BRITISH COLUMBIA DEPARTMENT OF MINES Hon.HERBERT ANSCOMB, Minister JOHN F. WALKER, Deputy Minister BULLETIN No. 16 DraglineDredging Methods Compiled by STUART S. HOLLAND 1942 This Bulletin is in large part a reprint from United States Bureau of Mines Information Circular 7013 VICTOIIIA, R.C.: Photoaffset by CH~LESF. BANPI~U).Printer to the King's Most Excellent Majsty. 1042. CONTEPJTS Page ' HISTORY AND DEVELOP1IZNT ..................................................................................................................................................................... 1 n LINITATIONS 'OF M~THOD................. 1............................................................... :........................................................................................... ' 5 Values ....................................................................................................... ......................................................................................................... 6 Depth .................................................................. ..... ............................................................................................................................. .. 6 7 Bottom ....................................................................................................................................................................................................................... Character of thegravel ................................................................................................................................................ ' 7 Surface ........................... ~ ................................................................................................................................................................................. 7 Quantity ............................................................................................................................................................................................................. 8 SAMPLIIJG AND RECOVERY ........................................................................................................................................................................ 9 FLOATINGPLANTS ....................................................................... I ................................................................ :.............................................................. 13 BIBLIOGRAPHY ............................................................................................................................................................................................................ 36 ILLUSTRATIONS Page Figure 1 Typicalset-up for floating washer 'andexcavator. ...................................................................................................................................... '2 .Figure 2 , Essentialfeatures of a floating washerand gold saving plant. ..................................................................... 14 -Figure 3 I Methods of rebuildingbucket teeth ................................................. 21 PHOTOGRAPHS Facing page .Plate I A. The first draglinedredge to operate in B.. C. Operation of A. G. Watkins on SimilkameenRiver about 2 miles up- stream from. Princeton. ...................................................................................................... 6 B. View of washingplant showing the stacker and sluices which discharge at the stern. ............................................................................................................................................. 6 Plate I1 A. Operation of NorthAmerican Goldfields Ltd. on low Fraser-River bench up- streamfrom Alexandria Ferry. Tailing pileslie behind the shovel, between it and the Fraser River, andback of.the washing plant. .................................................................................................................... :................... 14 5' B. Sideview of the washing plant showing bucket dumping into the hopper, riffle tablesdischarging at the stern, en- closed engine room. and control house on upperdeck, and stacking belt lead- ing off to the right. ........................................................................................... ........... 14 ,. 'DRAGLINE DREDGING METHODS HISTORY AND DEVELOPMENT A dragline dredge isa placer mining machine comprising two separate units (see PlatesI and 11). The gravel is dug by a ' standard dragline shovel which travels over the ground under its own power usually by meansof caterpillar tracks (someof the large shovels are "walkers"). The bucket, havinga capacity of from.one to three cubic yardsor more, is suspended froma structural steel boom50 feet or more in length. The gravel is washed in a separate unit whose equipmentis on a barge floa.ting in a pond. For washing the gravel and separating the gold from it, the barge hasa revolving screen (trommel) and riffle-tables similar tothose used on bucket-line dredges. The dragline shovel- digs away at the edge of the pond andcasts thegravel into the hopper of the washing plant. The pond consequently advance: as, tKe digging proceeds and the barge followsby being warped along by winches with cables anchoredon shore. The coarse tai1in.g.s are discharged from abelt-conveyo;, and sand-sluices. fillthe pond be'hind the dredge. "In the early daysof placer mining, depositsof gold- bearing gravels werefound that.could notbe hydraulicked or worked by hand. .The principal resultof efforts to work such deposits mechanically has been the developmentof the gold bucket-line dredge. The first efforts were mainly unsuccessful but the modern gold dredge is an efficient machine.1 "During the past45 yearssteam shovels and other mechanical. excavators have beenused,fcr mining gravel deposits not susceptible to dredging. The technique for dragline and power-shovel mining has not been developed toa comparable degree with dredging. Most of the operations have been spasmodic and, exceptin relatively 'few cases, unsuccessful up to about 1934. "However, standard washing, screening and gold-saving- *quip- ment similar to that used on bucket-line dredges is now.empl.oyed on floating washing plants and permits continuous operation." The successful development.of dragline .dredging equipment and methods has largely taken place in California in recent years. The first plant wasa home-made boat built at Oroville about 1932 equipped with a perforated tronmel 24 inches in diameter and about 12 feet long whose maximum capacity witha l/Z-yard bucket was The material in'quota'tion is reprintedfrom Uni,ted Statef; Bureau of Mines Information Circular 7013. -1- I N I I "Channel width up to 150 feet- A B Figure I.-Typical set-up,for floating washer and. excavator(not drawn to scale). Reprinted from U. S. Bureau of Mines Infornation Circular 7013. about 200 yards per day. Although the equipment had many mechanical defects, basically it used the principles embodied in the monster dredge installed recently at Dayton, Nevada, which a uses14-cubic yard dragline and whose washing plant a has oapacity of 15,000 cubic yards per day. From modest beginnings dragline dredges have been perfected mechanically and at the same time their limitations discovered so that the proportion of failures has been considerably reduced and'their value, in working certain types of placer ground, recognized. There are at the present time more than200 dragline dredges operating in the Western United States,l by far the greatest number being in California.In British Columbia the first dragline dredge began operationsin 1941. .Credit for being the first to operate in the Province goes to the one which began onworking the ,Sirnilkameen River about3 miles ,up-stream from Princeton.A second and somewhat larger dredge operated by North American Goldfields Ltd. is on the Fraser River about2 miles above Alexandria Ferry and began work about mid-July 1941. "Most of the unsuccessful ventures owe their failure in- to adequate sampling of deposits; the gravel did not contain the anticipated-amountof gold. Other factors contributing to failure have been poor washing-plant design, selectionof'a set- up not adaptedto the deposit, and lack of experience. ALthough this type of mining is primarilya dirt-moving job, onlya few of the excursions into the field by excavating cofitractors and sand and gravel men have proved successful. The majorityof the unsuccessful ventures have been run by men without'previous placer-mining experience; most ofthe.suocessfu1 ventures are run by men with this experience. "To be successful, gold mustbe recovered at Low cost per cubic yard of gravel, and the success of ofthe most enterprises is determined by the number of cubic yards handled per man shift. A successful plant mustbe designed'to fitexisting conditions; proven.equipment isused by virtually all successful operators. "The excavating machines are built by established responsible companies; mechanical troubles have beenlargely eliminated. On the other hand, washingand gold-saving equipment have been standardized only in the floating plantsin California. "The most efficient screening an'd washing device for placer mining is the trommel of the type usedon dredges. As far as is loiown no installations using flat screensfor washing and fine. sizing of placer gravels have proved successful.. Riffles, as used on dredges, are efficientin recovering gold, except.fine or flaky rusty particles. Jigs have been used as an auxiliary Mining