58

These rocks have been intruded by granites or gneisses of probably more than
one age.

Overlying these two groups is a series of younger rocks, not greatly
disturbed, consisting of sandstones, conglomerates, shales, limestones, and some
associated volcanic rocks that have been referred to as Keweenawan or Animikie.

Early Precambrian. Rocks that have been more or less doubtfully correlated
with the Keewatin or Huronian-and which consist mainly of schists, slates,
limestones, and quartzites occur here and there throughout the Precambrian of
the Mackenzie basin in areas usually small but sometimes many square miles in
extent, The characteristic feature of the rocks of all the areas is that they are
intruded by the granites or gneisses of the succeeding division, though they
probably represent formations of vastly different ages. They occur in isolated
bands which are merely remnants of formerly more widespread series of rocks
that at one time probably covered the greater part of the whole region. They
have, however, been so reduced in area by intrusions of granites and by deep
erosion that they now form apparently the smallest portion of the Precambrian
of this region.

Three main bands of these rocks on the north shore of Athabaska lake are
described by Tyrrell! under the name Huronian, and in a later report are referred
to by Alcock? as portions of the Tazin series.

The largest of these bands is situated on Beaverlodge bay “where it is
developed for 16 miles along the shore and extends back at least 10 miles to the
north. It consists of limestone, quartzite, slate, and sandstone. The limestone
is bluish in colour, weathering to a rusty brown, and occurs only in local patches
cut by gneiss. The quartzite is much the most abundant type in the series. It
is white and in places reddish, is very badly brecciated, and in several localities
contains considerable hematite.”? ‘The second band, which occurs on Slate
island and the adjacent mainland, consists of dark grey and brown schists,
quartzite, and breccia. The third band occurs near Sand point and runs parallel
to the shore. It consists of beds of quartzite and schist which form cliffs along
the lake shore for about 2 miles.

‘In the country north of Athabaska lake, rocks of the Tazin series are
described by Camsell* as occurring in seven distinct areas along the Tazin and
Taltson rivers. These areas are situated along the canoe route which follows
these two streams and are designated as follows: Thluicho Lake area, Thainka
Lake area, Long Reach area, Hill Island Lake/area, Thekulthili Lake area, Kozo
Lake area, and Tsu Lake area, They occur in elongated bands from 6 to. 28
miles in length. The rocks strike north or northwest, and consist of schists,
quartzites, argillites, limestones, and some voleanic rocks, all dipping at high
angles. All these rocks are intruded and completely surrounded by granite or
gneiss and have been highly metamorphosed thereby. They generally occupy
depressions that form the water-courses. The band on Hill Island lake, which is
at least 18 miles in length, is from an economic point of view probably the most
important in this region. It consists of narrow, interbedded bands of limestone,
argillite, and mica schist, which stand vertically and strike north and south.
Numerous veins of quartz mineralized by pyrite cut the beds; veins of the inter-

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1Geol. Surv., Can., Ann. Rept., vol. VIII, p. 17 D.
2 Geol. Surv., Can., Sum. Rept., 1914, p. 61.

3 Alcock, F. J., op. cit.

4Geol. Surv.,.Can., Mem. 84, DP. 25..

TAREE MONG Ep UIE > eT PRC Ean er eee Tee

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