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By R. O. Burt

"IntroductionThe introduction to this section on gravity concentration indicated the wide range of equipment types that exist for the concentration of minerals, in what is the broadest size range of any concentration process.The equipment described in this chapter includes jigs, tables and sHme plant equipment. In contrast to the equipment described in the two succeeding chapters, this range of equipment, in nearly every instance, superimposes a mechanical movement on the fluid motion to effect separation of the valuable mineral from the waste mineral. The motion may be vertical Gigs), reversing (tables), or rotary (slime plants): however, in common they ""dilate"" the bed of particles to allow preferential settlement of the heavier particles.Description of Process UnitsJiggingJigging is the sorting of different minerals by stratification, based on the movement of a bed of particles relative to a fluid in a vertical plane.The basic construction of a jig is shown in Figure 1. Essentially it consists of an open tank filled with a fluid, normally water, with a horizontal jig screen at the top and with a spigot in the ""hutch"", or bottom compartment, for removal of heavies. The jig beri consists of a layer of coarse heavy particles (ragging) on the jig screen. This ragging is of a specific gravity between that of the minerals it is intended to separate.In operation the bed is made fluid by a pulsating current of fluid to provide stratification. On the upward or pulsion stroke the bed of ragging and slurry is normally Hfted as a mass, then as velocity of the upcurrent decreases it dilates, loosening the whole mass. On the downward or suction stroke it closes slowly again. The ideal is to control this dilation of the bed of material so that the heavier and smaller particles penetrate the interstices of the bed, while the larger heavies fall under a condition akin to ""hindered"" settling."

Jan 1, 1989

By A. L. Craven, J. P. L. Bacharach, D. B. Stewart

"Inert gas use for underground mine fir e control is a well-established mature technology in some parts of the world. This paper reviews three candidate inert gases and describes three case histories where inert gas fire-fighting technology was used in actual underground fires.IntroductionInerting is the introduction of an inert gas into an atmosphere in contact with a fire to reduce the level of oxygen and hence the intensity of the fire 10 the point of extinction. The benefits of inerting include:a. Reduced Explosion HazardBy displacing oxygen from the atmosphere surrounding the fire the risk of secondary gas explosions is reduced. For example, simple methane-air mixtures at standard temperature and pressure are non-explosive below 12% oxygen. In actual mine fires, combustible gases may include hydrogen and carbon monoxide as well as methane. Such gases are also rendered non-explosive with oxygen removal to below 40/0. Fuel-rich oxygen-deficient mixtures can however be made explosive through dilution with air. Such dilution can occur downwind of the fire. It is also important to remember that the atmosphere in a sealed-off fire zone is rarely homogenous.b. Reduced Fire Intensity and SpreadIn a fire zone the initial combustion may well set alight materials surrounding the fire. Inerting can reduce the intensity and spread of secondary combustion and can cool the area surrounding the fire zone after the fire itself has been extinguished.c. Reduced Air LeakageLeakage of air into sealed areas in excess of the natural leakage may be reduced either by introducing inert gas into the leakage paths to replace air or by pressure balancing seals and providing a chamber of nitrogen on the outbye side of the seals. Both methods assist in the reduction of the intensity of combustion and hasten oxygen starvation."

Jan 1, 1986

By W. J. Farley

"The Sherritt Gordon mine is 100 miles north of The Pas in northern Manitoba. Copper-zinc ore was discovered on the property in 1922. Production began in 1931 and continued to June, 1932, when operations were suspended because of the low price of copper. Operations were resumed on August 1st, 1937, and have been carried on continuously from that time to the present (March 1947). The production of metals up to the end of 1945 was copper, 287,129,880 lb.; zinc concentrate (50 per cent) 104,419 tons ; gold, 79,388 oz.; silver, 2,529,974 oz.GENERALThe ore occurs in two deposits, the east and the west. Both are enclosed in gneisses that are highly metamorphosed sedimentary and volcanic derivatives. The rock beneath the deposits, and hence forming their footwall, is gneissoid quartzite; the hanging-wall rock is basic garnetiferous hornblende gneiss. Pegmatite commonly occurs along both foot- and hangingwall peripheries and as isolated blocks and fragments within the ore zone . These blocks and fragments are considered to be residuals of unreplaced host rock .The ore is relatively coarse grained and ranges from the massive to the disseminated type. The metallic sulphides composing these, named in the order of their abundance, are pyrite and pyrrhotite ( 2-1 ratio) , chalcopyrite, sphalerite (marmatite) , and minor chalmeriite; subordinate amounts of gold and silver are recovered . The insoluble content of the ore averages about 35 per cent.Another deposit known as the Bob Lake, much smaller and lower in grade but having very similar relationships, occurs about 3 ½ miles to the northeast of the main Sherritt Gordon ore masses.STRUCTUREThe Sherritt Gordon orebodies are of the replacement type, and lie within a pegmatite sill that has been intruded along a contact between quartzite and hornblende gneiss. The two main orebodies are intimately related, for the east deposit is an erosional remnant of the lower, easterly limit of an orebody once continuous with the west body. The ore lies along the southwest limb of an overturned syncline."

