Search Documents

By I. Bock

Selective Blast Mining (SBM) makes use of milli-second sequential blasting technology to separate the valuable reef material from waste rock in the blasting operation at stope faces in the mining of tabular ore bodies such as exist in the gold and platinum mines in South Africa. The waste rock is cast blast to the back of the stoping area, and the reef material is fractured and deposited close to the stope face. Only the reef material is transported to the surface. A simplified economic model is presented to evaluate the economic benefits of SBM. Although premature, in that adequate experimental demonstration of the validity of the model has not yet been possible, the model is presented since it indicates substantial benefits in the case of narrow reef gold mines. It is suggested that many marginal mines should seriously consider SBM. Benefits can also be realised in platinum mines, but a lot more experimental work is necessary to establish cost parameters more reliably. Some practical experience in the use of SBM in the mining of the UG2 reef is presented.

Jan 1, 1998

By K G. Fleetwood

This paper proposes an approach to determine the influence of non-ideal detonation characteristics related to the charge diameter, explosive type and confinement conditions on the available shock energy of ANFO and a representative chemically-sensitised (gassed) emulsion. The proposed degrees of non-ideality of the two different blasting agents are indicated by the Gurney ratios, determined from existing cylinder expansion testing data. The influence of the non-ideal detonation properties on blast design and performance are also compared using a series of theoretical, equal powder factor open pit blasting patterns with hole diameters ranging from 102 mm to 270 mm. The non-ideal shock energy factor (NSEF), which is the available shock energy per tonne of blasted material (MJ/t), is used to compare the different blasting patterns as charged with either ANFO or the gassed emulsion of equal charge density (0.85 g/cm3). The intended purpose of this investigation is to provide explosive users with an approach to compare different explosive types or charge diameters in the absence of dedicated non-ideal detonation modelling, which is generally not available to explosives users.The results of the comparisons suggest that at low charge densities, the example gassed emulsion displays a higher velocity of detonation (VOD) than ANFO in smaller charge diameters but similar degrees of non-ideality (based on proposed Gurney ratios). The results also suggest that the confined, non-ideal gassed emulsion VOD at hole diameters greater than 270 mm can be less than ANFO due to the low density effects on the emulsion matrix. The differences in non-ideal detonation properties and Gurney ratios between the ANFO and gassed emulsion resulted in gassed emulsion NSEF values ranging from 15 per cent lower to 65 per cent higher than ANFO for equal powder-factor patterns in blasthole diameters from 102 mm to 270 mm.

Nov 8, 2011

A pilot plant has been constructed for the low temperature carboni-zation of Wallarah (N,S,W6) coal at the rate of 300 pounds per hour. The plant was built and tested at Australian Mineral Development Laboratories for Broken Hill Pty, Ltd. Char product was required within the specifi-cation 15.5 `S' 1 per cent volatile matter. The design was based c atz an entrained state carbonizer developed by Parry and U.S. Bureau of Mines co-workers at Denver, U.S.A. The method involved the carbonizatioan of fine coal by entrainment with air in an externally heated reactor.. The heat required for carbonization of tits coal was supplied to the be, both through the reactor walls and also by internal cambustion of products .

Jan 1, 1963

By Paul Hatmaker

A primary, function of the Bureau of Mines is to encourage elimination of waste and the most profitable use of mineral raw materials. In line with this objective the Bureau has frequently stressed the importance of waste utilization at stone quarries. From time to tine studies both technical and economic in character have been made of problems pertaining to the most efficient use of natural, stone, particularly that which may be classed as a by-product of the higher grades of dimension stone. Every quarry producing ornamental or building stone yields large quantities of material that for one reason or another is unsuited for high-grade products, even though a great deal of work has been expended upon it more or less unavoidably. It is obviously good judgment to sell this odd-sized or off-grade stone at whatever price can be obtained rather than to spend more money to place it on the waste dump. In many cases, however, a really profitable side line has been developed.

