The Arrow Uranium Deposit, South-west Athabasca Basin

摘要

The Arrow uranium deposit, south-west Athabasca Basin, Saskatchewan, was discovered in February 2014. Arrow comprises structurally-controlled basement-hosted mineralisation concealed beneath c 100 m combined thickness of four subsequent sedimentary depositional packages.Uranium mineralisation at Arrow is hosted in numerous stacked subvertical mylonitic structural zones and ancillary splay structures within a known strike length of over 515 m, total known width to date of over 215 m, and a known depth extent of over 905 m. Mineralisation is open along strike, at depth and potentially in other parallel zones laterally and at depth.The host Taltson Domain basement lithologies include high-grade blue quartz charnockitic coarse-grained quartz-feldspar-garnet-biotite gneisses and granulite, with subordinate fine-to-medium grained similar assemblages. Local zones of granitic gneiss and massive metagabbro occur, with minor pegmatite. Graphitic material is very restricted, comprising only trace amounts in the host gneisses, while larger accumulations occur only locally within the structurally-disturbed zones. The basement package is subvertical, trends NE-SW, and with dips reversing between NW and SE due to a NNW cross-cutting wrench structure at the present core of Arrow.The main U-mineral is uraninite, with local minor coffinite. Mineralisation styles at Arrow include massive to semi-massive veins and pods, stockworks, fracture linings and minor disseminations.Definitive observational evidence of several generations of reactivation includes alteration minerals (clay, chlorite, illite, smoky quartz, dravite, hematite), minor sulfides (<10 per cent locally), and cross-cutting structures with associated uranium mineralisation and alteration. Three geochronological samples provided ~(207)Pb/~(206)Pb ages of 1316 + 14 Ma, 611 ± 43 Ma and 363 + 34 Ma. All represent re-setting ages, almost certainly related to tectonic events. The uranium localisation at Arrow is due to the contrasting basement lithologies, the initiation and reactivation of structures, the generation of the U-bearing fluid, and the local physico-chemical depositional mechanisms. Interpretation of observed features at Arrow differ from conventional Athabasca models, with consequent implications for genesis and exploration methodology.