Geochemical Studies Research Articles

Investigating the Effect of Water Softening on Polymer Adsorption onto Carbonates through Single-Phase and Two-Phase Experiments

Summary Polymer retention is considered a major challenge in polymer flooding applications, especially in carbonates. This is due to the prevailing conditions of low permeability (<100 md), high temperature (>85°C), and high salinity (>100,000 ppm) generally found in these formations, which limit the effectiveness of commonly used polymers such as hydrolyzed polyacrylamide (HPAM) and xanthan gum. To address these challenges, a polymer based on acrylamide tertiary butyl sulfonate (ATBS) has been used due to its tolerance to high-temperature and -salinity conditions. However, the high cost of manufacturing these polymers, combined with their anionic properties that promote adsorption onto positively charged carbonate rocks, necessitates the exploration of methods to reduce polymer retention. In this study, we aim to determine the sufficient concentration of hardness ions (Ca2+ and Mg2+) required to significantly reduce the adsorption of this polymer. The study is unique in its focus on mitigating polymer retention in carbonate formations using softened brine, as no prior research has investigated this aspect. Four different brines were investigated with a salinity of 8,000 ppm total dissolved salts (TDS) and varying ionic composition designed mainly by eliminating the hardness-causing ions, Ca2+ and Mg2+. A geochemical study was performed using the PHREEQC software to analyze the interaction between these injected brines and the rock. Furthermore, comprehensive rheological and static adsorption studies were performed at a temperature of 25°C using the potential ATBS-based polymer to evaluate the polymer performance and adsorption in these brines. Later, dynamic adsorption studies were conducted in both single-phase and two-phase conditions to further quantify polymer adsorption. The geochemical study showed an anhydrite saturation index (SI) of less than 0.5 for all the brines used when interacting with the rock, indicating a very low tendency for calcium sulfate precipitation. Furthermore, the rheological studies showed that polymer viscosity significantly increased with reduced hardness, where a polymer solution viscosity of 7.5 cp was obtained in zero hardness brine, nearly 1.5 times higher than the polymer viscosity of the base makeup brine of 8,000 ppm. Moreover, it was observed that, by carefully tuning the concentrations of the divalent cations, the polymer concentration consumption for the required target viscosity was reduced by 40–50%. For the single-phase static adsorption experiments, the polymer solution in softened brines resulted in lower adsorption in the range of 37–62 µg/g-rock as opposed to 102 µg/g-rock for the base makeup brine. On the other hand, the single-phase dynamic adsorption results showed an even lowered polymer adsorption of 33 µg/g-rock for the softened brine compared with 45 µg/g-rock for the base makeup brine. Additionally, the single-phase dynamic adsorption studies showed a remarkable improvement in polymer injectivity using softened brine. The polymer retention in wettability-altered cores was further reduced. The study highlights that water softening improves the performance of polymers, specifically in terms of lowering polymer adsorption. It concludes that a threshold hardness level (Ca2+ and Mg2+) of approximately 100 ppm is sufficient to achieve a significant reduction in polymer adsorption for the tested experimental conditions. In this paper, we show that the softened water increases the polymer viscosity and reduces polymer adsorption, which leads to an overall reduction in polymer consumption. Hence, the softened makeup water has the potential to enhance the application envelope of this potential polymer for polymer flood, especially in the case of carbonate reservoirs.

Geochemical evaluation of Sarvak oil reservoir using biomarkers, carbon isotope and trace element: A case study from Southwest Iran

The crude oils of the Sarvak reservoir were studied by integrated geochemical, inorganic and isotopic analyses to evaluate the origin, depositional conditions, geological age, thermal maturity of the source rocks and possible facies from which these oils were sourced. This study provides new insights into the Middle-Jurassic age source rock in the Azar Oilfield. This is the first geochemical study in Azar Oilfield where non-biomarker parameters and biomarker parameters were utilized to achieve the objectives. The n-alkane distribution pattern along with their standard ratios, including CPI (0.83–1.03), TAR (0.18–0.29) and isoprenoids (Pr/Ph, 0.52–0.65) as well as pristane/n-C17 versus phytane/n-C18 cross-plot indicate a marine source of the organic matter deposited in an anoxic condition. The sterane parameters such as C27 and C29 are characterized by the predominance of C27ααα-20R steranes (41%–49%) and also depict the algal source of organic matter. The organic input and facies of the source units were also determined by terpanes C29/C30H, Ts/Tm, C35/C34-HH, and DBT/Phen. The relatively high ratio of C29/C30H along with the ratios of Ts/Tm (<0.5) and C35/C34 (>0.8) reflect the carbonate marine facies of the source rocks. Furthermore, the higher values of the homohopane index (>0.1) along with the low ratio of the gammacerane/C30-H (0.06–0.22) as well as the high ratio of V/Ni (>1) further indicate anoxic environments. The dibenzothiophene/phenanthrene ratios of the oil samples (from 2.43 to 3.25) indicate the marine carbonates/marl zone. This genetic classification is also supported by stable carbon isotopic compositions (δ1³C). Most of the maturity-related biomarkers and non-biomarker parameters such as CPI, steranes-C29S/(S + R), ββ/(αα+ββ), moretane to hopane (M29/C30H), pentacyclic terpanes C27Ts/(Ts + Tm), C32-S/(S + R) hopanes, and methyl phenanthrene index agree that the analyzed oils have originated from mature source rocks. Ultimately, this study has demonstrated that analyses of biomarkers and their stable isotope compositions (δ13C and δ34S) complemented with trace element data provide an excellent novel tool for better understanding the basic concepts in petroleum basins and for solving a wide range of problems during petroleum exploration.

