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By P Atkinson, M P. Simpson, J R. Kyle

BM37 is a bonanza-grade (>30 ppm Au) ore shoot of the Maria Lode of the Karangahake adularia-sericite epithermal deposit in the southern Hauraki Goldfield. Samples from BM37 contain up to weight percent gold. The ore shoot is a vein that pinches and swells, but is typically tens of cm thick, and locally exceeds 0.5 m in true width. Gold occurs as irregular anhedral electrum grains that range up to 300 microns across and contain 38 to 59 wt per cent Au (ave. 52 wt per cent Au). Electrum occurs in sulphide-rich bands in association with pyrite, chalcopyrite, acanthite, galena, sphalerite, and local covellite. Lower grade samples contain local to rare mckinstryite [(Ag, Cu) 2S] and polybasite [(Ag, Cu) 16 (As, Sb) 2S11]. Pyrite from BM37 is nearly stoichiometric; it lacks the As that commonly occurs at up to percent levels in pyrite from other veins in the goldfield. Acanthite also contains low quantities of trace metals, and typically has less than 2.5 per cent Se. The vein shows complex textures. Bonanza grade sulphide-rich ginguro bands form discrete layers adjacent to the vein margins, and occur as breccia fragments encased by later massive to comb quartz with local quartz after platy calcite. Both the breccia fragments and ginguro bands are cross-cut by later quartz veins. Textures thus indicate that formation of the high-grade portions of BM37 resulted from one or more discrete events that differed markedly from the events that formed the bulk of the vein.

Jan 1, 2006

By T Graham

The invention of the traditional belt and idler conveyor system is attributed to Thomas Robins in 1892. This basic concept, ubiquitous in most mining operations, has not changed markedly in 125 years and still suffers from five forms of energy losses. Firstly, Wheeler, Roberts and Jones (2004) showed that indentation rolling losses, a consequence of the indentation a roller inflicts on the belt, consume 60 per cent of all energy. Secondly, Wheeler (2006) explained that bulk solid flexure resistance resulting from material interaction and movement absorbs 20 per cent. The remaining energy is lost by idler rotating resistance (5 per cent), belt flexure resistance (5 per cent) and secondary resistances (10 per cent).Traditional conveyor systems are continuous as opposed to batch systems, implying both positive and negative features. On one hand, continuous systems have high availability (available infers ‘ready to run’), but, on the other, utilisation of availability is often low; for example, when a conveyor is running empty or below capacity. This converts into reduced system OEE (overall effective efficiency). Many attempts have been made to mitigate energy losses and low OEE issues, including development of rail-based systems. The key drawbacks have been higher capital cost, low flexibility, poor availability and lack of market acceptance.A recent conceptual development known as the ‘autonomous rail conveyor’ (ARC) promises to address issues of energy loss and poor availability and provide increased flexibility by offering solutions for difficult applications. The ARC uses a series of interconnected skeletal bogies covered with a conventional conveyor belt as a load bed running on relocatable light rail. The bogeys have two axles, each driven by integrated variable speed-geared motor and brake systems, and are connected to previous/next bogeys by specialised couplers. Power is provided by a generator (located in a dedicated bogey) and ‘daisy chain’ plug in cables. Centralised redundant control is provided at a preferred point. Although the system is batch in nature, the number of carriages and trains is flexible, meaning that the system is effectively continuous. Loading is achieved by feeding the ARC from a perpendicularly oriented apron feeder, while material off-loading is accomplished by a twist-dump operation in which the belt is twisted through an angle of 50° below the horizontal, causing material to flow from the belt into a receiving conveyor.The ARC system can run multiple trains over any distance, although benefits are more significant in distances of over two kilometres. Capital and operating costs are predicted to be lower than competitive products, with planned maintenance being simple to perform.CITATION:Graham, T, 2017. The autonomous rail conveyor significantly reduces ore haulage costs, in Proceedings Iron Ore 2017, pp 467–472 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 24, 2017

