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By C Jincheng, L. Liang, L. Wenjun

"Considering overgrinding in a grinding process, the grinding characteristics of comminuted hematite products using a HPGR and a conventional CC were comparatively studied. The major properties including particle size, grinding kinetics and grinding technical efficiency (Et) were investigated. Individual size distributions (ISDs) of -2.0mm in a HPGR product showed a more significant “double-peak” characteristic than a CC product. As a result, HPGR products were finer and had a wider full-size distribution because of the greater proportion of fines. The parameters m and zi in m-th order grinding kinetics were analyzed by the partial-derivative method and the critical time tc(tc = exp (1/ zi)) was obtained. zi mainly affected the breakage rate when t < tc; otherwise, m mainly affected the breakage rate. In these tests, tc was considerably higher than the grinding times, and HPGR products yielded a higher zi-value than the CC product for the same sieve size. This indicated that HPGR products had a higher breakage rate and needed a shorter grinding time for a certain grinding fineness. Et was calculated by simulating the size distributions of batch grinding products. HPGR products gave a lower Et at a decreasing rate than the CC products for -2.0 mm feed and -0.5mm feed, and then showed a slightly higher Et for -2.0+0.5 mm feed. This indicated that overginding in HPGR full-size products was more serious under the condition of coarse grinding, whereas the efficiency was higher and overgrinding weakened significantly in HPGR coarse products because of screening-out fines. Based on the above research, a new process of “ultra-crushing in HPGR – classified grinding” was advanced, reducing ores tonnage into first stage ball mill significantly, improving grinding efficient and weakening overgrinding in the whole grinding process.INTRODUCTIONIn mineral processing, comminution accounts for a substantial portion (approximately 60~70%) of the energy consumed in plants. As an ultra-fine crushing equipment,the application of the HPGR for industrial comminution has been paid close attention because of its low specific energy, low steel consumption, high capacity and high ratio of reduction, among others (Schonert, 1998; Norgate & Weller, 1994; Fuerstenau & Kapur, 1995). HPGRs comprise two counter-rotating rolls that draw feed material into the roll gap. One roll is fixed to the mainframe, while the other movable roll is mounted on slides and positioned by hydraulic rams. The specific pressing force (SPF) (i.e., total force divided by projected roller area) is typically in the range of 3~9 N/mm2 depending on the application, while pressures of up to 1000 N/mm2 have been measured within the operating gap (Maxton , Morley, & Bearman , 2003)."

Jan 1, 2016

By J. A. Brusset

Introduction I am indebted for most of the information in this paper to Mr. P. S. Lea, Deputy Chief Inspector of Mines of Great Britain, and Mr. A. E. Crook, Engineering Inspector of Mines, Ministry of Fuel and Power. Other coal-mining men in Canada may be as surprised as I was to learn that there are twenty-five Diesel locomotives in service underground in British gassy coal mines. Many more are in use underground in non-gassy coal mines and in metal mines. Approval has been granted for an additional fifty flame-proof locomotives to be used in gassy mines, and these should be in operation by the end of 1946, or as soon as manufacturing facilities permit.

Jan 1, 1946

By L. Garrigues, M. Jarvis, M. Halhead, O. A. Bascur

"Large variability of ore types, escalating variables operating costs and increased throughput require large investment in sensors and systems in mineral processing operations. Mining and mineral processing plants collect and manage more data than a small city with much in real-time. The data is changing rapidly as internal and external conditions evolve. As corporations buy and sell assets, and reengineer their staff, the structure and tools that were used to understand this data is lost. This results in significant deterioration in the ability to maintain a smart operation. When data is recognized as a critical asset and managed as part of an infrastructure, it become a key enabler to help transform the entire operations. In many situations, all partners in business collaboration—such as join ventures, contract manufacturer, expert service providers, and operations and maintenance companies—need access to production and asset data. The emergence and maturation of Cloud technologies make it possible to easily connect the plants to external equipment suppliers and operational support service.This paper will share examples of how mineral processors have adopted new data strategies such as self-service business intelligence, cloud computing and internal/external collaboration.INTRODUCTIONOne of the main challenges in mineral and metallurgical processing plants is effective energy and water management. The lowering of ore grades requires higher throughputs while the ores are getting more complex with variable mineralogical compositions. Electrical energy supply is becoming a restriction in many countries. Rising water management costs has a direct impact on the profitability of the operations. Grade recovery versus energy consumption in copper production for both open pit and underground mines has been described by Fuerstenau (2001). Comminution uses over 55% of the energy to produce nonferrous metals while other operations require much less energy (Nelson, Richins, & Lelinski, 2013)."

