Secondary Enrichment Research Articles

Sedimentary Environments of Cambrian–Ordovician Source Rocks and Ultra‐deep Petroleum Accumulation in the Tarim Basin

AbstractThe Tarim Basin is the only petroliferous basin enriched with marine oil and gas in China. It is presently also the deepest basin for petroleum exploration and development in the world. There are two main sets of marine Source Rocks (SRs) in the Tarim Basin, namely the high over‐mature Cambrian–Lower Ordovician (∊ –O1) and the moderately mature Middle–Upper Ordovician (O2–3). The characteristic biomarkers of SRs and oils indicate that the main origin of the marine petroleum is a mixed source of ∊ –O1 and O2–3 SRs. With increasing burial, the hydrocarbon contribution of the ∊ –O1 SRs gradually increases. Accompanied by the superposition of multi‐stage hydrocarbon‐generation of the SRs and various secondary alteration processes, the emergence and abnormal enrichment of terpenoids, thiophene and trimethylaryl isoprenoid in deep reservoirs indicate a complex genesis of various deep oils and gases. Through the analysis of the biofacies and sedimentary environments of the ∊ –O1 and O2–3 SRs, it is shown that the lower Paleozoic high‐quality SRs in the Tarim Basin were mainly deposited in a passive continental margin and the gentle slope of the platform, deep‐water shelf and slope facies, which has exhibited a good response to the local tectonic‐sedimentary environment. The slope of the paleo‐uplift is the mutual area for the development of carbonate reservoirs and the deposition of marine SRs, which would be favorable for the accumulation of petroleum. Due to the characteristics of low ground temperature, the latest rapid and deep burial does not cause massive oil‐cracking in the paleo‐uplift and slope area. Therefore, it is speculated that the marine reservoirs in the slope of the Tabei Uplift are likely to be a favorable area for deep petroleum exploration, while the oil‐cracking gas would be a potential reserve around the west margin of the Manjiaer Depression. Hydrocarbons were generated from various unit SRs, mainly migrating along the lateral unconformities or reservoirs and the vertical faults. They eventually brought up three major types of exploration fields: middle and lower Cambrian salt‐related assemblages, dolomite inner reservoirs and Middle and Lower Ordovician oil‐bearing karst, which would become the most favorable target of marine ultra‐deep exploration in the Tarim Basin.

Evolution of Gold in the Oxidation Zone of the Kopto Deposit (the Republic of Tuva, Russia)

Abstract —The Kopto deposit (northeastern Tuva) is assigned to gold ore objects with a combination of the Au–Cu–skarn and superposed quartz–gold–sulfide stockwork types of mineralization. From the surface, the ores underwent intense oxidation, which formed a zone of secondary gold enrichment, containing a supergene paragenesis with gold and silver chalcogenides and newly formed gold. The depth of distribution of oxidized ores from the surface is 80–90 m. The Au content varies from fractions of ppm to 150 ppm (on average, 30.8 ppm). Using computer thermodynamic modeling, it is shown how the ore gold–sulfide–quartz association transformed under oxidizing conditions with a decrease in the pH of solutions. Gold becomes more and more high-grade; acanthite appears and disappears; limonite prevails (pH = 1.65; Eh = 0.69 V). The conditions for the stability of pyrite, iron hydroxides, and gold and silver chalcogenides (petrovskaite (AgAuS) and uytenbogaardtite (Ag3AuS2)) have been estimated. It requires weakly acidic solutions with pH = 5–6 and Eh values close to zero, which ensures the stability of thiosulfate and hydrosulfide complexes of noble metals. The main difference between solutions in equilibrium with petrovskaite and uytenbogaardtite is the Ag/Au ratios, which are maximum in the first case and approximately equal in the second. The paper is concerned with a comparative analysis of the morphologic features of gold from primary and oxidized ores of the Kopto gold deposit. The aim of this work is to identify a set of signs of the supergene nature of gold and to assess the extent of its redistribution.

