Basin inversion and structural architecture as constraints on fluid flow and Pb-Zn mineralisation in the Paleo-Mesoproterozoic sedimentary sequences of northern Australia

Abstract

<jats:p>Abstract. As host to several world-class sediment-hosted Pb-Zn deposits and unknown quantities of conventional and unconventional gas, the variably inverted 1730–1640 Ma Calvert and 1640–1580 Ma Isa superbasins of northern Australia have been the subject of numerous seismic reflection studies with a view to better understanding basin architecture and fluid migration pathways. Strikingly similar structural architecture has been reported from much younger inverted sedimentary basins considered prospective for oil and gas elsewhere in the world. Such similarities suggest that the mineral and petroleum systems in Paleo-Mesoproterozoic northern Australia may have spatially and temporally overlapped consistent with the observation that basinal sequences hosting Pb-Zn mineralisation in northern Australia are bituminous or abnormally enriched in hydrocarbons. This points to the possibility of a common tectonic driver and shared fluid pathways. Sediment-hosted Pb-Zn mineralisation coeval with basin inversion first occurred during the 1650–1640 Ma Riversleigh Tectonic Event towards the close of the Calvert Superbasin with further pulses accompanying the 1620–1580 Ma Isa Orogeny which brought about closure of the Isa Superbasin. Mineralisation in all cases is hosted by the syn-inversion fraction of basin fill, contrary to most existing interpretations of Pb-Zn ore genesis where the ore-forming fluids are introduced during the rifting or syn-extensional phase of basin development. Syn-extensional normal faults of Calvert and Isa age are mutually orthogonal, giving rise to a complex compartmentalisation of sub-basins with predominantly NNW and ENE strikes. Basin inversion subsequent to 1640 Ma occurred overall in a transpressive tectonic regime linked to continent-continent collision accompanied by orogen-parallel extensional collapse and right-stepping strike-slip faulting. </jats:p>

Variscan U-Th-Pb age for stratabound Pb-Zn mineralization in the Bossòst dome (Pyrenean Axial Zone)

“…Finally, metal (re)mobilization during structural inversion periods is not specific to the Bossòst Pb-Zn deposits. Structurally-controlled mineralization has already been described elsewhere in the world, like in the Australia's world class Carpentaria zinc belt (Gibson and Edwards, 2020). As an example, the Century Pb-Zn deposit is described as synorogenic and has formed during crustal shortening in an overall compressive tectonic regime (Polito et al, 2006).…”

“…As an example, the Century Pb-Zn deposit is described as synorogenic and has formed during crustal shortening in an overall compressive tectonic regime (Polito et al, 2006). More generally, the structural and petrographical comparison between several Pb-Zn deposits of northern Australia by Perkins and Bell (1998) evidences a possible metal deposition during shortening events, as shown by structural architecture of the basins (Gibson and Edwards, 2020;Gibson et al, 2017). These structural arguments are supported by petrographic and chemical observations on Pb-Zn ores that highlight the key role of carbonate dissolution for sphalerite precipitation (Spinks et al, 2021).…”