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By A. C. Halferdahl

The Granby ores may be divided into three groups or classes. The No. I ore is a heavy pyrite, chalcopyrite, pyrrhotite, sulphide carrying some free silica, and calcite. No. 2 ore carries the same general group of sulphides as does No. 1, but in a lesser amount. The gangue is an altered greenstone. No. 3 ore has a smaller amount of sulphides than either of the others. Analyses of these ores is as follows: Cu. Si02 Fe. CaO S. Al 203 MgO No. I. Per Cent. 1.8 17.5 33.0 5.7 34.5 2.3 1.3 No. 2 Per cent. 2. 0 35. 6 23. 9 4. 3 I .5. 0 9. 2 6 .. 0 No. 3, Per cent. 1 . 5 40. 9 21 . 7 3. 0 I 1 . 3 11 . 0 5 . 4 The sulphide minerals in No. 2 and No. 3 ores occur largely in bands in the gangue, and for these portions comparatively coarse grinding serves to release the gangue. Drill cores show a certain dissemination of sulphides in portions of the rock, so that grinding to 5 per cent. + 65 mesh with 65 per cent.-200 mesh liberates the sulphide minerals very completely. The association of the sulphides is fundamental. The pyrite was probably deposited first and was followed by a portion of the chalcopyrite, or these two portions of the sulphide minerals were deposited together.

Jan 1, 1924

By Chris M. Healey

"Abstract - Perhaps the single most significant variable in the evaluation of a mining project is the reserve estimate. Many parameters are considered when estimating reserves, among them geology. This paper examines the link between the quality of a reserve estimate and a good understanding of the geological controls for the deposit. A clear understanding of the geometry is essential to the accurate definition of the shape and size of the deposit. This includes the definition of any structural controls as well as the proper interpretation of the stratigraphy. Further when the distribution of grades is erratic and there is consequently a high nugget effect, there are significant problems in estimating the true grade of the deposit.Two Saskatchewan examples are presented, one with good knowledge of the controls and therefore good estimates of reserves, and the other with a poor understanding of the geology and resultant problems in deriving good estimates. In both cases the reserve estimates at various stages in the project development are compared to actual results from underground work. The first example is the Star Lake Mine where just about all the estimates were within 10% of the actual on both tonnage and grade. The Laurel Lake deposit is discussed to show how problems in interpreting the geological data make reserve estimation very difficult. Laurel Lake has the additional problem of erratic grade distribution."

Jan 1, 1992

By G. E. Rowan

"DURING the dark ages, the cherished dream of chemists was to find a process for converting base metal into gold. Many a wealthy-but-gullible patron lost a fortune in the search. Men who work with metals today are a bit more realistic. I haven't heard of a metallurgist who expects to develop any one alloy that will resist all corrosive media. In the field of stain-less steels, there are about forty different types of alloys that are used where corrosion is a •problem.A stainless product is ordinarily selected because it offers one or more of the following qualities:(1) Resistance to corrosion (2) Resistance to oxidation at high temperatures (3) Good mechanical properties at room temperature (4) Good mechanical properties at high or low temperature (5) Attractive appearance (6) Ease of maintenanceToday we are interested in discussing the stainless steel family of alloys because of their .ability to resist corrosion. We• will not try to explain the Theory of Corrosion. Let us assume that, when surface potential and oxide formations are properly controlled, iron will resist attack in various chemi.cal solutions. The addition of alloying elements to iron does this for stainless steels. The principal stainless alloys used by various Canadian industries are listed in the accompanying Table."

