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By Henry Louis

The work performed by the Royal Commission on Mining Subsidence is likely to prove of permancnt value, less perhaps for the conclusions it has reached and for the recommendations it has based upon these than for the admirable exposition which it affords of the law concerning mining subsidence and of the legal status of the person who has suffered damage by reason of such subsidence, as also of him whose working has caused the damage. The Commission was appointed by Royal Warrant in the middle of 1925 and delivered its final report in the middle of 1927. The terms of reference to the Commission were as follows: "To consider the operation of the law relating to the support of the surface of the land, and of buildings or works on or under the surface, by underlying or adjacent minerals; to enquire into the extent and gravity of the damage caused by subsidence owing to the extraction of minerals and the incidence of the resulting liability; and to report what steps should be taken, by legislation or otherwise, to remedy, equitably to all persons concerned, any defects or hardships that may be found to arise in existing conditions." Report on the Doncaster Area The Commission submitted an interim report at the end of 1925, which referred solely to one area, usually spoken of as the Doncaster area, and recommended that a Commission of a more technical character be appointed to investigate this particular case. This recommendation was acted upon, and the Commission thus appointed reported early in 1928. Here it is necessary only to indicate the nature of the special problem that had to be solved, the proposed solution being mainly of local interest. The Doncaster area consists of about 330 sq. miles of low-lying land in the southeasterly portion of Yorkshire and adjoining parts of Lincolnshire and Nottinghamshire. No less than 78 per cent, of this land lies below the 25-ft. contour line, and a good deal is even below high-water level. It includes a large tract of land known as Hatfield Chase, swampy ground which has always been a source of trouble on that account, so much so that in 1626 a Dutchman, Cornelius Vermuyden, was called in by King Charles I to devise and execute schemes of drainage for its reclamation. The entire Doncaster area is

Jan 1, 1930

By C. R. Whittemore

Introduction The technical library in the service of industry is gradually becoming a well recognized and important part of all progressive industrial organizations. The larger mining, metallurgical, and chemical firms of Canada are establishing extensive reference libraries in connection with their research and operating departments in order that the members of the organization may keep abreast of the rapidly developing fields of engineering in which they are interested. It is the purpose of this paper to point out the usefulness of such a department in any industrial organization, to give a general outline of a system for filing and dispensing information, and to outline briefly the literature to be consulted and the procedure to be adopted in instigating a literature search. The technical library falls under the classification known as 'Special Libraries', and is quite different from the general library in that it is a storehouse of facts and owes its value to the ready presentation of information required for each specific case, and in a form most ready for use. The library brings all the available information relative to the interests of the corporation from without the plant to the organization within, and also keep in touch with each department of the organization.

Jan 1, 1930

By S. M. Marshall, B. M. Bird

For a number of years European investigators have used laboratory methods of predicting the probable strength of coke made from coal, and recently several investigators in the United States have reported the use of various tests for this purpose. There is at present no method accepted as standard, however, nor is there even agreement as to the general type of test that should be used. Furthermore, because the details of most of the tests have not been worked out carefully, one investigator can not hope to duplicate the work of another. The extension of coke manufacture to new localities in the United States, and the increasing need for cokes of exceptional qualities made from the most economical mixtures, made it desirable to have some simple laboratory test which will determine whether given coals, alone or blended with other coals, are more satisfactory from the standpoint of coke strenpth- than others of different cost. The work described herein has resulted in the development of a simple laboratory test which, it is believed, can be generally adopted in coal laborat,ories, and which will give concordant results even though performed by different investigators in different laboratories. The general method of predicting whether a coal or a mixture of coals will produce a strong coke, resistant to crushing and shattering, has been to correlate the known strengths of the cokes produced in commercial ovens with some measurable constituent or with some property of the coals, and then to use the relationship so found for forming an estimate of the coking strengths of coals unknown. Several such correlations have utilized the percentages of the various ultimate constituents of coal, such as the oxygen content and the hydrogen-oxygen ratio;(39)§ other correlations have involved the proportion of a, B and r com-pounds, (17,21,30c) or of "oil and solid bitumens."(16,30) Also a relationship has been traced between the coking properties of coal and the rate of change of the resistance offered to the flow of an inert gas by fine particles of the coal while being slowly heated. (11,176) But the most general corre-

