The modes of working adopted at the first start of the diggings were necessarily rude mad wasteful; the fortunes of the gold-seekers, too, were of course very variable under such a system, many of them having made large profits—as much, in a few instances, as a thousand pounds and upwards in a single week—but many more met with nothing but disappointment. A more systematic plan of mining, however, has now been intro-, duced, by which the auriferous deposits are more completely worked out, and milling undertakings rendered less precarious. But notwithstanding the improved methods of working, the average annual produce of gold in the Australian colonies for the five years ending 1874, was only about £7,000,000, which was less than two-thirds of the yield of-some earlier years. In the international exhibition. of 1862 there was a gilded pyramid 10 ft. square at the base and 45 ft. high, representing the mass of gold exported from Victoria between Oct. 1, 1851 and Oct. 1, 1861. Its weight in solid gold would have been 2.6,162,432 ounces troy, which, taken roundly at £4 per ounce, gives its value as £104,649,728. The produce of California since the discovery of its gold-fields in 1847, up to the present time, may be estimated at about 50,000,000 ounces, and its value at £200,000,000.
Since the two great gold regions of California and Australia became known, three new ones of considerable promise have been discovered—one of them in British Columbia, the value of which was proved in 1858, although previously it was to some extent known to the Hudson's Bay Company; another is.being successfully developed in Nova Scotia; and a third in the province of. Otago, in New Zealand. It would appear that there is a great similarity between the general rock systems and auriferous deposits of this region and those of Australia. Before passing from the subject of recent gold-fields, it is worth noting that, a few years ago, Dr. Livingstone, the African traveler, discovered gold near Tete on the which may be found to be rich in the precious metal, when more deliberately surveyed. Its position is remark able as occurring in the center of a coal-field.
The annual produce of gold in the whole world at the present time is somewhere between 30 and 40 millions sterling. Wherever gold is found, its origin can generally be traced to quartz veins in the pyimary or volcanic rock, such as granite, gneiss, ppr phyry, clay-slate, or greenstone. As these rocks became decomposed by the action of the weather, portions of the auriferous veins were carried down by streams and floods, i and so found their way into the deposits of sand, clay, and shingle in river-beds, and in the gullies and flats of hills. Many auriferous drifts are of great thicknesi, formed by
long-coutinti,ed wasting of the rocks of neighboring hills, and therefore require mining to a considerable depth. Gold for the most part is found in small grains, or scales, called gold-dust; sonic of it, however, in pieces, or nuggets of considerable size. One found at Ballarat in 1858, called " the welcome," weighed 2,166 oz., and its value was £8,376 10s. 10d. Another discovered in Donolly district, Australia, in 1869, weighed 2,520 oz., and its value was £9,600. A good deal of the Mexicali and European gold is obtained from auriferous pyrites. .
Nearly all the metals except gold are most usually found as ores chemically com bined with oxygen, sulphur, or other substances; and they therefore require to be separated by chemical processes. Gold ores, if we may use the term, require to be mechanically treated by the processes of crushing, stamping, and washing; the amal gamation process being resorted to when the gold occurs in a state of fine division.
One kind of crushing-mill consists of two large cast-iron rollers, which break the auriferous quartz into small pieces as it passes through between them. More usually now, a stamping- mill is used with iron-shod piles of wood, wrought by an axle with projecting cams after the fashion of flint-mills and beetlins-machines. The ore pounded by the stamps is next washed, and for doing this there is an almost endless number of contrivances. In one of the richest quartz districts of California, it is carried by a cur rent of water over coarse woolen blankets laid on slopino. boards. By this plan, the lighter particles of quartz are carried away, and the particles of gold become entangled in the fibers of the wool. The blankets are washed at intervals in a tank, where the gold and other matters caught on their surface accumulates. It is then ready for the amalgamation process.
The gold of auriferous drift is partly extracted by washing, but there still remain minute particles invisible to the naked eye mixed with the gangue; indeed, some auriferous soils contain all their gold in a state of extreme division. To recover the gold either from this or stamped quartz, an amalgam is made; that is, it is mixed with mercury, widch has the power of seizing on and dissolving the gold particles, however minute. The mercury is afterwards distilled off in a retort, leaving the gold nearly pure. Gold has of late been profitably extracted from sulphureted ores by Plattner's process, which converts it into a liquid chloride, and the gold is then precipitated from the solution by metallic copper.