Reconnaissance of Iron Occurrences in Colorado Page: 16
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16
Gulch. Surface rights belong to George E. Everett and mineral rights to the
Calcium Co., both of Salida. The mine is extensively developed underground
by shafts, inclines, and adits, but all the workings, except two opencuts,
are inaccessible (fig. 3). Early-day mining was done by square-set stoping,
which was changed later to the less selective system of open-stope mining.
During the 1890's an unsuccessful attempt was made to free the ore of sulfur
by roasting. Exploration in 1905 indicated that the remaining ore was high
in sulfur.
Magnetite, with some hematite, limonite, pyrite, chalcopyrite, azurite,
and malachite, occurs as a contact-metamorphic, replacement-type deposit on
or near the contact between white to gray Mississippian limestone and Tertiary
intrusives. The gangue minerals include calcite, diopside, epidote, garnet,
biotite, apatite, tremolite, and actinolite. The magnetite replaces a defi-
nite series of beds in the limestone. The ore body is reported to be 40 to
50 feet thick and about 500 feet wide and has been traced about 1,800 feet
downdip. The magnetite occurs mainly as bands parallel to the bedding, a
fraction of an inch to 2 feet thick and separated by light-green silicated
limestone. A section of the ore body exposed in a large opencut (fig. 3)
was measured as follows:
TABLE 4. - Measured section Calumet-Hecla-Smithville
magnetite ore body (feet)
Hanging wall, dip 38o-45 - bleached and siliceous limestone.
Brown layer of silicates and garnet.......................... 2.5
Brown massive beds with layers of magnetite up to 2 inches
thick........................................ ... 7.5
Altered greenish limestone with diopside and small stringers
of magnetite.......................................... ... 5.0
Solid magnetite........................... .................. 1.0
Barren layer of silicates....................................... .5
Solid magnetite .................. ............. 1.0
Layered or banded magnetite, epidote, and diopside........... 4.5
Solid-magnetite.............................................. 2.0
Foot wall - bleached and siliceous limestone.
Total thickness of exposed magnetite deposit............ 24.0
The enclosing limestone trends northeasterly through section 35 and
northwesterly through sections 26 and 27 and dips 40" to 60 northwesterly.
The ore first mined was very pure and contained up to 60 percent iron.
As mining proceeded, the grade of the ore gradually decreased, and the sul-
fur (pyrite) content increased. The ore last mined contained 43 percent
iron. The following analyses were obtained from various sources:
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Harrer, C. M. & Tesch, W. J., Jr. Reconnaissance of Iron Occurrences in Colorado, report, 1959; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc170710/m1/28/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.