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By Wolfgang Hermann

The ancit-process of the Eschweiler Bergwerks-Verein, an affiliate Company of ARBED S.A., Luxembourg, was developed in its principles by the Dutch State Mines, Limburg, in the mid-50's with the aim of producing a smokeless domestic fuel on the basis of low volatile hard coal. In 1967, the EBV erected a 10 t/h large- size pilot plant along these principles in the Aachen mining district and further developed the acquired know-how. In hardly 10 years more than 650 000 t of ancit briquettes with unit weights between 17 and 100 grams were produced and in the meantime stream rates of over 85 % of the yearly utilization hours have been reached. In more than 10 blast furnace trial runs involving substitution rates up to 100 p. c. ancit have proved the suitability of ancit as a metallurgical fuel both for a burden with a high and a poor iron content. Construction work for a minor process-step to enable processing of coal with a higher content of volatile matters is finished and first results are expected by summer this year. A pilot plant with a 30 t/h capacity working on a low-volatile coal basis is being planned. Engineering and construction are supervised by MecanARBED. Luxembourg, as responsible contractors.

Jan 1, 1977

By W. F. Carew, F. A. Crossley

IT has been reported that the Ti-8 pct A1 alloy is ductile as water quenched from 800°C but brittle as annealed at 650 °C." The present, somewhat limited, investigation was undertaken to discover the cause of the embrittlement. In order to evaluate to some extent the continuity of the embrittling phenomenon, alloys of 6, 8, and 10 pct A1 were studied. Subsequent to the completion of most of this work, Ence and Margolin reported that a Ti,A1 phase exists and that two or more unidentified compounds may exist in the Ti-A1 system.' Materials, Equipment, and Techniques The alloys were prepared using Kroll process sponge of 124 Bhn hardness. In addition, some 8 pct A1 material was made with iodide titanium. The sponge-base alloys were prepared as melts of 4 lb or more by double arc melting. The iodide Ti-8 pct A1 alloy was prepared as 200-g buttons. The alloys were forged at temperatures of 980" to 1150°C. Results of chemical analyses are given in Table I. A Baldwin-Southwark 60,000-lb capacity tensile machine, equipped with an autographic stress-strain recorder, was used for the tensile tests. Standard tensile test specimens, 0.252 in. diam, were used. Standard Charwy V-notch impact specimens were tested using a -kiehle machine. specimens were sealed in evacuated Vycor bulbs for heat treatment. Powder samples for Debye-Sherrer anal- ysis were prepared by filing and screening through 325 mesh. The —325 mesh fraction was taken in an effort to concentrate a microstructural constituent assumed to be less ductile than the a phase. The powder samples were stress relieve2 by annealing

Jan 1, 1958

By Walter Stephen

MODERN developments in alloy steels have been so rapid and diverse that engineering practice has scarcely had time to re-appraise all items of past experience wherein conclusions became axiomatic under conditions that no longer apply. A case in point is the wet screening of abrasive ores within the fine range still looked upon as belonging exclusively to classifiers. By virtue of the development of stainless steels (18 per cent Cr, 8 per cent Ni), it is no longer true that classifiers are more economical than screens in closed circuit with large-tonnage ball or rod mills at 65 or even 100 mesh, provided a selective overgrind of the higher-gravity constitu-ents of the ore is not desired. Wet screening of ores is a highly corrosive as well as an abrasive opera-tion, because of the inevitably high degree of oxygenation of the water. Screen cloth of ordinary or spring-steel wire almost at once becomes pitted and covered with a film of corrosion products, which causes rust-blinding of fine-mesh screens and offers high frictional impedance to the flow of ore particles. On the other hand, the well-known properties of stainless steel enable it to maintain a bright surface, and so to eliminate blinding either by ore particles or by corrosion products. That a large-tonnage mill grinding hard ore to 65 mesh can be oper-ated economically in closed circuit with screens instead of classifiers has recently been demonstrated at the Copper Cliff concentrator of the International Nickel Co.; in the test to be described, a 6 ½ by 12 ½ -ft. Marcy rod mill ground from 625 to 820 tons. of ore per day to approxi-mately 65 mesh, operating in closed circuit with three 4 by 5-ft. Hum-mer screens, without any classifier.. Stainless-steel cloth gave an indicated life of several months. There was no difficulty with blinding, yet dilution and spray water could be controlled so that screen undersize averaged not less than 40 per cent solids. In contrast, ordinary carbon steel was pitted and blind with rust within 40 hours.

