Table 9. Mineralogical composition of Guyet Formation conglomerate.
Rock Q 0 P Z B C C P 5 VR 3 M 0
no. T R L R 0 H H L L ee: T T T
Z | G C 1g R 5 T T Seog! Y X H
1 2 1 37 4 17 g 23 7
2 g 1 1 5 17 ‘4 2 2 37 22 + C,MC
4 12 34 16 1 20 + 16
5 46 1 + + 14 8 20 13
6 55 + 1 36 1 2 1 2 2 1
7 4 2 69 11 6 6 4
8 16 84 1 M
9 8 + 71 6 5 3 3 4
10 24 2 + 25 13 10 27
11 57 1 15 x 6 12 5
10-1 3 + 42 13 18 11 3 1 oe
26-3D 67 + + 23 4 3 1
46-16 66 2 16 5 12 1 T
46-28 35 3 4 7 CRB
113-1 ad + + 1 33 2 + + 5 2 7 + T
113-1A 59 2 + 4 +5 3 1 6 3 7
Lt3-2 42 + 2 35 E 3 + 3 + 10 1 QM,M,T
126-25 43 1 + + + 19 5 7 6 4 8 7 1 QM,B
126-26 48 3 + 1 2 1 3 1 + TZ 23 1 QM,B
Key
QTZ = Quartz PLT = Pelite C = Chlorite
ORT = Orthoclase SLT = Siltstone CRB = Carbonate
PLG = Plagioclase VLC = Volcanic M = Muscovite
ZRC = Zircon RXQ = Recrystalline quartz MC = Microcline
BOP = Black opaques STY = Stylolites QM = Quartz mylonite
CHR = Chert MTX = Matrix B = Biotite
CHP = Cherty argillite OTH = Others
+ = less than 0.5 per cent
All mineral percentages are rounded to the nearest integer
Note: Samples 1 to 11 have been analyzed for strain and are discussed further in Appendix B.

Reference areas for the Guyet Formation are at
Mount Guyet and Summit and Alex Allen creeks. Thick-
ness of the formation is variable because it is discontinu-
ous. The formation is thickest where the conglomerate
is predominant, as at Alex Allan Creek, Mount Guyet
and Mount Tinsdale. In general the formation is from
several metres to 400 m thick, commonly being between
100 to 300 m thick. It pinches out near Black Stuart
Mountain.

The lower contact of the Guyet Formation is con-
formable onto parts of the black pelite unit of the Black
Stuart Group and may be unconformable on the Waverly
Formation north of Mount Guyet. Basalt clasts of the
Guyet Formation conglomerate resemble basalt of the
Waverly Formation and may have been derived from it.

The sandy conglomerate (Fig. 19) underlies the area
of Alex Allan Creek, Mount Guyet, and the island at the
north end of Spectacle Lakes. Granule- to cobble-size
clasts of green, tan, and grey chert to cherty argillite, grey
to black chert, black pelite, light grey micaceous siltite
and quartzite, and minor limestone and basalt are sup-
ported in a sand-size matrix of quartz, chert, siltite and

minor feldspar. The matrix clasts are subrounded to
rounded. Granule to pebble chert fragments are angular
to subrounded and siltite and quartzite are subrounded
to rounded. Pebbles and cobbles of limestone are angular.
Pelite and cherty argillite are in most places too deformed
to estimate original shapes.

The bedding within the sandy conglomerate is defined
by layers of sand in which are supported coarse clasts and
layers of sand with no coarse clasts. The sand matrix is
continuous across the boundaries. Scoured contacts
between overlying conglomerate and underlying sand-
stone were seen locally but their frequency is unknown
due to the type of exposure. The sandstone is planar
bedded where bedding could be detected from trains of
opaques. Channels of Guyet conglomerate are cut into
the underlying black siltstone and pelite of the Black
Stuart Group at the junction of Tinsdale and Cunning-
ham creeks. The erosional relief is up to 75 cm and the
width of the channels is on the order of 1 to 2 m.

The sandy conglomerates of Alex Allan Creek and
Mount Guyet are very similar in clast content, size, shape,
percentage and distribution. The Spectacle Lakes occur-

29