Uranium and graphite mineralization in metamorphic rocks in the Kangding complex (Datian area), southwestern Yangtze Platform, Western China

• Published in: Arabian journal of geosciences 2022-08, Vol.15 (16), Article 1382
• Main Authors: Cheng, Long, Luo, Dejiang, Zhang, Chengjiang, Wang, Yuke
• Format: Article
• Language: English
• Subjects: Analysis; Carbon; Carbon isotopes; Decomposition reactions; Dehydration; Earth and Environmental Science; Earth science; Earth Sciences; Electron microprobe; Electron probe microanalysis; Electron probes; Fluids; Geochemistry; Gneiss; Graphite; High temperature; Isotopes; Metallogenesis; Metamorphic rocks; Mineralization; Organic carbon; Organic matter; Original Paper; Platforms (geology); Reducing agents; Schist; Schists; Scientific imaging; Spectrometry; Spectroscopy; Sulfur; Sulphur; Total organic carbon; Uranium
• ISSN: 1866-7511; 1866-7538
• DOI: 10.1007/s12517-022-10302-3

The Sandawan graphite deposit, Datian uranium and graphite deposit, and Lazishao graphite mineral occurrence in the Kangding complex in the Datian area are hosted by five types of metamorphic rocks: carbonaceous slate (CS), graphite-bearing phyllite (GBP), graphite-bearing schist (GBS), graphite-bearing gneiss (GBG), and graphite-bearing migmatite (GBM). Uranium mineralization and graphite mineralization are developed in these rocks, but whether there is a metallogenic relationship between graphite and uranium has not been studied. Based on geochemistry analysis, carbon isotope analysis, Raman spectrometry analysis, and Electron microprobe analysis (EMPA), the graphite and uranium mineralization in metamorphic rocks in the Datian area were analyzed. Geochemical analysis reveals that the uranium (U) contents increase from the CS and GBP to the GBS, and then decrease from the GBS, GBG, and GBM. From the CS to the GBM, the variation in total organic carbon (TOC) content is basically same with that of the U content. The CS, GBP, GBS, and GBG have extremely low total sulfur (TS) contents, but the GBM has significantly higher contents. From the CS to the GBG, Raman spectrometry shows that the crystallinity of graphite increases. Carbon isotopes (–17.1 to –30.0‰) show that source of the carbonaceous matter (CM) is organic matter in the metamorphic rocks. EMPA analyses revealed that the ore minerals are uraninite and coffinite. Uraninite (79.61–84.95 wt%) was formed by high temperature-hydrothermal fluids, and coffinite (47.24–61.24 wt%) is the alteration product of uraninite. In the CS, GBP, GBS, and GBG, uranium adsorbed to graphite was lost during dehydration metamorphic reactions. During the migmatization, graphite decomposition and S were likely the dominant reducing agents, leading to uranium precipitation and formation of uraninite.