Jan 1, 1930

By G. P. Moore

BOLIVIA still remains among the oil countries that have proved oil acreage but no production which is being marketed. No steps have been taken during the past year to provide facilities for transport of Bolivian oil to market nor are any known to be contemplated for 1930. The only active operator to date is the Standard Oil Co. of Bolivia, subsidiary of the Standard Oil Co. of New Jersey. The potential production from completed wells is practically unchanged from the 1928 figure of 6000 bbl. daily. As far as is known, there has been only one completion during the year 1929. This is the Machareti well, which is about 50 km. north of Villa Montes along the road to Charagua. The well is reported at about 250 bbl. daily initial production. The gravity of the oil is not known but is presumed to be about 40" Bé., the average for the region. The Standard Oil Co. of Bolivia has five strings working on various parts of its concession. No new locations have been made definitely. Company Activities There was no change in the situation of American holdings in Bolivia during 1929. The oil rights of an English company, acquired under a special colonization contract with the Bolivian Government, are being negotiated in New York and may mean the entrance of another of the large American oil companies in Bolivia. The Sucre Syndicate sold its holdings to the Standard Oil Co. of Bolivia during the past year. .A local company called the "Aguila Doble" was formed during 1929 to drill a well or wells near the town of Cochabamba on structures mapped by a local geologist. It is reported that the Government is buying about one-fourth of the capital stock of this company for 500,000 Bolivianos (about $180,000). The company has not yet raised sufficieht funds to buy drilling equipment so that no operations have been started. According to the statements published in La Pas, this company has acreage on seven anticlinal structures near Cochabamba. This area lies about 8500 ft. above sea level on the eastern Hank of the Andes Moun-

Jan 1, 1930

By C. R. Ince

The term "differential flotation" is used to denote a flotation operation in which separation is effected between two or more minerals of the same class; e. g., lead sulfide from zinc sulfide, pyrite from blende, chalco-pyrite from pyrite, chalcopyrite from blende. At present, so far as published work shows, there seem to be two theories as to the mechanics of differential flotation. The earlier and more generally accepted theory is that the so-called depressing agents alter the surface of one or more of the sulfides in the ore, either by chemical action or adsorption, so that it is no longer amenable to flotation, but that these depressed sulfides can be revived, after the unaffected sulfide has been floated, by reagents which react chemically with the altered surface and make it amenable to flotation. More recently, Professor Taggartl has advanced the theory that slime adsorption is an important factor in differential flotation. He believes that, with the proper use of a class of agents, which he calls dispersion agents and which include practically all the depressing agents, one can cause the slime to adsorb differentially on sulfide surfaces. A gangue-slime coated sulfide surface will act as a gangue particle and will not float. If, subsequently, an agent that will remove the gangue-slime coating is added, the sulfide again assumes its original surface and can be floated as an ordinary sulfide. This is the basis of the slime theory of differential flotation. Timber Butte mill at Butte, Mont., is a typical lead-zinc flotation concentrator. Neihart ore, chosen for investigation in this work, is one of the custom ores treated at that mill. Practice at Timber Butte mill in February, 1928, was as follows: A combined lead-zinc concentrate was first made using 0.2 Ib. per ton on the ore of potassium xanthate and 0.03 lb. per ton of Cleveland Cliffs oil after 1.5 lb. per ton of lime and 1 lb. per ton of calcium chloride has been added just before the ball mill. The concentrate was then thickened to 70 per cent. solids. Potassium cyanide to the amount of 0.3 lb. per ton and zinc sulfate in the quantity of 0.5 Ib. per ton were added to the thickened pulp and the whole

Jan 1, 1930

By James W. Wade

This paper describing the mining practices at the Tintic Standard mine is one of a series being prepared by the United States Bureau of Mines. In the preparation of this paper each subject has been presented by the engineer in charge. L. R. Dobbs wrote the part pertaining to tae technique of square-set mining, J. M. Snow the part on geology, and M. D. Paine, the part on ventilation. All of the drawings are the work of H. W. Waterfield of the engineering department. The statistics of the Tintic district ware prepared by A. G. MacKenzie. Each writer has attempted to show the difficulties that arise in operating and the practices used to overcome them.