Jan 1, 1959

By P. J. Urso

"The coal reserves of the Crow's Nest Basin in British Columbia have been known since the late 1860's. The 51.0-million-long-ton (over 15 years) sale of low-volatile coking coal to Japanese steel mills, as finalized in 1968, establishes the importance of these coal reserves in the world markets.In the early stages of the exploration program, which began in January, 1967, emphasis was placed on deter-mining the reserve of underground low-pitch coal within the No. 10 or Balmer seam of the Kootenay coal forma-tion. The finding of low-cover reserves in excess of 100,000,000 tons altered the initially planned underground program. Extensive tests were performed, establishing the excellent coking characteristics of the open-cast Balmer coal. Due recognition was given to the ultimate reclamation costs of mined lands and associated spoil areas.t was determined that, to achieve the costs desired, a high productivity was necessary, requiring large mining equipment. Operating criteria were set out, based on producing 4.2 million tons of clean coal per year. To optimize recovery, the preparation plant feed size was fixed at Yi in. x 0. The initial basic design capacity of the plant was 1,000 tph. The washing plant is composed essentially of four separate cleaning sections: a dedusting section; a multi-stage heavy media cyclone section; water cyclones; and flotation cells. Subsequent to the basic program, additional sales were made of 6.0 million long tons over the initial three-year period and the plant capacity was raised to 1,400 tph through the addition of a 400-tph coarse-coal treatment section. All wet coal products from the fine coal plant will be dried in a 70-tph (water) heat dryer. A unit-train concept of coal transportation between the mine site and the Westward Terminals at Roberts Bank has been negotiated with the Canadian Pacific Railroad. Facilities at the port will include a 4,000-tph rotary car bumper, 400,000-ton clean-coal stockpiles, and a bucket reclaiming system having a total ship-loading capacity of 6,000 tph."

Jan 1, 1969

By W. A. MacDonald, C. M. McGibbon, J. H. Reynolds

This paper traces the development of the Seaboard Power Plant, which plays such an important role in the industrial life of Nova Scotia. It also shows the involvement of the plant in the siting of a heavy water production facility in Cape Breton. The paper concludes with an outline of the new installations which the Nova Scotia Power Commission has undertaken as an extension to the Seaboard Plant.

Jan 1, 1966

By R. D. Westervelt

IN JULY 1954, the first iron ore from the deposits in the Knob Lake vicinity was mined and shipped to Seven Islands. The beginning of the production may well be the greatest advance in Canadian economy in the past fifty years. In 1955, the Canadian iron ore output was more than twice that of 1954, an in-crease due principally to the iron ore shipments from the Knob Lake area. Previous to this, Canada's iron production was 1.85 per cent of the world's output. Now, this percentage has risen to approximately 5.5 per cent and shows every indication of increasing further as the production rate from the area is increased. In 1955 the Iron Ore Company of Canada shipped over 7 million tons of iron ore and expects to ship over 10 million tons in 1956. Present facilities may be enlarged to handle up to 20 million tons per year. If the expected I 0 million tons per year are exported, Canada's iron exports will be second only to her wheat and newsprint exports. Before production began from the Knob Lake deposits, years of development were necessary in the area. Geologists spent several summers mapping the general area in order to unravel the complicated stratigraphy and petrology. Particular attention was paid to the mapping of the iron formation and all stages of alteration from fresh iron formation to ore were observed.

Jan 1, 1957

By R. B. Allen, E. E. N. Smith, B. C. MacDonald

"LocationTHE MAIN PROPERTY and townsite of Eldorado Mining & Refining, Limited, Beaverlodge Operation, is on the north shore. of Beaverlodge lake, •about seven miles north of the deserted town of Goldfields on lake Athabasca, and four hundred and ninety air-miles equidistant from Prince Albert, Saskatchewan, and Edmonton, Alberta. Both Eldorado Airlines •and Canadian Pacific Airlines maintain scheduled flights from Edmonton to the 4,000-foot airstrip on the north boundary of the Company property. Bi-weekly flights are made by Saskatchewan Government Airways from Prince Albert. Men and priority freight are flown by Company aircraft direct from Edmonton. From June to-September, when the waterways .are ice-free, freight is carried by barge from the •railhead at McMurray, Alberta, down the Athabasca river to Chipewyan, and across lake Athabasca to• Bushell, the terminal on Black bay, lake Athabasca, a total distance of 265 miles.The Eldorado Operation has been connected by a 12-mile, all-weather highway to Bushell. Where the highway crosses the park-land along the Fredette river, the townsite, Uranium, is under construction to provide services to the uranium-producing district. Spur roads have been built to the Ace, Fay, Eagle, •and Martin mines of the Eldorado operation, and to the properties of Pitch-Ore Uranium Mines, Ltd., and Rix Athabasca Uranium Mines, Ltd."

