Anomalous tungsten occurs in Archean banded iron formation from the previous Sherman and Adams mines, Ontario. In Sherman samples from three open pits and one drill core site, with one exception, anomalous tungsten occurred only in the Sherman North pit. Adams mine samples from three pits carried anomalous tungsten in samples of chlorite-rich silicate facies. Statistical evaluation showed that ≥10 ppm tungsten was anomalous with respect to the entire data set. The implications of restricted tungsten distribution, as seen in Sherman occurrences, were evaluated with respect to tungsten mineralization processes. Scenarios considered involve syngenetic, metamorphic, and magmatic-hydrothermal processes. Thermal constraints provided by iron-bearing silicate assemblages and oxygen isotopes attest to contact metamorphism as a potential mechanism for tungsten redistribution within iron formation. However, tungsten of magmatic-hydrothermal origin emplaced as an epigenetic component is considered the essential mineralization process.

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