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By J. E. Worthington, W. H. Spence, I. T. Kiff

Gold was discovered at the Haile mine in Lancaster County, South Carolina, in 1827 or 1828, and since that time the mine has been worked intermittently by both open-pit and underground methods until its forced closure in 1942 by World War II. Production figures are incomplete, especially for the early years, but the total gold produced is estimated to have been greater than 200,000 oz. Thus, the Haile mine has been the most productive gold mine in the eastern United States. The upper, residually enriched ores were relatively rich, but the bulk of the production has come from the mining of lower grade ores. General Geology The Haile mine is located in late Precambrian or early Paleozoic rocks of the Carolina slate belt at the edge of the Atlantic Coastal Plain [(Fig. 1)]. The metamorphic grade is lower greenschist facies and the rocks have been folded into a sequence of northeast-trending isoclinal folds. The gold is associated with siliceous, pyritic, and kaolinized felsic pyroclastic and tuffaceous rocks in an interbedded volcanic and volcanoclastic sequence of felsic to mafic tuffaceous rocks and argillaceous sediments [(Fig. 2)]. The ore bodies occur in two northeast trending zones approximately 500 m apart; each zone is 30-70 m wide and 600 m or more in length, with possible extensions to the east beneath the Coastal Plain sediments. Mineralogy. Gold in the Haile mine is always associated with siliceous and/or pyritic ores. The gold occurs in at least three states: As native gold as originally deposited; as residual gold derived from the breakdown of pyrite; and as gold included in pyrite. Major associated minerals in addition to quartz and pyrite are kaolinite, sericite, and iron oxides. Minor molybdenite, arsenopyrite, pyrrhotite, copper sulfides, sphalerite, rutile, and topaz are also present. Petrology. The gold-bearing ore zones vary from highly siliceous rocks to pyritic massive sulfide lenses. This variation is most easily seen today along strike from the Haile pit to the Red Hill pit. Ore grade material still exposed in the wall of the Haile pit consists of a highly siliceous and very thinly bedded rock containing minor pyrite. Along strike, the character of the mineralization changes to pyritic massive sulfide lenses occurring interbedded with siliceous horizons at the Red Hill pit. The siliceous rocks vary from the thinly-bedded material as just described from the Haile pit to silicified fragmental-appearing rocks to totally recrystallized cherty rocks lacking any recognizable primary features. Scattered, apparently at random, throughout the very thinly-bedded and very fine-grained ore face of the Haile pit are seemingly anomalous silica-rich clasts or concretions up to 5 cm in diameter which will be discussed later in this paper. Alteration. One of the most striking features of the Haile deposit is the alteration mineral assemblage which is intimately associated with the siliceous and pyritic ores. This altered material has been intersected in drill core at depths greatly exceeding the modern weathering profile and is, therefore, of hydrothermal origin rather than from supergene processes. This "sericite," actually a fine-grained mixture of sericite, kaolinite, and quartz, can be shown to stratigraphically underlie the gold- quartz-pyrite zone, and is well exposed in the open pit just southeast of the Haile and Bumalo pits. Relict textures indicate that this highly altered material was originally a felsic ash flow. Other similar alteration zones have been found in outcrop and drill core underlying the remaining ore bodies. Thus each of the mineralized zones consists of two parts: A siliceous and/or pyritic gold-bearing ore zone which is stratigraphically underlain by a zone of high alumina minerals, in this case sericite and kaolinite along with variable amounts of quartz. A green chrome mica, presumably fuchsite, is present in trace amounts in the high alumina zone. Genesis An adequate model to explain the origin and distribution of the gold deposits in the Carolina slate belt is presently lacking. Worthington and Kiff1 suggested a volcanogenic origin for certain gold deposits in the North Carolina slate belt from the waning exhalations of felsic volcanic piles. They also pointed out that such an origin has similarities to many epithermal precious metal deposits located in more recent volcanic piles in the western United States. A further key to the understanding of the genesis of the gold mineralization at the Haile mine is the close association of the mineralization in siliceous and sulfidic horizons to the genetically related and stratigraphically underlying high alumina alteration. Such high-alumina alteration is common around felsic volcanic centers in the Carolina slate belt and the mineralogy as seen today consists of some combination of kaolinite, sericite, pyrophyllite, kyanite, andalusite or sillimanite depending on the local prevailing grade of metamorphism. Accompanying the high-alumina alteration are large quantities of pyrite and iron-oxide minerals as well as characteristic minor accessory minerals often including base metal sulfides, fluorine-bearing minerals (topaz, fluorite, apatite), titanium-bearing minerals (ilmenite, rutile),

