Post-Archean Australian Shale Research Articles

New geochemical evidence constraining the water-rock-gas interaction on geothermal fluids of the Querétaro Graben, northern Trans-Mexican Volcanic Belt

This study examines the water-rock-gas interaction of the Los Geysers geothermal system in the northern Trans-Mexican Volcanic Belt (TMVB). Physico-chemical parameters, δ13C of total dissolved inorganic carbon (TDIC), and Rare Earth Elements (REE) composition on 14 thermal water discharges are reported and discussed. Waters had temperatures ranging from 40 °C to 98 °C, pH from 7.4 to 9.2, and total dissolved solids from 598 mg L−1 to 992 mg L−1. Signals of thermophilic biota, mainly diatom frustules, were found in the suspended particulate matter of spring waters. The range of δ13CTDIC was between −7.55‰ and −4.13‰ (avg. −7.10‰). Although potentially affected by secondary processes, the dissolved C species of the studied waters likely have a predominant deep, mantle-related component. The lanthanoids concentrations (∑REE) were variable over practically one order of magnitude, with average values between 1463 pmol L−1 for Ce and 9 pmol L−1 for Lu. Post-Archean Australian Shale (PAAS)-normalized patterns showed a slight enrichment in middle lanthanides, numerically expressed as [Sm/La]N and [Sm/Yb]N, ranging from 1.43 to 2.06 and 0.84 to 2.03, respectively. We propose that the overall signature of the REE is inherited during the regional migration of the liquid and from the primary aquifer. Moreover, PHREEQC computer code was run to calculate the dominant REE complexing ligands in the geothermal system at different temperatures. Our calculations indicate that F− complexes dominate over CO3 species at outlet temperatures, but oxyhydroxide complexes (REE-O2H, REE-O2–, and REE-O⁺) act as sinks after leaching from the source rock. The 143Nd/144Nd ratio of one of the studied samples was measured (0.512320 ± 0.000019; εNd = −6.20 ± 0.37, 2s.e.). The conceptual model in this paper highlights a mixing waters process between geothermal waters and cold shallow waters in the Queretaro Graben.

Indicator role of rare and rare-earth elements of the Northwest manganese ore occurrence (South Africa) in the genetic model of supergene manganese deposits

The authors analyzed the content of a number of rare and rare-earth elements in the rocks of the Northwest manganese ore occurrence, confined to the Neoarchean dolomites of the Malmani series of the Transvaal Basin. 30 samples of manganese ores and host rocks were analyzed by ICP-MS and XRF methods. Average values of Post-Archean Australian Shale (PAAS) were used as the geochemical standard for data calculation and normalization. The concentrations of elements normalized on PAAS reveal the LREE anomaly in manganese ores. Positive Ce and negative Y–anomalies indicate the hydro-genetical type of sedimentation of ore minerals from manganese-bearing aqueous solutions. This is consistent with the ratios of the elements: Ce and Y SN/Ho SN, Ce and Nd, Fe – Mn – (Co + Ni + Cu) × 10. A clear correlation between the contents of rare-earth elements in manganese nodules and the underlying Malmani dolomites indicates their close genetic relationship. Negative Ce and positive Y–anomalies in manganese wad minerals indicate differences in the conditions of their formation. The manganese wad formed earlier than the rest of the ore with the active participation of microorganisms.

Geochemical comparisons of weathering, provenance and tectonics in the fluvial sediments from Yarlung Zangbo to Brahmaputra River

Globally, large river sediments record crucial signatures of geology and climate change from source to sink. The Yarlung Zangbo River (YZR) is upstream of the Brahmaputra River (BJR). It originates in the active Himalaya-Tibetan Plateau (HTP) and finally enters the Indian Ocean. Therefore, YZR-BJR sediments are best for studying Earth surface processes and climate variations in Asia. However, few comparisons of their sediment chemistry have been conducted with respect to the weathering, climate, provenance and tectonic setting. Here, we examined 80 fluvial sediments measuring major and trace elements with chemical indicators. The YZR-BJR sediments are derived from a felsic source on an active continental margin with a continental island arc. Both the Lhasa terrane (LT) and Himalayan orogen are possibly the main sources of upstream (YZR) sediments that are chemically close to the upper crustal continent (UCC). In contrast, downstream BJR sediments, such as the post-Archean Australian Shale (PAAS), are predominantly sourced from the eastern Himalayan orogen, followed by LT. Due to the uplift of HTP and global cooling, the YZR sediments underwent low to moderate silicate weathering, while the downstream BJR sediments experienced weaker weathering processes with lower chemical index of alteration (CIA) values. This means dominant physical weathering and erosion in the source area and thus provides substantial sediments. Although the CIA values of finer overbank sediments are slightly higher than those in coarser riverbank sediments, they can still reveal weathering combined with other chemical indicators. The results suggest that there is no obvious contrast between YZR and BJR in the HTP due to river mixing and strong physical weathering.

