Bulk Geochemistry Research Articles

Catalogue of South African mine tailings for geochemical carbon dioxide removal purposes

South Africa has the potential to be a global leader in implementing strategies targeting geochemical carbon dioxide removal (CDR) using mine tailings, utilising methods for alkalinity production and mineral carbonation. This is due to the hundreds of millions of tonnes of geochemically and mineralogically suitable tailings produced annually from diamond, PGM, chrome, nickel, phosphate, copper, talc and magnesite mines, exploiting mafic and ultramafic rocks. This approach may offer an additional route towards emissions offsets and reduction targets for South Africa.Here, a catalogue of tailings has been developed to highlight overall national CDR potential, drawing attention to site opportunities for pilot schemes. It has been calculated, using bulk geochemistry and shrinking core modelling, that South Africa has an average 1.1-1.7 MtCO2 removal capacity per year across all suitable sites, while an additional 11-17 MtCO2 could be removed through weathering historic tailings. The total CDR that could be achieved over the 2030-2100 period, considering all annually produced tailings available to weather, is 79-119 MtCO2. The capacity may be higher if mines of limited production information are considered, and pre-2017 tailings production amounts, abandoned stockpiles, and other industrial by-products are included. Diamond mines hold the highest geochemical CDR capacities, along with high tailings producers in Phalaborwa, Nkomati and Mogalakwena metal mines. There are incentives for academia, industry and policymakers to revise the geochemical CDR potential of mine sites in the years to come, and for other countries to catalogue their own suitable tailings and geochemical CDR potential capacities for future Mt-scale opportunities.

The key role of volatile‐rich magma in the formation of porphyry molybdenum deposits: A case study of the Chalukou deposit, China

Volatile element abundance is a crucial factor triggering mineralization and controlling the enrichment of molybdenum in porphyry deposits. The Chalukou deposit is the largest porphyry Mo deposit in NE China, with an average grade of 0.087% Mo. In this contribution, we present petrology, bulk geochemistry, zircon U–Pb geochronology and Lu–Hf isotopes, and apatite geochemistry for the Chalukou deposit. The intrusive rocks include pre‐mineralization monzogranite, syn‐mineralization quartz porphyry, fine‐grained porphyry and granite porphyry, and post‐mineralization monzogranite and feldspar porphyry. These granitoids are metaluminous to peraluminous, and belong to alkali‐calcic to calc‐alkalic series. Zircon εHf(t) values of granitoids range from +0.2 to +5.7 with corresponding Hf crustal model ages of 805–1170 Ma, indicating a Mesoproterozoic juvenile crustal source modified by mantle‐derived magma. They are characterized by logf(O2) of −16.1 to −9.4, with an average of −12.5, ΔFMQ of +0.8 to +7.9, with an average of +4.5, showing a relatively high oxidation state for the syn‐mineralization magma. The apatites in quartz porphyry have the highest F contents, ranging from 3.61 to 4.62 wt%. At Chalukou, F‐rich magma is conducive to the convection of magma and promotes the efficient separation of differentiation magma, making the magmatic‐hydrothermal fluid circulate many times, eventually resulting in the accumulation of ore‐forming materials on the top of the magma chamber and gradually aggravating mineral enrichment processes.

Lithium isotopic constraints on the petrogenesis of the Jiajika two-mica granites and associated Li mineralization

Petrogenesis of two-mica granites and the associated Li mineralization from the Jiajika super-large Li deposit in Sichuan Province, southwest China, remains equivocal. This study analyzed Li contents and isotopic compositions of metasedimentary rocks (schists and slates) and two-mica granites in this deposit to investigate the issue. The metasedimentary rocks show large variations in Li (71.7 ppm to 1792 ppm) and δ7Li (–14.1 ‰ to +7.9 ‰), while the two-mica granites have Li contents from 60.2 ppm to 388 ppm and δ7Li values from –3.1 ‰ to +1.9 ‰. Integrated with bulk geochemistry and available Nd–Hf isotopes from this deposit, the two-mica granites probably originated from partial melting of the middle-upper crustal pelitic metasediments. The lower average δ7Li value of metasedimentary rocks (–2.9 ‰) than that of two-mica granites (–0.4 ‰) is possibly attributed to 6Li-rich garnets entering residuum during incongruent melting. We speculate that Li isotopic fractionation might have occurred during crustal anatexis. The partial melting that contributed to the transfer of volatiles and rare-metal elements into the granitic melts played an important role in Li mineralization. Li isotopes can potentially guide Li deposit prospecting as Li-bearing veins are likely to occur in regions with light 6Li.

