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By A. Papandreou

Industrial wastes nowadays constitute one of the most serious threats for the future of our planet. Researchers around the world have very often proposed many kind of solutions in the management problem of industrial effluents. However in most cases suggested solutions are either too expensive to be applied in industrial scale, or they just transfer the problem (e.g. precipitation creates dangerous sludge) and so they create an even greater problem and threat. In the present study the exploitation of valuable hydraulic and adsorption properties of fly ash is studied. Fly ash can easily and cheaply be shaped into stable pellets. After ageing for a sort period of time, these structures can be used as adsorbents for the removal of heavy metals from industrial effluents. Experiments in aqueous solutions have shown excellent adsorption behavior concerning the removal of cadmium, copper, lead, chromium (III) and zinc. The advantage of this technology, except low cost, is that after saturation the pellets can be easily removed from the liquid phase and stabilized in concrete structures without any problem of desorption or leaching. Moreover in these structures a significant amount of cement in the concrete can be replaced by raw fly ash. (Ashcrete as it is called). The utilization of an industrial byproduct as fly ash in the form of pellets as adsorption means and their stabilization with concrete (or ashcrete) combines the useful properties of a solid waste in the treatment of liquid effluents and constitutes a green low cost technology.

Jan 1, 2006

By R. D. Lama

Coal mining is one of the major sources of methane release to the atmosphere by human industrial activities and is believed to contribute to -30% of the total methane emissions from industrial activities. In 1993, world saleable black coal production, attained almost 3.5 billion tonnes from which around 65% was produced underground. Coal in underground mines can contain high quantities of methane and some deep coal seams have methane content as high as 50 cubic meters per tonne of coal. Gas is re- leased during coal mining from the mined seam and in a higher degree from the neighboring unmined seams and gas bearing strata which are fractured as mining advances. This paper de- scribes a study which was undertaken to estimate the extent of methane emissions from coal mining in the world. Measured emission related data were collected from most underground coal producing countries in the world. The data included methane flows in the ventilation system, methane flows in gas drainage system, in-situ gas content, methane utilization and coal production. More comprehensive data were collected from a range of gassy and non-gassy Australian mines. Residual gas content of samples from run of mine were also measured. Using the Australian data, mathematical expressions were established to evaluate methane emissions as a function of coal production and in-situ gas content for other mines. These emission models were then used to evaluate the emissions for the countries or coal basins without measured emission data. Trends in methane emissions from underground mining for the year 2000 and beyond were also estimated.

Jan 1, 1997

By Terry P. McNulty

During the last 30 years, at least ten authors have dealt with startup ("ramp-up') times for minerals beneficiation, hydrometallurgical, and/or pyrometallurgical plants. Most have attempted to identity the reasons for delays and some have suggested attributes common to successful startups, as well as those shared by unsuccessful ones. The most recent has advanced a project characterization matrix as a predictive tool for qualified users. This paper will summarize past work, will review cause and effect, will outline an approach for refining our ability to avoid costly delays, and will seek guidance from professionals most likely to use such a tool. INTRODUCTION During the last few decades, many billions of dollars have been lost by investors in mineral industry projects that did not perform as well as their developers had hoped. The most common form of failure has been the inability to generate a profit quickly, and delayed achievement of planned production rate has been the chief cause. Minerals processing projects are by no means the only kind of plant to suffer from startup delays, as some authors cited in this paper considered inorganic chemical plants and other types of facilities. Furthermore, mines are not without fault and there have been many that were closed after years of disappointing performance. However, our interests as a group are most sharply focused on mineral processing and our database for such projects is relatively extensive. It is sufficient to say that the conclusions made or repeated in the following text can be readily extended to most types of projects.

Jan 1, 2004

By Hisakazu Matsushita

1. Introduction This is a report on applications of the earth pressure type balanced shield tunneling projects executed under narrow streets on soft alluvial layers in Japan. Japan is a long island country surrounded by the sea. Steep mountain ranges run along the archipelago and numerous rivers originate from the mountains, leaving only limited areas of flat land along the upper and middle reaches of the streams. The majority of cities in Japan are on soft alluvial layers. Alluvium represents an extremely complex soil formation, sections bordering diluvium being characterized by sharp undulations. Various difficulties are therefore encountered in shield tunneling work undertaken in such ground conditions. Particularly, at work sites lying in an unstable, waterbearing layer with high permeability, shield excavation becomes utterly impossible, hampered by large amounts of underground water as well as land collapsing caused by the water. Even when work can somehow be accomplished by using chemical grouting or by lowering ground water level, which require extra expenses and time, undesirable effects such as ground surface settlement are unavoidable in projects undertaken in the past. The newly developed method allows safe and accurate tunnel excavation at normal speed and without giving any adverse effects on buildings above, even under such unstable ground conditions. An outline of this new method was announced at the "International Tunnel Symposium '78" held in Tokyo, and the method has since been employed in a number of tunneling projects in this country. This report provides further data on the new method with reference to some of those projects, explaining how it allows tunnel excavation with

