GEOCHEMICAL INVESTIGATION OF THE IRON SPRINGS DISTRICT

The Iron Springs District in Southern Utah hosts the second largest iron deposit in the United States. The main ore mineral is magnetite and it is unique for its large apatite inclusions. The district’s main mechanism of formation has yet to be identified despite its large size and economic importance. However, the presence of apatite suggests that the region was formed either from magmatic hydrothermal fluids or through silicate melt-oxide rich immiscibility. Geochemical microanalyses of the apatite and fluid inclusions has been used to determine which mechanism was the dominant system during crystallization. Thin sections were made in order to study the petrography of the samples and subsequent electron probe microanalyses (EPMA) were conducted in order to determine the bulk and trace chemical composition of the apatite and magnetite. Primary inclusions, which became trapped during formation, and secondary inclusions, which were formed from fracture lines, were both observed within samples. Additionally, primary inclusions were found to have multiple phases of development. The general fluid inclusion composition and minimum trapping temperature was determined using a USGS Fluid Inc. heating-freezing stage. Using the collected data, the formational environment and fluid inclusion geochemistry of the Iron Springs District has been determined.