Fe-oxide(-Cu-Au-REE)-rich hydrothermal systems have been of economic importance for centuries, and enigmatic in their origin for nearly as long. Recent work, stimulated by the discovery of the giant Olympic Dam deposit in Australia, has focused on three possible origins: (1) these deposits are fundamentally magmatic, formed by an immiscible oxide-rich melt separated from geochemically distinctive magmas; (2) the deposits are hydrothermal, formed from magmatic-sourced brines and can be considered as broadly analogous to porphyry Cu-Mo type deposits, and (3) the deposits are hydrothermal driven by magmatic heat, but generated from distinctive high-salinity surface or near surface, non-magmatic brines. The implications of these hypotheses are significant. Both magmatic hypotheses imply a correlation with particular types of magmatism and tectonic environments. In contrast the non-magmatic fluid hypothesis predicts a correlation with saline surface or ground waters thus a common direct link to the climate. This project builds on earlier work to test the importance of non-magmatic fluids versus the magmatic connection. A combination of field-based geochemical, petrological and theoretical approaches will be used to investigate the sources of fluids, the sources of metals, and the mechanisms whereby the metals may or may not be concentrated in economically significant quantities. Most field and analytical work will be done on U.S. and Mexican occurrences in combination with a global synthesis of Archean to Modern examples. One of the broader implications of this research is that these saline hydrothermal systems may provide direct evidence for ancient arid climates. This could be important where an independent record, for example from sedimentary rocks, is not preserved.
