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Stripping of the Exotica open-pit mine, which is proceeding at about 120,000 tpd, is dwarfed by its proximity to the 500-million-ton Chuquicamata tailing pile. The excavating work is being carried on smoothly and efficiently and, as of the end of October, accounts for the removal of 77 million tons of total material of which some 200,000 tons is stockpiled ore. Diamond drilling has outlined an orebody 5900 ft long and 3400 ft wide containing an estimated 153 million tons of ore at 1.35% recoverable copper based on 80 % extraction.

Jan 11, 1969

Andes Copper has an old camp and a new camp, both isolated until recent road improvements. The old camp is at Potrerillos and the new one at El Salvador, 25 road ,miles away. The company was incorporated in 1916 and the first mine, concentrator, leaching plant, smelter and town were built in the succeeding twelve years. The first blister copper was poured on January 24, 1927. Economic conditions determined the long development period but the end result was the design and construction of a mining complex that was all of a piece, unlike the piecemeal additions to El Teniente and Chuqui. The mining episode at Potrerillos came to an end in 1960 when the ore at La Mina became exhausted and the new mine, El Salvador was brought in. Both of these ore deposits come within four hpundred feet of the surface and had they been developed within the last five years might reasonably have been brought in as open pit mines. However, that is conjecture, and as it stands the operation at La Mina was so ideal for the mining method selected, blockcaving, it became a classic for the textbooks. On the other hand, El Salvador has turned out to be a blockcaving mine to test an engineer's skill. In mining the copper deposit at Indio Muerto mountain, there are ground conditions of every conceivable type. Tunneling in one section, the back can cave like sized pea gravel and only spiling can hold it; in another heading only the lifters are shot but often the rest of the round will sit down in one piece; elsewhere the bottom squeezes up and closes the drifts; and contrary to all other locations, there are sections where the block can be undercut without support. Today the scope of operations at Andes extends from mining to electrolytic copper. Ore is mined at El Salvador and the concentrator is also situated there. Concentrates pipelined 14 miles to Llanth, the water decanted, and then it is hauled by rail 40 miles and 5500 ft higher to the Potrerillos smelter and refinery. Potrerillos and El Salvador are respectively 90 and 70 miles from the port of

Jan 11, 1969

By John V. Beall, William F. Haddon

A long the mighty Andean Cordillera, there is splendor beyond imagination-in the natural beauty of the mountains and in daring engineering and lavish investment in the mines. This is the story of the great copper mines of Chile and Peru. Each mine has a special quality which has tested the physical and spiritual resources of the founder. In the early days of the older mines, the mining engineer of song and story was more the rule than the exception. He was physically tough, ingenious and a leader of men. In the current political and social environment of Chile and Peru, the foreign contract mining engineer is still needed; but he must be a different type of man. To John J. Selters at Cerro's Rio Blanco, the principal ingredient is still "toughness," but it is "toughness of mind" that is needed. "He probably should be a teacher." The copper mines are not new. They were, almost without exception, worked by Indians (La Exotica might prove the rule), and later by the intrepid Spaniards. Modern mining began after the turn of the century. In Chile, the first of the big ones was the Braden Copper Co. founded on the El Teniente deposit. This development was followed by Chile Exploration Co. at Chuquicamata and Andes Copper at Potrerillos. These properties have been developed over the years by vast expenditures of money and a monumental amount of labor. None was free of technical problems-metallurgy at Chuqui, marginal grade of the old mine at Andes, avalanches and the great fire at El Teniente. The evolution which has brought the established mines of Chile, and the new ones coming on stream, to their present state of development is in reality the work of wonders of input-money, engineering and responsible management in an atmosphere of political stability. Without any one of these, the result would have been failure.