Jan 1, 2016

By D. F. Coates

Slope problems arise on mining properties from cuts for roads and railroads and from open pits. When it is 'realized that 1,000,000 extra tons of waste may have to be mined as a result of an average slope being reduced by 1 ° it is easy to appreciate that the slope problems connected with open pits are of far greater importance than the others. The type of slope failure that can occur can be classified in different ways. The most useful classification would be one that separates the causes in such a way as to provide a basis for studies to deal with problems of prevention and control. Using this criterion the types of slope failures are classified into four groups. Having classified the problems in this way an understanding can be gained of the various mechanisms involved in failure ..

Jan 1, 1961

By R. Glenn Madill

Western Canada is defined, for the purposes of this paper, as that part of the Dominion bounded approximately by the 95th and 141st meridians of longitude and the 49th and 80th parallels of latitude. It is comprised of Manitoba, Saskatchewan, Alberta, British Columbia, Yukon, and that portion of the Northwest Territories lying to the west of the 95th. meridian. The first magnetic observations made in Western Canada were in the interests of navigation by sea. Observations were made by Captain Middleton in Hudson bay at Churchill and York Factory in 1725, and along the Pacific coast by Captain Cook in 1778 and Captain Vancouver in 1792. The first systematic magnetic survey in Western Canada was made between 1819 and 1826 by Sir John Franklin in his widely distributed explorations. It is of interest to find that while the first magnetic declination observations made in Hudson bay and along the Pacific coast were purely in the interests of navigation, the next investigations, which were made in the Western Arctic, included measurements of inclination and force with those of declination. There was a valid reason for this more complete research into the magnetic field as the construction of declination charts depended on the position of the north magnetic pole. Halley promulgated a theory 1683 that " the globe of the Earth may be regarded as one great magnet, having four magnetic poles, two of them near each pole of the equator, and that in those parts of the world which lie near any of those magnetic poles the needle is chiefly governed thereby, the nearest pole being always predominate over the more remote" . The position of a magnetic pole may be defined as a point where the inclination is 90 degrees and the horizontal force zero. It is obvious that the position cannot be&apos; defined by declination observations alone since, for some distance from the magnetic pole, .the horizontal force is too weak to give directive force sufficient to effect the pointing of a compass.

Jan 1, 1948

By D. F. Kidd

Introduction In a companion article, Surveys at Great Bear Lake, 1931, R. C. McDonald has described the general character, topography, and climate of the Great Bear Lake-Coppermine River area and the main means of access (l). The present paper will largely be confined to the geological features of the district. In the last two years, the rocks of the region have received considerable attention, and papers including references to .the geological succession have been written by Knight(2), Duncan(3), Norris( 4), Reid(5), Cameron(6),and Kidd(7). The writer confined his field-work during the 1931 season to the district between LaBine point and Hunter bay and northwest to the head of McTavish arm. Brief trips were made down the Sloan river from McLaren lake, 25 miles northeast of Hunter bay, to that place, to Dowdell (Sixty-six) point, the south point of Echo bay, and to the region north of the Dismal lakes and west of the Coppermine river. The inner part of Echo bay, which is the area discussed by Reid and Cameron, has not been seen by the writer and the geology there will not be discussed.

Jan 1, 1932

By H. R. Manouchehri

"It is well understood that, apart from particle hydrophobicity, the flotation process is strongly influenced by the cell hydrodynamics. Once the chemical conditions were optimized and fixed, the flotation rate is essentially determined by impeller speed and the air flow rate.The collection efficiency in flotation is a product of collision, attachment and stability/detachment efficiencies. The collision efficiency for a given particle diameter is increased by decreasing the bubble size and bubble velocity as well as increasing the power input to the cell. The attachment efficiency, however, is defined by bubble size and its velocity. The detachment/stability depends on the relative magnitudes of the attachment force between the bubble and particles and the detachment force acting on the bubble-particle aggregates. For the particles having specific contact angle, the stability decreases as the energy input increases. Therefore, there must be an optimum energy dissipation to maximize recover of defined size fraction.A comprehensive laboratory study was devoted to determine the effect of power input in recovery of finely grind Cu-Ni bearing ore. Several flotation tests were conducted to define the hydrodynamic parameters for a laboratory scale Runge cell under different impeller speeds. An increase in flotation recovery of finely ground ore was observed when the impeller speed was increased from 450 to 1,200 rpm. The experimental results have shown increasing in water recovery and improving in flotation kinetics of fines by increasing the power input to the flotation cell. Implementation of the Wark flotation model to the experimental data revealed a good correlation between the experimental data and the model. For the particles having enough hydrophobicity the flotation rate increases by increasing the impeller speed due to a higher value for collision efficiency within the cell."

