Mineral Associations Research Articles

Contrasting fates of terrestrial organic carbon pools in marginal sea sediments

Burial of terrestrial organic carbon (OCterr) in marginal sea sediments is a key component of the carbon cycle, exerting long-term influence on atmospheric CO2 and climate. Assessment of the burial efficiency of OCterr is of key importance, yet remains poorly constrained due to current gaps in our knowledge of mechanistic controls, including the influence of organic matter composition and age on the fate of OCterr in marine sediments. We measured bulk characteristics (δ13C and Δ14C of OC; mineral surface area, SA; grain size; n = 98 samples) and biomarker carbon isotopic compositions (fatty acid δ13C and Δ14C; n = 11) of a suite of surface sediment samples from the Bohai Sea and Yellow Sea (BS-YS). Combining with published results, bulk OC (n = 234) and biomarker (n = 19) carbon isotopic data are used to examine spatial variability in the sources and ages of OCterr in this shallow marginal sea system. Biomarker carbon isotopic values are used to constrain endmember values, and a dual carbon isotope mixing model was applied to all bulk samples to develop a spatially explicit assessment of contributions of different pools of OCterr. Although highly spatially variable, pre-aged OC (OCpre-aged) and fossil OC (OCfossil) when combined (i.e., “non-modern OC”) on average accounted for 51 ± 10% of the OC in BS-YS surface sediments. This was equivalent to the proportion of OCterr (ave., 51 ± 14%) estimated from a δ13COC binary mixing model, suggesting OCterr in the mixed layer of BS-YS sediments is predominantly composed of millennial-aged OC. The burial potential of pool-specific OCterr was then evaluated through comparison of corresponding mineral SA-normalized loadings of surface sediments with those of Yellow River suspended particulate matter. Both the regression slope and the arithmetic mean value approaches reveal high burial potential for all terrestrial OC pools delivered by Yellow River, which is attributed to the aged and refractory nature of OC exported from the Yellow River. However, differing relationships of pool-specific OCterr loadings between BS-YS and Yellow River sediments imply contrasting fates. In particular, we find that the burial potential of OCpre-aged is consistently greater than that of OCfossil. This surprising observation suggests either enhanced degradation of OCfossil during lateral transport (possibly as a consequence of different mineral associations and hydrodynamic sorting effects), or additional sources for OCpre-aged, such as from small rivers or aerosol deposition. Overall, OC age, mineralogical composition and hydrological settings contribute to the complex patterns of OC residing in northern China marginal sea surface sediments. This novel molecular-isotopic approach reveals significant spatial variability in proportions, contents and burial potential among terrestrial OC pools, and underlines the importance of considering organic matter age and composition in understanding and constraining the fate of OCterr in marine sedimentary environments.

Methodological aspects of regional metallogenic analysis

Relevance and purpose of the work are due to the need to formulate the conceptual base and essence that determine the methodology of regional metallogenic analysis. Results. The fundamental provisions that make up the methodological and conceptual-semantic basis of the regional metallogenic analysis have been determined and concretized. The conceptual basis of regional metallogenic analysis is the provision that the ore (deposit) is included as a natural component in certain structural-material associations (or complexes), i.e., in certain formations of igneous, sedimentary and metamorphic rocks. They are objectively existing and actually mapped geological bodies, which are expressed both in the form of stratified (series, formations, strata, packs, horizons) and intrusive (massifs) formations. On their basis, structural-formation (structuralmetallogenic) zoning is carried out. An important feature of magmatic, sedimentary and ore formations is their recurrence in the geological history of mobile belts, which confirms the concept of the conservatism of metallogenic processes in the geological history of the Earth. At the same time, along with repetitive ones, there are magmatic, sedimentary and ore formations formed in the geological history of the Earth only once. Lateral and vertical rows of rock and ore paragenetic associations are characterized. Examples of Caledonian and Hercynian lateral ore-formation series of the Urals are given. The main provisions of the quantitative assessment of the predicted resources of the predicted types of minerals are formulated. Conclusions. The regional metallogenic analysis consists of the following components: petro-lithoformational analysis, structural-formational zoning which is adequate to structural-metallogenic zoning, paragenetic analysis of mineral associations and geological-industrial typification of various-scale occurrences of a mineral, and quantitative assessment of expected mineralization predicted resources.

