|Author:||Petrella, 2011; Lafrance et al., 2018|
Chapiteau Lake area (NTS sheet 13M05)
|Geological province:||Churchill Province|
|Geological subdivision:||Mistinibi-Raude Lithotectonic Domain|
Table des matières
The Misery syenitic intrusion was discovered by Quest Rare Minerals in 2007 and was studied as part of a master’s project (Petrella, 2012). The term “Misery Syenite” was formalized by Lafrance et al. (2018) in their Southeastern Churchill Province regional synthesis.
The Misery Syenite is associated with an annular magnetic anomaly clearly visible on the residual total magnetic field map. It was divided into two units by Petrella et al. (2014): a ferrosyenite unit and a syenite unit. Given the small extent of the ferrosyenite unit, it is not distinguished from syenite. The description below is from the work of Petrella (2011), Petrella et al. (2014) and Quest Rare Minerals.
Unit mPmsy1 quartz syenite has homogeneous composition and mineralogy, but varies from fine to coarse grained. It is mostly composed of K-feldspar and a small amount of ferromagnesian minerals (5%). These, consisting of fayalite, hedenbergite and titanomagnetite, are interstitial with K-feldspar crystals and are surrounded by ferropargasite. Annite replaces ferropargasite locally. Quartz (1-5%) is interstitial, while plagioclase (5%) forms small euhedral to subhedral crystals. Accessory minerals include allanite, zircon, fluorapatite, fluorite, columbite-(Fe), carbonates and pyrite.
In the coarse-grained phase, K-feldspar forms rounded perthitic centimetric crystals with 1 cm to 5 cm clusters of interstitial ferromagnesian minerals. Fine and medium-grained facies are distinguished by the preferential orientation of K-feldspar crystals, perthitic and as laths. This orientation is often parallel to the contact of the Misery Intrusion with the Mistastin Batholith. In these phases, quartz syenite is more or less even grained and the content of ferromagnesian minerals ranges from 7% to 20%. Another feature of these phases is the partial albitization of K-feldspar crystals.
Misery Syenite 1a (mPmsy1a): Porphyraceous Fayalite Quartz Syenite
Porphyritic quartz syenite dykes cutting the coarse-grained facies of unit mPmsy1 are included in informal subunit mPmsy1a. These NW-SE to N-S oriented dykes are grey to green and fine to medium grained. Perthitic phenocrystals (1-2 cm) represent ~10% of the rock. The matrix consists of fine crystals of K-feldspar, plagioclase, quartz, fayalite and, in smaller amounts, ferropargasite and hedenbergite. Apatite, zircon and fluorite are accessory minerals.
Misery Syenite 1b (mPmsy1b): Quartz Syenite Containing Ferrosyenite Enclaves
In the eastern portion of the intrusion, some areas consist of coarse-grained quartz syenite of unit mPmsy1 containing many enclaves of ferrosyenite. These areas were distinguished in informal subunit mPmsy1b. Medium-grained quartz syenite enclaves, as well as fluorapatite-magnetite clusters, are present in smaller amounts in quartz syenite.
Ferrosyenite in enclaves is dark greenish grey and fine to medium grained. It comprises up to 50% ferromagnesian minerals including euhedral primary crystals of orange-green fayalite (15%), dark green hedenbergite (15%) and titanomagnetite (5%), as well as primary or secondary crystals of black ferropargasite (10%) and annite (5%). Fayalite is commonly surrounded by anhedral ferropargasite, locally replaced by annite, which concentrates in layers showing normal gradation, that is, the amount of fayalite decreases upward. Ferrosyenite contains 1% to 2% zircon and fluorapatite interpreted as primary minerals. Unlike quartz syenite of unit mPmsy1, subunit mPmsy1b K-feldspar is interstitial with ferromagnesian mineral phases.
The Misery Syenite forms an intrusion of ~6 km in diameter (31 km2) in the SE portion of the Mistinibi-Raude Domain (Charette et al., 2019), near the Quebec-Labrador border. The medium to fine-grained phase of unit mPmsy1 is located in the centre of the intrusion, while the coarse-grained facies surrounds this core and covers a larger area. Subunits mPmsy1a and 1b are small and cover only ~0.3 km2 each.
The crystallization age obtained on a sample (2010-LP-6738-A) of the Misery Syenite was defined around 1410 Ma.
|Isotopic System||Mineral||Crystallization Age (Ma)||(+)||(-)||Reference(s)|
|U-Pb||Zircon||1409.7||1.2||1.2||David et al., 2012|
The Misery Syenite intrudes into the Mistastin Batholith (mPmit). Petrella et al. (2014) report that contact with the batholith is gradual and characterized by the disappearance of the rapakivi texture in the Mistastin Batholith.
Does not apply.