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By E. A. Domínguez

La Espingarda kaolin deposit was formed by ?in situ? alteration of volcaniclastic rhyolitic rocks belonging to Jurassic Marifil Formation. Three volcanic lithofacies were identified: porphyric biotitic ignimbrites (PBI), a coarse lithic ignimbrite (ILG), a fluidal intrusive rhyolite (RFI), all kaolinized in different degrees. The alteration covers an ellipsoidal area of ~20,000 m2, with its alteration decreasing downwards and disappearing at 8-12 m from the surface. The length to thickness ratio of alteration is 60:1. An erratic silicification was found as small zones (<3 m2) of quartz stockwork. The mineralogy is kaolinite + quartz + feldspars + Fe-oxyhydroxides ± halloysite ± illite and interstratified I/S, although the relative proportions change in each rock type. Due to coarse grain size and high quartz content, natural kaolin is unsuitable for slip cast ceramics, unless beneficiated. Washed ILG kaolin has the best rheological properties and behavior in casting and drying for its mineralogy, particle size distribution, thin texture and surface activity, as well as a certain fusibility and firing kinetics. PBI and RFI kaolins, due to finer texture, smaller grain size, lower surface activity, and higher halloysite amount, have worse slip viscosity and thixotropy that are due also to soluble salts. For the same reason, they have good casting and drying properties, but their purity brings about higher softening temperatures and water absorption. Several parameters are used to discriminate between hypogene or supergene kaolinite genesis. The hydrothermal genesis is mainly sustained by fluid inclusion temperature (150-180ºC) in quartz veinlets, while weathering is supported by deposit morphology, simple mineralogy, kaolinite stable isotopes (d18O ? 18, 13; dD ? ?59; ?85) and paleoclimatic record. It is concluded that a weathering process formed the main alteration with some participation of steam-heated meteoric waters. Neither the contents of Au, Ag, As, Sb, Hg, nor drill data support the existence of any epithermal gold mineralization at the kaolinite bottom.

Jan 1, 2010

By David A. Campbell

There has been a long history of ironmaking on the North East coast of England centered around the River Tees. The industry developed here because of the availability of good coking coals to the North in Co. Durham, and the discovery in 1851 of ironstone in the nearby Cleveland Hills, South of the .River. Cleveland ironstone is relatively poor in quality, with an iron content not exceeding h% and high proportion of sulphur and phosphorous. The iron exists in chemical association with alumina and silica, and physical beneficiation processes involve a serious loss in iron unless the upgrading is limited, when the economics of the process become doubtful. Over the years, richer foreign ores have replaced the local ironstone, and the last operating mine was closed in 1964.

Jan 1, 1982

By G. Markopoulos

Every year thousands of people from all over the world come to Mount Parnasse, visiting Delphi, the Parnasse ski-resort and other sights in the area of Fokida, available to all ages all year round. This region of Greece, is not only gifted with natural beauty, but also with valuable underground natural wealth: inside Mount Parnasse and the adjoining Ghiona Mountain, there are rich bauxite deposits - the ore from which aluminium is made. In this magnificent part of our country, any mining activities undertaken must be adapted to coexist within such an ecologically sensitive area. This demands an enormous effort, knowledge and the use of technology. This is definitely our Company&apos;s primary objective. Our company&apos;s (Silver & Baryte Ores Mining Co. S.A.) activities in the area began in 1933, when Euripides Mavrommatis and the two Eliopoulos brothers, Elias and George, established "Bauxite Parnasse SA". Since then, ten thousand people have worked in these ore deposits, and 45 million tons of bauxite have been extracted. The full length of the underground excavations is more than 300 kilometers and 115 million cubic meters of limestone have been extracted on surface mining. In 1996, Bauxite Parnasse merged with Silver & Baryte Ores Mining Co. S.A. Now, the company exports more than 1.500.000 mt per year of bauxite to more than 15 countries around the world, offers a significant amount of job opportunities in the region, and imports valuable exchange into the country.

