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By Roman Z. Pyrih

Subsurface migration of cyanide is attenuated by naturally occurring geochemical and biogeochemical processes. Geochemical mechanisms which remove or immobilize cyanide and metal-cyanide complexes include precipitation/coprecipitation, sorption, and volatilization. Geochemical properties of soils and geochemical materials that promote the functioning of these mechanisms include the following: 1) acidic soil pH; 2) presence of illite and smectite clays; and 3) presence of iron hydrous-oxides and organic carbon. Naturally occurring soil microorganisms play perhaps a more important role in attenuating cyanide movement than previously realized. Biodegradation of cyanide is a "renewable" process, limited in its effectiveness by the avalibility of oxygen and micronutrlents (usually phosphate) to the microorganisms.

Jan 1, 1990

By J. C. Potvin

Although the occurrence of deposits of titanium minerals on Kenya’s present day beaches and adjacent dune systems has been well documented, the potential for older formations to host economically viable deposits had not been recognised until recently. The Magarini sands formation in Kenya has been found to contain deposits of ilmenite, rutile and zircon in quantities and grades that have the potential to be commercially exploited. Since 1995, Tiomin Resources Inc. has explored these deposits and has identified one deposit, the Kwale project, as being able to support the development of a mine producing some 300,000 tpa ilmenite, 75,000 tpa rutile and 37,000 tpa zircon. Tiomin plans to start production by late 2002. Construction of a US$137 million operation is set to commence in the first half of 2001.

Jan 1, 2001

By F. W. Schweitzer

The trend toward development of large low grade ore bodies has accelerated in recent years. It has been estimated within the copper industry that "porphyry" type deposits will provide the bulk of copper production during the next 30 years. It is further estimated that in these deposits the average ore grade by the year 2000 will be 0.25% copper (1). Many of the new porphyry copper discoveries are of such extremely low grade that they are particularly sensitive to small fluctuations in cost variables and copper prices. Because haulage constitutes a major item of surface mining expense, the capability to transport large tonnages of material at increasingly lower unit costs is vital to the profitable operation of many of these mines. High capacity conveyor belts appear to have considerable promise in this area. The heaviest use of high tonnage conveyors has been in the brown coal industry in Germany. In the past 20 years several such installations have proven successful. In addition to the German installations, several other successful systems have been put into operation. Some examples are: The Oroville Dam project in the United States; the tar sand operation in Northwest Canada; the pre-mine stripping and mining of the Twin Buttes Mine in the United States; the Kursk Magnetite 'dine in the U.S.S.R.; and the Nchanga Copper Mine in Zambia. Most of the systems mentioned are handling alluvial material consisting mainly of fines. The noteworthy point regarding these installations is their high continuous capacity. One of the largest lignite mines in the world is at Fortuna, Germany, where over 15,700 tons (15,250mt) per hour of overburden is transported on an 87 inch (221cm) wide belt running, at over 1000 feet (305m) per minute.(2). Another example is a 20,000 ton (18,150mt) per hour system for loading iron ore into barges on the Great Lakes (3).

Jan 1, 1976

By Robert H. Oliver

Flowsheet flexibility in new 750 TPH coal cleaning plant provides three unusual capabilities. Two compartment drum coarse H.M. washer can be adapted to provide two stage separation. Coarse section of plant can be operated without fine section when washing surface mined coal. Fine section can operate with flotation cells bypassed if strip coal oxidation kills the froth. Plant can be fed by belt from bulk storage, front end loader from storage piles and truck from the mines. Raw coal and each of four washed products can be fed by belts to three separate loading points on two separate railroads.

Jan 1, 1979

By Ron Robinson

Booster fans have been in regular use in British coal mines since the first half of this century, but a large increase in their use did not take place until after the Nationalization of coal mines in 1947. From that time the need was identified to improve standards of ventilation in general and mining engineers specializing in ventilation were appointed at all levels in the mining industry. A comprehensive approach to ventilation surveys and planning, together with the realisation of the benefits of booster fans, led to their more rapid introduction. Many coal mines in the U.K. are at moderate depth and have virgin strata temperatures of 30°C or less. The ability to control climatic conditions by increased ventilation rather than resort to cooling systems has led to the introduction of booster fans and recirculation systems in these mines. Large makes of methane and high levels of coal dust production due to increased mechanization have also required enhanced ventilation standards. This paper deals with the reasons for selecting booster fans and the specific safety considerations involved in their use. Numbers, types and sizes of booster fans in the U.K. are outlined, together with notes on installation and performance. Remote monitoring and control from the surface is dealt with, and current legislation. The evolution of controlled recirculation is also covered starting with auxiliary fan systems in 1970 and leading to very large district schemes in the late 1980s. The research at Newcastle upon Tyne University and other establishments in the climatic conditions associated with recirculation is summarised and its use in assisting existing and proposed conventional and recirculation systems is indicated.

