Cora C. Wohlgemuth-Ueberwasser

Fluorite mineralization associated with different types of magmatism is common in the Western Transbaikalia. This study deals with Arshan, Yuzhnoe, and Ulan-Ude fluorite occurrences, which are the most significant examples of carbonatite-related fluorite mineralization in the region. The present paper focused on new fluorite geochemistry and fluid inclusion data, is aimed at revealing conditions of the fluorite mineralization formation, highlighting its genetic relationship with magmatism, compared to other deposits of this type. All the three locations belong to the Late Mesozoic Central Asian carbonatite province. Fluorites here are characterized by high rare earth elements (REE), Sr, and elevated La/Yb values. Fluid inclusions data imply that the formation of fluorite mineralization is a long process extending from late magmatic to the hydrothermal stage. Early fluorite crystallized from sulfate-carbonate orthomagmatic fluids at temperatures up to 500 °C. True hydrothermal fluorite was formed from the same fluids that were probably mixed with meteoric waters, which caused the temperature to drop to below 420 °C and led to an increase in the chloride component. The REE compositions of fluorite from the studied locations are similar to compositions of REE-rich fluorites from carbonatite-related deposits around the world.

The Kovdor massif is a part of the Paleozoic Kola alkaline province and located in the eastern part of the Baltic Shield. Kovdor carbonatites host a unique complex baddeleyite-apatite-magnetite deposit from which iron ores and zirconium have been mined. New data on melt inclusions in olivine crystals from phoscorites and olivinites of the ore complex are presented in this contribution. Daughter minerals in crystallized melt inclusions were identified by Raman spectroscopy and scanning electron microscopy. The trace element composition of inclusions was determined using LA-ICP-MS.Melt inclusions in olivine from Kovdor phoscorites are negative crystal or round in shape, with sizes ranging from 5 to 50 microns. They form groups or line up. According to the mineral composition, two types of melt inclusions can be distinguished: carbonate and silicate-carbonate. In the first type, Ca-Na-Mg- (Sr?) - REE carbonates are dominant among daughter phases. In the second one, silicate phases (phlogopite, monticellite, diopside), Ca-Na-Mg carbonates and magnetite are found together. Melt inclusions in olivine from olivinites are isometric or elongated, 5–25 μm in size. They form groups or occur as isolated inclusions. Benstoneite, geylussit, ankerite, calcite and hydroxyl-bastnesite along with phyllosilicates (phlogopite, paragonite?) were identified among daughter minerals.The rare earth elements composition of melt inclusions from both types of rocks is characterized by the predominance of light REE. The content of REE, especially light ones, in inclusions from phoscorites is higher. Strontium and barium contents in most melt inclusions have negative correlations with niobium and zirconium concentrations.Melt inclusions from phoscorites and olivinites contain carbonate and silicate mineral phases in various proportions, which may imply heterogeneous trapping of crystalline phases and two immiscible melts, silicate and carbonatite. Inclusions from phoscorite represent a more evolved magma with higher concentrations of rare metals.This work was supported by the Russian Science Foundation, grant No 19-17-00013.

Baddeleyite is a key mineral in geochronology of mafic rocks as it crystallizes in silica-undersaturated systems that do not grow zircon.

We applied three different LA systems (213 nm nanosecond solid state, 193 nm nanosecond excimer, and 200 nm femtosecond laser) coupled to a quadrupole ICP-MS or a sector field ICP-MS, respectively, for the analysis of different sulfide minerals (pyrrhotite, chalcopyrite, and sphalerite). Ablation craters were investigated via back-scattered electron (BSE) images to compare the amounts of melt produced, and fractionation factors were calculated to determine the degree of down-hole fractionation. Our results show significant differences in melting between the three LA systems. While samples show massive melting when using the ns systems, no melting has been observed utilizing the fs laser. Fractionation factors for a variety of elemental pairs indicate the absence of down-hole fractionation even at the highest melt production. The extent of melting of different sulfide specimens is independent of melting temperatures of these materials. Although no down-hole fractionation has been observed, Fe/S fractionation as calculated from sensitivities deviate among pyrrhotite and chalcopyrite when applying the 193 nm ns and 200 nm fs systems. Analyses of synthetic pyrrhotite with known PGE concentrations using the 200 nm fs LA system yielded moderately precise and accurate concentration data (3–4%; 4–14% 2SD) utilizing sulfide as the external reference material. Application of NIST610 as the reference material improved the precision to 1.4–2.4% 2SD and the deviation from reference values to 5–7%.