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By M. A. Mahtab

When characterizing orientations of rock joints in an engineering site with respect to mean values of the existing clusters or joint sets, a need may arise for a similarity test that allows grouping of observations from several adjacent sampling stations. Subjective judgment, though based on experience, may not produce realistic groupings in the data. A similarity test is developed in this paper for objective grouping of samples of joint orientations in engineering sites. The test is applied to the data from a large, geologically complex site of a potential open pit mine.

Jan 1, 1984

By David A. Thomas, David N. French

The lrnrdness of WC crystals has been measured with the Knoop indenter at loads of 100 and 500 g on the (0001) and (1070) planes. The hardness as tneasitred on the basal plane is 2400 kg per sq mm and shows little anisotropy. The hardness on the prism plane, however, shows a marked orientation dependence, with a low value of 1000 kg -per sq mm when the long axis of the Knoop indenter is oriented parallel to the c axis and a high value of 2400 kg per sq mm when the indenter is perpendicular to the c axis. Slip lines (Ire observed surrounding the microhardness indentations and they show slip on (1010) planes, probably in [0001] and (1120) directions. This slip behavior can be explained by the crystal structure of TVC, which is simple hexagonal with a c/a ralio of 0.976. The hardness anisotropy call be explained by [0001]{1010} and (1130) {10l0] slii) and the resolved shear-stress analysis of Daniels and Dunn. HARDNESS anisotropy is a well-known phenomenon and has been reported for many metals, with both cubic and hexagonal structure.1-6 For hexagonal tungsten carbide, WC, a wide range of hardness values is reported in the literature. For example, Schwarzkopf and Kieffer7 give a hardness of 2400 kg per sq mm and report a value of 2500 kg per sq mm by Hinnüber. Foster and coworkerss give the average Knoop microhardness as 1307 kg per sq mm with a maximum value of 2105 kg per sq mm. Although these values and the structure of WC suggest the likelihood of hardness anisotropy, no such measurements have been made. We first detected a large apparent hardness anisotropy in WC crystals about 75 p large, in over-sintered cemented tungsten carbide. Prominent slip lines also occurred around many indentations. This report presents further observations and interpretations of hardness anisotropy and slip in WC crystals obtained from Kennametal, Inc. Both Knoop and diamond pyramid indenters were used on a Wilson microhardness tester with loads of 100 and 500 g. EXPERIMENTAL RESULTS The carbide crystals tended to be triangular plates parallel to the (0001) basal plane of the hexagonal structure. The side faces were parallel to the ( 1010) prism planes. Specimens were mounted approximately parallel to these two types of faces and metallographically polished. Laue back-reflection X-ray patterns were used to orient the specimens, which werethen ground to within ±1 deg of the (0001) and (1010) planes. The Knoop hardness values measured on the basal plane are plotted in Fig. 1. There is only a small anisotropy, with a hardness range of 2240 to 2510 kg per sq mm. The additional points at angles from 52.5 to 67.5 deg confirm the sharp minimum hardness at 60-deg intervals, consistent with the sixfold hexagonal symmetry. The average hardness of all values obtained on the basal plane is 2400 kg per sq mm. While the basal plane shows only slight anisotropy, the (1010) plane exhibits marked hardness anisotropy, from 1000 to 2400 kg per sq mm. Fig. 2 shows the hardness as a function of the angle between the long axis of the indenter and the hexagonal c axis, the [0001] direction. The minimum and maximum occur when the indenter is oriented parallel and perpendicular to the [0001] direction, respectively. The anisotropy of the prism plane is contrary to that reported for hexagonal zinc and hard- However, the basal-plane anisotropy is similar to these two metals.1'2 To check the accuracy and reproducibility of the measurements, a series of fifteen impressions was made at 100-g load in the same orientation in the same area of the specimen surface. The average for all was 2040 kg per sq mm, with a range of 1950 to 2130 kg per sq mm, giving an accuracy of about ± 5 pct. Thus the slight anisotropy on the basal plane is almost within experimental error. Fig. 3 shows slip lines around the Knoop indentations on the basal plane. The slip traces are in directions of the type (1130). The presence of slip steps on the basal plane indicates that the slip direction lies out of the (0001) plane. Because WC has a c/a ratio of 0.976,' the shortest slip vector is [0001], which suggests slip systems of the type [0001] (1010). Fig. 4 shows slip lines around the Knoop intentations on the (1010) plane. These slip lines are inconsistent with [0001] slip but can be

