Cross Lake Project (1983-86)

Geologist P.G. Lenton Year 83 STATION 5156
EASTING 576077 NORTHING 6048182 ZONE 14 DATUM NAD83
Date of mapping 07/21/1983

STRUCTURAL DATA

PETROLOGIC DATA

Rock Number: 1

Rock Type: pegmatite
Field Description:

DIKE A-1
-estimation of attitude on main body based on contact of core zone and upper intermediate zone 263/13
-upper wall zone:
-extensively exposed on the dip surface it comprises platy grey albite, quartz, small anhedral microclines, 0.5-2.0 cm beryls
-typically it has very little muscovite
-shows a strong development of quartz aggregate schistocity at 075/55
-transition into upper intermediate zone is gradational, marked largely by the appearance of book muscovite
-upper intermediate zone:
-very similar to the upper wall zone except for an increasing inward abundance of progressively coarser muscovite books
-beryl is abundant in crystals up to 2 cm in diameter
-small subhedral crystals of microcline up to 10 cm across increase in abundance toward the core zone
-muscovite books show the same general alignment as the quartz schistocity
-core zone
-transition into the core zone is very rapid, marked by a rapid increase in grain size
-albite becomes a minor phase with the majority of the core comprising pink and grey mottled microcline
-the boundary is marked by large inward growing columnar tourmalines
-coarse book muscovite, characteristic of the inner core zone
-spodumene first appears as club shaped crystals growing normal to the contact; within 50 cm the spodumene increases in grain size, becomes more equant, and randomly orientated
-white beryl increases in size from 5 to 7 cm
-quartz appears to be a relatively minor phase throughout the core zone
-blocky microclines range 50 to 80 cm in size
-the core zone appears to be in excess of 3 m thick
-there appears to be a very thin slice of lower into zone exposed for about 20 cm on the south face of the outcrop
-structure
-the dike appears to be a planar podiform body that bifurcates at the west end into two thinner dikes
-in addition to the tectonic fabric there are several cross fractures with significant movement involved (see plan view)
-the major fracture striking 313 with right lateral motion, appears to have elevated the core zone about 2 m
-at the western margin the bifurcate layers have become very shallow to nearly horizontal comprised mainly of core zone with a cap of upper intermediate

PHOTOS

Location of the main Tanco Island pegmatite group.

Anderson dike A-1
Basic geology of pegmatite 5156

Manitoba Geological Survey, 2017