Cross Lake Project (1983-86)

Geologist P.G. Lenton Year 83 STATION 5006
EASTING 572150 NORTHING 6040039 ZONE 14 DATUM NAD83
Date of mapping 06/18/1983

STRUCTURAL DATA

Planar Structures:
Structure type | Strike | Dip | Separation
cataclastic foliation | 65 | 75 |
mylonitic fabric | 311 | 68 | dextral

PETROLOGIC DATA

Rock Number: 1

Rock Type: tonalite
Descriptors:
gneissic
leucocratic
Field Description:

-Very old highly gneissic unit that has undergone extensive deformation, mainly shearing.
-Whiskey Jack Augen unit

Textural Features
Type | Mineral | Min. Size | Max. Size | Abundance (%) | Unit
mafic mineral | biotite | 0.0 | 0.0 | 5.0 | mm

Minerals of Note
Mineral | Abundance (%)
plagioclase
chlorite
biotite

Rock Number: 2

Rock Type: granodiorite
Descriptors:
porphyritic
dike
dark grey
homogeneous
boudin or boudinaged
Field Description:

-Dikes of homogeneous charcoal grey plagioclase porphyritic quartz diorite
-it intrudes an already highly deformed and sheared TNLT but has undergone extensive deformation
-exists now as a series of boudins

Textural Features
Type | Mineral | Min. Size | Max. Size | Abundance (%) | Unit
mafic mineral | biotite | 0.0 | 0.0 | 15.0 | mm

Minerals of Note
Mineral | Abundance (%)
plagioclase
chlorite
biotite

Rock Number: 3

Rock Type: pegmatite
Descriptors:
massive
granitic
Field Description:

Apparent history
1- oldest unit leucocratic tonalite
2- leucocratic tonalite is extensively intruded by old lit-par-lit veinlets or mobilizate
3- tonalite gneiss highly deformed and sheared
4- dikes of grey porphyritic granodiorite intrude the tonalite gneiss
5- grey granodiorite is intruded by leucocratic tonalite stringers
6- Tonalite and granodiorite intruded by an E-W set of pegmatite dikes of 3-5 cm thickness
7- Extreme deformation of all rocks, mainly cataclastic in nature broke the granodiorite dikes into agmatitic blocks and large boudins
8- Intrusion of N-S zones pegmatites (pegmatitic borders and aplitic cores) with 2 m sinistral offset
9- Continuation of cataclasis imposes fracture cleavage in late pegmatites with attendant pinch - and - swell and undulous folding. Deformation is still in the main shearing plane
10- Everything is crosscut by late, undeformed mylonites with pseudotachylitic margins with 120cm of dextral offset

PHOTOS

Large block boudin of grey porphrytic granodiorite in old sheared schlieric augen leucocratic tonalite. Notice how the laering/fabric in the old gneiss wraps around the boudin ends.

Detail of marginal deformation on grey porphyry boudin.

Overview of outcrop showing the schollen structure of the complex.

Younger cross cutting pegmatite containing small inclusion of grey porphyry granodiorite.

Late dextral mylonite with quartz filled extension veins.

Overview of t he schollen migmatite with the late mylonite zone central in the picture.

Manitoba Geological Survey, 2017