Indirect monitoring of heavy metals in volcanic gases by synchrotron X-raymicroprobe (mu-SRXRF) qualitative analysis of sublimates

The results of a photon microprobe study carried out on incrustations and s ublimates collected at active fumaroles of the Fogo Island volcano (Cape Ve rde Archipelago) following the eruption of April 1995 are reported. The min eral phases studied were previously identified by X-ray powder diffraction: sulfur, sodium and potassium chlorides, calcium sulfates with Variable deg rees of hydration and alums (hydrated Na/K A-sulfates). Amongst the minor a nd trace elements detected, P, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Ga, Se, Br, Rb, Sr, Y, Zr, Nh, 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 v olcanic fumarole sublimates, a result made possible by the unique character istics of synchrotron radiation used in the photon microprobe. Chemical dat a are discussed taking into account the crystal structure of the carrier mi neral phases. Comments are presented on possible geological implications of this micro-chemical study.