Source, transport and fate of terrestrial organic carbon from Yangtze River during a large flood event: Insights from multiple-isotopes (δ13C, δ15N, Δ14C) and geochemical tracers

Climate change-triggered episodic and intensive flood events are increasing in frequency globally; these events play a disproportionate role in the carbon cycle at land-ocean interfaces by influencing the delivery of terrestrial organic matter to the sea. However, the transport and burial of flood-driven terrestrial organic carbon (Corg) in river-dominated marginal seas remains poorly understood. Here, water column particles (surface, intermediate, and bottom layers) and surface sediments from the Yangtze River estuary system were collected during a large flooding event (>60,000 m3 s−1) for a multiproxy geochemical study. We analyzed N/C, δ13Corg, δ15N, F14C, grain size, and elemental (Al and Si) to characterize the sources, ages, and alterations of particulate organic carbon (POC) and sedimentary Corg from the river channel to the estuarine mixing zone to the continental shelf and fingerprint the fate of Corg burial in marine sediments.We found that terrestrial POC delivered by the Yangtze flood is characterized by low F14C (0.625 ± 0.002; Δ14C = −379.8 ± 2.3‰, 14C age = 4,135 yr before present (BP)) and δ13Corg (−27.1 ± 0.5‰) values and high δ15N (3.9 ± 0.6‰), and N/C (0.15 ± 0.01) values, and was adsorbed on fine-grained particles. Using a Bayesian-Monte Carlo simulation approach, we estimated that terrestrial POC is dominated by C3 plant detritus (42 ± 16% on average), followed by petrogenic organic carbon (33 ± 7%), and soil (26 ± 22%). Moving offshore, hydrodynamic sorting of lithogenic particles exerts first-order control on POC by selecting particles with unique signatures. Petrogenic organic carbon and aged plant debris associated with coarse-sized particles preferentially accumulated within the proximal delta, whereas POC derived from catchment soil and adsorbed on fine-grained particles was transported offshore along the sediment dispersion system. We estimated that, on average, 76 ± 18% of POC initially present in the water column is oxidized at the water column-seabed interface during seaward transport and constitutes a source of atmospheric carbon dioxide. In contrast, the stable form of the organic matter-aluminosilicate mineral association controls the preservation of the sedimentary Corg. Our results suggest that frequent flooding events in the near future will likely increase lithospheric Corg delivery to marine sediments and have the potential to promote petrogenic Corg burial efficiency in the river-dominated marginal seas and accelerate biospheric POC oxidation and CO2 release, thus generating a positive feedback to global warming.

Sulphide geochemistry of the superlarge Tiegelongnan Cu (Au) deposit in Tibet, China: Implication for the mineralization process

The Tiegelongnan deposit in central Tibet presents a typical high‐sulfidation porphyry Cu (Au) mineralization system. Optical microscopy, scanning electron microscopy–energy dispersive spectrometry (SEM–EDS), and laser ablation inductively coupled plasma mass spectrometry (LA–ICPMS) were used to understand the mineralization processes. The advanced argillic alteration zone directly contacts the phyllic alteration zone, which is linked to the Early Cretaceous porphyritic intrusions. In this study, the spatial distributions of chief copper sulphides with variable gangue minerals are illustrated. The deep inner phyllic zone typically produced an end‐member assemblage of chalcopyrite–sericite (±dolomite), which trended upwards to produce more bornite–sericite (±siderite ± magnesite), and subsequently, the advanced argillic alteration yielded the representative end‐member assemblage of tennantite–alunite ± (aluminium‐phosphate‐sulphate, namely, APS, ±kaolinite). In the phyllic–advanced argillic transition zone, intensive covellite precipitation with the widespread occurrence of sericite–kaolinite (±APS) assemblage is proposed as an important feature in this study, which is mainly produced on the southwest side of the ore‐body centre. The typical co‐occurrence of chalcopyrite with dolomite at great depths indicates that it was related to a gently acidic fluid containing CO2; however, the pervasive tennantite–alunite association present at shallower levels suggests that fluids with SO2 were mainly involved and produced stronger acidic conditions. Acidic fluids are demonstrated to highly accelerate water‐rock alteration. Trace element analyses of the copper sulphides reflect that Au concentrations of bornite and tennantite are higher than chalcopyrite and covellite and present small signal variations. Moreover, comparing the presence of micron‐sized Au‐telluride in tennantite under advanced argillic alteration with the nano‐sized native gold in bornite resulting from phyllic alteration suggests that to a certain extent, Au enrichment is affected by the shift of more Te contents in fluid towards shallower levels, which could promote Au precipitation. Additionally, the Se contents of the selected samples were typically concentrated in chalcopyrite, bornite, and covellite, which yielded contents an order of magnitude greater than those in tennantite, indicating the intimate hydrothermal origin of the first three sulphides. Overall, the sulphide–gangue mineral associations and their copper sulphide geochemistry indicate that the hypogene–chalcopyrite of low Au contents from the phyllic zone closely corresponds to the action of gentle acidic fluids with CO2, while more acidic fluids with SO2 are involved in the formation of supergene tennantite with relatively high values of Au and Te in the advanced argillic alteration.