Studies of radioactive minerals and geochemistry of uranium at the granitic rocks of Wadi Um Shillman Area, South Eastern Desert, Egypt

The northwestern part of Gabal Um Ara granitic pluton is represents a good example for uranium occurrence in the southeastern desert of Egypt. Among the different lithologies in the study area, the granitic rocks attract attention for more detailed geological, geochemical and radiometrical studies. Um Ara granitic masses cover an oval outline area of about 300 km2, which is characterised by moderate topography. The granitic rocks are classified as monzogranite and alkali feldspar granite. Both of them belong to the post-orogenic younger granite magmatic activity that intruded the Egyptian shield between 620 and 530 Ma. The intrusion of Um Ara monzogranite and alkali feldspar granite appears to have been controlled by deep-seated tectonic zones and block faulting. The studied area lies at southeast of Aswan City between 22ͦ 38′ 12˝–22ͦ 38′ 34˝ N and 33ͦ 47′ 27˝–33ͦ 48′ 14˝ E. Geochemically, the average concentration of the elements in North Um Ara granite shows that the relative abundance decreases gradually with decreasing incompatibility from Rb to Y. The common features are enrichment in more mobile elements Rb, Th and U. The monzogranite shows the lowest U and Th content, whereas the alkali-feldspar shows an enhanced contents of both elements, with average Th/U ratio = 3.0. the alkali-feldspar exhibits an expanded enrichment of Th relative to U. The U of the alkali-feldspar may be included within the structure of the refractory accessory minerals. The northern part of the Um Ara granitoids has subjected to different types of alterations. The radiometric survey of the northwestern part of Gabal Um area granitic pluton revealed the presence of several radioactive anomalies near the contact with the Dokhan volcanic and metavolcanic rocks in the north. Some visible uranium mineralisation of uranium minerals occur mainly along the NW, NE, E-W and N-S joints, of a highly sheared alkali feldspar-granite. Uranophane is visible secondary uranium mineral, characterised by bright yellow lemon colours and occurs mainly as filling fractures and joints associated with violet fluorite, iron and manganese oxides. The radioactive and accessory minerals studying and X-ray diffraction analysis that of the mineralised alkali feldspar-granite granite in the northwestern part of Gabal Um Ara granitic pluton revealed include the presence of fluorite, zircon, columbite, spessartine garnet whereas, the secondary uranium minerals are represented by uranophane, β-uranophane and kasolite. The hydrothermal origin was proposed as two possible alternatives for this uranium mineralisation.

Characterization and prediction of acid mine drainage potential and metal solubility: Critical data for tailings and waste rock management in high sulfidation gold deposits

Abstract In the Purnama gold deposit at the Martabe mine of South Tapanuli District, North Sumatra Province, Indonesia, gold is extracted from the ore and the remaining fine-sized material is stored in the tailings storage facility (TSF) and waste rocks are placed as TSF embankments. Without proper management, tailings and waste rocks from mining can create acid mine drainage (AMD) and release toxic chemicals, posing significant risks to local ecosystems and residents in mining areas. To address this, a mineralogical and geochemical characterization study was investigated, as well as the leaching behavior of heavy metals in the tailings leach column tests (LCT) was conducted. Geochemical characterization showed quartz hornblende andesite and hornblende dacite as NAF materials; clay breccia, volcanic andesite, carbonaceous clay, volcanic breccia, and silica breccia as PAF materials. Further tests revealed that volcanic breccia, carbon clay, and volcanic andesite were classified as high-risk PAF materials, supported by XRD test results. Finally, the LCT results showed that volcanic breccia produced rapid acid drainage, with arsenic (45.9 mg L−1), copper (41.4 mg L−1), and manganese (14.1 mg L−1) being the main dissolved metals. It is important to manage PAF rocks and ensure the water leachate does not contain high concentrations of these metals.

