DISCLAIMER: This English version is translated from the original French. In case of any discrepancy, the French version shall prevail.
|Author(s):||Midra et al., 1992a|
|Type area:||Area SW of Rachel Lake (QTS sheet 32G11-200-0101)|
|Geological province:||Superior Province|
|Geological subdivision:||Abitibi Subprovince|
|Lithology:||Tonalite, diorite, quartz diorite and granodiorite, tonalitic gneiss|
The granitoid mass of the Lapparent Intrusive Suite first appeared on the map of Retty and Norman (1938). Remick (1956, 1957) recognized different phases of the Lapparent Suite but did not differentiate them on the map. In 1970, Duquette described the Lapparent Pluton, to which is associated the Rachel Pluton, as a tonalite-diorite mass. The area corresponding to the Rachel Pluton was first identified on the map of Racicot et al. (1984). The Rachel Pluton itself was described by Tait and Chown (1987) and Tait et al.(1990). Midra et al. (1992a) further defined the contours and provided a more complete description of the pluton.
Rocks of the Rachel Pluton are generally granular with a brownish grey colour in altered surface and light grey in fresh exposure, which may be pink and white spotted (Tait et al., 1990; Midra et al., 1992a). According to Tait et al. (1990), “The typical lithology of the Rachel Pluton is an even-grained biotite tonalite.”
According to Midra et al. (1992a): “The eastern border, in contact with the Est Tonalite, is highly foliated. The foliation, parallel to contact, is therefore caused by the emplacement of the Est Tonalite. The NE border of the pluton contains amphibolitized basalt enclaves and early tonalite enclaves. Deformation at this location is more intense with the development of mylonitic textures in tonalites and a strong, moderately dipping lineation in volcanic enclaves.”
Tait et al. (1990) note that the marginal phase in contact with tonalitic gneiss consists of melatonalite cut by biotite tonalite veins forming a net-veined complex. This marginal deformation of the pluton and subsequent tectonics produced a rock with a gneissic appearance, identical to the marginal tonalitic phase of the Anville Pluton, as described by Gervais (1986). South of Rachel Lake, different phases of tonalitic and pegmatitic injection occur. Pegmatites are late and display little deformation, unlike tonalitic phases.
Still according to the lead authors (Tait et al., 1990; Midra et al., 1992a): “The subhedral-textured [tonalite] [ … ] is composed mainly of plagioclase, quartz, biotite and chlorite. Secondary minerals are hornblende, microcline, apatite, sphene and zircon. Subhedral plagioclase (An32) is slightly to highly zoned. It exhibits a sericite deuteric alteration. This alteration is uneven throughout the pluton. Anhedral quartz occurs as crystalline aggregates equal in size to plagioclase, stretched or polygonized. Biotite, in the form of laths, is usually chloritized [and forms large flakes that surround plagioclase]. Epidote aggregates are commonly associated with biotite. Microcline, where present, is interstitial with plagioclase.”
The Rachel Pluton stretches 36 km to the NW from Denning Lake to Lapparent Lake. In this segment, its thickness varies from 3 to 6 km.
According to Midra et al. (1992a): “the Rachel […] Pluton is located at the southern edge of the Lapparent Intrusive Suite. It is bounded to the east and NE by the Est Tonalite, to the NW by the Ouest Granodiorite and to the south by a volcano-sedimentary strip. On the west side, tonalite becomes very deformed and could be a separate intrusion of the Rachel Pluton. The eastern border, in contact with the Est Tonalite, is highly foliated. The foliation, parallel to the contact, is therefore caused by the emplacement of the Est Tonalite. The NE border of the pluton contains amphibolitized basalt enclaves and early tonalite enclaves. […] South of Rachel Lake, different phases of tonalitic and pegmatitic injection occur. Pegmatites are late and show little deformation, unlike tonalitic phases. The Rachel Pluton has a narrow metamorphic halo. To the south, host volcanic rocks are amphibolitized, whereas NE of Rachel Lake, a gabbroic mass has poikiloblastic amphiboles at its margin. These observations give this pluton a syntectonic character.”
Does not apply.
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TAIT, L., PILOTE, P., CHOWN, E H., 1987. GEOLOGIE DE LA REGION DU LAC A L’EAU JAUNE – DISTRICT DE CHIBOUGAMAU – RAPPORT INTERIMAIRE. MRN; MB 87-24MB 87-24, 120 pages, 4 plans. Disponible à https://gq.mines.gouv.qc.ca/documents/EXAMINE/MB8724.
GERVAIS, D. 1986. Le caractère de la zone de contact entre l’intrusion tonalitique syn à postcinématique d’Anville et le terrain de gneiss du massif de Lapparent. Université du Québec à Chicoutimi, Québec; projet de fin d’études, 56 pages.
RACICOT, D., CHOWN, E.H., HANEL, T. 1984. Plutons of the Chibougamau-Desmaraisville belt: A preliminary survey, dans: Chibougamau – Stratigraphy and Mineralization, (Guha, J. and Chown, E.H., editors). Canadian institute of Mining and Metallurgy; Special Volume 34, pages 178-197.
Ministère de l’Énergie et des Ressources naturelles (MERN). Rachel Pluton. Quebec Stratigraphic Lexicon. https://gq.mines.gouv.qc.ca/lexique-stratigraphique/province-du-superieur/pluton-de-rachel_en [accessed on Day Month Year].
Patrice Roy, P. Geo., M.Sc. email@example.com (redaction)
Mehdi A. Guemache, P. Geo., Ph.D. (coordination); François Leclerc, P. Geo., Ph.D. (critical review); Mélina Langevin, B.Sc. and Simon Auclair, P. Geo., M.Sc. (editing); Céline Dupuis, P. Geo., Ph.D. (English version); Nathalie Bouchard (HTML editing).