Crystallization, alteration, and ore-forming processes, of iron oxide apatite (IOA) ores and related host rocks in the Atacama Desert of northern Chile

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The overarching objective of my research program for the next five years is to gain a better understanding of the geologic processes that lead to the formation of what are commonly referred to as economic grade iron oxide apatite (IOA) deposits. This includes the initial emplacement and crystallization, the subsequent metasomatic alteration of the host rocks, the mineralization, and any post mineralization alteration. These deposits are a major source of iron from many well-known localities around the world. There are at least two major unresolved issues with our current understanding of IOA deposits. ******The first is how do these deposits form in nature? Are they magmatic, hydrothermal, or do they form along a continuum between those two end-member geologic processes? Related to that, what is the relationship(s) if any between IOA, so-called iron oxide copper gold (IOCG), and Cu porphyry deposits? Why are IOA deposits devoid of economic concentrations of Cu and Au? Are Cu-porphyry deposits similar to IOA deposits but form at a different level in the crust with IOCG deposits forming somewhere in between? Cu porphyry deposits and IOA and IOCG deposits share some common properties with Cu-porphyries including their association with calc-alkaline to mildly alkaline magmatism but there are also some distinct differences including IOA and deposits being magnetite rich and S poor? ******The Atacama Desert region of northern Chile is an ideal field area for studying these kinds of deposits and for training students in a geologically interesting and relevant locality. The exposure is excellent and the access to the mines where the samples are to be collected has already been arranged. This research program will be carried out on a selected group of deposits of the Chilean Central Andes in two areas. In the first, IOCG and IOA deposits are clustered in a narrow belt approximately 1000 km long of Late Jurassic-Early Cretaceous age, in the Coastal Cordillera, related to the Atacama Fault System. The project also will include - due to its special importance - the Holocene deposits of the High Andes, and in particular the El Laco deposit and minor nearby prospects that likely represent the shallow equivalent of the Mesozoic belt. ******The trace element, tracer isotope, and geochronology of selected minerals and melt inclusions, and whole rock samples will be investigated using a variety of in situ and bulk sample analytical methods to address the unresolved issues above. These include trace elements in apatite, zircon, magnetite, and melt inclusions, Nd-Sm isotopes in apatite, Lu-Hf and O isotopes in zircon, and Pb-Pb isotopes in melt inclusions, to gain a better understanding of the source region of the magnetite ores. Uranium-Pb geochronology of zircon, and 40Ar/39Ar geochronology of sanidine feldspar will also be used to constrain the timing of the emplacement of the host rocks, the later hydrothermal alteration, and the Fe mineralization. **