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By S. P. Polack

"INTRODUCTION The purpose of this circular is to correlate the information obtained during personal investigations at the sites of four rock tunnels in the process of construction and information obtained from the records and personal views of the constructors of two other tunnels that were not visited during the, excavation phase of construction and to present this information for the benefit of those who contemplate future construction of rock tunnels.Modern mechanized coal mining requires better, safer, properly alined haulageways and beltways; consequently, better understanding of tunneling methods by coal-mining men will be necessary. The possibility of future high-speed haulage systems utilizing rock tunnels in the more solid rock strata above or below the coal beds must not be discounted. In the past, tunnels have been driven for use in draining and unwatering inundated coal mines. At present, the need for such tunnels is very evident in some parts of the coal-mining regions, notably in the Pennsylvania anthracite fields, and studies along these lines are in progress. The average coal-mining man has little time or opportunity to visit tunnels while they are being exca-vated; therefore, it is hoped that this information will assist him in constructing tunnels safely if he is required to do so in the future.The tunnels described herein differ in size, shape, usage, and, in many instances, in their geological aspects. Full-face, heading and bench, and pilot-tunnel, and enlargement methods of excavation were utilized.The roof-support methods show diverse designs and materials of construction to suit each purpose and condition. The superiority of steel roof support over wood is demonstrated beyond doubt and is shown clearly in the photographs included in this circular.The illustrations (photographs taken by the U. S. Bureau of Mines, the U. S. Corps of Engineers, and others) show many of the necessary steps taken during the excavation and the erection of roof support in tunnels under construction."

May 1, 1950

By Gerald W. Elger

This report describes development of the fusion-leach crystallization precipitation process for producing a hafnium content feed material for hafnium-zirconium separation plants. Mixtures of zircon, potassium silicofluoride, and potassium carbonate (or potassium chloride) were fused to prepare soluble potassium zirconium hexafluoride-potassium hafnium hexafluoride salts. High extraction of these salts was obtained by countercurrent leaching the fused material in dilute hydrofluoric acid. About one-half of the hafnium was recovered in hafnium-enriched mother liquor by cooling clarified lead: liquor to crystallize most of the zirconium salt. Additional hafnium was recovered from the primary crystals in a multiple dissolution-recrystallization step. Hafnium-enriched oxides having a hafnium-zirconium ratio of more than three times that of zircon were precipitated from the combined mother liquors. The hafnium and zirconium recoveries in the precipitate were 83 and 24 percent, respectively. About 71 percent of the zirconium and the remainder of the hafnium were recovered in potassium zirconium hexafluoride crystals of low-hafnium content.

Jan 1, 1966

By Xuan Cheng

The electrochemistry of sulfide mineral flotation is reviewed with particular emphasis on galvanic interaction among minerals and grinding media, and its relevance to flotation of complex sulfide ores is discussed. Surface alteration due to galvanic interactions among chalcopyrite, pyrrhotite and mild steel is analyzed in terms of voltammetric and chronoamperometric studies on individual minerals and through galvanic current measurements in 2- and 3- electrode combinations. The results are related to laboratory flotation behaviors of chalcopyrite-pyrrhotite mixtures simulating copper-nickel bearing Duluth gabbro.

