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By R Rimmelin, C Vergara

Heap leach pads are composed of mined ore, usually crushed, disposed on liners to be processed with leach solutions, and the tail of the process is called “spent ore” which are then transported by conveyor belts to be disposed into dumps. It is often to observe stability problems in these dumps, that could affect the equipment working on it and the continuity of the whole mine process. These problems are related to an excess of water content at the spent ore, therefore the operational efforts are focused onto control this geotechnical parameter.This work presents the results of different geotechnical laboratory testing, using samples of spent ore of a mining operation in the north of Chile. In the last 10 years, 3 campaigns have been made to get samples. Valuable information was obtained to identify how specific operational/metallurgical factors could affect the geotechnical behaviour of the spent ore. Special attention is given to the decision to change the metallurgical process adding salt to the heap leach process and its impact to its hydraulic conductivity.Historically, the process has been based on the leaching of oxides and sulphides materials, in separate campaigns, in which it is possible to observe different geotechnical response in the spent ore generated. Recently, it was implemented a new process in which the materials are blended and salt is added, to improve metallurgical performance in terms of recovery. This change generate impacts in the dump, since the geotechnical parameters are affected; decreasing hydraulic conductivity in about one order of magnitude (explained by the salt added).Changes are shown in the geotechnical parameters of the spent ore, considering that the mining source is the same, and how the operational process and dump design are affected.CITATION:Rimmelin, R and Vergara, C, 2018. Geotechnical behaviour of spent ore – impacts of metallurgical factors, in Proceedings Mine Waste and Tailings Stewardship Conference 2018, pp 369–375 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 23, 2018

By A. H. Srnallbone

Over the past few years the rising production costs, shortage of skilled labor, and increased use of lower grade ore bodies have all added justification for the use of on-stream analysis. A rise in the number of on-stream units indicates that this type of assay is now being accepted as a necessity. On-stream analysis is a much more rapid means of obtaining true assays of a flowing product when compared to wet chemistry or "grab" samples dried, briquetted and assayed by x-ray. In contrast, on-stream analysis uses real time samples assayed every 30 seconds while each stream is assayed every 5 to 15 minutes. It is very important not only to know that a change has occurred in the process, but to know what caused the change and how to correct for the change. For example, in a tailing sample the elements of interest comprise between 1% and 10% of the sample. The remainder is water and gangue. Previously the gangue was not assayed nor were the low atomic number elements used for corrections. In addition to the demand for higher accuracies some concentrators were being penalized for excessive Ca or in some cases 5i in their concentrates. This penalty was being imposed by the smelter in order that they could better cope with pollution problems and prolong the life of their furnaces. But until Ca, 5i, and S are measured on-line, nothing can be done about their control. By accurately measuring these light elements on-line, a complete assay is obtained of the total sample providing improved accuracy for the important products. The justification for complete accuracy assays is now even more obvious because they are possible at very 1ittle increased cost and at no increase in analytical time.

Jan 1, 1977

By Guo Wenbing

"INTRODUCTIONThere is a great amount of coal (about 140 billions tons) left unmined under the surface structures, water bodies, railways (referred to as the “three-body”). Coal mining under “threebody” especially that under surface structures has become a major problem in the mining area. The key problem of mining under surface structures is to control overburden strata and surface movements. At present, the major surface subsidence control methods are strip pillar mining, backfilling mining method, room and pillar mining, grouting of bed separations, harmonic mining, and so on. Wongawilli mining method is a high-efficient shortwall mining method developed based on the room and pillar mining, and named after the first successful trial in Australia “Wongawilli” coal seam. The room and pillar mining equipment such as continuous miner is employed in this method. Its major advantage is flexible face layout. It can be used to mine the small wedge coal blocks and those that are difficult to be mined with retreat longwall mining method. It requires less capital investment, short lead time for production, flexible equipment operation and face move and high productivity. It has been applied in some China’s coal mines.The “Wongawilli strip coal mining technology” is a new coal mining method for mining under surface structures. It combines the strip mining longwall layout and Wongawilli high efficient mining technology. This technology can fully utilize the advantages of both the strip pillar and Wongawilli mining methods, and overcomes the disadvantages such as frequent face move, and low mining efficiency in strip pillar mining, and poor ventilation condition and poor long-term stability problems of coal pillars. In this paper, the Wongawilli strip mining method was designed for Wangtaipu mine and its feasibility was studied using numerical modeling and surface subsidence prediction.Geological and mining conditionsAt present, most of the No.15 coal seam reserves totaling 377.07 million tons in Wangtaipu mine are located under surface structures. In order to mine the coal under the surface structures, the Wongawilli strip mining method was employed. An appropriate panel was selected for trial and the surface movement monitoring lines were set up. The trial area is located in panel XV2214 (East) ( re 1). In this area, the floor elevation of coal seam is +634~646m, the surface elevation is +810~817.5m, and the average depth of coal seam is about 174m.The average panel length is 282m and average panel width is 73.5m. The seam dips 1~3° and is 1.8~2.5m thick with an average of 2.15m. The roof and floor rock characteristics are shown in Table 1."

