Earth Sciences Report 2006-02
A reconnaissance field program was conducted in the summer of 2005 in the Andrew Lake area. Selected geological traverses and uranium prospecting, using a sensitive GR130 spectrometer and two STRAT SPP2N scintillometers, were carried on over the main lithological units and more focused around selected radioactive sites previously identified by Godfrey. Preliminary field and microscopic observations added by microprobe and fluid inclusion analyses have been integrated in the regional geological evolution of the region that includes: a) the development of the ca. 2.4-2.1 Ga Taltson biotite and hornblende granite gneiss complex, related to the tectonothermal recycling of the western Archean Churchill Province; b) a subsequent tectonothermal event in which well-layered migmatized bands of possibly supracrustal rocks were incorporated in the granitoid gneissic complex; and c) emplacement of the ca. 1.96 Ga Andrew Lake and ca 1.97 Ga Colin Lake granitoids, local representatives of the regional Talton plutonism. The metamorphic transformations observed in thin sections, the polyphase ductile deformation of the well-layered and migmatized rocks (routinely interpreted as bands of supracrustal rocks) and the exclusive association with the ca. 1.93 Charles Lake and the ca. 1.92 Sonja Island anatectic granitoids suggest that they represent discontinuous domains of deformation and partial melting of the Taltson granite gneiss complex. Migmatization appears to be a first phase of uranium enrichment as many of the pegmatitic dykes and veins show radioactivity four to eight times the background level (e.g., Spider Lake). Subsequent zones of strain and fluid-flow concentration within the supracrustal units resulted in lower grade metamorphic tectonites often associates with higher concentration of uranium, sulphide, arsenide and possibly gold (e.g., the uraniferous zone southwest of Holmes Lake). The intense carbonatic metasomatism commonly associated with the Athabasca-type uranium deposits has not been observed. The hematite cemented breccia and quartz stockwork within the examined segments of Bonny Fault are apparently uranium depleted. Future exploration for uranium and base metals in the Andrew Lake area should concentrate on detailed examination of the entire belt of fault rocks that define Bonny Fault, the belts of chlorite-zone retrogression and the pegmatite units particularly within supracrustal rocks.
Pana, D.I., Olson, R.A. and Byron, S.J. (2006): Geological reconnaissance work in the Andrew Lake area of northeastern Alberta; Alberta Energy and Utilities Board, EUB/AGS Earth Sciences Report 2006-02, 29 p.