Jan 1, 1965

THE writer of this paper well realizes that the majority of engineering and metallurgieal works have from time to time evolved mechanical devices which are of great value as regards application in an operating plant.Many of these deviees would not be apparent to an individual making a brief inspection of works such as these, and it is for this reason that the writer proposes to outline a few of the devices which have been evolved by the engineering department of the Broken Hill Associated Smelters Pty. Ltd.NOVEL METHOD OF MACHINING A SPHERICAL JOINTFig. 1 represents one half of a casing for a ball-joint coupling. In the ordinary methods of boring an external spherical casing, that is with a radius bar attached to the tool rest of a lathe, there is always an error in the bore. It has two flat sides, and this error is inherent in the ordinary orthodox method and cannot be corrected. The engineers of the Broken Hill Associated Smelters Pty. Ltd. undertook a job that had to be extremely accurate, and the tool shown in Fig. 2 was evolved. The tool is not exactly fool proof, but in the hands of an average mechanic an absolutely perfect FIG. 1. sphere can be bored. The casing has to be held in the lathe in such a manner that one half can be removed without affecting the setting of the work. The business end of the tool is then placed inside the...

Jan 1, 1922

By R. Sandefur

Recent advances in personal computer technology allow movies of various types to be made and displayed on PC and Macintosh computers. An interesting application of this movie technology is animation of computerized geological models. These movies, which can be most easily constructed along rows, columns, and benches of block models, allow an ore body to be more easily and quickly visualized than the traditional method of flipping back and forth through various sections.

Jan 1, 1994

By K Zic, P Pickering, P Fraser

Water is a defining feature of the Pilbara. Its management was and remains vital for the pastoral industry which European settlers established when they first came to the Pilbara, and for the mining industry which now dominates economic activity in the Pilbara. Water availability in the Pilbara is, however, problematic. Severe droughts and major floods can occur at close intervals. In response to this uncertainty, the Department of Water undertook a Prefeasibility Study to determine, at a high level, the water requirements and opportunities in the Pilbara region. This paper reports on the outcomes of this study and the water integration opportunities in the region, identifying the sources of water supply and offers possible options for managing this water sustainably for the present and future demand. A range of supply opportunities is reviewed including: dewatering from mining operations, surface water, and desalination. All opportunities were subject to order of magnitude costing, including capital, whole of life and retail unit pricing with preferred options receiving further interrogation through triple bottom line (TBL) analysis to prioritise solutions. Options were also subject to intangible quantification (IQ) including benefits from the reduction of carbon emissions to ensure that the preferred option is based on factors other than just the least cost. Demand analysis was undertaken to identify current and future requirements and were assessed through review and integration of regional and sub regional master plans and consultation with mining, agriculture, industry and the community. The paper concludes that the viability of a Pilbara integrated water supply scheme depends on the development of a financial mechanism involving both government and industry participation models. The agreed scheme formed the basis of a submission to Infrastructure Australia for funding assistance.

Jan 1, 2009

By C. H. Mathewson, Kent R. Van Horn

Copper and the copper-base solid solutions readily form twin crystals when plastically deformed at a suitably elevated temperature or annealed after cold deformation. In fact, no feature of the microstructure of these materials is more prominent or characteristic than these straight-sided bands or simple lines of division which sometimes come from groups of thin polysynthetic lamellae, penetrating part way or wholly through the parent grain substance, but often divide the grain into a few or perhaps only two crystallographically related parts. Nearly always the bands as seen in the usual microscopic examination of a specimen come into vivid contrast with the adjacent crystalline material owing to the inherent difference in orientation. Bands which under special conditions of orientation cannot be seen with vertically incident light are often visible under oblique illumination and, when this fails, contrasting effects usually may be obtained by using polarized light. There is no longer any doubt that these synthetic banded structures obtained in the ordinary course of working and annealing are due to twinning of the spinel type which was observed long ago in a number of metals crystallizing in the isometric system.' It has been customary in metallurgical literature to designate these synthetic twins, which grow into prominence during an annealing process, as "annealing twins" without regard to the actual mode of their formation, which is, indeed, obscure and with scant recognition of the fact that prior deformation is essential, no twins having been observed in metal of known unstrained history. This is questionable; especially in view of the fact that in a number of metals and minerals, reorientation into the twin configuration is known to occur as a result of a simple shearing mechanism along the recognized twinning planes and the

