Scanning Microscopy


Spectral patterns were obtained for zoned dolomite and unzoned calcite gangue, and dolostone breccia fragments from the Right Fork area in the central Tennessee zinc district (U.S.A.). The samples had been analyzed previously for Fe, Mn, and other trace elements using a synchrotron XRF probe. Spectra were obtained for zoned dolomite, breccia fragments, and unzoned calcite using an ELM2-B cold-cathode Luminoscope attached to an Oriel Multispec Compact Spectrograph. Spectra obtained for the prominent dolomite zones, which luminesce medium-bright to bright red to the eye, revealed a broad peak in the vicinity of 460 nm and a more intense peak in the vicinity of 655 nm. Several trial least squares spectral decompositions suggest that the spectra are composites of five peaks. The broad peak at 460 nm appears to consist of two peaks at 439 nm and 546 nm. The intense peak at 655 nm, which is normally assigned to Mn, appears to have two less intense peaks as shoulders at 704 nm and 727 nm. These shoulders do not appear to be artifacts. They may be due to additional Mn2+ peaks or to the presence of Mn in a higher valence state. Fe, which is assumed to quench Mn-activated luminescence in carbonates, produces peaks in orthoclase and plagioclase which are very close to the peaks observed here. The integrated intensities for the peak at 655 nm appear to be related most closely to Fe/Mn ratios. In spite of a three-fold difference in the intensity of the dominant peak, as recorded by the spectrograph, differences in intensity from sample to sample were not obvious to the eye.

Included in

Biology Commons