Contrasting arc and MORB-like assemblages in the Paleoproterozoic Flin Flon Belt, Manitoba, and the role of intra-arc extension in localizing volcanic-hosted massive sulphide deposits

Abstract

The Flin Flon Belt (Trans-Hudson Orogen, Manitoba and Saskatchewan) is the largest Paleoproterozoic volcanic-hosted massive sulphide (VMS) district in the world, with 118.7 million tonnes (Mt) of Zn-Cu-(Au-Ag) sulphide ore in 25 past or presently producing mines and 64.3 Mt in subeconomic deposits. The orebodies are restricted to isotopically juvenile volcanic-arc sequences, dated at 1.903-1.881 Ga at Flin Flon. Sequences of ca. 1.904-1.901 Ga back-arc and ocean-plateau basalts and related plutonic rocks, structurally juxtaposed with the arc assemblages at 1.880-1.870 Ga, are not known to contain economic base metal deposits. The juvenile arc tectono-stratigraphic assemblages are generally marked by older and stratigraphically lower tholeiitic submarine volcanic packages (ca. 1.903-1.886 Ga) that are observed or interpreted to be overlain by extensive and lithologically varied sequences of calc-alkaline and alkaline (shoshonitic) arc rocks and arc rift deposits (ca. 1.888-1.881 Ga). VMS deposits occur in both the tholeiitic and calc-alkaline arc sequences, but the 62 Mt Flin Flon deposit occurs in a 1.903 Ga tholeiitic primitive arc package. It can be demonstrated that for the Flin Flon - Callinan - Triple 7, Cuprus, and White Lake VMS deposits, whose stratigraphic context is preserved, deposition of the massive sulphides was temporally associated with inferred arc rifting processes. Critical observations for arc rifting include evidence for extensional faulting, erosion, and development of unconformities; extrusion of MORB-like basalts and associated rhyolites; and development of depositional basins with thick sequences of shoshonitic turbidites. As has been proposed for other major VMS camps (e.g., Kuroko, Kidd Creek, Bathurst), arc rifting can generate the loci of sustained high heat flow and fluid pathways required for the development of long-lived hydrothermal convection systems.