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By P. Lin, S. G. She

"In June 1985, Chinese Society for Rock Mechanics and Engineering (CSRME) was established. During the past 30 years, various major achievements are made in the discipline of rock mechanics and rock engineering field, especially in the last ten years. This paper will discuss the main rock engineering progress in association with China National Science and Technology Awards, “973 Program”, and “Tan Tjongkie Lecture”. The current status of rock engineering in China and some hot problems are summarized. Furthermore, some suggestions are given for addressing those problems. INTRODUCTIONThe modern concept of rock mechanics and engineering was initiated and developed after the Second World War. In this regard, the International Society for Rock Mechanics (ISRM) was established in 1962, subsequently further promotes its development. In June 1985, the Chinese Society for Rock Mechanics and Engineering was established. Various chief scientists, including professors Tan Tjangkie, Pan Jiazheng, Sun Jun, Wang Sijing, Qian Qihu, have made their huge efforts to the development of Rock Mechanics and Engineering in terms of the large-scale rock engineering projects in China.The achievements in the last 30 years significantly promote the development of China in different fields, such as energy, transportation, national defense and other national economy and major infrastructure facilities (Wang et al. 2004; Qian 2010, 2011). In other words, these projects also promoted the science and technology progress in rock mechanics and engineering across the world. Reviewing and analyses of the experiences on those key rock projects are beneficial to its technological development. She and Dong (2013), in view of literature statistical analysis, discussed the status and research progress in rock mechanics field associated with the last 30-year China's developments, including the rock strength and deformation theory, rock fracture and damage mechanics, the constitutive relation of rock dynamics, rock field coupling, rock reinforcement and stability analysis, etc. The challenging issues in rock mechanics were also proposed, which are the main concerns in rock engineering practices, engineering exploration, design, construction and operation."

Jan 1, 2015

By Kyle A. Perry

Pillar design formulae have existed for decades, and the guidelines for design stability factors are generally accepted by regulatory agencies and broadly used within the coal industry. Nearly all design pillar formulae are based on geometrical parameters of pillars resulting from empirical investigations, with primary focus on the pillar width-to-height (W/H) ratio and associated shaping constants from regression. The most widely used modern pillar design formula in the coal industry, the Mark- Bieniawski equation, also adheres to this principle. Common practice when applying Mark-Bieniawski equation is to use a coal compressive strength of 900 psi. This reduces the design equation to sole dependence upon geometry. However, recent studies have shown that pillar strength is highly dependent on roof and floor properties, particularly the interfaces between the roof-pillar and pillar-floor. This study utilized numerical modeling using FLAC3D to evaluate the relative effects of varying roof and floor interface and mechanical properties. The results confirm that pillar strength is significantly influenced by the properties of the coal pillar interfaces with roof and floor. The mechanical properties of the roof and floor material have only a minor impact on pillar strength when compared with interface effects. These results were used to formulate design recommendations for existing pillar design methods.

Jan 1, 2013

By Ju-hyung Ha

New automated curing system for mass concrete has been developed to improve the quality of concrete structure and to save construction time and cost. The principle of this system is the automated water circulation system of heated curing water. Applied curing water on the surface of mass concrete keeps the temperature difference between center and surface of the structure below the threshold of specification. Mock-up test and field application have been conducted to investigate the performance of this system. In the results, new automated curing system reduced the chance of thermal crack occurrence and improved quality of the concrete structure as well.

