Changes In Physicochemical Conditions Research Articles

Spatio-Temporal Distribution of Phytoplankton and Water Quality of Some Rivers of Haute Sanaga Department (Central Africa)

In Cameroon, rivers are subjected to physicochemical disturbances, which increase the degradation of water quality. The aim of this study was to determine the spatio-temporal diversity of the phytoplankton groups and to evaluate the environmental parameters of the sampling sites in order to assess the quality of water in two hydrographic networks. Physicochemicals analyzes were carried out according to the standard methods while phytoplankton organisms were harvested by direct sampling and analyzed by the Utermöhl method. The analysis of Ammonia Nitrogen, Dissolved Oxygen, Electric Conductivity, Nitrates, Orthophosphates, pH, Temperature, and Turbidity.of water revealed the poor state of health of the water. Data from the Long Dry Season differed significantly (p < 0.05) from those recorded in other seasons. The phytoplankton communities were made up of Chlorophyta, Chrysophyta, Cyanophyta, and Euglenophyta with 11 classes dominated by Bacilliarophyceae (12 210 Ind/mL) and Cyanophyceae (6 208 Ind/mL). Phytoplankton densities were higher the Long Rainy Season and much lower in the Small Dry Season than in the Long Dry Season. Station near NODISCAM indicated significant organic pollution under the effect of agro-industrial discharges operating upstream of this company. For this station, the different values showed significant differences (p < 0.05) from one station to another. Finally, spatio-seasonal variations of phytoplankton densities showed logical responses to changes of physicochemical conditions in the environment. This work highlights the need to treat wastewater from collection channels before its dump into the natural environment, to prevent progressive eutrophication of the receiving aquatic environment, and poisoning by water consumption.

Redox controls on H and N speciation and intermolecular isotopic fractionations in aqueous fluids at high pressure and high temperature: Insights from in-situ experiments

Aqueous magmatic fluids are essential to the transport of hydrogen (H), carbon (C), and nitrogen (N) from the mantle to the surface, during which changes in pressure, temperature, and redox conditions affect the chemical speciation and intermolecular isotopic fractionations of H, C, and N. Here, we performed a series of hydrothermal diamond-anvil cell experiments to evaluate the role of pressure, temperature, and redox conditions on the speciation and intermolecular fractionations of H and N during the decompression and cooling of aqueous fluids from 780 MPa to 800°C to 150 MPa and 200°C. We used Raman spectroscopy to investigate the distribution and exchange reactions of H and N isotopologues between water, methane, ammonia, and di-nitrogen molecules under changing physicochemical conditions. Our experiments show that upon decompression, a C- and N-bearing fluid will preferentially degas D-rich methane and 15N-rich N2, depleting the residual aqueous fluid in those isotopes. If this fluid precipitates N-rich (i.e., NH4+-bearing) minerals, the observed N isotopic fractionation is opposite to that during N2 degassing, enriching the aqueous fluid in 15N. Because these fractionations result from changes in H, C, and N speciation in the aqueous fluid, their magnitudes depend on redox conditions as well as pressure and temperature. Our new in-situ experimental results are consistent with the large H and N isotopic fractionations observed between water, methane, and ammonia species in aqueous fluids at high pressures and temperatures, although the magnitude of the fractionations in our experiments cannot be quantified. Nonetheless, our results suggest that statistical thermodynamic models likely underestimate isotopic fractionation effects for isotopic molecules under these conditions, and should account for solubility and isotopic effects of the solvent associated with the solvation of water, methane, and ammonia isotopologues in aqueous fluids.This work has significant implications for interpreting isotopic measurements of natural samples from hydrothermal systems because it offers insights into isotopic fractionations in multicomponent and multiphase systems under hydrothermal temperatures and pressures.

