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By R. M. Bustin

"Extensive deposits of tectonically sheared coal of the Mist Mountain Formation occur in the south eastern Canadian Cordillera. The quality of the coal varies markedly; it is commonly partially oxidized and poor washability characteristics.Oxidation of the sheared coal has been promoted by its fine grain-size and by fractures in adjacent rocks which have facilitated penetration of atmospheric oxygen and circulation of oxygenated waters. Oxidation has resulted in a loss of coking power, a decrease in vitrinite reflectance, and an Increase In oxygen and decrease in carbon content.The relatively low clean coal yields of the sheared coal are primarily the result of the greater volume of mineral matter present, which in turn reflects both the greater susceptibility to shearing of coal with abundant rock partings and the shearing and dissemination throughout the coal of formerly discrete rock partings. The high ash content of some sheared coal seams may be artificial, resulting from the difficulty in distinguishing and separating sheared roof rock and floor strata from the coal seam during mining. There is little variation between the quality of the washed sheared and unsheared coal, with the exception of the somewhat higher ash content of the clean sheared coal compared to clean unsheared coal. This poorer separation of the ash from the organic fraction of the sheared coal is considered to be a product of the large amount of fines present as well as the local formation of aggregates of organic material and ash resulting from plastic flowage of the vitrite and clarite during shearing.IntroductionIn the southeastern Canadian Cordillera, coal seams of the Lower Cretaceous Mist Mountain Formation (Gibson, 1979 were in part sheared and comminuted during Late Cretaceous and Tertiary tectonism . Extensive deposits of sheared coal exist, and even in areas of mild deformation the coal may be locally sheared (Bustin, 1979). The quality of the sheared coal varies notably; it is commonly oxidized even far from the present weathering horizon, and locally has a disproportionately large amount of ash and poor washability characteristics even far from the present weathering horizon and locally has a disproportionately large amount of ash and poor washability characteristics."

Jan 1, 1982

By Unkown

The Province-wide road ban on movement of heavy loads has had the effect of curtailing or stopping development in several areas. In the Leduc area, the discovery well has been restricted in flow to only a fraction of normal due to limited storage space, but drilling at Imperial Leduc Nos. 2, 3, and 4 has been continued for the past few weeks. The No. 2 well is within 100 feet of the producing horizon and should be completed within the next few days. According to reports, it has been logging slightly lower, structurally, than the discovery well, but, regardless of the outcome, it has been an important test to determine westerly cross-section of the Leduc structure. No official reports have been made available of any tests made during the drilling of the well, but it is understood that promising oil and gas shows have been indicated in higher formations. Actual drilling operations have not been commenced by any of the other companies holding leases in the immediate area but it is expected that, when road bans are removed and equipment is assured, several wells will be commenced. Announcement has been made that Imperial Oil, Limited, will drill a well near Battle lake, about thirty-five miles southwest of the Leduc field. Location of the well has been made following an extensive seismograph survey of the area, with total depth of the test well expected to be in the 8,000- to 8,500-foot range. Drilling will be done with the heavy-duty rig last used at the De Winton test. Imperial Oil have abandoned hope of oil production in the Provost area after drilling nine wells, but will retain their interest in the gas field that has been developed. Of the wells drilled, four indicated gas flows ranging from 1,060 to 13,200 M.c.f. per day.

Jan 1, 1947

By J. L. Bowlby

OWING to the pressure of routine analyses at the laboratory during the past year, work of an investigational nature on water problems has been greatly curtailed. Favourable reports by the boiler inspectors indicate that the operators are giving satisfactory attention to feed-water treatment at the several . power plants. Some of the operators prefer lime and soda, others the phosphate and soda treatment. Springhill is still on the same commercial treatment as they were using last year, and satisfactory results are being obtained. This individual preference for a particular treatment, although it may be different for feed waters of similar nature, indicates that so long as proper conditions of alkalinity and concentration are maintained within the boiler, it is immaterial what chemicals are used in the treatment. This statement refers, of course, to the low-pressure boilers. In high-pressure boilers, a treatment such as lime and soda cannot be satisfactorily employed, on account of the precipitated calcium carbonate unduly increasing the amount of suspended matter. Only one case of impending trouble was reported during the year. That was at Seaboard, shortly after the new unit was placed in operation. Dissolved oxygen, considerably in excess of the permissible 0.030 cubic centimeters per liter, was detected at various points on the feed line. It was suspected that a de-aerating heater was being operated at too low a temperature, and chemical tests, made before and after the necessary adjustments, proved that this was the source of the trouble. While it has been impossible to give mine waters the attention they require, progress can be reported in the work carried out by the Mechanical Department. Past investigation of the action of mine water on various acid-resisting alloys is now bearing fruit, and it can safely be said that repair work on mine pumps has been reduced by nearly one-half.