Jan 1, 1954

By Ron Tessier, Claude Bazin, Robert Grant, Mike Cooper

"Grinding simulators are now widely available to assist in the optimization of industrial circuits. They provide circuit operating conditions or flowsheet designs that yield a given product size distribution. However, they do not provide information of the impact of a change of product size distribution on the subsequent flotation or leaching stages. This paper presents a method to predict grade and recovery indices for a flotation plant as a function of the flotation feed size distribution. The application of the method to various size distributions allows the determination of the optimal fineness of grind. A case study for a CuPb rougher circuit of a New Brunswick complex sulphide processing plant is presented to illustrate the method.IntroductionIs the grinding circuit product fineness optimum for the subsequent separation steps? This is a question that is certainly very difficult, but critical, to answer. Laboratory and pilot plant testworks can provide clues as to whether grind should be finer or coarser. For a full scale operation there is no other way than trying to change the setup of the grinding circuit and verify the effect on flotation. True effects can, however, be masked by the numerous and unexpected disturbances inherent to grinding and flotation circuit operations. A good preliminary investigation requires a noise free environment to elaborate possible solutions for the question.Plant simulators provide this noise free environment. However, despite grinding and flotation simulators having evolved significantly for the last 20 years, very little is available on the integration of both simulators to analyze the effect of fineness of grind on metallurgical performances. For instance, a grinding circuit simulator may help to find the tuning of a grinding circuit that will yield the desired fineness of grind, but does not inform on the effect the new product size distribution will have on the separation stages. Linking grinding and flotation would require a flotation plant simulator with the rate and infinite recovery parameters for each mineral in each size interval considered. This approach is seldom used because of the tedious work required to estimate the model parameters. Recently Leroux(1992) proposed a method to predict mineral liberation from grinding ore of known mineralogical texture. Although the method is still at its infancy it may provide, when combined with a reagent conditioning model (e.g Niemi et al., 1982; Bazin et al., 1988), a way to simulate flotation without the need of entering the numerous parameters of a flotation model."

Jan 1, 1994

By H. R. Banks

SHORTLY after the commencement of operations at the Sullivan concentrator, the use of a pilot table was instituted in order to present a visual control of various products by showing the amount of galena still present in the tailing from several stages of flotation. Among the products so treated, the final tailing was later included. It was sratifying to note that very little free galena was escaping, but a fine streak o a whitish mineral appeared at the concentrate zone. This mineral was identified as cassiterite. The amount was small and the newly recognized component in an already complex ore was considered primarily as of academic interest. However, the problem of recovering a usable metal was intriguing and, as opportunity presented itself in temporary lulls in research on Sullivan and other ores, the concentration of tin was a useful 'bit of knitting' to go on with. It was recognized from the start that the bulk of the mill tailing would have to be floated and the residue subjected to gravity treatment. Since one of the predominating features of Sullivan concentration operation has been the necessity of fine grinding, the problem of gravity concentration was thereby intensified. Several batch runs were made, and sufficient pulp was treated to produce about one ton of final tin concentrate assaying 67 percent tin. The overall recovery was under 30 percent and the estimated profit at full tonnage was only marginal. Testing was resumed several years later, when the price of tin again appeared attractive, in an attempt to develop a more compact plant with better recovery of tin. The weakness of the original plan of concentration was the large number of tables required to treat a feed so low in tin.

Jan 1, 1941

By John J. Barakso

A summary of geochemical dispersion processes is presented. Secondary and tertiary dispersion of uranium was examined at several uranium prospects in British Columbia. The vertical migration of uranium from bedrock (primary dispersion) through overburden into the various soil horizons, and into snow and plants, was studied, and relationships were sought to explain the dispersion patterns in the secondary and tertiary environments. Soil developments were examined to obtain information on factors affecting the dispersion of uranium in soil profiles and tertiary substances; samples were analyzed for a number of elements. Biogeochemical data indicate that plant geochemistry is a possible exploration aid in areas of heavy overburden owing to the high selectivity of certain plants for specific elements. Some new data on the geochemistry of snow are discussed as a matter of research interest in the tertiary dispersion of uranium. Analytical techniques and problems are discussed, particularly extraction techniques, which must be carefully chosen to give reliable information on uranium dispersion.

Jan 1, 1979

By W. N. B. Armstrong

CORROSION of metals, for the purpose of this talk, may be divided into two general classes, namely, atmospheric and chemical. Atmospheric corrosion is caused by the natural agents -water, air, salt, and temperature -as well as by the agents arising from industrial operations which pollute the atmosphere. Chemical corrosion affects metals in refineries and chemical plants where severe conditions exist due to .acids, alkalies, salts, solvents, gases, ?steam, etc. A special condition is encountered on road equipment and motor vehicles due to the large amounts of corrosive salts which are used on our roads in the winter. Exposure to corrosive conditions such as those referred to above causes metal to be destroyed and, therefore, it has to be protected. The non-metallic or organic coatings used to protect the metal are themselves destroyed ultimately by these same conditions. Since all types of organic coatings do not have the same kind and degree of resistance to degradation, a particular kind of -coating must be used for a particular set of conditions in order to obtain the maximum benefit. In ?addition to the above mentioned agents, organic coatings are degraded ?by sun-light, which is probably the severest single factor in the breakdown of organic coatings exposed outdoors. We can divide organic coatings, in a general way, into the following classes: (1) Conventional coatings, and (2) Special coatings.