Extreme variability in atmospheric oxygen levels in the late Precambrian.

Mapping the history of atmospheric O2 during the late Precambrian is vital for evaluating potential links to animal evolution. Ancient O2 levels are often inferred from geochemical analyses of marine sediments, leading to the assumption that the Earth experienced a stepwise increase in atmospheric O2 during the Neoproterozoic. However, the nature of this hypothesized oxygenation event remains unknown, with suggestions of a more dynamic O2 history in the oceans and major uncertainty over any direct connection between the marine realm and atmospheric O2. Here, we present a continuous quantitative reconstruction of atmospheric O2 over the past 1.5 billion years using an isotope mass balance approach that combines bulk geochemistry and tectonic recycling rate calculations. We predict that atmospheric O2 levels during the Neoproterozoic oscillated between ~1 and ~50% of the present atmospheric level. We conclude that there was no simple unidirectional rise in atmospheric O2 during the Neoproterozoic, and the first animals evolved against a backdrop of extreme O2 variability.

Using Rover-analogous Methodology to Discriminate between Volcanic and Sedimentary Origins in Successions Dominated by Igneous Composition

We tested rover science operations strategies to determine best practices for interrogating geologic sections where the bulk composition is igneous but depositional/emplacement processes range from sedimentary to volcanic. This scenario may mirror locations on Mars interrogated by mobile vehicles (e.g., Perseverance rover in Jezero crater). Two field teams studied a 60 m vertical outcrop on Iceland’s Tjörnes peninsula as an analog for a Martian site containing interleaved layers of sedimentary and volcanic units. A Rover team commanded a human rover to execute observations based on common Mars rover sequences; the resulting data were used to characterize the geologic history of the location. Results were compared to that of a Tiger team using traditional terrestrial field methods to interrogate the same site. The goal was to understand which instruments, at what resolution, are required to assess the provenance of volcanic or sedimentary layers of similar chemical composition. Results suggest that, in a succession dominated by rocks having basaltic composition, current rover-driven decision-making protocols are sufficient to support a first-order interpretation of a sequence of sedimentary and volcanic layers. Two crucial data sets in maximizing science return in this scenario are (1) handlens-scale images revealing grain morphology and relationships and (2) data sets that allow comparison between surface and bulk geochemistry. Certain sedimentary features can be difficult to confidently identify if not viewed at a specific angle and resolution, and confident interpretations appear to require lateral scanning of beds at meter scales. This work illuminates the need for strategic planning, particularly of resource-intensive observations.

Controls of Geochemical and Hydrogeochemical Factors on Arsenic Mobility in the Hetao Basin, China.

High arsenic (As) groundwater is frequently found in inland basins, but little is known about As pools in sediments and their influences on aqueous As distributions. The Hetao Basin is a typical inland basin, where groundwater As concentrations generally increase from alluvial fans to flat plain. Two sites are only 1700 m apart, but groundwater As concentrations at the depth range of 15 to 80 m are quite different, ranging from 7.0 to 31.7 μg/L at site B1 and from 5.2 to 99.8 μg/L at site B2. Sediment geochemistry and groundwater hydrochemistry at two sites were characterized. No distinct differences were observed in the bulk geochemistry of sediments. Sequential extractions of 39 sediments were conducted to determine why As was easily released to groundwater at one site and not the other. Results showed that at site B1 most of solid As was associated with amorphous Fe-(oxyhydr)oxides, whereas at site B2 the strong adsorption pool dominated. Furthermore, higher dissolved Fe2+ and lower ORP in groundwater at site B2 suggested more strongly reducing conditions compared to site B1. High concentrations of NH4 + and HCO3 - at site B2 were consistent with As release coupled to microbially induced reductive dissolution of Fe-(oxyhydr)oxides. Other processes, such as the competitive adsorption of HCO3 - , As desorption under weakly alkaline pH conditions, may also influence the partitioning of As between groundwater and sediments. This study highlights the differences in how As is associated with sediments between high and low As aquifers and the contribution of chemical characteristics to As release.

