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By H. L. Hartman

The drop tester has proved an invaluable tool for the investigation of percussion drilling in the laboratory in "slow motion". It has allowed the process of rock penetration by impact to be studied a single blow at a time. In the present work, the relation of cratering to indexing has been determined under conditions simulating those in the bottom of the hole at atmospheric pressure. Indexed blows form craters which are influenced by others adjacent to them. Two unique effects are involved: (1) the provision of additional free faces in proximity to the point of impact and (2) the creation of subsurface damage by the previous blow(s). Both have a pronounced influence on the volume of rock removed per blow, which governs the rate of penetration in actual drilling. The emphasis in this study was placed on determining effects of index distance and impact energy on crater volume when blows were struck on a previorusly "drilled" or damaged surface, a situation most representative of down-hole conditions. The results indicated that (I) the optimum index distance on a damaged surface is greater than on a fresh, undamaged rock surface; (2) the volume of rock broken at optimum index distance is about the same for both surface conditions with die-shaped chisels but tends to be greater on a cratered surface with wedges; (3) the optimum index distance and maximum crater volume are proportional to the energy level; (4) at a given energy level, the volume of rock broken by dies generally exceeds that by wedges; and (5) maximum crater volume varies, approximately, inversely with width of die but is nearly independent of included angle of wedge. INTRODUCTION This is the third of a series l,2 of papers reporting on one phase of a continuing program of drilling research being conducted in the Rock Mechanics Laboratory at The Pennsylvania State U. The phase under consideration is crater geometry — blow energy relations in percussion drilling. While the previous papers have discussed mainly craters produced by single blows, indexed-blow studies are the subject of this paper. The basic mechanism of drilling under study here — that of penetration of a chisel-shaped bit subjected to impact — is the one employed in probably 90 per cent of all rock drilling in mining, percussion drilling. It also forms the fundamental action in nearly all oil well drilling with the so-called rotary (roller-bit) method. Here, the action is more complex, however, and may in actuality comprise rotary-percussion drilling. Certainly, the down-hole air and mud hammer drills, which superimpose percussion on rotation, belong in this latter category. In any event, impact blows constitute one of the principal mechanisms in the vast majority of drilling, mining or petroleum, and it is essential in drilling research to study percussion in all its basic aspects. Percussion drilling can be simulated in the laboratory by means of an impact drop tester. Striking one blow at a time with chisel-shaped bits, the drop tester permits study of most of the parameters in the drilling process except blow frequency and the interrelationship of certain variables. Single-blow craters, the simplest to produce, allow the determination of basic relationships, such as volume vs blow energy; while indexed craters most closely resemble the action in real drilling and provide data for the establishment of optimum operating criteria. Indexed-blow craters are those which are influenced by others in proximity. The simplest case to visualize, and the one studied in detail here, is that in which a given crater is formed adjacent and parallel to a previous crater, such that the second crater breaks into the first. A more complex situation usually exists downhole, where indexing is achieved by rotation of a radial-winged or rolling-cutter bit. But, admittedly, the phenomenon of indexing is more likely to be understood eventually if it is first studied in its simplest form, that related to parallel craters. Limited research has been conducted on indexed blows. The most complete study was that by Simon, 3,4 who proposed universal indexing curves to relate the important variables. His work, however, was conducted entirely with rows of craters formed on a

By Chester O. Ensign

Results of the application of geologic knowledge to grade control have been remarkable. Grade reduction from dilution has been diminished from greater than 9% at the time of the program's beginning to about 2% at present. This has resulted in an increase of about 1.8 lb of copper per ton of ore mined and has made a substantial contribution to earnings at White Pine during the past two years. Even more improvement is expected in the future. The White Pine orebody, situated in the southwestern portion of the Keweenaw peninsula of upper Michigan, is a gently dipping stratiform or bedded deposit. Copper distribution is stratigraphically controlled with higher values being confined to specific beds in the ore column. Room-and-pillar mining is practiced. Mining technique and geologic characteristics present a special array of problems in controlling the grade of ore.

Jan 4, 1964

By Jr. F. M. Perkins.

