Abstract

The paper presents U–Pb ages on zircon, baddeleyite, titanite, rutile, and monazite from volcanic and plutonic rocks of the Red Lake greenstone belt in the northern Superior Province. The purpose of the study was to refine a previously outlined time frame for the volcanic evolution of the belt, define the time of major plutonism and deformation, and constrain the age of formation of gold deposits.Volcanism spanned at least 270 Ma between 3000 and 2730 Ma. New ages of 2989 ± 3 and 2894 ± 2 Ma for units of a lower volcanic sequence and graphic and 2744 ± 1 Ma for units of an upper volcanic sequence corroborate and refine the previously established relationships. Local gabbroic and felsic intrusions cutting through the lower sequence yield ages of 2870 ± 15 and graphic, respectively.Volcanism was succeeded by major plutonism, deformation, alteration, and metamorphism between about 2730 and 2700 Ma. These processes were interrelated and progressed as a relatively continuous sequence of events accentuated by major activity during two phases at about 2720–2715 and 2705–2700 Ma. Early plutonism recorded at 2731 ± 3 Ma in the northern batholith complex was succeeded in the eastern part of the belt by a major tectonic – plutonic phase that includes intrusion of the McKenzie Stock at 2720 ± 2 Ma, the Dome Stock at 2718 ± 1 Ma, alteration and deformation of the Abino dyke at graphic, and emplacement of a late tectonic dyke at 2714 ± 4 Ma. A subsequent phase is recorded at 2701 ± 1.5 Ma in the Wilmar dyke. Major deformation and metamorphism in the western part of the belt is constrained by an age of 2729 ± 1.5 Ma for the deformed Red Crest Stock and a titanite age of 2705 ± 8 Ma for an undeformed crosscutting mafic dyke at Rowan Lake. Peak activity was probably coeval with emplacement of the adjacent batholithic phases at 2717 Ma. In the central part of the belt the deformation is constrained by ages of 2718 ± 1 Ma for the Dome Stock and 2699 ± 4 Ma for titanite of a crosscutting, undeformed diorite dyke and probably peaked during intrusion of the main phase of the Killala–Baird batholith at 2704 ± 1.5 Ma.Gold mineralization, which is spatially related to zones of intense shear deformation and alteration, is constrained within the time interval of 2720–2700 Ma by U–Pb ages on several felsic to mafic intrusive rocks that both pre- and post-date deformation and mineralization in different sections of the belt. These data indicate that mineralization occurred significantly later than the termination of volcanism.

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