Jan 1, 1958

By J. Awmack, M. A. Tomlinson, P. J. Lind

"Peñasquito is a complex polymetallic deposit containing gold, silver, lead, zinc, and copper and is one of the largest producers of gold in Mexico. Mining activity is currently transitioning to a second open pit, Chile Colorado, which will be mined concurrently with the existing open pit, Peñasco. The ore bodies are located within diatreme pipes and into the surrounding sediment formation. In the coming years, mining will be carried out in more sedimentary zones, which are significantly higher in organic carbon content. Organic carbon in the feed influences both flotation and leaching operations. Several changes are being implemented to the Peñasquito flowsheet to mitigate the effects of increased organic carbon in the plant feed. These include the use of alternate reagent schemes, construction of a carbon pre-flotation circuit, implementation of a pre-leach flotation circuit ahead of pyrite leach, and evaluation of a tertiary process for separation of carbon and precious metal minerals.INTRODUCTION Goldcorp’s Peñasquito operation is located in the Mexican state of Zacatecas, approximately 200 km from the city of Zacatecas in the Mazapil municipality (Figure 1). Peñasquito has been in operation since 2009, with mining carried out by open-pit methods. Oxide ore has been processed in a heap leach facility and sulfide ore is treated in the sulfide processing plant. The processing capacity of the sulfide plant is 130,000 tonnes of ore per day and in 2016 production amounted to 465,000 ounces of gold, 17.6 million ounces of silver, 109 million lb of contained lead in lead concentrate, and 263 million lb of contained zinc in zinc concentrate (Goldcorp Inc., 2017). To recover more of the contained gold and silver and to mitigate the impact of increasing organic carbon content in the ore, a number of significant changes are being made to the operation."

Jan 1, 2018

By C. E. White

The depletion of higher grade mineral reserves will accelerate the trend toward production from progressively larger and lower grade deposits. The discovery of adequate reserves of leaner ores will require the development of improved exploration techniques with a greater depth range. The principal challenges to the Canadian mining industry are to find the mineral resources required to meet fast growing world demand and to develop mining methods and equipment to ensure production costs which will strengthen our position in export markets in the face of in-creasing world competition. The challenges cannot be met without intensive efforts to attract more technical men to the industry and to improve their training.

Jan 1, 1967

By F. Bélanger, P. Fournier

"The Detour Lake Mine is located in northeastern, Ontario, approximately 300 kilometres northeast of Timmins and 185 kilometres by road northeast of Cochrane. The mill processes a free milling gold ore using both gravity circuit and leaching with a state-of-the-art carbon-in-pulp circuit. The grinding circuit is a conventional SABC circuit with a tonnage of 60,000 mtpd at 95 microns with the addition of pre-crushing upstream of the SAG mill. This paper will highlight the impact of a pre-detox thickener on the cyanide consumption in a gold leach/CIP circuit. While the pre-detox thickener was built with the intention to reduce the cyanide consumption, the opposite effect was observed when the thickener was put temporarily offline. It will show how the re-circulation of a dilute stream of cyanide into the grinding circuit, increases the overall slurry temperature and by the same effect, increases the dissolved copper concentration in the leaching circuit which subsequently increases the cyanide consumption.INTRODUCTION The processing plant is using a conventional gravity, cyanidation and carbon-in-pulp processing facility currently operating at approximately 60,000 mtpd. The comminution process is based on two parallel SABC lines, each fed from an individual reclaim tunnel. Cyclone overflow from the two ball mill circuits is directed to the pre-leach thickener. The thickener underflow is distributed to two (4) parallel leach trains of 5 tanks each, each leach train providing 29 hours of leaching retention time. After leaching, the gold in solution is recovered in a carrousel CIP circuit consisting of two (2) parallel leach trains. Tails from each CIP circuit are combined and sent to a pre-detox thickener to recover as much cyanide solution as is economically practical before being diluted and fed to a cyanide destruction system. The detoxified tailings are sent to the Tailing Management Area (TMA) for settling and retention. The excess water from the TMA is reclaimed and recycled back to the processing plant. The pre-detox thickener is designed to thicken the leach tails slurry to 64% solids with the overflow being recycled to the grinding circuit. It is estimated that the pre-detox thickener will recover 60% of the cyanide in the CIP discharge solution. It is also designed to reduce the SO2 consumption by diluting the thickener U/F to 50% solid using the tailing pond reclaim water which has very little cyanide content."