Jan 1, 1979

In the UK as existing face capacity is replaced, many of the new faces will have higher installed powers and be located in zones of higher strata temperature. These factors coupled with the need to increase production will result in more faces experiencing environmental difficulies, especially with respect to climatic conditions. In many cases these problems are unlikely to be solved, as in the past, by simply increasing the face air quantity. Therefore other techniques including refrigeration will be necessary, possibly requiring major capital and operational expenditure. It is easy to spend large capital sums and incur high operational expenditure without achieving the desired amount of climatic control. There is therefore a great need for reliable prediction techniques to aid in the making of sound, informed decisions which will have a significant influence in the long term on the level of production costs. A computer program able to predict the heat flows and resultant climatic conditions on a long¬wall coalfaces has been developed. Throughout it's development underground measurements have been used to validate the computer model and it has been shown that for an advancing coalface under normal production conditions that the program predicts the climate to within 1°C of the measured conditions. This paper outlines a number of methods available to improve climatic conditions on longwall faces. The coalface temperature prediction program is used to quantify the effects of these methods on the climatic conditions for a model coalface and a comparison is given. In conclusion a cool¬ing strategy for longwall faces is outlined.

Jan 1, 1991

By Virgil R. Huff, Ihor Havryluk

P. T. Pacific Nikkel Indonesia (PTPNI) was incorporated in Jakarta, Indonesia in February, 1969 by a group of Dutch and North American companies. At the same time, a Contract of Work with the Government of the Republic of Indonesia was signed, granting Pacific Nikkel all the necessary licenses and permits to explore and develop all nonradioactive minerals in two separate areas in Irian Jaya, eastern Indonesia. Nickel mineralization occurrences were confirmed by Dutch geologists in the two areas in 1952 and 1955, however, detailed exploration began in June 1969 after the Contract of Work was signed. Since that time, numerous studies and investigations have been conducted to determine the feasibility of producing metallic nickel in Irian Jaya. Four engineering studies, two bulk sample tests, an oceanographic survey, and a preliminary site investigation indicated that construction and operation of a nominal 100 million pounds per year metallic nickel plant on Gag Island were technically feasible. The fourfold increase in the price of oil in late 1973 without a corresponding adjustment in the price of nickel necessitated a reevaluation of the project, the results of which showed that the project required other conditions to be viable. Subsequently, analysis of: the future projected nickel supply-demand and cost-price relationships, the economics of treating a higher grade feed, and participation by the Government of Indonesia, indicate that the project will be viable. Therefore, planning of the Gag Island Nickel Laterite Project is continuing with the objective of commencing production to supply the market in the 1983-1984 time period.

Jan 1, 1979

By Terence G. McCusker, E. Roy Anderson

A four-mile length of interceptor sewer tunnel in Manhattan has finished sizes ranging from 10'6" to 14'6" horseshoe. Mixed face conditions were anticipated in three areas and encountered in five. All were short but since the tunnel lies well below the water table and failures would involve important utilities, major structures and human lives, great care had to be exercized in choosing a construc¬tion method. Chemical consolidation was selected as the best approach with compressed air working as a backup system. Initially grouting was accomplished from within the tunnel, but treatment from the surface was more successful and was later adopted. The soils consisted largely of impermeable weak silts and it was found possible to inhibit access of water to this material so that it could be controlled by breasting within the tunnel without loss of stability. It is concluded that in the interlayered permeable and impermeable soils encountered, chemical grouting would successfully stabilize the working face. INTRODUCTION An interceptor sewer is currently under construction along the entire length of the west side of Manhattan. When complete, the tunnel will intercept and divert to a treatment plant (also under construction) a daily flow in excess of 200 million gallons per day. About 9 miles of the interceptor sewer is in tunnel and the remain¬der is cut-and-cover construction. The tunnel is almost entirely in Manhattan schist but where its alignment crosses major faults at comparatively shallow depths, mixed face and earth conditions are

