81-2 Rare Earth Element scavengers in terrestrial Manganese Formations

Session: Investigating Earth’s History With Continental Scientific Drilling

Presenting Author:

Harshitha Gangula

Authors:

Gangula, Harshitha Reddy¹, Yadav, Jayant Kumar², C, Manikyamba³, Reddy, I. Panduranga⁴

(1) CSIR-National Geophysical Research Institute, Hyderabad, India, India; Department of Geology, Osmania University, Hyderabad, Telangana, India, (2) CSIR-National Geophysical Research Institute, HYDERABAD, Telangana, India, (3) CSIR-National Geophysical Research Institute, Hyderabad, Telangana, India, (4) Department of Geology, Osmania University, Hyderabad, Telangana, India,

Abstract:

Poorly crystalline manganese and iron oxides, such as δ-MnO₂ (vernadite and nanocrystalline birnessite), are known for their high adsorption capacity due to their large surface area (~260 m²/g) and low point of zero charge (pHₚzc ~2.25). This enables them to efficiently scavenge metal cations from natural waters. Minerals derived from the transformation of δ-MnO₂, such as todorokite, have an even higher pHₚzc (~3.39), further enhancing their ability to adsorb cations like REE³⁺, Ni²⁺, Cu²⁺, and Zn²⁺, particularly under alkaline conditions. This study examines the role of todorokite, a tunnel structured tectomanganate Mn-oxide as an efficient REE+Y scavenger in terrestrial supergene enriched Mn-ore, as identified in the Mn-formations of the greenstone belts of Dharwar Craton, southern Peninsular India. The studied Mn-ores show REE enrichment of up to 15 times that of post-Archean Australian Shale (PAAS), with mineralogical analysis identifying goethite, pyrolusite, psilomelane, hausmannite and todorokite as the dominant phases. Principal component analysis depicts strong correlations between REE, Mn and Sr suggesting that Todorokite [(Na,Ca,K,Ba,Sr)_1-x(Mn,Mg,Al)₆O₁₂.3-4H₂O] is the primary host of REE+Y in these formations. Hierarchical cluster analysis further reveals the clustering of redox-sensitive trace elements (Co, Ni, V, U) and large-ion lithophile elements (Sc, Sr, Pb), indicating that fluid Eh-pH conditions considerably influenced the mobilization and sorption of REEs onto the corner sites of todorokite. Additionally, extreme Ce enrichment and negative Ce anomalies in the Mn ore suggest that Ce was transported and mobilized in its (IV) oxidation state, along with Mn⁺² and U⁺⁶ (as HUO₄⁻). This corresponds to REE mobilization under circumneutral to alkaline fluid conditions, with a conservative Eh estimate of -0.2 to +0.4. Our studies suggest that, contrary to current understanding, the formation of secondary Mn-minerals in highly weathered terranes significantly influence the REE mobility and may serve as a valuable geochemical tool for exploring alternate REE resources in sedimentary terranes.

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

doi: 10.1130/abs/2025AM-4432

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