Page:Encyclopædia Britannica, Ninth Edition, v. 10.djvu/767

Rh GOLD aﬁluents, and the rivers of the central granitic mass of France. In the Austrian Alps the gold quartz mines at the Iiathausberg, near Gastein, at a height of about 9000 feet above the sea~level, and at Zell, in Tyrol, are of interest historically as having developed the system of amalgamation in mills, although they are economically of small importance at present. On the Italian side, in the Valanzasca and Val Toppa above Lago Maggiore, a group known as the Pestarena mines have yielded from 2000 to 3000 ounces annually for several years past; and more recently a discovery of great interest of a highly auriferous copper ore has been made at Ollomont in the Val (l’Aosta. In Hungary the gold-bearing veins of Scheinnitz occur in greenstones and trachytes of Tertiary age, the most power- ful example, the ;S'pz'laIcr-gr.In_r/, being ﬁlled with a mixture of quartz and brovn iron ore known as zinnopal, and contain- ing gold associated with silver ores, galena, and pyrites. In Transylvania, at Nagyag, the gold—bearing tellurium mine- mls previously noticed are found in small veins traversing greenstone trachyte. These are often very thin, as low as —:-th to T1,,-th of an inch, but each is carefully traced out, the rock being impregnated with gold and silver to :1 certain depth on each side. At Viirospitak, another Transylvanian locality, gold with a very large proportion of silver and associated with gypsum is worked in veins traversing a Tertiary sandstone, being almost the only known instance of such a mode of occurrence. The Russian empire has the largest gold production among the countries of the Old World, most of the produce, however, being derived from its Asiatic territories. The more important localities are situated on the eastern slope of the Ural chain, extending in a nearly north and south line for more than 600 miles from 51° to 60° N. lat. The chief centres are Miask (5.7 N. ), Kamensk (:30° 30' N.), Berezovsk (57° N .), N ijne Tagilsk (:38" N .), and Bogoslowsk 030° N.), the known deposits, which include both veins and alluvial mines, extending for about one degree farther north. The geological age of the Ural veins is not very well dctined——strata of the Silurian, Devonian, and Car- boniferous periods, which form regular parallel alternations on the European slope, being present on the Asiatic side, but in much disturbed and contorted positions, in associa- tion with piutonic rocks, diorite, diabase, and granite, with which the gold veins are intimately connected. The latter are therefore of post-Carboniferous and probably of Permian date. At Berezovsk the mines cover an area of about 25 square miles, mainly composed of talcose, chloritic, and clay slates, vertical or sloping at high angles, and pene- trated by dykes of beresite, a ﬁne grained rock made up of quartz and white mica with some felspar and pyrites, the latter usually transformed into brown iron ore. These dykes, which have a general north-and-south direc- tion are vertical, and are from 20 to 70 feet and upwards in thickness, are traversed perpendicularly to their direction by veins of quartz from the thinnest string to a maximum of or 4 feet thick, in which gold is associated with brown iron ore or ochres, resulting from the decomposition of pyrites. The workings being essentially shallow, none of the associated sulphides, galena, disulphide of copper, &c., have as yet been found, as a rule, to be gold-bearing. The valuable parts of the veins are almost entirely restricted to the beresite dykes. The richest of the Ural mines are those of Smolensk, near Miask, and Ouspcnsk, near the village of Katchkar, in 52° N. The alluvial deposits which, though called sands, are but very slightly sandy clays, ex-_ tend to the north beyond the inhabited regions, and to the south into the Cossack and Bashkir countries. The most valuable diggings are in the district of Minsk, where the largest nuggets have been found, and in the Katchkar, which are remarkable for the great number of gems, pink topazes, 743 emeralds, &c., found in connexion with the gold. Mag- netite, quartz, and platinum are very common in all the Ural gold sands; less common are hematite, titani- ferous and chromie iron, pyrites, garnet, and, least of all, zircon, kyanite, and diamond. These alluvial deposits are of later Tertiary age, some of them containing traces of pre- historic human work ; others are post-Pliocene, with the remains of the mannnoth, tichorrhine, rhinoceros, and other mammalian fossils. Somewhat similar conditions prevail in the alluvial gold region of the Altai. Besides the veins and alluvial deposits, the Ural rocks, such as serpentine, diorite, beresite, agrairite, &c., are at times auriferous. The gold deposits of the Caucasus, though immortalized in the tradition of Jason and the Argonauts, are now entirely abandoned, the last attempt at working them having been suspended in 1875. In India gold is obtained in small quantities by native gold washers in various parts of the highlands of southern Bengal, and more recently quartz veins and alluvial deposits of considerable promise have been discovered in the district of Wynaad, in the southern part of the Madras presidency. On the Atlantic slopes of North America the chief gold-- bearing localities are on the Chaudiere river, near Quebec, and in Nova Scotia. In both instances the quartz veins worked are contained in slates belonging to the Quebec group of the Lower Silurian period, those of the latter province being specially remarkable for their quasi—stratified character, as they penetrate the slates at a very low angle of inclination, and have been folded and corrugated together with the containing rocks by subsequent disturb- ances. Other deposits of old geological periods are found in Tennessee and North Carolina. On the Paciﬁc side of America gold is found under very different conditions, and on a much larger scale than on the Atlantic side. The whole distance from Mexico to Alaska may be said to be more or less auriferous, the most extensive deposits being in the great north-and-south valley of the Sacramento, which runs parallel to the coast, between the so-called. Coast Mountains and the Sierra Nevada, the latter being distinguished further to the north in the Cascade range. Others of less extent are known in the Klamath, Columbia, and Fraser river basins; they extend in the last two far back into the interior, to the region between t'he Cascade range and the Rocky Mountains. In many of these valleys alluvial deposits are developed to an extent unparalleled elsewhere, the river channels being bordered by banks or benches of gravel and sand, rising in terraces to considerable heights on the ﬂanks of the hills. For example, at the Methow a tributary of the Columbia, there are sixteen lines of such terraces, the highest about 1:200 feet above the river; and at Colville, on the Columbia, traces of old terraces, much degraded by frost and rain, are seen at 1500 feet above the river. These gravels, which are of Pliocene and more recent origin, are in many places, though very unequally, auriferous, the richest points being found in the bars or shingle banks of the river after the summer floods, and in the channels of the smaller tributary streams, where the poorer material has been partially enriched by a process of natural washing. The most extensive, or rather the best known because most completely explored, deposits of this class are those of the Upper Sacramento valley, in California (see vol. iv. p. 701)} Others of considerable importance are worked iii the Cariboo district on the Upper Fraser river, yielding very coarse gold. Another discovery of a singular character, the produce being a regular gold gravel, was made some years back at Salmon river in Oregon, but the deposit, though exceedingly rich was soon exhausted. Gold- ~-1 1 See also Vhitne_v, On the .114-nifernzls (-'rnr:2ls of the Sfrrrn .'e1'(1(lr(, ('.1mbiidge, U.S., I979.