Jan 1, 1954

By R. W. Zeindler, D. A. Fawcett

"A summary is presented of the report completed by the Coal Mining Research Centre in 1980. This report was of a cross-pit conveyor system applied as an auxiliary mining complement to the major stripping unit, a dragline. The purpose of the CMRC report was to evaluate selective mining and replacement of the upper horizons of the strata as an aid in reclamation. These strata were the topsoil, subsoil and glacial till.Past utilization of cross-pit conveyor systems and related engineering studies were assessed. The parameters of the study were based on the mining and geological conditions of the Alberta prairie coal mines. The principal excavator for stripping was a dragline. Excavation of the upper horizons was done by a bucket-wheel excavator discharging onto the crosspit conveyor. Alternative equipment applications were economically compared. Four cases or geological sections were evaluated in detail. The economics of the alternative mining systems for each of the cases were determined. In all instances, the most economical solution was a tandem system utilizing a dragline with a bucket-wheel excavator/ cross-pit conveyor system."

Jan 1, 1981

By P. Blonde

Recent analysis has suggested that a balanced recovery profile can improve flotation bank performance. Test work was conducted to test the balanced profile concept at the Penhorwood talc mine near Timmins, Ontario, Canada. Plant trials were devised to determine how to control the recovery profile and the resultant impact on grade and recovery in a rougher bank of four cells. Accompanying gas dispersion measurements revealed a maintenance issue with one cell that was corrected. By manipulating air and frother addition it was possible to bring the bank closer to a balanced recovery profile and the down-the-bank grade/recovery improved. Plant production showed an increased talc grade at similar yield with the balanced profile. The results provide justification for a long term plant trial.

Aug 1, 2013

The rate of liquid copper deoxidation during top blowing of reducing flames has been investigated using a high capacity thermogravimetric unit at 1200 °C. For 1 kg copper samples, it was observed that the rate of deoxidation was proportional to the flow rate of the reducing reagent (H2 or CO). Under similar experimental conditions, it was found that H2 is more effective than CO even though both have similar thermodynamic potential to deoxidize liquid copper. The rate of deoxidation of liquid copper with reducing 0 2/CH4 flames was measured for 0 2/CH4 molar ratios of 1.5 to 2. The deoxidation rate depends on the 0 2/CH4 ratio and decreases as it approaches the stoichiometric ratio (02/CH4 = 2). Estimation of the rate of deoxidation of liquid copper with top blowing flames based on the thermodynamic composition ofH2 and CO in the product gases, agrees well with measured values.

