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By Dwayne D. Tannant

The Adra tunnel near Naramata BC experienced a fire in 2010 that burned timber sets within the tunnel and caused severe spalling of rock from the roof and tunnel walls. The nature of the damage is documented and efforts completed to rehabilitate and open a portion of this tunnel to the public are described. The use of shortcrete and rock bolts is a technically and economically superior support system to timber sets as well as being far more fire resistant.

Jun 1, 2012

By G. E. Wittur

"The twenty-one members of the Organization for Economic Cooperation and Development, comprising eighteen western European nations plus Canada, the United States and Japan. account for two-thirds of world steel production. The Special Committee for Iron and Steel was formed by the OECD to study trends and problems in the steel industries of member countries. The paper begins with a summary on the Organization, including an historical sketch, its structure, member-ship and objectives. The steel industry of the entire OECD is briefly described before proceeding to a more detailed discussion of various aspects of the steel industries of European OECD members, emphasizing practices and conditions that differ from those in North America. Benefits to Canada of representation at meetings of the OECD Special Committee for Iron and Steel are described."

Jan 1, 1967

By E. H. Henderson

Introduction Stamp-Milling and amalgamation is, perhaps, one of the oldest processes of recovering gold from its ores. Many papers, theses, and textbooks have been written on the subject of stamp-milling practice in general, but, to my knowledge, there have been no publications describing the modern stamp-mill as designed, developed, and operated in Nova Scotia. Although it may be said that the gravity stamp-mill is the most primitive, and perhaps the crudest, crushing machine in existence, it is at the same time the most satisfactory all-round milling and amalgamating device yet contrived. Originating in Saxony, and used in North America first in Virginia and Georgia, the stamp-mill, in a primitive form, later found its way to California and Colorado. Here, it speedily developed from an affair of wood shod with iron, and operated with the crudest gearing, to substantially its present form. Briefly, it consists (see Figure 1) essentially of a series of hammers (the stamps), which fall upon a mixture of ore and water contained in a cast-iron box (the mortar). The resulting crushed ore (the pulp) is splashed out through a screen on the front of the box. For some years after the discovery of gold in Nova Scotia, in 1861, the ? arrastra and Chilean mill were used to recover the gold from the rich ores. The stamp-mill followed, and various types were used, principally the California and Gilpin County types. Then, in 1895, Mr. M. R. O'Shaughnessy, one of our foremost amalgamators, conceived the idea of a new type of stampmill, which has since become standard in Nova Scotia gold mines. This mill, unique in its design and operation, is specially adapted for the most efficient extraction and recovery of gold as it occurs in our Nova Scotian ores. It is commonly known as the Underwater Feed type, as opposed to the usual Overwater or Top Feed type, and it may be rightly termed The Nova Scotia Self-Classifying Stamp Amalgamation Mill. It is conceded by experienced mill-men that it is superior to any other type of mill for recovering the very coarse and granular gold typical of the ores of this Province. The particular installation and practice to be described in this paper is that of the Guysborough Mines, Limited, at Goldenville, Guysborough county. Emphasis will be laid on certain operating innovations of extreme simplicity and high efficiency.

Jan 1, 1935

By Eric D. Monrad

Supply chain simulation modeling is taking on a more prominent role in mining project planning and decision making. Transportation costs for the supply chain can form a significant component of the overall cost to provide product to the end customer. In recent years, computing power has increased, simulation software has advanced, and simulation specialists have become even better equipped to provide sophisticated analysis and recommendations. This has led to a virtuous cycle of owners expecting and supporting data-driven analytics, which drives further advancement. This paper discusses developments in supply chain planning and two case studies from recent simulation modeling analyses.

