Geochemical Investigations Research Articles

Scavenging and release of REE and HFSE by Na-metasomatism in magmatic-hydrothermal systems

Exploitable or potentially exploitable deposits of critical metals, such as rare-earth (REE) and high-field-strength elements (HFSE), are commonly associated with alkaline or peralkaline igneous rocks. However, the origin, transport and concentration of these metals in peralkaline systems remains poorly understood. This study presents the results of a mineralogical and geochemical investigation of the Na-metasomatism of alkali amphiboles and clinopyroxenes from a barren peralkaline granite pluton in NE China, to assess the remobilization and redistribution of REE and HFSE during magmatic-hydrothermal evolution. Alkali amphiboles and aegirine-augites from the peralkaline granites show evolutionary trends from sodic-calcic to sodic compositions, with increasing REE and HFSE concentrations as a function of increasing Na-index [Na#, defined as molar Na/(Na+Ca) ratios]. The Na-amphiboles (i.e., arfvedsonite) and aegirine-augites can be subsequently altered, or breakdown, to form hydrothermal aegirine during late- or post-magmatic alteration. Representative compositions analyzed by in-situ LA-ICPMS show that the primary aegirine-augites have high and variable REE (2194–3627 ppm) and HFSE (4194–16,862 ppm) contents, suggesting that these critical metals can be scavenged by alkali amphiboles and aegirine-augites. Compared to the primary aegirine-augites, the presentative early replacement aegirine (Aeg-I, Na# = 0.91–0.94) has notably lower REE (1484–1972) and HFSE (4351–5621) contents. In contrast, the late hydrothermal aegirine (Aeg-II, Na# = 0.92–0.96) has significantly lower REE (317–456 ppm) and HFSE (6.44–72.2 ppm) contents. Given that the increasing Na# from aegirine-augites to hydrothermal aegirines likely resulted from Na-metasomatism, a scavenging-release model can explain the remobilization of REE and HFSE in peralkaline granitic systems. The scavenging and release of REE and HFSE by Na-metasomatism provides key insights into the genesis of globally significant REE and HFSE deposits. The high Na-index of the hydrothermal aegirine might be useful as a geochemical indicator in the exploration for these critical-metals.

Late Paleoproterozoic magmatism in North Hengshan: Final collapse of the Trans-North China Orogen

Post-collisional magmatism carries important information for understanding when and how an ancient continental collisional orogen unrooted and collapsed. However, the post-collisional magmatic response to the final collapse of the Trans-North China Orogen, one of the 2.1–1.8 Ga collisional orogens that formed in coincidence with the assembly of the Paleo–Mesoproterozoic Columbia supercontinent, remains controversial. Here we present the results of a combined geochronological and geochemical investigation on a suite of Late Paleoproterozoic potassic granites in the North Hengshan terrane of the Trans-North China Orogen, the North China Craton. In situ zircon U-Pb dating shows that these potassic granites, as the last phase of Precambrian magmatism in this terrane, were emplaced between 1790 Ma and 1774 Ma. Their enriched bulk-rock Nd and zircon Hf isotopic compositions point to an ancient crustal source, and their zircon O isotopic variation indicates the involvement of weathered supracrustal rocks in their sources. Considering their bulk-rock major and trace elements, the Late Paleoproterozoic potassic granites in North Hengshan are best explained to be produced by melting of immature metagraywacke that belonged to the Neoarchean–Early Paleoproterozoic sedimentary sequences, at middle–lower crustal depths. The 1.79–1.77 Ga potassic granites in North Hengshan postdated the main phase of the Late Paleoproterozoic collisional orogeny, and were a magmatic response to the final collapse of the Trans-North China Orogen. These 1.79–1.77 Ga potassic granites, along with other 1.80–1.75 Ga magmatism in the Trans-North China Orogen, were most likely generated in a post-collision extensional setting, possibly superimposed by an Andean-type continental arc at its southern margin. The 1.80–1.75 Ga magmatism marked the end of collision between the Western and Eastern Blocks that gave rise to the final consolidation of the North China Craton and the assembly of the Columbia supercontinent, and recorded the outgrowth of this supercontinent through accretion at its continental margins.