Jan 1, 1981

By James Boyd

Scientists and engineers must concern themselves not only with technical problems, but with the socio-economic difficulties of our scciety. The author states that raw materials are basic to the economic process and that mineral raw materials occur naturally in nearly limitless quantities. He feels that the economic pocess will provide sufficient raw materials for man's needs, and discusses in some detail the world economic environment. As our society grows in complexity, it becomes more urgently incumbent upon scientists and engineers to bring their experiences to bear on the solution, not only of technical problems, but also on socio-economic difficulties. It is to this field that I have directed a large part of my energies. RAW MATERIALS BASIC TO THE ECONOMIC PROCESS There are certain premises, frequently overlooked, which bear emphasis. As economics concerns the production, distribution, and consumption of goods, so our whole society is based on raw materials. Without the basic extractive industries of agriculture and mining, there would be no economic problems with which to deal. This principle has been expressed as "All productivity is based on three factors: 1) natural resources, whose form, place, and condition are changed by the expenditure of 2) human energy (both muscular and mental), with the aid of 3) tools.77* It seems strange that such an obvious statement needs to be made. It is forgotten by all of us, however, at one time or another when we get involved in the complicated theories of economics dealing with the financial and fiscal policies of the various governments, in the financing of enterprises, in marketing, and in labor relations. Unless decisions in all of these fields are made with this, and the rest of the "Ten Pillars of Economic Wisdom," consciously in mind, the resultant policies are doomed to eventual failure, whether these are policies of individuals, companies, or governments. The economic process is basic to society. But economics and the social aspects of humanity are inevitably intertwined. If human needs are not provided for within the basic economic structure, conflicts arise to disrupt the most carefully laid social plans. Similarly, it is the failure of society to cope with basic economic prerequisites that leads to discord within the body politic and thus to eventual economic disaster. We who are engaged in the various aspects of the mineral industry, therefore, have a large part to play in society's future development. MINERAL RAW MATERIALS OCCUR NATURALLY IN NEARLY LIMITLESS QUANTITIES Throughout my career in and out of government, I have formed my decisions on two principles: 1) Fundamentally, all mineral raw materials exist within the earth's crust in quantities greatly exceeding man's needs; 2) Any problems of supply of these materials are primarily economic in nature. With respect to my first assumption, analyses by geochemists enable them to estimate the quantities in which each of the known elements exist in the earth's crust. One of the most cautious and famous suggests that the average copper content of the lithosphere to a depth of ten miles is about 55 ppm. If this is valid, then the lithosphere contains about 1.4 quadrillion (1.4 x 10 ") tons of copper metal — an unimaginable quantity. This is 8,500,000-fold that which has been consumed by man in his existence. To illustrate further, consider that the deepest copper mine in history went to about 9000 ft below the surface; the present copper mines of the world now average less than 1500 ft in depth. We can assume that in most continental land areas of the world it is technically feasible to mine to a depth of at least one mile. The land areas of the world to an average depth of one mile, then, contain 343 billion tons (343 x 10') of copper metal, or 2000 times that which has been extracted to date. I don't believe man will ever expend his energies to extract copper from rocks which contain only a few parts per million, but he knows that each element

