The Salt Lake herald. [volume] (Salt Lake City [Utah]) 1870-1909, 1908-08-03
IRON ORES IN
SOUTHERN UTAH
Geological Survey Experts
Describe Tremendous DepoS-
its of Iron Springs District.

Washington, Aug. 1.-The rapidly in
creasing cons Imption of iron ore in the
United States during the last few years
has led to careful investigation of all
available supplies. both in producing dis
tricts and in relatively unknown fields
with the result of emphasizing the linn
itation of the deposits now worked and of
pointing out the need for the early eX-
ploitation of new ones. At present less
than per cent of the iron ore mined an
nually comes from the region west of the
Mississippi. where large deposits have not
been worked because of lack of transpor-
tation facilities or distance from centers
of consumption. These deposits are now
becoming of steadily increasing import
ance.
One such deposit. in Iron county, south
ern Utah, in what is now known as the
Iron Springs district, is described in
bulletin (No. 33S) by c. K. Leith and Z.
c. Harder just published by the United
States geological survey. The region has
been explored by about 800 pits, but as
the deepest pit was carried down only $50
feet, the vertical extent of the ores Is not
known. Their total area is ). 10000 square
feet, and their total tonnage, so far as
can be measured by the areas and pits
explored is 100000 tons. Probably this
estimate is much too small, as the ores
doubtless continue for some distance be-
low the depths Indicated by the deepest
twenty-five miles distant.
The Iron Springs district was selected
for examination. because the deposits are
large and well located for study. and the
ores are typical OF many Others in the
west. and are of such quality that their
commercial development seems likely
within short time.
The ores occur in disconnected masses
within a general area that is one and one
half by twenty miles in extent. most of
them at or near the contact of the coun-
try rock. with certain igneous rocks
known dndeSiteS.
These were long ago forced up from the
earth's interior against or partly into a
great bed of limestone. The force was not
great enough to break through the lime
stone. however. and the molten rock
spread out, prying its way between the
limestone and the underlying bed
and forming what are known to biologists
as laccoiths or sills. The force and heat
of the intrusion and the later shrinkage,
consequent on cooling fractured and fis-
sured both the andesite and the limestone.
Hot ore-bearing solutions rose through
the assures filling them with iron ores
and other minerals, which were deposited
as fissure veins everything limestone.
Finally erosion wore away the rock and
exposed the laccOliths and the ores.
In the opinion of the authors the ores
in the andesite may extend downward TO
very considerable depths. the exact dis
lance being determined by the depths of
the assures in which they were deposited.
The depth of the replacement deposits in
the limestone depend on the depths to
which the andesite-limestone contacts eX-
tend The only one of the laccolths
whose thickness can be even estima ted
with the present information probahl
does not extend further down than 900
feet
The uniform associatio of ore with lac
coliths in this and many other western
iron districts outlines the first rule for the
prospector who is searching for SUCH ores
to find the laccOliths and determine their
boundaries. This is easily done, for as
the laccOliths are harder than any of the
other rocks Of the region they stand out
above il conspicuously. The contact with
the sedimentary rocks should be carefully
explored In places the ores stand out IL
great black ridges but elsewhere they are
concealed beneath the debris that has slid
down the mountain sides.