Reconstructing the paleoshoreline of Bukit Choras based on geochemical and microfossil studies

The archaeological findings in Bukit Choras are among the best preserved structural remains of Bujang Valley. Previous studies have revealed sacred buildings made of laterite blocks, ancient water reservoirs, as well as a Buddhist inscription which can be dated back to the 6th/7th Century C.E. Although Bukit Choras is currently located 8 km inland, in ancient times, it could have been nearer to the shoreline similar to other pre-14th Century coastal sites of Bujang Valley. Thus, this research attempts to reconstruct the paleoshoreline of the area by determining whether the dryland surrounding Bukit Choras was once submerged under the sea. In this study, hand-augered soil samples from the surrounding areas of Bukit Choras were analysed by using X-Ray Fluorescence (XRF), Scanning Electron Microscopy (SEM) and digital microscopy, while 14C dating was carried out on two organic samples extracted from the sediments. The possible locations of the paleoshoreline were deduced based on the analysis of geochemical and microfossil contents of the sediments while taking into account the sea-level fluctuations and the geomorphology of the area. Thus, it is concluded that Bukit Choras was once a coastal site, surrounded by a marine and swampy environment, while the archaeological site functioned as one of the coastal settlements of the Bujang Valley.

Hydrological dynamics and manganese mineralization in the wake of the Sturtian glaciation

The Cryogenian Sturtian and Marinoan glaciations stand as the most extreme climate events in Earth history. Intriguingly, large-scale Mn carbonates characterize the nonglacial interlude of this period in South China. The formation mechanism of Mn carbonates and the potential correlation underlying this temporal association remain elusive. Here, we present an integrated petrographic and geochemical study of drill core materials intercepting the Mn-bearing Datangpo Formation. Rare earth element patterns of these Mn carbonates exhibit positive Ce anomalies and a lack of Y anomalies, which differ from those of modern seawater but resemble marine Mn-Fe oxides. These features, combined with negative carbonate carbon isotope compositions (δ13Ccarb as light as −9.9 ‰ VPDB), indicate the presence of oxide precursors and the incorporation of light carbon during Mn-carbonate precipitation. Phosphate oxygen isotope ratios (δ18Op) of HCl-extractable apatite reveal a ∼4 ‰ difference in the average δ18Op between Mn-rich and Mn-poor rocks. We propose that the more positive δ18Op of Mn-rich samples may result from the dominance of phosphate released by reductive dissolution of metal oxides or a heavier oxygen isotope signal of surrounding waters with which isotopic equilibrium has been reached. We further illustrate how marine invasions into coastal anoxic basins could have triggered the formation of Mn oxides and highlight the role of glaciation–deglaciation in the development of giant Mn deposits.

Ferric Iron in Eclogitic Garnet and Clinopyroxene from the V. Grib Kimberlite Pipe (NW Russia): Evidence of a Highly Oxidized Subducted Slab

Abstract Estimates of oxygen fugacity of eclogitic rocks are linked to the redox evolution of the oceanic protolith during subduction and its residence in the lithospheric mantle, and, based on knowledge of pressures and temperatures, allow modelling of the speciation of volatile elements and diamond (or graphite) versus carbonate stability. To date, the oxygen fugacity of mantle eclogites has been shown to vary between −6 (Kasai, Congo and Udachnaya, Siberia) and −0.1 (Udachnaya, Siberia) log units (relative to the fayalite–magnetite–quartz buffer, FMQ), linked to the low Fe3+ contents of garnets. In this study, we investigated the Fe oxidation state of coexisting garnet and clinopyroxene hand-picked out of 17 diamond-free high-MgO and low-MgO mantle eclogites (dated at 2.84 Ga) from the Grib kimberlite pipe (East-European platform). Measured Fe3+/∑Fe values range between 0.03 and 0.19 for garnet and 0.18–0.38 for clinopyroxene, the former being higher than what was measured previously in garnets equilibrated at mantle conditions. The Fe3+/∑Fe of the reconstructed bulk rock ranges between 0.10 and 0.15 for high-MgO eclogites and 0.10 and 0.24 for low-MgO eclogites (with uncertainties of ± 0.02 and ± 0.03 in both cases). Thermobarometric calculations result in equilibration pressures and temperatures of 3.0–5.2 (± 0.4) GPa and 720–1050 (± 60) °C for both high-MgO and low-MgO eclogites, slightly lower than previous P–T estimates of mantle eclogites from the Udachnaya kimberlite pipe (Siberian craton). At these conditions, ∆logfo2 (FMQ) calculated using the available oxythermobarometric model varies from −1.7 to −0.6 log units for high-MgO eclogites and from −2.9 to 0.9 log units for low-MgO eclogites. Samples recording ∆logfo2 (FMQ) ≤ −1 log units overlap with North Slave, West Africa and Udachnaya eclogites, with no difference among eclogite types. The average values of −1.2 (± 0.4) log units for high-MgO and −0.6 (± 1.1) log units for low-MgO eclogites suggest different redox conditions of basaltic protoliths during subduction worldwide. Previous geochemical studies on the same rock samples reported evidence of cryptic metasomatism in both garnet and clinopyroxene that we demonstrate being not recorded by their major elements, while modal metasomatism evidenced by the presence of phlogopite as a product of interaction with a kimberlitic melt only affects the MgO of the bulk rock. Therefore, we suggest that high Fe3+/∑Fe ratios for garnet (&amp;gt; 0.10) and for reconstructed bulk rocks in the case of both low-MgO and high-MgO samples cannot be due to metasomatic interaction with an oxidized fluid, but rather are the consequence of Fe3+ redistribution in an unusually oxidized mafic protolith upon metamorphism. Our results highlight the redox variability of eclogites of Archaean age at conditions more oxidized than present-day mid-ocean ridge basalts (MORBs) and imply an oxidizing nature of the convective mantle source where magma was formed with consequent speciation of C in the form of carbonate fluid explaining, therefore, the lack of eclogitic diamonds in V. Grib kimberlite pipe.