Formation conditions of noble metal mineralization in sulfide cobalt-copper-nickel ores of Kamchatka (on the example of Annabergitovaya Schel ore occurrence)

The authors present research results, the purpose of which is to study the specifics of noble metal mineralization and its genesis in sulfide cobalt-copper-nickel ores of the Kamchatka nickel-bearing province. The paper is dedicated to one of its many ore occurrences called Annabergitovaya Schel (Annabergite Gap). The material composition of platinoid, silver, gold, bismuth and tellurium minerals, as well as sulfarsenides in the ores of this occurrence was investigated. Based on the data of mineral formation sequence and the use of geosensors, conclusions were drawn regarding the genesis of noble metal mineralization.
 Formation of platinoid minerals, silver and gold at the Annabergitovaya Schel ore occurrence is mainly associated with the epigenetic effect of post-ore granitoids on ore-bearing intrusion rocks of the Dukuk complex of the cortlandite-norite formation and on syngenetic ores. An early association of noble metal minerals is represented by sperrylite, irarsite, and rare unnamed phases of Pt + Ir + Te. Irarsite and Pt + Ir + Te phases were formed at the contact-metasomatic stage. Sperrylite can be assumed to be of magmatic origin. Silver sulfides and tellurides, silver and palladium bismuth tellurides, and native gold were formed at the late, hydrothermal-metasomatic, stage. The occurrence conditions of mineral parageneses, associated with noble metal mineralization, correspond to the formation of shallow-depth metasomatic rocks (5 km). Sub-developed quartz-feldspar metasomatites, associated with the formation of early platinoid arsenides and sulfarsenides, are in equilibrium with circumneutral solutions (pH of 4.5-6.5) at temperatures of 350-600 °C. Late hydrothermal association with Pd, Ag and Au minerals is close to propylites and was formed at pH values of 4.5-6.5 and temperature of 150-350 °C.

Mineralization and fluid inclusion characteristics of Pb-Zn-Fe-Ba (Cu, F, Sr) ore-deposits in northern east of Algeria

The northern east of Algeria represents the most important metallogenic zone for Pb-Zn-Fe-Ba (Cu, F, Sr) ore-deposits. The mineral association consists of galena, sphalerite, barite, and celestite with gray copper, pyrite, chalcopyrite, and marcasite associated with a carbonate (dolomite and calcite) matrix. Quartz, siderite, fluorite, and oxidation products like hematite, limonite, magnetite, smithsonite, and hydrozincite are also abundant. The ore-bodies are hosted in carbonate sedimentary rocks of lower Cretaceous, from Hauterivian to Aptian. Mineralization is mainly in vein fillings in fractures and in epigenetic lenticular or strata-bound ores. Most of the ore-bodies are structurally controlled by NE-SW-, NW-SE-, and E-W-trending faults, localized along the margins of subsiding sedimentary basins and diapiric zones, either inside hinges or on the flanks of anticlinal structures. Micro-thermometric data from sphalerite, dolomite, fluorite, quartz, calcite, and barite samples show relatively high temperatures, varying between 90 and 160°C. Salinity is variable, generally with high values (between 10 and 29.92 wt% NaCl equiv). These results combined to geological and metallogenic observations suggest an epigenetic origin for these mineral deposits. The saline fluids responsible for mineralization are related to basin fluids (formation water), which are classified as Mississippi Valley type (MVT), diluted locally by meteoric water. Eutectic temperatures measured in the fluid inclusions indicate an H2O-NaCl-CaCl2 system. The presence and variability of Na+ and Ca++ in the aqueous solutions suggest interaction with host rocks (contamination by dissolution respectively of Triassic gypsum and carbonate formations).