Jan 1, 2016

By Mohamad Kharseh

There is general acceptance that climate change, which is the most important challenge facing humanity, is anthropogenic and attributed to fossil fuel consumption. Therefore, improving the performance of our existing energy systems and deploy more renewable energy resources is an urgent issue to be addressed. Geothermal refers to existing of heat energy in deep rock and sedimentary basins. This energy can be used to drive a power turbine to generate electricity. Traditionally, geothermal has been exploited in places with the plentiful hot water at relatively shallow depth. In the light of fact that ground temperature increases with the depth everywhere on the Earth, engineered geothermal systems (EGS) can be installed in any place to exploit the geothermal in generating energy. Unfortunately, the high exploration and drilling costs of boreholes is the main barrier to commerciality of EGS worldwide. In addition, there are technical problems associated with drilling big depth. In oil producing countries such problems can be addressed by utilizing whether active or abandoned oil or gas wells and, consequently, EGS can produce power at profit. The current study presents an analysis of a binary geothermal power generation system for commercial electricity generation in Qatar. For this purpose, two binary cycles are assumed the main difference between them is that the first one is air cooled while the other will be water cooled. The performance of the two cycles and the possibility of improvement has been shown. Economic analysis the power plant shows that the levelized costs of electricity is 3.6US¢/kWh and the pay-back time is less than 8 years.

Aug 1, 2013

By N. Aslin, R. Clark, G. Heferen

The methods of harvesting copper from stainless steel mother plates has been investigated from fundamental and operational experience perspectives. At least five different harvesting techniques have been identified that have different effects on product quality, current efficiency, current distribution, growth morphology and ease of stripping. Each method is examined from fundamental principles to understand what occurs during the harvesting process and why the particular effects are manifested. Experience from plants operating the harvesting method is provided to show that the fundamental understanding is relevant. Best practice harvesting method and harvesting management are described.

Jan 1, 2014

By Dean Gerhardt

Why the need for proactive loose detection? ?? Past history of ground falls in Saskatchewan mines prompted research into new techniques for ground control. ?? Traditional tools for ground assessment (i.e. visual inspection, sounding with scaling bars) are not proactive and can often be time consuming. ?? Need existed for a system that was non-evasive, time efficient, and could be managed by a single operator. Ground Penetrating Radar (GPR) immerged showing the greatest potential.

May 1, 2008

By A. L. Mackie

Arsenic is a highly toxic element and a known human carcinogen. It is often a contaminant in mine water discharges, particularly from gold mining and roasting operations, and has been found at concentrations as high as 4 g/L. Increasingly stringent controls on the concentration of arsenic allowed to be discharged into the environment cannot always be met by current treatment processes and thus enhanced technologies are required to achieve low treated effluent concentrations at reasonable costs. A novel two-step physicochemical treatment process was developed and tested at the bench-scale using synthetic mine water solutions (SMWs) in order to reduce arsenic concentrations in treated effluent to exceed current discharge regulations. The process includes chemical coagulation with ferric sulphate and ballasted flocculation for enhanced solid-liquid separation. The SMW contained 59 ± 2 mg/L arsenic with a slightly alkaline pH. The effect of arsenic speciation on the process was tested by using either arsenite, As(III), or arsenate, As(V), in the SMW solutions. Tests were performed at cold temperature (3 ± 1 °C) to ensure the process? efficacy year-round in northern climates. Arsenic in As(V) SMW solutions was removed to a final total concentration of 0.0054 ± 0.002 mg/L, almost half the current recommended allowable drinking water concentration of 0.010 mg/L. As(III) was removed to a concentration below the Metal Mining Effluent Regulations? (MMER) current limit of 0.50 mg/L, to 0.32 ± 0.06 mg/L, with double the coagulant dose used in Stage 1 for As(V) removal. Oxidant addition at a concentration of 5 mg KMnO4/L in Stage 2 resulted in final total arsenic concentrations of 0.017 ± 0.002 mg/L and pH adjustment with lime in Stage 2 resulted in 0.0415 ± 0.0007 mg As/L in treated As(III) SMW. Both of these modifications to the process reduced arsenic concentrations to below proposed new MMER limits (i.e., 0.10 mg/L). This two-stage treatment process was shown to reduce arsenic concentrations to well below current treatment guidelines while reducing or eliminating chemical oxidant demand.