Jan 1, 1938

By Ron Doucet

Industry today is now more than ever dependent on its assets and on the standard of maintenance. Changes in technology, environmental regulations, a continually improving focus on safety and global competitiveness has made maintenance a key activity in sustaining safe, financially viable and environmentally integral operations. Maintenance used to be looked upon as a cost centre with a sole focus of fixing equipment to attain high availability. Maintenance today affects all aspects of the business: safety, environmental integrity, energy efficiency, productivity, costs, and product quality. These new demands on the function of maintenance requires us to think vastly differently about what maintenance is all about, even to the point of contradicting old beliefs. In the following paragraphs we will examine some of the changed thinking that has evolved over the last 50 years. These new concepts will lay the foundation for the implementation of 21st century best practice maintenance.

May 1, 2003

By D. Marotte, M. David

"A new exploration procedure is proposed for volcanogenic massive sulphide deposits of the Abitibi belt. ""Samples"" of acidic volcanic rocks (Si02 > 60%) were compiled from the literature. From the 574 samples collected, 322 were used in each of a number of experiments. Forward inclusion linear discriminant analysis performed on the untransformed geochemical data shows a general depletion in Na20 and CaO along with an enrichment in MgO for a ""proximal"" group of samples relative to a ""distal"" one. The percentage of misclassified samples reaches 20% to 30%, but test sets shows good stability.The exploration procedure was applied to the Normetal deposit, where the authors took 160 samples during the summer of 1977. It quickly leads to the definition of targets for more detailed exploration together with a good recognition of the old known deposit.IntroductionVolcanogenic massive sulphide deposits in the Abitibi belt (Quebec) are mainly found in rhyolites or acidic pyroclastics in the uppermost portion of a calc-alkaline volcanic series (Descarreaux, 1972). The deposits are thought to have formed syngenetically by the action of volcanic hydrothermal exhalations during the waning episode of a felsic volcanic cycle (De Rosen Spence, 1976). Alteration pipes of disseminated sulphides are commonly present. Metal deposition from hot springs, initiating convection cells in a submarine environment, may have been the dominant process in ore formation (De Rosen Spence, 1976)."

Jan 1, 1981

By G. Macfarlane

"In 1985, a crushing plant, located in the feed preparation area of Kidd Creek's copper smelter, was modified. The plant, which originally had treated only copper-bearing materials for the smeller, at a rate of 10 tonnes per hour, was expanded to 40 tonnes per hour capacity and modified to treat silica ores to meet the smelter’s flux requirement and also gold ores from the company's Hoyle Pond property. In the storage area adjacent to the crushing plant a 300 tonne per day gold mill was constructed.This paper outlines the construction and first year of operation of the crushing plant and gold mill with emphasis placed on the capital and operating advantages to be gained by utilizing an existing metallurgical infrastructure.IntroductionThe Kidd Creek Mines Ltd. copper-zinc-silver orebody is located 24 km north of Timmins, in Northern Ontario . Mining of this massive sulphide de posit commenced in 1966 and, in the ensuing years, a concentrator and zinc plant were constructed at the metallurgical complex, approximately 17 km by rail from the mine site . At this same site, in 1981, a copper smelter and refinery were commissioned. The smelter which utilizes the Mitsubishi smelting process for the continuous production of blister copper from copper concentrate, has been comprehensively described in previous papers.At the time of the smelter construction, a small (10 tonnes per hour) crushing plant was installed in the smelter's feed preparation area. This plant was used to treat the copper-bearing revert material produced by the smelter, and, apart from periods when slags and matte were produced through furnace drainage at the end of each operating campaign, it was generally under-utilized. This fact, together with the requirement to devise a more cost effective method of providing silica flux for the smelting operation, was the basic rationale for modifying and expanding and crushing plan t. At the same time, development at Kidd's Hoyle Pond orebody had progressed to such a stage that a gold mill of 300 tonnes per day was warranted."

