Enrichment Of Trace Elements Research Articles

A new kind of invisible gold in pyrite hosted in deformation-related dislocations

Abstract Mining of “invisible gold” associated with sulfides in gold ores represents a significant proportion of gold production worldwide. Gold hosted in sulfide minerals has been proposed to be structurally bound in the crystal lattice as a sulfide-gold alloy and/or to occur as discrete metallic nanoparticles. Using a combination of microstructural quantification and nanoscale geochemical analyses on a pyrite crystal from an orogenic gold deposit, we show that dislocations hosted in a deformation low-angle boundary can be enriched in Ni, Cu, As, Pb, Sb, Bi, and Au. The cumulative trace-element enrichment in the dislocations is 3.2 at% higher compared to the bulk crystal. We propose that trace elements were segregated during the migration of the dislocation following the dislocation-impurity pair model. The gold hosted in nanoscale dislocations represents a new style of invisible gold.

Geochemical and sedimentary facies study – Implication for driving mechanisms of organic matter enrichment in the lower Silurian fine-grained mudstones in the Baltic Basin (W Lithuania)

More than 100 m-long core sections from Western Lithuania (Baltic Basin), presenting an almost continuous lower Silurian fine-grained siliciclastic organic matter-rich sedimentary record from Aeronian to Homerian, were investigated to evaluate the main forces governing the organic matter enrichment. The methods applied include organic and inorganic geochemistry, organic petrology, sedimentological and petrographic studies along with framboidal pyrite analysis, as well as analysis of stable nitrogen and organic carbon isotopes. The petrographic observations showed distinct mudstone diversity reflecting a variety of paleoenvironmental depositional conditions evolving against a backdrop of post-Ordovician climate, thus, sea level variations, and progressing development of foreland basin throughout the early Silurian. Reflectance measurements on vitrinite-like particles, supported by molecular organic geochemical and Rock-Eval data prove that kerogen from the studied section reached the oil window maturity stage. Rock-Eval pyrolysis, organic geochemical and petrographical as well as δ13Corg data clearly confirm the marine origin of the organic matter. Various geochemical proxies and sedimentary features indicate that in Aeronian a period of more humid climate favored enhanced nutrient input, which in turn intensified organic matter productivity resulting in large amounts of organic matter accumulation. Redox proxies (TOC/TS ratio, trace elements enrichment, molecular organic geochemical indices, framboidal pyrite analysis, TOC/P ratio) demonstrate a rather broad spectrum of bottom water oxygenation levels in the lower Silurian sediments accumulated under oxic - dysoxic – anoxic conditions interrupted by several episodes of euxinia. A highly condensed section of Aeronian black-grey mudstones manifests a very good organic matter preservation under sediment-starved and oxygen-depleted settings. Here, the oxygen-depleted water bottom conditions are well evidenced by low values of δ15N and δ13Corg pointing to the presence of diazotrophic N-fixing and chemoautotrophic organisms. The Sheinwoodian-Homerian section of monotonous grey calcareous mudstones evenly and moderately enriched in organic matter reflects the most steady environmental settings developed under more arid climate in comparison to Llandovery. Throughout the early Silurian sedimentation rates were overall low, although probably enhanced in Wenlock, and played a role in organic matter preservation. It was a critical factor during sedimentation of grey-greenish mudstone of the Telychian characterized by comparatively the lowest organic matter preservation efficiency. Variations in the intensity of the pycnocline, thus organic matter preservation, were probably controlled by climate-triggered sea level changes, although tectonically-driven paleoenvironmantal effects, bathymetry, and, at some point, intensified paleoproductivity inducing oxygen-restricted conditions, were likely contributing. Although MoEF/UEF ratios mainly indicate fully open marine settings during the entire early Silurian, Mo–TOC covariation clearly displays strict basinal restriction in the Aeronian. The profile of δ13Corg demonstrates six carbon isotope excursions along the lower Silurian section. The identified Late Aeronian and Early Sheinwoodian Carbon Isotope Excursions are linked to global sea-level changes, thus, changes in oceanic water circulation pattern. A high percentage of tiny pyrite framboids within the interval of Early Sheinwoodian CIE could reflect an increased pyrite burial under highly reducing conditions and might be associated with an Oceanic Anoxic Event. The three positive δ13Corg excursions within the Telychian seem to be related to an early diagenetic partial oxidation of organic matter.

