Ch. 1: Gold in Ceylon

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	GOLD IN CEYLON.	81

	Proportion of (told in Deposits,—A rich gold-bearing deposit is quantitatively very different from one to which the same term is applied when containing ores of other metals. In the latter the useful material must as a rule from a considerable proportion—one or more parts in a hundred—of the mass ; while in the former, owing to the superior value of the product, it rarely at. tains as much as I per cent, and is generally very much less, the amount of gold contained in easily-worked alluvial deposits being often extremely small. For example, the yield of the Siberian gold washings ranges from 12 grains to I cwt. 12 grains per ton; (a) while in the lodes, which are more difficult and expensive to work, the proportion is about 8 dwts. per ton. In the alluvial washing of California it is estimated at about two shillings worth, equal to about i-40th of an ounce, per ton of gravel. In Australia the alluvail ground worked in the colony of Victoria in 1878 is returned as averaging 25 grains (1 dwt. 1 gr.) per ton, or about double the above quantity. In vein mining, which is more difficult and costly, a larger yield is necessary, but probably 5 dwts., or about £1 in value per ton, will in most places represent paying quantities from quartz containing free gold ;'. e., not associated with pyrites. The proportional yield and quantities of the different kinds of auriferous materials treated in the colony of Victoria during the last three months of 1878 were:—

	In the less tractable minerals, such as arsenical pyrites occurring in the lower portions of the veins, as much as li to 3 oz. may be required for profitable working. When associated with the ores of other metals, such as silver, lead, and copper, the extraction of the gold is in most cases an incidental and final operation in their metallurgical treatment, and may, therefore, be best considered in the articles on these metals. Mining.—The various deposits of gold may be divided into two classes— "veins" and "placers." The vein mining of gold does not greatly differ from that of similar deposits of metals. It will only be necessary to refer here to certain details of the extraction of gold in such cases. In the placer or alluvial deposits, the precious- metal is found usually in a water-worn condition imbedded in earthy matter, and the method of working all such deposits is based on the disintegration of the earthy matter by the action of a stream of water, which washes away the lighter portions and leaves the denser gold. In alluvial deposits the richest ground is usually found in contact with the " bed rock"; and, when the overlying cover of gravel is very thick, or, as sometimes happens, when the older gravel is covered with a flow of basalt, regular mining by shafts and levels, as in what are known as tunnel-claims, may be required to reach the auriferous ground. In the early days of gold washing in California and Australia, when rich alluvial deposits were common at the surface, the most simple appliances sufficed; the most characteristic being the " pan," a circular dish of sheet iron with sloping sides about 13 or 14 inches in diameter. The pan, about two-thirds filled with the "pay dirt" to be was>iied, is held in the stream or in a hole filled with water. The miner, after separating the larger stones by hand, imparts a gyratory motion to the pan by a combination of shaking and twisting movements which it is impossible to describe exactly, so as to keep its contents suspended in the stream of water, which

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