160 CORUNDUM, ITS OCCURKENCE AND DISTRIBUTION. 
means of open cuts, but to confine the mining to a system of tunnels 
and shafts. This method of mining will be found the cheapest in the 
end. Moreover, all the tunnels and shafts should be well timbered 
and the mine kept as thoroughly drained as possible. 
A large amount of the material that must be handled is easily 
worked with pick and shovel, as it consists of the crystals and frag- 
ments of corundum in the zone of chlorite and vermiculite. In those 
veins in which the corundum is associated with feldspar, as at Laurel 
Creek and Buck Creek, and those in which there is considerable 
amphibole or enstatite, as at Corundum Hill, blasting is necessary. 
If the mill is located some distance from the mine and if a line of 
sluice boxes can be built between the two, the more or less finely 
divided ore may be carried to the mill by means of these boxes. In 
this way the ore is partly cleaned by the time it reaches the mill. 
This is the method employed at the Corundum Hill mine. 
All of the gem corundum is mined by hydraulic methods similar 
to those used in sluicing placer gold, with the exception that the con- 
centrates containing the sapphires are removed from the sluice boxes 
and further concentrated in a circular sieve either held in the hand or 
mounted; and bv Sfivino- this sieve a certain circular motion the 
grains and crystals of corundum are collected in the center and at the 
bottom of the sieve. In accomplishing this separation it is neces- 
sary to screen the grains of the concentrates to nearly the same size 
before using the sieve. From the nearly pure sapphire concentrates 
the good stones are picked out by hand. 
METHODS OF CLEANING. 
The difi'erence between the commercial product and the ore as it 
comes from the mine is that the latter has been freed as far as pos- 
sible of all impurities, so that the resulting product is or should be 
nearly pure corundum or emery. 
Formerly there was but one method in use for cleaning corundum 
or emery ore, principally because the ore to be cleaned occurred either 
in peridotites or .amj^hibolites ; but now there are many differences 
to be noted in the various mills erected for the cleaning of corundum. 
This is due to the connnercial sources of corundum being in syenites, 
etc., as well as in peridotites. It may be of interest to give a short 
description of the old method of treating the corundum ores, and of 
one which, with a fcAv modifications, is applicable to corundum 
obtained from syenites. 
The ore is crushed and sieved, and all that will not pass through a 
No. 12 screen is recrushed and passed between rollers until it is 
reduced to the desired .size. Most of the impurities are then easily 
removed by conveying the crushed ore into boxes through which runs 
