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By Thomas O. Glover

Cameroon's mineral industry continued to be dominated by crude petroleum, The economic development of the country depended on the production and export of crude on. Output was estimated to be 49 million barrels in 1985 compared with 56 million barrels in 1984 and 47 million barrels in 1988. The country's only refinery consumed approximately 12% of the daily production of crude oil while operating at slightly over 50% capacity. The refinery output, however, supplied the domestic need for motor fuel and heating oils. Cameroon's economic prospects were heavily dependent on the oil sector, which bad been responsible for the recent strong growth in the economy. The country consistently sought to avoid the problems associated with an overdependence on oil and followed a relatively broad-based development strategy, using oil revenues to sustain and encourage growth in other sectors. Approximately 75% of the gross domestic product (GDP) was attributed to the mineral industry in some form. GDP growth was approximately 6.5% during 1985.

Jan 1, 1987

By Curtis H. Elder

In studies conducted by the Bureau of Mines, two test areas were hydraulically stimulated and exposed by mining: One in the Pittsburgh coalbed at the Vesta No. 5 mine, Washington County, Pa.; and one in the Illinois No. 6 coalbed at the Inland mine, Jefferson County, Ill. Induced fractures were contained totally within the coalbed with no adverse effect on the stability of associated rock strata. Induced fractures were vertical and were propagated normal to the direction of least residual tectonic stress. Gas production was increased fivefold to twentyfold by hydraulic stimulation.

Jan 1, 1977

By J. C. Nigro

Hematite-to-magnetite reduction kinetics were investigated mainly in CO-CO2 atmospheres at temperatures ranging from 500° to 1,000° C. Reduction rates were measured with a thermobalance, which recorded the weight loss as the specimen was reduced. Reduction data on both synthetic and natural hematite spheres showed good linearity of ro [1-(1-R)1/3] with time, t, up to over 85 pct conversion to magnetite; the rate coefficient (k[L], cm/min) obtained from the linear portion of the plot was used to characterize the penetration rate of the hematite-magnetite interface. Gas composition, porosity, and silica content were major factors affecting the rate. Temperature dependency of the reaction rate was small, yielding a mean activation energy of about 3 kcal/mole. Silica additions increased the reaction rate, probably through an increase in the effective surface area and diffusion; however, above 900° C, silica can react to form fayalite. Experimental data showed that the linear thickening rate of the magnetite layer, normally evidence of a chemically controlled reaction, can also be indicative of a reaction controlled by both mass transfer and diffusion. Evidence from this study indicates that the dominant rate-controlling factor in the reduction of hematite to magnetite at high temperatures is transport in the gas phase.

Jan 1, 1973

By J. W. Paul

This paper deals with the third phase of on extensive research on coal-mine ventilation factors. A comprehensive report of the entire work is in course of preparation, but abstracts of the various chapters are being prepared in order to make the results public as rapidly as possible. Parts I and II of this paper were issued Serial 2621 and Serial 2647 of the Bureau of Mines in July and October, 1924. They dealt with the resistance of unobstructed entry and the resistance caused by mine cars in untimbered entry. Description of the Tests After the resistance of unobstructed entry and of mine cars in untimbered entry had been determined by tests in the Experimental Mine, three different types of timbering were installed in the test section and the increased resistance caused by the timbering was determined.

Jan 1, 1925

By d&apos, Kathleen J. Amico

THIS summary appears in Minerals Yearbook volumes I and III, which cover mineral production in the United States, its island possessions, the Canal Zone, and the Commonwealth of Puerto Rico, as well as the principal minerals imported into and exported from the United States. The several commodity and area chapters contain further details on production. A summary table comparing world and U.S mineral production also is included.

