Occurrence of native selenium in Yutangba and its environmental implications

Abstract

Rare native Se has been discovered in Yutangba, Enshi City, Hubei Province, China, where a sudden incidence of Se poisoning occurred in the early 1960s. It was first found in a small area where native Se was produced on a large scale and was diverse in forms due to different formation mechanisms. Genetically, native Se can be divided into 3 categories: the primary native Se occurring in carbonaceous-siliceous rocks and tiny Se crystals formed in cracks of rocks during tectonic activities; micro-Se crystals formed in the weathering processes of Se-rich rocks; and larger Se crystals derived from natural burning of stone coal on the subsurface of abandoned stone coal spoils. The different forms of native Se found in Yutangba demonstrate that Se can be activated, transformed, remobilized and enriched at special sites such as in the unsaturated-subsurface zone or in the saturated zone. This discovery of native Se has not only resolved a long-standing controversial question on modes of occurrence of Se, which has puzzled many researchers in China, but has provided new possible evidence for the pathogenic explanation of the sudden prevalence of Se poisoning in Yutangba. The research results also have important implications for studying the mineralogy, ore geochemistry and environmental geochemistry of Se.