PETROGENESIS AND HYDROTHERMAL ALTERATION OF AN EVOLVED RHYOLITE, THE BLAWN FORMATION, SOUTHERN WAH WAH MOUNTAINS, UTAH
Some critical element-bearing mineral phases within the Blawn Fm. are anhedral, porous, and present in the groundmass or in pores within the rhyolite, whereas others are euhedral and typically present as inclusions within phenocrysts. These variations in crystal texture and mineral associations indicate different primary igneous and secondary hydrothermal mineral assemblages. Alteration indices as a proxy for hydrothermal alteration indicate that alteration and secondary mineralization did not affect trace element concentrations (REE, Nb, Ta, Y, etc.) of the rocks, neither upgrading nor degrading them beyond the concentrations established during igneous processes. However, the change in mineralogy and porosity during alteration may have concentrated these elements into smaller volumes of secondary minerals that are more easily processable during potential mining and extraction. This study indicates that although concentrations of elements of interest, such as the REE, Nb, Ta, Y, and others, may not increase during the alteration of A-type rhyolites, this alteration may significantly increase the economic potential of these units by increasing leachability and processability of the altered units.