Geological and Geochemical Study of Gold and Base Metals Mineralization in the Surupa Area, Borena Zone, Southern Ethiopia

The paper reported the information on geology, alteration pattern, ore minerals and geochemical investigation for gold and base metals and to delineate potential area of gold and base metals mineralization. The results showed that the study area consists of heterogeneous sequences of medium to high-grade poly-deformed gneisses with igneous and sedimentary precursors and structurally affected by three phases of deformation (D1 to D3) like foliations, mesoscale folds, veins and fractures/joints respectively. The nickel and cobalt are highly anomalous elements indicating the source for the mineralization controlled by different structures such as fractures and joints. Pyrite, magnetite, goethite and hematite are ore mineral assemblages characterize the mineralization of the area.

Geochemical Investigation of the Cretaceous Crude Oil Reservoirs and Source Rock Samples in One of the Abadan Plain Oilfields, SW Iran

AbstractCrude oil and source rock samples from one of the main oilfields of the Abadan Plain, Zagros, Iran were analyzed geochemically. Rock‐Eval pyrolysis was conducted on Kazhdumi (Upper Cretaceous) and Gadvan (Lower Cretaceous) formations, which are the probable source rocks for the oil in the region. The results indicated that the Kazhdumi Formation can be classified as a fair‐to‐excellent source rock, while the Gadvan Formation can be identified as having poor‐to‐good source rock in the basin. Based on the cross‐plots of HI versus OI and S2 versus TOC, types II and III kerogen were identified from studied source samples in the area. Determination of the main fraction percentages of the Sarvak and Fahliyan crude oils represented that the oils from the Sarvak reservoir are paraffinic‐naphthenic and aromatic‐intermediate, whilst that from the Fahliyan reservoir is paraffinic and paraffinic‐naphthenic. Biomarker ratios of the saturated fractions of oil from both reservoirs indicate that the source rocks formed in reducing marine environments with carbonate‐shale lithology. Furthermore, biomarker data helped to distinguish the degree of biodegradation in the studied oils. According to geochemical analysis, oil samples from the Fahliyan reservoir were generated at a higher thermal maturity than the Sarvak reservoir samples.

Rate and capacity of cation release from ultramafic mine tailings for carbon capture and storage

Solid wastes produced during hard-rock mining have capacity to capture and store atmospheric CO2 via dissolution and precipitation of Mg-bearing carbonate minerals. However, there is a discrepancy in our understanding of weathering and dissolution in these wastes, with dissolution and reaction rates in field studies exceeding those predicted by experiments under far-from-equilibrium conditions. To reconcile these differences, a series of flow-through dissolution experiments at 25 °C and 1atm were performed to investigate the short-term dissolution kinetics of ultramafic tailings and minerals. Results show that mineral and tailings samples have two stages of dissolution: a fast, transient (or labile) stage, and a slow, stoichiometric stage. Fast releasing labile cations (i.e. labile Mg2+) are sourced from trace minerals with a high reaction rate (e.g. brucite) and from non-stoichiometric surface reaction processes of major minerals (e.g. serpentine). These cations are missing from most geochemical models for mineral weathering. The implication of these results is that the initial transient dissolution of minerals, which is typically ignored during geochemical investigations into bulk dissolution rates, is the missing ingredient for understanding dissolution of mine tailings. Labile cations released during the initial transient dissolution process have value for rapid and low-cost carbon capture and storage techniques as they represent reactivity, capacity, and the best opportunities to deploy low-cost carbon sequestration techniques using mine tailings and other industrial wastes. The presence of labile cations and changing reaction rates over time may also suggest that short-term reactivity examined during field tests may overestimate long-term carbon capture potential of some sites.