Depositional framework and trace fossil assemblages of the Lower Triassic Montney Formation, northeastern British Columbia, Western Canada Sedimentary Basin

Hydrocarbon production from the Lower Triassic Montney Formation in northeastern British Columbia, occurs primarily from unconventional reservoirs consisting predominantly of fine-to coarse-grained siltstone beds. In this area, the lithostratigraphy of the formation is difficult to characterize due to the complexities associated with subtle grain-size variation, diminutive biogenic structures, lateral facies variability, and distribution of local discontinuities. Detailed sedimentologic and stratigraphic analyses are essential for understanding and refining the depositional models and stratigraphic framework of the Montney Formation. Based on detailed core examination focused on sedimentological, paleontological and ichnological characteristics, eleven lithofacies and three recurring facies associations are identified within the Lower Triassic Montney Formation in northeastern British Columbia. The lithofacies identified are interpreted to have been deposited in offshore, offshore transition and lower shoreface settings, along a storm-dominated mixed siliciclastic-carbonate ramp. Facies associations include FA(A): siliciclastic distal offshore transition to distal offshore; FA(B): mixed siliciclastic carbonate, storm-influenced offshore to offshore transition; and FA(C): storm-dominated siliciclastic offshore transition to lower shoreface. Trace fossil assemblages correspond to a stressed Cruziana Ichnofacies, and are overall characterized by low diversity (1–6 ichnogenera), small size trace fossils (1–12 mm in diameter), and variable bioturbation intensity (0–6). The vertical variation in SDI values reflect changes in physico-chemical conditions during deposition of the Montney Formation, particularly across the Smithian-Spathian boundary. Understanding the lateral-facies variability and overall stratigraphic architecture of the Montney Formation in northeastern BC, constitute key elements in defining and correlating existing and new potential hydrocarbon reservoirs in the area.

Episodic ore-forming fluid evolution processes in the Jiudian gold deposit, Jiaodong Peninsula: Constrains from texture, trace element and S isotope composition of pyrite

Jiudian is a representative quartz vein-type gold deposit in the Jiaodong world-class gold province, southeast of the North China Craton. Four stages and ten pyrite generations can be identified based on the paragenetic relationships: (1) pyrite (Py1)-milky quartz, (2) pyrite (Py2-1 and Py2-2)-smoky grey quartz, (3) siderite-pyrrhotite-pyrite (Py3, Py3-1 and Py3-2)-quartz, (4) quartz-polysulfide-siderite-marcasite (Py4-mc)-pyrite (Py4-1, Py4-2 and Py4-3), suggesting the complex and multistage ore-forming processes.The course-grained euhedral Py1 from the pre-ore stage 1 quartz veins is enriched in lattice-bound Co, Ni, and Se with relatively low δ34S values (+4.7 to + 5.5‰), precipitated from the equilibrated fluid environment with higher temperature (ca. 400 ℃). The dissolution-reprecipitation textures are characterized by the pristine As-rich Py2-1 as parent phase and porous Py2-2 as product phase hosting abundant microscale galena enriched in low-melting chalcophile elements (LMCE, e.g., Pb, Bi, Ag, Te, and Sb) and minor electrum. Both of Au-HS and Ag-Cl complexes destabilized by decompression would result in the precipitation of electrum with low gold fineness (672 to 713). Py3 is a poor host for majority of trace elements coexisting with pyrrhotite, precipitated from the late second pulse fluid.Py3 was overprinted by the third ore fluid pulse and replaced by siderite into sieve-shaped Py3-1 and anhedral aggregates Py3-2. Subsequently, fluid oxidation caused by pyrite replacement and meteoric water influx would result in the precipitation of marcasite (Py4-mc). Furthermore, euhedral pyrite aggregates were directly deposited from this ore-forming fluid, characterized by the Co-rich core (Py4-1) with abundant inclusions of LMCE-dominant sulfosalt (lillianite homologues) and galena, overgrown by pristine As-rich rim (Py4-2). The decoupled As and Co in Py4-1 and Py4-2 were probably attributed to abrupt temperature drop due to meteoric water influx. Nevertheless, the precipitation of visible gold with higher gold fineness in siderite or intergrown with Py4-mc was primarily resulted from fluid oxidation which has significant effect on the stabilities of Au-HS complexes but little on those of Ag-Cl complexes. The last generation Py4-3 was the post-oxidation product, evidenced by the extremely negative δ34S values (-34.3 to −28.4‰).Hence, the textural and geochemistry characteristics of different pyrite generations of Jiudian have revealed the presence of three fluid pulses as well as the distinctive evolution processes and changes of physicochemical conditions leading to the characteristic mineral assemblages and multiple-stage gold mineralization, which could provide implications for the genesis of siderite-rich gold deposits in the Jiaodong district.