Jan 1, 1930

By J. O. Brittain, N. R. Adsit

A number of zinc bicrystal specimens with the grain boundary loaded in simple shear were plustically deformed in creep in a vacuum at 200°C and under an argon atmosphere at 350°C. The results indicated that the amount of grain boundary sliding at a given time was controlled by the slip in the grains and was proportional to the resolved shear stress on the slip plane. Curves of grain boundary sliding vs time were found to be cyclic with no regular periodicity. ALTHOUGH grain boundary sliding (G.B.S.) has been investigated in a number of different types of tests on various materials there is substantial disagreement on the interpretation of the various observations. Gifkins1 has presented a comprehensive review of the subject of G.B.S. and fracture. He reports that the activation energy for high-temperature creep is equal to that for volume self-diffusion and that pure metals show less tendency towards intercrystalline fracture than alloys. Pure metals show appreciably greater grain boundary migration than alloys, and both grain boundary migration and grain boundary sliding follow the same general trend in time as plastic deformation during creep.' While there have been a number of different mechanisms proposed to account for G.B.S., none of the models explains all the results. Since zinc has only one prominent slip system, it was hoped that experiments on G.B.S. in zinc bicrystals might enable us to separate the effect of grain boundary angle and the effect of matrix slip and thereby resolve at least one part of this complex phenomenon. EXPERIMENTAL PROCEDURE Bicrystals of pure zinc (99.99 pct) were grown by a Bridgeman technique in a furnace having a gradient of 20°C per in. The bicrystals were seeded to a desired orientation and grown in a split graphite mold which was 3/4 by 5/8 by 8 in. The mold was enclosed in a Pyrex tube and the tube was evacuated and then filled with a small amount of argon before it was placed in the furnace. The growth rates were 1/2 to I in. per hr for the bicrystals and 1/2 to 3 in. per hr for the single-crystal seeds. The longitudinal V notches served to hold the grain boundary in position during the growth process. A schematic rep- resentation of a specimen which had been cut with a jewelers saw from the bicrystals is shown in Fig. 1. All specimens of a series were cut from the same crystal, some of which were 7 in. in length. After specimen preparation the boundary was approximately 5/16 in. long and the V notches had a radius of 1/16 in. The boundaries were straight at a magnification of X100 with the exception of a few which had a gradual radius of curvature of greater than 3.2 in.-1. Laue back-reflection photograms were taken on the specimens to check the orientation of grains in the bicrystals. The method of relating the orientation of the two lattices is shown in Fig. 1, where 0 is the angle between normal to the boundary and the trace of the basal plane, is the angle in the boundary between the trace of the basal plane and a line parallel to the V notch, and x is the angle in the basal plane between the Burgers vector and the perpendicular to the grain boundary. After mechanical polishing the specimens were chemically polished.2 Subsequent to the polishing operation the specimens were encapsuled under a vacuum of better than 25 annealed at 340°C for 1 hr to remove the effects of this handling, and again chemically polished. Finally, fiduciary marks were scribed on the specimen using a micromanipulator. Creep tests, which were conducted in a modified Bausch apparatusS with the boundary loaded in simple shear, were run at a constant load (since the boundary area remained essentially constant this is approximately constant grain boundary stress). The temperature was controlled to ±1/4°C as measured on a semiprecision potentiometer with a calibrated thermocouple. The specimens were tested in a vacuum of better than 0.5 at 200°C and in purified argon at a pressure of 1/2 atm at 350°C. The op-

Jan 1, 1965

By R. V. Ramani, K. V. K. Prasad

Forecasting mined grade variability from exploration information is a challenging task in mine planning. For effective planning of activities, such as workplace scheduling, ore grade quality control, etc., development of realistic numerical simulation models of in situ variability from exploration information is an essential first step. Geostatistical conditional simulation (GCS) is one of the well known methods to develop such simulations. Recently, stochastic fractal models based on the assumptions of scale-invariance and self-similarity have been used for developing simulations of several natural phenomena. It has been suggested that these models might permit the generation of short-scale variability information from exploration data with greater fidelity when the data satisfies the attendant assumptions. In this paper, stochastic fractal models are reviewed, and their relationship to geostatistical variogram models is examined. A comparison of the two simulation techniques has been performed using coal sulfur data from a mined-out coal property. The results of this comparative analysis are also presented in the paper.

