Smirnite is the natural equivalent of Bi2TeO5, a compound that has piezoelectrical and nonlinear optical properties. The mineral has rarely been described worldwide. Here, we describe the finding of a Bi–Te oxide, compositionally similar to the mineral smirnite, from an alluvial gold nugget. The mineral occurs within a goethite pseudomorph after arsenopyrite, forming an aggregate with the nugget gold. Electron-microprobe analyses gave an empirical stoichiometry of (Bi1.6,Fe0.2)1.8Te1.1O5, on the basis of five atoms of oxygen. The occurrence of smirnite in the municipality of Ouro Preto, Minas Gerais, Brazil, is noteworthy because the mineral: (i) is described in South America for the first time; (ii) represents a provenance indicator, connecting the gold nugget to auriferous quartz lodes with primary Bi–Te minerals in the Mariana anticline; (iii) indicates that Bi and Te were retained by goethite formation during oxidative weathering of gold deposits; (iv) has the critical metals Bi and Te as essential components, which should be considered in the economic evaluation of gold prospects as strategically important byproducts, in addition to the potential use of Bi and Te in the weathering zone as pathfinder elements to gold mineralisation at depth.
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