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By J. K. Whyatt

In situ stress on the scale of a tunnel or mine may be distorted by geologic structures. The resulting variations of in situ stress have a direct bearing on the potential for mining-induced seismicity. New evidence from the Lucky Friday Mine collected by U.S. Bureau of Mines researchers, as well as a review of case studies, demonstrates that in situ stress variations affect the spatial distribution of mining-induced seismicity. Although overcore stress measurements have been useful in these studies, they are too expensive and, depending on conditions, may be too difficult, to use routinely in mapping stress variations. However, information from borehole and raisebore breakouts; deformation of mine openings; and patterns of seismicity, ground control problems, and rock burst damage can be used to build a stress database. This database can then be used in con-junction with maps of mine structure and geology and models of rock mass behavior to build a map of in situ stress variations. Such a map provides a means to anticipate patterns of mining-induced seismicity that are likely to be encountered and, hence, provide a means for planning appropriate measures to ameliorate rock-burst hazards.

Jan 1, 1995

By J. R. Dyni

The lacustrine Green River Formation of Eocene age in the Green River Basin, southwest Wyoming, contains the world's large resource of natural sodium carbonate in bedded trona (Na2CO3? NaHCO3? 2H2O). In this study, 126 billion tons are estimated to be present in 22 beds, ranging from 4 to 36 feet in thickness. These 22 beds underlie areas of about 50 to more than 775 square miles at depths ranging from about 650 to more than 3,000 feet below the surface. The total resource of trona ore in the basin for which drilling information is available is estimated to be about 149 billion short tons. The undeveloped deeper trona beds in the southern part of the basin may be exploitable by solution mining. Additional unevaluated sodium carbonate resources are present in disseminated shortite in strata interbedded with the trona and in shallow sodium carbonate brines in the northeast part of the basin.

Jan 1, 1995

By R. Hogg, R. H. Weiland, P. Bunnaul

The dewatering of flocculated clay suspensions by compression in a centrifugal field was investigated. The results were analyzed with respect to the direct applicability of centrifugal dewatering (as in solid-bowl centrifuges) and indirect applications to gravity sedimentation systems. An important objective of the study was to evaluate the self-weight effect using centrifugal forces to simulate consolidation of deep sediments. Experiments were conducted in which the sediment mass and initial structure were maintained constant while the effective sediment weight was varied by centrifuging at different speeds. The relationship between the limiting sediment density and the applied consolidation stress was found to be the same for both gravity and centrifugal consolidation, indicating that small-scale laboratory tests can be used to predict consolidation in deep beds. The effects of the initial structure were also studied using controlled variations in flocculation conditions. The results imply that, for the flocculated suspensions studied, the longterm consolidation behavior is relatively insensitive to the actual extent of flocculation.

Jan 1, 1995

By Debra W. Struhsacker

Waste characterization plays an essential role in proactive project permitting, design, reclamation, and remediation strategies. Traditional TCLP tests and chemical analyses used in many studies do not provide adequate data to predict the long-term geochemical behavior of the mineralized system. Mineralogic and geologic data are needed to assess the homogeneity of the system, the potential for acid generation or metals leachability, and the amenability of the material to traditional and unconventional closure and reclamation measures. The characterization efforts done from the evaluation stages through final closure can aid in better cost evaluations, more representative sampling, more effective neutralization and waste containment measures, and optimized reclamation designs.

Jan 1, 1995

By D. R. Kalasky, J. M. Mutmansky, B. Kolonja

This paper considers simulation of truck dispatching systems using maximum expected production of the truck-shovel system as the measure of performance. Two analysis methods are utilized: multiple comparisons with the best (MCB) and the combination of MCB with the variance reduction technique known as common random numbers (CRN). These two techniques are compared via simulation experiments. Results show that the combined procedure of MCB with CRN is the superior tool to use to reduce the total number of replications needed to ensure the specified probability of correct selection from a number of systems. In this case study, MCB with CRN reduced the variance by 29% and the number of required replications by 48%. Also, the MCB with CRN procedure narrowed the confidence interval by 18%.

Jan 1, 1995

By R. L. Amelunxen

P. T. Freeport Indonesia (PI) in conjunction with Crescent Technology Inc. has developed a method to predict the metallurgical performance of ores blends based on the behavior of their component ores. The question addressed in this paper is whether ores treated individually could be extrapolated to predict the behavior of a blend of ores. The work further investigates the use of modal analysis to establish individual mineral flotation kinetics in each of the ore zones. This information would lead to the prediction of grade-recovery curves of ores made up of those minerals. Nine samples of ore, representing various zones of FI's Grasberg ore deposit were tested metallurgically and examined microscopically. The same testwork was performed on blends depicting the 1994 mill quarterly feed. Flotation kinetics of the individual ores were then "mathematically" blended and compared to the results obtained from the quarterlies. The calculated kinetics of the actual blends of ore received by the mill were fed to the simulation program and compared to the actual mill performance.

