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By Andrea Brickey, RICHARD AMOAKO, Akshay Chowdu

Production forecasts derived from the medium-term schedule represent the best path forward for underground mining operations to achieve corporate and operational goals. Unforeseen circumstances, such as equipment breakdown, can cause significant deviations from established production forecasts in the short term. Such situations require timely mitigation of the effects of the deviations in order to stay as close as possible to the medium-term plan. This paper presents a deterministic mathematical formulation for short-term scheduling that addresses this challenge. The formulation is able to make up for deficits resulting from operational disruptions by minimizing deviations from medium-term production goals and medium-term activity start dates. We demonstrate this in a case study by simulating disruptions involving reduction in ore extraction capacity and development advance rate. Aside from the rescheduling capability, this formulation can help mine planners conduct analysis on the impact of various disruptions on the schedule. The formulation can help identify those conditions or disruptions that are more detrimental to the achievement of forecast targets, or otherwise. The formulation also affords mine planners the flexibility to prioritize one production goal over the other, depending on operational conditions at the mine. In the future, we seek to incorporate in the formulation respirable dust, diesel particulate matter and ventilation constraints in order to create more realistic schedules, and enhance miners’ health and safety.

Jan 1, 2024

By Desiree Willis

At 6 percent downgrade to a low point beneath California?s Sacramento River, the Lower Northwest Interceptor Sewer was a difficult project from the outset. Project owner Sacramento County Regional Sanitation District (SRC-SD) planned to excavate the V-shaped tunnel in two sections using an earth pressure balance (EPB) machine in soft ground. Muck removal, due to the steep downgrade, was a tricky proposition. ?We did look at muck cars, but determined they were not the best option due to the relatively steep slope of the tunnel alignment. The safety benefits of conveyors on this job were obvious, as there were not the potential hazards associated with muck cars traveling on an incline or derailing,? said Steve Norris, senior civil engineer for SRCSD The successful project represented one of the first instances of a conveyor system being used for a soft ground tunnel boring machine (TBM) application. Several projects in California, including a recent tunnel completed in 2009, have highlighted a growing acceptance of conveyor muck removal in a variety of ground conditions. Conveyors offer higher system availability than more common methods, such as muck cars, as they allow for continual operation of the TBM. The design of conveyor systems must, however, take into account the differences in material between soft ground and hard rock, including belt cleaning features, sealed transfer points and other elements.

Jun 1, 2010

By T. Klemetti, W. H. Su, M. A. Van Dyke

Entry stability in coal mines is dependent on geologic conditions and engineering controls. Most engineering controls in ground control are predictable and standardized for typical geologic conditions. However, geologic anomalies may exist that are difficult to detect with traditional core hole drilling. Borescopes offer a cost-efficient way to gather more geologic data between core holes. Additional data obtained from borescope results provide a clearer picture to enhance detection of hazardous conditions due to geologic anomalies. The equipment, methods, and analysis of borescope results provide geomechanical engineers with a clear understanding of strata behavior and the best information to implement roof control plans and supplemental support to enhance miner safety and health. INTRODUCTION Borescope technology has changed very little since its inception. However, the idea to use borescopes to examine roof strata started with the U.S. Bureau of Mines in 1979 with the production of a fiber-optic borescope (FitzSimmons, et al., 1979). The first documented use of a borescope in the coal mining industry began during the 1980s in Australia by researcher John Shepherd. Shepherd’s idea was to use a borescope to collect a series of data points from the roof lithology and compose a geologic cross section. The cross section was then used to identify key features that suggested the beginnings of roof failure. The features Shepherd identified were bedding plane separations in the roof and low angle, extension, and tensile failures. Shepherd also suggested that the borescope findings could be used for geologic mapping for lithological variation, fracture distribution, and determining if supplemental roof support was needed (Shepherd, et al., 1986). In the United States the first publication about borescope usage for coal mine stability assessment was by Su and associates in 1999, who specifically related the combination of using borescope, geophysical, and corehole data to produce geologic hazard maps (Su et al., 1999). This work directly linked the usage of a borescope with the design of supplemental roof support. The use of borescopes in mining was adopted industry wide by the 2000s. Operator case studies were being published using borescopes to aid in supplemental support recommendations and hazard mapping. An Australian study published in 2007 based the optimization of secondary support after each longwall pass on the results of borescope data. The study stated that the borescope was an invaluable tool for understanding roof behavior (Black, et al., 2007). In 2009, a publication by the National Institute for Occupational Safety and Health (NIOSH) took the concept of borescoping one step further. The work centered around creating a roof quality index (RQI) for limestone mines based on borescope data. The RQI attempted to assign a ranking to establish the nature of the roof and its stability (Ellenberger 2009). In theory, this would have been a very useful tool, but the RQI system has not been widely adopted in the industry.

