Geology, Montresor River area, Nunavut, parts of NTS 66-H and NTS 66-I

Abstract

The Montresor River area (parts of NTS 66-H/13, 14, 15, 16, and NTS 66-I/1, 2, 3, 4, 5, 6, 7, 8), part of the Rae structural province, is underlain by granitic rocks of Archean (ca. 2.6 Ga) age and the Paleoproterozoic (<2.19 Ga) Montresor group of metasedimentary rocks. Quartzite, dolostone and metapelite of the lower Montresor group are structurally imbricated (D1) with granitic gneisses and metamorphosed to the amphibolite facies. This structural footwall complex is separated from greenschist-facies rocks of the upper Montresor group by a detachment fault (D2). A third set of structures including mylonites juxtaposes the basal footwall complex and surrounding granitoid rocks carrying concordant augen gneissic fabric. The Montresor syncline, outlined aeromagnetically by prominent magnetic siltstone beds, may be a D4 structure. Previously unrecognized breccia and hydrothermally altered alkaline igneous rocks occur as a stratabound layer in the southwestern Montresor syncline and have elevated Cu, Ag, Au values.

Toward 3D structural constraints from magnetic models: an example from the Montresor belt, Nunavut, Canada

“…Where available, strike and dip information from Frisch (2000) and Percival et al (2015) was incorporated into the models.…”

“…2.35, 2.0, 1.9 and 1.85 Ga (Figure 1). Initially considered to be a simple syncline (Frisch, 2000), the Montresor belt consists of a footwall complex made up of structurally interleaved (D1) Archean gneiss and quartzite-carbonate units of the lower Montresor group (<2190 Ma), and above a D2 décollement, low-grade sandstone and siltstone of the upper Montresor group (<1940 Ma; Percival et al, 2015), the focus of this study. Heavy-mineral beds in the upper Montresor give rise to magnetic marker units defining two doublyplunging synclines (D3-D4 interference patterns) resembling elliptical bulls-eyes on aeromagnetic maps (Figure 2).…”

Quantifying the Pressure, Temperature, and Timing of Metamorphism in the Montresor Belt, Nunavut, Canada

“…The lower Montresor group is commonly cut by granodiorite, granite, and pegmatitic dykes (Percival et al, 2015A, C). Previous studies suggested that these higher-grade amphibolite facies rocks belong to the basement Percival et al, 2015A). (Frisch, 2000;Frisch and Patterson, 1983), but recent work has demonstrated that these units are part of the Montresor belt (Percival et al, 2015C).…”

“…The belt is 73 km long and 8 km wide, extending from the Montresor River in the northeast to the Back River in the southwest (Frisch, 2000). It structurally forms an open synclinal fold with the southeast limb dipping at 30˚ and the northwest limb dipping 40 -70˚, with localized dip up to 80˚ (Percival et al, 2015A). The base of the syncline is prominently visible as a magnetic low in modern aeromagnetic maps (Tshirhart et al, 2015).…”

“…It has been suggested the Montresor belt formed in a shallow water or continental depositional environment (Rainbird et al, 2010). Archean basement rocks to the Montresor Belt are dominantly of a tonalite-granodiorite-granite composition (Frisch, 2000;Percival et al, 2015A).…”