Preliminary source rock evaluation, paleo-depositional environment and hydrocarbon generation potential of the cretaceous organic-rich outcrops of Mayo-Figuil River, Babouri-Figuil Basin, Northern Benue Trough (Yola arm) Cameroon: Insights from bulk geochemistry

Babouri-Figuil sedimentary basin is considered the most northerly and one of the most attractive intracontinental Cretaceous basins in North Cameroon, which contains organic-rich deposits presumed to be oil shale levels. The fieldwork carried out as part of this study enabled to delineate six lithological units mainly consisting of black shales, marls, orange clay, black to grey clays and limestones. Twenty-two samples from the studied section were subjected to bulk organic (Rock Eval pyrolysis) and inorganic (biophiles XRF-trace element) geochemistry to investigate their hydrocarbon generation potential. Field data and organic geochemical analysis of organic matter reveal that three of the six lithological units are potential hydrocarbon source rocks; these are units 1 (1.50 ≤ TOC ≤3.98%), 2 (0.47 ≤ TOC ≤1.17%) and 4 (TOC = 24.74%) consisting mainly of black to grey clays and black shales. These source rocks are discontinuously distributed throughout the studied section with a cumulative stratigraphic thickness of 275 cm. The organic matter contained in unit 1 is mainly Type II/III (182 ≤ HI ≤ 382 mg HC/g TOC) with a significant contribution in Type II kerogen. It is mature (443 °C ≤ Tmax ≤448 °C) at the base (MF-1, -2, -3 and -4) and immature (Tmax = 416 °C < 435 °C) at the top (MF-5). Unit 2 contains early-mature type III organic matter (98 ≤ HI ≤ 155 mg HC/g TOC; 438–439 °C). Organic matter in unit 4 is also early-mature and has generated mainly oil (Type I or IIS). The combination of proxies of biophile trace elements (cross plots Ni/Co vs. V/Ni and V vs. Ni) indicates that this organic matter is of mixed source, both marine and terrestrial origin, deposited under oxic-dysoxic conditions. Thus, subject to further geochemical analyses and given the pessimistic predictions from outcrop samples, these units are conventional effective source rocks in place of the early reported immature oil shale levels.

Mineralogy and bulk geochemistry of a fumarole at Hverir, Iceland: Analog for acid-sulfate leaching on Mars

AbstractIceland’s Námafjall geothermal area exhibits a range of alteration environments. Geochemical and mineralogical analyses of fumaroles and hot springs interacting with Holocene basaltic lavas at Hverir, and with Pleistocene hyaloclastites atop nearby Námaskar∂, reveal different patterns of alteration depending on the water/rock ratio, degree of oxidation, and substrate composition and age. The focus of this study is a transect of a Hverir fumarole that has formed a bullseye pattern of alteration of a Holocene basaltic lava flow. Surface samples and samples collected from shallow pits were analyzed by X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM) to constrain changes in mineral assemblage and major elemental composition with both distance and depth. Elemental sulfur is concentrated near the vent, with leached deposits with amorphous silica and anatase nearby and kaolinite, hematite, and jarosite/alunite-group sulfate minerals farther out, with smectites and less altered material at the margins, though smaller-scale mineralogical diversity complicates this pattern.Silica phases include amorphous silica (most samples), cristobalite (some samples in the leached part of the apron), and quartz (minor constituent of a few samples). The silica was concentrated through residual enrichment caused by leaching and is accompanied by a significant enrichment in TiO2 (in anatase). The presence of abundant cristobalite in a surface fumarole-altered Holocene basaltic lava flow most likely reflects cristobalite formed during the devitrification of volcanic glass or precipitation from fumarolic vapors, rather than high-temperature processes. Minor, localized quartz likely reflects diagenetic maturation of earlier-formed amorphous silica, under surface hydrothermal conditions. Natroalunite, natrojarosite, and jarosite are all present and even exhibit compositional zonation within individual crystals, showing that under surface hydrothermal conditions, these minerals can form a significant solid solution.The high iron content of the substrate basalt and the prevalence of Fe-sulfates and Fe-oxide spherules among the alteration products makes this geothermal area an especially useful analog for potential martian hydrothermal environments. The residual enrichment of silica in the leached deposits of the Hverir fumarole apron could serve as an acid-sulfate leaching model in which amorphous silica forms without appreciable sulfur-bearing phases in many samples, a possible analog for silica-rich soils in the Columbia Hills on Mars. The coexistence of hematite spherules and jarosite-group minerals serves as an intriguing analog for a volcanic/hydrothermal model for hematite and jarosite occurrences at Meridiani Planum.