Jan 1, 2007

By A. Ghahreman, M. Oliazadeh

"Heap leaching is an attractive process for low grade deposits where the metal content of ore does not justify the high cost of milling and agitated leaching. In general, the heap leaching capital cost is low, construction is rapid, and production costs are low. The primary disadvantage of heap leaching is low recoveries (typically 65% of agitated leach recovery); thus, recovery improvements could convert more lower-grade deposits into minable reserves. This will also allow to process primary sulfide ores and result in a dramatic expansion of the technology, as ~80% of total ore types are sulfidic in nature. The old gold operations tailings are another massive source of low-grade gold material that can be retreated by the heap leach process. The major parameters affecting the recovery rates are ore characteristics (mineralogy, particles size of metal and host minerals, ore permeability), and operational conditions (segregation of ore, compaction, leach cycle time, lift height, and solution application rates). The design of a percolation leach process is based on a limited number of coarse ore bottle roll and/or column tests under ideal conditions. The economics of the projects and engineering design of the process facilities are developed based on the bench scale test work results and the application of the conventional engineering scale up factors. This paper will deal with the parameters affecting the HL efficiencies and focus on the potential improvement of gold heap leach recoveries. This would include design of heap leach operation and evaluation of processes such as fine crushing and bioleaching.INTRODUCTION Gold heap leaching is a hydrometallurgical process designed to treat amenable low-grade gold ores that contain typically 0.5 to 1.5 g/t gold (Marsden and House, 2006; Wong Wai Leong and Mujumdar, 2010). Ore is stacked by various types of equipment on an impermeable barrier, and a sodium cyanide solution is applied to the surface of the stacked ore. Gold, silver, and other metals contained in the ore are dissolved to various degrees by the cyanide application, as it percolates downward through the stack of the ore. The pregnant leach solution (PLS) is then collected at the bottom of the heap. The PLS is then sent to the gold recovery plant where the metals are extracted. The barren leach solution (BLS) is then reapplied to the top of the pad. Ore is placed on a pad or previously leached lift by various means, including ramp conveyor belts, radial-arm and self-leveling stackers, and trucks. Once trucks are used to construct the pads, the pad can be compacted and hence the pad should be graded and ripped or scarified (roughened up) with wheeled or tracked equipment to produce shallow cuts to increase surface area exposure to the leachate."

Jan 1, 2019

By B. A. Monkman

"IntroductionONE OF :THE most effective methods by which the construction industry is combatting mounting building costs is by making increased use of lightweight materials, thus reducing the dead load to be carried •by structures. This applies to non-metallic materials as well as to metallic ones, and particular attention has been given to developing lightweight aggregates for use in concrete.The use of lightweight aggregates is not new and, in fact, dates back to the Roman Empire, when pumice was used in the walls and domes of the Roman buildings. More recently, and up to a decade or so ago, the demand for these aggregates was met from deposits of volcanic cinders, pumice, scoria, etc., and from the by-products of blast furnaces and coal burning boilers. However, these sources of supply are no longer sufficient to meet the demand, for transportation costs pretty well restrict the use of the natural lightweight aggregates to the western cordillera regions where the deposits of these materials occur, and the use of expanded slag aggregates to the areas neighbouring the plants where slags are produced. As for cinders, the supply has been greatly reduced by the conversion of industry to fuel oil, natural gas, and powdered coal, and the large stockpiles which existed previously have been pretty well exhausted.Industry's approach to the problem of a decreasing supply, in the face of an increasing demand, has been characteristically direct. The solution has been to construct plants whose sole .purpose is to produce economically an acceptable light-weight aggregate from materials close at hand."

Jan 1, 1955

By H. Soto, P. Lacombe, R. del Villar

"During the summer of1989, Les Mines Selbaie, with the cooperation of Université Laval initiated a research project to evaluate the column flotation technology for its concentrator near Joutel, Quebec. The experimental work involved both a 5 cm by 11 m laboratory column and a 45 cm by 10 m home-made pilot unit Amenability tests were conducted using both units on various streams of the plant. Results showed that columns are not suitable for the copper cleaning circuit because the loss of precious metals, associated with the rejected pyrite, overcome the improved copper metallurgy. On the other hand, column testing at the zinc circuit showed improved zinc selectivity.Scale-up testing was', therefore, conducted on the first zinc cleaner concentrate using the laboratory-size column. The influence of variables such as porous parger grain size, wash water flow rate, airflow rate and froth depth values on column performance was' first assessed. Scale-up parameters were then determined using the optimal operating conditions from the previous tests. Simulation facilitated the determination of the most convenient plant-scale column arrangement.A number of conclusions concerning the experimental determination of scale-up parameters are also presented."