Jan 1, 1938

By Mark D. Zoback, Bezalel C. Haimson

INTRODUCTION A Workshop on Hydraulic Fracturing Stress Measurements was convened by the authors in December 1981 in Monterey, California under the auspices of the U.S. Geological Survey and the U.S. National Committee on Rock Mechanics. There are now over a dozen groups of investigators around the world who are actively using the hydraulic fracturing method for making in-situ stress measurements. Because of the extensive recent experience of these different groups, the Workshop enabled forty investigators from eight countries to comprehensively assess the status of the method. Based on the presentations and discussions at the Workshop, in this paper we briefly discuss the current status of the hydraulic fracturing stress measurement method concentrating on problem areas where further research needs to be done. A complete account of the presentations at the Workshop will be available through the Proceedings of the Workshop which will be published by the U.S. National Committee on Rock Mechanics in early 1983. The most exciting aspect of the Workshop was the discovery by the various groups of investigators that others were having very similar experiences with the method. The consensus among the different groups of investigators at the Workshop was that they were recording very similar pressure-time data in the field, they were able to interpret them in similar ways, and they were achieving results that were quite encouraging because of several factors. First, the results at various locales were found to be internally quite consistent. This was reported by investigators from Germany (Rummel, Baumgartner, and Alheid, 1982), Japan (Tsukahara, 1982), Australia (Enever, 1982), and the U.S. (see, for example, Haimson, 1978, 1982a; Zoback

Jan 1, 1982

By R. G. Mallon, A. E. Lewis, R. L. Braun, C. J. Sisemore

Large ore-bodies, too deep to mine economically by underground methods, may be mined using nuclear explosives and a high pressure leaching technology. Breaking of a hypothetical ore-body with a series of nuclear explosives is described. The leaching would be accomplished by pumping oxygen into the flooded rubble under the normal hydrostatic pressure. The injection of oxygen gas into the bottom of the rubble chimney induces a circulation of the solutions which carries dissolved oxygen to all parts of the chimney. Copper and other metals would be recovered from the solutions by solvent extraction as they are circulated through a surface plant in a closed system. This provides for control of pH as well as containment of radioactivity. Radioactivity levels in the solution are low, and no radioactive impurities are expected in the copper. This technology will allow production from deposits too deep to be of interest with present technology and will reduce or eliminate some environmental effects of conventional mining, such as open pits, mine dumps, tailings ponds, and SO2 effluent. Close proximity of cities and towns is a limitation because of seismic damage. The technology requires further development for commercial application, and exploration targets must be enlarged to include deeper deposits, before the technology can be applied on a large scale.

