Cross Lake Project (1983-86)

Geologist P.G. Lenton Year 83 STATION 5209
EASTING 572659 NORTHING 6049190 ZONE 14 DATUM NAD83
Date of mapping 08/18/1983

STRUCTURAL DATA

Planar Structures:
Structure type | Strike | Dip | Separation
cataclastic foliation | 261 | 51 |

PETROLOGIC DATA

Rock Number: 1

Rock Type: pegmatite
Field Description:

Dikes A15 and A16
-highly deformed podiform body 10 m wide. Has a strongly developed cataclasic foliation at 261/51.
Strong development of rolled spodumene augen. Quartz is microfractured and annealed into a beige saccharoidal textured rock. The dike appears to have been under directed stress during crystallization as spodmene and tourmaline crystals show preferred orientation in the foliation plane that precedes the cataclastic disruption.
- 4 photos showing cataclastic deformation of dike with augening of feldspar and spodumene
- 1 photo shows primary alignment of spodumene; another to show alignment of tourmaline and spodumene.
- mineralogy: dominant phases are grey-white microcline and pale white to greenish spodumene. Quartz accounts for about 20 %.
Primary muscovite is present but relativly rare.
Beryl is fairly common as milky white crystals up to 1 cm across.
-apatite is very rare and bright green in colour.
Blue black tourmaline is most abundant near the contact.
Columbite crystals occur sporadically, mainly near the margins.
There is no discernable zoning in the pod. Quartz is more or less evenly distributed with no development of blocky-feldspar zones.
Any zoning that may have existed has been obliterated by shearing.
Spodumene counts for around 20 % of dike and was crystalized as elongate columnar crystals betweeen 5 mm and 4 cm across, and probably up to 15 cm long
- There is no significant exomorphic effect on the surrounding amphibolites

PHOTOS

Cataclastic deformation of dike with augening of feldspar and spodumene.

Cataclasis in the pegmatite caused by a westerley shear zone running along the top of Spodumene Island.

Extreme shearing with augening of feldspars and stretching of spodumene crystals. Much of the very fine grained ground mass is shattered and annealed quartz. The band of massive grey quartz was protected from shearing being in a pressure shadow behind large feldspars.
Because of the abundance of quartz it is assumed that this portion of the exposure is sheared quartz core.

Dextral rotation of feldspar and spodumene porphyroclasts.

Large spodumene crystals aligned in the shear plane. The spodumene shows extension in the shear plane with the crystals breaking in the c direction, moving apart and then being healed by late quartz infill. This suggestes that the pegmatite crystallized in a directed stress field and was therefore synchronous with late deformation.

Same features as previous photo but with tourmaline aligned in the shear plane, pulled apart and then healed by quartz.

Manitoba Geological Survey, 2017