Jan 1, 2019

By John J. Stetler

The Companhia Vale do Rio Doce in Brazil operates one of the most extensive systems in the world for the mining, transportation, processing, pelletizing and shipping of high grade hematite iron ore and pellets. Current shipping of unbeneficiated, sized, high grade ore from its ports at Tubarão and Vitória is now at the rate of 17,500,000 metric tons annually. An increase in this annual rate is now under study. Using the technology and facilities of Lurgi (1) and Arthur G. McKee company CVRD undertook a program to process and pelletize two types of fines - "Blue Dust" and ?Itabira Fines?. Blue Dust is a high grade fine ore which was bypassed while mining the direct shipping ores and which, also, exists as a very large ore body called the Conceição Mine. Itabira Fines is a lower grade of fine ore which is comprised of in-situ fines and, also fines which are generated in sizing the direct shipping ores for a rigid specification market.

Jan 1, 1970

By John L. Ellenberger

Virtually no two mines operate with the same geographic, geologic, and mining conditions. It follows chat problems vary with the conditions from mine to mine or often from one section to another in the same mine. Actual situations are described, and a technique of "stacking" maps to predict hazards is presented. Two case histories of the use of multiple overlays are de- scribed. The first deals with a property that was examined before the start of mining. The second is a property in which severe ground control problems were encountered and the relationship between the problem areas and known conditions were found to be related.

Jan 1, 1981

By Donald E. Hendrickson

A new prinicple of side dumping front end loading for underground mucking machines has completely changed the concept of underground loading and haulage equipment arrangement both in production and development work loading. Versatility and adaptability of this type of machine permits combinations with a broad range of haulage means not possible with -conventional overhead loaders. Steel "armored" conveyors serving this type of loader are replacing conventional rail mounted car haulage to give a continuous loading operation and effect important economics of reduced manpower, faster loading rates and fewer working areas for a required production. First used in Germany this easy to control and highly efficient means of placing rock from the muck pile on or into haulage means has advanced the art of underground rock loading more in the past three years than any other advancement since the first successful small crawler mounted air powered loader was introduced in 1954. Bucket type loaders with a relative new side dump principle are gaining in popularity for underground loading. They are replacing conventional overhead loaders in present applications and becoming first choice in new ones. Primarily for hard rock development and production loading they are also widely used in production loading of coal and other soft materials. This discussion briefly traces the historical development of hard rock underground loaders to the new side dump type and its present population. In more detail various applications, loading techniques and the advantages of operation, production and economy with the side dumper in hard rock loading will be dealt with.

Jan 1, 1966

By Y. Lv, H. Ye, D. Du

Electrolytic manganese residue (EMR) is a kind of industrial solid waste with high silicon content that contains harmful metal elements such as chromium (Cr), copper (Cu), lead (Pb), cadmium (Cd), nickel (Ni) and cobalt (Co). Developing a highly effective and environmentally friendly process to treat EMR is important, both for the reutilization of metal resources and for environmental sustainability. In this study, the bioleaching of available silicon from EMR using silicate bacteria is investigated, with flask experiments conducted to optimize the parameters in the bioleaching system. For metal ions, the concentrations of manganese (Mn), Co, Ni and Pb in solution were measured to determine the environmental safety effects before and after bioleaching. The results show that the bioleaching rates of available silicon in the slag were mainly affected by the temperature, pH and pulp density. Under the optimal conditions of temperature of 30 °C, pH of 7.0, pulp density of 5 percent, shake flask rotational speed of approximately 210 rpm, particle size of approximately 0.150 mm and leaching time of 16 d, the concentrations of available silicon in the bioleaching system rose to approximately 110 to 140 mg/L. The metals remaining in the residues were mainly bonded in stable fractions, with concentrations lower in the leachate after bioleaching. This study demonstrates that silicate bacteria can be used to increase the contents of available silicon from EMR, and that bioleaching technology can realize the harmless resource utilization of EMR.

