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By J. B. Warriner

S. A. TAYLOR, Pittsburgh, Pa.-What was the distance of haul? J. B. WARRINER.-There is practically no limit to the haul. The length is determined entirely by the feasible location for a dump. -I have known of hauls up to 2 miles in length. R. V. NORRIS, Wilkes-Barre, Pa.-This paper was originally presented to the Anthracite Section as the result of the appointment of Mr. Warriner as the Chairman of the committee to study this matter and present this paper. As he has stated, he obtained data very freely from all the stripping operations in the region, and it is a type of paper of which we should have more in the Transactions. Two or three things in it strike me as particularly valuable. The two tables, 1 and 2, showing the coal remaining, have been the result of a great amount of study, as it is not an easy matter to obtain data as to the amount of coal left in mining. As an example, one of the, anthracite mines was mined and robbed out in 1850, so the maps show. That mine is today producing 250,000 tons of coal, over 50 per cent. from the bed which on the maps is marked as exhausted. What actually happened is that the seam was on a light pitch inconvenient to mine. There was ample thickness of coal and the chambers were driven at a convenient pitch through this 30,-ft. bed, leaving top and bottom, taking out about 10 ft. The pillars were removed and the working caved and marked as gone. That is the type of area that is now being stripped, which explains the reason for the enormous amount of coal left in, and the fact that Mr. Warriner has worked out the actual results from a large number of strippings is of great interest to the operators in any region handling thick coal which has been mined over in the past, generation. The modern mining, of course, is different. We do not have all the coal we want in big veins, and we do not mine it that way. Another interesting feature of the paper to me was the study of losses. It is not uncommon to assume that after you have stripped off the overburden all the coal goes to market. Mr. Warriner has shown that there is a loss ranging up to 10 or 15 per cent. that does not go, so 'that estimates made on stripping, figuring on all the coal, are subject to this very material correction.

Jan 4, 1917

The Wheeler Condenser & Engineering Co., of Carteret, N. J., is now building a line of horizontal and vertical shaft centrifugal pumps for general services, as well as for condenser work.. This company has been building centrifugal pumps for over 20 years, most of them being used, however, in connection with condensers. The new line of pumps is suited for all services. A small motor-driven unit for tank or stand pipe operation is shown in Fig. 1. Referring to the sectional illustration (Fig. 2), it will be seen that this pump conforms to the most recent advances in centrifugal pump construction, having a two-part divided casing, with the suction and discharge nozzles in the lower half. The impeller is of the closed double-suction type, protected by labyrinth wearing rings. The shaft is protected from the water by bronze sleeves, which screw on to the shaft and extend clear through into the bearing bracket boxes. Bearings are of the ring-oiled type, and in the outboard bracket, is a ring-oiled thrust bearing, which is a refinement not usually found in double-suction

Jan 4, 1916

By L. H. Hart

Because of a widely recognized association between breccia pipes of one form or another and many important copper deposits, conditions under which breccia pipes develop have been of great scientific interest for many years. Since these phenomena first attracted attention, many theories have been advanced to explain their origin. This is not unexpected, since it is likely that they have been formed by and under a wide range of conditions. Moreover, the entire subject is confused by the fact that the term breccia pipe is applied to a wide variety of occurrences. To discuss any part of the subject intelligently, therefore, it is necessary to start with definitions of the terms used. In their discussion of the Toquepala deposit, Richard and Courtright have carefully defined the terms they have used in their presentation of a very logical geo- logical history of Toquepala breccias. This is a real contribution, as there is no reference in the literature known to the writer where the history of a series of breccia pipe epochs, confined essentially within one channelway, may be read with the degree of certainty that appears to be possible at Toquepala.

Jan 6, 1958

By Hobart M. Kraner

THE mineralogy of blast furnace sinter is of interest because its mineral content is one of the important factors contributing to its character. There are so many other factors affecting the properties of the sinter, however, that it is well to mention them here. The proportion and character of the raw materials, that is, raw ores, concentrates, returns, and fuel, as well as the mixing and the water content, all have a marked effect on the physical properties of the product and the degree to which sintering action can be carried on. The process of sintering is a relatively fast operation. In as much as appreciable time is required to carry on processes of fusion in such masses of low thermal conductivity, large lumps of hematite ore frequently remain unfused and partly unchanged in state of oxidation in the sintering process. The kind, the grain size, and the amount of fuel used affect both the completeness of the fluxing reaction and the prevailing atmosphere. The rate of reduction in laboratory tests is not only dependent upon the state of oxidation of the sinter but also upon the sizing and porosity.

