AN ALUMINOPHOSPHATE MINERAL ASSEMBLAGE IN THE CENTRAL MOJAVE DESERT, CA

A suite of rock samples from the Soda Mountains, Mojave Desert, CA contains an unusual aluminophosphate rich mineral assemblage including an enrichment in Sr and Ti. Understanding these rocks is important because they contain rare elements that are critical to the future of clean energy. In order to understand the processes responsible for these samples we utilized optical microscopy and SEM-EDS to study two samples.

Sample 1 (BB-RA3-1A), contains major sillmanite and quartz (90%), with minor rutile (5%), scorzalite, zircon, monazite, barite, svanbergite; two additional aluminophosphates were tentatively identified as trolleite and matulaite. Svanbergite and barite occur in the contact between silicate and phosphate minerals and appear to be texturally later. Sample 2 (BB-RA3-4A), contains major lazulite (80%), muscovite (5%), Fe-Ti oxide (5%), and minor xenotime defining the first stage of mineral growth. In sample 2, second stage minerals formed along grain boundaries and cracks, including minor quartz, svanbergite, woodhouseite, apatite, rutile, topaz, barite, and crandalite; A third textural stage of mineral growth in sample 2, includes apatite, berlinite, whiteite, and additional rutile.

The mineral assemblage implies that the bulk composition is rich in Fe, Ti, Al, and P in sample 1, and Fe, Ti, Al, P, and Mg in sample 2. Enrichment in these elements appears to have occurred early in the sample’s formation process. The texturally first alteration enriched the samples in Ca, Ba, S, and Sr, and is interpreted to be hydrothermal. The texturally second stage is also interpreted as hydrothermal but did not result in significant element enrichment. Understanding the element enrichment processes in these samples could help future exploration for critical elements.