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Jan 1, 1934

By E. A. Moulder

The mining industry is continually faced with problems involving dewatering, pollution, water supply, leaching and hydrochemical mining and prospecting. Greater application of the principles of ground-water hydrology to solution of these problems promises improved operating efficiency, increased safety and better public relations. Estimating the magnitude of dewatering for a proposed mine may be a major factor in determining the feasibility of proceeding with mine development. Diverting the source of ground water to an abandoned mine may save costly treatment of acid-mine drainage. Development of a large ground-water supply near an ore deposit may enhance the possibilities of a leaching operation. Detection of certain dissolved minerals in water from springs or wells may lead to hitherto unknown mineral deposits. Current efforts of industry, educational institutions and government are making these kind of events more commonplace. Dewatering of Mines The magnitude of dewatering problems was dramatized by a flooding that occurred last year in a gold mine in South Africa. During drilling operations at the West Driefortein mine, a major fracture was encountered from which large volumes of water issued necessitating evacuation of 1350 men from the mine. Dewatering required an increase in pumping of more than 80 million gpd. Models of ground-water systems are being used to test alternate plans for dewatering mines. Using the models in conjunction with computer optimization programs may lead to minimizing costs of operation. In addition to computer simulation of aquifers associated with phosphate deposits in North Carolina mentioned in last year's report, two USGS employees developed a model to estimate the amount of pumping required to dewater a mine site in Colorado.

Jan 1, 1970

By THOMAS J. CLIFFORD

IN 1926, finer grinding began to be a feature of the milling practice of the Southeast Missouri lead district. Nothing since the adoption of flotation has caused greater changes and greater improvement in results. The trend toward finer grinding, with the consequent discarding of tailing at finer sizes, and consequent lower assays in lead, continued to progress until 1931, when the abnormally low price of lead brought a halt: that is, the better metallurgical results obtained would not offset the increased costs due to higher power and necessary maintenance. Since 1931 a slight tendency toward the discard of coarser tailing has taken place. , In 1926, larger rod mills i.12 ft. 1 in. by 6 ft. 6 in.) than any previously used in the district were installed in cue plant, and a new primary crushing plant, of greater capacity was built. This combination demonstrated immediately the better metallurgical results obtainable by finer grinding and all the mills now running have adopted the practice.

Jan 1, 1934

By A. W. Hesse

Twelve years ago, some coal-mine operators, mining engineers, oil and gas operators, Bureau of Mines engineers, geologists and state mine inspectors met in Pittsburgh, Pa. to discuss and solve if possible, the problems in connection with the drilling of oil and gas wells through or near coal mines and through the future coal reserves. Regulations were drafted and presented by O. P. Hood and A. G. Heggem of the Bureau of Mines.' . There was considerable discussion of the various articles, practically all of which appear in Bulletin 65, but the interest aroused at that meeting was short lived. Practically none of the important coal-producing states gave the matter the consideration it should have received. Notwithstanding the marked progress in safety work, coal mines still have an unenviable reputation for mine explosions. Our mining laws have become stricter and the enforcement, especially in Pennsylvania, more rigid, but what good will come from a rigid enforcement of the mining laws if some source of danger exists all around the mines, over which the operators have no control ? It is hardly necessary to recite all the cases of natural-gas explosions published in Bulletin 65, but with some of them I am especially familiar. In 1912, while visiting the Miners' Hospital, at Fairmont, W. Va., my attention was called to a patient swathed in in bandages so that no part of his face and hands were visible. He had not been told that his two sons, mere boys, had died of the burns they had received in the same accident—explosion due to natural gas leaking into a country mine at Peora, Harrison Co., W. Va.