Jan 1, 1993

By L. Adler

The proper transfer of roof loads from props and bolts to ribs and pillars can result in appreciable savings. The author shows how to plan such load reduction in underground mines. For openings in bedded rocks, analyzed by simple beam theory, it has been shown that roof loads can be shifted from one support to another.&apos; This transfer is effected by controlling the relative deflection of adjacent supports. If this action is used to reduce loads in the props or bolts and increase them in the ribs or pillars, it could be productive of economies averaging 30 pct. Such savings can be realized by: 1) using smaller artifical supports such as props and bolts, and 2) increasing loads in the rib to induce eventual failure for longwall caving. Since the rib is relatively load-insensitive, it provides a natural load sink. However, caution must be used in applying such permissive deflections, for while the supports are being handled properly, the stresses in the roof itself are very sensitive to such manipulations.1 An underground opening overlain by a relatively thin immediate roof, and a thick main roof, is usually laid out as shown in Fig. 1. The total open span (T) between pillars or ribs is calculated on the basis of the main roof, and the secondary spans (L) on the basis of the immediate roof, so that a complete accounting of the existing loads is made. For this purpose the immediate roof is treated as a uniformly loaded continous beam, which is an indeterminate structure as shown in Fig. 2(A). The term systematic supports places the following two restrictions on the continuous beam: 1) Spans between all supports are equal: uniformity of spans. 2) Loads on all supports (excepting ribs) are equal: uniformity of supports. The usual mode of analysis of such a structure by beam theory is to divide it up into a series of simply supported beams with end moments as shown in Fig. 2(B)2 The problem now is to transfer a maximum roof load to the rib from the span immediately adjacent to it by permitting its support to deflect, and yet not fail the roof. Once this has been done, the load can be equalized on all other supports by permitting further degrees of relative deflection. It is necessary, therefore, to determine an expression for the constant load on each support, and the required deflections, in terms of properties of the roof. From Fig. 1: T/L0 = No and T/L = N [1] Where: T = allowable span of main roof, ft. (Calculated from S = Mc/l) S is allowable modulus of rupture, psi. M is maximum moment, lb-ft (in this case wT2/12). c is distance from neutral axis to extreme fiber, ft. I is moment of inertia with respect to the neutral axis, ft4. L,, = allowable span of immediate roof, ft (calculated as was T). L = actual span of immediate roof, ft. N0 and N are pure numbers where No < N and N is the integer just higher than Nu. For example: If T =100 ft and L0 - 15 ft 100 N0 =100/15= 6.667 . . .N= 7 L = T/N = 100/7 = 14.28 ft Consequently N = No + n where n is a positive fraction i.e.: 0< n < 1 Since from Eq. 1, T = NL = N0L0 Lo /L = N/No = N/N-n

Jan 1, 1961

The integration of historic exploration geoscientific data with high precision multi-element and isotope geochemistry can provide explorers fundamental information on mineral potentiality, tectonic setting, source signatures, fluid migration, mineralisation environment and the timing of mineralising events. Such knowledge is crucial for ore modelling and target generation, particularly for concealed ore systems in both brown and greenfields. An&nbsp;EXTENDED ABSTRACT&nbsp;is available for download. A full-length paper was not&nbsp;prepared for this presentation.

