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Replacement origin for hematite in 2.5 Ga banded iron formation: Evidence for postdepositional oxidation of iron-bearing minerals

2014; Geological Society of America; Volume: 126; Issue: 3-4 Linguagem: Inglês

10.1130/b30944.1

1943-2674

Birger Rasmussen, B. Krapež, Daniela B. Meier,

Paleontology and Stratigraphy of Fossils

Research Article| March 01, 2014 Replacement origin for hematite in 2.5 Ga banded iron formation: Evidence for postdepositional oxidation of iron-bearing minerals Birger Rasmussen; Birger Rasmussen † Department of Applied Geology, Curtin University, Kent Street, Bentley, WA 6102, Australia †E-mail: B.Rasmussen@curtin.edu.au. Search for other works by this author on: GSW Google Scholar Bryan Krapež; Bryan Krapež Department of Applied Geology, Curtin University, Kent Street, Bentley, WA 6102, Australia Search for other works by this author on: GSW Google Scholar Daniela B. Meier Daniela B. Meier Department of Applied Geology, Curtin University, Kent Street, Bentley, WA 6102, Australia §Present address: School of Earth and Environment, The University of Leeds, Leeds LS2 9JT, UK. Search for other works by this author on: GSW Google Scholar Author and Article Information Birger Rasmussen † Department of Applied Geology, Curtin University, Kent Street, Bentley, WA 6102, Australia Bryan Krapež Department of Applied Geology, Curtin University, Kent Street, Bentley, WA 6102, Australia Daniela B. Meier §Present address: School of Earth and Environment, The University of Leeds, Leeds LS2 9JT, UK. Department of Applied Geology, Curtin University, Kent Street, Bentley, WA 6102, Australia †E-mail: B.Rasmussen@curtin.edu.au. Publisher: Geological Society of America Received: 11 Jun 2013 Revision Received: 10 Oct 2013 Accepted: 06 Dec 2013 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2014 Geological Society of America GSA Bulletin (2014) 126 (3-4): 438–446. https://doi.org/10.1130/B30944.1 Article history Received: 11 Jun 2013 Revision Received: 10 Oct 2013 Accepted: 06 Dec 2013 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Birger Rasmussen, Bryan Krapež, Daniela B. Meier; Replacement origin for hematite in 2.5 Ga banded iron formation: Evidence for postdepositional oxidation of iron-bearing minerals. GSA Bulletin 2014;; 126 (3-4): 438–446. doi: https://doi.org/10.1130/B30944.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Banded iron formations (BIFs) are central to interpretations about the composition of the Precambrian ocean, atmosphere, and biosphere. Hematite is an important component of many BIFs, and its presence has been used as evidence for the former presence of hydrous ferric oxyhydroxides that formed from the oxidation of dissolved ferrous iron in seawater. However, textural evidence for the origin of hematite is equivocal. New petrographic results show that hematite in unmineralized BIF from the ca. 2.5 Ga Dales Gorge Member of the Brockman Iron Formation, Hamersley Group, Western Australia, including morphologies previously interpreted to represent ferric oxyhydroxide precipitates, formed via fluid-mediated replacement of iron-silicates and iron-carbonates along sedimentary layering. The lateral transition from stilpnomelane- and siderite-rich laminae to hematite-dominated laminae is interpreted to reflect progressive stages of in situ alteration of reduced mineral assemblages by oxygen-bearing fluids rather than changes in the chemistry of the water column during deposition. Although morphologies previously ascribed to “primary” hematite are present, they are related to mineral replacement reactions, raising doubts about the petrographic criteria used to identify original hematite. Hematite replacement in unmineralized BIF postdated deposition and possibly metamorphism, and predated modern weathering. From a regional perspective, it appears to be a distal signature of the processes that were responsible for iron-ore mineralization, which involved the deep infiltration of oxygen-bearing meteoric fluids. The mineral replacement reactions recorded in the Dales Gorge Member are unlikely to be unique and probably occurred in BIFs elsewhere at some point in their history. The observation that at least some of the hematite in unmineralized BIF did not form directly from ferric oxyhydroxides implies that hematite is not a reliable proxy for the composition of the precursor sediment or the redox chemistry of the ocean. The oxidation of ferrous-rich phases after deposition suggests that the precursor sediments of BIF originally had a more reduced bulk composition. This raises the possibility that, in an ocean with negligible molecular oxygen and elevated Si and Fe, the growth of iron-rich clay minerals was favored over hematite. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.