Detailed stratigraphy, 1:500 scale mapping, and clast counts and descriptions have established several distinctive eruptive and volcaniclastic members of the “Flin Flon Formation”, which comprises the footwall stratigraphy to the Flin Flon, Triple 7, and Callinan volcanogenic massive sulfide deposits. The volcaniclastic rocks were emplaced within a structurally controlled depression or “basin” by high and low concentration mass flows. Stratigraphy is repeated by early thrust faults and associated drag folds. The aim of this work is to produce a more comprehensive analysis of the present position of the VMS horizon in three dimensions.
In the Yathkyed Lake area the Tyrrell shear zone (TSZ) marks the boundary between the northwestern and central Hearne subdomains of the Western Churchill Province. The TSZ is dominated by Proterozoic dextral strain, but in areas of low dextral strain, older shear fabrics are consistent with an earlier thrusting event. Four syntectonic granite sheets from within low-dextral-strain zones in the TSZ and contiguous shear zones at the base of the Yathkyed belt have ages of 26362629, 2652 ± 8, 26652639, and 2644 ± 3 Ma. The Yathkyed belt occurs in the hanging wall of these shear zones and comprises a greenschist- to amphibolite-grade, overturned panel that is overlain by an upper amphibolite-grade polydeformed panel. The geometry is consistent with a thrust-imbricated stack. Two episodes of deformation in the hanging wall are bracket between ca. 2660 and 2616 +6 4 Ma and between 2616 +6 4 Ma and ca. 2.60 Ga. The Yathkyed belt is interpreted to have initially been emplaced as a thick-skinned, thrust nappe along the TSZ, during 2.662.62 Ga tectonism, and reactivated at ca. 2.622.60 Ga, causing further crustal thickening. In the Upper Panel, protracted upper amphibolite-grade metamorphism and associated anatectic melting are recorded by zircon, titanite, and monazite ages ranging from ca. 2561 to 2492 Ma. This thermal event is in part attributed to burial in response to ca. 2.622.60 Ga thrust reactivation. The timing and means of emplacement of the Upper Panel on top of the Lower Panel is uncertain; however, ca. 2.50 Ga thrusting elsewhere in the northwestern Hearne subdomain provides one possible mechanism.
The objective of this sub-project of the Flin Flon Targeted Geoscience Initiative (FFTGI) is to gain a better understanding of the nature and distribution of hydrothermal alteration within the hanging-wall strata, herein informally called the “Hidden Formation” 3 , to the Flin Flon-Triple Seven-Callinan volcanogenic massive sulphide (VMS) deposits of the Paleoproterozoic Flin Flon belt. Important findings to date from this study include: 1) The recognition of extensive zones of hydrothermal alteration within the hanging-wall strata, including both distal and proximal alteration facies. 2) The definition of two distinct, synvolcanic dyke swarms within the “Hidden” and “Louis” formations, one of which includes felsic dykes. Dyke swarms are important for localizing hydrothermal fluid upflow zones. 3) The recognition of a rhyolite flow unit with associated sulphidic sedimentary rocks called the “Tower Member” of the “Hidden Formation”. This increases the exploration potential for another VMS-bearing horizon in the Flin Flon area at the upper contact of the “Hidden Formation” with the “Louis Formation”.
The Walmsley Lake area of the southeastern Slave Province, Northwest Territories, exposes a crustal transect from greenschist through to upper amphibolite facies. Two tectonothermal crustal domains are proposed based on disparate tectonic histories and rock types. Within the upper tectonothermal domain, D 1 deformation reached lower amphibolite facies prior to 2614 Ma and associated M 1 metamorphic conditions outlasted D 1 . Peak M 2 conditions reached middle amphibolite facies prior to 2603 Ma and outlasted D 2 deformation. Deformation style and metamorphic sequencing during these two pre-2600 Ma events are consistent with regional crustal shortening and thickening in the upper tectonothermal domain. At mid-crustal levels in the lower tectonothermal domain, a third tectonothermal event (D 3 M 3 ) produced uppermost amphibolite-facies peak metamorphic conditions, transposed preexisting fabrics to shallow dips, and produced a subhorizontal foliation and recumbent folds at ca. 2583 Ma. D 3 structures are not present in the upper tectono thermal domain, however, evidence of M 3 heating is locally displayed in rocks at the base of the upper tectonothermal domain. Upper and lower domains were structurally decoupled during the D 3 M 3 event. In rare places where the zone between the two domains outcrops, it comprises a narrow high-strain zone. The metamorphic and structural topology of the Walmsley Lake area is consistent with the topology predicted from thermomechanical modeling and modern observations of gravitational accommodation in structurally thickened crust.
