Abstract:

Algoma-type banded iron-formation units are generally Archean chemical sedimentary rocks comprised of alternating layers of iron-rich minerals and chert that are stratigraphically associated with submarine volcanic rocks and localized within greenstone belts. Although much research has been done on Algoma-type banded iron-formation units, their depositional and overall geological settings are conten- tious due to overprinting effects of postdepositional deformation and metamorphism and the absence of modern analogues for comparative studies.<br/>Geochemical study of the gold-hosting Algoma-type banded iron-formation units at the Musselwhite and Meadowbank deposits provide comparable information on their depositional context. Geochemical tools, such as rare-earth element REE+Y systematics, indicate that chert bands in Algoma-type banded iron-for- mation record contributions from: 1) seawater, characterized by enrichment in HREEs relative to LREEs, and positive La, Gd, and Y anomalies; 2) hydrothermal fluids, characterized by a positive Eu anomaly and a flat pattern; and 3) hydrogeneous contamination. A detailed study of both of the aforementioned deposits was undertaken to evaluate the origin of the chert in these banded iron-formation settings. A hydrother- mal overprint on banded iron-formation from the Musselwhite deposit is proposed to explain negative Ce anomalies that may be due to late hydrothermal fluid circulation in the chert bands replacing the initial seawater component. This hydrothermal alteration phase may be associated with the gold mineralization.