Jan 1, 1933

By David R. Skuse, Jacek A. Kostuch, Steven M. Fortier

"Particulate ground calcium carbonate (GCC) is used as a filler and coating pigment in a wide range of applications including papers, paints, plastics and films. In this paper we will overview the requirements for GCC used in both filling and coating applications in the paper industry and highlight the processes used in the production of these materials.INTRODUCTIONCalcium carbonate is both abundant and very widely distributed occurring most commonly as limestone, marble and chalk (Harben 2002). Given, the high purity, whiteness and relative inertness of these materials it is not surprising that they are heavily utilised in a range of industrial applications. Worldwide ground calcium carbonate (GCC) capacity is estimated at 50.5 million tonnes per year (Roskill, 2002). This usage is divided between relatively coarse materials that are used in applications such as landscaping, cultured marble and carpet backing and finer grades that find application in plastics, rubbers, inks, paints and paper. Given the usage of calcium carbonate products across a very wide range of consumer products, the outlook for GCC is very promising with growth expected in many markets. Growth is anticipated across many applications in the emerging nations and more specifically in paper applications on a global basis.Over the last several decades the GCC processing industry has evolved to be well adapted to both the cost effective production and delivery of standard products and the production of high performance speciality products. Many of the standard unit operations found in the metaliferous raw material processing industry are also used, albeit in some cases in modified form, in the processing of GCC. Coarse products (diameter > 3 - 10 µm) are typically produced by dry processing routes. Whereas, the finer products are typically produced by a combination of wet and dry processing."

Jan 1, 2004

By M J. Shearer

An investigation into the reliability of the data being collected at the Mount Isa Mines site operated by Glencore in Queensland allowed on-site ventilation personnel to scrutinise pressure and volume measurements collected from the primary surface fans. The investigation effectively identified discrepancies being reported to the on-site remote monitoring system. The difference between the real-time and static measurements on the P63 RAR shaft identified that the in situ differential pressure transducer and piezo annubar system was not operating correctly. This indicated a deficiency of approximately 30 per cent reporting back to the remote monitoring software versus the live readings measured with the Pitot tube bomb and ALNOR AXD610 pressure micro-manometer.Constant monitoring of an operations ventilation network is imperative to ensuring that the underground atmosphere provides a safe and healthy workplace. Further benefits to real-time monitoring allows for the early indication of network failures and promotes increased availability. An innovative approach to out engineer and improve the existing measuring equipment from the 1970s was sought.The use of ultrasonics in the mining industry is not new with ventilation management systems (VMS) equipment available within the marketplace. The introduction and implementation of a reliable product for real-time monitoring was a challenge to overcome due to limited access and suitable measuring points within the mine. The available equipment on the market through mainstream suppliers was not suitable for the unique application required due to the in situ installation of the surface fans. A solution was identified in the oil and gas industry through collaboration and innovative thinking. This paper describes the sustainable approach to implement a reliable air flow monitoring system on-site.CITATION:Shearer, M J, 2017. Case study – an analysis of reliability and efficiency: ultrasonic versus annubar technologies, in Proceedings Australian Mine Vent Conference 2017, pp 51–56 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 28, 2017

By Henry E. Blake

The Bureau of Mines has been engaged in a continuing research effort to develop processes for increasing the recovery and utilization of fluorine from low-grade resources. This current research has shown that over 98 percent of the fluorine in phosphate rock is extracted when the ore is treated with excess phosphoric acid in the presence of water vapor at 150° to 180° C. More than 80 percent of the fluorine can be recovered as fluosilicic acid, which can then be converted to commercially useful hydrogen fluoride or fluorspar by previously developed Bureau processes. Extraction of P205 from the ore was about 98 percent in batch tests and 90 percent in semicyclic tests.

Jan 1, 1974

By Joseph W. Mussey

Bio-epigenetic sulphur deposits occur in Pecos, Reeves and Culberson Counties of far West Texas. Sulfate reducrng bacteria, utilizing hydrocarbons as energy, transformed gypsum into replacement limestone and hydrogen sulfide. Hydrogen sulfide, retained in the porosities of the replacement limestone, was subsequently oxidized by highly oxygenated groundwaters, and native sulphur precipitated. West Texas sulphur was first recognized at surface exposures by William P. Blake, a geologist attached to the Captain Pope Military/ Scientific Expedition of 1854. Attempts were made in the early 1900's to mine these sulphur vent exposures by a retort method, but the ventures met with little success. In 1967, Duval discovered a large sulphur deposit near some of the old sulphur works in Culberson County. Duval also extended a small sulphur deposit in Pecos County. The Frasch process, developed for producing sulphur from Gulf Coast salt domes, proved successful in West Texas type sulphur deposits also. However, modifications of the process were necessary to provide economical and efficient sulphur recovery from the varied ore modes. West Texas conditions and logistics require the ultimate in productivity to be competitive in the domestic and foreign sulphur markets. Several companies, in addition to Duval, are producing or have produced sulphur in West Texas. As of the first of June 1984, a total of 29.4 million long tons of sulphur had been produced west of the Pecos -aver. Duval produced more than 88 percent of that total.

