26 The Extraction of Gold. 
made at the works of the Port Phillip Company gave the 
following results .— 
Contents of waste tailings before going 
on to the table - - - : - 17 dwts. 22 er. of gold per ton. 
After leaving the table - - - it eS Aha 
Amount retained on the table - - i 
Proportion of total gold contents saved, 82°3 per cent. 
99 99 
99 99 99 
In the gold-bearing material saved on the table was found 
fine free gold, and gold still attached to particles of sand, but 
it principally consisted of decomposed pyrites converted by 
exposure in the vein above the water level into oxide of 
iron. It is probable that each of these particles of oxide 
contains a nucleous of undecomposed sulphide, yet the partial 
oxidation is sufficient to so reduce the specific gravity as to 
materially increase the difficulty of separating it from the 
quartz sand, and the saving of such a large proportion of 
this gold-bearing ore is equivalent to a saving of from ninety 
to ninety-five per cent. of the undecomposed sulphides. 
Three of these tables are now in course of erection at the 
Good Hope mine, and one at the Clunes, where its effective 
working on different kinds of material will be -carefully 
observed, and the results laid before the Society at a future 
meeting ™ 
Another important matter is the separation of the sul- 
phides mixed with as small a proportion of waste sand as 
possible, but hitherto this close concentration could not be 
effected without such an increase of loss as more than 
balanced the gain through having to treat a smaller quantity 
of pyritous sand. With the improved percussion table a 
much higher degree of concentration can be effected without 
risk than by any other means previously discovered, and 
there will be a corresponding decrease in the cost per ounce 
of gold extracted. No doubt time and experience will lead 
to improvements in the working and construction of this 
table, but it now surmounts the difficulty which has so long 
stopped the way; it is simple, inexpensive, and easily 
erected, and when worked in conjunction with the system 
now in use at Clunes for extracting the gold, will retain 
from seventy to seventy-five per cent. of the gold at present 
lost in the waste tailings, at a cost not likely to exceed ten 
shillings per ounce obtained. 3 