Jan 1, 1968

By G. W. Ostroot, S. Shryock

Cementing deep, high-temperature oil wells where static temperatures range from 350 to 400F has become routine in the part decade. In the United States there were 271 wells drilled deeper than 15,000 ft during 1963. Many of these wells had static temperatures higher than 400F. Bottom-hole static temperatures near 700F are now realities in the geother-mal (steam producing) wells of California's Salton Sea area. The detailed planning initiated prior to drilling the wells is discussed together with the methods, materials and equipment used in solving the cementing problems which are encountered. Data are also presented that lead to development of cementing compositions that provide adequate thickening time, do not retrogress in strength, and maintain low permeability under these extreme temperature conditions. Field data include the cementing programs used on eight relatively trouble-free geothermal steam wells in the Salton Sea area. INTRODUCTION Not too many years ago cementing oil wells with temperatures in the range of 300F caused considerable anxiety. In some areas of the United States it is now fairly common to cement wells having bottom-hole static temperatures in excess of 400F. We are now confronted with the problem of cementing wells with temperatures ranging from 500 to 700F. Temperatures in this order of magnitude are often found in geothermal steam wells. From where does this extreme heat emanate? There are many theories as to the source of this steam flow. The most widely held views are: (1) heat- ing of ground water fairly close to the surface by an intrusive mass of hot rock; (2) steam generation from a reservoir of metamorphic rock, normally found below 25,000 ft and not at the shallower depths of the Salton Sea reservoir; and (3) high-temperature gases (water vapor) escaping and migrating from molten or semi-molten rock (magma) at a considerable depth. Of these. No. 3 seems to be the most generally acceptable explanation. Heat from springs and fumaroles has been used for years as a means of heating and cooking; however, significant progress in harnessing the vast power of underground steam reservoirs has been relatively slow. The first large-scale attempt to use the heat generated by steam from wells was made in Italy around the beginning of the 20th century. In excess of 250,000 kw of electrical power is now being produced from holes around Larde-rello, Italy. Another very active drilling program was initiated in the volcanic area of New Zealand in 1949.' Natural steam for power projects in the United States began in the early 1920's. An early commercial steam field is located at the Geysers, approximately 75 miles north of San Francisco, an area discovered in 1847 and used for many years as a health resort. Steam originates from 15 wells that have been drilled since 1957. The present output from this project is 25,000 kw. Success of the Geysers operation has been responsible for several companies taking a careful look at the feasibility of producing steam for power generation in the Salton Sea area of Southern California's Imperial Valley. Geothermal steam activity in this latter area began in 1961 when O'Neill, Ashmun and Hilliard completed Sportsman No. 1, at that time the hottest wellbore in the world.' Since its References given at end of paver. completion seven additional wells have been successfully completed in this area. Many problems encountered in drilling steam wells had to be overcome to make the ventures successful. Formation temperatures encountered in the Salton Sea seemed to be a straight-line function (a gradient of 13F per 100 ft of depth).' This imposed severe conditions on all aspects of drilling and completion. This varied, to some extent, from gradients in the older geothermal areas. Not to be overlooked is the effect of these temperatures on casing creep or elongation by thermal expansion (Table I), because standard API flanged wellhead equipment makes no provision for this kind of performance. Floating equipment was redesigned, and changes in types of downhole equipment were made in an effort to eliminate anticipated problems. In the later completed wells, standard oil-well cementing equipment has been used. During the early development of geothermal steam wells there were some problems resulting from blowouts. However, these were eliminated in the deeper Salton Sea wells and no problems were encountered with the drilling mud. A sodium surfactant mud was used on the Sportsman No. 1 to drill from 2,690 to total depth. Nevertheless, it was necessary that a cooling system be added and the mud cooled before circulating it back into the well. The difficulty in evaluating the size of the steam area and its potential in terms of pounds of steam and years of productivity still has not been resolved. Economic complexities have also entered into the steam play in the Salton Sea. The wells at the Geysers were drilled at a cost of $15,000 to $20,-000, whereas the Salton Sea wells will cost more than $150,000. This cost differential has to some extent been accounted for because of the heavily

