Cl, Ca, Si, and Al the grey level will be higher. Micrinite has an unusual response in that it behaves like an exinite maceral in the SEM rather than an inertinite maceral. It either has a low grey level when relatively free of inherent mineral matter, or a low grey level background with high level granules corresponding to Si and Al dominantly. Similar structures have been found in exsudatinite and resinite. It is thought that micrinite results from the migration of hydrocarbons out of exinite giving a porous structure which usually accommodates inorganic matter.

Jan 1, 1991

By Daniel E. Walsh

A pilot scale study was performed to evaluate the potential for gravity concentration of gold from -13 mm (-1/2"), crushed ore from Ester Dome, Alaska. 9.04 tonnes (9.94 tons) of crushed ore were sampled and processed through a Pan-American jig -Wifley table pilot plant. Plant products were sampled for assay and material balance calculations. Gold recovery through one stage of jigging and two stages of tabling was 17.4% at a concentration ratio of 615:1. Concentrate grade was 766.3 g/tonne (22.4 oz/ton). The feed grade to the plant was calculated at 1.71 g/tonne (0.050z/ton). Jig tailings, primary table tailings and secondary table tailings grades were 1.44 g/tonne (0.042), 1.30 g/tonne (0.038), and 5.47 g/tonne (0.16 oz/ton) respectively. Significant, coarse, free milling gold values were shown to remain in the jig tailings. Concentrate mineralogy is discussed.

Jan 1, 1991

By Beer G

The recent re-emergence of an Integral Pressure Stripping system which operates with both cell and column in closed circuit at elevated temperature and pressure, requires no cyanide in the eluate solution and has greatly reduced carbon reactivation requirements in seen as a progressive step in this area. Several of these re-configured IPS systems have been placed in service in Australia and overseas in the last three years, with the first of the new generation units constructed and commissioned by Como Engineers Pty. Ltd. at Mt. Fisher in the East Murchison of W.A. in September 1987. This plant was relocated to a new ore body at Darlot W.A. in February 1989. Use is made of a data base of raw plant performance figures from both Mr. Fisher and Darlot and its performance compared with other operating plants. Initial commissioning difficulties of the Mt. Fisher prototype and dis- cussed together with the modifications and operational procedures required to overcome these problems. Stripping times of less than 6 hours at 145 degrees have been achieved with barren carbon values less than l O ppm from loaded carbon values above 3000 ppm and with cell pass efficiencies reaching 90 per cent.

Jan 1, 1991

By C. J. Hall

The simplest natural ventilation cycle is similar to a Joule or Brayton cycle. This comprises two reversible adiabatic processes in the shafts and constant pressure processes underground and on surface. The thermal efficiency of such a cycle is given by the temperature increase in the downcast shaft divided by the absolute temperature of the air at the bottom of the downcast shaft, and is independent of the temperature increase underground. This efficiency is comparable to the Carnot efficiency, which is the greatest possible value between constant temperature reservoirs, source and sink. Two variations of the Joule cycle are investigated, using numerous work examples. In the first, dry air is used as the working substance, a fan is provided at the top of the upcast shaft, and various mass rates of flow are used with frictionless shafts and a constant resistance value in the horizontal mine workings. The lost work less the fan work gives the natural ventilation work, and this divided by the enthalpy increase in the workings gives the thermal efficiency. The thermal efficiency increases dramatically with mass rate of flow, although the enthalpy increase remains constant. This appears to violate the second law of thermodynamics, since the frictionless case has a Carnot efficiency. When the lost work is added to the enthalpy increase, however, the efficiency decreases slightly from the Carnot value, to conform with the second law. This increase in efficiency with mass rate of flow is often referred to as the reheat effect, although the air is not heated. The second investigation is similar to the first, except that the air entering the downcast shaft contains a small amount of water vapor, and there is evaporation in the mine workings only, until the air entering the upcast shaft is saturated. There is, of course, condensation in the upcast shaft. In this case, it is not possible to calculate the Carnot efficiency, but the thermal efficiency is 20 to 40% of the similar dry air values. This decrease is much more than can be accounted for by the larger value of specific heat for water vapor. In addition, the natural ventilation work is almost constant with increased mass rate of flow, and the thermal efficiency based on heat addition tends to decrease. The thermal efficiency based on heat and lost work decreases in conformity with the second law. The reasons for the differences in behavior between dry and moist air are not readily apparent.