Petrological, chemical, and chronological study of breccias in the Chang'e‐5 soil

AbstractWe carried out a petrological, mineralogical, and geochemical study of fragmental and regolith breccia clasts separated from two Chang'e‐5 (CE‐5) soil samples, CE5C0000YJYX03501GP and CE5C0400, which provide an opportunity to investigate the compositional change of regolith at the landing site through time. Fragmental breccia CE‐5‐B3 contains a diverse range of basaltic clasts and basaltic mineral fragments, and some rare Mg‐suite‐like minerals. Regolith breccias CE‐5‐B006, CE‐5‐B007, CE‐5‐B010‐08, CE‐5‐B010‐09, CE‐5‐B011‐07, and CE‐5‐B016‐03 contain mare basaltic fragments, mare vitrophyric clasts, rare Mg‐rich fragments possibly derived from the Mg‐suite rocks, and impact‐derived glass spherules. Pb‐isotope data obtained for baddeleyite grains found both inside some of the basaltic clasts identified in breccia fragments and in the breccia matrices yield Pb/Pb dates similar to the 2 Ga crystallization age of the CE‐5 basalt fragments, extracted directly from the soil sample. Seventy‐four Pb isotope analyses of Ca‐phosphate grains also indicate that the majority of these grains have Pb/Pb dates of 2 Ga, suggesting that they originate from the CE‐5 basalts. In addition, a Pb–Pb isochron drawn through analyses of four Ca‐phosphates in breccia CE5‐B006 yielded an intercept corresponding to a date of 3871 ± 46 Ma, which is the best possible estimate of the formation age of these four grains. Electron probe microanalysis shows that the breccias contain components similar to CE‐5 mare basalt fragments extracted directly from the soil sample, implying that the fragmental and regolith breccia fragments are mostly composed of material sourced from the underlying basalts. The general absence of impact melt breccia clasts, along with the general lack of Fe–Ni metal and absence of added meteoritic debris all suggest that the regolith at the CE‐5 landing site is immature and dominated by material mixed together by small local impact cratering events. Trace element analyses show that the glass beads in the regolith breccias have a Th abundance of 4.06–5.28 μg g−1. This is similar to the Th content of the regolith above the Em4 unit at the landing site as measured from orbit, as well as the estimated bulk Th content of CE‐5 basalts, suggesting that Th of the local regolith is predominantly sourced from the underlying mare basalts, without significant Th addition from Th‐rich exotic clasts sourced from evolved lunar lithologies.

Geochronology and Geochemistry of Granitic Pegmatites from Tashidaban Li Deposit in the Central Altun Tagh, Northwest China

The Central Altun orogenic system is a result of the amalgamation of multiple micro-continental blocks and island arcs. This complex system originated from subduction–accretion–collision processes in the Proto-Tethys Ocean during the Early Paleozoic. Research has reported the discovery of several Li-Be granitic pegmatite deposits in the Central Altun Block, including the North Tugeman granitic pegmatite Li-Be deposit, Tugeman granitic pegmatite Be deposit, Tashisayi granitic pegmatite Li deposit, South Washixia granitic pegmatite Li deposit, and Tamuqie granitic pegmatite Li deposit. The Tashidaban granitic pegmatite Li deposit has been newly discovered along the northern margin of the Central Altun Block. Field and geochemical studies of the Tashidaban granitic pegmatite Li deposit indicate: (1) Spodumene pegmatites and elbaite pegmatites, as Li-bearing granitic pegmatites that form the Tashidaban granitic pegmatite Li deposit, intrude into the two-mica schist, and marble of the Muzisayi Formation of the Tashidaban Group. (2) Columbite–tantalite group minerals and zircon U-Pb dating results indicate that the mineralization age of Tashidaban Li granitic pegmatites is 450.2 ± 2.4 Ma with a superimposed magmatic event at around 418–422 Ma later. (3) Whole-rock geochemical results indicate that the Kumudaban rock sequence belongs to the S-type high-K to calc-alkaline granites and the Tashidaban Li granitic pegmatites originated from the extreme differentiation by fractional crystallization of the Kumdaban granite pluton.

