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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

Skridlaite, Grazina LU ; Siliauskas, Laurynas ; Söderlund, Ulf LU and Næraa, Tomas LU (2024) In Lithos 482-483.
Abstract

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,... (More)

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.

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author
; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Baddeleyite, East European Craton, LA-ICP-MS geochronology, Monazite, Ore dating, Ore origin, Zircon
in
Lithos
volume
482-483
article number
107736
publisher
Elsevier
external identifiers
  • scopus:85199782912
ISSN
0024-4937
DOI
10.1016/j.lithos.2024.107736
language
English
LU publication?
yes
id
7582b44c-017f-4284-9ed2-1cf0c844823f
date added to LUP
2024-09-03 15:47:27
date last changed
2024-09-03 15:48:24
@article{7582b44c-017f-4284-9ed2-1cf0c844823f,
  abstract     = {{<p>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 H<sub>2</sub>O 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.</p>}},
  author       = {{Skridlaite, Grazina and Siliauskas, Laurynas and Söderlund, Ulf and Næraa, Tomas}},
  issn         = {{0024-4937}},
  keywords     = {{Baddeleyite; East European Craton; LA-ICP-MS geochronology; Monazite; Ore dating; Ore origin; Zircon}},
  language     = {{eng}},
  publisher    = {{Elsevier}},
  series       = {{Lithos}},
  title        = {{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}},
  url          = {{http://dx.doi.org/10.1016/j.lithos.2024.107736}},
  doi          = {{10.1016/j.lithos.2024.107736}},
  volume       = {{482-483}},
  year         = {{2024}},
}