Basement rock parameters that control the genesis of high-grade unconformity-type uranium deposits in the Athabasca basin

Category Other
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Annesley, Irvine R.۱; Wheatley, Ken۲; Wasyliuk, Ken۱; McCready, Alistair J.۳; Hajnal, Zoltan۴
Holding Date 07 October 2008

Exploration strategies concerning uranium deposits, in particular unconformity-type, have changed significantly over the last 40 years. For the most part, the exploration strategy in the Athabasca Basin is well formulated. But until recently (e.g. Shea Creek and Millennium deposits), no major deposits have been discovered since finding the McArthur River and Sue deposits. We present some of the specific geological, geochemical, and geophysical signatures of basement rocks that are considered useful guides for uranium exploration in the Athabasca Basin.
To help define these characteristic signatures, many new and improved technologies and analytical techniques have been used for exploring in the Athabasca Basin over the last 10 years (e.g. 3D visualization/modeling, high-resolution seismic surveys, Raman/synchrotron analyses, Pb isotopes, PIMA, U-Th-Pb chemical age dating, ion microprobe dating). Here we provide recent results from some of these technologies and analytical techniques, mainly from the eastern Athabasca exploration district.
In the eastern Athabasca Basin, the sedimentary fill is comprised mainly of flat-lying Manitou Falls Formation sandstones and conglomerates, overlying unconformably a crystalline basement complex of highly folded, variably metamorphosed Paleoproterozoic metasediments and Archean orthogneisses. Numerous examples show the complex lithostructural basement environments associated with the high-grade unconformity-type uranium deposits. Positive/distinctive signatures of the Archean/Paleoproterozoic basement complex proximal to major unconformity-type uranium deposits are outlined as follows: • Fertile (radioelement-enriched) heterogeneous basement complex
• Basal metasedimentary package, comprising graphitic pelitic gneisses, Fe-rich garnetites, and Mg-Al-B-S-rich pelitic gneisses
• High-Heat-Production Hudsonian intrusions, comprising evolved porphyritic calc-alkaline granites/granodiorites, strongly peraluminous granitic pegmatites, and strongly peraluminous microgranites
• Pre-existing complex ductile structures of Hudsonian age with significant ductile-brittle and brittle reactivation producing cataclastic/breccia zones with graphite altered to carbonaceous matter
• Significant rheological and geochemical heterogeneity between basement footwall (e.g. Archean granitoid gneisses) and hanging wall (e.g. pelitic gneisses) rocks
• Significant episodic fluid flow/infiltration/alteration over time within fault cores and associated damage zones
• Pre-existing Hudsonian mineralization (i.e. protore) within a major plumbing system. Essentially mono-metallic basement mineralization may represent the root zone to the classical unconformity-type uranium deposits.
In summary, more basic/applied research is required to identify cryptic mineralogical/geochemical signatures in the basement lithologies underlying the Athabasca Basin, so to provide new constraints for mapping the complex mineralizing systems of these uranium deposits.