BY E. D. PETERS, JUN., M.E.., M.D. 197 
exist in every pound of sulphides in the entire deposit. This is the well- 
known mineral heavy spar, or sulphate of baryta, a common enough 
gangue-rock in} many regions, and one that is always dreaded from its 
stubborn and infusible character. In the average ore of the Mount 
Lyell mine there is too little heavy spar to have any perceptible effect 
upon the metallurgical treatment of the ore. This mineral is absolutely 
insoluble and undecomposable under any ordinary conditions, and thus 
during the oxidation and removal of the sulphur, copper, and part of 
the iron, the heavy spar remains behind together with the gold and the 
rest of the iron. If you will take the trouble to examine an average 
sample of the Mount Lyell gossan, you will find that instead of contain- 
ing, as does the ore, about 2 per cent. of heavy spar, this mineral has 
risen to 30, 40, or even 50 per cent., whilst the iron has diminished 
accordingly, and the gold has increased from 3dwt. to 20dwt., 30dwt., 
40dwt. or more. Surely no prettier harmony between theory and fact 
could be asked for. There is little more to be said about the rest of the 
deposit. As already explained, it is a great leus-shaped mass of mixed 
iron and copper pyrites set slantingly on edge, with its upper edge 
slightly decomposed on the extreme surfaces. Its average width may 
be regarded as 300ft., while it has been followed for about 1,000ft. in 
length, and about 300ft, in depth, at which point it is: raduaily widening. 
After getting a few feet from the wall-rock, and fairly into the deposit, 
the pyrites is so pure and massive, that in four months’ residence at 
the mine I never saw a fragment of gangue rock as large as a cherry. 
The average composition of the unaltered ore is about as follows :— 
Iron pyrites_... oh ats a ... 83 per cent, 
Copper pyrites ... oe aoe Be, aot De. a 
Heavy spar ae sh ae ate sade ieee 4 
Silica -...... Ses co ‘si ne comnae. (al ee 
Total... as 52, ... 100 
And the average contents of the ore in the valuable metals, throwing off 
enough to cover ordinary losses, is 
Copper Me ae i Ns ... 43 to 5 per cent, 
Silver Bie ae ans 205 .. 3 to 40z, 
Gold... kee ae is A ... 24 to 3dwt. 
Although the ore is simply an ideal sulphur ore for the manufacture of 
sulphuric acid, not only containing 50 per cent. of sulphur, but also 
being an almost perfect burning ore mechanically speaking, the company 
will be obliged to forego this advantage for the present. For the new 
process for making soda has so injured the acid market that pyrites ores 
are simply a drug, even if it would pay to trausport the Lyell ores to 
the coast, and thence to England. To make acid on the spot can of 
course not even be considered, as there is no market for it at home, and 
the cost of the very lowest freight to a market would be about twice and 
one half the value of the best acid. I need hardly say that the creat- 
ment must necessarily be the amplified form of the old blast-furnace 
method, 7.¢., roasting in stalls under cover, smelting the roasted ore for 
a natte containing the copper, silver and gold, blowing this natte up to 
a 96 per cent. pig-copper in Bessemer converters, shipping the pig-copper 
to England, where the gold and silver will be separated by electrolysis, 
which consists in dissolving the pigs of copper in weak sulphuric acid at 
one pole of the battery, whilst chemically pure copper is re-deposited 
at the other pole, and the gold and silver fall to the bottom of the tank 
as mud, , To institute a business commensurate in importance to the site 
