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Carbonate Rocks. In various parts of the area, assoc- 

 iated with Keewatin rocks, are carbonates to which various 

 terms have been applied, such as dolomite, ferro-dolomite, 

 ferruginous carbonate and ankerite. 



There is much uncertainty as to the origin of this rusty 

 carbonate rock in different parts of the area. The carbonate 

 may occur in at least four different forms, namely, as 

 original bedded material, as a replacement, as vein filling, 

 and as a decomposition product of basic, igneous or other 

 rocks. 



That there has been considerable migration of carbonate 

 solutions is shown by the manner in which almost all the 

 rocks of this area are more or less impregnated with it. 

 Sections of quartz-porphyry schist show the presence of 

 much calcite as a secondary mineral. Veins and veinlets 

 of ankerite occur frequently, not only in basic rocks, but in 

 the quartz-porphyry. 



LaurSntian. 



A few outcrops of granite occur in the township of 

 Whitney. This granite is a medium-grained biotite variety, 

 and not typical of that occurring in large volume to the 

 north and south of the area. In south Whitney it intrudes 

 light-colored porphyry of Keewatin age, but its relation to 

 the Temiskaming is not known. 



While typical granites do not outcrop in the immediate 

 vicinity of Porcupine, they occur in large volume to the 

 north, west and south of the area, and are known to intrude 

 the Keewatin. Where the granites are exposed over large 

 areas they are medium to coarse in grain, and have been 

 exposed at depth by extensive erosion. It is considered 

 that some of the granophyre, porphyry and felsite rocks are 

 dike representatives of the granites, which very likely under- 

 lie the Keewatin and Temiskaming formations at Porcupine. 

 The predominant feldspar of the acid dikes is a plagioclase 

 (near albite), which is also prominent in many of the 

 erranites. 