Jan 1, 1925

By A. J. May

THE Star shaft is near the north boundary of the group of mining claims belonging to the Ground Hog Unit of the American Smelting and Refining Co., near Vanadium, N. Mex. The shaft bins and surface plant are served by a siding from the Atchison, Topeka and Santa Fe railroad, and this factor of railroad transportation influenced the choice of site. This paper describes the shaft sinking only, and does not cover the surface plant or other parts of the mine or its equipment. A. J. MAY is Engineer in Charge of Shaft Sinking, Ground Hog Unit, American Smeling and Refining Co, Vanadium, New Mexico. El Paso Meeting, October 1948. TP 2737 A. Discussion of this paper (2 copies) may be sent to Transactions AIME before Feb. 28, 1950. Manuscript received Nov. 29, 1948; revision received June 22, 1949. Experience with this shaft seems of interest because of the mechanical mucking, good rate of progress, and the costs obtained at the present level of labor and material costs. The shaft has four compartments, as shown in fig. 1. Equipment: Riddell Mucker: The mucking was done by a clamshell bucket and a Riddell mucker, which, as in other shafts sunk with this machine, consisted of a carriage mounted on axles with double flanged wheels that traveled back and forth on a swinging track, parallel to the long axis of the shaft (fig. 2 to 6). Three air motors were mounted on the carriage; one hoisted the clam, one operated the bucket opening and closing device, and the third moved the carriage along the track. The carriage was designed with guide shoes and could be hoisted to the surface in either skip compartment without trouble (fig. 4). During blasting operations the clam was tied on the rails and the carriage was hoisted up a few sets to protect it from flying rock. No attempt was made to hoist the carriage and clam together lest the clam catch in the timbers. The track on which the carriage operated was built of extra heavy 6 in. pipe with 1x2 in. strap welded on top for rails. A Yzx4 in. angle was welded on the bottom of the 6 in. pipe with a 1 in. round rod welded in the angle for a filler and additional strength. The end or cross pieces of the track which kept the track to gauge, were also made of reinforced, heavy 6 in. pipe and were bolted to the long members on which the carriage traveled (fig. 2 and 3). This section of track was used, instead of heavy railroad rails, for two reasons: (1) this section would bend before it snapped and was much safer for the men in the bottom; and (2) it was a better blasting shield, and protected the timbers better, in fact, only five wall plates were broken by blasting in 1926 ft of shaft, although 150 to 225 lb of 40 pct powder was loaded per round, depending on the ground conditions. The swinging track was supported by four % in. hoisting cables anchored to the end plates. There were also four safety cables fastened two to three sets above the carriage, which would catch the carriage if one of the supporting cables should fail for any reason (fig. 7). Clamshell Buckets: Two clams were used, each of % yard capacity, both manufactured by Blaw-Knox, Nos. 662 and 663. The No. 663 clam was 4 in. wider and 5 in. shorter than the No. 662, but seemed to dig and load more satisfactorily. It was easier to hoist and lower when it came up for repair. It did not turn over as easily, had less spill

