Ml-TALS 



79 



It is of interest to note that the United States paid $7,200,000 

 for the Alaskan territory. It was catalogued as the "white 

 clt -pliant" on the hands of the United States government. Yet 

 (lit- total gold brought out of Alaska exceeds $150,000,000 with 

 an output in 1910 of $20,947,600 or nearly three times the 

 amount paid for the territory. 



The Lodes: Gold quartz lodes occur most abundantly along 

 the coast, especially near Sitka and on Douglas Island. The 

 ore bodies are dikes of diorite traversing black slates. The hang- 

 ing wall of the ore body is a much altered intrusive greenstone 

 and the foot wall is a black slate. (See Fig. 58.) 



Treadwcll Mine 



440 



FIG. 59. Section through the Alaska Treadwell mine, Douglas Island, 

 near Juneau, Alaska. 



Two sets of fractures at right angles to each other seem to 

 have been incident to the epirogenic movements of the region. 

 According to Spencer, the mineralization was caused by hot as- 

 cending solutions of magmatic origin. Secondary concentra- 

 tion is not in evidence. The actual depth to which the ores can 

 be worked depends more upon the increased cost of mining at 

 great depths than upon the exhaustion of the ore body. An 

 almost continuous ore body has been developed for more than 

 half a mile. (See Fig. 59.) 



The Placers: Gold occurs most abundantly in Alaska in 

 placers. The placer deposits of Seward Peninsula alone are about 

 equal in area to those of California and approximately ten times 



