5o 



Miles add 

 Kilometres 



of the Coast Range batholith is clearly expressed 

 in the sedimentary rocks (argillites and schists) 

 outcropping along the shores. Pegmatite dikes 

 are also more abundant near the batholith 

 contact. 

 335 m. Juneau. — Near Juneau the rocks exposed 



540 km. along the shores are greenstones alternating 

 with black slates. Toward the east the green- 

 stones (originally lava flows and tuffs) are less 

 common, and the entire formation consists of 

 black slates in different stages of metamorph- 

 ism. These slates pass in turn into the highly 

 schistose rocks of the Silver Bow basin. The 

 planes of cleavage, and usually also of stratifi- 

 cation, strike northwesterly and dip at high 

 angles northeast into the mountains. Intrusive 

 dykes of diorite and related aplitic rocks occur 

 frequently and are intimately associated with 

 the mineralization in this region. The Tread- 

 well group of gold mines on Douglas island 

 opposite Juneau are located on mineralized 

 diorite dykes intrusive along or near the 

 contact between black slate and greenstones 

 bands. These dykes were much fractured after 

 intrusion, and the fracture cracks were subse- 

 quently filled with gold-bearing quartz veinlets. 

 The zone of mineralization here is nearly 400 

 feet (122 m.) in width and has been traced for 

 over 3,500 feet (1 km.) along the strike. 

 Much of the gold is free milling and is associ- 

 ated with pyrite and some pyrrhotite and mag- 

 netite and many other less abundant minerals. 

 The Treadwell group alone has produced 

 nearly $50,000,000 worth of gold and is one of 

 the largest gold mines in the world. 

 391 m. Lynn Canal. — Continuing north from 



630 km. Juneau the route enters Lynn canal and grad- 

 ually approaches the Coast Range batholith. 

 At 416 miles (670 km.), or abour 25 miles 

 (40 km) above Berners bay, the east shore of 

 Lynn canal is bordered by the batholith, which 

 is continuously exposed to Skagway at the head 

 of Taiya inlet and beyond to White pass and 

 Lake Bennett in British Columbia. The elon- 



