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By R. Taggart, R. H. Ericksen, D. H. Polonis

Transmission electron microscopy techniques hare been used to study the spontaneous marfensite phase that forms during the thinning of Ti-Cr alloys. The structure of this phase has been found to differ. from the hcp martensite and has been identified as a clisforted fcc lattice. The spordaneous marlensile in this system is interpreted as a metastable isomorph of the equilibriunz TiCr, phase. WHEN thin-foil specimens for transmission electron microscopy were prepared from metastable alloys of the Ti-Cr system, a spontaneous transformation occurred' when the foils contained the untrans-formed 0 phase or two-phase mixtures of the 0 and w phases. The purpose of this paper is to examine the relationship that exists between the crystal structure of the spontaneous product and that of the matrix. The differences between the martensite transformation that occurs in the bulk material and the spontaneous reaction that occurs during the preparation of thin foils are compared with the observations that have been reported for similar phenomena in a commercial titanium alloy.' A spontaneous reaction that exhibits characteristics similar to a martensite transformation has been reported to occur in thin foils prepared from the retained metastable structures of several alloy systems.1'3"7 ~ull~ observed such a spontaneous reaction in 0 brass and attributed the apparent increase in the martensite transformation temperature to a decrease in the non-chemical free energy associated with bulk strain energy. He also showed that the spontaneous product did not have a specific habit plane, but that its orientation relationships to the parent matrix were dependen on the thickness of the transforming region. It has also been pointed out by Breedis6 that in thin films the absence of the constraints imposed by a bulk matrix can cause different requirements for the martensite plate interface and lattice distortion which is reflected bv a dependence of the transformation mechanism on the specimen geometry. In the case of the spontaneous reaction reported for Au-Zn alloys7 a definite habit plane was determined and shown to correspond with the habit plane calculated on the basis of the Bowles and Mackenzie crystallographic theory of the martensite transformation.'- lo EXPERIMENTAL PROCEDURE A series of titanium alloys containing 5.5, 5.9, 6.4: 7.6, 8.0, 11.3, and 18.7 at. pct Cr were prepared from high-purity (iochrome) chromium and iodide-grade titanium by levitation melting. The experimental procedure used for sectioning the alloys and for thin-foil preparation has been reported in an earlier paper.' X-ray diffraction patterns were obtained using a 114-mm Debye-Scherrer camera and Cu-Ka radiation. In order to minimize fluorescent radiation from the specimen, a strip of aluminum foil 0.002 in. thick was placed in contact with the X-ray film. After a specimen was removed from the camera: an additional X-ray experiment was performed, to insure that no spurious lines were obtained due to the presence of the aluminum foil. The interstitial impurity analysis for the alloys used in this study was as follows: oxygen, 100 ppm: hydrogen, 30 ppm: nitrogen, 28 ppm. EXPERIMENTAL RESULTS Electron diffraction patterns were obtained from several individual crystals of the spontaneous marten-

Jan 1, 1970

The Library of the above-named Societies is open from 9 A.M. to 9 P.M. on all week-days, except holidays, from September 1 to June 30, and from 9 A.M. to 6 P.M.. during July and August. The Library contains about 55,000 volumes, including sets of technical periodicals and the publications of scientific and technical societies. Members of the Institute, with few exceptions, are forced to spend a portion of their time in localities isolated from sources of information. To these the Library can render valuable service through correspondence; letters requesting information-will receive special attention. The Library is prepared to furnish references and copies of articles on mining and metallurgical subjects; to determine the existence of mining-maps, and to furnish general information as to the geology and mineral resources of all countries: All communications should be made as definite as possible so that the information received may be what is desired and not include collateral matter which may not be of interest. The time spent in searching for such collateral matter will be saved, and the information will be sent more promptly and in more usable shape. The members of the Institute. can be of service to the Library by forwarding copies of mining-reports, maps privately issued, and similar material, which will he classified, indexed, and made available to other members. Suggestions for additions to the Library, either by purchase or personal solicitation as gifts, will be welcomed. It is hoped that members while in the city will use the Library freely, and assurance is given that most careful service will be rendered to them.

