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By John L. Schroder, Woods G. Talman

EXPERIENCE has shown that certain known natural conditions and other indefinite characteristics combine to make a mining area vulnerable to mountain bumps. Some of the known conditions are heavy overburden, an overlying stratum of strong non-elastic rock, a structurally strong coal seam that does not crush easily and yet is the weakest stratum in the series, and a floor stratum of more than ordinary firmness. The indefinite characteristics could include resistance of top or bottom of a coal seam to lateral flow, effect of immediate top and bottom strata, nature of the coal seam, and other factors about which very little is known. It is in this area that exhaustive study is needed to achieve positive control of the dreaded mountain bump hazard.

Jan 8, 1958

THE term mountain bump describes the sudden rupture of one or more coal pillars under excessive stress. These bursts occur with varying degrees of violence and sometimes include adjacent strata, especially the bottom rock. Many failures do not develop enough violence to be dangerous and are regarded as an aid to coal production, but severe occurrences are accompanied by tons of flying coal, dense clouds of dust, and excessive gas emission. Such bursts sometimes throw heavy machinery several feet. Major factors to be considered in the problem are the nature of the strata above and below the seam and the depth of cover. Bumps are classified as to their nature, extent of damage, and point of occurrence, e. g., face bump, coal bump, high side bump, low side pavement bump, and district bump.

Jan 8, 1958

By James V. Thompson

ENGINEERS from industrialized countries are frequently called upon to examine mining operations in primitive areas and make recommendations regarding mechanization and modernization. They often set forth with self-confidence, knowing full well that all that is needed is their experience and several shiploads of mining machinery, and at times they mentally provide the answers before the problems have been clearly stated. In primitive areas it is absolutely essential that the examining engineer spend enough time at the site to acquire a thorough understanding of what is being done now and why it is done the way it is. The objective here is to state in simple terms some of the problems that may be encountered, in- as much as solutions, if they can be found at all, will differ with each experience.

Jan 8, 1958

ORE at the Jeffrey mine of Canadian John Mansville at Asbestos, Que., is hoisted by two 12 1/2 - ton capacity aluminum skips, counterbalanced. When the loaded skip reaches the surface it empties, via its sliding door, into a bin. Simultaneously, the skip tender, who operates at the 940 level, loads ore into the alternate skip from a 12 ½ -ton measuring pocket. This done, he sets the skips in motion. Problem: When moisture content of the asbestos ore is high, the ore, unknown to the skip tender, some- times sticks in the dumping skip, preventing complete discharge. Moreover, the sliding skip doors sometimes jam and stay open after the ore is discharged. If a skip in this condition is lowered, the result is either an overflow of ore, or the ore discharges through the open skip door, down the shaft. Spilled ore must then be mucked out of the spill pocket and hoisted in 2-ton cars. Cost is high, time is lost, and the shaft is sometimes damaged. Solution: A television apparatus was installed so that the skip tender might quickly spot improper door operation or hang-ups at the dumping station.

Jan 8, 1958

By John M. Warde, Eileen P. Burke

ORES of manganese and chrome have a high order of strategic importance, both metals are basic to the metallurgy and usefulness of steel, the fabric on which our economy rests. Looking beyond the current recession and short range picture of oversupply in these ores, this review attempts to answer the following questions regarding the longterm outlook for these key commodities: By 1970, what will be the probable demand here and abroad, what are future supply prospects, and what effect is the USSR likely to have on the world market? (See summary forecast on facing page.)

Jan 8, 1958

By John F. Myers

Since the art of comminution has lain practically dormant for many years, it is very interesting that R. T. Hukki approaches the subject with a new concept. One is reminded of the research carried on by A. W. Fahrenwald of Moscow, Idaho, a few years ago. Fahrenwald mounted a steel bowl on a vertical shaft. The balls and ore placed in the bowl were rotated at fast speeds, thus simulating the supercritical speeds used by Hukki. The rolling action of the balls against the smooth shell liner has pretty much the same effect. The action is horizontal in one case and vertical in the other. Both researchers report good grinding activity.

Jan 8, 1958

SUDBURY ore processed by International Nickel Co. of Canada Ltd. was recovered for many years as two mill concentrates, one primarily of copper, and the other mixed pentlandite-pyrrhotite, But, Since iron content of the nickeliferous pyrrhotite concentrate was ten times its nickel value, capacity of smelting was limited by the need for slagging the excess iron. A process for recovering the iron con- tent was developed after some years of research and a $20-million plant was constructed to employ the new method. Built near Copper Cliff, Ont., the plant started operation early in 1956, scheduled for separate treatment of 365,000 tons of pyrrhotite each year. It is only the first unit of an installation which will have a capacity of more than 1 million tons per year of pyrrhotite. By early 1958, production totaled more than 200,000 long tons of 68 pct Fe pellets containing 0.003 pct P, 1.5 pct SiO2, 0.01 pct S, and 0.15 pct Ni.

