66 ALASKAN MINERAL RESOURCES IN 1906. 
KETCHIKAN MINING DISTRICT. 
All the copper-producing mines of southeastern Alaska are on Prince 
of Wales Island, in the Ketchikan district. The ore bodies are genet- 
ically related to the intrusive rocks and occur either as contact or 
replacement deposits in the form of lenses or irregular masses. They: 
are found in limestone, quartzite, or a greenstone-schist country rock. 
The chief copper ore is largely chalcopyrite, accompanied by pyrite, 
magnetite, and pyrrhotite, besides various gangue minerals. Enrich- 
ment zones are lacking, evidently on account of the absence of the 
zone of weathering which was removed during the glacial epoch ; and 
at only one locality (Copper Mountain) are secondary ores present 
in quantity. At this place they extend only a few hundred feet 
below the surface. 
KASAAN PENINSULA. 
Kasaan Peninsula is a promontory 12 miles long and 3 to 6 miles 
wide, projecting into Clarence Strait and sheltering Kasaan Bay, aj 
deep embayment. Its high points reach elevations of 500 to 3,000 
feet, and the mountain mass is made up principally of eruptive rocks.) 
The sedimentaries exposed are small areas of marbleized limestone 
and schists varying in composition. These are invaded by wide 
diorite masses and by dikes of felsite, diabase, andesite, and basalt, 
in many places forming an intricate complex of intrusives, both pre- 
vious and subsequent to the deposition of the ore bodies. Faulting 
was observed locally, but displacements were small and their effect 
on the ore bodies was slight. 
The ore bodies occur as lens-shaped masses within the contact 
aureole of the invading diorite batholiths. The diorite is not invari- 
ably exposed on the surface at the mine, but its presence may be usu- 
ally found in the near vicinity. The presence of a huge underlying 
mass of igneous rock is clearly shown by the vast amount of contact 
metamorphism and contact minerals within the ore bodies. Garnet, 
epidote, hornblende, calcite masses, and many other secondary min- 
erals are present and form the gangue of the copper deposits. Asso- 
ciated with the chalcopyrite is a large percentage of magnetite, thus 
making a base ore and necessitating the addition of much siliceous 
ore on its reduction in the smelter. This latter problem has been a 
source of difficulty the last few years, but has apparently been over- 
come by the development of extensive bodies of copper-bearing quartz 
at Maple Bay, on Portland Canal. 
There is every reason to suppose that these copper deposits origi- 
nated from considerable depth and were laid down from the solutioi 
given off during the solidification of the dioritic batholiths. It seen 
safe to assume, therefore, that other ore bodies similar to those exposec 
on the surface may be found within the contact zones in depth. 
