The Millungera Basin—new geoscience supporting exploration

Abstract

An unknown sedimentary sequence was first recorded during a Geoscience Australia/ Geological Survey of Queensland/ pmd*CRC deep seismic reflection survey in the Mount Isa Inlier and adjacent undercover terrains, during 2006/07. The sequence occurs unconformably underneath the Carpentaria Basin succession in the Julia Creek area, east of Cloncurry in north Queensland, and is named the Millungera Basin. A section through the basin is recorded along seismic line 07GA–IG1, recorded between north of Cloncurry to east of Croydon. In this section three internal sequences are noted—with two strongly reflective units separated by a poorly reflective unit. As well as deep crustal seismic reflection profiles, magnetotelluric profiles were collected along the same traverse. These data show a moderately conductive Millungera Basin underlying the strongly conductive Carpentaria Basin. Zones of limited reflectors beneath the basin in the seismic sections have been interpreted as granites, raising the possibility of raised geothermal gradients. The Millungera Basin may comprise a potential geothermal target. The Millungera Basin sequence is interpreted to overlie granites. Adjacent Proterozoic granites of the Williams Batholith are known to be high heat producing granites, containing high levels of potassium thorium and uranium. The hydrocarbon potential of the basin is similarly uncertain. Strong reflectors in the seismic sections may be coal beds. Although the depth of the basin in the seismic section is insufficient to have reached the oil window, interpretation of gravity profiles by Geoscience Australia suggest the basin deepens to the south, possibly reaching 4,000 m. If fertile beds have reached the oil window, the structurally more complex eastern side of the basin may contain petroleum traps. The age of the rocks in the Millungera Basin is not known. Constraints from the seismic suggest between the early Mesoproterozoic and the Middle Jurassic. Investigations into the nature of the basin are continuing. A more detailed magnetotellurc survey is being undertaken to better define the shape of the basin. In order to reliably describe the basins components, a deep drilling program is required.