Systematic variations in trace element composition of pyrites from the 26°S hydrothermal field, Mid-Atlantic Ridge

Variations in trace element composition of pyrites in inactive chimneys from the SMAR 26°S hydrothermal field provide important insights into the genesis and evolution of volcanic-hosted hydrothermal mineralization. Petrographic observations of zoned chimney samples integrated with in-situ LA-ICP-MS analysis of morphologically different pyrites allowed the assessment of fluid evolution during the chimney growth. Pyrite varieties precipitated with increasing temperatures from the outermost chimney wall (zone A) through the intermediate zone (zone B) to the inner zone (zone C). At the late mature stage, pyrite precipitates as interstice pore fillings. The distribution of trace elements in pyrites across the chimney indicates a strong dependence on time, temperature, and associated sulfide minerals. Variations in the trace elements composition of the different pyrite varieties indicate that the hydrothermal system evolved from low-temperature low-chloride liquid-dominated fluids (enriched in Zn, Cd, Tl, Ag, Pb, Mn, Mo, and V) to higher temperature, vapor-dominated fluids (Cu, Au, Te, and Bi), and then to high-temperature fluids (Co and Se). In the waning stage of the hydrothermal system, circulating hot fluids in auxiliary conduits were depleted in most trace elements. The systematic variations in trace element compositions of hydrothermal fluids induced by changes in physicochemical conditions are properly governed by the law of normal distribution of trace elements. The LA-ICP-MS time-depth analysis indicate that Cu, Zn, Cd, Tl, Ag, Te, and Bi are related to micro-/nano-inclusions, whereas Co, Se, and Mo may occur as substitutions in pyrite lattice. The As, Pb, Au, and Sb show both modes of occurrences as substitutions and as inclusions. Adsorbed films on pyrites control the distribution of V and Mo. The incorporation processes of trace elements in pyrites change with fluid evolution during the chimney growth: trapping of micro-/nano-inclusions and surface adsorption is seen more frequently at the low-temperature stage, and lattice substitution mainly at the elevated temperature stages.

МИГРАЦИЯ ТЕХНОГЕННЫХ РАДИОНУКЛИДОВ (137CS, 152EU, 60CO) В ДОННЫХ ОТЛОЖЕНИЯХ Р. ЕНИСЕЙ (БЛИЖНЯЯ ЗОНА ВЛИЯНИЯ КРАСНОЯРСКОГО ГХК)

The distribution nature of the artificial gamma-emitting radionuclides (137Cs, 152Eu, 154Eu, 155Eu, 60Co) in vertical columns of the Yenisei River bottom sediments selected in the near zone of influence of the Krasnoyarsk MCP was revealed. It is shown that the mineral composition of bottom sediments does not change with the depth and is mainly represented by quartz, plagioclase and potassium feldspar, with a small amount of amphibole, chlorite, mica. It was found that the exchangeable and carbonate forms contain, on average, 16% of 152Eu, 22% of137Cs and 15% of 60Co being found in bottom sediments. Radionuclides presented in these forms can pass into an aqueous solution and be involved in secondary migration under stable, natural conditions. Other fractions of the absorbing complex in the absence of catastrophic changes in physico-chemical conditions in the river ecosystem do not pass into an aqueous solution, and the redistribution of radionuclides associated with them can occur only with mechanical transfer of the matter.

Formation, remobilisation and alteration processes at inactive hydrothermal vents: insights from elemental analysis of Cu-(Fe-)S sulfides from TAG, Mid-Atlantic Ridge

Chalcopyrite is the main Cu mineral in mafic-hosted marine hydrothermal systems. Its trace element budget and that of its alteration products may hold valuable information on formation, remobilisation and alteration processes of the hydrothermal system. In this study, we analysed chalcopyrite from five inactive seafloor massive sulfide (SMS) sites from the TAG hydrothermal field on the Mid-Atlantic Ridge by electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for 24 elements. Twelve of them are discussed in detail. In general, trace element concentrations range between sub-parts per million (ppm) to several hundreds of ppm. The elements Se and Co are incorporated into the lattice at high temperatures of > 300 °C, whereas As, Ge, Ga substitute into the structure at intermediate to low temperatures. Other elements, e.g. Zn, are either accommodated into the mineral lattice or form inclusions, whereas V and Mn, which originate from seawater, get adsorbed onto the mineral surface. Idaite, chalcocite, and covellite exhibit similar trace element patterns to those of the precursor chalcopyrite. However, the secondary copper minerals show enrichment of Ag and Mo. Factors controlling the incorporation are predominantly related to changes in physicochemical conditions with the host rock composition playing only a minor role.