Jan 1, 1988

By I. A. Cameron, F. Ham, R. Sriram

"Planned increases in electric furnace productivity and higher matte temperatures needed for the Sudbury Smelter's S02 Abatement Plan, require an improved matte tap hole. Since startup in 1978, the matte tap holes have been incrementally improved by the addition of copper cooling blocks around the refractory tap blocks. These improvements provided a tap block life of about 100 taps per campaign.In July 1993, a prototype matte taphole was installed in Number 2 Electric Furnace to develop the technology to increase tap hole service life. The design was based on a heat transfer model of the tapping process to determine candidate refractory materials and cooler arrangements. The prototype tap hole features increased copper cooling, high conductivity refractories and extensive instrumentation. Eight trial campaigns are reviewed outlining the performance of silicon carbide and graphite refractories and typical heat loads during tapping.IntroductionFalconbridge Limited operates two 36 MYA, 6 electrode submerged arc electric furnaces in Falconbridge, Ontario. The furnaces, commissioned in 1978, smelt a partially roasted nickel-copper calcine, to produce matte for converting and slag for discard. Additional details of the smelter are available in the literature(1-4).Each furnace was equipped with two matte tap holes located in the furnace end wall. Early in the campaign, matte tap holes were identified as a weak area in the furnace which could be improved. From 1981 to 1987, incremental improvements were made to the design by the addition of water cooled copper blocks. In 1993, a prototype matte tap hole was designed and installed in Number 2 electric furnace to develop the technology to increase tap hole service life. Improved service life is required to meet planned increases in electric fWl1ace productivity and the higher matte temperature needed for the smelter's S02 Abatement Plan.This paper reviews matte tap hole development since 1978; outlines the prototype matte tap hole design, refractory selection and installation; and details the performance of the prototype tap hole during the first eight campaigns."

Jan 1, 1995

By J. Mullins

Coal was first banked by the Dominion Coal Company, Limited, in 1898, near No. 2 Colliery, the same site as is presently used for that purpose. Though today there are banks at Glace Bay, Sydney, and Sydney Mines, these notes, except when otherwise desirable, will be confined to describing the practice as developed at the No. 2 Banking Station, Glace Bay, as being typical of methods obtaining at all sites. Storing The manner in which the coal was piled is illustrated diagrammatically in the accompanying sketch. A train of coal was brought on the main trestle, which extended the full length of the banking ground at a height of 22 to 39 feet above the natural surface, and dumped into bins which were integral with the trestle work. Chutes from these bins permitted the coal to be fed into 3-ton cars, which were horse drawn laterally on narrow gauge tracks laid about 10 ft. centres, to a maximum distance of 400ft. from the trestle. These cars were end-dump and as the pile extended laterally the narrow gauge tracks were lengthened by shorter or longer filling pieces, so that their ends were always kept at the brow of the bank. Much coal, however, had to be dumped directly on the tracks and hand trimmed to fill the valleys, and level off, between the tracks.

Jan 1, 1931

By Stephan Day

Comments on Robust M3 to Protect Water Quality ?Regulatory and philosophical thinking have tended to evolve at decade scale since 1970s. ?Mines typically last more than a decade. ?Robustness is defined by the ability to adapt to new realities. Managing Water Quality in BC ?1973 ?BC Pollution Control Objectives ?1977 ?Federal Metal Mine Liquid Effluent Regulation (Fisheries Act) ?Late 1980s ?Philosophy of ?Designing for Closure? ?1990s ?Designing for Acid Rock Drainage Management ?2000s ?Awareness of need for water quality management in general, regardless of acidity