Jan 1, 1951

By A. J. May

THE Star shaft is near the north boundary of the group of mining claims belonging to the Ground Hog Unit of the American Smelting and Refining Co., near Vanadium, N. Mex. The shaft bins and surface plant are served by a siding from the Atchison, Topeka and Santa Fe railroad, and this factor of railroad transportation influenced the choice of site. This paper describes the shaft sinking only, and does not cover the surface plant or other parts of the mine or its equipment. A. J. MAY is Engineer in Charge of Shaft Sinking, Ground Hog Unit, American Smeling and Refining Co, Vanadium, New Mexico. El Paso Meeting, October 1948. TP 2737 A. Discussion of this paper (2 copies) may be sent to Transactions AIME before Feb. 28, 1950. Manuscript received Nov. 29, 1948; revision received June 22, 1949. Experience with this shaft seems of interest because of the mechanical mucking, good rate of progress, and the costs obtained at the present level of labor and material costs. The shaft has four compartments, as shown in fig. 1. Equipment: Riddell Mucker: The mucking was done by a clamshell bucket and a Riddell mucker, which, as in other shafts sunk with this machine, consisted of a carriage mounted on axles with double flanged wheels that traveled back and forth on a swinging track, parallel to the long axis of the shaft (fig. 2 to 6). Three air motors were mounted on the carriage; one hoisted the clam, one operated the bucket opening and closing device, and the third moved the carriage along the track. The carriage was designed with guide shoes and could be hoisted to the surface in either skip compartment without trouble (fig. 4). During blasting operations the clam was tied on the rails and the carriage was hoisted up a few sets to protect it from flying rock. No attempt was made to hoist the carriage and clam together lest the clam catch in the timbers. The track on which the carriage operated was built of extra heavy 6 in. pipe with 1x2 in. strap welded on top for rails. A Yzx4 in. angle was welded on the bottom of the 6 in. pipe with a 1 in. round rod welded in the angle for a filler and additional strength. The end or cross pieces of the track which kept the track to gauge, were also made of reinforced, heavy 6 in. pipe and were bolted to the long members on which the carriage traveled (fig. 2 and 3). This section of track was used, instead of heavy railroad rails, for two reasons: (1) this section would bend before it snapped and was much safer for the men in the bottom; and (2) it was a better blasting shield, and protected the timbers better, in fact, only five wall plates were broken by blasting in 1926 ft of shaft, although 150 to 225 lb of 40 pct powder was loaded per round, depending on the ground conditions. The swinging track was supported by four % in. hoisting cables anchored to the end plates. There were also four safety cables fastened two to three sets above the carriage, which would catch the carriage if one of the supporting cables should fail for any reason (fig. 7). Clamshell Buckets: Two clams were used, each of % yard capacity, both manufactured by Blaw-Knox, Nos. 662 and 663. The No. 663 clam was 4 in. wider and 5 in. shorter than the No. 662, but seemed to dig and load more satisfactorily. It was easier to hoist and lower when it came up for repair. It did not turn over as easily, had less spill

Jan 1, 1951

By Carl E. Swartz

ALTHOUGH a number of articles appeared during the war advocating the use of cadmium in lead-tin solders, very little information of value can be found in the literature regarding the properties of solders containing cadmium. In most of the published articles the cadmium seems to have been considered merely as a partial substitute for tin in a tin-lead alloy rather than as an essential constituent of a ternary alloy. The primary object of the substitution of cadmium for tin was to lessen the amount of tin required, at a time when the latter was scarce and high-priced, and thus to produce a cheaper solder. While this object was accomplished, the new properties resulting from a change from a binary lead-tin alloy to a ternary lead-tin-cadmium alloy were not given proper consideration in many cases. For the past few years, the American Smelting & Refining Co. has been marketing a very considerable amount of cadmium in the form of lead-tin-cadmium alloys for use as solders for certain special purposes, and the successful use of these solders suggested that if more extensive knowledge were available concerning the properties of lead-tin-cadmium alloys of various compositions their field of usefulness might be materially extended. The investigation described in the present paper was undertaken to obtain this information and, by means of tests under conditions approaching those of practical use, to determine the suitability of cadmium solders for various purposes. CHARACTERISTICS AND REQUIREMENTS OF SOLDERS IN GENERAL General Physical Properties.-When cast into bars, solder should present a smooth and bright appearance free from oxide inclusions and bubbles. Ductility should be as great as possible without sacrificing tensile strength, and vice versa. Hardness and specific gravity are not of any great importance. Melting Characteristics.-The melting or solidification range is important. This statement applies both to the extent of the range and to the actual temperature at which complete solidification occurs. A rather narrow solidification range is desirable in soft solders in order that solidification may take place quickly. The solder should have high fluidity at temperatures only slightly above its melting range. For a

