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Ulf Söderlund

Ulf Söderlund

Professor

Ulf Söderlund

Iron-rich Ca–Mg skarns from the SW East European Craton (Lithuania) : Microstructural study, mineral reactions and direct age constraints of ore-forming events using LA-ICPMS

Author

  • Grazina Skridlaite
  • Laurynas Siliauskas
  • Ulf Söderlund
  • Tomas Næraa

Summary, in English

The Varena Iron Ore deposit in the SW East European Craton is a significant ore body that occurs within metamorphosed and hydrothermally reworked Paleoproterozoic dolostones. We have performed microstructural investigations supplemented with mineral chemistry and geochronological investigations (LA-ICP-MS) to obtain age constraints on the ore-forming event(s) and improve the understanding of the conditions during mineralization process. Mineral chemistry and textures suggest a drop in pressure after the event of peak metamorphic skarn formation. Influx of oxidized, iron-rich H2O fluids resulted in (1) Mg mobility that caused secondary dolomitization of calcite, (2) dissolution of metamorphic magnetite and formation of a new, inclusion-rich (Mag-1) and inclusion-poor (Mag-2) magnetite, and (3) replacement of the peak skarn assemblages. During these fluid-related processes, accessory phases of monazite, baddeleyite, and zircon were formed. Their U–Pb dating yield individually robust ages of 1721 ± 9 Ma (monazite, 23 spots), 1703 ± 10 Ma (baddeleyite, 18 spots) and 1706 ± 54 Ma (zircon, 14 spots), respectively. The weighted mean age of 1713 ± 7 Ma (2σ internal) is considered to represent the best age estimate of the iron-ore mineralization in the Varena Iron Ore deposit, and possibly also dates influx of P, REEs etc. into the system. This mineralization event is contemporaneous with ca. 1.73–1.70 Ga metamorphic reworking of the host rocks in the region and may be linked to regional continental-margin type Transscandinavian Igneous Belt (TIB) magmatism in south-central Sweden.

Department/s

  • Lithosphere and Biosphere Science

Publishing year

2024-10

Language

English

Publication/Series

Lithos

Volume

482-483

Document type

Journal article

Publisher

Elsevier

Topic

  • Geology

Keywords

  • Baddeleyite
  • East European Craton
  • LA-ICP-MS geochronology
  • Monazite
  • Ore dating
  • Ore origin
  • Zircon

Status

Published

ISBN/ISSN/Other

  • ISSN: 0024-4937