Custer chronicle. [volume] (Custer City, Black Hills, D.T. [S.D.]) 1880-1890, 1885-11-28
The Mines Around Custer.
Continued from our last.
THE TIN MOUNTAIN BELT.

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about six miles west of Custer City, on
the southern slope Of the high divide
south Of French creek, and are directly
drained by Warren gulch and several
lesser gulches tributary to Warren.
These gulches all run in a northerly
direction leaving ridges between that
are very high and precipitous. The
country rock is here micaceous slate and
gneissoid granite, partially blended with
the slate in places, containing considers
bic oxide Of iron and other mineral in
mass. The slate being OF sedimentary
origin and the black granite an igneous
intrusion, coming up through the mica
ceous or archaan slate, always running
with and conforming to the grain of the
slate. The upheaval caused BY this
intrusion Of black granite must have
been at an age very remote. and long
before any system Of veins were formed
We arrive at this conclusion from the
fact that all the veins of quartz, feldspar
and mica schist are found to run through
the slate and the black granite alike
without regard to their contact.
Now, having described the formation
the country rock, We will proceed to
describe the character Of the veins in
which the tin is found, j. e. in this par
ticular locality. We find here the for
nation running northerly and souther-
ly, the gulches and ridges and the strike
of the stratas of slate all conforming and
having the same general inclination or
trend, while across this formation,
across the ridges and gulches runs the
great zone or belt Of veins. which we
here designate as the Tin Mountain belt
1t consists of alternate dykes Of coarse
crystalline granite, We call it granite be-
cause it has all the constituents of gran
lite, to.wit: quartz, feldspar, and mica,
but unlike ordinary granite, these con-
each to have crystalIized separately or
nearly SO. The blending not being OBJ
servable as general thing except
where they come in contact at the sur
face, or are crossed by veins Of quartz
which seem to have caused blowout
at that point, and the upwelling or out
spew has flowed together forming a
coarsely crystalline mass. These blow.
outs only occur where two or more
veins cross each other and is shown
here on such a grand scale as to attain n
vertical height above the level of the
gulch I'VE estimate) $50 feet The tin
occurs in the form Of casiterite through.
out the mass, but it il noticeable that il
Is richest in the quartz and mica schist,
or rather ii is the richest where the
quartz predominates and poorest i'm the
ieldspar. We said the tin occurred in
the form of casitcri,e To those not
familiar with the tenn We will say
casiterite is the crystallixed oxide Of tin.
These crystals are sometimes large and
coarse and sometimes fine, always dark,
nearly black, and are very heavy. The
course crystals in some cases resemble
the crystals Of tournaline with which
they are often associated, much to the
perplexity of the prospector The differ
ence, however, is readily detected by
the practiced eye, the tin stone being
much more dense in grain and almost
twice as heavy. There are other forms or
conditions in which tin is found often
in the form Of powder in cavities in
the rock which apparently were once
occupied by a crystal, the same having
become decomposed and carried in
solution, to again crystallizs lower in the
vein. This powder. and sometimes
grains, is Of various colors, grey, brown,
and white but is nevertheless always an
oxide of tin, the difference in color be-
ing attributed to other mineral with
which in that case it is or has been in
combination.
The main outcrop of the Tin Meun
tain lode proper occurs where it cuts
the formation and crosses the high
ridge that separates the wet and dry
forks Of Warren gulch. And as We have
remarked in a previous article, every.
thing indi Gates the existence Of at least
three veins running parallel through
this mountain, vary .ng in distance from
each other from so to 100 feet, making
this groupe of veins about 800 feet
across from south to north and about 400
feet from east to west, when it is covered
by the two 9ulches before mentioned.
1t is presumable that the veins continue
on right through the country, holding
their easterly and westerly course, but
are here covered bv the loose depris
and soil of the gulches, which has the
appearance of being very deep. The
work of development has thus far been
confined to the west end of the blowout,
where one of these veins has been
opened in three different places. One
at the foot Of the mountain, one about
half way up, and one at the top of the
mountain. In every opening this vein
shows itself to be rich in tin. The
largest excavation is at the foot of the
hill very nearly on q level with the
Lob