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By H. Colijn

Introduction Bulk commodity prices are ever increasing. This forces buyers and sellers in world markets to look more carefully at methods for obtaining an accurate accounting of commodity transactions in commerce and materials utilization in processes. Weighing and sampling inaccuracies can result in loss of income, product quality, and cost controls. So weighing and sampling accuracies are extremely important. They are the key components of managing the quantity and quality control aspects of bulk materials handling. This article will confine itself to the weighing systems and will deal with various aspects of system design, calibration, and operations. Emphasis will be placed on new developments and requirements in this field. Weighing methods To measure the gravimetric pull on a body being weighed (the load), the gravimetric force must be countered by an opposing force. Measuring this counter-balancing force thus becomes the measurement of weight. The conventional even-arm balance shows the concept of balancing an unknown mass with an equal known counterbalancing mass. But the loads encountered in industry generally range up to many thousands of pounds. So it is obvious that the even-arm approach is not practical. Thus, with the exception of direct load-bearing load cells, most of the weighing equipment uses some form of lever system. This is usually a combination of first- and second-class levers, to gain a mechanical advantage. These levers permit the load force to be counter-balanced and hence measured within a practical range. Lever systems not only perform this force-reducing action, they also serve to focus the load force at a single point, for convenient measurement. They align the force vertically in one direction so that measurement accuracy will not be affected by unrelated side forces. There are five basic methods of gravimetric weight measurements. That is, there are five basic types of opposing forces. • The first is the standard weight counterbalance. It uses a known weight to counterbalance the load directly or through a lever system.

Jan 9, 1988

By Akram Marseet, Andrew J. Petruska, Rik Banerjee

Underground mine roof bolting is a crucial operation for miners’ safety and mine sustainability. Since roof bolting is a manual or human-supervised operation, miners’ safety is at risk due to dust or rock falls. Traditional machine learning algorithms have shown limitations to detecting drillable areas, mainly due to harsh lighting conditions. The authors propose an adaptive deep-learning framework for autonomous roof bolting. The proposed framework is based on implementing a binary semantic segmentation algorithm on color images to classify pixels that belong to rock from those that belong to non-rock. Significantly, the proposed framework implements deep learning semantic segmentation on images from traditional and neuromorphic vision sensors in underground mines. The performance of the proposed model shows an impressive accuracy level of at least 98% at a low number of training epochs with smooth learning curves. The high accuracy enables the implementation of autonomous roof bolting, greatly improving miners’ safety and operational efficiency while reducing human exposure to safety hazards. This research will advance the use of deep learning in mining automation and has the potential to revolutionize the traditional mining industry.

