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By St. E. Deák

This paper focuses on maintenance of underground salt air curative quality using environmental friendly solutions. Possible ways to preserve its curative properties, in relation with the admissible salt air quality parameters, are analyzed. In situ investigations regarding microbiological impregnation in walls and the air inside the Romanian salt sanatorium were initiated. The results of a pilot project, which is in progress at Praid salt mine, are presented. After the end of the investigation at this site, investigations will continue in other Romanian salt mines, such as Slanic Prahova, Targu Ocna and Cacica.

Jan 1, 2006

By D. E. Ranta, M. G. Hester

The ore reserve modelling of stratiform uranium deposits to be mined by selective underground mining methods must be done with consideration of the erratic nature of the ore-forming processes that produced the mineralization. Estimation methods that model the uranium grade as a smooth transition between high-grade and low-grade drill hole intercepts tend to greatly overestimate the ore tonnage. Care must be taken to first establish realtistic ore pod geometries and then estimate the grade of the reserve units within the pods.

Jan 1, 1992

By L. H. E. Weyher

A mine is essentially a vast materials-handling system. All other systems found in the mine exist to one degree or another to support the materials-handling functions, from the cutting at the face to the hoisting in the shaft. In this chapter computerized planning of underground materials-handling systems will be examined by dividing this function into: (1) the planning of the production section, and (2) the planning of underground rail or belt haulage from the production section to the shaft, slope, or surface. While alternative divisions might focus on the different materials- handling functions, i.e., production, supply, and manpower transportation, historical computer analysis has focused on the various systems rather than functions. The emphasis in this chapter is directed toward coal mine applications; however, most of the programs and methods are equally applicable to other underground mines. Markedly different methods are encountered in each system, and moreover, marked differences exist in the nature and the degree to which the materials-handling subsystems in each interact with the environmental or support systems. The most intimate interaction exists at the faces where geologic, human, and machine performance factors are closely related and constantly varying. In view of this, the planning of the materials-handling systems for the face will usually stress flexibility, while the outby materials-handling systems will generally place decreasing emphasis on flexibility and more on system reliability, capacity, and cost effectiveness. Thus, hoisting and main haulage systems are generally designed and constructed as permanent installations and cannot be readily changed, whereas secondary haulage systems and face operations are relatively mobile. These differences may have considerable significance for the mine planner in making technical and financial comparisons of alternatives to provide the scheduled mine production.

Jan 1, 1979

By Peter Ralph

All copper ore haulage at Isamine was transferred to the new 19 level haulage network by mid 1975. Previous experience together with design studies had indicated that a three train operation would be required to haul the scheduled ore production. The ore train with a gross weight of 600 tonne is made up of 15 bottom dumping trucks hauled by twin electric locomotives (Figure 1). Present train speeds reach 40 km/hr and, in the future, this speed could be increased to 55 km/hr. The planned operation on the restricted track network and the relatively high train speed meant that the train driver operated block light system would be inadequate on the grounds of haulage safety and meeting production targets. Some form of Centralised Train Control (CTC) system emerged as a necessity, and as an initial step, tenders were called for a relay control type CTC system. The high cost of these systems and the anticipated high maintenance costs and inflexibility of the offered systems led to the rejection of the tenders. It was decided to develop a CTC system locally and to use a digital computer to perform the basic track [ ] equipment interlocking tasks and monitor haulage operation.

Jan 1, 1979

By S. Crewdson

Vertical hoisting of materials using hoists and skips is common in the Mining Industry. These systems have a number of drawbacks, one being limited hoisting capacity at medium depths. FKC-Lake Shore and Metso Flexowell have been developing and installing vertical belts for medium depth shaft applications for many years, progressively going deeper whilst increasing belt capacity. The latest development from Metso the Pocketlift® belt advances this technology allowing higher tonnages to be lifted from greater depths. The design, manufacture, installation and operational experience of a 1818 tonnes capacity, 273 meters vertical lift Pocketlift® system at the White County Coal Pattiki 2 mine is the subject of this work.

