64 ALASKA GEOLOGY 



in the mill, but it is not conspicuous in the ore. Chalco- 

 pyrite was found in small amounts in both Treadwell 

 and Mexican ores, but no other sulphide was seen except 

 pyrite. Small veins of short-fibred asbestos are some- 

 times formed on shear planes in the altered gabbro. 



As regards the tenor of the deposit in gold, I was in- 

 formed that there was no apparent change with depth to 

 the lowest parts reached (the 440 level) although, as stated 

 above, there was here a considerable body of syenite that, 

 while containing pyrite in abundance, was practically bar- 

 ren of gold. The slate was everywhere found to be barren. 

 The serpentine forming the hanging-wall on the 440 

 level was said to show low values, not to exceed fifty 

 cents a ton. 



At the time of our visit the Treadwell Company had 

 five mills running continuously with 880 stamps, and were 

 crushing approximately four tons of ore per day per stamp. 

 It was interesting to note the encroachments made in the 

 shallow water of that side of Gastineau Channel by the 

 vast amount of tailings thus being continuously poured 

 into the bay. 



The town of Juneau stands on the mainland just across 

 the channel from the Treadwell Mine. The black slate 

 which is so conspicuous on Douglas Island about the 

 mine is not found in Juneau, its place being taken by a 

 series of much more highly crystalline schists. 



In the town of Juneau on top of a little hill above the 

 wharf were found outcrops of a bluish hornblende schist 

 (NOS. 24 and 26). This rock is highly schistose but of 

 rather coarse texture, showing to the unaided eye only 

 fibrous bluish hornblende. In section it was found to 

 consist largely of hornblende, which is in large irregular 

 crystals and also in slender needles, embedded in the 

 granular quartz-feldspar groundmass of the rock. The 

 hornblende is strongly pleochroic in blue and brown tints, 



