Extreme light rare earth element mobilization by diagenetic fluids in the geological environment of the Oklo natural reactor zones, Franceville basin, Gabon

Abstract

Research Article| August 01, 2000 Extreme light rare earth element mobilization by diagenetic fluids in the geological environment of the Oklo natural reactor zones, Franceville basin, Gabon Michel Cuney; Michel Cuney 1Unité Mixte de Recherche G2R-7566, Université Henri Poincaré, BP239, F-54506 Vandoeuvre-lès-Nancy Cedex, France Search for other works by this author on: GSW Google Scholar Régis Mathieu Régis Mathieu 1Unité Mixte de Recherche G2R-7566, Université Henri Poincaré, BP239, F-54506 Vandoeuvre-lès-Nancy Cedex, France Search for other works by this author on: GSW Google Scholar Geology (2000) 28 (8): 743–746. https://doi.org/10.1130/0091-7613(2000)28<743:ELREEM>2.0.CO;2 Article history received: 11 Feb 2000 rev-recd: 08 May 2000 accepted: 19 May 2000 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Michel Cuney, Régis Mathieu; Extreme light rare earth element mobilization by diagenetic fluids in the geological environment of the Oklo natural reactor zones, Franceville basin, Gabon. Geology 2000;; 28 (8): 743–746. doi: https://doi.org/10.1130/0091-7613(2000)28<743:ELREEM>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The anomalously high Th/La ratio (∼1.14) of the Early Proterozoic silicified sandstones of the Franceville basin (Gabon), compared to Archean and Proterozoic metasedimentary rocks (Th/La ∼0.27), results from extreme light rare earth element (REE) migration during diagenesis. Monazite, which represents the main light REE-bearing phase in the sandstones, was altered by diagenetic brines at 140 °C and 1 kbar. The alteration phase is a microcrystalline Th-silicate phase, indicating low Th solubility at these conditions. Light REEs are simultaneously leached out together with P and U. The increase in Th/La from detrital monazite to residual Th-silicate phase indicates that about 76% of the light REEs were leached out, corresponding to a global amount of 2.01 × 109 metric tons at the scale of the FA Formation in the Franceville basin. Uranium was also leached during monazite alteration and may have contributed significantly to the genesis of the high-grade uranium deposits of the Franceville basin that host the natural nuclear reaction zones. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.