Geological and Geochemical Characterization of Variscan Pegmatites in the Sidi Bou Othmane District, Central Jebilet Province, Morocco

The Sidi Bou Othmane (SBO) pegmatite district is situated in the Central Jebilet massif, Western Meseta domain, Morocco. The SBO district is hosted essentially in a volcano-sedimentary series composed of Late-Devonian Sarhlef shales. Pegmatite bodies crop out as dykes, which are oriented from N-S to E-W and are generally variably deformed with ductile and/or brittle structures with ante, syn- or post-kinematic criteria. Petrographic observations of pegmatite dykes show that feldspars (i.e., albite, microcline) are the most abundant mineral phases, followed by quartz and micas, with tourmaline and accessory minerals such as garnet, and zircon also featuring heavily, as well as secondary minerals such as clinochlore, sericite, and illite. The geochemical study of the SBO pegmatites indicates that they have mainly S-type granitic compositions, which are peraluminous granites with calc-alkalic affinities. The study of trace elements indicates that SBO pegmatites were formed in post-orogenic syn-collision context during the Variscan orogeny by the partial melting of argilliferous sediment. They can be ascribed to the muscovite-bearing pegmatite; moreover, they have good potential regarding ceramics. They also contain minerals, such as feldspar, which have been recently assessed as critical raw materials by the European Union.

Petrological and geochemical insights into the magma plumbing system of the Daliuchong dacite eruption, Tengchong Volcanic Field, SW China

The formation of highly evolved, dacitic magmas has been attributed to various processes, including crystal fractionation, partial melting of overlying crust, and/or assimilation of crustal material into an evolving magma chamber. These processes are undoubtedly primary processes involved in the formation of dacites, but they may not be the only mechanism involved in the formation of high-silica dacites. For instance, mafic magma replenishment has been proposed as an additional mechanism but has not been assessed, and thus, its role has not been well-constrained. The Daliuchong volcano is the result of one of the largest eruptive events within the Tengchong Volcanic Field (TVF) in southwest China during the Early-Middle Pleistocene. Here, we conducted detailed mineral textures, mineral chemistry, and geochemical studies on Daliuchong pyroclastic rocks to explore the pre-eruptive storage conditions and evolution processes of the magma. The Daliuchong pyroclastic rocks are dacitic in composition. The samples show porphyritic textures characterized by phenocrysts of plagioclase, amphibole, clinopyroxene, orthopyroxene, and Fe-Ti oxides. Additionally, two distinct types of glomerocryst are identified: a gabbroic glomerocryst containing plagioclase + clinopyroxene + orthopyroxene ± Fe-Ti oxides assemblage and a dioritic glomerocryst containing plagioclase + amphibole ± pyroxene ± Fe-Ti oxides assemblage. Both phenocryst and glomerocryst show rich micro-textures. The Daliuchong dacite exhibits bulk compositional heterogeneity. Analysis of bulk-rock data suggests that this heterogeneity may arise from both the differentiation of the dacite itself and the injection of mafic magma. The compositional similarity between the Daliuchong dacite and experimentally produced partial melts of metamorphic basalt supports that the Daliuchong dacite was predominantly formed through the partial melting of the mafic lower crust. Thermobarometry estimation indicates that clinopyroxenes with high Mg# crystallized at 560–870 MPa, whereas amphibole and clinopyroxenes with low Mg# crystallized at 185–300 MPa. Based on the observed phase relations and the calculated crystallization conditions, we propose that during the differentiation of the Daliuchong dacite, heterogeneous dacitic magma formed by partial melting accumulated in a deep magma reservoir (21–32 km) before subsequently ascending toward shallower depths. Crystallization of plagioclase, amphibole, Fe-Ti oxides, and small amounts of pyroxene and apatite occurred at a shallower depth (7–10 km). The presence of coarse-sieve texture, fine-sieve texture, and oscillatory zoning with high amplitude in plagioclase suggests intermittent injection of mafic magma into the shallow magma reservoir, with the eruption of dacitic magma occurring after the final mafic magma replenishment. The petrological evidence above advocates that primitive magma replenishment could have been involved in the formation and triggered the eruption of dacite in the Daliuchong volcano.

Geochemistry and origin of the Late Carboniferous ultramafic, mafic, and felsic plutonic rocks (NW Iran)

