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By F Kelly

"A central composite experimental design was used to determine empirical relationships between the operating variables of a ball mill and the characteristics of the ground products. The independent variables selected for the study were the work index and size distribution of the feed material, the feed rate and the pulp density. The measured responses included product size distribution, product surface area, viscosity of pulp discharge, weight of dry solids in mill, mill time constant and emitted sonic vibrations. The ball mill was operated continuously in open circuit during each experimental run.Multivariable regression techniques were used to derive linear empirical models from the experimental results. Of the four factors studied, the grindability of the feed material significantly affected every measured response. The size distribution of the ground product was affected significantly by the feed rate and the size distribution of the feed, but not by the pulp• density. Feed throughput capacity and pulp density were significant to the viscosity of the pulp discharge, the weight of solids in the mill and the mill time constant. Significant first-and second-order models are given for the above relationships. The relation-ships between the characteristics of the sonic vibrations of the operating mill and the various dependent variables have not as yet been established."

Jan 1, 1970

By C. A. Rowland Jr

"I. INTRODUCTIONFred C. Bond's ""Third Theory of Comminution"" (1) was published in 1952. The mathematical statement of the Third Theory is the well-known Bond Formula:where W - Kw H per short tonWl - Work IndexP - Product size in microns which 80% passesF .. Product size in microns which 80% passesWork Index, as defined by Fred Bond, "" ... is the comminution parameter which expresses the resistance of the material to crushing and grinding. Numerically, the Work Index is the KwHrs per short ton required to reduce the material from theoretically infinite feed size to 80% passing 100 microns."" (2)Work indices for grinding can be obtained tram Bond grindability tests and can be calculated from plant grinding mill operating data when power consumed per ton of ore ground, the feed size analysis and the product size analysis are known.Work indices obtained tram Bond grindability tests, having been obtained from standard and controlled laboratory procedures, are reproducible and for the sample tested are accurate. The degree of accuracy relative to plant mill operation depends upon how representative the sample is of the total mill feed.The results of the Bond closed circuit rod and ball mill grindability tests (3) are given in grams of product sized material produced per revolution of the test mill. In developing a method to evaluate plant operating data and results from his grindability test, Fred Bond developed the ""Third Theory of Comminution."" In the process formulae were developed for converting grams per revolutionobtained from grindability tests to work index.The standard feed sizes for the Bond grindability tests are:Rod Mill Test ore crushed to minus 1ll inchBall Mill Test ore crushed to minus 6 mesh (Tyler)The formulae for converting grams per revolution to work index incorporate the 80% passing sizes for the feed to and the product produced in the specific test. Therefore, accurate work indices can be obtained from Bond grindability tests when the feed size is finer than standard. To obtain accurate test results, the ratio of reduction should be greater than 6 to 1."

Jan 1, 1972

By Zou Lisheng

The culture of safety is very important to coal mining production. About 90% of mine accidents are caused by human error. This paper analyzes the status of China?s coal mining accidents, and accident cause. This paper explains the concept of safety culture, the value of safety culture, as well as the relationships between safety culture and safety behavior, and between safety culture and science and technology. The paper proposes the model of safety culture and the ways to enhance safety culture of coal enterprises. Safety culture and safety production is closely related and are significant to the improvement of mine safety situation in China.

Aug 1, 2013

By Jeonghwan Kim

Intelligent Excavation System (IES) has been considered to be one of the desirable solutions to improve the productivity, quality and safety of the current earthwork processes. IES is composed of various hardware and software modules including task planner (work command generator), local and global work environment sensors, GPS and other sensors to acquire the excavator?s status, robotic controller and electronic valves, and the manipulator (excavator). A data communication manager was required to coordinate the signal or data-flow in between these modules considering the operational status of IES such as; excavation start/completion, truck detection, terrain model update, emergency stop, local sensing, GPS/motion sensor data handling, and so on. This paper presents the role and functions of this data communication manager. After every possible operational status of IES operation was identified, a protocol of each communication process in the form of string-type was made. The components of IES are connected with either wired or wireless network. Therefore, they can communicate with the manager using socket (TCP/IP) communication. The data communication manager is also capable of accessing a web-based project management information system, which constantly updates the performance of excavation robot to online database.

