The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1915-02-04
Copper Beds of the Occur dAlene
District

District


Occur dAlenes have been the object
of my study over period of seven
years. The areal geology was covered
for seven miles in length by one mile
wide. observations were made UNI
derground all over the area to the ex-
tent of $4,000 feet of tunnel, shaft and
open cut work.
Mullan and Larson are the nearest
towns to these beds. from which Is de-
rived the copper ore Of the SnoWstorm
and National mines. A large amount
of development Is In progress along
their strikes with fair chance of
bringing In more producers. The COM
inercially mineralized beds consist OF
highly sillcious pref ambrian quartz
les occurring In what Is known as the
Granite peak syncline, situated in the
east central portion of the Occur
d'Alene region. The syncline course or
trend is nearly north-south for slight
Nv more than half of tne distance, af-
ter which it swings or swerves to
more east-west course. The upper
half Of the area north of Canyon creek
is of minor Importance. From this
stream south and east, a distance OF
about $4,000 feet, the trend may be
divided into two divisions according to
the strike, the north division for a.
500 feet and the south division for the
same distance. The former stretches
from a point just above the upper
workings of the National mine to the
workings of the Great Western group
lon Canyon creek. The south runs
east south from this point to the No
3 adit level of the Snowstorm mine
The Granite peak syncline Is one Of
the most plainly marked structural
features of the region. 1t Is traceable
seven miles and probably reaches a
greater distance. The trough is filled
with sedlmentary rocks of the usual
Occur d'Alene series, in age downward
namely, the Wallace, ST. Regis and
Revett formations. 1t contains no
visible igneous rocks. Side pressure
against the limbs has fractured a
plane line down about the center Of
the trend on a scale sufficient to pro-
duce MASKING and faulting with an
overturn effect on the vest limb, The
pitch is south and the syncline is un-
symmetrical.
At the junction of the two divisions
the syncline swerves more to the east
the pressure effects being found ir
rocks of both limbs, agreeing with the
strike. The wrenching effect has open
ed assures across the brittle beds OF
the east limb, which are quartz filled
These show copper and galena in the
immediate neighborhood of the i'm
pregnated beds, but the naturalization
quickly dies out with distance and tht
assures themselves fade away intc
branching velnlets They are of NJ
commercial value.
Revett Formation.
Each formation, the Wallace, st
Regis and Revett, contains a group o
beds containing copper, but the frs
two are not profitable for reasons t
be named. The Revett contains ;
group of beds from 20 to 60 feet II
thickness. impregnated with cope
sufficient to make pay ore at inter
walls. These beds lie in the first or tol
$50 feet OF the formation. and THU
holds good over the entire area. Th'
transition from st. Regis to Revett il
somewhat indeterminate, but recogni
tion is possible within so feet. S,
plainly defined Is the trend that al
experienced observer can follow it OF
the surface, in it's sinuosities and fault
ing, for the length of seven miles
knowing the position within convenien
prospecting distance at any point.
The west limb of the syncline i
practically barren, the east limb hold
the copper beds, and these terminate
on the dip into the center plane o
fracturing and faulting. The faultinl
as noted, follows about the center lin
Of the trough, the Sonora fault on tn
Canyon creek slope connecting through
with the Snowstorm fault on the Mul
Ian side. There is minor faulting tina
may influence the ore beds, between
them and the Sonora fault. The plan
line OF the fault agrees with the cours
of the syncline. Looking from tn
lower end of the south division to tn
upper end of the north. the faults o
horizontal throw are right hand faults
The swing change In strike governs tn
throw direction, fact useful to tn
operator in finding lost copper beds.
Lateral pressure over restricte,
area on the southeast end of the soutl
division has elevated the syncline bot
tom, folding ST. Regis strata agains
the Revett ore beds This is seen Of
the No. 3 level of the Snowstorm mine
1t cuts the ore strata of at about 470
feet above sea level. The pressure eff
feet dies out to the west. giving in
creased strata length with distanc
before reaching the fault again. !
slight elevation apparently took plac,
around the National mine near tn,
strike change, and the ore beds enricl
to the commercial stage again. al
though the difference allows the or,