May 1, 2013

By C. G. McLaughlan

The Noranda concentrator was placed in operation in October, 1928, and the object of this paper is to outline operations during the twelve months which have elapsed since that time. The ores milled are massive sulphides carrying copper and gold, and, in certain cases, zinc. These ores have a specific gravity of about 3.8. The average assay of the copper-gold ore so far treated has been 2.0 - 3.5 percent Cu; 0.10 - 0.20 oz. Au; 40 - 51 percent Fe; and 6 - 15 percent SiO2. In this ore the copper occurs almost entirely as chalcopyrite, and the iron which is not combined with the copper is present mainly as pyrite and pyrrhotite. ?some iron is also combined with the silica, the ratio being about 1 to 4, and a small percentage is present as magnetite. The occurrence of the gold has been shown by microscopic work carried out by Prof. L. C. Graton, of Harvard University, to be very variable. Some of it is free, and is included within the base-metal sulphides or occurs at their boundaries. A similar distribution also holds for a portion of the gold which is combined as a telluride. Little is so far known of the occurrence of the silver other than that some of it may be combined with the gold in the telluride, petzite. The copper-zinc ore contains up to 6 percent copper, and has a very variable zinc content. The copper in such ore is present as chalcopyrite, and the zinc as sphalerite. In starting the mill we had three conditions to face; the first of these was climatic, the second was the lack of skilled flotation operators, and the third was the ore itself." The last of these three proved much more difficult to contend with than the other two combined.

Jan 1, 1930

"Accelerated expansion of Western Canada's metallurgical coal industry has again stimulated considerable exploration activity in the Rocky Mountain Foothills Belt and influenced much of the R&D related to transportation, processing and carbonization. Preparation R&D has included further pilot-plant work on desulphurization, spherical agglomeration and modified compound cyclones (which are also proving themselves in other mineral beneficiation studies). Combustion research, aside from increasingly stressing control of combustion source pollution, has directed special attention to lignite PF firing and problems arising from lignite ash. Studies directed toward the non-fuel utilization of coal have centered on such diverse topics as active carbons, carbonaceous filter media, plant nutrients and industrial applications of humic acid derivatives. In addition, a number of long-range research projects related to such matters as coal chemistry and pyrolysis have been actively pursued, and further attention has been given to improved sampling techniques and analytical methods."

Jan 1, 1969

By The Staff

"THE Wabana iron ore mines, owned and operated by the Dominion Steel and Coal Corporation, Limited, .are on Bell Island in Conception bay, on the east coast of Newfoundland. Mining began on surface in 1895 and, although open-pit work is still done on a small scale, the entire output may be considered to•be derived from extensive submarine workings. In 1958 the average daily production of hematite ore was close to 12,000 tons, almost all of which was concentrated in a heavy-media plant. SUMMARYThe character, occurrence, and extent of the submarine bedded deposits enabled early operators to meet prevailing market demands with the minimum attention paid to exploration. Mechanization of the mine and the pressure for sustained high tonnages since 1955 have emphasized the importance of an expanded exploration and development programme.A serious handicap has been the impossibility of utilizing normal diamond drilling methods to explore ore conditions in advance of mining faces. Drilling between tl1e bedded zones has been done but the major difficulty has been to delineate ore reserves in the lower bed, which has the greatest ore potential of the three mineable seams."

Jan 1, 1960

By P. D. R. Maltby

This paper describes the background and markets for calcium carbonate and silica sand in Canada, as well as the results of recent test work carried out at the Ontario Research Foundation. Tests on sericite, tremolite, vermiculite, barite and graphite are also mentioned.

Jan 1, 1979

By P. Leo

The Al-Zn-Mg alloys (e.g. 7004, 7020) are employed for land transport and architectural applications whereas the Al-Zn-Mg-Cu alloys (e.g. 7075, 7050) provide the high strength aircraft alloys. The Cu gives rise to suitably sized and distributed precipitation but causes high quench sensitivity. Their hot work processing also has marked differences; the Cu-free alloys have good extrudability whereas the Cu-bearing alloys have low extrudability and are difficult in rolling as well. The behaviors of the two classes are described in terms of flow stresses and ductility over 300 - 500°C, along with constitutive contrasts. The ductility of the alloys with Cu is much reduced above 400°C by precipitation of a phase at the grain boundaries that can be avoided by suitable heating schedules. The high strength alloys are subject to de-lamination corrosion of sheared edges due to severely pancaked grains; this can be alleviated by holding between passes, in mid-rolling schedule. In torsion tests at 10-1 to 10 s-1/ 250 - 500°C, the stresses (ductilities) at 300°C/ 1s-1 and activation energy Q for 7004 were 118 MPa (2) and 262 kJ/mol. The 7075 was tested after several pretreatments: completely over-aged (softened): 107 MPa (5), Q=150 kJ/mol; whereas, solution and quick cooling to testing caused extraordinarily high peaks related to dynamic precipitation resulting in 160 MPa (1.2), Q=300 kJ/mol.

