REE distribution (ICP-MS) in fluorite and Low Riphean country rocks from Bashkirian mega-anticlinorium allow to decipher the nature and stages of formation of vein fluorites in the Suran deposits and fluorite impregnations in recrystallized host dolomite of the Suran formation.
The chondrite normalized patterns of country rock dolomite and disseminated fluorite reveal low contents (about x ppm) and typically decreasing trends of HREE which are characteristic for REE pattern of continental sedimentary rocks. Similar distribution with smooth REE pattern was obtained for sellaite and white-milky fluorite from the selvages of a vein (Suran deposit) and can be regarded as primary precipitation of fluorite. Another type of REE pattern is shown by the green fluorite, which is the larger part of the vein. It has a high level of REE contents (about 100x ppm), always shows strongly negative Eu anomalies and a subhorizontal trend of REE distribution. The transparent, optical fluorite has not such a high level of REE content as the green fluorite and decreasing LREE content, sometimes with a negative Eu anomaly.
Differences in the REE distributions of the studied fluorites depend on the various formation conditions of these deposits. Fluorite and sellaite with low REE fractionation, smoothly decreasing of HREE, and without Eu anomalies in sellaite and selvage fluorite, might be considered as primary hydrothermal crystallizates with typical Ca/ligand >>1 (Möller, 1991). This is in agreement with removal of fluorine from country dolomite (Krupenin, 1992) into a paleohydrogeological basin. The green fluorite with negative Eu anomalies might be related to an unknown source, of a probably felsic burried pluton or the influence by riftogenic fluids, interacting with the country rocks. It is a second generation of fluorite (metasomatic replacement of primary sellaite). The REE pattern of optical fluorite indicates processes of remobilization of fluorite, because their LREE are decreasing due to their enhanced adsorption during migration of fluids. The complicated formation of fluorite deposits in the S. Urals Low Riphean rocks represents a long geological history of this region (Precambrian riftogenic stage, Paleozoic ocean stage).
This study was supported by INTAS grant 94-1857.