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Significant uranium mineralization represented by a typical assemblage of uranyl supergene minerals in a quartz-uraninite vein hosted in the exocontact zone of the Variscan-Tanvald granite was found at a new construction site in the municipality of Jablonec n. Nisou. Activities of 222Rn in soil gas reached 1 MBq/m3 around two houses, with a maximum of 3.33 MBq/m3 between them on a uranium ore lens outcrop. The uranium content reaches up to 291 ppm eU (3595 Bq/kg 226Ra), and it is possible to find many ‘hot’ pieces of uranium ore fragments with a high percentage of uranium in the Quaternary cover in this place. This unfavourable situation is a result of an improper spatial planning process. The constructor was given the permission to construct the building even though the construction site did not meet safety requirements and the geological survey had failed. Not only geological prospecting was underestimated, but also the radon risk assessment was undervalued.

The Beaverlodge district in northern Saskatchewan is known for “vein-type” uranium mineralization. Most of the uranium deposits are spatially related to major structures, and hosted by ca. 3.2–1.9 Ga granitic rocks (and albitite derived from them) and by ca. 2.33 Ga Murmac Bay Group amphibolite, all of which are unconformably overlain locally by deformed but unmetamorphosed redbeds of the ca. 1.82 Ga Martin Group, and by the flat-lying ca. 1.75–1.5 Ga Athabasca Group. The uranium mineralization is mainly hosted in fault rocks (breccias) and carbonate ± quartz ± albite veins, referred to as breccia-style and vein-style mineralization, respectively, with the latter being the focus of this study. Most of the mineralized veins occur in the basement rocks, although some crosscut the Martin Group. This study examines the field, petrographic, fluid inclusion and C-O isotope characteristics of mineralized and non-mineralized veins from 19 deposits/occurrences as well as from the Martin Group, with an aim to better understand the mineralizing environment and processes. The coexistence of liquid-dominated (L + V), vapour-dominated (V + L) and vapour-only (V) fluid inclusions within individual fluid inclusion assemblages (FIAs) in the veins suggests fluid immiscibility and heterogeneous trapping. The L + V inclusions with the lowest homogenization temperatures (T h ) within individual FIAs are interpreted to represent homogeneous trapping of the liquid phase, which yield T h values from 78° to 330 °C (mainly 100° to 250 °C), and salinities from 0.2 to 30.8 wt.% NaCl equivalent. Mass spectrometric analysis of bulk fluid inclusions shows that the volatiles are dominated by H 2 O (average 97.2 mol%), with minor amounts of CO 2 , CH 4 , H 2 , O 2 , N 2 , Ar and He. Fluid pressures were estimated to be < 200 bars based on the inference of fluid immiscibility, fluid temperatures of 100° to 250 °C, and low concentrations of non-aqueous volatiles (< 3 mol%). The δ 18 O VPDB and δ 13 C VPDB of carbonate minerals associated with mineralization range from − 20.5 to − 8.9‰ and − 10.1 to − 0.9‰, respectively. The δ 18 O VSMOW values of the parent fluids calculated using the T h values range from − 9.6 to + 17.0‰, with the majority from 0 to + 5.0‰. O isotopes of paired equilibrium quartz and calcite, analyzed by secondary ion mass spectrometry (SIMS), yield temperatures from 161° to 248 °C, which are consistent with the fluid inclusion data. The new fluid inclusion and stable isotope data are inconsistent with a metamorphic or magmatic-hydrothermal model as proposed in some previous studies (for breccia-style and vein-style mineralization), but rather support a model in which the vein-type uranium mineralization took place at relatively low temperature (100° to 250 °C) and shallow (< 2 km) conditions, with fluid pressure fluctuating between hydrostatic and sub-hydrostatic regimes, possibly related to episodic faulting. The mineralizing fluids were mainly sourced from the Martin Lake Basin, and uraninite was precipitated as a result of mixing between this basin-derived fluid and fluids carrying reducing agents (Fe 2 + , CH 4 ) derived from the basement, although fluid-rock reactions and fluid immiscibility may have also played a role. [ABSTRACT FROM AUTHOR]