116 ALASKAN MINERAL RESOURCES IN 1906. 
North of Matanuska River, on the southern margin of a granif 
mass, occurs a band of highly crystalline mica schist. It is closel 
folded and infiltrated with fine quartz stringers, and streams cuttin 
it yield gold placers. It is noteworthy that the igneous rocks, gn 
nitic and volcanic, to which this schist gives way on the north an 
east have so far proved barren of workable placers. 
To the northwest, near the mouth of Talkeetna River, a slate-schis 
series, folded, intruded by granite, and containing abundant quart 
stringers, represents the gold-bearing rocks. Eldridge a reports tr. 
occurrence of similar rocks north of the Susitna-Tanana divide. Sou 
gold has been found in the past on streams heading within this fo: 
mation. The gold-bearing gravels of the new Yentna district ai 
reported to have a slate bed rock, indicating the presence of the sair 
formation. 
Though there is yet some question as to the relative ages of the* 
several series of rocks, there is little doubt that their economic impo: 
tance is due to the mineralization accompanying local infiltration ( 
quartz stringers. In the subsequent wearing away of the rocks tl 
gold content therein has been concentrated in the form of placers. 
Though placers have not been found within the areas of older vo 
canic rocks, some mineralization has occurred. West of Hicks Cree 
a large cropping of gossan was found. This gossan is due to the ox 
dation of finely divided pyrite disseminated through a quartz po: 
phyry. A sample selected for assay showed a trace of gold and a 
silver. 
The whole southern flank of Sheep Mountain, at the head of Mats 
nuska River, is colored a strong red from the oxidation of pyrite in tl 
greenstones. At some points the sulphuric acid formed during tl 
oxidation of the pyrite has bleached the greenstones entirely whii 
and this bright color, contrasting vividly with the red, produces 
marked scenic effect. Certain streams emerging from the range are g 
highly charged with iron salts as to coat their gravels red with oxi 
The mineralization of the greenstones, which are here roughly s< 
tose, is extensive but diffuse. An assay showed the presence of a tra 
of gold, but no silver. 
DESCRIPTION OF LOCALITIES. 
WILLOW CREEK. 
Placer gold is being mined in commercial quantities only at 01 
locality within the area covered during the season — on GrubstaJ 
Gulch, a southern tributary of Willow Creek, which enters Susiti 
River about 30 miles above its mouth. Willow Creek proper w 
staked by M. J. Morris and L. Herndon in 1898, and it is reported tli 
aEldridgo, G. I!.. A reconnaissance in the Susitna basin and adjacent territory, Alaska: Twentii 
Ann. Rept. U. S. Geol. Survey, pt. 7, 1900, pp. 15-16. 
e g 
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