High-Precision U-Pb Geochronology of the Late Archean Kidd Creek Deposit and Kidd Volcanic Complex

Abstract Results from a comprehensive U-Pb geochronology study of the Kidd Creek deposit and the surrounding Kidd Volcanic Complex are presented. Eleven new zircon and two titanite ages are reported and integrated with U-Pb age results on five related samples, which were published in a previous study. Zircon ages for rhyolite volcanism of the Kidd Volcanic Complex range from 2717.0+–22..56 to 2711.5 ± 1.2 Ma. This age range is established on immediate footwall and hanging-wall rhyolites of the Kidd Creek orebody. Since both footwall and hanging-wall rhyolites can be linked to ore formation, the conclusion must be that the giant Kidd Creek deposit is the product of unusually long-lived, albeit episodic, sea-floor hydrothermal activity. Our most precise estimate for the age of footwall rhyolites at Kidd Creek is provided by results on two nearby rhyolites that have been dated at 2716.1 ± 0.6 and 2716.0 ± 0.5 Ma, respectively. The age of at least one large massive sulfide lens at Kidd Creek, the North orebody, has been tightly bracketed between the age of footwall rhyolites and the age of an overlying rhyolite lapillistone horizon dated at 2715.8 ± 1.2 Ma. Hence, ore formation of individual massive sulfide lenses appears to have been rapid and well within the resolution limits of current U-Pb dating techniques. Based on the large number of ages, it appears that volcanic activity of the Kidd Volcanic Complex can be divided into four general phases, each of which is supported by at least one or more high-precision ages: phase I, onset of bimodal komatiite and rhyolite volcanism, probably as early as 2717.7 ± 1.1 Ma, and extrusion of the footwall assemblage at Kidd Creek at ca. 2716 Ma; phase II extrusion of ca. 2714 Ma rhyolites; phase III, extrusion of ca. 2711 Ma rhyolite, including the quartz porphyritic hanging-wall rhyolite at Kidd Creek; and phase IV, extrusion of the hanging-wall basalt sequence and intrusion of subvolcanic gabbro sills sometime after 2711 Ma. The Kidd Creek deposit probably formed along the axial zone of a slow-spreading rift basin that developed during extension of an older volcanic-arc assemblage. This older arc assemblage, which included ca. 2723 and 2735 Ma components, is probably represented by the Deloro Group and correlative assemblages exposed to the south of Timmins. Rifting of the older volcanic substrate, and partial melting to produce the rhyolites, was induced by the arrival of a hot mantle plume that gave rise to the komatiites of the Kidd-Munro assemblage. Graywacke turbidites in the Kidd Creek area are all younger than ca. 2699 Ma and do not form the deeper stratigraphic footwall to the deposit. Instead, the graywackes probably overlie, unconformably to disconformably, all the volcanic assemblages in the region. From the sub -sequent protracted structural-metamorphic evolution in the area, two discrete events have been dated: the 2663.3 ± 3.3 Ma intrusion of the Prosser porphyry granitoid stock and a discrete 2639.1 ± 7.2 Ma metamorphic-hydrothermal event. The timing of both events corresponds closely to ages for granulite facies metamorphic events in lower crustal rocks of the nearby Kapuskasing structural zone.