Impacts of tracer type, tracer selection, and source dominance on source apportionment with sediment fingerprinting

Sediment fingerprinting estimates the proportional contribution of fine sediment from distinct catchment sources delivered to downstream receiving environments. Increased attention has focused on assessing the accuracy of source contribution estimates, particularly in relation to tracer selection and statistical un-mixing procedures. However, no studies have systematically tested the impact of source combination or dominance on the accuracy of source estimates. Here, we assess sensitivity to tracer type, selection, and number of sources, and examine how variations in the dominant sediment source affect the accuracy of source apportionments using numerical mixtures. Sources were sampled according to erosion process and land cover from a New Zealand catchment. Topsoil and subsoil (landslide) samples were collected from pasture, harvested pine, kānuka scrub, and native forest, while banks were sampled along the main channel. Samples were analysed for bulk geochemistry, fallout radionuclides, and compound specific stable isotopes (CSSIs). Source apportionment accuracy tended to decrease as source number increased, which reflected decreasing source discrimination. Tracer selection showed variations in accuracy but exhibited no clear pattern overall. Source combination and particularly the dominant source had the largest impact on accuracy, reflecting the level of discrimination for each source. Notably, channel bank was frequently identified as the dominant source when using CSSI tracers. While this partly reflected lower levels of discrimination, the CSSI apportionment was particularly sensitive to the use of post-unmixing corrections routinely applied to derive soil proportional contributions from isotopic proportions. This sensitivity likely related to the low organic carbon content in bank material and the assumption that source apportionments based on isotopic proportions can be corrected using a linear relationship with organic carbon content. These results indicate that the use of CSSI tracers in catchments where erosion sources exhibit large differences in soil organic carbon content may introduce significant unquantified error in source apportionments.

Fingerprinting historical tributary contributions to floodplain sediment using bulk geochemistry

Sediment deposition on floodplains is essential for the development and maintenance of riparian ecosystems. Upstream erosion is known to influence downstream floodplain construction, but linking these disparate processes is challenging, especially over large spatial and temporal scales. Sediment fingerprinting is thus a robust tool to establish process linkages between downstream floodplain development and sediment production in distal headwater basins. Here we use sediment geochemistry to connect historical erosion in several tributaries of the Yampa River in Colorado and Wyoming, USA, to the construction of downstream floodplains on which extensive cottonwood forests established. Using a combination of conventional techniques and the relatively novel machine-learning random forest algorithm, we build multiple fingerprints of diagnostic geochemical tracers that are then input into a Bayesian mixing model to apportion provenance of floodplain sediment. Sediment samples for provenance analysis were collected from an excavated floodplain in Deerlodge Park on the Yampa River at the rooting surface of the surrounding cottonwood forest and dominantly comprised of very fine (4Φ) sand. Fingerprinting analysis of the 4Φ fraction of collected floodplain sink (n = 38) and tributary source (n = 218) samples revealed floodplain sediment to be dominantly sourced from the tributaries of Muddy Creek (45 ± 4%) and Sand Wash (42 ± 6%). Dendrochronology results moreover indicate the Deerlodge floodplain sediment was deposited in ∼1912, which falls squarely within the time (1880–1940) these tributaries were actively eroding. Taken together, study results indicate a demonstrable link between historical tributary erosion and downstream floodplain construction and concomitant forest establishment. Our findings suggest processes operating in tributary watersheds play an important role in the dynamics of large rivers and emphasize both the need for holistic, collaborative management of sediment as an essential resource and the potential to utilize sediment fingerprinting to inform and direct river ecosystem management.