Aug 1, 2013

By K. K. Clark, W. H. Somerton

The feasibility of reducing pressures needed to fracture formations by heating the borehole intensively has been investigated on a laboratory scale. Reductions in fracture pressures of heated Bandera, Berea and Boise sandstone cores were observed at various confining pressures, simulating reservoir stress conditions to a depth of 5,000 ft. Both permeable and impermeable borehole boundary conditions were tested. Three heating conditions were used in the tests. One group of samples was heated in a furnace to a temperature of 600C, cooled to room temperature., and then tested for fracture pressures. Two other groups of samples were heated with a borehole heater to maximum borehole wall temperatures of 625 and 792C, then cooled and tested. In all cases, heated samples showed substantial reductions in fracture pressures compared to unheated samples. The higher temperature borehole heated samples showed the greatest reduction, amounting to 70 per cent in the extreme case. In actual application to wells, it was concluded that fracture pressures may be reduced by 20 to 50 per cent by intensive borehole heating before fracturing. INTRODUCTION Hydraulic fracturing of oil and gas wells is an accepted and effective technique for increasing well productivity in many areas, but is notoriously unsuccessful in other areas. The technique becomes less interesting for production stimulation purposes when excessive fracture pressures are necessary. Formations which do fracture but require high pressures, probably form horizontal fractures. There is good evidence to indicate that some formations do not fracture at all, but yield plastically under high pressure. Thus, any technique which will make formations easier to fracture or will reduce fracture pressures is potentially interesting to petroleum producers. Horizontal fractures generally occur in planes of weakness, such as bedding planes, and at pressures equaling or exceeding the effective overburden stress. In the unusual case where planes of weakness do not exist, a slightly higher pressure must be applied to overcome the tensile strength of the rock. In general, high fluid-loss fracturing fluids are conducive to the formation of horizontal fractures.1 Vertical fractures, when they do occur, are initiated at pressures generally lower than overburden pressure and are favored by low fluid-loss fracturing fluids or impermeable boreholes. The pressure necessary to create a vertical fracture in an impermeable, elastic medium can be predicted from the so-called "thick-walled cylinder" equation: Pf = 2 or+ st.............(1) where pf = fracture pressure or = radial stress st = tensile strength of medium. This equation indicates that to fracture it is necessary to overcome a tangential compressive stress, induced by and equal to two times the radial confining stress, plus the tensile strength of the medium. If the above equation held strictly true for rocks, very little could be done to reduce fracture pressure. The tensile strength of the rock might be reduced somewhat, but any change in st would be small compared to the magnitude of the tangential stress at reasonable subsurface depths. Laboratory tests have shown that actual fracture pressures exceed values predicted from Eq. 1 by factors of 1.4 to 28.6.1,2 Eq. 1 thus does not properly describe the

Jan 1, 1966

By Tim Miller, Michael M. Murphy, John L. Ellenberger, Gabriel S. Esterhuizen

"A limestone mine in Ohio has had instability problems that have led to massive roof falls extending to the surface. This study focuses on the role that weak, moisture-sensitive floor has in the instability issues. Previous NIOSH research related to this subject did not include analysis for weak floor or weak bands and recommended that when such issues arise they should be investigated further using a more advanced analysis. Therefore, to further investigate the observed instability occurring on a large scale at the Ohio mine, FLAC3D numerical models were employed to demonstrate the effect that a weak floor has on roof and pillar stability. This case study will provide important information to limestone mine operators regarding the impact of weak floor causing the potential for roof collapse, pillar failure, and subsequent subsidence of the ground surface.IntroductionMassive roof falls extending to the surface at a limestone mine in Ohio have been studied collaboratively by the National Institute for Occupational Safety and Health (NIOSH) and the mine owners. This paper provides a summary of the sequence of events leading to observed instability and presents a numerical modeling analysis that investigates the role a weak floor can have on roof and pillar stability.This study builds upon previous NIOSH research in underground limestone mines undertaken by way of a survey that analyzed performance of pillars in 34 different stone mines in the Eastern and Midwestern United States between 2005 and 2009 (Esterhuizen et al., 2011). This survey led to the development of underground stone mine pillar design guidelines based upon a “stability factor” for the pillar system. The factor is compared to operational experience to determine ranges of values that are typical of stable pillar systems. A software package titled Stone Mine Pillar Design (S-Pillar) was developed for easy application of these guidelines (Esterhuizen and Murphy, 2011).Weak floor in the present case study departs significantly from cases included in the previous NIOSH research, in that none of the 34 study mines had weak floor issues. Moreover, this case study is the first in which a weak floor has been monitored routinely as roof falls are occurring. A detailed report on the observations and measurements taken at the mine has been published (Murphy et al., 2015). The previous observations led to the conclusion that although there were weak bands in the pillar, the weak floor was the significant defect that led to the instability issues. The pillars were initially mined in 2004, approximately 10 years before the instability issues began to occur. The objective of this study is to use numerical models to analyze a variety of floor strengths and the impact of moisture content to find the critical point at which the floor becomes unstable, leading to long-term instability issues."

