The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1913-09-25

downthrow on the south. Between
wallace and Muilan the rocks on the
south side OF the Osbusn fault belong
chiefly to the Newland formation,
while those on the north side are
quartzite Of the Burke formation and
Revett quartxite. The areal relations
along the old valley indicate a throw
OF the same order Of magnitude; the
rocks ON the south belong 10 the 81.
Regis formation, and those on the
north are aacribed to the Burke and
Revert. This is the main evidence of
the fault. but II Is corroborated by
abundant evidence that the old valley
comedies with zone Of fracture. Brec-
elias abound on the slope to the north
and every prospect exhibits remark
able amount Of shattering in the coun-
try rocks. The poor exposures In the
deeply decayed rocks on the floor II
the trench make 1t difficult to follow
the line Of the fault precisely, but the
main fracture Is apparently north Of
Meadow mountain and the knobs
aligned with It.
The course Of this great fracture,
which may, without serious risk Of err
ror, be called, as a whole, the Osburn
fault, Is convenient line of reference
In characterizing briefly the other
structural features Of the region, which
are by no means thoroughly worked
out.
The structure Is simpler south Of the
fOsburn fault than north Of It. The
largest structural feature of the south
ern area is an anticline. well shown by
the map southwest Of Mullan. This fold
becomes indistinct to the east, but
there IL some phcation along the gen.
Ieral line Of Its axis as far as the l9ngi-
tude Of Saltese. The area between the
Bitter Root divide and st. Regis river
lis occupied chiefly by the southwest
flank Of this anticline, and here south
westerly dips are remarkably persist
ent. Farther south there is rather COM
pick folding, some Of which is clearly
expressed by the sinuous trace Of the
Wishards sill.
In the area mapped south Of the Os-
burn fault few conspicuous faults have
been found except at the extreme west,
and the only important fault newly
mapped in 1912 is that designated the
Roland fault. This causes large dis
placement Of the folded Wishards sill
near Roland and is probably the same
fault that displaces the sill abut zoo
feet In the divide. Brecciation. saddles
In the spurs, and sharp disturbances OF
dip in the srata mark the line connect
ing the points at which the fault GUS
the sill. The Roland fault might have
failed Of detection, however had 1t not
lbeen for It's clear effect on the diabase
intrusion, and there are indications OF
other faults which may be consider
liable. although the evidence Of them IS
not very tangible. A few Of the more
tdistinct lines Of fracture lying in the
lNewland formation are shown on the
map, An Indication Of faulting, which
there was no opportunity to trace far
Their, Is afforded by the strong Jog III
1.-The st. Regis Newland boundary
northwest Of Taft.
The structure north OF the Osburn
fault Is characterized near and west
of Mullan by very complex faulting'
which is not fully represented IN the
Imam. The fractures r1c51 IN strike
from east-west to north south. NJ
folds can be traced here for any con-
siderable distance. The structure along
the old valley Is Of the same general
character, but the slight variations in
the prevailing quartzitic country rocks
and the poor exposures make 1t very
difficult to work out structural details.
The quartzitic zone is thanked on the
north by an area Of the Newland for
mation. in which there Is an eastward
pitching syncline.
Orc peposits--General Features and
Grouping.
| The ore deposits of the northern
part Of the zone described in this re-
port are chiefly valuable for lead and
silver, and the poential value Of the
prospects in the southern part depends
mainly on their copper content. M
sharp division can be made, however,
between silver-lead belt and a cop
per belt, for copper deposits. typified
by that of the Snowstorm mine, north
east Of Mullan. occur in the northern
part Of the area and there are at least
two lead prospects in the southern
copper belt. The prevailing form Of
the deposits Is that of assure veins,
mostly trending east-west to north
west southeast; but in this respect
Iagain the copper deposits Of the Snow
storm type are exceptions, for their
minerals are finely disseminated in the
lcountry rock. The prevailing gangn2
mineral throughout the region is sid
jerite, the Snowstorm deposits once
more furnishing the most conspicuous
exception to the rule In view Of
these diversities and others, 1t is con-
|yenicnt to recognize the following
lmore or less distinct subdivisions OF
the region.
! 1. The area Of silver, lead and zinc
deposits north Of the river near Null
llan--the Mullan area.
2. The area Of silver, lead and zinc
ideposits along the old valley In Mon