By Scott Chesman

Increased TBM performance is leading the way for resurgence in tunneling activity in NYC. Tunnels will be excavated in the same geologic formations as previously excavated D&B tunnels whose construction records are providing valuable insight into the prediction of rock mass behavior. This report compares an eight mile stretch of NYC Water Tunnel #2 with the recently excavated eleven mile stretch of the TBM driven Water Tunnel #3. Comparisons of the type and amount of rock support installed as well as water inflows and grout quantities are made. Rock mass characteristics specific to TBM performance are also evaluated.

Jan 1, 2005

The material presented in this paper describes experimental work to determine the effect of variations in suction nozzle design upon inlet flow conditions. Four entrance profile shapes were examined under controlled conditions of slurry flow and it was found that the straight ended nozzles had consistently higher entrance losses than the straight taper or the ellipse, and that the circular arc profile nozzles were the most efficient. Subordinate considerations were the measurement of the quantities and the forces involved.As the work progressed, three distinct phases in the pattern of flow were apparent and the static pressures in each were carefully examined. An inlet zone was found to be unstable in changing boundary conditions, a transition zone was largely independent of slurry density and in a zone of stability the pressures were found to be directly related to the characteristics of the flowing pulp. In this zone pressure measurements were reproducible within ± 2 per cent regardless of changing boundary conditions.The effect of varying the "1" parameter of nozzles with a part circular entrance profile was examined and it was found that flow conditions approaching the ideal were obtained when the radius of curvature was between 0·40 and 0·550.

Jan 1, 1966

By W. Dziurzynski

The present article sets forward the results of field tests that made it possible to validate the mathematical model used in the VENTGRAPH ventilation engineer programmes. The case considered relates to the introduction of a new heading to the ventilation network of the mine. The utilisation of computer programmes in practice is justified by the necessity of ensuring expected performance and secure conditions in the network of mine headings, where - for example - plans are being made to utilise the transport dip-heading, taking into consideration fire and methane hazards. In the article we have presented the methodology of preparation of a database for computer programmes of the VENTGRAPH system, obtained on the basis of ventilation measurements. The next step consists in the execution of a design of the modified network and prediction, this on the basis of heading geometries, of parameters characterising the flow of air for the designed headings. Due to the fact that the heading was in the final stage of driving, following its introduction to normal operation and the stabilisation of flow values it was possible to retake ventilation measurements, which validated the results obtained through computer simulations. In order to execute measurements of the volume flow in the dip-heading, we employed a new wireless multipoint measurement system to determine the velocity field of air in the mine heading; the results are characterised by a high accuracy of measurement. As a part of fire prevention and incident management planning, a series of underground fire case studies for the a validated network flow model has been made. Results of simulations show the capabilities of the FIRE module of the mentioned software, including assessment of stability of flow directions and hints on counter and preventive measures for particular locations of fire.

Jan 1, 2009

By Hans von Michaelis

"INTRODUCTIONThe renaissance in gold and silver recovery technology has continued to unfold and it is appropriate to review some of the useful new technologies as well as try to identify some of the industry's future needs and frontiers.The remarkable strengthening in the US dollar has resulted in a relatively low gold price in US Dollars of around $310/oz at the time of writing and silver at $6.25/oz. This general softening in the dollar prices and the recent confusion as to environmental compatibility of cyanidation tailings and effluents, has led to a slowdown in announcements of new operations. Another reason for the slackening off in the USA is that in the past few years a large part of the capital has come from oi I and gas companies that now seem to be losing interest in mineral ventures, and foreign investors for whom the dollar is becoming out of reach. In the author's opinion this represents an unprecedented window of opportunity.Elsewhere in the world where local currencies have weakened, the price of gold is at or close to its all time high.For example, in South African Rands, the gold price was R571.00/oz when the rand was US$1.47 and the gold price reached US$800. Now at US $309/oz and with the Rand at US$0.51 = Rl .00, the local gold price is R600. The price of si Iver in Mexican pesos is not much less than it was when silver reached US$50/oz. Gold, and silver prices in local currencies outside North America are still buovant and at levels where additional investment in new projects is more encouraging.Even in Canada where the dollar is worth about US$0. 75, this provides a smaller but significant cushion compared with US operations. Considering the present strength of the US dollar and even the Canadian dollar relative to many other gold producing countries, there should be significant investment opportunities at today's prices. Mining companies have started to descend on Brazil, for example, where in a matter of just a few years annual gold production has increased from 10 to 70 tons. In South Africa, a Canadian company backed by Swiss financing has been able to take over a Witwatersrand gold mining operation and is installing a huge new tailin9s retreatment plant to process about 1 million tons per month of tailings."