Jan 1, 2015

By M Mohammad Khani

An economic block cave is dependent to the characteristics of the rock mass at stages of caving. These are cave initiation, propagation and ore flow. In this research, the rock engineering system (RES), first established by Hudson (1992) to solve complex rock engineering problems, is introduced and verified against the well-established caving parameters established by Laubscher. There are two types of factors influencing caving and these are natural (cannot be controlled) and induced (operator controlled). A RES based interaction matrix is developed by determining the rating parameters required to reproduce the caving database using Laubscher’s caving parameters. This provides the relative importance of the parameters in the interaction matrix. After discussing the rock mass caving process and identifying all the effective parameters, an interaction matrix is introduced to study the cave initiation of rock masses. The expert-semi-quantitative (ESQ) coding method is utilised to assign the numerical value to each parameter’s interaction. Thereafter, the interaction intensity and dominance of each factor in the system is determined to classify these factors. Finally, all the parameters affecting caving operation and their weights on the RES system are identified. This new application of RES in block caving is very efficient and useful for any stage of caving studies and helps experts to make decisions more accurately.CITATION:Mohammad Khani, M, 2016. The application of rock engineering systems to block caving to identify the effective parameters, in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 853–860 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

By D. R. Dolinar, J. Pablic, D. C. Oyler, T. P. Mucho

At a mine in central PA, high horizontal stresses have caused long running roof falls resulting in hazardous conditions for the miners and the premature abandonment of panels. Because of these conditions, the mine requested assistance of the National Institute for Occupational Safety and Health (NIOSH) in utilizing the 'advance and relieve method to mitigate the affects of horizontal stress on the mine roof. "Advance and relieve" mining involves the removal of a pillar or a portion of a pillar during development, thereby creating a cave along one side of the panel. Following cave development, the horizontal stress is relieved over the workings adjacent to the cave in the active panel. The mine has used this system in three panels with a significant reduction in stress damage and no large roof falls.

By E. J. Gleim

In keeping with past custom, it is the purpose of this publication to bring up to date previously published lists of equipment that meets safety standards of the bureau of Mines so that the mining industry may be informed as to the development and availability of equipment that can be used safely. The present lists supplement those in Bulletin 543. Permissible Mine Equipment Approved to January 1, 1953; Information Circular 7722, Permissible Equipment Approved During the Calendar Years 1953-54; and Information Circular [40], Permissible Equipment Approved During the Calendar Years 1955-56. These [ew] lists also contain equipment meeting those standards revised since the last listing. A revision of Schedule 16C (now Schedule 16D4/) was officially approved on September 28. 1958. Schedule 29 was another standard revised in 1958. The revision was officially approved on September 8. 1958, and is known as Schedule 29A5/ .