Sierra Gorda 013: Unusual CBa‐like chondrite

AbstractThe new metal‐enriched anomalous chondrite Sierra Gorda 013 (SG 013) contains two different lithologies. Lithology 1 (L1) is represented by anomalous CBa‐like chondrite material containing ~80 vol% of Fe,Ni‐metal particles and globules up to 6 mm in size; chondrules and clasts of types POP, BO, and SO (up to 5 mm in diameter); rare sulfides; and shock melted silicate–metal areas. It does not contain any fine‐grained matrix. Several chondrules contain chromite–pyroxene symplectites. Lithology 2 (L2) has a recrystallized texture with evenly distributed olivine, pyroxene and plagioclase. L2 does not have any chondrules or sulfides, and contains less Fe,Ni‐ metal (~25 vol%) than L1. Both lithologies contain reduced olivine (Fa2–4) and pyroxene (Fs3.5), similar to CBa chondrites. Similar to CBa, there is no Ni‐Co correlation in the SG 013 metal. Rare sulfides in L1 are enriched in V. Chromite was observed in both lithologies. Oxygen isotope compositions of both lithologies are different but in the range of CBa chondrites. Bulk major and trace element geochemistry of nonporphyritic chondrules and bulk siderophile compositions in metal globules of L1 indicate elemental fractionation during formation of metallic and silicate objects with records of the evaporation process: depletion in moderate and volatile elements with the exception of Cr. Bulk geochemistry of porphyritic chondrules of L1 and the silicate portion of L2 is similar and also indicates evaporation processes. The rare Earth element (REE) distribution of L1 chondrules records a very fractionated signature corresponding to possible differentiated precursor material, while the REE pattern of L2 is primitive chondritic. The formation of SG 013 could be explained by collisions of planetesimals producing an impact plume, the precursor material of which could be chondritic and possibly differentiated. Both lithologies were affected by secondary processes: L1 preserved the traces of shock events and partial melting resulting in formation of symplectites in chondrules, melt pockets, and metal–silicate melt between the metal globules; L2 was affected by shock thermal metamorphism (up to 900 °C) resulting in recrystallization.

Increased Erosion Rates Following the Onset of Pleistocene Periglaciation at Bear Meadows, Pennsylvania, USA

AbstractDirect measurements of erosional response to past climate change are scarce, but mid‐latitude landscapes can record how shifts between cold and warm periods altered erosion outside glacial margins. To study hillslope responses to periglaciation, we measured bulk geochemistry and cosmogenic 10Be and 26Al concentrations in colluvium and weathered bedrock in an 18 m regolith core from Bear Meadows, Pennsylvania, ∼100 km south of maximum glacial extent. Using core lithology, cosmogenic nuclide concentrations, and regional 10Be‐derived erosion rates, we show the onset of 100‐Kyr glacial cycles at the Mid‐Pleistocene Transition (1.2–0.7 Ma) instigated multiple periglacial episodes in central Appalachia, increasing erosion rates compared to the relatively warmer Neogene. Our results show the higher efficiency of periglacial versus temperate erosion processes and highlight a pervasive Pleistocene periglacial erosion signal preserved in the 10Be inventory of surface sediments in central Appalachia, where erosion rates are slow enough to integrate previous cold‐climate processes.

Middle Jurassic climate oscillations from paleosol records of the Sichuan Basin, SW China

The Middle Jurassic is characterized by major plate tectonic changes, variable atmospheric CO2 concentrations (pCO2), and climate oscillations in both marine and terrestrial realms. However, the limited evidence from the terrestrial sedimentary records hampers a comprehensive understanding of global climate state in this period. Well-exposed strata of the Shaximiao Formation in the Sichuan Basin, Southwest China, preserve successions of paleosols that offer the possibility of evaluating the terrestrial paleoclimatic changes during the Middle Jurassic (Bajocian to Callovian). A total of 151 paleosol profiles belonging to four paleosol types (Entisol-like, Inceptisol-like, Aridisol-like and argillic Inceptisol-like paleosols) were identified and characterized. The quantitative paleoclimate reconstructions based on the bulk geochemistry of paleosol horizons and depths of carbonate nodules indicate a generally semiarid–subhumid climate alternating with arid–humid and cool/warm–temperate climates during this time interval. This dynamic climate terminated in a dry, subhumid, humid/perhumid and superhumid moisture regime characterized by steppe/wet or rain forest floral provinces. We suggest that these climatic fluctuations may have been related to global geodynamic (e.g., the fragmentation of Pangea, “megamonsoonal” circulation, and bolide impacts) and regional tectonic uplift (e.g., the uplift of the Longmenshan Mountains in the South China Block) during the Middle Jurassic. The pCO2 estimates suggest relatively low pCO2 levels within the range of ∼100 ppm–∼890 ppm during the Bajocian to Callovian. Our results coincide with the threshold for the initiation of glaciation and may help to explain the occurrence of cool intervals in the generally warm Jurassic. These pCO2 fluctuations, which coincide with paleotemperature variations in the low paleolatitudes of the Northern Hemisphere, are possibly attributable to global geological events (e.g., wildfire events, eustatic sea-level oscillations, and the transient development of glaciations) in the Middle Jurassic.

