Custer weekly chronicle. [volume] (Custer City, S.D.) 1890-1931, 1910-08-20
MICA I'm THE BLACK HILLS
OF SOUTH DAKOTA.

: After two score years ofquiescence the
mica industry of the Black Hills was re-
vived four years ago, when the Westing
! house Electric & Manufacturing Co. tool
over, under purchase, the New York
White Spar and other properties in the
vicinity of Custer.
II Perhaps in this case revived" is moi
the proper word butto be more accurate
the term Established" should be used
for prior to 1905 the mining of mica wat
conducted in desultory, haphazard
manner, and was not considered profit
. able. Through shortage of supply, the
Westinghouse Co. was forced to seek
on its own responsibility, and since pur.
chasing the properties mentioned, has
gradually and consistently brought up
the production and carried forward the
development work, until its mines alone
are sufficient producers to place South
Dakota in the first rank.
In 1879 the Crown known then as the
McMackin) mine, was exploited as q
mica prospect, and for five years was
worked to some purpose. During that
time the production amounted to 46, 000
lbs. of cut mica, worth an average of So
a pound. The New York, Lost Bonanza
and Climax were opened little later,
producing in four years total of 1885,
600 worth of cut mica. Other mines
were producers to nearly as great extent
This work, all done previous to the ad-
vent of railroads, at time when it was
necessary to haul the mica by wagon 200
and more miles to railroad, resulted in
some profit to the operators.
With the output of 1884 most of the
mines practically ceased working, the
work during subsequent years until 1893
consisting of scarcely more than such
development work as is necessary to
hold claims. During 1900 scrap mica
was shipped 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 $4,000. In 1900
the sheet mica output reached $4,000
lbs, value $45, 900, while the production
of scrap mica amounted to 222 tons,
worth 1854.
Of the mica produced in the United
States during the year 1908, amounting
to 972,264 lbs. of cut mica worth 1924, ,O2l
and 24l7 tons of scrap worth $4,000
South Dakota produced over one-third.
This was the year following the panic,
and the Westinghouse properties were
not worked to full capacity. During
1909 the production was materially in
creased, and the present year will far
outstrip any previous one. At the pres
ent moment the New York mine alone
is producing 1000 lbs. per week of cut
mica, in addition to scrap of varying
amounts.
Pegmatite dikes in the Archasn gran
ite region of the Harney Peak district
are the mica producing deposits of the
Black Hills. The Harney Peak district
is an area Of Archaen granite several
miles in extent. rising at one point 724O
it,, the highest point in the Black Hills,
and is region of steep peaks, deep can
yons and rolling mountain prairies, or
parks" as they are locally known.
The primary formation is mica schist
occasionally grading into garnetiferous
schist. The pegmatite occurs in dikes
in this schist, and the later granite,
while these dikes are occasionally cut
by the granite. The exact age of the
pegmatite is matter of some specula-
ton among the geologists who have ex-
amined the deposits. d. B. Sterret says:
whatever the age of these formations,
| that in which
the mica deposits occur, is composed OF
true gneisses and schists in which the
MASKING has been extreme and the de-
velopment of ofmetamorphic minerals ex-
tensive."
The pegmatite occurs in dikes of vary
ing thickness, few inches to 80 and 40
#. being the extremes. The deposits
are often lenticular, and at the lowest
point quite often carry the highest per-
centage of mica. The general trend ap-
proximates north and south, with the
dip as rule running from vertical to
southwest. This is in conformity with
the enclosing schists.
In addition to mica, these dikes carry
a variety of minerals, among which
might be mentioned spodumene, lepi.
dolite and amblygonite, beryl, columbite
cassiterite, tourmalins, etc. In nearly
every mine in the Custer district tour
maline is found in large crystals and in
considerable quantity. j. A. Holmes
mentions this occurrence and contrasts il
with the general scarceness of tourma-
line in the tin-bearing pegmatites north
of Harvey Peak. He states that mica
is apparently not found plentifully in
commercial sizes in the pegmatites o.
the tin region.
AS rule the portion of the mica
bearing pegmatite dixie is along the walls
In the New York mine, where the dixie
is 40 it. in thickness, 8 to #. along tht
wall is about all that is worked. From
this area the pegmatite extracted carrie.
6 or per cent mica. In the center o
the dixie it is much leaner, probabl,
carrying less than 10 per cent. Yer,
likely the entire dixie would average fo
the entire 40 #. something like 24 pc
cent.
As an instance of the richness of th,
dikes when they pinch, it may be men
toned that at the mine of the Electrica