Custer weekly chronicle. [volume] (Custer City, S.D.) 1890-1931, 1910-09-03

I ped for the first time, all Of the
earlier product having been sold In
the form of sheets. The output IN
1899 was 20,299 lbs. valued at $751;
900. In 1900 the sheet mica output
reached $4,000 lbs, value $4,000,
while the production Of scrap mica
amounted to 222 tons, worth $1,554.
| OF the mica produced in the Unit
ed States during the year 1908,
amounting to 972,264 lbs. of cut
mica, worth $234,021, and 2417
tons of scrap, worth $33.904, South
Dakota produced over one-third, and
the Westinghouse properties were
not worked to full capacity. Dur
ing 1909 the production was ma
terially increased, and the present
year will far outstrip any previous
one. At the present moment 1000
lbs. per week of cut mica, in addi- |
ton to scrap of varying amounts, is
being produced.
Pegmatic dikes in the Archaen
. granite region of the Harvey Peak
|, district are the mica producing de-
posits of the Black Hills. The Har-
ney Peak district is an area OF Arch
aen granite several miles in extent,
rising at one point 7240 it., the
, highest point in the Black Hills, and
, is a region of steep peaks, deep can
2 yons, and rolling mountain prairtes,
, or parks" as they are locally known
+ The primary formation is a mica
schist, occasionally grading into a
garnetiferous schist. The pegma-
4 tite occurs in dikes in this schist
a and the later granite. while these
n dikes are occasionally cut by the
: granite. The exact age Of the pegma-
: tite is a matter of some speculation
q among the geologists who have exam
: lined the deposits. d. B. Sterret says
q l"Whatever the age Of these forma-
, tions, that in which the mica de-
4 posits occur, is composed Of true
gneisses and scists in which the
- MASKING has been extreme and the
- developments Of metamorphic miner
N els extensive"
: The pegmatite occur in dikes of
,s varying thickness a few inches to
80 and 40 IT. being about the ex-
tremes. The deposits are often len
40 ticular, and at the lowest point quite
a. often carry, the highest percentage OF
>. mica. The general trend approx.
. mates north and south with the dir
80 as a rule running from vertical tc
80 southwest. This is in conformity
with the enclosing schists.
=, In addition to mica, these dike'
"a carry a variety Of minerals, among
- which might be mentioned spodu
meme, lepidolite and amblygonite
!, beryl, columbite, cassiterite, tourma
line, etc. In nearly every mine II
the Custer district tourmaline II
found in large crystals and in con
siderable quantities. ]. A. Holme
= mentions this occurrence and con
trasts it with the general scarcenes
of tourmaline in the tin-bearing peg
" matites north of Harvey Peak. H
states that mica Is apparently no
e' found plentifully in commercial siz
w es in the pegmatites in the tin re
gion.
40 AS a rule the best portion Of tn
- mica bearing pegmatite Is along tn
'" walls. In the New York mine, wher
1o' the dixie is 40 #. in thickness, t
GU it. along the walls Is about a.
~ that is worked. From this area tn
III pegmatite extracted carries to
ne per cent mica. In the center Of tn
n9 dixie it is much leaner, probably cal
"s rying less than 10 per cent. Yer
Vi likely the entire dixie would averag
III for the entire 40 #. something lik
DIT 1-2 per cent.
20 AS an instance of the richness G
ne the dikes when they pinch it ma
H. be mentioned that at the mine {
the Electrical Mica Co., near Harne
Peak, where the pegmatite narrow
IA ed to 3 it., in running 25 IT. alon
the vein Is tons of mica was extrac
ed. This particular dixie varies frol
Sc to or to 60 #. in width and hs
ok been traced for 1000 It along II
90, strike.
N distinct
er, being worked by the Westinghous
ite Co. in the Custer district. Two {
vi them are regular producers Of MIC
the New York and Crown, while th
is others are in varying stages of deve
ore opment.
ID" The New York situated mile
O6 southwest of Custer, the largest PR
in ducer of the company, is on a hoi
nd back overlooking Hay creek an
lie. about zoo #. above the water lev
the in the creek.
to The mine at the present time
ty, 315 TT. deep 15 #, Of this depth b.
les ing accounted for in a slump belo
on the 300-ft, station. Starting we
ion of the outcrop of a pegmatite dil
op- ping southwest, the shaft, which
are vertical, cuts through the dixie b
lth tween the 100 and 2O0-ft level
From the SCOTT. level it will be ne
len essary to drift in the neighborhoc
,it- of $50 #. to open the dixie. TIL
i've work is now in progress. There al