Jan 1, 1960

By N. W. Xu, M. D. Wei, F. Dai, B. Li

"Chevron notched samples achieve general acceptance for measuring the Mode-I (opening mode) fracture toughness of rocks. The cracked chevron notched semi-circular bending (CCNSCB) sample, which is developed from the International Society of Rock Mechanics suggested the cracked chevron notched Brazilian disc method, has recently received much attention. However, these chevron notched methods have not been fully mastered, some ideal assumptions based by their theories and formulas, such as the straight-through crack assumption (STCA), have not been verified detailedly. Fractures of CCNSCB specimens were numerically simulated considering different heterogeneities, geometrical and mechanical parameters. The results show that, the real fractures of CCNSCB specimens are never satisfied with the STCA. In fact, micro fractures not only occur in the notch tip but also the two chevron edges. Consequently, the crack front features prominently in a shape of parabolic curve, far from being straightthrough. Moreover, curvature of the crack front is only affected by shape of the chevron ligament. Cracks usually start from two sides of the notch tips rather than center of the notch width, and propagate deviating from the postulated fracture routes. These fracture mechanisms induce errors with the measurements, and thus more attentions should be paid to the real fractures of the chevron notched samples for measuring fracture toughness more accurately. INTRODUCTIONWith the increasing requirement of people for resources and energies, frequent rock engineering activities have been conducting, such as underground excavation, oil exploration and deep burial of nuclear waste. Many problems appear in rock fracture. Consequently, there are more and more attentions paid in rock fracture mechanics due to its broad application prospects for solving these engineering problems. Since Mode-I (opening mode) fracture is the most common failure mode in rocks, Mode-I fracture toughness is a primary parameter to predict rock mechanical properties in actual engineering, and thus its accurate values are necessary to the researches of rockburst, rock mass slope stability, rock cutting, hydraulic fracturing, tunneling, et al. Therefore, it is thus significant to evaluate and study relevant methods to obtain the reliable value."

Jan 1, 2015

By J. Hantelmann

The Yanaquihua gold-bearing vein-fault deposit is associated with a sinistral strike-slip fault system, hosted within granite to granodiorite of the Tiabaya Super Unit of the Coastal batholith. The deposit is located near the northwest striking Cincha-Lluta-Incapuquio (System 11) regional fault system . Mineralization exhibits vertical trends and is primarily controlled by sub-vertical vein-fault structures. Mineralization includes variably abundant quartz, clay minerals, pyrite, calcite.

May 1, 2008

By Nicolás Guevara Alvarado

Las energías renovables son aquellas que se producen de forma contínua,+ y cuya disponibilidad energética es mayor que las fuentes de energía convencional. Sin embargo, su utilización es escaza, así como el desarrollo de las fuentes de energía convencional. En ese sentido, el presente trabajo plantea medidas que incrementen estas fuentes de energía, las preserven y mejoren su relación con el medio ambiente a través del avance de energías alternativas como la éolica, solar, etc.

Apr 1, 2014

By Donelson A. Robertson

Literature was searched and cases of alleged water well damage were investigated. Occurrence of ground water in Appalachia is primarily in low yield, fractured, water table aquifers. Four test sites were chosen based on geographic and geologic diversity. Test wells were drilled at each site and base line data on water quality, static water level, and drawdown characteristics were obtained before surface mining commenced. Blast induced ground vibrations were measured at the surface by the wells at levels up to 5.44 inches per second maximum resultant particle velocity. Measurements made at the bottom wells indicated that vibrations were considerably attenuated at depths of 140 to 160 feet. No direct evidence of change in water quality or well performance was produced by blast vibrations, but removal of downslope support by excavation does cause lateral stress relief which permits the water-bearing fractures to become more open. This additional storage capacity causes the static water level to drop and for well-bore permeability to improve. Static water level recovers if sufficient recharge is available and well performance is improved.

Jan 1, 1980

By L. Gutierrez, M. Pawlik

The rheology artificial mixtures of bitumen with fine quartz of varying bitumen content, as well as actual oil sand ores, was investigated under different physicochemical conditions (pH, temperature). All rheological measurements were conducted using a Haake Rotovisco VT550 rotational viscometer, connected to a fixture specifically designed to measure properties of settling suspensions. It was found that at low bitumen contents (1 %, wt.) the pH of the slurries was the most important parameter that controlled the rheology of quartz-bitumen slurries. At higher bitumen contents (10%, wt.), it was a combination of high temperature and high pH that gave the lowest apparent viscosities and yield stresses of the model mixtures. These model observations correlated well with the rheology data obtained for slurries of actual oil sand ores. The overall results were discussed in terms of aggregation-dispersion phenomena between bitumen and mineral particles.

