50 ALASKAN MINERAL RESOURCES IN 1904. [bull. 259. 
of extensive lode systems traceable over great distances, and it appears 
from the evidence already gathered that, beyond the boundaries of the 
main-lode system, mineralization is widely and irregularly distributed. 
However, on Admiralty Island a mineralized zone may be traced from 
Funter Bay through the Mammoth group south of Young Bay and 
to the Johnson prospect on Seymour Canal, 4 miles north of Wind- 
fall Harbor. Another may be said to occur on Baranof Island, begin- 
ning at Billy basin east of Sitka, traversing the properties in the 
vicinity of Silver Bay and striking southeastward through the Luck} 7 
Chance property, a distance of 12 miles. This zone may also be 
represented by mineral outcrops which have been located recently at 
the head of Red Bluff Bay, an indentation on the east shore of Baranof 
Island. 
Mineral-bearing veins and impregnations of copper and gold ores 
may follow or recur along certain schistose and sedimentary beds, or 
near contacts of igneous rocks, for several miles, but no well-detined 
belts of mineralization have yet been traced on the islands to the south. 
ORE DEPOSITS. 
The ore deposits themselves vary greatly. Some are strong gold- 
bearing quartz fissures containing free-milling ore of moderate grade, 
as at Berners Bay, Sitka, and Snettisham. Some are rich stringer 
leads, occurring in slates and schists, as at Sheep Creek and Funter 
Bay. Others follow wide dikes of a mineralized basic rock intersect- 
ing the slates, as in the Silver Bow basin. Both slates and dikes are 
cut by numerous gash veins accompanied by sulphides, which also 
penetrate the inclosing rock and form wide bodies of low-grade ore. 
Still others are mineralized belts of slate or schist impregnated with 
sulphides of iron and intersected b}^ numerous stringers of quartz and 
calcite and occasional concentrations of massive auriferous sulphide. 
Deposits of this character occur at the Yakima and Nevada Creek 
properties on Douglas Island, the Portland group on Endicott Arm, 
the prospects up Spruce Creek at Windham Ba} r , and the Rodman Bay 
mines. However, for the most part these ores are of too low grade 
for profitable mining. 
The ore bodies of the Treadwell group of mines, as shown by 
Becker a and Spencer^ are brecciated masses of intrusive syenite inter- 
sected by a network of quartz and calcite veinlets and impregnated 
with pyrite, which is found both in the veinlets and the rock itself. 
These deposits occur in carbonaceous slates, the structure of which they 
closely follow. Similar ore deposits have not been discovered else- 
where in Alaska. 
« Becker, G. F., Reconnaissance of gold fields of southern Alaska: Eighteenth Ann. Kept. U. S. Geol. 
Survey, pt. 3. 
b Spencer, A. C, The geology of the Treadwell ore deposits, Alaska: Trans. Am. Inst. Min. Eng., 
vol. ;;•">. 
