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The present joint pattern of the Abraham Creek body commonly
bears no apparent relation to the local gneissic structures of the body or
of the surrounding younger phases of the Hogem batholith, or to the
attitudes of the myriad dykes, stringers, and healed fracture systems
by means of which many of the different rock masses were emplaced.
There is ample evidence that most of the rock has been through a condition
of plasticity, which appears to have completely relieved stresses connected
with the formation of the Abraham Creek body itself. The stresses
producing most of the present fractures are clearly of later origin, and
may be related to the intrusion of the acidic phases of the Hogem batholith.
The attitudes of four hundred and sixty-six dominant joint sets from this
body were plotted (See Figure 11). It can be seen that most of these
joints dip very steeply to vertically with a southeast, east, and northeast
trend. Analysis of the relation of the shear and tension joints in this
pattern, assuming the easiest relief to be vertically upward, leads to the
suggestion that the main fracturing has been in relief of forces that were
directed to the northeast, upward at an angle of 5 to 25 degrees.

CONTACT RELATIONS AND MANNER OF INTRUSION OF THE HOGEM BATHOLITH

The only melanocratic, quartz-free body in the Hogem batholith whose
contact with the Takla group is well exposed is the Tutizzi Lake body,
whose relations suggest a forcible invasion of a heterogeneous, apparently
viscous magma into much shattered andesites and tuffs. The actual con-
tact of the Abraham Creek body with the Takla group to its northeast is
nowhere exposed, but outcrops of each rock unit close to the contact show
that the contact plane is relatively regular and steeply dipping for a
vertical interval of at least 2,400 feet.

The more widespread, light-coloured, younger rocks show a variety
of types of contact, both against Takla group rocks and against the older
phases of the Hogem batholith. Contacts with Takla group rocks are well
exposed on the ridges between Thane and Kliyul Creeks, and are of three
main types, two of which appear to be related in a general way to the
composition of the intruding rock.

Gradational Contacts

The first type of contact is that shown by a few, relatively dark
granodiorites and quartz diorites, and is typically developed on the ridges
on each side of the east branch of Matetlo Creek. In these places the
batholith has been emplaced in comparatively coarse-grained porphyritic
andesite, against which there is no sharp contact with the lighter coloured
coarse granodiorite. Across a distance of about 300 feet, the granodiorite
becomes progressively finer grained and darker, and passes into a slightly
sheared, sugary, grey-green rock in which ‘phenocrysts’ of feldspar are
vaguely visible, and which in turn grades into saussuritized porphyritic
andesite. All the observed contacts of this type are sheared, but no single
fault, bringing rocks of noticeably different nature into contact, was found.
East of Matetlo Creek, the planes of shearing strike parallel with the
contact and dip about 45 degrees towards the batholith; the contact itself,
as shown by its trace over a vertical interval of 2,500 feet, is nearly
vertical. Slickensides on the shear planes trend directly down the dip and