Feb 1, 2024

By A. L. Frank, Benton

INTRODUCTION The selective sensitivity of plastic nuclear track detectors (PNTD's) to low energy 4He particles in an environment which also contains gamma and beta radiations has made these detectors prime candidates for the dosimetric measurement of the concentrations of radon and its daughter products in mine air. Their passive, integrating mode of measurement, small size, low weight and inexpensiveness are attractive characteristics for large scale personnel dosimetry. The detectors can be used in either active or passive dosimeters. In active devices, the PNTD is placed in close proximity to a sampling filter. The filter collects, from a calibrated air flow, all the daughter nuclei which are in suspension. As the daughter nuclei pass through the decay chain, through 214Po, a fraction of the 4He particles emitted are registered as latent tracks in the plastic. In passive devices, the PNTD is placed in direct contact with the ambient air containing the radio-nuclei concentrations to be determined. The active dosimeters have the advantage of excellent sensitivity, and the measured track densities yield very close approximations to accumulated Working Level (WL)** exposures. They have the disadvantage that the simplicity of the passive PNTD is lost, since a battery-driven constant flow-rate air pump is a necessity. The passive dosimeters are simple in construction and use, but they have the disadvantage that WL exposures are not directly measured and certain assumptions concerning radon and daughter equilibrium conditions must be made in determining WL exposures from the measured track densities. Also the sensitivities, in track densities per Working Level Hour (WLH) exposure, are much less than for active dosimeters. Dosimeters of both types have been investigated. Passive devices have been tested extensively both in the laboratory and in mines. Active devices have been laboratory tested. In our earlier measurements, cellulose nitrate plastic detectors were used exclusively, since this material had the highest sensitivity of the PNTD's then in use. When the properties of CR-39 plastic were discovered (Cartwright, 1978; Cassou and Benton, 1978), this material was used, where possible, to take advantage of its superior sensitivity. The results of our earlier work have previously been published (Frank and Benton, 1977). * Research sponsored by the Bureau of Mines, U.S. Department of Interior, under Contract No. JO-188003. ** A Working Level is defined as any combination of the short-lived radon daughters containing 1.3 x 105 MeV of potential 4He-particle energy per liter of ambient air. PASSIVE DOSIMETRY In the earliest testing of PNTD's for passive WL dosimetry, a single strip of cellulose nitrate plastic was used to determine the total cumulative 4He-particle activity in the air of simulated uranium mine and uranium mine environments (Rock, 1968; Rock [et al], 1969; White, 1969). The measurements yielded a close relationship between track densities and WL exposures in a controlled, static environment, but poor accuracy in the active mine tests. It was assumed that equilibrium differences contributed largely to the variations found. The response of PNTD's to airborne 4He-particle emitters, derived by Lovett (1969), demonstrated that detectors such as cellulose nitrate, which has a sensitivity cutoff at 4He-particle energies below the emission energies of radon and its daughters, are equally sensitive to the activity concentrations of radon, 218po(RaA) and 214Po(RaC'). Since radon does not contribute to WL as it is defined, and since, under normal ventilated uranium mine conditions, the radon activity constitutes about 40% to 70% of the total 4He-particle activity, the WL exposures calculated from measured track densities are very sensitive to the particular radon daughter equilibrium conditions. Also, the detector does not weight the individual daughter activities in proportion to their importance to WL. The equation for WL is WL = 0.00103C2 + 0.00507C3 + 0.00373C4 (1) where C2, C3 and C4 are the activity concentrations of RaA, RaB and RaC-C', respectively, in pCi/[L]. The detector leaves C3 unmeasured and weights C2 and C4, equally. [This problem has been approached by Domanski et al (1975, 1979), for some non-uranium mines, by measuring equilibrium conditions throughout the mines to determine a mean value for A, the inverse of the Working Level Ratio (WLR = 100 WL where C1 is the activity of radon-222 in pCi/[L].) The distribution of values allowed Domanski to determine probable errors in calculating WL exposures from track densities. However, measurements of equilibrium conditions in U.S. uranium mines (Breslin et al, 1969; Holub and Droullard, 1978) indicate that this method would not be accurate enough for uranium miner personal dosimetry.] A two-element dosimeter was designed at our laboratory to compensate for equilibrium variations. The first element is a radon detector; the second is a detector for the total 4He-particle activity in the ambient air, just as in the single element dosimeters cited above. The addition of the radon detector allows the equilibrium conditions for the individual nuclei to be determined, given certain assumptions concerning the interrelationships between the nuclei concentrations in mine air. The two detectors and the problems involved in calculating WL exposures from their measurements are discussed below.

Jan 1, 1981

By William C. Ellis

Underground water is part of a continuing hydrologic cycle, which involves all elements of water occurrence. All groundwater of economic importance is in process of movement through a porous rock stratum from a place of intake or recharge to a place of disposal. Groundwater moves and is contained in fractures in the rock and/or in intergranular spaces of porous formations. Where there have been no water developments by man, groundwater is in a state of approximate equilibrium and the forces of replenishment and discharge are in balance. Thus, groundwater, unlike other mineral resources, is constantly being replenished in most areas at a rate which is measurable and which is important in the planning of its utilization. As illustrated by Figure 1, replenishment of groundwater supplies results from the direct penetration of rainfall through the soil to the water table, by seepage from surface streams or ponds, and/or by subsurface movement from an adjacent groundwater body. Under natural discharge conditions, water is commonly consumed by transpiration of trees and other types of vegetation, by flows from springs, by evaporation from shallow depths below the surface, and seepage into streams that traverse the area.