Jan 1, 1930

During the war period of quicksilver activity there were a number of departures from what may be termed the classical quicksilver metallurgy. Attempts were made to beneficiate low-grade ores by gravity concentration and flotation; mechanical furnaces began to replace the Scott furnace and the vertical coarse-ore furnaces, and condensers of sewer tile and redwood tanks were used in place of the older brick and stone condensing chambers. Other developments that have occurred during the current period of quicksilver activity are mainly in the nature of improvement and further refinement of those started during the war period. Each period of quicksilver activity has been accompanied by the proposal of various new processes, including wet methods for the treatment of quicksilver ores and innovations in furnaces, retorts and condenser equipment. As far as the author knows, nothing of economic significance in the way of "new processes" has been developed. There is in fact no real need for any essentially new process for the treatment of quicksilver ores; the direct furnace treatment is simple and inexpensive. Moreover, with rare exceptions, the quicksilver industry has no complex or refractory ore problems corresponding to those which are receiving more and more attention from metallurgists in other branches of the nonferrous field. Untler these conditions improvements in quicksilver metallurgy must be looked for through the adaptation of current developments in engineering and metallurgy generally to the particular needs of quicksilver practice rather than through the invention of new processes. Preliminary Treatment of Quicksilver Ores At Sulphur Bank, in the treatment of old dump material left by the early operators, wet screening is being used as a preliminary step in concentration ahead of flotation. Power shovels and trucks are used to deliver some 400 tons of ore per day to the lower terminal of a hoist, which in turn discharges the material at the top of the screening plant. Wet screening is carried on in two stages. Depending on the character of the material, 1-in. or 2-in. punched screens are used on the first trommel.

Jan 1, 1930

W. H. Blauvelt, New York, N. Y.—One thought lias been running through my mind during the wholc of this meeting and that is that the scientific and the practical men must recognize very clearly their interdependence. The value of scientific classification of coal is going to be of the very greatest importance to the users, the practical men. Is not the scientific investigation and the great amount of work that is being done in a measure at least lost to the world? Therefore the scientific investigations and the practical needs of the users should bo brought as close together, and the work should be done as closely together, as possible; that is, the scientific man should know what the practical man needs, and the practical man should not feel that the scientific man is merely a theorist. Scientific investigation is going to have a great effeet and be of great valuc to the practical man who is trying to solve his problems. In the subject which I discussed' for instance, we must look to the scientific man to tell us why coal cokes in one way and not In another and why certain coals will do certain things and others, which appear on the surfacc to be generally similar, do not act in the same way. Need or Physical Data on Coal H. J. Rose, Pittsburgh, Pa.—There is a subject which is a sort of hobby of mine; that is, the need for what might be called critical tables of constants for coal. The chemist has big volumes giving constants, such as the density, solubility, specific heat, thermal conductivity and all other physical and chemical data that have been determined for chemical compounds. Data arc also available on many common materials, for example, the density, hardness, modulus of rupture or maximum crushing strength of swamp white oak as compared with some other wood. In fact, physical data for practically cvery hype of wood commercially produced in the world can he found. In the same way the metallurgical man has handbooks giving the properties of alloys, etc., but we havc very little tabulated information about coal. Our principal reference works are the volumes published by the U. S. Bureau of Mines on the proximatc and ultimate analysis and calorific values of coals of the United States. That is 3 pioncer work of enormous value, but we have reached the point where we need more diversified information. Mr. Fulweiler raised the question of the relative strength of the different coals and cokes. Dr. Campbell and Dr. Ashley wanted to have some information on the resistance of coal to air slacking. It was brought out in the discussion that we want to know something about the coking properties of coal. There are any number of physical tests that we need, such as the thermal conductivity of certain coals, the coefficient of expansion, or the coefficient of friction; or other constants. A smattering of such information is scattered through the literature; for instance, a research worker in Wales will report a coefficient of expansion on Wclsh coals and one in South Africa will report something else for one or two kinds of African coals, hut it is difficult to find the information that is needed on our own coals. Would it not be worth while to consider collecting reliable critical

