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By J. W. Cooksley

Pyrometasomatic zones are a type of replacement deposit, normally in a carbonate rock unit, which consists of a zoned, coarse-grained, generally iron-rich mixture of calcium and magnesium silicates. These zones or rock masses are also called ?skarn,? and ?tactite?. They are formed as a result of the interaction of a shallow intrusion of magma with a carbonate or calcareous host rock and are considered to be of hydrothermal origin. Three environments of pyrometasomatic deposits are depicted in Figure 1. Of course, the interaction takes place at high temperatures. Pyrometasomatic zones are categorized as calcic or magnesian, depending on whether the intrusive interacts with a limestone or a dolomite. Common pyrometasomatic zone minerals are garnet, epidote, quartz, calcite, wollastonite, actinolite, hedenbergite and diopside. Pyrometasomatic zones are of considerable economic importance because they contain ore deposits of tungsten, molybdenum, copper, lead, zinc and iron. According to Rose and Burt (1979), the chronological sequence in the formation of a ?typical? pyrometasomatic deposit is as follows: 1. Shallow intrusion of magma at 900-700°C into carbonate sediments.

Jan 1, 1981

By G. H. Thomas, M. C. O’Riordan, S. Rae

INTRODUCTION The British mining industry comprises 228 nationalised coal mines producing some 113 million tonnes of deep mined coal and employing 242,600 persons of whom 185,200 work below ground. There are in addition 174 small privately-owned coal mines employing 1500 persons underground and producing 1.5 million tones of coal. In the non-coal sector there are 108 privately-owned mines producing some 20 different minerals, including tin, wolfram, fluorspar, potash, rock salt, china clay, ball clay and fireclay. There are currently 4,100 persons employed in these mines of whom 2,346 are employed below ground. One mine producing potash employs 870 persons of whom 465 are underground workers. Since 1975 all matters relating to the health and safety of persons at work and of the general public who are exposed to industrial hazards have come within the purview of the Health and Safety Executive (HSE). The Mines and Quarries Inspectorate (MQI) is a constituent part of that organisation and enforces legislation applicable to all mines and quarries. The National Radiological Protection Board (NRPB) is a statutory and independent body that was established in 1970 to advance knowledge and provide information and advice about radiological protection. The NRPB has an agency agreement with HSE to provide advice and services relating to radiological protection, including protection against exposure to radon decay products in mines. There are as yet no statutory requirements controlling exposure to this source of radiation in Britain. Investigations for the presence of radon in British coal mines were begun in the mid 195Os. The concentrations found were of low order, typically around 2 pCi/l (Duggan et al., 1968). This was not surprising since big coal mines are well ventilated to control methane and airborne dust and it is now generally accepted that radon and its decay products do not constitute a health hazard in British coal mines. At one or two small mines where igneous intrusions were in close proximity to the coal workings, slightly higher readings were recorded. The MQI then commissioned NRPB to make investigations at metalliferous mines and in these much higher readings were detected. It was later agreed that the NRPB should undertake a survey of all non-coal mines in Britain to establish the extent of the problem. This survey was conducted mainly in 1973, (Strong et al.,1975) and follow-up surveys at various mines have since been conducted by the MQI. These investigations revealed that radon readings could be high in mines producing tin, haematite and fluorspar. Some small mines working other minerals in the same localities also showed high readings. More recently owners have been making environmental measurements at mines where there was some cause for concern. LEGISLATION AND RADIATION STANDARDS As a result of the survey work for MQI the Board in 1975 recommended an occupational limit of 4 WLM in a year from radon decay products together with a programme of radiological supervision (Strong et al., 1975). The MQI accepted the recommendation and advised employers and employees that the 4 WLM limit should be adopted. The limit corresponds to a concentration of 0.3 WL, equivalent to 30 pCi/l of radon-222 in equilibrium with the decay products, and was in accordance with an earlier recommendation by the International Commission on Radiological Protection (ICRP, 1959). ICRP recommendations are usually endorsed in Britain. It was recognised that some years would probably be required to achieve general compliance, and this is proving to be the case. Some confusion has been caused in Britain by the conflict between successive Euratom Directives on this and other standards of safety. As relative newcomers to the Community, we were not affected by earlier Directives, but the situation is different now. In 1959, the Commission of the European Communities provisionally recommended a maximum permissible concentration for radon-222 and daughters of 3 x 10-7 µCi/cm3, which corresponds to 300 pCi/l (CEC, 1959). The number was affirmed in 1962 (CEC, 1962) and reaffirmed in 1966 (CEC, 1966) but without any specification of the state of equilibrium. In 1976, the CEC again recommended 300 pCi/l, but on this occasion, the daughters were assumed to be present in the same quantities as in unfiltered air (CEC, 1976): this implies 40 WLM a year in poorly-ventilated mines. The formula is repeated in the latest version of the Directive (CEC, 1980), but the value is now said to be an interim one because it might not ensure compliance with the appropriate dose limit. ICRP (1955) recommended 300 pCi/l in equilibrium with the decay products in 1955 and reduced this value to 30 pCi/l for unfiltered air in 1959 (ICRP, 1959), endorsed it for equilibrium conditions in 1976 (ICRP, 1976), and held to it until 1980: these values imply respectively 40 and 4 WLM a year. The recent recommendation of the ICRP (1980) that the annual limit of intake for the decay products should be 0.02 J in a year corresponds to 5 WLM, but there is a rider that reduction should be made for exposure to gamma rays and long-lived airborne radioactivity. An allowance of 20% is suggested for uranium mines, implying 4 WLM a year for the decay products. The