Jan 1, 2019

By G. A. Sutton

"At the San Manuel mine (Arizona, USA), in-situ copper leaching of a copper porphyry deposit was carried out from 1986 to 1999 during underground and open-pit mining. In 1993–1994, well¬field testing of the supergene zone, composed primarily of chrysocolla and copper-rich clay minerals, led to estimates that 52% of the acid-soluble copper (ASCu) could be recovered during in-situ leaching; however, the actual recovery from zone 6, which had the longest leach history, was approximately 42%. Comparing drillcore assay data from holes drilled before and after leaching also indicated an approximate recovery of 42%. The discrepancy between the predicted (52%) and actual (42%) recovery is probably related to several factors, including difficulty maintaining fluid saturation, channelling effects, and gypsum precipitation. ¦ KEYWORDS Copper oxides, in-situ leaching, Modelling, Porphyry, Solvent extraction and electrowinning (SXEW), Well-to-well RÉSUMÉ À la mine San Manuel (Arizona, États-Unis), on a procédé de 1986 à 1999 à la lixiviation in-situ de cuivre d’un gisement porphyre cuprifère pendant l’exploitation minière souterraine et à ciel ouvert. En 1993 et 1994, des essais effectués dans des champs de captage de la zone supergène, composée principalement de chrysocolle et de minéraux argileux cuprifères, ont abouti à des estimations selon lesquelles on peut récupérer 52 % de cuivre soluble dans l’acide (ASCu) pendant la lixiviation in-situ ; toutefois, la récupération réelle dans la zone 6, qui affiche l’histoire la plus ancienne en matière de lixiviation, était d’environ 42 %. La comparaison des données d’analyses de forage obtenues à partir de trous forés avant et après la lixiviation indiquait également une récupération approximative de 42 %. La différence entre la récupération prévue (52 %) et réelle (42 %) réside probablement dans plusieurs facteurs, notamment la difficulté à maintenir la saturation des fluides, les effets de canalisation et la précipitation du gypse. ¦ MOTS CLÉS d’un puits à l’autre, extraction par solvant et extraction électrolytique (SXEW), lixiviation in-situ, modélisation, oxydes de cuivre, porphyreINTRODUCTION in-situ copper leaching at the San Manuel mine, Arizona, USA (Figure 1), began in 1986. It was recognized that some of the copper oxide resource was not economically recoverable by conventional open-pit and heap leach methods using solvent extraction and electrowinning (SXEW) and a high stripping ratio would be required to access part of the resource. At the time, in-situ leaching was becoming popular in the uranium industry, but the approach was virtually unknown in the copper industry, especially at a large scale."

Jan 1, 2019

By The Satff

"TEXADA Island is situated in the Strait of Georgia, about 100 miles northwest of Vancouver. The property of Texada Mines Ltd. lies on the southwest coast of the northern end of the Island. A part of the ""Sunshine Coast,"" the climate is moderate, with about 30 inches of rain during winter months and relatively dry summers. Texada has been shipping high-grade magnetite concentrate continuously since 1952 to Japanese ore buyers. In 1959, a 3,000-foot tunnel was driven just above sea level to explore the possible downward extension of known orebodies then being mined by open pit. In January of 1961, because the open-pit operations had a limited life, C. C. Huston and Associates were brought in as mining consultants to do a feasibility study on the possibility of going underground for production. This study was completed in March, 1961. With the completion of the report, the Company went to Japan seeking a ,long-term contract to justify the capital outlay necessary for setting up an underground operation. Concurrently, underground diamond drilling revealed more ore, and the Company planned some modifications to the concentrator for increasing the copper recovery. By November, 1961, a ten-year contract was signed with Japanese ore buyers for the sale of 450,-000 long tons of concentrates beginning in October, 1963. Since that time, the Company has built its own 65 000-ton ore carrier and an additional three-year contract has been negotiated, with an annual tonnage increase of from 450,000 to 550,000 tons."