Jan 1, 2003

By Wayne Taylor, Martyn Dawborn

Simulation modeling of portions of two platinum mines using General Purpose Simulation Software (GPSS/H™) is presented in this paper. Both mines, located in the Bushveld Igneous Complex PIC) of South Africa, exploit Merensky and UG2 reef horizons, which are processed separately and therefore handled individually from the stope face to surface, requiring duplication of storage arrangements and batch operation of transport facilities. The first simulation assignment concerns the upgrading of a shaft system operating exclusively on Merensky ore, to hoist UG2 ore and increase production. The second assignment comprises a simulation of rock flow from the stope face to surface by way of tramming, inclined conveying and vertical hoisting. Development ends and stope boxholes were modeled down to individual hoppers (cars) demonstrating the versatility of the GPSS/H™ language.

Jan 1, 2002

By A. E. Isaacson

Researchers at the Bureau of Mines, U.S. Department of the Interior, developed and tested equipment to measure corrosion rates on a commercial-scale mill. Bench-scale experiments were also designed for duplicating ore grinding conditions closely enough that realistic rate determinations can be made in laboratory tests. Rates measured in a laboratory system compared favorably with those measured in the field. Cast steel was found to have corrosion rates in a copper mill and laboratory test cell of 22 and 21 mpy, respectively. Corrosion was found to account for less than 5 pct of the total grinding media wear in the operations studied.

Jan 1, 1989

By Peter G. Chamberlain

Novel and innovative mining methods are attracting the attention of mining engineers at an unprecedented level. Historically, the US mining industry has responded rather conservatively to new technology. The financial difficulties affecting the domestic mining industry in the early 1980s changed attitudes toward new technology. The market contraction during that period, coupled with an expanding world mine capacity, created a serious oversupply of many raw mineral products. Many mining companies found that retaining a share of world markets while making a profit required drastic cost-cutting measures.

Jan 1, 2008

General. Data for the operating information given in the 15 tables in this chapter was obtained from voluminous questionnaires sent to over 100 operating companies in 1972. There has been a considera¬ble change since then in supply and power costs and many companies have had expansions or revisions since that time, so it must be realized that information is valid for the year 1972. This is true except for the three new properties of Sacaton, Metcalf, and Pinto Valley. These three operations started up since 1972 and all information for them was obtained in 1975. The questionnaires were sent to all major copper properties throughout the world as well as to many smaller units and to some mines that had complex or unusual conditions. Properties for which no information is given did not submit completed questionnaires. Several operations were unable to supply information requested be¬cause of company policy prohibiting it. However, data is presented for 75 different operating properties. The reference number of the left-hand column is the same for all 15 tables of data. If the company had several operating properties as of 1972, then subsequent properties use the same number but a different letter. For example, Anaconda's property at Butte, Mont., is IA, whereas Anaconda's (now Anamax) Twin Buttes property in Arizona is IB. Table I gives general data for the properties including exact loca¬tion, milling rate, pertinent assay values and recoveries, and a brief listing of ore and gangue minerals. It was not possible to obtain any more information from the properties in Chile except that given in Table I. Crushing. Crushing plant operating data is given in Table 2. This table gives data on the crushers, feeders, and screens used at each property. The data obtained on feeders was confusing, but, rather than completely eliminate this information, it was decided to report it as given. The confusion lies only in the description of where the feeder is located. Where a primary feeder is listed it was not possible to determine if this feeder was on primary feed or primary discharge. For secondary feeders it is known that the feeder listed usually is feeding the secondary crushers, but at some properties it is handling the secondary crusher discharge. The same reasoning holds true for tertiary feeders-they handle either tertiary feed or discharge. This table contains a voluminous amount of data. A column giving tons per day per square foot of screen area would have been very informative, but some properties included circulating load in the feed rate and others listed new feed only, so calculations were meaningless. Autogenous Mills. The use of autogenous or semiautogenous mills for any property must be given serious consideration in the future. Table 3 lists data for four properties that are fully autogenous and four more semiautogenous mills that use balls to supplement the chunks of ore. This method of grinding is especially applicable when the ore is of such a nature that crushing problems would be severe, such as when ore is wet or sticky or contains a lot of fines. Paradoxically, it should also be considered when ore is tough and hard and blocky because then the competency of the ore means it can serve well as the grinding media. Where the ore varies greatly in hardness, as at Cyprus Pima and Lornex, semiautogenous grinding has been especially beneficial with capital costs and operating costs both 10-20% lower than could be obtained with conventional crushing and grinding. Rod Mills. For a great many years the standard milling operation used two- or three-stage crushing followed by open circuit rod mills and then ball mills in closed circuit with classifiers of some kind. A surprising number of properties crush to the fine size of about 3/8 in. and then use ball mills only, in closed circuit, with no rod mills. It is difficult to say whether rod mill-ball mill circuits or ball mill only is the best. One can be certain of two things: (1) the argument will go on for a long time and (2) for some mills one method obviously was superior over the other. As ball mills of 14, 15 ft, and larger came into use, more properties like Duval Sierrita (16b ft diam by 19 ft long) and Bougainville (18 x 21 ft) were built with single-stage ball mill grinding. Although there are larger rod mills used, especially in the iron ore industry, the largest rod mills on copper ore are at Twin Buttes (14 x 18.5 ft) and at Gibraltar (13'A x 20 ft). Table 4 lists operating data for rod mills. If a company is listed in Table I