By Ralph J. Holmes

INTRODUCTION Although sampling techniques used by the mineral industry continue to improve, sampling is still an area which is often neglected. Frequently, sampling and sample preparation requirements are left to personnel who do not fully appreciate the significance and importance of sampling. Consequently, plant evaluations are often based on seriously biased samples, leading to mass balance problems and incorrect assessments of plant performance. The basic rule for correct sampling is that each particle of ore or concentrate must have an equal probability of being collected and becoming part of the final sample for analysis. If this is not the case, bias is easily introduced and the sample is not representative. For example, when ore is travelling on a conveyor belt, the lumps may come to the surface. Consequently, a grab sample taken from the top layers only will contain a greater proportion of lumps, i.e., the sample is biased. There seems little point in making major investments in precise analytical equipment, if the sample provided to the analytical laboratory is not representative in the first place. This paper describes the sources of plant sampling errors, reviews the methods of estimating their variance, presents some worked examples, and provides some practical advice for reducing sampling errors and their variance. SAMPLING BASICS It is generally accepted that the discharge point of an ore or concentrate stream is the most suitable sampling location. The stream can be intersected at regular intervals, and representative samples, referred to as increments, can be obtained by taking a complete cross-section of the ore stream. On the other hand, sampling devices that take part of the stream on an intermittent or continuous basis, e.g., a bleed from a pipe, may introduce serious bias, and should be avoided at all cost. Increments may be taken at completely random times or tonnages during the sampling operation, in which case it is called "random sampling". However, as shown below, random sampling results in the largest sampling variance, so it is preferable to divide the ore or concentrate stream up into strata of equal time or mass and take one increment from each stratum. This operation is called stratified sampling and may be either systematic sampling, in which increments are taken at the same point in each stratum, or stratified random sampling in which the increments are taken at random within each stratum. Systematic sampling results in the smallest sampling variance, provided periodic variations in quality or quantity are not present which may coincide with, or approximate to, any multiples of the proposed sampling interval. In such cases, it is strongly recommended that stratified random sampling within fixed time or mass intervals be carried out.

Jan 1, 1991

By Randall E. Hughes, John F. Burst

This chapter describes the nature and occurrence of the principal clay minerals that are used as ceramic raw materials, explains how these raw materials are used to produce finished goods, and summarizes positive and negative trends that will affect future demand for raw materials and products in the ceramic industry. The term ceramics was derived from the ancient Greek keramikos (a clay jar). A ceramic product is a material that has been fired to at least 468.3°C (Mitchell, 1983). In addition to being one of our earliest manufacturing and construction materials, ceramic products are among the earliest records of civilization. The enduring significance of ceramics is shown by the fact that, even today, the manufacture of whitewares, brick and related red-fired wares, refractories, and engineered ceramics continues to be a major sector of the US economy. A wide range of materials can be made into ceramic products, although relatively few earth materials make up most of the ceramics in today's markets (Table 1). Most ceramic products are made from clay or a related material. The long history of clay use in the ceramics industry stems from its variable and sometimes unique physical and chemical properties, as well as its ubiquitous occurrence and relatively low cost. Clay is important to ceramics because of its plasticity, moldability and filterability, chemical content, color. refractoriness, solubility. corrosion resistance, electrical properties, and other properties that result from the essentially two dimensional morphology of the individual clay mineral platelets. Because of their basic relationships to the chemical and physical properties of clays, the chemical and mineralogical content have been the subject of continuous studies over the past few decades. Advances in knowledge about the chemical, mineralogical, and physical properties of clays are responsible for most of the advances in processing. The need to remove off-colored contaminants, minerals with low melting points, and soluble salts has resulted in beneficiation by wet processing methods such as water washing. Water washing is restricted to kaolins, although low cost methods of water washing have been extended more recently to ball clays in Europe. High intensity magnetic filtration and flotation technologies have noticeably improved the quality of kaolins and broadly expanded their use in the ceramics industry. In addition to products for construction (e.g., brick, tile, sewer pipe, field drain pipe, cement, fiberglass, roof granules, and paint) and manufacturing (e.g., refractories, kiln furniture, sanitary ware, pottery, and dinnerware), clays are used in calcined form as ceramic fillers, carriers, extenders, and grogs. Ceramics suppliers are under economic pressure in several of these product areas. Manufacture of refractories in America has declined as steel production has decreased. Similarly, dinnerware and tile production have declined because of foreign competition. Fortunately, new uses for clays,