The Late Carboniferous Gharabagh-Mamkan-Mingol plutonic complex (GMMP) consists of a variety of ultramafic, mafic, felsic intrusive rocks, including the 325–315 Ma Gharabagh gabbroic, granitic, and monzonitic rocks and Mamkan-Mingol 320–315 Ma massive appinites (hornblende-rich gabbros) and 300–295 Ma layered mafic-ultramafic (gabbro, appinitic gabbro, and appinite) rocks in the northwestern Sanandaj-Sirjan zone, Iran. The relationships between various rock types in the plutonic complex are unknown. To address these issues, we conducted a detailed petrologic and geochemical study of the complex, and its country rocks.The abundance of major and trace elements and isotopic ratios of 87/86Sr (0.70379–0.70428) and 143/144Nd (0.51228–0.51245) systems showed that the Gharabagh gabbros formed from a metasomatized amphibole-bearing spinel lherzolite from an ancient subduction-modified mantle source with OIB characteristics including high contents of light rare earth elements (LREEs), Ti, Nb, Ta, and Ba, as well as low concentrations of Sr, Hf, and Zr. The geochemical data show that monzonites had high concentrations of LREEs, Ba, U, K, Hand Zr, and the low contents of Th, Nb, Ta, Sr, P, and HREEs and Eu-positive anomalies and originated from the melting of the continental crustal base in the subducted mantle wedge. The granites are similar to monzonites, with their difference being in the high concentrations of Th and Eu-negative anomalies. Combining petrographic, petrological, geochemical, and isotopic data suggests that Gharabagh plutonic rocks were formed as a result of Paleo-Tethys slab break-off, and slab sinking, during trans-tensional collision between the Central Iranian microplate and Gondwanaland during the Late Carboniferous. As a result of this event, decompression melting began in the upwelling mantle, coeval with the formation of the pull-apart basin, during major strike-slip faulting, leading to a hydrous mafic melt with about 10–12% partial melting.The Mamkan-Mingol massive and layered masses have a tholeiitic affinity. The Mamkan-Mingol rocks are characterized by different trace element patterns, especially in the concentrations of REEs and high field strength elements (HFSEs) such as Nb, Ta, Hf, Zr, and P and large-ion lithophile elements (LILEs) such as Th, U, Sr, K, Rb, and Ba. The massive and layered rocks mostly show a variably developed negative anomaly in HFSEs, and widely varying ratios of (La/Yb)n (1.0–5.2). Massive appinites and layered gabbros of GMMP originated due to different partial melting in the upwelling zone of metasomatized OIB-like amphibole-bearing spinel lherzolite and a less hydrous- to dry upwelling mantle zone, respectively, in an environment associated with the initiation of rifting, where the remnants of the Paleo-Tethys subducted slab plunges deep into the mantle. Contrasting Nd isotopic ranges are present between the massive appinites (ɛNd = +0.39) and different types of mafic-ultramafic rocks in layered outcrops (ɛNd = +1.12 to +2.07) of the complex. Based on the geochemical and isotopic (ratios of Sr, Nd, and Pb) data, we suggest that variations in of contribution of slab-derived fluids or crustal components in the primary melt caused the generation of massive appinites and different types of layered gabbros.

The relationship between total organic carbon and bottom water redox state in North American black shales

It is clear from modern analogue studies that O2-deficient conditions favor preservation of organic matter (OM) in fine-grained sedimentary rocks (black shales). It is also clear that appreciable productivity and OM flux to the sediment are required to establish and maintain these conditions. However, debates regarding redox controls on OM accumulation in black shales have mainly focused on oxic versus anoxic conditions, and the implications of different anoxic redox states remain unexplored. Here, we present detailed multi-proxy sedimentary geochemical studies of major Paleozoic and Mesozoic North American black shale units to elucidate their depositional redox conditions. This is the first broad-scale study to use a consistent geochemical methodology and to incorporate data from Fe-speciation – presently the only redox proxy able to clearly distinguish anoxic depositional conditions as ferruginous (H2S-limited) or euxinic (H2S-replete, Fe-limited). These data are coupled with total organic carbon (TOC), programmed pyrolysis, and redox-sensitive trace element proxies, with almost all measurements analyzed using the same geochemical methodology. Consistent with expectations based on previous geochemical and paleontological/ichnological studies, these analyses demonstrate that the study units were almost exclusively deposited under anoxic bottom waters. These analyses also demonstrate that there is wide variance in the prevalence of euxinic versus ferruginous conditions, with many North American black shale units deposited under predominantly ferruginous or oscillatory conditions. TOC is significantly higher under euxinic bottom waters in analyses of both preserved (present day) TOC and reconstructed initial TOC values, although sediments deposited under both redox states do have economically viable TOC content. While this correlation does not reveal the mechanism behind higher organic enrichment in euxinic environments, which may be different in different basins, it does open new research avenues regarding resource exploration and the biogeochemistry of ancient reducing environments.

Revisiting the rocks discovers turbidites and a new exploration play in the Penola Trough, Otway Basin, South Australia

As part of an integrated geological, geochemical, and geophysical study, conventionally cored intervals from the lower-most stratigraphic section of the onshore South Australian part of the Penola Trough, Otway Basin have been reviewed and reinterpreted. Three conventionally cored wells; Bungaloo-1, Jolly-1ST1 and Sawpit-2, were described using a quick-look approach to determine gross lithological and sedimentological information. Seven lithology types were observed: clay-siltstone with horizontal lamination, diamictite (claystone with horizontal lamination and dropstones), clay-siltstone with massive-horizontal lamination, silt-sandstone with horizontal lamination, sandstone with ripple lamination, sandstone with parallel lamination and sandstone with massive bedding ± rip-up clasts. The first two lithologies are interpreted as representing deposition in a cold climate, profundal-lacustrine depositional environment. The first, containing interpreted varves is the most distal and the second, containing dropstones indicates relatively colder freeze/thaw conditions. The last five lithologies are interpreted as lacustrine turbidite depositional environments, specifically Bouma sequences Te, Td, Tc, Tb and Ta, respectively. Seismic facies interpretation has identified canyon-like and mound features and interpreted them as slope-feeder channels and fan/s respectively, at and away from well control. This rock-based turbidite interpretation provides an alternative to the current alluvial channel/crevasse splay/floodplain lake model for reservoir deposition and as such presents a new exploration play. Further the reservoirs’ immediate lateral association with gas/oil-prone source rocks and seals in the clay-rich lithologies potentially provide for stratigraphic trapping in addition to the previously targeted fault-controlled structural traps.

