Search Documents

By Carle Hayward

THE effect of copper on steel has been studied by numerous investigators. Before modern testing methods had been developed, blacksmiths noted red shortness in iron, the cause for which was ascribed to the presence of copper. Numerous papers have been published on the corrosion of steels containing various amounts of copper, and a few writers have discussed the effect of copper on the mechanical properties of steel. The purpose of the investigation described in the following paper was to obtain additional data on the mechanical properties of medium-carbon steel containing small quantities of copper. Among those who have published results of mechanical tests on copper steels are Ball,1 who states that copper increases the tensile strength and 'hardness but lowers the elongation. Stead2 states that copper steels closely resemble nickel steels containing equivalent percentages of nickel,, as regards tensile strength, resistance to shock, corrosion and hardness. Wigham 5 found that copper in small amounts had no injurious effect on steel. Breuil4 found that with 1 per cent. carbon, copper lessened the brittleness of steel and in low-carbon steel it increased the tensile strength and lowered the ductility slightly. H. H. Campbell 5 states that copper up to 0.25 per cent. slightly raises the elastic limit, elongation and reduction of area.

Jan 1, 1918

By A. J. Lena, M. F. Hawkes

Changes in hardness, tensile properties, microstructure, electrical resistance, and X-ray diffraction effects indicate that lattice strains are necessary for the embrittlement of ferritic stainless steels when heated for relatively short times at 475°C (885°F). It is suggested that 475°C (885°F) embrittlement is due to the accelerated formation of an intermediate stage in the formation of s under the influence of these strains. FERRITIC stainless steels (low carbon alloys of iron with more than 15 pct Cr) are subject to two forms of embrittlement when heated in the temperature range of 375° to 750°C. The embrittlement which occurs after long time heating between 565" and 750°C is well understood; it is caused by the precipitation of the hard, brittle s phase. Sigma is an intermetallic compound of approximate equi-atomic composition with an extended range of formation in Fe-Cr alloys. The maximum temperature at which this form of embrittlement can occur is dependent upon chromium content; and is approximately 620°C for a 17 pct Cr steel and 730°C for a 27 pct Cr steel. The other form of embrittlement occurs after relatively short heating periods in the range of 375" to 565°C; in the higher chromium steels, hours may be sufficient as compared to months for s embrittlement. This phenomenon is not at all well understood and several controversial theories have been proposed. The rate and intensity of embrittlement increase with increasing chromium content but the maximum rate occurs at 475°C re-gardless of chromium content. As a result of this, the phenomenon has been termed 475°C (885°F) embrittlement. The effect of 475°C embrittlement on the properties of ferritic stainless steels has been thoroughly reviewed by Heger.1 The embrittlement causes a pronounced decrease in room temperature impact strength and ductility, a large increase in hardness and tensile strength, and a decrease in electrical resistivity and corrosion resistance. Microstructural changes accompanying embrittlement are minor and difficult to interpret with a general grain darkening, appearance of a lamellar precipitate, grain boundary widening, and precipitation along ferrite veins having been reported at various times. With the exception of reported line broadening, X-ray diffraction studies by conventional Debye analysis of solid samples have been of little value. BY making use of electron diffraction methods, Fisher, Dulis, and Car-roll' have recently shown the existence of a chromi-um-rich, body-centered cubic phase in 27 pct Cr steels which had been aged at 482°C (900°F) for as long as four years. Two types of theories have been advanced to account for the embrittlement. The first of these requires the precipitation of a phase not inherent in the Fe-Cr system with various investigators suggesting a carbide,3 nitride,3 phosphide,4 or oxide." Theories of this type have difficulty accounting for the influence of alloying elements on the embrittlement and for the facts that a minimum chromium content is necessary for embrittlement and the intensity of embrittlement increases with increasing chromium content. The second type of theory that has been proposed relates 475°C embrittlement to s phase formation which is inherent in the Fe-Cr system. An assumption of this kind can adequately explain the influence of alloying elements, for they exert an effect on 475°C embrittlement similar to that on s phase for-mation as can be seen in Table I. The minimum chromium content is essentially the same for both phenomena and it has been shown12,13 that s is a stable phase in the embrittling temperature range. In addition, it has been reported14,15 that pure alloys embrittle to the same extent as commercial type alloys. There are, however, several factors which have prevented complete acceptance of a s phase theory. Foremost of these is that the embrittlement can be removed by reheating for short time periods above 600°C, which in the higher chromium steels is within the stable s region. No s has ever been observed after one of these curing treatments, nor has any s been found as a result of embrittlement at 475°C. In addition, the simple precipitation of s cannot explain the time-temperature relationships for reactions between 350°and 750°C. This behavior is shown schematically in Fig. 1. Newell 16 and Ried-rich and Loib4 have shown that 475°C embrittlement follows a C-type curve as illustrated, while Short-