Jan 1, 1995

By J. A. Organiscak

This paper describes the research con-ducted on bit wear and respirable dust generation conducted by the US Bureau of Mines (USBM) and West Virginia University (WVU), a member of the Generic Technology Center on Respirable Dust. The USBM investigated wear, energy and dust characteristics of various conical bit designs when cutting rock. WVU studied the functional relationships between wear, cutting force, energy, and dust of one conical bit type when cutting coal. The objective of the USBM study was to identify qualitative bit selection guidelines for cut-ting rock; WVU's research objective was to determine optimum bit replacement guidelines. These research studies both found that bit geometry (a function of bit design and wear) influences energy consumption and dust generation. Bit selection and replacement recommendations are given.

Jan 1, 1995

By Z. Yu

The effect of particle size on coal dewatering has been well recognized However, there are no systematic studies on ultrafine coal dewatering. The results discussed last year revealed the effect of flocculant type and coal wettability on the filtration of ultrafine coal In this paper, the differences in dewatering between -25 µ m ultrafine and -500 µ m fine coal with addition of flocculants, surfactants and oil-emulsions in vacuum filtration are further investigated Significant differences were observed in the reduction of the cake moisture. The utilized emulsions were found to be very powerful and promising filtration aids for both ultrafine and fine fractions of hydrophobic and hydrophilic coal

Jan 1, 1995

By Spencer R. Titley

Nearly three decades of intense research, corresponding with a period of unparalleled discovery and the advent of scientific advances and hypotheses of ore formation, has resulted in a great body process-focused research concerning how ore deposits form. The development of process models and their application has proceeded more or less in step. Discoveries have been made in mineralized regions such as provinces and districts but generally without a comparably developed understanding of why provinces and ore bodies exist and, except in general terms, where ore deposits are within districts and regions. The process of discovery is still referred to as search and exploration budgets are heavily weighted toward exploration drilling.

Jan 1, 1995

By Steve Wirch, Robert Jankowski

The issue of dust control in underground coal mines has been extensively studied by both government and industry. This research work has resulted in many techniques which control the dust or help miners avoid it. Control techniques either prevent the dust from becoming airborne or cleanse the air before it can be inhaled. Avoidance measures minimize the exposure of miners to the airborne dust by blowing the dust away from work areas or making it unnecessary for a miner to occupy a dusty region. One of several successful dust control measures in continuous miner sections is the use of a machine mounted scrubber which cleanses the air and helps to prevent the contaminated air from reaching areas frequented by mine personnel. Research on the application of scrubbers on longwall shearers began in the 1970s and continued into the 1980s. The most successful projects showed only moderate improvement when a scrubber system was mounted on a longwall shearer, and the less successful projects actually increased worker dust levels. There are many reasons that scrubbers have not been successfully applied on longwalls. The most significant of these is that longwalls have across the face ventilation and generally have high face air flows. Scrubbers tend to work best when they are the primary cause of ventilation. Therefore, their capture efficiencies on longwalls tend to suffer because of the exposure of the drums to the primary airflow. Other reasons scrubbers have not been implemented on longwall s include the successful application of an excellent water spray system, effective cutting techniques, and dispersion of dust sources. These techniques can help control drum generated dust, increase production, and limit the relative effectiveness of a scrubber.

Jan 1, 1995

By Gail Moulton

Searles Valley is located approximately 125 miles northeast of Los Angeles in the Basin and Range Province. Occupying the lowest part of the valley is Searles Dry Lake Playa, which is about 9 miles long and 7 miles wide. Three major subsurface evaporite horizons have been identified and are termed from bottom to top, the Mixed Layer, Lower Salt and Upper Salt. The evaporite beds were formed by desiccation of runoff from the eastern Sierra Nevada during Quaternary time. The saline beds are generally brine saturated with the important ions being sodium, potassium, carbonate, bicarbonate, sulfate, chloride and borate. These ions are present in the brines in various concentrations and have combined to form the minerals halite, hanksite, trona, nahcolite, burkeite, borax, thenardite, sulfohalite, glaserite and others. North American Chemical Company selectively pumps the interstitial brines to feed their chemical plants located on the western edge of Searles Lake. Minerals have been mined since 1873, beginning with borax and trona scraped from the surface. Brine processing began in 1914 with potassium chloride and borax recovery. Expansions have added sodium sulfate and soda ash to the product mix. Currently, dredging of trona ore is also taking place.