Jan 1, 1991

By Swift J. D

A key parameter affecting the performance of gravity thickeners in hydrometallurgical processing operations is the aggregation state of the feed after the addition of a flocculant. New procedures which measure the settling ratelsize relationship and the size distribution of aggregates in their process liquors have been used to quantify the aggregation state of the feedwell, overflow and underflow streams in a tailings thickener. The data obtained have been related to the thickener's operation and to a change in the flocculant dosage. A comparison is also made between the settling rate/size relationships determined with these new procedures and the mud-line settling rates from cylinder tests.

Jan 1, 1991

By J. J. Peshel

As per the current conceptual design presented by the Department of Energy, the exploratory shaft facility (ESF) becomes a part of the repository if the Yucca Mountain site is found suitable for repository development. Therefore, the design of the ESF should be compatible with the performance requirements for the repository. The construction methods selected should limit to the extent practical, the degree and the extent of damage to the surrounding rock mass. The ESF construction and operation should be compatible with the site data gathering activities, such as geological, thermomechanical, hydrological and geochemical testing.

Jan 1, 1991

By H. R. Weischedel

The art of wire rope inspection has advanced rapidly over the past decade. Present electromagnetic (EM) wire rope inspection instruments provide an important and often vital element of wire rope inspection. Some instruments are easy to operate and offer simple and clear data interpretation. Simultaneously, wire rope inspection and retirement standards are becoming simpler and more lucid. Future guidelines will he easy for inspectors to apply and for rope operators to fulfill. The thrust of evolving regulations is clearly toward periodic EM inspections supported by visual inspections. These development sallow even moderately skilled personnel to perform EM inspections of wire ropes. Therefore, it is now possible and cost effective for wire rope users to have EM and visual inspections performed by in-house personnel. In-house EM inspections have many advantages and offer an excellent return on the initial investment. Since EM inspections can detect rope deterioration in its beginning stage, wire rope users recognize that they are an effective preventive maintenance tool. For instance, the early detection of wear or corrosion allows immediate corrective action. This can easily double, or even triple or quadruple, the service life of a rope.

Jan 1, 1991

By Norman L. Kotraba

In Electric Arc Furnace (EAF) steelmaking, dust emissions are collected in a baghouse to prevent their escape to the Environment. This fine dust, predominantly iron oxide, also contains oxides of various other metals introduced into the EAF from the scrap charge. For example, mixed or galvanized scrap brings with it zinc, lead, and small quantities of cadmium which preferentially accumulate in the collected off-gas dust. Stainless steel scrap brings chromium into the charge, some of which also makes its way into the baghouse dust as hexavalent chromium-containing oxides. Because many of the contained heavy metal oxides are water-leachable, the U. S. Environmental Protection Agency has listed EAF dust as a hazardous waste which, as of August 8, 1988, cannot be 1andfi11ed without first being treated. Moreover, beginning August 8, 1991, all dusts with zinc concentrations of 15% or greater will be required to undergo high temperature thermal treatment to remove the heavy metals prior to any further disposal. This deadline represents several EPA-granted time extensions to the original requirements; extensions which were granted to allow for further development of process technologies.

Jan 1, 1991

By Fred N. Kissell, Jeffery L. Kohler, Edward D. Thimons

Aerodynamic stall of vane-axial fans is both an operational problem and a safety concern. While deep stall is relatively easy to detect, the diagnosis of a partial stall is often more difficult. Its transient nature and the fact that its symptoms can mimic electromechanical problems of the fan and fan drive assembly, or vice-versa, compound the difficulty of making a timely and accurate diagnosis. A knowledge-based expert system known as FANPRO has been developed to aid in the diagnosis of these problems. FANPRO and its application are the subject of this paper.

Jan 1, 1991

By Hassan Madani

Kushk lead-zinc mine is located in central part of IRAN. The mine is owned by Bafgh Mines Co., which is a nationalized company. Exploration results show that ore occurs in the area that extends for 800m length and 180m depth. The approved, probable and possible reserves of the mine is 900,000 tons, 1,120,000, tons and 1,450,000 tons respectively with average grade of 17.7% zinc and 4.3% lead. The total annual output of the mine all was by underground mining, is in the order of 100. 000 tons. The main entry to the mine is via an inclined shaft with a cross-sectional arp of 8 m2, length of 263m which dips at 20°. The ore is mined mostly by sublevel stopinq method. The major difficulty in ventilating the mine was that related to spontaneous combustion of pyrite, which was more serious in some parts of the mine than others. In order to reduce this risk, a new ventilation system for the mine was designed, using 4 exhusting fans.

