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Bauxite is the world’s main source of aluminium and typically consists of gibbsite, boehmite, and minor amounts of diaspore. However, bauxite deposits from the North and South China blocks consist mostly of diaspore and associated minerals, including anatase and illite. Much of this illite is authigenic and occurs as three polytypes (1M, 1Md, and 2M1), with Kübler indices ranging from 0.23 to 0.47 indicating precipitation temperatures of 175 to 300 degrees C. The Raman spectra of anatase show an intensity ratio less than 1.5 for G (ca. 1 600 cm–1) and D bands (ca. 1 350 cm–1) diagnostic of organic matter, suggesting its presence during bauxite sedimentation followed by heating (165 to 270 degrees C). The K-Ar ages of authigenic illite from the South China block (178–137 Ma) and the North China block (214–203 Ma) are synchronous with known regional Mesozoic tectono-thermal events generating hydrothermal overprints resulting in the formation of illite, the conversion of some diaspores from thermal of gibbsite and boehmite, and the heating of anatase postsedimentation of the Carboniferous bauxites. (Authors.), Bauxite is the world’s main source of aluminium and typically consists of gibbsite, boehmite, and minor amounts of diaspore. However, bauxite deposits from the North and South China blocks consist mostly of diaspore and associated minerals, including anatase and illite. Much of this illite is authigenic and occurs as three polytypes (1M, 1Md, and 2M1), with Kübler indices ranging from 0.23 to 0.47 indicating precipitation temperatures of 175 to 300 degrees C. The Raman spectra of anatase show an intensity ratio less than 1.5 for G (ca. 1 600 cm–1) and D bands (ca. 1 350 cm–1) diagnostic of organic matter, suggesting its presence during bauxite sedimentation followed by heating (165 to 270 degrees C). The K-Ar ages of authigenic illite from the South China block (178–137 Ma) and the North China block (214–203 Ma) are synchronous with known regional Mesozoic tectono-thermal events generating hydrothermal overprints resulting in the formation of illite, the conversion of some diaspores from thermal of gibbsite and boehmite, and the heating of anatase postsedimentation of the Carboniferous bauxites. (Authors.)

This paper reports geophysical anomalies and intra-crystalline quartz lamellae in drill cores from the Warburton West Basin overlapping the border of South Australia and the Northern Territory. The pre-Upper Carboniferous ~450 × 300 km-large Warburton Basin, north-eastern South Australia, is marked by distinct eastern and western magnetic, gravity and low-velocity seismic tomography anomalies. Quartz grains from arenite core samples contain intra-crystalline lamellae in carbonate–quartz veins and in clastic grains, similar to those reported earlier from arenites, volcanic rocks and granites from the Warburton East Basin. Universal Stage measurements of quartz lamellae in both sub-basins define Miller–Bravais indices of {10–12} and {10–13}. In-situ quartz lamellae occur only in pre-Late Carboniferous rocks whereas lamellae-bearing clastic quartz grains occur in both pre-Late Carboniferous and post-Late Carboniferous rocks — the latter likely redeposited from the pre-Late Carboniferous basement. Quartz lamellae in clastic quartz grains are mostly curved and bent either due to tectonic deformation or to re-deformation of impact-generated planar features during crustal rebound or/and post-impact tectonic deformation. Seismic tomography low-velocity anomalies in both Warburton West Basin and Warburton East Basin suggest fracturing of the crust to depths of more than 20 km. Geophysical modelling of the Cooper Basin, which overlies the eastern Warburton East Basin, suggests existence of a body of high-density (~2.9–3.0 gr/ cm3 ) and high magnetic susceptibility (SI ~ 0.012–0.037) at a depth of ~6–10 km at the centre of the anomalies. In the Warburton West Basin a large magnetic body of SI= 0.030 is modelled below ~10 km, with a large positive gravity anomaly offset to the north of the magnetic anomaly. In both the Warburton East and Warburton West the deep crustal fracturing suggested by the low velocity seismic tomography complicates interpretations of the gravity data. U