The composition of subduction zone fluids and the origin of the trace element enrichment in arc magmas

The partitioning of major and trace elements between eclogite and aqueous fluids with variable salinity was studied at 700–800 °C and 4–6 GPa in piston cylinder and multi anvil experiments. Fluid compositions were determined using the diamond trap technique combined with laser ablation ICP-MS measurements in the frozen state. In addition to NaCl, SiO2 is the main solute in the fluids. The fluid/eclogite partition coefficients of the large ion lithophile elements (LILE), such as Rb, Cs, Sr, and Ba as well as those of the light rare earths (LREE), of Pb, and of U increase by up to three orders of magnitude with salinity. These elements will therefore be efficiently transported by saline fluids. On the other hand, typical high field strength elements, such as Ti, Nb, and Ta, are not mobilized even at high salinities. Increasing temperature and pressure gradually increases the partitioning into the fluid. In particular, Th is mobilized by silica-rich fluids at 6 GPa already at low salinities. We show that we can fully reproduce the trace element enrichment pattern of primitive arc basalts by adding a few percent of saline fluid (with 5–10 wt% Cl) released from the basaltic slab to the zone of melting in the mantle wedge. Assuming 2 wt% of rutile in the eclogite equilibrated with the saline fluid produces a negative Nb Ta anomaly that is larger than in most primitive arc basalts. Therefore, we conclude that the rutile fraction in the subducted eclogite below most arcs is likely < 1 wt%. In fact, saline fluids would even produce a noticeable negative Nb Ta anomaly without any rutile in the eclogite residue. Metasomatism by sediment melts alone, on the other hand, is unable to produce the enrichment pattern seen in arc basalts. We, therefore, conclude that at least for primitive arc basalts, the release of hydrous fluids from the basaltic part of the subducted slab is the trigger for melting and the main agent of trace element enrichment. The contribution of sediment melts to the petrogenesis of these magmas is likely negligible. In the supplementary material, we provide a “Subduction Calculator” in Excel format, which allows the calculation of the trace element abundance pattern in primitive arc basalts as function of fluid salinity, the amount of fluid released from the basaltic part of the subducted slab, the fluid fraction added to the source, and the degree of melting.

State-of-the-art and perspectives in the heavy mineral industry of Sri Lanka

Heavy minerals have become an essential commodity in modern-day technology. The objective of this study is to examine the current status of the heavy mineral industry of Sri Lanka. The present study also examines the economic viability of potential heavy mineral placer deposits, based on geochemical data. Field investigations suggested the occurrence of heavy minerals as beach-placers, and inland/raised beach deposits along the coastline of Sri Lanka. Geochemical results showed the enrichment of TiO2, Fe2O3, Al2O3, and trace elements, and depletion of other major oxides such as Na2O, K2O, MnO, MgO, CaO, and P2O5. Consequently, it suggests the abundance of ilmenite, leucoxene, rutile, sillimanite, garnet, and rare earth element (REE)-bearing heavy minerals in potential placer deposits. In contrast, this study illustrates the exported quantity (in the weight ratio of 35:3:1) of ilmenite, rutile, and zircon minerals during the last decade. Ilmenite is the dominant heavy mineral in Sri Lanka, and thus, its production and price volatilisations are essential to understand the current status and predict the future behaviour of the heavy mineral industry. Statistical observations suggest that the global production and unit price variations of ilmenite have increased gradually from 1950 to 2015. Besides, the forecasted variations in annual global production and unit price changes of ilmenite indicate healthy compound annual growth rates of 1.27% and 1.43%, respectively. However, Sri Lanka has less contribution (< 1%) to global ilmenite production. Consequently, the value addition of ilmenite must be highly encouraged with at least an immediate stage (e.g. synthetic rutile). The present study also highlights possible value addition stages of available heavy mineral resources (low-, intermediate-, or high-level value addition), and discusses action plans to improve the quality of the heavy mineral industry of Sri Lanka. In recommendations, imposing sustainable regulations and policies would uplift the heavy mineral industry of Sri Lanka. For example, value addition to local heavy minerals and terminating raw commodity export are highly recommended.

Transient deep-water oxygenation recorded by rare Mesoproterozoic phosphorites, South Urals

The Mesoproterozoic deep ocean is thought to have been largely anoxic, dominated by ferruginous conditions. Phosphate was scavenged from the water column by iron oxyhydroxides, and dissolved nitrate was rapidly reduced along the redoxcline. Primary productivity was therefore generally low, and eukaryotic life was restricted to oxic marine margins. This model is supported by new nitrogen isotope data from the Lower Riphean (ca. 1.55 Ga) strata of the South Ural Mountains, where we find evidence for strong redox stratification, coupled with low organic carbon content. In contrast, unconformably overlying siliciclastic sedimentary rocks of Middle Riphean age (ca. 1.33 Ga) preserve a rare occurrence of apatite concretions, associated with relatively high concentrations of organic carbon (up to 4 wt%). The Pb-Pb isochron age for the apatite concretions of the Zigazino-Komarovo Formation is 1330 ± 20 Ma (MSWD = 3.7). We measured nitrogen isotope ratios across this interval and found δ15N values up to + 7.6‰, which are similar to those in modern upwelling zones and indicative of a significant nitrate reservoir. These observations are most parsimoniously explained by upwelling of phosphate- and nitrate-bearing waters, suggesting that the deep ocean was at least regionally and temporarily oxygenated. The lack of redox-sensitive trace element enrichment in these strata and the general scarcity of apatite accumulations in the Mesoproterozoic sedimentary record suggest that oxic deep-waters were not a global and persistent phenomenon, but our results confirm that oxic, nutrient-rich refugia existed in Mesoproterozoic oceans and were perhaps important for the radiation of early eukaryotes.