Assessment of potentially toxic elements (PTEs) sources on soils surrounding a fossil fuel power plant in a semi-arid/arid environment: A case study from the Sonoran Desert

Understanding the sources of potentially toxic elements (PTEs) in soils is a worldwide challenge that requires effective discrimination between geogenic and anthropogenic contributions, particularly in areas with certain geological complexity. This study aims to examine the chemical contents of 23 topsoil samples collected from the surroundings of a fossil fuel power plant in the village of Puerto Libertad (Sonoran Desert, Mexico). The study did not exclusively focus on the source identification of the priority PTEs to evaluate soil pollution. Furthermore, major oxides and immobile trace element (Zr, Hf, and REE: La→Lu) data were provided for a reliable assessment of the provenance of the soils. The relatively high SiO2 contents (65.26–75.42 wt%, anhydrous basis), the Post-Archean Australian Shale (PAAS)-normalized REE patterns, and the uniformity of the values of the Index of Compositional Variability (ICV = 1.11–2.72) and the Chemical Index of Alteration (CIA = 31.65–51.79) suggest that the soils were derived from intermediate to felsic source rocks, controlled by the local weathering of the parent bedrocks, under a low degree of chemical weathering conditions. The PTE data were treated following a robust workflow, which included the use of the enrichment factor (EF), the Spearman rank correlation (ρ), and multivariate statistical analyses allowed the generation of significant elemental associations and the identification of pools related either to the geological background or to anthropogenic activities. The results suggesting that Mo and Zn concentrations present a moderate anthropogenic influence while the concentrations of Pb, Sn, Cu, Cd, As, Cr, and Co are predominantly of geogenic origin. Vanadium (avg. EFV = 3.4) and Ni (avg. EFNi = 4.6) were the most enriched elements in the soils. Moreover, the highest values of the integrated Nemerow Pollution Index (PIN>3) were recorded at the sampling stations closer to the village, suggesting point-source pollution by the emissions of the power station. Finally, in this paper is traced the extent of the particulate released into the atmosphere, which can be dispersed in a wide area into the Sonoran Desert.

Characteristics and formation mechanism of mesogenetic dissolution: A case study of Ordovician carbonate in the western slope of the Shulu Sag, Jizhong Depression, Bohai Bay Basin

Mesogenetic dissolution has the potential to enhance the quality of carbonate reservoirs, and thus it is critical to identify the source of corrosive fluids and establish the mechanism that leads to mesogenetic dissolution. An integrated study using cores, thin sections, seismic profiles, and geochemistry was performed to investigate the characteristics, discuss the possible corrosive fluids, and establish the formation mechanism of mesogenetic dissolution in Ordovician carbonates in the western slope of the Shulu Sag, Bohai Bay Basin. The Shulu Sag underwent a four-stage growth history, and the carbonate rocks in the study area experienced three episodes of diagenetic alteration (i.e., syngenetic, telogenetic, and mesogenetic). The micro- and macroscopic occurrences of mesogenetic dissolution were ubiquitous, including, for example, stylolites, solution seams, tiny pores, laminar dissolution pores, dissolution pores and vugs associated with stylolites, dissolution enlarged fractures, erosion of late minerals (e.g., saddle dolomite), and related hydrocarbon inclusions. The partition patterns of trace elements normalized to Upper Crust Continent (UCC) and rare earth elements (REEs) normalized to Post-Archean Australian Shale (PAAS) were consistent between eroded and uneroded samples. Compared with uneroded samples, eroded samples had higher contents of some trace elements (e.g., Co, Cr, Cu, Ni, V, and Zn) and REEs, and relatively higher average δ13C values and 87Sr/86Sr ratios. These characteristics indicate that the most likely corrosive fluids causing dissolution were organic acids in hydrocarbon-bearing fluids, which may have been derived from the maturation of organic matter in marlstone in the lower part of the Sha3 member (Es3l). The combination of the tilted basin structure and presence of good conduits (i.e., unconformity, stylolites, and fractures) promoted the migration of corrosive fluids and the occurrence of mesogenetic dissolution in Ordovician reservoirs from the Neogene-Quaternary period to the present. A geologic model for the formation mechanism of mesogenetic dissolution has been proposed, which provides new insight for future hydrocarbon exploration.

