MINERALOGY AND GEOCHEMISTRY OF THE HONEYCOMB HILLS RHYOLITE, JUAB COUNTY, UTAH

The Honeycomb Hills, a 4.7 Ma topaz rhyolite complex of west-central Utah, are composed of two different sequences, a pyroclastic sequence in which the eruptive phase resulted in the formation of welded tuffs composed of ash and breccia and an upper rhyolite sequence that is characterized by flow banding. The rhyolite has extensive honeycomb weathering. The Honeycomb Hills complex is very intriguing. It has been described as eruptive pegmatite magma (Gongdon and Nash, 1988, 1991), has been explored for beryllium, Rare Earths, and uranium deposits, and is now being explored for specialty minerals (rare earths, lithium, beryllium, and rubidium). Samples were collected in 2011 and 2012 on experiential learning field trips by mineralogy students from the University of West Georgia.

Our ongoing research includes the production of many thin sections for analysis under a petrographic microscope in search of zoning and inclusions as well as with a scanning electron microscope (SEM) to produce elemental maps of major elements and the rare earth elements (REE) present in the samples. Samples that have been studied with the SEM indicate elemental values consistent with the presence of quartz, several compositions of feldspars, topaz, fluorite, ilmenite, and possibly amphibole in the groundmass. One notable line traverse of a sample with a possible amphibole crystal indicates some compositional zoning with high iron content at the rim and a change in the calcium content from core to rim. On the August 2012 recent field trip to Honeycomb Hills, samples were collected from several different locations. At one of the locations visited, there was the presence of amphibole in some of the samples taken. Various other crystals were also collected for analysis as well.