COKUNDUM^ ITS OCCURKENCE AND DISTRIBUTION. 159 
TECHNO JA)C4^ OF ( ORUNDU3I. 
METHODS OF MINING. 
In considering tlio methods used in nnnini>- cornnduni it must bv» 
borne in mind that up to the past few years this mineral had only 
been obtained in (]uantity where it Avas associated with pcMidotite 
rocks. These rocks, as will be shown later, present certain difficulties 
which, if not overcome, will cause consideral)le delay and danger in 
mining. AVliere the corundum occurs in amphibolite, as at Chester, 
Mass., these difficulties are not so evident, and the mining operations 
can l)e carried on as in any metal mining. If the corundum occurs 
in gneiss, (piai'tz-schist, or syenite, the ore can often be advanta- 
geously mined by means of open cuts, as at the Craig mine, Ontario, 
Canada. If the corundum-bearing portion of the rock is narrow it 
will be found more economical to mine by shafts, drifts, and crosscuts, 
as at the Montana deposits. As these latter occurrences of corundum 
offer no serious problems in mining, no description is given of their 
mining operations. As, however, corundum in peridotite does pre- 
sent certain difficulties to the miner these are treated briefly. 
Nearly all of the peridotite formations in Avhicli the corundum 
deposits occur are bold outcrops on mountain sides and hilltops, hav- 
ing almost perfect natural drainage. At all the localities Avhere there 
has been no mining the little prospecting has been usually by means 
of open cuts supplemented by tunnels. While at first mining by 
means of cuts may seem to be the most advantageous, it is soon found 
to be expensive. These cuts, or any other openings made over the 
surface of the peridotite, offer a much greater opportunity for surface 
w^ater and frost to penetrate the mass of the rock formation. These 
rocks are more or less seamed or cracked, usually to the depth that 
alteration can extend, and thus they offer opportunities for the infil- 
tration of water. As most of the alteration products of this perido- 
tite formation are slippery, hydrous magnesium minerals, such as 
serpentine and talc, and as these are developed in the seams and cracks 
of the peridotite, anything that is done to disturb them will make 
them very liable to slip. At the Corundum Hill mine there are large 
masses of peridotite that have become loosened and have gradually 
slipped down and closed up some of the tunnels, and there is constant 
danger that fragments of the rock will fall into the cuts and some of 
the tunnels. At the Laurel Creek mine a mass of peridotite with soil, 
etc., nearly a 200-foot cube, has become loosened and slipped down- 
ward, effectually closing up the tunnel and shaft of the Big vein. 
In mining corundum associated with peridotite rocks it is therefore 
advisable not to break the surface of the formation any more than is 
absolutely necessary ai_d to do no work at all along the contact by 
