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Triple oxygen isotope variations in magnetite from iron-oxide deposits, central Iran, record magmatic fluid interaction with evaporite and carbonate host rocks

Stefan T. M. Peters, Narges Alibabaie, Andreas Pack, Seann J. McKibbin, Davood Raeisi, Niloofar Nayebi, Farhad Torab, Trevor Ireland and Bernd Lehmann
Triple oxygen isotope variations in magnetite from iron-oxide deposits, central Iran, record magmatic fluid interaction with evaporite and carbonate host rocks
Geology (Boulder) (December 2019) 48 (3): 211-215

Abstract

Oxygen isotope ratios in magnetite can be used to study the origin of iron-oxide ore deposits. In previous studies, only (super 18) O/ (super 16) O ratios of magnetite were determined. Here, we report triple O isotope data ( (super 17) O/ (super 16) O and (super 18) O/ (super 16) O ratios) of magnetite from the iron-oxide-apatite (IOA) deposits of the Yazd and Sirjan areas in central Iran. In contrast to previous interpretations of magnetite from similar deposits, the triple O isotope data show that only a few of the magnetite samples potentially record isotopic equilibrium with magma or with pristine magmatic water (H (sub 2) O). Instead, the data can be explained if magnetite had exchanged O isotopes with fluids that had a mass-independently fractionated O isotope composition (i.e., MIF-O), and with fluids that had exchanged O isotopes with marine sedimentary carbonate rocks. The MIF-O signature of the fluids was likely obtained by isotope exchange with evaporite rocks of early Cambrian age that are associated with the IOA deposits in central Iran. In order to explain the triple O isotope composition of the magnetite samples in conjunction with available iron isotope data for magnetite from the deposits, we propose that magnetite formed from magmatic fluids that had interacted with evaporite and carbonate rocks at high temperatures and at variable water/rock ratios; e.g., magmatic fluids that had been released into the country rocks of a magma reservoir. Additionally, the magnetite could have formed from magmatic fluids that had exchanged O isotopes with SO (sub 2) and CO (sub 2) that, in turn, had been derived by the magmatic assimilation and/or metamorphic breakdown of evaporite and carbonate rocks.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 48
Serial Issue: 3
Title: Triple oxygen isotope variations in magnetite from iron-oxide deposits, central Iran, record magmatic fluid interaction with evaporite and carbonate host rocks
Affiliation: University of Goettingen, Department of Isotope Geology, Gottingen, Germany
Pages: 211-215
Published: 20191217
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 43
Accession Number: 2020-006819
Categories: Economic geology, geology of ore depositsIsotope geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2020057
Illustration Description: illus. incl. geol. sketch map
N25°00'00" - N39°30'00", E44°00'00" - E63°19'60"
Secondary Affiliation: Technical University of Clausthal, DEU, GermanyTehran University, IRN, IranYazd University, IRN, IranAustralian National University, AUS, Australia
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 202006
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