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MINING IN CALIFORNIA AND NEVADA.
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APPENDIX.
When
it is taken into consideration that the investigation of mining in all
its collateral branches, as relating to gold principally, had been the
object of the delegate's mission, it was, however, not to be said that
he should lose sight of or pass over any other matter that could be
advantageous to miners not engaged exclusively upon auriferous
deposits; and, in a rich metalliferous country like the two States
visited, it could not be avoided to see and investigate, though such
action has not materially infringed upon the general instructions of
the committee under whose authority these matters were proceeded with.
A. Novel Treatment of Poor Copper Ores.—About
18 miles north-west of Grass Valley City, California, a cupriferous
belt has been discovered, giving rise to extensive operations both in
the mines and in their reduction; and, as the new mechanical treatment adopted—instead of the older and slower process hitherto in vogue—has given daily results
from an ore scarcely yielding 6 per cent, of copper, it may be of
advantage to introduce that system in Australia with similar low-graded
copper ores.
The
ore occurs in almost unlimited quantities, in the form of an irregular
deposit, having one well-defined wall only; its extreme width has been
ascertained at 110 feet, but its extent in the strike of the wall is so
far unascertained. The ore is a liighly ferruginous copper pyrites, and
it yields as low as 2 -1/2 per cent., though 6 per cent, appears to be
a very fair average, and the mining proper of this ore costs, under
contract, but 1 dollar 50 cents per ton. After raising the ore from
below, it is piled under very extensive sheds in heaps of 40 tons each,
upon large logs, &c, of firewood, and roasted. At the centre of
each pile a rough chimney of loose bricks and large lumps of ore is
built, upon which a movable stack of stout sheet-iron is placed, so as
to project above the roof of the sheds, and thus conduct the very
noxious fumes away from the works. This ore, after complete
calcination, is allowed to cool for subsequent removal to other sheds.
Large wooden tanks are there constructed at the hill side, in the form
of terraces, so as to permit the various products falling from one set
of tanks to the other without much handling. It may be remarked that in
the construction of all these tanks and shoots, iron bolts, nuts, and
nails, &c, are entirely covered with lead or wood, to prevent their
destruction by the strong liquors obtained. The higher series of tanks
are filled with water for 3 inches ; the calcined ore is placed in
layers therein, each layer receiving a coat of coarse rock-salt; then
water is turned on to fill the tanks within a couple of inches from the
top. After this, superheated steam is turned on through a leaden pipe
at the bottom of each tank for about one hour, when the whole contents
begin to boil. Gaseous bubbles rise to the surface, which increase both
the ebullition of the liquor, whilst also facilitating and sustaining
the dissolution of the ores and other ingredients. The first solution
is drawn off every evening from each tank, in order to increase the
body of the liquor to about double its strength originally; and this
fluid, strongly impregnated with copper, and of a deep-green color, is
passed to the large receiving-tank located near the revolving barrel.
This tank when once full is kept so, in order to carry on the
operations every day in the year (Sundays included), as it is
impossible to stop when the processes are once in fair working order.
The liquor possesses that well-known acrid taste of copper solutions,
and it is periodically gauged by graduated instruments, and it is then
pumped into the revolving barrel. This barrel appears to be the
principal feature in the process, as it takes the place of the usual
shoots in which cupriferous mine or other water is made to run over old
iron, which latter is very gradually transmuted into chemically pure or
"cement copper." This old style of utilizing the water so impregnated,
however, is a very slow process, and the Californian method is much
more expeditions and economical. The revolving barrel is 16 feet long
by 6 feet in diameter; the staves are 6 inches thick, and so are the
two bottoms; inside a false lining of clear pine is inserted, with a
view of covering any iron that has been used in its construction. In
this huge barrel all kinds of old iron (preferably hoops), nails,
&c, are placed with the solution, and the trap-door is at once
hermetically closed, whereupon the driving gear is thrown into motion,
making the barrel to revolve but three times per hour. As the solution
and iron combined generate hydrogen gas, every care has to be taken, in
order to prevent explosions, from fire being brought into its vicinity.
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