ments during the period of 30 years beginning with 1860 than had been made during the preceding 500 years.1 The Homestake mine has always been worked by shafts and stoping with square-sets. However, in the summer of 1878 it was decided to remove the large ore-bodies lying close to the surface by means of an open-cut. This was accomplished by running long drifts into the deposit from the hillside and connecting them with the surface by raises. Work of breaking down the ore is then begun at the surface, the ore being run down the raises, caught in cars and hauled through the drifts to the surface on the drift-level. When the level of the drifts is reached other drifts are run at a lower level thus opening up a new level or block of ground. This system of open-cut working is in reality a milling method and is practically identical with the milling methods employed in the iron mines of Lake Superior. The resulting open pits are called "Glory Holes." Mining began on Douglas Island about 1881 and as late as 1904 it was estimated that fully 75 per cent of all the ore mined had come from the open pits or "Glory Holes" of the Treadwell mines. One such Glory Hole at the Alaska-Treadwell mine had reached a depth of 220 feet below the adit-level and about 450 feet from the surface with a maximum width of 420 feet and length of 1,700 feet. The method of procedure here is similar to that at the Homestake mine and it is in fact becoming the usual method employed with the proximity of large deposits to the surface. A similar method is employed in the Mercur mines, Utah, and at the Combination mine, Goldfield district, Esmeralda County, Nevada.5 A modified caving system was employed in mining the gold ores of Mercur, Utah, as early as 1897 and has been successfully operated up to the present time. The peculiar conditions obtaining here renders this method applicable, a method that has been used extensively for many years especially in the iron deposits of the Lake Superior region, but was not, to our knowledge, applied to gold and silver deposits prior to its use in these mines. In those localities where there is lack of water to carry on hydraulic-mining operations successfully, also where the grade is 1 Min. and Sci. Press, Vol. 76, p. 109. Min. and Sci. Press, Vol. 90, pp. 392 and 404. T. A. I. M. E., Vol. 34, p. 351, 1904. Mines and Minerals, Vol. 25, p. 3. not sufficient for sluices and dumping of gravels, the working of auriferous deposits has always been a serious problem. The first attempt to overcome these difficulties was the introduction of a hydraulic nozzle into the lower end of a section of straight wooden box or spout which was leaned against the pit bank, thus delivering the gravel with sufficient water for sluicing at a considerably higher level. However, it was found that to thoroughly mix the water and gravel, and make a mobile mass the lower end of the box needed to be given a curve, when the gravel could be elevated with little difficulty. The first hydraulic elevator, built on the proper lines, is claimed to have been used in California by the Yreka Creek Gold Mining Company, Siskiyou County, in 1880. This was a Cranston elevator and was operated under a head of 266 feet, using about 800 miner's inches of water and raised the gravel 40 feet. In 1889 the Joshua Hendy works erected a hydraulic plant at the North Bloomfield mine. This elevator raised the gravel 96 feet with a head of 540 feet and used 1500 miner's inches of water.1 Hydraulic elevators were not generally used until comparatively recent times but are now in common use in most of the Western states and to a limited extent in the Southern goldfields. The first hydraulic elevator was used in the South at Brindletown, North Carolina, in 1883, also at Dahlonega, Georgia. A Crandall elevator was installed at the Chestatee mine, Georgia, in 1895.' As early as 1893 electric power for the operation of mine plants was installed at Bodie, California, and since that time many other installations have been made in the gold and silver mines of the West. About 1900 the electrical equipment of the C. and C. shaft at Virginia City, Nevada, was begun. Power is generated on the Truckee River not far from Floriston. Extensive hydraulicing operations along the Truckee River are also furnished with power from the same plant.3 The hydraulic system of raising water was adopted by the California and Consolidated Virginia Company of the Comstock lode, in 1899 and proved very successful. Many mines are now being operated by electric power in whole or in part in the Cripple Creek district as well as in numerous mining camps throughout the United States. 1 Min. and Sci. Press, Vol. 34, p. 24, and Ibid., Vol. 72, p. 261. 3 U. S. G. S., 20 Ann. Rept., Pt. 6, p. 116, 1898-99, and T. A. I. M. E., Feb., Eng. and Min. Jour. Vol. 74, p. 243. The discovery of dynamite by Nobel, in 1866, furnished the mining industry with one of its most important and powerful agencies which may be considered as standing second to none in its influence on the advancement of mining. Exactly when dynamite was introduced into the United States as an explosive for mining purposes is not known, but an early mention of it occurs in the Mineral Resources of the States and Territories for the year 1869, about three years after its discovery. In this connection the following statement is made: "Now since the small holes with giant powder do as much execution as the larger ones with common powder, the comparative cost of using the two materials is as 51 to 92 in favor of the former. . . The miners foresee that this change reduces the necessity for skill on their part, and will lead to the introduction of unskilled labor." Power or the so-called machine drills were first used in the mines of this country, about 1850, although the "drop drill," a hand operated machine, was first used in 1838. A German engineer, Sommeiller, operated the first air drill in the Mt. Cenis tunnel, which was being driven through the Alps. Steam or air operated drills were used in 1848, but it was not until several years later that they were introduced into the mines