Jan 11, 1969

Cobriza can only be described as the Machu Picchu of the mining business. This relatively new mine of the Cerro de Pasco Corp. in Peru, subsidiary of The Cerro Corp., was put on stream in December 1967. The best way to get there is to go in the company's HelioCourier with pilot Paco Perez. The plane is mostly engine and the pilot is without nerves. The trip starts at an elevation of 12,000 ft at La Oroya and ends at the Cobriza air strip near the top of the Continental Divide at 14,200 ft. Perez says this is the highest air strip in the world. The flight is made at an altibude below many of the peaks and it is easy to pick out the Inca Trail which follows the ridge line of the top of the Andes. Inca ruins are also visible from the aircraft. The drainage pattern, with a surprising number of lakes and rivers, can be seen and so, too, can a great deal of structural geology and numerous agricultural settlements dotting the altiplano. Cobriza is in the monta[n]a on the east side of the Andes, which is characterized by tropical climate and vegetation, an abrupt change from the frosty mountain atmosphere. The mountainsides are precipitous and the bottoms of the steep valleys are channels for roaring rivers. Such is the setting of Cobriza, above the swift cataracts of the Mantaro, benched out precariously at about 8700 ft elevation. The mountains rise in majestic splendor and the sun comes up late and sets at 3: 30 on winter afternoons. One of the lowest of the Cerro de Pasco camps, it is the most remote.

Jan 11, 1969

Hunkered up against the spine of the Andes in a tight valley where natural refuge from avalanche hardly exists is the daring Rio Blanco project of Cerro Corp. The deposit here was found in 1904, but nature has foiled all previous attempts to open it. To an experienced mountaineer or a highway engineer with mountain experience, the avalanche hazard in the valley of the Blanco river would be immediately apparent. The collar shaft is at the head of the valley at an elevation of 3600 m and for 12 km down the valley there is no space on the floor for building very much; the dissected rock walls are roadways for avalanches and even a highway could not be maintained sufficiently passable. This is the proposition taken on by the Cerro Corp. Chilean National Decree #1699, passed on December 9, 1966, signified "Go" to the Compania Minera Andina, a company whose shares are held 70% by the Cerro Corp. and 30% by the government of Chile. The orebody, although only partially delineated, contains proven reserves of 120 million tons of ore averaging 1.58% Cu. When the operation comes on stream in the last quarter of 1970, it will be at the rate of 11,000 tpd. Annual production will be 65,000 tpy of recoverable copper in concentrates.

Jan 11, 1969

A mine that staggers the imagination is Chuquicamata, the granddaddy of them all. In 1968 production exceeded 300,000 tons of copper. Production began in 1915 and mining proceeded solely on oxide ores until 1953 when the first treatment of sulfides began. Today the company has mined about 1.2 billion tons of all types of material since inception. The accelerating rate of output can be gauged by the comparable 1946 figure of production-to-date which was 350 million tons. No single mine comes close to touching Chuqui for productivity at its high annual metal yield mining only 90,000 tpd of ore at the luxurious waste-to-ore ratio of 0.6 to 1. However, the complexity of the operation is enormous and the experience required to synchronize the various processes is masked by normal operations and only becomes apparent in times of emergency such as when the slide took place in the pit in February.

Jan 11, 1969

E1 Teniente made blockcaving look easy. Ore rolling out the Teniente 5 level has the appearance of nicely screened riprap ready for road dressing. Actually it has been mostly size-reduced by nature abetted along the way by the occasional nudge of a double jack wielded by a buitrero (grizzly-man). It is the famous upside-down mine at Sewell, where the ore flow is down and the people flow is up. Sewell (rhymes with jewel) is the impossible cluster of dwellings clinging to a high Andean spur where 13,000 inhabitants find that staircases must substitute for sidewalks. There is no mining man who is not familiar with the picture of Sewell-by day a pyramid of barracks huddled on the high ground out of harm's way and by night a surprising Christmas tree against the mountain top. Until April 1967, Kennecott's Braden Copper Co. rocked along producing a not inconsequential amount of copper, 180,000 tpy (all tonnages cited here are short tons), attributable to its not unspectacular mountaineering and engineering achievements. These latter included expertness in building avalanche-control fencing; operation of a 35,000-tpd concentrator on the Sewell mountain spur; a spectacular aerial tramway to move 1600 tpd of concentrates to the smelter at Caletones, and occasionally to provision Sewell when snow blocks the road; a cliff hanger of a railroad 43 miles down to the rich bottom land at Rancagua; and last but not least, a 40-mile tailing launder that sweeps across deep valleys on trestles that rival those of the Romans.

