INTEEESTIXG LOCALITIES OF ISHPEMINd FOKMATION. 435 



formation at Champion are diflfereut from those at an}- otlier h)caHty. It is 

 to be noted that just nortli of the Ishpemhig formation in this vicinity occur 

 mingled sedimentar)- and volcanic rocks of the Clarksburg formation, and 

 further, one of the volcanic centers was probably just east of Champion. 

 It is doubtless due to this volcano that the absence of pui-c quartzites is to 

 be attributed. The pecuhar conglomerate above mentioned may perhaps 

 be really volcanic rather than sedimentary. 



In thin section certain of the impure ores have a backgi-ound consist- 

 ing of small granules of quartz between which are leaflets of biotite, 

 sericite, and chlorite, and in which are very numerous crystals and clusters 

 of crystals of magnetite. Where the quantity of tlie micaceous minerals 

 is small and the granules of quartz are almost wholly derived from the 

 Negaunee jasper, the recomposed rock simulates to a remarkable degree 

 the original formation. Where the chlorite Ijecoraes verj- abundant, as 

 it sometimes does, the background is predominantly of this mineral, but it 

 still contains clastic grains of quartz derived from the Negaunee jasper, and 

 the whole is studded with crystals of magnetite. There are also present 

 large crystals of chloritoid. As usual, the micaceous hematite is easily 

 discriminated from the brightly reflecting, secondary, crystal-outlined mag- 

 netite. As the ore body at the Champion mine is so largely magnetite, it 

 appears that the secondary replacement, after dynamic action had ceased, 

 was the most important process in the production of the ore deposits. 



By the appearance of coarse-grained fragmental quartz from tlie 

 Basement Complex, the rocks at the bottom of the formation grade up 

 into biotitic, sericitic, and chloritic quartzites or quartz -schists, which 

 contain much iron oxide as a secondary impregnation. In the more 

 mashed phases the quartz grains are flattened so that their longer axes 

 are in a common direction. Accompanying the flattening is granulation. 

 Sericite is the predominant mica, and this secondary mineral wraps around 

 the particles of quartz in the usual mesh-like fashion. In certain of the 

 rocks many fekkpars are seen, and these are parth?- decomposed, the mica 

 and quartz forming from them. The mica -slates and mica-schists are 

 in all respects like similar rocks of the Michigamme formation, described 

 on pages 449-450, and they will therefore not be here fully considered. 



