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The implementation of NAFTA in January 1994 was expected to have small but beneficial effects on the Mexican economy, mostly through increased investments. Mexico's mining industry was especially likely to benefit, as mineral investment funds would be diverted to the now safer Mexico and away from similarly endowed but more risky Latin American mineral economies. The results during the past two years have shown that it is government and macroeconomic factors that influence investment flows, rather than the fine tuning of trade flows through so called 'free-trade" agreements.

Jan 1, 1997

By T. Weimer

Gasification of carbonaceous energy carriers with simultaneousCO2 removal is a new and interesting alternative e.g. ZECA [1],HyPr-Ring [2], AER [3]. In the ZECA process lime supported Hydrogen generation from Methane is a basic process unit and the Hypr-RING process investigates Hydrogen generation from hard coal with addition of lime. Here the main objective is a further development of the AER process. High energetic efficiencies for gasification in the range of 90 % can be achieved if the humidity of the energy carrier is already sufficient for steam reforming reaction. The aim of the overall process is upgrading coals and biomass yielding into three valuable products: • A fuel gas ready for power generation • A CO2gas stream containing >95%, ready for transportation to disposal or chemical fixation • A pre-calcined feed for cement clinkering consisting ofCaO and coal ash Thus power generation and gasification are independent. A promising industrial application is the combination of gasification and cement production. Then only one additional reactor is required and the precalcination mass flows have to be increased.

Jan 1, 2004

By S. D. Van Nort

Editor’s note: This is the first of two MINING ENGINEERING articles about the Grasberg deposit. The second, focusing on open pit mine development, will appear in the April issue of the magazine. The Grasberg porphyry copper-gold deposit of Freeport Indonesia Inc. lies within the Ertsberg Mineral District in central Irian Jaya, Indonesia. The Grasberg deposit was discovered during a drilling campaign initiated in the mid-1980s. Production at the open pit de- posit commenced in December 1989. The Grasberg copper-gold ore body is contained within a young igneous complex of dioritic composition that intrudes limestones of the Tertiary New Guinea Group. Alteration is typical of porphyry copper deposits worldwide except that higher grade primary chalcopyrite with significant gold values is associated with a centrally located zone of strong quartz stockwork. Irian Jaya comprises the western half of the island of New Guinea. The Ertsberg District lies 70 km (43 miles) inland from the Arafura Sea at an altitudeof3500 to45OOm (11,480to 14,764 ft). It straddles the Papuan fold belt. This belt forms the east-west trending chain of mountains that extend the entire length of New Guinea and is the site of numerous mineral districts.

Jan 1, 1991

By Wang Yingmin, Xu Zhuyun

There are 3 steps in the process of forming a mine ventilation system, (1) selecting a reasonable ventilation pattern (included pit shaft arrangement); (2) optimizing of the ventilation network and (3) computing and outputting the flow splitting results of the network with the optimal ventilating equipments selected. In the past, the first step was relied on artificial decision-making. In order to design a common ventilation system, some ventilation experts were needed to participate or do some examinations. Even so, the design made was reasonable only for those experts. If there is a mistake in the first step, then even the followed 2 steps are best done, the losses are very difficult to retrieve. So that, the first step is very important. The development of expert systems provided an efficient means and tool for all engineering fields. This paper presents an expert system of selecting mine ventilation pattern and pit shaft arrangement. After testing many times, it is shown that the system can perform the first step of designing a mine ventilation system, and can help the experts doing their study works more efficiently.

Jan 1, 1991

By Antti J. Niemi

Radioisotope tracers have so far been used for extraction of residence time distributions of flotation devices. They have also been proven applicable to evaluation of rate coefficients k of industrial flotation. It is now shown how values of k are scaled up on the basis of laboratory data on flotation and chemical conditioning, and of laboratory testing of samples from output of industrial conditioning vessel. Subsequently a model of conditioning and flotation is obtained which may be used for simulation and control of the steady state of the combined process. Discussion extends to modelling, simulation, CAD and opti- mization of flotation plants with re- circulation, and of ore dressing systems which consist of grinding and flotation plants.