Jan 1, 2011

By Nicholas Bonderoff, Amily Xu

The evaluation of battery electric vehicles (BEVs) in underground mines involves comprehensive business case analysis beyond just the capital and operating costs of the equipment itself. BEVs demonstrate benefits from an EHS perspective, reduced mine ventilation costs, lower energy operating costs, reduced overall GHG emissions (dependent on the source of electricity), elimination of DPM, lower equipment maintenance costs, and reduced cooling requirements in deep mines. When including batteries and supporting infrastructure, BEV capital costs are approx. 80% greater than that of diesel equipment. The project economics are highly dependent on the cost of electricity and diesel fuel, and these can vary widely depending on the location of the mining operation. Battery charging and swapping methodologies must be evaluated as there are a variety of approaches that can be employed which vary by manufacturer and type of equipment. Careful consideration of the cycle times, charging methodologies, and location of the battery charging infrastructure is necessary. Specific operating conditions must also be taken into consideration. For example, the time for blast gases to clear will be increased by reducing ventilation flow, and the potential impact on production needs to be evaluated. Similarly, the electrical distribution system needs to be evaluated for peak loading conditions when BEVs are charging. Criteria including maintainability, reliability, commercial availability, and performance need to be evaluated. BEVs have fewer components than diesel equipment and this correlates to lower overall maintenance costs, however, BEVs require maintenance personnel with specific skill sets in order to maintain the equipment. Battery lifecycle costs need to be considered as battery replacement incurs significant capital expense. Some manufacturers offer services to offset these capital costs through usage agreements. Recycling and disposal of batteries at the end of their lifecycles also need to be considered. With the increased selection of BEV equipment that will be available in the next 2-4 years, 100% BEV adoption is also possible. We recommend a holistic approach when evaluating BEVs for underground mines. This will ensure that everything is considered in order to evaluate the full impact of BEV implementation.

Jan 1, 2023

By Randy McMeekin, Chris Twigge-Molecey, J. Peter Blake

The business objectives of a metallurgical project determine targets and constraints, such as the range of products, production capacities, in-service dates, and capital and operating cost parameters. Permitting is usually left to the project team, as are decisions regarding site location, technology, and construction approach. Success requires an orderly methodology, represented in this book by front end loading (FEL) phases: FEL1 examines several alternative approaches; FEL2 ranks and eliminates less economically or technically attractive options; and FEL3 develops the preferred option to the point of major permit completion, with defined scope, schedule, and cost to submit for approval to proceed with implementation in FEL4. Working through FEL1, FEL2, and FEL3, the project definition improves, estimates become more accurate, and project risks are reduced. The project design basis at the end of FEL3 is the control document for project implementation in FEL4.

Jan 1, 2015

By J. A. Scott, K. Moreau, H. Shang

"Trials of automated technology at underground mine sites around the world have reported increased production and the potential for lower energy consumption. Autonomous mining eliminates a range of delays related to operator downtime and travel to the workface and facilitates continuous operation in conditions that are unsafe for workers. Automation also introduces complexities and safety hazards arising from equipment–personnel interactions; automated processes must be isolated from other stope-cycle–related activities such as production drilling, development, loading, and backfilling, poten¬tially requiring changes to the mine design to maintain an efficient and safe operation. This paper reviews and discusses the implementation of automated equipment in deep underground mining operations and the challenges and advantages associated with the technology. ¦ KEYWORDS Automated equipment, Emissions reduction, Energy, Productivity, Sustainability, Technology, Underground mines RÉSUMÉ Des essais de technologies automatisées dans des sites miniers souterrains aux quatre coins du monde ont indiqué une production accrue et la possibilité de réduire la consommation d’énergie. L’exploitation minière autonome élimine tout un éventail de retards liés aux temps d’immobilisation des opérateurs et aux déplacements vers le front de taille, et facilite l’exploitation continue dans des conditions qui s’avèrent peu sécurisées pour les travailleurs. L’automatisation introduit également des complexités et des risques pour la sécurité, qui surviennent en raison des interactions entre l’équipement et le personnel. On recommande d’isoler les procédés automatisés des autres activités liées au cycle des chantiers telles que le forage de production, le développement, le chargement et le remblai, ce qui pourrait entraîner des changements au niveau de la conception de la mine afin de préserver rendement et sécurité dans l’exploitation. Cet article examine et aborde la mise en oeuvre de l’équipement automatisé dans des exploitations minières souterraines profondes, ainsi que les enjeux et les avantages associés à cette technologie. ¦ MOTS CLÉS durabilité, énergie, équipement automatisé, mines souterraines, productivité, réduction des émissions, technologieINTRODUCTION As the mining industry continues to exhaust easily accessible orebodies, the need for efficient, deep (typically below 2,500 m) mine operations increases (Atlas Copco, 2013a); however, the mining process can become economically infeasible at great depths because operation costs drastically increase. This has resulted in investigations into automating mining operations as the industry strives for improved productivity (Schunnesson, Gustafson, & Kumar, 2009) and ways to remove personnel from hazardous work areas."