Jan 1, 1928

Jan 1, 1932

By P. A. Toynbee

An experimental air-slide classifier1 has been applied to the de-dusting of ground dolomite in an attempt to produce a grade of -30 +150 mesh (B. S. Sieves) material from a raw material containing 30-35% of the -150 mesh fraction. Air flows varying between 1.5 and 2.5 cu ft/sec sq ft of screen area were used. The throughput of dolomite was between 80 and 100 lbs/h. inch of screen width. The size analyses of the de-dusted material and of the original dolomite are shown in table at right. The proportions of the +100 mesh material in the feed and in the de-dusted products have been used to calculate materials balances, on the assumption that there is no loss, as dust, of this +100 mesh fraction. By interpolation, it can be shown that a de-dusted product recovery of 68.5% will be obtained at an air flow of 2.13 cu ft/sec sq ft of screen area. The feed material contains 68.5% of +150 mesh material, so that if the de-dusting gave a perfectly sharp cut, the product would contain no material less than 150 mesh. Further calculations based on the size analyses, show that, at an air flow of 2.13 cu ft/sec sq ft of screen air, the -150 mesh fraction in the de-dusted product will fall just below the specified maximum limit of 5%.

Jan 1, 1964

By J. W. Downey, A. E. Dwight, R. A. Conner

In a previous paper' we have reported the existence of a number of AB2 Laves phases in which A is a member of the scandium group (including the 1an-

Jan 1, 1967

By George A. Packard

THE experiments here described were made under my supervision while temporarily acting as head of the Department of Metallurgy at the Missouri School of Mines, at Rolla. The work was done by Messrs. W. E. Brown, W. C. Richards, and F. L. L. Wilson, and the description of the results forms a portion of a thesis presented for the degree of Bachelor of Science. These results are submitted because I have seen no description of the application of pot roasting to the treatment of a copper-concentrate. This work followed that already described in the discussion of the ' Lime-Roasting of a Galena-Concentrate,"' and was similarly occasioned by the lack of a furnace of the reverberatory type in which the copper-concentrates could be smelted. The material for the tests was a mixture of three lots available. The first consisted of 8-mm. jig-concentrates and the second of 0.5 mm. table-concentrates, from the San Juan district, Colo. Both contained pyrite, chalcopyrite and galena. The third was a lot of copper-ore, found in the laboratory, which had been crushed through 8-mm. screen, and had at some previous time, before the laboratory roasting-furnace was torn down, received a partial roasting. The analyses of these ores are given in Table I. In order to determine the applicability of pot-roasting as to each lot of ore, and the effect of varying proportions of lime, six preliminary tests were made in a " size N " Battersea crucible, 9 in. high by 6 in. in diameter at top, with a 5/8 in. hole bored through the bottom. The crucible was set in the upturned elbow of a 2-in. pipe, the joint being luted with clay; and air was obtained from a receiver supplied by a compressor. The

Jan 1, 1908

By George A. Komadina

From its modest beginning in 1957 with one mill grinding section handling 3000 tpd Pima has steadily expanded. In July 1966, work was completed that allowed the concentrator to treat in excess of 18,000 tpd. Almost immediately Pima embarked on another expansion program that will increase plant capacity to 30,000 tpd during the summer of 1967. This repeated expansion has corresponded with the development of additional low-grade ore deposits and with the improved operating economics realized by handling larger masses of material. Early in the life of Pima it was known that a mineralized area was present on the flanks of the high-grade orebody which systematic drilling had shown to be a low-grade copper orebody. Many months of engineering studies revealed that this was sufficient to allow Pima to compete with other large scale, low-grade copper operations in the Southwest.

