Genesis of sedimentary- and vein-type magnesite deposits at Kop Mountain, NE Turkey

Sedimentary- and vein-type magnesites were deposited within and on ultramafic rocks of the Kop Mountain region in Bayburt province. In the field, magnesites are exposed along NE-SW trending normal faults and in fractures in the ultramafic rocks. Petrographic studies reveal that magnesite is predominantly micrite, but also occurs as microsparite formed by recrystallization of micrite. The ultramafic rocks hosting the magnesites consist of serpentinized olivine, hypersthene and diopside. Ni, Co and Ti contents of magnesites suggest precipitation from percolating water through the serpentinized ultramafic rocks. The sedimentary- and vein-type magnesites have different d18O and d13C values, characterizing formation under different conditions. Temperature estimates using the average d18O values reveal precipitation from water at ~24.5°C for sedimentary magnesite and ~37.0°C for vein-type magnesite. The d13C values of vein-type magnesites are distinctly more negative than those of sedimentary magnesites, indicating carbon isotopes derived from predominantly decarboxylation of organic sediments in shales and carbonate dissolution. Less negative d13C values in the sedimentary magnesite are mainly due to outgassing of mineralizing water. Our data suggest a petrogenetic model in which the surface water percolates through the ultramafic and sedimentary rocks becoming heated by volcanics at depth and enriched in Mg+2 and light carbon isotopes, followed by migration upward to form magnesite near the surface in ultramafic rocks as fracture-fill and as sediment at the surface.

Genesis of sedimentary- and vein-type magnesite deposits at Kop Mountain, NE Turkey

Sedimentary- and vein-type magnesites were deposited within and on ultramafic rocks of the Kop Mountain region in Bayburt province. In the field, magnesites are exposed along NE-SW trending normal faults and in fractures in the ultramafic rocks. Petrographic studies reveal that magnesite is predominantly micrite, but also occurs as microsparite formed by recrystallization of micrite. The ultramafic rocks hosting the magnesites consist of serpentinized olivine, hypersthene and diopside. Ni, Co and Ti contents of magnesites suggest precipitation from percolating water through the serpentinized ultramafic rocks. The sedimentary- and vein-type magnesites have different d18O and d13C values, characterizing formation under different conditions. Temperature estimates using the average d18O values reveal precipitation from water at ~24.5°C for sedimentary magnesite and ~37.0°C for vein-type magnesite. The d13C values of vein-type magnesites are distinctly more negative than those of sedimentary magnesites, indicating carbon isotopes derived from predominantly decarboxylation of organic sediments in shales and carbonate dissolution. Less negative d13C values in the sedimentary magnesite are mainly due to outgassing of mineralizing water. Our data suggest a petrogenetic model in which the surface water percolates through the ultramafic and sedimentary rocks becoming heated by volcanics at depth and enriched in Mg+2 and light carbon isotopes, followed by migration upward to form magnesite near the surface in ultramafic rocks as fracture-fill and as sediment at the surface.

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  • Abu-jaber, N. & Kimberley, M. 1992. Origin of ultramafic-hosted vein magnesite deposits. Ore Geology Reviews 7, 155–191.
  • Aharon, P. 1988. A stable isotope study of magnesite from the Rum Jungle Uranium field, Australia: implications for the origin of strata-bound massive magnesite. Chemical Geology 69, 127– 1
  • Bashir, E., Naseem, S., Akhtar, T. & Shireen, K. 2009. Characteriscs of ultramafic rocks and associated magnesite deposits, Nal Area, Khuzdar, Baluchistan, Pakistan. Journal of Geology and Mining Research 1, 034–041.
  • Ece, Ö.I., Matsubaya, O. & Çoban, F. 2005. Genesis of hydrothermal stockwork-type magnesite deposits associated with ophiolite complexes in the Kütahya-Eskişehir region, Turkey. Neues Jahrbuch für Mineralogie- Abhandlungen 181/2, 191–205.
  • Deines, P. 1980. The carbon isotopic composition of diamonds: relationship to diamond shape, color, occurrence and vapor composition. Geochim. Et Cosmochim. Acta 44, 943–961.
  • Fallick, A.E., Ilich, M. & Russell, M.J. 1991. A stable isotope study of the magnesite deposits associated with the Alpine-type ultramafic rocks of Yugoslavia. Economic Geology 85, 847–861. Frank, T.D. & Fielding, C.R. 2003. Marine origin for Precambrian, carbonate-hosted magnesite. Geology 31, 1101–1104.
  • Gartzos, E. 1990. Carbon and oxygen istotope constaints on the origin of magnesite deposits, North Evia (Greece). Schweizerische Mineralogische und Petrographische Mitteilungen 70, 67–72.
  • Horkel, K., Ebner, F. & Spötl, CH. 2009. Stable isotopic composition of cryptocrystalline magnesite from deposits in Turkey and Austria. − EGU General Assembly Geophysical Research Abstracts, v. 11. EGU 2009-11881.
  • O’neil, J.R. & Barnes, I. 1971. C 13 and O 18 compositions in some freshwater carbonates associated with ultramafic rocks: Western United States. Geochimica et Cosmochimica Acta 35, 687–697. Şengör, A.M.C. & Yılmaz, Y. 1981. Tethyan evolution of Turkey: A plate tectonic approach. Tectonophysics 75, 181–241.
  • Smykatz-Kloss, W. 1974. Differential Thermal Analysis, Application and Results in Mineralogy. Springer-Verlag, Berlin, 185 pp.
  • Sun, S.S. & McDonough, W.F. 1989. Chemical and isotope systematics of oceanic basalts; implication for mantle compositions and processes. In: Saunders, A.D. & Norry, M.J. (eds), Magmatism in the ocean basins. Geological Society Special Publications, 42, 313–345.
  • Van Der Marel, H.W. & Beutelspacher, H. 1976. Atlas of IR Spectroscopy of Clay Minerals and Their Admixtures. Elsevier, Amsterdam. 396 pp.
  • Webb, T.L. & Krüger, J.E. 1970. Carbonate. In: MacKenzie, R.C. (ed), Differential Thermal Analysis, volume 1, fundamental aspects. Academic Press, London and New York, 303–341.