Jan 1, 1993

The brown coal deposits of the Latrobe Valley are ideal for open cut mining and this method has been used since the start of coal winning in 1894. Operations at the main Yall9urn open cut commenced in 1922, but after a few years the main excavators were replaced by German continuous excavators and subsequent developments of Yallourn and the newer Morwell open cut have been based on this type of plant. The reasons for preferring continuous to intermittent excavators in the Latrobe Valley are indicated in this paper.Under the pressure of post-war conditions, and from their long experience and ability, German engineers have recently made substantial improvements in their continuous excavators and these developments have been enhanced by some American innovations. These changes have extended the economic limits of open cut mining and also serve to emphasize the close inter-relation between the nature of coal and overburden deposits, excavator design and methods of operation.As an aid to descriRing recent excavator developments, this interdependence is demonstrated by means of diagrams which show typical methods of operations, together with examples of actual machines using these methods. The types of excavator dealt with are mainly those in use at, or destined for Yallourn or Morwell open cuts, together with additional types used in U.S.A. and Western Europe. For completeness, and also because they will continue in service at Yallourn and Morwell for some years, rail-mounted dredgers have been included in this paper even though in Europe they are now regarded as obsolescent.Explanations are given of how the intrinsic qualities of Latrobe Valley brown coal and overburden have sometimes prevented overseas plants from operating with the full efficiencies and/or in the methods visualized by the manufacturer, and references are made to the modifications and investigations being undertaken to overcome these problems.A compresensive bibliography is given. Dates shown on illustrations are not commissioning dates of the plant concerned, but the year when photographed.

Jan 1, 1960

The mineral chromate is the sole current source of commercial chromium Chromite varies compositionally within limits permitted by the formula ((Mg,Fe,Zn,Mn)(A1,Cr)2O4) No chromate has been mined in the United States since 1961 In the past, almost all the chromate mined in the United States came from Alaska, California, Maryland, Montana, Oregon, and Pennsylvania, with about one-half of all production coming from Montana Primary chromate deposits occur only in certain kinds of ultramafic or closely related anorthositic rocks The two major types are stratiform (layered) and pod-shaped The Stillwater Complex of Montana is the largest known United States resource It is a stratiform deposit where several exposed zones of high-iron chromiferous material extend in length Since there is no commercial chromate mining in the United States, there are no environmental problems related to underground mining

Jan 1, 1975

By Nick Hasenack

In the pelletizing plant of Hoogovens, Estel BV, a varying mixture of hematites and magnetites is used for the production of acid and (occasionally) fluxed pellets. Optimum results regarding productivity, quality and process control are obtained with mixtures containing 30-40 % magnetites. A decrease of the magnetite ratio or an increase of the basicity has a great influence on both productivity and heat and power consumption. Tests have been carried out to find the extent to which magnetite can be replaced by b.f. dust, mill-scale and coke breeze. Pilot plant tests show that about 80-100 % of the production loss due to a decrease in magnetite content or to the increase in basicity can be regained without damage to the quality by adding coke breeze. The amount of coke breeze should be limited tot 1,5 %; if this percen¬tage is chosen higher, the quality of the pellets deteriorates rapidly. The amount of coke breeze to be added should be about 30 % above the theoretical value, based on heat balance considerations. The results achieved by incorporating b.f. dust and mill-scale into the pelletmix were also encouraging, but as some types of mill-scale are very difficult to grind and the supply of b.f. dust is limited, the research has not been carried out extensively in this field. The pilot plant tests on replacement of magnetite by coke breeze have been followed by industrial tests, during which the breeze was added to the ore feed before the dry-grinding system.

Jan 1, 1977

By Maria I. De Rosa

The U.S. Bureau of Mines conducted experiments for predicting materials' ease of combustion (smoldering onset, smoldering, flaming, and decomposition rates) by means of submicrometer smoke particle characteristics for the development of a simple test method. The experiments were carried out in an approximately 20-L furnace, with a 10-L/min airflow through the furnace for a 14-min duration, at set furnace temperatures of 150°, 250°, and 1,000° C. The variables studied as a function of time were the onset time of smoke particles, time and duration of maximum smoke particle generation, average concentration of smoke particles, and particles' average diameter, mass weight loss, and furnace temperatures. Results show that the onset time of smoke particles is predictive of materials' ease of smoldering, and the time of maximum smoke particle generation and its duration, coupled with mass weight loss, are predictive of materials' ease of smoldering and flaming (depending on the experimental temperatures), and decomposition rates.