Jan 1, 1989

By Anthony Peach, Lok Home

Introduction Raise boring is the most accepted form of mechanized hard rock boring in the mining industry. It appeared logical to take this mechanization one step further by introducing computers. Atlas Copco Jarva has produced a series of raise boring models that use an integrated computer. The company decided to use electronics and computerization, not for marketing purposes, but to make its equipment more cost-effective. Basis of Cost-Effective Design From the manufacturer's standpoint, it is possible for the equipment owner to reduce the cost of putting in raises by: • Replacing existing components with less expensive components that produce the same results; • Replacing existing components with more expensive components that make the equipment more productive; • Mechanizing equipment to reduce associated labor costs; and • Combining the above. Analysis of a standard raise boring machine (RBM) system showed that little could be done with less expensive components. It appeared, however, that the RBM could be more productive by transmitting more horsepower through the expensive drill string, while being precisely controlled by computers. An RBM system includes a basic machine, drill pipe, accessories, reamer, and cutters. The approximate percentage cost of various components on a standard system capable of boring 300 m (985 ft) long and 3-m-diam (10-ft-diam) aises in medium to hard rock is shown in Table 1. Also shown is the increased cost above standard of the Jarva computerized machine, and the productivity of both. Increased Productivity Penetration is important during the reaming cycle for more productive raise boring. This is possible by increasing the cutter load with constant rpm or increasing the rpm with constant cutter load. To increase thrust and maintain rpm requires increased capacity in the cylinders, drive train, main thrust bearings, drill string, electrical motors, and power units. To increase rpm and maintain cutter load requires only increased capacity in the electrical motors and power units. This is possible because the torque requirement remains constant for a constant thrust load. Only the horsepower increases, proportional to rpm. Since cutter costs are a big factor in raise boring, changes in machine performance must be analyzed to assess the effect on cutter performance. With a standard or typical carbide cutter, as used on raise boring machines, the effects of increased thrust or rpm are shown in Table 2. The assumption is made that the base data is the current rpm and thrust range where the cutters are now operated. It is also assumed one variable is held constant while the other increases. The result of this comparison, approximately, is that a 50% penetration increase can be achieved with little or no increase in cutter cost if rpm is increased 50% and cutter load is maintained constant. A similar 50% penetration increase can be achieved with a 45% increase in cutter cost, if the cutter load is increased by 20% and maintained constant. From an equipment standpoint, it is significantly less expensive to increase rpm 50% than it is to in-

Jan 7, 1984

By Anna Eleria, Joseph Welna, Jim Herber, Nathan Campeau

Constructed by stonemasons over 120 years ago, a portion of the Trout Brook Storm Sewer Interceptor (TBI) owned and operated by the Capitol Region Watershed District in Saint Paul, Minnesota, needed rehabilitation. A routine inspection of the 10-foot limestone block tunnel revealed degraded and missing mortar between the blocks, allowing significant infiltration and soil migration through the tunnel joints. Conditions, including damaged and missing blocks, were considerably worse in a 250-foot-long segment beneath a busy mainline railroad corridor. Barr’s solution included tuck-pointing to repair the mortar joints, shotcrete overlay, and construction of a hybrid cast-in-place/shotcrete “tunnel within a tunnel” to support the mainline railroad loads.