Jan 11, 1967

By C.H. Lorig, M.C. Udy

Through the years much interest has been centered in attempting to develop a direct method of iron-ore reduction, to replace or supplement the present indirect blast-furnace process. It would not be difficult to produce a list of more than 500 patents dealing with the direct production of iron and steel, but the few of this type of process that have proved successful do not produce in competition with the blast furnace; they produce special products. A survey of the literature reveals that the equilibrium conditions for the reduction reactions (iron oxides with carbon monoxide and with hydrogen) have been fairly well established but that data on the rate of reaction are discordant, although the genera1 effects of the variables are known. This dissertation deals with the rate of reduction of a magnetite concentrate with hydrogen. The following variables have been studied: bed depth, gas velocity, particle size and temperature. The behavior of a single particle was also studied. Literature Two general factors should be considered in a study of reduction of iron oxide: (I) equilibrium relations, and (2) rate of reaction. The first factor, equilibrium, has received the attention of many investigators and the equilibria Fe304-FeO-H2-H2O, Fe3O4-FeO-CO-CO2, FeO-Fe-H2-H2O, FeO-Fe-CO-CO2 are fairly well established. Of the second factor, the rate of reaction, much less is known. Data are comparatively scarce and there is very little concordance. The discordance probably results from the large number of variables influencing the reactions. However, the general effect of the variables is known. Among these variables are temperature, gas velocity, particle size, porosity, gas composition (distance from equilibrium), presence of impurities, greater or less prevalence of side reactions, and even design of the apparatus itself. Wetherill and Furnasl published an excellent paper in 1934. They point out that any one or more of five processes (the chemical reaction, diffusion of the reactant through the gas film, diffusion of the reactant through the solid phase, diffusion of the reaction product through the solid phase, or diffusion of the reaction product through the gas film) may be the slow process, and thus the rate-controlling process. It is regretted that the work of these authors was limited to experiments at One temperature, and that the range of gas compositions was limited. Langmuir2 has shown that heterogeneous reactions take place at phase boundaries.

Jan 1, 1943

By M. C. Udy, C. H. Lorig

Through the years much interest has been centered in attempting to develop a direct method of iron-ore reduction, to replace or supplement the present indirect blast-furnace process. It would not be difficult to produce a list of more than 500 patents dealing with the direct production of iron and steel, but the few of this type of process that have proved successful do not produce in competition with the blast furnace; they produce special products. A survey of the literature reveals that the equilibrium conditions for the reduction reactions (iron oxides with carbon monoxide and with hydrogen) have been fairly well established but that data on the rate of reaction are discordant, although the genera1 effects of the variables are known. This dissertation deals with the rate of reduction of a magnetite concentrate with hydrogen. The following variables have been studied: bed depth, gas velocity, particle size and temperature. The behavior of a single particle was also studied. Literature Two general factors should be considered in a study of reduction of iron oxide: (I) equilibrium relations, and (2) rate of reaction. The first factor, equilibrium, has received the attention of many investigators and the equilibria Fe304-FeO-H2-H2O, Fe3O4-FeO-CO-CO2, FeO-Fe-H2-H2O, FeO-Fe-CO-CO2 are fairly well established. Of the second factor, the rate of reaction, much less is known. Data are comparatively scarce and there is very little concordance. The discordance probably results from the large number of variables influencing the reactions. However, the general effect of the variables is known. Among these variables are temperature, gas velocity, particle size, porosity, gas composition (distance from equilibrium), presence of impurities, greater or less prevalence of side reactions, and even design of the apparatus itself. Wetherill and Furnasl published an excellent paper in 1934. They point out that any one or more of five processes (the chemical reaction, diffusion of the reactant through the gas film, diffusion of the reactant through the solid phase, diffusion of the reaction product through the solid phase, or diffusion of the reaction product through the gas film) may be the slow process, and thus the rate-controlling process. It is regretted that the work of these authors was limited to experiments at One temperature, and that the range of gas compositions was limited. Langmuir2 has shown that heterogeneous reactions take place at phase boundaries.

Jan 1, 1943

By Walter Weeks

CONSIDERABLE difference of opinion seems to exist as to whether the rate of air flow when a fan is placed on a given duct should be determined by the use of static pressure or total pressure characteristics. A little study will show that both methods are correct. Assume that a fan is connected to a duct by an expansion piece as shown in Fig. 1, and that steady flow is established. Considering the atmospheric pressure as zero pressure, let the static head at the outlet of the fan be h and the velocity at this point be v1. The total head at the outlet is then h + v1/2g? The total head at this point must be equal to the total head at the end of the duct plus the losses that have occurred between the two points. Let f be the friction loss in the straight duct, s the shock loss in the dif- fuser, and V2 the velocity at the end of the duct. Then h+ v12/2g=v22/2g + f + s FIG. 1.-FAN ON DUCT. A curve showing the value of the left-hand side of the equation for different rates of flow is the total pressure characteristic of the fan, while a curve showing the value of the right-hand side is the total pressure characteristic of the duct. If these two curves are plotted on the same chart, the intersection indicates the rate of flow when steady flow is established.

