Montgomery-Shoshone Mill
The following is details of the operation of the Montgomery-Shoshone Mill located in Rhyolite,
Nevada.
Ore was crushed in rolls, with cyanide solution, then elevated, and treated by amalgamation,
concentration, and cyaniding. The descent of the pulp from the top of the 60-foot bucket elevators was by gravity
throughout. The sand was treated by percolation, the slime by agitation, and filtering was done in the Butters
filter.
The plant of the Bullfrog Reduction and Water Company at Rhyolite, Nevada, was built under
contract by the Traylor Engineering Company, of New York, and was described in full in Mines and Minerals by P E
VanSaun. The following paragraphs contain a condensed statement of this paper:
All of the mill machinery is driven by electric motors in units to suit the installation, the
concentrators being driven with independent motors to avoid any possible fluctuation in speed. The pumps, likewise,
are driven by a separate motor so as to regulate the speed and capacity of each set. Water for the plant is pumped
for a distance of about one mile into a large storage tank placed on the hill in order to give ample gravity
pressure for the plant. The values are approximately $30 per ton in gold and silver, contained in a quartz and clay
gangue. The coarser particles of gold and silver are extracted by amalgamation on regulation copper plates, after
crushing and sizing; the finer sulphides, consisting of about two per cent of the weight of the ore, are recovered
in the shape of a high-grade concentrate on reciprocating concentrating tables. The values contained in the slimes
and sand tailings from the above processes are recovered in the cyanide department.
The sand treatment in this description by Mr. VanSaun will be kept separate from that of the
slime product in order to avoid confusion.
Sand Treatment
From the reciprocating tables the sand product is run to the hopper of a swinging lauder, by
which the sand may be sent to either of the two receiving sand tanks 36 feet in diameter by 6 feet 6 inches deep.
These two tanks are used alternately, and each is provided with three roller gates so that as they are filled with
the sand product the water and slimes will overflow, the gates being raised as the tank is filled. This overflow
product is run into a sand trap or classifier, from the bottom of which the settled sand products, together with
the necessary water, are pumped by centrifugal pumps to the distributing launder and thence back into the sand
tank. The slime product is pumped by centrifugal pumps for slime treatment, as described below. When either of the
receiving tanks has been filled with sands a vacuum connection is turned on under the filter, covering the entire
bottom of the tank so as to thoroughly drain the contents. The vacuum connection is then closed and the accumulated
liquid is allowed to flow by gravity into the above referred to sand trap. After the sands have thus been freed of
superfluous moisture in the receiving tank, the center plug gate is removed and the Blaisdell excavating machine
run over the tank, by means of which the sands are discharged onto belt conveyors and are delivered to the
Blaisdell distributing machine for uniformly feeding and aerating the product in the leaching tanks. There are five
of these sand leaching tanks each 36 feet in diameter by 6 feet 6 inches deep; they are of steel as are all the
other tanks in the cyanide department. After a leaching tank is filled it is treated in the usual way with cyanide
solution, the piping being so arranged that the solution may be admitted either on top of the charge or beneath the
filter, as may be advisable.
The resulting gold solution is allowed to flow from beneath the filters to either of two
gold-solution tanks, 20 feet in diameter by 8 feet deep, one for weak and the other for strong solution. The sands
are drained by means of a vacuum which withdraws the solution and delivers it to a sump tank, and from thence
either directly to the zinc boxes, or if it is desired to store the solution it may be run to the two gold-solution
tanks before mentioned, from which it is drawn to the zinc boxes. Ten improved steel zinc boxes are provided, each
with seven compartments, arranged so that each compartment can be cleaned separately. From the sump tank the
solution is dumped into either of two solution tanks placed on the hill above the plant, one for weak and one for
strong solution, and restandardized as required. The zinc-box products will be treated as described farther on in
connection with the slime treatment.
The sands in the leaching tanks, having been treated with cyanide solution, are washed, drained,
and delivered by a belt conveyer system to the dump.
Slime Treatment
The slime product coming as tailings from the vanners is run by gravity launder to the sand trap
before mentioned, the trap also receiving the slime overflow from the roller gates of the two receiving tanks. The
overflow product from this trap, which will contain all of the slimes from the entire previous treatment is pumped
by means of centrifugal pumps into either of two 20' by 12' steel thickening tanks. These are provided with an
overflow launder around their entire top circumferences. The thickened pulp is drawn off from a large cone in the
bottom of each tank by means of flexible connection, so as to vary the head against which the flow occurs and thus
regulate the density of the pulp discharge. The overflow from the top of the tank is clear water and is pumped into
water-storage tank of the plant. The thickened slime is then carried by gravity launders to any one of four
agitating tanks 28 feet by 16 feet, one of these being filled at a time. The slime solution in these is allowed to
settle and decant by means of a special apparatus, the supernatant liquor going into a sump tank, or if of
sufficient value, to an intermediate tank of about the same size as the sump tank before referred to. The slime in
the agitation tank is then treated with cyanide solution, settled, and decanted. The supernatant liquor is again
allowed to go into the intermediate tank and from there directly to the zinc boxes. In leaching the slimes in the
agitating tanks, the contents are thoroughly stirred by means of a mechanical agitator. The resulting slime
product, after treatment and settling to a proper consistency, is conveyed by means of a centrifugal pump to stock
tank of about the same size as the agitating tanks, this acting as a reservoir or receiver for the product to be
filtered, where it can be allowed to settle, and, if desired, can be decanted into a wash-water tank provided in
connection with the Butters filter. From the stock tank the slime product is pumped by a suitable by-pass
arrangement into the Butters filter tank containing 100 leaves. The vacuum connection is then turned on the filter
and the resulting gold solution drawn through the vacuum pump and delivered to a 30' by 8' tank, from which it is
run by gravity through the zinc boxes.
After the slimes have thus been filtered, the cakes hanging on the filter frames are removed by
turning water under pressure into the vacuum pipes, which frees the cake of slime accumulation and deposits it in
the bottom of the filter tank, a special gravity pressure tank being provided for this purpose. To free the filter
frames more effectually a compressed-air connection is provided so that the filter leaves will be thoroughly
cleaned and gotten in a satisfactory condition for the next charge. By means of a suitable valve arrangement, the
same centrifugal pump is made to draw the water from the tank provided for this purpose, discharging it into the
filter in order to thoroughly wash the slime product, which is then settled and decanted back into the wash-water
tank, after which the discharge gates provided on the bottom of the filter tank are opened and the contained slime,
which values have been extracted, is sluiced out to the dump.
The gold solution resulting from this slime-filtering process is allowed to flow to the zinc
boxes combined with the resulting from the sand treatment before described. Some of this solution, after passing
through the zinc boxes, is restandardized in the sump, then pumped into the agitating tanks for retreatment of the
slime products. The remainder of the solution goes to the solution restandardizing tanks before mentioned. When it
is desired to clean up a zinc box, after removing the zinc shavings from the compartment, the cock at the bottom of
same is opened and the gold slimes are washed through a launder to a portable receptacle which is taken directly to
the clean-up room. The gold slimes are there washed in a suitable tank and decanted, and are then treated in an
acid tank, from which they are drawn to a sand filter. A boiler is provided for furnishing steam for heating and
agitating solutions in connection with the above operations. The resulting filtered slimes are then roasted and
melted down to bullion.
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