Jan 1, 2002

By C. E. Capes

The spherical agglomeration process provides an attractive method for the cleaning and recovery of fine coals in the form of compact oil-bonded pellets. In treating a washery effluent containing 50% minus 20 micron material by this technique, the slurry was first mixed under vigorous agitation with oil to deash and dewater the fine coal. The flocculated coal pulp was then formed into larger agglomerates on a modified balling disc. The operation of a semi-pilot scale process is described and an analysis of some of the operating and system variables is given. A semi-theoretical expression to predict the final agglomerate size under various conditions is derived and compared with the experimental data. Coal producers are faced with a growing requirement to clean and recover fine mesh coals. Greater mechanization of the extractive and preparation processes has resulted in finer-sized products containing larger quantities of associated foreign matter and preparation plant effluents contain quantities of fine coals which are potentially valuable. These losses will probably increase with the expansion of production and will require the development of effective disposal and utilization processes under pressure of the lack of adequate disposal areas, the enforcement of air and stream pollution laws, and the economic need to obtain the maximum yield of salable product(1)

Jan 1, 1970

By C. G. Hunkin

In situ, or in-place leaching is concerned with the extraction of metals from natural mineral disseminations without removal from their geologic location which, in many cases, amounts to the reversal of the deposition process accompanied by a presumed increase in velocity of the processes, if the project is to be profitable. Solution mining processes involve removal of minerals such as sulfur, common salt, and potash, generally leaving cavernous voids, in contrast to in situ leaching which term is applied to the selective dissolution of a mineral from its gangue without sensible disturbance of the formation. Where such a process can be operated, the advantages are manifold and have been so recognized by miners from the earliest days of mining. Recent technological developments have encouraged a reassessment of the status of in situ leaching, and it now appears possible to extend the application of the method from a few isolated special situations to many uranium and copper deposits. Anaconda&apos;s interest in the techniques stems from long experience with vat and heap leaching, &apos;dump leaching, and natural leach activities associated with several established mines. Increasing activity through-out the industry has been noted, particularly in leaching low grade pillars and the peripheral zones of operating mines, often by the introduction of leach solutions via boreholes drilled from surface. Reactivation of dormant mines] using similar techniques has been successful. Over the long term, environmental improvement activity will lead to excess sulfuric acid production, even to a disposal problem. The cost of leach solutions and reagents must be reexamined in this light. The mineral industry now classifies as uneconomic deposits of readily soluole minerals whose potential value, on a per acre basis, may De several times that of many currently profitable oil field reser-

Jan 1, 1971

By O. W. Kamper

To most of you present here the word "refractories" is not new and you are familiar with the materials and use. To many people though the question is asked, "What are refractoriness and what are they used for?" Refractories are non-metallic products which are so resistant too melting at very high temperatures that they can be used for building or lining furnaces of all kinds. A large variation occurs in the size, form, and composition depending on the service for which they are intended. They are made from a wide variety of raw materials, of which fire clay and quartzite are used in largest quantities. Other refractory raw materials include magnesite, chrome, diaspore, bauxite, kyanite, sillimanite, olivine, zircon, and many others. Most of these are assembled from-widely-&apos;separated points in the United States while others come from the far corners of the earth. Chrome is imported from the Philippines and South Africa, and, to a lesser extent, Turkey and Greece Kyanite and sillimanite come: from India and bauxite from the Guianas. And there&apos;s "magnesite from brines," produced in chemical plant&apos;s by treatment of sea water or inland deep-well brines with hydrated lime. The proportion of magnesia available in sea water is so small, less than one pound from 500 pounds of water,, that millions of gallons must be pumped and processed each day in a sea water magnesite plant. The realm of refractory raw materials, therefore, is very extensive and continues to grow because of the endeavor to find-better raw materials from which to produce better products for refractory service.

Jan 1, 1960

By William F. Riggs

Inspiration Consolidated Copper Company, located in a semi-arid climate in Arizona, continually struggles with a water problem. This applies to quality as well as quantity. When the EPA considered installing a new centralized sewage plant to handle the combined waste from the municipalities of Globe and Miami, Arizona, they automatically assumed that He could use the sewage effluent for process water in flotation. The treatment plant was to be a tertiary system producing 1600 gpm of sewage effluent. Inspiration decided that this could possibly be a source of additional process water. It was decided to test sewage effluent from Miami Treatment Plant at the rate of 400 gpm since it was only a primary treatment plant. The 400 gpm was combined with the 5000 gpm of process water going to the Concentrator. After one week the results were disastrous. The recovery and final grade had each dropped approximately 5%. With the results from this brief run, it was concluded that sewage effluent from a primary treatment plant could not be used. Research was then brought into the problem to begin an evaluation of sewage effluent in flotation.