Jan 1, 1985

The principles of geometry and trigonometry are so continuously used by mining engineers for the purpose of accurately and intelligibly recording their measurements, that the writer is prompted to lay the following cursory remarks upon mine surveying before the members of this Institution in the hope of eliciting a free interchange of opinion upon details of this interesting branch of the profession. He proposes to deal with surveying only so far as it concerns the mining engineer, not to intrude upon the domain of the professional surveyor, and, in this instance, to discuss more especially that which may be termed the mechanical, rather than the mathematical side of surveying.In the latter part of the eighteenth century and the beginning of the present one, the usual underground surveying equipment in the English metalliferous mines, consisted of a magnetic needle in a fiat square wooden box of about 9-inch sides, a two-foot rule, a long cord, aud a stool, upon which to place the needle and box. The operator took his bearing by sending his assistant with the end of the cord as far in a straight line as the length of the cord would admit.On its being drawn that he held its end in one hand and placed the side of the compass-box against it with the other, and noted the bearing thus found either by a book entry, or by ticking it off with a piece of chalk on the board the compass lay in. He then measured the cord with a two-foot rule. It is needles to say that with these appliances the accuracy of the results were open to question, and mining surveying was not unduly popular.In the present day, engineers have the advantage of using instruments brought to such a state of perfection, and of employing such an exact system of underground surveying, that inaccurate work must usually be attributed either to lack of care, or lack of ability in the operator.

By Robert Bittner

The following is a report on the development of two unique and separate cofferdam systems used in the construction of the marine foundations for the I-205 Columbia River Bridge at Portland, Oregon for the Oregon Department of Transportation. The first of these two systems utilized interlocking H-pile 100 ft long to form a cofferdam 145 ft by 58 ft in plan and 100 ft deep. The second system consisted of two immense bell shaped steel forms. The larger of the two forms was 83 ft by 66 ft in plan, 62 ft high and weighed 450 tons. This form was externally stiffened for a designed hydrostatic head of 54 ft. Both forms were designed, except for the top 14 ft, to be set and stripped in one solidly welded unit. The supporting geological formation for the bridge foundations is the Troutdale, a cemented sand and gravel. This formation is at the ground surface on the Washington Shore and slopes downward to a depth of 115 ft below normal high water at about mid-channel. In this area the Troutdale formation is covered with a layer of fine to medium sand 90 to 100 ft thick. It was the variable depth of the Troutdale which determined the two types of foundations and the corresponding to the two cofferdam systems.