Jan 1, 1984

By Gerrit V. R. Goodman

Future coal mining systems will be able to cut from crosscut to crosscut where advances could exceed 100 ft. However, limitations arise when ventilating such mining systems. In deep advance mining, there would be no workers at the face to advance ventilation tubing or curtain manually. Traditional methods also provide no means for maintaining face ventilation after the miner backs away from the face. U.S. Bureau of Mines research is studying means to provide effective ventilation at cut depths beyond the current limit of 4D ft. Several innovative ventilation schemes are currently being considered. One such method is the use of a jet fan to ventilate a deep cut. A jet fan is simply a freestanding fan using little or no ducting to direct the ventilation flow. Jet fan testing in a 90-ft entry revealed that higher exit velocities and greater penetration depth occurred when various configurations were used to confine and direct the air flow. Additional testing also indicated that 2,200 cfm of fresh air was delivered to the face? 90 ft distant when a check curtain was used to limit entrainment around the fan. Without this curtain, this quantity dropped to only 1,000 cfm. This testing indicated that a jet fan was capable of providing ventilation to a distant face area. It also highlighted potential problems, such as recirculation at the fan and reentrainment in the jet flow. Despite these potential problems, jet fans may be adequate for ventilating cuts exceeding 4D ft.

Jan 1, 2010

By A. R. Elsea, E. E. Fletcher

Cast X-40 alloy with the lowest nitrogen content studied had a 100-hr rupture stress at 1500°F about equal to the reported value for the commercial alloy. Increases in nitrogen content progressively decreased the rupture strength, and with about 0.1 to 0.2 pct N a minimum strength was reached, but there was no accompanying change in microstructure. Further increases in nitrogen resulted in the fomzation of progressively increasing amounts of a lamellar, pearlitic-type structure at the grain boundaries, with accompanying increases in rupture strength, and above about 0.25 to 0.33 pct N, the rupture strength exceeded the normally reported values. Two series of melts representing different melting stocks exhibited minimum rupture strengths at different nitrogen contents. This suggests that some unidentwed trace element not removed by vacuum melting has a strong influence on the response of this alloy to variations in nitrogen content. In a series of melts with manganese contents ranging from 0.6 to 3.2 pct, the material with the lowest manganese content had the highest 100-hr rupture strength at 1500°F. The manganese variations had no appreciable effect on the microstructure. CAST cobalt-base alloys such as X-40* exhibit high strengths at elevated temperatures (1500°F and above), but they also show considerable scatter in high-temperature properties. Since the design of parts for critical applications must be based on the minimum expected properties, this broad scatter appreciably lowers the design strength of the alloy. If the relatively poor properties exhibited by a few test parts from any given group could be improved, the spread in properties would be narrowed, and the design stress could more closely approach the average expected properties. The purpose of this research investigation was to learn what were the causes of these erratic properties and, if possible, to find methods for eliminating them. Earlier unpublished work showed that vacuum melting markedly influenced the high-temperature strength of cast X-40 alloy. There were indications that this behavior may have been the result of changes in the nitrogen or manganese content of the castings. Consequently, in the current investigation, the influence of variations in nitrogen and manganese content on the structure and high-temperature properties of cast X-40 alloy was studied. In this program, X-40 melting stock was vacuum melted to produce a base material that was very low in nitrogen content and in volatile trace elements. Additions were then made to this base material to produce alloys of the desired composition. The metal was cast into investment molds producing coupons which were machined into stress-rupture bars. These bars were subjected to stress-rupture tests and me-tallographic study to determine the influence of changes in analyses (nitrogen and manganese content) on the structure and properties. Material—The melting stock used for these experi-ments was in the form of shot from two master heats of commercial X-40 alloy. Only one master heat was used in a given series of melts. Thus, any differences in structure or properties that showed up in the specimens from a given series would be the result only of the intended variations in composition. The certified analyses of the master heats were as follows: C Mn Si Cr Ni Lot No. 2 0.50 0.71 0.66 25.44 10.53 Lot No. 3 0.54 0.73 0.70 25.95 10.00 W Fe Co P S Lot No. 2 7.45 1.34 Bal. 0.011 0.013 Lot No. 3 7.58 1.53 Bal. 0.005 0.016

Jan 1, 1960

By James S. Browning

The Bureau of Mines conducted laboratory batch and pilot plant flotation tests to determine the technical feasibility of recovering commercial-grade mica from a California micaceous schist. Best results in the laboratory batch tests were obtained using sodium carbonate and sodium silicate for pH control and quartz depression, and a combination of fatty acid and cationic reagents as the mica collector. In continuous pilot plant flotation tests, an alkaline fatty acid-cationic method recovered about 70 percent of the mica in a concentrate analyzing 95.6 percent mica.