Jan 1, 2015

By Donald I. Kurth

This Bureau of Mines report describes the development and application of a computer model of aquifer hydrology associated with in situ leaching of uranium. The model provides uranium resource developers with a simulation of leachant flow characteristics in a preproduction or pilot five-spot leaching operation. Various types of aquifers are modeled using closed form solutions of the partial differential equations describing the change in fluid head (pressure) as the leaching operation is carried out. User-supplied descriptive input consists of aquifer, well, and leachant flow characteristics. Numeric and graphic outputs such as isopressure, iso-velocity, and isotime contours are available. A typical application is shown.

Jan 1, 1978

By C. Richard Tinsley

Non-ferrous econometric metal models available from consultants are reviewed for structure and computer access, using copper as an example The evolution of a computerized metals price forecasting system for a consumer of non-ferrous metals is outlined including front ends, bridge equations, and supporting databases. An empirical sensitivity analysis technique is described. A postscript discusses the subscription costs of these models.

Jan 1, 1977

By P. Nayak

"Comminution is an energy intensive and expensive process consuming approximately 40-50% of the total processing costs in a mining operation. This process poses an even greater challenge with gold ores due to their low elemental concentration and small particle size. Over 99.9% of the ore fed to the mill is waste which must be removed during the ore processing stage. Preconcentrating the Run of Mine (ROM) ore before feeding the mill will result in significant cost savings. In partnership with Sacré-Davey Engineering, Agnico Eagle Mines Limited identified this opportunity and is currently evaluating the implementation of sorting technology to preconcentrate the ore or upgrade the waste material at its operations. This paper will discuss the steps adopted by Agnico Eagle in the evaluation and installation of sorting technology at its operations. Since the Company has a large portfolio of operations, the first step in the project was to shortlist the operations that had the highest probability for successful application of the technology. Following this, the top three operations were selected for bench scale evaluation. The projects which showed the most economic potential were then considered for detailed evaluation and pilot plant installations. This paper provides an insight into the methodology followed by Agnico Eagle and Sacré-Davey in the evaluation of the technology.INTRODUCTION The benefits of ore sorting technology are being increasingly understood by the mining industry today. The application of ore sorting in gold mining is attractive due to the nature of the mineral distribution. The presence of high value minerals distributed in an extremely small mass of the ROM ore creates a tremendous opportunity for preconcentration with ore sorting. Since Agnico Eagle currently has a portfolio of eight operating mines and numerous development projects and exploration properties, the challenge was to identify the deposits which had the most favourable mineralogy and grade distribution for successful ore sorting. The success of ore sorting is mostly based on the minerals present in the deposit and the grade distribution. The minerals signify the amenability of the deposit for ore sorting and the kind of sensing technology to be used. On the other hand, the grade distribution demonstrates the amount of material that can be rejected without losing value. In order to understand a deposit’s characteristics, it is important to examine the sample’s behaviour with various sensors and then assay it to know its actual value. It is a common practice in the mining industry to document assay value of drill cores and/or material feeding in and out of the mill. However, those VALUES (are insufficient to understand the grade variability on a granular basis. To capture the ore variability in very high resolution and significantly improve the selectivity of the material feeding the mill, it is vital to assay the samples on a rock-by-rock basis, as this is the level of resolution which will be examined by the ore sorter during sorting. A careful and elaborate procedure was followed in evaluating the technology at Agnico Eagle’s operations which is discussed in this paper."