Jan 1, 2013

By H. M. Lawrence, E. Roca

"INTRODUCTION Of the phosphate rock deposits of the United States that are being exploited actively at present, the land-pebble area in Florida is the largest producer. In recent years the land-pebble district, in Polk and Hillsborough Counties, has produced about 80 per cent of the raw phosphate rock that has supplied the requirements of the several national industries based on this essential commodity.In the land-pebble deposits sizes finer than 16 to 22 mesh are below the commercial limit in phosphate content, and washing-plant practice has been directed to the recovery of the coarser material. Recently, more extensive control of the washery plan has resulted in the saving of additional amounts of phosphate, the loss of which had been considered unavoidable. However, strict requirements of the trade regarding the lowest acceptable grade of phosphate rock prevent the inclusion of more than a very small proportion of the low-grade phosphatic sands with the washery output of phosphate roe:. Further advances in practice resulting in larger recoveries of phosphate can only be effected by the application of processes that are based on other principles than merely a difference of particle size. Research is be conducted actively along these lines by the industry and by cooperating agencies.Flotation has been studied for several years by the International Agricultural Corporation and its allied company, the Phosphate Recovery Corporation. J. T. Burrows, vice-president of the International Agricultural Corporation, in a letter dated July 10, 1929, states:"

Aug 1, 1931

By S C. Dominy

The grade of ore at Marvel Loch mine is directly related to the presence or absence of shear zones and quartz-sulfide-rich hornblende (¦ diopside) veining within areas of plagioclase alteration. An experienced geologist can identify these features in hand specimen. Practical rules have been developed to assist this visual identification. The structural sites and styles of alteration and veining most conducive to gold mineralisation have also been determined. The work has enabled a better understanding of the geological controls on mineralisation at Marvel Loch, and has clarified geological understanding for optimisation of grade control modeling, ore block mark-ups, and minimisation of ore loss and dilution during excavation. In addition to this, it has enabled a detailed understanding of mine scale structural controls, geometry and relative grade relationships.

Jan 1, 2003

By L. Russell Van Wert

DURING an investigation in which the solubility relations of the phases in Muntz metal (60 per cent. copper, 40 per cent. zinc) were under study, certain phenomena that had no immediate connection with the main problem were observed, which were thought sufficiently interesting to study further. Because of lack of time, only a preliminary survey was made of two of these; namely, the cleavage structure developed under certain conditions in a 60:40 brass and abnormal grain growth in this alloy. CLEAVAGE STRUCTURE IN HEAT-TREATED MUNTZ METAL Carpenter noted many years ago that cold-working a brass of the Muntz metal type, which had been quenched previously from within the beta field, results in a partial breakdown of the supersaturated beta solution and the precipitation of the solute (the alpha solution) in the cleavage planes of the beta grains. This manner of rejection of a solute from a metastable solid solution is not peculiar to this particular alloy, for among others, it occurs in the cold-working of certain austenitic steels; for example, the austenitic nickel steels. In these ferrous alloys, cold deformation produces a partial decomposition of the austenite, with the formation of martensitic "needles" and zigzags in the austenitic poly-hedra. It is interesting to note that while the two solid solutions-austenite and quenched Muntz metal- are metastable and in their mode of decomposition behave quite alike when deformed in the cold, the metastability of each results from a different cause; viz., that of the austenite from the fact that it is a supercooled solution (its solvent, gamma iron, at ordinary temperatures is below its normal stable range) whereas the metastability of the quenched Muntz metal is the result of supersaturation.

Jan 1, 1929

By Edward A. Barrett, Kathleen M. Kowalski-Trakofler

This paper discusses the application of a training intervention that uses degraded images for improving the hazard recognition skills of miners. Method: NIOSH researchers, in an extensive literature review, identified fundamental psychological principles on perception that may be employed to enhance the ability of miners to recognize and respond to hazards in their dangerous work environment. Three studies were conducted to evaluate the effectiveness of the degraded image training intervention. A model of hazard recognition was developed to guide the study. Results: In the first study, miners from Pennsylvania, West Virginia and Alabama, who were taught with the aid of degraded images, scored significantly better on follow—up hazard recognition performance measures than those trained using traditional instructional methodologies. The second and third studies investigated the effectiveness of the training intervention at two mining companies. Data collected over a3—year period showed that lost—time injuries at mines in Alabama and Illinois declined soon after the training intervention was instituted. Impact on Industry: Further exploration of the hazard recognition model and the development of other interventions based on the model could support the validity of the steps in the hazard recognition model.