May 1, 2010

By K. C. Sole

In most copper solvent-extraction operations, an important consideration in choice of extractant is the requirement for high selectivity of copper over iron. Ester-modified aldoxime extractants presently offer the best Cu:Fe selectivity. In some plants, however, the process feed liquors contain significant amounts of manganese but little iron. Although manganese is not chemically extracted by oximes, trace amounts are carried over to the electrowinning circuit by physical entrainment. This may result in anodic oxidation of manganese which, in turn, can cause oxidative degradation of the organic phase when returned to the solvent-extraction circuit in the spent electrolyte. Many of these operations prefer to operate with higher levels of iron reporting to the advance electrolyte, as appropriate control of the Fe(II)/Fe(III) couple will ensure that manganese remains in the benign Mn(II) form. A new reagent, LS 4202, designed by Cytec, now offers the possibility of tailoring the iron co-extraction, so that appropriate Cu:Fe selectivity can be achieved in the solvent-extraction operation to maintain an electrolyte Fe:Mn mass ratio of >10:1, while retaining the other benefits offered by ester-modified aldoximes. The results of an integrated solvent extraction-electrowinning pilot-plant trial are presented, in which the performances of the conventional extractants ACORGA® M.5774 and LIX® 984N are compared with LS 4202. The Cu:Fe selectivity is demonstrated, along with results on the transfer of other impurities to the advance electrolyte.

Jan 1, 2007

By S. A. Willis

For the past several months 1 have been considering the functions of this Society and its reasons for continuance. The fact that it is now sixty years old indicates that it must have been of value and we all know that it has contributed much that was worthwhile to Nova Scotia and the Maritime Provinces. The question arises: "What is the future of the Society, and how might its activities be altered to suit present-day activities and to be of even greater value?" Let us analyse the various activities in which we are interested and determine which, if any, are of more value than others. First of all, at least once a year we have a two-day convention which constitutes a holiday for the members and their wives. This has always been well planned and has been much enjoyed. Second, there are many social and business contacts made during the meetings and interim meetings. These certainly tend toward better relations and co-operation between the various people concerned. Mine operators meet other mine operators, engineers, people from the education fields, Department of Mines, and so forth. Various sales contacts are made at these meetings which can be of value and use to both the Company selling and the customer. Third, and of greatest importance in any conference, is the exchange of ideas by the members and by authorities from outside, and the presentation of slides and drawings, or actual visits to operations. It is upon this phase that 1 wish to elaborate. These papers are not only presented to our meetings but are generally published in the C.I.M. Bulletin so that members throughout the Dominion have access to them. Many important papers describing new phases of operations have originated through our Society.

Jan 1, 1947

By W. F. Moore

"In January 1981, Quintette Coal Limited (QCL) signed a 2a-year coking coal sales agreement with the Japanese Steel Industry which was followed by the commencement of mining operations in October 1982 and preparation plant operation in November 1983. During the mine 's startup, the town of Tumbler Ridge, the Anzac rail spur line, coal port facilities at Ridley Island plus numerous related elements of infrastructure were completed to support QCL and the neighbouring Bullmose operation in northeastern British Columbia. QCL's annual product coking coal levels have accelerated from 2.9 to 5.2 Mt between 1984 and 1986 with related increases in total mined volume from 14.8 to 41.0 M BCM between 1983 and 1986. This paper presents an overview of QCL 's current operation and related infrastructure. Development BackgroundDuring the 1970s, the Japanese Steel Industry (JSI) was forecasting a steady and significant growth in its steel production. By 1980 they were expecting crude steel production to increase from about 105 Mt in 1980 to 125 Mt by 1985 and almost 140 Mt by 1990.Discussions between Quintette Coal Limited (QCL) and the JSI for the development of the QCL project began in the 1970s and continued over a period of several years. During that time detailed and regular meetings took place, at which technical and commercial presentations were made to the JSI. The geology of the project area and the alternative mining methods and sequences were studied in detail. The new rail line which would connect the mine to tidewater was a critical factor and received particular attention. Alternate routes for the rail line from Tumbler Ridge to Prince George were the subject of much detailed study and discussions. The Anzac route was chosen in the best long-term interest of the northeast area development, after careful consideration and advice from the Japanese side.The new bulk coal terminal on Ridley Island at Prince Rupert was also a key factor and completed the development of an independent and new major coal field to supply the JSI. The QCL project and the development of the northeast area of British Columbia was a major strategical initiative of the JSI. It provided Japan with an important new coal field which was both self-sufficient and distinct from the traditional Japanese coal field resources in southern Canada, Australia, and the United States."