Jan 11, 1953

By E. A. Stevens

IT has been ascertained in recent years that certain rocktypes, geological formations and structural conditions may be used as fairly reliable guides, when prospecting in recognized mineral belts or mining districts, with a reasonable certainty of discovering "pay-ore;" and that such is considered as a practically established conclusion may be inferred from a perusal of the recent reports of the U. S. Geological Survey and the literature of the several scientific societies discussing minim, geology, and kindred subjects. Cripple Creek is no exception to this conclusion, and the rock-type or association, rather than the structural condition, is the most infallible guide.† These guides consist of four, possibly five, dike-rocks, three of which are extremely basic, while the fourth is an acid rock of an entirely dissimilar character. The basic rocks are nepheline-basalt, limburgite, feldspar-basalt and tephrite. There are grounds, however, for believing that the two latter are subdivisions of one type, and therefore will be described under one head. The acid rock is quartz-porphyry. Nepheline-basalt is-a rock encountered in but few localities elsewhere on this continent, and occurs in narrow dikes cutting various formations. When typical‡ it is composed of

Jan 1, 1913

By D. R. Miller

The use of fully grouted cables for ground reinforcement in underground mining is becoming widespread. Reinforcement design for this application has tended to be empirical although some two- dimensional design techniques have been developed. This paper describes a technique based on a model of the behaviour of cables placed across planes moving in shear. The model is three- dimensional and includes a simple model of the 'dowel' effect which arises from the bending of the cables. The model determines the shear resistance developed at a particular shear displacement assuming joint friction and cable parameters. Using data for twin 15.2mm dim. steel strand cables, and a concept of reinforcement efficiency, the application of the model to design wall support in open stopes is demonstrated. The examples consider the cases where major planar structures are known in location and orientation and where, as is more common is open stope development, mapping has indicated that a distribution of potential shear failure structures may be present. The actual location and orientation of potential shear planes is not known. These two cases highlight the underdesign of reinforcement that may arise if the distribution of orientation of potential shear planes is not considered.

Jan 1, 1984

By Marius R. Campbell

Every mining engineer who has engaged in prospecting for coal in flat-lying rocks understands the importance of constructing geological sections across the territory which he has to prospect. If the area is small and the time and means at his command are unlimited, he can construct such sections with the transit and level; but if the area is great and the examination hurried, as it frequently is, he will doubtless be puzzled how to proceed. Under this pressure of time and means, his work will probably be, to a great extent, devoid of any system, being simply a hap-hazard opening of such seams as show in outcrop at some point on the territory, without any determination of geologic structure or stratigraphic succession. Prospecting carried on in this manner is never satisfactory to the intelligent mining engineer, for he must realize that the information which he is able to furnish to his employer is totally inadequate to determine the economic value of the property. To the owner of the land such a report is no more satisfactory than to the engineer. Unless the latter can show both

