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TIDBITS OF INFO- AUSTRALIAAugust 25, 1928— Engineering and Mining Journal
Mining Ore at the Broken Hill Proprietary
A Brief History of the Methods Used
By E. J. HORWOOD
Superintendent of Mines, Broken Hill Proprietary Company, Ltd.,
Broken Hill, New South Wales
Abstract of an address made by Mr. Horwood in New South Wales early this year, tracing the development of mining and metallurgical methods in his forty years’ connection with the con,pany. An article in a coming issue will be devoted to the developmont of concentration methods.
UNTIL recent years the mode of occurrence of the Broken Hill ore was supposed to be by the replacement of the country rock in and adjoining the original fissure, by lead and zinc in solution in underground waters. Though such action has admittedly taken place, it is now considered to have been subsidiary to the igneous origin of the ore, there being strong evidence of its having been forced into the fissure in a molten condition. Early development disclosed rich oxidized silver-lead ores, but subsequent exploration has shown that, varying from 300 to 500 ft. below the surface downwards, the ore consists of sulphides of about equal percentages of lead and zinc, the assays also showing silver.
As the oxidized ores were in places much richer in lead and silver than the sulphide ore from which they were derived, and were almost devoid of zinc, it was evident that the original sulphides were acted on by the oxygen of the atmosphere carried down by the surface waters of past ages, when the rainfall was doubtless much greater than at present. Much of the silver and lead was dissolved and redeposited in the oxidized ore lower down, while the zinc was carried away in solution in the underground waters and to a certain extent redeposited on the sulphide ore below. This enrichment is illustrated by the fact that, although the average grade of the unaltered sulphides is from 11 to 13 per cent of both lead and zinc and about 11 oz. of silver per ton, some of the oxidized ores contained up to 75 per cent lead and several thousand ounces of silver per ton, and some of the semi-oxidized sulphide ore assayed as high as 30 to 35 per cent zinc.
There are two distinct classes of ore in the lode, one with a calcitic or carbonate of lime gangue, and the other with a rhodonitic or silicate of manganese and iron gangue. The calcitic ore occurs at the extreme north and south of the known ore deposits, pitching northward at the north end and southward at the south end. It would appear that in some very remote age the calcitic ore was continuous from one end to the other, as indicated in the sketch, and, owing to the volcanic earth movements pushing the central portion much higher than the remainder of the ore deposit, the calcitic ore originally in the central portion was exposed to denudation by torrential rains of past ages. Though this action robbed the company of much ore, it was largely compensated by the enrichment below the calcitic zone, which provided much easily smelted, rich, oxidized ore, of which other companies were devoid, and which enabled Broken Hill Proprietary to earn, for a time, up to £1,000,000 per year.
Owing to the great width of the orebodies, which vary from 20 to over 250 ft., and average over 100 ft., the usual Australian mining methods proved unsuitable. An American mining engineer by the name of Patton was then called in as general manager. He instituted the square-set system of stoping, consisting of lO x lO-in. timber forming a framework 7 to 8 ft. high and 6 ft. long, horizontally, center to center. Each set represented a block of ore 7 ft. high and 6 ft. square. One of the advantages of this system was the number of working faces made available; another was the ease with which the broken ore could he sent down to the level below. A set alongside the level was lined off, forming a vertical box, into which the miners shoveled the ore and from which truckers on the level received the ore, taking it to the shaft to be hauled to the surface. The square-set system worked well so long as the excavation or stope was of moderate size. But, after experiencing a number of collapses, it became necessary to fill sections of the stopes with waste rock to reinforce the timbering. The ore in the American mines that Mr. Patton had worked was evidently much harder and more self-supporting than the oxidized ore at Broken Hill. Hence it could be supported by square-set timbers supplemented by bulkhead timbers, generally built in every fourth set.