Jan 5, 1913

By Allan M. Harvey

Asbestos production in the United States is no match for the vast operations of Canada and the U.S.S.R. The majority of U.S. production is limited to the states of Vermont, California and Arizona, and the type of asbestos is limited to the variety of serpentine known as chrysotile. What little production of other varieties of asbestos such as tremolite and anthophyllite that has occurred over the past 100 years since asbestos became a useful commodity is of practically no significance. However, new developments in the field of environmental and occupational health hazards has startled the mining industry in this country and has already given a few particular companies reason to be concerned about the profitability and probability of their continued operation in the business of mineral processing. At the heart of these developments is the question and controversy over just what constitutes asbestos and what exactly is the definition of a fiber. To the mineralogist or, in fact, to practically anyone engaged in the process of mining and separating minerals there is little or no question about asbestos. It is not a distinct mineral but rather a commercial product serving specific applications for which a number of fibrous mineral types can qualify. To the hygienist pr health authority this definition is too general. They demand something they can detect, measure and control. To suit their purposes and simplify their task of detection, they have labelled the minerals chrysotile, crocidolite, amosite, tremolite, anthoph-yllite and actinolite as asbestos, and any particle of these minerals with an aspect ratio of 3:1 as an asbestos fiber. It does not

Jan 1, 1976

By J. W. Stevenson

The Bureau of Mines investigated the influence that atmospheric pressure changes exert in a gassy coal mil on a ventilating air current with a system of bleeder entries. During the season when abnormal barometric fluctuations usually occur, recording instruments monitored the air current ventilating an active coal-producing area. It HL he rate of coal production caused a more significant change in methane concentration than did barometric change. The hazard that accompanies methane release due to expansion of the gob gases during atmospheric lows was minimized by the effective bleeder system.

Jan 1, 1966

By Raymond B. Ladoo

Wollastonite is a calcium metasilicate, with the formula CaSiO3; containing theoretically 48.3 pct CaO and 51.7 pct Si02. It is one of many natural and synthetic silicates with varying CaO/SiO2 ratios, with and without water of crystallization. While it is a very common mineral, deposits of sufficient size and purity to be of commercial interest are unusual. There is only one producer (1958) of wollastonite for industrial use in the United States, Godfrey L. Cabot, Inc. at Willsboro, New York. There has been a small production of surface material for ornamental use from near Blythe, California. Carload tests have been made on California wollastonite for making mineral wool and a commercial plant for this purpose was projected in 1957. Properties Wollastonite is monoclinic and commonly occurs in masses or aggregates of bladed or needle-like crystals. It has a perfect cleavage parallel to the long prismatic axis. It is rather brittle and some types grind easily to a very finely fibrous product, but other types, due to interlacing of fibers, are tough and difficult to grind. Mobs hardness is 4.5 to 5; specific gravity 2.8-2.9; index of refraction 1.616 to 1.631; melting point 1,512°C. Color when pure is a brilliant white, but when less pure it may be gray or brown. Luster is vitreous, transparent to translucent. Common mineral associates are garnet (several varieties), diopside, calcite and quartz. The nature of the mineral impurities determines to a large degree the commercial value of a deposit. At Willsboro, New York, the impurities consist chiefly of iron garnet and iron diopside which are both magnetic and so are easily removable by magnetic separation, yielding a nearly theoretically pure product. Some deposits in California contain calcite and quartz which cannot be removed cheaply, thus limiting market possibilities. Occurrence Wollastonite is a contact metamorphic mineral occurring in most places within or associated with impure limestones. The deposits at Willsboro, New York1,2,3,5 consist of two or more beds dipping 15-50°E and striking NW-SE. The main bed, 30 to 70 ft thick, may be traced on the surface for at least 2 ½ miles. In this belt, the Pre-Cambrian Grenville limestone has been injected and partially replaced by the more liquid portions of an anorthositic magma. Buddington and Whitcomb3 have described the rock as "Mixed gneisses, pyroxenite and garnetiferous gneisses and skarns." Prospecting revealed the wollastonite at ten different places in the belt, overlain in most places by a garnet rock. Diamond drilling has proven several million tons with probable reserves around 15 million tons. Interbedded with the wollastonite are beds of garnet from a few inches to several feet in thickness. In the wollastonite ore itself the chief and almost only associated minerals are garnet (mostly almandite but some andradite and grossularite) with small amounts of green hedenbergite. Inasmuch as the almandite and diopside are magnetic they are easily separated from the wollastonite in high intensity magnetic separators. If grossularite should occur in quantity other means of separation would be needed. Wollastonite has been reported at 35 localities in California12 but only those in the Big Maria and Little Maria Mountains, 16 to 20 miles north of Blythe, Riverside County, are

