SOilE CONCLUSIONS CONCERNING GOLD MINING. 153
to use less than two 4-foot belts to every five stamps. The degree of concentration (cleanness of the concentrates) must depend upon the ratio between the cost of subsequent treatment per ton, on the one hand, and a greater loss in tailings occasioned by close concentration on the other, the cost of concentration itself being practically the same in either extreme.
For the economical treatment of the concentrates clilorination by the Thies process furnishes in almost all cases a ready solution. The process is a simple one and is not patented; the cost of plant is comparatively small, and the percentage of extraction is high (91 to 97 per cent.). It has been in active operation on a continuous working scale at the two most successful mines in the South (Ilaile and Franklin mines). The presence of copper is objectionable in this process, as it increases the consumption of chemicals, and if in too large a quantity it may preclude the adoption of the process. At the Phcenix mine, X. C, ores running as high as 3 per cent, copper were, however, successfully treated. Ingredients which make dead-roasting difficult may also add to the cost of the process.
Sulphuret ores assaying only $3 per ton, when existing in extensive bodies, so as to permit operations on a larger scale, other conditions being favorable, might be worked at a profit by the application of this process.
Should-concentration, on account of the too finely divided condition of the gold and sulphurets, prove impossible without a heavy loss in tailing's, the cyanide, bromination or Swedish clilorination process might prove of value for a direct treatment of the ore: or the ore might be treated in bulk by the modification of the Thies process in use at Deadwood. Dakota: or by the Thies process proper on an enlarged scale, using, if necessary, closed filtering-tanks under pressure. In all of the above previous roasting is necessary, excepting perhaps in the cyanide process. Attempts with the latter have so far been unsuccessful. It will lie of interest to watch the outcome of the plant at the Dusscll mine, X. C. Lack of success in the use of cyanide cannot always be laid to its lack of applicability: it certainly has, however, this disadvantage, that it requires a careful experimental trial, best made on a large scale and therefore expensive, as well as a continuous supervision afterwards by an experienced chemist, together with more or less skilled assistance, which is a requirement not always conformable with Southern conditions.
.V small class of the Southern ores, referring particularly to those containing lead, copper and zinc, would have to be treated by smelting. A smelting plant would, however, only prove a financial success under the concerted action of all or at least most of the mines producing such