Jan 1, 1995

By Jon Y. Kaneshiro, Blake D. Rothfuss, Gregory E. Korbin

A critical aspect of the planning, investigation, design, and construction of an underground excavation project is the portal. The portal is the primary access through which most if not all tunnel construction is carried out and it is the lifeline of the tunnel. Planning considerations include depth of cover, slope stability, economics of open cut versus shaft access, environmental impact, and contractor staging area. Critical aspects of planning, investigation, design, and construction of portals are considered by discussing portal design and portal failure case histories.

Jan 1, 1995

By S. Shankar

Available literature on the effect of re-entrainment on overall airborne dust concentration in mine airways or the fundamental mechanisms of coal dust re-entrainment in mine atmosphere is scant. Therefore, as part of the Respirable Dust Center's ongoing research, a three part study was envisaged: study of the re-entrainment phenomena of anthracite and bituminous coal dust particles in a wind tunnel under the influence of varying air velocities; study of the same in the Lake Lynn Laboratory Mine of the USBM with both airflow and walking by personnel causing re-entrainment; and mathematical modeling and computer simulation of the re-entrainment phenomenon. In this paper, results from the re-entrainment studies in the wind tunnel and the Lake Lynn Laboratory Mine are presented. Further, the results from the wind tunnel studies are compared with the results from in-mine studies conducted at the Lake Lynn Laboratory Mine of the USBM. Comparing the results from the two studies it was observed that increasing air velocity increased the rate of re-entrainment, but increased time of exposure decreased the airborne dust concentration. Compared to same size particles, a mixture of sizes created more airborne dust concentration when re-entrained. It was also observed that contribution of airborne dust concentration due to airflow was negligible compared to the contribution due to walking.

Jan 1, 1995

By Howard Brown

High purity, high brightness limestone deposits in the San Bernardino Mountains and Mojave Desert region occur in upper Paleozoic carbonate rocks which are part of an upper Precambrian and Paleozoic sequence that unconformably overlies crystalline basement. The Paleozoic strata are divided into formations and members, and correlated with strata of the inner Cordilleran miogeocline. The region has been affected by multiple Mesozoic intrusive, contact, and regional metamorphic events. Structure is complex, and includes polyphase Mesozoic folding and thrusting, and complex Cenozoic structures. The area continues to be seismically active. High brightness (white), high purity crystalline limestone deposits are uncommon because their formation is dependent on several geologic processes which include; 1) depositional environment, 2) contact and or regional metamorphism, 3) folding and faulting, 4) uplift and erosion, and 5) preservation through geologic time. The complex geologic history of the San Bernardino Mountains and Mojave Desert region has allowed the formation of several large high brightness, high purity limestone deposits which are currently being mined or will be mined in the future. Specialty Minerals, Inc. (formerly Ptizer), Pluess-Staufer (California), Inc. and Partins Limestone, Inc. produce high brightness, high purity limestone from several quarries in the San Bernardino Mountains. These active mines combined with undeveloped deposits controlled by Pluess-Staufer in the San Bernardino Mountains, New York Mountains, and Bristol Mountains in the Mojave area, contain proven and or indicated reserves sufficient to sustain production through the 21st century Detailed geologic mapping, intimate knowledge of stratigraphy, recognition of complex structures, sampling, drilling and assay data, are proven tools in the discovery and delineation of high brightness, high purity limestone deposits in the San Bernardino Mountains and Mojave Desert region of southern California.

Jan 1, 1995

By P. J. Suardini, S. K. Kawatra

A number of on-stream coal slurry analyzers are presently being developed and commercialized for measuring ash and solids in coal process streams, particularly around flotation circuits. The eventual goal of these efforts is to develop on-line quality control systems for flotation circuits and other fine-coal cleaning operations. As part of this on-line monitoring and control effort, it is important to gain a better understanding of the response of industrial flotation circuits to changing operating conditions. This paper summarizes the results from a detailed sampling program performed at an industrial coal flotation circuit in western Pennsylvania. The testing focused on evaluating the response of the circuit to changes in reagent dosages, operating conditions and feed compositions. The testing indicated that it is desirable to maintain high collector-to-frother ratios to enhance coarse particle flotation. The recovery of fine impurity particles was also proportional to water recovery, due to hydraulic entrainment. Key words: Industrial, Coal, Flotation, Circuit, Reagent, Response.