Jan 1, 2009

By S. Storchheim

MORE and more attention is being paid to the bonding of metals in their solid states. For a better understanding of this technique for joining metals and how it is affected by changes in temperature, pressure, and time at temperature and pressure, a detailed report concerning nickel to aluminum bonding has been published.' In order to broaden the knowledge accrued, some additional work concerning solid state joining of aluminum to copper and aluminum to zirconium was performed. The investigation of the Al-Cu system was considerably more extensive than the investigation of the Al-Zr system. For the A1-Cu system, not only were tensile sudies made but intermetallic penetration rate investigations also were carried out. The effect of temperature on intermetallic penetration rate for the A1-Cu system was determined at 11 tsi pressure, held 2 min. Procedure Apparatus: The hot pressing technique was the means of solid state reaction used and required the equipment depicted in Fig. 1. The following procedure was involved: The two metals to be reacted were placed in an aquadag-lubricated 18-4-1 tool steel die, 16 in. high by 1.440 in. ID, between punches of 1.366 in. diam made of the same material. A thermocouple well was located in the die body 3½ in. down from the top of the die, while another well was located centrally in the bottom punch 8½ in. from the bottom of the die. This die assembly was located in three cylindrical ceramic heating furnaces placed in tandem. Each furnace was controlled individually by a Variac power transformer. In turn, the die and furnaces were placed in a water-cooled stainless steel pot which could be evacuated. A cover, which contained a centrally located Wilson seal with an 18-4-1 1 in. diam ram running through it, was bolted on the pot. After sealing, the pot was evacuated by a roughing pump to 200 microns pressure, after which a diffusion pump was used to bring the pressure down to 5 to 15 u. At this pressure, the furnaces were turned on. As soon as they started to heat, out-gassing of the entire unit raised the pressure to 30 to 400 p. By the time the specimens were at temperature ready to be pressed, approximately 4/2 hr, the vacuum pumps had re-established the 5 to 15 u pressure. Once the desired temperature was reached, the required pressure was applied for a predetermined length of time to the 1 in. ram, through to the top punch, and to the specimen. When the time for keeping the specimen under pressure had elapsed, the pressure was released, the energizing coil current turned off, and the assembly allowed to cool. After cooling, the die was removed from the pot and the specimen was ejected. Specimen Preparation: Two different types of specimens were made for this investigation. One was for subsequent tensile testing, while the other was for determination of intermetallic alloy zone penetration into the parent metals. Tensile Bars—Commercially rolled copper pieces in. thick or zirconium sheet pieces 1/32 in. thick and 1.366 in. diam were placed between commercial 2-S aluminum rod 1 in. thick and 1.366 in. diam. This sandwich in turn was slipped into a 2-S aluminum sleeve 1.438 in. OD and 1.370 in. ID. This sleeve lined the couple up and prevented the aquadag lubricant from getting in between either the A1-Cu or Al-Zr interfaces. Immediately prior to the specimen assembly, the copper or zirconium was abraded on the flat surfaces with 320 grit silicon carbide paper, producing clean smooth surfaces. The aluminum was chemically cleaned just before assembly by: l—degrease in acetone, 2—distilled water rinse, 3—immersion for 3 min in 5 pct NaOH at 70" to 80°C, 4—distilled water rinse, 5—immersion for 2 min in 50 pct HNO3 solution at room temperature, 6—distilled water rinse, and 7—drying in a blast of gas. After the A1-Cu sandwiches were hot pressed and ejected, the specimens were machined such that the aluminum sleeve was removed, and the remaining aluminum was then threaded; the bar so produced was tested later for tensile strength. In all the instances where Al-Cu couples were tested, the specimens broke during the test at the Cu-A1 interface and never within the aluminum or copper. The ultimate tensile strength values at times showed considerable scatter for a set of given reaction conditions. Because of this, as many as three to five specimens were made for a particular set of conditions. The trend of the average tensile strengths obtained was not as conclusive as was the trend of the maximum tensile strengths, the latter values being obtained under optimum reaction conditions. Therefore, the values of ultimate tensile strength given herein are maximums.

