60

syenites, and granites are described by: J. M. Bell as occurring all the way from
Great Bear lake to Great Slave lake, and on the east arm of Great Slave lake

“sranites and gneisses rise as a sea of half rounded hummocks to a general height
of nearly 1,000 feet all along the northwest side of this part of the lake and also
around the northeastern extremity.”?

Associated with the granites and gneisses, but possibly of a later period of
intrusion, are bodies of gabbro and norite occurring notably on the north shore
of Athabaska lake and the country to the north.

’ This whole group of rocks belongs not to one period of intrusion alone, but
represents different intrusions. In the main, however, the rocks cut the series
of stratified rocks locally known as the Tazin series and others that have been
referred to as Keewatin or Huronian. They are not in themselves mineralized |
to the extent of forming workable ore~bodies, but they are in places believed to
have produced mineralization in the rocks into which they have been intruded.

Late Precambrian. The youngest Precambrian formations of this part of
Canada consist chiefly of sandstones associated with basic intrusions and flows.
These rocks are of wide distribution; they lie to the northeast of Great Bear
lake, at the east end of Great Slave lake, and north and south of lake Athabaska;
they also cover large areas lying to the east of the Mackenzie basin.

In the Lake Athabaska district the rocks consist chiefly of reddish,
moderately coarse-grained sandstones, becoming in places fine-grained, thin-
bedded, and shaly, and in places passing downward into conglomerate. These
constitute what have been designated the Athabaska series.

8“The total area underlain by this sandstone formation is very large,
extending from Cree lake on the south to Athabaska lake on the north, and from
Wollaston lake on the east, doubtless to the vicinity of the valley of Athabaska
river on the west, and perhaps much farther under the covering of later rocks.
- Cree lake lies largely within the area underlain by these rocks, and Athabaska
lake seems to lie entirely within it, for the red sandstones compose TARDY, of the
islands and more prominent points of its northern shore.” |

North of Beaverlodge bay on the north shore of lake Athabaska, hig bedded
sandstones, arkoses, and conglomerates of the Athabaska series are found, and
interbedded with these is a number of flows of vesicular and amygdaloidal
basalt. The series is also intruded by sills and dykes of diabase. The strata
here form an open syncline and have a maximum dip of 40 degrees. There is a
thickness of about 8,800 feet.* Conglomerate and shaly sandstone exposed at the
northeast end of Tazin lake possibly belong to the same series.®

Concerning the formation as exposed on Great Slave lake, Robert Bell
says:

8“The northeastern continuation of the main lake-basin is excavated out of
the older Cambrian or Animikie rocks resting in a long physical depression or
trough in the Archean foundation. These strata have a thickness of over 1,000
feet and they are thrown into gentle anticlines and synclines, parallel to the
axis of the general trough, in which they lie. They have been deeply eroded
along the anticlinal folds and the waters now filling the depressions form the

-1Geol. Suryv., Gan. Ann. Rept., vol. XIII, p. 101 A.

2 Bell, Robt., Geol. Surv., Can., Ann. Rept., vol. XII, p. 106 A.
3 Tyrrell, J. Bs Geol. Surv., Can., Ann. Rept., vol. VIII, p. 18 D.
4 Alcock, F. Is Geol. Surv., Can., Sum. Rept., 1/916.

5 Camsell, C., Geol. Surv., Can., Mem., 84, p. 36.

6 Geol. Surv., Can., Ann. Rept., vol. XII, p. 106 A.