A new type of Nb (Ta)-Zr(Hf)-REE-Ga polymetallic deposit in the late Permian coal-bearing strata, eastern Yunnan, southwestern China: Possible economic significance and genetic implications

This paper describes a new type of Nb(Ta)-Zr(Hf)-REE-Ga polymetallic deposit of volcanic origin in the late Permian coal-bearing strata of eastern Yunnan, southwestern China. Well logging data (especially natural gamma-ray), geochemical data (high concentrations of Nb, Ta, Zr, Hf, REE, and Ga) and mineralogical compositions (Nb(Ta)-, Zr(Hf)-, or REE-bearing minerals rarely observed), together with the volcanic lithological characteristics indicate that there are thick (1-10 m, mostly 2-5 m) ore beds in the lower Xuanwei Formation (late Permian) in eastern Yunann of southwestern China. The ore beds are highly enriched in (Nb,Ta)(2)O-5 (302-627 ppm), (Zr,Hf)O-2 (3805-8468 ppm). REE (oxides of La-Lu + Y) (1216-1358 ppm), and Ga (52.4-81.3 ppm). The ore beds are mainly composed of quartz, mixed-layer illite-smectite, kaolinite, berthierine, and albite. Four types of ore beds in the study area were identified, namely, clay altered volcanic ash, tuffaceous clay, tuff, and volcanic breccia. Preliminary studies suggest that the high concentrations of otherwise rare metals were mainly derived from the alkalic pyroclastic rocks. The modes of occurrence, spatial distribution, and enrichment mechanism of the rare metals, however, require further study. (C) 2010 Elsevier B.V. All rights reserved.