The daily sentinel., 1912-09-11
MICA IN MESA COUNTY. COLO.
tBy Douglas B. Sterrett)


A deposit of mica was located some
10 to Is years ago in Ladder canyon,
Mesa county, S miles south of Grand
Junction, Colo. The discovery is said
to have been made by Benton Can
non, but the prospect is now held by
S A. Grady, OF. Grand Junction The
locality is at present reached by trail
only, though a road was once made
up the canyon withon a mile of IL.
The trail leaves the Grand junction
road and enters the canyon about a
mile north of the prospect. This part
of Ladder canyon is from 200 to 800
feet deep.
The development consists of q short
tunnel about ] 0 feet long and an open
cut about 20 feet long In the side of
the canyon. The deposit occurs in
u dome of pre-Cambrian rocks ex-
posed In the bottom and lower wallsof
the canyon. Red sandstone. probably
Of Carboniferous age, overlies the
dome and forms the country rock of
the region, even outcropping in the
bottom of the canyon one-third of
mile farther north. Near the mica
prospect the older rocks outcrop to
height of 100 feet in the canyon
walls. They consist of biotite and
muscovite schist and gneiss cut by
pegmatic. The pegmatic is over 200
feet wide in the bottom of the canyon
and IL thinner at the top of the eA-
posure. Apparently IL is at the top OF
an anticline whose axis strikes nearly
east and west. The main anticline
has smaller folds upon 1t and the peg
matte exhibits these irregularities.
The minerals of the pegmatic are Sc
gregated in large masses. The field
spar is chiefly the potassium variety
and has a pinkish or flesh color. 1t
occurs In an irregular mass or streak
over 10 feet thick in the interior of
the pegmatic and grades into ma
terial containing considerable quartz
or with the composition of ordinary
pegmatite. A large segregation OF
massive quartz the thickness of which
is not exposed, lies below the feldspar
mass, and more massive quartz over
lies 1t. A few blocks of translucent
lrose-colored quartz were observed in
the bottom of the canyon, but the
quartz is too pale for use as gem ma
terial. The upper part of the peg
Matte outcrop is concealed by talus
/ from the overlying red sandstone.
The mica occurs principally along
The contact between the feldspar and
quartz masses, where ii forms an al
most continuous streak across the
lace CT the pegmatic outCrop. The
mica streak ranges from | to feet in
| 4 ickness and is composed of nearly
Q masses of mica orystalys. These
ge arm ess than | inch to over L
tri 81 euGth and are mere commonly
r-A ca N TUFTS and radiating
arcups. In places quartz, feldspar,
d hib X -ourmaline are assoc lated
( Iwitl TIE mica. Rosettes of radiated
mica crystals cover the south wall of
te open tut for n space II feet long
~ s feet high. The exposure here
teB an impression of very thick
mica streak but an examination
shows that the cut has opened the
vein" along its wall. The fun thick
ness of the streak OF mica Is not ex-
posed but is probably 8 feet or more.
rhe mica crystals are much ruled
and broken and nearly all have either
the "A, wedge" or 'herrins-bone'
structure. 1t is probable that the en-
tire yield of mica from this deposit
will be suitable for grinding only
and that little If any mica valuable
for cutting into sheets will be obtain
ed, The quantity of scrap mica for
grinding that can be mined near the
surface iS Onsidprahle