Jan 1, 1930

By E. P. Barrett, T. L. Joseph

The large iron-ore producers on the Mesabi Range are able to maintain the silica in their shipping products at from 8 to 10 per cent. by mixing ores of various grades, some assaying 4 per cent, silica and some as high as 18 per cent. silica. For each ton of 4 per cent. silica ore mined, a ton of 14 per cent, silica ore can be mined and mixed with it and the average grade maintained at 9 per cent. This mixing operation has made possible the utilization of large quantities of ore too lean to be used alone, and herein lies the advantage of the producers who operate a number of mines at the same time. As the grade of the ore from one of the properties falls off, a little high-grade ore from another property can be mixed with it and the average maintained, while if one property alone were being operated all of the ore below grade would be left behind. This mixing operation, however, can continue only as long as there is high-grade ore available for mixing with the high-silica ores and, while the tonnage of iron ore in the Mesabi Range is still enormous, the tonnage of high-grade ore suitable for mixing with any quantity of low-grade ore is being rapidly depleted. Obviously, if an 18 per cent. silica ore can be reduced by concentration methods to 12 per cent. silica, considerably more of it can be utilized with a given amount of high-grade ore. The operators on the Mesabi Range recognize this situation and are energeticdly endeavoring to reduce the silica in their concentration plants because every unit of silica that can be removed by concentration is a conservation of their high-grade ores. More Elaborate Processes Will Be Needed At the present time there are thirty-seven concentrating plants on the Mesabi Range, and about one-third of the total ore shipped is beneficiated in these plants. In about one-half of these plants no reduction is made in the silica but the moisture or structure of the ore is improved. The washing process is by far the most important method for the removal of silica, and it is interesting to observe that the tonnage of "wash" ore during the past five years has shown practically no increase although the total tonnage of ore shipped has increased. This is due to the fact that the available tonnage of wash ore is being depleted and the amount

Jan 1, 1930

Jan 1, 1930

By Anthony Folger, Charles E. Straub

Kansas produced 38,150,878 bbl. of oil in 1928 and 40,658,170 bbl. in 1929, thereby retaining its rank as fourth among the oil-producing states of this country. Production for 1928 was less than that for 1927 (Fig. 1) because of a decrease in the number of completions, but the average initial production per well (Table 1) shows an increase due to the completion of wells of comparatively large capacity in the new Valley Center pool of Sedgwick County. This increase in average initial production per well was further augmented during 1929 by completion of additional wells of comparatively large capacity in the Valley Center pool and the new Greenwich pool of Sedgwick County. Production for 1929 exceeded that for 1928 and threatened to exceed all records except that of 1918, however, production was prorated in

Jan 1, 1930

By H. J. Struth

A glance into the immediate future of the refining industry, and a retrospective view of 1929, cannot fail to emphasize the need for effective measures of control of refinery still runs. With oil producers alert to the need for control of the crude supply, it has become more than ever necessary for refiners to complete the movement toward stabilization by concerted determination to maintain still run schedules within the limitations prescribed by the demand for gasoline. The outlook for continued growth in the demand for gasoline appears to be well sustained by a preliminary survey of requirements for 1930. In fact, it is apparent that the industry will be assured of a market for gasoline that will aggregate in volume at least 472,000,000 bbl. this year. This indicates a gain in total demand over 1929 of about 9 per cent. or about 4.6 per cent, less than the gain recorded during 1929 over 1928, which amounted to 13.6 per cent. Despite the indicated increase in gasoline demand this year, it is apparent that little, if any, more crude will be required than last year. This is shown in Table 1, presenting estimates of gasoline demand and probable crude requirements for 1930. Table 1.—Preliminary Survey of 1930 Gasoline and Crude Run Requirements Millions of Barrels Doniestic gasoline demand................................... 397 Foreign gasoline demand..................................... 75 Total indicated demand...................................... 472 Natural gasoline content..................................... 53 Net gasoline from crude...................................... 419 Imported gasoline........................................... 13 Net gasoline required from refineries.......................... 406 Indicated excess stock Dec. 31, 1929........................... 10 Maximum protluction required................................ 396" At 40 per cent. gasolitlc recovery, this represents a maximum crude converson of 990,000,000 bbl., or a daily average for the ycar 2,712,000 barrels. Year after year, the refining branch of the petroleum industry has been found guilty of running crude to stills greatly in excess of normal requirements, causing frequent periods of market depression. A review

Jan 1, 1930

By C. E. Wethered

This paper describing the mining methods employed by the Federal Mining and Smelting Co., operating the Morning mine at Mullan, Idaho, is one of a series being prepared by the United States Bureau of Mines on mining practices, methods, and costs in the various mining districts of the United States. The daily tonnage produced at the Morning mine, including that mined by leasers, is 1,100 tons. Mine run of ore will average 9.1 per cent lead, 5.8 per cent zinc, and 4.4 ounces silver per ton. A stull set and fill method of mining is employed.

