Abstract

The granite cupola at Zinnwald (Germany) or Cínovec (Czech Republic) consists of highly evolved, weakly peraluminous and variably altered topaz – albite – Li mica leucogranites of A-type affiliation. In the apical part of this cupola, As-bearing REE–Y–Th–U–Zr minerals, including arsenoflorencite-(Ce), chernovite-(Y), hydrated chernovite-(Y) – xenotime-(Y) solid solutions and As-bearing thorite, coffinite and zircon, formed locally. Accompanying minerals comprise As-poor bastnäsite-(Ce), synchysite-(Ce), synchysite-(Y), fluocerite-(Ce), and columbite-(Fe). Electron-microprobe analyses show that arsenoflorencite-(Ce) contains low to moderate concentrations of P, Pb, and particularly Sr (4.0–8.3 wt% SrO), reflecting substitution of florencite, arsenoflorencite, goyazite, and kintoreite components. Relative to published data, chernovite-(Y) is the most REE-rich yet recorded, with up to 0.51 apfu REE substituting for Y. All REE arsenates display a variably kinked REECN pattern and a negative Eu anomaly. Thorite, coffinite, and zircon accommodated maximum concentrations of As of 14.4, 5.3, and 1.3 wt% As2O5, respectively. The results of this study demonstrate that As-rich hydrothermal fluids are susceptible to dissolve and severely alter primary magmatic REE–Y–Th–U–Zr minerals.

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