Aug 1, 2013

By J. S. Stachulak, K. A. Mackinnon

This paper deals with specifying and evaluating fans for mine ventilation projects. Topics such as fan and equipment design life, operating points, and operating conditions are discussed. Common operating problems, such as vibration, parallel operation, mechanical failure, erosion, corrosion, and deficient fan performance are covered. Apart from identifying the potential operating problems, likely causes and suggested remedies are given. Fan type, fan accessories, and likely system effects and fan testing are discussed. Suggestions on what should be covered when evaluating different fan options and proposals and suggestions on the verification of supplier claims and guarantees, including cost of operation, the evaluation of initial capital cost, estimate on maintenance costs, and likely replacement expenditure over the life of the fans. In addition, fan reliability, operational flexibility, suggested construction details and fan vendor past history and experience are reviewed.

Jan 1, 2004

By S. Broda

Waste rock piles (WRP) are made of heterogeneous, coarse grained waste rock, with inclined layers due to segregation along the slopes and haul traffic compacted layers, creating highly contrasted hydrogeological conditions. The internal structure of the pile has a major impact on water and oxygen movement and pore water pressure distribution. In the presence of reactive minerals, this influences the production of acid mine drainage (AMD) or contaminated neutral drainage (CND) with metal leaching from the WRP. Water flow and distribution may also affect slope stability, particularly following major infiltration events (rain/snow melts).The prediction and interpretation of water distribution in WRP is a challenging problem. Numerous numerical investigations of short and long term forecasts have been conducted, and many of these were found of limited reliability. The shortcomings of existing approaches are typically due to difficulties in representing preferential flow processes in macropores. Such phenomena are in fact often neglected in the assessment of water flow in WRP because these are unattainable with the classical porous media approach typically used in this field. This paper focuses on the use of modeling techniques originally designed for massive fractured rock media to simulate flow in WRP. Waste rock properties used in this study are retrieved from large scale laboratory permeability and water retention tests and from in situ infiltration tests. The effect of WRP configurations on water flow into potentially reactive zones is examined with the numerical 3D fully-integrated surface/subsurface, variably saturated flow model HydroGeoSphere. Material properties retrieved from the laboratory tests are represented by means of stochastic facies distribution generated within a probability framework. Modelled soil water contents and hydraulic head distributions, as well as fluxes within a simple waste rock pile, with compacted layers, are compared with results retrieved from simulations based on the classical equivalent porous medium approach. Results indicate significantly increased flow towards the looser waste rock zone by considering heterogeneous material distribution, causing weak or absent capillary barriers and preferential flow paths. Practical implications for the design of waste rock piles are also discussed.

Aug 1, 2013

Several inorganic reagents and organic polymers were tested as depressants in the single mineral flotation of ultrafine iron oxide and hydroxylapatite with Dowfroth 250 as a frother. It was observed that the inorganic reagents and the low molecular weight polymers generally caused dispersion of the ultrafine particles, and consequently their recovery into froth products more or less equaled the recovery of water. On the other hand, the high molecular weight polymers caused different degrees of flocculation of the ultrafine particles, and their recoveries were much lower than the recovery of water. These observations pointed to a need to re-define flotation depressants in fine particle flotation. The traditional definition of a flotation depressant, i.e., to make particle surfaces hydrophilic by forming a hydrophilic film and/or by removing collector and activator coatings, is sufficient for relatively coarse particles. However, to prevent fine and ultrafine particles from floating, a successful depressant should not only make the particles hydrophilic, but also enlarge the particle sizes so that they do not enter the froth product by mechanical entrainment. Polymeric depressants are ideal for these purposes. The different schemes to use polymeric depressants in the selective flotation of fine and ultrafine particles were discussed These schemes involve the integration of the polymeric depressants into other size enlargement processes such as shear flocculation, oil agglomeration, etc., for hydrophobic particles.