Jan 1, 1897

By M. Prats

The effect of a sand-filled vertical fracture of limited radial extent and finite capacity (fracture capacity is the product of the permeability and width of the fracture) on the flow behavior of a cylindrical reservoir producing an incompressible fluid through a centrally located well has been investigated mathematically. The shape of the lines of equal pressure near the fracture is essentially independent of the size of the reservoir, provided that the field radius is of the order of the fracture length or larger. For reasonable values of production rates and of fluid, reservoir and fracture properties, the total pressure drop between the end of the fracture and the well is gelrerally negligible compared with the pressure drop in the reservoir. With regard to production response, the effect of vertical fractures can be represented by the production response of an equivalent or effective well radius. For a high-capacity fracture, the effective well radius is a quarter of the total fracture length, decreasing with the fracture capacity. When invasion effects are simulated by decreasing the width of the damaged zone with distance from the well, the effect of formation damage around a fracture on the production response is not so seriolls as indicated by the literature. This suggests that frac fluids with a conventional filter-loss response are better than high-spurt-loss frac fluids, provided the effective permeability of the damaged zone is the same. INTRODUCTION This paper considers the effect of the fracture capacity, as well as the formation damage which can result from fracture treatments, on the productive capacity of vertically fractured wells. Other publications, notably those of van Poollen,l,2 consider these same effects. In addition to providing more general results for vertical fractures than are available from the liter- ature, the present paper gives the equivalent well radius of fractures having different lengths and capacities and, also, includes pressure distributions in and around the fractures. The effect of a damaged zone around a fracture on the production response was not found to be so great as that reported by van Poollen. 2 This difference probably stems from the fact that we consider a damaged zone which is widest (but is still small) near the well and thins out toward the extremities of the fracture, whereas van Poollen considers a damaged zone having a uniform width for the entire fracture length. Simple, but adequate, equations which describe the effect of these variables on production response are presented (in Appendixes A and B). Thus, results can easily be extended to values of the variables not specifically considered here. IDEALIZATION AND DESCRIPTION OF THE FRACTURED SYSTEM It is assumed that a horizontal oil-producing layer of constant thickness and of uniform porosity and permeability is bounded above and below by impermeable strata. The liquid is incompressible. It is assumed that, after the well is fractured, the cylindrical outer "boundary" is at a uniform potential, provided that it is not too near the fracture. The fracture system is represented by a single, plane, vertical fracture of limited radial extent, bounded by the impermeable matrix above and below the producing layer (reservoir).3 Fig. 1 indicates the general three-dimensional geometry of the fractured reservoir described above. If gravity effects are neglected, the flaw behavior in the reservoir will be independent of the vertical position ill the oil sand. This means that the flow behavior in the fractured reservoir can be described by the two-dimensional flow behavior shown in the horizontal cross section of the reservoir, Fig. 2. PARAMETERS The effect of a fracture on the pressure distribution in the fracture itself and in an otherwise undamaged (no skin) reservoir indicates that the pressure distribution is a function of three parameters.

By P. E. Arnold, G. S. Ansell

RELAXATION in metals has been studied in detail by many workers in recent years.1-5 These studies have shown that there is an energy-loss peak observed in a metal placed in mechanical resonance at low frequencies which may be correlated with various metallurgical processes. These experiments have been largely used to study single-phase materials. In order to study the effect of a finely dispersed second phase in a metal matrix upon this phenomenon, the relaxation behavior of an aluminum-aluminum oxide SAP-Type alloy in both the fine-grained as-extruded and coarse-grained recrystallized conditions was investigated by the use of internal-friction measurements. The alloys studied, designated MD 2100, consist of a matrix of commercial-purity aluminum containing a finely dispersed second phase of aluminum oxide. The aluminum oxide is present in this alloy in the form of fine platelets approximately 130A units thick and several microns on edge. The mean free path betwen dispersed platelets is approximately 0.5 p. The grain size of this alloy is extremely stable at temperatures as high as the melting temperature of the aluminum matrix. In the as-extruded condition the grain diameter is several microns, while in the recrystallized condition it is several millimeters in diameter. The damping characteristics of the alloy samples were determined using a torsional-pendulum device. The internal-friction constant was determined for this alloy in both the fine-grained as-extruded and coarse-grained recrystallized conditions over the temperature range from 343" to 923°K at frequencies of 0.9, 1.3, and 1.8 cycles per sec. An internal-friction peak was observed in testing the fine-grained alloys which was not observed for the coarse-grained alloys. This peak, which might be associated with a type of grain-boundary relaxation, was observed at each of the three different test frequencies for the fine-grained sample. The temperature at which the relaxation peak occurred for each of the three different frequencies is shown in Table I. From these data an activation energy of relaxation for each pair of frequencies was determined by comparing the temperature shift of the relaxation peak with frequency between each of the test frequencies, assuming that an Arrhenius-type rate equation is applicable. The activation energy of relaxation determined from these data is also shown in Table I. The mean value of the activation energy was about 6 kcal per mole. The activation energy for the relaxation process determined in this investigation indicates that the relaxation associated with the grain boundaries in this aluminum-aluminum oxide SAP-Type alloy is quite a different process than grain boundary relaxation in single-phase aluminum alloys. In these latter alloys, the activation energy for relaxation has been found to be the activation energy for self-diffusion, approximately 36 kcal per mole1,2 Where the activation energy is the same as the activation energy for self diffusion, it has been proposed that the relaxation phenomena is dependent upon vacancy formation and motion. It is apparent therefore, that, in this aluminum-aluminum oxide SAP-Type alloy, the relaxation must be due to another type of atom transport. It has been shown previously in studies of the high-temperature, low-stress, steady-state creep behavior of as-extruded aluminum SAP-Type alloys, that the activation energy for steady-state creep is one that may be characterized by the nucleation of dislocations from the grain boundaries. It is proposed that the relaxation behavior observed here is due to a similar effect. In this case, the internal-friction peak is a resonance behavior due to the time-dependent nucleation of dislocations from grain boundaries in the sample. A process of this type would have an activation energy which is undoubtedly stress-dependent and of the form Q = Q, + (dQ/du)u