Jan 1, 1930

By H. A. Wilhelm, P. Chiotti, G. A. Tracy

A summary of analytical, X-ray, thermal, and metallographic data obtained in the study of the Mg-U system is presented. No intermetallic compounds are formed by these two elements, and their mutual solubility is limited at temperatures up to 1255°C. The compositions of the liquids which coexist at 1135°C under a pressure of 3 atm are 0.14*0.05 wt pet U in magnesium, and 0.004 wt pet Mg in uranium. The solubility of uranium in magnesium decreases to 0.0510.03 wt pet at 675OC, and to about 0.0005 wt pet at 650°C. Due to the reactivity of both uranium and magnesium toward crucible materials, the choice of a suitable crucible presented a problem. Crucibles made from high purity magnesia to which 10 wt pet MgF2 was added to reduce porosity proved to be satisfactory. Some observations made with the use of other crucibles are given. THIS investigation was made to establish the phase diagram for the Mg-U system. Ahmann,' formerly of the Ames Laboratory, did some work on the system. He used several methods in an attempt to prepare Mg-U alloys. One of the methods involved the reduction of UF, with a large excess of magnesium. In these experiments, the magnesium wet the surface of the uranium, but there was no evidence for compound formation. The maximum solubility of magnesium in uranium was indicated to be 0.01 wt pet. In another set of experiments, uranium chips as well as uranium powder were heated in contact with molten magnesium in a graphite crucible for periods of time up to 48 hr. A reaction layer was found at the Mg-U interface in several instances. X-ray analysis of the layer material showed the presence of UC and some additional unidentified lines which were interpreted as indicating the possibility of an intermetallic compound of uranium and magnesium. These studies indicated the maximum content of magnesium in uranium to be 0.043 wt pet. One sample of magnesium which had been heated at 1025°C in contact with excess uranium was found by chemical analysis to contain 0.275 wt pet U. Rules, based on empirical or semi theoretical considerations, which attempt to predict the alloying behavior of metals have been presented in the literature. Although these rules are not infallible, they nevertheless serve as useful guides. Using them, several generalizations can be made concerning the Mg-U system. According to Hume-Rothery's' atomic

Jan 1, 1957

By T. M. Morris

R. T. Hukki (Finland Institute of Technology, Helsinki, Finland)—Two schools of thought are developing concerning the order of the rate of flotation. The paper by Morris is intended to show experimental evidence in favor of the first order rate. Arbiter, on the other hand, has presented an earlier paper" to demonstrate the validity of the second order rate equation. Unfortunately his method of plotting is open to criticism, as pointed out by Morris." A more sensitive method of plotting has been described by the writer,= whereby the data presented by Arbiter demonstrate the superiority of the second order plot. The general rate equation may be written in the following forms for the integrated first and second order equations: (A) t = -1/k In Co-R/Co (first order) [4] 1 (B) 1/t = - kCo + kCo2 1/R (second order) As a first approximation the value of Co may be taken as a unity, 100 pct or 1. Whether or not this is the case in all tests performed by Morris is impossible to judge, owing to the fact that the flotation times are extremely short, e.g. 150 sec in tests A. It would, indeed, be very interesting to know what the total recovery R would be after 1 hr of flotation, for example, instead of after 150 sec. Certainly there are circumstances when C, approaches unity within a very small margin of error. Morris has used the same approximation in his example D "since the feed to this cleaner

