28 
MUSEUM BULLETIN NO. 30 . 
A second type of mineral deposit, very subordinate both as 
regards quantity and value, is the magnetite-pyrrhotite deposits. 
Under the course of differentiation as previously outlined, such 
deposits might be formed at two periods in the history of con- 
solidation of the gabbro. They might have resulted from the 
early separation and aggregation of iron minerals from the body 
of the gabbro magma, as at Sudbury, and thus in age antedate 
the consolidation of nearly all its phases; or they might have 
been formed in the last stages of differentiation at the time of 
the formation of the hornblendite veins, had the waters that 
formed these been laden with excess of iron. That these waters 
did carry iron in excess of that required for the conversion of the 
rock into hornblendite is shown by the almost universal presence, 
in the middle of the small hornblendite veinlets, of strings of mag- 
netite and pyrrhotite grains. 
One of the two deposits observed on the peninsula belongs 
without doubt to the second type, as it is found in a large shear 
zone, in the form of lenses, greatly cracked and cut by the later 
depositions of chalcopyrite. This is the deposit at Iron mountain, 
section 79. Here the only gangue mineral is hornblende, in 
bladed forms and granulated, and the metallic minerals are 
magnetite and pyrrhotite. The pyrrhotite is found in fairly 
large, comparatively pure, masses. The other body is found on 
section 83 ; it was not examined by the writer. 
These massive deposits are too low grade in copper to be 
even of prospective value. They are rich in the valueless metallic 
minerals, and it would be difficult and expensive to separate the 
chalcopyrite from them. The deposits have been exploited for 
iron as well as copper, but the sulphur is too high for the deposit 
to be a possible source of iron with the present conditions 
existing in the iron industry of this continent. It is possible 
that at. some future time they may have some value as a source 
of sulphur for the manufacture of sulphuric acid. Their chief 
value has been as an iron flux in copper smelting. 