Jan 1, 2010

By William Rachunis

This publication describes the construction of 43.64 miles of underground tunnel to be used as an aqueduct, known as the West Delaware aqueduct. In the past, the accident history of tunnel operations has not been favorable, the "rule of thumb" being a death for each mile of progress, according to the meager accident statistics available for the tunnel-driving industry. The accident experience at this project and the use of modern equipment established safety and progress records that were accepted by tunnel people as a record at the time. The city of New York comprises 5 boroughs, with a total population of approximately 8 million people, and uses about 1,210 million gallons of water each day. The water supply for the city is the responsibility of the New York City Board of Water Supply. This organization has constructed an extensive aqueduct system, the Delaware aqueduct, to convey water to the city from the distant mountain and river sources in the Catskill Mountains in the Southern Tier areas of New York State (figs. 1 and 2).

Jan 1, 1962

By R. E. Fryxell, E. C. Duderstadt, P. K. Conn

Permeation rates for nitrogen through are-cast tungsten were measured in the temperature range 1800° to 2600°C at nitrogen pressure differentials of 1.0 and 0.1 atm. Gas chromatography was used to measure the quantities of nitrogen which permeated through 0.26-and 0.53-mm-thick membranes. Permeation rates were proportional to the difference between the square roots of the nitrogen pressure on each side of the membrane and inversely proportional to membrane thickness, indicating that atomic nitrogen was the difjusing species and that diffusion was the rate-limiting step of the process. Permeation coefficients calculated from the rates may be represented by the equation: where P is expressed in the units cu cm (stP)-mm per 1/2 sq cm-min-atm"' and 70.0 * 0.8 is the activation energy in kcal per mole of permeating species. In a previous paper' permeation rates were reported for hydrogen and for oxygen through tungsten. The permeation cells used for the hydrogen measurements were suitable for measuring nitrogen permeation under similar conditions, so the study was extended to include nitrogen. Permeation rates of nitrogen through the polycrys-talline arc-cast tungsten membranes were measured in the temperature range 1800" to 2600°C using two membrane thicknesses and two nitrogen pressure differentials. Permeation coefficients were calculated and the activation energy of the process determined. THEORY For diatomic gases which dissociate prior to diffusion, the quantity of gas which permeates through a membrane or wall at an elevated temperature where bulk diffusion is the rate-limiting step of the process is given by the equation: where: q = total amount of gas permeating a membrane, P = temperature-dependent permeation coefficient, A = area of membrane, t = time, p1 = gas pressure of high-pressure side, p2 = gas pressure of low-pressure side, and d = thickness of membrane. When bulk diffusion is the rate-controlling step, and the solubility of the gas obeys Henry's law, a further relationship is that, for any given temperature and pressure, the permeation is the product of diffusivity and the amount in solution. The permeation coefficient, P, is temperature-dependent according to the equation: where: Po = permeation constant, Q = activation energy, R = gas constant, and T = absolute temperature. EXPERIMENTAL PROCEDURES Cell Design and Experimental Apparatus. Two of the permeation cells used for the previous measurements of hydrogen permeation are shown in Fig. 1. Each consisted of a cylindrical chamber divided into two parts by a permeation membrane fabricated from high-purity (>99.9 pct W) wrought tungsten sheet made from vacuum arc-cast tungsten. The membrane in one cell was 0.26 mm thick and the other was 0.53 mm. The fabrication of these cells was described previously.' The permeation cells were mounted vertically in a high-temperature tungsten resistance furnace and the membranes and the center portions heated to test temperatures. Temperatures were measured by sighting an optical pyrometer on the edge of the membrane through a small hole in a tungsten plate which was fastened to the side of the cell. This arrangement provided an approximate black-body condition and eliminated the need for emittance corrections. Appropriate corrections were made for the quartz window through which the temperatures were measured. Argon gas flowed through the 10-liter volume of the furnace at the rate of 4.7 liters per min. An impurity