Understanding Necrosol pedogenetical processes in post-Roman burials developed on dunes sands

In Archaeology much emphasis is dedicated to bone preservation, but less attention is paid to the burial soil (i.e., Necrosol), despite its crucial role in governing the geochemical environment. The interaction between human remains and sediments starts after inhumation, leading to bidirectional physico-chemical changes. To approach these complex, bidirectional processes, we sampled at high resolution (n = 46) two post-Roman wooden coffin burials (one single and another double), and the coeval paleosol (n = 20; nearby pedo-sedimentary sequence). The samples were analysed for physical (grain size, colour) and chemical (pH; LOI; elemental composition: FTIR-ATR, XRF, C, N) properties. Principal component analysis enabled to identify five main pedogenetical processes: decalcification, melanization, acidification, neoformation of secondary minerals (i.e., clays) and enrichment in phosphorus. Melanization, acidification and phosphorous enrichment seem to be convergent processes in Necrosols—irrespective of the parent material. Decalcification may be restricted to carbonate containing soil/sediments. Despite not mentioned in previous research, clay formation might also be an overall process. Compared to the local, coeval paleosol, pedogenesis in the studied burial soils was low (double burial) to moderate (single burial). Our results also emphasize the need to study the finer soil fractions, as they provide clues both on soil formation and bone diagenesis.

Geochemical Reconstruction of the Provenance, Tectonic Setting and Paleoweathering of Lower Paleozoic Black Shales from Northern Europe

Lower Paleozoic black shales from Estonia, Sweden, and Russia were analyzed for major and trace elements to reconstruct the provenance, tectonic setting, and paleoweathering conditions of these shales. The black shale is highly enriched in U, V, Mo, and Pb (except in samples from Sweden where Pb is slightly enriched), slightly enriched in SiO2, Fe2O3, K2O, and TiO2 and highly depleted in CaO, Na2O, and MnO, with respect to average shales. The provenance signatures (Th/Sc versus Zr/Sc, Al2O3 versus TiO2, Zr versus TiO2 plots, and Zr/Sc ratio) of the Baltoscandian black shales suggest that they were derived from rocks of intermediate to felsic composition and from recycled sediments. The likely provenance region was the Paleoproterozoic igneous and metamorphic basement of southern central and southern Finland, which consists predominantly of felsic to intermediate metamorphic (acidic to intermediate gneisses, felsic volcanics, microcline granites and migmatites) and igneous rocks (small granitic intrusions and large rapakivi granite intrusions), and reworked older Ediacaran and Lower Cambrian sediments; however, the proportion of clastic input from these sources is not uniform in the three regions studied. The discrimination of the tectonic settings of source materials of the black shale using the SiO2 versus K2O/Na2O plot and a new discriminant method (APMdisc) favors a passive margin setting. The Chemical Index of Weathering (CIW) indicates that the clastic material in the black shale of the studied regions has experienced an intense degree of chemical weathering. Weathering indices (Chemical Index of Alteration CIA and CIW) also show that the black shale has experienced significant secondary potassium enrichment.

Distribution and ecological risk assessment of heavy metals in the sediments of Changli ecological monitoring area, northwest of Bohai Bay, China

ABSTRACT The concentrations of six heavy metals were determined in the sediments of the Changli ecological monitoring area, northwest of the Bohai Bay. The spatial distribution of the metals was discussed, and the ecological risk was evaluated using the potential ecological risk index (PERI) and secondary phase enrichment factor (KSPEF ). The content ranges of Cu, Pb, Cd, Cr, Ni, and Zn were 1.38–25.78, 11.13–21.96, 0.12–0.54, 15.44–120.60, 0.48–57.11, and 44.21–156.38 mg·kg−1, respectively. Based on the results of the geochemical speciation analysis, the residual phase was the main form for all five metals (Cu, Pb, Cd, Cr, and Zn). Compared to the assessment results of KSPEF, PERI is more suitable for the pollution evaluation of heavy metals. The results indicated that all the sediments pose a moderate to considerable level of risk, except site S14 (low risk), and Cd was found to be the main contributor of the ecological risk due to heavy metals.

Geochemical, mineralogical and geostatistical modelling of an IOCG tailings deposit (El Buitre, Chile): Implications for environmental safety and economic potential