Jan 1, 1955

By V. S. Swaminathan

This year, Great Britain is looking back over a century to August 14, 1850, the day when the first "Act for the Inspection of Coal Mines" was passed in that country, an act which signaled the end of over two hundred years of hitherto uncontrolled and dangerous mining practices. It was back in the time of Queen Elizabeth that . thousands of pounds were invested in mining, particularly coal mining in England and Scot- land. By 1640 there were collieries producing 10,000 to 25,000 tons of coal per year. In the seventeenth century the Tyne district coal industry was organized into powerful partnerships, and coal took an even larger part in industry, as a source of power and as fuel for the iron industry. In the early 19th century a "phenomenal, almost devastating expansion" characterized Britain's coal industry, and it was sparked by a 111 pct in- crease in the population of England and Wales in the first half of the century. Coal production for those 50 years increased 470 pct and pig iron production was up 946 pct for the period 1801-51.

Jan 1, 1950

Jan 1, 1935

By S. R. B. Cooke, R. O. Huch, C. S. Chang

IN the flotation of iron ores laurylamine derivatives have been used for considerable time.1, 2' To effect satisfactory separation of the gangue, pre-dominantly silica, from the iron oxide minerals, the addition of specific depressants for the iron oxides has been found necessary. Starches and starch products have been used for this purpose.V here is, however, very little published information on the effects of these materials and other variables on this process. In some cases it has been found that prior acid scrubbing and desliming are essential," and depending upon the efficiency of the subsequent washing step, there will be accompanying changes in pH. It was the object of this investigation to test and observe the effects of the above factor as well as to examine and compare the action of various starches and starch products. Ore Preparation The ore used in this experiment was a wash-ore tailing obtained from the western Mesabi range. Microscopic examination and x-ray analysis of the ore showed it to consist of hematite, goethite, and quartz. Physical properties of the iron minerals ranged from hard and crystalline to earthy and ocherous. The quartz grains were discolored either because of iron-oxide inclusions or because of a sur-face coating of iron oxide. The ore assayed 27.52

Jan 1, 1954

By Anthony Sharkey

Introduction In Europe, longwall mining accounts for over 95% of coal produced from deep mines, whereas in the U.S.A., longwall accounts for less than 5% of deep mine coal production. There are many reasons for the difference, but in general: a. U.S. mine operators have invested heavily in continuous mining or conventional equipment which continues to produce acceptable results; b. There 1s a reluctance to change from, a familiar (and proven) mining method to an unfamiliar one, despite promises of huge production increases,; c. Multi-seam mining in Europe has made longwall the only really viable mining method, whereas In the U.S.A. multi-seam mining (particularly in "below-drainage" mines), is relatively rare; d. Although some spectacular results have been achieved by longwall in the U.S.A.(I), the general performance of longwall in this country has not been good enough to generate much enthusiasm for its wide application; e. The much higher level of investment in face equipment required for longwall when compared to alternative methods (approximately $7.5 million for a medium seam longwall installation and $1 million to $1.5 million for a continuous miner section). However, declining productivity, national energy requirements and safety legislation are creating a situation in which longwall as a viable mining method is being examined more closely and in more places than hitherto. This paper, therefore, attempts to identify some of the principal criteria needing examination in any assessment of the feasibility of longwall application, the limitations of information for those criteria in the decision making process and the need for further research and development to assist the mine operators make the decisions.

