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The most frequently applied project evaluation criteria are the Net Present Value, the Internal Rate of Return, and the Pay Back Period. Unfortunately, the Internal Rate of Return and the Pay Back Period, if interpreted according to their traditional definitions, easily produce results which contradict the Net Present Value. The reasons for the Net Present Value incompatibility of the two criteria are that these criteria have not been adequately defined and so new, complete definitions are recommended. The concept of the True Rate of Return is proposed as a substitute for the interest rate that the Internal Rate of Return has been believed to represent. The redefined Internal Rate of Return and Pay Back Period criteria, as well as the True Rate of Return are all Net Present Value compatible and can, therefore, serve as independent project evaluation criteria. Also, the correct approach to the evaluation of mutually exclusive alternatives and the status of the often neglected borrowing projects in project evaluation are found to be quite important.

Jan 1, 1991

By O. Ofor

Finely-ground hematitic ore, too high in silica (quartz) to be commercially viable, was treated by emulsion flotation. A three-component emulsion mixture was used at temperatures ranging from ambient (22° C) to 30° C, 40° C, 49 °C, 59° C and 68° C. The optimal emulsion dosage and composition at ambient temperature were used to determine that dosage for higher-temperature flotation tests. The crushed ore (100%, -8 mesh) was repeatedly washed with tap water, and the filtrate's ionic content was analyzed. The separation efficiency values (a measure of the selective separation and concentration of hematite from gangue minerals) demonstrated temperature dependence, with marked increases at temperatures above ambient. The optimal separation efficiency occurred within the range from 30° C to 60° C. The improved separation efficiencies at temperatures exceeding ambient are explained by quartz depression. This depression is attributed to: • the precipitation of quartz-activating cations, principally calcium and magnesium, at increasing temperature; and • temperature's effect on the collector's solubility and attachment to the aqueous hematite surface.

Jan 1, 1993

By Frank W. Bowdish, T. M. Plouf

The purpose of this writing is to make available additional data, not previously published, on the zeta potential at various pH values of chrysocolla from the Inspiration mine, Arizona. Much research has been performed on chrysocolla, its physical properties, and its flotation, the results of which have not yielded a commercially acceptable flotation process for its recovery. The present data were collected and are presented to further advance chrysocolla research. Experimental For this investigation a carefully prepared sample of chrysocolla was used. This sample was obtained by crushing specimens from the Inspiration mine and picking out by hand the solid blue particles at -3+8 mesh, by grinding these to 10 mesh and repicking the +28 mesh sizes, by cleaning this product using magnetic separation, and by grinding and screening the material into fractions for final magnetic treatment on a Frantz Isodynamic Separator. All testing was done on the -100+150 mesh fraction. A chemical analysis was made on a portion of this fraction which was washed in dis-

Jan 1, 1974

By Samuel L. Hoyt

The present report represents that part of the work that has been done by the War Minerals Investigation, Manganese Section, of the Bureau of Mines, on the use of manganese alloys in open-hearth practice. The magnitude of the work and the number of people participating in one way or another make it difficult to acknowledge adequately the services of all who have contributed to the success of the work. It would be amiss, however, to pass to the body of the report without mentioning the hearty cooperation and willingness to assist of the various manufacturing interests. With such a sympathetic attitude toward this investigation, our work was assured of success. Inasmuch as the unhappy circumstances that rendered this investigation necessary have now passed, this report is made in the hope that the results may prove of some permanent value to the peace-time operation of our open-hearth industry. Broadly speaking, the purpose of the manganese investigation was to consider the most suitable means of utilizing our domestic supply of manganese and thus relieve, to the maximum extent possible, our shipping of the burden of importing manganese ores. It was not held that any decided shortage of manganese was imminent but rather that every legitimate means should be utilized for making our ship tonnage available to European service. While we have considerable metallic manganese in this country, it occurs largely as a low-grade mixture with iron or silica or with both. The open-hearth investigations, therefore, were carried on to determine the extent to which domestic or low-grade alloys could properly be substituted for high-grade alloys without materially impairing the steel production as to either quality or quantity. Also, it was held that such an investigation would yield valuable results to the steel industry as well as contribute, in no small way, toward directing future investigations in the same field. To the practical steel manufacturer, especially to him who felt no immediate concern about

