The Homestake-King Mill
The following is details of the operation of the Homestake-King Mill located in the Bullfrog
Mining District at Rhyolite, Nevada.
The 25-stamp mill of the Homestake-King Consolidated Mining and Milling Company, at Rhyolite,
was started up in June, 1908. The process of working the ore was devised and elaborated by the California Ore
Testing company, of San Francisco, California, and the mechanical features of the plant were designed by John E
Rothwell, of a Colorado Iron Works, Denver (the constructors), and William B Milliken, of Rhyolite. The mill was
driven by electric power furnished by the Nevada-California Power Company. The building was a steel structure
covered with galvanized iron. The stamps weighed 1,050 pounds each and the mortars were of the Homestake narrow
type without inside copper plates. It was a plate-amalgamation mill without concentrators.
From the plates the crushed sands and water flowed direct to a Dorr classifier for the
separation of the coarser sands from the fine or slimes. The sands or oversize from the classifier went to two
Colorado Iron Works trunnion tube mills 45 inches in diameter by 15 feet in length, inside measurement, lined with
El Oro tube-mill liners and half filled with silex pebbles. In the mills the sands were ground to a very fine
product, after which they flowed over another set of amalgamated copper plates to save any gold released in this
regrinding.
From these plates the tube mill product was returned by belt elevator to a second Dorr
classifier for further separation of sands. This sand product was returned to a third tube mill similar to the two
already spoken of and the reground product of this mill was passed over amalgamated copper plates and then returned
to a third classifier. The sand product of this third classifier, a very small percentage of the whole ore, was in
an extremely fine granular condition and was delivered with a strong cyanide solution through an automatic
distributer to one of the other of two 50-ton sand tanks and the gold and silver values leached out, the leach or
gold-bearing solution going direct to the gold tanks, thence to the zinc boxes for the recovery of the values.
The slimes or fine product floated out from the classifiers flowed to two Dorr settling and
thickening tanks. In these tanks all the solids settle to the bottom and the excess of water overflowed at the top
and was pumped back to a water tank above the mill for use in the stamp batteries again.
The settled product of these tanks, carrying approximately 50 per cent of moisture, was
delivered to one of the two Hendrix agitators, in which, as soon as a charge had accumulated, cyanide solution to
bring the whole to a required strength was added, and the charge was agitated from 6 to 8 hours, in which time the
gold and silver values to a high percentage were dissolved and held in solution. The charge was then delivered to a
storage tank, preparatory to the separation of the solution from the barren solids. This operation was accomplished
in the Butters filter plant, containing about 40 standard leaves, the valuable solution going to the gold tanks and
the solids, after thorough washing with weak solution and water were discharged to the tailings dump.
The gold solution collected in the gold tanks was passed through six zinc boxes of eight
compartments and with a capacity for 60 cubic feet of zinc shavings each. In these the gold was precipitated and
caught, and the barren solution went to tanks above the mill to be regenerated and used again. At suitable
intervals the zinc boxes were cleaned up and the gold precipitates separated from the excess of zinc. This product
was then dried, calcined, and placed in crucibles with the necessary fluxes, fused, and cast into molds, and then
usually remelted and cast into the regular shaped gold bars and shipped either to the United States mint, if of
sufficient fineness, or to the refineries for the separation of the gold and silver values, and in turn sent to the
mint.
|