Jan 1, 1965

By Leonardo Flores

"Minera Escondida operates two open pits on a porphyry copper district, southeast of Antofagasta, Chile. During 2005, ore will be delivered exclusively from one pit to two concentrators, while from 2006 both pits will provide ore to these plants. Annual testing programmes on drillhole samples, have allowed for the construction of hardness block models since 2000. These models have delivered two main hardness descriptors, the Bond work index and the SAG power index. These parameters and plant operational specifications have been used as input information to forecast, the expected throughput and ball mill product size (P80) for each block of ore. Two forecasting techniques have been used, an in house model, strongly dependant of bond work index and MinnovEx´s CEET2, dependant of Bond work index and Sag power index and other parameters. Model performance has been evaluated from reconciliating on a monthly basis, the forecasted throughputs against a recalculated plant throughput which accounts for losses in tonnage not caused by ore hardness but instead by unscheduled plant operation problems. The model performance for 2003 was ± 2% yearly and ± 5% quarterly, well within the expected ± 3% and ± 10%. INTRODUCTIONThe Escondida porphyry copper district is located 140 km SE of Antofagasta, Chile at 3150 m.a.s.l, at 24°16’ South latitude and 69°04’ West longitude (figure 1)."

Jan 1, 2005

By G. R. Gardner, D. H. Davis

INCREASING realization of the importance of dust control, and the recommendations of various agencies, have led the mining industry to become actively concerned with this problem. The background and necessity for adequate dust-suppression measures have been discussed in a number of publications, including those of the U. S. Bureau of Mines, and the use of spray water to reduce dust at the face and on roadways has been recommended. The problem resolves itself into obtaining adequate dust reduction at a reasonable cost. Inasmuch as the term "adequate dust suppression" has never been clearly defined, nor have permissible limits of dustiness (in terms of dust count) been established, it is apparent that any method selected may be required to meet additional demands. Until the industry has been given some indication of permissible limits of dustiness, no permanent solution is possible. Progress will be somewhat handicapped until such information is available. In addition, dust reduction must be obtained without the addition of any excessive moisture to the coal, since consideration must often be given to: I. Quality standards, particularly reduction in heat value. 2. Handling characteristics, particularly in regard to unloading from railroad cars and bins. 3. Application of dry methods of coal cleaning. 4. Necessity for fine screening within specified limits of oversize and undersize. Little detailed information is available as to the advantages and disadvantages of the several methods of water distribution, the location and protection of sprays, operating data on pressure, quantity of water, and so forth, and results obtained. In 1940 an investigation was undertaken to determine and evaluate the principal factors involved. This paper constitutes a progress report on this work and cannot in any way be regarded as complete on any one of the several phases. CLASSIFICATION OF DUST SOURCES The various sources of underground dust may be classified as primary or secondary. A primary source is one associated with appreciable degradation of size, that is, where the greater part of the actual fines capable of becoming air-borne dust are produced. A secondary source may be considered as one in which the greater part of the fines have been produced at some previous operation and are in such condition that they can be dispersed as air-borne dust. These conceptions appear to be of practical significance, as experience indicates that when dust is controlled at the primary sources the importance of secondary sources is minimized. For these reasons, investigations to date have been concerned principally with the primary sources of dust, and this paper is concerned particularly with one of these-namely, undercutting. In accord with the foregoing definitions, the sources to which the following opera-