Jan 1, 2004

By P. Venkatasubramanian

"In recent years, computer based ""expert systems"" have been taking on large complex tasks for which no exact algorithmic solutions are feasible; tasks previously reserved for human experts requiring empirical knowledge, judgment, experience, developing a ""best solution "" by the use of plausible reasoning. Mining method selection is an appropriate area for the application of an expert system because extensive and detailed knowledge is required to make a ""best"" interpretaion of frequently ambiguous geological information. The expert system model presented here would enable users to apply expert knowledge to the evaluation of methods for coal deposits mineable by underground methods. IntroductionIn an increasingly complex and specialized world, human expertise spanning scientific, economic, social and political issues plays an increasingly important role in all branches of engineering. This is especially true of mining engineering. The number of scientific and professional disciplines involved in mine planning and evaluation, illustrates the problem. A conservative list includes geology, geophysics, geotechnics, hydrology, mining, environment, and economics.Engineers are almost obliged to be experts in at least one of the above disciplines if they are to handle the volume of information required in the planning process. Although computers have become indispensable tools in many endeavours, there is continued reliance on the human expert's ability to identify and synthesize these diverse factors, to form judgments, evaluate alternatives , and make decisions . This is especially true with regard to problems that are not easily amenable to precise formulations.The precious resource of human expert is also fragile and transient. The departure of a crucial expert from an organization ma y cause serious dislocations. Senior experienced people impart their knowledge of younger colleagues, but the demand for their talent may not leave sufficient time for such educational efforts. In recent years, computer based "" expert systems"" have been taking on large complex tasks for which no exact algorithmic solutions are feasible; tasks previously reserved for human experts, requiring empirical knowledge, judgment , experience, developing a ""best solution"" by the use of plausible reasoning."

Jan 1, 1988

By John B. Hodgeson

AMMONIA is an essential constituent in the production of the ammonium-sulphate and ammonium-phosohate soil fertilizers manufactured by the Consolidated Mining and Smelting Company of Canada, Limited. The fertilizer plant, built in 1930 at Warfield, near Trail, provides a means of utilizing the large amount of sulphuric acid produced from the sulphur dioxide which is removed from the smelter smoke. The plant has an avail-able source of cheap power which makes the production of fertilizer economically possible. The fundamental operations involved in the production of ammonia at the Warfield plant are, first, the manufacture of hydrogen by the electrolytic dissociation of water; next, the recovery of nitrogen by the fractional distillation of liquid air; and finally, the combination of hydrogen and nitrogen in proper proportions and under suitable conditions to form ammonia.

Jan 1, 1938

By F. Weinberg

"The recent development of the continuous casting process for steel has required basic understanding in a number of areas in the metallurgcal sciences. In some areas, information is still lacking. The success of the application of basic knowledge and research to the process is evidenced by the fact that a large percentage of the steel now produced in the world is produced by continuous casting.A number of areas in which metallurgical science has contributed and is currently contributing to better design and control of the continuous casting process and leading to a better quality product will be considered. These include:(a) heat transfer studies of the entire casting process;(b) fluid flow in the tundish, strand and liquid metal stream;(c) solidification structure and segregation;(d) strength and ductility of steel at high temperatures related to bulging and cracking; and(e) problems related to horizontal casting developments.IntroductionThe continuous casting of steel is a relatively new technology in steelmaking. It is now used extensively throughout the industry. In Japan, for example, continuous casting accounts for approximately 40010 of steel production, and this value is expected to increase to over 50% in the near future . New steel plants are now designed to use continuous casting exclusively. This means the process must work well and be completely reliable, because all the steel produced must go through the caster.The development of the continuous casting process in a short period of time has required concerted research and development in many areas . I shall cite a number of examples of these developments and refer to work done in Canada when applicable. No attempt will be made to review all of the research in continuous casting, nor refer to all of the workers in the field.The developments in continuous casting are based in many cases on metallurgical science, as described below. The use of metallurgical science in these developments is qualitative, in that concepts and idea s are used, as opposed to quantitative values calculated from fundamental equations. In general, most metallurgical problems are too complicated to enable fundamental equations to be used without the introduction of uncertain approximations and boundary conditions in the calculations.Starting at the beginning of the steelmaking process, very extensive research and development has been carried out to produce liquid steel of the required composition and temperature. The replacement of open hearth furnaces with BOF furnaces reduced refining time from many hours to roughly 30 minutes for 250 tons of steel. Two BOF furnaces effectively enable a continuous flow of steel to be available in a plant, essential for the introduction of the continuous casting process. This area of research will not be considered here."

