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A detailed geochemical and mineralogical study was carried out on the Lokpanta oil shale (OS), Nigeria. Samples from three drill cores and several outcrops were studied in order to understand OS general geochemistry and reconstruct tectonic and depositional settings as well as paleoredox conditions. The mineral phases in OS include calcite, quartz, dolomite, feldspar, illite, kaolinite, halloysite, pyrite and gypsum, as well as a trace amount of anatase. The Lokpanta oil shale shows little variation in geochemistry. It is depleted in trace elements Ba and Rb and major compounds except CaO, and is enriched in trace elements Mo, Sb, As, V, Zn, Ni and U with reference to the Post-Archean Australian Shale (PAAS). These enrichments are, however, in most cases lower than those in the Estonian graptolite argillite (GA). Trace element ratios (U/Th, Ni/Co, V/Ni, V/(V + Ni) V/(V + Cr)) indicate that the Lokpanta oil shale was deposited in an anoxic environment. Discriminant diagrams also suggest its deposition in an active continental margin setting and a transitional to marine environment. The geochemical and paleoenvironmental features of the Lokpanta oil shale were compared with those of the Estonian graptolite argillite.

This research focuses on the geochemical analysis of Paleoproterozoic metasedimentary and metavolcanic units in the Alutaguse region of northern Estonia, shedding light on the geodynamic evolution during the Svecofennian orogeny in eastern Fennoscandia. The metasedimentary units consist of micaceous gneisses (± Grt ± Crd ± Sil), and the metavolcanic units include amphibolites and pyroxenic gneisses. Geochemical analyses utilized both historical and new whole-rock geochemical data. Weathering indices indicated their applicability for provenance studies and tectonic setting analyses. Metasediments are classified by their silica content: high-SiO2 (>63 wt%) metasediments resemble litharenites, implying higher maturity and felsic origins akin to the upper continental crust reference; low-SiO2 (

The Jõhvi magnetite quartzites (MagQ) occur as subvertical beds with a complicated structural outline in biotite-garnet-cordierite and pyroxene gneisses which in places also contain high concentrations of iron. Drill core study shows that the complex of MagQ and magnetite-rich gneisses may be up to 100 m thick. The MagQ provide a wide range of chemical composition: SiO2 ranges between 40.3 and 60.1 wt%, Al2O3 between 1.7 and 19.7 wt% and total iron between 15 and 45.2 wt%. This study also revealed unusually high manganese contents of 1–6 wt%. The rare earth element (REE) patterns of MagQ and the surrounding gneisses partly overlap. Cutting granitoids form two different REE patterns. Magnetite occurs as anhedral grains elongated along rock fabric, as rounded inclusions in other minerals or as tiny platelets along grain edges and along cleavage planes of amphibole and biotite. Sulphides are present as pyrite, pyrrhotite and other minor sulphide minerals (chalcopyrite, galena and sphalerite). Analysis of the magnetite grains from drill core J-1 shows that classifying Jõhvi magnetites into a certain deposit type is not unambiguous. The garnet–biotite geothermometer revealed metamorphic temperatures between 650 and 750 ºC. The garnet–biotite–plagioclase–quartz geobarometer yielded the pressure range of 2.9 to 4.9 kbar. However, having in mind that the entire Jõhvi ore complex may be a result of repeated metasomatic events, which have influenced the primary volcanic-sedimentary sequences, the estimate of primary pressure–temperature conditions might not be a straightforward task. The current understanding of the geological-geochemical correlation hints at geological similarities between the Bergslagen area in Sweden and the Jõhvi Zone in Estonia.

In a very broad meaning, oil shale is defined as a fine-grained sedimentary rock containing organic matter that yields economic amounts of oil and combustible gas upon destructive distillation. In many cases oil shale contains valuable metals. Some of metal-enriched organic-rich shales are known as black shale and used for extraction of metals. During the last decade, organic-rich sedimentary rocks, commonly shales, have been targeted for shale gas extraction; this trend seems to be still increasing. It is well known that the world oil shales range widely in mineral composition, organic matter content and oil yield. The deposits range from Cambrian to Tertiary in age and greatly vary in layer thickness and lateral size. Thus, the thickness of oil shale beam can reach up to 700 m and the largest deposits occupy several thousands of square kilometers. This variability is created by differences in original depositional environments and other conditions.

