Ore-Deposit of the Treadwell Mine. • 87 
to bo cut by (juartz-voins of greater width, which hold visible 
gold. The association of metalliferous quartz-veins with 
masses of granite or other intrusive rocks traversing sedimen- 
tary deposits is a fact of general observation. Had the higher 
portions of the rocks, which may at one time have completely 
covered this particular granitoid intrusion, remained, it might 
be anticipated that it would be found to pass upward into one 
or more ordinary auriferous quartz-veins, these filling fissures 
through which the heated waters ultimately reached the then 
surface. In depth the present ore-mass should be found, on 
the other hand, to pass gradually into ordinary unaltered 
granite. Many cases of course occur in which intrusive masses 
have led to the formation of metalliferous veins without pro- 
ducing extensive low-grade metalliferous deposits of an inter- 
mediate character, such as the one here naturally exposed by 
subsequent processes of denudation appears to be. This 
deposit therefore affords an interesting example of the manner 
in which intrusive masses may directly give rise to ordinary 
metalliferous veins. 
The quantity of gold contained in the ore of the Treadwell 
mine is small. Though not informed as to the actual yield, I 
believe it to be on the average less than $10 to the ton. The 
ore is, however, easily and cheaply obtained by work resem- 
bling (juarrying rather than mining, and can in consequence 
be profitably worked on a large scale. It is not intended here 
to enter into particulars as to the mode of working, but it may 
be stated that at the time of my visit 120 stamps were con- 
stantly employed, and that since that date this has been 
increased to 240, the quantity of ore milled daily being now 
reported at from 500 to 600 tons. A considerable proportion 
of the gold is "free" and this is saved on amalgamated plates. 
The remainder is contained in the iron pyrites, which is sepa- 
rated by Frue Vanners. The pyrites was then formerly 
roasted in revolving cylinders, but these were being replaced 
at the time of my visit by continuous automatic furnaces sim- 
ilar to those employed in sulphuric acid works. The gold is 
dissolved from the roasted product by chlorine gas, and pre- 
cipitated by sulphate of iron. 
As the geological conditions are very similar along the west 
coast all the way from Lynn canal to the strait of Fuca, it 
appears highly probable that other deposits of a similar char- 