Jan 1, 2019

By Fabio Mielli

In these times of increasing costs and diminished returns, energy consumption is one source of savings that remains relatively untapped in the mining sector. Typically, 15% to 40% of operational costs can be attributed to energy in mining operations. This ?process variable? is a complex, multi-faceted variable that involves government regulations, societal pressures, cost and competitiveness. A mining company able to successfully embrace an energy efficiency program is more often than not a successful mining company. Production optimization programs, relatively common today, provide increased production, increased availability of assets and, in many cases, improved quality. They generally ignore the energy question altogether. Production Energy Optimization combines reductions in energy consumption with production improvements to reduce the cost per unit of production while improving emissions reporting. An energy strategy in mining and mineral processing operations is a critical component of Production Energy Optimization. This strategy must support the financial and operational integrity of the business. Developing a successful energy strategy requires a well structured approach such as following: ??Understanding where energy is being used and why, ??Recommending and implementing energy conservation measures, ??Driving visibility to targets and results, ??Re-evaluating continuously. The objective of this paper is to help you better understand the process, tools and technologies that enable mining organizations today to address energy and sustainability issues more tactically and proactively.

Aug 1, 2013

By Eldon L. Brown

Location and History The Sherritt Gordon property is located in northwestern Manitoba, about 100 miles north of The Pas and 40 miles northeast of Flin Flon. It is connected with the Manitoba Northern railway, which runs from The Pas to Flin Flon by a branch line, 42 miles in length. The location of the property is shown on the sketch-map, Figure 2. The ore deposit was first discovered by Philip Sherlett, a Cree Indian, in 1922. In 1924 Sherlett's claims lapsed and the ground was re-staked by Carl Sherritt and Dick Madole, and was optioned by them to J. P. Gordon in the summer of 1925. Gordon re-optioned the property successively to three well-known mining groups, one of which did some surface trenching .and put down 28 shallow diamond-drill holes before dropping their option. In the latter part of 1927, a Company known as Sherritt Gordon Mines, Limited, was formed to take over the property, and preparations were made for systematic development work. Preliminary Development In order to fill-in gaps left by the original drilling, a light diamond-drill outfit was flown-in to the property from the Hudson Bay railway in the early fall of 1927. Ten shallow holes were put down before freeze-up .and a considerable amount of surface trenching was completed. Based on the results of the surface trenching and the shallow diamond-drilling, an extensive development campaign was outlined. A winter road, 90 miles in length, was cut from mileage 55 on the Hudson Bay railway, and during the winter of 1927-28 a total of 2,600 tons of freight was hauled-in to the property. This freight included four complete diamond-drill outfits, two complete mining plants, building material for two sets of camps, and supplies for one year's operations, including 105,000 gallons of fuel-oil for Diesel engines.

Jan 1, 1933

By P. Nos, L. Kolbeinsen, M. W. Kennedy, A. Filzwieser, R. T. Jones, A. MacRae

Modern furnace designs often incorporate extensive use of cooled elements to achieve long campaign lives at high operating intensities. However, contact between water and high temperature fluids can result in powerful Boiling Liquid Expanding Vapour Explosions (BLEVEs). Therefore cooling such elements with water carries inherent risks when used under slag and particularly below molten metal or matte. Alternative cooling media exist that can reduce or eliminate the risk of BLEVEs. These media are analysed and discussed in the context of deeply cooled furnace elements. Important factors in selecting alternative coolants are explored including: critical heat flux, thermal limits, toxicity, flammability, unit cost, etc. Key cooling system design criteria are reviewed in the context of both traditional and alternative coolants. Results of Computational Fluid Dynamics are presented for an example tap-block cooler design using a number of selected coolants. Research needs to advance the safe use of alternative coolants are presented.