Jan 1, 1993

By Antoine Fournier, Karen St. Seymour

"Responding to market developments, interest in locating deposits of wollastonite has grown significantly. The many occurrences in the Grenville marbles of Quebec can be grouped into disseminated type and discordant vein-type deposits. Disseminated-type wollastonite occurrences have the disadvantages of lower grade, the need for more elaborate mineral separation, and failure to meet ""long grain"" technical specifications. Vein-type deposits have better grades and technical characteristics; exploration should be focussed on these and in the contact-metamorphic aureoles of fluid-rich intrusions. SOMMAIREEn réactions aux nouveaux de bouches, l'interet pour les gîtes de wollastonite a crû de façon marquée. Les nombreux indices sis dans la province de Grenville au Québec peuvent être regroupes en deux catégories soit: les indices dissémines et les indices en veines discordantes. Les indices dissémines ont le désavantage d'être moins enrichis, de requérir une séparation minéralogique plus complexe, et leur wollastonite ne possède pas le degré d'acicularité voulu. Les indices en veines sont plus enrichis en plus de rencontrer les critêres techniques; les efforts d'exploration devraient se porter vers ce type de gites et aussi, sur les auréoles métamorphiques de contact d’intrusions riches en fluides."

Jan 1, 1992

By C. O. Aksoy, H. Kose, K. Ozfirat, T. Malli, A. Gonen, S. Gurgen

In selecting mobile mining equipment, factors including availability, useful economic life, maintenance and operating costs, and spare parts availability are considered. Given these factors, trucks and shovels with different capacities are selected. Optimizing equipment for pit and hillside quarry cases, where 8% and 10% ramps are commonly in use, were examined; the effect of other mining activities such as drilling and blasting on unit cost were considered. In principle, 20 m to 25 m high benches should be economical for downhill haulage, and 7 m to 10 m low benches economical for uphill haulage. However, practice of both mining styles favours 10 m to 15 m bench heights. Hence, the analysis here was carried out with the field experience bench height range. In the study, a truck-shovel optimization was based on the movement of 5 to 20 million cubic metres (in 2.5 million cubic metre increments) of overburden stripping at the Eynez open pit mine in the Soma region of Turkey. The outcome showed that low-capacity shovels were unfavourable due to high production expectations. High-capacity shovels were also unfavourable due to health and safety issues causing high instances of impact vibration on trucks during the loading cycle and a decrease in foreseeable unit lifetimes. The number of shovel passes required to load a truck ranged from three to six. Trucks with high-capacity bodies were deemed uneconomical due to high investment and operating costs.

Jan 1, 2005

By R. G. S. Mussi

An inclined cooling plate is utilized as a modification in the compocasting process of magnesium alloy and the mechanical properties of the composites obtained are studied in this work. Based on crystal separation theory, molten AZ91D is poured onto an inclined plate in order to produce solidification nuclei inside the fluid metal, and is mechanically stirred while reinforcement is added. Particulate SiC was utilized as reinforcement in quantities varying from 0 to 15%vol. Dispersion of the reinforcement was observed by macro and microstructure analysis. SiC was properly mixed into matrix until 15%vol., and Vickers hardness tests were carried out for the composites produced. Results obtained for hardness were shown to increase with reinforcement addition and comparable to those of traditional compocasting. Utilization of Inclined Cooling Plate produced good inclusion and homogenization of SiC through an AZ91D matrix, at lower temperatures and shorter times than traditional compocasting.

Jan 1, 2006

By D. B. Haas

THE HYDRAULIC TRANSPORT of solids is becoming increasingly prevalent throughout the world. Major long-distance slurry pipelines currently in operation transport commodities such as coal and various ore concentrates distances of up to hundreds of miles. In the United States, a number of large-diameter, high-tonnage pipelines are under consideration for the transport of Western Plains coal to markets up to 1000 miles away. In these and other applications, the solids are generally quite fine, with 14 mesh being a typical limit of particle size for long-distance (over 100 miles) slurry transport. There are applications where it might be practical to transport solids consisting of larger particles distances of up t o 100 miles. Deposits of high-quality metallurgical coal are found in the inner foothills belt along the eastern edge of the Rocky Mountains on the Alberta-B. C. border. There are few existing railroad s and the possibilities of constructing extensions are limited because of environmental and economic factor s. In these circumstances, the most efficient transportation system might consist of a pipeline to transport the coal from the mine to beneficiation plants located near existing railroads 50 or 100 miles away. Such systems would minimize environmental effects, capital cost s and operating costs. To determine whether such a system would be technically feasible, experimental testing is needed to determine the energy requirements for transporting coarse coal in a pipe line. Currently, run-of-mine metallurgical coal is crushed to less than 1 1/2 inches before going to the beneficiation plant. In the proposed scheme, coal of this size would be transported through a pipeline to the beneficiation plant located at the railroad. The Transportation Development Agency and the Department of Supply and Services have awarded a contract to the Saskatchewan Research Council to study pipelining of coarse coal in pipelines ranging from 4 inches to 12 inches in diameter.

