AN INVESTIGATION INTO METAL-RICH TOPAZ CRYSTALS WITHIN THE TOPAZ MOUNTAIN RHYOLITE FORMATION IN JUAB COUNTY, UTAH

Large and abundant euhedral topaz crystals, ranging from a few millimeters to several centimeters in length, and appearing either partially or completely black in color, have been observed at a localized site in Juab County, Utah, and exploited for their value as gemstones. The topaz crystals are localized along a fault that cuts through the Topaz Mountain Rhyolite Formation, which has been dated to approximately 8 Ma. This area has undergone a complex history starting with rhyolite dome volcanic eruptions, as well as hydrothermal alteration and hydrologic events related to glaciation and deglaciation. Initial geochemical data organized by the claim owner and fulfilled by several third parties indicated a concentration of many economically valuable metals, including tungsten, titanium, gold, and a variety of REE’s. Further tests at Western Carolina University verified the presence of tungsten, titanium, and yttrium via handheld XRF. An examination of thin sections revealed that the dark color was caused by abundant inclusions, which appear to represent a wide diversity of mineral species. Additionally, several episodes of topaz crystal growth can be inferred based on zonation of the crystals and inclusions. Hand samples reveal evidence for hydrothermal metasomatism of the host rock, and the presence of secondary carbonate minerals. The goal of this project is to evaluate the various materials, including the topaz and host rock, to determine the properties of the ore minerals within them. This will be accomplished by using a combination of data obtained using scanning electron microscopy, micro-XRF analysis, and ICP-MS analysis of REE’s. Further goals may include examining the feasibility of using the black topaz as an indicator mineral for ores, and the possibility of using similar inclusion rich topaz as a source for critical minerals.