The Mt Buller igneous suite in the southeastern Lachlan Fold Belt encompasses a large variety of rock types, from gabbros through diorites to granites. Mafic rocks and enclaves have primitive, mantle-like initial 87Sr/86Sr values, 0.7037-0.7045, and εNd values +5.6 to +4.1. The granites do not show distinctively more radiogenic initial 87Sr/86Sr values, suggesting they are derived from the same parent as the gabbros. Most of the Mt Buller rocks do not show a positive correlation between silica and initial 87Sr/86Sr, or between silica and 143Nd/144Nd values, indicating that neither crustal contamination nor mixing between mantle- and crustal derived melts has been important and that these rock types are likely to have formed by fractional crystallization from a common mantle-derived parent. Some scatter in compatible trace elements, particularly in granites and diorites, may be explained by mixing. Geochemical modelling confirms a comagmatic origin of the suite. Magma generation probably took place in the subduction-modified upper mantle. This mechanism may play an important role in I-type granite petrogenesis in particular tectonic settings such as during an efficient slab roll-back or sinking of oceanic crust in divergent subduction conditions.

The Jõhvi magnetic anomaly is situated within the Jõhvi structural zone that is part of the Bergslagen–Livonia microcontinent. Drilling in the 1930s and 1960s has revealed a complex of magnetite ore alternating with granites, pegmatites and gneisses. The study presents the results of ground magnetic mapping, measurements of drill core (Jõhvi I and II) petrophysical properties (density, magnetic susceptibility, intensity and inclination of the natural remanent magnetization), modelling of the anomalous magnetic field in the Jõhvi area and frequency domain electromagnetic (FrEM) measurements. The magnetic anomaly is composed of three major peaks named western, eastern and northern anomalies. The maximum amplitude of the western total field anomaly is 19 290 nT, of the eastern anomaly 15 880 nT and of the northern anomaly 8080 nT. The 3-dimensional model along five profiles extends from the basement surface to a depth of 1000 m. The direction of strong remanent magnetization coincides with the dip of the iron ore formation. The strong remanence hints at the significant presence of small (

The occurrence of Cambrian to Ordovician organic-rich black shale deposits has been known in Baltoscandia, including Estonia, for a long time. The Estonian graptolite argillite (GA) shows high to very high concentrations of U (800 ppm), Mo (1000 ppm), V (1600 ppm), Ni and other heavy metals, and are rich in N, S and O, unlike normal shale. The present study provides a new estimate of the total GA tonnage in Estonia, including estimates for U, Zn and Mo. The total preserved volume of GA is about 31.92 billion [m.sup.3], while about 9.02 billion [m.sup.3] has been eroded between the Estonian mainland and western islands. The total mass of GA is about 67 billion tonnes at a specific gravity of 2.1 g/[cm.sup.3]. About 18.93 billion tonnes of GA has been eroded and re-deposited, including 1.8 million tonnes of U, 22.7 million tonnes of Zn, 6.6 million tonnes of Pb, 4.4 million tonnes of Mo and 13.3 million tonnes of V. In Estonian GA the total [U.sub.3][O.sub.8] reaches 6.7 million tonnes, ZnO 20.6 million tonnes and Mo[O.sub.3] 19.1 million tonnes as calculated using a cell size of 400 m.

The study focuses on chemical composition of stream and subsurface water in the catchments of two small arctic alpine lakes in the Kilpisjärvi area (northwest Finland). Differences and changes in chemical components of both water types are followed in order to detect spatial variability and impact of environmental factors. To achieve this, ion compositions of subsurface water and streams were measured at 12 sites in the catchments of Lakes Saana and Saanalampi during four years (2008–2010, and again in 2017). In the Lake Saanalampi catchment, the salinity of stream water (7.0 to 12.7 μS·cm−1) corresponded to that of snow. In the catchment of Lake Saana, however, the conductivity in stream water was much higher (40 to 220 μS·cm−1), connected mainly to the increase of SO42− and less with Mg2+ and Ca2+ contents, especially in the western part of the Saana catchment. These results demonstrate that arctic conditions do not preclude intense chemical weathering where conditions are favourable. Although chemical composition of the soil fluid does not match the geochemical signal from the local soil, rock composition, especially the presence of pyrite, is the main controller of chemical weathering rates of the rocks on the area. This supports earlier views that the character of precipitation mostly controls water chemistry of local lakes in the Kilpisjärvi area.

This paper describes vertical fine-scale geochemical heterogeneity of Estonian graptolite argillite (GA). GA samples from Pakri and Saka outcrop sections were collected at 20 cm intervals for chemical analysis of major and trace elements, including rare earth elements. The study indicates GA enrichment in U, V, Mo and Pb with respect to the average black shales and thus confirms the formerly reported data on GA geochemistry in general. However, the content of enriched elements and other trace metals was recorded to vary greatly across the sequences suggesting that trace metal distribution in GA is notably more heterogeneous than previously assumed. The origin of the observed complex distribution of trace elements was likely controlled by the interplay of different primary metal supply-sequestration factors/processes, such as synsedimentary redox-driven sequestration of redox sensitive elements, the provenance of clastic input, the post-sedimentary redistribution, etc.