Jan 1, 1942

By Hongbo Zhu, Jinhui Peng, Linqing Dai

"To optimize the process variables for making direct reduced iron (DRI) by microwave heating, the reduction temperature, reduction time and the ratio of coal to material were studied with the central composite design (CCD) and their interactions on the Metallization rate were also investigated. The predictive polynomial quadratic equations model was analyzed by ANOVA. Optimal conditions of making DRI can be concluded as follows: 28 min at 1139?, the ratio of coal to material is 20.95%. Under these conditions, the metallization rate is up to 97.06%.1. IntroductionThere are some technical problems in making direct reduced iron (DRI) or sponge iron using iron ore concentrates containing coal and lime. In reduction of the iron ore concentrates containing coal with microwave heating, the strength of pellets needn’t to be considered. It reduces the costs and improve quality of materials, but also eliminates the need for pellet preparation process, simplifying the process and achieving a cleaner production.Microwave energy is a clean energy, and has characteristic of selective heating. The speed of heating is also fast. It researched by Chen Jin that when the mole mass of C: O is 0.627 and the microwave power is 15KW, it only spends 15min from 15? to 1021.6? with 1 kg iron ore containing coal with microwave heating [1]. There are many factors affecting metallization rate. In order to find a suitable condition for reduction process, it is necessary to design a series of suitable experiments.Response surface methodology (RSM) is one of the relevant multivariate techniques which can deal with multivariant experimental design strategy, statistical modeling and process optimization [2–5]. It is used to examine the relationship between one or more response variables and a set of quantitative experimental variables or factors. This method is often employed after the identification of the vital controllable factors to find the factor settings that optimize the response. Designs of this type are usually chosen when a curvature in the response surface is suspected. The process optimization of the microwave reduced iron ore was seldom reported in literature. Hence the present work intends to assess the effects of variables such as reduction time, reduction temperature and the ratio of coal to identify the optimum conditions using a central composite design (CCD). The characteristic of product was assessed using scanning electron microscope (SEM)."

Jan 1, 2011

By John Carson

Belt feeders are commonly used to meter the flow of bulk solids from bins and hoppers. If the interface between the hopper outlet and belt feeder is not designed correctly, flow from the bin may be severely compromised, resulting in problems of no-flow, segregation, flooding, etc. By knowing the flow characteristics of the bulk solid being handled and applying proven design techniques, such problems can be avoided. Relevant bulk solids flow characteristics are identified, along with measurement techniques. Design procedures for correcting problems with existing feeders as well as proper design of new feeders are presented, along with case histories of successful application of these procedures.

Jan 1, 2008

By Dan B. Kivari

A key operation of any milling circuit is grinding. Over the last two decades, large diameter semiautogenous grinding (SAG) mills have become the preferred primary grinding mills. The drive systems became more complex as the size of the mills became larger, during which time operating and design experience for SAG mill accumulated. Considerable reliance is now placed in power electronics to provide flexibility in SAG mill operation to meet the demands of lower operating costs. Most earlier SAG mills were designed to operate at fixed speeds. Present day SAG mills can operate at a fixed speed or variable speed through the use of an ac synchronous motor or dc motor. This flexibility, however, comes with an increase in capital and operating costs. Since the capital and operating costs of a project directly affect the project's rate of return, the selection of a SAG mill and its drive system should depend, in part, on the impact that the extra cost makes on the project. This impact can be measured by performing an economic analysis based on net present cost (NPC) calculations. Although the NPC calculation is an important factor in the grinding mill selection, other factors, such as reliability of mill drives and power source, are important elements in the decision making process. This article examines how the NPC calculation, plus reliability and power source, influence SAG mill selection.

Jan 1, 1992

By Bright Oppong Afum, Kojo Boakye, Kwaku Boakye

This research developed and simulated a novel multi-indicator Fatigue Detection and Alert System (FDAS) designed to enhance fatigue detection accuracy in mining environments. The system integrates a comprehensive set of inputs: eye blink rate, eye closure duration, yawning frequency, distraction levels, Pre-shift Check-in Scores (Self-report) and Electroencephalography (EEG) Levels. Using MATLAB’s Fuzzy Logic Rule Viewer (FLRV) and Simulink, simulations demonstrated the FDAS’s robust ability to process these diverse physiological and behavioural indicators accurately. It effectively classified operator fatigue into low, moderate, and high fatigue levels, consistently providing appropriate outputs and corresponding intervention recommendations across various mixed-signal scenarios. The system achieved a calculated accuracy of 85.19% across 27 test entries, with a standard deviation of approximately 1.8459, confirming its reliability for real-time fatigue monitoring. These findings highlight the significant potential of this fuzzy logicbased approach to proactively identify early signs of fatigue, substantially enhancing safety and operational efficiency in demanding mining operations.

