146 Tlie A}nerican Geologist. September, i898 
shaft were in magnetite with the oHvine increasing in pro- 
portion. 
The ore has a shining black hister, is brittle and usually 
coarse grained. Thin sections of the apparently pure ore 
generally show the presence of small particles of plagioclase, 
and sometimes of other minerals. Copper and chalcopyrite 
are associated with magnetite. Native copper was found by 
the writer in outcrops north of Tucker lake in the north part 
of T. 64 N., R. 3 W., and from the shaft in the N. W. \ of S. E. 
\ sec. 21, T. 63 N., R. 4 W. It is reported from other localities 
near these locations. Some specimens of rock contain over 
five per cent of copper. 
Chemical analyses show quite a variation in the compo- 
sition of these ores. An analysis by the writer of an ore from 
section 21, T. 63 N., R. 4 W., gave silicia, 6.08; alumina, 3.82 ; 
lime, 1.69; titanium oxide, 14.73; magnetite, 71.; nickel oxide, 
2.65 ; sulphur, trace. The lime and alumina are accounted for 
by the presence of a triclinic feldspar. 
Titanium is sometimes absent. Cobalt, manganese and 
chromium are sometimes found in addition to the constituents 
given in the above analysis. The metallic iron varies from 49 
to 60 per cent. These extensive magnetite deposits at pres- 
ent afford the only ores from the gabbro of probable economic 
value. An exhaustive study of the rarer metals in this ore 
has not yet been accomplished. Some analyses show the 
presence of small quantities up to two or three per cent of 
these metals in certain localities. 
Orthoclase gabbro. This variety is so called on account 
of the presence of the mineral orthoclase. Since this mineral 
is never abundant the orthoclase gabbro is quite limited in ex- 
tent. It seems that the orthoclase might be regarded as an 
accessory mineral rather than to form a separate variety. 
It is hard to distinguish the relative age of each variety. The 
granulitic noryte is slightly older than the rest of the mass, 
which may be considered as of one age. The noryte in places 
forms angular blocks cut by and enclosed in the rest of the 
gabbro. In other places the noryte and gabbro grade into 
each other. The relative age of the individual minerals may 
assist in determining the relative age of the varieties of the 
■gabbro mass. The minerals were formed in the following 