Jan 1, 1964

By A. Tarigan

The integration of the ESZ orebody and DOZ orebody resulted in a much larger footprint than the original DOZ Mine shape. The significant change in footprint geometry presented new cave front management challenges, specifically: longer undercut drifts. Using a constant blasting rate, more time is required to complete caving in each drift which ultimately influences the number of active faces at any point in time. The number of manageable active drifts is controlled by the planned square-meters of undercut blasting, lead/lag restrictions and other specific conditions such as the need to blast pre-charged explosives. In early 2008, an evaluation of the existing plan showed that significantly more active undercut drifts and longer cave fronts would occur in the next five years. Difficulties associated with the long cave fronts led to a decision to redesign the caving sequence. Several different boundary options based on operational, geotechnical and ore grade parameters were investigated. This paper describes the issues faced with long cave fronts, the constraints and requirements to effectively manage the caving sequence and the options considered to mitigate this situation.

Jan 1, 2010

By M. J. van der Meulen

"The Netherlands has major resources of sand, gravel and clay, exploited mainly for construction works and the building materials industry. As in most western countries, mineral extraction meets with considerable societal resistance. To this end, Dutch minerals policy aims to prevent extraction by promoting economical use of materials, and the use of alternative (secondary or renewable) materials. Up till recently, it also included a system of production planning to sustain supplies of regionally scarce materials. Dutch policy development is reviewed and discussed in terms of pitfalls and possibilities for mineral planning in general. Promoting secondary substitution has been quite successful, and presents an example. In contrast, the production planning system has been controversial from the start and ineffective as a result, mainly because it attempted to solve supply problems without properly addressing the underlying resistance. For this reason the system is in the process of being abandoned. The full paper will be published in: Petterson, M., McEvoy F, & Marker, B.R. (Eds) 2005, Sustainable minerals operations in the developing world, Geol. Soc. Lond. Special report series, in press. This abstract is reprinted with kind permission of the publisher."

Jan 1, 2005

By Aki Fujii, Hiroshi Dobashi, Mitsuro Matsuda, Yoshinari Kondo

INTRODUCTION The Metropolitan Expressway Central Circular Route with a total length of approximately 47 km is located outside the Inner Circular Route of Tokyo (at a radius of approximately 8 km from the city center). Sections with a length of approximately26 km, slightly less than 60% of the total length, on the east and north sides are in ser-vice. Completing the Central Circular Route (Figure 1) is expected to enable through traffic concentrated at the city center to get around, and to form a well balanced trans-port network, which will alleviate traffic congestion considerably. The Central Circular Shinjuku Route, a section with a length of approximately 11 km on the west side, is now being constructed at a fast pace. The route is being built mainly by the shield tunneling method to carry out work smoothly under a trunk highway carrying heavy traffic and to reduce adverse effects of tunneling work on residents in the neighborhood. Shield tunnels have recently been becoming longer and deeper, and no secondary linings have been used in an increasing number of cases because of the over-crowding of cities or the reduction of budgets for public works. Economical, durable and high-quality segments have been required for linings of shield tunnels. Segments are made of concrete, steel, cast iron or combination thereof. Concrete segments are generally used in shield tunnels of medium to large diameter. Concrete segments are highly durable and resistant to compression, so they are highly resistant to earth pres-sure, water pressure and jack thrust. They are, however, heavy and have low tensile strength, so they are brittle and their corners are likely to spall. Concrete segments should therefore be handled carefully.[1] The authors have developed a steel fiber reinforced highly flowable concrete segment (referred as SFRC segment) that overcomes the weaknesses of concrete segments[2] to construct economical, durable and high-quality linings. SFRC segments have been applied to outbound sections SJ51 through SJ53 of the Central Circular Shinjuku Route. Unlike conventional concrete segments (referred as conventional RC segments), SFRC segments are made of steel fiber reinforced self-compacting highly flowable concrete. SFRC segments require less reinforcing bars than conventional RC segments because steel fibers are expected to work as reinforcements. Steel fiber reinforced concrete is a composite material that overcomes the brittleness of plain concrete, and has higher resistance to bending, tension and shear than