In the mining industry deposits of tailings represent large volumes of the mining wastes, reflecting the mineralogy and chemistry of the ore deposit type of origin. In this paper, we report the results of a mineralogical and geochemical characterization study and geostatistical modelling of an Iron Oxide Copper Gold deposit with neutral pH, in an arid climate. Twenty-eight boreholes allowed recovery of 755 samples for analysis. Modelling by means of co-kriging spatial interpolation allowed determination of the distribution of concentrations for elements of interest in the deposit. Low water flow and near neutral-pH paste restrict the mobility of the chemical elements, limiting the development of an oxidation front and inhibiting the appearance of a secondary mineral enrichment zone and the precipitation of secondary efflorescent salts on the tailings surface. Our observations determine that the composition of the gangue material, and to a lesser extent the effect of the tailings gravitational deposition and the geometry of the deposit, control the geochemical and mineralogical associations and distributions present in this deposit of tailings. The observed low mobility along the tailings profile of some potential pollutants (e.g., As, Mn, Cr and Ni) allows to anticipate a low groundwater pollution risk as long as the current environmental conditions remain. Additionally, the depositional history of the tailings had a great influence on the vertical and horizontal distribution of pyrite. However, the grades of elements economic interest such as Fe, Cu and Co are uniformly distributed, which would facilitate the application of tailings reprocessing technologies. In addition, it would allow maximizing the number of necessary boreholes for its economic evaluation.

Increase in fluoride concentration in mine water in Shendong mining area, Northwest China: Insights from isotopic and geochemical signatures

Mine water poses severe threats to the quality of the water supply and ecological environment of the Shendong mining areas owing to its excessive fluoride (F-) content. However, the geochemical behaviours and enrichment mechanisms responsible for F⁻ enrichment during mining activities are not fully understood. In total, 18 Yanan groundwater and 45 mine water samples were collected to analyse the spatial distribution, hydrogeochemical behaviours, and formation mechanisms related to elevated F- levels by analysing the stable isotopes and water-rock interactions. In this study, F- concentrations in mine water samples varied from 0.16 to 12.75 mg/L, with a mean value of 6.10 mg/L, and 77.78% of the mine water samples had a concentration that exceeded China’s national standards (1.00 mg/L) for drinking water. The F- concentration was markedly high in the mine water samples, with the mean F- concentration being 1.58 times of that in the Yanan groundwater samples. The results of stable isotopes (18OH2O, D, 34SSO4, and 18OSO4) and water-rock interaction analyses suggested that cation exchange and competitive effects were the dominant factors responsible for elevated F- concentration in mine water during mining activities. Thus, the weathering of F-bearing minerals, agriculture, and domestic activities do not play a significant role in the secondary enrichment of F- concentration.

Assessing trace-element mobility during alteration of rhyolite tephra from the Dinaride Lake System using glass-phase and clay-separate laser ablation inductively coupled plasma mass spectrometry

AbstractThis paper reports a novel approach in the study of trace-element mobility during the argillization of volcanic glass that is based onin situlaser ablation inductively coupled plasma mass spectrometry glass analyses and that of spatially related illite-smectite collected in the form of fraction separates. The material studied originates from lacustrine sediments of the Dinaride Lake System that bear evidence of intensive weathering of distal tephra during the Miocene climatic optimum. Yttrium andHREEwere probably mobilized from decomposing glass in the form of carbonate complexes and were consequently depleted significantly in the clays studied. On the other hand, the Mg-rich illite-smectite demonstrates an elevated adsorption potential of solvatedLREEcomplexes. This may be explained through clay surface geochemistry controlled largely by Mg for Al octahedral substitution. This paper highlights the role of eogenetic 2:1 clay aluminosilicates that, under favourable geological conditions, may be conducive to secondaryREEenrichment and the formation of potential ion adsorption-type deposits.

НАЗНАЧЕНИЕ ШАХТНЫХ ПЕЧЕЙ ЗАПАДНОАЗИАТСКОЙ МЕТАЛЛУРГИЧЕСКОЙ ПРОВИНЦИИ

The article addresses the problem of the functional purpose of shaft-type furnaces with chimneys found at the Late Bronze Age sites of Northern Eurasia. This category of thermal engineering structures became widespread in the eastern wing of the West Asian (Eurasian) metallurgical province. Thermal sets with flue channels are physical evidence of the implementation of technological algorithms of the pastoral model of metal production based primarily on multistage processing of secondary copper sulfides. Shaft furnaces with flues of the Ural-Kazakhstan region are functionally similar to the more structurally simple fi re pits-furnaces present in the structure of mining and processing complexes of the steppe Cis-Ural region. They were intended for decrepitation, pyrotechnic enrichment, and refining of ore protolith during a long fi re setting using brushwood and wood fuel at relatively low temperatures in the range of 600–800 °C. The degree of complexity of thermal engineering structures was determined by the nature of the raw materials used. Ordinary fi re pits turned out to be acceptable for ore-bearing complexes in the copper shales and sandstones of the steppe Cis-Ural region. The ores of the ultrabasic deposits of the Ural-Mugodzhar region were difficult to be processed and required the use of mine furnaces with flues, which were also characteristic of the metal production centers of the Kazakhstan mining and metallurgical region. Further improvement of thermal engineering structures with flue channels was due to the need to overcome the raw material crisis caused by the exhaustion of available sulfide reserves in secondary enrichment zones within ultrabasic deposits, and copper shale ore occurrences at the end of the Bronze Age. It required the transition to the use of chalcopyrite and greatly contributed to the discovery of iron metallurgy.

