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Rocks with still less orthoclase and quartz pass into typical quartz
diorites, and finally into dark grey syenodiorites and true diorites. The
typical diorite of this series consists of about 60 per cent dark grey or
greenish plagioclase and 40 per cent augite or amphibole. A few small
bodies of pyroxenitic and amphibolitic material are associated with the
diorites. These may represent remnants of engulfed older rock or parts
of the earlier, melanocratic phase of the Omineca intrusions. ~

Approximately 234 miles of outcrop of these rocks in the Hogem
batholith were traversed within the map-area. Along the lines so investi-
gated, the adamellite-granite rocks occupy 35 per cent of the batholith,
in bodies with an average estimated diameter of 4,000 feet; the largest
body encountered was 28,000 feet across. The granodiorite (monzotona-
lite) constitutes 87 per cent of the rocks traversed, in bodies with an
average intercept of about 3,000 feet; the largest single body recorded
was 7,500 feet across. Rocks that appear to be best described as quartz
diorite make up 22 per cent of the total within the main body of the
batholith; the average diameter of masses of this rock is about 3,400 feet,
and the largest single body observed has a diameter of 12,600 feet.
Diorite and syenodiorite, with very minor pyroxenitic and amphibolitic
rocks, constitute 6 per cent of the rocks traversed, in bodies about 2,000
feet across.

The modal (mineral) composition of thirty-nine specimens of these
rocks, distributed as shown in Figure 9, is presented in Table I and
plotted on Figure 10. The rocks appear to represent all stages in a
progression from diorite toward relatively quartz-rich, orthoclase-poor
granite.

Bodies of pegmatite composed mainly of quartz and microcline-
microperthite are found as dykes and irregular masses up to 1,000 feet
by 500 feet in all parts of the batholith, and in some of the Takla group
rocks near the contact. Most of the pegmatites are salmon-pink or orange-
brown, and contain about equal amounts of feldspar and quartz, commonly
in graphic or myrmekitic intergrowth. They are associated with a smaller
number of dykes of aplite, alaskite, and leucogranite. A few of these
dykes are remarkably straight and persistent; one exceptional body of
leucogranite about 150 feet thick may be traced from Detni Creek to the
ridge south of Klakring Creek, a distance of 11 miles.

STRUCTURAL RELATIONS
MUTUAL RELATIONS OF THE VARIOUS INTRUSIVE BODIES

The individual igneous bodies that compose the Hogem batholith
and its satellites are almost all separated by sharp, intrusive contacts.
As has been described, the melanocratic, quartz-free, hornblendite-appinite-
hornblende diorite series of rocks forms separate bodies within or adjacent
to the batholith. Among the other rock types the sequence of intrusion
is in most places fairly apparent, and although widely diverse in detail,
was found to show a more or less constant trend in all parts of the
batholith from which information was obtained. It is not meant to be
inferred, however, that all bodies of similar-appearing rocks are directly
related. The general trend of successively younger rocks is from diorite,
through quartz diorite and granodiorite, to adamellite-granite. Evidence

7h