Petrographic and geochemical features of Gimo marble, Gole area, Kurdistan Region, Iraq: constraints on its protolith's origin and depositional environment

It is essential to identify marbles' petrographic and geochemical characteristics to determine the palaeo-environmental settings where their carbonate protoliths formed. The petrogenesis of massive Gimo marbles in the Gole area, Kurdistan Region of northeast Iraq, was investigated in this study through a combination of field mapping, petrographic, and geochemical techniques. Petrographic examination of these marbles reveals that mineral compositions are similar in all samples, with both homeoblastic and mosaic textures occurring, in addition to opaque grains that provide evidence of mineralization. Geochemical analyses show that the average calcium carbonate content of the marble is 94.96%; hence, the marble is lithologically characterized as a pure calcite marble. In most samples, the silica content was below 2 wt.%, with high values related to quartz veinlets. A range of geochemical indices and Post-Archean Australian Shale (PAAS–normalized rare earth element (REE) patterns) suggest that the limestone protolith was deposited in a shallow, near-shore marine environment on a continental margin, with very low input of detrital material. The negative Ce anomalies indicate that the protoliths of the Gimo marbles were carbonate rocks of a sedimentary origin.

Geochemical behavior and fractionation characteristics of rare earth elements (REEs) in riverine water profiles and sentinel Clam (Corbicula fluminea) across watershed scales: Insights for REEs monitoring

The increasing global demand for rare earth elements (REEs) has led to their recognition as emerging contaminants; however, the effect that biota have on the cycling of these elements at the watershed scale is not currently well understood. In this study, water samples and field freshwater clams Corbicula fluminea were concurrently collected along watershed gradients, and concentration profiles of 14 naturally occurring REEs were measured in operationally defined water fractions and soft tissues of the freshwater clams. Moreover, Post Archean Australian Shale (PAAS) normalized REE patterns, fractionation indices, and anomalous values were determined to further extract characteristic features. As a result, both the water and biological samples had variable REE compositions, with higher concentrations of light REEs (LREEs) than middle REEs (MREEs) and heavy REEs (HREEs), while decreasing concentrations were generally observed as filter pore size decreased, implying that large colloidal and particulate fractions were important carriers of REEs. The spatial distribution patterns of REEs revealed a clear site effect among profiles, with variability more pronounced among watersheds and with peaks in sites from a small watershed near the hotspots of the mining area, and then exhibited a decreasing trend with distance from there. Meanwhile, significant bioaccumulation of REEs was observed potentially reflecting different degrees of contamination gradients among the watersheds. The PAAS-normalized distribution patterns tended to be slightly enriched in MREEs, producing a peculiar “roof-shaped” feature and characteristic fractionation. Remarkably, bio-concentration factors (BCFs) highlighted the importance of large colloidal and particulate phases in assessing biologically available REEs for filter-feeding species. Collectively, our study strongly favored that accumulation patterns and fractionation characteristics of REEs in C. fluminea can serve as a reliable indicator of geochemical behavior, providing a promising biomonitoring tool to quantitatively denote different degrees of REE contamination and assess possible impacts in mining watersheds.

Isotopic and geochemical constraints on the protolith, redox state and paleo-tectonic setting of the Malagarasi Supergroup of north-western Tanzania

