Journal
GEOLOGY
Volume 41, Issue 2, Pages 99-102Publisher
GEOLOGICAL SOC AMER, INC
DOI: 10.1130/G33244.1
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Funding
- Curtin Research and Teaching Fellowship, Australian Research Council Discovery [DP1090475]
- Core to Crust Fluid Systems
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Banded iron formations (BIF) are the protolith to most of the world's largest iron ore deposits. Previous hypogene genetic models for Paleoproterozoic Lake Superior BIF-hosted deposits invoke upwards, down-temperature flow of basinal brines via complex silica and carbonate precipitation/dissolution processes. Such models are challenged by the necessary SiO2 removal. Thermodynamic and mass balance constraints are used to refine conceptual models of the formation of BIF-hosted iron ore. These constraints, plus existing isotope and halogen ratio evidence, are consistent with removal of silica by down- or up-directed infiltration of high-pH hypersaline brines, with or without a contribution from basinal brines. The proposed link to surface environments suggest that Paleoproterozoic BIF-ore upgrade may provide a record of a critical time in the evolution of the Earth's biosphere and hydrosphere.
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