Jan 1, 1962

By Nick Barton, Stavros Bandis

The descriptive term "rock mass" encompasses individual block dimensions ranging from centimeters to many tens of meters. Strength and deformability vary both qualitatively and quantitatively as a result of this size range. A key issue is therefore the appropriate size of the test sample. A large body of test data was reviewed to determine the influence of block size on the displacement required to mobilize peak strength. It is shown that the shear strength and shear stiffness reduce with increased block size due to reduced effective joint roughness, and due to reduced asperity strength. Both are a function of the delayed mobilization of roughness with increasing block size. A method of scaling shear strength and shear displacement from laboratory to in situ block sizes is suggested. It is based on the assumption that size effects disappear when the natural block size is exceeded. This simplification appears to be justified over a significant range of block sizes, but is invalidated when shearing along individual joints is replaced by rotational or kink-band deformation, as seen in more heavily jointed rock masses. Recent laboratory tests on model block assemblies illustrate some important effects of block size on deformability and Poisson's ratio.

Jan 1, 1982

FIRE tubes are commonly made in order to frighten horses or to harm enemy soldiers, but although fire issues from them, they do not cause much damage because they cannot be used at a distance. If you wish to use them, you are not able to approach close to the enemy, for if there is anyone who is afraid, he does not let you approach nor does he come near you until he sees that they have finished burning. Thus, in short, the assault with this is one that is seen beforehand, and for which there is always time to decide on some action in defense. It is indeed true that they are beautiful things to see and when the name tubes of fire is heard it terrifies those who do not have a defense ready. When four, six, or indeed ten or twelve of these are put in the hands of as many courageous and united men, they are surely good in forcing passage on a guarded bridge, or in entering or holding a gate, road, or other narrow place. They serve also for setting fire to dwellings or the enemy's supplies,