Soils and landforms of war — Pedological investigations 75 years after World War II

Seventy-five years after World War II, the legacy of the last war in Germany is still visible in near-natural and anthropogenically shaped urban and rural soilscapes of the Berlin/Brandenburg Metropolitan Area (BMA). Shooting ranges, trenches, and artificial mountains consisting of war debris can be identified across the study area. Our study has been carried out to show how acts of war influence the pedosphere and the geomorphology in the study area. Analysis of war-related landforms and soil profiles in the BMA has been conducted to achieve morphological and pedological characteristics of “soils of war”. Emphasis was placed on geochemical investigations on shooting ranges and war debris soils as acts of war may induce elevated soil heavy metal contents.Our study displays how humankind, by relocating and reworking natural soil material and depositing war debris, substantially altered the rural and urban landscapes within the BMA. Approximately, 4% of the BMA have been used for indirect or direct military purposes. Our research revealed that “soils of war” on anthropogenic landforms show distinct soil physical and chemical characteristics as well as pedoturbations. We furthermore found out that “soils of war” often contain elevated amounts of heavy metals. On the other hand, these ruderal soils are often habitats for endangered species of the red list and can provide specific ecosystem services. As studies on “landforms and soils of war” in urban areas are still insufficient, further efforts are needed in the future to research the characteristics of these specific landforms, evaluate their ecological risk but also the potential worth of protection.

The Marsili Seamount Offshore Geothermal Reservoir: A Big Challenge for an Energy Transition Model

Renewable energies have been the only sources recording a clear increase in total installed capacity, setting a record in new power capacity in 2020, despite the pandemic. The European Union Green Deal represents a strategy towards a sustainable economic model. In this framework, land-based geothermics has seen very limited development; however, offshore geothermics is almost completely absent in the discussion on energy source alternatives, even though it represents a real challenge for energy transition, including the production of green hydrogen. This article discusses an excursus on the activities carried out on offshore geothermal areas worldwide. We focused on the energy potential capacity of the Marsili volcanic seamount located over the bathial plain of the Tyrrhenian Basin, describing the detailed geological, geochemical, and geophysical investigations that have been carried out on that seamount since the 2000s. All the collected data have shown evidence supporting the existence of an exploitable geothermal system in the Marsili seamount consisting of a reservoir of supercritical geothermal fluids of about 100 km3. We discuss and evaluate the actual consistence of the impacts associated with the occurrence of potential risks. We also describe the necessary further steps towards the pilot well. An important breakthrough in the short-medium term that allows for an exit from the predominance of fossil sources may come from the development of energy production derived from offshore high-enthalpy geothermal fields, especially in areas such as the Southern Tyrrhenian Sea. There is a natural clear predisposition for its exploitation combined with a low ecological footprint, which is the target objective of international agreements in the context of a blue economy strategy.

Evolution of Paleogene weathering intensity in the Qaidam Basin, northeastern Tibetan Plateau: Insights from clay geochemistry

An integrated multiproxy dataset involving both mineralogical and geochemical investigations of the northern Tibetan Plateau helps in assessing regional weathering processes linked to topographic evolution and environmental change. However, changes in landscape and drainage reorganizations caused by active tectonics and remarkable climate change during the Cenozoic characterize the basins in and around the Tibetan Plateau by frequent facies changes and coarse lithologies, which largely limit the reliability of bulk geochemical indicators for revealing the regional weathering history. Here, we present detailed geochemical investigations of clay-sized sediments collected from the Hongliugou section (54–26 Ma) in the northern Qaidam Basin to reconstruct high-resolution chemical weathering records of the northern Tibetan Plateau. To prevent chlorite bias when calculating the chemical index of alteration (CIA) in the clay-sized sediments, we propose a modified CIA formula (CIAMg+), in which Mg is added as a soluble cation that can be removed during weathering, similar to Na, K and Ca; thus, CIAMg+ = Al2O3/(Al2O3 + Na2O + K2O + CaO* + MgO) × 100. The CIAMg+ and illite chemistry indices are generally the highest values in the early Eocene Climate Optimum (∼52–49.5 Ma) and a long-term decreasing trend is present from ∼ 49.5–26 Ma; the Mg/Al ratios of the clay-sized sediments and hydrochloric acid leachates are the lowest during the EECO and present a long-term increasing trend in the following 49.5–26 Ma, thus collectively indicating a continuous decrease in the regional chemical weathering intensity. The weakening weathering process during the Paleogene is mainly attributed to the decreasing global temperature and decline in precipitation caused by global cooling. Our study suggests that the proposed geochemical index based on clay-sized sediments can serve as an efficient proxy for regional chemical weathering reconstruction, even in thick sedimentary sequences with frequently changing facies and lithology.

