Geochemical comparison of woodlawn and mount painter acid volcanics, Southeastern Australia

Major- and trace-element chemistry (including rare-earth elements), total-rock Rb-Sr and U-Pb and zircon U-Pb data are used in an attempt to distinguish between two essentially coeval, felsic volcanic suites: the predominantly submarine Woodlawn suite which is associated with massive Cu-Pb-Zn sulphide mineralization and the terrestrial Mt Painter suite, with minor vein-type mineralization. The Woodlawn samples are the unmineralized equivalents of the volcanics in the immediate ore environment. Alteration perturbs some of the major- and trace-element chemistry, particularly Ca and alkalis, thereby precluding their usefulness. REE patterns exhibit a significant light to heavy rare-earth enrichment with an average La/Yb of 12 in the Mt Painter volcanics compared with 5.6 in the Woodlawn volcanics. Both suites have a marked negative Eu anomaly, with that of the Woodlawn samples more pronounced (-45.5) than in the Mt Painter volcanics (-29.2). A hydrothermallyaltered sample from Woodlawn has apparently lost about 50% of its light rare-earth elements. Initial 87Sr/86Sr ratios at about 0.711 are the same for rocks from both suites and differences in initial lead-isotopic ratios appear negligible. Zircons from both suites are a mixture of clear euhedral crystals and rounded discrete crystals or rounded cores overgrown by clear zircon. The U-Pb data substantiate the morphological features in that the zircon suites both contain older inherited Pb but the Mt Painter zircons contain a greater proportion. Cs concentrations and Cs/Rb and Ti/Zr ratios can be used to distinguish between the Woodlawn suite and the Mt Painter suite.