Discovery of two carbonatite intrusive complexes in Yanyuan area of western Sichuan and its geological significance

The Masilei and Gangou carbonatite intrusive complexes were discovered in the Yanyuan area of western Sichuan based on geological and mineralogical investigations. Tectonically, the two complexes are located in the Chapuzi-Bazhe brittle- ductile fault of the Yanyuan-Lijiang Nappe Belt. The carbonatite complexes are veins in shape without fossil, and intruded the wall rocks. The rocks are mainly composed of calcite, plagioclase, rutile and exhibit magmatic crystallization structure. In addition, lamprophyre and diabase dykes occurring along the fault belts are also found in the adjacent area. The distribution, occurrence, rock association, mineral paragenesis and wall-rock alteration of the two complexes, argue that they are igneous carbonatite intrusives rather than the metamorphic sedimentary carbonate rocks previously suggested. Both of them are similar to the other carbonatite-alkaline igneous complexes along the Mianning-Dechang Rare Earth Element (REEs) Metallogenic Belt. The polymetallic, rare earth, uranium mineralization is also found in the Chapuzi-Bazhe Zone. Therefore, the discovery of the two carbonatite intrusive complexes provided new evidence for the tectonic evolution and regional metallogenic system along the Yanyuan-Lijiang Nappe Belt, and new clue for the prospecting of the Maoniupingt-Type Deposit.