Page:The New International Encyclopædia 1st ed. v. 09.djvu/18

* GOLD. 6 GOLD. amounted to $1,350,000,000, or about one-eighth of the entire output uf the world since 14!>2. The gold occurs in three types of deposits: River gravels or pincers, high gravels, and veins. The river gravels, found in the beds of the numerous streams that flow down the western slopes of the Sierras, have been derived from the higher levels, where the erosive processes have cut deeplj' into the auriferous rock formations, ilost of the gold is generalh- found near bed-rock, and it is neces- sary to remove a heavy overburden before the values can be obtained. The gold particles vary from minute pellets or dust to nuggets of consid- erable size. The high gravels represent the work of ancient rivers whose channels are more or less parallel to those of the present day, but have been filled in with detrital materials and frequently buried beneath lava flows. They lie along the higher slopes of the Sierras up to 5000 feet aboe sea-level, and sometimes attain a thickness of 500 feet. The veins, which have fur- nished the gold found in both the placers and high gravels, occupy fissures in slates, schists, and igneous rocks, and are, of variable extent and rich- ness. Quartz is generally the gangue material, while the gold occurs in a free state or combined with sulphides, most commonly pyrites. A great series of these veins, called the 'mother lode,' extends across Tuolumne. Calaveras. Ainador, and El Dorado counties ; for a number of years it has been the source of much of the gold mined in the Stjite.. The Comstock IjO<le (q.v.) is situated on an eastern spur of the Sierras, extending into Nevada. Placers and veins similar to those of the Sierras are found also in Oregon and Wash- ington. The Rocky Mountains and the outlying ranges, which were first prospected by Californian miners in the early sixties, include an immense area of gold-bearing territory. Rich gravels have been worked near Leadville, Fairplay, and in San Miguel County, Colo. : near Helena and Butte, Mont.; along the Snake River. Idaho: near Dead- wood. S. D. ; and at Santa Fe. N. il. Leadville was originally settled by gold-miners, but the chief industry for a long time has been the mining of lead-silver ores: it is now coming to the front again as a gold-producer. About 1890 important discoveries of telluride ores were made in the granite hills surrounding Pike's Peak, and since then Cripple Creek has liecome the cen- tre of the richest sold field in America. In 1900 more than .$18,000,000 in gold was taken from these deposits. The Black Hills of Wyoming and South Dakota have a well-developed mining in- dustry which is based largely upon the occur- rence of extensive but low-grade ore bodies. Much of the ore is refractory, yielding only a portion of its gold to amalgamation, so that large cyanide plants have been installed here. There are numerous small fields in Montana, Utah, Idaho. Arizona, and New Mexico, which in the aggregate yield considerable amounts of gold anniuilly. See Map with United States. Alaska, the seat of the most recent discoveries, gives promise of great future importance. With the exhaustion of the rich placers and beach de- posits, such as were found at Cape Nome and in the interior districts, attention will bei directed to quartz mining, which affords a more permanent basis for the industry. It is noteworthy that the Territory was a producer of gold several years before the surface deposits were discovered ; the quartz mines on Douglas Island, near Juneau, have yielded a large output from ore that av- erages only $2 per ton. Canada. The rich alluvial deposits of Yukon Territory furnish the larger part of the output, the remainder coming from British Columbia, C)ntario, and Nova Scotia. In the Yukon region the gold is concentrated in the recent gravels along the rivers and in the terraces on the sides of the valleys. A few quartz veins have been found, but so far the production from this source is small. See Yukon Gold-Field. RlssiA. Most of the gold is derived from placer workings on the eastern slope of the Urals. Little progress has been made in the introduction of improved methods and appliances, and only the richer deposits can be exploited at a profit. There are small quartz mines in the interior districts of Siberia. Transvaal Colony. The Witwatersrajul gold- field, near Johannesburg, is one of the most re- markable and productive in the whole world. The deposit is a conglomerate, commonly called 'banket,' varying from a few inches to several feet in thickness and averaging about $10 per ton in gold. It can be traced for several miles along the strike, and, as it retains its auriferous tenor with depth, there is an enormous reserve of ore for future working. The output of the Trans- vaal mines in 1898 was $78,071,000, but it fell to about $7,000,000 in 1900 owing to the w^ar. Wlien operations are again resumed in full force Die Transvaal Colony undoiibtecUy will assume the premier position as a producer. The amount of gold available in the ore for future working runs into billions of dollars. AusTR.Li.. Oold-mining holds a prominent place among the industries of the Commonwealth. The rich alluvial deposits that first attracted the attention of miners are largely exhausted, but there are still considerable areas of surface grav- els which repay working with modern methods. An increasing proportion of the output each year comes from quartz veins. The most productive fields are those of Murchison and Coolgardie in Western Australia: Charters Towers and Mount Morgan in Queensland: and Ballarat. Sandhurst, and Beechworth in Victoria. OoLD-MiNiNG. Gold-mining operations may be divided into two classes, which are commonly called placer mining and quartz mining. The de- posits of gold first mined were called placers, and were the river-bed deposits of gold-bearing sand and grav«l. These deposits are knowTi as dry placers when they are ancient river-beds from which the water has gone, and as wet placers when they are the beds of existing streams. The process of dry-placer mining consists in excavat- ing the gold-bearing sand and separating the gold from it by washing, according to one of the methods described in the succeeding section on iletallurgy. Dry-placer workings are divided into surface placers and deep placers. The most important method of placer mining is the hy- draulic method, which was first attempted in a crude way in 1852 in Placer County. Cal.. and is now practiced on an immense scale. Briefly described, hydraulic mining consists in directing a powerful stream of water from a pipe against the gold-bearing gravel bank, which breaks down the material and washes it away through sluices, where the separation of metal is accomplished as described below. Wet-placer mining from the