Digital ultraviolet petrography: approaches and applications

Abstract

Integrated data on the approaches and applications of the rock fluorescent macro- and micropetrography is presented. Fluorescence in minerals is caused not by the major chemical elements but a wide range of chemical impurities (activators). As a result, fluorescence cannot be used for the mineral identification in the different deposits because of the different activators prevailing in the different localities. Nevertheless, fluorescence is the reliable typomorphic feature because the minerals with specific fluorescence forms in the same geochemical condition. This methodical approach is based on the combination of the epifluorescent microscopy and multifocal petrography of the rocks. Ultraviolet (UV) investigations by the reflectance microscopy method reveal some advantages, mostly in the sedimentary rocks studying – improving an optical resolution of the images, avoiding the microparticles overlapping inside the thin sections. On the contrary to the classical petrography which uses light source, fluorescent minerals are the source of light themselves, and this feature improves the optical resolution of this method as well. Ultraviolet investigations of the samples of Starobin UpperDevonian bed reveal polygenic processes of their forming. Silt-sized minerals with the different fluorescence features, small and high quantum yields, have been brought from the different sources. Prevailing marls, consisting of the clay minerals and dispersed calcite reveal invisible for the other methods structures – colloform aggregates, metasomatic replacement of the marls in the fracture zones of the rocks. Fluorescent features let to define hydrothermal and chemogenic minerals in the sedimentary rocks. For example, fluorescent borates in the salt formations of the evaporates. Nevertheless, complex methodical approach, such as XRD and XRF, needs for the accurate mineral definition.