| Summary: | Minerals are a key constituent of ore deposits that are the source of metals and non-metals required for our global society to function. In this dissertation, I use field and laboratory methods to understand the processes that lead to the formation of iron oxide - apatite deposits — an important source of iron — and as a tool for discovering new ore deposits. The analytical methods used include backscattered electron (BSE) imaging, cathodoluminescence (CL) imaging, and energy dispersive X-ray spectroscopy (EDS) element mapping, as well as electron probe micro-analysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Chapter 2 describes an investigation of the chemistry of apatite from the Los Colorados iron - oxide apatite deposit, in Chile, that tested existing ore genesis hypotheses. My work indicates that apatite grains in the deposit contain distinct domains with chemistries that show statistically significant differences. The major, minor, and trace element chemistry of the apatite grains are consistent with growth from silicate melt and magmatic-hydrothermal fluid. The data are supportive of ore formation via magmatic/magmatic-hydrothermal fluids, according to a new model developed at the University of Michigan. In Chapter 3, I investigated the chemistry of magnetite and apatite from outcrop and drill core samples from five of the seven ore bodies at the El Laco iron - oxide apatite deposit, in Chile. Magnetite grains in the deepest samples have chemistries and textures consistent with growth of magnetite from a silicate melt, whereas the chemistries and textures of magnetite from the shallow samples and outcrops indicate growth of magnetite from magmatic-hydrothermal fluid. Apatite grains have major, minor, and trace element chemistry consistent with growth from a silicate melt or a magmatic-hydrothermal fluid. Magnetite and apatite grains contain mineral inclusions that preserve evidence for re-equilibration with hydrothermal fluids. Together, the data suggest that the ...
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