Deciphering multiple ore-forming processes of the Shuangqishan orogenic gold deposit, Southeast China by in situ analysis of pyrite

Gold deposits are characteristically formed via multiple mineralization and remobilization events. Inferences on the complex formation history of such deposits from ore textures can be ambiguous in the lack of chemical and isotopic evidence as exemplified by the Shuangqishan orogenic gold deposit in Southeast China. We, therefore, conducted LA-ICP-MS spot analysis coupled with LA-MC-ICP-MS sulfur and lead isotope analysis on texturally complex gold-bearing pyrite from the Shuangqishan deposit. Gold distribution in different syn- to late-ore pyrite generations indicate initial evenly deposition of nano- to micro-inclusions of Au-Ag-Pb-Bi tellurides within pyrite grains and subsequent Au remobilization following brittle deformation and fluid-mediated coupled dissolution-reprecipitation (CDR) reactions. Gold dissolved from the pyrite during the reworking event became re-concentrated and re-precipitated as visible gold either as inclusions in pyrite or larger free gold grains within microfractures of pyrite. The distribution of Bi-Te-Pb-Ag assemblage is comparable to that of Au, illustrating that these trace metals became redistributed in a similar fashion. Early, undeformed pyrite has the least radiogenic Pb isotopic compositions. Late, porous and inclusion-rich pyrite, brecciated pyrite, and recrystallized Te-Bi minerals have variable but in general more radiogenic Pb isotope ratios (higher 206Pb/204Pb and 207Pb/204Pb ratios), which are attributed to modification and precipitation from a more evolved crustal fluid during the re-precipitation of native gold. The Pb isotopic signature of the younger pyrite generations was likely inherited from Pb released during modification of earlier proto-pyrite and a second, crustal lead source that was involved in the hydrothermal system during later remobilization. The δ34S values for the early proto-pyrite and the reworked pyrite generations within the individual vein stage are broadly similar. The variations in sulfur isotope compositions reflect the change in physicochemical conditions (temperature and oxygen fugacity) during proto-ore formation. Our study highlights the importance of metal recycling from early proto-auriferous pyrite during later reworking and gold remobilization, which led to visible gold and high-grade ore shoot formation. The extensive variations of trace element concentrations and S-Pb isotope compositions of proto and reworked pyrites record the complicated Au mobilization and deposition processes and help to understand how gold ores evolved.

WaterQuality Guidelines for Metal Contaminants in Stormwater Runoff: Insights and Considerations.

WaterQuality Guidelines for Metal Contaminants in Stormwater Runoff: Insights and Considerations.

Composition of garnet from the Yongping Cu skarn deposit, South China: Implication for ore-fluid evolution