Pegmatitic granite fluid compositions and thermochronometry in the Seridó Belt, Borborema Province, Brazil: Insights from trace element advection-diffusion-partitioning halos in host schist and gneiss

At the Seridó Belt pegmatitic province, fluid advection from dykes and sills led to trace element diffusion and partitioning in biotite, producing sub metric concentration halos in host mica schist and gneiss. We analyzed trace element concentration vs. distance profiles in the host rock of pegmatitic granite intrusions showing enrichments in Li, F, Cl, Zn, Rb, Nb, Sn, Cs, Ta, U and depletions in Sr and Ba. We estimated fluid temperatures in the range 600 to 700 °C using methods of Ti in biotite, F-OH in biotite-apatite and Tschermak component in biotite-muscovite. We analytically modeled thermal profiles around pegmatitic planar intrusions and found that cooling by thermal flats in the first meters into the host rock is reached in 100 years for a 10 m thick sill. The model constraints sustained heat flow during pegmatitic melt emplacement into a colder host rock. The measured trace element profiles were fitted with solutions of differential equations modeling advection-diffusion-partitioning in porous media under isothermal and cooling conditions. Each trace element profile is equally fitted by values of pegmatitic fluid concentration vs. fluid flux duration plotting as a straight line. We obtained a theorical framework combining pegmatitic fluid trace element composition, fluid flux duration and velocity, rock/fluid trace element partition coefficient, and cooling rate. Using published fluid inclusion trace element composition, we obtained fluid flux duration between tens of years to several centuries for the studied profiles. In the case of low temperature fluid flux at 450 °C the modeled flux duration is increased by less than one order of magnitude. The results allow us to interpret the trace element halos as sub millennial hot isothermal fluid influx from the pegmatites into their host rock. Trace element partitioning from the fluid into host rock falls mostly within the range of 0.01 to 25 and decreases in the order Nb, Cu, Rb, Zn-Li, Cs-Sn. The model constraints fluid advection velocity between 1 × 10−11 m/s and 1 × 10−9 m/s, typical of regional metamorphism to shear focused fluid flow regimes. The trace element enrichment of biotite along the profiles reproduces the observed pattern for whole rock, indicating that biotite is their main sink during pegmatitic fluid influx. Using experimental F in biotite diffusivity we obtained a minimal planar diffusion distance, or the effective porosity, between 7 and 15 μm for the total F re-homogenization of metamorphic biotite by pegmatitic fluid. As shown from others fluid-present petrogenetic systems, the trace element contents of biotite in host rock at the contact with pegmatitic intrusions can be a potential tool for the assessment of their rare metal potential.

Systematic LREE enrichment of mantle harzburgites: The petrogenesis of San Carlos xenoliths revisited

The dichotomy between partial melting and metasomatism is a paradigm of mantle geochemistry since the pioneering work of Frey and Prinz (1978) on the occurrence of LREE-enriched harzburgites. However, the thermo-chemical implications of such two-stage scenarios are often poorly considered, and the latter fail to explain why trace-element enrichment and major-element depletion are often proportional. We here re-envisage the petrogenesis of the famous San Carlos peridotites based on new petrographic observations and detailed modal, major- and trace-element compositions. The lherzolites (and pyroxenites) are characterized by homogeneously fertile mineral chemistry and LREE-depleted patterns consistent with low degrees of partial melting of the lherzolitic protolith. Bulk compositions and mineral zoning suggest that opx-rich pyroxenites formed by pressure-solution creep during melt-present deformation, locally accompanied by magmatic segregations of cpx. The harzburgites are characterized by stronger mineral zoning with low-Mg# and Na-, Al- and Cr-rich cpx rims, and can be discriminated in a low-Jd and high-Jd cpx groups. The high-Jd group is interpreted as the result of local elemental redistribution in the presence of a low-degree hydrous melt, in good agreement with their wide range of LREE enrichment. In contrast, the MREE-to-HREE fractionation and increasing Cr# in spinel of the low-Jd group indicate that they experienced higher degrees of melting. Open-system melting simulations of trace-element fractionation during hydrous flux melting suggests that the high-Jd harzburgites are the result of low fluid influx producing poorly extracted melt, while higher influx led to higher melting degrees and efficient melt extraction in the low-Jd harzburgites; the lherzolites mostly remained below or near solidus during that process. The lithological and chemical heterogeneity of San Carlos mantle is thus compatible with a single-stage evolution, which is also supported by the striking consistency between Fe-Mg exchange and REE thermometric estimates (1057 and 1074 °C on average, respectively), indicating that harzburgites and lherzolites probably followed a similar P-T path and relatively little sub-solidus re-equilibration. These interpretations suggest that the development of melt extraction pathways promoted by reactive channeling instability is able to produce complex lithological heterogeneities during hydrous flux melting. This process provides a self-consistent explanation for the systematic enrichment of harzburgites observed in many mantle terranes and xenoliths worldwide. We argue that San Carlos is one of such examples where a ca 1.5-Ga continental lithosphere experienced localized flux melting and deformation during the tectonic reactivation of a Proterozoic subduction zone, providing new constraints on the mantle sources of volcanic activity in the Jemez Lineament.