Petrography and Geochemistry of the Harzburgite Xenoliths of Lake Guinnadji and Ngao Djalsoka Volcano from the Dibi Area (Adamawa Plateau - Cameroon)

Petrographic and geochemical studies have been carried out on the peridotite xenoliths included in the pyroclastite deposits from the Lake Guinnadji and Ngao Djalsoka volcano close to the Dibi locality in the Adamawa plateau, central Cameroon. The peridotite xenoliths exhibit protogranular and porphyroclastic textures, and are composed of olivine, orthopyroxene and minor amount of clinopyroxene, amphibole (?) and spinel, typical of harzburgite type. ICP-MS and ICP-OES analyses of representative samples show that they are in the range of those of the primitive mantle origin (42.4-45.0 wt.% MgO, 65.7-79.0 wt.% normative olivine). Decreasing SiO2, TiO2, Al2O3 and CaO contents vs increasing MgO trends evidence depletion from more fertile mantle by extraction of basaltic melts, leaving a refractory residue of harzburgite composition. High contents of REE and incompatible elements point out secondary enrichment processes which have affected the peridotite xenoliths. For this, metasomatism caused by silicate fluids is invoked. In that way, peridotites of Dibi area witness of the nature and the evolution of lithospheric mantle under the Adamawa plateau.

Mineral inclusions in the late bronze age metal objects оf Southern Transurals

The paper is devoted to the determination of copper raw material types based on the analysis of mineral inclusions and the composition of metal objects from the Late Bronze Age settlements of the Southern Transurals (XIX–XIII centuries BC). The composition of alloys, inclusions of sulfdes, oxides and metals of objects was established by scanning electron microscopy. The composition of objects is dominated by copper and tin bronze, with a subordinate role of arsenic bronze. The presence of chalcocite and bornite inclusions in most objects indicates the use of rich ores from secondary sulfde enrichment zone. In comparison with analogs, the low total amount of sulfdes in the Southern Transuralian metal objects may indicate the use of mixed oxide and sulfde concentrates. The high Se and Te concentrations of sulfdes are indicative of using of ores of volcanic-hosted massive sulfde or skarn deposits. Keywords: metal objects, copper, bronze, sulfdes, Late Bronze Age, Southern Transurals

Microwave-assisted one-pot rapid synthesis of mesoporous silica-chitosan composites for efficient recovery of rhenium(Ⅶ)

• Mesoporous silica-chitosan composites were prepared by one-pot rapid microwave-assisted method. • The adsorbents were prepared without the use of expensive silane coupling agents or organic amine reagents. • The adsorbents have high adsorption capacity and selectivity for Re(VII). Rhenium (Re) is a rare element in the earth’s crust and has wide range applications in industry, its effective secondary enrichment plays a crucial role in environment and energy field. On the basis of economy and resource sustainability, we report a facile and rapid process to prepare chitosan (CS) functionalized mesoporous silica composites for recovery of Re by a one-pot microwave-assisted synthesis method. Schiff base groups inside the nanostructure were functioned as active sites for Re adsorption. A series of characterization analysis indicated that the optimal adsorbent (SS-KIT-6-M4-15-CS3) possessed mesoporous channel and retained the ordered morphology of mesoporous silica skeleton. The maximum adsorption capacity for Re(Ⅶ) of the as-prepared adsorbent reached 261.81 mg·g −1 at pH 4, higher than that of other reported adsorbents. The SS-KIT-6-M4-15-CS3 showed excellent regeneration performance after eight adsorption–desorption cycles, and exhibited high selectivity for Re(Ⅶ). The prominent adsorption performance was attributed to the chelation between C = N and ReO 4 ¯ according to FT-IR and XPS analysis. These findings showed encouraging potentiality of the adsorbent for recovering of Re(Ⅶ) in real industrial effluents.