Jan 1, 1997

By Crone Duncan

The search. for massive sulphide orebodies is steadily being extended to greater depths as well as expanding outward into the large portion of the earth's surface where the sulphide bodies are deeply weathered. Massive sulphide orebodies are generally not large in dimensions. They are not like disseminated type sulphide bodies that form large ground exploration targets that can be detected at greater and greater depths simply by increasing the geometrical spacing between the geophysical transmitter and receiver. In¬creasing the transmitter-receiver spacing with massive sulphide bodies eventually "waters down" the anomaly from the body until it disappears into noise. If high surface conductivity is present, as is common in areas of deep weathering, the problem is compounded by the increasing response of the surface layer, as the receiver-transmitter spacing is expanded. The search to greater depths has important implications other than just detection of the orebody. Drilling costs are increased and the probability of missing the target are increased. Missing an orebody is an expense that is difficult to evaluate in dollars per line mile of survey especially since one does not know the value of what was missed. A ground Pulse EM method has the capabilities of solving the problems of deeper exploration particularly in areas of surface weathering it can attain deep penetration without large coil spacings, it also provides information from a complete range of frequencies. The method has other operational advantages since it is free of geometrical restrictions as to coil alignments and can operate in areas of high power line noise.

Jan 1, 1975

By D. M. Jepsen

One of the first things we tell a potential new client is that they have only one chance to make a first impression with an Aboriginal community; all future communications and engagement will be predicated on that first impression. The key components of this most critical meeting are not your power point, your maps, or your draft plan for development ? they are instead a genuine, evident and clear demonstration of a sincere desire to develop a positive relationship that is based upon respect, and consideration and understanding of local communities and their interests, needs and desires. Relationship building is the foundation of proactive and positive consultation and accommodation with Aboriginal communities and the tone is set with the first meeting. C3 has refused more clients than we have accepted due most often to the fact that relationships between the company and the Aboriginal community have already devolved into a tense and toxic scenario. Land access and tenure certainty for exploration and mine development is critical to the foundation of a healthy, sustainable and environmentally and economically sound mineral exploration and mining sector. Without certainty confidence to invest in mineral exploration will be severely eroded. We all understand that substantive investments in exploration are required to increase the possibility of discovering, defining and developing new mines. The development of positive relationships based on a shared commitment of understanding, mutual respect and trust by Aboriginal Peoples and the mineral sector can provide the required business certainty and deliver social and economic benefits for local Aboriginal communities.

Jan 1, 2012

By Donald D. Haas

Contract mining has a definite place in the mining industry, both in the United States and around the world. A mine owner should evaluate the utilization of contract mining in the devel­opment and production of mining properties. This evaluation of contract mining should be performed at various times in the life of a mining prope1iy from the development and initial operation of a new mining project, periodically throughout the mine's life, and at mine closure. Many factors must be considered in ana­lyzing and evaluating the potential of contract mining and those factors are both quantitative and qualitative. Quantitative factors are those factors for which costs or measures can be determined or estimated objectively; and qualitative factors are those factors for which costs or measures must be determined subjectively and do not lend themselves to objective determination or estimation. Some of the qualitative aspects may provide only yes, maybe, or no answers while others will provide a tendency or partiality toward one answer or the other without a quantified cost. The major quantitative aspects include operating and capital costs, monitoring costs, capital preservation, acquisition and disposal of new and used equipment, direct payroll and administrative costs, recruiting and training costs, and employment and termi­nation of staff and hourly personnel. The major qualitative areas include corporate philosophy, risks associated with capital and operating costs, financing the project, operating control, operat­ing flexibility, recruiting and training of personnel, employment and termination, administrative concerns, and owner/contractor relationship.

