164 THE VERMILION IRON-BEAEING DISTRICT. 



which one would be likely to find in the Archeau greenstones with those in 

 the adjacent Keweenawan gabbro, we see that they would probably be 

 very much smaller than those in the gabbro, since the greenstones with 

 which they would occur are of much finer grain than the gabbro. More- 

 over, as the size of the mass of magma has an important bearing upon the 

 rate of cooling, we may say that the larger the mass of magma the larger 

 the ore body. For this reason also we should expect to find smaller bodies 

 of oxides in the greenstone than in the gabbro. 



In many portions of the world very important ore bodies containing- 

 other metals than iron are found associated with rocks of essentially the 

 same composition as those forming the greenstone complex. The question 

 may well be asked, What are the chances of finding silver, nickel, and 

 cobalt ores, to mention some of the most important, in association with 

 these greenstones'? I would answer that there is practically no chance. 

 In other regions the ores mentioned occur as contact deposits which owe 

 their occurrence to the intrusion of rocks allied to these greenstones into 

 younger rocks, the deposits being found iu fissures occurring within the 

 younger rock, within the older rock, partially in both, or along the contact 

 between the two. Although these greenstones cover a broad area, )''et, 

 since they are themselves the oldest rocks, we can not expect to find such 

 deposits in them in very large quantity unless they occur within the 

 greenstones themselves as the j^roduct of processes of segregation — pro- 

 cesses which, as has been intimated, may have given oi'igin to certain iron- 

 ore deposits reported to occur in them, but whose existence remains 

 unverified. Winchell refers to the occurrence of a gold-bearing quartz 

 vein in the following words:" 



At the west end of Long Lake, SW. i SW. i sec. 30, T. 63 [N., R.] 12 [W.], is a 

 'conspicuous display of quartz and granite, the former carrying gold. An average 

 sample selected from the dump, assayed by F. F. Sharpless, gave $8.64. Some casual 

 working has 1)een done on this vein, and numerous assays show, according to the 

 statement of Mr. Mcintosh, one of the owners, an average of over $10 per ton. The 

 vein is traceable about an eighth of a mile, a little north of east, with an irregular 

 width reaching a maximum of about 80 feet. It accompanies a granite dike. The 

 ore is not abundant, but is in irregular streaks in the quartz. 



Thus far no gold-bearing veins which have paid Tor the working' of 

 them have been found in the Vermilion district. 



aN. H. Winchell, Geol. and Nat. Hist. Survey of Minnesota, Final Kept., Vol. IV, 1899, p. 258. 



