Geologic, fluid inclusion, and stable isotope studies of the gold- bearing Breccia Pipe at Kidston, Queensland, Australia

Three phases of brecciation have been distinguished within the breccia pipe, all being associated with magmatic and or magmatic hydrothermal processes. Fluid inclusion data indicate that the present level of exposure was approximately 3500 m below the contemporary land surface at the time of mineralization. The lack of any significant input of meteoric fluid into the hydrothermal system suggests that the breccia pipe failed to breach the contemporary land surface. Stockwork veining and localized brecciation resulted from the multiple buildup and escape of a high-temperature, highly saline magmatic fluid associated with a number of crystallizing rhyolite stocks. Postbreccia mineralization was dominated by magmatic fluids which in turn were dominated by a liquid with a salinity of 2 to 10 wt percent NaCl equiv. This liquid resulted from condensation of a vapor produced by the boiling of a highly saline magmatic fluid at a deeper level within the breccia pipe. The structural control on the distribution of postbreccia mineralization was an inverted funnel-shaped zone of enhanced permeability produced by the forceful emplacement of the postbreccia rhyolite into the lower portion of the breccia pipe. -from Authors