Plate XXXI. — Ore Deposits. 



Fig. 1. Longitudiual sectiou of south deposit, Colby mine. This figure shows a very large deposit 

 of ore, whi(;h was found at the surface, but whirli, in following eastward, was found to pass 

 under the ferruginous chert. fSo far as tliis figure goes, no indication of a dike is seen, but 

 a drill hole put down from one of its deeper levels has passed through a thick dike rock. 



Fig. 2. Longitudinal section of north deposit, Colli.v mine. This deposit, before it had been devel- 

 • oped to siuh a diptli as tlie soutli deposit, reached a dike, and a little farther north this 

 sanu^ dike reaches the surface of tlu' ground. 



Fig. 3. Cross section of nortli and soutli deiiosits, Colby mine. The perpendicular line running 

 through tlie figure is drawn liecause the two parts of the section are not exactly upon the 

 same plane. They differ jrom this so slightly, however, that the true relations of the ore 

 bodies to the surrounding rocks are shown by the combined figure. 



Fi(i. 4. Longitudinal sectiiui of Trimble mine. This is a case in which the main deposit of ore is 

 above three parallel dikes very close to one another. This deposit, like many others, is founil 

 at the surface, but when traced eastward, passes below the ferruginous chert. Above tlie 

 lower dike, a little farther west, is a considerable ore deposit. 



Fii;. .5. Cross section of Trimble miue, showing quartzites, ferruginous chert, and <like rocks. 



Fig. 6. Cross section of Miunewawa miue, .showing the same relations of ((uartzite, dike roek, and 

 ore bodies; and also a faulting of the foot wall quartzite where cut by the dike rock. 



Fig. 7. Section designed to show variation from unaltered carbonate to ferruginous chert and ore 

 bodies in passing from higher to lower horizons, au<l to illustrate the manner of ore con- 

 centration. S. Upper slate ; Q. Quartzlte ; F. Q. Feldspathic Quartzite. 

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