Jan 1, 1981

By W. A. Cincilla, Z. T. Bieniawski, E. Unal

Although coal mine tunnels such as the main haulageways or roadways are the lifelines of coal mines, little attention has been paid to them in terms of pre-construction planning and design. This paper presents the results of research aimed at improving design methods for coal mine tunnels. Studies of the current practice and design needs in the United States were performed for coal mine development entries. A design approach evolved for coal mine tunnels is presented. It is based on field investigations and laboratory model studies aimed at integrating into reinforcement guidelines for coal tunnels. An up-to-date bibliography on coal mine tunnels is provided.

Jan 1, 1981

By Stanley J. LeFond

The Republic of Botswana, one of the newer countries of southern Africa, attained independence on September 30, 1966. It covers an area of about 225,000 square miles (582,000 square kilometers) which makes it slightly larger than France, or slightly smaller than Texas. It is bounded by Zimbabwe, the Republic of South Africa and Namibia, including the Caprivi Strip. Angola and Zambia are close neighbors. (Map 1). Botswana lies at the center of the southern African plateau at a mean elevation of 3,300 feet (1,000 m). It is a natural habitat for most species of African fauna. The rolling sands and extensive grasslands of the Kalahari Desert cover the southwest. The climate is sub- tropical. Summers, although tempered by north- easterly breezes, are hot, but mean maximum temperature seldom rises above 100°F (38°C). Winters are dry with wide temperature variations, which often give rise to frosts.

Jan 1, 1981

By D. Malhotra, R. M. Hoover, F. N. Bender

The paper discusses the effect of aeration and agitation on grade and recovery of molybdenite. A series of factorially designed flotation tests were carried out in a "Leeds Automatic Laboratory Flotation Cell." Analysts of flotation results indicate that molybdenite has fast floating and slow floating components. The rates of fast floating components, which do not create a problem inflotation, could be varied by changing agitation or airflow rates. However, the rate of slow floating components was stable and was only a function of residence time. Aeration has a significant effect on the grade of MoS2 and only a slight effect on the recovery of MoS2. Agitation has a slight effect on the grade, but does not effect the recovery of molybdenite. The implications of the results on the design of flotation cells and control and optimization of the existing circuits are also considered.

