50 ALASKAN MINERAL RESOURCES IN 1906. 
A second, less important zone of mineralization follows the east 
flank of the granitic belt already mentioned, though in this zone no 
ore bodies of consequence have been developed. The belt includes 
several prospects at the head of Hooniah Sound and Idaho Inlet. 
A northern continuation of this zone appears to traverse the head of 
the several bays northwest of Cape Spencer as far as Lituya Bay. 
On Kupreanof Island are scattered indications of a widespread 
mineral-bearing zone, which extends from the head of Portage Bay 
down the east side of Duncan Canal and includes prospects along 
the west shore of Wrangell Narrows. The ore bodies thus far opened 
carry small values in both copper and gold. No deposits of ore have 
yet been discovered on Kuiu Island. 
On Prince of Wales Island the regularity of the rock structure is 
locally interrupted by the broad and irregular intrusive masses, and 
for this reason the ore bodies are not traceable along definite lines. 
Where zones of mineralization occur they follow the lines of contact 
of the intrusive rock masses closely, as is well shown, for example, at 
Copper Mountain and on Kasaan Peninsula. 
ORE BODIES. 
Within the zones described above mineralization is widespread, 
metallic sulphides occur disseminated throughout most of the beds, 
and quartz veins or veinlets are everywhere present. A sample taken 
almost anywhere within such areas will usually yield, a trace of gold 
and silver, though concentrations of these metals into workable 
deposits are much less numerous than one would anticipate with the 
vast amount of mineralization present. 
The ore bodies are of many types. Strong gold-bearing quartz 
veins of moderate-grade ore, occurring either in the intrusive rocks or* 
adjacent metamorphic rocks, are mined at Berners Bay, Eagle River, 
and Sheep Creek, in the Juneau district; on the west coast of Chi- 
chagof Island, north of Sitka; at Helm Bay and Dolomi near Ketchi- 
kan; and at many other localities. Lodes or stringer leads in the 
slates and schists or following wide dikes of a mineralized basic rock 
are most strongly developed up Gold Creek in the vicinity of Juneau 
and at numerous other points along the mainland belt. 
Bands of heavily mineralized schist following the trend of the rock 
structure and cut by rich ore seams are shown at the Nevada Creek 
mines on Douglas Island, the Gold Stream mine on Gravina Island, 
and at other localities. The ore bodies of the Treadwell group of* 
mines, as shown by Becker a and Spencer, 6 are brecciated masses of 
intrusive syenite, intersected by a network of quartz and calcite vein- 
lets and impregnated with pyrite, which is found both in the veinlets 
a Becker, G. F., Reconnaissance of the gold fields of southern Alaska: Eighteenth Ann. Rept.U. S. 
Geol. Survey, pt. 3, 1898, pp. 1-86. 
b Spencer, A. C, The Juneau gold belt: Bull. U. S. Geol. Survey No. 287, 1906, pp. 93-115. 