Jan 1, 1967

By H. J. Burchell

"IntroductionTHE PURPOSE of this paper is to introduce the reader to rock bolting and its present application in mining.Rock bolting consists of bolting insecure rock to secure rock in order to form a safe structure. The insecure rock may be a weak beam or loose from arching or from sloughing. The material is strengthened and held in place before damage can result.Little is known of the limitations of rock bolting; to date, work has been carried on by trial-and-error, with large safety factors being used. Rock bolts have been principally used for roof support. Bolting offers a new field of support to the mining industry: it now has a permanent position as a ground control method.HistoryRock bolting is a relatively new means of support, its exact origin being unknown.Bolting has been in use at the St. Joseph Lead Company's property in Southeastern Missouri for the past twenty-six years, the first attempts having been hit-or-miss trials before a systematic attack was made. Many instances of occasional use of rock bolts have come to light .in widely separated mining camps, .some dating back forty years.The first installations were made as supplements to wooden timbering where space was restricted. The excessive costs compared to wooden timbering hindered their advancement for a number of years"

Jan 1, 1955

By Victor F. Hollister

Elemental sulphur occurs as aformational sedimentary deposit in Upper Devonian Wabamun evaporites near Coronation, Alberta. The deposit developed in a stratigraphic jacies-change lrap; it is assumed that petroleum reacted with anhydrite to form sulphur, calcite, hydrogen sulphide and other reaction products. The deposit contains about 362,800 tonnes of sulphur and lies at a depth of 1200 m. The Coronation deposit is expected to be geologically typical of such other native sulphur deposits as may be found in Wabamun Group sediments. Widespread sour gas sulphur production f rom the Wabamun suggests the possibility that additional native sulphur deposits will ·be found.

Jan 1, 1984

By C. Boudreault, M. Fortier, S. Fafard

In the forging industry, the increasing trend is to use DC cast billets as forging stock to replace extruded stock. However, there is little technical information available in open literature. In order to gain a better understanding of the behaviour of cast stock during deformation, a study was initiated to evaluate the impact of an homogenisation treatment on the billet prior to cold forging. Axisymmetric upsettings of cylindrical samples machined from DC billets were achieved in order to evaluate and compare flow stresses, crack initiation and propagation. Results show a 30% decrease in flow stress after homogenisation. Observations of the deformed samples show major cracking for the as-cast material. Optical microscopy and SEM observations have related the crack initiation to decohesion around ß -AlFeSi particles and subsequent growth along the constituent path. Homogenisation effectively breaks up and transforms the ß phase, present as platelets in the cast product, into smaller spherodised a-AlFeSi particles. This has the effect of preventing crack growth in the forged product. The homogenisation treatment also resulted in the reduction of Mg and Si in solid solution. The softer matrix generated 29% less die wear when compared to the as-cast structure. Based on the results of this study, it is thus recommended to homogenise cast billets prior to cold forging.

Jan 1, 2006

By A. M. Christie

Acknowledgements The following account has been compiled mainly from records and maps of Eldorado Mining and Refining (1944), Limited, hereinafter called the Crown Company. This work was done under the supervision first of R. F. Murphy, Chief Geologist, and later of E. B. Gillanders, Eldorado Mine Manager and Manager of Eldorado Exploration Division. W. F. James and B. S. W. Buffam are consulting geologists. Since 1946, S. N. Kesten has supervised geological work for the Company in the Goldfields area. Where maps of Eldorado properties have been included in this paper, the name of the geologist who examined the property is acknowledged on the map. Outline of General Geology The geology of the area is described in the Goldfields and Martin Lake preliminary maps of the Geological Survey and accompanying Paper 49-17. In brief, the Tazin series of Precambrian age, consisting mainly of sediments with minor interbedded volcanics and basic intrusives, is intruded and replaced by granite, now generally gneissic. The late-Precambrian Athabaska series of conglomerate and arkose, with interbedded basalt and andesite flows, rests unconformably on the older rocks. All these rocks are cut by small diabase dykes. The geological terms used in this paper and in the accompanying figures are standard with the exception of the term 'mafic rocks'. These include all the basic or dark coloured rocks of the Tazin group, such as amphibolites, biotite schists, and chlorite-epidote rocks (greenstones), whether they be of extrusive, intrusive, or sedimentary origin.

Jan 1, 1949