Jan 1, 1977

By George H. Davis

The Caribou sulfide deposit near Bathurst, New Brunswick (Figure 1) is illustrative of one variety of strata-bound sulfide deposits. It consists of numerous near-vertical sulfide lenses which are concordant to the foliation and lithologic layering of low-grade metamorphic host rocks. Pyrite is the chief mineral in these lenses, but appreciable quantities of sphalerite, chalcopyrite, and galena are also present. Rocks in the Caribou mine area belong to the Tetagouche Group of Ordovician age. They consist chiefly of (1) quartz-sericite and quartz- sericite- feldspar schists, (2) greenschists, and (3) slate and phyllite. The trends of these steeply dipping rocks define the trace of a tight, steeply plunging fold structure, the Caribou fold (Figure 2). This fold plunges approximately 750 to the north-northwest; its axial plane strikes N.20°E. and dips steeply westward. Sulfide lenses of the Caribou deposit are associated spatially with the Caribou fold. The deposit is located in the fold along the contact between quartz-sericite and quartz-sericite-feldspar schists on the hanging wall and quartz-chlorite-sericite phyllites and graphitic schist on the footwall (Figure 3). Genesis of the Caribou deposit is ambiguous because its strata-bound form suggests syngenetic sulfide deposition, whereas its location within a fold suggests structurally controlled epigenetic mineralization. Acceptability of a particular genetic model rests on establishing the time of mineralization relative to deposition, deformation, and metamorphism of the associated rocks. To establish the timing for Caribou mineralization, the deformational histories of rock and sulfide, respectively, were compared. Epigenetic and syngenetic models can be tested against this interpreted structural history of the Caribou deposit.

Jan 1, 1971

By F. L. Bazzanella

Cyprus Pima has two concentrators, one with a conventional crushing-grinding circuit and the other using semi-autogenous grinding followed by ball mills.

Jan 1, 1978

Coal has traditionally been an integral part of life in Kentucky. Coal mining produces a large part of revenue for the Commonwealth of Kentucky and provides a significant number of jobs to the residents of eastern (less in western) Kentucky. Recently, however, the coal industry of Kentucky has had to endure many hardships. The Clean Air Act set forth sulfur dioxide emission standards which have severely affected much of the coal mining industry in Kentucky, because much of the coal mined in Kentucky has a high sulfur content. In this paper, the background around the effects of Clean Air Act on the coal industry is introduced. The economic and social effects of the Clean Air Act on the Kentucky coal mining are addressed.

Jan 1, 1993

By W. C. Goldberg

This paper presents pit slope monitoring and back-analysis case studies con-ducted to evaluate and, if possible, stabilize slopes at the Berkeley Pit in Butte, MT. Two specific slopes were studied in detail. The first slope was determined to be near limiting equilibrium, as evidenced by its response to the initiation and cessation of mining, while the second failed on three occasions. Back-analysis of the failed slope verified the laboratory-derived geomechanical properties of the earth materials. Early detection of slope movement can show a need to take action, including modifying slope geometry, dewatering if the slope were wet, and/or investigating and implementing artificial supports. Monitoring slope displacements in open-pit mines can supply data for predicting collapses and preventing serious damage, injuries, and/or loss of life.

Jan 1, 1989

By Lennart Bergstedt

Boliden Aktiebolag, the prime base metal mining company of Sweden, annually treats some 11-12 million tons of sulphide ore in nine concentrators. Its first flotation plant was established in the early thirties for the complex Boliden ore. Since then, the number of mines and plants has gradually increased. Considerable effort has been devoted to the development of all phases of the technology of ore prospecting, mining, milling, smelting and refining. This has been necessary due to the complex and low-grade ores. The development of concentration has mainly been directed toward the arts of grinding and flotation. During the forties and fifties, open-stage fine crushing followed by two-stage grinding in rod and ball mills with cyclone classification was successfully introduced and used throughout the plants. The increasing cost of grinding media led to studies of an autogenous grinding technique as early as 1945. Basic test work commenced during the early fifties, with a. number of ores tested for pebble grinding. In 1956 a new pilot plant was built, with equipment installed for the continuous testing of pebble grinding and, later, for primary autogenous grinding of run-of-mine ore. The intensive test work showed that pebble grinding was feasible in almost all of the plants. At this early stage of testing, however, the merits of autogenous grinding could not be fully evaluated. As a. consequence the rod mill/ball mill grinding systems were converted to rod mill/pebble mill systems whereever possible. In parallel with the converting of grinding systems the development work concerning the merits of autogenous grinding went on. The major result