Jan 1, 1981

By Kris Inwood

"In 1879, when the Dominion government initiated its controversial program of industrial promotion, iron smelting in Canada was limited to one company producing coke iron on the mainland of Nova Scotia and three small charcoal blast furnaces in Quebec. There was no steel production. By the eve of the First World War, iron and steel were being produced in very large quantities, the companies active in 1879 had disappeared and new centres of integrated iron and rolled steel production at Hamilton, Sydney and Sault Ste. Marie had come to resemble the industry as we know it today. The most dramatic change was that at Sydney, Nova Scotia, where in the early 1900s, two steelmaking companies established works. The Sydney developments have been explained as the result of resource discovery and technical change. W.J. Donald, in his authoritative account of the Canadian iron and steel industry, observes:(1) ""The most rapid growth of the Canadian iron and steel industry has occurred since 1897 ... The remarkable growth has been caused largely by the new conditions of the industry. The discovery and use of Newfoundland ores, together with the availability of Cape Breton coal, has made the Nova Scotia industry not only possible but profitable .... It is a safe conclusion that the Canadian industry would not have been an important one, had it not been for the discovery of the Michipicoten and especially the Wabana (Newfoundland) ores:' Donald also argues that metallurgical progress had been necessary to render the ores valuable. ""Newfoundland ores ... contain a considerable amount of phosphorus, and were made available for steel-making by recent inventions:' The purpose of this paper is to re-examine Donald's story. It will be argued that the origin of steel-making at Sydney is somewhat more complicated than Donald has indicated. The difficulty with Newfoundland ore extended beyond its phosphorus content and a resolution required more than the basic open hearth furnace identified by Donald. Moreover metallurgical change was only one of several developments necessary to induce industrial investment at Sydney. Surprisingly, however, the discovery of iron ore in the late nineteenth century does not appear to be part of the explanation."

Jan 1, 1999

By Denis J. Kemp

The 20th Century saw changes in the mining and metallurgical industry not only technically but also in social and environmental expectations. As projects continue to become larger to maintain competitiveness the visibility of their potential impacts raise concerns among many groups. The need for transparency, openness and early engagement of all parties are fundamental to assure success. An equally important task is to anticipate the standards that will be required to meet society?s expectations in the 21st Century. Historical Observations The mining industry of the 18 and 19th Century was dominated by opportunistic Companies and individuals with an entrepreneurial flair for adventure and risk. Those who promoted had the chance of great reward, while those willing to risk their life were assured a short one for their efforts because of the physical and health dangers that abounded. Disregarding conditions miners rewards were high even in those days, with an average Cornish miner known to be earning two pound a month in 1800. Coal and iron ore mines were driven by the needs of the industrial revolution and were the first to embark on larger scale output. Base metal mines were smaller as industrial demands for their use did not start to expand greatly till the late 19th Century. Electrification, the automobile and the 1st World War drove the increased demand for a variety of metals. Early mines were foul smelling and dusty and what was taken from below ground left spoil piles around the surface countryside after recovery of the coal or concentrate. The image of barren blackened hills is one that is easily conjured up and is an environmental legacy that still lives with us today.

May 1, 2002

By L. Lafrenière

A trend in mining exploration is to increase the number of geophysical parameters collected and interpreted for geological features in a given area. Airborne technology now allows us to simultaneously combine electromagnetic, gravity, aeromagnetic and radiometric surveys. We report the results of a multiparameter survey conducted in the area of Kamiskotia, Ontario. This area is located near and on the West side of the multi-metalliferous Kidd Creek deposit. Various metallic occurrences are reported in the studied area. Integrating multiple parameters in the interpretation produces a more detailed pseudogeological map than what has already been published. 3D interpretation has been undertaken using some of these parameters and suggests that future work is required in 3D earth model solutions in order to fully use all parameters.

Aug 1, 2013

By Åke Krukka, Heribert F. Broicher

"The iron ores of the Kiruna Mine in Sweden are of exceptional quality but for the phosphorus content in certain zones of the orebody. The prevention of mixing ores high in phosphorus with those low in phosphorus has always been of significant economic importance. The ongoing introduction of tele-mining and automatic haulage by LHDs requires new means in the field of quality control underground, as the experienced miner as well as the underground laboratory assistant no longer are involved in the process. As of 1998 LKAB has been testing prototypes of LIF Analysers for non-contact and real-time measurement of the phosphorus content of ore being transported by LHDs from the stopes to the respective ore pass assigned to a certain ore quality. The principles of the analysis of laser-induced fluorescence, the different test phases and results are described and conclusions made. With bulk sorting of ore underground the mining engineer supports the efforts of the metallurgist in the processing plant.INTRODUCTIONThe Kiruna Mine of LKAB, Sweden is the largest underground iron ore mine in the world. In the early nineties LKAB decided to develop the Kiruna orebody further down from the 775m main level to a new main level at 1045m. This development programme was realised while in the mineral processing section and in the pellet plant further capacity was added (Wyllie 1996).In addition to deepening of the mine, which opened up 330 million tonnes of ore, the exploitation of the so-called lake ore was included in the future planning, adding another 1 15 million tonnes of mineable ore. At an annual production of approximately 20 million tonnes of ore the Kiruna Mine today looks at a developed ore reserve sufficient for the next 20 years.All of the competitors’ ores traded in the world market are from open pit operations. LKAB compensates for the obvious disadvantages by continuous efforts to make the best possible use of her high quality magnetite ore deposit. This objective is realised by combined efforts in the pellet plant, the mineral processing plant and the mine. Propriety processes, latest big scale equipment and high tech solutions for automation lead to high quality sales products at a reasonable cost."