Jan 1, 1920

By Bruno Bussière, Michael Aubertin, Robert P. Chapuis

Covers with capillary barrier effects (CCBE) have been used in recent years as gas barriers for the isolation of wastes, including reactive mine tailings. Capillary barrier effects help to maintain a high degree of saturation in the moisture retaining layer, which then reduces gas flux. Various factors affect the degree of saturation of the moisture retaining layer in a CCBE, such as the material water retention characteristics and layer thickness. Slope geometry can also influence the hydrogeological behaviour of a CCBE, but this factor has frequently been ignored in the past. In this paper, the authors show some results of a numerical study that illustrates the influence of slope on the behavior of capillary barriers made of different types of material. The numerical model calculations are based on an actual case of a CCBE constructed in northern Quebec. This investigation shows that the water content profile is greatly affected by the position along the slope. Thus, it is necessary to evaluate the influence of the geometry to properly establish the performance of a cover system.

Jan 1, 2000

[Note.—The paper of Mr. Hoffman on " Practical Results in the Magnetic Concentration of Iron-Ore " (page 602); that of Mr. Langdon on "The Use of Magnetic Concentrates in the Port Henry Blast-Furnaaces" (page 599); and those of Mr. Landis on "The Determination of Iron in the Tails from Magnetic Concentration " (page 609) and "Note on Sampling Iron-Ore" (page 611), were all prepared as contributions to this discussion.] The papers of Mr. Langdon and Mr. Hoffman were presented. W. H. Hoffman, Croton Mines, N. Y.: I will add a few remarks, by way of answer to inquiries for further details. The Croton Mines are particularly well located for cheap mining. The ore-bed is very large, and so lies in relation to the railway tracks of the Harlem and other railroads that a very large proportion of our mining for several years to come can be done above these tracks. The concentrating-mill is now 400 feet from where we are working in the quarry. In blasting we never remove less than 2500 tons at a blast,

Jan 1, 1892

By M. Bailey-McEwan

The application of refrigeration on deep South African gold mines is mostly achieved through the medium of chilled water which is produced in central installations either on surface or underground. The amount of refrigeration has been increasing rapidly over recent years, and the total installed capacity on all gold mines now exceeds 1000 MW(R), with annual running costs exceeding R100 million for electricity alone. Hence, there are strong incentives to design such installations for optimal cost-effectiveness. The duty required of these installations varies considerably, owing to daily and seasonal climatic changes and the varying nature of the water demand. It has long been recognized that a computer program to predict installation performance as a whole under any given conditions would be highly desirable. An interactive computer program, CHILLER, is described which enables the user to build an installation, consisting of any configuration of cooling towers, water storage reservoirs and packaged water chilling machines. Externally-dictated conditions such as the weather and chilled water demand must be specified, and all quantities under control of the installation, including internal water flow rates and compressor capacity regulators, must be set. The time-varying performance of the installation can then be simulated. Examples are given of the application of the program in the design of a new installation, and in evaluating the effect of any modifications to existing installations.

Jan 1, 1987

By Thomas J. Peters

The U.S. Bureau of Mines studied the 3,500-acre Winegar Hole study area, Idaho, a legislatively proposed (101st U.s. Congress) addition to the Winegar Hole Wilderness, Wyo.; it adjoins the western boundary of the Wilderness at the Idaho-Wyoming border, about 15 m; east of Ashton, Idaho. The study was part of an Idaho Land Assessment Program to provide minerals information for land-use decisions, and ensure domestic mineral supplies. The study area is an east-west elongated, wooded plateau south of Falls River. Although the area is covered with surficial glacial deposits, it is probably underlain by volcanic flows; light-colored and mafic flow rock were noted in sparse outcrop. No mines, prospects, mineralized areas, or mineral resources were found in the study area during a literature and field search. The only nearby prospects include geothermal and rock aggregate (volcanic cinder) sites, and several placer claims. Although the Winegar Hole study area lies within a region of potential geothermal resources, no evidence of geothermal activity was observed. Rock in the area does not split into flat slabs, which could be useful as dimension stone, and would require crushing to be used 8S aggregate. Alluvium (placer) samples contain less than SO.01 per cubic yard gold (at a $350 per oz price); alluvial deposits are too small to contain gold resources.