The Shahejie Formation in the Dongpu Depression, Bohai Bay Basin, China: Geochemical investigation of the origin, deposition and preservation of organic matter in a saline lacustrine environment during the Middle Eocene

The Eocene Shahejie Formation in the Bohai Bay, Eastern China is known to contain important petroleum source rocks. Here, a new, large set of geochemical, petrographical and mineralogical data obtained on 41 samples from 9 wells within the North Dongpu Depression is presented in order to investigate organic matter precursor material, thermal maturity as well as paleoenvironment during deposition of the Es3U, Es3L, Es3M and Es4U members within the Eocene Shahejie Formation. These shales and marlstones from the four sub-members show low to moderate TOC contents (up to 5%) with highest values in the Es3U member; quartz content is at about 10% and carbonate content is variable, partly reaching more than 40%. A range of different maturity parameters was determined indicating early mature to peak oil mature stages, and maturity increase with burial depth. Throughout, alginite is the predominant maceral, whereas both vitrinite and inertinite are rare. Hydrogen index values are highly variable, ranging from about 100 to 700. Distinctly different biomarker assemblages indicate variable depositional environments and organic matter inputs between the four intervals. The Eocene Shahejie shales and marlstones in the study area were deposited under episodic photic zone anoxia as revealed by the presence of aryl isoprenoids. Bottom water conditions were anoxic during most of the time, except for Es3M, as indicated by several parameters, e.g. low pristane/phytane ratios. In north Dongpu Depression Es4U displays a fairly uniform biomarker composition, which indicates relatively stable hypersaline lake conditions with a shallow chemocline based on the high Gammacerane Index > 0.6 and abundant aryl isoprenoids. Water salinity changed during deposition of Es3L according to variable C24 tetracyclic terpanes related parameters and evaporite minerals content. The aquatic algal organisms, i.e. haptophyte algae, diatoms and bryophytes which are reflected by abundant nC37–39 alkanes, a variable sterane pattern and other biomarkers, were flourishing during Es3L. Additionally, specific PAHs, i.e. retene, cadalene, fluoranthene, indeno[1,2,3-cd]pyrene and benzo[ghi]perylene also have been identified in small concentration in Es3L, which may be attributed to limited terrigenous organic matter input. Es3M was deposited in a normal lacustrine environment under rather low salinity conditions with substantial input of organic matter derived from algae. During Es3U, saline lake conditions were re-established accompanied by input of both algal and microbial organic matter, especially cyanobacteria as deduced from MMAs and 2α-MeHs, methanogens as deduced from abnormally abundant phytane, PMI, squalane, and methanotrophs from 3β-MeHs.

Contrasting Modes of Carbonate Precipitation in a Hypersaline Microbial Mat and Their Influence on Biomarker Preservation (Kiritimati, Central Pacific)