Jan 1, 1965

By Glenn S. Wyman

CHUQUICAMATA, located in northern Chile in the Province of Antofagasta, is on the western slope of the Andes at an elevation of 9500 ft. Because of its position on the eastern edge of the Atacama Desert, the climate is extremely arid with practically no precipitation, either rain or snow. All primary blasting in the open-pit mine at Chuquicamata is done by the churn drill, blasthole method. Since 1915; when the first tonnages of importance were removed from the open pit, there have been many changes in the blasting practice, but no clear-cut rules of method and procedure have been devised for application to the mine as a whole. One general fact stands out: both the ore and waste rock at Chuquicamata are difficult to break satisfactorily for the most efficient operation of power shovels. Numerous experiments have been made in an effort to improve the breakage and thereby increase the shovel efficiency. Holes of different diameter have been drilled, the length of toe and spacing of holes have been varied, and several types of explosives have been used. Early blasting was done by the tunnel method. The banks were high, generally 30 m, requiring the use of large charges of black powder, detonated by electric blasting caps: Large tonnages were broken at comparatively low cost, but the method left such a large proportion of oversize material for secondary blasting that satisfactory shovel operation was practically impossible: Railroad-type steam and electric shovels then in service proved unequal to the task of efficiently handling the large proportion of oversize material produced. The clean-up of high banks proved to be dangerous and expensive as large quantities of explosive were consumed in dressing these banks, and from time to time the shovels were damaged by rock slides. As early as 1923 the high benches were divided, and a standard height of 12 m was selected for the development of new benches. The recently acquired Bucyrus-Erie 550-B shovel, with its greater radius of operation compared to the Bucyrus-Erie 320-B formerly used for bench development, allowed the bench height to be increased to 16 m. Churn drill, blasthole shooting proved to be successful, and tunnel blasts were limited to certain locations where development existed or natural ground conditions made the method more attractive than the use of churn-drill holes. Liquid oxygen explosive and black powder were used along with dynamite of various grades in blasthole loading up to early 1937. Liquid oxygen and black powder were discontinued because they were more difficult to handle due to their sensitivity to fire or sparks in the extremely dry climate. At present ammonium nitrate dynamite is favored because of its superior handling qualities and its adaptability to the dry condition found in 90 pct of the mine. In wet holes, which are found only in the lowest bench of the pit and account for the remaining 10 pct of the ground to be broken, Nitramon in 8x24-in. cans, or ammonium nitrate dynamite packed in 8x24-in. paper cartridges, is being used. This latter explosive, which is protected by a special antiwetting agent that makes the cartridges resistant to water for about 24 hr, currently is considered the best available for the work and is preferred over Nitramon. Early churn drill hole shots detonated' by electric blasting caps, one in each hole, gave trouble because of misfires caused by the improper balance of resistance in the electrical circuits. Primarily, it was of vital importance to effect an absolute balance of resistance in these circuits, the undertaking and completion of which invariably caused delays in the shooting schedule. Misfires resulting from the improper balance of electrical circuits, or from any other cause, were extremely hazardous, since holes had to be unloaded or fired by the insertion of another detonator. The advent of cordeau, later followed by primacord, corrected this particular difficulty and therefore reduced the possibility of missed holes. After much experimentation, the blasting practice evolved into single row, multihole shots, with the holes spaced 4.5 to 5 m center to center in a row 7.5 to 8 m back from the toe. Such shots were fired from either end .by electric blasting caps attached to the main trunk lines of cordeau or primacord. The detonating speed of cordeau or primacord gave the practical effect of firing all holes instantaneously. Double row and multirow blasts, fired instantaneously with cordeau or primacord, proved to be unsatisfactory in the type of rock found at Chuquica-

Jan 1, 1952

By Ernest Wiltsee

The Half-Moon mine, situated three miles west of the town of Pioche, exhibits geological features which are peculiar and interesting. The general formation in the vicinity of Pioche consists of a quartzite, usually covered with an overlying limestone containing strata of shale. In the camp itself, where the original mines are situated, the quartzite has been denuded, and the principal veins outcrop in this formation; to the west, the quartzite is again covered with limestone, containing thin strata of shale.

Jan 1, 1893

By Martin J. Conway

DURING the past year, the intense interest shown by the metallurgical industry in the use of relatively pure oxygen has been evidenced by the number of papers dealing with its application and production. The reason for this interest is apparent when it is realized that, weight for weight, oxygen enters into the formation of steel equally with iron. In the manufacture of steel, approximately one ton of oxygen is required to produce one ton of ingots. Until the recent development of plants capable of producing oxygen at far lower costs than had ever previously been considered possible, the oxygen required for steel manufacture was used as it occurs in air, where it is associated with approximately four times its volume of nitrogen. Because of the diluent nitrogen more than 4 tons of total gaseous material per ton of steel must be handled rather than only approximately one ton required when pure oxygen is used. In addition, provision must be made to handle the large quantity of waste, gases resulting from the process. There are cases where the reduction in gas volume alone can justify the installation of an oxygen plant.

Jan 1, 1947

By AIME AIME

THE quarters provided for the session on Milling Methods, Monday afternoon, Feb. 17, were filled to capacity. Galen H. Clevenger presided and notables, such as A. W. Fahrenwald, A. O. Gates, F. A. Thomson, W. L. Zeigler and others who had not graced a milling meeting in New York in recent years, or per- haps even never before, were actually present and spoke "in person." The first paper, by A. W. Fahrellwald (T. P. 275), entitled "Classifier Efficiency ; An experimental Study," was summarized by the author, who clearly showed the inconsistency of determining the efficiency of a classifier by means of sizing tests, especially where the material classified consists of a mixture of minerals of different specific gravities. In place of sieve analysis the procedure recommended involves the use of a glass settling-tube which is considered to give ideal classification and thus serve as a standard against which mill classification will be compared and relative efficiency calculated. This procedure sounds logical. Perhaps the greatest difficulty may lie in securing an ideal classifier acceptable to every one.

Jan 1, 1930

By F. M. Sandoval, R. E. Ries, J. F. Power

Returning the original soil material to the surface of smoothed mine spoils is a practical means of restoring agricultural productivity. Research has established that high-sodium spoils in North Dakota: (1) must be covered with about 70 cm of soil material to achieve maximum production; (2) top-soil must be segregated and spread separately from subsoil; (3) potential production depends on the quality of the soil material returned; and (4) erosion and upward salt movement must be controlled for sustained production. Erosion is best controlled by reducing final grades as much as possible during the smoothing process followed by prompt establishment of vegetation.