Jan 1, 1977

By R. L. Christie

"THE ISLANDS lying north of the Canadian mainland, and the large Boothia and Melville peninsulas, form one of the great archipelagos of the world; this sparsely vegetated and nearly unpeopled region extends about 1,500 miles east to west and 1,200 miles from the mainland to the northern tip of the northern-most island. Sea access to most of the islands is restricted by ice to the summer season, and the 'polar pack' ice of the Arctic Ocean presses the year round against the northwest margin of the archipelago. Although the region is remote, the accessibility has greatly increased through a network of weather stations, airfields and air routes connecting with southern centres.The area considered in this paper is that part of the island region underlain mainly by sedimentary rocks. In broad terms, this includes the land and sea areas of the archipelago and the adjacent continental shelf, but excludes the dominantly 'Shield' terrain of Baffin Island, and of Melville and Boothia peninsulas. An impression of the size and potential of this sedimentary region may be gained by comparing some areas: the land area of islands underlain mainly by sedimentary rocks is over 300,000 square miles or about 50,000 square miles greater than the area of Alberta. The total area of the region, including the continental shelf and the inter-island areas, may be double this figure, and may approximate one-seventh of the land area of Canada."

Jan 1, 1970

By M. Jiang, X. Fan, W. X. Chen, Z. K. Guo, H. H. Zou

"Some improvements are carried out for elasto-plastic model by taking the shear dilation effects and relaxation effects of deep rocks into accounted. The high pressure equations of states with Mie-Grüneisen form are also introduced to describe the relation of pressure-volumetric strain. Numerical simulations of free field responses for deep underground explosions are conducted by using the user subroutines which compiled by means of the secondary development functions of LS-DYNA9703D codes. It is indicated that the dynamic responses of free field are well simulated based on this improved elasto-plastic model, and the analytical results are in good agreement with the data of U.S. Hardhat nuclear test.INTRODUCTIONDynamic behaviors of deep rocks for underground explosions are obviously different from that of shallow underground explosions and have aroused great attentions of international experts who work for rock engineering. The dynamic models of deep rocks could be roughly divided into classic elasto-plastic model and fracture damage model according to different theoretical foundation. M. E.Kipp and D. E.Grady et al. are the outstanding representatives who engaged in the researches of fracture damage mechanics. Researches of dynamic problems for geomaterials were carried out by C.C.Grigorian and the conclusion that incompressible elasto-plastic medium model could not be used to solve the problems of closed underground explosion was derived, and therefore C.C.Grigorian model was proposed. In this model, C.C.Grigorian assumed that the average hydrostatic pressures and the densities of medium had one to one relationship, and the path of loading or unloading is different from each other. For shear deformations, analytical solutions of the problems were derived according to the model which was slightly different from Prandtl-Reuss model, the constitutive equations were closed by Mises-Schleiher constitutive model. However, the analysis showed that there were two inadequacies in C.C.Grigorian model. Firstly, the shear dilation effects of fractured medium after wave front could not be considered. Secondly, the relaxation characteristics of the rocks in fractured region were not taken into account."

Jan 1, 2015

By Greg Gosson

These materials are provided for general information purposes only and do not constitute legal advice. Readers are advised to seek specific legal advice from their own counsel in relation to any decision or course of action contemplated. Outline ??What is meant by a ?current technical report? under NI 43-101? ??When is a current technical report required? ??Who makes the decision regarding whether a technical report is current? ??Examples of the types of information that make a technical report no longer current for securities filing purposes.

