The Shirley May (Garo) uranium deposit near Garo, Park County, Colo., consists of tyuyamunite
and carnotite that occur as disseminations and as fracture fillings in three beds of medium- to coarse-grained
sandstone. The sandstones are in the Maroon formation of Permian age. This deposit was explored by means
of 12 core-drill holes, totalling 2,003 feet.
The deposit is on the northeast flank of the Garo anticline, a local structure that probably is related
to Tertiary tectonic movement. In the vicinity of the deposit the sedimentary rocks strike northwest and
dip steeply. They are cut by numerous northerly-trending faults that have horizontal displacements of as
much as 1,000 feet. The ore minerals tyuyamunite, carnotite, volborthite, calciovolborthite, malachite,
azurite, chalcocite(?) , and an unidentified yellow to dark-red vanadium oxide are restricted to a complexly
faulted area. The ore body that has yielded most of the uranium ore is in the uppermost ore-bearing sandstone
(bed no. 1) and is stratigraphically 50 and 150 feet above the ore horizons in sandstones nos. 2 and 3,
respectively.
The uranium content of samples from the mine workings ranges from 0. 001 to 0. 48 percent uranium;
dump samples contain as much as 2.39 percent uranium. A total of 40 tons of uranium ore, averaging 1.0
percent uranium, was produced in 1919.