Jan 1, 1981

By David T. Kao

The energy situation the world faced during the decade of the Seventies resulted in actions throughout the free world to reduce its dependence on OPEC oil. Many nations heeded the indicators early in that decade and commenced efforts to reduce their oil requirements. Those nations which did not heed these warnings had the message brought to them more emphatically in the last portion of the decade with the further rapid and continuing rise in prices of OPEC oil. Furthermore, the demonstrated unstable nature of large oil-producing countries has made it clear to all free world nations that their energy demands of the future must be provided for by some more stable and assured supply. Now, early in the decade of the Eighties, we see the need for expanded use of coal as an energy supply to be essential. The result in 1980 and 1981 has been a great increase in demand for steam coal worldwide. In essence, a new business for the United States has developed in steam coal export. In the United States, the large growth in foreign demand for our steam coal is now well recognized and documented. A major impediment in meeting this growing demand became abundantly clear in 1980. This impediment is the congestion existing at U.S. coal export ports. With the recognition of this constraint, a plethora of activity has been observed in announcements for alleviating the problem by improving and expanding current export port facilities. In addition to improvement and expansion, an abundance of totally new facilities has been announced in an effort to find ways to meet this large demand in the new business of steam coal export. This is needed; and hopefully, many of these plans will be translated into action. While total implementation of all stated plans is not expected, much of the implementation depends upon large- scale dredging, large waterside ground storage sites, and improved handling equipments in the conventional type of export ports. The time and capital required for implementation is great, and environmental problems associated with dredging are substantial. Host significantly, and unfortunately, implementation that does include dredging our ports will still not permit use of the truly large colliers of 140,000 DWT and greater, which are evolving as the "state of the art" in long-distance sea transport.

Jan 1, 1981

By William L. Carter

Through your presence here this morning and your membership in the Society of Mining Engineers, you have shown that you are interested in keeping abreast of the latest technology and mining procedures, want to be part of the continuing progress made by those in your profession, and are looking for ways to participate in expanding your professional and personal experiences and skills. All of these factors are part of your continuing education, the need for peer identification or recognition, and the desire to make a specific contribution to strengthening your profession. However, you may be here with or without your company support and financial backing, unless you are self-employed. Whether you are here for the above reasons, or for many others, your presence reflects a recognition of the importance of participating in the organizational structure of your profession.

Jan 1, 1981

By H. L. Fraser

A review of the possibilities of performing microchemical analysis in thin sections using a combination of scanning transmission electron microscopy and energy dispersive spectroscopy of x-rays is given. Particular attention is paid to the factors that limit accurate analysis at the highest spatial resolution. As an example of the use of these techniques applied to a potential problem in minerals processing, the identification of iron pyrite and pyrrhotite particles in Illinois, Herrin #6 coal is presented.

Jan 1, 1981

By P. S. Daly

"The purpose of this paper is to describe the types of instrumentation used at Sherritt Gordon's Ruttan Mine to monitor the"" effects of mining. The aim of the monitoring program is to establish parameters to achieve a maximum ore recovery with minimum dilut ion in a safe environment.The copper-zinc Ruttan Mine is in northwestern Manitoba, approximately 760 km from Winnipeg (Fig . I) . Production commenced in 1973 from the open pit at the rate of 10,000 tons per day. Pit bottom lies 58 metres above the first mine level. Underground development has overlapped with open-pit mining throughout. The open pit was phased out in the latter part of 1980.Underground production began in early 1979. The mining method employed in the first lift is sub-level blasthole open stoping with delayed hydraulic filling. Large-diameter (6.5-in.) holes are being drilled in the crop stope area and are also planned for some other areas for vertical retreat mining into a slot. GeologyThe orebody consists of numerous sulphide lenses of variable size, geometry and geology . The lenses occur within volcanoclastic host rocks which exhibit a strong variability in intensity and type of alteration and structural characteristics. Stope design and sequencing were based on these complex geological factors."

Jan 1, 1981

The need for a carefully prepared set of special conditions, to be used with general conditions of contract or, alternatively, a purpose written contract for adoption in tunnelling work in Australia is discussed. Recent decisions on the proprietor's liability for tender information and arbitrator's power to award interest are examined. A new clause for inclusion in contracts specifically giving arbitrators power to award interest is suggested. Similarly, a new clause covering delays due to environmental disputes is suggested, particularly for marine outfall tunnels. An alternative method for the settlement of disputes by negotiation is suggested for consideration and contracts and contract administration are discussed as the possible weak point in the construction process. At the conference it is intended to present a method or process to be used in contract administration which should reduce disputes, result in a better quality and efficiency of administration and ultimately in better contracts'.