Investigating the Combined Use of Enrichment Factor and Weather Research and Forecasting (WRF) Modelling for Precipitation Sample Source Identification: A Case Study in North Carolina, USA.

Pollutants emitted into the air not only have local effect but can also affect areas further from the source. The goal of this study was to assess a method for identifying the sources of element pollution in rainwater using enrichment factors supported by Weather Research and Forecasting (WRF) model. In this study, we collected nineteen rainwater samples at the two locations of Durham and Chimney Ridge in North Carolina, USA in July of 2014. The samples were analyzed for pH, conductivity and levels of major ions and a range of trace elements. These data showed that the pH of precipitation ranged between 3.91 and 6.65, with an average value of 4.98. The average electrical conductivity was 15.58 and 17.7 μS/cm for rainwater collected at Durham and Chimney Ridge, respectively. The lowest concentration of the elements analyzed was for thorium (Th) with an average concentration of 0.002ppb, whereas the highest elemental concentration was for calcium (Ca) with an average concentration of 980.3ppb. Enrichment factors for trace elements were assessed within three different groups as: (1) rarely enriched, (2) significantly enriched, and (3) highly enriched. Copper (Cu), zinc (Zn), arsenic (As), molybdenum (Mo), silver (Ag), cadmium (Cd), and lead (Pb) were highly enriched trace elements. The wind fields acquired by the WRF model indicated the probable contamination sources. Source identification indicated that the highest contribution of elements to precipitation was from industry. The results showed that the combined use of enrichment factors and the WRF model can be used to identify the sources of pollutants in precipitation samples.

Spatial heterogeneity of redox-sensitive trace metal enrichments in upper Ediacaran anoxic black shales

The Ediacaran radiation of metazoans is widely thought to have been triggered by an increase in atmospheric and oceanic oxygen levels. Although supported by other proxies, rising oxygen levels were deduced to a significant degree from sedimentary enrichments of redox-sensitive trace elements (RSTEs). However, some organic-rich shales of this period show only minor enrichments in RSTEs, leaving the significance of RSTE data for palaeo-oxygenation interpretations in doubt. We measured and compiled proxies for marine redox conditions (Fe species, RSTEs), total organic carbon (TOC) and water mass restriction (Mo/TOC and Co × Mn v. Cd/Mo) in the intra-shelf Jiulongwan and basinal Sandu sections of the Nanhua Basin in South China. Compared with the same proxies from coeval sections in the Nanhua Basin and globally, our results document a strong spatial heterogeneity of RSTE enrichments in anoxic black shales during the late Ediacaran. We infer that RSTE enrichments were strongly influenced by local factors, such as basinal restriction, seawater RSTE concentrations, and differential elemental responses to redox conditions and other influences. The broader significance of our findings is that they highlight the difficulty of investigating global redox conditions based on an analysis of local RSTE proxies within a single depositional basin or a limited number of study sections. Thematic collection: This article is part of the Advances in the Cambrian Explosion collection available at: https://www.lyellcollection.org/cc/advances-cambrian-explosion Supplementary material : Tables S1–S3 are available at https://doi.org/10.6084/m9.figshare.c.5325047

Uniform oxygen fugacity of shergottite mantle sources and an oxidized martian lithosphere

Martian meteorites are the only available samples that can be directly measured to constrain the geological evolution of Mars. It has been suggested that the oxygen fugacity (fO2) of martian shergottite meteorites, which have low (∼7 wt.%) to high-MgO (∼30 wt.%) compositions, correlates with incompatible trace element enrichment (i.e., La/Yb), and 87Sr/86Sr, 143Nd/144Nd, 187Os/188Os and 176Hf/177Hf at the time of crystallization. These relationships have been interpreted to result from early magmatic processes segregating enriched and more oxidized from depleted and more reduced reservoirs in Mars. Here we use the V-in-olivine oxybarometer to constrain the fO2 of shergottites and the dunitic chassignites. These data, utilizing early crystallizing silicate phases, constrain the shergottite fO2 range to between −3.72 ± 0.07 and −0.21 ± 0.55 ΔFMQ (log units relative to the fayalite-magnetite-quartz buffer), with no correlation with trace element enrichment or Nd isotope systematics. Previously employed oxybarometers that use later-formed or multiple mineral phases, and that show such correlations, likely differ from the V-in-olivine oxybarometer in that they record effects from late-stage magmatic processes. In contrast to shergottites, chassignites are relatively oxidized, at +2.1 ± 0.4 to +2.2 ± 0.5 ΔFMQ. The chassignites, along with the nakhlites, have been proposed to be sourced from metasomatized lithospheric mantle, and their high fO2 strengthens this model. The new data implies that the martian mantle sources of shergottites have fO2 of −2.1 ± 1.8 ΔFMQ. This estimate indicates that the mantle and core of Mars are not in redox equilibrium and therefore that oxidation of the martian mantle following core formation is required.