Jan 1, 1981

By C. F. Floe, M. Cohen, M. B. Bever, V. G. Paranjpe

NITROGEN is becoming recognized as one of the important elements in ferrous physical metallurgy. Several investigations indicate that nitrogen plays a significant part in such phenomena as strain aging and temper brittleness. Nitrogen is known to be a powerful austenite stabilizer and may be a useful alloying element in stainless steels. The hard-enability of steels has been found to be increased by nitrogen. The nitriding and carbonitriding pro- cesses are examples of successful industrial application of nitrogen in ferrous materials. For a complete understanding of the various roles played by nitrogen in ferrous metallurgy a knowledge of the phase relations in the binary iron-nitrogen system is essential. The literature contains a variety of iron-nitrogen phase diagrams. Those suggested by Fry, Sawyer,² Epstein and his coworkers,³,4 Lehrer,5 Eisenhut and Kaupp, and Hägg7,8 differ significantly from one another. Moreover, the most recent of these investigations dates back about twenty years. A re-determination of the entire diagram, therefore, appeared desirable. In addition to the published phase diagrams, investigations have been carried out on portions of the iron-nitrogen system. Bramley and Haywood determined the composition and temperature of the iron-iron nitride eutectoid. The maximum solubility of nitrogen in a iron was investigated by Portevin and Seferian10 and by Diikstra. 11 Several investigators have determined the crystal structure of the various iron-nitrogen phases. In fact, Eisenhut and Kaupp6 and Hägg7 based their entire phase diagrams on the results of such studies. Epstein' and Emmett12 reported lattice-parameter measurements on the E (hexagonal close-packed) phase. Osawa and Iwaisumi13 also studied the change in lattice parameters of the a, ? and E phases with nitrogen content. Brill" and Hägg7 showed that the y' phase has an ordered structure, and Hendricks and Kostingsl5 suggested a structural relation between the E and phases. In a recent investigation Jackl6 arefully studied the super-lattice reflections from the y' and phases. Experimental Procedure A large variety of experimental methods has been used by previous investigators in studying the iron-nitrogen system. These methods include thermal analysis, microscopic examination, X ray diffraction, magnetic measurements, dilatometric analysis and anelastic experiments. Thermal analysis is of low accuracy in determining changes in the solid state. This accuracy is further decreased for iron-nitrogen alloys since composition changes will occur during heating or cooling unless extreme care is taken to use a proper atmosphere. Metallographic methods are of small value . because homogeneous iron-nitrogen alloys of sufficient size can be produced only with great difficulty. The dilatometric method is open to the same objections as thermal analysis in that changes in composition may occur during heating and cooling. Lattice parameter measurements by X ray diffraction can be used satisfactorily for determining phase boundaries if cooling is fast enough to prevent structural changes. In view of the limitations of the various other techniques two methods only were adopted in this investigation, (1) X ray diffraction measurements, and (2) a controlled nitrogenizing method. The second method is an innovation for investigating the iron-nitrogen system, and will be described at length. Materials: All iron-nitrogen alloys were prepared from carbonyl iron powder of the analysis shown in table I. The average particle size was about 20

Jan 1, 1951

Jan 1, 1935

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 Robert G. Johnson, Richard J. Prosen