Jan 1, 1992

By Boyd Dudley

The material presented in this paper is an abstract of a thesis submitted by the writer to the faculty of the Massachusetts Institute of Technology, as part requirement for the degree of Master of Science. The investigation was undertaken at the suggestion of Prof. H. 0. Hofman, and it was conducted, under his direction, in the laboratories of the Mining Department of the Institute. The purpose of the work was, first, to study some of the reactions that have been considered as a part of the mechanism of the chloridiz-ing roast, and second, to study the conditions under which nickel oxide and copper oxide may be chloridized. While the production of chlorine gas by various reactions during the chloridizing roast may not be primarily useful in the chloridation of metal oxides and compounds, it nevertheless serves a useful purpose in preventing the dissociation and decomposition of chlorides once they have been formed; for example, the dissociation of cupric chloride into cuprous chloride and chlorine. Therefore it was thought that a study of some chlorine-producing reactions would prove of interest, and the first series of experiments dealt with this phase of the subject. he object of the latter part of the work was to show the possibility of treating heavy sulphide ores, such as those of Sudbury, Ontario, containing much iron and small amounts of copper and nickel, by chloridizing and removing the copper, leaving an iron-nickel oxide product suitable for smelting in the blast furnace for nickel-bearing pig iron. The chloridizing of the copper would, of course, be preceded by a roast for the removal of sulphur, the sulphur oxides being available for the manufacture of sulphuric acid, if under the local conditions this product would be of commercial value. Reactions of the Chloridizing Roast Reaction of Sodium Chloride, Sulphur Trioxide, and Oxygen.—The first reaction studied was that involving the production of chlorine

Jan 1, 1915

By John S. Marshall

The purpose of this paper is to present to the profession data and experience obtained over a period of 5 years in the operation of 87 shaker-conveyor units, and the production of 2,169,638 tons of run-of-mine anthracite coal. The data are not generally available and should be of interest to those concerned with the operation of anthracite and bituminous mines. To simplify comparison, a ton of 2000 lb. of raw run-of-mine coal has been used as the production unit throughout this paper. Mining Methods and Equipment The mine is in the vicinity of Wilkes-Barre, Pa., in the Buried Valley area of the Susquehanna River. Seven veins were mined, varying in thickness from 18 in. to 8 ft. The cover overlying the veins varied from 200 to 800 ft. Three-fourths of the 1200 acres of property was covered with from 100 to 200 ft. of water-bearing gravels and clays, which prevented first mining under rock cover less than 50 ft. and pillar removal under rock cover less than 100 ft. The property was opened by two shafts sunk on the mountainside to avoid the sand and gravel present in the river valley. The veins dipped an average of 5" from the shafts. In certain areas the veins were practically flat and in some places a reverse pitch as high as 5" was encountered for short distances. A daily output of 3800 tons was hoisted on a two-shifi; hoisting operation. The mining consisted of 75 per cent pillar removal, and of the total production in the later years of operation 80 per cent was loaded by shaker conveyors, chain conveyors and scraper loaders. Shaker conveyors accounted for 70 per cent of the total output; chain conveyors and scraper loaders for 10 per cent. All conveyor work was double-shifted and 25 per cent was triple-shifted. A total of 87 shaker-conveyor units were on the property, of which 75 were kept in operation at all times.

