Deposit or prospect? example from the Miaoya, Hubei province, China

The Miaoya carbonatite-syenite complex is prospective for REE and is ideal for studies of the formation of REE deposits. Mineralization at this prospect includes carbonatite-, syenite-, and mixed -type, all are low REE grade (below 1 %). XRD and EMPA analyses reveal that REE minerals are low in all samples (<5%), consistent with the fact that few monazite, bastnasite and other REE minerals are visible under the microscope. LA-ICP-MS analyses reveal that apatite and calcite in carbonatite have the highest REE concentrations. Isotope ratios of Sr and Nd for REE-mineralized and altered carbonatite and syenite rocks are similar to those of fresh carbonatites and syenites. These observations are interpreted as recording REE mineralization that originates directly from the unmineralized carbonatite syenite complex rather than other host rocks. Carbon and oxygen isotope ratios of hydrothermal calcite are consistent with low-temperature alteration subsequent to ore formation. The low REE of the Miaoya prospect compared with other carbonatite-syenite hosted deposits may reflect: 1) as supported by petrography, minimal tectonic deformation in the area resulting in 2) restricted cycling of hydrothermal solutions that led to 3) minimal fluid scavenging from REE-rich apatite and calcite for local REE re-deposition and concentration.