Jan 1, 2007

By David G. Adam

Introduction Syncrude Canada Ltd. is the operating company for a consortium of industry and government participants that produce synthetic crude oil from their leases in the Athabasca Oil Sands. Production from the $2.3 billion (1978) integrated mining, extraction, and bitumen upgrading and utility complex started in September 1978. Production is currently about 6.4 Mm3/a (40 million bbl per year) of high quality synthetic crude oil. This is done by upgrading the extracted bitumen from the oil sands mined. Plans are to increase the production to 8 Mm3/a (50 million bbl pier year) by 1989. At that time, the mining operation will be required to deliver 100 Mt/a (110 million stpy) of oil sand (ore) to the extraction plants, and handle quantities of waste ranging from 50 to 75 Mt/a (55 to 83 million stpy). The Syncrude plant is located at Mildred Lake, 40 km (25 miles) north of Fort McMurray and 480 km (300 miles) north of Edmonton, Alberta. Climate, particularly winter, is therefore a major factor affecting the design and operation of all the Syncrude production facilities. Bitumen production, consisting of overburden removal, oil/sand mining, bitumen extraction, and tailings disposal, account for about half the total SCO production costs. Considerable research and development, therefore, continues to be applied to improve both material handling and bitumen recovery methods. Potential applications for feeder breakers were identified in the material handling aspects of both overburden and oil sand mining to reduce cost and to attain planned production increments. Overburden removal Overburden materials on the leases comprise thin Pleistocene sands, gravel and fill, and sands, silts and clays of the thicker Clearwater Formation with the silt to clay components predominating. The latter contains multiple leases of hard siltstone with unconfined compressive strengths up to 148 MPa and thicknesses up 0.1 to 0.9 m (1 to 3ft). Characteristics of the overburden as well as the climatic environment and scale of operation present unique problems for the efficient removal of the material. In a bucketwheel/conveyor system, the weak silty clay formations require relatively flat working slopes for safe operation, while the siltstone lenses and frozen overburden require blasting or selective removal by other equipment. These factors, combined with the normal bucketwheel/conveyor design parameters, lead to high capital investment and relatively inefficient use of that capital. Hydraulic mining alternatives, including dredging, are constrained by severe clay settling problems in the waste disposal

Jan 6, 1986

The authors provide a discussion of the paper, ?Coal workers? pneumoconiosis prevalence disparity between australia and the united States,? a peer-reviewed paper that appeared in the technical papers section of the July 2012 issue of Mining Engineering magazine. The original authors, G.J. Joy (gjoy@cdc.gov), J.F. Colinet (jcolinet@cdc.gov) and D.D. Landen (dlanden@cdc.gov), respond.

Jan 1, 2013

It is widely accepted that particles stabilize flotation froths and that stable froths result in improved flotation performance. Predicting the effect of particle addition on froth stability is, however, challenging. Furthermore, there is currently no technique that allows the prediction of the effect of different flotation reagents on froth stability, without carrying out froth stability experiments.

By L. R. Moore

Arsenic is among the list of major contaminants in mining aqueous waste streams. Though the elemental form is toxic, the aqueous oxyanions are more so. The most common forms of arsenic released during mining processes are arsenate and arsenite. The common treatment technologies to date can be summed up in these major categories: oxidation, coagulation, absorption, and media filtration. These methods can often involve many expensive processing steps that may also be limited by variables, such as total dissolved solids, other cations and anions, and the oxidation state of the arsenic. An innovative technology, falling in the absorption category, was developed that can successfully reduce such aqueous forms to a level below the EPA recommendations. This new technology offers a unique and viable solution which is transparent to the above mentioned limitations.

