학술논문
Banded iron formation to iron ore: A record of the evolution of Earth environments?
Document Type
Article
Source
Subject
*BANDED iron formations
*IRON ores
*EVOLUTIONARY theories
*CARBONATES
*SILICA
*MAGNETITE
*ISOTOPES
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Language
ISSN
0091-7613
Abstract
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. [ABSTRACT FROM AUTHOR]