Dutsen Wai (Duchin Wei)

This intrusion, just over 3 km in diameter, is expressed as a group of small hills. Most of the intrusion is occupied by biotite granite, which underlies most of the high ground. It is made of perthite, a little albite, quartz and fluorite. In places the granite is cut by quartz veins which carry minor cassiterite (Raeburn et al., 1927). Post-dating the biotite granite is a riebeckite granite which is highly variable and often pegmatitic. Riebeckite, which may form centimetre-long prisms, is commonly intergrown with aegirine and there is generally plentiful pyrochlore and cryolite, which has usually been altered, possibly to thomsenolite. A narrow zone of explosion breccia is located along part of the southern margin and consists of fragments of basement rocks.