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Tracing ancient hydrogeological fracture network age and compartmentalisation using noble gases, Geochimica et Cosmochimica Acta (2017), doi: https://doi. AbstractWe show that fluid volumes residing within the Precambrian crystalline basement account for ca 30 % of the total groundwater inventory of the Earth (> 30 million km 3 ). The residence times and scientific importance of this groundwater are only now receiving attention with ancient fracture fluids identified in Canada and South Africa showing: 1. microbial life which has existed in isolation for millions of years; 2. significant hydrogen and hydrocarbon production via waterrock reactions; and 3. preserving noble gas components from the early atmosphere. Noble gas (He, Ne, Ar, Kr, Xe) abundance and isotopic compositions provide the primary evidence for fluid mean residence time (MRT). Here we extend the noble gas data from the Kidd Creek Mine in Timmins Ontario Canada, a volcanogenic massive sulfide (VMS) deposit formed at 2.7 Ga, in which fracture fluids with MRTs of 1.1-1.7 Ga were identified at 2.4km depth (Holland et al., 2013); to fracture fluids at 2.9km depth. We compare here the Kidd Creek Mine study with noble gas compositions determined in fracture fluids taken from two mines (Mine 1 & Mine 2) at 1.7 and 1.4 km depth below surface in the Sudbury Basin formed by a meteorite impact at 1.849 Ga.The 2.9 km samples at Kidd Creek Mine show the highest radiogenic isotopic ratios observed to date in free fluids (e.g. 21 Ne/ 22 Ne = 0.6 and 40 Ar/ 36 Ar = 102,000) and have MRTs of 1.0 to 2.2 Ga. In contrast, resampled 2.4 km fluids indicated a less ancient MRT (0.2-0.6 Ga) compared with the previous study (1.1-1.7 Ga). This is consistent with a change in the age distribution of fluids feeding the fractures as they drain, with a decreasing proportion of the most ancient endmember fluids. 129 Xe/ 136 Xe ratios for these fluids confirm that boreholes at 2.4 km versus 2.9 km are sourced from hydrogeologically distinct systems. In contrast, results for the Sudbury mines 3 have MRTs of 0.2-0.6 and 0.2-0.9 Ga for Mines 1 and 2 respectively. While still old compared to almost all groundwaters reported in the literature to date, these younger residence times compared to Kidd Creek Mine are consistent with significant fracturing created by the impact event, facilitating more hydrogeologic connection and mixing of fluids in the basin. In all samples from both Kidd Creek Mine and Sudbury, a 124-128 Xe excess is identified over modern air values. This is attributed to an early atmospheric xenon component, previously identified at Kidd Creek Mine but which has to date not been observed in fluids with a residence time as recent as 0.2-0.6 Ga. The temporal and spatial sampling at Kidd Creek Mine is also used to verify our proposed conceptual model which provides key constraints regarding distribution, volumes and residence times of fracture fluids on the smaller, regional, scale.

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The metal-reducing bacteria Geobacter sulfurreducens, Shewanella oneidensis and Veillonella atypica, use different mechanisms to transform toxic, bioavailable sodium selenite to less toxic, non-mobile elemental selenium and then to selenide in anaerobic environments, offering the potential for in situ and ex situ bioremediation of contaminated soils, sediments, industrial effluents, and agricultural drainage waters. The products of these reductive transformations depend on both the organism involved and the reduction conditions employed, in terms of electron donor and exogenous extracellular redox mediator. The intermediary phase involves the precipitation of elemental selenium nanospheres and the potential role of proteins in the formation of these structures is discussed. The bionanomineral phases produced during these transformations, including both elemental selenium nanospheres and metal selenide nanoparticles, have catalytic, semiconducting and light-emitting properties, which may have unique applications in the realm of nanophotonics. This research offers the potential to combine remediation of contaminants with the development of environmentally friendly manufacturing pathways for novel bionanominerals.

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