Garnet typically occurs as a major constituent in skarn deposits. It commonly displays variations in texture and composition due to changing physicochemical conditions. In this study, we integrate textural and geochemical studies of garnet from the Yongping Cu skarn deposit (South China) to constrain the nature and evolution of the ore-forming fluids. In the Yongping deposit, garnet shows red or brown colors in proximal skarns, and shows green color in distal skarns. All types of garnet grains show a core-rim texture. The cores generally have higher proportions of Fe and lower proportions of Al than the rims. In red or grown garnet grains, the Fe-rich cores have relatively high contents of REE, typically with an upward-facing parabola pattern with a peak at Ce or Pr. The rim domains have lower contents of REE, in particular La and Ce, than the cores. The compositional differences between the cores and rims reflect a transition from oxidized, Fe3+- and REE-rich fluids to fluids with lower contents of Fe3+ and REE. In green garnet, the Fe-rich cores have obviously lower contents of REE than the red/brown garnet cores, and their REE patterns resemble those of ore-hosting marbles. It indicates that the distal fluids were relatively poor in REE, and partial REE in garnet may be sourced from the ore-hosting marbles. The rims of green garnet usually have obviously higher contents of REE than the cores, which may imply ingress of new pulses of REE-rich, magmatic-hydrothermal fluids during the garnet growth process. In both proximal and distal skarns, the prograde garnet grains may be partially replaced by Al-rich domains in the retrograde skarn alteration stage. The replaced domains generally have higher contents of F, Ti, HREE and lower contents of LREE than the original domains. It indicates that the metasomatic fluids were relatively reducing, and have higher contents of F, Ti and HREE than the earlier-stage fluids. In general, the composition of garnets can record multiple pluses of fluid activity and the complicated physic-chemical evolution paths of the fluids. The influence of wall-rocks on the compositions of minerals is also indicated. Thus, garnet from skarns can preserve a wealth of information regarding mineralization processes in their crystal growth stratigraphy.

Effects of arsenic on the distribution and mode of occurrence of gold during fluid-pyrite interaction: A case study of pyrite from the Qiucun gold deposit, China

Abstract This paper presents the results of an investigation of the incorporation of Au within pyritic ore from the Qiucun epithermal Au deposit, China. The new data provide insights into the mode of occurrence of Au during fluid-rock interactions within epithermal systems. The distribution and mode of occurrence of Au within arsenian pyrite were investigated using a chemical and structural characterization-based approach combining laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) trace element analysis, megapixel synchrotron X-ray fluorescence analysis (MSXRF), and atom probe tomography (APT). The resulting data indicate that invisible Au is present at elevated concentrations in the form of a homogeneous solid solution within As-rich pyrite domains, which yields Au concentrations that positively correlate with As. Arsenic-induced lattice defects, such as stacking faults and the expansion of the pyrite unit cell, provide evidence of the effect of As on the incorporation of Au into pyrite. The nucleation and crystallization of electrum preferentially occurred at the fluid-pyrite reaction interface or along fractures and grain boundaries within the pre-existing pyrite. This study indicates that changes in physicochemical conditions (e.g., temperature, pH, and sulfur fugacity) during fluid-pyrite interactions are key controls on the development of nanometer- or micrometer-scale clusters of gold. The systematic compositional and textural observations documented in this study provide new insights into the mechanisms responsible for the different modes of occurrence of Au (ionic vs. particulate) and enable us to further understand the processes involved in the formation of Au mineralization.

Compartmentalization of bacterial and fungal microbiomes in the gut of adult honeybees

The core gut microbiome of adult honeybee comprises a set of recurring bacterial phylotypes, accompanied by lineage-specific, variable, and less abundant environmental bacterial phylotypes. Several mutual interactions and functional services to the host, including the support provided for growth, hormonal signaling, and behavior, are attributed to the core and lineage-specific taxa. By contrast, the diversity and distribution of the minor environmental phylotypes and fungal members in the gut remain overlooked. In the present study, we hypothesized that the microbial components of forager honeybees (i.e., core bacteria, minor environmental phylotypes, and fungal members) are compartmentalized along the gut portions. The diversity and distribution of such three microbial components were investigated in the context of the physico-chemical conditions of different gut compartments. We observed that changes in the distribution and abundance of microbial components in the gut are consistently compartment-specific for all the three microbial components, indicating that the ecological and physiological interactions among the host and microbiome vary with changing physico-chemical and metabolic conditions of the gut.

Identifying hydrothermal quartz vein generations in the Taiyangshan porphyry Cu-Mo deposit (West Qinling, China) using cathodoluminescence, trace element geochemistry, and fluid inclusions