Jan 1, 1974

By S. R. Goodman, Hsun Hu

PREVIOUS investigations on the temperature dependence of rolling texture transition in high-purity silver1'2 and in electrolytic copperS have shown that a brass-type texture is favored at low rolling tem- peratures, whereas a copper-type texture is favored at high rolling temperatures. The transition takes place gradually as a function of the temperature of deformation, and a general correlation between texture transition and stacking-fault frequency or probability exists—a copper-type texture is associated with low stacking-fault frequencies, and a brass-type texture is associated with high stacking-fault frequencies. If the stacking-fault energy is calculated from the stacking-fault frequency and the dislocation density of the specimen, one finds that with low stacking-fault energies a brass-type texture will be developed, and that with high stacking-fault energies the texture will be of the copper-type. These findings are consistent with the idea that the formation of rolling textures in fcc metals may depend on their stacking-fault energy, although results of such nature always involve the ambiguity that a change in the density (or width) of stacking faults produced by deformation at different temperatures may be actually due to a variation in the stress, rather than due to a change in the specific stacking-fault energy per se. It has also been shown that the type of annealing texture depends entirely on the deformation texture. From a copper-type rolling texture, a strong cube texture will be formed upon recrystallization, whereas from a brass-type rolling texture, the annealing texture will be quite different from the cube orientation. Based on these results on texture transition in pure fcc metals, it appeared possible to effect a

Jan 1, 1963

By Roy Thomas

SOON after the Waelz plant for the fire concentration of low-grade zinc ores was put into operation in the early part of 1929 at Katowice, it was found that the conveyor equipment for transporting the hot residue from the furnace dust chambers was inadequate. Hand tram-ming with water cooling was used for a time, but that method was injurious to the workmen as well as costly. The problem was to find some practical mechanical means of conveying flue dust at temperatures of from 450° to 600° C. as it was drawn from the dust chambers. After considerable preliminary investigation it was decided to install pneu-matic equipment for conveying the hot materials to a central mixing plant, where it would be mixed with slime and from which it would be returned to the furnace feed hoppers. The first pneumatic equipment was installed in 1930, and has been in successful operation since that time. The pneumatic method of transportation has shown a considerable saving in operating costs over the former methods of dust handling and a decided improvement in working and hygienic conditions at the plant, through the elimination of the dust hazard. Additional pneumatic equipment was installed in 1933 for conveying the furnace fume from the baghouses to the roaster plant. At the same time pick-up lines were provided for collecting the cleanings from the vertical and horizontal cooling pipes that are between the furnace dust chambers and the baghouses. The latter installation has practically eliminated a dusty and costly hand-tramming operation.

Jan 1, 1939

By E. G. Leonardon, C. Schlumberger, M. Schlumberger

Last year the authors presented a paper that discussed the various electrical measurements they perform in drill holes, which they name "electrical coring."' The object of the present paper is to give a brief account of the points of scientific interest that have been elucidated by further field work and laboratory research, as well as the economic results that have been attained recently. The practical examples given in this paper are drawn, for the most part, from the field work performed in Russian oil fields during the years 1931 and 1932. This is due to the fact that, thanks to the comprehensive cooperation of the Russian geologists and scientists, the authors are allowed to make public a large amount of recant information. In other countries in which the authors are engaged in similar work, the competition between private companies makes it imperative, for a considerable lapse of time, to avoid publication of the results obtained. The following points will be discussed successively, under separate headings: 1. Electrochemical phenomena in drill holes. 2. Stratigraphic correlations and tectonic studies. 3. Relations' between the productivity of oil horizons and their electrical resistivity. 4. Location of coal seams. 5. Summary and conclusions. Electrochemical Phenomena in Drill Holes Technical Publication 462l described the author's discovery concerning the existence of important differences of potential spontaneously gener-

Jan 1, 1934

By M. R. Campbell

You have just heard several papers on the classification of coal as this subject appears to the chemist; I shall approach it from the point of view of the geologist who, perforce, has to deal with coal as it occurs in the ground and with the miner of coal who knows certain phases of the physical characteristics of coal better than the scientist can possibly know them. The chemist is familiar with coal as it reaches him in the laboratory, but he seldom has an opportunity to see it in its native condition and to study its physical characteristics and its behavior under varying conditions of weather, transportation and use. He naturally regards the chemical composition of coal as the all-important feature upon which to base a system of classification and he is sometimes inclined to ignore as unscientific any scheme of classification that is based on characteristics other than chemical. The geologist, on the other hand, although he is glad to use the data furnished by the chemist, must depend largely upon the differences that he can see and feel. Classification Understandable to the Layman In the very comprehensive program of examination of the coal fields of the West which the U. S. Geological Survey undertook in 1906, it fell to my lot, as the responsible head of the work, to classify the coals in advance of much knowledge of their chemical composition and in regions where mining had not begun. In this work I was forced to devise some sort of classification that would work practically and that would be understandable to the layman in the field. Much of the classification was based on the work of those who had gone before me, but in the low rank coals of the West the field was unoccupied and I was forced to devise a scheme embracing both chemical and physical characteristics. This scheme has stood the test of actual practical application for several years but it needs revision and the sharpening of the limits between the different ranks. I feel that my experience warrants my saying that physical characteristics must be considered and I have faith to believe that some scheme embodying both can be devised.