Jan 12, 1979

By L. P. Teas

Although 1927 in the Arkansas-Louisiana territory will probably pass into history as a year of small profits and little new production, nevcrtheless during this period two large gas fields were developed; two new oil fields were discovered, and two new oil horizons, hitherto of minor annual production Fig. 1.—Production of North louisiana and ARkansas by fields, for 1926 and 1927. (Upper blocks represent 1926 production; lower blocks, 1927 production ) importance, were developed. In spite of the "hard times" some of the leading supply houses did more business this year in this district than in any year since 1920.

Jan 1, 1928

By Orson Cutler Shepard

RECENT research work in the flotation concentration of minerals has been concerned mainly with flotation reagents and the mechanism by which collecting reagents are held to the surface of certain mineral particles. The fundamental question of why air bubbles cling to properly prepared mineral surfaces is usually dismissed with the statement that the surface is air-avid or water-repellent. In my article in MINING AND METALLURGY for June, 1932, I showed theoretically that surface tension relationships govern bubble attachment in Rotation. This explanation has not been accepted by many; probably be¬cause the difficulty of measuring solid-solution surface tensions prevented obtaining experimental evidence. If the surface tensions involved in the system [solution, mineral, air bubble] are responsible for attachment of the air bubble to the mineral, any change in the surface tensions should cause a corresponding change in the attachment of the air bubble. An example in which the mineral-solution surface tension could be varied was found with mercury. When mercury is in contact with solutions of certain electrolytes the surface tension at the contact of mercury and solution can be altered by electrical polarization of the mercury. The surface tension rises to a maximum as the mercury is given an increasing negative potential and then decreases with further increase in potential. The theoretical relation between the surface tensions and the attachment of an air bubble is given by the following equation:

Jan 1, 1936

No. 364.-Asbestos mine in Canada desires assistant mine superin¬tendent to supervise mining of ore and delivery of same to mill bins. To be successful, applicant should be good organizer and able to get production at right cost; one with experience on steam-shovel rock work preferred. Knowledge of French desirable. Salary $175-$200 per month; permanent position; chance for advancement. Company¬ owned houses available at nominal rental. No. 365.-Research metallographist. Man of commercial experience in alloy steels for position offering opportunity for constructive work over wide range of alloys, with large concern providing ample working facilities. In replying please give full details of training; experience, age and salary desired. No. 366.-Engineer to do surveying and making of mine maps cover¬ing inside development of mine as well as property outside of the-mines. Matter of salary depends on man's experience and efficiency. No: 367.-Engineer, preferably single man to be detailed mostly on mine surveying. Salary to start $130 per month and expenses while on the road.

Jan 2, 1919

By E. H. Crabtree

Research on the iron ranges begins to bear fruit in big plant construction -Big coppers raise capacity, build at new Arizona, Michigan, Nevada, properties - Hydrometallurgy comes to fore with new uranium ore treatment and the Chemico process for nonferrous metals -

Jan 2, 1953

By Robert B. Schlosser

Anaconda's Jackpile uranium mine is a multi- million-ton open pit sandstone deposit, producing some 3000 tpd for the company mill. With minor exceptions, the orebody is in equilibrium, and the backbone of ore-grade control is the radiometric assay, which fortunately is dependable. Preparatory Sample Drilling: Before it is stripped, the orebody is diamond-drilled on 200-ft centers N-S and 100-ft centers E-W. Drill core is logged, split, and assayed radiometrically, and several samples are assayed chemically to check the equilibrium status. This information establishes the pit outline and the first rough estimate of ore. After stripping, diamond drill data is supplemented by rotary drillholes on 50-ft centers. Dry chip samples, collected every 2 ft, are prepared and assayed radiometrically at the mine. Details of the orebody are then available for study, and the basic mining plan is drawn up.