Source of selenium in Handan geochemical anomaly belt: Evidences from petrology and geochemistry of Upper Paleozoic in western Handan, China

Handan lies in a geochemical anomaly belt characterized by enrichment of selenium (Se) in rock, soil, and water, contrasted with deficiency of Se in the North China Plain. In this study, 27 environmental soil samples and 96 rock samples in the Upper Paleozoic were analyzed by inductively coupled plasma optical emission spectrometer (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) for major and trace element concentrations to determine the source of Se in the environment.Se concentrations in soil vary from 0.054 μg/g to 2.869 μg/g, with an average of 0.598 μg/g. Ignoring the anthropogenic contamination, Se concentrations in soils elevate with the decrease of distance from outcrops in Mountain Zishan (Mt. Zishan). There is a strong positive correlation between Se and Al2O3 (r = 0.679, P < 0.01, n = 27), and between Se and TiO2 (r = 0.638, P < 0.05, n = 27). Furthermore, Se is significantly negatively correlated with MgO, Na2O, K2O, and Sr (r = −0.674, −0.755, −0.716, −0.739, respectively, P < 0.01 for all, n = 27). It indicates that Se in the soil is derived from weathering products.Se is the most highly enriched trace element within Upper Paleozoic, which is composed of Benxi Formation (BX Fm.), Taiyuan Formation (TY Fm.), Shanxi Formation (SX Fm.), and Shihezi Formation (SHZ Fm.), in outcrops in Mt. Zishan area, western Handan. Se concentrations of rock samples vary from 0.021 μg/g to 4.971 μg/g, with an average of 0.401 μg/g. The maximum of Se concentration is 99.41 times higher than the Upper Continental Crust (UCC). The order of the rest trace elements enrichment degrees is S > Pb > As > Ga > Li > Bi > Th > Sc > In > U > Cd > Y > Rb > Ba > Cr > V > Be > Cs > Ni > Zn > Tl > Sr > Co > Mo > Cu. Se enrichment appears in two types of rocks, which are gray clay rocks and black mudstones and shales (including coal and gangue). Stratigraphically, Se is more highly enriched in TY Fm. and SX Fm., with average enrichment factor (EF) values of 14.64 and 5.59, respectively.Chemical index of alteration (CIA) and several environmentally sensitive elements, such as Th, U, Sr, Ba, V, Cr, and Ce, were employed for sedimentary environment analysis. The results revealed that Se-enriched rocks were deposited mainly in a weak, reducing freshwater environment, and their sediments were subject to an intermediate chemical weathering process. The discrimination diagrams of SiO2-TiO2, F1-F2, ∑REE-La/Yb, and La/Sc-Co/Th indicate that the terrestrial clastic sediments were dominated by multiple types of original rocks. Se-laden clastic materials derived from mafic and ultramafic rocks in Yinshan ancient land provided main source of Se in Upper Paleozoic in western Handan, and adsorption of clayey and organic materials and biological accumulation induced Se enrichment ultimately.

The trace-element composition of a Polish stalagmite: Implications for the use of speleothems as a record of explosive volcanism

Identification of volcanic signals preserved in paleoenvironmental records can provide key insights into the timing and consequences of explosive volcanism. Yet the eruption record is incomplete and this confounds our ability to link volcanic eruptions to their impacts on climate and environments. Studies have suggested that stalagmite records can help to address these gaps, through the identification of transient geochemical variability associated with incorporation of elements derived from erupted material. However, the utility of stalagmites for tracing volcanism is poorly constrained globally. Here, we present a high-resolution geochemical dataset for stalagmite NIED08–05 from Niedźwiedzia Cave (Poland). We do this with two primary aims: (1) to test the suitability of NIED08–05 as a record of volcanism since 3 ka BP, and (2) to ascertain whether stalagmites grown in temperate regions preserve volcanic signals with success comparable to those grown in tropical regions. We find transient enrichments of 16 trace elements and the rare-earth-elements Y, La, Nd, which coincide with the timing of some known eruption events. Using Principal Component Analysis (PCA) we find that elements atypically incorporated into calcite (e.g., Fe) co-vary. Similarly, filtering PC1 (17% of the dataset variability) for high magnitude deviations from a baseline signal yields tentative agreement between PC scores and some known large eruptions with tephra found in Poland. We use our analysis to discuss the complexities involved in associating volcanic signals with stalagmite chemistry in temperate regions far from the source of large eruptions. The transport pathway from volcanic source to stalagmite growth surfaces includes the complex Niedźwiedzia Cave hydrological system and is influenced by dense forest above the cave site. Together these factors increase the potential for attenuation of volcanic-derived chemical signals prior to reaching the stalagmite, and so make it difficult to unambiguously link trace element enrichments in NIED08–05 to volcanic eruptions. Our results provide strong evidence that in a temperate depositional environment far from active volcanoes, climate and hydrology conspire to mute the strength of volcanic geochemical signals. Therefore, this work provides important incentives for future research in this area by highlighting that stalagmites grown in a comparatively simple hydrological regime and grown in caves overlain by thin vegetation and soil cover , may preserve volcanic signatures with greater success than those grown in temperate environments.