Jan 11, 1969

By A. M. Starfield

Discussion J. de V. Lambrechts (Fellow): The author's paper is a brilliant follow-up of an earlier paper by Starfield and Dickson.1 I have no quarrel with Dr Starfield's computerization of a complex problem, but I do not believe that he is getting quite the right answers from his programme. My impression is that his predictions about wet bulb temperature increases in very deep mines are over optimistic; in other words, that it will be hotter than Dr Starfield predicts. This is putting my views in a nutshell. This is not the occasion on which to indulge in lengthy argument about the original paper by Starfield and Dickson, but the present paper is, after all, based directly on that earlier paper and if the one fails, the other cannot succeed. I did level certain criticisms at the first paper and cannot say that the authors' replies were very convincing. I do not think it is a sin to admit that I belong to the old school which believes in thorough field experimentation and practical trials and no amount of mathematical manipulation or physical theorizing, no matter how excellent, can make up for inadequate practical confirmation. This, as I see it, is still the crux of the matter. The original paper by Starfield and Dickson still rests on somewhat scanty practical evidence and I would be much happier if Dr Starfield's computer programme, based on the Starfield-Dickson model, had been checked against a large mass of observations in the practical mining situation. This is what both Wiles2 and myself3 had tried to do previously. What we lacked in mathematics and/or computer aids, I think the present paper by Dr Starfield lacks in practical substantiation. This is no condemnation of the author's paper which, taken by itself, is excellent but I think the final stage is still lacking, namely the bringing together of theory and empiricism in a manner acceptable to all. This may be wishful thinking on my part but I hope, within the next year or so, to come up with a modified Starfield-Dickson model in such a way that the computer answers will agree in the majority of cases with the few hundred field observations which are already on record. It might be a case of applying the proverbial 'Cook's Law' to the Starfield-Dickson model! REFERENCES 1. STARFIELD, A. M., and DICKSON,A. J. 'A study of heat transfer and moisture pick-up in mine airways.' J. S. Air. Inst. Min. Metall., 68, (5), 1967. 2. WILES, G. G. 'Wet bulb temperature gradients in horizontal airways.' J. S. Air. Inst. Min. Metall., 59, (7), 1959, p. 339. 3. LAMBRECHTS, J. DE V. 'Prediction of wet bulb temperature gradients in mine airways.' J. S. Air. Inst. Min. Metall., 67, (11), 1967, p. 595. R. Hemp (Visitor): Dr Starfield's paper has very effectively rounded off one particular aspect of the general problem of heat flow in mines. The ease with which this computer programme can be used to calculate temperature increases in horizontal airways must lead to its wider use in ventilation planning and, in developing this rapid method, Dr Starfield has indeed rendered a valuable service to the mining industry. One could consider further instances of heat flow in airways in which the availability of a rapid computer method would be desirable, e.g. the flow of air down a shaft, where there is an increase in temperature due to adiabatic compression, as well as an increase in virgin rock temperature as the depth increases. However, this particular case would not present any new problems and would merely require an extension of the exisitng work. I should like in this contribution to talk about an aspect of environmental control in mines which, I think, will become more important in the future. It is well known that wet bulb temperatures are subject to fluctuations underground. In some instances, particularly in stopes, the fluctuations, both with time and position, can be considerable. The theoretical work which has been carried out on temperature increases has been aimed at the prediction of mean temperatures, and no account has been taken of fluctuations around this mean. It is questionable whether this approach will, on its own, be sufficient, particularly when temperature increases in stopes are considered. The fluctuations in air temperatures underground arise from two causes. The first of these would be the fluctuations in surface conditions, and here one could list random, diurnal and seasonal fluctuations. The second cause is the multitude of things which vary in a mine and here one could list variations in air flow quantity, sources of evaporation, heat transfer from pump and compressed air columns and, particularly in the stope, variations in air flow patterns. Fluctuations arising from surface temperature variations should be amenable to calculation, and here one envisages figures relating the decay of temperature variation with distance to factors such as air flow quantity. Fluctuations resulting from changes in the mine are perhaps more difficult to tackle theoretically and the best approach could well be to analyse underground observations. In this connection, there is a good case to be made for the increased use of statistical methods in the analysis of underground temperature measurements, and it might be of value to look at current air-conditioning practice. When carrying out cooling load calculations for a particular location it is customary to use design wet bulb