Jan 1, 1969

By John W. Shield

Oxide gold reserves are being rapidly depleted, especially in regions with long histories of gold mining, such as the Black Hills of South Dakota. However, these districts often have substantial additional deposits, where gold is refractory. It is not amenable to traditional cyanide extraction due to the presence of sulfide minerals that encapsulate or otherwise preclude the economic extraction of the gold. Several technologies have been developed to render refractory sulfide deposits amenable to traditional cyanide processing. These include roasting and pressure autoclaving. Unfortunately, these oxidation processes require substantial capital investment and incur significant operating costs. Microorganisms that obtain energy for their life processes by the oxidation of iron sulfides can be used to treat gold-bearing refractory sulfide minerals. As the bacteria convert the sulfide to sulfate, they expose any gold associated with the sulfide matrix. This makes the gold amenable to cyanide extraction.

Jan 1, 1996

By Jr. Smith

The equilibrium compositions of product gases for mixtures of air with methane, propane, or ethylene at and around flame temperatures are reported. For each hydrocarbon, compositions are given for five fuel-to-air ratios--two lean, two rich, and one stoichiometric--at five pressures, from 1 to 20 atmospheres, and at an ambient temperature of 25° C.

Jan 1, 1965

By Thomas T., Read

ALTHOUGH the first colonists in the area that is now the A United States, whether Spanish, French or English in nationality, were usually keenly interested in the possibilities of mineral wealth, it is a curious and interesting fact that none of them happened upon the mineral deposits that eventually were to make this the greatest mineral-producing country; up to 1800 it would probably have been rated as rather poor in minerals. Spanish explorers traversed the southeastern United States with- , out finding the Appalachian gold deposits that aroused so much interest in the early nineteenth century; Coronado sought in vain for the seven golden cities of Cibola; and the important gold \ deposits of California were not discovered until the political sovereignty of the region had passed from Mexico, which had held it for three centuries. The French also held Canada for nearly two centuries (and the British for another century) without finding the mineral deposits in Ontario and Quebec that now are so important. Though they knew of the copper of the Keweenaw peninsula, the lead ores. of Wisconsin and Missouri, and the coal of Illinois in the seventeenth century, these deposits were all too remote for exploitation. In the area held by Great Britain, iron smelting was planned at Jamestown as early as 1619 and was actually begun at Lynn, Mass., in 1643. The industry grew slowly, at first, but had reached considerable importance before the Revolution. Commercial bituminous coal mining began about 1750 in Virginia but anthracite mining in Pennsylvania was not started until 1800. As a result there was naturally little interest in the technical aspects of mineral prodnction here before 1800 by any except the few people who were actually engaged in it. Students of natural science were much interested in minerals, however. The activities of those who rank as geologists are so thoroughly covered in

Jan 1, 1941

By A von Johannides, G J. van Hout, L F

In the past various systems have been used to plan the extraction of ore from block cave operations. These systems have varied from rather sophisticated models with empirical ægravity flowÆ rules applied to the very rudimentary models where only the recorded mined tonnageÆs have been accounted for against the available resource. The normal requirement of these models has been to only plan the movement of ground through the drawpoints. Little cognisance has been taken of the other parameters that affect the total mining operations. The intended purpose of the linear program planning system is to not only include the management, resource availability and geotechnical constraints, but to also include the mining rules. The paper will discuss the various constraints that have been considered, and attempt to illustrate where the system better serves the production system than previous ones. A brief technical discussion on the linear programming system is included.