Jan 1, 1964

By John C. Edwards

The Bureau of Mines has developed a time-dependent droplet vaporization model (in the absence of forced convection) that can be applied to the vaporization of liquid Halon 1301 droplets (vapor pressure at 300 K = 14 atm) sprayed from an extinguisher. It was found that rapid surface vaporization quickly lowers the droplets' surface temperature very near to the boiling temperature, and the vaporization becomes diffusion controlled. Although the lifetime of the droplet is proportional to the square of the initial radius of the droplet, the elapsed time prior to complete droplet vaporization is not proportional to the square of the droplet radius, as an equilibrium model would indicate.

Jan 1, 1982

By Donald R. Johnson

Apparatus developed by the Bureau of Mines for thermal analysis of oil shale was used to determine the thermal properties of shortite. Dissociation of shortite near 470° C occurs as an endothermic reaction that could consume significant quantities of heat in the oil-shale retorting process that produces shale oil. The shortite dissociation products undergo other thermal reactions that would not affect the retorting process. These reactions include crystal inversions near 365° C and 425° C and melting and decomposition endotherms above 500° C. Two separate reaction route for fusion and decomposition of the shortite decomposition products are dictated by the presence or absence of CO2 around the sample.

Jan 1, 1974

By Robert A. Jankowski, Ellsworth R. Spencer, Jay F. Colinet

Longwall mining is the most productive method of under- ground coal mining in the United States (U.S.), and record levels of production have been reached in recent years. These ever-improving production levels have the potential to generate significantly higher quantities of respirable dust. Consequently, the longwall industry continues to struggle with controlling dust liberation and maintaining compliance with the federally-mandated respirable dust standard. In response, longwall operators have increased the application of primary dust controls, airflow and water flow, in an effort to improve respirable dust control and reduce worker exposure. Pittsburgh Research Center (PRC) personnel conducted dust surveys at 13 longwalls operating throughout the U.S. and collected information to: identify current operating practices on these longwalls, identify the types of dust controls in use, document the levels at which these controls are being applied, and measure the respirable dust levels present. This data was analyzed to quantify the dust levels generated by the major sources on the longwall section and to evaluate the relative effectiveness of the control technologies in use.

Reduce longwall shearer operators' dust exposures by more effectively suppressing the dust generated by the upwind cutting drum. Approach Direct more of the shearer water supply to the upwind drum, thus reducing the shearer operator's exposure to respirable dust while making more efficient use of water. How Proportioning Permits More Efficient Use of Water On most longwall mining operations, the cutting action of the shearer drums is the primary source of dust. Al-though the amount of dust generated is directly related to the amount of coal and rock cut by the drum, the exposure or the shearer operators to dust depends more on their work position relative to the upwind drum. When cutting with the airflow, the upwind drum, cutting bottom coal and floor rock, is the primary generator of dust reaching the operators. The lead drum is downwind of both shearer operators and is thus of less concern. (See diagram). When cutting against the airflow, the lead drum is upwind-taking a full cut, including roof rock-and both shearer operators may be exposed to very high levels of respirable dust. Currently, water sprays mounted on the cutting drum provide the most effective method of controlling dust from longwall shearer drums, and all longwall mining operations use some type of bit flushing or cavity filling water spray system on the cutting drums. Bureau surveys of longwall operations, conducted as part of its research program to reduce respirable dust, have indicated that six longwalls with better than average compliance records use higher than normal water flowrates to the cutting drums. The average water flow to the shearers at these six operations was approximately 60 gpm-about 50 percent more water than is normally supplied to double-drum longwall shearers.

Jan 1, 1982

By George H. Johnson

An evaluation of the diamond-bit-performance data accumulated from core-drilling cherty limestone and cherty dolomite reveals that the percentage of core recovered and the physical characteristics of the bits and diamonds used are economically significant. One of the established trends, of particular interest to those engaged in diamond drilling, is that bits set with small, low-quality, West African drill bort are the most economical. Detailed analysis of the factors that affect diamond-bit performances, such as diamond size and quality, bit size and type, percentage of core recovered, and the physical characteristics of the bit matrices are assessed in the tables, charts, and discussion.

