Chen Wei, Radiogenic Pb reservoir contributes to the rare earth element (REE) enrichment in South Qinling carbonatites

Chen Wei, Radiogenic Pb reservoir contributes to the rare earth element (REE) enrichment in South Qinling carbonatites

Title:Radiogenic Pb reservoir contributes to the rare earth element (REE) enrichment in South Qinling carbonatites

Author(s): Chen Wei, Lu Jue, Jiang Shao-Yong, Ying Yuan-Can, Liu Yong-Sheng

Addresses: State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China

Collaborative Innovation Center for Exploration of Strategic Mineral Resources, Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China

Source: Chemical Geology Volume:494, Issue:5 Pages:80-95

DOI: 10.1016/j.chemgeo.2018.07.019

Published:18 July 2018.

Abstract: Carbonatite and related alkaline silicate rocks contain one of the most significant rare earth element (REE) reserves in the world. It is well-known that these REEdeposits are characterized by a strong light REE enrichment with a steep fractionation from La to Lu in the chondrite-normalized diagram. However, the origin of their REE enrichment remains debatable. The Shaxiongdong (SXD) carbonatite in the South Qinling orogenic belt hosts one of the most important REE deposits in central China. In this study, in situ chemical and isotopic data have been obtained for carbonate minerals from the complex. Our results show that calcite has variable trace element abundances, especially REEs. In situ Pb isotope data for calcite reveal extreme variations of 206Pb/204Pb (18.05–31.71) and 207Pb/204Pb (15.49–16.36) ratios. Interestingly, Pb isotope variations display positive correlations with REE enrichments [i.e., (La/Yb)N and (La/Nd)N]. Calcite with extreme radiogenic Pb isotopic compositions displays upper mantle C and O isotopic compositions (δ13Cavg = −5.74‰, δ18Oavg = 7.13‰) and depleted 87Sr/86Sr isotopic ratios (~0.7030). The observed various REE enrichments accompanying the variable Pb isotopic composition within SXD calcite possibly result from a closed-system metasomatic event. The U-bearing mineral (i.e., pyrochlore) accumulating abundant uranogenic lead since their Silurian formation serves as the radiogenic Pb and LREE source for the metasomatism. Alternatively, the chemical and isotopic composition observed might suggest involvement of two mantle sources (PREMA and the distinct radiogenic Pb mantle reservoir).

Full Text from Publisher: https://doi.org/10.1016/j.chemgeo.2018.07.019