Jan 1, 1994

By M. D. Bath

Minproc Engineers Inc. (Minproc) recently completed the construction and start-up of a process facility to treat 14,000 t/d of gold-silver ore at Kori Kollo, Bolivia. The comminution circuit consists of crushing and SAG-ball mill grinding. Breakage characteristics of the ore were determined and a circuit model developed. This enabled variations of the circuit to be simulated, and evaluated in terms of predicted performance to provide the criteria for final engineering design. Subsequently, analysis of the operating circuit provided data for circuit model-fitting. The validity of the original model and circuit performance predictions are discussed.

Jan 1, 1994

By A. J. Basu

Computer assisted mine planning and design applications are routinely used by many Australian mining companies, However, the design process requires human expertise to recognize and evaluate the potential pitfalls. This paper introduces the application of a commercial optimization software (WHITTLE 4D) for strategic planning of an open pit mine in Western Australia. The authors present their experience in intelligent application of the optimization program while incorporating many technical and nontechnical obstacles. This paper provides some guidelines on how to apply the optimization software without loosing sight of practicalities. Moreover, this paper also shows how to build project evaluation guidelines for non-experts.

Jan 1, 1997

A joint research effort by Newmont Gold and Du Pont, working with Kurtis Mooney, of Tri-Combined Resources has developed a new ore-sample bag made of "Tyvek," a spunbonded olefin. "The goal was to find a bag with the best trade-off between efficient draining of moisture, minimal fines loss and compatibility with the conveyor drying process we were developing for our new assay lab," Charles Bucknam, analytical development coordinator for Newmont Metallurgical Services states. None of the available polypropylene, cotton or canvas bags had the needed combination of properties. "Our original tests in 1987 on the plastic bags we had been using showed an average loss of 5.4% of mud sticking to the bags when they were emptied into drying pans. Part of the sample was still in the bag as a residual." Tests on bags of "Tyvek" showed low residuals when the samples were dried in the bags before they were emptied, but about 3% of the fines were lost through the seams. Mooney recommended a new bag design, with fold-over seams.