Jan 1, 1956

By H. Jung

The microstructures and grain sizes of nanocrystalline Co and Co-1.1 wt % P alloys were characterized by X-ray diffraction. The corrosion properties of as-deposited and annealed Co-l.l wt % P alloys and pure nanocrystalline Co were studied in a deaerated 0.1M H2SO4 solution using electrochemical measurements and XPS surface analysis. Potentiodynamic polarization testing and impedance measurements revealed that an addition of P to pure nanocrystalline Co improved the anodic-corrosion resistance, however, this enhanced corrosion resistance was compromised by the heat treatment process at 350 and 800°C. The corroded surface of annealed nanocrystalline Co-1.1 wt % P at 350°C exhibited a more porous P-enriched layer compared with the as-deposited case. A sample annealed at 800°C corroded uniformly showing second-phase precipitates. The enhanced corrosion resistance of as-deposited nanocrystalline Co-1.1 wt % P was attributed to the elemental P on the surface that acted to hinder the anodic dissolution kinetics of surface Co following an initial selective dissolution of Co. However, at a higher anodic overpotential region, the superior corrosion resistance of Co-l.l wt% P alloys did not last because of the formation of a non-protective surface film consisting of mainly hypophosphite and phosphate as well as elemental P.

Jan 1, 2005

By Thomas Mütze, Petya Atanasova, Kai Bachmann, Urs A. Peuker, Thomas Leißner

"A method is presented for the evaluation of mineral processing by liberation and upgrading. The method bases on the plot of recovery of valuables versus the recovery of gangue (Fuerstenau upgrading curve). The locking curve of a feed material was plotted together with the upgrading curve in a Fuerstenau diagram. The assessment of liberation and upgrading is done by a comparison of surfaces formed by the curves and some characteristic lines of the diagram. This plot allows the calculation of two new quantitative measures for liberation and upgrading. Both parameters can be combined to a third parameter describing the quality of the whole technical setup for mineral processing by subtracting the upgrading parameter from the liberation parameter. The third parameter shows a positive value in cases of upgrading determined processes, a negative value in cases of liberation affected processes and about zero for processes affected equally by liberation and upgrading. Thus it is easily possible to distinguish between poor results in the mineral processing caused by insufficient liberation or poor results caused by insufficient upgrading. Preliminary results from two case studies, performed on two different ore types, are very promising illustrating the practical use of such an approach."

Jan 1, 2014

By Hani S. Mitri

Overhand cut-and-fill mining of narrow vein orebodies inevitably leads to the creation of horizontal pillars. As the thickness of the overlying crown pillar diminishes, stresses build up in the pillar. More often than not, this situation causes an increased level of seismicity and possible pillar burst. One well-known strategy to reduce the hazard of crown and sill pillar burst in cut-and-fill vein mining is that of destress blasting. The paper first reviews the methods used for the monitoring and assessment of potential pillar burst in narrow vein cut-and-fill mining. The influence of horizontal stress, mine depth and pillar thickness on stress build-up in the crown pillar is examined through a characteristic narrow vein numerical model. The paper then presents, with reference to three mine case studies, the benefits of destress blasting and the factors affecting its success as a ground control technique.

Oct 1, 2001

By L. Shang

In conventional continuous hot rolling processes, metals are usually reheated to a temperature such that the workpiece will maintain appropriate hot working characteristics as it proceeds through the rolling mill, assuming that the temperature is continually decreasing. Metallurgically, reheating will reduce micro-segregation in the as-cast material, may increase the as-cast grain size and will affect any second phase particles present in the as-cast structure. All these changes can affect the hot working characteristics, and the final as-hot rolled microstructure. In order to study the effect of reheating on AZ31 magnesium alloy, a plate sample was cast in a water cooled copper mould and a series of compression tests was performed at a temperature of 350 °C, strain rate 0.01 5-1, and strains from 0.2 to 1.0, after different reheating schedules. It was found that there is no significant difference in flow behavior between the as-cast sample and all but one of the reheated ones. The reheat treatment of the 'anomalous' sample was a two stage heat treatment; it was first reheated to 450 °C, cooled to room temperature, then reheated to 350 °C. The effect on the flow curve was to increase the flow stress. This result may be related to changes in second phase particle characteristics.

