ABSTRACT Early Archean spherule layers, widely accepted to represent distal ejecta deposits from large-scale impact events onto the early Earth, have been described from several stratigraphic levels of the Barberton greenstone belt in South Africa. Recently, exploration drilling at the Fairview Gold Mine (25°43′53″S, 31°5′59″E) in the northern domain of the belt resulted in the discovery of a new set of spherule layer intersections. The Fairview spherule layers in drill cores BH5901, BH5907, BH5911, and BH5949 were intersected just a few meters apart, at about the same stratigraphic position within the transition from the Onverwacht Group to the Fig Tree Group. The Fairview spherule layers have petrographic and chemical similarities to at least three other well-known Barberton spherule layers (S2–S4), and multiple spherule layer bed intersections in drill cores BARB5 and CT3, all from about the same stratigraphic position. They are not uniform in composition, in particular with respect to abundances of highly siderophile elements. The highest concentrations of moderately (Cr, Co, Ni) and highly siderophile (Ir) elements are within the range of concentrations for chondrites and, thus, reinforce the impact hypothesis for the generation of the Fairview spherule layers. Iridium peak concentrations and Cr/Ir interelement ratios for spherule layer samples from drill cores BH5907, BH5911, and BH5949 suggest admixtures of 50%–60% chondritic material, whereas for the BH5901 spherule layer, only an admixture of 1% chondritic material is indicated. We discuss whether these four Fairview spherule layers represent the same impact event, and whether they can be correlated to any of the S2–S4, CT3, and BARB5 intersections.

ABSTRACT The Bon Accord nickel body has been known since the 1920s to contain rocks with up to 50 wt% NiO. Numerous nickel-rich minerals have been described from this deposit. However, none of these minerals contains significant Cu or S, making the deposit chemically distinct from all other known Ni deposits. The origin of the Bon Accord nickel body is highly contentious, with previous studies suggesting three major possible origins: (1) a hydrothermal origin; (2) an Fe-Ni meteorite that fell into and was altered by an active ultramafic lava flow; or (3) a deep mantle plume that contained a fragment of nickel-rich material. Here, we present new field, petrographic, and geochemical data in an attempt to constrain the origin of this enigmatic body. Based on our fieldwork, there are at least two distinct Ni-rich bodies. Based on the trace-element chemistry, the protolith of the body was a komatiite, likely belonging to the Weltevreden Formation. Because the Ni end member of olivine (liebenbergite) is present in the form of euhedral crystals, this mineral most likely crystallized from a Ni-rich melt. The redistribution of the nickel appears to be due to hydrothermal activity that occurred during the intrusion of the Stentor pluton. Consistent with previous studies, we find that the komatiitic affinity of the host rocks, the stratigraphic controls on the deposit, and the regional distribution of Ni-rich material are inconsistent with a meteorite origin; instead, a komatiite plume sampling a Ni-rich portion of the mantle is currently the best explanation for the origin of the Ni-rich material.