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preservation of a uranium-rich Paleozoic epithermal system with a surface expression (Northern Flinders Ranges, South Australia): radiogenic heat driving regional hydrothermal circulation over geological timescales, Astrobiology, 2011; 11(6) Authors may also deposit this version on his/her funder's or funder's designated repository at the funder's request or as a result of a legal obligation, provided it is not made publicly available until 12 months after official publication. Research ArticlesGenesis The surface expressions of hydrothermal systems are prime targets for astrobiological exploration, and fossil systems on Earth provide an analogue to guide this endeavor. The Paleozoic Mt. Gee-Mt. Painter system (MGPS) in the Northern Flinders Ranges of South Australia is exceptionally well preserved and displays both a subsurface quartz sinter (boiling horizon) and remnants of aerial sinter pools that lie in near-original position. The energy source for the MGPS is not related to volcanism but to radiogenic heat produced by U-Th-K-rich host rocks. This radiogenic heat source drove hydrothermal circulation over a long period of time (hundreds of millions of years, from Permian to present), with peaks in hydrothermal activity during periods of uplift and high water supply. This process is reflected by ongoing hot spring activity along a nearby fault. The exceptional preservation of the MGPS resulted from the lack of proximal volcanism, coupled with tectonics driven by an oscillating far-field stress that resulted in episodic basement uplift. Hydrothermal activity caused the remobilization of U and rare earth elements (REE) in host rocks into (sub)economic concentrations. Radiogenicheat-driven systems are attractive analogues for environments that can sustain life over geological times; the MGPS preserves evidence of episodic fluid flow for the past *300 million years. During periods of reduced hydrothermal activity (e.g., limited water supply, quiet tectonics), radiolytic H 2 production has the potential to support an ecosystem indefinitely. Remote exploration for deposits similar to those at the MGPS systems can be achieved by combining hyperspectral and gamma-ray spectroscopy.

Cleusonite, (Pb,Sr)(U 4+ ,U 6+) (Fe 2+ ,Zn) 2 (Ti,Fe 2+ ,Fe 3+) 18 (O,OH) 38 , is a new member of the crichtonite group. It was found at two occurrences in greenschist facies metamorphosed gneissic series of the Mont Fort and Siviez-Mischabel Nappes in Valais, Switzerland (Cleuson and Bella Tolla summit), and named after the type locality. It occurs as black opaque cm-sized tabular crystals with a bright sub-metallic lustre. The crystals consist of multiple rhombohedra and hexagonal prisms that are generally twinned. Measured density is 4.74(4) g/cm 3 and can be corrected to 4.93(12) g/cm 3 for macroscopic swelling due to radiation damage; the calculated density varies from 5.02(6) (untreated) to 5.27(5) (heat-treated crystals); the difference is related to the cell swelling due to the metamictisation. The empirical formula for cleusonite from Cleuson is (Pb 0.89 Sr 0.12) 7 =1.01 (U +4 0.79 U +6 0.30) 7 =1.09 (Fe +2 1.91 Zn 0.09) 7 =2.00 (Ti 11.80 Fe +2 3.44 Fe +3 2.33 V +5 0.19 Mn 0.08 Al 0.07) 7 =17.90 [O 35.37 (OH) 2.63 ] 7 =38. Cations were measured by electron microprobe, the presence of structural (OH) was confirmed by infrared spectroscopy and the U 6+ /U 4+ and Fe 2+ /Fe 3+ ratios were determined by X-ray photoelectron spectroscopy. Cleusonite is partly metamict, and untreated crystals only show three major X-ray diffraction peaks. Because of this radiation-damaged state, the mineral appears optically isotropic and shows a light-grey to white colour in reflected polarized light. Cleusonite is trigonal, space group R3, and unit-cell parameters are varying from a = 10.576(3), c = 21.325(5) Å (untreated crystal) to a = 10.4188(6), c = 20.942(1) Å (800°C treatment) and to a = 10.385(2), c = 20.900(7) Å (1000°C treatment). The three cells give a common axial ratio 2.01(1), which is identical to the measured morphological one 2.04(6). The name cleusonite also applies to the previously described "uranium-rich senaite" from Alinci (Macedonia) and the "plumbodavidite" from Huanglongpu (China).

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