Jan 1, 1990

By A. Hayatdavoudi, E. Apande

Introduction Troublesome shales have plagued the petroleum industry for more than 50 years. Unstable boreholes have been experienced when drilled into shale formations; sane have been studied almost at the beginning of rotary drilling. A little progress has been made since then, but much is still to be learned. No simple solution exists so far, but good drilling practices combined with good mud practices have been helpful. It is well known that shales in general have a strong affinity for water, and when water is adsorbed, the stability of the shale section of a well is reduced; cohesive strength will be re- bed, properties will be altered and shale will generally expand and/or crumble. The amount of water a shale will adsorb depends on the characteristics of its clay mineral and the ionic concentration of surrounding fluid. Fluid loss and the resulting hydration of an unstable formation can lead to serious downhole problems. The rate of fluid loss depends greatly on the permeability of the deposited cake. In impermeable formations, however, there is no loss of fluid into the formation. As such, shale, because of its very low porosity and almost no permeability, could be termed impermeable. Yet there is strong evidence that shale surfaces are wetted by an invasion of fluid into the formation through microfractures and jointed planes. It is this wetting that causes the shales to swell and slough into the hole, resulting in problems such as increased mud volume and treating costs, bridges and fill-up, stuck pipe, overgauge hole, poor cement jobs and increased cement requirements, and logging and completion difficulties. Drilling operations have been defeated by severe shale problems, resulting in & hole being plugged and abandoned after several weeks of drilling. Shales are we1l known as being difficult and costly to drill. Numerous fishing jobs have plagued drilling operations, and the cost of reaming tight holes ad weighting up the drilling mud to control shale sloughing has been high. The concept of controlling water loss to stop sloughing was introduced in the 1920's. It was known-then that calcium in fresh water re- strains clay £ran excessive swelling (theory of osmosis) . This reinforced the belief that calcium-based muds such as lime, gypsum and calcium chloride should minimize hydration of clays. Lime muds were then introduced for this purpose and others in the 1930-1940 decade1. They were used for shale inhibition but were not effective. In an attempt to improve them, a special calcium-type mud beam popular during the 1950's. Hole enlargement continued and they too were considered ineffective. During & early 1960qs, papers were published claiming that shale swelling could be prevented by using high concentrations of chemical thinner called Chrane Lignosulfonate1. This began the era of highly treated lignosulfote muds. Unfortunately, the hole enlargement problem continued. During & mid-1960’s, oil based muds were used for the purpose of inhibition of shales. Not until 1966 did Mondshine2 suggest that the water phase be saturated with calcium chloride. The cost of using oil based mud was considered by most operators not worth the additional hole stability. The potassium chloride-polymer muds were also used in many fields in the United States and western Canada. The use of these muds has been claimed to prevent clay swelling by inhibition and encapsulation in sane areas of western Canada. They are also expensive and their ueneral application is still experimental. To reduce filtrate loss when sloughing shale becomes a problem during drilling is a reasonable practice. This study will investigate the use of cationic organic additives to mud to form a protective barrier between the shale - which are primarily composed of clays - and water that will keep water from entering the microfractures and will also prevent them from hydrating. In so doing, an understanding of modern clay chemistry and & dispersive properties of cationic additives in water based systems will be our most valuable tools. This study will also present and solve a mathematical model for simulating cation transport phenomena in fractured shales using the Framdlich equilibrium adsorption isotherm. The studies will analyze wellbore failure and stability as affected by cationic organic material.

Jan 1, 1986

"When boring a tunnel, homogeneous hard rock is the exception rather than the rule. While contractors can set goals such as meters per month and performance incentives, it is also prudent to plan for difficult ground. A properly designed tunnel boring machine (TBM) can tackle fault zones, water inflows, squeezing ground, or whatever the risk may be. The alternative is not a good one: modifying the machine in the tunnel after bad ground is encountered. Not only does this result in increased downtime, but it also needlessly exposes the crew to the tunnel conditions. In the worst case scenario, the entire operation grinds to a halt.However, an accurate GBR cannot always be obtained, particularly for mountainous, high cover tunnels in remote locations. And even with a thorough GBR, unforeseen geological events can occur. What can be done in these situations? Difficult Ground Solutions (DGS) is ground investigation system with a suite of options that can be added to a shielded hard rock machine or dual-mode, Crossover machine to better enable advance when conditions are unknown or difficult conditions are anticipated.DGS consists of a set of integrated features tailored to a specific project’s geology. The main components of the system allow for ground investigation ahead of the TBM, increased monitoring and methods to keep a machine shield from becoming stuck.In fault zones and squeezing groundIf fault zones or squeezing ground are known or suspected, or if there is even a possibility of encountering them, this can greatly affect the TBM operation. Shielded machines protect the crew from the surrounding rock, and they can bore and line a tunnel efficiently, but in fault zones and converging material their shields can be their downfall. Avoiding a stuck machine is paramount to project success. DGS employs several features to avoid the problem of a machine becoming stuck. The first of these is multi-speed cutterhead drives. These drives effectively give the machine multiple modes of operation—high speed, low torque for hard rock, and low speed, high torque for difficult ground. Designing a machine with high-torque, continuous boring capabilities allows that machine’s cutterhead to restart with break-out torque in difficult ground. The net effect is that the machine can keep boring in the event of a face collapse and can bore through fault zones and running ground where the potential for cutterhead jamming exists. Going one step further, multi-speed gearboxes give the machine the ideal earth pressure balance- (EPB-) type torque if larger sections of soft ground are anticipated.Secondly, TBMs can get through squeezing ground and faults using Continuous Shield Advance. This design utilizes a stepped shield configuration — where each successive shield is slightly smaller in diameter — to avoid becoming stuck in converging ground. External shield lubrication is an added insurance against becoming stuck, using a series of radial ports that can pump Bentonite into the annular space to act as a lubricant in squeezing material.As a last effort, if a machine has already become stuck the TBM can utilize augmented, or “super” thrust. Additional thrust jacks can be added to supply an extra boost in a short stroke, generating enough force to break loose a trapped shield."