Jan 1, 1981

By Paul H. Johnson

Resource Engineering and Development, Inc. is designing and building a portable 150 to 225 TPD, flotation-cyanide leach plant with unitized, skid-mounted components. This plant design, with its portability, low capital investment, and high recovery of silver and gold from many partially oxidized ores, is well suited to treat many small, high-grade deposits, old waste dumps, and old mill tailing piles. A description is given of flotation and/or cyanide leach tests run on about 17 partially oxidized, newly mined ores; waste dump materials; placer slimes; and old mill tailings.

Jan 1, 1981

By Oscar Auerbach, Marvin Kuschner, Rosemarie Mick, Geno Saccomanno, Stephen Wood, Victor E. Archer, Marlene Egger

INTRODUCTION Excess bronchogenic carcinoma has been demonstrated among underground uranium miners in the United States, Czechoslovakia, and Canada (Archer 1981). This excess cancer is attributed largely to radiation from the alpha particles delivered to the tracheobronchial epithelium by the decay of short-lived daughters of radon. Interaction between the radiation and cigarette smoking has been demonstrated in production of the excess cancer (Archer 1973). The distribution of histologic types of bronchogenic cancer among uranium miners was established as different from that in other men in 1964 when an analysis of the first 51 cases among United States uranium miners was published (Saccomanno 1964). It was confirmed five years later by Yugoslavian studies (Horacek 1969). A later analysis, using a relative frequency method, indicated that oat cell and other small cell undifferentiated carcinomas increased markedly with increasing exposure to radiation in uranium mines (Saccomanno 1971). A subsequent analysis used only cases from an epidemiological study so as to enable calculation of expected numbers. It showed that there was an elevation in incidence of epidermoid, adenocarcinomas, and possibly other types, as well as small cell undifferentiated carcinomas (Archer 1974). At that time, it was felt that the histological distribution of cancer among uranium miners was well established. However, one of the authors (GS) has noted that fewer oat cell carcinomas were appearing among uranium miners in recent years. In his material the fraction of oat cell carcinoma, in successive 5 year periods between 1960 and 1980 was 59, 46, 37, and 22 percent. The association with calendar years is almost certainly spurious, reflecting some other factor associated with time. From the standpoint of tumor biology such a change must be important. This is a preliminary report which attempts to determine the cause of that change. POSSIBLE REASONS FOR OBSERVED CHANGE IN CELL TYPES 1) It might reflect a decrease in radiationinduced carcinomas, so that most of the ones being seen now are cigarette-induced. This appears to be a possibility because radiation levels in mines had been markedly reduced in the early 1970s, and because most of the uranium miners now developing carcinoma had quit mining during the 1965-1975 period. 2) It might represent a change in interpretation by the pathologists involved. 3) It might represent a real change in distribution as a result of increased latency, an aging population, cessation of smoking, increasing pack years of cigarettes, or other factors which have changed with time. Each of these possibilities is being checked. Dr. Waxweiler, later in this conference, is presenting an updated mortality analysis of United States underground uranium miners. His data indicate that lung cancer incidence among the Study Group of uranium miners is still quite high, but the ratio of observed to expected is falling somewhat. It is apparent that decreasing exposures in uranium mines is not yet reflected in normal lung cancer mortality rates. Reason #1 is therefore very unlikely. Thirty-five percent of the histologic types of carcinomas in this study were classified by a panel of three pathologists, 45% were classified by one of the panel members, and 20% were classified by a number of

Jan 1, 1981

By G. L. Finfinger, J. Cervik, L. J. Prosser

The Bureau of Mines has completed an underground degasification project in which an underground piping system was used to transport methane from the coalbed to the surface. In a 10-month period four horizontal holes were drilled to an average depth of 1,450 feet. All four holes were surveyed vertically and azimuthally. In 991 days of degasification, 255 MMcf of gas was drained from the coalbed. The underground piping system proved to be a safe and effective means of transporting methane from the coalbed to the surface.