Research on the exploitation and utilization degree of mineral water based on ecological base flow in the Changbai Mountain basalt area, northeast China.

Mineral water from the Changbai Mountain basalt area is China's most important source of drinking water. Mineral water with abundant output and enriched trace elements has driven the rapid development of the local economy. However, the extensive exploitation of mineral water and the neglect of ecological base flows threaten interdependent river ecosystems. In order to ensure the sustainable use of mineral water, it's necessary to calculate the exploitation and utilization of mineral water according to the ecological base flow. In this study, four hydrological methods were used to analyze the intra-annual and inter-annual ecological base flows, namely the Tennant method, the base flow ratio method, the driest monthly average flow method and the Texas method. The results show that the ecological base flow during the flood season is about 3-4 times that during the non-flood season. Affected by rainfall and runoff, the inter-annual ecological base flow also fluctuated within a small range. This study divides the mineral water exploitation coefficient into five categories and proposes an assessment of the mineral water exploitation potential based on the ecological base flow. It shows that the flow of Baijiang River spring group is the largest, but it's exploitation potential is normal. Huangni River spring group at weak level for exploitation because of its small flow rate. It's obvious that river runoff is not the only factor that determines the exploitation coefficient of the spring group. The proportion of ecological base flow and the proportion of river base flow are also important factors.

Organic Matter Accumulation Mechanism in the Lower Cambrian Strata from Well Luntan 1 in the Tarim Basin, NW China

A large amount of light crude oils have been found within 4000 to 7000 m deep strata of Cambrian, Ordovician, and Silurian reservoirs in the Tarim Basin, NW China. To enhance the understanding of parental materials of deep oils, a set of high-quality source rocks from the Yuertusi Formation in well Luntan 1 (maximum drilling depth of 8882 m) was studied in terms of their sedimentary condition and mechanism of organic matter enrichment. Total organic carbon (TOC) content, carbon isotope of kerogen (δ13Cker), and major and trace elements of the rocks from the Sinian Qigebulake, Cambrian Yuertusi, and Xiaoerbulake Formations in well Luntan 1 were analysed. The results showed that the δ13Cker value of the Yuertusi Formation barely changed with an average of -31.19‰. High TOC contents accompanied by enrichments of the bioessential trace elements, such as cadmium, chromium, copper, nickel, and zinc, occurred in the lower part of the Yuertusi Formation. Excess barium (Baxs) and phosphorus concentrations revealed high primary productivity during the deposition of the Yuertusi Formation. Moreover, variations in the enrichment factors of molybdenum, uranium, and vanadium and molybdenum-uranium covariation pattern indicated suboxic-anoxic conditions in the Qigebulake Formation, anoxic-euxinic conditions in the Yuertusi Formation, and suboxic-oxic conditions in the Xiaoerbulake Formation. The TOC contents were significantly correlated with the paleoproductivity and paleoredox parameters, indicating that high productivity and reducing conditions jointly controlled the organic matter accumulation and preservation in well Luntan 1.

High-temperature fluids in granites during the Neoarchaean-Palaeoproterozoic transition: Insight from Closepet titanite chemistry and U-Pb dating (Dharwar craton, India)

The aim of this paper is to determine the composition and age of high-temperature (HT) hydrothermal fluids in Closepet granites (Dharwar craton, India). The magmatic origin of the Neoarchaean Closepet batholith has been recognized and dated many times, whereas a HT fluid system, strong evidence for which has been partly investigated, has never been dated. Titanite was chosen for a geochemical study on its pristine and altered domains to illustrate the fluid composition; the domains were dated to recognize the timing of fluid activity.Titanite presents distinct trace element enrichments in non-altered domains and strong depletions in trace elements in marginal, irregular, patchy zones. The high total rare earth element (REE) concentrations and the marked negative Eu anomalies suggest crystallization from a residual melt. The negative Eu anomalies diminish progressively in the REE patterns of altered parts and become positive. Trace element ratios (Nb/Ta, Y/Ho, and U/Th) indicate fluid-crystal interactions. Strong U/Th fractionation might be linked to the presence of CO2 and Cl−. Zr-in-titanite thermometry yields a crystallization/recrystallization temperature of ~700 °C for both magmatic and altered domains. The titanite factor Ti+4/(Al+3 + Fe+3) reveals an affinity with significant mantle input to the fluid system.Pristine and altered titanite domains have been successfully dated by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Reversely discordant apparent ages suggest interaction with fluids, which modified the Pb composition of the magmatic titanite. The oldest semi-concordant analyses of titanite cores indicate an age of approximately 2500 Ma, which we interpret as the minimum age of magmatic titanite crystallization. Narrow dark rims of titanite with considerably lower Th/U ratios form a more coherent group of analyses defining an upper concordia intercept age of 2345 ± 0.016 Ma, interpreted as the best estimate for the time of complete titanite resetting associated with the metasomatic event. The HT fluid system appears to have remained active into the Palaeoproterozoic.Confirmation by dating that the tested fluids belonged to the Archaean hydrothermal system gives us information about this system at the time, but the information that it worked at least until the Palaeoproterozoic provides additional valuable information about the hydrothermal systems during the Neoarchaean-Palaeoproterozoic transition.