May 1, 2009

By Peter N. Blakey, Jean-Paul Paquette, Barton A. Thomson

"FROM THE BEGINNING OF THE PIT, it was known that the surface mining method had a projected life of about ten years, and that the ore extended to depths recoverable only by underground mining. When serious consideration was given to underground mining in 1968, it was realized that tremendous advantages could be gained by starting the underground mine as early as• poss1ble. These included: 1. The availability of underground ore for grade control, which would become more difficult as the pit deepened. 2. The need to develop new systems, equipment and skills to take full advantage of the technological revolution in underground mining. 3. Early knowledge of rock behaviour through trial mining on a small scale prior to finalizing plans for major blocks. In addition, the pit would be available to guarantee the mill supply if problems were encountered. 4. With sufficient time and early mining experience a much better job could be done on all mine planning. Because ample reserves of economic underground ore were virtually assured, the desired underground mining capability became a function of two restraints: first, the time required to excavate and construct the permanent headframe, shaft and ore-handling facilities necessary to handle large volumes of stope ore; second, the time for lateral and stope development on at least one level which would normally follow shaft sinking. The decision made was to move immediately on the permanent hoisting installations and at the same time embark on the planned ramp from surface, which would allow much stope preparation to be completed prior to .bringing the shaft on stream. Both projects were placed on an urgent basis early in 196S' and the following decisions made shortly thereafter."

Jan 1, 1974

By K. Shikaze

"For the last three years (1967-9) the value of the output of mineral resources in the Province of Ontario exceeded one billion dollars per year. To produce this great wealth, it was necessary for the mining industry in Ontario to dispose of an estimated 80 million tons of waste mill tailings. Some of these tailings were returned underground but the greater proportion was disposed of above ground in lakes, watercourses, marshy areas and in engineered impoundment basins. This volume of tailings, if accumulated in one location would cover an area of 1000 acres to a height of almost thirty feet. The provision of proper disposal of the waste mill tailings in a manner such that they will not create problems in the environment is one of the costs which must be borne from the extraction of such a wealth from our mineral resources. It is principally the potential water pollution which may occur as a result of the indiscriminate discharges of waste mill tailings which is of concern to the Ontario Water Resources Commission.ONTARIO WATER RESOURCES COMMISSIONThe Ontario Water Resources Commission was formed in 1956 and operates under the Ontario Water Resources Commission Act. The Act has been broadened and amended many times by amendments."

Jan 1, 1970

By M. L. Jeremic, G. J. P Delaire

"The mechanical aspects of cable bolt failure are considered from the point of view of properties of grout and cable, as well as of the rock in which it is anchored. The results from recent investigations made in-situ as well as in the lab are combined and presented with reference to other work done in the area. An attempt is made to stimulate the thinking along these lines so as to initiate further research which may enhance the design of cable bolting as it applied to mining operations.IntroductionIn the past twelve year s systematic cable bolting has found application in many areas. In civil engineering rock anchors have been used to provide tension at the heel of a dam permitting the reduction of its cross section. They have been used in retaining walls to reduce construction time and costs by eliminating the need for struts and braces which complicate pouring the foundation walls. It is also possible to use rock anchors in providing reactions where tall buildings are subjected to uplift on one side due to wind forces. Cantilever bridges may be constructed by implementing rock anchors to provide anchorage requirements. Anchorage piles or dolphins or mooring ships have also been built using these. In the mining area rock anchors, commonly known as cable bolts because they are made of hoist cable may be implemented in the reinforcement of hanging walls or to retain rock slopes.In order to sustain de-pressurized ground where rock separation developed along the pressure arches, cable bolts were utilized at the Tsumeb Mine in South-West Africa and also at the Strathcona Mine in Sudbury, Ontario, In both places old degreased hoist ropes were installed in downholes from crosscuts above a given stope and then grouted without tensioning. Jeremic and Cassidy described the use of cable bolts to increase hanging wall stability and postpone fracturing, in addition to producing pre-support for improvement of stope back stability."

Jan 1, 1983

By The Staff

Introduction In this paper it is proposed to discuss briefly some of the problems confronting the management of a gold mine in choosing a method of milling to recover the gold from various classes of ore. In order to simplify the discussion, the more common types of gold ores are classified from a metallurgical point of view as follows: Class 1?A: Free-milling ores which require only relatively coarse crushing. B: Free-milling ores which require finer grinding to release the gold. Class 2?A: Gold ores which contain the gold partly in the flee state and partly associated with a small amount of iron sulphide, and which do not require fine grinding. B: Gold ores similar to 2A, but which require fine grinding. Class 3?A: Gold ores containing copper in quantities insufficient to interfere to a serious extent with cyanidation. Gold ores containing copper in sufficient quantity to interfere with cyanidation but in which a large proportion of the gold is in the free state, the remainder being chiefly associated with the copper mineral, chalcopyrite. Gold ores containing copper and other sulphides, such as pyrite, etc., in which the gold is principally associated with these sulphides.

Jan 1, 1931