Jan 1, 1940

By John S. Marshall

The purpose of this paper is to present to the profession data and experience obtained over a period of 5 years in the operation of 87 shaker-conveyor units, and the production of 2,169,638 tons of run-of-mine anthracite coal. The data are not generally available and should be of interest to those concerned with the operation of anthracite and bituminous mines. To simplify comparison, a ton of 2000 lb. of raw run-of-mine coal has been used as the production unit throughout this paper. Mining Methods and Equipment The mine is in the vicinity of Wilkes-Barre, Pa., in the Buried Valley area of the Susquehanna River. Seven veins were mined, varying in thickness from 18 in. to 8 ft. The cover overlying the veins varied from 200 to 800 ft. Three-fourths of the 1200 acres of property was covered with from 100 to 200 ft. of water-bearing gravels and clays, which prevented first mining under rock cover less than 50 ft. and pillar removal under rock cover less than 100 ft. The property was opened by two shafts sunk on the mountainside to avoid the sand and gravel present in the river valley. The veins dipped an average of 5" from the shafts. In certain areas the veins were practically flat and in some places a reverse pitch as high as 5" was encountered for short distances. A daily output of 3800 tons was hoisted on a two-shifi; hoisting operation. The mining consisted of 75 per cent pillar removal, and of the total production in the later years of operation 80 per cent was loaded by shaker conveyors, chain conveyors and scraper loaders. Shaker conveyors accounted for 70 per cent of the total output; chain conveyors and scraper loaders for 10 per cent. All conveyor work was double-shifted and 25 per cent was triple-shifted. A total of 87 shaker-conveyor units were on the property, of which 75 were kept in operation at all times.

Jan 1, 1940

By Pierre Bernard

Contents of the presentation ? Overview of Brunswick 12 Mine ? Brief description of the mine geology ? Summary of the current Mineral Reserves and Additional Mineral Resources ? Review of the ongoing mining remnants evaluation process, particularly emphasizing the integrated work between the mine geologists, the mine engineers and the metallurgists ? Challenges and opportunities to extend the mine life

Apr 1, 2005

By H. Groeneveld, C. A. Connally, P. J. Hoenmans, J. J. Justen, W. L. Mason

A miscible displacement pilot using a slug of LPG driven by separator gas was conducted in the Cardiurn reservoir of the Pembina field. The injection pattern was a 10-acre, inverted, isolated five-spot. Upon completion of the LPG-gar phase, an experiment was conducted using a slug of water followed by gas. Calculated performance of the pilot is compared with actual performance. Equations are developed to calculate the distribution of LPG into zones of varying permeability, to estimate the progress of the flood at different times in the various zones and to estimate gas rates after breakthrough. The analysis indicates that permeability stratification was a dominant factor in controlling oil recovery and that oil was completely displaced from the swept pore volume. The results of the pilot indicated that miscible flooding is a practical means of pressure maintenance in this reservoir. The total recovery from the pilot area was good in spite of the early breakthrough of LPG. The effects of stratification were reduced by injecting a slug of water into the partially swept reservoir. INTRODUCTION The Pembina field,' located in Alberta, is the largest oil field in Canada and one of the largest in the North American continent. The reservoir is a stratigraphic trap producing from the Cardium sand. Neither bottom water nor free gas has been found. The recovery of oil by the natural depletion mechanism has been estimated at 12.5 per cent. Pressure maintenance studies of various areas have indicated that the recovery can be increased 21/2 times by water flooding, and a large area of the field is presently under water flood. However, reservoir studies of the North Pembina area indicated that miscible flooding might be competitive with water flooding. A pilot test was conducted to evaluate the performance of a miscible flood. A 10-acre, inverted, isolated, five-spot pattern was selected for the pilot. The pattern area was large enough to minimize wellbore fracturing effects and contained sufficient oil to provide significant working numbers. The performance of each of the four producers could be evaluated individually and compared. In the event of breakthrough in one direction, the effect would be isolated from the other producers. The use of a single injector minimized the volume of LPG required, and, because of the high mobility of gas, one well was sufficient to inject the necessary daily volume to replace the high rate of production. With four producers, the test could be completed in time for results to be evaluated, additional engineering studies to be made and a unit to be formed before the reservoir pressure in the North Pembina area declined below the bubble point. The pilot was located in an area developed on staggered, 80-acre spacing. The injection well was drilled at a regular location, while the four producers were drilled 467-ft north, east, south and west of the injector. Each quadrant and its associated producer were identified according to their direction from the injector— that is, north, east, south or west. The eight surrounding producers on 80-acre spacing were shut in to isolate the pilot area and provide for reservoir pressure observation. The pilot wells were completed using permanent-type completion techniques. After coring, casing was run through the pay section and cemented. Inside 51/2-in. casing, 2 1/2-in. tubing was hung. The wells were perforated opposite the Upper Cardium sand and lightly fractured. Fracturing volumes, rates and pressures were low to minimize the extent of the fractures. The fracturing treatments average 1,000 lb of 20-40 mesh sand in 700 gal of a low fluid-loss sand-carrying agent. Feed rates and wellhead fracturing pressures averaged 5.5 bbl/min at 2,535 psig, respectively. After fracturing, the productivity index was measured in each of the five pilot wells. The average PI of the four producers was 0.41 BOPD/psig drawdown. The measured PI'S were approximately the same as PI'S calculated from core analysis data, indicating that the fracturing treatments were just sufficient to overcome