We report detrital zircon U–Pb ages, radiogenic Sm–Nd isotopic compositions, major and trace element compositions of the intra-plate extensional rhomb-shaped Neoproterozoic Malagarasi Supergroup of north-western Tanzania in order to elucidate the paleo-tectonic setting, source rocks chemistry and paleo-oxygenation in the basin. Assuming that provenance trace element proxy ratios, including the rare earth elements (REE) contents, behave as closed systems during sedimentation and diagenesis, we suggest that the detritus for the Malagarasi Supergroup originated from more felsic rocks than those for upper crustal composites (i.e. Post-Archean Australian Shale; PAAS, Proterozoic Shale; PS). This observation is also supported by enriched chondrite-normalized light REE (La/SmCN = 2.36–7.84; mean = 3.85), overall negative Eu anomalies (Eu/Eu* = 0.56–0.93; mean = 0.69) and flat heavy REE patterns (Gd/YbCN = 1.01–2.04; mean = 1.47). Paleo-weathering proxies using the Chemical Index of Alteration (CIA ~59–78%) protocol indicate an overall moderate weathering intensity in the basin. V/Cr ratios (mean = 1.18; range = 0.48–1.69) coupled with intra-sample Ce anomalies reveal an overall oxidizing state during deposition. Mantle extraction ages (TDM = 1594–2394 Ma) suggest a diverse mixing of protolith terranes including Archean (Tanzania craton), Eburnian (Ubendian Belt) and possibly the nearby Mesoproterozoic Kibaran Belt. Radiogenic laser ablation detrital zircon U–Pb ages of between 1826 and 2656 Ma may preclude contribution from the Kibaran. Given that Nd systematics in sedimentary rocks provide mixing ages of different hinterland source rocks (1594–2394 Ma; in our study), we suggest relatively juvenile sources such as the local post-orogenic effusive bodies farther south of the basin in the realm of Rodinia Supercontinent. Thus, a northerly flow direction of the of the proto/paleo river system in the region is inferred.

Major and Trace Element Geochemistry of the Permian-Triassic Boundary Section at Meishan, South China

We report extensive major and trace element data for the Permian-Triassic boundary (PTB) at Meishan, China. Analyses of 64 samples from a 2.5 m section span the last 75 kyr of the Permian and the first 335 kyr of the Triassic, from beds 24 to 34. We also report data for 20 acetic acid extracts that characterize the carbonate fraction. Whole rock major element data reflect the change of lithology from carbonate in the Permian to mudstone and marl in the Triassic, indicate an increase of siliciclastic input and MgO in and above the extinction interval (beds 24f–28), and silica diagenesis in carbonates below the extinction horizon. Above bed 27, enrichment factors calculated with respect to Al and Post-Archean Australian Shale (PAAS) are ∼1 for most trace elements, confirming that siliciclastic input dominates trace element distributions in the Triassic. Within the extinction interval, beds 24f and 26 show increases in As, Mo, U and some transition metals. V, Cr, Co, Ni, Cu, Zn, Pb, and Ba are variably enriched, particularly in bed 26. Below the extinction interval, the top of bed 24d shows enrichment of V, Cr, Co, Ni, Cu, Zn, Pb, and Ba in a zone of diagenetic silicification. Trace elements thus reflect siliciclastic input, diagenetic redistribution, and responses to redox conditions. Trace element patterns suggest either a change in provenance of the detrital component, or a change in the proportion of mechanical to chemical weathering that is coincident with the beginning of the extinction in bed 24f. Ba, Zr, and Zn behave anomalously. Ba shows little variation, despite changes in biological activity and redox conditions. The enrichment factor for Zr is variable in the carbonates below bed 24f, suggesting diagenetic Zr mobility. Zn shows a sharp drop in the extinction horizon, suggesting that its distribution was related to phytoplankton productivity. Rare earth element content is controlled by the siliciclastic fraction, and carbonate extracts show middle rare earth enrichment due to diagenesis. Ce and Eu anomalies are not reliable indicators of the redox environment at Meishan.

Genesis of REY-rich deep-sea sediments in the Tiki Basin, eastern South Pacific Ocean: Evidence from geochemistry, mineralogy and isotope systematics

Deep-sea sediments in the eastern South Pacific Ocean were recently found to contain high concentrations of rare-earth elements and yttrium (REY). To understand the genesis of REY enrichment in the sediments, we performed detailed element and isotope geochemical analyses on samples from gravity core S028GC23 recovered from the Tiki Basin in the eastern South Pacific Ocean.The REY-rich sediments in core S028GC23 are dark-brown to black zeolite clays, with REY (∑REY) contents of 1136–2213 ppm (average of 1857 ppm). The ∑REY contents in the sediments are positively correlated with P2O5 and negatively correlated with Ce anomalies. The REY-rich sediments display obvious Ce depletion and positive Y anomalies in the post-Archean Australian shale (PAAS)-normalized REY diagrams. Bioapatite fossils contain the highest REY concentrations (average of 8921 ppm) among the constituents, indicating that they are the primary hosts of REY. The REY enter through the roots and diffuse to the tops in the bioapatite fossils. Fe–Mn micronodules are divided into two different types based on Ce and Y anomalies in the PAAS-normalized REY patterns, and they have average REY concentrations of 781 ppm and 937 ppm, respectively. The phillipsite has low REY contents (average of 106 ppm) and is associated with a low sedimentation rate. REY patterns and Sr-Nd isotopic signatures show that seawater was the main ore-forming fluids during the formation of REY-rich sediments. The sedimentation rate of the sediments calculated by the 230Thex activities was 0.8 mm/Ka. The REY accumulation process can be explained by two-stage fluid-bioapatite fossil interactions and small contributions of Fe-Mn micronodules in an oxidized environment with slow sedimentation rate.