Jan 1, 2012

By P. D. Georgescu

Gold, like no other metal, has a fascinating and special place in the world. It is used in a range of every day applications essential to modern life. Gold has long been considered the most precious metal in the world. Gold is used mainly for making jewellery as well as for dentistry, adornments on building and artistic expression. For thousands of years it has been used as an ornament of kings, a currency and standard for global currencies, and more recently, in a wide range of electronic devices and medical applications. Gold?s many unique properties have secured in a central role in history and human development. Today, more often than not, gold is extracted from ores. It occurs in vein and alluvial deposits and is often separated from rocks and other minerals by mining and processing operations. Some of these processes cause environmental concern (cyanidation, amalgamation, roasting). Besides primary gold ore resources, a series of secondary resources can be taken into account and processed for gold and silver recovery. There are two main types of waste produced. The first type is process waste, which includes tailing consisting of processing residues and waste rock. The other type is refuse from other different processes and recyclable materials. Among other secondary resources and/or by-products containing precious metals, which have been studied some processes and technologies with low ecological impact are presented in this paper. Heaps and tailing ponds resulted from gold-bearing ore exploitation and processing, refractory gold-bearing pyrite concentrates, slag resulted from electrolytic slime melting, gold-bearing chlorous slime are taken into account. In order to establish environmental friendly technologies for precious metals recovery from these secondary resources, laboratory experiments have been carried out on a pilot scale and in some cases on semi-industrial scale by applying specific technological processes, namely hydro-gravitational concentration, bio-oxidation, non-ionizing electromagnetic radiation (microwaves), solubilization without utilizing cyanide and gold recovery by ion-exchange resin. This paper presents the research results, technological principles as well as the possibilities of applying combined processes in order to treat different secondary gold-bearing resources.

Jan 1, 2006

By Henry J. Schwellenbach

The New York Trap Rock Corporation has four plants located along the Hudson River, all within 70 miles of New York City. The company produces crushed stone for use as construction aggregate, with a total annual production amounting to 6 million tons. The crushed stone is moved to markets in metropolitan New York, New Jersey and Long island areas by water transportation. There are daily deliveries of approximately 35 scowloads to the market area. Its customers are contractors with ready-mixed concrete and asphalt plants located on the water, where the aggregate is unloaded for its ultimate use. For a number of years capital equipment was replaced only when the current operating machinery was no longer serviceable, or when' a need was apparent for a different type of equipment. There was no particular regard for efficiency or for operating and maintenance costs. Such lack of system often resulted in the emergency purchase of equipment which was later found to be unsuitable for the job. A few years ago it became apparent that a systematic procedure was necessary. After evaluation of several systems, an individualized plan was evolved from the basic pattern developed by the Machinery and Allied Products Institute. The system adopted by New York Trap Rock has proved wholly satisfactory.

Jan 1, 1959

By Joseph M. Denk, John N. Baran, William J. Francart

Filling or sealing shafts of underground coal mines is required when the mine is declared inactive by the operator, permanently closed or abandoned for a period of time greater than 90 days. Although shaft filling requires the use of incombustible materials for the first fifty feet of the shaft, a sparking potential may exist which has been reported to be the cause in at least one shaft-filling explosion. This paper outlines the method used at the explosion site to monitor mine gases within the shaft to assure the safety of the workers involved in the remainder of the shaft-filling operations. Gases which were monitored include methane, oxygen, carbon monoxide and carbon dioxide. Continuous sampling was conducted twenty-four hours per day to determine the methane liberation and accumulation of gases within the shaft. Once gas concentrations were evaluated, the need for ventilation in the shaft was obvious because methane accumulations within the shaft were in the explosive range. Several methods to ventilate the shaft were explored. The most practical seemed to be the dilution of gas concentrations with compressed air to inject a quantity of fresh air into the shaft. But, when the compressed air was stopped, a buildup of an explosive mixture reoccurred. The pattern of gas accumulation was then studied to find the correct combination of ventilation and shaft-filling time periods which would a1 low for the greatest reduction of the potential for an explosion. Gas concentration sampling continued during the remainder of shaft-filling operations at this shaft and four others at the same mine. In conclusion, this paper illustrates some of the problems which are often overlooked in a shaft-filling operation. If addressed, the work can be done in a safe and feasible manner.