Jan 1, 1930

By C. McLean, Erickson, S. G. Kolb, S. C. Moore

The Grossschloppen vein-uranium deposit, Bavaria, West Germany, was examined with underground workings during 1980-82 by Esso Erz GmbH, an affiliate of Exxon Minerals Company (EMC). Geologic evaluation entailed dense drilling of a portion of the deposit from workings constructed specifically for the program. Discovered in 1977, the deposit was initially explored by surface diamond drillholes which allowed definition of a 30-60 m wide vein system discontinuously mineralized along a 1000 m strike length and to at least a 450 m depth. The underground program was conceives as a cost-effective procedure to answer quest ions on vein correlation, grade continuity and variability. A 1200 m decline allowed access for detailed sampling of approximately 10% of the known area of mineralization. Fanned drillholes, logged by gamma probe, were spaced to provide intersections of veins at 10 to 20 m intervals. Six cross-cuts also penetrate the pitchblende and uranophane mineralization which occurs in 0.1 to 2.5 m thick quartz veins. Detailed cross-sections and level plans were constructed for resource estimates of the intensively studied portion of the vein system. The program resulted in the discovery of local, high grade areas and an average grade in the evaluated area nearly double that expected from surface drilling.

Jan 1, 1984

By Benjamin Smith Lyman

There seems to be dire need of repeated preachment against the too-frequent sad neglect of instrumental surveying and mapping in geological surveys. The value of the map as an illustration of the statements and opinions of a report is too apt to be overlooked; and its essential necessity in working out during its construction the proper conclusions from the observed facts is generally altogether misunderstood. Practical geology seeks, of course, to ascertain and indicate the character of workable or unworkable beds or veins, their depth, position, dip, and horizontal course, or strike, even below the surface; also their outcrops, and therefore, if workable, their extent; and so, taking account of their thickness and specific gravity, their weight in tons. It might, therefore, be called quantitative geology. For the study of more abstruse geological questions, too, it is in many cases necessary to gain some knowledge, or reasonable opinion, in regard to such hidden facts. In some cases, careful instrumental surveys are made; in others, from necessity or choice, there are few or no instrumental observations. It was said, 15 or 20 years ago, that there was an engineer in the anthracite-regions who was capable of telling, on first glancing at a new place, exactly what coal-bed was to be found there at a certain depth, and how thick—a splendid second-sight! "' 0, there be,' " you may be tempted to exclaim, " geologists ' that I have seen' geologize ' and heard others praise, and that highly, not to speak it profanely, "'—but let them pass without being fully characterized, lest the temptation towards profanity be altogether too strong. Yet such second-sight does not exceed the expectations of many men of imperfect geological knowledge, men who have heard of marvel-ously successful geological predictions, but are unaware of

Jan 1, 1910

By Charles H. Jacoby, Leo E. Read

IN diamond coring salt beds to evaluate deposits, special techniques are applied to standard slim hole drilling to obtain a representative sample of the water soluble sodium chloride. Industrial consumers generally require a run-of-the-mine material of 98.0 pct sodium chloride. Since no commercial beneficiation has yet been devised to upgrade the lower quality salt beds, the only processing is crushing and screening to the size required by the customer. Coring salt sections has recently become important not only in dry mining, but also in the development of brine cavities by hydraulic fracturing and the formation of jugs for storing liquid petroleum products. Drilling Fluid: The fluid used in coring salt beds in New York, Ohio, and Michigan is a thoroughly saturated brine made from 3.0 lb rock salt per gal of make-up water. This mined rock salt, -4 mesh +10 mesh, is dissolved in a lixator, a double-bottomed cone hopper that turns fresh water to fully saturated brine.