Fostering the Sustainability of Artisanal and Small-Scale Mining (ASM) of Barite in Nasarawa State, Nigeria

The exploration and mining of Nigerian barite are primarily by artisanal and small-scale miners (ASM) whose operations are characterized by poor productivity. As a result, the quantity and quality of barites produced do not satisfy the nation’s oil sector demands and other industries that require the mineral. This situation leads to massive importation of the mineral with negative impact on the country’s drive toward increasing the contribution of solid minerals to the gross domestic product (GDP). This study reviews the existing policies and government interventions on ASM of Nigerian barite; evaluates the operations of ASM through a survey of mines in Nasarawa state, Nigeria; identifies factors that affect sustainability of the sector and proffers solutions to foster sustainability of ASM of barite in the region. The study adopted the 4Is optimization technique (Information gathering, Interpretation, Implication, and Implementation) through personal interactions with the stakeholders at the barite mining sites, and government agencies, regarding policies and interventions specific to ASM of barite. Challenges identified include: weak implementation and enforcement of mining laws; inadequate support from government and development partners; poor access to mining equipment and technology; poor infrastructure (access road, water, electricity); poor pricing of products (marketing challenges); poor remuneration of mine workers; poor mining skills; inadequate formal education; limited awareness on environmental health and safety hazards; fragility and conflict; insufficient information and data on mines and miners; security issues; lack of access to finance; lack of formalization of operations and poor legal framework for operations. The strategies suggested for fostering the sustainability of ASM of barites include: enhanced policy and legislation formulation and implementation, strengthening of institutions, formalization of ASM operations, training of miners, awareness campaign, improvement in environmental and safety of operations, empowerment and support by government and development partners for individual miners and processors and organized groups within the sector (such as Miners Association of Nigeria, Association of Miner and Processors of Barite, AMAPOB). Implementation of these strategies will lead to sustainable operations of the sector and hence improved rural livelihoods, stimulation of entrepreneurship in an environmentally responsible manner, and improvement in the contribution of the mineral sector to the nation’s gross domestic product (GDP), and hence national development.

Identification of continental-type eclogites in the Paleo-Tethyan Changning–Menglian orogenic belt, southeastern Tibetan Plateau: Implications for the transition from oceanic to continental subduction

As a record of ancient subduction, eclogites preserve critical information for exploring geodynamic processes at convergent plate boundaries. The Changning–Menglian orogenic belt (CMOB) in the southeastern Tibetan Plateau is situated between the Gondwana-derived Baoshan–Tengchong Block and the Eurasia-derived Lanping–Simao Block. The belt has long been accepted as a typical cold subduction–accretion belt associated with the closure of the main Paleo-Tethys Ocean, owing to the development of oceanic-type lawsonite-bearing eclogites. However, this viewpoint is challenged by the presence of newly discovered continental-type eclogites hosted by metasedimentary rocks in the CMOB. The continental-type eclogites are depleted in high field-strength elements (e.g., Nb, Ta, and Zr), enriched in Th and U, and preserve highly negative ɛNd(t) values varying from −15.26 to −13.04, indicating derivation from continental mafic protoliths that underwent extensive crustal contamination. Inherited zircons from both the continental-type eclogites and their host schists have characteristic detrital age distributions, with dominant Pan-African age peaks at 630–505 Ma that match well with those in the Baoshan–Tengchong Block. Combined with published age data, our new geochemical and geochronological data provide convincing evidence for the presence of significant volumes of subducted continental fragments derived from the Baoshan–Tengchong Block. Thermodynamic modeling of the continental-type eclogites indicates a clockwise P–T path with a steep prograde path consistent with a geothermal gradient of 5–8 °C/km, which was followed by near-isothermal decompression. Calculations suggest the eclogite-facies assemblage of garnet + omphacite + glaucophane ± talc ± lawsonite ± phengite records peak conditions of 28.5–29.6 kbar and 580–594 °C, equivalent to depths of 85–90 km. U–Pb dating of metamorphic zircon rims from the eclogites gives an age of 234–233 Ma, which is interpreted to reflect the timing of continental subduction. The continental-type eclogites show mineral associations, paragenetic sequences and metamorphic P–T–t evolutions similar to those of low-temperature oceanic-type eclogites in the CMOB. As a result, we propose that rapid, cold subduction of continental crust, and its subsequent rapid exhumation, occurred shortly after the closure of the dense and long-lived Paleo-Tethys oceanic lithosphere. The discovery of continental-type eclogites imparts significant insights into the dynamics of Gondwana–Eurasia convergence in the Paleo-Tethyan domain. The CMOB provides a well-exposed example of the tectonic transformation from final oceanic subduction to the onset of continental subduction and collision in a cold geothermal regime.

Bone Mineral Density Measurements and Association With Brain Structure and Cognitive Function: The Framingham Offspring Cohort.