Jan 1, 1930

By E. Stansfield, J. W. Sutherland

It is well known that the ash left when coal is burned is not the same either in chemical composition or in weight as the mineral matter originally present in the coal. This mineral matter has been referred to as "mineral impurity," "ash-forming constituents" and "corrected ash." The authors prefer the simple name used in the title and throughout this paper. The mineral matter in a sample of coal cannot be isolated unchanged and then weighed; but if the relation between the weight of mineral matter in the coal and the weight of ash remaining when the coal is burned can be ascertained, the weight of mineral matter in the sample can be calculated from the determined weight of ash. When the weight of mineral matter in the sample is known, the weight of pure coal can be found by subtraction. This pure coal must be the basis of accurate coal classification. W. F. Wheeler,l,3 W. Brinsmaid,2 S. W. Parr, and many subsequent workers have studied the relation between mineral matter and ash. Wheeler and Parr and others have deduced formulas for calculating this ratio, and used heavy-solution separations for checking the accuracy of their formulas. Brinsmaid hand-picked and analyzed two separate samples (and mixtures of these) and based thereon a graphical method of deducing the ratio. In the Fuel Testing Laboratories of the Scientific and Industrial Research Council of Alberta, a graphical method, based on heavy-solution fractionation of coal samples, has been used with marked success for the past 7¼ years for determining the mineral matter-ash ratio. This method resembles that employed by Brinsmaid in 1907.

Jan 1, 1930

By Elford H. S

Mr. H. W. GEPP said he desired to bring particular attention to this paper. The underlying intention of the Development and Migration Commission when the paper was prepared was to place at the disposal of Australian miners and metallurgists the story of the development of tin metallurgy as it had been advanced in other countries, particularly Great Britain. They had very considerable resources of low-grade tin-bearing metals in the eastern coast of Australia particularly, and they need not anticipate that tin was going to remain at the extremely low price at which they saw it to-day. The Commission felt that it was most desirable to place 'on record, and make easily available, the story of the treatment of comparatively low-grade tin ores in other parts of the world.Arrangements were made that the technical staff at Australia House, in conjunction with Mr. H. S. Elford; should collect this information so that in due course, when Australia awoke to an interest in low-grade deposits, of which there were many throughout Australia, this story would then not,have to be gathered from other areas and other places of the world. The -paper was a contribution which would turn out to be of very great value. He suggested to the younger members that this thorough contribution could be made the subject of study so that they would be ready to assist in the developments which must come. Mr. WM. APLIN said there was one point in connection with the paper upon which he would like to speak. While at Mount Morgan he had occasion to test some highly pyritic tin ore by flotation, with a view to separating the cassiterite from the pyritic mineral.Instead of accomplishing that, it was discovered that it would be possible to eliminate as much as 50% of the total weight of ore in the form of a pyritic flotation concentrate, which would contain...

Jan 1, 1930

By A. J. Kraemer

[During the past several years a great deal of discussion has centered around the question of the permissible limit of sulphur content in fuels for automotive and aviation motors. Under certain conditions of operation, sulphur in motor fuels causes the formation of corrosive substances which attach bearings, wrist pins, and other parts of engines. On the other hand, in making gas¬oline from certain stocks, the gasoline fraction normally contains a relatively large proportion of sulphur compounds. By the generally used processes of reducing the sulphur content, a significant part of the gasoline fraction is lost as motor fuel, and added expenses are entailed for chemicals, labor, and other process costs. This condition has been an economic burden to some refiners of high-sulphur crudes. In some instances the treating losses have been rather severe and the treating costs relatively high, but the data presented in this paper indicate that the reduction of sulphur content of motor fuel is a problem to a relatively small number of refiners and of little or no concern to the remainder; in fact, more then 90 per cent of the 153 samples analyzed passed the Federal specification requirement, which limits the sulphur content to 0.10 -nor cent. 3 This report is based upon the results of an examination for sulphur content, Doctor test, copper strip corrosion, and color of the samples collected during January, 1930, for the twenty-first semiannual gasoline survey of the Bureau of Mines. The results of the gravity and distillation tests of the survey were published as Report of Investigations 2995. The numbering of the samples given in this report is the same' as in Report of Investigations 2995; for example, No. 25 of this report is the same sample as No. 25 of Report of Investigations 2995.]