Jan 5, 1957

By Howland Bancroft

This article is not presented as a treatise on tin mines and mining in Bolivia. It deals primarily with the tin situation, and but fragmentary information is given regarding individual properties, generalizations being necessary in so short an article. Data on general subjects related to tin mining in Bolivia are necessarily abbreviated and very incomplete. It is believed that the references to be found in this article will help those interested to a more thorough understanding of the general conditions extant in Bolivia. Bolivia produces from one-fifth to one-fourth of the world's supply of tin. The United States consumes about one-half of the world's supply and produces practically none. Tin ore is not reduced in the United States. These facts are not generally appreciated by American mining men. Many conflicting data have been published regarding tin in Bolivia. The Transactions of the Institute contain practically no mention of this subject.' I have made a study of mines and mining conditions in the west coast republics of South America and have been particularly impressed by the possibilities of the Bolivian field.= In consequence the thought seems justified that the present meeting would present a fitting occasion to bring the tin situation in Bolivia to the attention of American mining men.

Jan 1, 1914

By R. W. Raymond

The sudden death of Captain Jones, September 28,1889, became known to his fellow-members on the eve of the Ottawa meeting of the Institute; and at that meeting, Mr. Charles Albert Ashburner, of Pittsburgh, expressed with unaffected feeling and unpremeditated eloquence the sorrow of all. Mr. Ashburner subsequently undertook to revise and extend, for in in the Transactions, the remarks he had made at Ottawa; but death surprised him also, in the midst of his labors; and it has become my duty and privilege to prepare from the memoranda he left behind, the present brief and inadequate notice. To me, who knew and loved them both, this task of double sorrow recalls them both, with a peculiar sense of presence and of absence. They seem to speak from another land, not far away, yet not with human voices—like an echo and its echo. William Richard Jones was born in Luzerne county, Pennsylvania, February 23, 1839. His father was Rev. John G. Jones, a Welsh minister, who had immigrated to the United States in 1832. William was the eldest son, and his father's failing health made it necessary for him to begin early the work of self-support. At the age of ten, he was apprenticed to the Crane Iron company, of Catasauqua, and in this humble capacity entered upon the profession in which he was to become famous. Unquestionably, the thorough acquaintance with all details, acquired by working his way from the bottom to the top, was one secret of the conspicuous executive ability which characterized him in the height of his career. According to a letter from Mr. J. H. Geer, Assistant Chief Engineer of the Cambria Iron Company, Mr. Jones entered the service of that company in 1858 or 1859 as a machinist, and continued to work in that capacity until July, 1862, when he enlisted as a private in the 133d Regiment of Pennsylvania Volunteers, in which he afterwards commanded a company. The regiment was mustered out of service in 1863, and Captain Jones re-enlisted in the 194th