Jan 1, 1995

By D. B. Sikka, R. B. Bhappu

Porphyry-type copper-molybdenum (Cu-Mo) deposits typically occur in the Phanerozoic rocks and have been well-documented. During the past two decades, a number of porphyry-type Cu-Mo deposits that range in age from 1055 Ma to 2970 Ma have been identified in the Precambrian rocks of Australia, Canada, China, Finland, India. Namibia and Zambia. The Malanjkhand porphyry copper deposit M.P., India is estimated to contain 789 Mt (870 million st) averaging 0.83% copper (mill headgrade); 0.004% molybdenum; 0.2 g/t (0.006 oz/st) gold; 6 g/t (0.175 oz/st) silver and a cap of 7.5 Mt (8.2 million st) of oxide ore averaging 0.8% copper. The economic potential of the expanded copper mining milling, smelting and refining complex is expected to yield cathode copper 118.6 kt (130,700 st); molybdic oxide 830 t (914 st); gold 1.9 t (61,732 oz); silver 46.6 t (1.5 million oz); sulfuric acid 240 kt (264,500 st), copper from leach dumps 11.5 kt (12,600 st); nickel 24 t (26,400 st); cobalt 84 t (92,600 st); bismuth 16 t (17.6 st); selenium 48 t (53 st), tellurium 4.8 t (5.3 st).

Jan 1, 1995

By J. Gathje

Normal process development for pressure-preoxidation treatment of refractory gold ores starts with laboratory batch autoclave tests. That is followed by continuous autoclave pilot-plant testing to confirm the process options. This scheme will generally provide good information showing the effects of grind size, time and temperature. And it will indicate whether autoclave preoxidation will produce solids that are amenable to cyanidation for gold recovery. However, several test programs have shown that the cyanide-leaching responses of treated solids from the batch tests can differ considerably from those achieved by the continuous pilot-plant autoclave. It has become apparent that laboratory investigations should extended to include the use of a semicontinuous autoclave test procedure. Santa Fe Pacific Gold conducted several months of metallurgical investigations for a major refractory sulfide gold deposit. The project started with batch tests to investigate and optimize the primary variables, such as grind size, retention time and temperature. These tests were conducted using a representative whole ore composite.

Jan 1, 1995

By L. F. Zeiler

In the past, health concerns in coal mines have primarily centered on those elements which have been essentially inherent to the mining environment. These would include respirable coal mine dust, respirable crystalline silica, excessive noise levels, and diesel exhaust particulates. Commercially-available chemical products are prevalent on mine property. These potentially toxic materials are chemical formulations that can degrease, clean, and lubricate metal parts, separate coal from rock in float/sink operations, and aid in roof consolidation, among other uses. As the general public has become more aware of the hazards of chemical exposures, miners have likewise become more concerned about working with an ever-expanding variety of chemical products on the job. Often, product or chemical specific hazard communication training is inadequate or ineffective, and miners do not know exactly what the ingredients are in the products they handle, or the health hazards involved with their use or misuse. Currently, the Mine Safety and Health Administration (MSHA), by law, enforces 1972 Threshold Limit Values (TLV). MSHA is making preparations to adopt new personal exposure limits for enforcement. The values given throughout the article are 1994 TLV's and are not enforcement standards, but are used for discussion purposes. They reflect the current scientific thinking regarding personal exposure to these chemical agents. An overview of these products is presented, and the potential health hazards associated with their use are discussed. Controls needed to prevent overexposures, such as proper handling procedures and personal protective equipment, are covered. Methods used to collect and identify contaminants are presented.

Jan 1, 1995

By Martin L. Smith

Mine waste characterization and risk assessment currently focesses on water quality and largely ignores boththe charteristics of the wastes themselves and how wastes interact with the environment. Characterization of the parameters that control contamination of pore waters and their migration can quantitatively assess risk and remediation strategies in terms of cost effectiveness and risk reduction. Since mine waste characteristics are spatial, geostatistical methods should be used for characterization and assessment. A number of geostatistical methods are reviewed in terms of their application to mine waste sampling, modeling and risk assessment and management.

Jan 1, 1995

By Terry Mudder

Long-term anaerobic biochemical treatment for draindown of residual solutions is a cost-effective way to close a heap-leach pad. This article presents a laboratory evaluation of anaerobic biochemical treatment of cyanide heap-leach pad solutions. The traditional approach to heap-leach pad closure is to rinse the pads with multiple pore volumes of fresh or recycled treated water. The effluent from an initial rinse is often treated and recirculated until the solutions passed through the heap meet the appropriate numeric and narrative water quality standards. Column rinsing tests are completed during project planning to determine the number of pore volumes of fresh or recycled treated water required to rinse the pad to meet long-term closure requirements. A traditional closure plan generally includes provisions to sample the rinse effluent and rinsed solids (the Meteoric Water Mobility, Procedure or USEPA 1312) to verify that chemical requirements are being met.

Jan 1, 1995