Jun 13, 2021

By W. M. Kidd

INTRODUCTION Uranium mine inspection in Canada forms one element of the enforcement of the Atomic Energy Control Act; it is under this Act that all Canadian uranium mines and mills are licensed to operate. Inspection duties are carried out by a small core staff of federal government inspectors (working for the Atomic Energy Control Board (AECB)) largely supplemented by provincial mine inspectors working on behalf of the AECB. Unlike most resource extraction in Canada, uranium mining is under federal jurisdiction and consequently it was the AECB who decided in 1975 that changes in the Canadian uranium mining industry, particularly its expansion and the expanding role of the mine inspector in the limiting of exposures, warranted the offering of a special radiation protection training course. The Uranium Mine Inspector Training Course (UMITC) was first conducted in 1976 at the Elliot Lake Centre in Elliot Lake, Ontario. Subscription for the course was not limited to mine inspectors to enable union stewards, management personnel and provincial/federal labour inspectors to attend. This paper will present an outline of the course content, the format of its presentation and non-curriculum aspects of running a course of this type in uranium-producing community. The core lecturers for UMITC are drawn from the Radiation Protection and Uranium Mine Divisions of the AECB. In addition, guest lecturers are invited from universities and medical research centres together with industry professionals and government researchers. In all some twenty-four plus presentations are made over the first five days of lectures. The program topic areas, hazards, controls, measurements, record-keeping and health effects are preceded by an intensive half-day session on radiation fundamentals. TOPICS Hazards [Dust] A review of the dynamics of airborne particles including the effects of particle size, gravity and wake-turbulence on the behaviour of dust clouds. Associated topics are migrational aspects of dust particles and specific dust-generating mine operations. [Radiation] Canadian uranium mines are increasingly diverse in nature ranging from large scale low-grade underground operations in Elliot Lake to smaller high-grade open pits in Saskatchewan. Papers are presented on assessments of internal and external exposure, the metabolic pathways of ingested or inhaled radiation and the specifics of mine and mill hazards. Radiation hazards are further broken down into gamma surveys of uranium mines, radon daughter concentrations and problem areas. Controls The relationship between mining methods and the operating environment is critically important to ensuring safe working conditions. This refers to both the selection of machinery/devices, etc., and to engineering controls which are instituted to remedy problems created by new technology. UMITC examines a number of possible mining techniques, their criteria for selection and impact on the working environment. Control measures, ventilation practices and design, the need for continuous water misting and special open-pit precautions are presented. These lectures frequently conclude with suggestions for better operating guidelines for mine ventilation systems and the need for greater co-operation between the ventilation department and the underground crews. Measurements Uranium mining regulations stress the need for a high standard of exposure monitoring, statistical planning and record-keeping. [Statistics] Although many course participants are well versed in statistics, certain fundamentals are repeated and include, the concepts of mean, variance, standard deviation and standard deviation of the mean. Confidence levels, decision-making based on sample statistics and statistical records are also discussed. [Dust Measurement] Dust measurement is particularly critical in the mines where the high silica content of the ore body, such as those at Elliot Lake, results in the continuous generation of dust. Sampling practices, filtration, impaction, thermal impaction and electrostatic precipitation are explained together with the methods of counting samples to determine free silica. Konimetric and gravimetric techniques for dust sampling are compared and contrasted. [Radiation Measurements] Both collective and personal dosimetry systems are used in the Canadian uranium mining industry and lectures are presented on each. Techniques and possible sources of error are discussed for a variety of radon and radon daughter measurement methods - Lucas method, Tsivoglou and modified Tsivoglou, Kusnetz, Rolle. Instant working level meters and personal alpha dosimeters are explained in terms of calibration, maintenance, readout and estimation of accuracy. A lecture outlining dose estimation by means of bio-assay, whole-body counting and the use of TLD's concludes the topic. Record-Keeping An overview of the problems of changing limits,

Jan 1, 1981

By David Lynn Passmore

The reliability of mine operators reports to the Health and Safety Analysis Center of the U.S. Deparetment of Labor of days lost from work by injured miners is .267.

Jan 1, 1985

By Robert M. Dreyer

Although lateritic deposits have long been a principal source of bauxite and are becoming an increasingly important source of nickel, the problems in the evaluation of such deposits are not generally understood. In the evaluation of lateritic bauxite and nickel deposits, there are many similarities, but there also. are significant differences. It has long been recognized that laterites with commercial concentrations of trivalent metals represent the ultimate in the intense leaching of tropical soils. Any factors which effect-the rate of soil leaching will effect the form of local lateritic concentrations. Although the most intense leaching generally occurs on somewhat elevated areas of gentle relief where there is a free downward flow of rain water, the- effect of local rock structures in effecting varia¬tions in soil metal concentrations has-not been well understood - primarily because the laterite forms a masking blanket over the rocks from which the laterites were derived. All of the-factors which facilitate downward movement of water may effect greater surficial concentrations of trivalent metals. Such features as zones of fracturing, zones of greater rock permeability, and areas of karst topography may, therefore, be responsible for greater leaching. The variations in rock structures and the vagaries of ground water flow pat¬terns impart, to the laterites, rapid lateral and vertical variations in thickness and metal concentrations. Because of such rapid