Capillary forces play a controlling role in water-drive displacement processes both in laboratory experiments and in actual reservoirs, but their quantitative importance may be quite different in the two cases. Because of the importance of conducting laboratory experiments which are representative of field conditions, it is necessary to understand exactly the role of capillary forces in the displacement process. Though a number of experimental investigations related to this subject are contained in the literature, there appears to be a lack of information pertaining to unsteady-state experiments in water-wet media. This experimental study was conducted to obtain additional laboratory data to clarify further the role of capillary forces in both the macroscopic and microscopic flow of oil and water in porous materials. THEORETICAL CONSlDERATlONS The capillary pressure is defined as the difference in pressure between a continuous oil phase and a continuous water phase in a porous material.' The magnitude of this pressure difference depends on the interfacial curvature and the interfacial tension. The interfacial curvature is determined by the geometry of the pore spaces, the wettability of the rock surfaces, and the quantity of cach phase present. Capillary forces are involved in a water-drive displacement process in that they exert a controlling influence on the microscopic fluid distribution which in turn is reflected in the saturation or macroscopic flow behavior. Microscopic Fluid Distribution Because of the microscopic nature of the displacement of oil by water, it is necessary to consider the flow and the fluid distribution in individual pores. On this microscopic scale the capillary Forces, which act over a distance of one or two sand grain diameters, control the distribution of oil and water under static equilibrium conditions. When an external force is applied to the fluids, such as in a water-injection experiment, the applied forces tend to distort the oil-water interfaces. However, in most fine-grained, water-wet sands, the applied pressure difference across one or two grain diameters is usually several orders of magnitude less than the capillary pressure difference. These con-siderations lead to the theory' that even during flow the capillary forces continue to control the microscopic distribution of oil and water within the pores of a porous material for all practical reservoir and laboratory flow rates. This concept of capillary forces controlling the microscopic distribution of fluids has been substantially verified by other investigators3-7 who have found a lack of dependence of relative permeability and residual oil saturation on rate of fluid injection. Macroscopic Distribution The microscopic influence of capillary forces cannot be observed easily and only the effect on the macroscopic or average saturation can be detected. The saturation, of course, is really the point of interest. During a water flood, large differences in saturation at the flood front cause large capillary pressure gradients. This, in turn, causes water to advance ahead of the flood front thereby reducing the capillary pressure gradient in this region. The result is that in homogeneous porous media capillary pressure gradients tend to cause a diffuse displacement front. At low rates in laboratory columns, the front may extend over the entire column length. When the advancing water first reaches the outflow face of a core, the water, which is the wetting phase, cannot be produced because the pressure in the water just inside the core is lower than the pressure in the oil-filled space around the outflow face. This difference in pressure is equal to the capillary pressure for the water saturation existing at the outflow face. Water, therefore, accumulates at the outflow end of the core which causes a reduction in the capillary pressure. Because the capillary pressure does not vanish except at the residual oil saturation,7,8,9 water will not be produced until the residual oil saturation exists at the outflow face. This entire effect,"' which is called the "boundary effect", results in a region of relatively high water saturation near the outflow face. At low rates of injection in a short column, this region of high water saturation may extend over a considerable portion of the column. The influence of capillary forces on the macroscopic flow of oil and water have been described by Leverett.10 For unidirectional, viscous flow in the absence of gravity segregation, the expression in dimensionless form for the fraction of water in the flowing stream, f, is