of the United States, when all such drills went by the name of Burleigh." The improvements made in methods of reducing ores together with the processes of extraction of values were largely responsible for the rapid advancement in mining made during the sixties and seventies. The invention of the Blake crusher and the gravity stamp, and the application of the lixiviation methods to the treatment of ores must be considered of vital importance in the building up of the mining industry to its present status. However, a discussion of the methods of treating ore in the extraction of values is given in another chapter, under the heading of Milling. DESCRIPTION OF METHODS OF MINING. In the following pages are given descriptions of the methods of mining employed at various times in the mines of the United States. Gravel-mining is first considered in its varied and multiform phases, following which is a discussion of vein-mining. When available, extracts are given of descriptions of typical operations; otherwise 1 Mineral Resources of the States and Territories West of the Rocky Mountains, 1869, pp. 33-36. 2 Min. and Sci. Press, Vol. 87, p. 19. descriptions, incorporating the best practice, are used instead. Numerous references are appended in order that the reader may verify statements made and enlarge upon the information given should he so desire. Gravel Mining. Prospecting. -The prospecting of auriferous gravel deposits is more readily accomplished than similar work in veins owing to the comparative shallowness of the deposits, and the greater regularity and uniformity of occurrence of the gold-content. The first work of this character is done by pits which are sunk to bed-rock, but where water occurs in considerable quantities such work is impossible, except in special localities, as in Alaska, where, during the winter months, the miners even prospect the beach of Bering Sea, by sinking pits through the ice and underlying sands. Such work has been carried on at a distance of one-quarter of a mile from the shore, where the water was shallow and consequently froze solid to the bottom. Prospecting of the tundra of the Cape Nome goldfields was first accomplished by shafts, but owing to the expense is now done almost entirely by drills. Both drilling and shaft sinking are readily accomplished as the tundra is frozen except in open spots, which usually occurs near growing trees. The testing of gravel deposits, especially those of considerable depth, is now almost universally done by churn drills. Such work is now successfully carried on in all of the large hydraulicing and dredging fields, that at Oroville being typical of such operations. Here a 7-inch drill is employed, the casing of the hole being driven as far in advance of the drill as possible, the core being cut out by the bit. The volume and contents are thus readily determined as measured, when raised by the sand-pump. This material is rocked and panned, and from the results the value per cubic yard of the deposit for that particular locality is determined.1 Ground-Sluicing and Booming. Detailed descriptions of the early methods of working gravels, while interesting are not of sufficient importance to warrant elaboration in this connection. However, as ground-sluicing and booming, or hushing, especially the former are still used, and will probably continue to be employed by individuals with small capital and in new districts, brief mention is made regarding them. 1 Min. and Sci. Press, Vol. 90, p. 266. Ground-sluicing consists in digging a ditch, either by hand or by the use of a stream of water, which is cut down to bed-rock. If the bed-rock is smooth, boulders and stones are thrown in, often very irregularly, while in other cases they are carefully placed on edge with the upper edge inclined slightly upstream; but if the bed-rock is rough it may serve to arrest the gold, from which irregular depressions it is removed at certain intervals. After the ditch or ground-sluice has been made and prepared with riffles, the work of washing is begun; all of the water and gravel passing through the sluice to the waste bank. As the face of the bank recedes the sluice is advanced thus maintaining the same relative position between the two. Many of these sluices may be in close proximity, each having an independent discharge, or several and possibly all may feed one large sluice, which may be a ground-sluice or wooden sluice, in either case provided with some sort of riffles. Ground-sluicing is, however, pre-eminently a poor man's method, and the equipment is usually of the roughest sort. In the early days in California ground-sluicing yielded the greater part of the gold produced, but was soon superseded by hydraulicing and other improved methods by which it was possible to obtain larger returns at small cost. Nevertheless ground-sluicing did not cease as a source of gold production, for the Chinese still persisted in the work, even working over many times ground long since abandoned by the white man. Furthermore, the Chinaman excelled the white miner in saving gold, and especially fine gold, under difficult conditions. In fact the Chinese became adepts in collecting gold from clayey gravels, black sands, etc., and were thereby able to work profitably ground considered too low-grade for the American miner to spend his time upon. Taking the case of black sands, the Chinese so arranged their sluices that all materials passing through them dropped into a large shallow box floored with perforated iron. All material too large to pass this screen was shoveled out, while that passing through the screen was carried by a stream of water into a wide sluice provided with blanket riffles, and is practically identical with the operation known as "blanket sluicing." By this means it is evident that the bulk of the material in the sluices is considerably reduced, the coarser being thrown out by shovels, while the finer and lighter earthy material is permitted to escape with the water. The black sand, gold, quicksilver and amalgam are thus concentrated into a comparatively small bulk.1 1 Min. and Sci. Press, Vol. 43, p. 6. |