HISTORY AND TECHNOLOGY OF THE GOLD DEPOSITS. 
141 
be crushed to about 20-mesh size and then fed into the roasters. These are of the 
Holthoff-Wethey type, have a capacity of 100 tons per day each, and employ an 
average temperature of about 1,600° F. The roasted ore is cooled in its journey back 
underneath the furnaces, and is then conveyed on an inclined belt to the barrel house, 
where it is loaded into hopper cars and finally charged into the chlorination barrels. 
The 10 barrels, of a capacity of 10 tons, are about 20 feet long and 5 feet in 
diameter. The exact composition of the lixiviating solution is not made public, 
but it consists essentially of a solution of electrolytically generated chlorine in water. 
The strength of the solution used is determined not so much by the value of the 
ore as by the composition of the gangue. About 100 gallons of the solution are 
used for each ton of ore, and this amount contains 1 to 2b pounds of chlorine. 
When the barrels have been charged with ore and solution, they are sealed 
and rotated for two or three hours, at the end of which time a valve at the bottom 
of the barrel is opened and one at the top is connected with water pressure. The 
solution is thus made to pass through an interior filter of the Sloan type, and the 
pulp is washed for two to four hours. About 100 gallons of water per ton of ore are 
added during the washing, making the total bulk of gold-bearing solution about 200 
gallons for each ton of ore. After the pulp is sufficiently washed the manhead is 
removed from the barrel, the barrel is rotated, and the pulp emptied into a launder 
by which it is conveyed to Wilfley tables on a floor beneath. There are 20 of these 
concentrators, arranged in batteries of 5. The headings from four of the five pass 
to the fifth, and the concentrates from this table, which represent about one two 
hundred and fiftieths of the total pulp, are saved and sent to the smelters. They 
have a value of $20 to $30 per ton. For the presence of the greater part of the 
gold in them the following explanation is offered: When the ore is roasted, pyrite 
is oxidized and converted partly into magnetite (Fe 3 0 4 ), which is only slightly 
attacked b} 7 the chlorine solution. Any gold which may have been inclosed in t^he 
pyrite is thus protected from the action of the solvent, and without concentration 
would be lost. Besides magnetite other iron oxides and barite are noticeable con¬ 
stituents of the final concentrates, and a molybdenum mineral is said to be present 
at times. Finely divided free gold is occasionally seen on the last table. 
After passing through the filters the lixiviating solutions together with the 
wash water pass to the sand boxes where the coarser sediment which has escaped 
the filter quickly falls and is returned to the barrels; then to the settling tanks, 
where they remain for eight hours and allow practically all the material in suspen¬ 
sion to separate out. During this time a gelatinous precipitate, said to be a basic 
aluminum silicate, forms and falls to the bottom. On account of the difficulty 
of washing this precipitate thoroughly, a small loss of gold may take place. 
From the settling tanks the solution is drawn into lead-lined monte-jus, and 
thence forced by air pressure into precipitating tanks. Into these the precipitating 
agent, hydrogen sulphide, is introduced direct from the generator. Precipitation 
is continued until tests show no more gold in solution, the time required being 
thirty to forty minutes. After the precipitate settles the supernatant liquor is 
drawn off and run through filter presses, and before leaving the building is passed 
through a sand filter to counteract possible leakage or breakage of these presses. 
13001—No. 54—06-11 