Jan 1, 2015

By P. B. Queneau, Peter V. Avotins, Lauch F. Farris

"The Lang Bay germanium property is a carbonaceous sandstone deposit outcropping near the Pacific coast, 100 km north of Vancouver. The germanium-bearing seams are up to 5 m thick. Where one such seam outcrops, it averages 50 to 60 g Ge/tonne. Drill core analyses have shown considerably greater concentrations of germanium at depth. Additional drilling to establish continuity and grade of the germanium-b earing strata is scheduled for 1986. The germanium occurs in association with lignite, which makes up 1 to 2% of the seam. American Cyanamid Company engineers have developed a proprietary flotation reagent effective for concentrating the germanium rich vitrain portion of the Lang Bay lignite. Ongoing laboratory studies are developing procedures for further upgrading and refining of this germanium. This paper outlines progress made by Fargo Oil Corporation on Lang Bay geology, reserve estimation, mine planning, ore dressing, refining, and economic evaluation.IntroductionIn 1871, Mendeleyev specula ted on the properties of a ""missing"" element between silico n and tin on the periodic table. The discovery of germanium fifteen years later proved the Mendeleyev predictions to be remarkably accurate. Almo half a century later, the pioneering work of McCutcheon of Eagle-Picher led to production of germanium dioxide from Oklahoma zinc smelting residues. Demand for the element surged due to development of the Ge02 diode rectifier during World War II, followed by development of the transistor in 1947. The chief commercial sources for germanium during the following two decades were the Cu-Zn mines in the Congo and the Zn-Cu-Pb mines of Tsumeb in Southwest Africa. The germanium was chemically combined in complex Cu-Fe sulphides (germanite and renierite), from which the element was recovered either by leaching the selectively roasted sulphide, or by direct fuming of GeS(I). Although these deposits have reportedly been depleted (2), new deposits of renierite have been discovered in Zaire. Alternative sources of germanium are therefore being sought worldwide for use in infrared optics, semiconductors, fibre optics, and catalysts. One such source is germanium-rich coal (2)."

Jan 1, 1986

By Dan Miners

"This presentation will provide an overview and understanding of Mine Safety and Health Administration (MSHA) and Ontario Regulations for Mines and Mining Plants. It includes discussions on the history and practical development of the standards and an overview of engineering best practices from a construction, maintenance and operational viewpoint. INTRODUCTION Ontario is one of the safest mining jurisdictions in the world and has some of the most comprehensive regulations for the construction, operation and maintenance of a mine. In the USA, several operators have adopted some or all of the practices prescribed by the Ontario Regulations as an internal procedure. Experience has demonstrated that these plants are indicating less unplanned downtime and fewer issues with MSHA inspectors in their hoist plants. HISTORY AND THE REGULATIONS Both Canada and the USA have had some form of laws governing the operation of mines since the late 1890s. The paths of legislation have run in reasonably parallel lines, continually improving the health and safety conditions in the mining industry. Ontario Mine Health and Safety In the 1970s the accident rates in mining were higher than any other industrial sector; this prompted a Royal Commission on the Health and Safety of Workers in Mines (the Ham Report). The recommendations of this report, published in 1976, generated several changes in the regulations regarding worker safety in mines. Following the release of the Ham report, the Occupational Health and Safety Act (OHS) was passed by the Legislature in 1978. The Act is a set of comprehensive laws governing almost all Ontario workplaces, and it replaced separate laws governing different industrial sectors. OHS is enforced by the Ministry of Labour (MOL), and this discussion will focus specifically on Ontario’s Occupational Health and Safety Act, R.R.O. 1990, Regulation 854, Mines and Mining Plants, Part X Mine Hoisting Plant (Ontario Regulations). USA Mine Health and Safety A coal mine explosion in West Virginia and medical studies on occupational disease led to the 1969 Federal Coal Mine Health and Safety Act (Coal Act). The Coal Act was the most comprehensive and stringent Federal legislation governing the mining industry to date. The Mining Enforcement and Safety Administration (MESA) was formed, following the 1973 Act, as a new departmental agency to assume the enforcement of safety and health in mines. The Federal Mine Safety and Health Act of 1977 (Mine Act) transferred enforcement responsibilities from the Department of the Interior to the Department of Labor and named the new agency the Mine Safety and Health Administration (MSHA). This agency enforces the Code of Federal Regulations (CFR), and this discussion refers to CFR Title 30 Mineral Resources, Chapter I Mine Safety and Health Administration, Department of Labor, Subchapter K—Metal and Non-metal Mine Safety and Health (MSHA)."

