Banded iron formation to iron ore: A record of the evolution of Earth environments?

Autor:	David J. Leach, T.C. McCuaig, Steffen Hagemann, Thomas Angerer, Katy Evans
Rok vydání:	2013
Předmět:	Hypogene Geochemistry Geology engineering.material chemistry.chemical_compound chemistry Iron ore Genetic model engineering Carbonate Banded iron formation Dissolution Protolith Hydrosphere
Zdroj:	Geology. 41:99-102
ISSN:	1943-2682 0091-7613
DOI:	10.1130/g33244.1
Popis:	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 fl ow of basinal brines via complex silica and carbonate precipitation/dissolution processes. Such models are challenged by the necessary SiO 2 removal. Thermodynamic and mass balance constraints are used to refi ne 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 infi ltration 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.
Databáze:	OpenAIRE
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