Section IV., 1915 [175] Trans. R.S.C. 



A British Columbia Example of the Contact Metamorphism of a Granite 



Rock to a Garnet. 



By R. W. Brock, F.R.S.C. 



(Read May Meeting, 1915.) 



In the Summary Report of the Geological Survey for 1902, the 

 writer gave a brîef description of the contact metamorphic deposits 

 of the Boundary Creek District of British Columbia, calling attention 

 to the fact that heie the metamorphism to garnet, epidote and other 

 typical contact minerals was not confined to limestone but that other 

 rocks, even granodiotite, were altered in like manner to a similar and 

 indistinguishable product. 



As this type of deposit had just been recognized and the observed 

 contact metamorphic deposits had been in limestone, gfologists con- 

 sidered such deposits to be peculiar to this rock, and its presence as a 

 host to be essential to their formation. The writer's Boundary Creek 

 observations weie therefore discredited. Since that date a number of 

 such deposits have been found and described in which the altered rock 

 is not limestone, and it is now fully recognized that the action is not 

 confined to a rearrangement of the molecules present in a limerock, 

 with the addition of silica, but that there are other important chemical 

 changes and that these may occur in many rocks, though limestone 

 appears to be most susceptible. 



While it is therefore no longer necessary to corroborate these 

 Boundary Creek observations, the alteration of the Boundary Creek 

 granodiorite to a garnet rock furnishes such a clear and striking instance 

 that it seems desirable to have it placed on record with the Society. 



The geology of the District^ is complicated through deformations, 

 igneous intrusions and flows, and metamorphism. 



The chief formations may be grouped as follows : 



Glacial and Recent Deposits Pleistocene 



Pulaskite and Pulaskite porphyry 1 



Augite Porphyrite \ Miocene 



Midway Volcanic Group J 



Kettle River Formation (Conglomerate Sand- 



stone Shale) Oligocè ne 



i.In addition to the Summary Report, 1902, page 95, description of the geology 

 will be found in Memoir 21, G.S.C., "The Geology and Ore Deposits of Phoenix" 

 by O. E. LeRoy, Memoir 19 "Geology of Mother Lode and Sunset Mines" by O. E. 

 LeRoy; Memoir 38, "North American Cordillera, Forty-Ninth Parallel" by R. A. 

 Daly. 