The nature, timing and control of Archean crustal architecture on the distribution of Proterozoic reworking in Western Churchill Province are investigated in the Yathkyed Lake area, central Nunavut. The Tyrrell shear zone (TSZ) marks the boundary between the northwestern and central Hearne subdomains, respectively, in the hanging wall and footwall. Metamorphism and deformation in the hanging wall are ca. 2.662.50 Ga. Two episodes of metamorphism are recorded in a foliated granodiorite in the footwall, at 1818 +5 2 and 1827 ± 5.6 Ma. The latter age is interpreted as the time of amphibolite-facies metamorphism and deformation in the footwall. A crosscutting dyke provides a minimum age of 1818 ± 2 Ma for this metamorphism and deformation. The TSZ is dominated by dextral oblique-slip shear fabrics. A suite of leucogranite dykes provide a maximum age of 1816 ± 2 Ma for dextral shearing. Dextral deformation is bracketed between 1815 ± 2 and 1811 ± 1 Ma, the ages of two other granitoid dykes. In an area of low dextral strain, there are proto-sheath folds related to Neoarchean thrusting. Paleoproterozoic transtensional shearing in the TSZ was localized along a preexisting late Archean thrust fault. The prior existence of this structure resulted in localization of penetrative Paleoproterozoic deformation in its footwall. This domain of high-grade Proterozoic deformation was uplifted in a regional, antiformal, metamorphic culmination, in part, by dextral-normal shearing along the TSZ. Penetrative basement deformation at depth played a role in transmitting farfield stresses related to the Trans-Hudson Orogen into its hinterland.
The Aylmer dome is a prominent geological feature in the northeastern Walmsley Lake map sheet (NTS 75 N), southeastern Slave Province. The dome is composed of a granitoid core rimmed by a narrow volcanic belt, overlain by regionally extensive metaturbidite of the Yellowknife Supergroup. The volcanic stratigraphy comprises a con- formable succession of basal mafic flows and gabbroic sills, overlain by a fine-grained, intermediate to felsic volcaniclastic sequence with a lens of intermediate breccia in the northwest. The upper felsic sequence is capped by iron-formation deposited at the volcanic-sedimentary interface. Airborne magnetic and electromagnetic geophysical surveys defined several conductive and magnetic horizons within the volcanic belt, and a continuous magnetic and conductive response coincident with the capping iron-formation. Ongoing work is aimed at resolution of a more detailed stratigraphy and petrogenesis of the volca- nic rocks and will aid in assessing the mineral potential of the belt, in particular the magnetic and conductive hori- zons identified by geophysics.
Regional mapping in the Yathkyed greenstone belt has revealed two distinct tectonostratigraphic units in the hanging wall of the Tyrrell shear zone. The geometrically lower tectonostratigraphic unit comprises mainly amphibolite and monzogranite, whereas the structurally higher unit consists of a package of mixed flows and associated volcaniclastic and clastic sedimentary rocks intruded by foliation-parallel sheets of tonalite. A shear zone of unknown displacement sense separates the two tectonostratigraphic units. The Tyrrell shear zone at the base of the greenstone belt records early (possibly Archean) reverse displacement, followed by Paleoproterozoic dextral-normal movement. Foliation- parallel gossans with strike lengths up to 3 km and alteration assemblages containing sericite±chlorite±carbonate were documented in volcanic rocks of the upper tectonostratigraphic unit. The timing of formation of these mineralized zones is unclear, although evidence for a Proterozoic thermal overprint suggests late remobilization of metals may have contributed to the mineral potential of the area.
