This project proposes to examine two areas of contrasting Fe-P mineralization in the mid-Mesozoic of the northern Great Basin and compare them with results from ongoing cooperative studies of the Proterozoic Fe-P deposits in southeastern Missouri. Areas for selected study are: (1) the Humboldt Lopolith (western Nevada); (2) the Cortez Mountains (central Nevada); and (3) the granite- rhyolite terrane of the St. Francois Mountains. It is planned to: (1) characterize selected deposits, associated alteration, and related magmatism, (2) evaluate the conditions of formation and the sources of components, and (3) investigate reasons for similarities and differences. Selective mapping and sample collection will be followed by petrographic and geochemical work. The Missouri portion of this project extends a joint effort with the Missouri DLGS and USGS to understand mid-continent "Olympic Dam" systems. Radiogenic isotopic analyses (Sr, Nd, Pb) from well- characterized samples will be used to: (1) improve geochronometry of mineralization, and (2) help resolve sources of components and mechanisms of ore formation. Regional stable-isotope studies (O, H, S) and selected radiogenic isotopic analyses will investigate the timing, distribution, and intensity of hydrothermal systems and their relationship to mineralization. The Missouri and Nevada investigations combine two complementary ongoing efforts with the long-term aim of quantitatively interpreting the genesis of Fe-P deposits.
