Under
these circumstances, and after mature consideration, I would strongly
support any movement for a test to be made on a fair and comprehensive
basis, between the complicated Californian methods of treatment with
gold-bearing and pyritous quartz and that which obtains the most favor
on Bendigo or elsewhere. In one of my reports published by the Argus I
have already given the results of a crushing of quartz, that, owing to
its "hungry " appearance, would be held as worthless or nearly so. The
return, however, proved a very profitable one indeed, and can only be
ascribed to the superior treatment adopted in that State. And it should
also be borne in mind that our appliances deal principally with the
saving of free gold ; secondarily, with the rough concentration
of pyrites ; and, thirdly, with- the calcination and grinding of the
latter. The exclusive calcination and grinding of desulphurized pyrites has been abandoned in California for the last twelve years or more.
Having
given a concise description, and a few out of the original diagrams
prepared for the report, for the purpose of comparing them with our
most approved systems, I would now add a few facts concerning machines
that are giving great satisfaction under certain conditions, both in
crushing and concentrating of ores.
In
the opinion of many American mine superintendents, the present stampers
are both too costly and require too much power in order to achieve
certain results ; certain kinds of ore need different kinds of
machinery to reduce them than what is done by the fall of the
stamp-head. Amongst these the Bruckner's pulverizer operates
upon ore passed through the stone-breaker, and this machine I saw at
work, when it crushed 18 tons of very hard quartz in 24 hours, at an
expense of only 6 horse-power; the result was an impalpable powder, and
the same amount of work would take 10 heads and 10 horse-power to
accomplish;—As this machine is very compact, needs no extra
foundations, and, besides, requires very little repair, it has been
recommended in many cases to take the place of stamping batteries. It
is simply a large horizontal cylinder, worked off a belt and pulleys,
with a speed of 22 revolutions per minute ; there are two central
shafts inside of each ather, one to receive the coarse ore, and the
other is used for the removal of the crushed ore, which latter should
be nearly or altogether dry. The inner cylinder, 4 feet in diameter,
contains 1,500 lbs. weight of chilled cast-iron balls, each from 1 to 4
inches in diameter, which act as crushers on the ore fed through one of
the two hollow shafts; the finer powder thus produced would necessarily
interfere with rapid crushing were it not for the lining of this drum
or cylinder, which consists of chilled cast-iron ribs laid
longitudinally, and riveted so as to provide very narrow slits between.
Through these slits the crushed ore fells on to a rather coarse screen
and the finer particles on other and much finer screens, so that
eventually a very fine sand is produced by these disintegrating balls.
This fine sand falls through the inner hollow shaft into a receptacle,
whence it is conveyed to the appliances ordinarily used for
concentration and amalgamation. Inasmuch as these screens separate the
fine from the yet coarse ore, the latter falls into recesses, having
direct radial communication with the inner drum, when they are
subjected to repeated crusliings by means of the iron balls until fine
enough. This machine, complete for work as exhibited, would cost in San
Francisco about £330, and its work is certainly equal to that of a
10-head battery.
The Frue Ore Concentrator.—This machine is simply an improvement in many respects upon the well-known " endless blankets," first brought under notice, I am informed, by Mr. Thomas Carpenter, M.E. Its Californian
