Cross Lake Project (1983-86)

Geologist P.G. Lenton Year 83 STATION 5071
EASTING 572509 NORTHING 6041718 ZONE 14 DATUM NAD83
Date of mapping 06/26/1983

STRUCTURAL DATA

Planar Structures:
Structure type | Strike | Dip | Separation
schistosity | 71 | 64 |
fault | 309 | 68 |

-several 1 to 3 cm minor mylonites
PHOTOS
2 or 3 photos of offset by youngest mylonite
2 photos of brecciation of older cataclasis
1 photo of refraction of younger mylonite along old slip plane (younger is fine fracture going left to right)

PETROLOGIC DATA

Rock Number: 1

Rock Type: two component schlieric gneiss - intimate mixture of 2 major units
Descriptors:
white to pink or white and pink layers
leucocratic
layered
pegmatite
aplite veins/dikes present
Field Description:

-light white and pink layered gneiss complexly layered with pegmatite/aplite of more that one generation

Rock Number: 2

Rock Type: tonalite
Descriptors:
light grey
grey
gneissic
augened
intrudes rock #1
boudin or boudinaged
pegmatite lit present
cataclastic
Field Description:

-grey-white subgneissic augen tonalite/granodiorite
- intrudes(?) the old tonalite/pegmatite complex and is now rafted in it because of cataclasis
-Could be cataclastic equivalent of the younger porphyritic grey granodiorite that is a major component of the two component migmatites.

Textural Features
Type | Mineral | Min. Size | Max. Size | Abundance (%) | Unit
mafic mineral | biotite | 0.0 | 0.0 | 12.0 | %

Rock Number: 3

Rock Type: amphibolite
Descriptors:
black and green mottled or banded
layered
occurs as a raft
possibly pillowed
diopside clots
layering 1 metre
Field Description:

-large inclusions up to 4-5 m across of mafic black and green weathering gneiss
-layering discontinuous with numerous diopside-plagiclase clots and stringers; almost certain to be a pillowed or brecciated flow.
-several thin 1 m layers are almost featureless black amphibolite that may be massive flows

Textural Features
Type | Mineral | Min. Size | Max. Size | Abundance (%) | Unit
raft size in metres |  | 4.0 | 5.0 |  |

Minerals of Note
Mineral | Abundance (%)
hornblende
diopside
plagioclase

Rock Number: 4

Rock Type: pegmatite
Descriptors:
granitic
intrudes rocks 1 through 3
young phase / unit
aplite veins/dikes present
dike
Field Description:

-younger pegmatites that post date above units but are extensivly sheared and brecciated
-contain graphic microcline, plagioclase, biotite, garnet and traces of silver metallic mineral; probable specular hematite
-Pegmatite is associated with black-speckled aplite (sample)

Minerals of Note
Mineral | Abundance (%)
biotite
garnet
specular hematite

PHOTOS

Young dextral mylonitesbrecciating multicomponent gneisses

Detail of consistent dextral offsets by late NW trending mylonite. Note the pseudotachylite development near the scale card.

Sinistral folding in old cataclasis in the augen tonalite.

Old shearing in augen gneiss with sinistral form. Quartz veins in shear are boudinaged and rolled.

Refraction of younger mylonites (309°) along old slip plane of the main deformation fabric (071°).

Manitoba Geological Survey, 2017