Sequence stratigraphy of the Bowthorn Block in the northern Mount Isa basin, Australia: implications for base-metal mineralization process

Precipitation of base metals, dolomitization, and paleothermal anomalies all occur near the top of organic-rich highstand system tracts within the Paleoproterozoic-Mesoproterozoic (1800 to 1500 Ma) northern Mount Isa basin, Australia. These highstand systems occur below major regional unconformities (and their correlative conformities) in the foreland sequence of the basin. The mineralization appears to be epigenetic, associated with migration through lowstand system tract aquifers. Deposits associated with maximum flooding surfaces at the tops of transgressive system tracts are different from epigenetic mineralization. Transgressive system tracts fine upward to maximum flooding surfaces where phosphate, manganese, and glauconite are commonly concentrated in condensed sequences. These syndepositional minerals are in contrast to epigenetic ores, such as zinc, lead, silver, and copper, that are precipitated from brines migrating through lowstand deposits and along sequence boundaries overlying line-grained highstand systems tracts that act as basal seals. Both these mineral-rich systems are clearly identifiable in the Bowthorn block of the northern Mount Isa basin and it is possible to predict facies distribution from seismic interpretation, preferred migration pathways from regional basin analysis, and likely trap sites from structural analysis in conjunction with the above.