Improved isolation and detection of toxigenic Vibrio parahaemolyticus from coastal water in Saudi Arabia using immunomagnetic enrichment.

BackgroundVibrio parahaemolyticus is recognized globally as a cause of foodborne gastroenteritis and its widely disseminated in marine and coastal environment throughout the world. The main aim of this study was conducted to investigate the presence of toxigenic V. parahaemolyticus in costal water in the Eastern Province of Saudi Arabia by using immunomagnetic separation (IMS) in combination with chromogenic Vibrio agar medium and PCR targeting toxR gene of species level and virulence genes.MethodsA total of 192 seawater samples were collected from five locations and enriched in alkaline peptone water (APW) broth. One-milliliter portion from enriched samples in APW were mixed with an immunomagnetic beads (IMB) coated with specific antibodies against V. parahaemolyticus polyvalent K antisera and separated beads with captured bacteria streaked on thiosulfate citrate bile salts sucrose (TCBS) agar and CHROMagar Vibrio (CaV) medium.ResultsOf the 192 examined seawater samples, 38 (19.8%) and 44 (22.9%) were positive for V. parahaemolyticus, producing green and mauve colonies on TCBS agar and CaV medium, respectively. Among 120 isolates of V. parahaemolyticus isolated in this study, 3 (2.5%) and 26 (21.7%) isolates of V. parahaemolyticus isolated without and with IMB treatment tested positive for the toxin regulatory (toxR) gene, respectively. Screening of the confirmed toxR gene-positive isolates revealed that 21 (17.5%) and 3 (2.5%) were positive for the thermostable direct hemolysin (tdh) encoding gene in strains isolated with IMB and without IMB treatment, respectively. None of the V. parahaemolyticus strains tested positive for the thermostable related hemolysin (trh) gene. In this study, we found that the CaV medium has no advantage over TCBS agar if IMB concentration treatment is used during secondary enrichment steps of environmental samples. The enterobacterial repetitive intergenic consensus (ERIC)-PCR DNA fingerprinting analysis revealed high genomic diversity, and 18 strains of V. parahaemolyticus were grouped and identified into four identical ERIC clonal group patterns.ConclusionsThe presented study reports the first detection of tdh producing V. parahaemolyticus in coastal water in the Eastern Province of Saudi Arabia.

Selenium Geochemical Characteristics and Influencing Factors of Paddy Fields in Du'an County, Guangxi

This study used 21 rock samples and 193 sets of paddy soil and rice grain samples collected form Baiwang Town, an area of clastic sedimentary rocks in Guangxi, China, to evaluate the potential for selenium-rich agriculture. We analyzed the concentrations of selenium and heavy metals in the soil and rice samples, and discuss the influencing factors by means of statistics and correlation analysis. The results showed that the selenium-rich rate of paddy soil and rice grain in Baiwang Town were 67.4% and 64.8%, respectively, but the content of cadmium in the selenium-rich soil samples was generally higher than the baseline value for China and the background value for Guangxi. In comparison to the screening value of soil pollution risk for agricultural land(GB 15618-2018), the over-standard rate of cadmium was 46.1%, while the over-standard rates of other heavy metals were negligible. The comparison shows that the selenium-rich rate of rice was 61.1% in the southern area of Baiwang Town with a negligible heavy metal content, and the advantages of green selenium-rich rice planting were clear. The correlation analysis showed that secondary enrichment was the main form of selenium enrichment in the study area. The soil pH and texture of the root-zone soil also affected the selenium content of the soil. The selenium content of rice seeds was mainly affected by the selenium content, active selenium content, pH, and aluminum oxide content of the root-zone soil. The risk assessment showed that the level of dietary exposure to cadmium is generally within safe limits, but it is still necessary to strengthen the monitoring of cadmium in rice and control cadmium pollution to reduce the levels of dietary exposure, especially in the central region of Baiwang Town.