Jan 10, 1958

By G. F. Fix, R. E. Esarey

During 1939, Indiana experienced a grcat increase in prospecting and drilling for oil and gas. Major activity, as during the preceding year, was in the southwestern part of the state, the Indiana portion of the Eastern Interior Coal Basin. An increasing interest was evident during the year, however, in the entire state, chiefly in northern Indiana (on the south flanks of the Michigan Basin) and in the old Trenton field of east central Indiana. In the latter area several tests to deeper horizons in the Trenton and to the underlying St. Peter sandstone were completed. Results in this area have been discouraging, however, since these deeper horizons are very erratic. The regional structure in the Indiana portion of the Michigan Basin is generally favorable to oil accumulation, but the picture is complicated by a uniform mantle of glacial drift and a lack of subsurface information. Several wells were started during the last half of 1939 to test the Devonian and Trenton formations in this area. Production from these formations was found at several localities many years ago, hut, no sustained effort has been made to locate pools in this area, which covers perhaps 20 counties. There were 377 wells completed in Indiana during 1939, and 77 others were in various stages of drilling at the close of the year. Of the 377 completed, 255 were classed as field locations and 122 as wildcats. The field wells were divided as follows: 156 oil wells, 39 gas wells, and 60 dry holes; the wildcats: 98 dry holes, 19 oil wells and 5 gas wells (wildcat oil and gas wells include deeper production in oil fields and field extensions as well as new field discoveries). During the year 218 more wells were completed than during 1938. Outstanding developments for 1939 include the discovery of several new oil and gas fields. In the Griffin field, which was discovered during the closing days of the previous year, 103 wells were drilled, including field extensions. Of these, 97 were productive oil wells. This field now covers more than 2000 acres of productive area and has not as yet been defined. There are five producing horizons in the field, including the Waltersburg, Tar Springs, Elwren, and Aux Vases sandstones of Chester age and the McClosky horizon of the Ste. Genevieve limestone. Produe-

Jan 1, 1940

By G. F. Fix, R. E. Esarey

During 1939, Indiana experienced a grcat increase in prospecting and drilling for oil and gas. Major activity, as during the preceding year, was in the southwestern part of the state, the Indiana portion of the Eastern Interior Coal Basin. An increasing interest was evident during the year, however, in the entire state, chiefly in northern Indiana (on the south flanks of the Michigan Basin) and in the old Trenton field of east central Indiana. In the latter area several tests to deeper horizons in the Trenton and to the underlying St. Peter sandstone were completed. Results in this area have been discouraging, however, since these deeper horizons are very erratic. The regional structure in the Indiana portion of the Michigan Basin is generally favorable to oil accumulation, but the picture is complicated by a uniform mantle of glacial drift and a lack of subsurface information. Several wells were started during the last half of 1939 to test the Devonian and Trenton formations in this area. Production from these formations was found at several localities many years ago, hut, no sustained effort has been made to locate pools in this area, which covers perhaps 20 counties. There were 377 wells completed in Indiana during 1939, and 77 others were in various stages of drilling at the close of the year. Of the 377 completed, 255 were classed as field locations and 122 as wildcats. The field wells were divided as follows: 156 oil wells, 39 gas wells, and 60 dry holes; the wildcats: 98 dry holes, 19 oil wells and 5 gas wells (wildcat oil and gas wells include deeper production in oil fields and field extensions as well as new field discoveries). During the year 218 more wells were completed than during 1938. Outstanding developments for 1939 include the discovery of several new oil and gas fields. In the Griffin field, which was discovered during the closing days of the previous year, 103 wells were drilled, including field extensions. Of these, 97 were productive oil wells. This field now covers more than 2000 acres of productive area and has not as yet been defined. There are five producing horizons in the field, including the Waltersburg, Tar Springs, Elwren, and Aux Vases sandstones of Chester age and the McClosky horizon of the Ste. Genevieve limestone. Produe-

Jan 1, 1940

By T. A. Rickard

In southeastern France, among the magnificent alpine masses of the Dauphine, there is a group of celebrated mines of silver-, nickel- and cobalt-ores, the deposits of which present many features

Jan 1, 1895

By Robert B. Paul

This paper describes the new lead smelter and refinery recently completed by the American Smelting and Refining company in Southeast Missouri.

Jan 1, 1970

EUGENE WESLEY SHAW,* Washington, D. C. (written discussion ?).-Studies of the probable future production of oil wells and fields-particularly those in the nature of the recent work by Lewis and Beal, having the object of increasing the percentage of recovery-rank, in both practical and theoretic value, very high, if indeed they do not outrank all other petroleum investigations except structural surveys. Even such surveys, although saving untold millions that might have been spent in prospecting unpromising territory, may have less ultimate value than generally supposed, for it may perhaps be argued that much if not most of the condemned territory will sooner or later be tested-some is already productive-and the most that can be rightly claimed is the recovery of cream first; also that the consumption of the richest portions first cannot be extenuated, as it might with some resources, on the ground that if the best is not taken now it will deteriorate.