Jan 1, 1958

By R. D. Stover, F. O. Shuck

The variation of binary-diffusion coefficients with composition in the liquid Bi-Sn system at 300°C was measured using the capillary-reservoir technique. The experimental coefficients did not exhibit a simple composition dependence. A number of tests were also made to determine the effect of variation of density with composition on convection within the capillaries. These tests indicate that the density changes arising from composition duferences may give rise to high diffusion coefficients unless care is taken to maintain a stable configuration. In recent years there has been considerable interest in diffusion in liquid metals. However, the bulk of the work done to date has involved measurements of self-diffusion or diffusion of dilute concentrations of "solute" metals. Because there are possible applications to liquid phase processing of metal alloys and since additional data may help to clarify the nature of diffusion in liquid metals, investigations of the concentration variation of diffusion coefficients in binary alloys have been undertaken. Of past studies only two have covered large ranges of binary composition. Niwa et al.' investigated the Pb-Sn, Bi-Pb, and Bi-Sn systems and Grace and Derge2 investigated the Bi-Pb system. Because of the discrepancy between the data of these investigators, it was deemed desirable to check the possibility of convection arising from the variation of density with composition. The capillary-reservoir technique of Anderson and saddington3 was chosen for the present investigation since it has been widely used for measurements involving dilute solute concentrations and it was the technique used by Grace and Derge.2 It was necessary, however, to modify the normal procedure of using a pure metal bath to avoid measurement of integral diffusion coefficients over large concentration ranges. The alloy system chosen for study was the Bi-Sn system for which there are some data available.' EXPERIMENTAL PROCEDURE In order to utilize the capillary-reservoir technique for measurements of diffusion coefficients as a function of composition, it was necessary to modify the normal procedure slightly. This modification consisted of using a reservoir composition which was only slightly different from that in the set of capillaries, in order that the integral coefficients measured might be taken over a small composition range and might thereby be assumed to approximate the differential coefficient at some average composition between that of the capillary and that of the bath. It was found that a composition difference of approximately 0.10 mass fraction provided a satisfactory compromise between a small increment in composition and reasonable accuracy in measuring changes of composition. The alloys were prepared from tin and bismuth of 99.999 pct purity. The materials were first cleaned of surface oxides, then weighed and melted to form a homogeneous alloy in a Pyrex filling apparatus. The capillaries used were of precision bore Pyrex tubing 1.000 *0.005 mm bore. Capillaries of various lengths (from 2.85 to 5.85 cm) were cut and sealed at one end by fusing a 3-mm Pyrex rod to the end. The capillaries were filled by inserting them into the filling chamber, evacuating the chamber, submerging the capillaries, and pressurizing the chamber with argon. Two sets of capillaries were prepared for each run. One set contained an alloy more dense than the bath alloy and one set a less dense alloy. This procedure was followed so that the effect of density difference on the measurement could be determined. After filling one set of capillaries, these were placed open end up in a capillary holder and transferred to the diffusion chamber which consisted of a Pyrex tube inserted into a graphite block. The second set of capillaries was then filled and placed into the diffusion chamber. The reservoir alloy, which had been melted in a separate crucible, then was poured carefully into the diffusion chamber. Sufficient reservoir alloy was used to cover all capillaries to a depth of several centimeters. All of these operations: capillary filling, melting of alloys, and diffusion anneal, were carried out in a fused-salt bath which maintained a temperature of 300"*1°C. All capillaries were permitted to diffuse for approximately 48 hr. At the end of the diffusion period the capillary holder was removed from the bath and

Jan 1, 1969

By WALDEMAR T. SCHALLER, EDWARD P. HENDERSON

THE material available for mineralogic study, consisted of drill cores, 2 to 3 in. thick, supplemented by small well cuttings. Such study has added no essential new information regarding the minerals, though the refractive indices, used for determinative purposes, have been determined more accurately than before, permitting the development of a scheme for the rapid identification of these minerals. The essential points brought out by the investigation are two: (1) that certain mineral associations evidently point the way to an understanding of the geologic history and (2) that a definite sequence of mineral formation has taken place so that the original minerals formed have been in part-reacted on producing new compounds and associations; Twenty minerals have been found. The most important are :

Jan 1, 1929

By H. Nakazawa, I. Iwasaki

Galvanic contact, occurring between electrically conducting minerals in flotation pulps, may affect the nature of mineral surfaces and influence their floatabilities. Rest potential and galvanic current measurements were made on an electrode combination of pyrite and pyrrhotite under nitrogen, air and oxygen aeration conditions. The results were correlated with their oxygen-consuming characteris- tics and flotation behaviors. The galvanic contact improved the floatability of pyrrhotite, but adversely affected that of pyrite. Auger electron spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy indicated that the formation of hydroxide or oxide and sulfate species of iron on pyrrhotite decreased, whereas that on pyrite increased when these minerals were held in contact. An electro- chemical mechanism was proposed for the observed behaviors.

Jan 1, 1986

The following list contains the names of members of whose deaths notices have been received at the Secretary's office during the year 1934 Biographical sketches published in MINING AND METALLURGY are indicated in the last two columns YEAR OF ELECTION - NAME - DATE OF DEATH - ISSUE IN 1934 CONTAINING BIOGRAPHY - PAGE 1885 AMY, ERNEST, J H - Oct 17, 1933 1906 BABB, P A - Sept 17, 1932 1883 BANKS, JOHN H - Oct 3, 1934 ? November - 466 1893 BARNETT, MAURICE - October, 1933 1892 BASSETT, WILLIAM H - July 21, 1934 ? August - 354 September 393 1928 BAUTZ, ROBERT A - Dec 13, 1933 ? January - 74 1927 BAXTER, J C July, 1933 1930 BELL, IRA J 1934 1895 BENNETT, RUSSELL M Oct 31, 1934 December 512 1884 BENTLEY, ROBERT 1928

