Biomarkers, stable carbon isotope, and trace element distribution of source rocks in the Orange Basin, South Africa: implications for paleoenvironmental reconstruction, provenance, and tectonic setting

Aptian to Campanian sediments from the Western offshore to Central Orange Basin were studied by integrating molecular geochemistry, inorganic and isotopic studies to recognize their geochemical characteristics via the reconstruction of the Orange basin’s paleoweathering, paleosalinity, paleovegetation, paleoclimate, and tectonic records. Molecular analyses of both aliphatic and aromatic compounds reveal an input dominantly from a marine source. The source rocks accumulated in a reduced, anoxic, saline water column. Based on various biomarker proxies and vitrinite reflectance data, some samples are thermally mature to produce petroleum, while others are not. According to the V/Ni ratio, samples from the Orange Basin in South Africa are mainly anoxic, with only a few samples ranging from suboxic to anoxic. This is congruent with biomarker and isotope analyses that further indicate the presence of marine-derived source rocks with some terrestrial remains generating hydrocarbons. The investigated sediments are made up of intermediate igneous rocks that have undergone moderate chemical weathering. Geochemical figures on tectonic setting discriminant function diagrams revealed a continental rift of passive margin settings. As a result, the extrapolated crustal processes are directly analogous to the genesis and evolution of the Orange Basin, demonstrating Gondwana’s breaking up and the opening of the Atlantic Ocean Margin.

Testing Trace-Element Distribution and the Zr-Based Thermometry of Accessory Rutile from Chromitite

Trace element distribution and Zr-in-rutile temperature have been investigated in accessory rutile from stratiform (UG2, Merensky Reef, Jacurici), podiform (Loma Peguera), and metamorphic chromitites in cratonic shields (Cedrolina, Nuasahi). Rutile from chromitite has typical finger-print of Cr-V-Nb-W-Zr, whose relative abundance distinguishes magmatic from metamorphic chromitite. In magmatic deposits, rutile precipitates as an intercumulus phase, or forms by exsolution from chromite, between 870 °C and 540 °C. The Cr-V in rutile reflects the composition of chromite, both Nb and Zr are moderately enriched, and W is depleted, except for in Jacurici, where moderate W excess was a result of crustal contamination of the mafic magma. In metamorphic deposits, rutile forms by removal of Ti-Cr-V from chromite during metamorphism between 650 °C and 400 °C, consistent with greenschist-amphibolite facies, and displays variable Cr-Nb, low V-Zr, and anomalous enrichment in W caused by reaction with felsic fluids emanating from granitoid intrusions. All deposits, except Cedrolina, contain Rutile+PGM composite grains (<10 µm) locked in chromite, possibly representing relics of orthomagmatic assemblages. The high Cr-V content and the distinctive W-Nb-Zr signature that typifies accessory rutile in chromitite provide a new pathfinder to trace the provenance of detrital rutile in placer deposits.

Diamondiferous kimberlites from recently explored Upper Muna field (Siberian craton): petrology, mineralogy and geochemistry insights

Petrographic, geochemical and mineralogical characteristics of diamond deposits from the Upper Muna field have been investigated. Geochemically, diamondiferous kimberlites from Upper Muna belong to the most widespread Fe-Mg-rich rocks in the Yakutian kimberlite province (average FeOtotal = 8.4 wt%, MgO = 32.36 wt%, TiO2 = 1.6 wt.%). Striking mineralogical features of Upper Muna kimberlites are: 1) abundance of monticellite and perovskite in the groundmass; 2) rare occurrence of Mg-ilmenite; 3) abundance of phlogopite megacrysts (up to 8 cm across); 4) coexistence of low-Cr (0.1–4wt. % Cr2O3, with 0.8–1.2 wt.% TiO2), and high-Cr (3–8 wt.% Cr2O3, with 0.1-0.6 wt.% TiO2) garnet megacrysts with contrasting REE patterns. The compositional features of groundmass minerals, the relatively low CaO and CO2 contents in kimberlites, and few deuteric alteration in Upper Muna kimberlites suggest high-temperature melt crystallization during pipe emplacement. Based on the compositional data of garnet and Cr-diopside from megacrysts and peridotites, we suggest a poor Cr dunite-harzburgitic and lherzolitic mantle source beneath the Upper Muna field where Cr-diopside crystallized within a wide P-T range (40–65 kbar and 900–1350 °C). Mineral geochemistry, trace element distribution and Sr-Nd isotope variations of Upper Muna kimberlites are typical for group I kimberlites and reflect a deep-seated asthenospheric (convective mantle) source for the kimberlites.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5442956

New identification and significance of Early Cretaceous mafic rocks in the interior South China Block

Early Cretaceous mafic rocks are first reported in the northern Guangxi region from the western Qin-Hang belt in the interior South China Block. A systematic investigation of zircon U–Pb dating, whole-rock geochemistry, Sm–Nd isotopes and zircon Hf–O isotopes for these mafic rocks reveals their petrogenesis and the mantle composition as well as a new window to reconstruct lithospheric evolution in interior South China Block during Late Mesozoic. Zircon U–Pb dating yielded ages of 131 ± 2 Ma to 136 ± 2 Ma for diabase and gabbro from Baotan area, indicating the first data for Early Cretaceous mafic magmatism in the western Qing-Hang belt. These mafic rocks show calc-alkaline compositions, arc-like trace element distribution patterns, low zircon εHf(t) of − 9.45 to − 6.17 and high δ18O values of + 5.72 to + 8.09‰, as well as low whole-rock εNd(t) values of − 14.27 to − 9.53. These data suggest that the studied mafic rocks are derived from an ancient lithospheric mantle source that was metasomatized during Neoproterozoic subduction. Thus, the occurrence of these mafic rocks indicates a reactivation of Neoproterozoic subducted materials during an extension setting at Late Mesozoic in the western Qin-Hang belt, an old suture zone that amalgamates the Yangtze and Cathaysia blocks.

Effect of Land Reclamation on Soil Properties, Mineralogy and Trace-Element Distribution and Availability: The Example of Technosols Developed on the Tailing Disposal Site of an Abandoned Zn and Pb Mine

Land reclamation is a common practice leading to the restoration of areas affected by industrial activity. Soil studies in reclaimed areas are very useful to determine the effectiveness of reclamation works. The goal of the study was to investigate soil properties, mineral composition, total concentrations of Zn, Pb, Cd and As and chemical forms of these elements in order to assess the success of land reclamation of the abandoned mine tailing disposal site of the “Trzebionka” Zn-Pb mine in Trzebinia, southern Poland. The disposal site was reclaimed by covering tailings with a layer of inert material with a thickness up to 25 cm. The topsoil of the studied soil profiles was comprised of sandy loamy/loamy materials and the subsoil was comprised of sandy tailing materials. The soils were characterized by a neutral or slightly alkaline reaction due to the high content of carbonates. The dominant mineral in the subsoil was dolomite. The studied soils were considerably contaminated with Zn, Pb, Cd and As. A high load of mobile Zn, Pb and Cd was typical of the subsoil material. The reclamation layer does not provide sufficient isolation of toxic tailings from the environment and there is still a high risk of element uptake by plants.