Jan 1, 1890

By E. J. Bruderlin

A metallurgical process to be economically successful must be carried on under proper conditions of control and equipment. The question of equipment is always of primary importance. In the distillation process for the recovery of zinc by retorting, the retort is the all-important piece of equipment. Each retort in a working blóck must function as a separate unit. Over-all block efficiency is the result of the ability of the individual retort to withstand the severe conditions of operation for a maximum period of time. Therefore retort manufacture has been an ever present problem with the operator of a zinc-retorting plant. During recent years the zinc-plant operator has been faced with rapid changes in the character of the ores and concentrates. Operating costs have increased as a result of the introduction of the flotation process and the amount of flotation concentrates to be handled. To counteract increasing costs, the operator has found it necessary continually to attempt heavier loading of retorts, until a 45 to 50-lb. charge per cubic foot of retort space has become common practice. Heavy loading has brought about severe firing conditions, which, in turn, have emphasized the necessity for further improving the quality of the retort. Increasing percentages of detrimental impurities in the retort charges have also added to the operator's difficulties. Amarillo Silicon Carbide Retorts At the Amarillo plant of the American Smelting and Refining Co. a retort made of a suitable plastic clay grogged with silicon carbide has been found to best meet the present-day requirements. Retorts of this kind have been in use at Amarillo for 8 years and have shown an average furnace life of approximately 175 calendar days. The Amarillo retort is cylindrical in shape and after burning is approximately 83/4 in, inside diameter by 60 in. over-all length. The wall thickness is 136 in., except for the butt of the retort, which is approximately 2½ in. thick. The retort mud has a shrinkage of 3 per cent, or approximately % in. per foot. The silicon carbide retort after being properly dried weighs about 211 lb. When the retort is fired and ready to go into use the weight decreases to approximately 203 lb.

Jan 1, 1937

By Richard B. Greenwalt

INTRODUCTION Direct reduction of iron ores has unquestionably become established as an important step in the worldwide steelmaking industry. The history of this development has been long and fraught with difficulty. In 1800, Champlain suggested the direct reduction concept using carbon and a shallow hearth vessel. Roughly 100 years later, Jones attempted a commercial process using carbon and producer gas in a rotary kiln. During the early years of this century, numerous attempts were made to start commercial direct reduction plants using such processes as Hoganas, Wiberg, Krupp-Renn, and others. Most of these were short lived, being abandoned due to a variety of technical and economical factors. Today, however, a new generation of direct reduction processes has emerged. We enter 1977 with at least 40 commercial plants in operation using 15 processes in 14 countries. These plants have combined total annual capacity of roughly 10 million tonnes of direct reduced product. Many articles have been written, and projections made, concerning the future growth potential for direct reduction. As is al- ways the case with projections, the numbers vary, but the outlook does not. Anyone who participated in the years of effort that have gone into this field of endeavor should be excited and justly rewarded by noting the shape of the curve in Figure 1.

Jan 1, 1977

By Michael Tenenbaum

RECENT researches on the reduction of iron ores have stimulated interest in the effect of increased pressures within the iron blast furnace. From a physicochemical viewpoint, it seems logical to suppose that the increased pressure would increase the rate of reduction of the iron ore within the furnace. This increased reaction velocity would in turn be reflected in an increase in the output of the blast furnace. Any sub-stantial effect of elevated blast-furnace pressures should accordingly be of both technical and economic interest to the operator. It is doubtful whether it is possible to increase the pressure in the stack of the blast furnace beyond two or three atmospheres without incurring severe mechanical difficulties. The benefits to be procured by elevations in pressure must therefore be restricted to pressures below two, or at the most, three atmospheres. Within this range it would seem both economically and mechanically feasible to modify the present design of the upper portion of the blast furnace to accommodate these more stringent operating conditions. This investigation was undertaken to study the effect of moderate pressures on the rate of reduction of iron ore with hydrogen. The use of carbon monoxide is contemplated for later work. Although any results that are obtained in the laboratory cannot be interpreted directly in terms of large-scale commercial operations, it is possible, through such an investigation, to ascertain the order of magnitude of the effects of higher pressure. A more quantitative conception of the effects that would result from the use of increased pressures in the modern blast furnace is needed.