Jan 1, 1977

By J. R. Schafler, J. L. Brinkman

"The US coal mining industry has suffered a recent decline in profits caused by a combination of decline in commodity demand and more restrictive government regulation, forcing coal mining companies to cease production in numerous mines. A 40% decrease in the total number of coal mines occurred from 1994 to 2000. The number of mines remained relatively constant until 2008 when a change of government sparked a series of new environmental regulations which have contributed to another 15% decrease from 2008 to 2016. In contrast, production has only decreased by 3%, increasing from 1994 to 2008, and then decreasing since 2008. However, this value is skewed by large increases in sub-bituminous coal production and decreases in other coal ranks. Several aspects assist in executive decisions on mine longevity and economic worth. Studies of open source mine data collected by mandated government surveys coupled with commodity history can be used to find relationships between mine closures and these elements, which include statistics on production tonnage, seam height, coal rank, etc. This paper looks at coal mining trends since 1994 by comparing mine, market, and regulation factors that may influence mine closure. INTRODUCTION The US coal mining industry is currently experiencing a decline in both demand and commodity price while facing implementation of more stringent air and water pollution regulations. Company profits have decreased significantly, forcing several major companies to declare bankruptcy. The industry was required to adapt to survive. Many of these companies have adjusted by abandoning mines; the last two decades have seen a drastic decrease in the number of mines. To discover the primary causes of this downturn, three major aspects must be studied: properties of abandoned mines, commodity history, and regulatory impact. TRENDS SINCE 1994 Each year, US coal mines are required to submit data on a wide variety of categories to the Mine Safety and Health Administration (MSHA) and the US Energy Information Administration (EIA). This data includes administrative records, production values, and information regarding the attributes of the mined material and the mine itself. Each year since 1996, EIA has released a report summarizing the data from two years prior. Additionally, MSHA maintains a database containing a collection of all the most current data. These resources are the primary sources for the following figures."

Jan 1, 2017

By F. S. Knoll

Magnetic separation employing superconducting technology is now accepted within the Kaolin processing industry, proving the value of this technology and its ability to operate reliably even at the most remote site. Developments in superconducting magnet engineering, including cryogen free operation, combined with experience in mineral processing enables new forms of Wet and Dry superconducting magnetic separation to be developed. Applying the high magnetic force advantages at 5 T else available from such magnets to other materials is now a reality. High magnetic force mineral separating system developments are reviewed allowing the mineral processor to take advantage of a technology that is no longer confined to the laboratory.

Jan 1, 1997

By S. R. Titley

Results of regional analyses of precious metal habits in Arizona ores lead to interpretations of a fundamental ore control related to geographic location that corresponds with crustal contrasts. Measurements of isotopic and trace element characteristics of Laramide ore-related intrusions lead to interpretations of crustal derivation of apparent ore-related magmas. Interpreted regionally, the numerous kinds of Laramide ores, which include porphyry copper deposits of this southern cordilleran region appear to be phenomena of a specific crustal lithology characterized by a basement of Proterozoic turbidites and (an interpreted) lower crust of amphibolite. This association with a specific basement terrane may be extended in principle from the United states into Mexico where faulted offsets of this basement are similarly favorable to formation of Laramide porphyry ores -to the exclusion of adjacent terranes. Whereas plate tectonic mechanisms may have triggered evolution of these ores, it is hypothesized here that crustal setting and crustal composition are more profound influences of metallogenesis.