THE present work was done in connection with a program for investigating metal-to-ceramic braze techniques using the well-known reactivity of titanium with certain ceramic oxides. The investigation extended over the range of 0 to 30 pct Ti. The indium was obtained from the Indium Corp. of America and was specified to be 99.97 pct pure. The titanium was supplied by Metals Disintegrating Co. and was stated to be 99.5 pct pure. Each 2 to 4 g quantity of the alloy compositions studied was prepared using a mixture of 300 mesh powders pressed into pellet form. The pellets were heated in thin-walled molybdenum crucibles using a resistance-wound furnace in a vacuum less than 10-4 mm of Hg. Little reaction occurred between the molten alloy and the crucibles at the temperatures and short time intervals used. Only slight spectroscopic traces of molybdenum were found in the melt after a typical period of heating. The points shown on the phase diagram of Fig. 1 represent thermal arrest measurements. The phase boundaries shown are consistent with the thermal arrest and X-ray data obtained. The temperatures were determined using a Pt-Pt 10 pct Rh thermocouple with the junction spot-welded to a short molybdenum rod. The rod was almost completely immersed in the liquid metal, so that good thermal contact with the melt was achieved. The small mass of the crucible and its contents made it possible to obtain many heating and cooling curves in a few minutes time, an advantage which helped to minimize the effects of indium evaporation at the higher temperatures. A Brown strip chart recorder was used to display the thermal arrest curves. To check the technique, the melting point of 99.999 pure Al was measured and found to be within 1 of 660.2c, the accepted melting point. The upper limit of temperature with this technique was about 900°C beyond which the evaporation rate of indium became great enough to alter appreciably the alloy composition during the runs. A peritectic transition was found at 796°+ 5°C from 1.5 to 30 wt pct Ti. It was not found at 0.5 or 1.0 pct. A small super-cooling effect was observed. The melting-point transition to the B + L phase was found up to 20 pct Ti but not at 25 pct. Within the 1 deg accuracy of the measurement, the transition temperature was that of pure indium, 156°C. The liquidus line to the left of the 1.5 titanium point was located only approximately. The two crossed circle points at 1.0 and 0.5 pct Ti place a lower limit on the liquidus line and were determined by observing visually the cessation of vibrations in the melt caused by the damping effect as B-phase crystals were formed during cooling. The B-phase boundary was found at 23.8 pct Ti by X-ray analyses of small single crystals of the B phase isolated from 2 pct Ti melts. The compound was found to be Jetragonal with lattice dimensions of c = 3.052A and a = 10.094W. From the unit cell dimensions and the measured density of 6.42 i 0.05 g per cc, the compound was determined to be In4Ti3 which has 23.8 pct Ti. The calculated density of 6.44 g per cc is obtained assuming 2 mol

Jan 1, 1962

By R. I. Jaffee, H. R. Ogden

AT the present time, there appear to be two conflicting opinions on the solubility of boron in titanium. P. Ehrlich' has indicated from X-ray diffraction work that boron is soluble in titanium up to TiB0.8 (17.8 wt pct, 44 atomic pct). The X-ray diffraction pattern for titanium was found in compositions up to TiB0.05_0.07 (1.1 to 1.6 wt pct); then, without a phase gap, superlattice lines appeared up to TiB0.8 On the other hand, Craighead, Simmons, and Eastwood' have estimated the solubility of boron in both alpha and beta titanium to be less than 0.1 wt pct, based on results of metallographic analysis. In some recent work done at Battelle, results were obtained which shed more light on the titanium-rich end of the titanium-boron system. Iodide-type titanium and high-purity crystalline boron were used in this investigation. The boron was prepared by hydrogen reduction of boron tri-bromide and deposition on a hot tungsten wire. The alloys were prepared by arc melting in an argon atmosphere of 10 cm Hg pressure on a water-cooled copper hearth. The ingots were hot rolled to strip at 850°C. Alloys containing up to 1 pct B could be hot rolled. Those containing 2 pct or more B could not be hot rolled. Metallographically, it was found that a second phase was present in alloys containing as little as 0.4 pct B, and that the quantity of second phase increased with increasing boron content. This is illustrated in Figs. la and lb, which show the microstructures of a Ti-0.4B and a Ti-1B alloy annealed in argon at 850°C. X-ray diffraction patterns of alloys containing 1 and 5 pct B revealed the presence of extra lines which correspond to the superlattice lines reported by Ehrlich.' However, no evidence was found of a shift in the lattice constants of alpha titanium indicating that there is very little, if any, solubility of boron in alpha titanium. This fact, coupled with the fact that the alloys were definitely two-phase, indicates that the extra lines are not superlattice lines, but are more probably the result of a second phase of a hexagonal structure almost identical in cell

Jan 1, 1952

By James A. Lewis

It is the purpose of this paper to show the importance of sand characteristics, when combined with other physical data, in evaluating production obtained by secondary recovery operations, and to indicate the benefits to be gained from the application of these principles to primary production.