Jan 1, 1930

By Harley A. Coy

This paper, describing the mining methods and practice at No. 2 mine of the American Zino Co. of Tennessee at Mascot, Tenn., is one of a series of papers issued by the Bureau of Mines presenting the mining methods and costs in various districts throughout the United States. Its purpose is to summarize methods recently put into practice whereby increased efficiency has been effected. These improvements have to do principally with mill-hole mining, slushing, contract labor, and bonuses. In general, this paper supplements earlier articles and brings them up to date. ACKNOWLEDGMENTS The author acknowledges the assistance of M. H. Newman, geologist of the American Zinc, Lead & Smelting Co.; of William Black, assistant superintendent of mines; of P. M. Arthur, director of personnel; and of the engineering staff. The paper has been approved by H. I. Young, vice president and manager of operations.

Jan 1, 1930

By Cyril Stanley Smith

Although not of the same importance as electrical conductivity, the capacity for conducting heat is nevertheless a very important property of metals and alloys. A knowledge of thermal conductivity is of value in selecting alloys for many purposes and in the calculation of the efficiency of apparatus which is being designed. Unfortunately, the determination of thermal conductivity is extremely slow and tedious, consequently few data have been obtained. A further reason for the lack of information is that there has long been an impression that the thermal conductivity of an alloy is directly proportional to the electrical cónductivity and that it can therefore be calculated from the latter. The Wiedmann-Franz-Lorenz law of constant ratio of the two conductivities holds with a considerable degree of precision for all the pure metals, but appreciable deviations occur in certain alloys—particularly those containing nickel—and it seems difficult to predict exactly what the ratio will be. Therefore direct determinations of thermal conductivity should be made whenever the results are needed with any accuracy. This research is intended eventually to cover all the alloys of copper that are of commercial importance, including the binary alloys of copper with zinc, tin, aluminum, nickel, silicon, manganese, cadmium and phosphorus, and the ternary alloys copper-nickel-zinc, copper-nickel-silicon, copper-manganese-silicon, copper-zinc-tin, etc. Most of these alloys are customarily used in the wrought condition and therefore were tested in the form of annealed rods. A limited number of sand castings were also obtained and examined. This paper contains a complete review of all the previous work that has been done on copper alloys, and includes a detailed description of the apparatus and method of procedure used in the present research, together with the new results obtained on the copper-zinc series, which is the only one completed at the present time. Subsequent papers describing the other alloys will contain the experimental results and discussion only. Previous Work Copper The conductivity of copper has been studied by many observers since the pioneer work of Wiedemann in 1859. The majority of these measure-

Jan 1, 1930

By Howbert Van Dyne

THE Presidio mine of The American Metal Co. is situated in the "Big Bend" region, some 45 miles over state highway south of Marfa, a station on the Southern Pacific R.R. It lies 20 miles by road north of the Mexican border, in semidesert surroundings typical of this general section of the United States and the adjoining part of Mexico. All supplies are hauled in by truck from Marfa under contract. The concentrates and precipitates produced by the mill are carried by the same trucks to Marfa, from whence they are shipped, respectively, to the El Paso and Selby plants.

Jan 1, 1930

By Oscar Glaeser

THE United Verde Copper Company's mine is at Jerome, Ariz. The orebodies are of the schist replacement type, the main sulfide mass being a large lens-shaped body approximately 7 acres in cross-sectional area. In general, the mineralization is found along the iron schist contact, with the orebodies extending about 1000 ft. along this contact and varying from a few feet to 250 ft. in width. Three types of ore are mined; schist porphyry and the so-called "heavy" or "massive sulfide" ore. Approximately 50 per cent. of the total tonnage mined at present is of the latter class. A representative analysis of this ore indicates 42 to 46 per cent. sulfur. Because of the high sulfur content, blasting in this ore is an extremely hazardous operation. Not only does it endanger the lives of men who may be in the mine at blasting time but it also becomes a potential fire menace when timber is in close proximity to shots being fired in these massive sulfides. The origin of the fires of 38 years ago, embers of which are glowing to this day, may perhaps be attributed to dust explosions due to blasting in the massive sulfides of those, early square-set stopes.

Jan 1, 1930