The Autunite #8 Prospect

This small but interesting prospect is located on the east side of Topaz Mountain.

There was an abundance of Radioactive Opal, which upon later inspection proved to be fluorescent!

A sample under ordinary light...

Under ultraviolet light!

Down into the belly of the beast! (Quicktime Movie 430k-Sound)

An excerpt from:

Uranium-Lead Apparent Agres of Uraniferous Secondary Silica As A Guide For Describing Uranium Mobility

By R.A Zielinski, K.R. Ludwig, and D.A. Lindsey, USGS

Uraniferous opal veinlets 1 cm wide occur in fractures in 38- to 39-m.y.-old rhyolitic ash-flow tuff at the Autunite No. 8 prospect (SW 1/4 sec. 10, T. 13 S., R. 11 W.) in the Thomas Range. The veinlets may have been deposited by hydrothermal activity related to nearby beryllium, fluorspar, and uranium mineralization.

Mineralization in the Thomas Range accompanied or followed topaz rhyolite volcanism that began 21 m.y. ago and ended with extrusion of voluminous flows of topaz rhyolite 6 to 7 m.y. ago. The areas of most intense mineralization occur in water-laid tuff associated with 21-m.y.-old rhyolite at Spor Mountain, but traces of mineralization are present in tuff interbedded with 6- to 7-m.y.-old rhyolites in the Thomas Range.

The opal veinlets in the Autunite No. 8 prospect were dated to obtain additional information concerning the age of mineralization and its relationship to volcanism in the Thomas Range. Fission-track maps (fig. (b) revealed U distribution to be very homogeneous within concentric growth zones (500-l,OOO ppm U). The analyzed opal fragments contained 1,220 ppm uranium and 0.88 ppm lead, and gave nearly concordant apparent ages of 3.5 m.y. The results support the hypothesis that some, and possibly all, of the beryllium-fluorspar-urani um mineralization occurred after the eruption of voluminous topaz rhyolite 6-7 m.y. ago.

Bell Hill Mine

This is the entrance to the adit.

Looking down one of the shafts.

A nice fluorite specimen.

This photo was taken at a fluorite mine directly
to the north of the Bell Hill Mine.


Byron J. Sharp
U. S. Atomic Energy Commission
From "Guidebook To The Geology of Utah" Number 17, 1963

The fluorite pipes of Spor Mountain contain variable quantities titles of uranium associated with the fluorite. These pipes are described in detail by M. H. Staatz and F. W. Osterwald in USGS Bulletin 1069. The U. S. Atomic Energy Commission sampled many of the pipes for uranium and the results indicated that some of the fluorite contained nearly commercial quantities of uranium. Yellow secondary minerals occur locally in the fluorite, but for the most part, the uranium ion apparently substitutes for the calcium ion in the crystal lattice of the fluorite. Although this intimate association renders the uranium non-amenable in existing uranium mills, it may be possible to extract some as a byproduct in a hydrofluoric acid mill.

The fluorite pipes at the southern end of Spor Mountain contain about 4 times as much uranium as those at the north end and those in between show a general gradational increase in a southern direction

The Bell Hill pipe is the most significant fluorite pipe as far as uranium is concerned. Near commercial grade uranium samples have been taken from the lowest levels of the pipe, as well as near surface from many places in between. The Bell Hill pipe is considered to be near the center of a high uranium zone in fluorite, and pipes which may be discovered in this area would probably be high in uranium content.

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