Jan 1, 1960

By Takeshi Tanaka, Shinya Ono, Tsuyoshi Kato, Masaji Kato, Yuusaku Tominaga

The knowledge of the macroscopic characteristics of a ventilation network is of fundamental importance for taking counter- measures to increase air quantity in-specified branches, such as those corresponding to working faces at advancing entries or longwall panels. Because the ventilation characteristics are inherent properties of each mine, it takes a long time for an engineer to accumulate experience on how a specific regulator may affect the air quantity in a specific branch of a mine with a complicated ventilation system. A computer-simulation training system, based on the macroscopic ventilation characteristics, is presented in this paper. When a trainee selects a specific condition from five regulator option (closed, almost closed, slightly open, half open, open), the change in air quantity for a network branch is indicated by the color allocated to the ratio of the new air quantity to the old or planned air volume. After the ventilation simulation, the colors in the specified branches are defined by using the fuzzy set theory. The trainee continues practicing the selection of closed/open conditions for different regulators until each of the specified branches is displayed in good state of airflow. The ventilation net- work of the Horonai coal mine is used as an example of the training system to control air quantities in six working faces with 33 regulators.

Jan 1, 1996

As previously advised, two of the raw materials for Wilsons Portland Cement are cement rock and limestone, both of which are quarried by the company. We now wish to give you a brief outline of these operations. The major material, cement rock, is obtained for our Portland Quarry at Tikorangi Hill, which is one mile west of the Works and a familiar landmark to travellers on state Highway 1. The geological structure of this deposit is involved, having intensive and irregular earth movements interpreted as large scale slumps where older rocks overlay younger rocks - numerous folds, faults and overthrusts are clearly visible.

Jan 1, 1978

By Robert E. Blackett

To help local governments plan for long-term supplies of sand and gravel for buildings and infrastructure, the Utah Geological Survey is assessing natural aggregate resources (mainly sand and gravel) in the St. George, Utah area. Whereas much of the aggregate in the study area is adequate for road-base construction, high-quality aggregate for Port- land cement concrete is limited due to geology, and also due to land administration and environmental issues. Virgin River alluvial gravels southwest of St. George are generally poor sources of aggregate because they contain clasts of soft sediments and soluble minerals derived from Mesozoic rocks. Elsewhere, widespread secondary calcium carbonate (caliche), as rinds and matrix in gravel, lower the quality of material. Young river-terrace deposits in Fort Pearce Wash, and along the Virgin River above St. George are the primary sources of sand and gravel for the area. Alluvial fans on the east side of the Beaver Dam Mountains, and on the west side of the Hurricane Cliffs are also sources of aggregate. Stream-channel deposits associated with "inverted valleys" north of the towns of St. George and Hurricane, Utah, and older pediment gravels on the west flank of the Beaver Dam Mountains may be future sources of high-quality aggregate. Accelerated urban development during the 1980s and early 1990s has caused St. George and other communities in Washington County to encroach upon sand and gravel pits originally located in rural, undeveloped areas. Urban residents often view nearby sand and gravel operations as undesirable neighbors and pressure elected officials to close the pits. Pit closures effectively eliminate the remaining reserve from the sand and gravel resource base of the area. More- over, resources may also be lost as new homes are built upon undeveloped sand and gravel deposits. The St. George area is particularly susceptible to loss of aggregate resources because high-quality natural aggregate for construction is already in short supply. Moreover, most of the land in the study area is administered by the U.S. Bureau of Land Management and subject to various land-use restrictions. Much of this public land cannot be developed for mineral materials, such as sand and gravel, because of federal regulations protecting rare plants and animals, archaeological sites, and important watershed areas. Of particular concern to resource development are areas designated as Areas of Critical Environmental Concern, Wilderness Areas, and Wilderness Study Areas. Protection for Endangered Species is a critical element in all planning efforts. Those species present in the St. George area or in areas near- by include: the desert tortoise, southwestern willow flycatcher, Virgin River chub, and dwarf bearclaw poppy. As the St. George area is depleted and/or deprived of sand and gravel resources through extraction and urbanization respectively, construction costs will rise unless conservation measures are instituted. To avoid the loss of aggregate resources, the UGS is pursuing a program of data gathering and field surveying of surficial deposits to determine tonnage and quality of the remaining sand and gravel resources. The resource information from this program will help land planners, developers, and government officials make informed decisions concerning urban development throughout the region.

