Secondary Sulfate Minerals from Thallium Mineralized Areas: Their Formation and Environmental Significance

Abstract

Thallium is a highly toxic metal and is predominantly hosted by sulfides associated with low-temperature hydrothermal mineralization. Weathering and oxidation of sulfides generate acid drainage with a high concentration of thallium, posing a threat to surrounding environments. Thallium may also be incorporated into secondary sulfate minerals, which act as temporary storage for thallium. We present a state-of-the-art review on the formation mechanism of the secondary sulfate minerals from thallium mineralized areas and the varied roles these sulfate minerals play in Tl mobility. Up to 89 independent thallium minerals and four unnamed thallium minerals have been documented. These thallium minerals are dominated by Tl sulfosalts and limited to several sites. Occurrence, crystal chemistry, and Tl content of the secondary sulfate minerals indicate that Tl predominantly occurs as Tl(I) in K-bearing sulfate. Lanmuchangite acts as a transient source and sink of Tl for its water-soluble feature, whereas dorallcharite, Tl-voltaite, and Tl-jarosite act as the long term source and sink of Tl in the surface environments. Acid and/or ferric iron derived from the dissolution of sulfate minerals may increase the pyrite oxidation process and Tl release from Tl-bearing sulfides in the long term.