Gold and silver deportment in sulfide ores – A case study of the Freiberg epithermal Ag-Pb-Zn district, Germany

Deportment data is essential for the planning of mining and minerals processing operations. This need is particularly tangible for deposits of noble metals, such as gold and silver. Therefore, the current paucity of published gold and silver deportment data for individual ore deposits and districts – and the concomitant lack of understanding how this relates to salient geological and mineralogical features of these deposits – is surprising. In the present study, we apply a combination of bulk geochemistry, laser ablation-inductively coupled plasma-mass spectrometry, electron microprobe analysis, and mineral liberation analysis to gold- and silver-rich samples from the epithermal Freiberg Ag-Pb-Zn district, to investigate variability in gold and silver deportments, as well as the corresponding geological/mineralogical controls. The results show that the main carriers of gold are electrum and arsenopyrite, whereas silver is mostly hosted by Ag-sulfosalts (pyrargyrite, miargyrite, polybasite) and fahlore (freibergite). Deportments vary greatly between samples. These variations can be related to the relative abundances of different minerals within the samples, which in turn reflect their spatio-temporal position within the district. Comparisons with other epithermal Ag-Pb-Zn districts similar to Freiberg indicate that the results presented here are of general significance.

Paleoenvironmental variations in a sedimentary Jurassic sequence from Lusitanian Basin (Portugal)

Gaiteiros-1 borehole, located in the central Lusitanian Basin (Portugal), drilled a continuous Jurassic (Hettangian to Kimmeridgian) sedimentary sequence. Forty-one samples were selected for this study to characterize the dispersed organic matter and its vertical variation along Gaiteiros-1 borehole and to evaluate the environmental changes based on palynofacies and bulk geochemistry analyses.Gaiteiros-1 borehole lithological sequence is characterized by a low organic carbon content, which varies between 0.10 wt% and 0.83 wt%, in Candeeiros carbonates and Lower Jurassic Coimbra Formation, respectively. The insoluble residue content indicate a carbonated character in almost the entire sequence, except for Kimmeridgian samples. The palynofacies analysis evidences the presence of the main groups of kerogen (Phytoclats, Amorphous and Palynomorphs) with a dominance of the amorphous group in the carbonated samples and phytoclasts in Kimmeridgian detritic samples. Different types of amorphous particles were identified, suggesting periods of reworking by bacterial activity and primary bioproductivity in depleted oxygen environments. Despite the dominance of amorphous particles, the kerogen groups vertical variation provides information that reveals changes in the depositional environment. The kerogen assemblage of the Candeeiros facies suggests a stratified water column, with well-oxygenated layers, responsible for high primary productivity periods, which allowed for the development of zooplankton, preserved in the form of zooclasts fragments and foraminiferal test-linings. The contribution of the Palynomorph group is scarce during the Lower-Middle Jurassic but increases in the Upper Jurassic. This modification in the kerogen assemblage reflects changes in the sea level, oxygenation conditions, climate and proximity to the terrestrial source area. The presence of Coleochaete-like freshwater algae was detected for the first time in the Lusitanian Basin, suggesting more restrictive conditions during the Late Oxfordian. During the Kimmeridgian, the amorphous material disappears and phytoclasts, mainly opaque phytoclasts, come to dominate the kerogen assemblage, as a result of terrigenous sediments input, due to the great proximity to the terrestrial source area.

