|Author:||Leclerc and Caron-Côté, 2017|
|Age:||Precambrian / Archean / Neoarchean|
|Type area:||The Whitefish Intrusion (nAwf) outcrops mainly between the Quénonisca and Rocher lakes (NTS 32K09 and 32K10).|
|Geological province:||Superior Province|
|Geological subdivision:||Opatica Subprovince|
|Lithology:||Purple gabbro, monzonite|
The Whitefish Intrusion is a lithodeme introduced by Leclerc and Caron-Côté (2017) to describe an intrusion located west of Rocher Lake which belongs to the Rocher-Quénonisca Intrusive Suite. This unit is elongated in a NE-SW direction just over 25 km long by 1.5 to 5 km wide.
The Whitefish intrusion is divided into two informal units: a purple gabbro unit (nAwf1) and a monzonite unit (nAwf2).
Whitefish Intrusion 1 (nAwf1): Purple Gabbro
The dominant unit of the Whitefish Intrusion is a homogeneous, massive, medium-grained gabbro characterized by dark gray to purple plagioclase crystals. The rock comprises 20 to 45% mafic minerals and has a well-preserved subophitic structure (Franconi, 1974). Minerals observed in thin sections are plagioclase, alkali feldspar, clinopyroxene and orthopyroxene, biotite, apatite and opaque minerals. Olivine appears only locally. Geochemical analyses indicate a calc-alkaline affinity (Bandyayera and Sharma, 2001).
Whitefish Intrusion 2 (nAwf2): Monzonite
Monzonite is massive and medium-grained with potassium feldspar phenocrysts. It has a pinkish to greyish color (Brisson et al., 1998). It also contains 10 to 20% of mafic minerals (biotite and hornblende). Under the microscope, plagioclase and microcline form perthitic intergrowths and clinopyroxene is almost entirely replaced by hornblende. Accessory minerals include iron oxides, apatite, quartz, biotite and titanite (Franconi, 1974).
Thickness and distribution
The Whitefish Intrusion forms an intrusive NE-SW unit a little over 25 km long by 1.5 to 5 km wide. It cuts tonalites of the Salamander Intrusive Suite (nAsam), as well as volcano-sedimentary rocks of the Rocher Complex (nAroc) and Broadback Group (nAbk).
The Whitefish Intrusion cuts both tonalites of the Salamandre Intrusive Suite and volcano-sedimentary rocks of the Rocher Complex and Broadback Group. The latter also occur as xenoliths in purple gabbro of the nAwf1 unit. The Rocher-Quénonisca Suite is thus considered a late-tectonic intrusion by Bandyayera and Sharma (2001).
Does not apply.