Jan 1, 2008

By Harold S. Davis

SURROUNDING the nuclear core of an atomic energy plant there are usually one or more thick walls of concrete, as required to protect instruments and personnel from the harmful effects of nuclear radiations. Sometimes these massive walls are of ordinary concrete weighing about 150 pcf. To reduce wall thicknesses, concrete weighing 200 to 350 pcf may be used. Such high densities are obtained by using natural aggregate processed from heavy ore, or by using steel slugs or iron shot in concrete. Mix data for a number of high-density concretes are summarized in Table I.1 High density at low cost is of prime importance in shields designed to absorb gamma rays. On the other hand, biological shields located near the reactor core must attenuate neutrons as well as gamma rays. In general, a biological shield should contain: 1) heavy elements to slow down high energy neutrons and to absorb gamma rays, 2) either light elements or hydrogenous materials to moderate neutrons of intermediate energy, and 3) materials to absorb neutrons once they have been slowed down to thermal energies. Some shield materials, iron and water for example, are effective in one or more of the above ways. On the other hand, some otherwise excellent shield materials have certain undesirable radiation properties that limit the ways or number of places they can be used. For example, when iron absorbs neutrons it emits secondary gamma rays of high energy. On the other hand, boron absorbs neutrons avidly without producing high energy gamma rays. In spite of its high cost, boron is sometimes used in concrete to minimize production of secondary gamma rays. In some shielding applications it is necessary to avoid materials that become radioactive when subjected to neutron bombardment, continuing to give off high energy gamma rays for long periods after being removed from a neutron field.

Jan 5, 1957

By Arnt Solbu, Jomar Thonstad

The reaction between CO, and aluminum in cryolite-alumina melts in contact with aluminum has been studied by passing CO2 over the melt. In unstirred melts a homogeneous reaction between dissolved metal and dissolved CO2 was observed. In stirred melts in which convection was induced by bubbling argon through the melt, the dissolved metal apparently reacted mainly with gaseous CO2. The rate of formation of CO increased slightly with increasing depth of the melt, and it did not depend on whether CO2 was passed over or bubbled through the melt. The rate of formation of CO increased with increasing area of the metal/melt interface and with the application of anodic current to the metal. It is concluded that the dissolution of metal into the melt is the rate-determining reaction. THE current efficiency in aluminum electrolysis is determined by the rate of the recombination reaction between the anode gas and the metal: 2A1 + 3CO2—A12O3 + 3CO [1] as originally stated by Pearson and waddington.1 The occurrence of this reaction in cryolite-alumina melts in contact with aluminum was first verified experimentally by Schadinger.2 Thonstad3 has shown that the reaction may proceed further to give free carbon: 2A1 + 3CO— A12O3 + 3C [2] Normally only a few percent of the CO formed undergoes such reduction. The mechanism of these reactions has not yet been clarified. Aluminum, as well as CO,, is soluble in the melt. The solubility of aluminum in cryolite-alumina melts at around 1000°C corresponds to 75 x 10- 6 mole A1 per cu cm,4 while that of CO2 is only 3 x 10-6 mole CO, per cu cm.5 Taking into account the stoichiometry of Reaction [I], the ratio between dissolved aluminum and dissolved CO2 available for the reaction in a saturated melt is about 40. Therefore, as will be shown in the following, the reaction probably mainly occurs between gaseous COa and dissolved aluminum. The dissolved aluminum presumably consists of subvalent ions of aluminum and sodium.4&apos;6 Since the interpretation of the present results is not dependent upon the nature of this solution, the dissolved metal will be designated solely as Al+ in the following. The reaction can then be divided into four steps: A) dissolution of metal, e.g., 2A1 + Al3 — 3A1+ [3] B) diffusion of dissolved metal through a boundary layer; C) transport of dissolved metal through the bulk of the melt; D) Reaction [1]. If dissolved CO, takes part in the reaction, three additional steps embodying the dissolution and transport of CO2 must be added. schadinger2 observed, when bubbling CO2 through the melt, that the rate of formation of CO (in the following designated rfco) did not depend on the distance from the metal surface. The results also indicate that the rate of bubbling did not affect the rfco. When passing CO, over the melt, Revazyan7 found that the loss of metal did not depend on the depth of the melt above the metal or on the flow rate of CO2, and concluded that Step A is rate-determining. In an unstirred melt, however, Gjerstad and welch8 found that the rfCo decreased with increasing depth of the melt, indicating that step C was rate-determining. It thus appears that the rate control of the process depends on the experimental conditions, particularly on the convection. In the present measurements the reaction has been studied in unstirred as well as in stirred melts. EXPERIMENTAL AND RESULTS The experiments were carried out at 1000°C in a Kanthal furnace with a 10-cm uniform temperature zone (±0.l°C). The melts were made up of "super purity" aluminum (99.998 pct), hand-picked natural cryolite, and reagent-grade alumina. In experiments where alumina crucibles were used, the alumina content in the melt was close to saturation (13.5 wt pct9); otherwise it was 4 wt pct. Pure Co2 (99.85 pct) was passed over the melt, and the exit gas was analyzed for CO2 and CO by the conventional absorption method.3 From the weighed amount of CO (as CO2) the rfco was calculated as the number of moles of CO formed per min per sq cm of the surface area of the melt. The amount of carbon formed by Reaction [2] was not determined. As already indicated the rfco is much higher than the rfC, by Reaction [2]. Since the rfC probably is proportional to the rfco, the measured rfco should then the proportional to, but slightly lower than, the total rate of Reactions [I] and 121. In general the scatter of results obtained in duplicate measurements was ±5 to 10 pct, while within a given run a precision of ±3 to 5 pct was obtained. The various crucible assemblies that were used will be described below. Measurements in Unstirred Melts. When carrying out aluminum electrolysis in small alumina crucibles. Tuset10 observed that after solidification the lower part of the electrolyte was gray and contained free metal, while the upper part near the anode was white and contained no metal. One may test for the presence of free metal by treating with dilute hydrochlorid acid.