Geochemical and molecular characteristics of ferromanganese deposits and surrounding sediments in the Mariana Trench: An Implication for the geochemical Mn cycle in sedimentary environments of the trench zone

Trench systems are some of the most important geodynamic settings on Earth and have a substantial influence on the global metal cycle. Trench environments are affected not only by episodic deposition of volcanic ash, but also exhibit a continuous water–rock chemical exchange. Ferromanganese nodules, which are archives for the marine Mn cycle, were first discovered in the southern Mariana Trench during China’s major 10,000-meter hadal trench scientific expedition in 2016. Nevertheless, their geochemical characteristics and formation mechanism in sedimentary environments of the trench zone remain enigmatic. In this study, these ferromanganese nodules and surrounding sediments were examined by geochemical and microbial methods. Bulk geochemistry indicated that trench nodules are characterized by high Mn/Fe ratios and nodule textures indicate a rapid growth rate, with Mn mainly from two sources: volcanic ash alteration and fluids discharge from the trench seabed. High-resolution in situ geochemical analysis categorized microlayers of an individual nodule into three types. Type I is the interior part that has a high Mn/Fe ratio (>20) and high growth rate (52.19–3571.73 mm/Myr), and formed by the influence of fluid discharge activities around this region. Type II is laminae from the exterior part that have a hydrogenetic origin with lower Mn/Fe ratio (0.01–2.50) and lower growth rate (4.54–9.86 mm/Myr). Type III is laminae from the exterior part that have a diagenetic origin with moderately high Mn/Fe ratio (2.5–15.0) and moderately high growth rate (12.40–18.93 mm/Myr). 16S rRNA gene sequence analysis revealed that the bacterial community structures in the nodule-bearing sediment samples, dominated by Shewanella and Colwellia, were substantially different from those of reference sediment samples. For the first time, we propose a conceptual model for a geochemical Mn cycle and nodule formation in trench sedimentary environments using both geochemical and microbial data.

Rare and Critical Metals in Pyrite, Chalcopyrite, Magnetite, and Titanite from the Vathi Porphyry Cu-Au±Mo Deposit, Northern Greece

The Vathi porphyry Cu-Au±Mo deposit is located in the Kilkis ore district, northern Greece. Hydrothermally altered and mineralized samples of latite and quartz monzonite are enriched with numerous rare and critical metals. The present study focuses on the bulk geochemistry and the mineral chemistry of pyrite, chalcopyrite, magnetite, and titanite. Pyrite and chalcopyrite are the most abundant ore minerals at Vathi and are related to potassic, propylitic, and sericitic hydrothermal alterations (A- and D-veins), as well as to the late-stage epithermal overprint (E-veins). Magnetite and titanite are found mainly in M-type veins and as disseminations in the potassic-calcic alteration of quartz monzonite. Disseminated magnetite is also present in the potassic alteration in latite, which is overprinted by sericitic alteration. Scanning electron microscopy and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of pyrite and chalcopyrite reveal the presence of pyrrhotite, galena, and Bi-telluride inclusions in pyrite and enrichments of Ag, Co, Sb, Se, and Ti. Chalcopyrite hosts bornite, sphalerite, galena, and Bi-sulfosalt inclusions and is enriched with Ag, In, and Ti. Inclusions of wittichenite, tetradymite, and cuprobismutite reflect enrichments of Te and Bi in the mineralizing fluids. Native gold is related to A- and D-type veins and is found as nano-inclusions in pyrite. Titanite inclusions characterize magnetite, whereas titanite is a major host of Ce, Gd, La, Nd, Sm, Th, and W.

Geochemical characteristics and genetic families of crude oil in DWQ oilfield, Kuqa Depression, NW China

As one of the most petroliferous oil producing area in Kuqa depression, Dawanqi (DWQ) oilfield is supplying with great attention. In this regard, the geochemical characteristics and oil families from DWQ field were investigated using molecular compounds analysis of GC, GC–MS techniques. The bulk geochemistry of oils from DWQ oilfield displays complicated molecular composition characteristics, including relative higher indices of Pr/Ph (1.4 ~ 4.26, with an average of 2.4), high concentration of light hydrocarbons and certain abundant pentacyclic triterpene and steranes. The C7 light hydrocarbon and isoprenoids ratios indicate the oils were derived from terrestrial and higher plant input in weak oxidizing and reducing environment. Most of the oils are among the mature oils in the study area, except a few samples that are identified as slightly biodegraded by C7 hydrocarbon. Three oil families are identified in DWQ oilfield of Kuqa depression by biomarker analysis and geochemical parameters. The family A shares the attributes with higher amount of tricyclic terpanes, such as C19- C20 tricyclic terpane, higher C24-tercyclic terpane, lower concentration of gammacerane (< 0.6) but poor diasteranes. Family C is characterized with lower content of C19-tricyclic terpane than C20 tricyclic terpane, low C24-tercyclic terpane than C23-tricycli terpane, relative high concentration of gammacerane (> 0.6) but poor diasteranes. The oils of family B are mixed from the two types, showing mixed features of family A and C. The results can shed light for the exploration of the studied area.

