Custer weekly chronicle. [volume] (Custer City, S.D.) 1890-1931, 1909-09-18
RARE METALS.
TIN. Tungsten. and Tantaium Deposits Of
South Dakota-by Frank L. Hess.
From Bulletin No. $50, Contributions to Eco
nOmic Geology, 1908, Part L.



an excellent paper by J. d. irving or
the tungsten deposits at Lead, was pub
lished in 1901. Nothing is known tc
have been published on the Tungsten
deposits of the Southern Black Hills,
but several articles have been written
on the deposits Of Tantalum. Nearly all
the papers on these different deposits,
however, are number Of years old, and
later developments have given several
of the deposits an aspect somewhat diff.
ferent from their apr earance at the time
they we're described. 1t therefore seems
we'll to give brief account of observa-
tions made by the writer during short
reconnaissance trip in September, 1908,
together with such reviews of the his
tory and the literature of the region as
may seem advisable.
All the known deposits of tin, tung-
sten, and tantalum in South Dakota,
occur in the Black Hills, in Lawrence
and Pennington counties, in the south
western part of the State. Although
designated as "hills", these elevations
reach height of 1915 feet in Harvey
Peak, 500 feet above the highest Appa-
lachians Mount Mitchell, 6,7ll feet and
almost thousand feet above the White
Mountains (Mount Washington 6,279
feet. They are about 60 to IS miles
long by so miles wide, the longer axis
lying nearly north and south.
There is considerable diversity of
topography in the different parts of the
area to be considered In the southern
part, near Hill City and Keystone, the
hills exhibit rounded contours with
fairly well graded valleys, the only
jagged or precipitious features where
the harder dikes of pegmatite or coarse
granite have resisted erosion, while the
more easily weathered schists have
worn away.
North of Hill City, in the vicinity of
Lead, the hills are fiat topped at many
places and the valleys are steep-sided
(though not precipitous), narrow, and
deep. The fat tops are given to the
hills by approximately horizontal Ca M
brian sandy dolomites and conglomer-
ates unconformably everything Algonkian
schists which are more easily eroded.
Farther north lies the linton area'
which resembles much of the country
between Hill City and Keystone, though
with a somewhat more marked relief,
and on the east it is adioined by the
great Speartish Canyon, which, were it
on great trunk railroad, would be one
of the well-known scenic features of the
country. The hills are covered with a
fair growth of pine except where it has
been cut off or burned.
GeologicaIly the Black Hills consist of
central mass of granite and metamor-
phic rocks from which dip away on all
sides the concentrically out-cropping
younger rocks of the plains. The gran.
ite is coarse pre-Cambrian pegmatitic
intrusive cutting Algonkian schists
which are exposed from linton to the
region south of Hill City. The schists
are amphibolitic, staurolitic, andalusitic,
and quartzitic, in places containing a
great many small garnets. There are
also imbeded quartzites. The schists
generally stand at high angle and on
their eroded edges rests Cambrian
conglomerate, though in places the con-
glomerate is lacking and an everything
quartzite 10 to % feet thick takes its
place. Above the quartzite are dolo-
mite and shale. These are members of
a series of Cambrian rocks which have
been eroded frcm large part of the
area.
The schists are cut by numerous dikes
of many kinds of igneous rocks. Of
these dikes this paper is most concerned
with the pegmatites, which are particu-
larly numerous in the Hill City, Key
stone and linton areas. A series Of
quartz veins are closely related to the
pegmatites in the Hill City-Keystone
area. With these dikes and veins the
tin and tantalum deposits are insepara-
bly, connected. Tungsten ores are close
ly associated with them, but at Lead are
also found, apparently with other rela-
tions. From place to place there is
considerable difference in both the
physical structure and the mineralogical
composition of the pegmatltes, especially
as concerns the accessory minerals. This
is particularly true in the Southern
Hills.
The deposits of tin, tungsten and tan
talum are closely connected, both geo.
graphically and genetically, and though
workable deposits carrying more than
one of these minerals haye not yet been
proved, this is not out of the range of
possibility.
Tin deposits occur in the Northern
Black Hills at linton, and in the South
ern Black Hills near Hill City, Key.
stone, Oreville and Custer.
Tuogsten, in the form of Wolframite,
has been found sparingly at linton;
in greater quantity at Lead, in the Gen.
trail Hills; and at many places near Hill
City. Scheelite has been found only
occasionally and in small quantity.
Tantalum, in tantalite and columbite,
has been found to very small extent
near linton and in considerable GUAM
tity near Keystone, whence there has
been some output.
Tin was first discovered in the Black
Hills in 1876, when Richard Pierce, of
Denver, recognized cassiterite in placer
gold from the northern part of the Hills,