Jan 11, 1969

By B. Fagerberg, P. H. Fahlstrom

Crushing and grinding practice in Sweden follows closely the international pattern. Certain special circumstances, however, have had an influence on its development. Most mines are worked underground. These mines are either quite small or very large. Sulfide ores are commonly treated by custom milling and, apart from the cement industry, the rock species treated are hard and abrasive. Another important factor is the increasingly strict requirements placed on the mechanical condition of different products, especially lump ores and coarse iron-ore concentrates. Increasing requirements are being placed on the concentrate grade to suit the new steel processes. As a result, iron ore beneficiation has expanded considerably for the production of fine pelletizing concentrates. This applies especially to magnetite ores in the intermediate phosphorus range 0.1-1% P. In 1969, about 5.5 million tons of pellets will be manufactured. It should be pointed out, however, that fairly large quantities of coarse products are still being made at mills where the right conditions are available. Crushing and grinding is also of great importance in the production of rich concentrates at high recovery from sulfide ores. In fact, a large part of the development work on the concentration of sulfide ores has been devoted to the crushing and grinding processes. Boliden has played an important role in this connection.

Jan 10, 1969

While great strides have been made in the machinery for mining rock on the surface of the land, comparable advances have not been made with underground equipment. In fact, excavation of underground openings has actually declined in importance. On the other hand, surface mines are getting deeper and approaching the economic limits at which they can be worked. In the face of these approaching limits and the added problem of escalating labor costs, James Boyd, President of Copper Range Corp. and AIME, has suggested that "science and engineering must come to grips with the need for making subsurface openings more quickly and cheaply.

Jan 10, 1969

By K. C. Strebig, C. W. Schultz, A. A. Selim

For some time researchers have attempted to in- crease drilling efficiency (and therefore reduce costs) by adding certain chemical agents to the circulating medium. The effect of some organic additives on the diamond drilling of quartzite was recently investigated in the laboratory by personnel of the U. S. Bureau of Mines. In these tests, the penetration rate and bit life were found to increase with the use of additives. In addition, an economic analysis of a hypothetical 1000-ft hole showed that additives can reduce drilling costs by 30%. Wetting Agents Improve Drilling Efficiency Much of the interest in the use of wetting agents to improve drilling efficiency is the result of an observation made by Rehbinder, Shreiner, and Zhigach.1 These investigators postulated that drilling creates a region of increased crack formation directly below the bit and that a circulating medium that wets the rock will also penetrate the micro- cracks of the predestruction zone. Increasing the molecular affiinity (wetting ability) of these circulating media for the surface of the rock helps the deformation and destruction by softening the rock in the zone of increased crack formation. In this manner, the hardness or strength of the rock is decreased as the medium wets the rock in the predestruction zone. This is known as the "Rehbinder effect." Rehbinder's work has prompted many investigators to examine the relationship between the use of additives and the mechanical destruction of rock. Engelmann, Terichow and Selim reported that the maximum penetration of the rock by a diamond point in a solution environment was at the isoelectric point of the mineral and solution interface.2 Improvement in rock breakage with the use of additives was observed by Frangiskos and Smith.3 Joris and McLaren suggest that additives having a lower surface tension than water will also be more efficient in cooling the diamonds.4 Additives help remove fine cuttings from the face of the bit and improve efficiency. The latter two authors also report an improvement in impregnated bit life and penetration rates with the use of soluble oil additives. All of these investigations were initiated in the hope of discovering what economic benefits will accrue with the use of additives.