Jan 1, 1991

By A. B. Cron, R. MacPhail, L. Melis, K. Armstong

"Mt. Milligan is a porphyry gold/copper deposit in north-central British Columbia. Diluted and mineable drill-indicated reserves total 449 million tons at an average grade of 0.013 oz gold/ton and 0.19% copper. Large-scale commercial development of the deposit will make Mt. Milligan Canada's third largest gold mine.Metallurgical investigations for the Mt. Milligan project were done in three phases: scoping tests in the first half of 1989; bench-scale work from October 1989 to April 1990; and a pilot plant program in May and June 1990. Various process alternatives for the recovery of gold and copper are described and results are presented. Net smelter return evaluations led to the selection of optimum process conditions for maximizing revenue from gold/copper flotation concentrates.The selected flotation circuit and basic design criteria are described. Forecast average recoveries over the presently-defined 20-year project life are 75.2% for gold and 90.5% for copper in a copper concentrate averaging 17.6% copper and 1.0 oz gold/ton. 1.0 PROJECT LOCATIONThe Mt. Milligan porphyry gold/copper deposit is located in northcentral British Columbia, 150 km north of Prince George, British Columbia. The site is at an elevation of 1,100 m in an area of logged, gently-rolling topography. Nearby communities include MacKenzie and Fort St. James. Climate in the area is moderate and there is direct road access to the property. A location map is presented in Figure 1-1."

Jan 1, 1991

By Peter T. Luckie, Joseph W. III Leonard

INTRODUCTION In a bed of fine coal, water can be found in the interstices created by the particle surfaces and in the pores within the coal particles. The extent of the interstices voidage is obviously a function of the particle sizes and morphologies, as shown by the fact that the bulk density of coarse coal is greater than that of fine coal. After drainage, the voids can be completely or partially filled. By increasing the suction pressure across the bed, as is done in vacuum filtering, the quantity of water in the voids can be reduced. But eventually the increased suction pressure has little influence on the moisture reduction. In addition, the moisture in the pore structure of the coal is unaffected by the mechanical removal of the moisture in the interstices. When this condition is reached, the total moisture content of the coal can only be reduced further by evaporating the water. Evaporative drying is done for one or more of the following reasons: 1. To avoid freezing difficulties and to facilitate handling during shipment, storage, and transfer to the points of utilization. 2. To reduce the heat loss due to evaporation of the moisture from the coal during the combustion process, thus increasing heating efficiency. 3. To decrease transportation costs. The heating value of coal is equally improved for each percentage point reduction in the noncombustibles in coal. It is estimated that a reduction of 1%22 in the total moisture in the coal increases the thermal efficiency of the heat-raising process by about 0. Some coal buyers consider 1 % moisture content to be the equivalent of a 4% ash content.23 It is important to avoid drying the coal to too low a moisture level, since the complete removal of surface moisture to produce a bone dry product can result in a serious dust, wind lost, and safety problem. Surface moisture con- tents of 3% or less for shipped coal are not uncommon. However, the evaporatively dried coal may be lower, Y, to 1%, since the mechanically dewatered coal may be higher. Evaporatively dried coal can be treated (sprayed) with chemicals in order to control the dustiness and any freezing difficulties, thereby providing the producer with more operational flexibility. The evaporative drying of coal is essentially a process of simultaneous transfer of energy, usually in the form of heat, and water, in the form of vapor, from the coal. In order to remove the undesired moisture, it is necessary to raise the temperature of the water from the entering temperature of the feed stream, TF, to the boiling point of the water (usually taken as 212"F), vaporize

Jan 1, 1991

By R. S. Ondrey, R. A. Haney, T Tomb, R. T. Stoltz, Novakowski D. L. Chiz, E. J. Gerbec, D. J. Atchinson