Jan 1, 1942

By Akira Ishizu, Nobuo Matsui, Hideo Yamamoto, Tatsuya Nagahama

At Kamioka Mine of Mitsui Mining & Smelting Co., Ltd., Japan there are three mills, treating a total of 6400 t/d of lead-zinc Ore. In the lead-zinc bulk differential flotation at Shikama Mill the addition of reagents is automatically controlled by the feed rate, the lead and zinc content in feed, froth and tailing, the pH and the concentration of cyanide ion in the pulp. As the zinc thickener overflow at Shikama Mill contains CU(CN)3--, ZnS, CdS, CN-, xanthate and frother, all the ingredients in the over- flow other than CN are floated by using the Nagahm flotation machine, and the water containing only CN- is effectively recycled to the lead- zinc differential flotation circuit. In the lead-zinc straight differential flotation at Mozumi Mill, the overflow of tailing pond is recycled especially to the cleaning flotation circuit by decreasing the pulp density. Thus the integrated recycling of wastewater greatly reduces environmental problem and in addition, it generates sizeable profit.

Jan 1, 1977

By Arthur F. L. Bell

Discussion of the paper of ARTHUR F. L. BELL, presented at the San Francisco meeting, September, 1915, and printed in Bulletin No. 105, September, 1915, pp. 1769 to 1799. WILLIAM A. WILLIAMS, San Francisco, Cal.-Is the Union Avila plant run as a topping plant or as a dehydrating plant? A. F. L. BELL, San Francisco, Cal.-Both. It takes off an average of 20 per cent. water besides topping the oil. Part of the crude oil is run through an electrical separator before running to the topping plant, but the entire crude averages about 20 per cent. when it enters the topping plant. DAVID T. DAY, Washington, D. C.-I suppose most of the work contemplated in these large topping plants is simply to deal with topping the oils with only a small percentage of water in them. A. F. L. BELL.-Not more than 2 per cent. of water can be handled in ordinary stills without causing trouble. At our Gavotte refinery, where the oil runs from 15 to 30 per cent. water, we carry 20 lb., pressure oil our stills to hold the framing down, we can do that with small stills, with large one's it would not be safe; but with a retort, the quantity of water contained in the oil does not affect its working. It simply means additional fuel to evaporate the water.

Jan 12, 1915

By A. W. Ashbrook

There are essentially three main classifications for extractants: acidic, basic, and neutral. The acidic and basic are also referred to as cationic and anionic, respectively. Some extractants are shown in Table 11-1. Acidic Extractants Acidic extractants which are of use, because of cost and/or insolubility in water, are alkylphosphoric, sulphonic, aliphatic monocarboxylic acids and naphthalene derivatives.

Jan 1, 1978

Jan 1, 1932

By E. Alan Haley

Accurate and economic control of line and grade on long tunnels, large structures, excavations and waterways has been a problem to surveyors and engineers for decades. The conventional method of surveying, incorporating a level, transit and a number of surveying technicians, has proven to be a very expensive and time-consuming operation. Now, however, engineers have adapted the laser to help ease the problems of surveying, at the same time increasing the efficiency of such operations. The laser, which projects a continuous, narrow red beam of brilliant light, provides a constant alignment reference that does not interfere with personnel or equipment. A complete laser alignment system, specifically designed for and suited to a variety of mining and tunneling operations, has been developed by the Perkin-Elmer Corp. The engineering significance of this development can be fully realized when it is noted that, aside from potentially tremendous economic advantages in terms of labor savings, the laser beam provides a system of alignment that is at least ten times more accurate than presently used optical systems. The new laser system provides accuracies within 10 microinches per foot (1 x 10-5in.) when used with an accessory centering detector. In one of its first field trials, the laser was used for alignment of a two-mile tunnel which showed a total deviation of less than 5/8 in.