Jan 1, 1958

Decrease dust concentra¬tions of longwall face workers by keeping them up¬wind of the headgate stage loader and crusher. Approach Direct the face airflow from tailgate-to-headgate, the direction of coal transport. How It Works Ventilation is the primary method of dust control on longwall faces, and the most effective ventilation control is to put workers upwind of dust sources. Recent ad¬vances in longwall dust sampling by the Bureau have shown that on some faces, the headgate crusher and transfer points are signifi¬cant sources of dust -some¬times making up more than half of the total dust to which the face workers are exposed. Also, when the air is coursed from head-to-tail, the relative velocity between the air and moving coal on the face conveyor can cause dust entrainment from the conveyor, particularly if the coal is dry. On the faces where these dust sources are a signifi¬cant problem, they may be eliminated by coursing the air from tailgate-to-headgate, provided that the mine roof is stable enough to permit the necessary intake of the tailgate along with an aux¬iliary intake at the headgate.

Jan 1, 1982

By W. E. Robinson

Sixty samples, selected from a 2,300-foot core of the Green River Formation in Colorado, were studied to ascertain differences in the structure of the organic material present in the oil shale samples. Emphasis was placed upon relating differences in the aromatic content of the insoluble kerogen and the alkane content of the extractable material obtained from the selected samples. The methods used in determining these differences consisted of fractionation of the soluble material, carbon and hydrogen analysis, volatile material determination, carbon residue determination, oxidation rate determination, and infrared analysis. In general, it was concluded that the organic material in this core does vary in chemical structure and that same of these variations resulted from factors related to depth of burial. Other observed changes in structure of the organic material were not depth-dependent and resulted from other factors such as source material variations, biological alterations, or ecological differences.

Jan 1, 1971

Validate the premise that there is measurable seismic activity associated with abandoned mint lands and that this activity can be used to determine stability of the abandoned mine openings, failure cycle of these openings, and susceptibility of the area to surface subsidence. Approach The U.S. Bureau of Mines conducted field investigations at two geologically contrasting sites, Colorado Springs, CO, and the Allegheny Portage Railroad Historical Site near Cresson, PA, to demonstrate that developing monitoring technology can be applied to any site. An array of seven geophones (velocity-measuring sensors) were strategically located to encompass an area at each site where failure in the underground mine openings could be expected, based on historical, geological, and engineering information. How It Works Bureau research has effectively demonstrated that stress changes within a rock mass can stimulate the development of cracks and fractures, resulting in the release of strain energy that generates seismic waves. These seismic waves, traveling outward from their source, can be detected, and the point of origin can be located in three-dimensional space. Furthermore, these seismic signals contain information that defines the source mechanism and the conditions between the source and the receiving sensor.

Jan 1, 1992

By J. H. Perry

The Bureau of Mines is conducting research to determine the effectiveness of long holes in degasifying an area of the Upper Split of the Lower Sunnyside coalbed at Kaiser Steel Co.'s Sunnyside No.1 mine. These holes were drilled from the two outside entries of a section that was closed to mining because of excessive methane emissions. Two holes drilled to 430 and 450 feet produced initial gas flows of 160,000 and 127,000 cfd, respectively. Sixteen days after the completion of the second hole, the total gas production declined to just over 144,000 cfd. In 9 months of degasification, over 35 MMcf of commercial-quality gas has been removed from the coalbed. The combined gas flows declined to 106,000 cfd in the 9-month period. The two holes have reduced face emissions by about 40 pet.

