Zinc Deposits and Related Mineralization of the Burketown Mineral Field, Including the World-Class Century Deposit, Northern Australia: Fluid Inclusion and Stable Isotope Evidence for Basin Fluid Sources

The stratiform Century Zn-Pb deposit and the discordant Zn-Pb lode deposits of the Burketown mineral field, northern Australia, host ore and gangue minerals with primary fluid inclusions that have not been af-fected by the Isan orogeny, thus providing a unique opportunity to investigate the nature of the ore-forming brines. All of the deposits are hosted in shales and siltstones belonging to the Isa superbasin and comprise spha-lerite, pyrite, carbonate, quartz, galena, minor chalcopyrite, and minor illite. According to Pb model ages, the main ore stage of mineralization at Century formed at 1575 Ma, some 20 m.y. after deposition of the host shale sequence. Microthermometry on undeformed, primary fluid inclusions hosted in porous sphalerite shows that the Zn at Century was transported to the deposit by a homogeneous, Ca2+- and Na+-bearing brine with a salin-ity of 21.6 wt percent NaCl equiv. δDfluid of the fluid inclusion water ranges from –89 to –83 per mil, consis-tent with a basinal brine that evolved from meteoric water. Fluid inclusion homogenization temperatures range between 74º and 125ºC, which are lower than the 120º to 160ºC range calculated from vitrinite reflectance and illite crystallinity data from the deposit. This discrepancy indicates that mineralization likely formed at 50 to 85 Mpa, corresponding to a depth of 1,900 to 3,100 m. Transgressive galena-sphalerite veins that cut stratiform mineralization at Century and breccia-fille