Figure 53. Pillow basalt of the Antler Formation near
Mount Murray. (GSC 191043)

Plagioclase,
er aay BE ee St ae 10-35%
microphenocrysts, 0.4 to 3mm An(25-35) 3- 8%
Augite,
erysiais, 0.0) (0 0.0: ue 2... St ee. 10-35%
microphenocrysts, | to 3 mm ........ 0- 3%
Chlorite,
filling 0.1 to 1 mm interstices ........ 7-15%

Semiopaque groundmass,
sheaths and irregular clumps of very fine

chlorite, epidote and minor calcite .. 15-40%

Opaques,

nyrne, O04 16° US ain. fo) Fee Te 0- 7%

otners, 0.1 10-0: 7 Mme a: S. oe CF. 3- 5%
Pebitcte 08 $6 OD I on! sien 0- 5%
ee a Re Ee ene ee ear 0- 3%
Amygdules,

0.1 to 0.4 mm from edge to core of

quartz, calcite, chlorite, and epidote .. 0- 2%

The amount of augite decreases with a decrease in the
overall crystal size. The finest grained volcanic examined
contains less than the 10% augite (cited above), but on
average the pillow basalts are more coarsely crystalline
than this sample. The groundmass plagioclase laths are
highly altered to a fine intergrowth of feldspar, chlorite,
epidote, and minor calcite and sericite. Plagioclase pheno-
crysts are saussuritized. Augite is altered along fractures
but is fresh in most specimens. Locally the basalt is
picritic containing fine olivine phenocrysts.

Diabase forms sills, dykes and coarse equivalents of
the finer pillow basalt. Its mineralogy is similar to that
described for the pillow basalt except that the augite is
coarser and the rock has an ophitic texture. Alteration
products are similar, with the addition of pumpellyite as
an interstitial filling and as rims to augite in diabase from
the ridge between mounts Guyet and Tinsdale. Coarsely
crystalline diabases, which are transitional to gabbro, do

74

not have the fine grained feldspar-lath groundmass and
instead have plagioclase crystals up to 4 mm long,
interstitial to 0.5 to 4 mm euhedral augite and subhedral
hornblende. The plagioclase is saussuritized and the
hornblende partly altered to chlorite.

Agglomerates and breccias are mineralogically similar
to the pillow basalts and are intimately associated with
them.

Ultramafic rocks were found near Mount Murray and
these have a mineralogy distinct from the diabase and its
associated gabbro. The ultramafics consist of olivine,
altered to talc and serpentine; clinopyroxene and/or
orthopyroxene; hornblende and the alteration product,
chlorite. From the limited number of samples collected
they range from lherzolite to harzburgite. The strati-
graphic relationship between the ultramafic and other
Antler Formation rocks is unknown. The ultramafic
rocks form pods and sheets mixed with pillow basalt,
diabase, gabbro, and chert on Mount Murray.

Chemical analyses of Antler Formation mafic igneous
rocks are listed in Table 15 and others have been pre-
sented by Sutherland Brown (1957, p. 44) Campbell
(1971, p. 104 and 108), and Hall-Beyer (1976). Suther-
land Brown’s (1957, p. 44) samples 3 and 4, Table IV,
may be from the Waverly Formation. Both Hall-Beyer
(1976) and Campbell (1971) considered their chemical
analyses to represent tholeiitic basalts and Hall-Beyer also
postulated komatiitic affinities for some. Sutherland
Brown (1957) reported his analyses as representative of
spilites.

The cherty pelite and pelitic chert (Fig. 54) forms 1 to
7 cm even beds varying from grey to light grey, grey green
to olive, very light green and maroon. Thicker beds are
primarily of pelitic chert or cherty siltite and thinner inter-
beds are of cherty pelite. These well bedded ‘‘ribbon
cherts’’ are best exposed on Sliding Mountain and Mount
Tinsdale. Sutherland Brown (1957, p. 37-38) provided a
good description of the mineralogical characteristics of
the ribbon cherts. They consist of:

Detrital quartz,
0.01-0.05 mm mostly but some to 0.2 mm variable
Detrital muscovite and biotite,

Oy RN ts a ee eee a 0- 3%
Detrital plagioclase,
ee NTN ag sg ee a ie all rare

Detrital accessories,
zircon, tourmaline, epidote(?)

GCs hee Oe oes ier ee oe 0- 1%
Matrix chert,
pervasive through various layers ...... 20-90%

Ovoids of chert,

probably recrystallized radiolaria,

Se ME ne ee ed aes Cone ce 5-25%
Secondary micas,
chlorite and sericite

may or may not be aligned,

stilpnomelane is not aligned,

Were Ts 0550 2G RE ae A 0-10%