Jan 1, 1970

By SAHENDRA SINGH, SANJIT KUMAR PAL, DHARMITA HORO

The North Singhbhum Mobile Belt (NSMB) lies between two crustal-scale shear zones, the South Purulia Shear Zone (SPSZ) at the north, and the Singhbhum Shear Zone (SSZ) at the south. The Babaikundi-Birgaon Axis (BBA) is an east-west trending secondary shear zone in the NSMB lying south of SPSZ, which is known for the occurrence of gold along with other sulfide minerals within the quartz reefs. The present study has been carried out at north of Ichadih village, which lies on the BBA. The present study attempts combined electrical resistivity tomography (ERT) and self-potential methods along a profile of 470-m length in the Ichadih area to map the potential mineralized zones. Initially, ERT sections generated by Wenner, Wenner- Schlumberger, dipole-dipole, and joint inversion of the combined array have been analyzed, and results are validated through the analysis of model resolution. A prominent low resistivity (10–100 Ωm) associated with quartz reef/limonitic quartz reef at a depth of approximately 30–85 m, encircled by a high resistive (more than 10,000 Ωm) formation associated with metasedimentary rock, has been delineated using joint inversion of the combined array. Further, analysis of self-potential (SP) anomaly using particle swarm optimization inversion also confirms the prominent low SP anomaly at a depth of 77.3 m, which is analogous to the low resistivity anomaly identified in the joint inversion of the combined geo-electric array. Subsequent analysis of a complex synthetic geo-electrical model analogous to the present field situation proves the efficacy of the joint inversion of combined arrays. As a whole, joint inversion of multi-array data is established as an efficient technique for better subsurface imaging in case of the complex subsurface structure. In-depth analyses confirm the possibility of sulfide mineral-rich deposit (quartz reef/limonitic quartz reef) which requires further geological drilling and lithogeochemical sample analysis, for possible future exploration.

Oct 26, 2020

By Robert Bohman

I truly free enterprise system requires free and unrestricted competition among a diversity of suppliers, in order to function properly. The natural attrition of the marketplace tends on the one hand to narrow the competitive field ... but the flow of new competitors entering the arena provides a "diluting" effect, and a "balanced" market place. Without the ready flow of new business entrants, the market becomes increasingly concentrated in the hands of fewer and. fewer firms. Competition among suppliers is diminished and the "free" marketplace suffers accordingly. A number of organizations, both governmental and private, have recently expressed grave con¬cern over the competitive future of the Western coal market. While most have noted that there is currently adequate competition within the Western market, some have cited the growing con¬centration of coal ownership ... particularly federal lease ownership ... in the hands of a relatively few firms. They suggest that unless this apparent trend is reversed or at least stemmed, the number of new firms entering the federally-dominated West may become reduced to the point where competition will suffer.

Jan 1, 1982

By L. Spiers

Motorized Conveyor Pulleys contain all the traditional conveyor belt drive components inside the pulley. Light duty airport check in, grocery stores and food processing conveyors; requiring compactness, elimination of guarding and component containment have been using them for years. Portable Aggregate Processing Equipment require these features but with higher belt pulls and severe duty beyond the capacity of traditional components in a limited space. New materials, design technologies and automation; converging with safety issues, higher energy and operating costs; have created a pressing need. The challenge is to integrate new technologies and traditional components into a reliable, compact, conveyor belt drive system.

