Cross Lake Project (1983-86)

Geologist P.G. Lenton Year 83 STATION 5077
EASTING 571922 NORTHING 6039122 ZONE 14 DATUM NAD83
Date of mapping 06/27/1983

STRUCTURAL DATA

Dikes and Sills:
Rock Number | Type | Width (m) | Strike | Dip
0 | gabbro | 0.00 | 185 | 34

PETROLOGIC DATA

Rock Number: 1

Rock Type: gabbro
Descriptors:
Molson dike
Field Description:

Very large mafic dike
Cross section of thin sections taken from across this large Molson dyke:
samples 1,2,3,4,5,6,8,9,10,11,12,13,14,16A,16B,16C,17,18
Cross section:
1) 0m - chill margin on hanging wall contact
2) 3m along shore - plagioclase glomerocrysts in fine grained norite
3) 12m - clinopyroxene rich melagabbro. Small 2 cm coarse diorite clots analygous to pegmatite. 20cm triangular inclusions of leucotonalite. Invaded by quartz veins and pegmatitc stringers. Not a Molson dike as I first thought.
4) 18m - hornblendic gabbro
5) 24m - hornblende pyroxene gabbro
6) 35m - waxey grey fresh surface with clinopyroxene phenocrysts. 054/72; 8mm mylonite that predates late faulting
7) 52m - cumulous pyroxene gabbro - cumulous layers at 182/78 topping to west based on graded plagioclase. Two photos of layering with tops to top of photo.
8) 53m - gabbro with gabbro pegmatite pod (55x23cm)
9) 80m - 098/82 minor mylonite shears in coarse hornblende gabbro
10) 95m - leucogabbro with 1-2cm oval mafic clots
11) 125m - pyroxene porphyritic gabbro with pyroxene/plagioclase cumulous layering - grading tops to west
12) 150m - 20m of laminated cumulous zones in coarse gabbro
13) 175m - as 12
14) 210m - at farthest tip of point - coarse leopard spot leucogabbro with sulfides. Photo 4m above footwall of small gabbro pegmatite. 2 photos of base of glomeroporphyritic gabbro in contact with underlying mafic gabbro
15) 225m - around corner of point - anorthositic gabbro
16) 245m - glomeroporphyritic anorthositic gabbro in contact with mafic gabbro: samples 16a glomeroporphyritic anorthositic gabbro, 16b mafic gabbro, 16c contact between a & b.
17) 260m - pyroxene cumulate gabbro
18) 275m - footwall contact - sample of fine grained gabbro 40cm above contact.

PHOTOS

Plagioclase - pyroxene cumulous layering in large Molson dike. Top is toward top of photo

Close-up of pyroxene cumulous with plagioclase indicating tops upward on photo.

Gabbro pegmatite pod. Note the growth of elongate hornblende crystals perpendicular to contact. The amoeboid light grey patches are quartz.. This type of pegmatite was sampled for geochronology at station 6022 and produced a precise age of 1884 ± 2 Ma.

Contact between coarse gabbro-norite (bottom) and a "leopard spotted" glomeropophyritic gabbro.

Close-up of glomeroporphyritic anorthositic gabbro with orthopyroxene (?) crystals mantled by palgioclase crystals.
Note the penetrative fabric in this rock which is located near the middle of the dike. This shows that the 050° deformation was still active post intrusion of the Molson dike at 1884 ± 2 Ma.

Manitoba Geological Survey, 2017