Jan 1, 1935

By Ernest R. Dickie

IN 1945 the Bagdad Copper Corp. decided to change from block caving to open-pit mining. By early 1948 the conversion was completed and production was increased from 1500 tons per day to 4000 tons per day. Open-pit mining costs decreased approximately 40 pet from the cost of producing ore by the underground method. At present one P & H model 1400 all-electric 4 1/2-yd shovel and one P & H model 1055 Diesel 3-yd shovel are used continuously for stripping. One 21/2yd North- west shovel handles the ore. Delivery of a new P & H 1055 electric shovel for stripping is expected this month. Blasthole drilling is performed with two Bucyrus model 22 and two Bucyrus model 27 churn drills.

Jan 9, 1951

By AIME AIME

DESPITE the meetings and discussions on over- production the situation still continues to grow worse instead of better. The demand for oil has dropped to 2,700,000 bbl. per day. On the other hand domestic production has risen to 2,700,000 bbl. with prospects of further increases, and if imports and natural gas-gasoline be added to this the current supply is about 3,100,000 bbl. per day. Though during the summer and early fall the demand may exceed this figure for a few months the prospects are that 'the average demand during 1929 will be at least 200,000 bbl. per day less than the present current supply, meaning additions to stocks over the year of about 75,000,000 bbl.

Jan 1, 1929

By John G. Hall

The pumping operations at the Chief mine have been unique in the respect that for many years the entire flow of water into the mine has been disposed of by pumping into natural underground " caverns" or "sinks." Volumes up to 4000 gpm have been pumped into these caverns with no apparent tendency for the caverns to fill with water, and it has never been proven that any of the water returns to the mine workings. Major pumping operations have been carried on during two periods, the first from 1918 to 1927, and the second from 1942 to the present time.

Jan 1, 1949

By M. T. McDonough

THE data relative to the effect of metal depth on slag volume was obtained from the operation on two acid electric furnaces in which heats of various sizes were produced. The furnaces used were of 3 and 5-ton rated capacity; the heats investigated ranged from 6 to 8 tons. Heats of 7 and 8 tons were made in the larger furnace; heats of 6 tons in the smaller one. Bath depths and diameters were measured on the furnaces when cold and each is accurate to one inch. Both the metal charge and the slag were weighed on a track scale accurate to ± 25 lb. All other components added to the furnace were weighed on a wheelbarrow scale accurate to ±5 lb.

Jan 1, 1947

Extractive Metallurgy Division Institute of Metals Division Iron and Steel Division Council R R McNaughton, Chairman (EMD), Ernest O Kirkendall, Secretary, J H Scaff, (IMD), Morris Cohen, (IMD), T J McLoughlin, (ISD), J S Marsh, (ISD), P T Stroup, (EMD), R D Parks, (MED), D S Eppelsheimer, (MIED) Journal of Metals Editorial Advisory Committee J S Smart, Jr, Chairman, W A Dean, T D Jones, Evan Just, J C Kinnear, Jr, J S Marsh, M Tenenbaum Pacific Northwest Regional Meeting F X Cappa, General Chairman, W W Wiltschko, Chairman (Metals Branch), Program Chairmen H E Lee (EMD), S E Maddigan (IMD), G R Heffernan (ISD), L C Richards (Ind Min Div), James Bell (Finance Committee), Ed Vestica (Registration), Donald Johnson (Special Events)

Jan 1, 1954

By Ross W. Smith, Nikhil Trivedi

The variation of point of zero charge (PZC) of both simple and complex oxide minerals was studied as a function of aging time in water. In most cases the PZC's of the simple oxides moved toward more basic pH values with aging time. Evidence to date suggests that this phenomenon relates to dissolution of disturbed layers on the mineral's surface accompanied by later readsorption of metal hydroxy species back onto these surfaces. The readsorption takes place after the solution becomes supersaturated with respect to some crystalline phase. The variation of PZC's of complex oxides as a function of aging time in water is apparently related to several different mechanisms. In a few cases PZC shifted toward more basic values with time. This shift could be attributed to much the same mechanism as for simple oxides. In most cases, however, PZC of complex oxides shifted toward more acid values with aging time, probably because of loss to solution of soluble cations whose oxides possess basic PZC's.