Jan 1, 2019

By Martin B. Zimmerman

It is becoming evident that traditional methods of econometric analysis are inadequate in estimating-the long-run supply of minerals. Econometrics is limited to extracting estimates from observations of the theory predicts that the least cost deposits will be exploited first.1 The estimation of parameters from past data then must lead to biased projections of the future. Mining conditions in the future will be worse than in the past and it is the impact of the future conditions on cost that we need to know. In this paper we present a methodology for dealing with this problem. We estimate a "cumulative cost" function that yields the long-run marginal cost of mining as a function of cumulative output produced over time.2 This is relatively easy to do for coal mining in the United States where exploration for new deposits is not a major factor in supply. The first step of the procedure relates cost to the rate of output and to the geological conditions of the mine. The second step combines geological information on remaining deposits with the cost function to yield the cumulative cost function. A central theme of both these steps is the interaction of economics with geology. The best deposits are selected first and in each step of the estimation allowance must be made for this fact. The problem of depletion is part of the general problem of structural change. The change through depletion in the nature of the exploitable mineral stock is only one factor that calls for an analysis sensitive to the changing circumstances of the industry. The factors impinging most heavily on the coal industry today are the strict environmental regulations legislated

Jan 1, 1977

By G S. Anderson, N W. McDonald

"The IsaMill™ was originally developed to address liberation issues at Mount Isa Mines (now Glencore) operations, McArthur River and Mount Isa in the early 1990s. Following on from the industrial success at those operations, the IsaMill™ was commercialised. In the year 2000, Kalgoorlie Consolidated Gold Mines (KCGM) became the first external user of the technology with a 1.1 MW M3000 IsaMill™ installed to supplement the roaster capacity at its Gidji Processing Plant. The IsaMill™ was used to ultra-fine grind about 10 t/h of pyrite flotation concentrate to 10–12 µm prior to gold cyanide leaching. Based on the success of the Gidji installation, another was installed at the processing plant at KCGM’s Fimiston operation in 2002 in a similar duty.In 2014, a 3 MW M10 000 IsaMill™ was selected to replace the roasters at Gidji as part of the A$98 M emissions reduction project. The mill was commissioned in April 2015 at the design 30 t/h, allowing the immediate shutdown of the two roasters. Replacement of roasting with ultra-fine grinding completely eliminated air emissions at Gidji while maintaining overall plant production rates.This paper details the history of the IsaMill™ at KCGM from the original M3000 to the latest M10 000. It covers the basis of the process selection, circuit design, operating and maintenance data.Citation:Anderson, G S and McDonald, N W, 2016. IsaMill™ at Kalgoorlie Consolidated Gold Mines - from the M3000 to the M10 000 and Replacement of the Roasters at Gidji Processing Plant, in Proceedings 13th AusIMM Mill Operators’ Conference 2016, pp 29–38 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Oct 10, 2016

By Samuel M. Cassidy

The exact date of man's first use of coal is lost in antiquity. The discovery that certain black rock would burn was undoubtedly accidental and probably occurred independently and many times in the world over thousands of years. It is quite likely that these independent discoveries were made when primitive man chanced to build camp fires on exposed ledges of a black rock, then was amazed when it caught fire. The Chinese recorded the use of coal 1100 years before the Christian Era and from the Bible we learn that King Solomon was familiar with coal in what is now Syria. In Wales, there is evidence that the Bronze Age people used coal for funeral pyres, and it is known that the Romans used this fuel. There are other ancient references. So the knowledge that coal would burn, and even some uses of that knowledge, go back thousands of years. However, practical and consistent use of coal seems to date to England in the Middle Ages. COAL IN AMERICA In the Americas, there is evidence here and there of occasional use by the Indians. However, the first recorded discovery of coal, in what is now the US, was by French explorers, who reported an outcrop exposure on the Illinois River in 1679. Following this, other discoveries were made by French and British explorers, but the first recorded actual usage was in Virginia in 1702, where a French settler was granted permission to use coal for his forge. Earliest recorded commercial mining was in 1750, from the James River coalfield near Richmond, VA, a deposit now abandoned. Besides local consumption from this field, shipments were made to Philadelphia, New York, and Boston. During the Revolution this coal was of importance in the manufacture of shot and shell; so important, in fact, that the British sent an expedition in 1781 to destroy the iron works and

