MOSSBAUER AND OPTICAL SPECTROMETRY OF SELECTED SCHORL-DRAVITE TOURMALINES

Spectrometric studies were carried out on samples of tourmaline (schor l-dravite series) from geological environments where first-phase-forme d tourmaline underwent influence of geochemically different fluids. Sa mples are from a differentiated magmatic complex of Trento-Alto Adige, Italy, and from hydrothermal gold and silver deposits of the Humboldt Range, Nevada, USA. Chemical data were obtained from electron micropr obes. The results of Mossbauer measurements suggest three to five doub lets. Fe occurs in two valence states. The Z-site, usually fulfilled w ith Al3+ and Fe3+, is assigned only to Al3+ and Fe2+. This location wa s found in nearly all samples studied. In the Y-site Fe2+ and Fe3+ are obviously present. Isomer shifts with intermediate values can be assu med to be related to intervalence charge transfer (IVCT). Optical spec troscopy reveals absorption bands at 9000 and 14000 cm(-1), which are assigned to a charge transfer between Fe2+ and Fe3+, the 23000 cm(-1) absorption band is supposed to be due to Fe2+ --> Ti4+ charge transfer . The occupation of the Z-site only by Fe2+ and the coexistence of div alent and trivalent Fe in the Y-site could be explained by selective o xidation in Y-site through a late process.