Jan 1, 1981

By Martin T. Broome

INTRODUCTION The Luanshya Mine is situated in the southern part of the Zambian Copperbelt. The copper ore deposit is stratiform, and is preserved in a synclinorium known as the Roan/ Muliashi basin. Roan shaft (formally called No.14 shaft) is located at the eastern end of the syncline and is theoldest of the presently operating hoisting shafts, being sunk during the 1930's. It presently hoists some 45 per- cent of the total Luanshya Mine production. A cross-section through the shaft is shown in figure 1. The ore formation on the south limb is unmined on this section because until recently it was believed that such mining might cause damage to the shaft. This paper examines the influences of adjacent mining on this so-called 'shaft pillar', and describes the mechanics of subsidence of the pillar itself. GEOLOGY AND STRUCTURE Figure 1 shows the general form of folding in the vicinity of Roan shaft. The north and south limbs of the main syncline approach parallelism, with the bottom of the trough fairly smoothly rounded. The axis of the - trough plunges to the west-north-west at 6° - l0°. A brief summary of the major lithologies present in the Roan basin is given in table 1, however, the performance of the overall structure during progressive mining of the ore horizon is controlled by the following features in addition to the mining method. Intraformational Contacts These are characteristically weak in most geological environments. The BC/RL7 contact is an unconformity between moderately weak quartz-biotite schists below (unconfined compressive strength 40 - 80 MN/M 2), and strong quartzites above (U .C .S. 170-200 MN/M2) Subsequent formations are conformable, and planes of weakness are generally the result of contrasting lithology (see below). Weak Interbeds The Rt7, RL6, RL5, RL3 and RU2 horizons consist predominantly of quartzitic rocks, i.e. conglomerates, quartzites and argillites, and as such are generally strong and considered suitable for the positioning of development. Between these however, lie two much weaker dolomitic horizons, the RL4 and RU1. The Rt4 is the main hangingwall aquifer, and must be drained prior to mining. Drainage results in an extremely weak, blocky cavernous horizon which usually requires support if exposed by development. Similarly, the RU1 formation is comprised mainly of dolomites and dolomitic arqillites which are weak and cavernous. In the eastern part of the Roan/

Jan 1, 1981

By L. W. Helle

In this investigation, which was conducted at the Metallurgical Research Plant, Lulea, Sweden, a series of experiments were carried out using a water-model to simulate the gas rinsing of a ladle containing liquid metal. The factors examined include the effect of gas flowrate, the position of a porous plug or lance, the immersion depth of the lance, and the geometry of the bath at the time of complete mixing. Mixing times were recorded by conductivity measurements. The results showed that there is a threshold level for mixing above which no advantage is to be gained from an increase in the gas flowrate. It is suggested that the results can be applied to rinsing ladles in working situations, the levels being approximately 270 dm3/min for 40 t ladles and 780 dm3/min for 150 t heats. The optimum siting of the lance or porous plug is a position that is three-quarters of the internal radius from the centre of the ladle with the lance penetrating as deeply as possible into the ladle. The best design of liquid bath is that having a diameter-to-height ratio of I. An equation was developed for the calculation, by dimensional analysis, of the time required for mixing during gas rinsing, and a comparison of the calculated mixing times with the results from production trials shows a satisfactory agreement (with a correlation factor of 0,91). Thus, an equation is available for the calculation of the stirring time needed to completely mix the bath in production situations.

Jan 1, 1981

Lower the respirable dust exposure of longwall shearer operators with improved water spray systems on the shearer. Approach Orient sprays (rather than relocate them) so that dust is held against the face. How It Works Research by the Bureau has indicated that shearer operator dust levels depend largely on how fast dust from the upwind drum spreads into the walkway. Water sprays on the shearer body can greatly affect the spreading of this dust because each spray moves air like a small fan, generating strong cross-currents of air around the shearer. Poorly designed spray systems, especially those with nozzles pointing upwind, will stir up much more dust than they sup-press. On the other hand, Improved systems may be designed to hold the dust cloud against the face while also suppressing It. In such arrangements the water is sprayed downwind and used with screens made from conveyor belting.

Jan 1, 1981

This Bureau of Mines publication contains the texts of the four papers presented at the May 6-7, 1980, seminar on the role of overburden analysis in surface mining. Coverage includes the geologic distribution of pyrite and calcareous material and its relationship to overburden sampling, overburden sampling and analysis, use of soil-overburden data in mine planning and development, and minesoil classification.

