The lower contact of the Midas Formation is con-
formable and gradational over about a metre interval with
the Yanks Peak Formation quartzite.

On Roundtop-Middle Ridge the base of the Midas
Formation is a dark grey limonitic siltite resting sharply
on medium grained dark grey quartzite of the Yanks Peak
Formation. South of Cariboo River, in fault packages
east of those which include the Roundtop-Middle Ridge,
the base of the Midas Formation is usually an impure
quartzite or siltite similar to beds found in the underlying
Yankee Belle Formation.

Slate and phyllite of the Midas Formation are grey
and grey olive, much like those of the Yankee Belle For-
mation; generally not as olive. There are some localities
where they are dark weathering and the primary one is
described in the measured section from 4.5 km southeast
of Black Stuart Mountain. Outcrops on Anderson Ridge,
continuous with this section, are lighter weathering and
equivalent strata north of Kimball Creek contain only
minor dark grey phyllite.

Siltite and fine grained quartzite are light grey to dark
grey, flecked with less than 1% hematite grains and
weather light olive grey to rusty brown. They are sorted
to poorly sorted with a micaceous matrix, interbedded
on a 3 to 30 cm scale with grey pelite, and may grade
normally upward into that pelite. They are not confined

Table 6.
Midas Formation (from point-count data)

to any particular part of the formation, however, they
are more common near the base and top.

Vic Sandstone. It is proposed that the Vic Sandstone
be a formal member of the Midas Formation. It consists
of olive-grey to light grey quartzite and is distinguished
from other quartzite of the Midas Formation by being
coarser grained and containing crossbedding. It occurs
in most areas underlain by the formation. A reference
locality for the Vic Sandstone is approximately 3.5 km
upstream along Cunningham Creek from its junction with
Cunningham Pass Creek (52°57’10’’N, 121°21°40’’W).
This locality was described by Holland (1954, p. 21, Plate
IVA) and Sutherland Brown (1957, p. 27, Plate IVA).
Geoff Hodgson (personal communication, 1978) named
the unit after the Vic claim block in which it lies. The
thickness at the reference locality is approximately 5-8 m
and varies to 12 m throughout the area.

The quartzite is medium grained, sorted to poorly
sorted and micaceous. Its most distinguishing character-
istic is its 10 to 50 cm trough and planar crossbeds marked
by concentrations of ilmenite and other heavy minerals
(Fig. 9). The quartzite is commonly graded normally from
medium grained olive grey to fine grained or silty, grey
to dark grey. The mineralogy and grain size as determined
with a microscope are listed in Table 6, with those of
several other rocks of the Midas Formation.

Mineralogical compositions (volume per cent) and quartz grain size (microns) of samples from the

1 2 3 “

ies 8 g 10

Quartz 2220. 40 56 10.2

Potassium feldspar Bs) 1
Plagioclase 8
Muscovite 6 1.4 ade
Biotite
_ Chlorite
_ Opaques 29.8 5.4 =
Zircon v3
| Epidote
Sphene
| Tourmaline 5
Apatite
| Secondary minerals
Sericite and clays 38.9
Chlorite 4
Biotite

>™N
nn

| Matrix 85.8

| Average quartz size
| (x10° mm) 70 40 70 40

9
94. 52.4 5.8 9 68.
8.

WHUONwDYN
WWM

4.3

oo Pr
aN

90 80 40 55 70 80

1 Siltite from junction of Antler and Pleasant Valley creeks. ie
2 Siltite from Loskey Creek area.

| 4 Phyllite from headwaters of Roundtop Creek.

3 Fine grained quartzite (Vic) 3.5 km upstream along Cunningham Creek from junction with Cunningham Pass Creek.

5 Fine grained quartzite (Vic) from saddle between Roundtop and Middle mountains.

6 Very fine grained quartzite from ridge south of Middle Mountain.

7 Slate from same locality as 6.

8 Very fine grained quartzite (Vic) from ridge northeast of Middle Mountain.
9 Fine grained quartzite from 4.5 km southeast of Black Stuart Mountain.

10 Fine grained quartzite from top of section 4.5 km southeast of Black Stuart Mountain.

18