Bone mineral density (BMD) is a potential surrogate marker of lifetime estrogen exposure previously linked to increased risk of Alzheimer dementia among elderly women. We examine the association between BMD in the "young old" with imaging biomarkers of brain aging and cognitive performance. Offspring participants (N=1905, mean age 66) of a population-based cohort who had BMD, brain imaging and detailed cognitive assessment were included in the study. Sex-stratified, linear, and logistic regression models were used for analysis. Higher femoral neck BMD was associated with lower white matter hyperintensity burden and better performance on Trails B-A in both sexes, even after adjustment for cerebrovascular risk factors. Among women, the positive association with Trails B-A performance was seen only in APOE4 allele carriers. Higher BMD measurements were linked to better visual reproductions test performance in men. Finally, among women, higher femoral trochanter BMD was associated with better logical memory and Hooper visual organization test performance. Among the "young old," higher BMD is associated with less white matter hyperintensity burden and better, domain-specific, cognitive performance. This suggests that lifetime estrogen exposure may modulate the degree of cumulative vascular brain injury independent of cerebrovascular risk factors.

An overview of some dating methods of mineralization

One of the most important achievements of applying radioactive isotope in the geological study is to determine the age of mineralization. Based on the synthesis, comparison, and evaluation of the popular isotopic systems in dating mineralization, the Rb - Sr, Re - Os, and Ar - Ar dating methods are discussed in this study. The results show that the Rb - Sr dating method is likely to be successfully applied to sulfide mineralization. If the mineralization contains little or no sulfide minerals, then the method is applied to other minerals in an ore mineral association. The Re - Os dating method has shown great success when it is applied to hydrothermal deposits, especially for the molybdenite - bearing vein deposits. The limitation of the method is that when the concentration of the Os element in molybdenite is low, it is difficult to establish the Re/Os ratio in a single mineral. The Ar - Ar isotope system for dating mineralization often uses mica or feldspar minerals, which are minerals with blocking temperatures ranging from 150÷350 0C, and later metamorphic periods have higher than 350 0C often overprinted these minerals. Generally, tectonic, magmatic, and metamorphic events, which occur after mineralization, can cause difficulty in determining the age of mineralization and collecting analysis samples.

The surgeon Wilhelm Wagner and the Upper Silesian Miners Association

This article describes the life of the Hessian physician Wilhelm Wagner (1848-1900) and his great importance for Upper Silesia. The initial years of Wagner's effectiveness in Königshütte (Upper Silesia) coincided at that time with the just beginning dissemination of antisepsis and its success. Parallel to this development Wagner turned more and more towards surgery. Without having undergone any surgical training, he was admitted into the German Society of Surgery as a young physician and later voted into its executive board. In the emergent industrial region of Upper Silesia he achieved pioneering work in surgery and social medicine. This was made possible and promoted by the Upper Silesian Miners Association. Wagner created fundamental and lasting innovations in surgery. His main work was "The injuries of the spinal column and the spinal cord" (1898). Despite his enormous private practice he always remained a "true friend and benefactor of the working man".

Vertical Distribution of Mercury in Forest Soils and Its Transfer to Edible Mushrooms in Relation to Tree Species

Soil pollution by mercury (Hg) is a global problem that poses risks to natural ecosystems and to human health. Forests represent an important recipient of Hg deposition, however, so far, very little is known about the tree species identity effects on the distribution of Hg in forest soils and its accumulation in edible mushrooms. To clarify the effect on the two main Central-European commercial forest tree species, soil samples were collected from organic F+H horizons and from mineral soil depths of 0–2, 2–10, 10–20, and 20–30 cm in mature Norway spruce (Picea abies (L.) H. Karst.) and European beech (Fagus sylvatica L.) dominated stands. Mushroom samples of the Boletaceae family were also collected at each sampling site. The highest Hg contents were found in the F+H layer and were significantly higher in spruce- (mean 0.46 ± 0.03 mg/kg) than in beech- (mean 0.29 ± 0.10 mg/kg) dominated stands. The variation in Hg contents in F+H was best predicted by pH, the overall lower soil pH in strongly acidic spruce stands might induce Hg immobilization in the F+H layer to cause a decrease in the bioavailability of Hg for Xerocomellus chrysenteron (Bull.) Šutara. In mineral soil, the Hg contents did not differ significantly between the spruce- and beech-dominated stands. The Hg content strongly correlated with the S, N, and C contents only in mineral soil; at the depths of 2–10, 10–20, and 20–30 cm, significantly also with the silt vs. sand, Alo, and Feo contents. Studied mushroom species were not Hg-contaminated and, therefore, their consumption does not pose serious health risks regardless of the forest type. The results suggest that species-related soil chemistry and mineral associations, rather than different atmospheric Hg interception by spruce vs. beech, drive the vertical distribution and accumulation of Hg in forest soils.

