An oval body of about 8x4 km, Bigspruce Lake is emplaced in Precambrian equigranular and porphyritic biotite granites. Almost all of the complex is now covered by the waters of Bigspruce Lake because of a power dam built on the Snare River.
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Northwest Territories, Mackenzie
This dyke, orientated approximately east-west, extends over a distance of 29 km but there are discontinuities due to shearing and displacement. Deeper levels of the dyke are exposed to the west, and a higher heterogeneous roof zone to the east.
The Blachford Lake complex intrudes Archaean granites and granodiorites and metasedimentary schists of the Yellowknife Supergroup, and is cut by diabase dykes and small plutons of diorite and granodiorite.
A strong nearly circular aeromagnetic anomaly 3-4 km in diameter occurs some 3 km north of Thomas Lake. Exposure is poor, only three outcrops having been sampled.