Because of complex geological environments, a number of coal reserves occur in inclined or dipping coal seams in certain parts of the world. Longwall top coal caving using split-level a singleentry panel system (SSPS) has been widely used for extracting such coal seams with large thicknesses (greater than 6 m) in China because SSPS can reduce or mitigate problems of coal outbursts, gate road deformations, overturning of shields, downhill sliding of shearer and armored face conveyor (AFC), and so forth, during mining of inclined coal seams. Depth of yield is the range of yield coal from the rib of the pillar to the boundaries where yield ends. It plays a significant role in maintaining the gate pillar stability. This paper presents a study on the stability of an unconventional water-obstruction gate pillar (UWGP) formed by SSPS to prevent water inrush in mining of an inclined thick coal seam in a coal mine in China. As the shape of this pillar is non-cuboidal, nonparallelepiped, a conventional empirical or analytical method is not applicable for studying its stability.

Jan 7, 2020

By E. A. Mihok

A pilot plant for treating mine drainage by neutralization with limestone was designed, fabricated, and operated by the Bureau of Mines. The process consists of (1) producing a very fine (minus 400-mesh) limestone slurry, (2) mixing the slurry with the mine water, (3) aerating the resulting mixture to remove carbon dioxide and precipitate iron, and (4) separating the solids from the liquid by sedimentation. A mine discharge of pH 2.8, containing 1,700 ppm total acidity, 36 ppm ferrous iron, and 360 ppm total iron, was treated at rates from 300 to 400 gpm. The treated water ultimately reached a pH of 7.4 and contained no detectable iron. The resulting sludge compacted to approximately one-third the volume of sludge from mine water neutralized with lime. The advantages of the limestone process, compared with the conventional lime process are as follows: Widespread distribution and lower cost of run-of-mine, indigenous limestone; simplicity of plant design; reduced hazards and plant operating and maintenance costs accruing from the use of a less reactive chemical agent; higher solids concentration of the precipitated sludge; and no deleterious effect caused by accidental overtreatment. While total process costs could not be determined, it is conservatively estimated that the cost of treating mine water by the limestone process is one-third to one-half the cost of the lime process, depending on the characteristics of the water to be treated and the availability and quality of limestone used.

Jan 1, 1968

By Buse Florian

This paper presents the specific features of the large-scale production and transportation systems (LSPTS), describing the main notions and characteristics of the LSPTS elements. A methodologically unitary approach of the formulation, formalization and solution of the problems regarding the planning of the LSPTS structure development is offered, based on the system description by the aggregation-decomposition method, as weil as on the complex of interreloted models for the planning optimization. The paper describes the characteristics of the complex of dynamic models for investments, utilized in solving the planning problems of the LSPTS structure development.