Jan 1, 1942

By Peter H. Fletcher

THE ECONOMIC THEORY It will assist in the understanding of the Resource Rent Tax ("RRT") proposals in Australia if the economic theory behind the tax is briefly explained. The idea goes back to the concept of rent put forward by the nineteenth century economist David Ricardo. His analysis was broadly as follows: A tenant who farms land which is just on the margin of economic viability cannot afford to pay his landlord any rent, because the value of the crop produced by such marginal land is equal to the cost of producing the crop, plus the cost of keeping the tenant alive. There is nothing left out of which to pay rent to landlord. A tenant who farms good land can afford to pay his landlord rent -- but the maximum amount of rent that he can be asked to pay is the excess of the value of the crop produced by the good land over the cost of producing the crop and of keeping the tenant alive. Adapting this theory to the taxation of mining projects, modern economists who favour this system of taxation say that a profitable mining (or resource) project produces rent in the Ricardian sense. The amount of the rent is the excess of the profits by the project over the amount of profit which is required to attract the taxpayer to invest in the project in the first place. This explains why the tax is called "Resource Rent Tax". PAPUA NEW GUINEA PRECEDENT Although Papua New Guinea ("PNG") is now independent of Australia, there are still close links between the two countries, and strong similarities between their respective tax regimes. PNG introduced an Additional Profits Tax ("APT") in 1978. In many respects, Australia's RRT proposals follow the precedent set by PNG1s APT. However, in practical terms, not a great deal can be learned at this stage from PNG's experiences since, according to the writer's understanding, no PNG mining project has yet paid any APT. The Bougainville mine is not liable to APT, being subject to tax under its own separate Act, which contains a different formula. Outline of PNG Additional Profits Tax. PNG has two versions of Additional Profits Tax ("APT) - one applying to general mining, the other to petroleum mining. The two versions are very similar. The general mining version is described below. The tax applies on a licence by licence basis. This means that losses on Licence A cannot be offset against profits on Licence B. Expenditure relating to two or more licences, is apportioned "in such manner as the Chief Controller thinks reasonable". Tax is levied on the "accumulated value of net cash receipts" at the rate of (70 - n)% where n=the rate of income tax. The accumulated value of net cash receipts ("av") is calculated as follows: Calculations commence from the first year in which substantial expenditure was incurred on the construction of facilities for the carrying out of mining operations on the licence. For that year the av consists of the total allowable expenditure to date on that lease. For the second year, the av is the av at the end of year one indexed in accordance with the statutory formula set out below, plus the total allowable expenditure in year 2. For year 3, the av is the av at the end of year 2 adjusted by the index factors, plus the total allowable expenditure in year 3. This process is repeated year after year. When the licence starts to earn revenue, the revenue is deducted from total allowable expenditure for that year. If revenue exceeds total allowable

Jan 1, 1985

By L. G. Austin, R. R. Klimpel

This article demonstrates that the Gilvarry and Klimpel-Austin equations for the random fracture of solids are incorrect by deriving intuitively correct expressions for simple cases and showing that the foregoing equations do not reduce to right answers. It is the purpose of this article to point out serious errors in some existing treatments of the random fracture of solids. Gilvarry ' gives the equation where B(y,x) is the cumulative fraction by weight of particles which fall below size y when particles of size x are broken. The constants i, j, k contain shape factors and densities of flaws leading to propagating fracture surfaces. The authors believe this equation to be incorrect. Klimpel and usttin' give where r~ is the number of fracture planes originating from edge flaws (per L where L is the edge length of the original particle), rs is the number of fracture planes originating from flaws on the particle surface (per S where S is the surface of the original particle) and rv is the number of fracture planes originating from flaws within the particle volume. This equation is also incorrect. The failures of these equations will be demonstrated by deriving intuitively correct expressions for simple cases and showing that the Eqs. 1 and 2 do not reduce to the correct answer. In this process, the flaws in statistical reasoning inherent in the derivations of Eqs. 1 and 2 become apparent. THE KLIMPEL-AUSTIN EQUATION Eq. 2 was derived by considering a set number of fracture planes occurring spatially at random within a given particle. This case will be treated here in its simplest form: a line with 1, 2, 3, etc., fractures occurring at random. This is illustrated in Fig. 1, with the original length of the line as Vo. The breakage of a long, thin, brittle fiber is a corresponding physical case, with the volume of a fragment proportional to its length. Assuming independence of the occurrence of the fractures, the probability of any one fracture occurring in length dV is dV/V0. The probability of the first fracture occurring at a length V to V + dV is dV/Vo. For the case of only one fracture per particle, formation of a number-size distribution of the left-

