76 



The zone of lime-silicates is of contact metamorphic 

 origin and consists essentially of garnet and epidote with 

 calcite, quartz and chlorite and trifling amounts of actino- 

 lite and zoisite. Irregular lenses and masses of crystalline 

 limestone are also included in the zone and represent 

 unreplaced portions of the original calcareous formation. 

 The zone or rather zones occupy basin-like depressions 

 in the jasperoids. They are for the most part economically 

 important and contain the large bodies of low grade 

 copper ore which have been deposited in certain favourable 

 areas usually along the edge or base of the contact zone. 



Jurassic f 



The granodiorite batholith so extensively developed 

 throughout the Boundary district and which probably 

 underlies Phoenix at no great depth, is represented at 

 Phoenix by a small stock of augite syenite and two dykes 

 of syenite porphyry which cut the Brooklyn formation. 



Tertiary. 



Oligocene. Kettle River formation. — An isolated area 

 of this formation occurs at Phoenix overlying uncon- 

 formably the Brooklyn formation and Knob Hill group. 

 The exposure is about one mile (i -6 km.) long and from 40 

 to 960 feet (12 to 292 m.) wide and 260 feet (80 m.) thick. 

 The formation here consists of conglomerate, coarse and 

 fine feldspathic sandstone, and cherty carbonaceous 

 shales and light grey indurated silts. The strike is nor- 

 therly and the dips are prevailingly eastward at angles 

 varying from 10 to 60 degrees. The formation has suffered 

 from warping, tilting and erosion before being covered 

 by the Miocene lavas (see section p. 80). 



Miocene. Midway Volcanic group. — An erosion rem- 

 nant of one of the younger lava members of the Midway Vol- 

 canic group overlies the Kettle River formation and Knob Hill 

 group. The exposure is a little over a mile (i -6 km.) long 

 and from 1,100 to 2,000 feet (335 to 609 m.) wide. The 

 thickness varies from a few inches (cm.) to about 300 feet 

 (91 m). The rock, though varying in texture from por- 

 phyritic to amygdaloidal, is an augite trachyte composed 

 of phenocrysts of orthoclase, soda-orthoclase, andesine, 

 augite and biotite in a base of the same minerals with 