Cattle manure loadings and legacy effects on copper and zinc availability under rainfed and irrigated conditions

Long-term cattle manure applications build up nutrient pools and can lead to trace element enrichments in soils. The objectives of this study were to evaluate copper (Cu) and zinc (Zn) loadings in the soil during continuous annual cattle manure applications and determine the time required for soil to return to its pre-manure available Cu and Zn levels after manure is discontinued. The manure application rates were 0, 30, 60, and 90 Mg·ha−1 for rainfed and 0, 60, 120, and 180 Mg·ha−1 (wet weight) for irrigated plots. Although manure was applied for 45 yr in some plots, applications were terminated in one subset of treatments after 14 yr and in another subset after 30 yr to study legacy effects after 31 and 15 yr, respectively. Soil samples were collected in the fall of 2003, 2008, 2013, and 2018 and analyzed for available Cu and Zn. Crops were grown in all years continuously with Cu and Zn concentrations measured in both silage and grains harvested. The regression model developed using data collected suggests long legacy effects with recovery time to pre-manure levels ranging from 10 to 20 yr for Cu and 23 to 41 yr for Zn at irrigated and 10–24 for Cu and 21–32 yr for Zn under rainfed, respectively. Long-term applications of cattle manure could lead to accumulation of Cu and Zn, creating long-lasting legacy effects in soils with the increased environmental risk of leaching to groundwater.

Genesis of Palygorskite in the Neogene Baiyanghe Formation in Yangtaiwatan Basin, Northwest China, Based on the Mineralogical Characteristics and Occurrence of Enriched Trace Elements and Ree

AbstractPalygorskite-rich mudstone interbedded with gypsum occurs in the Neogene Baiyanghe Formation in the Yangtaiwatan basin, northwest China, but the genesis of palygorskite in the mudstone is unclear. The objective of the present study was to clarify the manner by which the palygorskite evolved by analyzing the mineralogical and geochemical characteristics of the mudstone. The mineralogical composition of bulk-rock mudstone consisted of clay minerals, quartz, feldspar, dolomite, calcite, and gypsum. Palygorskite is dominant in the clay fraction together with illite and accessory chlorite and kaolinite. The interwoven rod-like palygorskite aggregates and delicate palygorskite particles indicated an authigenic origin. The bulk rock of palygorskite-rich mudstone was rich in the trace elements Cs, U, B, Li, Sb, Bi, and As, which, together with REE, all showed very positive correlation with major element oxides Al2O3, Fe2O3, MgO, K2O, and TiO2 of the mudstone, indicating that the REE and trace elements occurred mainly in the clay minerals. The detrital illite, chlorite, and kaolinite were the main original host of the REE and enriched trace elements. Statistical analyses showed that the authigenic palygorskite had strong affinity to such elements compared to the detrital clay minerals. In addition, the chondrite-normalized REE of the bulk mudstone showed essentially the same pattern irrespective of the proportions of detrital illite, kaolinite, chlorite, and authigenic palygorskite present in the samples. Thus, the conclusion reached was that palygorskite was generated from the dissolution of detrital clay minerals. The REE and enriched trace elements in authigenic palygorskite were inherited from the detrital clay minerals.

Oceanic water chemistry evolution and its implications for post-glacial black shale formation: Insights from the Cryogenian Datangpo Formation, South China