Jan 1, 1985

In early March 2011, a 6.2 m (20.3 ft) diameter Rob-bins Double Shield tunnel boring machine (TBM) crossed the finish line in Sochi, Russia. The machine completed a 4.5-km- (2.8-mile-) long section of tunnel that will ultimately become part of the transportation infrastructure for the 2014 Winter Olympic Games. The TBM advanced through difficult ground at aver-age rates of 100 to 120 m/week (330 to 390 ftpw) for contractor OJSC Bamtonnelstroy, a division of the SK Most Company. The section of tunnel will ultimately become a service tunnel for Complex #3 - a section of Sochi?s transportation infrastructure under construction, which includes road and rail tunnels. A second, 10 m (32.8 ft) diameter Robbins Double Shield TBM is currently excavating the parallel 4.6-km- (2.9-mile-) long main railway tunnel using a continuous conveyor system for efficient muck removal. A 13.2 m (43.3 ft) diameter highway tunnel is also under construction. The 6.2 m (20.3 ft) Robbins TBM achieved high rates despite difficult conditions. The tunnels run through mixed ground including massive to completely fractured limestone with clay seams. Some sedimentary rock including sandstone and siltstone is present, along with fault zones consisting of breccias and conglomerates. In May 2010, the machine was stopped after encountering a significant fault zone consisting of broken rock and running soft ground. Field service personnel and crew successfully freed the machine by excavating a bypass tunnel around the TBM, freeing the cutterhead. Following the restart, a combination of continuous probe drilling and ground treatment with cement silicate and foam kept the machine moving forward.

Jan 1, 2011

By Michael L. Maniocha

Most magnesia (MgO), whether of natural or synthetic origin, is used in the dead-burned or periclase form as refractory linings for the production of steel. Continued research in refractory science, combined with good refractory maintenance and improvements in steel-making processes, have resulted in decreased use of magnesia. To make up for this loss of business, producers of synthetic magnesia have started to manufacture a variety of magnesium-based chemicals that are used in many industries. There are three primary methods of producing MgO. The first involves the calcination of naturally occurring minerals species. Most of the magnesia produced by this method uses the rhombohedra1 carbonate mineral magnesite, MgCO,. To a lesser extent, the mineral brucite, Mg(OH), is calcined to magnesia. Magnesia produced by the calcination of minerals is called natural magnesia. The second production method uses magnesium-rich brines, or sea water reacting with lime or calcined dolomite to produce magnesium hydroxide. The magnesium hydroxide is subsequently calcined to magnesia. Material produced in this way is called synthetic magnesia. The third major method of production uses saline lake brines to produce magnesium chloride. Magnesium chloride brine is sprayed into a reactor where it thermally decomposes into MgO and HCl. The magnesia is purified by slaking to magnesium hydroxide followed by calcination. Magnesia produced in this manner is also know as synthetic magnesia (Duncan and McKracken, 1994). The degree to which the magnesium minerals or the synthetically prepared magnesium hydroxide is calcined governs the physical properties of the resulting MgO. It is the physical properties that dictate the end use for the product. The terms used to describe magnesia vary along with the degree of calcination. Table 1 summarizes the terminology used when discussing the various forms of magnesium oxide.

