Table 12. Compositions of diabase from the
Cariboo Terrane

Baas Se
| Plagioclase (altered)
laths 0.3-1.5 mm long ..... 40
blocky crystals 0.3-2.5 mm
ANos at Anas Phy sire rss Se tak ae 50 65 50

Augite (partially chloritized)

Sh 5

eT ton! 2esiciy.. .4): 13
Chlorite (interstitial) .......... 27 30
Biotite (secondary)

COW om... le. 10 Te

| ele eo a rs vu 8 10
Stilpnomelane (secondary) .... 5 |
Muattz, 0.05-0:3 mm ..°..... o 5
Sericite (secondary) ......... 2 5
Fe-dolomite (Secondary) ...... 10 5
Opaque

ee 8 4 )

is dedeoe eb 2 ae a a
Myrmekite (Secondary) ....... 8 re

| Key
1. Dyke on ridge south of Middle Mountain
2. Black Stuart Mountain area
3. Black Stuart Mountain area
4. Black Stuart Mountain area, olive-brown biotite is an
alteration of hornblende

Quartz porphyry intrusives

A quartz porphyry to quartz-feldspar porphyry sill can
be mapped intermittently from Jubilee Creek to the area
west of Two Sisters Mountain. It ranges up to approxi-
mately 8 m in thickness. A similar intrusive is found in
the Antler Formation near its base in the Mount Tinsdale
area. The Proserpine dykes may be ankeritized equiva-
lents of this quartz porphyry series.

The mineralogical content of the sill was estimated
from thin section:

‘(Juartz, phenocrysis, 1-5 mm ..........- 5-15%
Potassium feldspar, phenocrysts, 1-6 mm 0- 8%
Oligoclase, phenocrysts, 2-4 mm ........ 0- 3%
Matrix of fine quartz, sericite and fine

piitesrof oligoclase eit eek 8: 80-85%

The sill intrudes Guyet Formation and strata overlying
Middle Pennsylvanian Alex Allan Formation limestone
and therefore must be Pennsylvanian or younger. It is
folded and therefore was emplaced during, or prior to,
the major folding event.

The felsic intrusives were intruded prior to some fold-
ing and after the emplacement of the Antler Formation
in the early Mesozoic. The major folding event is Jurassic
and/or lower Cretaceous. The age of the quartz porphyry

intrusives is therefore bracketed between Permian and
Late Cretaceous.

Lamprophyre intrusives

The only occurrence of lamprophyre found is the one
reported by Holland (1954, p. 23) and Sutherland Brown
(1957, p. 45). It intrudes the northeast-trending fault at
Roundtop Mountain. The dyke is later than the fault and
is therefore younger than the pervasive deformational
event (Columbian). It is considered to be Tertiary, but
may be Late Cretaceous.

Economic geology

The Cunningham Formation is host to some replacement
deposits of galena and sphalerite. For example, on the
Cunningham Forest Road at Roundtop Creek, limestone
is altered to dolostone with minor galena.

The Black Stuart Group on Anderson Ridge hosts
quartz-barite veins with galena and lesser amounts of
sphalerite (Reed and Lovang, 1981). Although the miner-
alization is reported to be from the Mural Formation it
is more likely to be hosted in the chert-carbonate unit of
the Black Stuart Group.

Structural and metamorphic geology

The Cariboo Terrane consists of essentially one structural
package; defined as a deformed sequence of rock sepa-
rated from others by an angular unconformity. The pack-
age consists of all units from Kaza Group to Permo-
Triassic sedimentary rocks.

The structures of the package form a spectrum but
for purposes of discussion are divided into 3 categories
based on conditions of formation and superposition. .
From oldest to youngest they are 1) flow, 2) ductile short-
ening, and 3) brittle shortening and extension. The strain
environment is emphasized over the superposition of
structural elements. As a consequence little importance
is attached to designating structures as S, or S etc.;
although for comparison purposes this is done in its sim-
plest form in Table 13. The metamorphism is included
in the discussion of the structures because it reflects to
a large degree the strain parameters. The structural spec-
trum began with flow folding possibly in latest Triassic
and ended with brittle extension due to uplift in the
Eocene.

Flow

This category of structures includes isoclinal, small scale
rooted and rootless folds in limestones of the Cunning-
ham, Yankee Belle and Mural formations. The limbs of
these folds are parallel to a colour lamination and part-
ing that parallels bedding as displayed by lithological tran-
sitions. They are found only locally in recrystallized lime-
stones, and no larger scale isoclinal structures have been
found associated with them. Too few measurements of

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