Jan 1, 2006

By L. Frost

"Since the late 1990s, increased prevalence of severe lung disease among US coal miners has been observed, particularly in central Appalachia where thin-seam mining is prevalent. While respirable silica exposures have been implicated in many cases, the available dust monitoring data from mines shows no explanatory trends. One possible factor could be differences in the relative toxicity of silica particles based on their surface condition. Previous research has indicated that particles with occluded surfaces (e.g., by a thin layer of clay) may be less toxic than those with non-occluded surfaces. However, this dust characteristic has not been investigated before now in central Appalachian mines. In the present study, 18 respirable dust samples from seven central Appalachian mines and two northern Appalachian mines were analyzed to assess the relative occurrence of surface-occluded silica. Results showed that the dust from central Appalachian mines actually had higher fractions of occluded silica, which may be due to extraction of large amounts of rock strata along with the coal. However, the central Appalachian mines also more silica particles overall (i.e., occluded + non-occluded) in terms of total number percentage of respirable particles.INTRODUCTIONResurgence of occupational lung disease among US coal miners, especially in the central Appalachian region, has been observed since the late 1990’s (Gibson, 2016; Zosky et al., 2016; Suarthana et al., 2011; Gamble et al., 2011; Antao et al., 2005; Attfield & Sexias, 1995). In addition to increased prevalence of simple Coal Workers’ Pneumoconiosis (CWP, or “black lung”), the prevalence of severe and rapidly progressive disease has risen dramatically (Almberg et al., 2018; Blackley et al., 2018a, 2018b, 2016, 2014; Graber et al., 2017; Cohen et al., 2016). While exposures to respirable silica have long been known to cause or play a role in diseases such as silicosis or progressive massive fibrosis (PMF), which is conventionally considered as the most advanced form of CWP, it is unclear whether silica is the only culprit in the recent outbreak of severe disease. Indeed, as disease rates have risen, both total respirable dust and silica concentrations generally appear to have declined since the late 1980s, based on regulatory monitoring data in the most affected mining districts (i.e., MSHA coal Districts 4, 5 and 12, which cover central WV, eastern KY and southwestern VA, and southern WV, respectively) (Figure 1). Of course, the latency of disease can vary and may be or more 10 years, but many of the most recent cases are likely to have resulted from exposures that occurred since the late 1980s."

Jan 1, 2019

By W. D. Mcmillan

"Magnetic surveys made by the Missouri Bureau of Geology and Mines in 931 and 1932 disclosed a large positive anomaly about a mile south of Bourbon, Mo. 3/ Electrical resistivity measurements made by the Division of Geophysical Exploration of the Bureau of Mines in the winter of 1942-43 indicated that the source of this anomaly was in the pre-Cambrian rhyolite at a depth of more than 1,400 feet. 4/In order to determine the character of the material that caused the magnetic anomaly, which might be either a body of magnetite or a large intrusive of basic rock, the Bureau of Mines drilled four holes to depths of 1,800 to 2,300 feet. Magnetite in rhyolite porphyry was encountered at 1,600 to 2,000 feet, and this is doubtless the main source of the magnetic anomaly, although it is possible that additional iron ore exists at greater depth.Hole 1 was apparently located southeast of the source of the anomaly and encountered only small stringers of magnetite. Hole 2 penetrated four mineralized zones having a total thickness of 125.7 feet and an average weighted content of 43.52 percent iron and 31.62 percent silica. These zones were tested again by a deflection hole, 2A, which gave nearly identical indications. Hole 3, 500 feet north of hole 2, penetrated 58 foot of mineralized rhyolito containing an average 43.4 percent iron.Metallurgical tests showed that the silica in the ore is tightly locked with the magnetite. After grinding to minus 100 mesh, a 66 percent iron con¬centrate with 7 percent silica was obtained by flotation."

Oct 1, 1946