Jan 1, 1978

By Michael J. Brnich

Since 1991, Pittsburgh Research Center (PRC-formerly part of the Bureau of Mines) researchers have recorded extensive interviews with 30 individuals who are experts in the area of mine emergency response. These individuals, who have an average of 35 years of mining experience and 29 years of mine emergency response experience, related stories and observations from events that they experienced during their combined 850 plus years in mine emergency response. The purpose of this effort was to gather information that could be passed on to both today?s and tomorrow?s mine emergency responders to train and guide them in handling future events. This is the first of two articles which report the responses that these experts gave when asked how they think people who may have to respond to a future mine emergency should be trained. During the interviews they discussed how training should be conducted, who should be trained, and what topics should be included. This article will cover the first two areas: what training methodologies would be most effective and who needs to participate.

Jan 1, 1997

Detemine the elastic properties and structural integrity of a rock mass in situ. Approach An acoustic device that transmits and receives high-frequency seismic waves between boreholes was designed, built, and field tested. How It Works The acoustic cross-borehole apparatus operates by sending a seismic wave from a transmitter in one borehole to a receiver in a second bore? hole which may be located as far as fifty feet away, depending on the wave transmission quality of the rock. By measuring the wave's travel time and the distance between boreholes, the acoustic velocity of the rock mass can be determined. Characteristics of the seismic wave arriving at the receiver (such as the wave velocity, amplitude, and frequency content) are related to the physical properties of the geologic media, as calcu-

Jan 1, 1982

By R. O. Kneisley

Rock mechanics measurements indicate that the present two-bed mine design used at the Big Island trona mine, Green River, Wyo., results in stable workings. Vertical pressure changes in the lower panel pillars and horizontal pressure changes in the lower bed roof and floor indicated negligible upper bed mining influence. Pillar stresses stabilized soon after upper bed mining was completed. Strata movements in the pillar ribs, roof, and floor were also negligible and stabilized soon after completion of upper bed mining. Using tributary area theory, the confined core approach, and studies of model trona pillars it is shown that increased extraction ratio is possible. A program of gradually increased extraction ratio accompanied by simple measurements should result in a mine design that includes both higher recovery and long-term stability.

Jan 1, 1981

By Forrest T. Moyer

THIS CHAPTER of the Minerals Yearbook contains injury experience and related employment information for the coal-mining, coking, oil and gas, peat, and native asphalt industries in the United States for 1962. Injury experience is measured by the number of injuries sustained per million man-hours of exposure in each industry. No attempt has been made to combine these data and present rates reflecting the mineral-fuel industries because the hazards of the separate industries are not comparable. Tabulations showing the trend of injuries and employment for all mineral industries are presented in volume III of the Minerals Yearbook. COAL The injury-frequency rate for the coal-mining industry of the United States increased less than 2 percent, according to reports received by the Bureau of Mines. The number of fatal and nonfatal injuries per million man-hours in 1962 was 45.86, based on final data for anthracite mines and preliminary data for bituminous coal and lignite mines.

Jan 1, 1963

Develop methods to detect and repair poorly functioning dust collectors on roof bolters. Approach In conjunction with a research project to reduce silica dust in coal mines, a variety of roof bolting machines operating under different conditions were examined to find out how much these machines were contributing to the silica dust problem. Results The investigation concluded that if the bolting machines' dust collector is properly maintained, very little dust can be measured in the air, even with minimal airflow over the bolter. Poor maintenance, however, frequently results in high dust levels. Three major problem areas were found. These were: (1) filter leaks, which allowed dust to escape, (2) accumulations of dust in the collection system, and (3) low airflow at the bit due to hose, fitting, and relief valve leaks.

Jan 1, 1984

Avoid errors in determining the amount of trace elements in overburden when core drilling samples, particularly as required by PL 95-87, the Surface Mining Control and Reclamation Act of 1977. Reason Metal additives present in certain drill stem joint lubricants appear to contaminate overburden samples. If these lubricants are used in assembling the drill string, they can interfere with the analytical methods used to establish concentration of trace metals. Errors In trace element determination appear to be as much as 30 times true concentration, and may falsely Indicate that the amount of trace element in the overburden exceeds the

Jan 1, 1981