Jan 5, 1918

By C. E. Schwab

A lead-zinc orebody, in fairly strong quartzite and with a dip of 35" to 60°, is block-caved by use of scrams in a stair-step pattern up the ore footwall. Scram linings to handle coarse muck and permit the use of folding scrapers are developed by the use of end-grain wooden blocks to reduce maintenance and keep operating cost to a minimum. THE Bunker Hill mine, since its discovery in 1885, has steadily produced a high grade of lead-silver-zinc ore. By the end of 1952 over 21,000,000 tons of this high-grade ore had been produced by square-set mining, and reserves in the mine continue to be very satisfactory both as to quantity and grade. For many years prior to 1941, mine production and mill capacity had been 1200 tons of feed per day. Closely adjacent to the mill, and stored behind dikes, coarse jig tailings had been impounded during the time preceding the advent of fine grinding and selective flotation. When manpower became short in 1941 and sink-and-float preconcentration was proved successful, mill capacity was increased to 1800 tons per day to treat these jig tailings economically. By 1946, because the supply of jig tailings was limited, underground exploration was started to discover and prove ore reserves of low-grade material which could be mined by an appropriate bulk mining method. During the years of square-set mining many possible areas of low-grade mineralization had been observed. One chosen for the first exploration work was sufficiently remote from active mining areas so that subsidence, if an ore-body were proved, would cause no problem. Also, old adits and workings were still open and in good enough condition so that exploration in the mineralized zone could be started with a minimum of preparatory work. In 1948 an orebody was proved of sufficient tonnage, of a grade about 2 pct Zn, 0.5 oz Ag, and 1.0 pct Pb. It was decided to use block-caving, the only appropriate mining method by which this grade of ore could be economically recovered. Exploration for additional reserves in other areas of the mine is continuing, but ultimate results are not known at this time. With more sink-and-float capacity, larger ball mills, and more flotation machines, mill capacity was increased to 3000 tons per day, permitting the mining of ore in the square-set area at a maximum rate not usually achieved, because of the scarcity of labor. Increased mill capacity also permits block caving and the mining of jig tailings at variable rates to keep mill feed up to 3000 tons per day. Fortunately the three types of feed are amenable to the same mill circuit and reagents for recovery of Pb and Zn. For example, during the first 10 months of 1952 square sets produced 827 tons per day, block-caving 1421 tons per day, and jig tailings 643 tons per day, an average daily production of 2891 tons for all three products. Exploration had proved the existence of an ore-body 1000 ft long and 165 ft wide in horizontal section, see Fig. 1. Company engineers were concerned only with the vertical extension, about 300 ft, from an old level to the surface. Much of this almost outcropped, Fig. 2. The ore lies in the hanging wall of a major fault of the Bunker Hill mine, standing at 65" in one end of the zone and separated from the fault by a wedge of waste, see Fig. 3. This wedge pinches out near the center of the zone, at which point the ore dips 45", lying nearly on the fault, Fig. 4. The remaining portion lies on the fault and conforms to the fault dip of 35", Fig. 5. Open-pit mining for the top of the ore was considered, but since the ore zone dipped into and under the mountains, adverse waste-to-ore ratios precluded use of this method. The ore occurs in massive quartzite of sufficient strength to support untimbered drifts, crosscuts, and raises. Zones of weakness in the quartzite are bedding, jointing, and small faults or slips. The mineralization, which occurs as small stringers of sphalerite and galena as well as pyrite, creates another line of weakness. The mineral veins or veinlets in themselves are high-grade. Their size and regularity and the amount of barren quartzite by which they are separated determined the limits of mineable ore, which are all assay limits except for the one determined by the major fault. Block 1 Without any background of caving in this type of quartzite, engineers selected the first block on the very steep end of the zone. Compelling reasons prompted this decision. The steep portion of the ore in Block 1 was of the lowest grade, so that if difficulties were encountered no very valuable ore would be lost, while the experience gained might be applied in mining the remaining blocks. A block 200x200 ft was laid out, with four scrams spaced 50 ft apart for drawing and placed at a right angle to the strike. Finger raises were placed in a 25-ft interval grid pattern, with flat undercutting done by crosscuts at the undercut level 25 ft above

