Bearpaw Ridge

The Bearpaw Ridge alkaline complex is located in the Rocky Mountains of eastern British Columbia. It consists of an oval-shaped body of syenite 500x1000 m in size, flanked by two smaller sills of similar composition intruding the Silurian Nonda Formation volcaniclastics. These structures are all elongated north-south and display a low-grade metamorphic overprint. The sills and outer rim of the main stock are syenite, composed of 80-90% feldspar, altered from alkali-feldspar to albite due to metamorphism. Accessories include epidote and muscovite, also formed by metamorphism. In the core of the main stock is a feldspathoid-bearing syenite containing up to 10% sodalite and cancrinite, with an absence of nepheline. Minor aegirine and biotite are the primary mafic phases, with notable accessories in this unit including allanite, monazite, apatite, pyrochlore, thorite, and cheralite. In addition to the main intrusive units to the southwest end of the ridge is a second variety of “post-orogenic” syenite bears aegirine/aegirine-augite and riebeckite, with accessory pyrite, barite, monazite and sphalerite. The complex is believed to relate to the alkaline basaltic volcanics and volcaniclastics of the Silurian Nonda Formation into which it is emplaced. Whole rock and geochemical data can be found for both the plutonic and volcanic rocks in Pell (1987).