Jan 1, 1992

By J. Helton, J. L. Bellanca, M. McNinch, L. R. Swanson

DISCLAIMER The findings and conclusions in this paper are those of the authors and do not necessarily represent the official position of the National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention. Mention of company names or products does not constitute endorsement by NIOSH. ABSTRACT Accident data indicates that mobile haulage poses a significant pinning, crushing, and striking risk. Proximity detection systems (PDSs) have the potential to protect mineworkers from these risks. However, unintended consequences of mobile PDSs can undermine the safety benefit they provide. Soliciting iterative user input can improve the design process. Users help provide a critical understanding of how mobile PDSs may hinder normal operation and endanger mineworkers. Researchers explored users’ perspectives by conducting interviews with mineworkers from seven mines that have installed mobile PDSs on some of their haulage equipment. Mineworkers reported that mobile PDSs affect loading, tramming, section setup, maintenance, and general work on the section. Mineworkers discussed the operational effects and increased burden, exposure, and risk. Mineworkers also suggested that improved task compatibility, training, logistics, and PDS performance might help address some of these identified issues. This paper also gives additional insights into mobile PDS design and implementation. INTRODUCTION Pinning, crushing, and striking accidents are a large problem in underground coal mines, especially for mobile haulage. Between 1984 and 2014 there were 179 non-fatal and 42 fatal pinning, crushing, and striking accidents involving mobile haulage vehicles, including coal hauling machines and scoops [1]. Proximity detection systems (PDSs)—automated systems that decelerate and stop a vehicle in order to prevent a collision—have the potential to protect mineworkers in these situations. In fact, PDSs are now required on all place change continuous mining machines as of March 16, 2018, as a result of the final rule published in January 2015 (30 CFR 75.1732) [2]. To address mobile haulage, later in 2015 the Mine Safety and Health Administration (MSHA) also proposed a new rule that would require PDSs on mobile haulage vehicles [3]. Though there has been no additional actions related to the proposed rule and it is not currently required, mobile PDS can still help to save lives. MSHA estimates that the adoption of mobile PDSs could prevent approximately 70 injuries and 15 fatalities over the next 10 years [4]. As of June 2015, the underground coal industry had already equipped 155 of the 2,116 mobile haulage vehicles in use [1]. In order to capitalize on the projected safety gains afforded by PDSs, it is important that the systems are designed and implemented effectively. Along with others, researchers at the National Institute for Occupational Safety and Health (NIOSH) have been exploring PDSs for more than two decades [5-7]. Throughout this time, NIOSH has also held several stakeholder meetings (2010, 2014, 2016, and 2017) in order to disseminate information and provide an opportunity to discuss on ongoing issues and concerns. Despite some progress, human factors remain a key concern. Previous research examined mineworkers’ attitudes towards PDSs on continuous mining machines [8] as well as how continuous miner operators’ perceptions of risk have changed as a result of PDSs [7]. However, stakeholders have still expressed a need to better understand how mobile PDSs affect the mining process, the mineworker, and whether and how they may present previously unidentified risks.

Jan 1, 2019

By K. T. Brashear, N. Ripepi

"Over recent years, specifically following the MINER Act of 2006, an increasing number of manufacturers of underground mine seals in the United States have begun using a form of pumpable cement or shotcrete to create barriers separating the working and abandoned sections of underground coal mines. This seal material, while generally considered to be homogenous and solid, contains a network of microcracks, voids, and delaminations. Generally, it has been assumed that methane (CF4) leakage around these seals is a result of movement around the boundary interface between the seal and surrounding strata. Using a perfluorinated tracer compound, perfluoromethyl-cyclohexane (PMCH), the movement of gases can be monitored through seal material to observe how gases move though the material, both intact and with faulting in the material. This paper documents two large experiments where the movement of PMCH was monitored in the field, along with modeling confirmation using 3D visualization software. INTRODUCTION According to a report in 2007, there were over 14,000 active mine seals in underground U.S. coal mines alone (Zipf, Sapko, & Brune, 2007). These seals are used for both ventilation and safety purposes, to direct the flow of air away from the abandoned area of the mine and to help eliminate the propagation of explosions that can occur on the outby side of the mine seal. The atmosphere on the outby side of these seals typical consists of low levels of methane that have the potential of producing leakage along the face of the seal on the inby side. Methane leakage around mine seals has historically been attributed to the permeability between the seal and mine interface (McPherson, 1993). According to the United States Bureau of Labor Statistics (BLS) between 2003 and 2012 an average of 17 deaths occurred annually in underground bituminous coals mines. The only time during the ten-year period where the fatalities were higher than the average was in 2006 and 2010, years which had three major explosions occurring in underground coal mines in West Virginia and Kentucky. Two of the explosions were propagated through the mine by seal failure or methane leakage around newly poured seals (Light, et al., 2007) (Gates, et al., 2006). These recent events, and new regulations regarding seal strength (MINER Act), have created a need to monitor the condition of underground mine seals. BACKGROUND Measuring the permeability of solid materials, such as concrete or seal materials, can be a valuable tool in the field of non-destructible testing (NDT). By using an inert gas, such as nitrogen, injecting the gas into a solid structure, and measuring the resultant flow rate and pressure differential, this can provide valuable information about the structure. Studies have shown permeability can be affected by the stresses applied to the structure, as well as temperature and moisture (Choinska, Khelidj, Chatzigeorgious, & Pijaudier-Cabot, 2007) (Abbas, Carcasses, & Olliver, 1999)."