Jan 1, 1969

By E. W. Davis

IF the tonnage of merchantable iron ore remaining in the Lake Superior district is divided by the average of the annual shipments for the past 20 years, it will be found that this ore supply will be exhausted in approximately 35 years. This computed exhaustion period would be an indication of the future activities of the iron-mining industry if it were not for the fact that merchantable ore is being manufactured from low-grade ore, of which there is an almost inexhaustible supply in the Lake Superior district. It is true that at present only the simplest of these low-grade ores are being concentrated to any considerable extent, but progress is being made with the treatment of the more complex ores, and now, in addition to 20 washing plants on the Mesabi Range, three plants are equipped with jigs for the treatment of ore that cannot be concentrated simply by washing. The latest addition to the ore-treating plants of the Mesabi Range is a magnetic roasting and concentration plant at Cooley, Minn., in which ore that cannot be concentrated either by washing or by jigging is roasted to the magnetic state and concentrated on magnetic separators. This plant is beginning its third season of operation, and while it is too soon to make definite predictions, there are strong indica-tions that this new process may make commercially possible the manu-facture of high-grade, merchantable iron ore from large quantities of low-grade ore now considered worthless. After the iron oxide contained in an ore has been converted to mag-netite, almost any desired grade of concentrate can be produced, using magnetic-concentration equipment of the types now in general use for the concentration of the natural magnetites of New York, New Jersey and Pennsylvania. The conversion of hematite (Fe203) to magnetite (Fe304) is easily accomplished by heating the ore to a dull red tempera-ture in a reducing atmosphere. The reaction is slightly endothermic, and while it requires 200 B.t.u. to heat to 900° F. one pound of hematite ore containing 45 per cent Fe, it requires only 100 B.t.u. to convert the oxide into magnetite. In the laboratory, using small quantities of ore, this conversion is very simple, but large furnaces suitable for commercial

Jan 1, 1936

By Kenneth A. Gutschick, Robert S. Boynton

Lime has become a very general loosely used term that includes virtually all finely divided types of limestone as well as burned forms of lime. However, actually (and according to Webster) lime is only calcined limestone (known as quicklime, calcium oxide, or calcia). It also embraces the secondary product of quicklime-namely hydrated lime or slaked lime (calcium hydroxide). Fundamentally there are two basic types of limestone-high calcium and high magnesium (dolomitic). The dolomitic quicklimes and hydrated limes correspond to their "high calcium" counterparts in terminology. The only difference is that the dolomitic types are a combination of the elements, calcium and magnesium, whereas high calcium limes contain only 0.5 to 2 pct of magnesium. Both types, which are made through calcination at high temperatures, are shown chemically as follows: [ ] In the above reactions either type of limestone is burned (calcined) in furnaces known as lime kilns so that the carbon dioxide content of the stone is expelled as a gas. With high calcium limestone 44 pct of the weight of the stone is lost; with dolomitic limestone the loss is 48 pct. Also, both reactions are chemically reversible since quicklime absorbs carbon dioxide readily and in so doing transforms itself back to the original carbonate form. Most quicklimes correspond in size to the original rock, which varies from one to eight inches, depending upon the type of kiln employed. Slight shrinkage occurs during calcination. A few limestones when calcined will decrepitate (break down) into a fine powdery form; however, chemically it is the same as the pebble or lump-sized material. For some uses the lumps of quicklime are pulverized and packaged. Since quicklime has great affinity for moisture and carbon dioxide, it is perishable. When it absorbs moisture and CO2 slowly from the atmosphere, the resulting product is "airslaked." Consequently, it must be stored in dry, moisture-proof areas that are free from CO2. Because of its fugitive nature, it is usually consumed within a few weeks after manufacture. A more stable form of lime is hydrated lime-commercially made by adding water to the quicklime until the lumps break down into a fine, white powder. This product, which is usually packaged, can be stored more safely; and many of its uses are interchangeable with quicklime. The irreversible chemical reactions of hydrated lime for both high calcium and dolomitic types are: [ ]

Jan 1, 1960

By J. B. Austin

In considering so complex a process as the smelting of iron in the blast furnace, there is obviously no single method of calculating efficiency that gives a complete appraisal of the performance of the furnace in all its several functions; such a comprehensive view as is required to evaluate producing ability and manufacturing costs for a given furnace is obtained only by considering a group of efficiencies, each of which measures the performance of the furnace from a specific point of view. For instance, there is the rate of consumption of coke per ton of iron produced, which is probably the most frequently considered, and is certainly one of the most important of the group; there is the efficiency of recovery of iron charged; and there is the efficiency of utilization of energy, both chemical and thermal, in some respects related to the former two yet in other ways independent of either. In each of these cases, the calculation can be made on the basis of the actual input of material or energy, or it may be based upon a comparison with the minimum amount of material or energy that would be required by a "perfect" furnace; that is, an imaginary ideal furnace analogous to the perfect steam engine used in thermodynamic calculations, when this furnace is operating under optimum conditions. Moreover, the furnace itself can be considered either as an apparatus for smelting iron or, taking a somewhat less common point of view, as a gas producer yielding iron and slag as by-products. Some of these efficiencies are more useful than others, yet all are instructive; for a knowledge of them not only leads to good engineering practice from the standpoint of control but also discloses limits to possible improvement in performance and indicates the lines along which improvement is most likely to be profitable. Estimates of some of these efficiencies have appeared from time to time in the literature, but many of them are open to objection because they are based on data of uncertain accuracy or because they have been calculated without due regard to the thermodynamic principles involved. Moreover, so far as the author is aware, no general survey of the blast furnace comparing its performance in all the aspects mentioned has been made.