Constrains of eruption environment and hydrothermal fluid on the Permian pyroclastic reservoirs in the Sichuan Basin, SW China

A breakthrough has been recently made in the hydrocarbon exploration of the Permian pyroclastic rocks in the Jianyang Area, western Sichuan Basin, China. With an aim to decipher the impacts of the eruption environment, the temperature of hydrothermal fluids, and the paleo-salinity on the formation of authigenic mineral assemblage and pores, this study implements comprehensive petrographic and geochemical studies through the integrated core and thin section analyses. The data presented demonstrate that the Permian volcanic intervals are intensively affected by an event of Emei taphrogeny. During basaltic magma upward migration, fractional crystallization of anorthose results in slightly-alkaline magma. The specific pyroclastic rocks are formed by the eruption of slightly-alkaline magma in the sea or a salt lake and subsequent hydrothermal alteration. During deposition and diagenesis, the authigenic mineral association is constrained jointly by the sodium-rich and high salinity water environment, and mid-high temperature, high-salinity hydrothermal fluid. Specifically, the sodium-rich hydrothermal fluid, which may sustain till the late diagenesis stage, caused pervasive albitization of pyroclastic rocks, then leading to mineral transformation and formation of a series of mineral associations. Therefore, zeolitization of volcanic glass and vesicle-infillings of zeolite is an essential condition for later mineral transformation and dissolution. Albitization of analcite, recrystallization induced by deep hydrothermal fluids, and both meteoric and deep burial dissolution expanding the micro-pore space ultimately formed porous pyroclastic reservoirs.

Uncertainties in quantitative mineralogical studies using scanning electron microscope-based image analysis

Scanning electron microscope-based automated mineralogy studies are readily associated with quantitative results, providing one of the foundations of geometallurgical studies. Despite the importance of quantitative data for such studies, and efforts to reduce statistical errors, the reporting of uncertainties is rare. This contribution illustrates how bootstrap resampling can be used to provide robust estimates of statistical uncertainties for the modal mineralogy, metal deportment and all relevant textural attributes of a sample or a series of samples. Based on a case study of the Bolcana Au-Cu porphyry deposit in the South Apuseni Mountains, Romania, the impact of insufficient sampling statistics on quantitative mineralogical studies is illustrated. Quantitative analyses of the mineralogy and microfabric of milled ore samples from seven 40 m drill core intervals from the Bolcana Prospect were conducted using a Mineral Liberation Analyser (MLA), complemented by electron probe micro-analysis. Bootstrap resampling was then applied to assess how many grain mount surfaces should be analysed to achieve statistically robust results for both Cu and Au mineralogy, deportment and textural attributes. Despite variable mineralogy, grades and mineralisation styles, estimated statistical uncertainties on Cu deportment are consistently low. In contrast, uncertainties for Au deportment are so high that most reported values for important characteristics are statistically meaningless. This is mainly attributed to the pronounced nugget effect for Au mineralisation, exacerbated by the small sample size analysed by MLA. An unfeasible number of measurements would be necessary to provide robust figures for the deportment of minor/trace elements and minerals, along with other tangible mineralogical properties, such as mineral associations. The results of this case study demonstrate that statistical uncertainties need to be carefully incorporated when considering the results of automated mineralogical studies and their impact on geometallurgical models. This is particularly relevant for studies of precious metal ores.