Jan 1, 2003

By D. Leppert

Mr. Garrett brings up several interesting points with respect to the proposed API specification for "nontreated bentonite." However, although not explicitly stated, these specifications are being written based strictly on bentonites from the Wyoming/South Dakota area. Other sodium bentonites may be suitable for use as drill mud but will be unacceptable since the specifications are designed for Wyoming bentonites. Regardless of the API's intent that its specifications are intended only as guidelines, they are generally adhered to on an international basis and, for practical purposes, might as well be chiseled in stone. Estes (1986) notes that the quality of bentonite available from Wyoming producers has steadily declined since the early 1960's. The plastic viscosity: yield point (PV:YP) ratio was included in the current API 13A specification primarily to prevent excessive polymer treatment of lower quality bentonites to make drill mud. However, with development of polymers designed to control YP, this specification cannot ensure that only high-quality bentonites are used for drill mud. Nor will the new specifications for untreated bentonites. Other sodium bentonites are available. Bentonite produced in southeast Oregon demonstrates superior performance characteristics without addition of polymer or other chemicals. However, the exceptionally high purity of these deposits leads to a relatively high YP:PV ratio since the naturally high YP probably results from the higher purity and smaller particle size of this bentonite (Rath, 1986 and personal communication). These bentonites typically have a smectite component exceeding 90% (Rath, 1985), compared with 70% to 75% smectite for typical Wyoming bentonites, as determined by X¬ray diffraction and tests for colloid content. As evident from the accompanying table, the untreated Oregon bentonite has excellent rheological properties, though different from Wyoming bentonites due to the high purity. Additionally, this bentonite reacts well with polymers typically used in the oil industry, making it eminently suitable for use in a low-solids mud system. The extremely low grit content, less that 0.5% on a 75 mm (200-mesh) wet sieve, greatly exceeds the standards set for Wyoming bentonite. Optimum rheological properties are obtained at a higher moisture content than Wyoming bentonites. At 10% moisture, API 13A maximum, the clay is overdried, again reflecting the high smectite content. In summary, the specifications proposed by the API Task Group will ensure that only Wyoming producers can supply "nontreated" bentonite to the oilfield since specifications are

Jan 1, 1989

By H. E. Epstein, B. K. Parekh, W. M. Goldberger

Comminution is the single most expensive operation in mineral processing. It consumes about 50% of the energy required for mineral extraction (Agar, 1976). Current comminution technology is both energy-intensive and inefficient. A novel noncontact comminution process concept was developed in this study, whereby selective lib¬eration of minerals from an ore could be potentially achieved. The process involves application of electric and ultrasonic energy to liberate minerals from gangue particles. Introduction The mineral industry is a large user of energy in the US. Energy usage is increasing as the grade of ores processed decreases. It is es¬timated that comminution of ores uses about 32 000 kWh (115 trillion kJ), or 2% of the electric power produced in the US (NMAB-365, 1981). Among other minerals, ce¬ment, iron, and copper processing plants are the largest users of en¬ergy in comminution. Very little of this energy used in conventional grinding (about 1%) is used to gen¬erate new surface. The remainder is wasted (Table 1). Thus, there are substantial energy-saving and economic incentives to improve the efficiency of crushing and grinding techniques for mineral recovery. With an energy efficiency of only 1%, it would seem possible to devise methods to significantly improve comminution technology. This requires that breakage force be applied only where needed, not indiscriminately as in a conven¬tional ball mill (NMAB-365, 1981). Can apparatus and methods be de¬ veloped for large-scale commer¬cial use that allow energy to be fo¬cused at intergranular bounda¬ries? If this can be done, mono¬mineral grains would remain in¬tact and the grinding action would be selective and substantially more efficient. The novel comminution process concept described in this paper uses a combination of electric and ultrasonic energy. This energy breaks the ore and selectively lib¬erates minerals. The process has also been termed a two-stage or electroacoustical comminution process (Goldberger, Epstein, and Parekh, 1982). The mineral grain boundary is usually the weakest area in an ore. By applying electri¬cal energy to the ore, the rock frac¬tures mostly at grain boundaries. At the same time, the electric shock creates secondary hairline fractures in the ore. Additional application of ultrasonic energy to this ore provides further break¬age. The concept was proven on a molybdenum porphyry ore but needs additional study. Technical Background There have been substantial im¬provements in milling machinery and grinding operations, but rela¬tively few attempts have been made to develop alternatives to conventional impact milling. Sev¬eral methods, however, have been investigated that relate to this study. In the early 1970s there was considerable interest in a size re¬duction method known as the Snyder Process (Cavanaugh, 1972). It involved charging coarse ore into a pressure chamber, pressur¬izing with a gas, and activating a quick-opening (15 msec ) dis¬charge valve that connected the chamber to a discharge duct. This allowed solids to fluidize and ac¬celerate, subjecting the material to a variety of impulse phenomena that caused the desired size reduction. Other nonimpact means of achieving breakage and selective size reduction have been de¬scribed in technical and patent literature. Kanellopoulos and Ball (1975) considered using heat to induce thermal stress in quartz¬ite. This would cause cracking and, thus, increase grinding efficiency. The use of electrical energy to induce thermal stress was studied by the General Elec¬tric Co., in cooperation with the Montana School of Mines, under a research grant from the Anaconda