Microbial mats represented the earliest complex ecosystems on Earth, since fossil mineralized examples (i.e., microbialites) date back to the Archean Eon. Some microbialites contain putative remains of organic matter (OM), however the processes and pathways that lead to the preservation of OM within microbialite minerals are still poorly understood. Here, a multidisciplinary study is presented (including petrographic, mineralogical and organic geochemical analyses), focusing on a modern calcifying mat from a hypersaline lake in the Kiritimati atoll (Central Pacific). The results show that this mat has a complex history, with two main growth phases under hypersaline conditions, separated by an interruption caused by desiccation and/or freshening of the lake. The mineral precipitates of the mat are predominantly aragonitic and two contrasting precipitation modes are observed: the main growth phases of the mat were characterized by the slow formation of irregular micritic particles with micropeloidal textures and subspherical particles, linked to the degradation of the exopolymer (EPS) matrix of the mat; whereas the interruption period was characterized by the rapid development of a thin but laterally continuous crust composed of superposed fibrous aragonite botryoids that entombed their contemporaneous benthic microbial community. These two precipitation modes triggered different preservation pathways for the OM of the mat as the thin crust shows a particular lipid biomarker signature, different from that of other layers and the relatively rapid precipitation of the crust protecting the underlying lipids from degradation, causing them to show a preservation equivalent to that of a modern active microbial community, despite them being >1100 years old. Equivalent thin mineral crusts occur in other microbialite examples and, thus, this study highlights them as excellent targets for the search of well-preserved biomarker signatures in fossil microbialites. Nevertheless, the results of this work warn for extreme caution when interpreting complex microbialite biomarker signatures, advising combined petrographic, mineralogical and geochemical investigations for the different microbialite layers and mineral microfabrics.

Use of Cluster Analysis to Group Organic Shale Gas Rocks by Hydrocarbon Generation Zones

In the last decade, exploration for unconventional hydrocarbon (shale gas) reservoirs has been carried out in Poland. The drilling of wells in prospective shale gas areas supplies numerous physicochemical measurements from rock and reservoir fluid samples. The objective of this paper is to present the method that has been developed for finding similarities between individual geological structures in terms of their hydrocarbon generation properties and hydrocarbon resources. The measurements and geochemical investigations of six wells located in the Ordovician, Silurian, and Cambrian formations of the Polish part of the East European Platform are used. Cluster analysis is used to compare and classify objects described by multiple attributes. The focus is on the issue of generating clusters that group samples within the gas, condensate, and oil windows. The vitrinite reflectance value (Ro) is adopted as the criterion for classifying individual samples into the respective windows. An additional issue was determining other characteristic geochemical properties of the samples classified into the selected clusters. Two variants of cluster analysis are applied—the furthest neighbor method and Ward’s method—which resulted in 10 and 11 clusters, respectively. Particular attention was paid to the mean Ro values (within each cluster), allowing the classification of samples from a given cluster into one of the windows (gas, condensate, or oil). Using these methods, the samples were effectively classified into individual windows, and their percentage share within the Silurian, Ordovician, and Cambrian units is determined.

Mineralogical and geochemical investigations for subvolcanic hydrothermal alteration environments at an active volcano: An example of Hokkaido-Komagatake volcano, Japan

At active volcanoes, hydrothermal alteration related to subvolcanic hydrothermal systems can lead to volcanic hazards, such as edifice collapses and phreatic eruptions. Although it is difficult to investigate subsurface hydrothermally altered zones on active volcanoes directly because their edifices are rarely eroded, lithic materials derived from edifice interiors, such as debris avalanche deposits and phreatic ejecta, can contain information on subvolcanic hydrothermal zones and provide a way to investigate this. To reveal the hydrothermal system active during the historical eruptive stage of Hokkaido-Komagatake volcano, this study investigates the characteristics of hydrothermally altered lithic products in volcanic deposits and evaluates the hydrothermal environments using geochemical modeling. The debris avalanche deposits originally comprising the uppermost part of the edifice mainly contain smectite, kaolinite, and cristobalite, suggesting a low-temperature (approximately 100 °C) and weakly acidic to neutral environment. The deposits also have jarosite with a light-δ34S value which is formed from the oxidation of pyrite in a supergene environment, and the acid alteration induced by pyrite oxidation might weaken the edifice. Chlorite and mixed-layer chlorite/smectite comprise the altered rocks derived from the deeper part of the edifice, indicative of a higher temperature (150 to >200 °C) and nearly neutral environment at depth. Strongly acidic alteration, represented by alunite precipitation, is restricted to a fumarolic environment around the volcanic conduit, and this hydrothermal environment developed during the historical eruptive stage. Because the edifice mostly consists of permeable Plinian pumice and weakly welded tuff, the primary thermal water derived by the condensation of magmatic gas in groundwater flows while interacting with the edifice rocks, allowing meteoric water infiltration. Consequently, a relatively low-temperature and nearly neutral environment prevails in the edifice. This is consistent with the absence of acidic, SO4-rich thermal water in the crater area, and low-temperature and nearly neutral pH thermal waters discharge at the foot of the volcano. One of these waters showed heating and increased chemical concentrations related to an increase in magmatic gas flux. This thermal water is assumed to be derived from magmatic gas without scrubbing by the hydrothermal system. As a result, changes in magmatic gas flux directly affect the thermal and chemical changes in the thermal water. Thus, this thermal water can be an efficient monitoring tool for understanding volcanic activity of the volcano.