Jan 1, 1939

By A. A. Janke, G. J. Vogel, W. M. Swift

The combustion of fossil fuels in a fluidized bed of calcined limestone particles is a potentially efficient and economically attractive process for the generation of steam for electric power production and other uses. The process results in greatly reduced emissions of both sulfur oxide and nitrogen oxide pollutants. Development work, evaluations, and design studies are being carried out by various organizations under contract with the Department of Interior (Office of Coal Research, OCR) and with the U.S. Environmental Protection Agency, (EPA). The Atomic Energy Commission's Argonne National Laboratory is one of the principal participants in the development program under interagency agreements with EPA and OCR. The principal reasons for developing fluidized-bed combustion, its advantages and disadvantages over conventional combustion methods, and some of the potential applications of the process are covered in this paper. The participants in the multiorganizational program, the sponsoring agencies, the general status of development of the overall project, and the chief program areas that still require resolution are discussed. The main features of the program of work at Argonne National Laboratory and the results achieved so far are also included.

Jan 1, 1976

By William P. Blake

In addition to uintaite, the Uintah Mountains contain a deposit, or vein, of the peculiar hydrocarbon mineral, to which I have given the name wurtzilite, * in honor of the chemist, Henry Wurtz, Ph.D., of New York, who, in 1865, described grahamite, and who has added to our knowledge of the composition of the hydrocarbon minerals. Wurtzilite and uintaite are very similar in appearance, but are very different in their physical and chemical properties. Both are black, splendent and shining in fresh fracture; but the wurtzilite has a decided toughness, and a degree of elasticity, especially when warmed, which suggests to some persons a resemblance to caoutchouc. It was at first, at Salt Lake, believed and reported to be a mineral form of India-rubber, and great expectations of its value as a substitute for crude rubber were indulged in. It was, however, found that it would not act like rubber with sulphur; it would not incorporate with it and become "volcanized," and it was very refractory and insoluble in the ordinary solvents of rubber and of uintaite. The elasticity, though unlike the elasticity of rubber, led to the reference of the mineral to the species elaterite, the only name under which an elastic bitumen is described in the mineralogies; and it is so called in the list of the mineral products of Utah, given in the last message of the Governor of the Territory. The name elaterite, as used by Dana, covers at least three differing substances, ranging in specific gravity from 0.905 to 1.223. Two of the varieties are soft and elastic, much like India-rubber, and one is occasionally hard and brittle, imbedded in the softer kinds. All are rare, and comparatively unknown, and not generally represented in mineral collections. One of the varieties referred to here is the subterranean fungus from Derbyshire, described by Lister as early as 1673.

Jan 1, 1890

By R. J. Mechin

Top-slicing was introduced in the Pachuca district in 1917 by T. C. Baker, at that time mine superintendent of the Santa Gertmdis mine. There then existed 1200 ft. below the surface, lying between the fourteenth and eighteenth levels (a vertical distance of 354.2 ft.) a block of ore having a length of 295 ft. and an average width of 82 ft. and dipping at an angle of 65°. This block lay in the hanging wall of the vein and consisted of highly altered and fractured andesite, cut through with mineralized quartz stringers. On the foot-wall side, 26 ft. of old filling, left by former operators, was of payable grade. Stoping therein was first undertaken by the square-set filling system, but because of the extremely heavy hanging wall and loose dry filling in the foot wall, all square setting had to be accompanied by spiling, which made the operation exceedingly slow and costly. A system of mining was sought that would eliminate the difficulties inherent to the square-set system in heavy ground and that at the same time would effect the desired economies in mining. After several years, top-slicing has met all the conditions most satisfactorily, so that when similar conditions presented themselves in El Bordo mine, this method was adopted with necessary modifications. El Bordo mine is operated by the Santa Gertrudis company, and is situated about two miles north of Pachuca. Because of the diversity of the orebodies, a number of different mining methods are in use, among them top-slicing. Description of Block of Ore Former operators, when mining the original vein, left in the foot wall ore of too low grade to be profitable at the time; also, considerabe low-grade material was sorted out and stored as filling in the stopes. Some pillars were left in place, either for support or because they were not payable. All this has formed a body of ore that can now be exploited

Jan 1, 1925