Genesis of silica-rich carbonatite in the Miaoya complex, Hubei Province and its implications for REE mineralization

Abstract

The Miaoya complex in Hubei Province hosts one of the most important REE deposit in China. This complex is composed of syenite, carbonatite (SiO2 30%). The petrology and mineralogy of silica-rich carbonatite were investigated by the electron probe microanalyzer (EPMA), X-ray fluorescence spectrometer (XRF), laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) and other analytical methods, aiming to decipher the genesis and potential REE mineralization of silica-rich carbonatite from the REE ore bodies in carbonatite. First, silicate minerals of silica-rich carbonatite are dominated by K-feldspar, albite and quartz, which is similar with associated syenite, rather than adjacent Silurian Meiziya Group schist. This suggests that these silicate minerals are probably xenocrystals from syenite. Second, the captured K-feldspar in silica-rich carbonatite has irregular compositional zoning and higher Sr isotopes compared to marine sediments, implying the presence of postmagmatic fluid activity. In addition, the Th-Pb age of hydrothermal monazite associated with silicate minerals in silica-rich carbonatite yields (235.1±1.5) Ma, suggesting that this fluid activity is probably related to the regional metamorphic event related to the closure of the Mianlue Ocean (246-221 Ma) during the collision between the North China Craton and the Yangzi Craton. During the postmagmatic stage, Si and REEs are remobilized from silicate xenocrystals and fluorapatite into fluids, respectively. Moreover, Si in fluids could promote REE transport by these Sr-Ba-Si-rich fluids and ultimately lead to relatively low REE contents in these silica-rich carbonatites.

Keywords

• miaoya complex
• silica-rich carbonatite
• hydrothermal metasomatism
• k-feldspar zoning
• sr-nd isotopes