Jan 8, 1958

By D. H. Yardley

GEOCHEMICAL investigation of trace elements in surface materials was begun near Ely, Minn., in 1953 along the basal contact of Duluth gabbro with Giants Range granite (Fig. 1). This article presents data on the distribution of copper and nickel in till and in stream sediments in the area and proposes an explanation for the types of distribution found. The Duluth gabbro, one of the world's largest basic intrusives, intrudes rocks which range in age from Keewatin to middle Keweenawan. Within the test area the gabbro is in contact with granite except for short sections where it is in contact with remnants of iron formation. Sulfide mineralization occurs within the gabbro, near and parallel to the basal contact for a distance of several miles. Schwartz and Davidson1 have described the geologic setting of the mineralization.

Jan 7, 1958

As a service to its readers, MINING ENGINEERING is publishing the mineral industry portion of the 1957 list of Accredited Undergraduate Engineering Curricula in the United States. This list, revised annually, is issued by the Education Committee of the Engineers Council for Professional Development, and covers all phases of engineering education. The AIME is actively represented on ECPD, which was jointly organized by the Founder Societies and various other groups interested in the professional recognition of engineers. ECPD is merely authorized by its constituent organizations to publish a list of accredited engineering curricula for use as desired by those agencies which require such a list. It has no authority to impose any restrictions or standardizations on schools. (Date following school refers to year of initial accrediting.)

Jan 7, 1958

By R. J. Woody

DESIGN of the most economic continuous counter-current decantation (CCD) circuit is based on selection of the number of stages and the wash volume that will give the minimum summation of the following items: 1) Capital and operating costs of the CCD circuit. 2) Capital and operating costs of the precipitation circuit. 3) Value of the dissolved product lost.

Jan 7, 1958

By S. E. Craig

UPON entering the Uranium Field it was a pleasant surprise to find almost absent two factors that have always been a problem to the lead-zinc miner: 1) milling cost per ton, and 2) transportation cost to the milling site. Another interesting condition was the fixed price for the product. Under such conditions it seems rather simple to calculate the economics of a mining venture when grade and tonnage of a uranium ore deposit is known. That is assuming, of course, there is a market for the ore. It has been quite generally assumed by operators that a guaranteed price carried with it a guaranteed market, a subject about which there has been a great deal of discussion in the past several months. The fixed price for uranium in crude ore, calculated to U3O8, varies only slightly in value per pound from rather low grade ore to rather high grade ore. It is by taking advantage of this slight variation in price per pound in certain ranges that miners and shippers may increase substantially the monthly returns from ore shipments.

Jan 7, 1958

By Rudolph G. Wuerker

WITH the growing complexity of ore dressing processes and the diversity of equipment, efficiency control has become increasingly important in beneficiation. In the case of iron ore dressing, there have been sporadic attempts1-3 to establish the optimum separation for various ores so that grade and recovery would be readily predictable. But no rigorous statistical analysis and graphical presentation of such tests could be found in the literature of this country. Tests Made with Iron Ores Expanding upon existing methods of plant supervision and efficiency control, an investigation was started in the ore dressing laboratory at the University of Illinois on the applicability of distribution analysis to iron ores. A sample of crude ore was obtained from the Ohio mine of Cleveland-Cliffs Iron Co. at Ishpeming, Mich., consisting mostly of alternating bands of hematite and siliceous gangue, both about ¼ in. wide. The ore was heavily coated with limonite, which often filled the cracks.

Jan 7, 1958

By John B. Gayle

PRESENT flotation processes depend almost entirely on the buoyant properties of air bubbles to effect separations of mineral and gangue, but there is no convenient method for measuring aeration in flotation cells. Consequently the relation between aeration and cell performance has not been definitely established. In connection with a comparative study of kerosene and froth flotation processes, a modification of the displacement method' was developed in which air escaping from the cell surface is measured with a wet-test meter. The arrangement shown in Fig. 1 is satisfactory for use with a number of cells and is not critical, except that care must be taken to use connections and tubing large enough to avoid excessive back pressures. Attempts to use smaller tubing resulted in back pressures that caused displacement of the liquid level in the receiver, so that some air was lost around the sides, an occurrence readily visible when measurements were taken with only water passing through the cell. With the arrangement shown, the manometer indicated an average reading of about ½ -in. water pressure. No loss of air was evident.

Jan 7, 1958

By M. H. Brady, J. G. Roscoe

Continental No. 1 This mine in Lisbon Valley has an orebody about 1200 ft long and varying from 250 to 70 ft wide. Average width is about 100 ft and stope heights average about 9 ft. It was developed by a 350-ft, 11º inclined shaft for trackless haulage, although a hoist and track are installed for auxiliary hoisting. Mining has been done from horizontal open stopes with random pillar support, using a HD5 tractor for mucking and a 4-wheel drive Gettman shuttle car for tramming. Slushers have been used to some extent in thin ore zones. Back support for stopes and haulage ways has been accomplished by rock bolts and landing mat. The most interesting feature of this mine has been pillar extraction. Mining was done under contract during the first year of operations with little regard for an orderly plan of stope layout or regularity of openings. Most of this work was done in the largest area of the orebody; consequently, pillar recovery has been accomplished under conditions which are far from ideal. However, a workable system has been developed which is competitive, both in cost and production rate, with open stoping.

