The Precambrian region between Great Bear and Great Slave Lakes is characterized by large bodies of granitic rocks and quartz-feldspar porphyries. In Great Bear Lake area granitic rocks, about 1,800 million years in age, range in composition from granite to diorite. Some are high in potash and have the characteristics of rapakivis. Closely related to granitic rocks are large volumes of quartz-feldspar porphyries which exhibit the peculiarities of ignimbrites. These, when in contact with granitic rocks, are recrystallized but still retain evidence of volcanic origin.

Integration of field data, qualitative and quantitative mineralogy, and distribution of 19 trace elements from 250 samples suggests that the parent magma was acidic and that the phenomena of volcanism and plutonism are closely related, the difference between them being mainly the depth of activity.

End_of_Article - Last_Page 539------------