Jan 1, 1998

By Douglas R. Shaw

The results are discussed herein of laboratory and pilot scale research which has demonstrated some exciting prospects for the exploitation of refractory gold resources by heap leaching. The research examined practical and cost effective methods of chemical; i.e., non-biological, oxidation pretreatment of refrac­ tory old ores to enable successful conventional cyanide heap leachmg. The work has focused on regenerable chemicals, in order to minimize process consumable costs. A nitric acid method has emerged which offers rapid oxidation rates (eg, 0.5 to 6 hours) on ore samples crushed typically to% to ¾-inch. Gold recoveries in simulated heap leaching tests, after nitric acid oxidation of crushed ores, were as high as approximately 80 to over 90%, in contrast, typically, to negligible gold solu­bilities without oxidation. Nitric acid oxidation was effective when applied to several sulfide-bearing refractory gold ores which required either partial or essentially complete sulfide sul­fur conversion for high gold solubilities in cyanide. Ores rich in organic preg-robbing matter also were treated successfully, as were ores which contain significant quantities of acid-consum­ing constituents. Base metals also were recovered with nitric acid oxidation from some of the ores which contain these ele­ments. The work related oxidation and solution diffusion behav­iors and the important physical, textural, and mineralogical characteristics of the different ore types. Conceptual-level feasi­bility studies have defined the principal capital and operating cost components of the nitric acid method, sufficient to allow reliable comparisons with other oxidative technologies.

Jan 1, 1996

By S. Serata

Background Results of the above study in the August 1991 issue of Mining Engineering offer valuable lessons in the solution of cutter-roof problems. The original study plan was initiated by the discussion authors to solve the problems using the "stress control method" of mining (Serata 1976,1982; Serata, Carr and Martin, 1984; Serata and Gardner, 1986; Serata, Gardner and Preston, 1986; Serata, Gardner and Shrinivasan,1986; Serata and Kikuchi, 1986; Serata, Preston and Galagoda, 1987) However, the plan and the planner were changed to the arrangement reported in the paper. The change was considered reasonable at the time due to the mine engineers' uncertainties about the stress control method. Consequently, the basic principle of the study was shifted from the original stress control method to the method described in the paper, which will be called the "yield pillar method" for the purposes of this discussion. The paper convinces the reader that the yield pillar method fails to solve the cutter-roof problems. This doesn't mean that the stress control method also fails. Actually the contrary is true, as discussed below. Limitation of the yield pillar method The paper illustrates clearly how poorly the yield pillar method performs in solving the problem. The reason for this failure is the lack of the protective stress envelope needed to stabilize the cutter roof. Unfortunately, the protective envelope cannot be formed properly without utilizing the stress control method of mining. Changing the pillar size does not make much difference in the roof stability.

Jan 1, 1992

By Edward C. Krug

"You are to use the word ... purely for its selling power. It is a name they venerate. As a result, you can use the word ... to ... get [them] to practice, not only without shame bit with a positive glow of self-approval, conduct which, if undefended by the magic word, would be universally derided." (C.S. Lewis, The Screwtape Letters, 1982, p. 162). "We need to tear everything down over a period of time and reconstruct a whole new world, planned top to bottom. "Right now there are just way too many people on the planet [5.3 billion]. `If we had ... an ethic ... we could cut back to 250 million-350 million people. `The United States is ... a bunch of pigs ... the average citizen ... [uses] maybe 70 to 80 times as much as anyone in the Third World.` "The indigenous pople were the ones that were right! I mean, they had their own religion, their own ethics and their own technology. We just went down a wrong road. "So when he says, `We got to rebuild the whole world,' you have no doubt this is serious sentiment .... And it is finally this world view that distinguishes (Ted) Turner as a media mogul and an environmentalist. It is why Worldwatch's Lester R. Brown told me Turner was `truly a visionary. "'(Interview of Ted Turner, Audubon magazine, November-December 1991. On Dec. 28, 1991, Ted Turner was name Time magazine's "Man of the Year." Clearly, media and environmental leadership agree with Turner's openly stated beliefs.)

Jan 1, 1992

By Ann M. Gosier

Over the past 20 years, diesel-powered equipment has been introduced into the underground mining environment in increasing numbers. While the introduction began years earlier in the metal-nonmetal sector, the exponential growth in coal mining use during this time has been more pronounced. Reasons for the continued use and rapid growth of diesel equipment in underground mines are easily understood. The safety and operational advantages afforded by this equipment in production and support systems are demonstrable. As other mine operators witness the advantages enjoyed by their competitors, they too move to introduce an increasingly diverse array of such equipment into their underground mines. As with any industrial technology, the use of diesel-powered equipment entails potential safety and health concerns. Existing Mine Safety and Health Administration (MSHA)approval regulations (30 CFR Parts 31, 32 and 36) apply only to diesel locomotives and mobile diesel-powered equipment for noncoal mines. In the absence of specific regulations, MSHA has required the use of equipment approved under Part 36 (gassy noncoal mines) for areas of underground coal mines where permissible electrical equipment is required. However, a considerable amount of diesel-powered equipment without explosion-proof or fire prevention features is in use in areas of coal mines where permissible electrical equipment is not required. It is on the use of this latter class of equipment that MSHA is focusing much of its regulatory attention relative to coal. The agency also is focused on revising existing occupational exposure limits for gaseous emissions and instituting limits on diesel particulate emissions for both coal and metal-nonmetal mines.

