Uraniferous quartz ? hematite breccias at Mt Painter (South Australia): palaeomagnetic dating of hydrothermal activity

Abstract

The Radium Ridge Breccias are an unusual sequence of coarse terrestial clastics which contain a major amount of hydrothermally precipitated quartz and hematite, and locally host uranium and base metal deposits (Drexel and Major, 1987). The breccias are up to 500 m thick, are distributed over an area of at least 100 km2, and unconformably overly multiply deformed and metamorphosed Proterozic to early Palaeozoic rocks of the Mount Painter Inlier. The dominant lithological type is a granitic breccia that comprises dominantly clasts of local basement granite, gneiss and schist. Uranium mineralization occurs mostly in lens-shaped bodies of hematitic breccia within the granitic breccia pile. The granitic breccia also contains a diamictite comprising well- rounded clasts of rocks not found in the local basement, and is capped at some localities by a quartz-hematite-rich sedimentary rock, the Mount Gee Sinter. At Mount Gee the sinter was deformed, apparently while still plastic, into metre-scale domes and basins. The origin of the breccias, their age, and association with the diamictite and sinter have been poorly understood.