Jan 1, 1981

By Fiedler VA, Threadingham GM, Leckenby DF, Clarkson CJ

The Utah Development Company Research and Development Laboratory has embarked upon a programme of optimisation of the company's coal preparation plants. This goal is being accomplished in a three-fold manner - use of pilot plant equipment for optimisation and modelling of the various unit operations, evaluation or development of on-stream ash analysis for process control, and evaluation or development of alternative processes. In each of these areas, digital data acquisition- and at a later stage, process control feedback, is being extensively utilised, based largely upon the use of the HP85 and HP9915 desktop computers. A variety of input/output configurations such as HPIB, BCD, GPIO are used, and at times supplemented by microprocessors such as the Intel 80/05 to assist in data transfer. This paper will discuss a number of specific projects, especially in relation to the manner in which the variables are monitored, and the data later retrieved and analysed.

Jan 1, 1983

By A. M. Gaudin, F. W. Bowdish

MINERAL dressing is an industrial art concerned with the treatment and separation of solids suspended in fluids. Knowledge and evaluation of the area of solid-fluid interface is important in all cases except those involving only large pieces of solid. In fact, many problems relating to comminution, to flotation, to thickening and classification, could be dealt with more rationally if the interfacial area were known. A number of methods have been proposed for the measurement of the surface of certain finely divided solids. Among them are methods using rate of dissolution of the solid,7 its magnetic remanence,3 the turbidity of its suspension,8 and the character of the size distribution of the material.9 The first two are limited to one mineralogical species per sample; the third has certain optical limitations, especially for mineral mixtures, and the fourth is based on an extrapolation of uncertain validity. The need of a better and more general method of surface determination has long been felt, therefore. The method of P. H. Emmett,4 based upon the low-temperature adsorption of vapors, appears to fulfill this need. This method consists in determining the amount of nitrogen that is adsorbed by a given sample of solid at the temperature of boiling nitrogen. The more surface there is on the solid-both internal and external-the more nitrogen is abstracted. In actual operation, the method is somewhat less simple than has been stated so far, in that the nitrogen is adsorbed in an incomplete layer, the completeness and thickness of the layer being related to the pressure of the nitrogen in contact with the sample .2 This circumstance makes it necessary to determine the nitrogen adsorption for three or more values of the nitrogen pressure. APPARATUS In the Richards Mineral Dressing Laboratories an Emmett apparatus has been built and tested (Figs. 1 and 2). A mechanical vacuum pump B and a mercury diffusion pump A work in series to give a high vacuum. The sample, placed in bulb D, can be evacuated by this pump train by suitable operation of the stopcocks in the glass tubing that connects the various parts of the apparatus. C is a McLeod gauge, used to ascertain the order of magnitude of the vacuum obtained, and not for accurate pressure measurements. Pressure measurements are made in the mercury manometer F and gas-volume measurements in the gas burette E. Gases are stored in flasks L (nitrogen) and K (helium), arranged so that definite quantities of these gases can be introduced into

Jan 1, 1944

By D. A. Livingstone

Abstract Golden Manitou Mines, Limited, nine miles east of the town of Val d'Or in northwestern Quebec, are presently milling, at the rate of 1,000 tons daily, a relatively complex 3.11-phide ore and producing, in decreasing order of value, zinc, silver, gold, lead, and copper. The products are a zinc concentrate, a silver-lead-copper concentrate, and a silver-gold precipitate from cyanidation. Although several independent pre-production metallurgical investigations into the treatment of the ore were carried out, current practice is different from any of the recommended methods and, while still leaving room for improvement, is considerably more effective than earlier performance. Flow-sheet developments from the commencement of operations in 1942 are dealt with briefly, showing the reasons for making numerous changes, the shortcomings of the various schemes tried, and, finally, covering data pertinent to present-day practice. From the recovery standpoint, silver has presented the greatest difficulty. The writer's association with the Company coincided with the start of production. Characteristics of the Ore The predominant metallic minerals present in the ore, in decreasing order of their abundance, are: pyrite, sphalerite, galena and chalcopyrite, with lesser amounts of argentiferous tennantite-tetrahedrite, arsenopyrite, covellite, bornite, and chalcocite. The sphalerite is mostly light in colour, sometimes colourless, and practically free from combined iron. Some of the sphalerite is very closely associated with minor amounts of pyrite, chalcopyrite, and galena. Pyrie is abundantly disseminated as medium to fine grains; more rarely it is massive and contains occasional grains of sphalerite, galena, and chalcopyrite.

