DEPARTMENTOF THE INTERIOR UNITED STATES BUREAU OF MINES JOHNW. FINCH*DIRCC~OFI INFORMATION CIRCULAR - PLACER MINING IN THE WESTERN UNlTED STATES - - PART Ill. DREDGING AND OTHER FORMS OF MECHANICAL. HANDLING OF GRAVEL, AND DRIFT MINING 1 I . .C. 6788. February 1935 Part I11 . .Dredeing and Other Forms of Mechanical Handling of Eravel . and Drift Miniqg CONTENTS Introduction ....................................................................................:..................... Acknowledgments ..................................................................:................................. Excavating by teams or power equipment ...................................................... General statement...................................................................................... Team or traotors...................................................................................... Teams .................................................................................................... Tractors.............................................................................................. Scrapers and hoists.................................................................................. Drag scrapers...... : ............................................................................. Slaokline on oablewags .................................................................. Power shovels and draglines.................................................................. Stationary washing plants............................................................ Movable washing plants.................................................................. Floating washing plants........................................................ ....... Summary or operations at mines excavating by teams or power equipment ................................................................-. ............................... Dredging .................................................................................................................. General.............................................. ..., ...................................................... Status of the dredgins, industry.......................................................... Discussion lf modern dredges.......,....................................................... Estabrook dredge.............................................................................. Falrbanka Exploration dredges.................................................... General operating practice...., .................. :............................................ Screening............................................................................................ Gold saving........................................................................................ Dredging recovery ............................................................................ Water consumption ............................................................................ Pore r .................................................................................................... Cost of dredging........................................................................................ Cost of dredges................................................................................ 1 Tbe Bwmm or Minee will weloome reprinting of thia papor. prwided the following footnote aoloowl~dpratla uaod: l.prl8t.d from U.S. Bureau or Unee Infomation Ciroolar 6788 .* . 2 SPp.rriring onginerr. U.S. Bureau of Miner . Southwat Experiment Station . Roeon. rrit. 3 lurirtmt .ising enginerri U.S. Burr- of Mine8. South.rrt Crp.ri.mt Station. ?boaon . rrix . 1m Resoiling...................................................................................................... Accident prevention .................................................................................. Drift 8ining.......................................................................................................... General .......................................................................................................... Development.................................................................................................. General developmoot ............................ < ........................................... Breaating. ............................................................................................ ......... Representative 8ining praotioe~.......................................................... Reoent grave 1s.................................................................................. Ancient gravols................................................................................ Milline.......................................................................................................... Representative milling praotioes.............................................. INTRODUCTION This paper is the third of a series of three on placer mining in the western United States. The first paper4 discusses the history of placer mining in tho Western States and the production of placer gold, geology of placer deposits, location of placer claim on pub lie lands, sampling and estimation of gold plaoers, and clarsifioation of plaoer-.ininc methods, together with hand-shoveling and ground-sluicing. The second paper6 deals with hydraulicking, sluice boxes and riffles, recovery of gold and platinum from placer concentrates, treatment of amalgam, and marketing of plaoer gold. The disoussion of aluice boxes and subsequent aubjects in tho reoond paper applies to all forms of plaoer mining. The present paper treats of dredging and other forms of mechanical handling of plaoer gravels, and drift mining. - The authors wish to acknowledge their indebtedness to the operators of placers in the Western States who generously supplied information without whioh thi8 paper could not hate been written. Descriptions of placer operations in Nevada were supplied by Alfred Y. S8ith of the Nevacia State Bureau of Mines and Wm. 0. Vanderburg of the United States Bureau of Mines, both of Reno, Nev., Francis C. Lincoln of the South Dakota School of Mines at Rapid City, S. Dak., supplied the description of placer operations in South Dakbta. The account of the dredging operations of the Fairbanks Exploration Co. at Fairbaaks, Alaska, was prepared by C. G. Rice, vice president of the United States Smelting, Refining, & Mining Co., Boston, Mass. Available literature upon placer mining, engineering, and allied subjects ha8 been oon- sulted; tha .authors have endeavored to make suitable reference throughout the text. * 4 rnrbnor, E. D.. .od Jobon. C. H.. Plaoor Untng in tho Iastarn Unitad State.: Psrt I. - Olnaral Inforution. Haad- Shoraling, snd EroPnbSloicing: Int. Circ. 6Ta6. Buram ot Mine., 1934. 75 pp. 5 ardaor. C. D.. and Jobnaon, C. H., Plwot Wng in tha Wootorn United St.tor: Part II. - Wdt..LiokLn~. Tnatnnt or plwrr Conornttstar rod Y.rhting of Gold: 1st. Ciro. 6787, Burom of Yinrr. 1934, 88 pp. EXCAVARNG BY TLSAYS OR POWER EQUIPMENT Nu8erous gold-bearing deposits ocOur throughout the western placer districts that oannot b. mined by the usual methods. Often there is insufficient water for hydraulicking or ground sluicing, or the deposits are too small to justify the building of ditches or pipe lines. Such deposits may not be amenable to dredging owing to lack of water or small size; also, the depth or character of the gravel or the topography and condition of the bedrock nay make dredging irpraotioable. A large number of operation8 were begun io 1931 and 1932 in which mechanical equipment waa used as the principal means of excavating the gravel prior to wash- ing This activity was due to two principal causes: (1) The increased general interest in placer mining and (2) the desire of excavating contractors and sand and gravrl operators to use otherwise idle equipment and to keep organizations together. A third b~iless important cause was the endeavors of inventors and manufacturers of "trick" gold-saving machines to find placers in which to install and test their equipment. Although the early placer miners were as adept as the present generation ?ad power shovels, scrapers, and other mechanical excavators have been tried for placer mining at many placss during the last 40 years, the modern operator has at his command greatly superior excavating units and more efficient pumps and other mechanical equipment. Most of the present meohanical installations, however, have been built as cheaply as possible, using second-hand or homemade' equipment. Often the equipment used was not the best for the purpose but was employed.because it was handy or cheap. For example, old automobile engines were used largely as power plants. At many mines mucb, better fuel economy could have been obtained With a different type of engine of a horsepower more nearly corresponding. to the work to' be done. In opencut copper and iron lining, as wll as in large coalitripping and quarrying operations, it is an axiom that all operations should be planned to sene the digging units and keep them working steadily and at full capacity. It is equally true An mechanical placer mining that both the excavator and washing plant must operate at capacity if the mine is to be worked at a profit. In the present stage of development of this form of placer mining the plants seldom work steadily at capacity. Standard power shovels or other forw of ex- oavators aan be obtained for digging the gravel. Standard set-ups, however, for washing