Jan 1, 2001

By W. Spencer Hutchinson

THE relative importance of mineral production in British South Africa is about as follows: Gold, $200,000,000; diamonds, $40,000,000; coal, $18,-000,000; asbestos; $3,000,000; chrome ore, $2,000,000. In 1926 the gold mines paid $42,000,000 in dividends, the diamond mines $13,000,000, coal nearly $3,000,000, others less than $500,000. The recorded history of South Africa starts with the visits of the Dutch and the English in the sixteenth century, followed by the settlement of Cape Colony by the Dutch East India Company in 1651: The English acquired Capetown in 1806 and conflicts between English and Boers were a part of the history, from that, time on. Transvaal was settled in 1835, following the Great Boer Trek. The mining of diamonds became im-portant in 1870; the production of gold from the Rand in 1890;' the export of chrome ore in 1910; and the dis-covery of platinum in 1925. South Africa has a race problem, resulting not alone from the disparity of numbers between whites and natives, more than seven blacks to each white, twenty to one in Southern Rhodesia, and three. hundred to one in Northern Rhodesia; but because of the division of the white race between English and Cape Dutch or Afrikaans. The natives are also of many tribes.

Jan 6, 1927

"The present and possible futures commercial production of potash from various sources in the United States is discussed below under the following heads:1. Potash from the saline lakes.(a),Nebraska lakes.(b),California lakes.(c),Other lakes.2. Potash as by-product from the cement kilns.3. Potash as by-product from the iron blast furnace.4. Potash from silicate rocks.(a),Feldspathic material.(b),Leucite rocks of Wyoming.(c),Sericite slates of Georgia.(d),Glauconite (greensand) of New Jersey.5. Potash from Alunite.6. Potash from organic sources other than kelp.7. Potash from kelp.In this discussion very little more than passing reference, if any, will be given to those projects which up to date have been de¬veloped only slightly, if at all, beyond the small scale laboratory stage, or for the development of which there appears to be very little financial and technical backing at the present time. Nether or not many of these proposed projects have merit can be determined only by an actual operating demonstration.Generally speaking, the potash industry of the United States has been hardly more than marking time since the armistice. This is, largely due to the fact that the consumers of potash have been expecting that heavy shipments of foreign potash to the United States would be resumed soon at somewhere near the pre-war prices, and they have not been buying domestic potash at present prices for many months. The result has been that domestic producers have been unable to sell their product at even cost and many producers of potash have been obliged to close down. Thu Nebraska lake plants were closed down in February. The California saline plants were operating at below capacity, and the only large alunite plant is closed down. Even the cement plants have little or no inducements to recover the potash being lost in their waste gases, and the production is very small at present."