Jan 1, 1969

G. M. TAYLOR,* Colorado Springs, Colo.-I do not think the plan outlined in this paper would work at Cripple Creek. Most of our men have had a pretty good education. The Cripple Creek district is a lessee district-I do not think there is one urine operating in Cripple Creek to-day that does not have the leasing system. We have as many men leasing on our property as we have mining and every man who is working for wages is looking for a lease-every man has mined for him-self, he has been his own boss on a lease, either on our own property or on some of the other properties, and it makes a different class of employees.

Jan 12, 1919

By Edward Wisser

The environment of an ore body is taken to mean not only its physical surroundings but every factor, passive or active, that conditioned the ore shoot, saving only the original composition of the solutions that formed the shoot. Collection of data related to the shape and characteristics of veins should be followed by correlation of the data and the formulation of generalizations regarding ore formation. The nature of the criteria used in arriving at these generalizations is discussed. Certain of the criteria, when used with an understanding of their underlying causes, become "ore-guides." In the course of his study the geologist must not confine himself to the immediate surroundings of the veins, but should attempt to work out the geologic history of events culminating in the crucial epoch for any mining district, the period of mineralization. The work may involve study of features far removed from the veins and related to them only indirectly. It commonly means thorough study of the geology of the entire region surrounding the ore deposits. THE following question has been suggested for discussion: ? "Are there any criteria by which one can determine when mining operations have reached the roots of an ore deposit?" The question deals less with the roots of a particular ore body than with the lower limit of the vertical range within which ore bodies may be expected. It concerns a critical line upon the longitudinal vertical projection of a vein. ? Below this line it is useless to look for ore shoots; above the line exploration below the bottoms of individual ore shoots may be justified. Can we learn to determine the position of such a line?

Jan 1, 1939

By Larry L. Wischhoefer

The Automated Breathing Metabolic Simulator (ABMS) is a versatile machine capable of performing almost any physiologically appropriate respiratory simulation. The first ABMS was delivered to the Bureau of Mines by IBM in 1973. Since then efforts have been made to refine the systems and components which make up the ABMS including the Breathing Simulator Module (BSM), Gas Analysis Module (GAM), and Supervisory Controller (SC)-each of which are also capable of stand-alone operation. Since September 1980, Reimers Consultants has been testing and modifying the ABMS and its components in order to improve the equipment and to develop simulation criteria and parameters. Changes have been made to the Phase I Design Plan and Performance Specifications; future improvements based on current experience are recommended; and test results of full scale testing conducted by Reimers Consultants in November 1983 on several types of breathing apparatus are reported and illustrated.

