Ontario Geological Survey
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MDI31E01NW00002
| Record Name(s) | Percy Lake - 1988 |
|---|---|
| Related Record Type | Simple |
| Related Record(s) | |
| Record Status | Discretionary Occurrence |
| Date Created | 1991-Jun-05 |
| Date Last Modified | 2022-May-25 |
| Created By | |
| Revised By |
Primary Commodities: Anorthosite
Township or Area: Bruton
Latitude: 45° 14' 20.41" Longitude: -78° 18' 35.98"
UTM Zone: 17 Easting: 711129.756 Northing: 5013021.515 UTM Datum: NAD83
Resident Geologist District: Southern Ontario
NTS Grid: 31E01NW
Point Location Description: Point near centre of anorthosite body.
Location Method: Conversion from MDI
Access Description: Accessible via a forest access road leading E from the N end of Haliburton Lake to Benoir Lake in NE Harcourt Township.
May 25, 2022 (Therese Pettigrew) - Like the Allsaw Anorthosite, the Percy Lake Anorthosite lies within the CMBBZ. Hanmer (1989) states that "the base of the (thrust) stack (which forms the CMBBZ) is defined by a particularly well developed zone of porphyroclastic gneiss which truncates structures in the (Percy Lake) anorthosite in the foot-wall" (of the porphyroclastic gneiss). This observation places the Percy Lake Anorthosite below the CMBBZ and in the Central Gneiss Belt. However, the northern margin of the anorthosite is also underlain by a classic porphyroclastic and straight gneiss, well exposed near the shore of East Lake, along the access road west of Clyde Creek, and on the prominent hill at the west end of Byers Lake. Thus the anorthosite is likely an integral part of the CMBBZ, but occupies a lower structural position than the Allsaw Anorthosite (Marmont, 1991).
| Rock Type | Rank | Composition | Texture | Relationship | Anorthosite | 1 | Anorthosite | Is |
|---|
May 25, 2022 (Therese Pettigrew) - The Percy Lake Anorthosite is exposed in Harburn and Bruton townships, Haliburton County. Bruton Township is part of Algonquin Provincial Park. The anorthosite is some 20 km long and up to 3.5 km wide. It strikes east-west and dips south at 30 to 50 degrees. The anorthosite is accessible via a forest access road leading eastward from the north end of Haliburton Lake to Benoir Lake in northeast Harcourt Township (Marmont, 1991).
May 25, 2022 (Therese Pettigrew) - The Percy Lake Anorthosite is the cleanest of the anorthosites studied (colour index commonly < 5). The feldspar is the whitest and, in the main, is free of oxide and silicate inclusions. Remnant grey plagioclase crystals up to 6 cm long were seen in only a small part of one outcrop - between North Lake and East Lake. These contain abundant inclusions of iron oxides. Hornblende is present in the more mafic parts of the body but in most anorthosites, biotite, epidote and chlorite prevail. In some places epidote is cored by ferrian zoisite. Up to 5% scapolite may be present, but commonly it has been altered to muscovite and calcite. Titanite, quartz, myrmekite and microcline occur locally in trace amounts. Irregular, narrow pegmatite veinlets spaced a few metres apart can be seen in most outcrops. A remarkable feature of this body is that at the base of the "scarp face" of most outcrops (usually the north and northeast sides of hills), and to a lesser extent within outcrops, a ductile shear zone can be found by pulling back the moss and vegetation. These shear zones range in thickness from one metre to possibly several tens of metres. The shears typically consist of granitic pegmatite exhibiting varying degrees of disaggregation and comminution. The most deformed varieties appear as medium grained, pink, gneissic granite ("meta-arkose") containing small remnant feldspar and quartz crystals. Above the sheared pegmatitic material, the anorthosite commonly exhibits a lenticular structure on a scale of 0. 3 to 1.0 m, produced by millimetre to centimetre-wide anastomosing shears of comminuted anorthosite. In places, rotated blocks of anorthosite can be discerned within a finer grained anorthosite matrix. This grades up into parallel foliated anorthosite, which in turn passes up into the regular, massive anorthosite. In some shears a plagioclase-biotite-quartz gneiss, sometimes containing disaggregated pegmatite schlieren and feldspar porphyroclasts, underlies the sheared pegmatite. Locally this contains a garnet-hornblende-quartz-plagioclase gneiss. (Marmont, 1991)
Mono - Building stone, feldspar and limestone resources in central Ontario
Publication Number: OFR5760 Page: 244, 319-330 Date: 1991
Author: Marmont C.
Publisher Name: Ontario Geological Survey
Location:
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