Jan 1, 1954

By Jerome Alexander

THE object of this paper is to show that many of the important phenomena of metals and alloys are due to the facts that, at some stage, metals and alloys, or some of their constituents, are in a colloidal state and that a portion of the metal or alloy tends to remain in this state. The so-called amorphous phase in pure metals is an isocolloid, consisting of colloidal groups of metal molecules that may be dispersed in still more finely subdivided metal; these colloidal particles are not truly amorphous, but may consist, in part, if not entirely, of ultramicroscopic crystals; as a result the expressions amorphous phase and amorphous theory might be replaced by the expressions colloidal phase and colloidal theory. Any substance is in the colloidal state when the constituent particles consist of molecular or atomic groups, whose size varies approximately from about 100µµ down to about 5µµ, that is from just below the limit of microscopic resolvability to the dimensions commonly ascribed to the larger molecules. Colloidality involves no assumption as to the shape, internal structure, or orientation of the colloidal particles; size alone is the critical factor. A colloidal system may therefore contain crystalline groups, or amorphous groups (non-crystalline, random or haphazard clusters), or a mixture of the two. All colloids consist of at least two phases, the subdivided substance, or dispersed phase, and the substance into which this is subdivided, the dispersion medium. It is not necessary that there be any chemical difference between the dispersed phase and the dispersion medium. As molecular forces are extremely powerful, their application may produce marked changes in the physical properties of metals. It is doubtful whether metal in the interior, especially of large masses, possesses the same properties as that on or near the surface, which alone is open to, inspection.

Jan 10, 1920

By Andrew Hodge

ISSUES IN MINING LABOR The examination of mining labor issues is often confined to health, and safety. There are other issues, including the present state of mining manpower availability and utilization, and the nature of mineral industries' industrial relations, which are worthy of consideration. The state of the labor market for mining skills, the availability and utilization of mining engineers and related disciplines, the state of research and its employment of scientists and engineers, and the condition of mining industrial relations with all these groups, all have an important effect on the viability and economic health of the minerals production sector. PRODUCTION LABOR Why examine an industry's production labor market? People involved in an industry should be aware of what labor supplies will be relative to industry requirements. This advance information allows industry and government to plan ahead to alleviate problems by moving to affect labor supplies or to accommodate production to expected labor supplies. This is less costly and less painful than responding after the fact to labor market changes. Any industry requires some form of labor. Labor is especially important to the mining industry. Mining labor is well paid. Average annual earnings are higher than in manufacturing. Average hourly wages are also higher. Payroll costs form a high percentage of total cost in coal mining and nonmetallic minerals mining. In metal mining the percentage is comparable to the average for manufacturing. Payroll cost in oil and gas extraction is quite low, but a major proportion of cost is in the form of income to proprietors, i.e., unincorporated businesses. Mining labor is worthy of specific attention. The minerals extraction labor is unique in many ways. Mining labor and especially underground miners are differentiated from other "unskilled" labor. Miners cannot be considered as part of a larger labor pool. The mining labor market has exhibited a unique combination of characteristics. Mining is the only large sector of United States employment in which hourly wages are high and continuing to rise, yet employment declines. Although industry has introduced new labor-saving investments, and labor requirements continue to decline, there is evidence of a mining labor shortage. Specific problems have arisen in the mining labor market such as a present labor shortage in nonfuels mining. Understanding the causes and remedies for these specific problems is also important. These various problems and questions may be handled in a unified manner by examining the relationships of certain economic variables. The relationship that exists between changes in output, employment, labor productivity, and hours worked per week may be stated explicitly:

Jan 1, 1976

By J. Boldy

Discovery of the Delbridge massive sulfide deposit in the Noranda district of Quebec resulted from an appreciation of the significance of a mercury leakage halo as a lithochemical pathfinder to blind ore. Its location, relative to a geologically inferred ore-bearing horizon within complex volcanic stratigraphy was also a factor. Systematic sampling of microfractures present in outcrops delineated a diagnostic anomaly, drawing attention to an area considered prospective for buried ore. The massive sulfide deposit was subsequently found to be blind and topped at the 110-m (360-ft) level.

Jan 1, 1985