Jan 1, 1981

Agnico-Eagle Mines Ltd. comprises a Gold Division at Joutel, Quebec, and a Silver Division at Cobalt, Ontario. In 1979 the Silver Division milled 41,700 mt (46,000 st) of ore at a recovered grade of 139 g per mt (4.06 oz per st) for a production of 5,816 kg (187,000 oz) of silver. The 100 -year -old mining, camp of Cobalt has long been noted for its high-grade silver ores, and now seems to be on the threshold of being revived with several companies operating in the area. In 1979, the Gold Division milled at the rate of 27,200 mt per month (30,000 st) and processed 333,000 mt (367,000 st) at a grade of 6.58 g per mt (0.192 oz per st) with a mill recovery of 91.670 to produce 2,013 kg (64,700 oz) of gold. The average total cost per ton milled was $22.10 per mt ($20.05 per st) which was $3.66 per g ($1 13.90 per 0s). These figures make Agnico-Eagle one of the lowest cost producers in North America. Gold occurrence in the Joutel ore is fine-grained and contained within sulfide facies composed mainly of pyrite with minor pyrrhotite. Two underground mining methods are employed with long hole stoping accounting for about 75% of the ore mined and shrinkage stoping the remainder. Ore from underground is hoisted into a 545 mt (600 st) coarse ore bin from where it is conveyed to a 45 mt (50 st) surge bin ahead of the 10-51 Hydrocone crusher. Crushed ore is then screened to make a 13 mm (112 in.) product with the oversize being recrushed in a 7-60 Hydrocone. Mill feed is conveyed to two 900 mt (1,000 st) fine ore bins. The Hydrocones were installed as part of a new crushing plant in March of 1980 and have contributed substantially to an increase in mill capacity. Space has been left to install a third crusher in the future. The fine ore bins discharge to a 2.75 m by 3.66 m (9 ft by 12 ft) rod mill, followed by a 3. 7 m by 5.5 m (12 ft by 18 ft) ball mill in closed circuit with a Krebs 380 mm (15 in.) cyclone to produce a 7070 minus 37 micron (400 mesh) .flotation feed. This pulp is first treated in a 34 cu m (1, 200 cu ft) Maxwell flotation cell and then in an additional twelve 2.8 cu m (100 cu ft) cells. Combined flotation concentrates are reground to 9070 minus 37 microns (400 mesh) in a 1.8 m by 4.9 m (6 ft by 16 ft) ball mill in closed circuit with a single Krebs 254 mrn (10 in.) cyclone. Flotation tailings are sent to the tailings dam. Reground concentrates are then aerated with lime to a single Pachuca and thickened in a 16.75 m (55 ft) diameter thickener with the addition of diesel fuel to render any activated graphite inert to adsorption of

Jan 1, 1981

By Robert C. Speck

Floor heave or deformation of the mine floor into the mine opening is a problem which has plagued coal mines in this country and others. In mining areas where room and pillar mining is practiced, floor heave generally occurs when the stress applied to the floor material by a coal pillar exceeds the bearing capacity of the floor strata. When the floor strata beneath the coal pillar fail, the pillar moves downward and displaces the material under it. This material, in turn, moves outward and upward into the mine opening (Figure 1). As the underlying materials fail, the load supported by the coal pillar may be transferred to adjacent pillars. If these are marginally stable, they too may become overloaded and push into the floor. Thus, floor heave can spread through a large portion of the mine in a progressive manner. As the pillars push into the floor, differential movement and flexure of the roof strata may cause them to weaken and fail, resulting in subsidence of the ground surface above the mine. This paper describes the problem as it was manifested in the Zeigler Coal Company No. 5 and Murdock room and pillar coal mines near Murdock, Illinois, and reports the results of a U. S. Bureau of Mines- sponsored study conducted by the University of Missouri-Rolla. During the course of the study, floor heave in the two mines hindered the transportation of men, machines, and coal to and from the working mine-face, interrupted ventilation plans, drastically increased roadway maintenance costs, intensified safety and strata control problems, destroyed large pieces of equipment, and, several times, pre- vented access to otherwise minable coal resources. The ultimate objective of the study was to develop one or more simple procedures to allow detection of a potential floor heave problem during the exploration phase of mine design--before initiation of production mining.