Jan 1, 2002

By J-S. Marois, F. Cappucitti, Y. Dodier, D. Downey, G. Matton

"The flotation processes of the Niobec Mine have been affected by a seasonal loss of recovery and a significant increase in reagent consumption over the past few winters. This paper discusses the problem-solving methodology that was used to identify the root causes, to develop solutions and to implement changes that resolved the problem to restore the process to summer-like conditions year-round. Mainly, it was found that the process water was contaminated by phosphates ions, which adversely affected the carbonate pre-flotation, and caused detrimental effects on the subsequent niobium flotation. The phosphate ions were being generated by the process itself, but were consumed by algae in summer conditions. It was determined in laboratory studies that concentrations as low as 5 ppm were enough to affect the circuit and that the multiple additions of process water throughout the circuit was worsening the effect. Also, temperature was found to have an impact on the reagent performance. The performance of the plant was restored by implementing a natural treatment of our process water with a simple cost-free rearrangement of our circuit streams. In addition to that, our extensive geometallurgical program was used to provide ore to the plant restricting phosphate generation in the process. Also, a modification of the collector was developed and introduced in the carbonate pre-flotation that provided improved performance during the periods of low pulp temperature.INTRODUCTION Niobec is one the three major global producers of niobium presently in operation. Situated in the Saguenay-Lac-St-Jean region of Quebec and in operation since 1976, the site produces ferroniobium (FeNb) to be used mainly in High Strength Low Alloy (HSLA) steel, which is known to have better mechanical properties than carbon steel. The Niobec operation consists of an underground mine, a concentrator and a converter plant. The concentrator concentrates niobium-bearing minerals, mainly pyrochlore and columbite, to produce a high-content Nb2O5 concentrate which is then converted to FeNb in the converter plant by an aluminothermic reaction. The Niobec concentrator flowsheet, which has gone through many expansions and optimisation over the years, consists of grinding, desliming, flotation and leaching steps. The flotation steps are numerous, sensitive and difficult to operate due to the non-selective nature of oxide mineral collectors. Thus, the pyrochlore concentration process at Niobec still faces many challenges and is constantly going through periods of continuous improvement."

Jan 1, 2018

By G. T. Lapidus, J. Trejo-Gallardo

A phenomenological model is presented for leaching silver from silver sulfide contained in mineral particles with ammoniacal thiosulfate solutions of copper in stirred reactors. Experimental results were used to adjust the kinetic parameters of the model, such as the reaction order and velocity. The incorporation of the cuprous sulfide-silver sulfide equilibrium at the reaction interface allowed the prediction of the conversion limits for different reagent concentrations. The information obtained from the reactor model was later integrated into a heap leaching simulation, whose results adequately describe tendencies observed in column tests, with respect to variations in copper and thiosulfate concentrations. Comp

Jan 1, 2005

By Julian Wills

The Candrill was developed with Soredem as a one-operator rockdrill for Canadian narrow vein mining. It provides the benefits of increased drilling rates, lower noise and vibration, mass reduction of 20% and system cost saving. The Candrill is to be commercialised at the end of 2001 together with a stoper drill through Parts Headquarters, Novatek's Canadian agent. The Candrill or pneumatic drills may be further exploited using a simple mechanised drilling system to further reduce operator labour, improve drilling speeds by up to 50% and to enhance drilling accuracy. Novatek's drilling system for simple mechanisation in gold and platinum mines is integrated with roof supports, can operate in stope widths as low as 800 mm and has resulted in labour savings of 50%, improved advances per blast of 20 to 50% and improved operator safety and ergonomics.