Jan 1, 1997

By Rasik H. Raythatha

Calcium carbonate is perhaps the most widely used mineral in the world. With total consumption of all calcium carbonate exceeding over 25 million tom per year, within this class of filler, a relatively smaller segment of precipitated calcium carbonates (PCC) is often misunderstood as a commodity product and bundled in the same category as ground calcium carbonate. However, each material has a distinctly digerent role and characteristics. Precipitated calcium carbonates are used to influence specific performance in a specific application whereas ground calcium carbonate is used primarily to reduce cost in many applications. In this paper, attempts are made to demonstrate the role of nano-fine-PCC in improving shear-thinning characteristics of common and specialized sealants and automotive underbody coating and how such "nano-particle" cal- cium carbonate properties can be exploited to process PVC plastics while reducing overall cost. We also review the role of precipitated calcium carbonate as "nano" material and why it must be viewed as a specialty additive.

Jan 1, 2003

By H. Jung, J. Kim, Y. Lee, Y. Seo

"Shale gas has become an increasingly important source of natural gas supply in North America and around the world. Horizontal drilling and multi-stage hydraulic fracturing are the two key enabling technologies for the economic development of these shale gas reservoirs. It is believed that gas in shale reservoirs is mainly composed of free gas within fractures and pores and adsorbed gas in organic matter (kerogen). It is generally assumed in the literature that the monolayer Langmuir isotherm describes gas adsorption behavior in shale gas reservoirs. In this work, we have analyzed several experimental measurements of methane adsorption from the Horn River Shale core samples that obey the Langmuir isotherm. INTRODUCTION In nature, gas shales are characterized by extremely small grain size, extremely low permeability on the order of nano-Darcy (10-6 md), small porosity, and high total organic carbon (TOC). Shale can serve as both source and reservoir rock. The amount of gas in place in shale is strongly affected by the TOC, clays, and the adsorption ability of methane on the internal surface of solid (Martin et al., 2010). Since a considerable amount of gas in shale reservoirs is adsorbed, investigation of gas adsorption can provide critical insights into evaluation of well performance and reservoir characterization. Generally, natural gas in shale reservoirs is stored as free gas in both larger mineral pores and natural fractures, as well as adsorbed gas within organic matter (Leahy-Dios et al., 2011). EXPERIMENT METHOD & THEORY Adsorption Experiment Several experiments were carried out on 9 shale core samples obtained in a vertical well drilled within Horn River basin (Figure 1). The CH4 adsorption isotherms were measured for the different depth. In order to measure the amount of adsorbed gas, the high pressure Belsorp-HP equipment applying volumetric method was used. The temperature was kept at 298 K and pressure was increased up to 18 MPa. Approximately 5 g of crushed sample was used for each measurement."

Jan 1, 2016

By David J. Akers

INTRODUCTION The variety of uses of coal and the wide range of characteristics of coal combine to produce a need for a wide variety of laboratory analysis. Coal is used to heat homes, produce electricity, and make coke for steel manufacture. It can also be used to produce both gaseous and liquid fuels as well as a variety of chemical products. Various applications may require specialized analytical procedures. For example, some of the procedures developed for the coke industry, such as expansion or contraction during carbonization, have little value to the power generation industry. Even for a single application, the type of analysis needed can depend on the source and/or general nature of the coal. This section provides a general overview of the types of analytical procedures commonly applied to coal from the perspective of the user of this information, not the producer. The intent is not to detail laboratory procedures, but rather to discuss the application of commonly used laboratory tests in coal preparation. Accordingly, laboratory procedures are categorized by type of information produced. Gravimetric Analysis Procedures that produce weight-based information (parts per million, pounds per cubic foot, or weight percent). Such analyses can relate to the coal's physical, chemical, or mineralogical characteristics. Volumetric Analysis Procedures that produce volume-based information (amount of a mineral present as a volume percent). The primary source of volumetric information is from petrographic analysis. Application Tests Procedures that measure some characteristic of coal that has been empirically related to some application or handling or processing step. Typically, these procedures attempt to duplicate some aspect of the commercial application at laboratory scale and may produce information in the form of an index. Applications procedures do not measure a single component of the coal but infer the combined effect of multiple components. Each class of information is discussed in the order listed. References are provided as a source of more detailed information. The American Society for Testing and Materials (ASTM) publishes the most inclusive reference to analytical procedures. This publication,16 which is revised annually, provides extensive information concerning generally accepted methods of laboratory analysis. ASTM also provides standards for sampling and some information concerning sample handling.

