434 THE GEOLOGY OF MINNESOTA. 



[Melacouite. Copper. Serpentine. 



No. 577. MELACONITE. 



Minong mine, Isle Royale. 



Ref. Annual Report, x, page 54. 



Mi'!/. With soda, on charcoal, this gave a bead of metallic copper. The ore is 

 purplish black, in form of a powder, associated with some malachite. 



Age. In Cabotian(?) rock. N. H. w. 







No. 578. COPPER. ( titamp ore.) 



Minong mine, Isle Royale. 



Ref. Annual Report, x, page 54. 



\ 



Metallic copper is spread through a brownish-red rock in a manner similar to 

 that of the Calumet and Hecla mine, on Keweenaw point, though not plainly con- 

 glomeratic. It is more or less coated and accompanied by small deposits of cuprite. 

 The rock appears to have been a somewhat open porphyryte, and the copper has 

 entered its cavities, and at the same time a change has come upon the rock by reason 

 of which a pseudamygdaloidal spottedness pervades it, /. e., foreign minerals have 

 been generated in nests at points in the mass of an originally non-amygdaloidal rock 

 subsequent to consolidation. In these nests sometimes is a central core of metallic 

 copper. 



No section. 



Age. Cabotian(?) 



Remark. The existence of copper in the Cabotian (i. e., in a dike in the 

 Animikie) was first noted by A. C. Lawson in the Thunder Bay region. (American 

 Geologist, vol. v, page 174,' 1890.) The environments of the copper .deposits at the 

 old Minong mine, at the head of McCargo's cove, Isle Royale, are apparently not 

 identical with those described by Lawson, but approach nearer those in Keweenaw 

 point, and it may be discovered that this copper is, instead, in a conglomeratic 

 outlier of the base of the Potsdam. The line of strike of the basal conglomerate at 

 the west end of Isle Royale probably would carry the northern boundary of the 

 Manitou and Potsdam to the vicinity of Conglomerate bay west of Rock Harbor. 



N. H. w. 



No. 579. SERPENTINE (?). (Cupriferous.) 



Minong mine, Isle Royale. Nodules in No. 578. 

 Ref. Annual Report, x, page 54. 



Meg. This is a massive, green, fine-grained rock, carrying nests and spangles 

 of metallic copper in a manner similar to No. 578, but less abundantly. Across the 

 rock run veins consisting of a finely fibrous, silky mineral which stands vertical to 

 the walls, apparently a form of asbestos. The source of this rock may have been 

 from change of a basic pyroxenous mass included in No. 578. Indeed there is reason to 