Aug 1, 2013

By R. J. T. Charles

Introduction An apparatus that will measure the surface area of a few of the simple minerals with a high degree of accuracy has been described by J. W. Bell (1). His apparatus consisted essentially of a photometric device that would measure the turbidity of fine particle suspensions. Turbidity, in this case, was considered as a function of surface area. Bell&apos;s method of surface area determination seemed to offer possibilities of extension and improvement to the point where it might approach a general method of particle size measurement. Theoretical and Practical Considerations of the Photometric Method In order to illustrate how turbidity may be considered as a function of average particle size, and to indicate the type of results expected from a photometric method of particle size measurement involving turbidity, the following theory may be hypothecated. If a number of particles, considered as spheres of uniform diameter, are placed at random in the path of a beam of light, the following expression, which will give the change in light intensity as a function of the diameter of the particles, the specific gravity of the material, and the weight involved, can be formulated from the Beer-Lambert Law:

Jan 1, 1951

By J. A. C. Ross

Introduction To enlighten those who may be wondering where anyone could find sufficient data to write a paper on underground concrete work, the author would like to explain that, at Copper Mountain, we have found it necessary to line numerous headings with a layer of concrete in order to keep them in a safe and serviceable condition. The majority of these headings are scram drifts and ore-pass raises. This paper will therefore deal, in the main, with the methods of and reasons for placing concrete in these headings. During recent years, radical changes have been made in the methods of mining ore at the Copper Mountain mine. After considerable experimenting, a mining system has been developed making use of diamond drills for primary breaking and transfering such broken ore through scram drifts with slusher hoists. With the advent of scram drifts, it soon became apparent that some substantial means of reinforcement and protection for the scram drifts themselves would be necessary. Since the orebodies in this mine are cut by numerous dykes or faults, and often both, it was anticipated that some means of support would be required where headings necessarily passed through these incompetent zones. Further, as experience was gained, scram drifts were driven into pillars and in close proximity to old workings so as to recover the maximum amount of ore. In such places, the ground is often severely fractured, either as a result of previous mining or from the effect of excessive rock pressures.

Jan 1, 1950

By Darrell McClarty, Roger Payne, Matt Haggis, Michael Courtin, Deborah Berthelot

"Over forty years of uranium mining in the Elliot Lake region of Ontario (I 956-1996) has resulted in the production of over 300 million pounds of uranium. With the completion of mining activity, Rio Algom Limited and Denison Mines Limited are utilizing progressive environmental technologies and management systems to reduce and manage the environmental risks associated with the 150 million tonnes of potentially acid-generating tailings in nine regional waste management areas. Water covers designed to reduce oxygen entry and thereby significantly inhibit acid generation have been applied at six of the sites with the Quirke site serving as a demonstration site for the Mine Environmental Neutral Drainage program. All five of Rio Algom Limited' s effluent treatment plants are monitored and controlled from a central control station utilizing a Supervisory Control and Data Acquisition (SCADA) system based on ""Fix Dmacs"" technology. Scheduling, auditing and reporting of plant operating and environmental monitoring programs for the entire watershed are controlled utilizing the Regional Environmental Information Management System (REIMS). Proper application of these technologies and management systems facilitates delivery of cost-effective environmental monitoring, care and maintenance programs at these sites and provides tools to demonstrate compliance with all environmental performance criteria.IntroductionCost-effective management of multiple tailings management areas distributed throughout a 35 km watershed requires the application of leading-edge environmental technologies. Long-term monitoring, care and maintenance costs must first be minimized through the application of decommissioning technologies that inhibit acid generation and minimize the release of contaminants from the sites. On-going operating costs must then be controlled through the application of environmental management strategies that optimize the allocation of resources while ensuring compliance with regulatory and Company environmental requirements.Using sites in the Serpent River Watershed as an example, this paper demonstrates the effectiveness of water covers as a decommissioning strategy to inhibit acid generation. In addition, the Telemetered Environmental Operating Control System and Regional Environmental Information Management System are reviewed as examples of the application of environmental technologies to the management of environmental programs."