Jan 1, 1991

By K. T. Valsaraj, L. J. Thibodeaux

Solvent sublation, the separation process for the removal of two hydrophobic compounds (penta- and trichlorophenols) from the aqueous phase, is discussed, as is a steady-state mathematical model for fire process. Solvent Sublation "'as conducted in a continuous countercurrent mode. The underlying mechanisms, theory and experimental details on the effects of process variables on removal efficiency are reported.

Jan 1, 1994

By C. S. Thompson, P. A. Ciullo

Pyrophyllite is a naturally occurring hydrous aluminum silicate with the molecular formula SiO,,AI,,(OH), or, as more commonly expressed, the oxide formula A120,~4Si02~H20. Pyrophyllite is rarely found in deposits as the pure mineral and is often intimately associated with quartz, sericite, kaolinite, and diaspore. These associated minerals, to a large degree, help determine the most appropriate commercial application for a given pyrophyllite ore. Structural similarities plus the generally soft platy nature of pyrophyllite has in the past caused it to be included with talc in applications and production data. The Minerals Yearbook, published annually by the US Bureau of Mines (USBM), still reports on talc and pyrophyllite together, although admitting that they do not share the same uses. Pyrophyllite has also at times been considered a clay mineral because of its structure and chemistry. The refractory properties of pyrophyllite have been known for nearly 200 years, but it has only been in the past 60 to 70 years that a variety of applications have been developed to exploit the unique characteristics of this mineral. Worldwide, pyrophyllite is a component of refractories, whiteware, foundry mold dressings, pesticides, paint, plastics, rubber, cement, fiberglass, and soap. Historical Overview The most salient refractory features of pyrophyllite are its low coefficient of thermal expansion, high thermal conductivity, low moisture expansion, and good resistance to corrosion by molten metals and basic slags. One of the first recorded uses of this mineral was as firebrick in Japan in the early 1800s. This followed its discovery in 1797 on Mount Omotoyama at the site of the present Mitsuishi mine. In addition to firebrick, sawn blocks of ore were used for carvings and in the manufacture of slate pencils and signature seals. The Mitsuishi mine is still one of Japan's largest. By the mid-1800s, refractories were being made in Japan from roseki (a pyrophyllite-bearing ore) for the construction of metal melting furnaces. The mineral did not get its name until 1829 when R. Herman, testing a sample of supposed talc from the gold-quartz veins at the Berezovo deposit in the Urals, showed that it was actually an aluminum silicate and designated it pyrophyllite. This name was derived from the Greek pur for fue and phullon for leaf, in allusion to the effect of heat in causing separation of the laminae in foliated varieties (Mellor, 1927). The exact date of the discovery of pyrophyllite in the United States is uncertain, but it is believed that the talc and soapstone deposits noted in an 1827 report on the geology of the slate belt of North Carolina were actually pyrophyllite occurrences (Olmstead, 1827). Pyrophyllite was first used in North Carolina on a local basis in the early 1800s. Blocks were sawn and cut for use as stove linings, mantels, chimneys, fireplaces, and gravestones. This was the material of choice because it did not shrink when heated, but cut easily and hardened as it weathered. Pyrophyllite crayons were sold commercially by local gold miners for steel marking and as tailor's chalk from about 1800 until 1922. It was during this period that pyrophyllite was discovered near the town of Hemp (later renamed Robbins), NC. The large quantity of scrap resulting from the sawing of crayons at this deposit prompted the construction in 1921 of a grinding plant. The ore scrap was ground to fine granules and sold to asphalt producers to prevent shingles from sticking together. By the mid-1930s, milled pyrophyllite from North Carolina was also being successfully utilized by the ceramics industry in whiteware for its low cost and ability to shorten firing time. Also during the 1930s, pyrophyllite was first used in kilncar furniture in the United States. Canada was another early entrant in the pyrophyllite business. Mining at the Foxtrap deposit on the Avalon Peninsula of Newfoundland began in 1904, with ore shipped to the United States. Production from this deposit was mostly sporadic in the ensuing years until 1956 when mining began for shipment and captive use in US tile manufacture. This production has remained continuous and still essentially captive to the present. The Foxtrap deposit is currently the sole commercial source of pyrophyllite in Canada.