Jan 1, 1984

The Lower Palaeozoic Woolomin Association is composed of chert and jasper (often radiolarian), siliceous argillite, the mafic volcanics with associated hyaloclastites, and occasional greywacke and limestone lenses. Several "Cyprus-type", conformable pyritic copper (+/- zinc and cobalt} sulphide lenses are spatially related to individual mafic volcanic units and manganiferous chert and/or jasper. The Association has been interpreted to represent an oceanic crustal remnant generated either in an island arc environment (Herbert, 1981) or at a divergent plate boundary (Scheibner and Glen, 1972; Leitch, 1974a, 1975) later to be obducted, or tectonically emplaced, into continental crust; the adjacent Peel Fault was considered to be the palaeo-obduction zone (Scheibner and Glen, 1972) and the associated alpine-type mafic/ultramafic complex, an ophiolite (Crook and Felton,1975).

Jan 1, 1990

By O. Benavente, M. C. Hernández

Selenium is obtained mainly from copper anode slimes, which is a by-product of the copper electrorefining process. Selenium is present in copper anode slimes as silver and copper selenides. Traditionally, selenium has been obtained by pyrometallurgical processes; however, hydrometallurgy has now been incorporated either full or partial to the conventional process. Some hydrometallurgical processes are been developed and used at laboratory level an industrial scale. This document describes theoretical background and results of characterization and dissolution of selenium from a decopperized anode slimes in an alkaline oxidizing system. The results have indicated that the oxidizing leaching process reaches a practically complete dissolution of selenium (up to 90 %); the undissolved portion is due to the generation of a AgCl around the particle surfaces that delays the progression of the reaction. The results indicated that 90% of selenium extraction can be obtained by dissolution under moderate conditions of pH, temperature and reagent concentration in oxidizing medium. INTRODUCTION Selenium is distributed in the earth's crust in most rocks and soils. Selenium is essential, as it has wide range of applications in the medical and food industries as well as, used in semiconductor, sensors and photochemical devices. Selenium is rarely found in the native state, 90% of selenium is obtained from copper anode slimes, which is a byproduct of the copper electrorefining process (Lu, Chang, Yang, & Xie, 2015; Xiao et al., 2017; Yang et al., 2018). In anode slimes, selenium is present as an intermetallic compound, as Ag-Cu selenides. Currently, selenium is recovered from the anode slimes via hydrometallurgical and pyrometallurgical processes (Lu et al., 2015). The traditional pyrometallurgical method recovers selenium effectively, but faces difficulty as a result of increased energy costs and strict environmental regulations associated with the process (Li, Yang, Jin, Chen, & Tong, 2017). Therefore, hydrometallurgical processes are proposed in oxidizing medium such as nitric acid, alkaline leaching with sodium nitrate, wet chlorination and pressure leaching, amongst others (Hait, Jana, & Sanyal, 2012; Kim & Wang, 2010; Xiao et al., 2017; Yang et al., 2018).

Jan 1, 2019

By F. Mendaña

The characteristics of the igneous and metamorphic bedrock, extra-hard and abrasive, of the Guadarrama Tunnels, a bi-tube project of length 28.4 km without any intermediate attack, are first commented upon. Next, a detailed discussion is given of the most relevant aspects of the performance of the four double shield type TBMs. The experience of this leads to various recommendations to be borne in mind in future designs of TBM having to work in rock of similar characteristics.