Jan 1, 1981

By R. Masse, J. Chameaud, J. Lafuma, R. Perraud

Estimating the risk of lung cancers for workers in uranium mines and defining the resulting dose equivalent limits have been made possible thanks to work carried out in two scientific fields : physics and epidemiology. Theoretical calculations on the basis of physical models for the former and epidemiological surveys on the mortality of uranium miners from lung cancer for the latter. However, even though considerable work has been done in these two areas, the results obtained still remain controversial on several points. The radioactive and physical instability of the aerosols present in the atmosphere of the mines and the biological complexity of the human lung which even the most sophisticated physical models can reproduce only very schematically have often proved to be insurmountable difficulties for physicists, explaining the uncertainties which subsist concerning the dose delivered to the various parts of the respiratory tract from the air breathed by miners during their work. Epidemiological investigations on the other hand, in spite of the high quality of the surveys carried out, remain open to criticism, essentially because of the very approximative estimation of the individual occupational exposure to radon daughters. This is due to the fact that uncertainties arise from the measurement of radon gas if the state of equilibrium with the daughters is not accurately known or, if the active deposit is measured, to the fact that these measurements are insufficient in number. The controversies and discrepancies which subsist with regard to the evaluation of the level of risk, and in particular for low doses, can thus be understood. In addition, epidemiological surveys cannot dissociate the carcinogenic action of radon from the synergistic or potentiating actions of tabacco and of other pollutants present in uranium mine air. Animal experiments have been largely taken into account for evaluating the toxicity of various radionuclides. This type of experiment is necessary when human data do not exist and has provided us with much information. For instance, the relative biological effectiveness of the various types of radiation, the metabolism of radionuclides and the mechanisms of cancer induction have been approached and satisfactorily resolved in this way. Concerning radon and its daughters, however, animal experiments have been used very little even though it seems apparent that they should complement epidemiological studies. For instance, whereas doubt can be cast on the data obtained from human epidemiology because of the uncertainty concerning the individual exposure of miners, those drawn from experiments are indisputable because in this case the dose is as perfectly known as the effect. In addition, the effects of radon can experimentally be appreciated separately whereas in the surveys, they cannot be dissociated from the effects of the other pollutants in the mine. Finally, there are no other means of dealing with the mechanisms of cancer induction. In order to gain any useful knowledge from this method however, the experimental model must necessarily present certain methodological guarantees and the effects seen in the animals must enable a comparison with those which appear in man. For this reason we will present here the animal model we have been using for 15 years, and will give the results obtained and compare them with human data and made a synthesis. Finally the conclusions which can be drawn will be discussed as well as their limitations with respect to the protection of uranium miners. I - MATERIAL AND METHODS Male SPF Sprague-Dawley rats were used. At the onset of the inhalations they were around 3 months old. Their small size makes it possible to expose a large number of animals at the same time. Their life-span is long enough to be able to follow the evolution of the cancers and to estimate the latency time. Finally, they present the advantage of having a very low rate of spontaneous lung cancers (SANDERS, 1979). I.1 - Three inhalation techniques were used. 1.1.1. – [Inhalation of radon decay products.] The inhalation apparatus has been described previously (CHAMEAUD et al. 1971). The first experiments utilized a room of a half cubic meter linked to a source made up of high grade uranium ore. Later on, a large installation was built with a 10 m3 inhalation chamber making it possible to expose up to 500 rats at one time at radon concentrations ranging from 100 to 10 000 WL for variable lengths of time (1 to 10 hours per day). These concentrations are higher than those to which the miners are generally exposed, but in order for the cumulated doses in man and in animal to be similar and delivered for the same fraction of their respective life-spans, the ratio of the concentrations should be approximately that of the life-spans. The concentrations of radon and its daughters during the experiments were carefully controlled thanks to multiple samplings of radon gas associated with measurements of radon decay products. I.1.2 – [ The dust inhalation chamber] has already been described : it is a dust-loading chamber where the dust content remains constant during the experiment and can hold over 20 - 30 animals (PERRAUD et al, 1970). I.1.3 – [Tobacco inhalations] take place in a smoke box

Jan 1, 1981