Jan 7, 1958

By Edwin T. Wood

THE term blending as used herein refers to the mixing of ores assaying more than 0.20 pct U3O8 with low grade material assaying less than 0.20 pct U3O8. Such blending when properly understood and controlled will produce more total dollars of profit from many mining ventures. The question whether or not to blend is particularly vexing when an orebody is surrounded by an envelope of low grade material or separate tonnages of low grade exist which could be extracted coincident with the higher grade ores. Should any, all or part of this low grade be mined? If so, in what proportion and what is the limiting assay of the low grade material?

Jan 7, 1958

By H. L. Miaw, A. M. Gaudin, D. W. Fuerstenau

IN spite of considerable study,1-5 the nature of slime coatings in flotation is still not completely understood. However, phenomena that control flocculation and dispersion of colloidal systems are now interpreted in terms of electrical double layers."' Colloids will flocculate even though the particles carry the same charge, but when two dispersed colloids of opposite charge are mixed, flocculation ensues even more rapidly. Analogous phenomena seem responsible for slime coating on minerals in flotation systems. To shed new light on the issue it was considered desirable to devise a tool that would measure slime coatings. The usual method has been to examine photographs of presumably representative surfaces, after an intervening washing in running water. But such an examination is non-quantitative, and the changes in chemical environment represented by the washing may have removed the slime coatings that existed during flotation. To provide the possibility for a correlation with electrical double layer phenomena, the experiments were made with quartz, corundum, and iron oxide, for which electrokinetic data are available.8-12 Since the properties of the electrical double layers of these oxides depend on the pH of the solution, pH will be the most important variable. Furthermore, because the zero point of charge for silica, iron oxide, and alumina occurs at pH 3.7, 8, and 9.5, respectively, the relative charge on the slime and mineral can be changed over wide ranges. Because of its practical importance in quartz flotation, iron oxide powder was chosen as the slime. Also, its uniform composition, contrasting color, and ease of analysis make experimentation simple.

Jan 7, 1958

By R. L. Curfman

WHEN the Uranium Reduction Co. mill was put on stream in October 1956, one of the many operational problems was that the sand-slime separation circuits could not produce a satisfactory RIP feed, inasmuch as production greatly exceeded de- sign capacity. The original cyclone portion of the circuits consisted of two stages of three 14-in. cyclones in each circuit, as shown in the condensed flowsheet. The high percentage of +325 mesh material in the over- flows of these 14-in. cyclones was not consistent with good operation, and flow rates per ton of ore were high, indicating that not enough of the total solids in the ore was being rejected as sands. It was inferred by members of the metallurgical department that returning the underflows, or sand fraction, from these cyclones back into the drag classifiers was the primary reason for dirty feed.

Jan 7, 1958

By James W. Lower

IN developing the orebody on lower levels of the Star mine at Burke, Idaho, Hecla Mining Co. is faced with a serious problem in driving raises. Levels are at 200-ft intervals. As a raise is being driven between levels, at points about 70 and 130 ft from the sill, heavy pressure arches develop and the raise becomes extremely hazardous. Eventually, following a blast, caving occurs, making it impossible to recover the raise. In February 1957 it was decided to attempt sinking a small winze on the vein from the 5500 to the 5700 level. This shaft (winze-raise No. 2) was to be used as a raise prior to stoping. It was assumed, and correctly, that the heavy ground pressure could be controlled by timbering close to the bottom after each advance.

Jan 7, 1958

By Karl W. Mote

CALIFORNIA'S iron and steel industry had its beginning in San Francisco in 1849 when the first iron casting was poured at the old Union Iron Works. Soon after, in 1856 at Grass Valley, enough iron ore was smelted to supply pig iron for the castings of a quartz mill there. From 1880 to 1886, iron ore was produced from the Hotaling mine in Placer County and converted to pig iron in a local blast furnace using charcoal. From 1907 to 1914, the Noble Electric Steel Co. produced pig iron from iron ore mined at the Shasta Iron Co. mine, and followed this for three years in the production of ferro-alloys. Between 1917 and 1941, the State's industry in- creased its capacity for open hearth and electric furnace scrap treatment, but the real impetus was supplied by the need for more steel at the beginning of World War II. The result was the State's first integrated steel plant-the Kaiser Steel Corp. facilities at Fontana.

Jan 7, 1958

By Petri Bryk, John Ryselin, Rolf Malmstrom, Jorma Honkasalo

THE theoretical possibilities for the realization of flash smelting have been known for a long time. Calculations concerning the same can be found in previously published literature,1 and suggestions for its accomplishment in practice are described in patents on the subject. Likewise a smaller number of practical test results are known. Autogenous smelting is closely connected with flash smelting, since in flash smelting techniques it is possible to use the heat evolved by oxidation of the sulfides for the smelting process to such an extent that under certain conditions smelting can proceed without additional fuel. However, in the event that insufficient heat is available from the oxidation of the sulfide concentrates, then additional heat may be supplied by preheating the air, using oxygen enriched air, on burning additional fuel with the concentrate.

Jan 6, 1958