Origin of Graphite–Diamond-Bearing Eclogites from Udachnaya Kimberlite Pipe

Abstract Kimberlite-borne mantle eclogites represent an important diamond source rock. Although the origin and stability of diamond, as opposed to its low-pressure polymorph graphite, have been studied for decades, their relationship in rare natural samples where both polymorphs coexist remains poorly constrained. To shed new light on this issue, seven graphite–diamond-bearing eclogites from the kimberlite pipe Udachnaya, Siberian craton were comprehensively investigated with respect to their petrography, mineral chemical composition and omphacite 87Sr/86Sr, acquired in situ by laser ablation multicollector inductively coupled plasma mass spectrometry. The calculated P–T conditions for basaltic group eclogites (Eu/Eu* < 1) correspond to a pressure range of 4·8–6·5 GPa and temperatures of 1060–1130 °C, whereas gabbroic eclogites with positive Eu- and Sr-anomalies have a smaller pressure variation (4·8–5·8 GPa), but a larger range in temperature (990–1260 °C). Reconstructed bulk compositions for gabbroic eclogites indicate an oceanic crustal origin for their protoliths, with accumulation of plagioclase and olivine ± clinopyroxene (gabbronorite or olivine gabbro). The protoliths of basaltic eclogites probably formed from the complementary residual melt. The presence of coesite and low Mg# in basaltic eclogites suggest that their light rare earth element depletion was the result of <10 % partial melting during subsequent subduction and emplacement into the cratonic lithosphere. Extremely unradiogenic 87Sr/86Sr (0·70091–0·70186 for six of seven samples) not only provides new evidence for the Archean age (2·5–2·9 Gyr) of Yakutian graphite–diamond-bearing eclogites and for formation of their protoliths in a depleted mantle source, but also suggests that they were not significantly metasomatically overprinted after their formation, despite their extended residence in the cratonic mantle lithosphere. The mineralogical and petrographic features indicate that the primary mineral association includes garnet, omphacite, ± coesite, ± kyanite, ± rutile, graphite, and diamond. Graphite occurs in the samples in the form of idiomorphic crystals (the longest dimensions being 0·4–1 mm) in garnet and kyanite and extends beyond their grain boundaries. Diamonds occur as octahedral cubic transparent, slightly colored or bright yellow crystals as large as 0·1–2 mm. Furthermore, idiomorphic and highly ordered graphite occurs as inclusions in diamond in four samples. The carbon isotope composition for diamond and graphite has a narrow range (−4 to −6·6 ‰) for both groups (gabbroic and basaltic), indicating a mantle source and limiting the role of subducted isotopically light biogenic carbon or reduction of isotopically heavy carbonate in diamond crystallization. Importantly, the presence of graphite and diamond inclusions in garnet, omphacite, and kyanite in three samples indicates a co-formation close in time to eclogitization. Combined, the petrographic and geochemical evidence suggests that both polymorphic carbon modifications can form in the diamond stability field, as also suggested by experiments and some natural examples, although the exact mechanism remains unresolved. Furthermore, this study provides natural evidence that graphite can be preserved (metastably) deep within the diamond stability field, without recrystallizing into diamond, for a long time, ≥2·5 Gyr.

AUTOMATIC IDENTIFICATION OF MINERALS IN IMAGES OF POLISHED SECTIONS

Abstract. Automatic identification of minerals in images of polished section is highly demanded in exploratory geology as it can provide a significant reduction in time spent in the study of ores and eliminate the factor of misdiagnosis of minerals. The development of algorithms for automatic analysis of images of polished sections makes it possible to create of a universal tool for comparing ores from different deposits, which is also much in demand. The main contribution of this paper can be summed up in three parts: i) creation of LumenStone dataset (https://imaging.cs.msu.ru/en/research/geology/lumenstone) which unites high-quality geological images of different mineral associations and provides pixel-level semantic segmentation masks, ii) development of CNN-based neural network for automatic identification of minerals in images of polished sections, iii) implementation of software tool with graphical user interface that can be used by expert geologists to perform an automatic analysis of polished sections images.

Clay mineralogy and lithogeochemistry of lutites from the Lower Cretaceous Crato Member, Araripe Basin, NE Brazil: Implications for paleoenvironmental, paleoclimatic and provenance reconstructions

The Aptian Crato Member of the Araripe Basin is a 50-m-thick succession of laminated limestones alternated with siliciclastic rocks. This unit has been receiving attention worldwide mainly because it is one of the most famous fossil Konservat-Lagerstätten, where were identified well-preserved paleofauna and paleoflora. Clay mineralogy and lithogeochemical data have been widely used in paleoenvironmental, paleoclimatic and provenance reconstructions. However, these techniques were not systematically used to study the Crato Member rocks. This study reports the mineralogical and lithogeochemical characterization of the Crato Member lutites looking for paleoenvironmental, paleoclimatic, and provenance reconstructions. Facies analysis, X-ray diffractometry, lithogeochemical, and scanning electron microscopy studies were carried out on thirteen Crato Member lutite samples in the Três Irmãos quarry, near Nova Olinda County. Regional arid paleoclimate conditions were identified using clay mineral assemblages and two paleoenvironmental models with subtle paleoprecipitation and provenance differences were interpreted. In the lower Três Irmãos quarry, a tidal-dominated delta mouth bar facies succession coincident with a clay mineral association with lesser kaolinite contents was identified, which indicates drier conditions. Lithogeochemical data suggests provenance from Archean felsic rocks. In the upper Três Irmãos quarry, a marginal paleolagoon facies succession coincident with a clay mineral association with higher kaolinite contents was recognized, which indicates wetter conditions. Lithogeochemical data indicate provenance from mixed Post-Archean to Archean felsic-mafic rocks. The paleolagoon water was interpreted as brackish and sudden paleosalinity increases indicated seawater inputs, which were also responsible for raising the paleolagoon water table in the marginal paleolagoon facies succession, which presented paleoenvironmental proxies suggesting a more expressive marine character.

