THE MINING INDUSTRY IN 1906. 25 
so that it may be correlated with that on Washington Creek. More- 
over, his geologic map shows the gold-bearing area to be intruded by 
many igneous rocks which are of the same general composition as the 
granites of southeastern Alaska. In other words, this occurrence 
appears to be closely analogous to the gold deposits of southeastern 
Alaska. Furthermore, some evidence is at hand which suggests a 
similar origin for the gold of the Susitna basin. 
It is safe, therefore, to assert that the intrusion of the Mesozoic 
granite in many parts of Alaska was accompanied or followed by the 
formation of auriferous veins. It is important, therefore, to draw 
attention to the distribution of this rock. As shown by Mr. Wright, 
it not only forms the major portion of the Coast Range, but also finds 
a wide distribution in isolated stocks among the islands to the west. 
The main granite mass passes into Canadian territor}^ in the Chilkat 
basin and has been traced northward to Kluane Lake, where, too, 
evidence of mineralization is found. It occurs again in the form of 
dikes and stocks along the northern margin of the Copper River valley 
and has been recognized at a number of places in the Alaska Range 
to the southwest. 
The genetic relation of the auriferous deposits of Seward Peninsula 
is still an unsolved problem, but so far no connection with the granitic 
intrusions has been established. Mr. Moffit shows elsewhere in this 
report (see pp. 130-132) that the placer gold of the Nome region proper 
finds its source in a series of closely folded and faulted metamorphic 
rocks and apparently most commonly along the contact between the 
schists and crystalline limestones. The only ore deposits in this prov- 
ince which have been found in association with granite intrusions are 
the cassiterite lodes, which, as Collier ° and Hess 6 have shown, are 
closely connected with the intrusions. The developments of the past 
year at Cape Mountain clearly show that the tin ores occur along the 
margins of the granite. It is unfortunate that little is known of the 
age of this granite. While it has generally been regarded as Paleozoic, 
it may be Mesozoic, but is certainly pre-Eocene. 
The matter already presented refers chiefly to the auriferous veins, 
but is probably applicable to some of the copper deposits, especially 
in southeastern Alaska. In Prince William Sound 6 the copper 
deposits are intimately associated with greenstones and greenstone 
schists, probably of Mesozoic age, which are relatively little altered. 
Granite intrusions are present in this province, but the ore bodies are 
not known to have any genetic relation to them. The copper ores of 
Copper River occur as contact deposits along a semicrystalline lime- 
's Collier, A. J., Tin deposits of the York region, Alaska: Bull. U. S. Geol. Survey No. 229, 1904; I ! 
development of Alaskan tin deposits: Bull. U. S. Geol. Survey No. 259, 1905, pp. 120-127. 
&Hess, F. L., The York tin region: Bull. U. S. Geol. Survey No. 284, 1906, pp. 145-157. 
c Grant, U. S., Copper and other mineral resources of Prince William Sound: Bull. U. S. ( teol. Survey 
No. 284, 1906, pp. 78-87. 