Jan 1, 1998

By S. B. Mishra

Ni-20Cr metallic coating was deposited on a Ni-based Superalloy (3Fe-19.5Cr¬0.3Ti-Balance Ni) by a shrouded plasma spray process; NiCrA1Y was used as a bond coat. Erosion studies were conducted on uncoated and plasma-spray coated superalloy specimens using an air-jet erosion test rig at a velocity of 40 m/s and impingement angles of 30° and 90°. The coating has been characterized for porosity, microhardness and microstructure and X-Ray Diffraction (XRD). An electron probe micro analyzer (EPMA) was used to obtain X-ray elemental mappings of the coating along the cross-section. Scanning electron microscope (SEM) with EDAX attachment was used to analyze the eroded surfaces.

Jan 1, 2005

By R. H. Nafziger

A novel process has been developed for preparing directly workable steel ingots from prereduced iron ore pellets by a two-stage process. The pellets are continuously charged into an electric arc furnace, where molten metal is separated from the gangue. The molten metal flows out of this furnace through a hollow nonconsumable graphite electrode immersed in a molten flux in an electroslag furnace. The molten metal solidifies on a continuously withdrawing base plate to form the ingot. A variety of standard carbon and alloy steel ingots . free of porosity , were produced using suitable decarburizers and ferroalloy additions. Some advantages of the two-stage process include: (a) consumable electrode fabrication is eliminated; (b ) no expensive deoxidizers are required; (c ) the uncontaminated electros lap flux can be reused; (d) energy consumption averages 25% less than in a conventional electric arc - electroslag operation ; and (e) the operation is continuous.

Jan 1, 1977

By Carol Odell

This paper was prepared as a brief for Prospectors and Developers Association of Canada (PDAC) to guide input at a series of round tables carried out by the Federal Government in response to the 38th Standing Committee on Foreign Affairs and International Trade (SCFAIT) report, on ?Mining in Developing Countries and Corporate Social Responsibility?. This document mandate is to provide background information, analysis and recommendations on the practice of Canadian exploration and mining companies abroad. This research was based on 11 case studies of Canadian companies which have experienced conflicts or controversies overseas. All case studies were assembled through an extensive literature review of publicly available documentation and communications with representatives of the mining companies to assist in deepening the insights into the drivers of the conflicts and the needs of Canadian companies in similar situations. The case studies include both exploration and mining operations. Our analysis begins with the identification of general and case specific drivers of conflict/controversy in each case study. Company names are kept confidential and only anonymous results are presented. We make ample use of simple flow charts and schematic diagrams to explain how contextual drivers and aggravators and company drivers and mitigators play varied and interrelated roles in conflicts. The diagrams also illustrate the cumulative analysis of drivers including the linkages among drivers/aggravators/mitigators across different domains (social, governance, NGO/media and company). Finally, we discuss needs of companies and propose recommendations for addressing social responsibility and human rights concerns.

May 1, 2007

By J. R. Dinn

On the afternoon of Saturday, June 23rd last; there was an unusual occurrence at the surface plant of the Dominion Coal Company&apos;s Caledorria mine, Glace Bay, which operates on the Phalen seam, here lying at a depth of 170 feet from the surface. On that day, the writer, who was attending a business conference in the General Office about a mile distant from the Colliery, received a telephone call to the effect that there was a strong odour of gasoline or kerosene in the wash-house and lamp-house of the Colliery, and that the attendants in both the wash-house and the lamp-house had become ill and had had to be sent home. Instructions were given at once to cut off the electric current, and to close all doors to prevent access to the building. When the writer arrived at the plant and questioned the workmen, he was led to the belief that the gasoline tank in the lamp-house (used in connection with flame safety lamps) had leaked and that the gas, having volatilized, had displaced sufficient oxygen to cause the trouble. Emphasis was being placed on the kerosene, or, as some said, the gasoline, odour. In the lamp-house, there is a small shuttered window which opens on a corridor. Here the workmen receive their lamps from the lamp attendant. An examiner, with a flame safety-lamp, proceeded to test the atmosphere within the building by passing his lamp through the open window, since, if the trouble was due to volatilized gasoline, a gas cap would be shown on the flame of the safety-lamp. After holding the lamp for a few seconds inside of the window, he withdrew it and remarked, "There&apos;s no gas cap" . Almost immediately the lamp fell from his hand and he dropped unconscious to the floor of the corridor. The writer, who was standing beside him, felt no ill effects and removed him at once from the corridor. Steps were immediately taken to revive him ( artificial respiration) , and in about ten minutes he became conscious and was breathing naturally. In making the examination, his head was not inside the window, but in line with the frame of it. It was apparent that some gas more deadly than the hydrocarbons from gasoline was present.