Jan 1, 1987

By P. E. Sperry, R. E. Heuer

The United States Bureau of Reclamation is constructing the $200 million Navajo Indian Irrigation Project to irrigate 110,000 acres of land on the Navajo Indian Reservation in northwestern New Mexico. Water from the San Juan River is impounded by Navajo Dam and will be conducted for 26 miles along a series of tunnels and canals to the area to be irrigated. Tunnel No. 3 is the third in a series of six tunnels along the route. Bids for construction of Tunnel No. 3 were received by the Bureau of Reclamation in September, 1970. Fluor Utah was low bidder at $8.7 million. Ten of the 12 bids were based on excavation by tunnel boring machine. The consulting firm of A. A. Mathews, Inc., was retained by the contractor to advise on geologic and rock mechanics conditions after support problems developed in the tunnel. Tunnel No. 3 is 15,264 feet long, has an 18 foot lined diameter, rises approximately one-half inch per 100 feet in the direction being excavated, and is 6,000 feet above sea level. There is one short curve in the alignment. Minimum concrete thickness is 12 inches with eight inches from 'A' to 'B' line making a pay diameter of 21 feet, 4 inches. The tunnel is supported with rock bolts and steel pans. Mole excavation began on May 13, 1971 from a blasted starting chamber. After 46 feet were excavated the mole was shut down and the trailing muck handling equipment was pulled into place. After advancing 1,700 feet in 34 days, unanticipated ground water conditions and ground support problems were encountered slowing moling so that the next 1,000 feet of advance consumed 97 days until December

Jan 1, 1997

By M. Carvalho, R. Bicallho, M. Queiroz, R. Gomide, V. Silva, R. Toubes

Since it is becoming increasingly important, from an environmental viewpoint, to minimize blast vibrations induced in urban dwellings and improve rock fragmentation in order to reduce costs with loading, transportation crushing and grinding, a cooperative research project was established between Companhia Vale do Rio Doce - CVRD and the Blasting Research Group in the Department of Mining Engineering at Escola de Minas - UFOP to investigate which elements interfere on ground vibration, air blast, flyrock and rock fragmentation related to rock blasting activities at Conceição Mine, located in Itabira city, state of Minas Gerais, Brazil. This research also involved development of a new explosives formulation in order to minimize the total blasting cost. This paper presents the general scheme of the research running from May 1995 to May 1997 and a summary of the results obtained in the field tests that were carried out in this mine.

Jan 1, 1998

By B. R. Utz

The goal of the DOE Coal Preparation Program is to provide industry with the scientific and engineering knowledge base to produce economically competitive and environmentally acceptable clean coal products for both existing and new markets. The DOE/PETC in-house program continues to conduct fundamental, exploratory, and applied research in the areas of physical, chemical, and microbial coal beneficiation to assist in meeting these goals and objectives. The Coal Preparation Division now has a new Coal Preparation Process Research Facility that allows continuous bench-scale testing of emerging coal cleaning technologies and ancillary coal preparation equipment at feed rates up to 1,250 kilograms (1.25 tons) per hour. Bench-scale and laboratory-scale research projects at PETC cover areas such as 1) the use of micronized-magnetite for fine-coal, 2) heavy-media cycloning, 3) fine coal reconstitution, 4) development and testing of coal preparation process flowsheet simulators, 5) dry coal beneficiation using electrostatic methods, 6) tracer methods to determine the efficiency of density-based separations, 7) selective oxidation of organic sulfur, and 8) microbial removal of pyrite and organic sulfur from coal. This paper will discuss several of these research areas.

