Mineralogical Study On The Weathering-crust-type Rare Earth Deposit In The Gangxia Granite Area, Anyuan, Jiangxi Province

Rare-earth element (REE) mineralization in Southern Jiangxi is known for ion-adsorption type REE deposits. The deposit studied in this work is in the Gangxia Mining District, near Caifang Village to NE Anyuan City in the Ganzhou region, Jiangxi Province. The mine covers an area of about 491.22 hectares, has the resource reserves of 2072.3 kilotons, exploits 387.5 kilotons ores per year, and has the productivity of 200 tons/year REE oxides. Gangxia deposit is related to Sanbiao the Caledonian granite body, including majorly the biotite granite and secondly two-mica granite. In this area, REEs are adsorbed on clay minerals in form of ions (RE3+), and may be easily extracted by leaching precipitation. So far, no other forms of REE minerals have been reported. To unravel this interesting question, we collected different layers of weathering crust in the Ganxia granite area. Studies include petrography and petrochemistry of the granite weathering crust, mineralogy of REE minerals. Such studies will help to understand the different forms of REEs.On the basis of different degree of weathering and mineral assemblage type, weathering crust was divided into four different weathering crust layers, broken layer, weathered layer, semi-weathered layer and bed rock. Halos in biotite are very common in the bedrock of granite, probably caused by highly REE-bearing accessory minerals, related to later REE enrichment. Such a phenomena indicated REE mineralization. In these samples, REE contents are 1281.06ppm as high as the weathered layer sample. LREE/HREE ratio was 1.94-0.5 (average 0.90), relatively enriched in HREE.Certainly, the experimental results showed there truly exist other forms REE minerals, nano-sized polycrystalline cerianite and other nano-particles of REE Minerals. Primary LREE mineral wasn’t discovered in bed rock, but secondary bastnasite or parasite are present. Xenotime, apatite and other secondary minerals are the main source of HREE. Tungsten, tin and rare-metal mineralization characterizes South China granites. Owing to regional climate environments, granites in this area faced force weathering. So, REE in primary minerals may be leached during their weathering and decomposition. Rare-earth elements, complexed with fluids on the surface, may infiltrate and migrate downwards, and form secondary nano-sized REE aggregates after colloidal precipitation. In this study, we found colloidal REE minerals or absorbed REE partticles besides hydrated or hydrated hydroxyl ionic phases. These REE-containing minerals, normally existing in nano-sized (10-150nm) particles, are absorbed by clay minerals together. TEM investigation further proved some of REE minerals as nano-sized polycrystalline cerianite, indicating that Ce in weathering crust was oxidized into 4+ and precipitated as REE oxides.