Jan 12, 2017

By Deepak Malhotra

The first step in the development of a gold deposit is the detailed mineralogical examination of the ore types, major and minor mineral constituents and their association. It is extremely difficult and expensive mineralogically to characterize the occurrence and association of gold with other minerals for low-grade refractory ores (less than 0.1 troy oz/t Au). Even if a mineralogist can identify a gold-associated particle or two, one wonders how representative they are of the deposit. What alterative does a metallurgist have for characterization of gold-bearing ores? Diagnostic leach procedures, consisting of a series of sequential leaches, can provide the metallurgist/mineralogist with reasonably good Indication of the deportation of gold in the various mineral matrices. This information con help the metallurgist concentrate on the most promising process options In the Initial stages of the project development process.

Jan 1, 1993

By S. Partney

Waste clay ponds are a necessary part of the phosphate rock beneficiation process. They are large, averaging a square mile in size; unsightly, in that they protrude 20 to 50 feet (6 -15 meters) above natural grade; stabilization and reclamation is slow; and they have had a history of catastrophic failure. The State of Florida has never published a specific rule regarding the configuration or height of these ponds, but has enforced numerous policies along these lines. The current rules are given and interpreted, along with the reasoning for current policy. In addition, an overview of the history of the policies, and an attempt at explaining the reasons for the changes that have occurred is given. The industry has been forced to make major monetary decisions, having effect for decades on mine economics, in a constantly changing regulatory environment. The Bureau of Mine Reclamation is confident that a direction of regulation has been solidified, but changes are still to be anticipated.

Jan 1, 1998

By H. G. Stephenson

Canada and the United states are both developed countries with economies which are extremely dependant on oil. Canada exports 37% of its production (to the United states) and imports 35% of its consumption (mainly into Eastern Canada), making the country self-sufficient in oil. Canada is attempting to increase its oil production so as to simultaneously reduce its dependence on foreign oil while producing more oil for export. The United states -imports no less than 50% of its total consumption of 17 million barrels/day. Canada's exports to the United states form only 7% of the United States total imports. The United States would clearly prefer to achieve self-sufficiency in oil. Consequently both countries are dependent on foreign oil. The united States is however in the sensitive situation of depending, for its imports, on countries which are susceptible to destabilizing political events. It is the author's hypothesis that recent developments in underground oil recovery from the Athabasca oil Sands of Alberta may well, for both countries, form part of the solution to these problems.

Jan 1, 1991

By Helmut Mischo

For more than 100 years, diamond mining has been Namibia?s most important mining sector. Today, it provides the highest foreign currency income for the country?s development. Since the late 1970s, offshore mining of diamonds has gained more importance and now more than 60 percent of Namibia?s generally high-quality stones come from those offshore deposits, with a steady increase expected for the coming years. Diamonds in Namibia The mining industry is one of the three pillars of the Namibian economic development, along with tourism and fishing. Diamond mining is one of the two main mining activities in Namibia and diamond mining operations are rapidly moving from onshore to offshore deposits. This article provides a comprehensive overview of the current and future situation of the Namibian mining industry, with a special focus on the tasks and new technical developments for the successful excavation of beach and marine diamond deposits. The different deposits and the adequate applied mining technologies and methods are shown in examples.

