Isotopic signatures of REY mineralization associated with lignite basins in South Primorye, Russian Far East

Abstract

The paper is based on stable isotopic analyses (C, O, H) first obtained for the rare earth elements + yttrium mineralization of South Primorye and Southwest Japan in addition to recent exploration data and some K-Ar and U-Pb datings. The analyzed minerals include hydrous carbonates and clay minerals that are hosted by argillized (weathered) shale, granite, mafic rocks, and semi-lithified sediments of various (from Cambrian to Late Cenozoic) age. The data distinctly evidence that a major agent of rare metal leaching from the host rocks and their redistribution inside the lignite-bearing sediments and weathered crust was meteoric water. Its moderately acidic character was due to carbon dioxide flowing up from the mantle through faults associated with the lignite basins, in addition to organic matter and sulfides disseminated in the host rocks. Concentrated precipitation and sorption of rare earths and yttrium from the evolved meteoric water were probably caused by their neutralization or even alkalization that had resulted from CO2 release near the surface. The previous Sr-Nd isotopic data for lanthanite-(Nd) from South Primorye indicate the upper Earth’s crust origin of the ore metals. Thus, both endo- and exogenous factors significantly influenced the studied mineralization in Primorye. Juvenile CO2 made a key contribution to meteoric waters allowing them to mobilize and redistribute ore components in the near-surface conditions. The deep-seated faults cross-cutting and bordering the lignite basins and providing the necessary conduits for the upflows of carbon dioxide are suggested to control localization of the studied mineralization.