Oct 1, 2001

By A. E. Boudreau

Abstract-It has long been recognized that platinum-group-element (PGE) deposits in layered intrusions preferentially occur in intrusions that crystallized from high-Mg parent magmas. Recent studies suggest that evaluation of any given intrusion for economic PGE potential should also include assessment of the PGE, sulfur and chlorine concentrations in the cumulates and potential parent liquids. PGE: Magmas that contain relatively abundant Pt and Pd are the best candidates for forming economic deposits. Although analyses of coeval sills and dikes are the best indicators of primary magmatic PGE concentrations, analysis of the cumulates themselves is also valuable. For example, within the Stillwater complex, background PGE values in cumulates from the ultramafic sections of the complex contain, on average, several 10s of ppb Pt and Pd. Background concentrations of this order are suggestive that the magma was not depleted in the PGE. Sulfur: Conventional petrogenetic models for the formation of PGE deposits in layered intrusions require the PGE to have been concentrated during a magmatic sulfide-saturation event. In contrast, some hydrothermal models suggest that sulfur and the PGE were mobilized from footwall cumulates by upward- migrating, high-temperature hydrothermal fluids. Both models suggest that significant PGE deposits are likely to occur at and below the level where stratigraphic increases in whole rock sulfur concentrations occur. Chlorine: In both the Stillwater and Bushveld complexes the cumulate sequences below the major PGE-bearing zones contain anomalous Cl-rich apatite. The chlorapatite component of apatite in these rocks may exceed 40% and, in the Stillwater complex, typically exceeds 90%. It is stressed that pristine igneous mineral analysis and not whole rock data be used, as whole rock Cl concentrations may be affected by very localized (grain boundary), low-temperature alteration. Intrusions that crystallized from high-Mg, high-Cl magmas appear to have the best potential to host significant PGE deposits.

Jan 1, 1995

By P. P. Sinha, D. N. Bhatia, B. R. Ghosh, R. K. Gupta

Medium carbon, low alloy, high-strength steels containing Ni, Cr, and Mo are used for the fabrication of various types of high-strength fasteners required for launch vehicle structures. Cold heading properties and response to hardening and tempering are the essential requirements of the material for fabrication and application, respectively. Combining these two requirements is essentially warranted in high-strength fastener-grade steels. Cold heading properties require ductility, which can be achieved through spheroidizing treatments. In the absence of a suitable spheroidizing cycle for medium carbon 3.8 Ni, 1.8 Cr, 0.3 Mo steel, experiments were carried out with a theoretical understanding of the alloy system. This paper presents the experiments and results obtained after a spheroidizing treatment, which was carried out to optimize the process. Hardness measurements were carried out and microstructural studies were conducted to assess the spheroidization process and to determine the optimal spheroidization parameters.

Jan 1, 2007

By C. B. Webber, L. S. Diaz

"The paper presents the approach taken by Craigmont Mines to grinding circuit control. A detailed description is given of a fully automatic control system which bases its control actions on the continuous measurement of particle size in the cyclone overflow stream. The control system holds a specified particle size in the cyclone overflow, and grinds rod mi 11 ore feed at increased rates. The principles of operation of the system used for continuous measurement of particle size are described, end the improvements in mill throughput and copper recovery over several months of continuous operation are presented.INTRODUCTION Craigmont Mines Limited is located in the south-western interior region of the province of British Columbia, approximately 230 road miles north-east of Vancouver, and ten miles west of the town of Merritt. A moderate climate, good roads and service facilities provided by the Canadian Pacific Railway, Inland Natural Gas Company, and the B.C. Hydro and Power Authority, have provided a very favorable mine and plant site.The preliminary metallurgical design of the Craigmont mill was based on the test results of samples obtained from the original 2500' level drift during 1959. Pilot plant runs and other research testing for design pur¬poses were conducted at the Canadian Exploration Ltd. Laboratory, at Salmo, B.C. The design flowsheet was altered in progressive stages from 2,000 to 3,000, and finally 4,000 tons per day as the ore reserves became better defined. Construction work on the 2,400' level mill site commenced in late 1960. The official opening of Craigntnt Mines Limited took place on September 15, 1961, a little over two years from the time of the metallurgical assessment of the original ore samples.Mill throughput to date has varied widely both on a daily and a monthly basis, due to the varying hardness of the mine ores. The grindability af the ore appears to be related to the oxide iron content, which varies from lows of 9% to highs of 20%. Daily tonnage has ranged from 5,000 tons per day with 10% iron in the feed, to 6,000 tons per day with 20% iron feeds."

Jan 1, 1973