Jan 1, 1993

By R. McCulloch

Exploration activity in metallic minerals continued to decline in Montana in 1992 as companies either reduced budgets or left the state. The number of active projects dropped another 50% from 1991. Expenditures were 3% to 6% of 1989's 28.6 million. Many of the major mining companies closed offices in Montana. Although depressed commodity prices have hurried the exodus, continuous changes in environmental regulations, as well as the Mining Law of 1872, without regard to economic effect have had the most serious impact. Many companies indicate that Third World countries present a more stable business environment than the United States. Grassroots projects are nearly non-existent, while late-stage programs continue cautiously. Exploration activity continued at the following projects: Garnet, Pegasus Gold; Southern Cross, Asarco; Elkhorn, Goldfields; 7-Up-Pete, Phelps Dodge and Canyon Resources; Miller Mountain, Pegasus Gold; Sheep Creek, Cominco American Resources; Checkerboard, Kennecott and BHP Utah International; Emigrant Creek, Pegasus Gold; and Crevise, American Copper and Nickel. All mineral activity, whether on private, state or federal land, is regulated by the Montana Department of State Lands under three classes of permits - Small Miner Exclusion Statements (SMES), Exploration Licenses and Operating Permits. A total of 230 Exploration Licenses are active in the state with 26 of those being new. However, there are only 433 projects current in Montana, with many of those in the reclaiming stage. The majority of exploration projects consist of individuals expending time rather than money on properties. The number of mines functioning under operating plans declined by one when W.R. Grace closed its Zonolite operation.

Jan 1, 1993

By Pramod C. Thakur

Tunnels are defined as underground passages made without removing the overlying materials. From time immemorial men have driven tunnels for mining purposes. Even today tunnels are the building blocks for underground mines. The total length of such a network of tunnels in a mine may add up to 10-100 miles! In addition to this, rapid development of vehicular traffic, needs for air raid protection and metropolitan traffic problems have given a great impetus to underground tunnel construction. But for the successful drivage of any tunnel an adequate air environment has always been and remains an essential prerequisite. This is particularly true for tunnels in mines which are driven in gas bearing strata often at a substantial depth from the surface. An adequate air environment is designed to promote the health, safety and comfort of workers which results in greater productivity and efficiency. Its legal definition varies from country to country but, in general, it means the provision of sufficient circulating air, often at specified velocities, to maintain: (i) at least 19% oxygen in the working areas (ii) Concentration of pollutants, e.g., methane, carbon monoxide, respirable dust, etc. below specified limits. Table 1 shows the maximum allowable concentrations for some of these pollutants.1 (iii) Temperature and relative humidity below specified limits. Ventilation of tunnels in mines assumes ever. greater importance today because of increased mechanization and concentration of output which leads to higher rate of production of inflammable gases and respirable dust. Efficient management of the tunnel air environment, however, depends heavily on a thorough knowledge of how

Jan 1, 1974

By Joginder S. Bhore, Francis M. Keville, David E. Puza, Roger C. Borggaard

A portion of the Massachusetts Bay Transportation Authority's Red Line Extension through Somerville, Massachusetts consists of 1,553cm (5,092 LF) of hard rock tunneling 6.7m (22 ft.) diameter horeshoe, 148m (485 LF) of mixed face tunneling, 7.2m (23 ft.) diameter circular, beneath an active railroad in a heavily commercialized business district. This paper will deal with the excavation of the mixed face area without the use of a shield. It will address the special excavation and support problems encountered during tunneling operations using the floating crown bar and modified spiling methods. Topics covered will include excavation and support methods, cement grouting, compaction grouting, and instrumentation. PROJECT DESCRIPTION The Davis Square to Porter Square Tunnels and Shafts Somerville/ Cambridge, Massachusetts is part of the Massachusetts Bay Transportation Authority's (MBTA) 5.1km (17,000 ft.) Red Line Extension. This extension runs from Harvard Square, Cambridge, to Alewife Brook Parkway, Cambridge through Somerville. This portion (MBTA Contract #091-106) required the excavation and concreting of 1,701m (5,580 LF) of single track twin tunnels consisting of 1,553m (5,092 LF) of conventional hard rock tunneling under 56 residential properties and 148m (485 LF) of mixed face tunneling beneath an active railroad in a heavily commercialized business district. The mined diameter of the mixed face tunnel is 7.16m (23.5 ft.) Access to the tunnel was via the Summer Street vent shaft, and the two Grove Street access shafts where all tunnel excavated materials were removed.