Oct 1, 2009

By R. A. Bosch, F. V. Lenel, G. S. Ansell

RECENTLY, Ansell and aenel' proposed a dislocation model to account for the yielding behavior of dispersion-strengthened alloys. The criterion for yielding used in this model was that yielding occurs when the shear stress due to arrays of piled-up dislocations fractures or plastically deforms the dispersed second-phase particles. Calculations based on this model predict that the yield strength, uysof a dispersion-strengthened alloy containing particles whose geometry permits them to be considered as straight, i.e. not curved, barriers to dislocations follows the relation where and are the shear moduli of the matrix and dispersed phase respectively, b is the Burger vector of a dislocation in the matrix, A is the mean free path between dispersed phase particles and C is a constant. This yield stress, ys, is closely approximated in polycrystalline alloys by the proportional limit. The offset yield stress, uoy, is the yield stress, uys, plus the increase of stress due to strain hardening in the offset strain increment. Previous investigation1 has shown that Eq. [I] describes the yielding behavior of several different dispersion-strengthened alloys as a function of the mean free path between dispersed phase particles at a constant temperature. The purpose of this investigation was to investigate the temperature dependence of the yielding behavior of dispersion-strengthened alloys. The alloys studied, MD2100 and MD5100, are SAP-type alloys containing flake shaped aluminum oxide particles dispersed in a matrix of commercial purity aluminum. The proportional limit and 0.2 pct offset stress of both of these alloys were determined as a function of temperature over the temperature range from -190" to 500 C. All tests were conducted on an Instron tensile testing machine. Stress was measured by means of the Instron load cell. Strain was measured by means of SR-4 strain gages attached to the tensile specimens. Stress sensitivity was 80 psi. Strain sensitivity was 2 x 10F Fig. 1 shows the values received for the proportional limit and 0.2 pct offset yield stress plotted as a function of homologous temperature for both the MD2100 and MD5100 alloys. Inspection of Eq. [I] shows that of the terms which determine the theoretically predicted yield stress, uy,, only the shear moduli have an appreciable temperature dependence. From Eq. [I] the yield stress at any temperature T, UT, may be predicted from the yield stress at any arbitrary reference temperature, in this case 25 OC, u25, by the relation where the subscripts T and 25 refer to the values of the property at test temperature and at 25"C, respectively. The temperature dependence of the yield stress predicted by Eq. 121, based on the observed value for the proportional limit at 25OC, is also shown in Fig. 1. In evaluating Eq. [2] the following data was used. The values for the shear modulus of

Jan 1, 1962

By G. Coombs, L. Meade, J. Welshimer

Industrial Minerals commodity profiles are continued from May's Annual Review issue. Diatomite G. Coombs, Manville Sales Corp. Growth in US diatomite production continued to lag in 1986. The US Bureau of Mines estimated that 580 kt (640,000 st) were produced last year. This is a 1%0 growth over 1985. The cumulative growth from the 1982 low point is 4.4%. Present production, though, is still only 90% of the high tonnage of 1979. The industry will see increased competitive activity with the start-ups of two new mines and production facilities in California and Oregon. US production has come primarily from Lompoc, CA, Bassalt, Clark Station, and Lovelock, NV, and Quincy, WA. New production, probably with capacities of 45 kt/a (50,000 stpy) each, have started near Burney, CA, and Vale, OR. Eagle Picher's new, full-line filter aid and filler plant at Celatom, Vale, OR, was dedicated in August. The plant uses diatomite from the Celatom mining district in Juntura, OR. Grefco's new filter aid and filler plant near Burney, CA, was ready in July. It produced flux calcined products through a single kiln and can handle both bag and bulk shipments. The operations are in Shata County with the plant and mine at the same site. Manville Specialties Group is moving its Filtration and Minerals Division headquarters and research staffs to Lompoc, CA. The move is intended to strengthen response and performance by locating research, marketing, and production close together. Diatomite is processed in three methods: natural, calcined, and flux calcined. The natural is dried to remove water and is particle size classified. Calcined or straight calcined products have been sintered to modify particle size or permeability. Flux calcination, or flux sintering, has a stronger influence on permeability and also benefits color. The unique structure of diatomite is used in a range of particle sizes from fine paint fillers, to coarser filter aids, to granular aggregates. Dimension stone L. Meade, Geomapping Associates Ltd. 1986 was another good year for dimension stone production. The trend toward using marble, granite, limestone, sandstone, and slate has created an increasing demand. According to US Bureau of Mines 1986 estimates, 1.1 Mt (1.2 million st) of dimension stone, with a value of $173 million, was produced by 200 companies. This is an increase from 1985, where 220 companies produced 1 Mt (1.12 million st) valued at $172 million. The increased production volume and decreased unit value is due to the competition from imports. The net import reliance in 1986 was 68% compared to 62% in 1985. The value of imports was $374 million in 1986 versus $295 million the year before. In an effort to maintain their market share, domestic finishers, particularly in the granite industry, continued to upgrade plants and machinery during 1986. In addition, offshore dollars have financed a number of fabricating facilities in North America that will finish imported rough stock. It is hoped that this increased domestic production capability will capitalize on a devalued US dollar. The trend has been for growth in stone usage and market. This trend is continuing with increased public awareness and desire for natural stone in buildings. The area of greatest market growth is expected to be in residential and interior decorative stone usage. Use of sophisticated, automated equipment has made the cost more affordable. Now lobbies, foyers, and specialty rooms are being clad in stone. Dolomite J. Welshimer, National Lime & Stone Co. About three-quarters of dolomite production is used as construction aggregates and 10% to 20% is sold or used as an industrial mineral. Total limestone and dolomite consumed for chemical and metallurgical purposes is about 136 Mt/a (150 million stpy). Sales of industrial dolomitic products were somewhat stronger in 1986 than levels recorded in the early 1980s. Some of the sales' strength, however, can be attributed to reductions in the number of active mining and processing operations. The industry will probably undergo further consolidation by the end of this decade. This will be due primarily to the continued softening in demand by the steel industry. Dolomitic limestone deposits being mined for raw materials for the steel, glass, and refractory in¬dustries are generally 54% calcium carbonate and 45% magnesium carbonate by weight. Impurities composed of silicon, aluminum, iron, sulfur, and phosphorous, represent less than 1%. The heaviest concentration of high purity, surface mineable dolomite in the US is in northwestern Ohio. Crushed and sized dolomitic limestone is a basic raw material for the iron and steel industry. It is also used as feed stone or lime kilns. Soft-burned lime is a popular raw material for BOF steel production. It is also used extensively in insulating glass fiber manufacturing. A related material, hydrated