Most of the unaltered sulphide ore could be mined by the open-stope method, in which the only supporting timber necessary was where the ground appeared likely to flake off, when an occasional bulkhead, consisting of logs of timber, was built on the square. An open stope was generally started by widening an existing crosscut, the latter having a connection with the level above, to provide ventilation and a mains of filling. The first, or sill floor, stope was carried up about 16 ft. high and in strong ground for the full width of the orebody and from 200 to 300 ft. long. Before any filling was put in the stope was dose-floored with timber 3 to 4 in. thick. The object of this was to prevent the filling breaking away and running into the stope when the ore underfoot was being worked. Before filling was put into the sill-floor stope, drive timbers were erected to provide access and exit for trucking to and from the various parts of the stope as it advanced. When the sill-floor stope was sufficiently filled with waste (which, by the way, consisted of the residues of the original ore after the lead and zinc had been extracted), the ore was mined in the form of a horizontal slice about 8 ft. high, and when this slice had advanced sufficiently a layer. of filling 8 ft. deep was placed in the stope, and so on, layer after layer, until the back or roof of the stope reached within about 30 ft. of the level above. At this stage the ore overhead—owing to the large area undermined—became too weak to permit of its being safely mined by the open-stope method, and square sets worked in small sections then became necessary.
To prevent the filling of the worked-out ground above from breaking away, it was generally necessary to work the square sets underhand. The first thing done was to take the ore out immediately below the old bottoms, and as soon as room was made for the horizontal members of the square set, these were put in and were held in position by a cantilever, or boom, of timber 10 in. square, and blocking was placed between the set and bottom timber. The back or roof of the set or sets having been secured, the ore below was mined by underhand methods and square-set timbers were inserted as room was made, each frame being hung by laths from the one above. In strong ground it was sometimes safe to mine from the bottom upward, taking care to safeguard the old bottom flooring above.
The ore was run from shoots alongside the various drives and crosscuts under the stopes into trucks of over one-ton capacity. These were coupled up in rakes or trains, of up to ten trucks, and drawn by horses to the shaft. These horses were mostly fairly heavy draught stock, and were sent down and up again at the beginning and end of each shift. Before large shafts were made, about 30 years ago, the horses had to be let down in a sling and were kept underground continuously. As they retained their good condition, they evidently reconciled themselves to living underground, though in one case, before electric lights were installed in the underground stables, one horse went blind. A unique happening was the birth of a foal underground. These horses displayed remarkable intelligence, and• in some narrow crosscuts, where it was impossible to turn standing, the horse would practically sit on its haunches and swing its body around. The horses were trained not only to pull the trucks when ordered, but also to push them, a breast pad being attached below the collar for this purpose. A small lamp, with a piece of candle, was suspended from the collar to give light for the horse.
Considerable trouble arose from underground fires in the early days, and some curious specimens were found when fire areas were reopened for working. One example was a dumbbell formed by the action of fire on a wooden ladder in contact with carbonate of lead. Two lumps of lead were formed from the smelting of the ore, one at each end of an iron rung of the ladder. Although it was rarely seen in the working faces, there were traces of mercury compounds in the ore; the fire volatilized these traces, which, in the gaseous form, found their way with the products of combustion to the surface, where in the course of years, meeting the cool air, they were condensed and deposited on rocks near the surface cracks. Partly smelted ore, slag, and red oxide of lead were, of course, common occurrences.
About the year 1890, it was realized that the upper portions of the ore could be more advantageously quarried than mined by underground methods, and for nearly ten years this method was followed simultaneously with mining below, the deepest open cut being nearly 350 ft. below the original surface. Altogether about 4,500,000 cu.yds. was excavated, yielding I 500,000 tons of payable ore. The limit as regards depth was governed by the amount to be removed to give the sides of the open cut a safe slope, or batter.
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AUSTRALIA MINING NEWS EMJ 10 20 1928Melbourne Letter
By PETER G. TAIL
Special Correspondent
Wiluna Gold Will Mine and Treat 40,000 Tons of Ore a Month
MELBOURNE, Sept. 13, 1928.—In a report on the property of Wiluna Gold Corporation, Ltd., in Western Australia, Alfred James, of London, states that work has been centered on the lodes in the southern part of the property, where 1,000,000 tons of ore,, averaging 40s. in gold to the ton, has been disclosed. He recommends that a vigorous exploration program be undertaken on the northern leases. On the question of treatment, Mr. James has advised the directors that the methods evolved by the company’s metallurgical staff insure a recovery considerably superior to that on which the original estimates for the mine were based.
Steps have been taken to prepare the design of the treatment and power plants which will handle 40,000 tons of ore a month, and the sinking of the main shaft has been started. Development at the mine continues to show’ consistently good average ore at all points. The management is particularly’ encouraged by the enrichment of the 300 level on the west lode. Preparations have been made for the development of the Bulletin and Essex leases in the north of the property. In addition to undertaking the construction of a railroad to the mine, the government of Western Australia has decided to deepen Geraldton Harbor, thereby facilitating the landing of machinery, stores, and oil fuel for the company. The ministry has granted the company a special freight rate for oil.
