CIRCLE PRECINCT. 203 
probable that the conditions of occurrence of the placers are about the 
same. Apparently, however, from the reported discovery of a galena- 
bearing quartz vein on Colorado Creek, all of the basin is not under- 
lain by conglomerate. It is not known to the writer whether this vein 
carries values or what its dimensions are. 
Three or four claims are said to have been worked in this basin 
during 1906. Most of the gold is said to have been taken from bar 
diggings in the main creek. 
WOODCHOPPER AND MINERAL CREEKS. 
Woodchopper Creek, which is about 12 miles long, enters the Yukon 
from the west, about 30 miles above Circle. Its flood plain is about 
half a mile in width, and the alluvium is probably 8 to 15 feet deep. 
Five miles from the Yukon, Mineral Creek, the scene of some placer 
mining, joins Woodchopper Creek from the south. The floor of the 
Mineral Creek valley is 100 to 150 wide, and the slopes are broken by 
benches. Woodchopper Creek has a gradient of about 100 feet to the 
mile. Remnants of benches are to be seen along the creek, the highest 
of these being marked by the ridge on the northwest side, which is flat 
and slopes toward the Yukon. 
In the lower mile of Woodchopper Creek only massive greenstones 
were observed. Above these is a belt of black slate and limestones 
about a mile wide that continues nearly to the mouth of Mineral Creek, 
where it is succeeded by friable conglomerates in a belt said to be sev- 
eral miles wide. Chert and quartz pebbles dominate in the conglom- 
erate, which is only imperfectly consolidated and outcrops in few 
places. This fact often leads to its being mistaken for bench gravel 
by the prospector. 
So far as known the gold-bearing alluvium is confined to those 
creeks that cut the conglomerate, which, therefore, appears to be 
the source of the gold. Mineral Creek and its tributary, Alice Gulch, 
are the only streams which have thus far been found to be productive. 
Prospects are reported from Grouse and Iron creeks. 
At the mouth of Mineral Creek the alluvial floor of the valley is 
about 75 yards wide, but narrows upstream. A mile upstream, at 
the mouth of Alice Gulch, it broadens out again into a basin about 
75 yards wide. On the south wall of Mineral Gulch three well- 
defined benches were observed, having altitudes of about 20, 150, 
and 250 feet above the creek. 
Muck is encountered on some claims to a depth of 30 feet; the 
gravels underneath vary in thickness from 2 to 5 feet and are made 
up chiefly of well-rounded quartz and chert pebbles. The pay streak 
lies in parallel channels 12 to 14 feet wide, as many as three of these 
channels having been found in a width of 80 feet. The pay streak 
under present systems of mining is from \\ to 4 feet in thickness. 