Jan 6, 1987

By Gordon M. Matheson, Douglas A. Anderson, David K. Miller

"Traditionally, analysis of vibrations from blasting has been focused on peak particle velocity fordetermining the likelihood of both annoyance and damage. The US Bureau of Mines, in RI 8507,indicated the importance of frequency in vibration. Methods of controlling the vibration by reducingthe vibration concentrated in certain frequency bands using delays have been successful over the past decade."

Jan 1, 1997

The new legislative regime applying to the mining industry has been in force for nearly two years. However the parameters for the permits required under the Crown. Minerals Act 1991 and the resource consents required under the Resource Management Act 1991 are still being established. Mining operators will benefit from participating in the development of policies and plans currently being formulated by local authorities. The Energy Legislation Amendment Bill currently before the House contains amendments to the Crown Minerals Act to clarify points of uncertainty and to reduce transaction costs where possible.

Jan 1, 1993

By Jay C. Hanson

Various electrical and electromagnetic (EM) geophysical techniques are currently being evaluated by the U.S. Bureau of Mines for their effectiveness in the detection and monitoring of electrically conductive (1 to 5 S/m) lixiviant (leach solution) to depths of 600 m, either above or below the water table. These techniques include magnetotellurics (MT) , controlled source audiofrequency magnetotellurics (CSAMT), resistivity and focused resistivity, ground-penetrating radar (GPR), frequency-domain electromagnetics (FEM), and time-domain electromagnetics (TEM). Of these techniques, TEM may be the most effective, but CSAMT and focused resistivity also hold promise. Geophysical computer modeling of the borehole TEM technique was conducted based on an idealized geoelectric section (layered earth) with characteristics based on the Santa Cruz porphyry copper deposit near Cas a Grande, AZ. Layer resistivities and thicknesses were obtained from geophysical data and geologic logs available from the site. Modeling of borehole TEM in both preleach and during leach situations was conducted. Simulating the TEM method using computer modeling proved to be encouraging since there were substantial differences between leached and nonleached responses. The modeling does not prove the effectiveness of TEM in the field, but does indicate that detection of deep lixiviant zones is theoretically possible.

Jan 1, 1992