Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Mirnejad, H. Articles by Taylor, B. E. Search for Related Content GeoRef GeoRef Citation

MINERALOGY, STABLE ISOTOPE GEOCHEMISTRY, AND PARAGENESIS OF MAGNESITE DEPOSITS FROM THE OPHIOLITE BELT OF EASTERN IRAN

H. Mirnejad^1,, K. Ebrahimi-Nasrabadi², A. E. Lalonde³ and B. E. Taylor⁴

¹ Department of Geology, Faculty of Science, University of Tehran, Tehran, Iran 14155-64155
² Department of Geology, Ferdowsi University of Mashhad, Mashhad, Iran 917794897
³ Department of Earth Sciences and Ottawa-Carleton Geoscience Centre, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5
⁴ Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, Canada K1A 0E8

Corresponding author, e-mail: mirnejad{at}khayam.ut.ac.ir

A large number of magnesite deposits with reserves totaling several million tons occur in Eastern Iran. These deposits are found as veins within ultramafic rocks (Afzalabad vein-type) and as lenses overlying the surrounding flysch sedimentary strata (Torshak strata bound). The occurrence of both vein-type and strata-bound deposits is not common among magnesite deposits worldwide. The Afzalabad magnesite is texturally heterogeneous and characterized by higher Mg and lower Ca, Sr, As, Ba, and B contents than the Torshak magnesite. These compositional differences are also reflected by the unit-cell parameters of the magnesite. However, magnesites from both localities have similar carbon and oxygen isotope compositions that are characteristically heavy (¹³C values of 7.2 to 8.2, ¹⁸O values of 27.5 to 33.6). Such high -values are unlike those for magnesite found near and within other ultramafic complexes worldwide but are similar to the isotopic compositions of magnesite found in lagoon or hypersaline basin environments. However, the settings of Eastern Iran magnesite deposits differ from those formed in lagoons or hypersaline environments. Instead, we infer that evaporating surface water containing dissolved atmospheric CO₂ percolated through fractures in ultramafic rocks, acquiring Mg by hydrolysis of Mg-rich minerals. As the fluids subsequently ascended, magnesite precipitated in the fractures within the ultramafic complex and in the open channelways in the surrounding flysch strata.