Jan 10, 1969

By J. H. Viljoen, A. Heyns, J. F. Morrison, C. H. Wyndham, N. B. Strydom

Discussion M. J. Martinson* (Associate Member): This is another interesting paper in the series which the Human Sciences Laboratory is publishing on the physiological cost of the more strenuous manual tasks performed underground. As a mining engineer-albeit presently an academic one -this contributor is more concerned with the practical significance of the study in the field of stope cleaning than with physiological niceties, but before discussing some of the practical issues raised by the paper perhaps the authors would care to reply to lay comment on three physiological matters. Firstly, in two places the authors make statements to the effect that the maximum oxygen intake of 'average' (sic) Bantu mine workers is 3.0 l/min. What do the authors mean by 'average'? Maximum oxygen intake in the individual is probably some function of inter alia age, physical fitness, state of health, ambient partial pressure of oxygen, diurnal and/or seasonal changes in metabolism, and possibly cumulative exposure to dust and other occupational contaminants. Since maximum oxygen intake is apparently such an important quality in manual labourers we ought to have a clear picture of its distribution in the entire labour force, and also know precisely how the individual's quantum is affected by factors such as those mentioned above. Secondly, arising out of the same statements and ignoring the reservation implicit in the previous paragraph, is it correct to say that the 'average' Bantu mine worker has a maximum intake of 3.0 l/min? In the August 1966 issue of the South African Journal of Science four of the present co-authors reported the mean maximum oxygen intake of a random sample of 338 Bantu recruits of different tribes to be 2.63 l/min with a standard deviation of 0.542 l/min, and these figures were repeated in a paper published in the November 1968 issue of this Journal. Admittedly the mean maximum oxygen intake of the six subjects used in the present study was 3.05 l/min, but since they were selected on the grounds of previous shovelling experience they can hardly be regarded as being 'average' recruits. Thirdly, it seems to me that the authors are perhaps a little uncritical in their acceptance of the '50 per cent of maximum oxygen intake' level of activity for endurance work. I am not unmindful of the evidence upon which this level is based, but I suggest that the evidence is at best tenuous and that the whole topic of fatigue and 'optimum' levels of productivity under conditions of high muscular activity and considerable psychological stress is a lot more complicated than would appear from the authors' ready acceptance of the 50 per cent level. Under present working conditions the question is largely rhetorical because it would need an army of supervisors to ensure that all members of a typical gang work at 'optimum' levels throughout the shift, but if individual performance should ever become more readily determinable the issue might become crucial to management and malayisha alike. So much for physiological matters; now a few random thoughts on some wider, practical issues raised by the paper. In the paragraph headed Material the statement is made that 'The mixture (of fine, medium-sized and bigger rocks) was considered to be representative of an average underground rock sample'. Elsewhere in the report the authors specifically draw attention to the effect of particle size on the oxygen consumption of men shovelling graded material, and intuitively one imagines that the size distribution of the material being shovelled would be highly significant in a study such as this. Presumably the authors were forced to assess size distribution subjectively because of the lack of objective data on the subject, and possibly the necessity for this assumption highlights how little we know quantitatively about any of the variables in stope cleaning systems. In this connection it may be remarked that although the present study was largely designed to show how dip and stoping width effect energy expenditure in shovelling, no data are given-nor, probably, are they available-to show how the industry's stoping tonnage is distributed in terms of these two factors. It seems to me that if the mining industry seriously hopes to improve stope productivity it must start by measuring the basic variables in existing systems. Elaborating somewhat on the previous paragraph, there also seems to be a tremendous gap between the present study-and its predecessors-and the prospect of gainfully using the information so carefully garnered by the authors. It would be reassuring to hear from the authors that their work on the physiological aspects is being integrated in some master plan for increasing productivity of manual labour. This I fear is not the case, and if productivity has changed at all in recent years I would hazard a guess that the change has been brought about by random factors rather than by systematic engineering design. The Human Sciences Laboratory has worked extensively in stopes in the past, and possibly the time has come when it should widen the ambit of its operations to include engineering-type analyses of cleaning systems, with particular emphasis on the economics of rapid cleaning by manual labour. Perhaps experiments could be conducted with stakhanovite-type gangs consisting of men selected for their high maximum oxygen intake and superior motivation; these men might be offered special incentives in the shape of extra pay