Jan 1, 1988

By J. Lu

The impact of acid treatment in agglomeration/acid curing on copper extraction and acid consumption was investigated with respect to acid dosage and moisture. Without the addition of water, no agglomeration occurred. At an acid dosage above 15 kg/t, the acid was not completely consumed during acid curing. With the addition of 6.2% water, the particles agglomerated together. Copper, iron, magnesium and manganese were dissolved as sulfates and enriched in the fine fraction of the ore. The copper extraction and net acid consumption increased with increasing acid dosage. The copper extraction for acid curing with the addition of 6.2% water was higher than that without the addition of water due to the improved permeability and the increase in the contact with acid-soluble copper. During acid curing, the reaction of sulfuric acid with muscovite, abite and nacrite mainly took place on the surface of the particles while the reaction of sulfuric acid with clinochlore occurred not only on the surface but also inside the particles.

Jan 1, 2007

By J. C. Moreno, G. Rios, M. Palacios

The Huelva smelter was commissioned in 1970 coinciding with the shutdown of the old smelter in the Rio Tinto mine site. That new smelter consisted of two Momoda blast furnaces with a capacity of 500 dmtpd of concentrate. Nevertheless, soon after their start-up, it was clear that an increase in the smelting capacity was needed. After an analysis of the existing alternatives at that time, the flash smelting technology was chosen. The new Outokumpu Flash Smelting Furnace (FSF) came into operation on 18 September1975, with an initial capacity of 900 dmtpd of concentrate, using four Venturi-type burners and preheated atmospheric air. Since that date the Huelva Smelter team, together with Outokumpu (now called Outotec), have continuously improved our FSF design, process conditions and operational practices, leading to a present capacity of 3,500 dmtpd of concentrate. Since 1975, five smelting campaigns have been completed, the last ending in November 2013 with the rebuilding of the original FSF hearth. This paper describes the history of these improvements and the lessons learned.

Jan 1, 2014

By D. R. Murray

"A promising long-term solution to uranium tailings reclamation has been the establishment of vegetation directly on the waste material. The soil profiles of areas vegetated for 0, 3, 8 and 10years are characterized as to the extent of soil development . The characteristics are compared with the visually interpreted soil profile. Organic matter content is presently the best analytical judge of soil development. Vegetation procedures have produced a build-up of organic matter in the top 10cm of tailings where natural microbial populations flourish. The CN ratio is high and the profile depth shallow, suggesting the need for additional fertilizer applications.IntroductionThe reduction of surface erosion and improved aesthetics of uranium tailings has been accomplished by the establishment of a vegetative cover. In 1971 research concentrated on developing methods of plant establishment at minimal cost and soil amendments on uranium tailings in Elliot Lake , Ontario. One process of stabilization used on a large scale was direct seeding of grasses and legumes into the tailings which had received only limestone and fertilizer treatments. Fertilizer additions were made for varying lengths of time in subsequent years to maintain the established cover.Maintenance-free vegetation would be possible once a soil profile developed with sufficient nutrient recycle and plant regeneration capabilities(1). Tailings vegetated in 1971, 1973 and 1978 that had received either 3 or 5 years of maintenance fertilizers were examined for soil development profiles. The extent of soil development and the relative effect of time and fertilizer would provide direction on reaching the goal of a self-sustaining cover.This paper is an abridgment of Division Report MRP /MRL 81-126 of the same title(2)."

Jan 1, 1984

By Premil Agarwal, Alok R. Patnaik, Pulak Dhar, Prakash C. Patnaik

In this study, a physics based model has been presented, considering the growth of the thermally grown oxide (TGO) layer on the bond coating of a thermal barrier coating. Using diffusion equations, a model has been developed to physically describe the oxidation process. The mathematical equations representing the diffusion formulations have been solved numerically. The computed results show the depletion of Al in the bond coating as it diffuses both towards the super-alloy substrate and towards the TGO produced in between the bond coating and the ceramic TBC top layer.

Jan 1, 2004

By A. Dave Mackintosh

Historical closure data has provided a description of the stress distribution patterns occurring around mine openings and enabled the development of a time ? distance plot predicting the location of the stress peak and its migration away from mine openings with time. Data collected from active mining areas during the 1970?s and 1980?s indicated the peak appeared to stabilize approximately 135m (450 ft.) from openings after four years. The region of high load and accompanying poor ground conditions in which the peak was centred was spread over approximately 45m (150 ft.) to 60m (200 ft.). Recent data from new development headings cut adjacent to 25 year old extraction areas suggests load transfer takes place over a much greater distance and time frame than predicted.