Jan 1, 1975

[Appalachian Petroleum Section: Walter H. Chapman, chairman; Jean Freeland, first vice-chairman; John Galpin, second vice-chairman; Jack L. Trittipo, secretary-treasurer. Meets 4th Tues., Humphreys Restaurant, Charleston. Balcones Section: William E. Richards, chairman; William C. Miller, Jr., first vice-chairman; Brantley G. Myers, second vice-chairman; Harold Vagtborg, Jr., secretary-treasurer. Meets 4th Wed., Petroleum Center Club, San Antonio. Big Horn Basin Subsection: Donald G. Davis, chairman; B. E. Yester, vice-chairman; J. F. Keleher, vice-chairman; Samuel N. Conley, third vice-chairman; William O. Snyder, secretary; M. J. England, treasurer. Billings Petroleum Section: N. J. Matthews, chairman; Guy J. Lookabaugh, first vice-chairman; George O. Ellis, second vice-chairman; Robert L. Spottswood, secretary-treasurer. Meets 3rd Tues., Turf Penthouse.]

Jan 1, 1961

By Edward Steidle

Those who have followed the rapid progress in rock-dusting bituminous-coal mines must admit that opinion crystallized during the year just closed in support of this preventive of coal-dust explosions. Up to 1924 only one mining company in America practiced rock-dusting on a large scale, but during 1924 forty-two companies had adopted this safety measure, and the "boom" is expected to extend over the next two or three years. Alabama is represented by 1 company, Colorado by 3, Illinois by 4, Kentucky by 1, New Mexico by 4, Pennsylvania by 20, Utah by 8, and Wyoming by 1. A total of about 500 miles of entry has been dusted. Illinois leads with 275 miles of dusted entries and Pennsylvania holds second place with about 175 miles. In each case there is a sense of great security, not only on the part of the operator but by the miner as well. It is also interesting to note that during 1924 the compensation rating or inspection bureaus in twelve of our coal-producing states revised their rating schedules so that a credit would be given for rock-dusting. This credit ranges from 10 to 20 cents per $100 payroll. Recent drastic federal and state regulations approved by mine operators made rock-dusting compulsory in bituminous coal mines in Utah, beginning July 1, 1924. Legislative action favorable to rock-dusting may be expected in other states. Colorado has already proposed a change in its laws, and Pennsylvania, Maryland, Washington, and West Virginia are giving the matter consideration. If the rock-dusting problem is handled properly and proves to be entirely successful, no mining man of any standing will delay applying it in his mine. State legislation regarding this matter may or may not solve the problem. At present, the mining companies that are rock-dusting of their own choice are doing it carefully and thoroughly. In Utah, some are doing it conscientiously, trying to get what benefits can be obtained while others are reported to be doing it only to keep within state regulations. In any event, if we are to have new legislation, it is essential that the various states know what they are about and then, if possible, work for uniform regulations.

Jan 1, 1925

By Charles White Merrill

Money is one of the most .pervasive elements in human life. The compensation for a workman's daily efforts is expressed as a wage and is measured in money. What an individual may consume depends largely on his income which also is expressed in terms of money. If he would start an enterprise its size would be determined in large part by the amount of money available for capitalization and its success would be measured in net income expressed in money. In short, the most widely used common denominator for comparing merchandise, real property, jobs, enterprises, gross national product, or personal success is money. Despite this use of money by almost everyone past infancy to express his appraisal of the in- numerable values he sees around himself, the complexity of the device called money makes its nature and workings a mystery to most users. Some of the difficulty in understanding money results from the fact that it has three distinct but interrelated functions: (1) a medium of exchange, (2) a unit of account, and (3) a store of value. In many statements about money the discussion moves from one function of money to another without the speaker or the listener recognizing the changes. For example, the housewife says "We took the money we had saved up to make the down payment and after twelve monthly payments the television will be ours." When this housewife spoke of "saving up the down payment" she referred to money in its function as a store of value; when she spoke of "the down payment" she was using money as a medium of exchange; and when she referred to the "monthly payments" she spoke of money as a unit of account. Another cause of confusion in understanding money is its paradoxical nature in that it represents both the power to produce and the power to consume. For example, when the rich uncle dies one nephew may regard his inheritance as an opportunity to buy a farm and leave the ranks of the wage earners to become an independent producer, whereas the other nephew may regard his portion as the means of living in complete leisure as a pure consumer.

