THE TREADWELL ORE DEPOSITS/' DOUGLAS ISLAND. 
By Arthur C. Spencer. 
INTRODUCTION. 
Douglas Island, one of the smaller islands of the Alexander Arehi- 
)elago, is separated from the mainland of southeastern Alaska by a 
larrow fiord known as Gastineau Channel. The four mines of the 
rreadwell group are located near its inland shore, and the towns of 
Douglas and Tread well owe their 2,000 inhabitants to the mining 
>perations, while Juneau, with somewhat greater population, lies on 
he adjacent mainland, about 2£ miles northwest of Treadwell. The 
listance by steamer from Seattle, Wash., to Juneau slightly exceeds 
)00 miles, while Skagw T ay, the terminus of the Yukon and White Pass 
Railroad, lies 95 miles to the northwest, and Sitka about the same dis- 
ance in a southwesterly direction. 
The most southeasterly mine, the Ready Bullion, is 3,000 feet from 
he nearest workings of the Alaska-Mexican mine, and the intervening 
ground is supposed to be practically barren. The workings of the 
Viexican mine extend, however, almost to those of the Seven Hundred 
?oot property, and the latter connect at several levels with the tunnels 
)f the Alaska-Treadwell mine. There is thus an almost continuously 
leveloped ore body for a distance of about 3,500 feet. Although the 
workings have revealed several separate ore bodies, and certain dis- 
inctions are made in the character and occurrence of the ores, the 
nines are all located on the same lead, and the ore material is practically 
)f one nature and of identical origin throughout. As a whole, there- 
: ore, the deposits may be conveniently designated by the name of the 
irst discovered and largest mine. 
GEOLOGY OF THE REGION. 
The geology of the Juneau region and of southeastern Alaska as a 
vhole resembles, in many ways, that of the gold belt of California, 
rhe rocks of both regions are in large part of identical character, and 
|ome of them correspond in age and in the nature of their metamor- 
)hism. There is also a marked similarity in the occurrence of the 
aThis paper, with a more extended account of the geological features of the region, was printed in 
he Transactions of American Institute of Mining Engineers, Lake Superior Meeting, Oct., 1904. 
69 