Jan 1, 1952

By Toivanen R-M, Leinonen O, Pekkarinen H

This paper presents developments in designing an integrated mine control system at Kemi mine. The aim of this paper is to present the general structure of the system and to outline some features of the process control strategies. The results o

Jan 1, 1998

The present Pacific Ocean arose from rapid sea-floor spreading that commenced in the late Mesozoic, and continues to the present day. It started within what is here called the Medusa complex of seaways, basins and troughs with spreading ridges and volcanic arcs, that girdled the earth, including the Palaeotethys and Neotethys of Eurasia between Gondwanaland and Laurasia. Detailed mapping and analysis of palaeofaunas and volcanic arcs indicate that several seaways, rather than one or two, extended throughout Tethys, and into areas now occupied by the Pacific Ocean. The Medusa complex developed under a long sustained wrench regime, right lateral at least from New Zealand to Eur.ope, and saw the origin, maturation and closure of elongate and oval basins under erratic sea-floor spreading, in which no Eulerian pole of rotation remained fixed for long. The name Medusa stems from the analogy of snake-like writhing hair to the constantly shifting development of basins and orogens within the complex. The Indian Ocean split and opened up Gondwanaland concomitant with the later development and deformation of the Tethyan segment- of Medusa, whereas, to the east, the Pacific Ocean opened within Medusa itself, and dispersed Medusa around the rim of the Pacific through sea-floor spreading and strike-slip faulting.

Jan 1, 1987

By Richard E. Chism

SAN DIMAS, in the State of Durango, Mexico, on the frontier of the State of Sinaloa, is the centre of an extensive and rich mining region, which has been exploited for over a hundred years; and the patio process for working silver ores has there attained the highest perfection of which it is capable. Local modifications have been engrafted upon the underlying principles of the process, but, as a whole, the San Dimas practice so fully illustrates its typical capabilities, that I have undertaken to describe its workings in the hope of lightening, to some degree, the labors of my professional brethren who may have occasion to visit Mexico." As is tolerably well known, the patio process, like all other systems of free amalgamation, is not successful with ores containing more than a trace of zinc or lead, the presence of zincblende being especially obnoxious. Iron and copper in small quantities are not particularly disadvantageous. The process succeeds very well with all sulphide ores which do not contain much more than a trace of arsenic and antimony, provided the tailings are concentrated, although, of course, it is best adapted for free milling ores. For suitable silver ores that contain small amounts of free gold the process is still a good one, but where the gold is combined with sulphurets, a considerable and even an excessive loss is inevitable. Hitherto the Mexicans have submitted to this loss, but, since the introduction of American mills, they are gradually abandoning the patio process in favor of the other. The San Dimas ores have a gangue of quartz and feldspar. They are composed principally of silver sulphides, with some chloride and

Jan 1, 1883

By Paul R. Thimas, Edward H. Boyle

"The Bureau of Mines evaluated the long-term cost and availability of primary gold production from 135 mines and deposits worldwide. Collectively, the evaluated countries represent 93 pct of world gold production. Total recoverable gold available (as of January 1984) from a subset of 111 significant producing mines and developing deposits in 13 market economy countries (MEC's) is estimated at 810 million tr oz. The Republic of South Africa is estimated to account for 87 pct of total recoverable gold. The United States and Canada account for 4 and 4.5 pct of the total, respectively. Eighty-three percent of total recoverable gold is available at a constant 1984 break-even price of $400/tr oz, and 70 pct is available at $300/tr oz. South Africa accounts for 90 pct of the gold available at $400/tr oz or less.Major conclusions are that (1) South Africa should remain the largest world producer through the year 2000, (2) annual MEC output in 2000 should not be significantly different than current output given constant 1984 gold prices of more than $300/tr oz, and (3) there may be a significant decline in production after 2010 in the absence of major new discoveries and continued development of new mines to offset the depletion of the South African mines. INTRODUCTIONSince the late 1970's the world gold mining industry has been characterized by dynamic growth in production and volatility in price. World production in 1983 was almost 15 pct greater than in 1980, and the short-term trend continues upward. Annual dollar-based price changes since the early 1970's have been unprecedented in both magnitude and volatility. This commodity, which sold for $35/tr oz3 for over a third of a century, reached an annual average $612/tr oz in 1980. Until 1980, the future price of gold seemed set on an upward trend. Since that year, however, world gold prices have fallen by over 50 pct to slightly over $300/tr oz at the end of 1984.Against this background, this study was undertaken to determine (1) the level of world demonstrated gold resources, (2) total and annual availability of gold mine production, (3) long-run production costs per operation and by national aggregates, (4) the economic and technical factors that impact upon cost and availability, and (5) probable future mine production and cost trends."