By Arthur Phillips, Carl H. Samans

The study of anisotropy in metals has been greatly stimulated in recent years by the rapid development of X-ray methods for determining the crystallographic relationships of wrought and annealed materials. Prior to this time the knowledge regarding the directional properties of commercial alloys consisted almost exclusively of observations of a practical nature made during the fabrication of metal objects, supplemented by a limited number of mechanical tests on specimens cut at various angles to the direction of working. Such observations clearly indicate that the common methods of cold-working metals cause both a crystallographic and a mechanical fibering varying in character and degree according to the nature and extent of the deforming process. Even after annealing, following certain not too well known combinations of reductions and anneals, a preferred orientation may exist,, thereby constituting a residual fiber effect sufficiently pronounced to manifest directional properties. With the application of the X-ray the experimental horizon was extended chiefly because the study of anisotropic metals promised to offer direct and quantitative evidence regarding the involved mechanism of fragmentation and plastic flow. As a natural consequence the intensive studies in this direction have yielded a vast accumulation of data of ultimate potential value. Unfortunately, however, as is commonly the case in entering a virgin field of experimentation, many of the data cannot be molded into complete and coherent form because of the many unrelated conditions of the experimental projects. Again, the results of the study of single crystals have been rather naturally but at times indiscriminately applied to poly crystalline metals. Furthermore, sweeping statements have been made regarding the behavior during working and annealing of metals and alloys, entirely on the basis of similarity in lattice arrangement. There is abundant reason for believing that relatively small concentration variables, differences in magnitude and distribution of applied stresses, and the character of associated annealing treatments may in some cases greatly influence the mechanics of flow

Jan 1, 1933

By K. Morsy, S. S. Peng

A new method of pillar stability evaluation was proposed. The unique feature about the method is that it estimates two types of stability factors for the pillar. The first stability factor is to measure how much the applied stress at that point is smaller than its strength, and the second stability factor is to predict whether or not the pillar will fail violently. The strain-softening behavior of coal pillars was simulated by the Drucker-Prager yield criterion. A new algorithm that simulates the strain-hardening behavior of the gob was used. A numerical technique to estimate the local mine stiffness (LMS) was introduced and verified by both numerical and analytical methods. A case of massive pillar failure in a room-and-pillar mine was used to define the stability limits for the proposed method.