Jan 1, 1993

By Cyrus W. Field

Chemical, mineralogical, and petrographic data have been obtained for suites of plutonic rock samples from the Guichon Creek Batholith of British Columbia and the Mineral-Iron Mountain-Sturgill Peak- Cuddy Mountain-Peck Mountain areas of western Idaho. Intrusions at these two geographically separate localities represent composite plutons ranging from early gabbro through quartz diorite to late grano- diorite and more silicic-alkalic phases. They are early Mesozoic (200 m.y.) in age, and contain porphyry-type mineralization in close spatial and temporal association with late-stage intrusions of porphyry, aplite, pegmatite, and (or) breccia. Country rocks are eugeo-synclinal assemblages of metasedimentary and metavolcanic greenstones of Permian, Triassic, and Jurassic age. The petrochemical evolution of these intrusions, and the effects of subsequent hydrothermal alteration and metallization, are illustrated by standard ternary diagrams of the major oxide and mineralogical data. Samples plotted on an AFM diagram suggest a calc-alkaline magma trend. However, their distributions on NKC and Qz-Kf-Pf diagram show well-defined trondhjemitic (Na20-rich) and tonalitic (quartz-rich) variants to this trend, which are similar in part to those reported for mineralized island arc plutons of the northern Caribbean and southwest Pacific, but which contrast markedly to those for continental plutons of the Bingham District, Boulder Batholith, districts of southern Arizona, and elsewhere.

Jan 1, 1975

By Matthew A. Omofoma, Andrew P. Hampton

The application of the Cyprus Cyanisorb process was investigated using a pilot scale facility at the NERCO DeLamar Silver Mine (DSM) in Owyhee County, Idaho. The purpose of this process is to remove cyanide from the DeLamar mill tailings slurry prior to its introduction to the tailings impoundment. This will maintain the tailings impoundment solution in a detoxified condition and thus prevent migratory bird mortalities. The cyanide removed is to be collected and recycled to the mill. The process successfully recovered approximately 90 percent of the weak acid dissociable cyanide (WAD), reducing the effluent tailings cyanide concentration from about 300 ppm to less than 20 ppm. This was accomplished by stripping the slurry with air in a packed tower and recovering the volatilized HCN in a packed absorption tower. Data were obtained for the design of the full scale facility including the stripping and absorption towers, currently under construction at the DeLamar Mine site. Finally, test results indicated that the final pH of reneutralization can be optimized to provide for minimal gold and silver losses, while selectively precipitating unwanted metal impurities (Zinc, Selenium, Iron, and Copper) from solution

Jan 1, 1992

By S. M. Jarrett, W. B. Schmidt

Within the last year, the Nation has been shocked by two major tunneling disasters. Almost exactly a year ago 17 men died in the San Fernando Tunnel in an explosion attributed to gas. A few months later another 21 men died in an explosion laid to the same cause at Port Huron, Michigan. The analysis of the causes of these accidents is still continuing. While it appears that they differ substantially from each other in their specifics, they share the common trait that, like most industrial accidents, they might well have been prevented. Gas explosions in tunneling are neither new nor particularly unusual. Forty years ago, Assistant Director Jarrett was hired as a safety engineer on the Hetch Hetchy Aqueduct in California after an explosion that killed 12 men. Prior to 1946, in California alone, the Bureau of Mines had recorded 27 gas explosions incidental to hard rock mining and tunneling. The purpose of this paper is to review the status of the principal regulations affecting tunneling and to indicate some ways in which safer and more healthful conditions can be obtained. The Bureau of Mines was established by an Act of Congress of May 16, 1910. Since that time the Bureau has been making investigations and compiling and publishing health and safety data relating to mining and to tunneling. If any benefit is to come from an anaylsis of tunneling accidents, it must be the knowledge needed to prevent their repetition. The Bureau of Mines has also had informal discussions with the Department of Labor regarding the possibility of the Bureau's assuming that agency's responsibility for tunnel inspections.

Jan 1, 1997