Jan 9, 1984

By Keith A. Heasley, Lee W. Saperstein

This paper investigates the use of backfill zones and yielding pillars for subsidence control. The investigation begins by choosing an appropriate subsidence predictive technique to simulate the proposed subsidence-control schemes. Two case studies are performed in order to delineate the accuracy and utlility of the chosen predictive technique and then the results of these case studies are used to establish appropriate sets of regional site parameters. Next, a detailed analysis of the major variables affecting the outcome of the subsidence-control simulations is conducted and graphical displays of the exact sensitivity of the surface subsidence to these variables are given. Finally, alterations to the surface subsidence that are expected from using two major subsidence-control techniques are presented. The first technique to be assessed is a backfilled pillar centered longitudinally in a panel. With this arrangement, a minimal amount of backfill material can produce substantial decreases in vertical displacements. The second technique to be assessed is the use of yielding gate pillars to reduce the sinuosity of the transverse subsidence over adjacent panels. With proper design, this technique can greatly curtail surface strains and help minimize remedial drainage control.

Jan 1, 1986

By Malcolm Scoble

This contribution examines the motivation and prospects for mining companies to become Learning Organizations and integrate Lifelong Learning into their culture. Mining Schools have a potentially central role to play in developing Learning systems for access by industry. Reference is made to initiatives to develop a system that is based on collaboration between UBC, Edumine and the Canadian Institute of Mining, Metallurgy and Petroleum. Recent experiences with this model are reviewed.

Jan 1, 2005

By D. R. Wilburn

The worldwide budget for non fuel mineral exploration was expected to increase by 27 percent in 2003 from the 2002 budget, according to the Metals Economics Group (MEG) of Halifax, Nova Scotia. The increase comes after five years of declining spending for mineral exploration. For the first time in several years, all regional exploration budget estimates for 2003 as defined by MEG would increase from similar 2002 estimates. However, MEG included 193 more companies in its 2003 survey than in 2002. As with previous MEG survey reports, estimates reflect anticipated expenditures rather than actual dollars spent. Caution, therefore, must be taken when comparing 2002 and2003 estimates or evaluating the magnitude of regional changes from year to year. Sample variations and currency exchange rates may influence year-to-year variations of MEG data. Even so, it is likely that the general climate of improved metal prices in 2003 encouraged companies that had previously left the mineral exploration sector or reduced their exploration activity to once again focus on minerals exploration or increase exploration activity and budgets.

Jan 1, 2004

By G. Davis

It is well known that the anticipated mineral price at the start of a prospective mineral project can have an overwhelming effect on a property's ex ante value. However, possible price movements throughout the life of a project can also have an impact on this value. This paper demonstrates how different potential price paths can affect project value. When considering commodity price projections for mine valuations, it is thus necessary to estimate not only the expected commodity price at the start of the project, but also the manner in which that price is likely to fluctuate throughout the project's life.

Jan 1, 1995

By H. E. Cross

In a minerals-recovery context, the object of exercising control over milling operations must be threefold, 1) To achieve maximum recovery at 2) minimum operating costs and 3) making maximum use of installed equipment, Milling is one of a sequence of operations which have as their objective the economic recovery of minerals from mined ores, All operations in the sequence are interdependent and each is both influenced by and itself affects all other unit processes. The part which grinding plays in achieving each of the above objectives is indicated in the following analysis: In South Africa, the most important mining operations are still the gold mines, A vast reservoir of knowledge and experience in treating the Witwatersrand and associated ores has been accumulated. and recoveries are consistently high, However residue values do vary and frequently this is due to fluctuations in the degree of grind, The significance of changes in residue values is indicated by the following example: On a modern mine, the residue values varied from 0,25 to 0,33 dwi; per 2000 lb, during a period of 6 months, The cash value of the gold thus lost varied therefore between $0.44 and $0.58 per 2000 lb, ton. A residue which assays 0.30 dwt per ton would contain approximately 0.26 dwt as undissolved gold and 0,040 dwt per ton as dissolved gold present in residual solution after filtration. This dissolved gold loss is a function of efficiency of filtration and varies from 0.030 to 0,.070 dwt per ton of residue.

Jan 1, 1970