The Extraction of Gold. 17 
minute patches of gilding, and must be detached in thin flat 
pieces readily floated away in running water. A part may 
be pyritous gold lberated in the breaking up of the iron 
ores. In practical working some of this fine gold must 
always be lost, even where the greatest care is used, but a 
large proportion of that now carried away would be retained 
with the sulphides by any efficient mode concentrating the 
latter. 
The pyritous gold is so closely incorporated with the iron 
and other ores, that it cannot be separated by the means 
found to be most economical for extracting the free gold. 
Jt has been a moot question whether this pyritous gold 
exists in combination with the sulphides or in a metallic 
state. Experiments made at Clunes, using hypo-sulphite of 
soda as the dissolving agent, showed a trace of other than 
metallic gold in rich pyrites, but none in auriferous antimony 
ore. In the first case the quantity was evidently so small 
as to be of no practical importance, nearly all the gold being 
mechanically deposited with the sulphides. In a sample 
washed from the blanket strakes, in which the grains of 
pyrites average about one one-thousandth of an inch in | 
diameter, gold can be seen on the broken faces in still 
minuter particles, and I believe the great bulk of the pyrit- 
ous gold is in this finely-divided state. Sulphides have 
been found in this colony containing two hundred ounces 
to the ton, and in New South Wales over two thousand 
ounces of gold per ton; but these were no doubt picked 
specimens, and would not represent the average yield of the 
sulphides in the vein. I have, however, more than half-a- 
ton of pyrites ready for treatment at the Good Hope 
mine holding nearly one hundred ounces of gold per ton; 
and wherever quartz veins contain a paying amount of free 
gold, and carry from two to five per cent. of pyrites, the 
latter in every case yet tried has proved to be rich in gold. 
I have met with no instance where the yield of the pyrites 
was not in proportion to the per centage of it in the quartz, 
and the amount of free gold that could be obtained from the 
ore. From ten to forty ounces of gold per ton may be taken 
as the average yield of the sulphides in paying quartz mines, 
although both higher and lower yields are occasionally met 
with. | 
But it is not the sulphides existing in the quartz veins 
only that are auriferous. Many of the blue slate beds, at a 
distance of several fathoms from the mineral veins, contain 
C 