The Cryogenian Nanhua Basin in South China comprises one of the best-preserved Neoproterozoic glacial-interglacial sedimentary fills. The Datangpo Formation (ca. 663–654 Ma) was deposited after the Sturtian glaciation and is characterised by extensive organic-rich black shales and interbedded manganese deposits. Trace element data suggest overall anoxic waters with varying degrees of euxinia. These anoxic and sulfidic conditions, as inferred by high ratios of FeHR/FeT and Fepy/FeT and significant enrichments of molybdenum, developed due to high organic carbon loading, resulting in the formation of the black shales. The high organic matter flux was likely the result of increased nutrient supply from continental weathering, upwelling nutrient-rich deep seawater, and seawater exchange due to elevated sea levels after deglaciation, which resulted in a temporary connection with the open sea. An episode of oxygenation during deposition of the manganese-bearing interval shortly after deglaciation is indicated by a negative excursion in the iron speciation data, and generally low enrichments of trace elements. Muted sulfate reduction rates, and thus inferred less euxinic conditions, occurred due to decreased organic matter loading during deposition of the upper-part of the black shales. The lower marine primary productivity was likely a result of suppressed bio-essential elements due to progressively weaker chemical weathering under cooler climatic conditions. Superheavy pyrite with δ34Spy up to +61‰ for the Datangpo Formation is consistent with a compilation of published data. We propose that multiple processes contributed to the superheavy pyrite formation, and suggest a new, more accurate way of recalibration of the sulfate reservoir in sedimentary basins with similar geological and/or geochemical settings. This dataset and model serves as a reference for better understanding the formation of post-glacial organic-rich black shales, including the temporal evolution of oceanic conditions after low-latitude glaciations.

Multigeneration garnets record the fluid evolution of volcanic-hosted skarn iron deposit: Study of the Yamansu deposit, NW China

Three generations of garnets are distinguished in the Yamansu volcanic-hosted skarn iron deposit in NW China, and their detailed textures and geochemical characteristics are presented to reveal the mechanisms controlling the distribution of trace elements in the garnets and to discuss the physicochemical conditions and evolution of the ore-forming fluid. First-generation garnets (Grt1) show well-preserved core–rim growth zonation and have considerable variations in composition (And25-99Gro0-73). Second-generation garnets (Grt2) show complex core–mantle–rim zonation textures with high andradite components (And54-99Gro0-44). Third-generation garnets (Grt3) occur in veins and exhibit nearly monotonic textures and geochemical components (And48-51Gro46-49). Garnet crystals in different generations have variable trace element compositions, such as REEs, U, and Y. We speculate that Grt1 cores were derived from a magmatic–hydrothermal fluid and crystallized in a closed system with low water/rock (W/R) ratios, low oxygen fugacity, and neutral pH, with the distribution of trace elements in Grt1 cores being largely controlled by crystal chemistry. However, during the crystallization of Grt1 rims and Grt2 cores, the hydrothermal fluid system is interpreted to have been open with high W/R ratios and with internal complexes (Cl complex) and external fluid (seawater-like) integrally controlling the fluid properties. The incorporation of trace elements into the Grt1 rims and Grt2 cores was controlled by not only crystal chemistry but also crystal-liquid equilibrium. The Grt2 mantles and rims are interpreted to have formed in a closed system as a result of crack-seal fluid flow. The inferred stable conditions associated with low W/R ratios, a reducing environment, and nearly neutral pH favored Fe reduction in the hydrothermal fluid and provided a material basis for later deposition of iron ores. Grt3 likely formed under near-equilibrium chemical conditions, with low W/R ratios during periods of slow fluid influx determined by episodic supply of hydrothermal fluids, and their distributions were largely controlled by crystal chemistry. The special environment of multistage hydrothermal fluid in the Yamansu deposit was the key factor controlling the multiple enrichment and precipitation of trace elements into garnet.

High-frequency redox variation across the Ordovician–Silurian transition, South China

Mass extinction and extensive black shale deposition were associated with widespread ocean anoxia during the Ordovician–Silurian transitional interval, yet uncertainty among trace-metal proxies has precluded an improved understanding of redox dynamics at this time of Earth history and their relationship with animal evolution and accumulation of organic-rich shale. Herein, we describe results of a geochemical investigation of the Qianqian #1 section of South China that preserves the stratigraphic record of the inner shelf of the Upper Yangtze Platform. Specifically, newly acquired total organic carbon (TOC), total sulfur (TS), iron (Fe) speciation, and major element and trace metal abundances are considered with existing data from the studied section. Our results reveal that redox trends suggested by Fe speciation data are generally consistent with those based on Corg/P ratios and redox-sensitive trace element (RSTE) enrichment. However, documented differences among redox histories based on Fe speciation, Corg/P ratios, and RSTE enrichment may reflect the influence of high-frequency redox fluctuations. Comparison of bimetal ratios (U/Th, V/Cr, Ni/Co, and V/(V + Ni)) to Fe speciation, Corg/P ratios, and RSTE enrichment suggest that commonly cited thresholds of bimetal ratios for various redox states are unreliable, though variations in U/Th, V/Cr, and Ni/Co may provide a more robust indication of relative redox changes. A documented strong correlation of changing redox conditions and fossil distributions suggests that largely dynamic and ferruginous, perhaps euxinic, conditions contributed to biotic crisis and recovery. A strong coupling of TOC and redox proxies suggests that protracted anoxia or euxinia is critical to the accumulation and preservation of organic matter. Our study demonstrates that redox evaluations that rely upon a single geochemical proxy or elemental ratio are likely to be uncertain. Rather, multiple geochemical proxies are required to explore relationships among redox states, animal evolution, and deposition and preservation of organic-rich shale.