Jan 10, 1969

Inflation, tight money and keen competition spur companies to consider advanced material handling systems capable of reducing cost per ton of moving ore, waste or men and supplies. Since transportation charges account for an average of about 25% of the total delivered price of a product, then this cost center may actually determine the economic value of a new deposit. This being so, it is interesting to note that of the 1.4 billion tons of revenue freight carried by all Class I carriers of the nation in 1967, over 247 million tons or 17.5% were industrial minerals or products dependent on industrial minerals, i.e., glass, gypsum board, brick, etc. Because most bulk commodities have a comparatively low market value and are usually classified for lower than normal freight rates, railroads rely on large volumes and better equipment utilization to effect an equitable return. It is for this reason that the unit and shuttle train concept came into being. The average rate per ton-mile of all materials hauled by rail in 1968 was 1.31 cents. The low rates existing for industrial minerals contributed to this low average as did unit and shuttle train rates.

Jan 10, 1969

By Paul Averitt

In spite of recent trends in the United States toward construction of steam generating plants near mine mouths, and toward use of high-voltage direct current for long-distance transmission of electricity, coal in substantial amounts is being transported over relatively long distances to serve specific needs. As coal is a low-cost bulk commodity which is more suitable for use near the point of origin, some of these long hauls are of considerable interest because they show what can be done under the pressure for more and more coal to support industrial and economic growth. Japan has an Insatiable Appetite for Coal Perhaps the longest U.S. coal journey begins in the east Appalachian Basin of southern Pennsylvania, eastern West Virginia, and southwestern Virginia. High-quality coking coal mined in these areas is shipped by rail to Baltimore, Md., and to Hampton Roads, Va., where the coal is reloaded on freighters for shipment primarily to western Europe and Japan. In 1967, shipments of coal to western Europe totaled 19 million tons, and shipments to Japan totaled 12 million tons. Japan also imports coal from Australia, the U.S.S.R., Canada, Poland, the People's Republic of China, and to a lesser ex- tent from several other countries. In an effort to solve long-term needs, Japanese steel interests have contracted for the purchase from the Kaiser Steel Corp. of 51 million long tons of coking coal over the period 1970 to 1985. The coal will come from the Kaiser Steel Corp. mine near Fernie, British Columbia. This arrangement will reduce Japan's future dependence on Appalachian Basin coal.

Jan 10, 1969

By Daniel T. O’Brian

Exploration targets and results in the mining industry are commonly summarized in terms of tonnage and grade. Business appraisals require, as additional information, the expected profit or loss implied by the physical summary. The early incorporation of knowledge gained through financial analysis computations can provide a means for economically resolving many common exploration and development problems. Examples of such applications from the activities of exploration planning, reconnaissance, land acquisition and develoment planning follow. While prospecting for mineral deposits, geologists are frequently asked what they have found or hope to find. The response is usually descriptive, such as: "50 million tons of 1% copper," and the economic implications are deferred until a capital investment decision is required. At that time a financial analysis integrating the four analysis components-tonnage and average grade above cutoff grade, capital and operating costs, product value, appropriate profit or loss accounting-are completed.

Jan 10, 1969

By R. B. Schluter, M. M. Fine

The Bureau of Mines' Twin Cities Metallurgy Research Center has of late concerned itself with reduction-induration of iron ore. One development provided a flowsheet for the agglomeration of green concentrate pellets in a reducing atmosphere created by a solid reductant external to the agglomerate. The product pellets were well metallized and physically competent. Maximum recommended operating temperature was 2100º F. In these studies, it was observed that unflred iron ore pellets indurated in a bed of anthracite or certain lignite chars frequently acquired exceptional crushing strength. A diagnosis of the phenomenon revealed that sulfur in the fuel was the probable cause. Accordingly, a research program was established to test this premise and to put it to practical use. Gaseous reductants were employed initially because of the ease and accuracy with which they could be metered.

