Cross Lake Project (1983-86)

Geologist P.G. Lenton Year 83 STATION 5202
EASTING 575322 NORTHING 6059970 ZONE 14 DATUM NAD83
Date of mapping 08/10/1983

STRUCTURAL DATA

PETROLOGIC DATA

Rock Number: 1

Rock Type: pegmatite
Field Description:

-these dikes need further work-blasting is neccessary to determine form and zoning
-basically the dikes are composed of two textural phases, neither of which is typically pegmatite
-very coarse granite - albite+biotite+muscovite+quartz+tourmaline+apatite -homogeneous equigranular
-grain size about 4 cm
-in the west body (grid 0+0) it appears to form a thin cap near horizontal (?) altitude
-in the east body it is irregular in distribution BE is present but rare
-microcline is absent
-equal amount of biotite and muscovite or muscovite>biotite
Albite Pegmatite
-alkali feldspar syenite in composition but albite dominent with only around 2% microcline as blocky chocolate coloured masses
- beryl is abundant, particularly in the margin where it is common as 1 cm to 10's of cm long crystals of pale green, yellow green or lemon yellow euhedral crystals often intergrown with blue apatite, tourmaline and red garnet
-quartz is around 5% or less
-composed of sub to euhedral albite crystals averaging 6 x 20 cm with 5 % coarse -muscovite books (typically 2-10 cm wide and 1 cm orless thick) traces of tourmaline, apatite (locally 2 %), garnet, beryl, and 2 - 3% blocky microcline
-texturally is ultra coarse granite - essentially homogeneous equigranular except for microcline megacrysts
-contact between 2 phases marked by rich accumulations of blue apatite, tourmaline and red garnet
-mineral cross section and large sample of coarse granite

PHOTOS

Geological map of the south western portion of the 5202 pegmatite (Anderson A-37)

Geological map of the north eastern portion of the 5202 pegmatite (Anderson A-37)

Apatite rich marginal phase of the albite syenite pegmatite (33/+21). Note the coarse books and rosettes of muscovite.

Overview of previous picture showing the highly strained margin with country rock.

Additional detail of the apatite rich margin of the albite syenite pegmatite (33/+21).

Muscovite - tourmaline rich, coarse granitic phase of station 5202 (grid 33/+12).

Close-up details of previous photo.

Albite+muscovite granite/pegmatite.

General view of the pegmatitic granite at 41/+21.

Apatite rich margin between coarse granite and albite pegmatite (2/+1). Large green beryl crystals growing perpendicular to the margin.

Overview of apatite rich margin between coarse granite (on left) and albite pegmatite (on right) (2/+1). Large green beryl crystals growing perpendicular to the margin.

Large green beryl surrounded by white beryl, equant albite, corase muscovite books, quartz, blue apatite and tourmaline needles. Microcline is not common in the this phase of the albite pegmatite.

Concentrations of dark blue apatite with locally increased quartz on the margin between the coarse granite/syenite (top) and the albite pegmatite. to bottom of picture.

Very large yellow-green "scabbard" beryl (euhedral prism of yellow-green beryl with a quartz-feldspar core). Note the abundant large red euhedral garnet crystals, blue apatite, clevelandite and muscovite.

Concentration of pinhead red garnets and blue-black apatite along marginal contact at 0.5/-1.

Dense concentrations of green beryl, agrnet, apatite and very coarse fans of muscovite at location 0/+0.

Manitoba Geological Survey, 2017