Jan 1, 1919

By R L. Grogan

Regulators of deep-sea mining projects are becoming increasingly hesitant about the concept of adaptive management as a tool to facilitate compliance and continuous improvement. Adaptive management is a relevant and useful instrument to ensure that the mine plan is successfully implemented throughout the life of mine, in parallel with optimum environmental performance and compliance.CITATION:Grogan, R L, 2018. Adaptive management in deep sea mining – looking like you know what you’re doing when it’s never been done before, in Proceedings Life-of-Mine 2018, pp 20–22 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

Jan 1, 1984

By Wilhelm Borchers

In all special branches of the chemical and metallurgical industries, in which large electric furnaces became necessary for carrying out new processes or for the improvement of old ones, the development of the electric furnaces took place on much the same lines. The endeavors to make a success of a new idea brought forth many ingenious designs, which, however, almost without exception, furnished the proof that the safest and shortest way to practical success is the utmost simplicity of construction of the necessary apparatus. Our knowledge of the qualities of materials for building electric furnaces and of the constituents of the furnace-charges, especially their electric conductivity and their chemical affinity towards one another at high temperatures, is still far from being complete, and from this fact we must conclude that the smaller the number of elements in the construction of a furnace, the fewer the number of unreliable factors both in the construction and in the operation of the electric furnace. This conclusion deserves special attention when an electric furnace for making steel has to be chosen from the constantly-growing number of inventions, inasmuch as the chief constituent of steel, the element iron, is a substance which in its liquid phase has so great an affinity for those elemen'ts which are to be removed from the charge, that it is very difficult to comply with the following conditions: 1, to heat the refining-slag to the highest point of its chemical activity ; 2, to prevent the iron from entering the slag, or, where this cannot be done, to make it enter so that it finally appears in the end-product

Jan 1, 1911

By S Morgan, A Jakowetz, S Taylor, B Weekes, S Litson, P Bourke, T L. Do

In the current tough mining environment with lower commodity prices, operators need to improve operational profitability. Optimised equipment asset management is a sustainable way to achieve this objective. The increased efficiency of installed process equipment positively contributes to the circuit performance, affecting metallurgical performance, plant availability and operating costs. Nui Phao Mining Company Limited (NPMC) operates a polymetallic mine located in Vietnam. The circuit produces four main products, tungsten, fluorspar, bismuth and copper. Tungsten is the major revenue producer. The operation experienced the following equipment inefficiencies in its copper and bulk sulfide flotation (BSF) circuits:• lower than expected metallurgical performance - the BSF rougher flotation tails contained coarse (+106 µm) sulfur minerals which affected the downstream tungsten gravity circuit. The unrecovered sulfur competed with tungsten minerals affecting both tungsten recovery and product grade. • structural integrity and safety - the flotation circuit structures experienced excessive vibration beyond the acceptable tolerance levels. The vibration was attributed to the flotation mechanism design and impeller tip speeds. • equipment reliability and wear life issues - the flotation mechanisms were being replaced every six months, with reported failures at three months. This resulted in high operational costs. A mineralogical evaluation of the ore indicated that the coarse sulfur minerals were well liberated and relatively rich in pyrrhotite and pyrite. It was predicted that these particles should be recoverable by flotation under optimum conditions. NPMC worked collaboratively with Outotec to investigate options to improve the metallurgical performance of both sulfur and tungsten. A review of the copper and BSF rougher circuit infrastructure was also undertaken and focused on reducing the structural vibration and improving mechanism wear life. Prior to the circuit upgrade, laboratory and pilot testing was conducted to validate the circuit improvements. The final solution included the installation of Outotec FloatForce® mechanisms in the existing copper and BSF rougher circuits, and a new flash circuit (SkimAir®) treating the rougher tails stream ahead of the tungsten gravity circuit. The flash circuit is unique, as typically these types of cells are installed in grinding circuits. By March 2016, all circuit upgrades were complete, however the initial metallurgical performance was below expectations. NPMC and Outotec worked together to investigate and improve performance through further equipment modifications. Since October 2016, the metallurgical performance has improved significantly. Coarse sulfur mineral recovery has improved, resulting in an overall increase in recovery of sulfur and tungsten of 4.7% and 2.7% respectively. The Outotec FloatForce mechanism has also delivered operational benefits, with a reduction in structural vibration to within acceptable levels (<4.0 mm/s) and an improvement in mechanism wear life by 150%. This paper discusses the BSF circuit upgrades and compares operational data before and after the upgrade to quantify the improvements in metallurgical performance, structural vibration and mechanism wear life. CITATION:Morgan, S, Weekes, B, Jakowetz, A, Litson, S, Taylor, S, Do, T L and Bourke, P, 2017. Nui Phao mine – flotation circuit upgrade, in Proceedings MetPlant 2017, pp 230–253 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 11, 2017

