Cited by 275Geochemistry and Elemental AnalysisPaleontology and Stratigraphy of FossilsGeological and Geochemical Analysis

The Chemistry of Manganese Ores through Time: A Signal of Increasing Diversity of Earth-Surface Environments

Maynard, J. Barry·2010·Economic Geology

Abstract

Almost all economic manganese ores are ultimately or directly derived from hydrothermal vents associated with intermediate volcanic rocks. This source is in contrast to deep-sea nodules, which likely have a larger component of sediment-derived manganese and whose volcanic sources are more mafic. Manganese deposits can be divided into sedimentary rock-hosted, volcanic rock-hosted and karst-hosted, in order of predominance. Two genetic types of sedimentary rock-hosted deposits can also be identified: those with Mn derived via upwelling from oxygen-minimum zones and those formed on the margins of euxinic basins. Most of the large tonnage deposits appear to form by the euxinic mechanism. Manganese ores, like those of Fe, show a strong concentration of deposits in the Paleoproterozoic and a lesser occurrence in the Neoproterozoic, but, unlike Fe, there is an additional strong peak in the Oligocene. Therefore, Mn is not controlled entirely by the level of oxygen in the Earth’s atmosphere. At each peak of Mn deposition, the associated ore deposits are concentrated in a few districts, suggesting a more local than global control on manganese metallogenesis. Age trends can, however, be discerned in some chemical properties of manganese deposits. Overall, there is a trend to progressive increases in chemical diversity from the Archean to the Recent, with a particularly steep increase in the Neoproterozoic-Early Cambrian, corresponding in time to the radiation of metazoans. Also beginning in the Cambrian is the development of upwelling-linked deposits. There is another sharp increase in chemical diversity at the Jurassic-Cretaceous boundary, which includes increased SiO 2 /Al 2 O 3 ratios and corresponds to the radiation of diatoms. There is a conspicuous gap in sedimentary rock-hosted Mn deposits between 1800 and 800 Ma that may correspond to a monotonous, low-oxygen ocean, but one without sulfidic deep water. Alternatively, Mn may have been precipitated entirely in the deep ocean, beneath a sulfidic oxygen minimum layer. The positive Eu anomalies, which in iron formations are equated to vent-sourced metals, are not seen in most Mn deposits, although they are found in Mn-rich iron formations. By contrast, Fe deposits interbedded with major Mn ores lack the usual Eu signal. Therefore, mechanisms of transport between hydrothermal vents and the sites of deposition differed for Fe and for Mn deposits in the Archean-Paleoproterozoic. The dominant pattern in the time trend of Mn deposition is increasing chemical diversity, which reflects an increasing compartmentalization of the Earth’s depositional environments. This compartmentalization was a response to, but also provided a spur to, the diversification of life forms.

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Crossref · 10.2113/gsecongeo.105.3.535

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Authors
Maynard, J. B.
Affiliations
University of Cincinnati (US)
Corresponding author
Maynard, J. Barry
Venue
Economic Geology
Published
2010-05-01
Volume
105
Issue
3
Pages
535-552
ISSN
  • 0361-0128 (ISSN-L)
  • 1554-0774
OpenAlex
W2099572573
Cited by
275
References
189
Citations by year
2026: 28 · 2025: 49 · 2024: 27 · 2023: 13 · 2022: 22 · 2021: 30 · 2020: 21 · 2019: 16 · 2018: 15 · 2017: 10 · 2016: 11 · 2015: 4 · 2014: 6 · 2013: 10 · 2012: 8
FWCI
10.94
Type
journal article
Language
en
Open access
closed
Locations
Economic Geology (publishedVersion)
Topics
  • Physical Sciences › Earth and Planetary Sciences › Geochemistry and Petrology › Geochemistry and Elemental Analysis
  • Physical Sciences › Earth and Planetary Sciences › Paleontology › Paleontology and Stratigraphy of Fossils
  • Physical Sciences › Earth and Planetary Sciences › Geophysics › Geological and Geochemical Analysis
Keywords
manganese ore, ore genesis, hydrothermal vents, intermediate volcanic rock, deep-sea manganese nodules, euxinic basins, oxygen minimum zone, upwelling, Paleoproterozoic, Neoproterozoic, Cambrian, Jurassic-Cretaceous boundary, Eu anomaly, iron-formation

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