Mass-wasting processes input in proximal metalliferous sediments: A case study of the Pobeda hydrothermal fields

Metalliferous sediments associated with oceanic hydrothermal systems contain various amounts of metals of a dual origin: from suspended particulate matter of an overlying plume and from weathered massive sulfide edifices. This study investigates the influence of the latter component on metal enrichment in sediments proximal to sulfide bodies for the Pobeda hydrothermal fields of the Mid-Atlantic Ridge (MAR). This region consists of three separate venting fields Pobeda-1, 2, and 3 located at different depth levels in the MAR rift valley. Hydrothermal precipitates within the site occur as massive sulfide edificies and metalliferous sediments. Detailed mineralogical and geochemical analysis of all these components revealed that a significant amount of hydrothermally-derived material in the sediments derives from overlying plume particulate superimposed by mass wasted oxidized sulfides from the nearest edifices. This last component is mostly abundant in the sediments of the deepest Pobeda-2 field, which complicates using bulk geochemistry to decipher the history of hydrothermal activity there. For the two remaining fields, Pobeda-1 and Pobeda-3, a reconstruction of vent discharge history indicates that it began almost simultaneously at the time interval recorded in core sediments. However it waned steadily at the Pobeda-3 field, whereas at Pobeda-1 field it exhibited a significant decrease in intensity and then a reverse movement upward until recently.

Transport of fine-grained sediment in oceanic currents: Holocene supply to sediment drifts around Flemish Cap by the Labrador Current

Hemipelagic sediment on the upper continental slope is commonly transported from the adjacent continental shelf, but along-slope transport of sediment by thermohaline currents may be an important source of sediment. One such case is Flemish Cap, a promontory of the eastern Canadian continental shelf protected from direct continental sediment supply by the deep-water Flemish Pass. Pleistocene sediment drifts around Flemish Cap accumulated glacially derived sediment from the north, transported by the Labrador Current. This study determines the changing sources and controls on the accumulation of bioturbated hemipelagic sediment through the Holocene. From a set of >150 box cores in water depths of 600–1200 m, some 30 push cores, up to 55 cm long, were studied in detail for stratigraphic variation in grain size, bulk geochemistry (XRF) and detrital petrology (granule petrology and qXRD). Criteria were developed to identify trawling disturbance. Two Holocene stratigraphic units, A) almost lacking ice-rafted detritus and B) with some coarse IRD and higher detrital carbonate, correlate with similar units farther north on the Labrador Shelf and Slope. Sedimentation rates based on 26 radiocarbon dates were ~ 0.02–0.03 m/ka over much of the region below the 800 m isobath, locally reaching 0.1 m/ka in some sediment drifts, but as low as 0.01 m/ka on southeastern Flemish Cap. Where sedimentation rate was >0.03 m/ka, the record of flow vigor from the sortable silt proxy since 6 ka shows three different zones of Labrador Current flow with different timing of changes in flow vigor. The mid to early Holocene record shows that the meltwater-driven inner Labrador Current extended across the entire study area. Where sedimentation rates are lower, periods of sediment bypassing are inferred and the sortable silt record varies little. Correlation with external drivers is hampered by century-scale core resolution and sparse dating control. The distinctive abundance of dolomite rock flour in hemipelagic sediments around Flemish Cap indicates important supply from Baffin Bay icebergs during the entire Holocene, diluted prior to 6 ka by sediment from Hudson Strait and some Labrador ice streams. Baffin Bay icebergs melt preferentially in the southern Labrador Sea, dropping their load, with the fine grained component transported to the south by the Labrador Current. Similar partitioning of coarse- from fine-grained components of IRD may take place on other high-latitude outer continental margins.