Jan 1, 1981

By G. L. Dollinger, W. H. Hamilton

INTRODUCTION Design and development of new products generally proceeds through a phase of initial development and discovery based on the evolution of existing arts, followed by technical innovation and development based on both pure and applied research. The development of the mechanical tunnel boring machine (TBM) has followed a similar pattern, with the first machines closely resembling continuous coal miners. In general, however, the design of TBM's to date has been more a result of evolution and discovery than of new technical innovation, even though large sums of money have been spent on research and development. In particular, the results of experimental laboratory and field investigations have had little effect on tunnel boring machine design, and the better performance of TBM's today over those of 10 or 15 years ago, is due more to increased mechanical reliability and greater operating experience, than to improvements in penetration rates and rock fracture capability. The improvements made, have been mainly by the machine and cutter manufacturers who recognize the greater efficiency and economic advantage of utilizing large single row cutters with high load capacity along with large edge spacing. Are there any improvements to be made, therefore, in TBM performance without new and dramatic technological breakthroughs? Can TBM manufacturers design greater performance into their machines by a logical extension of the present art, and by applying what has been learned in the laboratory and field? Some, for example, believe that the kerf cutting system of boring rock is at, or close to, its opti¬mum and little improvement can be made in the present TBM concept.

Jan 1, 1979

By Michael Gauna, William J. Gray, Joseph C. Zelanko

Mechanized mining in the underground coal industry has continued to evolve since the introduction of the remote control mining machine. Remote control continuous mining machines without an onboard operator’s compartment are now the norm in the industry. Extended cuts in excess of 30 ft (9.1 m) are commonplace. Unfortunately, machine operator positioning has become an often unrecognized safety concern, particularly when remote control continuous mining machines excavate a turn (turn a crosscut). From January 2001 through July 2004, remote control continuous mining machine operators or helpers have been involved in ten roof fall fatalities and eight machinery crushing fatalities. The machinery crushing incidents occurred when machines were being repositioned or moved to another place. Of the ten roof fall fatalities, three occurred while a crosscut was being turned and a fourth fatality occurred while mining was being conducted adjacent to the crosscut. The operating time associated with turning crosscuts is a relatively small part of the mining cycle. In recent years, however, a disproportionate number of fatal incidents appear to have been associated with this activity. Procedures for reducing the incidence of operator fatalities while turning crosscuts are discussed. These techniques include: minimizing the number of turn cuts, limiting turn cut depth, establishing no work zones and using visual warning devices to designate them, installing more roof/rib support in the vicinity of the turn cut, using notch cuts prior to initiating a full turn cut, and positioning the remote control miner operator in nontraditional locations.

Jan 1, 2005

By James S. Redpath

"The ways of the world be many and most of the ways be tried, you follow in the footsteps of others till you come to the great divide". These words, written by Robert Service a long time ago, come to mind when I think of our original attitude upon entering into a contract with the International Nickel Company to sink the deepest shaft in the world outside of the Union of South Africa. This shaft was to be sunk to a depth of 7,137 feet from surface, and while it was recognized by all concerned to be a somewhat unusual undertaking in our part of the world, the fact that quite a few shafts had already been sunk to this depth in South Africa probably gave us the feeling that we were following in the footsteps of others. In retrospect, because this shaft was being sunk under entirely different conditions than those existing in South Africa, we were in fact venturing into an entirely new area of endeavour without properly recognizing this fact. It has occurred to me that others considering a similar type of job could benefit from our experience, especially in an assessment of the risks involved and how they compare to those encountered in an ordinary shaft. For comparison purposes, I would define an ordinary shaft as being sunk to a depth of 5,000 ft or less, and a deep shaft as one being sunk to a depth of between 5,000 ft and 8,000 ft. The sinking of the Creighton No. 9 Shaft has been de-

Jan 1, 1997