86 DIFFERENT METHODS OF MINING.
the number of men and extracts four to six times the amount of gold per lineal foot of channel.
The
yield of the North Bloomfield channel by drifting has been $150 per
lineal foot of channel, while hydraulick-ing the entire deposit in this
locality has given a yield of $750 per foot.
Requirements for Financial Success__From a
financial
point of view it is essential for profitable hydraulic mining that
there should be ample facilities for grade and dump and a sufficient
head and an abundant supply of cheap water, all of which requirements
vary in importance inversely with the richness and extent of the
gravel. Economical management may be considered in all classes of
mining a sine qua non to success; but it is especially
requisite here, as the value of this method is based on the great
facility with which profitable results can be obtained at trifling cost
from expeditiously and skilfully washing vast areas of ground which
contain relatively insignificant amounts of precious metal.
Strictly
speaking, in hydraulic mining, water does all the work, but in the
application of this process to the washing of cemented gravel and
masses of volcanic products, it has been found that water alone has
little effect on banks composed of such material, and to overcome this
difficulty recourse is had to blasting in order to shatter the bank
before water can be advantageously employed.