Depositional Environment and Genesis of the Nabeba Banded Iron Formation (BIF) in the Ivindo Basement Complex, Republic of the Congo: Perspective from Whole-Rock and Magnetite Geochemistry

The Nabeba high-grade iron deposit (Republic of the Congo) is hosted by banded iron formation (BIF) in the Ivindo Basement Complex, which lies in the northwestern part of the Congo Craton. The Nabeba BIF is intercalated with chlorite-sericite-quartz schist and comprises two facies (oxide and a carbonate-oxide). In this study, whole-rock and LA-ICP-MS magnetite geochemistry of the BIF was reported. Magnetite samples from both BIF facies had fairly similar trace element compositions except for the rare earth element plus yttrium (REE + Y) distribution patterns. The high V, Ni, Cr, and Mg contents of the magnetite in the Nabeba BIF could be ascribed to the involvement of external medium-high temperature hydrothermal fluids during their deposition in relatively reduced environment. The Post-Archean Australian Shale (PAAS)-normalized REY patterns of the Nabeba BIF magnetite were characterized by LREE depletion coupled with varying La and positive Eu anomalies. Processing of the information gathered from the geochemical signatures of magnetite and the whole-rock BIF suggested that the Nabeba BIF was formed by the mixing of predominantly anoxic seawater (99.9%) with 0.1% of high-temperature (>250 °C) hydrothermal vent fluids, similar to the formation mechanism of many Archean Algoma-type BIFs reported elsewhere in the world.

Paleoclimatic variability in the southern Tethys, Egypt: Insights from the mineralogy and geochemistry of Upper Cretaceous lacustrine organic-rich deposits

The effect of paleoclimate during global warming periods on Upper Cretaceous lacustrine deposits is not fully understood. In this study, comprehensive sedimentological, mineralogical, and geochemical data were used to unravel the past climatic changes and their influence on the accumulation of Campanian lacustrine organic-rich deposits in Egypt. Three sedimentary lithofacies associations are recorded within the uppermost part of the Quseir Formation. The laminated clay-rich mudstone lithofacies has the highest organic matter (TOC up to 1.2 wt.%). Sedimentological observations indicate that the bulk lithologic assemblage was originated in a shallow lacustrine setting. The studied samples consist of clay minerals, quartz, pyrite, carbonate, fluorapatite, and halite. The siliciclastic content reaches up to 78wt.%, whilst the carbonate content ranges from 3 to 22 wt.%. Compared to Post-Archean Australian shales (PAAS), the studied samples are significantly rich in Mg, Ca, P, Al, V, Ga, and Cr contents. The mudstone samples are characterized by high ratios (C-value, CIA, CIW, Mg/Ca, Fe/Mn, Ga/Rb) and low values (K2O/Al2O3), reflecting relatively warm and humid conditions during deposition of these sediments. The prevalence of smectite, as well as the sedimentary features, support that the lacustrine organic-rich mudstones are mainly deposited under warm seasonal climate (arid/humid). Additionally, the presence of dolomite and halite along with the Sr/Ba ratios (1.30–2.13), strongly suggest a saline water setting. The changes between aridity and humidity periods are probably the main reason for the significant variation in water chemistry, especially salinity. Therefore, the paleoclimatic variations largely controlled the depositional process during the formation of the Upper Cretaceous lacustrine organic-rich mudstones in the southern Tethys.

Major and Trace Element Characteristics of the Average Indian Post-Archean Shale: Implications for Provenance, Weathering, and Depositional Environment

We estimate the average chemical composition of Indian post-Archean Shale (IPAS) and conclude that it is comparable to that of global shale standards: post-Archean Australian Shale (PAAS) and North...

Provenance tracing of dust using rare earth elements in recent snow deposited during the pre-monsoon season from mountain glaciers in the central to northern Tibetan Plateau.