Indicative significance of biomarker parameters on crude oil cracking rate from the Dongpu Depression, Bohai Bay basin of North China

Molecular markers have a strong ability to maintain their own structure. The side chain fracture, isomerization and aromatization show regular response characteristics for the organic matter evolution process, which can measure oil maturity and identify oil cracking degree. In this research, 43 crude oil samples were collected for geochemical investigation in the Dongpu Depression from Bohai Bay Basin of North China. By the gas chromatography (GC) experiments of saturated hydrocarbon and aromatic hydrocarbon, a variety of molecular marker parameters were selected for quantitative evaluation of crude oil maturity and cracking rate, including pristane isomerization index (PIR), C29 sterane parameters, monoaromatic sterane, rearranged sterane (20 S/(20 S + 20 R)), hopane (Ts/(Tm + Ts)), methyl phenanthrene ratio (MPR), Methyl phenanthrene index (MPI), alkyl naphthalene, and alkyl dibenzothiophenes (DBTs). Thus, the crude oil cracking rate in the different regions of Dongpu Depression were calculated quantitatively. The results show that the increase of temperature, the pressure (<40Mpa) and thermochemical sulfate reduction (TSR) action promotes crude oil cracking, whereas the pressure (>40 MPa) generally inhibits the crude oil cracking. In addition, well Wei 20 does not experience prominent thermal history temperature and burial history pressure, but its oil cracking rate is higher than the average cracking rate curve value, suggesting other factors also have an important impact on crude oil cracking, which needs to be further discussed.

Geochemical investigation of low latitude black shale intervals of the Lower to Middle Jurassic succession, Indus Basin, Pakistan

Geochemical investigation of low latitude black shale intervals of the Lower to Middle Jurassic succession, Indus Basin, Pakistan

Environmental aspects of the carcinogenic situation in developed industrial region

The cancerous situation in Tatarstan Republic, in particular, the data on the disease incidence, mortality are estimated. The data on the content of some toxic substances in environment are analyzed. The necessity of studying the role of anthropogenous factors in population health formation is emphasized. The use of geochemical investigation methods in medicine is necessary to solve the topical problem to reveal the relation between environmental pollution and growth of the malignant tumor incidence.

A Neoarchean to Paleoproterozoic magmatic arc in the Trans-North China Orogen: Petrological and geochemical constraints from the Tianzhen gneisses in the Huai'an Complex

