Recent Changes in Gold Mining 
129 
1907] 
strength. This sump tank thus serves for a solution tank, 
from which the solution is raised by a small centrifugal 
pump to the sand leaching tanks. Most other mills have a 
small extra tank at the highest level in which the solution is 
made up and from which it flows by gravity to the sand 
tanks. 
The clear solution from the slime settling tank is stored in 
the tank 24x8 feet. From this it flows through an eight com- 
partment zinc box like the other one and to the sump and 
weak solution tank. 
In the zinc boxes zinc from a mass of fine zinc shavings 
enters the solution in place of the gold which is precipitated 
as a black coating upon the zinc. Each month the zinc in 
the boxes is sifted and the fine stuff saved, and the coarse 
stuff returned to the box. The deficiency of coarse zinc in 
the first box is made up by taking some of it from the second, 
which is in turn filled from the third and so on. All the 
fresh zinc required is added to the last compartment, and, 
since much of the gold sticks to the zinc until it is all dis- 
solved, most of the gold slimes are recovered from the first 
compartment where precipitation is also most active, as the 
solution passing through it contains the largest percentage of 
gold. 
The gold slimes, or finety divided gold, containing small 
scraps of zinc, is melted in a graphite crucible to which a 
little nitre is added to oxidize the zinc and cause it to unite 
with the borax used as a flux. The melted gold is cast into 
bricks and sent to the mint. 
All the tanks are in the open air. The pipes are wrapped to 
prevent freezing, and there is no trouble except that heavy 
rains increase the amount of solution which must be wasted 
and so cause a greater loss of potassium cyanide. The 
pumps, and the engine for driving them and the agitators, 
are housed in. In the same building is the room containing 
the zinc boxes and furnace for melting the bullion. About 
4-10 of a pound of potassium cyanide is consumed per ton of 
ore. In the ore are no copper minerals or similar sub- 
stances to consume cyanide. 