Jan 1, 1994

By S. P. Brown, J. E. Worthington

Increasingly, exploration geology seems to be growing into a practice overly separated from production geology, yet the eventual purpose of exploration is a producing mine. To help in the search for new deposits, exploration "lessons" will be drawn from the papers given at the Fall AIME Applied Geology Symposium. In addition, examples will be re-emphasized to show how early observation of matters now routine to mine work (for example, hydrology, rock mechanics, oxidation state) can help increase the effectiveness of exploration.

Jan 1, 1992

By J. Franko, M. S. Klima

Wet-drum magnetic separators are used extensively for upgrading iron ore and for magnetite recovery in dense-medium separation circuits. In this study, the performance of a continuous, laboratory wet-drum magnetic separator was evaluated both with and without the application of ultrasonic energy when processing dense medium slurries. Test variables included magnetic-to-nonmagnetic ratio, solids concentration and nonmagnetic material. The results indicate that, under certain conditions, the purity of the magnetic material increased after ultrasonic treatment. Key words: Ultrasonics, Wet-drum magnetic separation, Iron ore

Jan 1, 2003

By Glen L. Black

Choosing a mining method for an underground orebody is a complicated and often iterative process. Advances in technology have given design teams an array of possibilities for methods and equip¬ment. Hecla Mining's discovery of the deep Gold Hunter ore body challenged the staff at the Lucky Friday Mine to determine the optimum mining method. Taking an ore body from prospect to production requires traditional resource characterization. This includes drilling, delineating and modeling. Developing the mining plan is an evolving process, changing with each new piece of in¬formation as the project progresses through exploration and development. The Gold Hunter deposit is a steeply dipping vein system in the Wallace Formation of Idaho's Coeur d'Alene mining district. Gold Hunter is a misleading name for the ore body. The vein is a silver-rich, lead-zinc deposit with only traces of gold. The Gold Hunter ore body is located about 1.6 km (1 mile) north to northeast of Mullan, ID. The ore body is mined from the Lucky Friday Mine, located 0.4 km (0.25 miles) east of Mullan. Mining began on the vein from an access drift driven from the Lucky Friday Mine's 4900 level. Production from the ore zone is projected to be 771 t/d (850 stpd). The Gold Hunter ore is combined with Lucky Friday ore and milled in the Lucky Friday mill. The combined ore boosted Lucky Friday's 1998 silver production from 62.2 t/a (2 million oz/year) to more than 124.4 t/a (4 million oz/year).

Jan 1, 1999

New South Wales (NSW) and Queensland dominate Australian black coal production and exports. NSW produced 86 Mt (95 million st) of saleable coal in 1994, a doubling of output since 1980. Asian demand for thermal and coking coal has driven this growth. This high Asian demand is expected to continue and NSW will seek to secure its share. History The history of the New South Wales (NSW) coal industry can be traced to 1797 when coal was first taken from Newcastle to Sydney (Ellis, 1969). At that time, NSW was a British colony, independent from the other colonies, such as Victoria and Queensland. Australia, as a federation of colonies, did not exist until 1901. The Newcastle coal industry grew through the 1800s in line with the growth of the colonies. Several events spurred demand for Newcastle coal. These included: ? The NSW and Victorian gold rushes of the 1850s and associated population growth. ? The development of steamship traffic at the expense of sail. ? The development of railways and town gas supplies. By 1900, Australia was producing 6.4 Mt (7 million st) of coal, most of it from NSW. By then, NSW had established strong export markets in Indonesia, China, Japan and New Zealand. The history of energy consumption is marked by continual competition, changing intensity of use and substitution. From 1900 to 1940, the Queensland, Victorian and Indonesian coal industries developed at the expense of NSW exports. Similarly, New Zealand developed its hydroelectric industry and thus declined as the largest customer for NSW coal. Oil replaced steam in the shipping and railway markets and electricity replaced gas for lighting. Industrial efficiencies also affected coal. Between 1928 and 1938, coal consumed in generating power fell from by 17% on a kilowatt hour basis and, during the same period, the amount of gas produced per ton of coal rose by 18% (Shaw and Bruno). Faced with these pressures, production and exports stagnated. By 1941, Australian black coal production was 14.2 Mt (15.6 million st). NSW's production was 11.7 Mt (12 million st), up only 19% from 1912. Exports had virtually ceased (Fig. 1). In such circumstances, the industry had lost focus. Unions resisted the need for mechanization, for security of employment reasons, and owners were loath to invest. This reluctance to mechanize and the associated in-

Jan 1, 1997