Neoarchean convergent margin Ni-Cu mineralization? Axis Lake and Nickel King Ni-Cu deposits in the south Rae craton of the Canadian Shield

Abstract

The southern portion of the Rae craton in the Canadian Shield is host to multiple ca. 2.63 Ga Ni-Cu-rich metamorphosed mafic intrusions with noritic, noritic-anorthositic and pyroxenitic compositions, including those hosting the undeveloped Axis Lake and Nickel King deposits found in northern Saskatchewan and southeast Northwest Territories.In order to understand the setting of these intrusions, and their concomitant mineralization, we investigated their geochemical and isotopic characteristics. Mineralized intrusions at Axis Lake and Nickel King are metamorphosed up to granulite facies, with local partial melting. The intrusions preserve whole-rock major element geochemistry consistent with a sub-alkaline basaltic composition (e.g., SiO2 = 46–54 wt%; TiO2 < 0.5 wt%). In terms of their trace elements, these intrusions have: LREE to HREE enrichments (La/YbPM = 2–16), low HREE fractionation (Gd/YbPM = 1.0–2.6), well defined negative Nb (Nb/Nb∗ = 0.06–0.31) and Zr (Zr/Zr∗ = 0.24–0.41) and variable negative to positive Ti anomalies (Ti/Ti∗ = 0.25–1.38), and Th/Yb versus Nb/Yb distributions consistent with formation in an arc-like setting.The Nd isotope values of the Axis Lake intrusion (ɛNdt2630 = +0.3 to +2.1) are more juvenile and closer to the depleted mantle value, relative to those of the Nickel King deposit (ɛNdt2630 = −2.4 to −0.4). This agrees with their also distinctive Th/Yb and Nb/Yb distributions suggesting oceanic and continental arc-like settings, respectively. The Axis Lake and Nickel King Nd isotope compositions are indistinguishable from other arc-like 2.61 to 2.58 Ga mafic to felsic intrusions and volcanic rocks recognized in the Rae craton and the neighboring Chesterfield block. The age, spatial distribution and geochemistry of the studied intrusions coincide with the initial stages of a recently defined 2.63–2.60 Ga continental arc, the roots of which are found in the south Rae craton.Our data indicate that Neoarchean intrusions with an arc-like geochemistry may be a significant exploration target in the Rae craton. This broadens possible host suites beyond the established Paleoproterozoic rift-related rocks most commonly considered as the prime target for Ni-Cu-PGE mineralization.