Jan 1, 2003

By J. H. M. Thomeer

A method is presented that provides a mathematical description of capillary pressure curves and, probably, of differences in pore geometry of samples. The technique is based on the observation that the location and shape of a capillary pressure curve reflect characteristics of the pore structure of the sample. INTRODUCTION It has been noted1-5 that the observed differences in shape and location of capillary pressure curves reflect some basic properties regarding the pore geometry of the samples. For example, according to basic concepts of capillarity, the following statements can be made regarding the location and shape of a capillary pressure curve.* The location of the curve with respect to the (Vb)pc and PC axes is a measure of the interconnected pore volume and of the cross-sectional area of the pore first entered by mercury, respectively. The shape of the curve depends on the interconnection of the pores and the sorting of the pore sizes. It has been the object of this study to use this information as a starting point in an attempt to find a unique mathematical description of the PC — (Vv)p, relations of different samples. It may be expected that parameters in such a relation can then be used to describe differences in pore geometry of these samples. For a practical description of the PC — (Vb)p, relation, however, it appears desirable to describe each curve (i.e., each sample) by a limited number of parameters so that the curves taken from all samples form a family, each member of which is uniquely determined by one single combination of values of all parameters.

By G. R. M. Del Giudice

The term "slime-coating" is not new in the art of flotation; the phenomenon has been observed and described by Taggart;(l)† Taggart, Taylor, and Ince;(2) and by Ince.(3) Notwithstanding that flotation was introduced for the treatment of finely crushed ore, the adverse effects of slimes have been recognized since the earliest days of the process, and the Elmore, Delprat, Potter, and other processes actually specified desliming of the ore prior to treatment. The cause of this trouble has been studied and described by Taggart;(1) Taggart, Taylor, and Ince;(2) Ince;(3) Morrow and Griswold;(4) and by Gaudin and Malozemoff.(5) Old Theory of Slime-coatings At present, so far as published work shows, there seems to be but one theory for the mechanism of slime-coatings. Ince(3) states that they are due to attraction between electrostatic charges of opposite sign on the sulfide and on the slime particles, supporting this theory by migration experiments in the Burton tube. He also used the microscope in conjunction with a glass cell employed by Beans and Eastlack(6) in studying migration, but met with interference from endosmosis. Several attempts have been made in the Department of Mineral Dressing at Columbia University to duplicate Ince's experiments with the Burton tube, but the results have never been convincing. Formation of precipitates which settled through the pulp levels, and evolution of gas at the electrodes, which disturbed the interface between the pulp and the distilled water above it, seriously interfered with observations. However, by use of the migration cell shown in Fig. 1, endosmosis effects and the disturbances due to precipitation and gas evolution were avoided, and distinct and reproducible migrations or absence of migration were observed. The cell was made of bakelite and had platinum electrodes. Objectives were employed which had a working distance of at least three millimeters,1 and the parts of the mounting which came in contact with

Jan 1, 1935

By J. L. Liu

Long-term maintained load test on the bored pile group in unsaturated silty soil has been carried out. And the research on the time effects of bearing behavior of pile group has been done by the method of installing pressure cells and reinforcement stress gauges for measuring the soil reaction beneath the cap and the pile bottom as well as the shaft resistance. The test shows that, within a certain duration after loading, the soil reaction beneath the cap and the pile point resistance increase with time; but the shaft resistance decreases. The load distribution among the pile tops in the group tends to be even with time. The shaft resistance redistributes along the pile shaft with time, that is, getting less in the upper part, getting larger in the middle. The redistribution does not tend to stop till the distribution in both upper and middle part becomes to be uniform. The load-bearing conditions of soil beneath the cap of pile group and the variation in time effects with related factors also have been discussed.