To the question of raw material sources of mining and smelting centers of the Paleometal Epoch in Central Kazakhstan

The subject of this research is the copper deposits, copper-ore resource, and sources of alloying raw materials for mining and smelting production of the Paleometal Epoch in Central Kazakhstan, namely within the Kazakhstan mining and smelting region and Zhezkazgan-Ulytau mining and smelting center. The article provides the interim results of comprehensive research of geoarchaeological production facilities in the territory of copper deposits within the Zhezkazgan-Ulytau mining and smelting center, which allow determining the peculiarities of metallogenic complexes that used to be potential objects of the development of copper-ore reserves during the establishment of copper metallurgy, as well as making a predictive assessment of mineral raw materials potential of the region. The initial premise of this research lies in the authors' pursuit to integrate natural scientific methods of research into the field of humanities to the maximum effect via studying smelting slags and ore relics from the ancient settlements of the region for the purpose of reconstructing the mining and smelting process of the Bronze Age in Central Kazakhstan. The authors offer the variants of localization of the mineral raw materials complex of Zhezkazgan-Ulytau mining and smelting center within the Kazakhstan mining and smelting region. Based on examination of the ores and smelting slags of Bronze Age settlements in Central Kazakhstan, the authors believe that the main copper raw materials in the Zhezkazgan-Ulytau region were the oxidized malachite-azurite and rich sulfide ores, as well as the zones of secondary sulfide enrichment of copper sandstones of the Zhezkazgan ore region. The conducted research allow to get closer to establishing patterns of localization of various types of copper deposits and development of copper-ore resources for mining and smelting production of Zhezkazgan-Ulytau region during the Paleometal Epoch.

Insights into Distribution of Soil Available Heavy Metals in Karst Area and Its Influencing Factors in Guilin, Southwest China

The bioavailable contents of heavy metals in karstic soils are a subject of increasing concern since the uptake of heavy metals by plants can pose a severe threat to food safety and public health. However, the bioavailable contents of heavy metals and their effective factors are poorly understood in karst regions. Calcareous soil and red soil developed from carbonate and clastic rocks, respectively, were chosen from a typical karst region (Guilin) of southwestern China, and the total (CT) and available (CA) contents of 11 heavy metals, as well as their influencing factors in soil profiles, were investigated. The results showed that calcareous soil has greater soil organic carbon, total nitrogen, available nitrogen, available potassium, and calcium (Ca) contents than red soil, but lower available phosphorus and C:N. Acid-soluble Ca (Aca) was the dominant fraction in both types of soil. Heavy metals were highly accumulated in calcareous soil, mainly controlled by secondary enrichment in the processing of carbonate rock weathering. For the majority of metals, calcareous soil had higher CT and lower CA than red soil. According to a redundancy analysis (RDA) and Pearson correlation coefficient, the high pH and Ca content in calcareous soils were primary factors influencing both the CT and CA of the metals, especially residual Ca to CT and Aca to CA. Additionally, higher soil cation exchange capacity and clay minerals also probably improved the immobility of heavy metals.

Evidence for extreme Sm[sbnd]Nd fractionation during chemical weathering

During subaerial chemical weathering, submarine weathering and other intracrustal processes, SmNd chemical fractionation remains uncertain, while a little is known about the conditions, scale and magnitude, specific processes and actual mechanism for possible SmNd fractionation. Here, an in situ terra rossa weathering profile developed on dolostone is chosen for the study. Based on sequential extraction experiments and measurements of the mineral and geochemical compositions including SrNd isotopic compositions, we suggest that subaerial chemical weathering not only leads to considerable SmNd mobilization, redistribution and secondary enrichment, but also gives rise to extreme SmNd fractionation, apparent 143Nd isotope homogenization, nearly complete resetting of the 147Sm143Nd isotope system, anomalous initial 143Nd/144Nd ratios, and meaningless 143Nd model age (TDM) for weathering products. We found that the lanthanide tetrad effect, rather than mineralogical control, is responsible for the observed substantial SmNd fractionation and for the other rare earth element fractionation. Under domination of the lanthanide tetrad effect, the mobility of Sm is preferential to that of Nd during their migration in the form of dissolved organic complexes. Our results also illustrate that resetting of the 147Sm143Nd isotope system in weathering products is controlled by the combined effect of the extraneous dissolved SmNd input and additional SmNd fractionation. Finally, we argue that similar scenarios may occur in submarine weathering, diagenesis and other geological processes.