Jan 1, 1990

By Leonard Harris

Mining is a business and, therefore, is expected to make profit for its investors, like any other business. It is a risky business which requires the expertise of professionals from several disciplines to make it successful in the finding, evaluation and development of a new mining venture. Many of the same disciplines, as well as experts in some other fields are required to operate the facilities once they are built. To manage all this, wide-ranging, versatile and sharp managerial skills are required. On the U.S. domestic front, the most important management issues requiring attention today and tomorrow are the increasing unwarranted attacks by anti-mining groups and legislators on the industry and aided by an unchallenged, but widespread, public view that mining is not necessary and damages the environment. Higher costs to mine and process deeper and more refractory ores are also of great concern. More and more attention is being focused, therefore, on overseas projects under the belief that undeveloped countries will recognize the economic value of mineral production and that lower costs can be achieved.

Jan 1, 1993

By Li Changgen, A. Bahr

The adaptability of pneumatic flotation cells for the flotation of sulfide ore and the conditions for sulfide ore flotation in pneumatic cells were investigated. The advantages of pneumatic flotation cells over mechanical flotation cells, as well as flotation columns, for the flotation of sulfide ore were demonstrated. Test results indicated that the Cu grade and recovery for concentrates obtained when using the pneumatic flotation cell were 1 % to 2% and 4%, respectively, higher than those obtained when using the mechanical flotation machine.

Jan 1, 1993

By A. J. Hendron, G. Mesri, R. M. Semple

Squeezing ground conditions in hard-rock tunneling are associated with fault zones containing brecciated rock and gouge. Gouge is a stiff clay-like soil that exhibits a propensity to creep. The ground loads applied to tunnel supports in squeezing ground are known to be significantly time dependent. Accordingly, an experimental and analytical study is presented that deals with soil creep and its application to the prediction of tunnel support requirements in squeezing ground conditions. Relatively undisturbed samples of fault gouge obtained from Straight Creek tunnel in Colorado and Pacheco tunnel in California are classified as very stiff to hard clays of low plasticity. Constant-load undrained triaxial compression tests are performed on these materials. A simple, three-parameter creep equation is developed that adequately describes the observed deformation of fault gouge with respect to applied stress and time. The equation is shown to fit existing creep data of various soil types. The creep equation is used to modify an existing continuum-mechanics solution to the time-dependent behavior of unlined and lined cylindrical openings in a creepsensitive medium under a hydrostatic state of stress. Assuming properties for the medium that are representative of the fault gouge materials tested, parameter studies are performed for unsupported and supported tunnels in squeezing ground. The analyses permit estimates to be made of the steel set supports required for tunnels at different depths in various squeezing ground conditions.

Jan 1, 1974

By G. D. Trump, F. L. Stanley

Spirals have become one of the most popular methods for treating fine coal. Unfortunately, spirals tend to produce an undesirably high specific gravity cut point and often misplace significant amounts of coal and/or rock. In the present study, a process-engineering tool known as linear circuit analysis was used to identify problems with traditional spiral circuits and to suggest alternative configurations. These analyses indicate that a modified rougher-cleaner circuit incorporating a middlings recycle stream offers the best option for improving performance while maintaining a reasonable circulating load. In light of this finding, a full-scale test circuit was installed and evaluated at an existing preparation plant. Data obtained from the plant tests indicate that the new spiral circuit can simultaneously reduce the cut point and improve separation efficiency. Preliminary economic analysis show that the new circuit provides an attractive payback on capital investment.

Jan 1, 1999

By G. P. Brahmaprakash, K. A. Natarajan, N. Jyothi, K. N. Sudha

Some important electrochemical aspects involved in the bioleaching of mixed sulfides have been discussed with reference to selective sphalerite dissolution from different binary mineral combinations. Combination potentials and galvanic currents were measured in different binary combinations of sphalerite with other minerals such as galena, chalcopyrite and pyrite in order to under- stand the electrochemical dissolution behaviour of sphalerite when coupled with other minerals. The effect of applied DC potential was also studied with reference to selective sphalerite dissolution from a binary mineral mixture. An application of a potential of -500 mV (vs SCE) was found to enhance bacterial growth as well as selective sphalerite dissolution. Factors influencing bioleaching of sphalerite under a negative applied potential are discussed.

Jan 1, 1989

By Arpad E. Torma

The electrochemical behavior of a zinc sulfide concentrate during the microbiological leaching was investigated using ZnS-carbon paste electrodes and a cyclic voltametric technique. The effects of Zn2 [ ] , Fe2+, Fe3+ and Cu2+ on the cathodic and anodic currents associated with zinc sulfide leaching in presence and absence of microorganisms, were assessed. The semiconductor nature of zinc sulfide was discussed in terms of ability of microorganisms to obtain their metabolic energy (through removal of electrons) from this high energy gap substrate. The intermediate electrochemical reactions involved in the ZnS leaching were described.