In the past two decades, extensive investigations have been carried out on the Trans-North China Orogen (TNCO), a Himalayan-type continental collisional belt along which the Eastern Block and the Western Block amalgamated to form the basement of the North China Craton. There are now coherent outlines of the timing and tectonic processes involved in the Paleoproterozoic amalgamation of the TNCO. However, pre-collisional tectonic setting and driving mechanism of the TNCO still remain controversial. To resolve these issues, we carried out field petrological and geochemical investigations on the Tianzhen gneisses from the Huai9an Complex in the TNCO. The Tianzhen gneisses consist predominantly of tonalitic-trondhjemitic-granodioritic (TTG) series, which can be further divided into low-Yb and high-Yb types. Our results indicate that although both low-Yb and high-Yb TTG series were formed in a magmatic arc environment, their petrogenetic origins were different. The Huai9an low-Yb TTG magma was derived from the partial melting of subducted oceanic crust consisting of eclogite or 30% garnet-bearing amphibolite under 15 to 20 kbar or even higher pressure, with garnet, amphibole, and rutile as residues. In contrast, the high-Yb TTG magma was derived from the partial melting of subducted oceanic slab consisting of garnet-free or 7% garnet amphibolite under 10 to 15 kbar, leaving residual garnet and amphibole. Both magmas then interacted with the overlying mantle wedge during ascent. Thus, it can be concluded that the Tianzhen TTG magmas were derived from the partial melting of subducted oceanic crust and interaction with mantle peridotite, supporting a magmatic arc setting for the Huai9an Complex during Neoarchean to Paleoproterozoic time. Associated with other analogous gneiss complexes in the TNCO, a long-lived Neoarchean to Paleoproterozoic magmatic arc system is established in the Trans-North China Orogen.

Mineralogy, organic geochemistry, and microstructural characterization of lacustrine Shahejie Formation, Qikou Sag, Bohai Bay Basin: Contribution to understanding microcosmic storage mechanism of shale oil

Shale samples of lacustrine Shahejie Formation from the Well F39X1 drilled in Qikou sag were used to study microstructures, mineralogy, and organic geochemistry and their impacts on oil storage response. Samples are quartz and clay rich and contain a variable amount of calcite, dolomite, plagioclase, and pyrite minerals. The TOC content ranges between 0.33 and 2.59 wt %, Rock-Eval S 1 and S 2 values range from 0.05 to 1.07 mg/g and 0.12–9.57 mg/g, respectively. The maximum yield temperature (T max ) of pyrolysate ranges from 440 °C to 467 °C, and vitrinite reflectance calculated based on T max between 0.76 and 1.25%. High frequency 2D nuclear magnetic resonance (NMR) results show free oil contents are 1.176–1.909 μl/g, with an average of 1.542 μl/g. Mineral-related pores are dominant and volumetrically significant with a multimodal pore-throat size distribution, they could provide significant storage space and have good microstructural connectivity. Their roles in microscopic storage of oil molecules mainly depends on two mechanisms: (1) rigid mineral grains preserve large pore networks, within which residing a very large volume of free oil, and (2) clay particles existed within large interparticle pores alter pore throat size distribution, resulting in a slight increasing of adsorbed oil onto pore walls. The Well F39X1 is an important shale oil exploration well for Shahejie Formation. To reduce exploration risk and determine economic feasibility, knowledge of liquid hydrocarbon molecule microscopic storage mechanism is required so producible shale oil resources can be quantified. The investigation of oil-bearing shale mineralogy, organic geochemistry, and microstructures is an important step in better understanding of the pore network development and their related microscopic storage mechanism for oil in lacustrine shale. We suggested that siliceous Shahejie shales in Qikou sag with moderate TOC and suitable thermal maturity have well-developed pore networks and high residual hydrocarbons, which should be the important target for lacustrine shale oil exploration. Also, the well-developed mineral-related pore networks should be included in attempts to build realistic microscopic storage models of shales. • Four typical pore types in Shahejie Formation of Well F39X1 are identified. • Mineral-related pores are dominant and volumetrically significant in pore networks. • Oil molecule type, distribution, and content are identified by high-frequency 2D NMR. • Two microstructural models are proposed to reveal shale oil storage mechanism.

