OXYGEN ISOTOPE ANALYSIS OF THE IRON SPRINGS DISTRICT, UTAH

This project seeks to determine whether the ore deposit in Iron Springs, Utah is of hydrothermal fluid origin or whether it was the product of an iron oxide-phosphate rich magmatic immiscibility. If it is a hydrothermal fluid, this project will also differentiate whether it is magmatic or meteoric fluid. The Iron Springs District is one of the largest iron ore deposits in the United States and its geologic origin is still a topic of debate. Previous authors have argued for a hydrothermal fluid origin of magmatic-meteoric fluids carrying and precipitating the magnetite and hematite (Mackin, 1965; Barker, 1995). However, the Iron Springs District shares some similarities with Kiruna-type deposits and some authors classify it as such (e.g., Barton, 2013). Kiruna-type deposits are igneous-related and similar in that they are largely composed of magnetite and apatite, but the apatite typically has significantly elevated concentrations of rare earth elements (Frietsch and Perdahl, 1995) compared with average hydrothermal apatite. The apatite from the Iron Springs is significantly enriched in REE and that they are anhydrous (Barker, 1995; Jaeckel et al., 2014; Hughes et al., 2015). The Kiruna-type deposits of Sweden and Chile show little to no evidence for a hydrothermal origin, with this largely based upon their oxygen isotopes; they are often hypothesized to represent melt immiscibility between a silicate melt and an iron oxide-phosphate melt (Nystrom et al., 2008). Recent work by Jaeckel et al. (2014) on the Iron Springs district found no fluid inclusions within the apatite crystals, but found inclusions that were revealed to be melt inclusions based on the failure of freezing experiments on them. This study thus aims at analyzing the oxygen isotopes of the magnetite using mass spectrometry to further constrain the source of the magnetite and eliminate the possibility of a meteoric fluid. These analyses also will help to prove whether this system is actually caused by magmatic immiscibility and that the Iron Springs district should officially be reclassified as a sub-type of Kiruna-type iron deposits.