Although the number of operating longwalls in the United States (approximately 100) has remained relatively constant over the last five years, longwall production levels have significantly increased and in some cases more than doubled. As a result of this production increase, control of respirable dust continues to be a problem. Therefore, the Mine Safety and Health Administration (MSHA), Pittsburgh Health Technology Center, Dust Division, initiated a study to investigate the availability and adequacy of technology for controlling dust on longwall mining operations. The study involved 23 longwall mining operations in three different Coal Mine Safety and Health Districts. Each operation was visited for a full shift. Respirable dust samples were collected on face personnel and at fixed locations along the face. Methods being used to control dust were noted, with special emphasis placed on obtaining quantitative data relative to ventilation, headgate dust controls, cutting drum sprays, external machine sprays and cutting sequence. Attempts were made to correlate dust control practices in place at the time of the visit to dust concentrations measured at the tail and on the tail shearer operator and to the average of all the dust concentration measurements from the occupations sampled. The methods used to control dust were also compared to the gamut of methods known to be available. This paper presents a discussion on the effectiveness of the methods being used to control dust and on the availability of technology for the control of dust on longwall mining operations.

Jan 1, 1991

By William D. Leech, Ronald E. Romley, Gary N. Sheppard

The Price Road Drainage Tunnel was constructed for the Arizona Department of Transportation (ADOT) in 1988 and 1989 to provide surface water drainage for the proposed outer Loop Highway (SR 117). The 5.4 km (3 mile) long, 6.6 m (22 ft) excavated diameter tunnel was driven through sand, gravel and cobbles utilizing an open face digger shield. Precast concrete segments were erected for initial ground support. A second-pass reinforced concrete final lining was placed, which was followed by contact grouting. This paper will consider the owner's representatives' view of the effectiveness of using precast concrete segments for this project. Topics discussed include segment design and erection, ground support, geotechnical instrumentation, segment erection verses contact grout interactions and tunnel production.

Jan 1, 1991

By Xu Youzai

Static loading teets of five nodular piles and four non-nodular piles were performed in Tianjin soft clayey soil in which measurements of axial force and movements were made. Distribution of shaft resistance and load-movment curves for pile head and pile toe are presented in this paper. The applicability of nodular piles to soft soil and their effectiveness are also discussed. Based on the comparison, it is concluded that nodular piles have an advantage over non-nodular piles mainly in contri­bution to shaft resistance. Dynamic testing was also conducted through R. P. T. for evaluating the service load of tested piles.

Jan 1, 1991

By Harry J. Olson

Geothermal Energy has a great potential for meeting the electrical and thermal energy requirements of many countries and territories lying along tectonically active zones within and surrounding the Pacific Basin. Energy requirements for many of these small, scattered volcanic island nations preclude development of conventional generating facilities large enough to incorporate any economies of scale. However, by attempting to discover and develop shallow, relatively low temperature, geothermal reservoirs associated with recent vulcanism on many of the volcanic islands, exploration expenditures and risks, and problems associated with the development of high temperature resources can be reduced. Exploration and development drilling for these resources can be accomplished with truck mounted rotary drilling rigs that are less costly and more suitable for operations within the island infrastructures than the conventional rigs normally used in the drilling of deep, high temperature geothermal resources. Experience over the past decade with small, modular, binary (Rankine) cycle generating units indicates that geothermal energy can provide a reliable source of baseload electricity in the amounts required and at a cost that is competitive with other alternative and conventional energy sources. Development of shall, moderate temperature, geothermal resources with small, modular binary cycle generating units can provide ideal additions to the energy sources of many of the Pacific volcanic island nations within the framework of their island economies.

Jan 1, 1991

By David Kress

Grinding mills, both autogenous and ball can be powered by several basic means. The three methods used today are girth gear drives, gearless drives and trunnion coupled reducers. This paper will focus on the first of these methods -girth gear drives. The girth gear drive has been used on thousands of mills which continue to operate successfully. These drives are noted for their simplicity and low cost. In the past, the horsepower capacity of girth gears has been slow to keep up with the horsepower increase required by the mill builders, particularly since the advent of the SAG mill. Gear manufacturers had capacity for 2000 HP mills in the 1950's, 5000 HP in the 1960's and 6500 horsepower in the 1970's. The 70's and 80's brought dual pinion girth gear drives which allowed mill sizes beyond 10,000 horsepower. Gear manufactures who could not keep up with the pace of the horsepower demands and the quality and reliability demanded by the mill builders and users have fallen by the wayside.

Jan 1, 1991