Mudrocks and carbonates of the Isa superbasin in the Lawn Hill platform host major base-metal sulphide mineralisation, including the giant stratabound Century Zn-Pb deposit. Long-lived structures such as the Termite Range fault acted as hot fluid conduits several times during the Paleoproterozoic and Mesoproterozoic in response to major tectonic events. Illite and chlorite crystallinity studies suggest the southern part of the platform has experienced higher temperatures than similar stratigraphic horizons in the north. The irregular downhole variation of illite crystallinity values shows that clay formation was controlled not only by temperature increase with depth but also by high water/rock ratios along relatively permeable zones. Three major thermal events are indicated in the central and northern Lawn Hill platform, at 1500, 1440 to 1400, and 1250 to 1150 Ma. Siderite is the most abundant Fe-rich gangue phase in the Century deposit, which is surrounded by an extensive ferroan carbonate alteration halo. Modelling suggests that the ore siderite formed at temperatures of 120-150 degrees C, while siderite and ankerite in the alteration halo formed at temperatures of 150-180 degrees C. The data indicate that organic maturation and carbonate precipitation in the northeast Lawn Hill platform resulted from interaction with fluids of the 1250-1150 Ma event., Mudrocks and carbonates of the Isa superbasin in the Lawn Hill platform host major base-metal sulphide mineralisation, including the giant stratabound Century Zn-Pb deposit. Long-lived structures such as the Termite Range fault acted as hot fluid conduits several times during the Paleoproterozoic and Mesoproterozoic in response to major tectonic events. Illite and chlorite crystallinity studies suggest the southern part of the platform has experienced higher temperatures than similar stratigraphic horizons in the north. The irregular downhole variation of illite crystallinity values shows that clay formation was controlled not only by temperature increase with depth but also by high water/rock ratios along relatively permeable zones. Three major thermal events are indicated in the central and northern Lawn Hill platform, at 1500, 1440 to 1400, and 1250 to 1150 Ma. Siderite is the most abundant Fe-rich gangue phase in the Century deposit, which is surrounded by an extensive ferroan carbonate alteration halo. Modelling suggests that the ore siderite formed at temperatures of 120-150 degrees C, while siderite and ankerite in the alteration halo formed at temperatures of 150-180 degrees C. The data indicate that organic maturation and carbonate precipitation in the northeast Lawn Hill platform resulted from interaction with fluids of the 1250-1150 Ma event.

Studies of the least-deformed Zn-Pb-Ag deposits at McArthur River and Century provide support, respectively, for exhalation of ore fluids into the basin and ingress of hydrothermal fluids into reactive lithologies at depth. The interplay of stratigraphy, thermal flux and flow timing determined whether fluids reached the basin floor or interacted with reductant at depth to form sediment-hosted deposits. At Mount Isa, three sulphide mineralising systems are distinguished: early fine-grained pyrite, Zn-Pb-Ag and overprinting Cu. Other deposits also indicate multiple fluids. Pb isotope data suggest a common source for the Mount Isa Zn-Pb and Cu fluids whereas stable isotope studies indicate both local and deep-seated sources of volatiles. Progressive thermal leaching/metamorphism of a common source region and its periodic tapping in response to episodic tectonism may provide an explanation for apparently conflicting genetic observations across the McArthur-Mt Isa-Cloncurry province., Studies of the least-deformed Zn-Pb-Ag deposits at McArthur River and Century provide support, respectively, for exhalation of ore fluids into the basin and ingress of hydrothermal fluids into reactive lithologies at depth. The interplay of stratigraphy, thermal flux and flow timing determined whether fluids reached the basin floor or interacted with reductant at depth to form sediment-hosted deposits. At Mount Isa, three sulphide mineralising systems are distinguished: early fine-grained pyrite, Zn-Pb-Ag and overprinting Cu. Other deposits also indicate multiple fluids. Pb isotope data suggest a common source for the Mount Isa Zn-Pb and Cu fluids whereas stable isotope studies indicate both local and deep-seated sources of volatiles. Progressive thermal leaching/metamorphism of a common source region and its periodic tapping in response to episodic tectonism may provide an explanation for apparently conflicting genetic observations across the McArthur-Mt Isa-Cloncurry province.