Isotopic composition of Australian leads—III Northwestern Queensland and the Northern Territory—A reconnaissance

Abstract

Lead isotopic abundances are reported for a number of samples from Northern Australia, principally from the Mount Isa region of Queensland and Rum Jungle in the Northern Territory. Model ages ( t 6–7 of Russell and Farquhar, 1960) are deduced for Broken Hill, N.S.W., 1590 m.y.; Mount Isa, 1570 m.y.; and for Rum Jungle, where some lead of anomalous behaviour is also found, 1520 m.y. After some discussion of sources of error, the tentative suggestions are made that the Dugald River deposits are the same age as those at Mount Isa; and that the radiogenic contamination at Rum Jungle may have taken place over a long period of time by some non-catastrophic process. Finally, an example has been found, in the Macarthur River area, of lead which appears on present evidence to be considerably older (Lower Protorozoic) than the sediments (Upper Proterozoic) with which it is syngenetically associated.