Jan 1, 2015

By M. Z. Emad, M. U. Khan

"Coal mines opting for longwall mining or its variations rely on the main and tail gates for production. Stability of these entries or crosscuts is crucial in coal mining operations. Roof or strata failure can be fatal, may lead to property loss and delay in production. Failure of the gates depends upon many factors including the mining method, panel dimensions, pillar width, mine depth, caving rate, dimensions of gates and roof strength properties. In Pakistan coal is mined through a variation of longwall mining method with almost no mechanization while using timber as a primary support. Timber support as chock is very useful in coal mines especially in overhanging face. Similarly gate entries and coal faces are supported by chock supports throughout their length. In this paper the stability of the longwall gate is assessed for a typical coal mine in Pakistan by using finite element code. Numerical modelling considerations for gate entries are discussed. A model parametric study is performed for key factors. The results showed that the existing mining practice is not suitable and there is a need to review the mining approach. INTRODUCTION Main and tail gate entries leading to longwall mining panel play a crucial role in production cycle. Failure of any of these may lead to loss of life, property and production delays. The stability of gate entries depends primarily on the nature of loading and stresses incurred. It is relatively easier to assess the ground response to production for common longwall mining panel. In thin-seam coal mines the gate entries are generally supported throughout their length by timber made chock supports. The tailgates receive huge deformations and stresses during the mining and backfilling cycle. The chock supports are required to take care of rock falls leading to blockage of entries causing production delays and loss of capital. A number of supports are available for supporting the gate entries (Hoek and Brown 1980; Brady and Brown 1985). The support system can be selected based on load-deformation characteristics including the yielding behavior, pre- and post-yielding behavior (Barczak, 2003). The principal of support selection is that the support characteristics must match the ground response in order to maintain the gate entries (Mucho, et al., 1999). It has been observed that thin-seam mining (<1 m) is very challenging and it is necessary to develop an understanding of ground mechanics before the selection of an efficient support system Dolinar (2003). The chock supports have been tested for load-deformation characteristics in the laboratory (Barczak 2003). But the ground and support interaction, response and loads must be assessed for individual site. This can be accomplished by in-situ testing and observations at few locations. The generated data is generally insufficient for complete understanding. Numerical models can combine the data generated in the laboratory and on-site to fulfill the requirements."

Jan 1, 2017

By I. Weir-Jones

I. Introduction The experimental work described in this paper was carried out during 1967 and 1968 in an inclined reinforced concrete adit which had been driven during 1965 and 1966 to provide primary access for a new gypsum mine. The new mine was situated near the village of Sherburn-in-Elmet in central Yorkshire in an area of extensive post-glacial plains of deltaic and lacustrine origin. These plains cover a large area of this part of Yorkshire extending inland from the coast for a distance of about 35 miles. The gypsum deposit at Sherburn dates from Permian times and it is considered" to have been associated with the western-most edges of the ancient Zechstein Sea which was also responsible for the formation of the extensive evaporite deposits in north-east Yorkshire. The gypsum deposit, which varies in thickness from 10 to 15 feet, is extremely pure and it occurs quite close to the surface; in the Sherburn area the overburden is only 120 feet thick. The proximity of the deposit to the surface, however, tends to give a somewhat false idea of the magnitude of the problems associated with its extraction. These problems were all related to the nature of the overlying strata. As has already been mentioned, the surface deposits are post-glacial and they consist of an extremely large number of thin layers of varved clays, fine silts and sands extending down to a depth of 75 feet. From the bottom of the post-glacial deposits to the seam, a distance of about 45 feet, the strata consists of a succession of marls, weak sandstones, and siltstones, which although they are inherently incompetent materials, are appreciably stronger

Jan 1, 1971

By J. H. Fowler

Canada&apos;s gypsum industry began over two hundred years ago in the Maritime Provinces when farmers attempted to supplement their incomes by selling "land plaster" to traders bound for the United States. Rising from such humble beginnings, gypsum now contributes significantly to the economies of nine of Canada&apos;s ten provinces. Thirteen open-pit and three underground mines produced a total of 8.38 million tonnes of crude gypsum and seventeen processing plants manufactured 2.49 million tonnes of finished products in 1985. Recent economic growth in North America has resulted in steady increases in gypsum production, however, competition from foreign producers and by-product gypsum poses a growing threat to Canada&apos;s gypsum mining industry.

Jan 1, 1987