Adaptive multi-paddock grazing enhances soil carbon and nitrogen stocks and stabilization through mineral association in southeastern U.S. grazing lands

Grassland soils are a large reservoir of soil carbon (C) at risk of loss due to overgrazing in conventional grazing systems. By promoting regenerative grazing management practices that aim to increase soil C storage and soil health, grasslands have the potential to help alleviate rising atmospheric CO2 as well as sustain grass productivity across a vast area of land. Previous research has shown that rotational grazing, specifically adaptive multi-paddock (AMP) grazing that utilizes short-duration rotational grazing at high stocking densities, can increase soil C stocks in grassland ecosystems, but the extent and mechanisms are unknown. We conducted a large-scale on-farm study on five “across the fence” pairs of AMP and conventional grazing (CG) grasslands covering a spectrum of southeast United States grazing lands. We quantified soil C and nitrogen (N) stocks, their isotopic and Fourier-transform infrared spectroscopy signatures as well as their distribution among soil organic matter (SOM) physical fractions characterized by contrasting mechanisms of formation and persistence in soils. Our findings show that the AMP grazing sites had on average 13% (i.e., 9 Mg C ha−1) more soil C and 9% (i.e., 1 Mg N ha−1) more soil N compared to the CG sites over a 1 m depth. Additionally, the stocks’ difference was mostly in the mineral-associated organic matter fraction in the A-horizon, suggesting long-term persistence of soil C in AMP grazing farms. The higher N stocks and lower 15N abundance of AMP soils also point to higher N retention in these systems. These findings provide evidence that AMP grazing is a management strategy to sequester C in the soil and retain N in the system, thus contributing to climate change mitigation.

Геохимические особенности Тулалларского золоторудного поля

The article discusses the geochemical features of the Tulallar gold field in the Lesser Caucasus. Distributions of gold and accompanying elements (Ag, As, Hg, Bi, Cu, Zn) in metasomatically altered rocks taken from mine workings (ditches, adits, etc.) and wells are considered. The results of analyzes of furrow samples showed that the content of Au ranges from 0.4 ppm to 37.5 ppm, Ag - from 0.5 ppm to 48.4 ppm. In strongly kaolinized, weakly limonitized quartzites, the Au content ranged from 0.4 to 1.2 ppm, Ag - from 4.0 to 8.8 ppm. In the well drilled in the Central Block, closer to the surface, the siliceous breccias contain Au 309-363 ppm, Ag 132-250 ppm, and high As, Bi and Hg contents are also noted. A similar picture is observed in the silicified rocks of the wells of the Western block. Correlations between Au, Ag and other impurity elements were determined using the STAT program. A direct positive correlation has been established between Au and Ag, Au and Bi, Au and Hg. A positive relationship was also found between Ag and Bi, Ag and Hg. Cluster analysis revealed two different mineral associations: 1) native elements and their compounds - minerals and 2) polysulfide. The closest connection is observed between Ag, Hg and Au. Mineralogically, the Ag-Hg-Au-Bi cluster apparently corresponds to an early ore association - electrum, bismuth tellurides, possibly with inclusions of finely dispersed gold. The second, polymetallic cluster is characterized by a weak correlation bond Аs-Сu-Zn, which indicates that polysulfides were deposited later. The largest amount of Au was deposited in the early mineral association.

Золотая минерализация штокового рудного поля (Магаданская область)

The authors briefly characterize the geology and structure of the Shtokovoye ore field attached to the area where the Khurchan-Orotukan zone of tectonic-magmatic activation overlays the structures of the Yana-Kolyma ore-bearing belt. Studied are mineral associations and physicochemical conditions of gold ore bodies, located both in granites and in hornfelsed sedimentary masses. By the main features of its geological structure, ore composition, and physicochemical formation conditions, the Shtokovoye ore field mineralization corresponds to the "depth" group of the gold-rare-metal formation, analogous to the Butarnoye, Basugunyinskiye, Dubach, and Nadezhda occurrences. Its ores are peculiar in the late epithermal mineralization, which is associated with the Okhotsk-Chukotka volcanic belt and overlays the sinaccretional gold-rare-metal mineralization.