A New Type of Nb (Ta), Zr(Hf), REE, Ga Polymetallic Deposit in the Late Permian Coal-Bearing Strata, Eastern Yunnan, Southwestern China - 2010

Coal and Related Carbon Resources / Exploration, Production, Coal Ash, & Rare Earths

Dai, and 10 co-authors reported in 2010 on a new type of Nb(Ta)–Zr(Hf)–REE–Ga polymetallic deposit of volcanic origin within 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)₂O₅ (302–627 ppm), (Zr,Hf)O₂ (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.

The authors concluded that preliminary studies showed that Nb(Ta)–Zr(Hf)–REE–Ga polymetallic deposits, with a thickness of 1–10 m and mostly 2–5 m, in the lower late Permian coal-bearing strata (Xuanwei Formation), widely distribute in eastern Yunnan and probably in some areas of western Guizhou and southern Sichuan provinces of southwestern China. From the genetic view, the thick beds rich in Nb (Ta), Zr(Hf), REE, and Ga belong to a new type of ore deposit that has not been reported before. The high concentrations of otherwise rare metals were mainly derived from alkalic pyroclasts, similar to the intra-seam alkalic tonsteins in the late Permian coals from southwestern China. Four types of ore beds have been identified, namely clay altered volcanic ash, tuffaceous clay, tuff, and volcanic breccia. Minerals in the ore beds mainly consist of quartz, mixed-layer illite–smectite, kaolinite, berthierine, and albite.

Original working URL: https://www.sciencedirect.com/science/article/abs/pii/S0166516210000674