Jan 1, 1989

By Richard E. Gertsch

A century of experience with mechanical excavation machines is beginning to pay dividends to the mining industry. Mining is moving from mechanical excavators to mechanical miners. These mechanical mining systems are poised to make a significant impact on hard-rock mining, both underground and surface. Mechanical mining machines have had a long and successful career in coal and evaporites ("soft-rock") mining. Unlike most mechanical hard-rock mining, these systems actually mine ore. For example, the most productive underground method has been, arguably, longwall mining. Mechanical excavation machines are mostly used in civil tunneling or in driving mine openings such as vent shafts. Civil tunneling is a notable mechanical excavation success. Even with its high capital cost, a tunnel boring machine (TBM) can drive kilometers (miles) of tunnel at very low cost. In hard-rock mining, mechanical excavators bore tunnels, raises and shaft openings in the mine, but rarely mine ore. Like the soft-rock miners, their contribution to mining is important and their development must continue. Generally, they are used as excavators not miners. Current trends guarantee development of true general-purpose hard rock mechanical mining machines. Mechanical miners will become a complete mining system and will determine the design of the mine. Mechanical methods will reward the operator with lower costs and high productivity.

Jan 1, 1992

By W. Petruk

Mineral liberations that would be obtained by grinding an ore to a specific size can be predicted by analyzing unbroken ore pieces, and mineral liberations in ground ores and mill products can be determined directly by image analysis. Predictions of mineral liberations are made by measuring size distributions and textures of mineral grains by image analysis and using liberation models. Ground ores and mill products are analyzed to determine the proportion of mineral that is liberated, and the data are used to evaluate mineral behavior during mineral beneficiation. The liberation data for minerals in a suite of mill products from a circuit are processed by a materials balancing technique to calculate recoveries of minerals in different types of particles throughout the circuit. The liberation-materials balance data define mineral recoveries; define the behavior of an ore in a concentrator, pilot plant or bench test: and indicate whether recovery improvements are possible and/or feasible.

Jan 1, 1992

By Todd A. Duex

The Richmond Hill Mine has recently completed a reclamation plan to mitigate Acid Rock Drainage (ARD) which was identified at the toe of the former waste rock pile in 1992. Reclamation activities began in 1994 with the removal of ARD material from the waste rock pile and placement of this material in the former pit. This material was then isolated from the near surface environment by a low permeability capping system designed to minimize water and oxygen flow into the material. The capping system consists of, from bottom to top, six inches of limestone, 18 inches of low permeability clay liner, 4 and one-half feet of thermal barrier/drain layer, and six inches of topsoil. This capping system was completed in 1995. An extensive program is in place to monitor the effectiveness of the reclamation plan, and includes measurements on moisture content movement, temperature, oxygen content, and groundwater impacts. Monitoring has been ongoing since the completion of reclamation. This monitoring plan is demonstrating the success in isolating the material from the near surface environment and minimizing the impacts to the surrounding environment.

Jan 1, 2000

By Eugene V. Cilento, George B. Georgellis

The hypothesis that freshly-sheared quartz makes it more reactive in lung tissue than aged quartz was tested by its ability to stimulate superoxide anion (02-) release from single adherent pulmonary alveolar macrophages (PAM). Fresh quartz was prepared by grinding for 30 min and then used within 2 hr, while stale quartz was from the same stock but aged 15 days prior to use. Also, dipalmitoyl lecithin (DPL), the major constituent of lung surfactant coating the alveoli surfaces, was coated onto the particles. Release of 02- was measured after 40 and 180 min of direct contact with quartz dust (225 µg/ml). Fresh quartz was more reactive than aged quartz, as indicated by the 78 and 63% increase after 40 and 180 min, respectively. A time delay and suppression of 02- release was observed in the ability of the DPL- coated fresh or stale dust to stimulate PAM. These results supported the hypothesis that the natural process of surfactant coating of inhaled particles in the alveoli may play a role in their phagocytic removal by PAM.