Jan 1, 1938

By R. G. Paterson

THE usual procedure in determining the magnetic susceptibilities of rocks and formations has been to take samples in the field and measure their volume susceptibilities in the laboratory, using one of numerous methods available. In none of these methods is the measuring instrument suited for field use. Usually the sample is pulverized; sometimes it is machined to a desired size and shape, and in one method' a cast of the sample is made and the susceptibility of the rock compared with that of a material of known susceptibility of the same size and shape, made from the cast of the original sample. Some writers assert that the difference in susceptibility of a rock sample in powdered and solid forms is negligible, and while doubtless this is true in many cases there are others in which the difference becomes appreciable. Further, the susceptibility of a small specimen may differ from that of the rock from which it is taken, owing to the stresses produced by the hammering or other forces used to obtain the sample and shape it for testing. Wilson2 found that an individual specimen of granite had about the same susceptibility in the solid as in the powdered form, but that pieces from different parts of the rock varied as much as 750 per cent because of unequal distribution of magnetite. The most accurate value of susceptibility would, obviously, be obtained from averaging a number of tests on the undisturbed rock instead of from one or two samples. No such procedures have been published, to the writer's knowledge. It is the purpose of this paper to describe a method by which susceptibilities of rocks may be determined in place by means of a portable instrument. METHOD The principle involved in this new method is that there is a change in inductance of a coil due to the presence in its magnetic field of a paramagnetic or diamagnetic medium. In this case, however, the windings of the coil do not enclose any part of the rock under test. Instead, the coil is circular, being small in cross section as compared to its radius, and consists of several hundred turns of fine wire. It is placed flat on the rock of which the susceptibility is to be measured. Thus only part of the magnetic field from the coil penetrates the rock under test. The relation between the change in field strength or inductance of the coil and the susceptibility of the medium will be developed later. To measure the change in the inductance of the coil due to the presence of a magnetic material an alternating-current inductance bridge was chosen. DESCRIPTION OF APPARATUS Of many alternating-current bridge methods applicable,3 the one shown in Fig. I (Owen's bridge') was adopted for its simplicity and sensitivity. In Fig. I, the test coil is indicated by P1L1. It is connected to the bridge by about

Jan 1, 1941

By George G. Griswold

The Parkes process of lead refining is based on the fact that when zinc isemixed with molten lead bullion, it forms an alloy with the silver and gold. This alloy freezes at a higher temperature and is of a lower specific gravity than the lead. With proper regulation of the temperature, the alloy solidifies and floats on top of the lead bath, from which it is removed and the silver, gold, and zinc recovered. The alloy should contain the maximum amount of silver (Ag2Zn,). The usual practice is to make two additions of the zinc. The first addition gives an alloy, or zinc crust, the zinc of which is saturated and is treated for the recovery of its zinc and silver; the crust from the second addition contains an excess of zinc and is used for the first addition on the following kettle. The crust produced depends on a number of items: purity of bullion, temperature, care with which kettle work is performed, addition of zinc, pressure used in expelling lead from crust, etc. It is desirable to make the concentration of silver in the zinc crust as high as possible; otherwise an undue amount of byproducts is produced, which greatly increases the cost of refining. It was formerly considered good practice to make a concentration of 20 :1. That is to say, if the lead bullion assayed 150 oz. dorê per ton, the assay of the retort bullion recovered from the zinc crust should be 3000 oz. per ton. As a matter of fact, the concentration should never, except on bullion assaying over 300 oz., be so low, and with low-grade bullion it should be 50:1. In one lead refinery where, ordinarily, the work was good, on a bullion averaging about 200 oz. per ton, a concentration of 24:1 was common; but how it was obtained was known only to the foremen. Changes occurred, and under new foremen the kettle work fell off badly; the problem then was to bring about this greater concentration. As is customary, the refincry had a "schedule" for its 60-ton kettles, which gave the number of pounds of zinc required for all possible assays, on both the first and the second zincing. Using this schedule, high temperatures

