Indirect monitoring of heavy metals in volcanic gases by synchrotron X-ray microprobe (µ-SRXRF) qualitative analysis of sublimates

Abstract

The results of a photon microprobe study carried out on incrustations and sublimates collected at active fumaroles of the Fogo Island volcano (Cape Verde Archipelago) following the eruption of April 1995 are reported. The mineral phases studied were previously identified by X-ray powder diffraction: sulfur, sodium and potassium chlorides, calcium sulfates with variable degrees of hydration and alums (hydrated Na/K Al-sulfates). Amongst the minor and trace elements detected, P, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Ga, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Hg, Tl, Pb and Bi, the last four heavy metals may create an environmental concern due to their high toxicity. Thallium is reported for the first time as a chemical component of well identified minerals in volcanic fumarole sublimates, a result made possible by the unique characteristics of synchrotron radiation used in the photon microprobe. Chemical data are discussed taking into account the crystal structure of the carrier mineral phases. Comments are presented on possible geological implications of this micro-chemical study.