390 THE MAItQUETTE IKON-BEAKINO DISTKICT. 



the Negaunee rock is tlie grurierlte-magnetite-sehist. There are transition 

 varieties between the griiuerite rocks and the jaspihte. In certain of these 

 the layers of griinerite-schist have outer zones or borders of jasper, sug- 

 gesting that the latter developed from the same original rock under conditions 

 more favorable for oxidation. There are at Republic excellent transition 

 phases and interlaminated beds between the griinerite-magnetite-schist and 

 the Ajibik qiiartzite. These have already been described in connection with 

 that quartzite. (See pp. 292-294.) Between the griinerite-magnetite-schist 

 and the reil jasper, which occupies the upper horizon of the formation, there 

 is a rock tlie siliceous bands of which are Avliite and similar to those which 

 occur at the topmost horizon at Michigamme and Spurr. In a phase inter- 

 mediate between this rock and the jaspilite the white bands <:)r oval areas 

 of quartz have a jasper border (fig. 22, p. 362). The relations are here, 

 therefore, just the reverse of those at Michigamme, in the latter place the 

 red jasper being below the rock with white bands, while at Republic the 

 jasper is above. 



In thin section the jaspilites and griinerite-magnetite-schists are in 

 nearly every respect similar to those of Michigamme and Spurr, lint a 

 concretionary arrangement of the quartz is less common. While the 

 griinerite generally has the usual radiating arrangement, in one case it 

 has a parallel one, resembling that of muscovite in a perfectly lami- 

 nated mica-schist. At low horizons beautiful intergrowths of griinerite 

 and green hornblende are found. In one case the amphibole of alternate 

 bands consists predominantly of griinerite and of hornblende, but in some 

 bands intergi-owths of the two occur. As usual, garnet is plentiful, 

 especially adjacent to the intrusive greenstones and at low horizons. 

 At the transiti(iu liorizons to the Ajibik quartzite muscovite and chlorite 

 also appear. 



Magnetic mine area. — In the soutliwcst tougue, at tlic Maguctic mine, and at 

 various places to the south (Atlas Sheet VII), the Negaunee formation 

 consists of a coarsely banded griinerite-magnetite-schist. The amphiljole, 

 vmlike that of the major part of the formation, has a decided green color. 

 The quartz of the siliceous bauds is also more coarsely crystallized than 

 anywhere else in the formation. The magnetite occurs to a great extent in 