By P. S. Bagga, P. T. Luckie

Liberation (the process of destroying the interlock between unwanted materials, such as mineral matter and pyrite, and coal) is one of the most important precursors to the benefication of raw coal in order to produce high grade marketable coals at economical recovery levels. Liberation is achieved usually by comminuting the raw coal. However, because of the significant interaction between the production of fine particles to achieve liberation and the cost of separating fine particles, the coal industry needs a method projecting the change in washability with size reduction. Such a projection can be combined with size reduction and separation simulators in order to examine completely beneficiation circuitry to produce coals of stringent specification. This paper presents the development of an appropriate liberation model for coal and its solution by Monte Carlo simulation to predict the expected washability of the raw coal as a function of comminution. It includes model validation with a known binary mixture as well as with a known teritary mixture.

Jan 1, 1983

By T. F. Witherbee

ON the 22d of November, „1879, white iron unexpectedly appeared while working the Cedar Point Furnace, Port Henry, N Y., on the following burden, calculated to turn out mill and foundry iron: Anthracite coal, - 3000 pounds. Connellsville coke, - 1500 pounds. Total, - 4500 pounds. Old Bed ore, - 3750 pounds. New Bed fine ore, - 2000 pounds. New Bed chunk ore, - 1000 pounds. Kearnev hematite ore, - 750 pounds. Total, - 7500 pounds. Magnesian limestone, - 1865 pounds. Common limestone, - 885 pounds. Total, - 2500 pounds. The production per week since making mill iron-from September 1st, 1879, to date, seven weeks-was 412 gross tons. Ore was not immediately taken off, as nothing serious was looked for. The iron for the next week graded from No. 4 to white, and in. six days the make was 274 1/2 tons. At 10 P.M., Friday, the 28th, a slip of-..4 feet occurred, and on Saturday, at 5 A.M., another of 3 feet on the south side and. 7- feet on the north side took place. At this time it was found that the south side had been hanging for over a week--a fact which had not been reported. Throwing off the wind, to produce slips. and reduce pressure, had been tried with no effect. The stock, as seen through the tuyeres, seemed to consist almost entirely of coal, with just enough infusible cinder to cement it into a mass through which the blast could not be forced. At 3.50 A.M., Sunday, the 30th, the first cinder seen in seventeen hours came into tuyeres Nos. 1, 2, 3, and 6, At 9.30 A.M. No. 3 was taken out to see if the stock

Jan 1, 1881

By J. -C. Tricket, W. A. Düweke, S. Kock

The high-resolution three-dimensional (3-D) seismic reflection data acquired for Impala Platinum between 1998 and 2002 in the western Bushveld Igneous Complex form an integral part of Impala?s mine planning and development programme. These data are of sufficiently high quality to provide unprecedented 3-D models of the geological structure of the Merensky Reef and UG2Chromitite Reef, from which the mine deduces the size, geometry and distribution of mineable blocks. Conversely, the seismic data details zones of un-mineable ground caused by structural disturbances in the form of potholes, fault zones and pegmatoid intrusions. Furthermore, variations in dip and strike are well imaged, allowing the mine planners to optimize the mine design and layout. Current interpretation work is focused on enhancing the accuracy of these geological model seven further through the analysis of ?seismic trace attributes.? Preliminary testing on the Impala Platinum 3-D seismic volume has shown that attribute analysis has the potential to illuminate a number of geological reef disturbances that are otherwise ?invisible? in the original seismic time volume. Potential areas of improvement include inter alia: ?Improved definition of major fault zones ?Improved definition of zones of reef depression (?slumping?) ?Identification of reef terracing and/or reverse dip.. Keywords: 3D reflection seismics; Impala Platinum Ltd; seismic attribute analysis; Seismic Micro Technology (SMT); rock solid attributes; dip-azimuth; instantaneous phase and similarity.

