Arrow: A Recent High-Grade Uranium Discovery in a New District
by Garrett Ainsworth, PGeo., Vice President Exploration & Development, NEXGEN ENERGY LTD.
The Arrow zone (“Arrow”) is a recent basement-hosted uranium discovery made in February 2014 by NexGen Energy Ltd. (“NexGen”) at its Rook I property in the southwest Athabasca Basin, Northern Saskatchewan. A total of 29,228.7 m in 42 diamond drill holes has been reported at Arrow to date. Forty of the 42 drill holes have intersected uranium mineralization. Drill hole AR-14-30 has returned the best intercept to date with 63.5 m of 7.54% U3O8, which included the highest assay over 0.5 m of 66.8% U3O8. Uranium mineralization is associated with numerous sub-vertical graphitic mylonite shears contained within 515 m strike length, 215 m width, and 905 m depth extent, and remains open in all directions.
Arrow is a basement-hosted, structurally-controlled, and hydrothermally-altered system located within the Patterson Lake conductive corridor. The Patterson corridor constitutes a series of 3 to 4 “discrete” parallel northeast trending electromagnetic (EM) conductors. The Arrow zone was discovered on the first drill hole testing a coincident gravity low and disrupted EM conductor. The Patterson corridor is also host to Fission’s PLS deposit to the southwest, and Purepoint’s Spitfire zone to the northeast of NexGen’s Rook I property.
The geological sequence of sedimentary strata overlying crystalline basement rocks is comprised of i) Quaternary glacial tills, ii) Cretaceous sediments of the Colorado and Mannville Group iii) Devonian sediments of the La Loche Formation, and iv) Helikian-aged Athabasca quartz arenite sandstone of the Manitou Falls “A” member.
The basement metamorphic assemblages are part of the Taltson Domain (ex-East Lloyd Domain). Basement lithologies are vertically-oriented, dipping -75[Symbol] to the southeast to -90[Symbol]. The basement rocks hosting Arrow mineralization are comprised of a major package of variable quartz-rich psammitic to garnetifierous (+/- graphite) semipelitic gneiss and granofel that are occasionally intercalated with relatively narrow graphitic mylonite zones. A complex group of interleaved semipelitic gneiss, feldspathic granitic gneiss, pegmatite, and massive gabbro and mafics are observed along the southeast margin of known mineralization. A massive-textured garnetite (>50% garnet) is quite frequently observed between the metasediments and intrusive suite of rock types, which is likely evidence of some degree of aluminous metasomatism.
The main uranium-controlling structures at Arrow are a series of stacked, vertically-oriented (+/-) graphitic shears with evidence of multiple episodes of reactivation. These units are quite commonly referred to as mylonites on the project because of the observed cohesiveness, high-degree of foliation, ribbony quartz, and rotated clasts (+/- pressure shadows). Uranium forms within the graphitic shears or on either side of the structures in splay offsets to the main structures.
Hematite alteration is generally limited to a paleoweathering profile intersected immediately at the unconformity and down to approximately 50 m depth, or is intimately associated with uranium mineralization as part of redox fronts. Retrograde chlorite alteration of garnets is extensive and located throughout, whereas hydrothermal chlorite alteration is limited to extremities of uranium mineralization. Late hydraulic structures provide space for dravite alteration as seen by intensive breccias, sometimes with remobilized uranium mineralization.
A variety of mineralization styles occur at Arrow, which include disseminations and flecks, fracture face linings, quartz-carbonate-uranium network vein complexes, “worm rock” or redox fronts, and massive to semi-massive veins and pods.
The Arrow zone further enhances the potential for additional high-grade uranium discoveries to be made along the Patterson corridor, and other numerous graphitic conductive corridors within the Southwest Athabasca Basin.
Garrett Ainsworth is a professional geologist and the Vice President Exploration and Development for Nexgen Energy Ltd. He has a Diploma of Technology in Mining and Bachelor of Technology in Environmental Engineering with honours from BCIT, as well as a Bachelor of Science in Geology with honours from Birkbeck, University of London.
Mr. Ainsworth and NexGen’s technical team are focused on advancing the Arrow zone and other numerous fertile conductor corridors within the Rook I property in the southwest region of the Athabasca Basin. The Patterson Lake South (PLS) deposit is located 1.3 km southwest of the Rook I property. The PLS deposit, and Arrow, Bow, and Spitfire zones are part of an approximate 14 km long mineralized trend along the Patterson conductor corridor that has recently established the southwest Athabasca basin as a new and exciting uranium district.
Mr. Ainsworth was instrumental in the successful progress of the PLS project, where he was the Project Manager from its inception in 2007 until June 2013. During his tenure as Project Manager of PLS he oversaw the staking of new claims, the discovery of the boulder field, the initial high-grade uranium drill hole discovery (R00E zone), and the discovery of the high grade, near surface, uranium zones R390E and R780E during the winter 2013 drill program.
Apart from being involved with numerous uranium projects in the Athabasca Basin, Saskatchewan, he also obtained experience as a field geologist on gold projects in British Columbia, Nevada, and Mexico; and a diamond project in West Africa. Mr. Ainsworth worked as an environmental consultant on a variety of industrial and mining projects from 2002 to 2007.
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