The adsorption of cerium on synthetic δ-MnO2: Implications for Ce uptake behavior of hydrogenetic and early diagenetic ferromanganese nodules from the Western Pacific

Cerium (Ce) anomalies can be used to distinguish diagenetic and hydrogenetic nodules, making them an important discriminator for the genesis of marine ferromanganese nodules. To understand the enrichment and adsorption mechanisms of Ce in different types of ferromanganese nodules, we conducted mineralogical and geochemical studies on ferromanganese nodule layers formed through both hydrogenetic and early diagenetic processes as well as adsorption experiments on synthetic δ-MnO2 to monitor the Ce uptake during the different processes. The major and trace element contents of natural ferromanganese nodule layers were investigated by SEM, EPMA and LA-ICP-MS analysis. The marine nodule studied in this study consisted of a core of fish tooth and a rim that could be divided into the hydrogenetic (type I) and early diagenetic (type II) layers based on their mineralogy and Mn/Fe ratios. The Mn oxide mineral assemblage is composed of todorokite, buserite, birnessite, and vernadite (δ-MnO2) and occurred in both type I and II layers. The type I layer has laminated structures with a low Mn/Fe ratio (1.1–3.2; averaging at 1.7), and low Cu, Ni and Mg contents consistent with a hydrogenetic genesis. The type II layer has a columnar and stromatolitic structure with a high Mn/Fe ratio (5.1–54.0; averaging at 23.3) and high Cu, Ni and Mg contents that are similar to early diagenetic nodules. The ΣREE contents in type I and type II layers are 1405–3506 ppm (averaging at 2091 ppm) and 199–1232 ppm (averaging at 674 ppm), respectively, indicating that the REE is enriched in the hydrogenetic type I layers. Strong positive Ce anomalies are present type I layers ranging from 1.2 to 2.5 (averaging 1.9), but only slightly positive are seen in type II ranging from 0.4 to 2.4 (averaging at 1.0). Synthetic experiments to monitor the Ce uptake process show that Ce can be adsorbed onto δ-MnO2 with the XRD and FTIR patterns suggesting that the structure of δ-MnO2 did not change significantly, consistent with Ce behavior in hydrogenetic nodules. The results suggest that Ce is predominantly concentrated in hydrogenetic nodules in an oxic environment, whereas in the early diagenetic layer, there is less oxidation and fixation of Ce due to the suboxic conditions. Our findings are consistent with Ce anomalies in marine Fe-Mn nodules being the result of Mn oxide oxidation adsorption and then fixation (oxidation) after adsorption.

Granitoids of the western Himalaya and Karakoram as potential geothermal reservoirs – A petrological, geochemical and petrophysical study

Hot springs in various granitoid and gneissic complexes in northern Pakistan indicate elevated geothermal gradients, which warrants their evaluation for geothermal applications. Evaluation of such prospects requires extensive knowledge of rock properties and their interaction with reservoir fluids. Our contribution provides first-order information on petrophysical, geochemical, and petrographic descriptions derived from outcrop analogs. About seventy samples of (mostly) granitoids and gneisses from the Nanga Parbat Massif (NPM), the Kohistan-Ladakh Batholith (KLB), and the Karakoram Batholith (KB) were collected. Biotite, K-feldspar, and plagioclase in the granitoid and gneiss show weak to moderate alteration, which increases in shear zones, suggesting fracture-assisted fluid interaction. Geochemical results indicate that the gneisses and granites of the NPM are mostly peraluminous S-type and show enrichment in most LREEs and depletion in HREEs. In addition, depleted Sr and Ba and enriched Rb and U in granites indicate partial melting and high fractionation. On the contrary, granitoids from the KLB are of calc-alkaline I-type and characterized by the depletion of REEs and the enrichment in Ba and Sr. The granitoids of the KB, due to their different magmatic histories, are more diverse, ranging from older I-type calc-alkaline granodiorite, and younger I-type alkaline syenite and S-type calc-alkaline granite. They show an overall enrichment in HREEs along with Ba, Th, Ta, Sr, and Lu. Allanites from syenite of the KB show significant concentrations of Th and U.Petrophysical measurements reveal low matrix porosities (0.6–3.5 %), with primarily average thermal conductivities (1.48–3.37 W m−1K −1) and thermal diffusivities (0.68–1.95 ∙10–6 m2 s−1), with minor variation in specific heat capacities (744–767 J kg−1 K−1). The NPM displays higher average thermal conductivity, thermal diffusivity, and lower porosity than the KB, while the petrophysical properties of the KLB range between these two domains.The geothermal systems in the area operate due to the thickening of a granitoid-dominant crust, which is enriched with radiogenic elements. The fault zones provide channels for meteoric water to access deeply these hot and thermally conductive rocks in the subsurface. After heat exchange, the water is discharged back to the surface as hot springs. The present data set provides a better understanding of regional geothermal regimes from petrological, geochemical, and petrophysical perspectives and assists in numerical modeling for potential geothermal assessment.

