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ore body is located at the east end of the deep Sayers Lake basin, partly above and 

 partly below the old water level. The lake has now been drained, and the ores 

 appear in a great amphitheater opening out to the west. The rocks immediately 

 associated with the hematite are siliceous ore, ferruginous cherts, or grained silica 

 rocks. These are mapped as immediately surrounding the iron ore, and also as 

 forming for the most part the north wall of the amphitheater. The east wall of the 

 amphitheater is composed of iron carbonate which shows gradations into siliceous ore 

 and into hematite ore. The south wall is composed of Wawa tuffs. 



The ores are believed to have resulted from the secondary alteration of an original 

 iron formation consisting mainly of iron carbonate, grained silica, and limestone, in 

 part interbedded with the Wawa tuffs, but mainly deposited above them. The iron 

 formation and the tuffs were folded up together, with the result that the tuffs were 

 formed into a trough underlying the iron formation, and the iron formation within 

 this trough was folded and brecciated. Percolating waters then altered the iron 

 carbonates. Probably the chief solvent of the carbonates was acid ferric sulphate or 

 sulphuric acid resulting from the oxidation of the iron pyrites, which are found in 

 considerable quantity throughout the iron formation. The ore body has resulted 

 directly from the alteration of iron carbonate, the oxidation of the iron sulphide 

 having yielded but little ore. The oxidation of the iron took place where solutions 

 of iron carbonate came into contact with waters bearing oxygen. 



The principal areas of iron formation possibly bearing iron ore at Gros Cap, 

 Sayers, and Boyer Lakes, just east of the Helen mine, around Brooks Lake, south of 

 Long Lake, just east of Goetz Lake, in Parks Lake, and between Parks and Kimball 

 Lakes. 



The Upper Huronian rocks are represented principally by the Dore conglomerate, 

 occurring typically at the mouth of the Dore River and thence eastward beyond 

 Michipicoten Harbor, and to a less extent in other parts of the district. This con- 

 glomerate is unconformably above the Lower Huronian rocks of the district. It con- 

 tains pebbles of granite, felsite, conglomerate, granular silica of the iron formation and 

 breccia. 



The Dore conglomerate is cut by acid intrusives in dikes and bosses. These are 

 the latest rocks of the region. 



The Laurentian granites and gneisses have not been studied in detail in the 

 Michipicoten district, but their associations with both Lower and Upper Huronian 

 prove them to be post-Huronian eruptive masses. 



Commettt. — As noted in the above paper, there is very close similarity in lithology 

 and succession between the rocks of the Michipicoten district and the rocks of the 

 Vermilion iron-bearing district of Minnesota, although described under different 

 names. The rocks above called Lower Huronian and Upper Huronian are called 

 respectively Archaean and Lower Huronian by the United States geologists. 



There is substantial agreement in the matter of the origin of the ores in the two 

 districts.^ The Wawa tuffs are also similar to the Palmer gneiss of the Archaean of 

 the Marquette district. The granites and gneisses described as Laurentian for the 

 Michipicoten district are similar in character and relations to granites in United States 

 districts referred to the Lower Huronian. 



'J. Morgan Clements, "The Vermilion Iron-Bearing District of Minnesota, 

 Monograph XLVI, U. S. Geological Survey, 1903; C. R. Van Hise, "The Iron-Ore 

 Deposits of the Lake Superior Region," Twenty-first Annual Report of the JJ. S. 

 Geological Survey, Part III, pp. 305-434. 