Jan 1, 1924

By John K. Berry

The handling and disposal of mine water is a much larger problem than is apparent at first glance. Many more tons of water are removed from underground coal mines in the United States each year than tons of coal. In the old anthracite region of Pennsylvania the average was around 36 tons of water for each ton of coal produced, while bituminous mines average about 5 or 6 tons. Water encountered in the mines may come from several different sources. In mines with light cover and without a firm solid roof, rain may seep directly into the workings. This is also true of deeper mines where pillar falls have broken the roof to the surface. The top under creek beds is generally faulty and broken and water comes through the roof at this point. Deeper mines are frequently overlain by water-bearing strata and pillar breaks and faulty top can admit water, while places running to the dip often accumulate water which comes up through the bottom. In all cases, except where passing under a year-round stream, the amount of water made is usually pretty closely connected with the weather-more water during the rainy season, less in the dry, although the deeper a mine is, the longer it is before changes in rainfall are felt. Another source of water, not connected with seasonal changes, is old water, accumulated over a period of time in abandoned workings of the mine, or from flooded adjacent mines. Here the water filters through the coal, the parting, or comes up through cracks in the bottom. Similarly, core holes, drilled to prospect the property, can be a source of unexpected water and modern safety requirements for dust-allaying water at the working faces can turn a pleasant working area into a soggy mess over the weekend if the system is not properly maintained and operated. Why water must be disposed is obvious. If allowed to accumulate, sooner or later the mine will fill up, or at least it will become "roofed" in low places, blocking ventilation and traffic. But it must also be controlled long before it reaches this stage. Water standing in the working faces is unpleasant for the men who have to work there and also cuts down on the amount of work they can do, as they must watch where they step all the time. It is especially unpleasant in low coal.

Jan 1, 1973

By E. S. Moore

The Kolar gold field has been for a long time the most important gold-producing area of India. It is situated in the Skate of Mysore, southern India, and not far from the City of Bangalore. The productive field is about 3 miles long and in it a gold-bearing quartz vein varying in width from 1 in. to over 10 ft. is worked. The vein carries high values to great depths and many of the mines have paid large dividends. Geological Formations In KolaR Region The rocks of the Kolar region are pre-Cambrian in age and bear a close resemblance to some of the pre-Cambrian formations of America. The oldest rocks seen are basic lavas, now mostly altered to hornblende-schists, with which is associated some banded iron-formation; these rocks are similar to the Keewatin schists and iron-formation in the Lake Superior region. The schist is cut by the gold-bearing quartz vein. In certain parts of the area there is also a conglomerate containing pebbles of granite, jasper, and schist. The matrix resembles a hornblende-schist and is intruded by small granite dikes, which in some cases have been pinched off by squeezing of the rock. This has led Dr. W. I?. Smeeth, Chief Inspector of Mines of Mysore, to whom the writer is greatly indebted for information regarding this area and for his hospitality while visiting the field, to regard this conglomerate as a breccia due to crushing of granite dikes in the schist. Dr. J. W. Evans has regarded the conglomerate as probably a squeezed glacial boulder clay. From analogy with pre-Cambrian conglomerates in America, the writer regards it as a metamorphosed rock similar to our basal Huronian conglomerate. However, the main bearing which it has upon the problem under discussion is the apparent fact that it is younger than the schist and that it indicates the presence of a syncline in the rocks cut by the quartz vein. Surrounding the area of schist and conglomerate is a large mass of granite-gneiss resembling the Laurentian gneiss of the Lake Superior region. Still later than the rocks mentioned above are basic intrusions which cut the quartz and schists; in the mines these are known as trap. One dike of this type is 50 to 60 yd. wide.

Jan 1, 1920