230 THE VERMILION IRON-BEARING DISTRICT. 



bodies and transported elsewhere. The removal of the silica is ordinarilj' only less 

 important in the development of the ores than the addition of the iron. In many 

 cases the abstraction of the silica proceeded further than the deposition of the iron 

 oxide, thus making- the rocks very porous and further rendering the conditions 

 favorable for abundant circulation." 



As the result of the detailed study of the ores in the various Lake 

 Superior iron-bearing districts the conclusion has been reached that they 

 are essentially replacement deposits, and this conclusion, pronounced early 

 in the study of the district, has been strengthened by the observation of 

 numerous facts in all the other districts which have been studied since then. 

 The follov^ing facts from the Vermilion district alone seem to offer incon- 

 testable proof that this is the character of the deposits in this district, and 

 also gives clear proof of the time of the formation of these deposits. Near 

 the west end of the ore body woi'ked from shafts No. 7 and No. 8 on Soudan 

 Hill there is a large mass of jasper, already described by Smyth and Finlay,' 

 lying directly across the ore with banding corresponding to and continuous 

 with the banding of the adjacent ore. Again, on Lee Hill, along the south 

 and west sides of the old North Lee mine, a breccia between the iron 

 formation and the underlying schist has been produced. Some of the 

 fragments of jasper in this breccia have been replaced by hematite with, 

 however, a partial retention of the banded structure of the jasper. That 

 the iron ore at this particular place was deposited later than the movement 

 which formed this breccia is shown by the fact that the fragments of the 

 breccia are cemented in many places by hematite ore, and numerous similar 

 bodies may be seen which have been formed in cavities within the breccia. 

 A study of the ore remaining in place at the North Lee mine and the 

 adjacent banded iron formation also shows intimate connection between the 

 two. The iron formation has an approximately east-west trend and seems 

 to rest in a westward-pitching trough of chloritic schist, the schist occurring 

 both on the north and south as well as at the east end of the iron formation. 

 The ore body corresponds in trend with the strike of the formation itself, 

 and on its south and west sides lies next to the iron formation, the banded 

 jasjjers. As the ore body is followed westward, the ore is g-radually more 

 and more mixed with jasper, becoming lean ore, and then the stringers of 



«The iron-ore deposits of the Lake Superior region, by C. E. Van Hise: Twenty-first Ann. 

 Rept. U. S. Geol. Survey, Pt. Ill, 1901, pp. 326-328. 

 ''Op. cit., fig. 8, p. 42. 



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