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SOME COXCXCSIOXS COXCEKXIXG GOLD 3IIXIXG-. 119
Bottom-gravel mines were operated in the earlier days almost entirely by pitting, draining the excavations with water-wheels, and raising the gravel by hand to rockers and sluice-boxes, the tailings being left in large heaps. This work was often done in an unsystematic manner; portions of the ground could not be worked at all; and, in general, only the richest gravel received attention, the overlay and the bed-rock being neglected entirely. Some of these gravel heaps have frequently been reworked, in one case (on the Mills property, jST. C.) as often as seven times. The additional gold obtained in these operations was partially due to the incompleteness of the preceding washings, as well as to the subsequent further disintegration of vein-quartz carrying free gold and sulphurets. A number of these old bottom-placers may warrant a remunerative reworking on a large scale, either by the use of giants and bed-rock sluices when sufficient fall is available, or where the latter is not the case (a common feature in the South.) by the application of the hydraulic gravel-elevator.
Virgin placer deposits also exist, which, on account of the low grade of gravel, or the great depth of the overlay, could not be profitably worked by the more primitive methods. For such, the above appliances may also* furnish a solution. The Southern gravel deposits are far less extensive than those of California and Xew Zealand, and therefore as low a grade of gravel cannot be worked, although the South has cheaper labor in its favor. Systematic work has rarely been pursued, and records of such work have not been kept. For this reason, as well as on account of the unequal concentration of the gold in the deposits and the varying working conditions met with, it is impossible to give limitingvalues per cubic yard to guide operations in the future. For the same reasons, preliminary testing will be difficult, especially in ground that has already been worked.
In general, it may be said that the great extent of the rock-decomposition in the South (often from 25 to .100 feet in depth), and the easy disintegration of the same has resulted in a greater concentration of gold in the gravel, considering the richness of the ore-bodies in place, than in many other gold fields.
The auriferous saprolites and decomposed vein-matter have been most extensively worked in the Dahlonega district. Here the decomposed material, in which gold from the eroded vein-matter is more or less concentrated, has to a great extent been worked clown to the harder rock. In the Dahlonega method of working, everything seems to have tended towards the simplification of the process and plant, with the object of milling as large an amount of low-grade material as is possible with economy in labor and plant, irrespective of close working. Both on account of the greatly impoverished material and its increasing unfitness
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