Jan 1, 2000

By Elham Najafi, Sina Ghassa, Ata Akcil, Hadi Abdollahi, Sandeep Panda, Zohreh Boroumand

The present study investigates the influence of ferrous iron (as FeSO4) and ferric iron (as Fe2 (SO4)3), and pyrite (FeS2) on the ability of bacterial leaching of a high-grade sulfide Zn–Pb ore. In this regard, shake flask experiments were carried out at 5% (w/v) pulp density of the ore sample (having 40.7% Zn and 12.4% Pb initial metal content) using a consortium of mesophilic iron and sulfur-oxidizing acidophiles. A concentration of 0.04 mol/L of ferric iron in the leaching media was found to be optimum for zinc extraction without affecting growth of the microorganisms. Under this concentration, the dissolution of Zn, Pb, Cd, and As was found to be 57%, 0.2%, 0.03%, and 9.9% in 25 days. Using ferrous iron in the media, 0.16 mol/L of Fe2+ was found to be the optimum concentration for efficient bacterial growth and metal dissolution (54.6% Zn, 0.08% Pb, 0.03% Cd, and 10.2% As) from the sample in 25 days. On the other hand, using pyrite as the source of energy for bacterial growth, an initial 12-day lag period was observed when compared to the effect of ferrous iron in the media. Under the optimum concentration (test with 0.24 mol/L iron in the form of pyrite), the dissolution of Zn, Pb, Cd, and As was found to be 39.8%, 0.1%, 0.03%, and 10% in 25 days. The surface chemistry analysis indicated formation of a sulfur layer over the particle surface that hindered reagent diffusion and affected metal recovery through bioleaching.

By AIME AIME

WILLIAM ("BILL") EMBRY WRATHER, recently elected to a second term as Director of the Institute, is widely known as petroleum geologist, gentleman, and scholar. Born in Brandenburg, Ky., he was early endowed with a Southern accent which has remained with him strongly flavored by his later life in the oil-fields of Texas and the Mid-Continent region, and only thinly concealed by a Middle Western burr acquired during his student days at the University of Chicago. After graduating there with the Ph. B. in 1908, young Wrather (the adjective still fits!) joined the Gulf Production Co. Soon afterwards he married a charming Chicago girl, Alice Dolling, who, with their two daughters, has been his companion on many of his more distant trios.

Jan 1, 1945

By S. S. Peng

In dealing with the mining engineering problems, the traditional approaches of laboratory experimental simulations and/or analytical solutions are not very effective. Mainly because the field problems are too complex to be solved with a few simplified assumptions. Conversely it is also true that the experimental and analytical/ numerical models currently available are far from being able to model the actual cases. Under such conditions, the most effective mean of research into mining engineering problems is to combine the mine (field) investigations with laboratory and / or analytical modelings. It is with this concept in mind this research was initiated in 1973. 'The field investigations which began in the fall of 1978 consisted of mainly visiting the mines where surface subsidence monitorings had been or were being monitored and/or surface structural changes had occurred. From such visits, subsidence data were collected. A quick analysis of those data provided preliminary understandings of the characteristics of the surface subsidence parameters in the regions (1-5). Using those date, models of various types are being developed for subsidence prediction / control. So far, a total of 44 longwall subsidence profiles in 22 longwall panels and 10 room-and-pillar profiles in 5 room and-pillar sections have been collected. This paper summarizes the combined results published previously (1-5) and present the preliminary results of the predictive models developed.

