UTAH ACADEMY OF SCIENCES 143 
There are many ores containing minerals which are 
not only difficult but often impossible of separation by 
gravity concentration owing to the intimate association 
and fine dissemination of the different minerals. Then 
again there are low-grade ores which lack sufficient 
mineral values to permit concentration and subsequent 
shipment to the smelter on account of the distance of 
haulage and transportation. Such low-grade ores may 
include gold-silver ores which worked in the earlier days 
were free-milling and could be treated by stampmills 
followed by amalgamation, but with depth the ore 
gradually became more base and could no longer be 
profitably amalgamated. This necessitated changes and 
alterations in the mills, especially the addition of cyanide 
plants in order to effect higher extractions and produce 
bullion, thus eliminating the cost of haulage and trans- 
portation as much as possible. Cyanidation of gold ores, 
however, is by no means limited to low-grade ores but 
is applicable to gold ores in general, although its applica- 
tion may involve modification of the cyanide process in 
order to overcome the effects of detrimental ingredients 
present in the ores. 
Oxidized copper ores have yielded to hydrometal- 
lurgical methods of treatment and the leaching processes 
have been especially desirable in the treatment of low- 
grade ores as they have effected high extractions which 
otherwise would not have permitted economical treat- 
ment and on account of the simplicity with which the cop- 
per can be recovered from solution. Aside from the appli- 
cation to ores, hydrometallurgy has, of course, also been 
applied to the refining of copper by electrolytic means 
as well as to the refining of some of the other metals. In 
fact a solvent process may serve as a process complete in 
itself or it may serve only as part of a process in the 
treatment of an ore. 
A great deal of experimental as well as practical 
work has been done in the hydrometallurgy of zinc 
during the past few years. Perhaps of greatest impor- 
tance to the mineral industry along this line has been 
the application of electrolytic methods to zine ores. In 
this method of treatment the ore or concentrate is given 
a dead-roast the product containing only a few tenths - 
