T188 Linking Critical Minerals and the Geologic Framework of North America II: The USGS Earth Mapping Resources Initiative (Earth MRI) and Related Activities

Tuesday, 17 October 2023
1:30 PM - 5:30 PM
324

40AR/39AR GEOCHRONOLOGY OF HYDROTHERMAL MINERALS FROM IOA AND IOCG DEPOSITS IN THE SOUTHEAST MISSOURI IRON PROVINCE, USA – RELATION TO 1.4 AND 1.3 GA MAGMATISM

Paper number: T188-12
Program: Technical Sessions
Time: 4:15 PM – 4:30 PM

Authors

  • Albert Hofstra Presenting Author
    Geology, Geophysics, and Geochemistry Science Center, Denver, CO
  • Cameron Mercer
    Geology, Geophysics, and Geochemistry Science Center, Denver, CO
  • Leah Morgan
    Geology, Geophysics, and Geochemistry Science Center, Denver, CO
  • Corey Meighan
    U.S. Geological Survey, Denver, CO

Abstract

The southeast Missouri iron province contains several significant magnetite and hematite iron oxide apatite (IOA)-REE deposits, a breccia pipe REE deposit and a magnetite iron oxide copper gold (IOCG)-Co deposit. Previous U-Pb geochronologic studies of igneous zircon and hydrothermal IOA and REE mineralization were mostly conducted using in-situ SHRIMP and LA-ICP-MS U-Pb spot analyses of zircon (1.48-1.44 Ga and 1.34-1.27 Ga), apatite (1.47-1.38 Ga), monazite (1.46-1.38 Ga), xenotime (1.45 Ga), and rutile (1.46-1.42 Ga).TIMS analyses of apatite (1.47-1.46 Ga), a whole rock Pb-Pb isochron (1.46 Ga) and Re-Os analyses of molybdenite (1.44 Ga) yield similar ages. Previous 40Ar/39Ar analyses of muscovite and biotite from the Pea Ridge IOA deposit showed that K-bearing alteration minerals can yield meaningful ages (1.47 Ga). Therefore, K-bearing alteration and vein minerals from several other IOA deposits and the IOCG deposit were analyzed at the USGS Denver Argon Geochronology Laboratory and the results compared to previous U-Pb ages.

Abundant actinolite and phlogopite and minor biotite and muscovite from IOA deposits (Pea Ridge, Bourbon, Lower Pilot Knob, and Kratz Spring) yield 40Ar/39Ar plateau ages of 1.51-1.46 Ga that are the same or older than previous U-Pb dates on apatite, monazite, and xenotime. Barren amphibole veins from the Boss IOCG-Co deposit are also dated at ca. 1.46 Ga.

Abundant muscovite and biotite alteration at the Boss IOCG-Co deposit yield 40Ar/39Ar plateau ages of 1.36-1.31 Ga. A small patch of muscovite alteration associated with fluorite at the Pea Ridge IOA deposit records a ca. 1.28 Ga hydrothermal overprint.

Together, previous and new 40Ar/39Ar analyses of K-bearing minerals record two periods of hydrothermal activity that correspond to each pulse of bimodal magmatism in the iron province. IOA-REE deposits and the REE breccia pipe are associated with the older 1.4 Ga pulse and the IOCG-Co deposit is associated with the younger 1.3 Ga pulse.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-391036

© Copyright 2023 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.