Jan 1, 1934

By R. I. Grauch, Michael D. Glascock, Chen Nansheng, Jr Coveney, James B. Murowchick

"Unusually rich molybdenum ores (cutoff grade = 4.10/0 Mo) hosted by Lower Cambrian black shales have been mined since 1985 near Zunyi in the province of Guizhou in China. Similar ores were once worked for Mo and Ni near Dayong in the province of Hunan. In both mining areas, mineralization occurs in Lower Cambrian black shale (Niutitang Formation and stratigraphic equivalents) as a single sulfide bed or lens with exposed thicknesses up to 15 cm and reported thicknesses up to 35 cm. In addition to high Mo values (4% to 7%), ore samples contain up to 7% Ni, 2% Zn, 2.5% As, and several hundred ppb Au and Pt-group elements, but the precious metals have never been recovered from the ores. Sporadic occurrences of Mo-Ni sulfide ore beds are found in at least five provinces stretching approximately 1600 Ian from Yunnan to Zhejiang. None of the Mo-Ni ore-bed occurrences has any obvious connection with mafic or ultramafic source rocks. Similar occurrences containing elevated values for Ni, Mo, and PGE exist in Devonian black shale in the Yukon. Future exploration for Pt, Au, Mo, and Ni deposits should consider this previously unknown type of sediment-hosted mineral deposit.Sommaire - Des minerais anormalement riches en molybdène (teneur-limite = 4.1% Mo) provenant de schistes argileux noirs du Cambrien Inferieur ont été exploites depuis 1985 près de Zunyi dans la province de Guizhou en Chine. Des minerais semblables ont déjà été traire pour Mo et Ni près de Dayong dans la province de Hunan. Dans ces deux régions minières, la minéralisation se présente dans le schiste argileux noir du Cambrien Inferieur (Formation Niutitang et équivalents stratigraphiques) sous forme de couche ou lentille unique de sulfures avec des épaisseurs exposées de plus de 15 cm et des épaisseurs rapport6es de plus de 35 cm. En plus des fortes teneurs en Mo (4%-7%), des échantillons du minerai contiennent jusqu’ à 7% de Ni, 2% de Zn, 2.5% d&apos;As, et plusieurs centaines de ppb d&apos;or et d&apos;éléments du groupe du platine; toutefois, les métaux précieux n&apos;ont jamais été récupérés des minerais. Des présences sporadiques sous forme de couches de minerai sulfure de Mo-Ni se retrouvent dans pas moins de cinq provinces s&apos;etendant sur 1600 km de Yunnan a Zhijiang. Aucune de ces présences de minerais, sous forme de couches, ne semble associée a des roches du type mafique ou ultramafique. Des présences similaires contenant des teneurs élevées en Ni, Mo et EOP se retrouvent dans le schiste argileux noir Devonien du Yukon. L&apos;exploration future pour des gisements de Pt, Au, Mo et Ni doit prendre en considération ce type de gisement encore inconnu précédemment."

Jan 1, 1992

By R. H. Sheaphim

THE RECENT and continuing activity in the Boundary district, British Columbia, makes the publication of this paper timely. The following description and discussions are based on two years&apos; experience in the district as Field Manager and Geologist for Attwood Copper Mines, Limited. The Attwood project was organized by Dr. D. F. Kidd to re-examine the Boundary mining camp. Thanks are due to Dr. Kidd, both for his intelligent guidance during the project and for his permission to publish this paper. Much of the data and many of the interpretations presented are credited to the work of, and to discussion with, Dr. W. H. White, Consultant Geologist, who worked for two field seasons on the project. However, the author assumes the responsibility for this presentation. Dr. C. D. A. Dahlstrom worked with the author during the latter stages of the project. His assistance and advice are gratefully acknowledged.

Jan 1, 1956