Jan 1, 2011

By J. P. Ferro, W. H. Stewart

Wet ground and dry muscovite mica continued to be the most commercially significant types of mica in the US. Canada's phlogopite mica and some US deposits of sericite mica have also contributed to the overall application of mica in a variety of industries. Mica's major end uses are paint, rubber, and construction material. Its value was about $30 million last year. The southern Appalachian Mountains weathered granitic bodies and pegmatites continued to be the primary US muscovite mica source. North Carolina production of mica as a coproduct of feldspar, kaolin, and lithium processing accounted for more than 60% of the total output. New Mexico, South Carolina, South Dakota, Georgia, and Connecticut accounted for the rest. Flake mica was also produced from mica schists in North Carolina and South Dakota. It is also being investigated in Ontario, Canada. Wet ground mica Wet ground mica was produced by four companies: KMG Minerals, Franklin Mineral Products, J.M. Huber Corp., and Concord Mica. KMG and Franklin Mineral Products accounted for more than 80% of the production. Wet ground mica is a highly delaminated platey powder used to reinforce solvent and aqueous system paints for increased weatherability, durability, and greater resistance to moisture and corrosive atmospheres. In plastics, it is an excellent filler and reinforcing agent, providing better dielectric properties, heat resistance, and added tensile and flexural strength. In the rubber industry, wet ground mica is used as a mold lubricant to manufacture molded rubber products, such as tires. It also acts as an inert filler that reduces gas permeability. Miscellaneous uses include additives to caulking compounds, foundry applications, lubricants, greases, silicone release agents, and dry powder fire extinguishers. Wet ground mica prices range from $353 to $496/t ($320 to $450 per st) fob plant. Specialty products may be higher, depending on customer requirements. Dry ground muscovite mica Dry ground mica was produced by nine companies: KMG Minerals, Unimin, US Gypsum, Mineral Industrial Commodities of America, Spartan Minerals Corp., Asheville Mica Corp., Deneen Mica Co., Pacer Corp., and J.M. Huber Corp. Dry ground mica's primary market is wallboard joint compound. Here, it is a functional extender that improves the physical properties and finishing characteristics of the mud. It is also used in various grades as a filler in asphalt products, enamels, mastics, cements, plastics, adhesives, texture paints, and plaster. Dry ground mica became popular as an additive in oil well drilling fluids, where the mica flakes platey nature helps seal the well bore, preventing circulating fluid loss. But oil's dramatic price drop and consequent curtailing of well drilling brought this once booming market to a virtual halt. Forecasters predict that this business will gradually pick up during the next few years and most current dry ground mica producers will again produce the oil well drilling material. Dry ground mica prices range from $110 to $420/t ($100 to $380 per st) fob plant. High quality sericite mica, sometimes referred to as an altered muscovite, was mainly produced by two US companies. Mineral Industrial Commodities of America and Mineral Mining Corp. have equivalent capacities of about 27 kt/a (30,000 stpy). The majority of the material produced was consumed by the joint compound industry. Minor uses are in paint and oil well drilling. The lack of ground sericite penetration into the traditional ground muscovite markets is attributed to high silica content, typically in excess of 20%, and a bulk density. Prices range from $88 to $187/t ($80 to $170 per st) fob plant. Phlogopite mica is a dark colored, magnesium bearing mica rarely found in the US. Suzorite Mica Corp., a division of Lacana Petroleum, mines a deposit in Quebec that is 80% to 90% phlogopite. The dark color has prevented the material's entry into the traditional paint markets. But the physical properties and high purity make it useful as a low-cost reinforcing filler in many plastics and several asphalt applications. Phlogopite mica is ground to several grades and may be treated with various surface coatings for use in plastics or coated with nickel for EMI/RFI shielding applications. Prices for phlogopite products range from $144 to $580/t ($104 to $580 per st) fob plant. As in recent years, production of domestic muscovite sheet - block, film, and splittings - remained insignificant. These resources are limited and uneconomic due to the high cost of hand labor required to process sheet mica in the US. Imports from India and Brazil were the primary sources of the estimated 1 kt (2.4 million lbs) valued at $2.5 million consumed by US electronic and electrical equipment manufacturers in 1986. Reserves As a feldspar, kaolin, and lithium industry coproduct, flake mica will continue to provide a large percentage of mica re- This summary of 1986 mica activity was received too late to be used in the June issue.

Jan 7, 1987

By Carlos Viramontes Aldana

Mining in Mexico is one of its post traditional activities, whose influence in the development of important cities and communications has been decisive. Precious metals and, to some extent, copper and tin were known and used before the Colonial period, but from the sixteenth century to tie end of the nineteenth century, mining and metallurgical industries were concentrated in the precious metals, mainly silver. This silver was exported to Spain and other countries under the Spanish. Rule, Mexican peso was known world wide since the end of the sixteenth century and Mexico ranked as the first silver producer since the eighteenth century.

Jan 1, 1985