Jan 1, 1959

By F. H. Willcox

In Bessemer-steel practice, air is blown through a bath of iron, or projected strongly upon its surface to burn out silicon, manganese, and cafbon. Toward the end of the blow, when the iron is not protected from oxidation by these elements and the excess of air becomes great, there is oxidation of the iron. In open-hearth practice, the same difficulty is experienced with dissolved gas and oxides in the product, though not to as great or severe a degree as in the Bessemer process because the oxidizing conditions grow less severe as the end of the heat is approached, and if the bath is allowed to boil for a time it undoubtedly frees itself from a large part of the gas and oxides which have been absorbed in the earlier part of the process. Basic open-hearth steel is usually assumed to contain a larger proportion of oxides than acid open-hearth steel, but it may be said that all steel, Besserner and open-hearth, contains more or less oxide of iron dissolved in the fluid metal at the end of the "blow" or "heat." That certain metals are solvents for their respective oxides has been shown, in the case of copper, by Heyn, and, in the case of iron, by Law. It is indicated that the solubility of iron oxide in iron increases with the purity and temperature of the metal. This confirms what is observed and known by operating men, and these observations may be summarized as follows: 1. Cast iron. is rarely subject to oxidation, as is logical from its composition. 2. Normal steel, unless deoxidizers are added, contains blow holes. 3. Steel known to be oxidized is full of blow holes. 4. The addition of deoxidizers prevents, to a greater or less degree, the formation of blow holes in normal steel. With these observations in mind, it is logical to deduce that the cause of blow holes lies in part in the presence of dissolved oxide of iron in the molten steel and its consequent reaction with the carbon of recarburizers, when these are added, to form gases. (Another factor in the origin of blow holes is, of course, the solubility of gases themselves in the steel and

Jan 1, 1917

By Charles White Merrill

Money is one of the most pervasive elements in human life. The compensation for a workman's daily efforts is expressed as a wage and is measured in money. What an individual may consume depends largely on his income which also is expressed in terms of money. If he would start an enterprise its size would be determined in large part by the amount of money available for capitalization and its success would be measured in net income expressed in money. In short, the most widely used common de- nominator for comparing merchandise, real property, jobs, enterprises, gross national product, or personal success is money. Despite this use of money by almost everyone past infancy to express his appraisal of the innumerable values he sees around himself, the complexity of the device called money makes its nature and workings a mystery to most users. Some of the difficulty in understanding money results from the fact that it has three distinct but interrelated functions: (1) a medium of exchange, (2) a unit of account, and (3) a store of value. In many statements about money the discussion moves from one function of money to another without the speaker or the listener recognizing the changes. For example, the housewife says "We took the money we had saved up to make the down payment and after twelve monthly payments the television will be ours." When this housewife spoke of "saving up the down payment" she referred to money in its function as a store of value; when she spoke of "the down payment" she was using money as a medium of exchange; and when she referred to the "monthly payments" she spoke of money as a unit of account. Another cause of confusion in understanding money is its paradoxical nature in that it represents both the power to produce and the power to consume. For example, when the rich uncle dies one nephew may regard his inheritance as an opportunity to buy a farm and leave the ranks of the wage earners to become an independent producer, whereas the other nephew may regard his portion as the means of living in complete leisure as a pure consumer.

Jan 1, 1964

By H. Rush Spedden, A. M. Gaudin

ALTHOUGH the number of minerals that are ferromagnetic) or highly paramagnetic is strictly limited, it has been known for some time that many minerals have slight but supposedly characteristic magnetic susceptibilities. With the exception of pyrrhotite, however, sulphides have been thought nonmagnetic. A new magnetic separator has been made available recently in limited quantity to research laboratories. This device, the Frantz Isodynamic Separator, has been used for the separation of various nonsulphides from each other. Its application to the separation of sulphides, however, does not seem to have been reported. In the Richards Mineral Dressing laboratories, the success achieved through the use of this device in separating associated sulphides has been so startling as to lead us to believe that it constitutes a magnificent adjunct to heavy-liquid separation and to quantitative mineragraphy as a tool for the mineral investigator. THE SEPARATOR The separator (Fig. I) consists of: I. A powerful magnet, the strength of which can be adjusted by means of a rheostat; 2. A vibrating chute of nonmagnetic metal on which the mineral to be separated is made to flow (Fig. 2); 3. A feed bin and adjustable feeder; 4. Receptacles for the collection of products; 5. Means for changing, setting, and accurately reading the two slopes of the chute; viz., the cross slope and longitudinal slope. The separator is made operative by the special shape of its pole pieces, which ensures a strongly converging field. It is said by the makers of the machine that the pole pieces apply a constant mechanical force to a particle of given susceptibility, regardless of its position in the operating space of the separators.* Susceptible particles, therefore, behave as though of lower specific gravity than under ordinary circumstances. This effect, combined with the slopes of the chute and the action of the vibrator, causes a stratification not unlike that obtainable on a shaking table. The chute is of rectangular cross section, and shallow; it is broadened toward the discharge end and divided longitudinally by a partition into two compartments that lead to the collecting receptacles. Although the separator probably can be used to make separations at fairly coarse

