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100-10 A Billion Years of Hematite Ore Development in the Lake Superior Region

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

Presenting Author:

Anthony Fuentes

Authors:

Fuentes, Anthony J¹, Courtney-Davies, Liam², Flowers, Rebecca³, Zhang, Yiming⁴, Swanson-Hysell, Nicholas⁵

(1) Department of Earth and Planetary Science, University of California Berkeley, Berkeley, CA, USA, (2) Department of Geological Sciences, University of Colorado Boulder, Boulder, CO, USA, (3) Department of Geological Sciences, University of Colorado Boulder, Boulder, CO, USA, (4) Institute for Rock Magnetism, Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN, USA, (5) Institute for Rock Magnetism, Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN, USA,

Abstract:

Iron formation (IF)-hosted hematite deposits are the primary source of high-grade iron and are found globally. The mechanism(s) by which iron becomes more concentrated in these deposits remains contentious in many instances. Geochronology can provide an efficient means to test ore formation hypotheses by evaluating the temporal association of iron oxide crystallization with independently dated geologic events, however most of the existing age constraints on ore mineralization come from accessory minerals. The recent development of direct hematite U-Pb dating via LA-ICPMS has resulted in significant re-evaluations of the formation timelines of the world’s largest iron ore deposits, showing greater nuance than age information obtained from accessory phases alone. In this work, we paired in-situ hematite U-Pb and paleomagnetism to evaluate the enrichment pathway of Paleoproterozoic iron formation in Northern Michigan to an economic hematite ore deposit. Our geochronologic and paleomagnetic results demonstrate that growth of hematite in these units was far more protracted than previously interpreted, with hematite crystallization spanning the Proterozoic. Most notably, we have identified a previously unrecognized period of ore genesis from ca 580 to 460 Ma that is supported by both the U-Pb and paleomagnetic data. Our results indicate that the study locality would have been located at tropical latitudes at this time during an especially warm non-glacial interval and positioned in the shallow subsurface. These constraints implicate warm, downward propagated meteoric fluids as a mechanism for the enrichment of this deposit rather than Paleoproterozoic tectonism as had previously been argued. These results highlight how paleomagnetism and hematite U-Pb geochronology can yield complementary insights into hematite mineralization throughout Earth history. This integrated approach opens new research directions for evaluating valuable information from hematite-bearing units.

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

doi: 10.1130/abs/2025AM-9981

A Billion Years of Hematite Ore Development in the Lake Superior Region

Description

Session Format: Oral

Presentation Date: 10/20/2025

Presentation Start Time: 10:40 AM

Presentation Room: HBGCC, 304C

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