Jan 1, 1954

By R. C. Ferguson, Harlowe Hardinge

Oscar Johnson—In my opinion, the effect of mill speeds on grinding costs must be studied along with capital investment and dollars gathered together as profits. Comparing the entire groups of operators with those who have had the opportunity to make slow-speed mill studies, I think you will find the latter small in numbers. Most managers want the equipment worked to its maximum output. There are, however, some installations where plant and mill sizes are such that they can do the job with reduction of mill barrel speeds. The past and the present installations of the industry are laid out to get the most capacity for the least capital outlay. This is the case even with the plants of Chile Exploration, International Nickel, Morocco, and Anaconda, now under construction or being changed. The industry recognizes that most all equipment it buys today is good and can be depended upon for efficient performance. Under this scheme of things, I am doubtful that slow-speed ball mill operation will be generally applicable. With reference to the U. S. Bureau of Mines laboratory tests, I think table II could have been omitted. It is inconclusive as to maximum efficiency for the low-pulp level mill on hard ore. There should be no question about this point. However, data on mill speeds can be found to substantiate various theories as well as refute them. Gow, Guggenheim, Campbell and Coghill, in their paper on Ball Milling,' believe their 2 x 2 ft laboratory mill reflects results that can be expected from large mills. If so, then referring to their table 11, they state, "The conclusion to be drawn from this second series is that high speed, not exceeding 72 pct of the critical, favors capacity, as before, but that with proper conditions of operation high speeds may give as good efficiency values as low speeds. In this case the efficiency values are nearly constant. A horizontal curve would indicate that the amount of grinding was directly proportional to the power expended, and these tests suggest that such a coildition can be made to exist in commercial operations." Table II (From Paper by Gow et a1)2 Speed. Pot Critical 32 42 52 62 72 82 Capacity: Surface tons per hr (65- mesh) 266 42.1 54.4 65.9 74.3 74.1 Surface tons per hr (200- mesh) 56.1 87.4 112.7 137.1 154.2 153.0 Efficiency: Surface tons per net hp hr (65-mesh) 35.7 36.3 36.3 35.4 34.3 32.3 Surface tons per net hp hr (200-mesh) 75.3 75.3 75.1 73.7 71.0 66.0 Ore in mill, 1.b. 98 100 100 113 122 165 The field performance data, table 111, represents much effort in its collection and preparation. But, one must realize that there are many variables that effect the efficiency of grinding mill operation, and too much must not be assumed as to the effect of some specific change. Possibly with changes in mill speed, the results might be more consistent by also a change in ball rationing, type of ball, volume of ball charge,. p.ulp level and amount of pulp in the mill, pulp consisting, design of liner, circulating load, etc. Also, changes in ore character must be reckoned with when evaluating grinding performance. At present the Climax Molybdenum Corp. is running at much reduced capacity. Mr. James Duggan informs me that at mill speeds of 17 rpm, they save a $0.025 per ton on liners and $0.025 per ton in power, but, if the demand for molybdenum increased, he would go back to higher speed to obtain maximum tonnage, as the values from the increased tonnage would far more than offset the one half saving at the slower speed. The Jnspiration ran a six months' test between mills running 21 rpm and 23.5 rpm. The slower mills ground 10 pct less ore with a slight saving per ton, but when the reduced plant tonnage was checked back into the actual cost figures of concentration, the high-speed mills with their greater tonnage showed considerable advantage. To be convinced of possible practical results from the predictions in the conclusions, I think we would have to rely on the analysis of expert cost accountants to furnish the necessary proof figures. Hardinge and Ferguson are to be commended for the work in preparing this paper. I am convinced that our Massco engineers should go into higher speeds with our equipment. Harlowe Hardinge (authors' reply)—For one, I heartily agree with Mr. Johnson's opening statement that the effect of mill speeds on grinding costs must be studied along with capital investment and dollars gathered together as profits. It was on this basis and for this reason the paper was written. Mr. Johnson, on the other hand, takes the position that, on the whole, low speeds are not justified from the economic standpoint, basing his principal reason on the fact that lower mill speeds cut mill capacities and hence reduce the gross income from the product produced. There is no denying this point. It is almost axiomatic. It is for this very reason that the overall advantage of lower mill speeds has been discounted and even overlooked. It was for this reason mainly that the paper was written in the first place. It is one thing to plan an efficient operation at the outset, basing one's figures on the tonnage requirements at the time, and it is quite another to be confronted with the problem of increasing the output of an existing installation at a minimum of capital expenditure. Economic consideration of a new installation is greatly influenced by referring to an old one. Too often, the analyst assumes that if this practice is followed in the new installation, one would not go wrong. It is just here that he may be wrong. Past practice and low capital expenditure are all too frequently given priority over the engineer's analysis of operating costs. When we are able to start fresh, we should give proper weight to other economic factors which do not exist in an old installation. It is these economic factors that make it possible to spend at the outset just a little more money and get it back in a matter of months and effect big savings for years to come. F. C. Bond—This paper is of considerable importance in that it emphasizes a modern trend to operate ball mills at somewhat slower speeds than formerly. We have checked the data in the paper with that obtained

Jan 1, 1951