To provide insight into dust sources in snow deposited during the non-monsoon period on the Tibetan Plateau, detailed post-Archean Australian shale (PAAS)-normalized rare earth element (REE) distribution patterns and variations in REE tracers, such as La/Yb, La/Er, and Gd/Yb with depth, as well as the distribution of samples in the plots of REE ratio pairs, such as La/Yb vs. Y/ΣREE, La/Er vs. Gd/Er, and Y/La vs. Nd/Er, were compared in seven potential dust source areas in Asia. Snow samples from five glaciers, i.e., Qiumianleike (QMLK), Meikuang (MK), Yuzhufeng (YZF), Xiaodongkemadi (XDKMD), and Gurenhekou (GRHK), were collected from April 26 to May 13 before the onset of monsoon activity. The results show that dust trapped in snow pits from the studied glaciers, i.e., QMLK, MK, XDKMD, and GRHK, has varying degrees of contribution from the Taklimakan Desert, Qaidam Basin, and the surface soil of the Tibetan Plateau. There are signals of the Tengger and Badain Jaran Desert and Chinese Loess in the MK and XDKMD snow pit samples or in the QMLK and GRHK surface samples from the REE tracers; however, from the point of view of the land location, the three dust sources should not be the major contributors. Signals of dust from the Indian Thar Desert were occasionally detected from the MK, YZF, and XDKMD snow pit samples and GRHK surface snow samples, implying the intrusion of early Indian monsoon activities to the sites. The dust signal from the Thar Desert in India from the YZF glacier is significantly greater than that from the XDKMD and MK glaciers. These findings were also supported by the tracer of dust transmitted to the three snow pits through the air mass backward trajectories. The new finding of this study is that dust from the Indian Desert can even reach the Kunlun Mountains in the northern region of the Tibetan Plateau. The conclusions are helpful in interpreting the sources of dust and the pollutants absorbed by dust particles, as well as the extent of the impact of Indian monsoon activities at the end of the non-monsoon season on the plateau.

Paleogeographic Characteristics of the Mengyejing Formation in the Simao Basin during Its Depositional Period and Its Indication of Potash Mineralization: A Case Study of MZK-3 Well

In China, pre-Quaternary solid potash deposit has only been discovered in the Simao Basin, and the Lower Cretaceous Mengyejing (MYJ) Formation (Fm.) is the productive layer of potash deposit. In this study, we investigated the clay conglomerates which are distributed in upper and lower members of the potash-bearing salt rock layer. We analyzed the relative contents of major elements (Al2O3, Fe2O3T, MgO, CaO, Na2O, K2O) and trace elements (B, Ba, Co, Cr, Cu, Ga, Mn, Ni, Rb, Sr, V, Zn, Zr) in the samples. The results show that MgO and CaO in the major elements are rich relative to Post Archean Australian Shale (PAAS), whose average enrichment factor values of the MgO (EFMgO) is 2.61 and CaO (EFCaO) is 4.57, and the others major elements are relatively minor; trace elements (B, Ga, Mn, Zr) are rich relative to PAAS, and the others trace elements are minor relative to PAAS. The study of paleogeographic conditions using various parameters shows that the paleoclimate is generally dry and hot during the period of clay conglomerate deposition, but it was warm and humid in certain periods; the main sedimentary environment is weak oxidation condition with strong oxidation conditions in individual periods; the average value of paleosalinity is ~21‰, and the highest is no more than ~92‰. The significance of the paleogeographic characteristics of MYJ Fm. to potash mineralization are as follows: (1) they indicates that the clay conglomerates of MYJ Fm. are not clastic sediments in brine formed by seawater, because the paleosalinity of clay conglomerates deposition period is obviously lower than that of seawater; (2) MYJ potassic salt ore is not formed by evaporation and concentration of seawater in clay conglomerates in the sedimentary basin, because there is no carbonate rock and sulfate rock of corresponding scale after the deposition of clay conglomerates in the basin; (3) clay conglomerates of MYJ Fm. were deposited in continental shallow water basin; (4) the matter source of potash minerals is deep marine strata; (5) in the MYJ Fm. sedimentation period, deep source salt moved to the surface under the background of extensional structure, and the subsequent sedimentary clastic rock formed a protective layer of potash-bearing rock, thus completing the “deep source and shallow mineralization” metallogenic process.

