UNITED STATES. The gold-fields of the United States are widely distributed both geographically and geologically, but, as elsewhere, the occur rence of gold is limited to areas of crustal and volcanic disturbances, these apparently being the prime factors that govern the formation of ore bodies the world over. There are thus two distinct regions in which gold is produced, the eastern region along the Appalachian Mountains, throughout its extent from Maine to Alabama, although workable deposits occur only in the southern section. The auriferous belt, varying from a few miles to 75 miles in width, extends from Virginia in a southwesterly direction through North Carolina, South Carolina, and Georgia, into Alabama. Both quartz and surface deposits are worked, but the former are the most important at present. The veins cut through slates and schists, and carry iron and copper pyrites, with which the gold is usually associated. Dahlonega, Ga., and Haile Gold mine, S. C., are the chief mining centres. The Westeni goldfields, to which this country owes its prominent place as a producer of gold, are scattered over the whole region between the east ern foothills of the Rocky Mountains and the western slopes of the Sierra Nevada and Cascade Ranges. Only those of special importance will he mentioned here. as a general description of the gold resources of the West may be found under the titles of the different States (qq.v.).
The auriferous belt of California extends through the northern and central parts of the State, and from the summits of the Sierras to the San Joaquin and Sacramento valleys. Its wonderful, almost unparalleled richness has fur nished the incentive for the exploration and rapid development of the whole Far West. From the first discovery in 1848 to 1900 the output has amounted to $1,350,000,000, or about one-eighth of the entire output of the world since 1492. The gold occurs in three types of deposits: River gravels or placers, 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 deeply into the auriferous rock formations. Most of the gold is generally 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 above 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, Amador, and El Dorado counties; for a number of years it has been the source of much of the gold mined in the State. The Comstock Lode (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 Fd, N. M. 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 become the cen tre of the richest gold 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 annually. See Map under ORE DEPOSITS.
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 bel 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.