Distribution, contamination status and bioavailability of trace metals in surface sediments along the southwest coast of India

This study investigates the influence of upwelling induced seasonal hypoxia in the sediment-water interface on the distribution, bioavailability and geochemical partitioning of selected trace metals in surficial sediments along the southwest coast of India based on two successive cruises. The first cruise was during the southwest monsoon (SWM) season when coastal waters exhibited intermittent bottom hypoxia due to upwelling. The second cruise during the northeast monsoon (NEM) season was characterised by a uniformly warm and well-oxygenated water column in the study region. The results showed that grain size, organic carbon and Fe are the major factors influencing the distribution of trace metals in the surface sediments. Based on the geochemical indices (contamination factor, enrichment factor and geo-accumulation factor), the study region appears to be moderately contaminated by Ni, Cr, and Pb. Based on the ecological risk assessment criteria, the enrichment of Pb, Cr and Ni may cause adverse effects on the benthic organisms. The fractionation studies demonstrated that the major pathway of metal deposition in the sediment is lithogenic. The data also showed that labile and organic fractions are the second dominant forms, while other fractions (exchangeable and carbonate) are insignificant. The consistency in the reactive Fe concentrations during SWM and NEM could be due to the absence of Fe dissolution in sediments under mild reducing condition (intermittent hypoxia). In addition to the above, an enrichment of organic matter also leads to increased deposition of trace metals in sediments. Conversely, the secondary phase enrichment factor and risk assessment code calculated based on the metal fractionation data indicated low risk and contamination along the southwest coast of India except for Zn that showed moderate contamination in some transects. The study provides the need for regular geochemical assessment to control metal pollution in the coastal environment, which is a major resource of the fishery.

Distribution and secondary enrichment of heavy metal elements in karstic soils with high geochemical background in Guangxi, China

Karst environments are globally significant, and the soils that develop on these landscapes often have unique geochemical features, including elevated–levels of metals. However, it has not been determined whether the enrichment of metals in soils is mainly controlled by parent rocks or secondary enrichment during weathering. In this paper, we studied the control of the accumulation of heavy metals in soils by parent materials and/or the process of soil formation. We examined the un–weathered carbonate and clastic bedrocks, as well as surface soils in a typical karst area in Guangxi of China. The spatial distribution of heavy metal (Cd, As, Cr, Cu, Hg, Ni, Pb, and Zn) concentrations in soils was mainly controlled by the geological background. Except for Cd, the concentrations of heavy metals in carbonate rocks were much lower than those in clastic rocks, whereas the soils derived from the carbonate rocks were highly enriched with heavy metals than those in clastic area. The enrichment of Cd in surface soils from the carbonate substrates was the result of the dual effect of secondary enrichment and parent rock inheritance, whereas the enrichment of other metals was mainly the result of secondary enrichment. During the weathering process of carbonate bedrock, great majority of the quantities of inherent heavy metals were leached, with only 2% of Cd being retained in situ. The high concentrations of soil Fe, Al, and Mn oxides, organic carbon and clay content (Al2O3/SiO2) were closely related to the enrichment of heavy metals in studied surface soils.

Bronze Age metallurgical slags from the South Urals: types, mineralogy and copper sources

In the paper, an investigation of copper metallurgical slags found in the South Urals and dating to the Bronze Age between 4000 and 1300 BCE is carried out. Four main mineralogical types are distinguished according to their mineral composition: Cr-rich spinel containing olivine, sulphide-containing olivine, sulphide containing glassy and pyroxene type. First type of slags is composed of zoned olivine, magnetite and glass having relicts of Cr-rich spinels and serpentinites that indicate the use of azurite-malachite ores from ultrabasic rocks. These finds were determined in sites of the Early Yamna period in the Cis-Urals and are widespread in Sintashta culture. The second type is composed of skeletal olivine crystals, magnetite and wustite with copper sulphides droplets. It type belongs to Alakul period. The raw material sources are sulphide ores from a secondary enrichment zone of VMS, skarn and Cu-porphyry deposits. The sulphide containing glassy type is mainly composed of glass with copper and sulphide droplets. The slags were recovered in the Srubna sites. The raw material sources were rich sulphide ores of cupriferous sandstones. The pyroxene type is composed of augite, pigeonite and/or wollastonite with a small amount of glass and sulphide inclusions. According to the composition of glass, slags can be distinguished into the Cis-Uralian type, including cupriferous sandstones, and Trans-Uralian type having various volcanogenic-hydrothermal deposits as raw materials. Essential Ca, P, Ba and REE impurities in slag glass demonstrate the use of barite, calcite and bone fluxes. The phase diagrams, crystallisation temperatures and experimental data revealed that slag melt temperatures ranged between 1150–1300 ° C.