Recent mapping in the Duchess-Urandangi region, covering most of the southern part of the Mount Isa Inlier, has shown that felsic and mafic volcanics occur in most Precambrian stratigraphic units exposed there. Five distinct geochemical suites of felsic volcanics are recognised, each suite probably having been derived from a chemically unique crustal source region. The Leichhardt suite is distinguished by high Sr, and low Zr, Nb and Y abundances, whereas the Argylla suite has low Sr and very high Zr and Nb concentrations. The Bottletree suite is characterised by high Ba, Sr, Zr, and Nb, the Duchess-Corella suite by low Sr and Zr, and high Nb and Y contents, and the Carters Bore suite by high K2O and low Al2O3, Na2O, CaO, Pb, Sr, and Ba. Most of the analysed mafic volcanics from the region are chemically similar, and there is no systematic change in composition from west to east. The mafic volcanics are characterised by low incompatible-element contents and are similar chemically to continental tholeiites of the Karroo province of southern Africa. Silica values for the volcanics and their intrusive equivalents show a well-defined bimodal distribution, probably indicating an extensional crustal regime.