100-9 Hematite Double-Dating Defines Proterozoic Mineralization and Thermal History of Archean Banded Iron Formations, NE Minnesota, USA

Session: Snowballs, Unconformities, BIFs and Beyond: Navigating the Neoproterozoic Rock and Climate Records Using Geochronology

Presenting Author:

Zsuzsanna Allerton

Authors:

Allerton, Zsuzsanna¹, Courtney-Davies, Liam², Danisik, Martin³, Hudak, George Julius⁴, Teyssier, Christian P.⁵, Mitchell, Jennifer⁶, Larson, Phillip⁷

(1) Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, Minnesota, USA, (2) University of Colorado Boulder, Boulder, CO, USA, (3) Curtin University, Bentley, WA, Australia, (4) NRRI - UMD, Duluth, MN, USA; University of Minnesota, Minneapolis, Minnesota, USA, (5) Univ Minnesota, St Louis Park, MN, USA, (6) Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, Minnesota, USA; Characterization Facility, University of Minnesota, Minneapolis, USA, (7) Swenson College of Sciences and Engineering, University of Minnesota Duluth, Duluth, USA,

Abstract:

The age and origin of hematite deposits in the Vermilion District of Minnesota, Lake Superior region has been debated for over a century and inferred to be Neoarchean or Mesoproterozoic. Utilizing a new geochronological approach combining U-Pb and (U-Th)/He ‘double-dating’ of hematite, we present the first direct dates for hematite deposits at the Soudan mine, revealing a previously unknown Paleoproterozoic mineralization event and a thermal history recording the emplacement of the proximal Mesoproterozoic Midcontinent Rift System. Hematite phases yield U-Pb crystallization dates ranging between 1.8-1.6 Ga and (U-Th)/He dates in the range of 1.63-0.53 Ga, with a distinct cluster at ca. 1.1 Ga. We propose that replacement-style hematite mineralization was generated during Paleoproterozoic orogenic events, including the Yavapai (1.71-1.68 Ga) and/or Mazatzal (1.65-1.60 Ga) accretionary orogenies and associated magmatism related to the assembly of Laurentia that reactivated shear zones and facilitated hydrothermal alteration deep into the Archean craton. (U-Th)/He data suggest that hematite ore experienced a thermal overprint that did not reset the U-Pb system, with the most consistent dates coinciding with the establishment of the Midcontinent Rift System at ca. 1.1 Ga. Double-dating of hematite is demonstrated to directly link iron mineralization to thermal and tectonic events in Precambrian cratons and place constraints on genesis not available from coexisting accessory minerals.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11328

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