Geoelectrical and Geochemical Investigations of Selected Dumpsites for Potential Groundwater Contamination in Gusau, Zamfara State, Nigeria

Groundwater contamination has been a worldwide phenomenon. In this research, geoelectric and geochemical surveys were carried out on three active dumpsites in Gusau metropolis for detection of groundwater contamination. Vertical electrical Soundings (VES) were conducted on the dumpsites using Schlumberger array with maximum current electrode separations of 180 m. Five VES were conducted on each dumpsite making a total of fifteen VES along three profiles. Thirty five (35) points were assessed from three wastes dumpsites using portable XRF equipment for the in-situ testing while fifteen (15) representative groundwater samples collected were taken to the laboratory for hydro-geochemical analysis. The field data obtained from VES was analyzed using WinGlink software. The VES results revealed three subsurface layers. The topsoil has resistivity ranging from 1.5Ωm to 48.2 Ωm while the thicknesses vary from 0.47 m to 3.37 m across the profiles. The second layer’s resistivity varies from 5.4 Ωm to 144.35 Ωm and their thicknesses’ ranges from 1.36 m to 16.93 m. The third geoelectric layer has resistivity from 70.0 Ωm to 6003.0 Ωm. The geoelectric results revealed that the top soils in all the dumpsites were characterized by very low resistivity depicting possible pollution and contamination. Environmental pollution models applied to the geochemical dataset revealed Zn, Pb and Cu as moderately contaminants which generally indicated severe potential contamination in the investigated area. While other analytic parameters such as Mn, Cr, Ni and Fe showed low contamination factors. Hydro chemical analysis showed that pH values recorded from the water samples ranged between 7.26 to 8.12 with mean value of 7.50, whereas, recorded Total dissolve solid (TDS) ranged between 377 to 1393mg/L with average concentration of 751.27mg/L. Findings from the study indicated that there may be possible contamination of shallow groundwater system in the nearest future if proper mitigation measures are not taken into consideration at the dumpsites.

Petro-Mineralogical and Geochemical Evaluation of Glauconitic Rocks of the Ukra Member (Bhuj Formation), Kutch Basin, India

AbstractGlauconites occurring within the Ukra Member of Kutch Basin have remained unexplored in terms of their economic significance. The present study aimed to present a detailed physicochemical characterization of glauconite occurring in the siliciclastic rocks of Guneri and Umarsar area of the Kutch district, Gujarat, India to explore their economic potential. The study involved an integrated petrographical, mineralogical, and geochemical investigation of glauconitic rocks to highlight the occurrence, nature, and maturity of glauconite. The characterization was carried out using X-ray diffraction (XRD), X-ray fluorescence (XRF), and electron probe microanalysis (EPMA) combined with energy dispersive X-ray (EDX), Field emission gun scanning electron microscopy (FEG-SEM), Fourier-transform infrared spectroscopy (FTIR), and inductively coupled plasma mass spectroscopy (ICP-MS). Petrographic and bulk XRD analysis revealed that the glauconite occurs as green pellets constituting ~30 and 40% of the glauconitic sandstone and shale, respectively. Whole-rock analysis showed that the value of K2O varies considerably from 3.93 wt.% (sandstone) to 5.63 wt.% (shale). Mineral chemistry indicated the distinctive chemical composition of glauconite pellets containing 7.4–8.4 wt.% of K2O. The parameters, such as the distance between the (001) and (020) peaks and the large K2O content (~8 wt.%) of the glauconite fraction reflect an evolved to highly evolved stage of maturation. The morphological and spectral signatures further support the high degree of maturation in glauconites. Trace-element analysis implied that the glauconitic sandstone and shale contain elements such as Zn, Mn, Cu, Co, Mo, and Ni, which serve as essential micronutrients for plants. These data sets collectively constitute part of a preliminary study which is prerequisite to beneficiation, but further evaluation of its potential as a potash fertilizer also is needed.

Provenances of the Upper Precambrian Clay Rocks in the Southern Urals: Results of Geochemical and Sm–Nd Isotope Geochemical Investigations

Provenances of the Upper Precambrian Clay Rocks in the Southern Urals: Results of Geochemical and Sm–Nd Isotope Geochemical Investigations