Jan 1, 1982

By Henry Ferguson

THIS paper is a preliminary statement, intended to present the more important results of the recent studies of the ore deposits of the Alleghany district in advance of the publication of the complete report, now in preparation. The Alleghany district (Fig. 1) has been a producer of gold since the early days of California gold mining. As in other California gold camps, placers yielded the bulk of the earlier production, but during the last 30 years lode deposits have been the only important source of output. The district differs from other California gold-quartz districts in that nearly all the production is from small shoots of high-grade ore. The mining camps of Alleghany and Forest are on the western flank of the Sierra Nevada range about 20 miles west of the crest. The gently sloping lava-covered plateau which controls the upland topography has been trenched by deep canyons of the westward flowing streams, which are cut to depths of as much as 2000 ft. below the crests of the ridges. The district is about 18 miles from Nevada City but the automobile road which connects the two places is 31 miles long. The senior writer first visited the district in 1913 and published a short description of the lode deposits.1 The increasing importance of the district made further study desirable. A detailed topographic map was therefore made by W. B. Upton, Jr., of the U. S. Geological Survey, in the spring of 1924, and the senior writer spent parts of the field seasons of 1924 and 1925 in the district. For the second field season the Geological Survey was fortunate in securing the services of R. W. Gannett, who had already done geologic work in the district for several of the mining companies. Owing to the death of Mr. Gannett in October, 1925, just before the close of his field work, the work of preparation of the entire report fell to Mr. Ferguson. He takes this opportunity of acknowledging how deeply he is indebted to Mr. Gannett for his excellent work in the field, and his realization of how greatly the completion of the report on the district has suffered from lack of Mr. Gannett's assistance in the office. In October, 1.928, after the completion of the first draft of the manuscript, Mr. Ferguson made a short visit to the district.

Jan 1, 1929

By P. Latostenmaa, O. Forsén, M. Lundström, J. Aromaa

The history of electrolytic copper production in Finland is closely connected with the industrialization of Finland and events of the Second World War. Production of cathode copper by electrowinning from the processing of Outokumpu ore started in 1913 based on the Hybinette nickel process, however due to the poor performance of this process, the plant was closed in 1929. Outokumpu commenced copper smelting at Imatra in eastern Finland in 1936 producing blister copper for refining outside the country. Due to the threating military situation, a new electrolytic copper refinery was built in 1941 at Pori in western Finland to refine the anodes. This was the first electrolytic copper refinery in Finland. It was built with 108 cells having a capacity of 12,000 tonnes/y. In addition, the smelter was relocated to nearby Harjavalta in 1944–1945. To fulfill the war reparations included in the peace treaty with the Soviet Union, a doubling of the smelter capacity was realised, with the Pori refinery capacity increasing to 20,000 tonnes/y in 1946 by adding additional cells. The cornerstone of Finnish metallurgical technology — Outokumpu flash smelting — was invented with the new technology commissioned at Harjavalta in 1949 replacing the electric furnace and providing a further increase in copper output with subsequent enlargement of the refinery. By 1963, the plant consisted of 380 cells with a capacity of 48,000 tonnes/y of cathode copper. The Pori electrolytic copper refinery has operated continuously since 1941. Commencing in 2004 the Pori refinery has been part of the Boliden group of Sweden. The most recent plant upgrade was in 2007 with the installation of permanent cathode technology. In 2017, the production of the Pori refinery was 133,000 tonnes of copper cathode, 2,300 tonnes of nickel sulphate, along with 66 tonnes of silver and 4.6 tonnes of gold. This paper describes these outstanding achievements. INTRODUCTION In 1809 the Kingdom of Sweden was defeated by the Russian Empire in the Finnish War, and Finland was annexed by the Russian Empire as the autonomous Grand Duchy of Finland. Finland’s commercial and industrial interests were developed to serve the Empire’s needs. Finland had raw materials, but at the start of the 20th century Finnish industry was based on the use of wood as raw material and agricultural products. The mining industry was only a few percent of the country’s industrial production.