Jan 1, 2010

By E. N. Cameron, H. M. Bannerman

During the years 1942-1934, about 125 New England deposits were mined for sheet and punch mica, and many others were briefly prospected. During this period the Geological Survey, United States Department of the Interior, carried on detailcd studies of the deposits and the pegmatite bodies that contain them. The primary purpose of the studies was to provide geological information that would contribute toward efficient mine development and operation. The studies were aimed directly at practical production problems. Detailed maps showing the structure of the deposits were prepared, and geological findings were closely correlated with data on specific yields and costs of mining and processing. The result is information that permits a reasonably accurate appraisal of the mica deposits of New England and the mining industry that they support. At a time when the future of the industry is in doubt, it seems desirable to submit this appraisal for consideration. Domestic mica deposits supply only a small fraction of the country's needs in normal times? for only the richest domestic deposits can compete with the low-cost mines of India and Brazil. However, the possibility that this country may be cut off from its supplies in time of war gives domestic deposits an importance much greater than their peacetime production would imply. New England supplied about 22 per cent of domestic output in 1943 and 1944, the peak years of wartime production. Its actual contribution to the war effort was greater, for the proportion of sheet mica of high quality in the New England product is higher than the average for domestic mica. The data analyzed below were collected for the Geological Survey by D. M. Larra-bee, A. H. McNair, J. J. Page, V. E. Shai-nin, G. W. Stewart, and the co-authors of this paper. The cooperation of officials of Colonial Mica Corporation and of mine operators and owners in furnishing information is gratefully acknowledged. D. M. Larrabee, A. H. McNair, and V. E. Shainin have made various suggestions based on critical reading of the manuscript. Analysis oF Warrtime Operations In considering the data presented in this report, it must be remembered that the scale of mica operations is very small compared with that of many other mining industries. The typical New England mica mine of 1943 and 1944 was worked by a crew of five or six men. Equipment was varied but on the whole extremely simple. The first stage of operation at a deposit was normally opencut mining. Drilling was done mostly with jackhammers powered by portable compressors driven by gasoline engines. Muck was shoveled by hand into buckets with a capacity of 45 to 35 ton and commonly hoisted by derrick to a dump adjacent to the cut. As operations were carried to greater depth, and the tram sition to underground mining was made, these methods were modified to a degree depending largely on the attitude of the deposit mined. At steeply dipping deposits,

Jan 1, 1948

By H. M. Bannerman, E. N. Cameron

During the years 1942-1934, about 125 New England deposits were mined for sheet and punch mica, and many others were briefly prospected. During this period the Geological Survey, United States Department of the Interior, carried on detailcd studies of the deposits and the pegmatite bodies that contain them. The primary purpose of the studies was to provide geological information that would contribute toward efficient mine development and operation. The studies were aimed directly at practical production problems. Detailed maps showing the structure of the deposits were prepared, and geological findings were closely correlated with data on specific yields and costs of mining and processing. The result is information that permits a reasonably accurate appraisal of the mica deposits of New England and the mining industry that they support. At a time when the future of the industry is in doubt, it seems desirable to submit this appraisal for consideration. Domestic mica deposits supply only a small fraction of the country's needs in normal times? for only the richest domestic deposits can compete with the low-cost mines of India and Brazil. However, the possibility that this country may be cut off from its supplies in time of war gives domestic deposits an importance much greater than their peacetime production would imply. New England supplied about 22 per cent of domestic output in 1943 and 1944, the peak years of wartime production. Its actual contribution to the war effort was greater, for the proportion of sheet mica of high quality in the New England product is higher than the average for domestic mica. The data analyzed below were collected for the Geological Survey by D. M. Larra-bee, A. H. McNair, J. J. Page, V. E. Shai-nin, G. W. Stewart, and the co-authors of this paper. The cooperation of officials of Colonial Mica Corporation and of mine operators and owners in furnishing information is gratefully acknowledged. D. M. Larrabee, A. H. McNair, and V. E. Shainin have made various suggestions based on critical reading of the manuscript. Analysis oF Warrtime Operations In considering the data presented in this report, it must be remembered that the scale of mica operations is very small compared with that of many other mining industries. The typical New England mica mine of 1943 and 1944 was worked by a crew of five or six men. Equipment was varied but on the whole extremely simple. The first stage of operation at a deposit was normally opencut mining. Drilling was done mostly with jackhammers powered by portable compressors driven by gasoline engines. Muck was shoveled by hand into buckets with a capacity of 45 to 35 ton and commonly hoisted by derrick to a dump adjacent to the cut. As operations were carried to greater depth, and the tram sition to underground mining was made, these methods were modified to a degree depending largely on the attitude of the deposit mined. At steeply dipping deposits,

Jan 1, 1948