Muluozhai REE deposit in Sichuan Province, China: Stable isotope data and their implications on the dynamics of mineralization

The Muluozhai REE deposit, located about 60 km to the southwest of the Mianning county, Sichuan Province, is the third largest light REE deposit in Sichuan. The Muluozhai REE deposit is tectonically located on the northern Jinpingshan Mountains, a Cenozoic intracontinental orogenic belt in southwestern China. The authors analyzed the essential ores from two tunnels for their carbon, hydrogen, oxygen, and sulfur isotopic compositions of the mineralizing fluid. The δ

13

C

V-PDB

values of fluid from fluid inclusions of the quartz and fluorite vary from −2.5 to −9.0 per mil, which show characteristics of mantle-derived carbon. The δD

V-SMOW

values of fluid from fluid inclusions of the calcite, quartz, fluorite, and bastnaesite range from −63 to −87 per mil, which are characteristics of mantle-derived hydrogen. The δ

34

S

V-CDT

values of barite and galena vary in a narrow range of +0.1 to +2.2 per mil and −8.6 to −9.3 per mil, respectively, showing the isotopic characteristics of mantle-derived sulfur. The δ

13

C

V-PDB

values and the δ

18

O

V-SMOW

values of calcite range from −6.6 to −6.8 per mil and from +8.4 to +9.1 per mil, respectively, which are fallen into the range of the “primary carbonatites”, showing the carbon and oxygen in the ores of the Muluozhai ore veins were mainly derived from depths. The stable isotopic data suggest a mantle source for the rare earth elements mineralization and a dynamic process involving mantle materials and tectonics.