Jan 1, 2019

By N. I. Fisher, J. Shepherd

A rapid method of determining natural fracture trends in collieries has been developed. The method will yield information that is precise enough to permit fracture domain boundaries to be delineated in a coal seam. Instead of a survey of cleat trends in a colliery taking several man-weeks or even man-months, a reconnaissance survey can be carried out in only a few man-days. At each of a sequence of sampling sites along a traverse, five measurements of trend are recorded for each set of fracture directions. A sequential plot of the medians of each fracture set is then made manually underground or by a computer in the mine office. Changes in fracture pattern can be detected easily in colliery development work if a geologist visits advancing faces regularly, and forecasts can be made about the likelihood of forthcoming faults and dykes. A full description of this method is given in Shepherd and Fisher (1981). The concept of mapping fractures rapidly in a colliery is based on using a geological traverse (Compton, 1962), along which observations can be made at chosen, regular intervals. The technique has been widely used for surface mapping across outcrops and in follow-up work in photogeological studies (Hepworth and Kennerley, 1970). In these cases, the geologist surveys the traverse line as mapping proceeds. In a colliery, however, ready-made traverse lines already exist in panels and along main roadways, often in several directions. It is thus possible to traverse a colliery in different directions and record the fracture trends at intervals, generating a reconnaissance fracture map. This can also be done on a continuing basis as mine development takes place. Generally, a sampling traverse should be longer than 0.5 km with sampling sites at relatively close-spaced intervals along the traverse. For example, in room-and-pillar mines pillars are commonly formed on 40-m centers and the sampling sites can then be arranged at 20-m intervals [(Fig. 1)]. The sites might have to be closer together for mines known to have bad mining conditions. The predominant fracture trend is normally the face cleat and the subordinate trend is the butt cleat (McCulloch et al.. 1974). Various changes can occur in the cleat or joint pattern: the face and butt sets may disappear or an entirely new set or sets may appear. Therefore, it is best to record all prominent fracture sets. Sometimes there is only one; in other cases there may be as many as three or more. An odd number of measurements of each fracture set are made (generally five or more) to enable the median value to be determined easily. The median value can be plotted underground using graph paper or a computer plot can be made in the laboratory or mine office [(Fig. 2)]. The sequential linked median (SLIME) plot draws the median trend for each sampling site as a unit line segment. The segments from successive sampling sites can be connected together to form a long chain [(Fig. 2A)]. The needle plot, on the other hand, draws a straight line to represent the traverse and then plots out the median trend for each sampling site [(Fig. 2B)]. The SLIME plot is better for visual display, as it highlights small irregularities and gross changes in trend. However, some work is required to relate the individual segments to their site location along a traverse. In this respect, the needle plot is more convenient because each segment -can be plotted-at a point corresponding to its location. Also, there is precise match-up if needle plots of face and butt cleat are compared. A description and listing of the SLIME program is given by White et al. (1981). An example of the use of this method is given for Wallsend Borehole colliery in New South Wales (Australia) [(Fig. 2)], where domains II and IV are associated with mining hazards. Domain II is coincident with a normal fault of 2.6-m throw, and domain IV with a basic dyke 12 m thick. These hazards were approached driving in a southwesterly direction, and a pronounced change in trend of the cleat to a northwesterly direction occurred at a distance of approximately 45 m from each one. The northwestern joint trend is parallel to that of the dyke and fault, and it occurs at a higher frequency close to these structures. The association of a particular joint set with faults has been found elsewhere (Shepherd and Creasey, 1979). The two minor cleat direction changes within domain V are narrow joint zones that are less than 5 m wide. The fracture trends derived from a SLIME traverse can be verified by collecting larger quantities of data at selected sites, as shown in the balloon density (rose) plots depicted in [Fig. 2C]. We are grateful for the financial support provided by Thiess Bros. Pty. Ltd. and the National Energy Research, Development, and Demonstration Program administered by the Commonwealth Department of National Development and Energy. R.W. Miller Holdings Ltd. and Thiess Bros. Pty. Ltd. are thanked for their permission to publish data from their collieries.

Jan 1, 1982

The 2012 North American Tunneling (NAT) conference is expected to attract more than 800 tunneling and underground construction professionals. But don?t let the North American part of the meeting?s title fool you. Many of the attendees will come from all over the world. The meeting is scheduled for June 24-27 at the JW Marriott Indianapolis Hotel in Indianapolis, IN. In addition to two and a half days of technical programming, the accompanying exhibit has attracted 116 exhibitors in 140 booths. And the conference will include short courses, a field trip and plenty of social activities that will give attendees the opportunity to catch up with each other.

Jan 1, 2012