Nd-Sr isotope constraints on the age and origin of unconformity-type uranium deposits in the Alligator Rivers uranium field, northern territory, Australia

Abstract

The results of an Sm-Nd and Rb-Sr isotope study on the large and rich unconformity-type uranium-(gold-platinum-group elements) deposits in northern Australia indicate identical Sm-Nd ages for primary uranium mineralization at Nabarlek (1616±50 m.y.) and Jabiluka II (1614±132 m.y.), in excellent agreement with new and previously published Rb-Sr data on U ores and altered host rocks. Relatively high initial ε Nd values and low 87Sr/ 86Sr ratios in the ores indicate that ore fluids derive their metal content from two main sources, a preunconformity source comprising the local wall rocks (lower Proterozoic metasediments and amphibolites) and a postunconformity source including the volcano-sedime..