Abstract

Beryllium mineralization near Spor Mountain, Utah, has been the subject of intensive investigation for the past 25 years.

The beryllium district is on the west and southwest slopes of Spor Mountain. Five open-pit mines have supplied mill feed for approximately 15 years to a processing plant near Delta, Utah, owned by Brush Wellman, Inc. Bertrandite, a hydrous beryllium silicate (Be₄Si₂O₇(OH)₂) is the principal ore mined.

Spor Mountain is made up chiefly of westward-tilted and intricately faulted Paleozoic sedimentary rocks which are locally intruded by volcanic rocks of Tertiary age. Tertiary volcanic rocks are divided into four parts, each underlain by an angular unconformity.

Beryllium mineralization is limited to the tuff member of the Spor Mountain Formation. The beryllium tuff north of the Roadside Mine interfingers with the porphyritic rhyolite member of the Spor Mountain Formation. Vertically there are up to three beryllium ore zones in the tuff because of cyclic deposition.

The beryllium tuff deposits on the southwest slopes of Spor Mountain have been partially altered by hydrothermal (epithermal) fluids to a fine-grained mixture of clay, potassium feldspar, silica minerals, and fluorite. The beryllium tuff deposits contain sizable but uneconomical concentrations of fluorite, lithium (smectite), manganese oxides, manganese carbonates, zinc, and uranium as well as many trace elements. Distinctive zones of argillic and feldspathic alteration enclose the beryllium deposits.

The beryllium deposits are submicroscopic, disseminated in the tuff and concentrated in fluorite nodules. The relationship of topaz-bearing rhyolite flows in the Thomas Range to mineralized tuff established that some or perhaps all of the beryllium and uranium mineralization are younger than 6 m.y. (Lindsey 1977).

There are several million tons of bertrandite ore that will average 0.60 percent to 0.70 percent BeO. Ore thickness will vary from 0 to 60 ft (18 m).

Exploration by Brush Wellman in the Spor Mountain–Fish Springs Range area has discovered the presence of a ring structure. One can postulate that the ring structure is an incipient caldera formed by the collapse of a magma chamber from which the volcanics of the area were ejected.

The techniques used for mining beryllium-bearing ore from Brush Wellman properties in western Utah are considered unique. They are unique because of the requirements that must be met to identify the ore body and the rock materials overlying the ore.

The beryllium mineralization contained within the tuff member produces no visible physical characteristics which would help one identify the presence of mineralization. The beryllium mineralization is colorless and its crystal structure is too small for recognition by the naked eye.

A detailed mining operation is used by Brush Wellman having several procedures to follow in survey control, use of cross sections, structure contour maps, and field berylometer. The beryllium ore is mined from selected or predetermined areas of the ore body, placed in the stockpile in layers as blocks on top of each other. This method is successful in producing a homogeneous blend acceptable as mill feed.