amie

102

The pegmatite is found only as dykes and sills, commonly sharply curved,
usually less than 10 feet thick and 500 feet long. In places the pegmatites
form a reticulate network, which may occupy nearly 50 per cent of the
rock volume over an area 4 mile square.

The pegmatites are of simple mineralogical composition; almost all
are composed principally of quartz, in both opaque white and smoky trans-
parent forms, microcline microperthite, and muscovite. Other minerals,
rarely observed to comprise more than 5 per cent of the rock volume, are
sodic plagioclase, biotite, actinolite, garnet (almandine ?), magnetite,
sphene, sillimanite, and zircon. The pegmatites have the variable texture
characteristic of bodies of this type, showing much mutual replacement and
intergrowth. Muscovite, which is the only quantitatively important
mineral possessing a tendency to euhedral form, occurs in pseudo-hexagonal
books as much as 5 inches in diameter and 3 inches thick. Pockets in the
dykes up to 10 feet across, in which nearly half the rock is composed of
muscovite crystals more than 2 inches in diameter, have been found. A
fewsay ies contain biotite crystals up to 2 inches in diameter and 1 inch
thick.

Most of the pegmatite bodies have obviously replaced the rock in
which they lie. Inclusions within the pegmatite bodies retain the same
orientation as the wall-rock, and large, regular and irregular bodies cut
the quartzite and banded gneiss without producing any offset of contorted
structures (See Figure 5). One of the most remarkable features of the
pattern so produced is the apparent disregard for the banded structure
of the host rock; true sills are much less common than irregular, curving
bodies crossing the foliation at all angles. The contact between the pegma-
tite and the wall-rocks is in most places gradational across widths of about
3 inch. An exception to the common replacement pattern is shown by a
few pegmatites in the grey granodiorite stock; here they occur as narrow,
straight-walled dykes with knife-edged contacts, and appear to fill fractures.

The areas containing much pegmatitic material commonly also contain
many quartz veins, and the two rock types are probably genetically related,
although no gradational phases were observed. There are two distinct
types of quartz veins in the highly metamorphosed rocks northeast of
Blackpine Lake: one of white, milky, opaque quartz, almost completely
devoid of any other minerals, and one of bluish to smoky transparent
quartz, commonly rusty weathering and containing scattered grains of
arsenopyrite and chalcopyrite. The white quartz veins are the more
numerous, and larger, though bodies more than 3 feet thick and 200 feet
long are rare; they both cut and are cut by the pegmatites. The bluish
transparent veins are rarely more than a foot thick, and were only
observed to cut the pegmatites. Within the pegmatite bodies themselves,
the smoky, transparent quartz is found mainly as isolated pockets.

The pegmatites are associated with, and in places grade into, bodies
of aplite.

Aplhte
Bodies of aplite are much fewer than bodies of pegmatite in the

Wolverine complex rocks. They are restricted to areas where pegmatites
are abundant, and occur as narrow, fairly regular dykes, or as vaguely