Jan 1, 2007

R,. P. JaRvis,* El Oro, Estado de México, México.—The practical problem raised by Mr. Wisser—that is, the determination of the lower limit of ore deposition, below which it is useless to look for ore shoots—is one of the most important in economic geology. He asks: "Can we learn to determine the position of such a line?" For individual districts, yes; but its determination has always been by empirical methods; that is by actually exploring the veins to such depths that the values drop below the economic limits. Usually the signs are plain enough that values have been bottomed without confirmation by the chemist or assayer. Most veins, when approaching their limit, begin to split into branches or stringers; the vein matter itself undergoes a change from "lively looking" rock to one that is dull and unpromising, the quartz, instead of having segregated into clean vein matter, has simply spread itself into the country rock, rendering this more siliceous but no richer—these, together with inclusions of the country rock in the vein, are all positive indications of the limit. Mr. Wisser seems disposed not to accept the law of cause and effect, which he calls "empiricism." He says: "Empiricism embodies an assumption perhaps not evident at first glance. It is this: that like effects spring from like causes and therefore necessarily have a common meaning." There can be no doubt as to the validity of this law, since it is the foundation stone upon which are built all inductive sciences, including economic geology. When demonstrable, proved facts become confused with inferences, as they seem to be generally in the paper under examination, no sound conclusions can be reached. Mr. Wisser has failed to give sufficient data covering the two vein systems which he cites as examples. Presumably they are situated in the Pachuca District of Mexico, but not everybody is familiar with the vein systems there in spite of the fact that it is world famous as a silver producer. Are these two systems separated some distance horizontally from one another and how far? He has given no estimate of the amount and kind of rock that has been eroded from over the present veins. His description of the two systems appears on page 100, beginning: "1. East-west veins," and ends on page 101, "they would lack spaces there in which to deposit." On page 101, with the paragraph beginning "On the other hand," he gives a picture of what he believes takes place in class 2 veins. The sum of this seems to be, according to Mr. Wisser&apos;s observations, that, in the east-west veins, class 1, there has been an invasion of an "altering solution," which I judge has been responsible for the formation of extensive "alteration haloes"; that these alteration solutions have followed along pre-existing fractures or fissures; and that after these alteration solutions finished their work the mineralizing solutions deposited the vein matter and metallic values. Mr. Wisser does not specify clearly what the "alteration haloes" consist of; in other words, what change the original rock has suffered, whether oxidizing, carbonating, or sulphidizing. If they came from depth they could not be oxidizing or carbonating, and in this case it is a bit

Jan 1, 1941

R,. P. JaRvis,* El Oro, Estado de México, México.—The practical problem raised by Mr. Wisser—that is, the determination of the lower limit of ore deposition, below which it is useless to look for ore shoots—is one of the most important in economic geology. He asks: "Can we learn to determine the position of such a line?" For individual districts, yes; but its determination has always been by empirical methods; that is by actually exploring the veins to such depths that the values drop below the economic limits. Usually the signs are plain enough that values have been bottomed without confirmation by the chemist or assayer. Most veins, when approaching their limit, begin to split into branches or stringers; the vein matter itself undergoes a change from "lively looking" rock to one that is dull and unpromising, the quartz, instead of having segregated into clean vein matter, has simply spread itself into the country rock, rendering this more siliceous but no richer—these, together with inclusions of the country rock in the vein, are all positive indications of the limit. Mr. Wisser seems disposed not to accept the law of cause and effect, which he calls "empiricism." He says: "Empiricism embodies an assumption perhaps not evident at first glance. It is this: that like effects spring from like causes and therefore necessarily have a common meaning." There can be no doubt as to the validity of this law, since it is the foundation stone upon which are built all inductive sciences, including economic geology. When demonstrable, proved facts become confused with inferences, as they seem to be generally in the paper under examination, no sound conclusions can be reached. Mr. Wisser has failed to give sufficient data covering the two vein systems which he cites as examples. Presumably they are situated in the Pachuca District of Mexico, but not everybody is familiar with the vein systems there in spite of the fact that it is world famous as a silver producer. Are these two systems separated some distance horizontally from one another and how far? He has given no estimate of the amount and kind of rock that has been eroded from over the present veins. His description of the two systems appears on page 100, beginning: "1. East-west veins," and ends on page 101, "they would lack spaces there in which to deposit." On page 101, with the paragraph beginning "On the other hand," he gives a picture of what he believes takes place in class 2 veins. The sum of this seems to be, according to Mr. Wisser&apos;s observations, that, in the east-west veins, class 1, there has been an invasion of an "altering solution," which I judge has been responsible for the formation of extensive "alteration haloes"; that these alteration solutions have followed along pre-existing fractures or fissures; and that after these alteration solutions finished their work the mineralizing solutions deposited the vein matter and metallic values. Mr. Wisser does not specify clearly what the "alteration haloes" consist of; in other words, what change the original rock has suffered, whether oxidizing, carbonating, or sulphidizing. If they came from depth they could not be oxidizing or carbonating, and in this case it is a bit

Jan 1, 1941