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<p>Rare earth element (REE)-rich polymetallic mineralisations along the so-called REE-line in the Palaeoproterozoic Bergslagen ore province of south-central Sweden comprise a diverse array of mineralisation types, specifically the classical Bastnäs-type skarns. Despite their historical, scientific, and economic significance, the timing and evolution of this Fe–REE–polymetallic system remain incompletely understood. Here we present new Re–Os geochronological data from laser ablation inductively coupled plasma tandem mass spectrometry (LA-ICP-MS/MS) of molybdenite from multiple occurrences in the REE-line, integrated with petrographic-paragenetic relationships and trace element analyses. Two main stages of molybdenite formation are recognised: an early stage (~1.91–1.89&#xa0;Ga) and a younger one, initiated after ~1.87&#xa0;Ga. These results show that the mineral system evolved through a prolonged, multistage history involving syn- to late-volcanic hydrothermal activity, skarn formation, and subsequent metamorphic overprinting and remobilisation spanning the evolution of the Svecokarelian orogeny. The two main stages likely reflect first-order tectonic control on mineralisation, developed primarily during extensional or tectonically quiescent intervals. Molybdenite is commonly associated with allanite-group minerals, and locally with related gatelite- and dollaseite-group phases, in both early and late paragenetic assemblages. Trace element systematics show distinct and different signatures between mineralisation types, reflecting the structural, chemical, and mineralogical context in which the respective molybdenites formed, and demonstrate the complex and polymetallic nature of the REE-line mineralisations. The study highlights the utility of in situ Re–Os dating for resolving mineralisation histories in metamorphosed systems and provides new temporal constraints on ore formation and modification in the Bergslagen province.</p>

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Timing and evolution of REE–Fe–polymetallic skarn mineralisation in the REE-line, Bergslagen, Sweden: insights from molybdenite Re–Os geochronology, petrographic–paragenetic relationships and trace element chemistry

  • 期刊论文

  • 发表日期：

    2026年4月10日

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  • Stefan S. Andersson,
  • Erik Jonsson,,
  • Thomas Zack,
  • Delia Rösel,
  • Dan Holtstam,
  • Martiya Sadeghi

摘要

Rare earth element (REE)-rich polymetallic mineralisations along the so-called REE-line in the Palaeoproterozoic Bergslagen ore province of south-central Sweden comprise a diverse array of mineralisation types, specifically the classical Bastnäs-type skarns. Despite their historical, scientific, and economic significance, the timing and evolution of this Fe–REE–polymetallic system remain incompletely understood. Here we present new Re–Os geochronological data from laser ablation inductively coupled plasma tandem mass spectrometry (LA-ICP-MS/MS) of molybdenite from multiple occurrences in the REE-line, integrated with petrographic-paragenetic relationships and trace element analyses. Two main stages of molybdenite formation are recognised: an early stage (~1.91–1.89 Ga) and a younger one, initiated after ~1.87 Ga. These results show that the mineral system evolved through a prolonged, multistage history involving syn- to late-volcanic hydrothermal activity, skarn formation, and subsequent metamorphic overprinting and remobilisation spanning the evolution of the Svecokarelian orogeny. The two main stages likely reflect first-order tectonic control on mineralisation, developed primarily during extensional or tectonically quiescent intervals. Molybdenite is commonly associated with allanite-group minerals, and locally with related gatelite- and dollaseite-group phases, in both early and late paragenetic assemblages. Trace element systematics show distinct and different signatures between mineralisation types, reflecting the structural, chemical, and mineralogical context in which the respective molybdenites formed, and demonstrate the complex and polymetallic nature of the REE-line mineralisations. The study highlights the utility of in situ Re–Os dating for resolving mineralisation histories in metamorphosed systems and provides new temporal constraints on ore formation and modification in the Bergslagen province.