ALBERT

Description: We report on Precambrian microfossils from igneous rocks of the Volyn pegmatite district, associated with the Paleoproterozoic Korosten pluton, northwestern Ukraine. The fossils were recovered from meter-sized miarolitic cavities and show a well-preserved 3D morphology, mostly filamentous but with a large variety of types and also in irregular, flaky shapes reminiscent of former biofilms, as well as rare spherical objects. Based on literature data, pyrolysis experiments, and reflected light microscopy results, the organic matter (OM) is characterized as (oxy-)kerite. Further investigations with microscopic techniques, including scanning and transmission electron microscopy, and electron microprobe analysis show that fossilization likely occurred during a hydrothermal, post-pegmatitic event by silicification dominantly in the outermost 1–2 µm of the microfossils. The hydrothermal fluid, derived from the pegmatitic environment, was enriched in SiF4, Al, Ca, Na, K, Cl, and S. The OM shows O enrichment in which N and S content is low, indicating simultaneous N and S loss during anaerobic oxidation. Mineralization with Al silicates starts at the rim of the microfossils, continuing in its outer parts into identifiable encrustations and intergrowths of clay minerals, feldspar, Ca sulfate, Ca phosphate, Fe sulfide, and fluorite. Breccias, formed during collapse of some the miarolitic cavities, contain decaying OM, which released high concentrations of dissolved NH4+, responsible for the late-stage formation of tobelite-rich muscovite and buddingtonite. The age of the fossils can be restricted to the time between the pegmatite formation, at ∼1.760 Ga, and the breccia formation at ∼1.49 Ga. As the geological environment for the growth of the microorganisms and fossilization, we assume a geyser system in which the essential biological components C, N, S, and P for growth of the organisms in the miarolitic cavities were derived from microorganisms at the surface. Fossilization was induced by magmatic SiF4-rich fluids. The Volyn occurrence is a distinct and uncommon example of Precambrian fossils, and the results underline the importance of cavities in granitic rocks as a possible habitat for microorganisms preserved in the deep biosphere.

Description: Organic matter (OM) is known to be an important reductant in sediment-hosted base metal deposits like the European Kupferschiefer. However, the precise nature of interactions between OM and hydrothermal fluids are still debated as well as how the interconnected reactions develop over geological timescales. This dataset provides for the first time bulk, compositional and stable isotope data of hydrocarbons, biomarkers and organonitrogen, -sulfur and-oxygen (NSO) compounds for the mineralized Kupferschiefer Spremberg-Graustein field in Eastern Germany based on samples from two drill cores. The study aims to help to better understand the role that organic matter plays during the mineralisation and formation of the sedimentary ore deposit within the Kupferschiefer with a focus on stable hydrogen isotope compositions and NSO compositional data to especially address the origin and to assess the oxidative nature of the brines that caused the mineralization in the Spremberg-Graustein field. The data publication includes bulk, compositional and stable isotope data on inorganic metals and organic matter. The data about metal contents were generated using ICP-MS while those on the organic matter were generated using Rock-Eval pyrolysis, a microscope, a Soxhlet apparatus, medium pressure liquid chromatography (MPLC), gas chromatography with flame ionization (GC-FID) and mass spectrometric detection (GC-MS), gas chromatography isotope ratio mass spectrometry (GC-IRMS) and ultrahigh resolution mass spectrometry (Fourier Transform ion cyclotron resonance mass spectrometry, FT-ICR-MS) with Electrospray ionization (ESI) and Atmospheric pressure photoionization (APPI). The full description of samples, methods and data is given in the following sections.