Jan 1, 1991

By Thomas F. Martin

Contract 75-124-211 extends along the Chicago River from Roosevelt Road on the south to Ogden Avenue on the north. In addition a branch tunnel runs east from approximately mid-project ending near Lake Michigan. The contract was bid on December 14, 1977 with three joint-ventures submitting bids. Of these the joint venture of J.F. Shea Co., Inc. Walnut, California, (Sponsor), Peter Kiewit Sons' Co., Omaha, Nebraska and Shea Company and Associates, Walnut, California was low with a bid of $101,976,680.00. The MSD awarded the job to the Joint-Venture on January 5, 1978 with a scheduled completion date of January 23, 1983. The project consists of the following major items of work: (1.) A 25'-0" minimum diameter Construction Shaft, 220 feet deep (2.) 13,726 Linear Feet of 30'-0" Concrete lined Tunnel in rock (3.) 6,648 Linear Feet of 13'-0" Concrete lined Tunnel in rock (4.) Seventeen concrete lined Drop Shafts varying in finished diameter from 4'-0" to 12'-0", and each approximately 250 feet deep with chambers and connections to the tunnels varying from 100 to 1300 feet in length.

Jan 1, 1979

By Chris Crowl

Employee involvement does not directly correlate to performance improvement. A key ingredient is the introduction of new Human Resource Systems that promote both performance improvement and employee involvement. Many organizations have tried to use employee involvement as the ''fixer" of performance issues-and seen their performance deteriorate further. They failed to realize that the entire human resource strategy must be connected to the goals of performance improvement and that greater employee involvement is only one tool in that strategy. So what are Human Resource Systems? These are systems that all managers use to get work done. Most of us are familiar with basics such as planning, assigning work, checking progress (auditing), completing assignments. We also commonly think in terms of staffing, training, compensation, or corrective action. All of these are human resource systems. All must be designed to support what you are trying to accomplish with your people. We call that the Human Resource Strategy. Let's examine one part of a total strategy intended to support more employee involvement at Kennecott Utah Copper-the hourly job structure. The design of hourly jobs directly affects how many employees of different capabilities are required to get the work done. It begins to answer some fundamental questions: • What are the roles and accountabilities of each employee? Do they have enough information to make decisions, to take responsibility for their work?

Jan 1, 2004

By Denis Murphy, James Gusek, Carl Mann, Thomas Wilderman

An active underground lead mine produces water having a pH of 8.0 with 0.4 to 0.6 mg/L of Pb and 0.36 mg/L. of Zn. This water is pumped at the rate of 1.200 gpm into a five-cell, bioreactor system covering about 5 acres. The gravity flow system is composed of a settling basin followed by two anaerobic bioreactors arranged in parallel which discharge into a rock filter polishing cell that is followed by a final aeration polishing pond. The primary lead removal mechanism is sulfate reduction/sulfide precipitation. The discharge has met stringent in-stream water quality requirements since its commissioning in 19%. However, there have been startup and operational difficulties. The system was designed to last about 12 years, but estimates suggest a much longer life based on anticipated carbon consumption in the anaerobic cells.

Jan 1, 2000

By Heinz Distelmeier

The New Austrian Tunneling Method was, as is well known, developed from conventional rock tunnelling. In Germany about 10 years ago the NATM began to be applied to partially stable soils by incorporated excavation and support methods to allow its use with these soils. The advantages of this tunnelling technique - adaptability, ecomomy, and quality have resulted in its widespread usage. Today, about 85 % of all mined tunnels in Germany are produced with this technology. This rapid development has resulted in about 40 companies operating within a geographical area about the same size as the state of Illinois that are capable of utilizing the NATM. In most cases German contract/award procedures allow the contractor to develop alternate design and plans. As a result of this flexibility and intense competition, safety factors have been gradually reduced to the lower limit of what could be regarded as demonstrably safe, and the utilization of the NATM has expanded to include higher risk conditions, namely * excavating larger cross sections. * working with less overburden. * work undertaken under less stable soil conditions.

Jan 1, 1983

By K. J. Stanaway

Syngenetic concentrations in clastic sediments of valuable mineral particles with specific gravities exceeding that of quartz constitute placer deposits. Two fundamentally different modes of concentration characterize "trap" and "bed" placer variants. Trap placers originate during sediment erosion or reworking. Bed placers form during episodes of sediment accumulation in a variety of depositional environments and lithofacies where mineral supply and fluid dynamics are favorable. Because trap placers are thin and generally limited in area, they rarely yield economic heavy-mineral deposits. They can become economically significant if they contain more valuable "heavies," such as gold, or if they occur within or very close to much larger but characteristically lower-grade bed placers.

Jan 1, 1993