Jan 1, 1943

By Didyk M. Marko, Vásquez Ñ. Gregorio

INTRODUCTION The Salvador Division of Codelco Chile is an important copper molybdenum production center, located 1,200 km north of Santiago and 124 km east of the Pacific Ocean, in the foothills of the Andes Range. El Salvador Mine produces by block caving 8,600,000 t of ore with a content of 1 .l0% Cu and 0.02% Mo, from a copper porphyry ore body. The geology of the ore body shows a great heterogeneity as to rocks, grade distribution, ore height and undercutting levels. This has resulted in a variety of designs for the productive units (blocks) and in the mineral handling systems. Up to now, 4 systems have been employed: grizzly and intermediate haulage; slusher drifts with intermediate ore pass and haulage; slusher drifts with scraper loading directly into trains; and, LHD. On the other hand there is a marked dispersion in the final results from each block mined out. We report here the conclusions reached after analyzing the data gathered on the mining of 163 depleted blocks, representing a total production of 102,000,000 t, with an undercut area of 340,000 sq m. The final results of each block, characterized in terms of tonnage and fine cop- per recovery, were studied as a function of a number of design, geological, and operational parameters. BASIC CONCEPTS Indices of Efficiency In order to evaluate the final result of each block, or group of blocks, the following indices of efficiency were defined : Tonnage Recovery (TR) . It is the ratio between the ore tonnage extracted and the in situ tonnage estimate for each block or group of blocks. Grade efficiency (E) . It is the ratio between the Cu mill feed grade and the in situ Cu grade estimate for each block or group of blocks. Grade efficiency is numerically equal to the ratio between fine copper recovery (FR) and tonnage recovery (TR) . Figure 1 shows the final results for 163 mined out blocks, in terms of tonnage and fine copper recovery. Different grade efficiencies are also indicated. The marked dispersion in the final results of mined out blocks must be stressed since it greatly incides in mine planning. It must be kept in mind that an eventual concentration of low overall efficiency in the blocks during a given period (e.g., one year) will make it necessary to bring into production new blocks over the standard development schedule. It is worth noting that the final results in the 163 mined out blocks corresponding to a production of 102,000,000 t of ore with a mill feed grade of 1.445% were obtained from an ore estimate of 93,000,000 t and a grade of 1.671% Cu, which represents 110% tonnage recovery and 86% grade efficiency. Parameters Studied The following parameters are considered in this study: Geological Parameters. These parameters depend exclusively on the geological and geotechnical features of the ore body. IN SITU GRADE: The initial estimate of the block grade. Four copper grade categories were considered : (a) lower than 1.3% ; (b) 1.3 to 1.6%; (c) 1.6 to 2.0%; (d) higher than 2.0%. The overall initial in situ estimate of the ore body was 1.6% Cu. IN SITU TONNAGE: Initial tonnage estimate of the block. Four categories are considered: (a) below 500,000 t; (b) 500,000 to 1,000,000 t (c) 1,000,000 to 1,500,000 t; (d) over 1,500,000 t. CONTACTS SLOPE: Since up to 4 rock types can be found in a block, resulting in a corresponding number of contacts, a horizontal con- tact was defined as that which forms an angle of less than 45" with the horizontal and a vertical contact that which forms an angle of more than 45" with the horizontal. GRADE DISTRIBUTION: As in rock types, horizontal and vertical grades were defined. ORE HEIGHT: The distance measured between the undercut level and the top of ore. Four categories are considered: (a) less than 60 m; (b) 60 to 100 m; (c) 100 to 150 m; (d)over 150 m

Jan 1, 1981