36 



Moose Mountain, rising 280 feet above the plain and the 

 railway, though one of the most important examples of the 

 iron formation in the Kee.watin of Ontario, presents less 

 than the usual variety in the accompanying rocks, and the 

 structural relations are more obscure than in some other 

 regions, such as the Helen Iron Range. 



In most cases the iron formation of Ontario consists of 

 some forrn^of silica interbanded with iron ore, either jasper 

 with herfiaiite or cherty or quartzitic silica with magnetite 

 At Moose Mountain the latter-material is found. Commonly 

 the iron formation occurs as ' synclinal belts enclosed in 

 green Keewatin schist; but a definite relation of this sort 

 has not yet been proved at Moose Mountain, perhaps 

 because the regularity has been disturbed by intrusions of 

 greenstone and granite. The accompanying rock is a 

 banded schist alternately light and dark gray. The 

 iron formation here has the usual steeply tilted attitude. 

 Often the banding is fairly straight and uniform for con- 

 siderable distances, hut in many cases there has been 

 crumpling and sometimes crushing and faulting on a small 

 scale. The ordinary banded ore contains 36 per cent, of 

 iron, and from the results of stripping and diamond drilling, 

 the manager of the mine, Mr. F. A. Jordan, estimates that 

 there are 100,000,000 tons of ore of this grade. There are 

 also 6,000,000 tons of higher grade magnetite in which there 

 is much less silica and where the banding is less marked. 

 Here some green hornblende is interbedded with the 

 magnetite. 



Laurentian-looking gneiss occurs just south of the iron 

 formation but its relations to the ore bodies are not very 

 certain ; though dikes of granite and less often pegmatite 

 cutting some of the outcrops of ore have probably come 

 from it. 



The richer parts of the ore have been greatly fissured 

 and are penetrated in all directions by yellowish green bands 

 or veins of epidote, evidently the last mineral formed. 

 Beside these bands the magnetite is sometimes changed to 

 hornblende which gradually passes into the usual ore within 

 a few inches. The main ore body worked has been pro- 

 visionally classified by Prof. Leith as belonging to the 

 Pegmatitic type (Jour. Can. Min. Inst., Vol. XI, 1908, p. 

 93). He defines the type as including "ores which are 