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A REPRESENTATIVE of Russo-Asiatic Consolidated is at present in New Guinea inspecting the options on the Bulolo gold field. It is stated that if the company exercises the options, a light railroad will be constructed from the coast to the Edie plateau and that operations will be carried out on a large scale. Russo-Asiatic also controls the Mount Isa silver-lead mines, in Queensland.
636 Engineering and Mining Journal — Vol.126, No.16
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ASARCO TO FINANCE MT ISA MINE VENTURE TMJ 8 30 1930A. S. & R. Co. ACQUIRED SUBSTANTIAL INTEREST IN MINING TRUST, LTD.
Through arrangements with American Smelting and Refining Company, capital has been provided for the development and equipment of the Mount Isa Property, in Australia, and for construction of the Mining Trusts’ silver-lead bullion refinery. Mining Trust, Ltd., owns a majority of the shares of Mount Isa Mines, Ltd., one of the largest lead-zinc-silver mines in the world.
American Smelting has not only acquired a substantial interest in Mining Trust, but has also agreed to place at disposal of that company, for a minimum of ten years, the benefit of the experience, assistance, and advice, of its large technical staff, trained in the management and administration of mining properties, smelting, and refining plants.
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JULIUS Kruttschnitt TO HEAD UP MT ISA MINE TMJ 8 30 1930THE MINING JOURNAL
KRUTTSCHNITT TAKES CHARGE MOUNT ISA, LTD., IN AUSTRALIA
Julius Kruttschnitt Jr, for the past 18 years, Manager of the Southwest Department of American Smelting & Refining Company, with headquarters in Tucson, has announced his appointment as manager of the Mount Isa Mines., Ltd., properties in Queensland, Australia. He plans to leave in a very short time for that country.
Mr. Kruttschnitt has been associated with A. S. & R Co. since 1909, before taking over the managership of the Southwest Mining Department, having been Superintendent of the company’s Reforma Mine in Coahuila, Mexico, and, previous to that, Superintendent of the Asientos Mine, at Aguascalientes, Mexico.
In 1912, he established headquarters in Tucson, in charge of examination and operation of the A. S. & R. mines, throughout the Southwest Territory, and the West Coast of Mexico. In the years 1907 to 1909, Mr. Kruttschnitt was associated with the engineering department of the Arizona Copper Company.
Born in New Orleans, the son of Julius Kruttschnitt, former Chairman of the Executive Committee, of the Southern Pacific Railroad, he attended Belmont Preparatory School in California, and later Yale, of the class of 1906. It was at Yale that he received his Ph.B. degree.
The Mount Isa Mines, to which Mr. Kruttschnitt is going, is owned by The Mining Trust, Ltd., in which the American Smelting and Refining Company is heavily interested. Recent work has been concentrated upon the building of a mill, smelter, lead and zinc refinery, and power plant to handle 2000 tons of ore daily. These plants, which are now about completed, are anticipated to give an annual production of 10,000 tons of lead, 8,100,000 ounces of silver, and 4,800 tons of zinc.
The development and mining methods program has been laid out by Charles A. Mitke, who has been working in a consulting capacity with this company, for the last two years. Although but three miles of development work has been done, along with some 25,000 feet of diamond drilling, it is stated that the company ore reserves total about 25,000,000 tons, valued at about $400,000,000.
About 3,000,000 tons of this ore are carbonates running 8 to 22 percent lead, and 3 to 10 ounces in silver, and better than 20,000,000 tons of sulphide ores running 4 to 8 percent lead, 6 to 10 percent zinc, and 2 to 5 ounces in silver. The Black Star orebody, is stated to exceed 2,200 feet in length, with widths up to 280 feet, and, while ore reserves have only been included up to 750 feet in depth, diamond drilling has shown no change at 1,000 feet.
The 2,000-ton plant, now being completed, is stated to be only the beginning, as greater capacity will be installed soon. The main shaft and underground layout has been designed to handle 12,000 tons daily. Twelve hundred men are now employed.
The transfer of Mr. Kruttschnitt to Australia, is undoubtedly a part of the agreement “to furnish The Mining Trust, Ltd., with technical advice for ten years, in the management and administration of its properties and plants.”
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