USEFUL METALS 



5. The Crystal Falls District: This district, according to 

 J. M. Clements, H. L. Smyth, W. S. Bayley, and C. R. Van Hise, 

 comprises a geological section extending from the Archean to the 

 Cambrian. The ore bodies occur: (1) In the Mansfield slate 

 win -re only one ore body of considerable dimensions has In* n 

 worked. This varies from 10 to 32 ft. in thicknc anl stands in 

 almost vertical position, (2) also in the Negaunee or Groveland 

 iron formations where the ore bodies are comparatively small 

 and the ore mainly a hard and siliceous hematite, and (3) within 

 the Michigamme formation where the large deposits at Crystal 

 Falls occur. The ore is chiefly a soft red hematite, though fre- 

 quently hydrated and classified in the trade as brown hematite. 



No. 1 is in the Lower Middle Huronian formations. No. 2 

 is in the Upper Middle Huronian formations. No. 3 is in the 

 Upper Huronian formations. 



6. The Menominee District. This district, according to C. R. 

 Van Hise and W. S. Bayley, lies mostly in Wisconsin and the 

 geological section extends from the Archean to the Ordovician. 

 The ore bodies occur: (1) In the Traders ore-bearing member 

 which is Middle Huronian. (2) In the Brier slate which is 

 conformable with the Traders iron-ore-bearing member also of 

 Middle Huronian age. (3) In the Curry ore-bearing member 

 which lies conformably upon the Brier slate formation and of Mid- 

 dle Huronian age. Rare bodies of ferruginous slate and iron 

 oxide occur in the Upper Huronian formations. The ores of 

 the Menominee district are mainly gray, finely banded hematite 

 with lesser amounts of a flinty hematite which shows local banding. 



7. The Penokee-Gogebic District. According to R. D. Irving 

 and C. R. Van Hise, this district comprises a narrow belt south 

 of Lake Superior with strike north 70 degrees east. The most 

 productive portion of the belt lies in Michigan and the remain- 

 der in Wisconsin. The geological formations are the Archean, 

 Lower Huronian, Upper Huronian, Keweenawan and Cambrian. 

 Each is separated from its successor by an unconformity. The 

 ore bodies occur in the Upper Huronian terranes, which consist of 

 a quartzitic slate and the Ironwood formation, above which is the 

 Tyler slate. The ore bodies closely resemble those in the Mesabi 

 district in that they occur between two slate belts. 



Previous to the introduction of great masses of igneous rocks 

 in Keweenawan times the original cherty iron carbonate was 

 largely decomposed with the production of some magnetite, and 



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