Direct determination of rare earth elements in natural water samples by inductively coupled plasma tandem quadrupole mass spectrometry with oxygen as the reaction gas for separating spectral interferences

Rare earth elements (REEs) were measured by inductively coupled plasma tandem quadrupole mass spectrometer (ICP-MS/MS) with oxygen as the reaction gas to achieve monoxide ions of REEs for separating from spectral interferences. Production rates of REEs' monoxide ions were improved by optimization of the octopole bias voltage for the reaction cell of the ICP-MS/MS. The optimized operating conditions provided instrumental detection limits from 0.004 pg mL−1 of Er to 0.26 pg mL−1 of Nd and permitted the direct determination of REEs in natural river water and lake water samples. Analytical results of REEs in a certified reference material (SLRS-4) were in coincidence with reported values, which confirmed the validity of the method. Compiled values for REEs in SLRS-4 were calculated based on the present results and reported data. Isotope dilution was applied to the determination of Gd, Dy, Er, and Yb in SLRS-4, which results confirmed the accuracy of the compiled values. REEs in multiple river water samples and a lake water sample were determined, covering a range from 0.24 pg mL−1 of Tm to 130.9 pg mL−1 of Ce. The results of REEs in natural water samples were evaluated by normalization to the concentrations of REEs in post Archean Australian shale (PAAS).

Depositional and Environmental Constraints on the Late Neoarchean Dagushan Deposit (Anshan-Benxi Area, North China Craton): An Algoma-Type Banded Iron Formation

Abstract The late Neoarchean, ~2.53 to 2.51 Ga Dagushan banded iron formation (BIF), is a typical Algoma-type BIF located in the northeast part of the North China craton. Despite having undergone upper greenschist to lower amphibolite facies metamorphism, the Dagushan BIF retains evidence of varied depositional facies, making it an ideal archive to evaluate the paleomarine environment and the paragenesis of the ore minerals. A transition from oxide to silicate to carbonate facies BIF is evident in a northward direction. The mineralogical composition shifts from magnetite and quartz in the south through a magnetite-quartz-cummingtonite/stilpnomelane assemblage in the transition zone to magnetite-siderite in the north. Such a distinct distribution of mineralogical facies correlates well with the depositional environment of the BIF. The carbonate facies BIFs formed in a near-shore, proximal environment, whereas the oxide and silicate facies BIF assemblages formed in deeper waters, distal to the paleoshoreline. The BIF samples display characteristic seawater-like rare earth element + yttrium (REE + Y) profiles with positive La and Y anomalies and heavy REE enrichment relative to the light REEs when normalized to post-Archean Australian shale. Positive Eu anomalies suggest a high-temperature hydrothermal contribution to the BIF. The absence of a negative Ce anomaly in nearly all samples, coupled with positive δ56Fe in magnetite in all mineralogical facies, indicates a dominantly anoxic water column contemporaneous with deposition of the BIF. At ~2.53 Ga in the Anshan area, seawater was mostly anoxic and rich in ferrous iron. Dissolved ferrous iron in upwelling hydrothermal fluids was oxidized and precipitated as Fe(III) oxyhydroxides in the photic zone leading to BIF formation. Proximal to hydrothermal vents, magnetite formed via the reaction of Fe(III) oxyhydroxides and aqueous Fe(II) supplied from the hydrothermal fluids and microbial dissimilatory iron reduction (DIR) coupled to organic carbon oxidation. Proximal to a paleoshoreline, siderite formed through DIR, as evidenced by the depleted δ13C values and the presence of graphite. Silicates, such as stilpnomelane and cummingtonite, are considered to be the metamorphic products of early diagenetic silicates (e.g., nontronite) that formed in the water column from admixtures of Fe(III) oxyhydroxides and amorphous silica.

Provenance of Lower Carboniferous Bauxite Deposits in Northern Guizhou, China: Constraints from Geochemistry and Detrital Zircon U-Pb Ages

The Lower Carboniferous Jiujialu Formation bauxite deposits of northern Guizhou Province, China, are a Kazakhstan subtype of karst bauxite deposits. The provenance of the Jiujialu Formation has long been debated, with uncertainty about the formation of the bauxite deposits. Here we report new geochemical data that indicate the affinity between the Lower-Middle Ordovician clastic rocks and argillaceous dolostones and the overlying Carboniferous bauxite deposits, all of which are characterized by high Al2O3, K2O, and ΣREE contents, flat post-Archean Australian shale (PAAS)-normalized REE patterns, and uniform immobile element ratios (TiO2/Al2O3, Nb/TiO2, and Zr/TiO2). Their similar detrital zircon age distributions further indicate the link between the bauxite deposits and the clastic rocks and argillaceous dolostones. Zircon age spectra of clastic rocks of the Lower Silurian Hanchiatien Formation in northern Guizhou match those of the bauxite deposits, with a maximum age peak at ∼980 Ma and other secondary age peaks, suggesting these clastic rocks may represent the provenance of the bauxite deposits. The youngest detrital zircons (∼445 Ma) occur only in the bauxite deposits and are probably sourced from K-bentonite beds of the Ordovician-Silurian transition. Our analyses indicate that the source materials of the bauxite deposits in the Jiujialu Formation are of mixed provenance: Lower-Middle Ordovician aluminosilicate rocks and argillaceous dolostones of the underlying strata, and Lower Silurian clastic rocks and K-bentonite from adjacent areas. A comparison of Early Carboniferous bauxitic provenances in northern and central Guizhou indicates that paleotopography was the major factor controlling the provenance of these bauxite deposits.