Jan 4, 1968

At the meeting of the Board of Directors of this Institute on Feb. 16, 1915, the 14 members of the Board present unanimously elected Professor Kemp an Honorary Member. The nomination of Professor Kemp was signed by 21 members of the Institute, none of whom are members of the Board of Directors, and recited his qualifications for Honorary Membership in the following terms: Professor Kemp graduated from Amherst College in the class of 1881, and from the School of Mines, Columbia University, in the class of 1884. After serving as instructor in geology in Cornell University for a few years he was called back to Columbia as adjunct professor in 1891, was made full professor the following year, and has since filled that office with dignity and honor. Among the first to recognize they importance of igneous rocks in the formation of orebodies, his studies have contributed greatly to that increase of knowledge of economic geology in which the Transactions of the Institute has had an influential part, and he is recognized both abroad and in this country as one of the most distinguished scholars in geology which America has produced. This recognition is evident in the honorary degrees of Sc. D. conferred on him by Amherst College in 1906, and LL. D. conferred by McGill University in 1913, as well as by election to membership in the National Academy of Sciences, and a corresponding member of the Academy of Sciences of. Christiania, and the Geological Society of. Stockholm. Professor Kemp was a Manager of the American Institute of Mining Engineers from 1896 to 1898, Vice-President from 1903 to 1904, a Director from 1905 to 1912, President and President of the Board of Directors in 1912, and Past President since that time. During these years he has labored loyally for the upbuilding of the Institute, serving on many committees, as well as in the offices enumerated. He has also served as President of the American Association for the Advancement of Science, the New York Academy of Sciences, and on the governing board of the Geological Society of America and the New York Botanical Gardens. His service is not confined, however, to these labors for the good of the profession and his contributions to exact knowledge of geology. In his almost 25 years as a professor in Columbia University there have come under his influence a great group of young men in whom he has inspired unflagging zeal in the search for truth, and to whom he has set an example of unselfish service. The value of such a service cannot be overestimated and in electing him to Honorary Membership the Institute would officially recognize the measure of appreciation which his professional colleagues have long accorded to him.

Jan 4, 1915

By A. L. Slaughter

The Homestake mine, located in western South Dakota, was discovered in 1876. The first reported production was in I 878. Total production through 1965 is 6,554,249 troy ounces of silver and 27,961,276 troy ounces of gold, worth $987,000,000 at present prices. Precambrian sedimentary formations at Lead total 20,000 feet. The Poorman Formation, the oldest, is chiefly ankerite carbonate. The Homestake Formation is iron-magnesium carbonate. The younger formations are argillaceous with some quartzites. The Cambrian Deadwood Formation unconformably overlies the Precambrian. All are cut by Tertiary intrusives. Sideroplesite schist of the Homestake Formation was converted to cummingtonite schist in the zones of higher-grade metamorphism. The Precambrian rocks show the effects of extreme isoclinal folding. A second stage of folding ( cross folds) may have been caused by the Tertiary intrusives. All folds plunge to the southeast. The Homestake ore bodies are pipe-like replacements of the Homestake Formation in zones of cross folding. It is believed that dilatation of the schists has increased permeability in these zones. Chloritization of the schists is the most widespread effect of the mineralization which is divided into four stages. Principal minerals of the first stage are quartz, chlorite, and arsenopyrite; in the second stage, quartz, ankerite, and pyrrhotite. In the third stage only pyrrhotite was deposited. The fourth stage followed the intrusions of Tertiary dikes and deposited mostly pyrite and calcite. Gold accompanies all stages and is always the last mineral to be deposited. It is most closely associated with arsenopyrite of the first stage but can be interpreted as having been deposited during the fourth stage and superimposed on the products of the earlier stages.

Jan 1, 1968

By F. J. Escandon V.

The Plomosas stratiform lead and zinc deposits are located in northeastern Chihuahua in a sequence of folded Paleozoic and Jurassic rocks. They consist mainly of channel or blanket-like bodies of ellipsoidal cross section restricted to a 60-in-thick shaly limestone and a 30-m-thick marble horizon of La Casita formation, with some reemplacement veins and shoots within the Plomosas formation. The mineralogy consists of iron-poor sphalerite, galena with a small silver content, and pyrite, in a gangue of calcite, barite, and minor quartz. The ore bodies present a lateral zoning with zinc-lead ratios increasing to the northwest. Vertical zoning shows marked changes in zinc-lead ratios and in the width and tenor of the ore which cannot be related to sedimentary or diagenetic features. Transgressive mineralization and some small fissure veins and breccia pipes also point to an epigenetic origin. Sulfur isotope analysis and geochemical data indicate hydrothermal solutions. Texture of the ores in the Mina Vieja marble is coarse, but in the Cuesta shale it is banded along bedding. The low iron and silver content of the sphalerite and galena and the weak hydrothermal alteration (only marbleization) of the wall rock suggest a telethermal stage of the solutions. There is no evidence of a possible intrusive rock mineralization.

Jan 1, 1976