Unconformity-related rare earth element deposits: a regional-scale hydrothermal mineralization type of northern Australia

Nazari-Dehkordi, Teimoor, Spandler, Carl, Oliver, Nicholas H.S., and Wilson, Robin (2018) Unconformity-related rare earth element deposits: a regional-scale hydrothermal mineralization type of northern Australia. Economic Geology, 113 (6). pp. 1297-1305.

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Rare earth element (REE) orebodies are typically associated with alkaline igneous rocks or develop as placer or laterite deposits. Here, we describe an economically important heavy (H)REE mineralization type that is entirely hydrothermal in origin with no demonstrable links to magmatism. The mineralization occurs as numerous xenotime-rich vein and breccia orebodies across a large area of northern Australia but particularly close to a regional unconformity between Archean metasedimentary rocks of the Browns Range Metamorphics and overlying Proterozoic sandstones of the Birrindudu Group. The deposits formed at 1.65 to 1.61 Ga along steeply dipping faults; there is no known local igneous activity at this time. Depletion of HREEs in the Browns Range Metamorphics, together with the similar nonradiogenic Nd isotope composition of the orebodies and the Browns Range Metamorphics, indicates that ore metals were leached directly from the Browns Range metasedimentary rocks. We propose an ore genesis model that involves fluid leaching HREEs from the Browns Range Metamorphics and subsequently mixing with P-bearing acidic fluid from the overlying sandstones in fault zones near the unconformity. The union of P and HREEs via fluid mixing in a low-Ca environment triggered extensive xenotime precipitation. This mineralization is unlike that of any other class of REE ore deposit but has a similar setting to unconformity-related U deposits of Australia and Canada, so we assign it the label “unconformity-related REE.” Further discoveries of this REE mineralization type are expected near regional unconformities within Proterozoic intracontinental sedimentary basins across the globe.

Item ID: 55967
Item Type: Article (Research - C1)
ISSN: 1554-0774
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Copyright Information: Copyright © 2018 Society of Economic Geologists, Inc.
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A version of this publication was included as Chapter 4 of the following PhD thesis: Nazari Dehkordi, Teimoor (2018) The origin and evolution of heavy rare earth element mineralisation in the Browns Range area, Northern Australia. PhD thesis, James Cook University, which is available Open Access in ResearchOnline@JCU. Please see the Related URLs for access.

Funders: Australian Research Council (ARC)
Projects and Grants: ARC Future Fellowship FT120100198
Date Deposited: 28 Oct 2018 21:32
FoR Codes: 37 EARTH SCIENCES > 3705 Geology > 370508 Resource geoscience @ 100%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840107 Titanium Minerals, Zircon, and Rare Earth Metal Ore (e.g. Monazite) Exploration @ 100%
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