REPORT OF THE CHIEF ASTRONOMER 369 



SESSIONAL PAPER No. 25a 



This dike may, thus, be described as a somewhat porphyritic, olivine-free 

 missourite. No other intrusion of this rock has as yet been found in the 

 Rossland region, but closer search may lead to the discovery of other bodies. 



VARIOUS OTHER DIKES. 



There are undoubtedly many thousands of dikes in the area covered by the 

 Boundary belt within the Rossland mountains. Most of them are more or less 

 clearly apophyses of the stocks and batholiths of the region or else their more 

 aplitic derivatives. As such the types have already been briefly described. 

 The intrusion of certain of the dikes has been accompanied, or closely followed, 

 by the formation of large mineral deposits. Many others have been observed 

 which are of importance in showing the relative ages of the formations. From 

 a purely petrographic point of view, however, most of the dikes have few 

 features which make them worthy of special description. 



The relation of the Beaver Mountain group to the Rossland latites may 

 possibly be indicated by the occurrence of a dike of monzonitic porphyry 

 cutting the Beaver Mountain sediments at the 2,800-foot contour on the spur 

 running up eastward from Champion railway station. The dike (or sill?) is 

 about 100 feet wide and seems to strike clue east and west. It is a fresh, 

 medium-grained, dark greenish-gray rock, porphyritic through the prominence 

 of large, lustrous biotites. The mass of the rock is a hypidiomorphic-granular 

 aggregate of augite, hornblende, biotite, labradorite, and orthoclase, with 

 accessory ilmenite, apatite, and titanite. The specific gravity is 2-867. The 

 habit of this rock is much like that of the chemically analyzed porphyritic 

 olivine syenite, though the plagioclase seems here to be relatively much more 

 abundant. The rock has been classified as a porphyritic hornblende-augite-biotite 

 monzonite with phenocrysts of biotite. It may be contemporaneous with the 

 Rossland monzonite, which in that case, would be younger than the Beaver 

 Mountain sediments. The tuffs associated with those sediments are cut by 

 diabasic dikes and by labradorite porphyrite dikes which are doubtless the 

 intrusive equivalents of some of the basaltic and andesitic flows in this volcanic 

 group. One of the labradorite porphyrite dikes, bearing phenocrysts of 

 labradorite in a diabasic ground-mass of augite and basic plagioclase, forms one 

 of the walls of an auriferous quartz-vein at the Princess mining claim. 



The fern-bearing argillite at the Little Sheep creek locality is cut by a 

 thirty-foot, north-south, vertical dike of typical augite-biotite monzonite por- 

 phyry, which may fairly be regarded as apophysal from the large Rossland 

 stock of monzonite. Quite similar dikes cut the older members of the Rossland 

 volcanic group on the railway between Trail and Rossland. Dikes of horn- 

 blende^bearing augite-biotite monzonite porphyry cut the great intrusion-breccia 

 about the Trail batholith at the Columbia river. 



Close beside the last-mentioned dike but without evident age relation 



to it is a somewhat unusual rock occurring in the form of a two-foot dike 



cutting the Trail granodiorite near its contact, and striking N. 15° W., with a 



dip of 80° to the eastward. It is a dark gray-green rock, compact and diabasic 



25a— vol. ii— 24 