Jan 1, 2004

By J. E. Owen

A model of a porous body is presented in which the pore space consists of a system of voids and interconnecting tubes. Relationships between porosity and resistivity formation factor are determined partly by calculation, partly by experiment. Con triction effects characteristic of the model are shown to be sufficient to account for high formation factors. It is shown that constriction may be combined with moderate amounts of tortuosity to give model pore systems exhibiting to a first approximation porosity and resistivity properties similiar to those of natural porous bodies. INTRODUCTION The relationship between the electric resistivity of a fluid-filled porous body and the geometry of its pore space is so complex that the calculation of the resistivity of a natural porous rock is a practical impossibility. Both the resistivity of a body and its porosity are measurable quantities, however, and previous successes at relating them have been reached by an empirical approach. Efforts at obtaining theoretically derived formulae relating them have generally been unsatisfactory. One of the reasons for this may lie in the pore geometry that has been assumed. THE TORTUOSITY CONCEPT A Parameter called the formation factor is useful in dis-cussing the resistivity of a fluid-filled porous body. This parameter is the ratio of the resistivity of a fluid saturated porous body to the resistivity of the saturating fluid. Formation factors are often available from measurements on cores or from electric logs, and many attempts have been made to correlate formation factors and porosities of geological formations. Whenever a successful correlation is found, the engineer working with electrical logs has a useful tool for the determination of porsities of pay section?. One of the more successful formulae applicable to these correlations is the familiar equation empirically obtained by Archie.' which F is the formation factor. $ is the porosity, and rn is an exponent called the cementation factor. When the for- mula applies, the cementation factor usually is found to be between 1.3 and 2.2. The values for formation factors experimentally obtained are often higher than simple pore geometry would lead one to expect. In an effort to account for such high values certain formulae have been derived based on a so-called "tortuosity concept." In deriving these formulae a synthetic porous body is usually assumed in which the solid material is an electrical non-conductor. and in which the pore system consists of three sets of fluid-filled tubes of uniform diameter connecting opposite faces of the body which, for convenience, is considered to be cubical in shape. The three sets of tubes account for the whole of the effective porosity of the body, and usually, it is specified that they do not interconnect. By considering that the pore tubes are not straight but tortuous, their resistance to the flow of electric currents can be made as high as needed to explain high formation factors. Such an explanation has some basis in fact, but it appears that the tortuosity concept is often incorrectly applied when other factors are largely responsible for observed high resistivities. Recently, Wyllie and Spangler have recognized that tortuosity as calculated by conventional formulae has little if any physical significance.' RESISTIVITY AND THE CONSTRICTION CONCEPT Any explanation of high formation factors which depends solely on tortuosity of uniform pore paths necessarily ignores the effect that variations in the cross-sectional area of the conducting paths have on the resistivity of a body. Although, as previously pointed out, the calculation of such paths for an actual body is impossible, it will he shown that a synthetic pore network can be devised which will yield to analysis, and lead to results in agreement with the experimental data represented by Equation (1). The porous body to be considered is assumed to be homogeneous and isotropic or, for present purposes, identical in its characteristics in the three directions parallel to its coordinate axes. It will he assumed to be built of identical unit cubes, each of which contains a single pore network connecting all faces of the unit cube. A unit of such a pore network is shown

Jan 1, 1952

By C. G. McLachlan

Laboratory flotation tests carried out on massive sulphide ores may not be reproduced in plant practice, and when this occurs the discrepancy can be the result of differences between laboratory and plant grinding. Results of parallel flotation tests are given to support this contention, and data show how tailing losses are affected in corresponding size zones.

Jan 4, 1951

A study of the electrolysis of PbS in molten PbCl2 showed cathode efficiencies which increased with current density at fixed sulphide concentrations, and decreased with increasing sulphide concentration at fixed current densities. The anodically produced sulphur dissolved rapidly in the melt, the rate increasing with temperature and sulphide concentration. Experiments with diaphragm cells, made to determine the relative effects that dissolution of lead and sulphur have on the cathodic current efficiency, demonstrated that dissolution of sulphur was the major contributor to the lowering in efficiency.

Jan 1, 1973