Feb 22, 2026

By T. Panhorst

Evaluation of through-deck blasthole sample reliability at the Lone Tree gold mine revealed a non-systematic bias in the sampling system. Ore is primarily hosted within the Powerline fault zone. Clay gouge, present in the fault zone and typically enriched in gold content, forms agglomerates during blasthole drilling leading to a segregation error during sampling. Replicated samples split from blasthole cuttings piles show through-deck samples to be either significantly enriched or depleted by 1.5 standard deviations or more from the mean gold content of their respective cuttings pile quality of through-deck samples correlates strongly with quantity of clay present.

Jan 1, 1999

By D. Harrington

The mining industry of the United States has-long been severely criticized because of its high rate of accident occurrence, net only as compared with other major industries-in the United States but also with the mining industries of other countries particularly Europe. Statistics (often not of strictly comparable nature) indicate that the accident-frequency rate in all mining is currently about three times and the accident-severity rate is about seven times as great as the average for general industrial work in the United States. These figures are by no means comforting to humanitarian mining men, irrespective of their status in. the industry, and they constitute a challenge that certainly cannot continue to be ignored much longer. This picture becomes much darker when the above statistics are augmented with data indicating that. on an exposure basis our mines (more particularly our coal mines) have accident rates two, three, or even more times as great as more or less similar types of mines in Europe, particularly England and Wales, Belgium, France, and Germany. However, these foreign accident statistics should be carefully analyzed before we become very mush concerned about them, because they are clot strictly comparable owing to several considerations, not the least of which is the fact that foreign methods of compiling or recording accident statistics often differ materially from ours. Moreover, foreign mining and other conditions axe definitely dissimilar to ours in many if not most phases, and numerous ether factors affect the comparability of foreign mine-accident statistics with ours. Unquestionably it should also be taken into consideration that the accident rate of the 130,000,000 or more constituting the populace of the United. States as a whole is much higher than that of any other major country in the world and is two, throe, or more times the rate of the European countries that have more favorable mine-accident rates than those of the United States. Moreover, it is significant that the mine-accident-severity- rate of British mines is about six times the average accident-severity rate of the major industries of the British Isles, or but little mere, favorable than the comparable figures in the United States, namely, that mining-has an accident-severity rate about seven times that of the average of about 30 of the major industries of this country.

Jan 1, 1941

By G. R. Gardner, D. H. Davis

Increasing realization of the importance of dust control, and the recommendations of various agencies, have led the mining industry to become actively concerned with this problem. The background and necessity for adequate dust-suppression measures have been discussed in a number of publications, including those of the U. S. Bureau of Mines, and the use of spray water to reduce dust at the face and on roadways has been recommended. The problem resolves itself into obtaining adequate dust reduction at a reasonable cost. Inasmuch as the term "adequate dust suppression" has never been clearly defined, nor have permissible limits of dustiness (in terms of dust count) been established, it is apparent that any method selected may be required to meet additional demands. Until the industry has been given some indication of permissible limits of dustiness, no permanent solution is possible. Progress will be somewhat handicapped until such information is available. In addition, dust reduction must be obtained without the addition of any excessive moisture to the coal, since consideration must often be given to: I. Quality standards, particularly reduction in heat value. 2. Handling characteristics, particularly in regard to unloading from railroad cars and bins. 3. Application of dry methods of coal cleaning. 4. Necessity for fine screening within specified limits of oversize and undersize. Little detailed information is available as to the advantages and disadvantages of the several methods of water distribution, the location and protection of sprays, operating data on pressure, quantity of water, and so forth, and results obtained. In 1940 an investigation was undertaken to determine and evaluate the principal factors involved. This paper constitutes a progress report on this work and cannot in any way be regarded as complete on any one of the several phases. Classification of Dust Sources The various sources of underground dust may be classified as primary or secondary. A primary source is one associated with appreciable degradation of size, that is, where the greater part of the actual fines capable of becoming air-borne dust are produced. A secondary source may be considered as one in which the greater part of the fines have been produced at some previous operation and are in such condition that they can be dispersed as air-borne dust. These conceptions appear to be of practical significance, as experience indicates that when dust is controlled at the primary sources the importance of secondary sources is minimized. For these reasons, investigations to date have been concerned principally with the primary sources of dust, and this paper is concerned particularly with one of these—namely, undercutting. In accord with the foregoing definitions, the sources to which the following opera-

Jan 1, 1942