Geochemistry and zircon U-Pb ages of the Oligocene sediments in the Baiyun Sag, Zhujiang River Mouth Basin

In this study, element geochemistry and zircon chronology are used to analyze the Oligocene sediments in the Baiyun Sag, Zhujiang River Mouth Basin. The experimental results are discussed with respect to weathering conditions, parent rock lithologies, and provenances. The chemical index of alteration and the chemical index of weathering values of mudstone samples from the lower Oligocene Enping Formation indicate that clastic particles in the study area underwent moderate weathering. Mudstone samples exhibit relatively enriched light rare earth elements and depleted heavy rare earth elements, “V”-shaped negative Eu anomalies, and negligible Ce anomalies. The rare earth element distribution curves are obviously right-inclined, with shapes and contents similar to those of post-Archean Australian shale and upper continental crust, indicating that the samples originated from acid rocks in the upper crust. The Hf-La/Th and La/Sc-Co/Th diagrams show this same origin for the sediments in the study area. For the samples from the upper Enping deltas, the overall age spectrum shows four major age peaks ca. 59–68 Ma, 98–136 Ma, 153–168 Ma and 239–260 Ma. For the Zhuhai Formation samples, the overall age spectrum shows three major age peaks ca. 149 Ma, 252 Ma and 380 Ma. The detrital zircon shapes and U-Pb ages reveal that during Oligocene sedimentation, the sediments on the northwestern margin of the Baiyun Sag were supplied jointly from two provenances: Precambrian-Paleozoic metamorphic rocks in the extrabasinal South China fold zone and Mesozoic volcanic rocks in the intrabasinal Panyu Low Uplift, and the former supply became stronger through time. Thus, the provenance of the Oligocene deltas experienced a transition from an early proximal intrabasinal source to a late distal extrabasinal source.

ХАРАКТЕР РАСПРЕДЕЛЕНИЯ РЕДКОЗЕМЕЛЬНЫХ ЭЛЕМЕНТОВ В МЕЗОЗОЙСКИХ ОСАДОЧНЫХ ПОРОДАХ НИЖНЕГО ПРИАМУРЬЯ

The article presents original data on the contents of rare earth elements (REE) and characterizes their distribution in Mesozoic sedimentary rocks of the Lower Amur region. The author compares various parameters of the studied rocks with similar parameters in the standards of the same rocks. The stratigraphic divisions made on the M-54-I sheet of the 1:200,000 scale State Geological Map belong to the Amur (or Chayatyn) subzone (SFPZ) of the West Sikhote-Alin Structural-Formation Zone (SFZ). Among them, the Zhorminsky (K1 zm) strata, Silasinsky (K 1-2 sl) and Utitsky (K2 ut K2) formations are distinguished. The stratons are composed of sandstones and siltstones in different ratios. They also contain conglomerates, tuffs of different composition, and andesites. The REE content in siltstones is higher than in sandstones. Higher concentrations of elements were found in the studied rocks relative to the rocks of the Caucasian Folded System (CC). Compared to the aleuropes of the Russian platform, the sandstones of Priamurye subzone have less REE content, and the siltstones have more. Compared to PAAS (post-Archean Australian shale), the REE content is less. Chondrite normalized REE contents. The trend of the charts is negative. The same behavior of elements is characteristic of the distribution spectra in the studied sandstones, siltstones, RAAS, aleuropesstones of the Russian platform, and rocks of the Caucasian SS. In most of the rocks presented, the LRSE/TRSE is higher than 8, this indicates that the sedimentation basin of detrital material has a predominantly acidic composition. There is a significant negative europium anomaly – from 0.34 to 0.71 in sandstones, and from 0.47 to 0.75 in siltstones. It also indicates the acidic rocks erosion. Consequently, a set of parameters determines the rocks acidic composition in the demolition areas.