ORES OF LEAD, ZINC, AND SILVER 111 
only than Potosi in Bolivia and two fields in Mexico. The 
ores at Cobalt are associated with four pre-Palzozoic series. 
The lowest, the Keewatin Series, consists mainly of a basic 
Pillow-lava which is associated with cherts, jaspers, and 
iron ores, which form ‘the ironstone formation.’ Above 
the Keewatin is the Timiskaming Series of conglomerates 
and quartzites. The third division, the Cobalt, consists of 
quartzites and conglomerates. The fourth is the Nipissing 
diabase, 5 widespread sill which is in places 1000 feet thick. 
The veinstones are chiefly calcite and dolomite with 
duartz, barite, and fluorite. Native silver is associated 
With numerous silver, cobalt, and nickel sulphides and com- 
Pounds with arsenic and antimony. The chief minerals 
Present are argentite (AgsS), dyscrasite (Ag,Sh), pyrargyrite 
(AgsSbs,), smaltite (CoAs,), and cobaltite (CoAsS), with 
any rarer species. 
The mines are of three types. The characteristic type, 
which has yielded 90 per cent. of the silver, is of veins in the 
lower part of the Cobalt sediments, below the diabase sill, 
The veins are near the diabase, the greatest distance being 
550 feet in some of the Cobalt rocks, and 350 feet in the 
Keewatin lavas. The second type is that of the Timiskam- 
'ng Mine, where the diabase is intrusive into the Keewatin 
0d the veins occur in both. The third type, the Keeley 
Mine In South Lorraine, is in the Keewatin above the dia. 
dase, Into which the main vein continues though it is there 
Poor in ore, 
According to the generally accepted explanation the 
metals were originally disseminated through the diabase, 
from which they have been leached either by its own magmatic 
water or by surface waters which were heated by it. 
This theory ‘has serious difficulties + (1) the characteristic 
“Onstituents—silver, cobalt, nickel, arsenic, and antimony— 
Are Not apparent in the normal diabase, which shows no signs 
of leaching or of solution channels; (2) most of the diabase 
'S not accompanied by ore, which is almost confined to one 
Srea of 8 square miles ; (3) the Cobalt ores resemble those of 
mony where the country is gneiss and not diabase; (4) 
Imilar ore at Cobalt occurs in diabase, in the Cobalt sedi- 
ons, and in the cherts and lavas of the Keewatin; (5) the 
5 1s dependent on the mechanical and not on the chemical 
ects of the Intrusion, for the veins were formed after the