Jan 1, 2019

By T. J. Fee

Introduction The International Nickel Company have been pioneers in mine rescue work in Ontario. Following the fire in the Hollinger mine in the spring of 1928, the Company purchased ten self-contained oxygen breathing outfits, ten all-service gas masks, an oxygen high-pressure pump, life line, inhalator, ten cap-lamps with batteries, and a complete stock of spare and accessory parts. An instructor from the U.S. Bureau of Mines, Pittsburgh, came to the Creighton mine for one week and trained twenty men in the use and limitations of all equipment. Monthly training courses were commenced in the fall, and have continued to the present time. Of the original twenty men trained, ten are still on the Creighton mine rescue teams. In the meantime, and as an aftermath of the Hollinger fire, the Work-men's Compensation Board of Ontario and the Ontario Department of Mines established a central mine rescue station at Timmins. This was completed in the spring of 1930. It was then decided, in view of the great expansion in mine development in the Sudbury district, to build and equip a similar station to serve all the mines there, namely, Creighton, Frood, Garson, Falconbridge, Sudbury Basin, and Errington. An extensive survey was made and a central location selected opposite the Frood mine. The International Nickel Company donated a site, and the station was completed in the fall of 1930. The station is a two-storey brick building, 27 ft. by 47 ft., with a large garage adjoining it. The ground floor is used for equipment and for training the crews. On the second floor are living quarters for the superintendent and his family. The garage houses a closed truck, in which all necessary equipment can be taken to any desired point for training purposes or for actual mine rescue work, if and when necessary. The garage is also used as a gas room, where the men are trained in an irrespirable atmosphere. A gas-tight observation window between it and the training room enables the superintendent to see and direct the men undergoing training, weight exercisers and other devices being used.

Jan 1, 1935

By R. L. Dunsmore

Introduction If one had been called upon to describe petroleum oil refining seventy-five years ago, he could have acceded to the request quite satisfactorily in about fifteen minutes. Fifteen years ago, an hour and a half would have been sufficient to give a general idea of oil refining, and of the equipment used for this purpose. Today, so extensive has been the research into all phases of the refining and manufacturing of petroleum products, and so rapid the strides in improvement in technique and equipment, that I doubt if a week would suffice to give an adequate outline of ail the ramifications of present-day oil refining. I propose to only 'hit the high spots', dealing particularly with the equipment and methods employed at the Imperoyal refinery, which you are to visit. Crude oil, the refiner's raw material, contains essentially only two elements, hydrogen and carbon. These are not present in the free state but are combined in various proportions as 'hydrocarbons'. A given crude oil is not made up of just one hydrocarbon, but of myriads; some solid, others liquid, and still others gaseous at atmospheric temperature and pressure, ail dissolved one in the other. Moreover, the nature and the relative amounts of the several hydrocarbons vary very considerably in crude oils from different sources. That is, a 'crude' from Oklahoma will contain hydrocarbons not present in crude from Mexico, and is different again from the Venezuela crude. Not only this but oil in a certain well in, say, Peru may be differently constituted from that in a well half a mile distant from it.

Jan 1, 1931

By Gordon L. Draeseke

"Before getting into more specific aspects of my talk today I should put in one disclaimer - one week in Mainland China and one day with Premier Kosygin does not make me an expert on Sino-Soviet affairs nor on Canadian-Chinese relations. Perhaps though there is a message in the fact that one meeting took place in relative openness in China and the other was at least partly in a bullet-proof limousine in Canada. I thought it might be interesting and appropriate to explain something of the forest industry to you who are engaged in the mining industry. Our industry, like yours, is based on a natural resource and the basic activity that we engage in is the extraction and conversion of that resource into saleable materials. However, the fundamental difference between our industries is that our resource is on top of the ground - easily visible and easily measurable, whereas yours is under the ground - difficult to find and, having been found, expensive to measure. A second difference is that ours is renewable while yours is extractive, and you must keep finding more to keep up reserves."

Jan 1, 1971