Organic geochemical study of Aleksinac oil shale

Organic geochemical study of Aleksinac oil shale

Geochemistry and mineralogy of modern floodplain Nile sediments of Sohag area, Egypt: an environmental perspective

Understanding the characteristics of modern floodplain sediment (MFS) is important for geomorphological, paleoclimatic, sedimentation, and environmental investigations. We collected samples from present floodplain Nile sediments in Egypt’s Sohag area and used mineralogical and geochemical (i.e., major and trace elements) proxies to investigate the characteristics and establish their provenances, climatic conditions during deposition, and weathering influence. The study revealed that the Nile floodplain sediments are composed mainly of silt (26–77%), clay fraction (7–44%), and sand content (3–63%), and their texture is classified as clayey silt. These sediments are classified geochemically as greywacke to shale. The mineralogical studies revealed two main assemblages of heavy minerals: the first assemblage represented by magnetite, goethite, zircon, epidote, and garnet and reflects the basement complex in the Eastern Desert and its surrounding rocks; and the second assemblage of goethite, pyroxene, hornblend, and mica of fooldplain deposits derived from the Ethiopian highlands. The geochemical studies indicate that the Nile sediments are immature and formed due to the moderate degree and nonsteady chemical weathering of the parent rocks. The geochemical studies show different mixed sources of sediments, where fine sediments are mostly mafic igneous with a partial contribution from siliscic sedimentary rocks, while the coarser ones are derived mainly from siliscic sedimentary and acidic igneous rocks. The sediments of the presented modern fooldplain reflected two different tectonic setting source areas (collision and continental rift tectonic setting for high silica and low silica samples, respectively) that were shared in supplying the sediments to the present basin. The study revealed that the investigated area may become desertified as a result of climate change and human activities such as salinity, fertiliser use, sand encroachment, and pollution.

Combustion Completeness and Sample Location Determine Wildfire Ash Leachate Chemistry

AbstractUnderstanding past fire regimes and how they vary with climate, human activity, and vegetation patterns is fundamental to the mitigation and management of changing fire regimes as anthropogenic climate change progresses. Ash‐derived trace elements and pyrogenic biomarkers from speleothems have recently been shown to record past fire activity in speleothems from both Australia and North America. This calls for an empirical study of ash geochemistry to aid the interpretation of speleothem palaeofire proxy records. Here we present analyses of leached ashes collected following fires in southwest and southeast Australia. We include a suite of inorganic elemental data from the water‐soluble fraction of ash as well as a selection of organic analytes (pyrogenic lipid biomarkers). We also present elemental data from leachates of soils collected from sites in southwest Australia. We demonstrate that the water‐soluble fraction of ash differs from the water‐soluble fraction of soils, with trace and minor element concentrations in ash leachates varying with combustion completeness (burn severity) and sample location. Changes in some lipid biomarker concentrations extracted from ashes may reflect burn severity. Our results contribute to building a process‐based understanding of how speleothem geochemistry may record fire frequency and severity, and suggest that more research is needed to understand the transport pathways for the inclusion of pyrogenic biomarkers in speleothems. Our results also demonstrate that potential contaminant loads from ashes are much higher than from soils, with implications for the management of karst catchments, which are a critical water resource.

Geochemistry and mineralogy of beach sediments in the northern Gulf of Mexico, Tamaulipas state, Mexico: implication for provenance

Geochemical and mineralogical studies were performed in the La Pesca (LP) and Tesoro Altamira (TA) beach sediments, located in the Tamaulipas state, northern Gulf of Mexico. The main aim of this study is to infer the weathering history and provenance and to discriminate the tectonic environment of the beach sediments. The sediments are composed of quartz with small amounts of accessory minerals such as plagioclase, calcite, orthoclase, microcline, and zircon. Both beach sediments are classified as fine-grained and very well sorted, however LP has coarse skewed and leptokurtic sediments, whereas TA has fine-skewed and very leptokurtic sediments. The chemical index of weathering (CIW’) indicates intense weathering in the source area. The quartz grain microtextures in the LP and TA are classified into mechanical, chemical, and mechanical/chemical origin. Mechanical features such as fractures, pits, percussion marks, abrasion fatigue, and V-shaped marks favor high-energy littoral, fluvial, subaqueous-marine, and aeolian environments. The chemical features indicate solution pits and crystalline overgrowth, which suggests a silica saturated marine environment. The mechanical/chemical features display adhering particles and elongated depressions suggest formation in a sub-aqueous nearshore marine environment. Major and trace elements-based provenance discrimination diagrams indicate a felsic source derived from the Mesa Central (MC), Sierra Madre Oriental (SMOr) and Oaxaquia terranes. The major and trace element concentrations imply a passive margin setting for the northern Gulf of Mexico, which is consistent with the general geology.