Jan 1, 1985

By Hee-Young Chung, In-Mo Lee, Jeongjun Park, Hangseok Choi, Seok-Won Lee

"When using a Tunnel Boring Machine (TBM) during tunneling work, unexpected ground conditions can be encountered that are not predicted in the design stage. These reduce the stability of tunnels, and can result in considerable economic losses. This paper analyzes the potential risk events that may occur due to risky ground conditions. A resistivity survey is utilized to predict the risky ground conditions ahead of the tunnel face during construction. The potential risk events are evaluated considering both the occurrence probability and the impact. A TBM risk management system that can suggest proper solution methods for potential risk events is also developed. Multi-Criterion Decision Making (MCDM) is utilized to determine the optimal solution method to handle risk events. Lastly, an actual construction site, at which a risk event occurred during tunnel construction, is analyzed utilizing the Earth Pressure Balance (EPB) Shield TBM, to verify the efficacy of the proposed system.INTRODUCTION The Tunnel Boring Machine (TBM) method has been widely adopted in numerous tunneling projects because, as a mechanized tunneling method, it is also environmentally friendly, exhibiting minimal noise and vibration when compared with conventional tunneling method. In addition, it provides considerable economic benefits that allow for a high advance rate for long drives during construction. However, the TBM method has a limitation, as it is unable to deal with unexpected situations during construction, as the system is not capable of moving backwards. This leads to delays or even stoppages, and a corresponding increase in construction costs due to the need to arrange for alternative equipment and solutions. It is essential to retain systematic management in order to prevent or deal with unforeseen consequences such as the collapse of a tunnel face, ground surface upheaval or settlement, and construction delay due to water leakage during construction. Therefore, a systematic risk management system that is applicable during the construction stage of the TBM tunnel should be developed, taking into account the predicted risky ground conditions ahead of the tunnel face in advance."

Jan 1, 2016

By K. E. Wood, K. J. DiRocco, L. A. Becker

The Russia Wharf segment of the Silver Line Phase II Project for the MBTA incorporated ground freezing and underpinning during New Austrian Tunneling Method(NATM) tunneling through timber pile foundations, urban fill, and abandoned wharf structures beneath two historic 7-story buildings with steel frames and masonry facades. During construction, the project team implemented an extensive program to monitor, evaluate, and mitigate the ground and building movements caused by the various construction activities. Mitigation included freeze cycling and building raising/lowering to compensate for ground movements and safely maintain the serviceability and occupancy of the buildings. In this paper, we present the history of the freeze, tunnel construction, and thaw-related movements that occurred and the building response that we observed.

Jan 1, 2005

By B. Demoulin, J. Fontaine, R. Gabillard, P. Degauque

To realize a radiowave communication along mine galleries a few kilometers long without repeater, we show that it is possible to use a coaxial cable bearing an important surface transfer impedance like a transmission line with an inductive coupling to the transmitter and the receiver. We determine the electrical and geometrical constants of the cable and the optimal frequency.

Jan 1, 1973

By Merrill, Charles White

MOST extraordinary of the technical developments in placer gold mining during the last five years has been the rise of the dragline dredge, by which is meant a floating washing plant for auriferous gravel, fed by a dragline excavator. The idea originated in the fall of 1933, when Horace Onyett constructed a floating washing plant to which gravel was delivered by a dragline excavator standing on dry land. Onyett's operation near Oroville, Calif., and another started by H. F. England later on Wyandotte Creek, Butte County, Calif., yielded '75 oz. of fine gold before the end of 1933. Although the first operation was abandoned shortly as un- profitable, the dragline-dredge method of gold recovery soon began to expand at a boom rate. As a matter of interest, the Onyett operation was taken over later by Lord and Bishop, who are re- ported to have succeeded in making it the first financially successful drag- line dredge. In California alone drag- line dredges produced $3,294,970 worth of gold in 1937, and the pros-

Jan 1, 1938