May 1, 2001

By John E. Udd

"Mining research at CANMET is delivered by the Mining Research Laboratories Division (MRL), with facilities in Sydney, Nova Scotia; Bells Comers, Elliot Lake, and Sudbury, Ontario; and Val d'Or, Quebec. This paper gives an overview of the work of the Division as of early 1993. An addendum, at the end of this paper, describes the organizational changes that will take place in April 1994. IntroductionCANMET, the acronym for the Canada Centre for Mineral and Energy Technology, is the name by which the organization founded in 1907 as the federal Mines Branch is presently known. The name was changed in 1974, in order to give recognition to the importance of both minerals and energy technologies in the activities of the Branch. Further reorganizations have taken place since 1987. As a result of these, CANMET has assumed the status of a Sector (equivalent to the Geological Survey of Canada) and has been organized into four branches.The organization as a whole functions in an environment of semi-matrix management. Some of the ""line"" Divisions report to Directors-General for the appropriate branches while other, larger divisions, report directly to the Assistant Deputy Minister.The second dimension of the organizational matrix is composed of a number of ""staff' divisions which report to the DirectorGeneral for Policy and Planning. Each of these Divisions performs a function which is common to all of the ""line"" divisions. For example, the Research Projects Office is responsible for monitoring the range of research activities of CANMET and for recommending allocations of funds for both research contracts and operating budgets. The Library and Documentation Services Division is responsible for CANMET publications and information services. Likewise, the Engineering and Technical Services Division provides support through, among other services, the construction of specialized laboratory equipment."

Jan 1, 1994

By B. E. Jones

"The area of uranium deposition is situated within the Churchill Province on the western edge of the Wollaston Iithostructural domain where it underlies the eastern edge of the Helikian Athabasca Formation. The Collins Bay deposit is 6 miles north-northeast of the Rabbit Lake mine. Two principal zones of uranium mineralization are described.The ""A"" zone is a partly eroded, high-grade pod of metal oxide and arsenides sheathed by clay-like minerals. It trends north-northeast and lies under 25 to 40feet of water. Uranium mineralization is localized at or adjacent to the unconformity between the Athabasca Formation and the basement rocks. The basement comprises a granitoid Archean terrain overlain by paragneisses of the Aphebian Wollaston Group. ""A "" zone ore contains phyllosilicates, quartz, pitchblende, rammelsbergite, pararammelsbergite, carbonaceous material, galena, gersdorffite, niccolite, carbonate and a trace of sphalerite.The ""B "" zone lies 6,000 ft south of the ""A "", and subcrops under till cover. It is a partly eroded zone composed of metal oxide and arsenides which occur within variably altered Athabasca Formation. Minerals recognized are phyllosilicates, pitchblende, niccotite, gersdorffite, millerite, carbonaceous material, pyrrhotite, skutterudite and a trace of galena. The Athabasca Formation varies from 90 to 160ft thick. Granitoid gneisses of probable Archean age and paragneisses of the Wollaston Group underlie the deposit. An easterly dipping thrust fault transects its length.The deposit is typical of the ""unconformity-type"" uraniumnickel deposits of the Athabasca Basin. Observed features fit well with the ""diagenetic-hydrothermal"" model for such deposits, as envisioned by Hoeve and Sibbald (/978)."

Jan 1, 1980

By Richard Murphy

"The general geology of the Great Bear Lake area has been described by; D. F. Kidd in the Summary Report of the Geological Survey for 1932. A brief description of the Eldorado mine was prepared by C. S. Lord for Memoir 230; Mineral Industry of the Northwest Territories; published by the Geological Survey in 1941. Recently; a detailed geological examination of the mine area has been initiated by the Geological Survey and; under A. W. Jolliffe's leadershif; J. D. Bateman; H. B. Thurber; and M. Feniak have prepared a number of maps and reports; as yet unpublished. Detailed mapping of the mine has been carried out since August; 1943; by A. W. Esty.Kidd has shown that, in the largely granitic country along the east side of Great Bear lake, the Echo Bay district is one of several underlain by older rocks . These he has divided into the Echo Bay and Cameron Bay groups. The former are strongly altered sediments, .porphyries, and lavas; the latter and younger group is predominantly sedimentary and far less altered. Associated with the granite, which everywhere intrudes the sediments and volcanics, are earlier differentiates. Later than all these rocks are various basic intrusives, collectively termed diabase. All the rocks are of Precambrian age."

Jan 1, 1954