Jan 10, 1969

By C. H. Wyndham, N. B. Strydom

Discussion C. G. Hinds (Member): The climatic chamber at Kloof Gold Mine was built to the design referred to in the paper presented by Professor Wyndham and Dr Strydom. As no suitable underground facilities existed for the acclimatization of labourers at the rate required, mining operations would have been severely restricted had there not been a climatic room timeously built on surface. The climatic room can accommodate 120 labourers per 4-!-hour shift. The standards laid down by the Human Sciences Laboratory were and still are being adhered to as strictly as possible. Through a shortage of European personnel the recommended degree of white supervision could not be adhered to and the use of Bantu assistants with a minimum education of Standard 8 was introduced. This is considered to have met with sufficient success to warrant acceptance as policy. The climatic room was brought into operation on the 1st September, 1967, i.e. two months after stoping at Kloof was commenced. The figures quoted herein therefore pertain to the period between that date and the 31st March, 1969, when the main shaft and the main surface fans were commissioned. The areas worked were sited between 5016 ft and 6 365 ft below surface. Virgin rock temperatures ranged between 92°F and 99°F. Stopes are cleaned by hand lashing. During the 20 months of stoping prior to the commissioning of the main shaft, mining operations at Kloof were effected through the Harvie Watt shaft of the Libanon Gold Mining Company Limited. In this period 10 452 Bantu labourers were acclimatized in the following categories: Experienced workers 7 326 New to the industry 2 086 Re-acclimatized 1 040 It will be noted that during the period, labourers 'new to the industry' averaged 22 per cent of the intake. This percentage fluctuated from time to time and reached 42 per cent. (The present percentage is 60.) The greatest number acclimatized during anyone month occurred in February, 1969 when 1234 Bantu were treated. The greatest number of Bantu acclimatized during any 8-day period was 411. As many as four X 41/2 hour shifts were run in 24 hours. The number of men found to be heat intolerant over the period of 20 months was 33 out of a total 9 412 Bantu. The following tabulation illustrates the history of the build-up of manpower and the climatic conditions under which they worked: The average dip of the reef is 35°. The number of heat stroke and heat exhaustion cases during the period of 20 months under most difficult ventilation conditions was Nil.

Jan 10, 1969

By Fredrick C. Kruger

Risk capital for mining ventures becomes harder to get each year as the costs for exploration, construction and money continue to skyrocket in today's inflationary economy. Because of this and because mining prospects must compete for the same dollar as many other needs of a diversified company, then the success or failure of any new proposal depends on how well its return on investment compares with all other capital requests. Mr. Kruger presents case histories showing what it costs to explore for new mines, how many of these prospects reward their promoters with success and how well some of the more famous mines have paid off.

Jan 9, 1969

By Robert H. Merrill

During the period from 1960 through 1966, the U.S. Bureau of Mines and Kennecott Copper Corp. performed an experiment to determine the changes in stress, strain, and displacement created by changes in slope angles. The experiment was performed at Kennecott's Kimbley pit near Ely, Nev. The supporting laboratory studies were made in the Bureau's Denver Mining Research Center, where final reduction of the data and summary reports are now in progress. The experiment was divided into two phases. The first consisted of the laboratory and field investigations required to select a new slope angle and configuration; the second phase consisted of a full-scale instrumented study in the west wall of the pit. The west slope was changed from an average of 45º to a slope angle that started at 45º on the south wall and gradually in- creased to 57 ½ º at the center of the west wall, and to 61 º on the north wall. The pit was deepened from 500 to about 550 ft, and approximately 2.55 million tons of waste and ore were removed from the wall.

Jan 9, 1969

Ask any mineral industry executive what he considers one of the most expensive aspects of getting a product to the ultimate consumer and invariably the answer will be transportation. Some company officials say that transportation charges alone account for over half of the total cost of most products. If these judgments are correct and a recent invention turns out to be the long-awaited breakthrough that shippers have been looking for, then many producers can look forward to slashing their delivery costs by 90%.

Jan 9, 1969