A low temperature oxygen isotope thermometer for cerussite, with applications at Broken Hill, New South Wales, Australia

Slow precipitation experiments have been used to determine the oxygen isoto pe fractionation between cerussite (PbCO3) and water over the temperature r ange 20 to 65 degreesC. The temperature dependent fractionation for oxygen can be expressed as: 1000 ln alpha ((cerussiteCO3-water)) = 2.63 (10(6)/T-2) - 3.58 Independent determinations of the oxygen isotope fractionation factor for r ecent historical cerussite samples from the Bwlch-Glas Mine, Wales, UK, and the Pinnacles Mine, Broken Hill, NSW, Australia, plot close to our experim entally determined fractionation curve. Similarly, earlier high temperature cerussite experiments are in agreement with our thermometer. This new oxyg en isotope thermometer was used to examine data for 7 cerussite samples fro m the Block 14 and 3 from the Kintore open cuts on the main Broken Hill lod e, NSW, Australia. Broken Hill cerussite formed at temperatures significant ly greater than modern ambient air temperatures. This is consistent with ma lachite thermometry results at Broken Hill. It is suggested that these high er apparent temperatures result from the exothermic oxidation of concentrat ed sulphides. Results indicate that oxidation of sulphides in the Block 14 Mine produced shallow subsurface temperatures up to at least 50 degreesC. C arbon isotope data suggest incorporation of significant amounts of organic carbon, possibly from a subsurface bacterial carbon source associated with sulphide oxidation. Copyright (C) 2001 Elsevier Science Ltd.