Porphyry-style mineralization is characterized by superposition of multiple generations of quartz growth, punctuated by dissolution and juxtaposed within a single vein. Such superposition inevitably obscures temporal relationships between quartz formation, alteration events, and fluid inclusion assemblages (FIAs), and consequently complicates the interpretation of fluid origin and evolution. Very detailed information of these relationships recorded within hydrothermal quartz from the Taiyangshan porphyry Cu-Mo deposit (NW China) is obtained using integrated cathodoluminescence (CL) imaging, trace element analyses, and fluid inclusion petrography.The CL characteristics range from bright blue-CL quartz (Q1) associated with early high-temperature potassic alteration, to dark blue-CL quartz (Q2) broadly coinciding with metal precipitation, to post-ore dull red-CL fine-grained, anhedral, and recrystallized quartz (Q3) subgrains. Early bright blue-CL quartz (Q1) crystals, generally at the edges of stockwork veinlets close to wallrock, are characterized by oscillatory growth zoning, and exhibit alignment of primary, equant-shaped, brine-bearing FIAs along the banded growth zones. Later dark blue-CL quartz (Q2) crystals are generally euhedral in shape and grow with c-axes pointing inward to the vein center. They exhibit well-defined, but rarely preserved, growth zones truncating Q1 and crystal terminations projecting into pyrite and chalcopyrite in the vein center although they are not spatially associated with sulfides. These vein features clearly indicate that Q2 crystals grow into an open cavity or fracture during the ore precipitation. This is also evident by coexisting, secondary, irregular-shaped, liquid-rich inclusions and vapor-rich inclusions along fractures transecting Q1 oscillatory growth bands. The coexistence of hypersaline and vapor-rich inclusions moreover provides unequivocal evidence for phase separation during mineralization. Dull red-CL quartz (Q3) crystals appear to coincide with or follow sericitic alteration, and cut and encompass preexisting Q1 and Q2 crystals. They spatially associated with sulfides. The Q3 grains contain rare well-defined FIAs, but show scattered, secondary, irregular-shaped, low-salinity aqueous inclusions with small- to medium-sized vapor bubbles (10–30 vol%), as well as complex fluid inclusions that have migrated to the margins of anhedral Q3 subgrains due to quartz dissolution and recrystallization.Formation of early blue-CL Q1 and Q2 crystals at moderate temperatures are consistent with enrichment of Ti in the quartz lattice compared to neighboring younger Q3. The Q2 crystals are typified by elevated concentrations of Al and K concentrations when compared to Q1 and Q3. The substitution of Ti4+ for Si4+ in the tetrahedral sites of quartz leads to an increased CL intensity from Q1, to Q2, and then to Q3 corresponding to a decrease in quartz precipitation temperature. Ore deposition, recorded by integration of CL textures, FIAs petrography, and trace element variations in Q2, in the Taiyangshan porphyry Cu-Mo deposit must have occurred over a significant change in physicochemical conditions. This suggests that phase separation due to fluid cooling/pressure drops during the transition from lithostatic to hydrostatic regimes is critical to porphyry mineralization. We further propose a complex hydrothermal quartz vein formation history involving multiple fluid inclusions under varying pressure and temperature conditions.

Appraisal of geochemical composition and hydrodynamic sorting of the river suspended material: Application of time-integrated suspended sediment sampler in a medium-sized river (the Sava River catchment)

The suspended particulate matter (SPM) carried by the rivers shows a wide range of particle size classes, mineralogical and chemical compositions and is mainly influenced by hydrodynamic sorting and provenance during the transport. Here, we have investigated the composition of the SPM in the Sava River and its tributaries (Ljubljanica, Savinja and Krapina) using a time-integrated suspended sediment sampler (TIMS). The representativeness of material collected by TIMS was evaluated comparing fine-grained sediments, single-point SPM and SPM collected using a shallow and deep-positioned sampler. The main results have revealed that the mineralogical and geochemical composition of the material is largely dependent on hydrological conditions. The differentiation of element composition is especially emphasized at low water stage when most of the SPM consists of slow-settling mineral phases (clay minerals and metal oxyhydroxides) which can be trapped in the sampler. During periods of high discharges, differentiation is less prominent, and homogenization of the SPM occurs, mainly as a part of bed load is also taken into suspension. These conditions have proven unfavorable for sampler efficiency, as at least part of the finest particles could not be retained. Additional issues that may occur during TIMS employment relate to biologically driven carbonate precipitation, which is triggered by changes in physico-chemical conditions at low water table in the summer period. Increased concentration of Ca, related to that process, influences the elemental composition of the SPM, which is particularly important when anthropogenic impact or sediment source is assessed. Hence, in order to interpret the geochemical and mineralogical data collected by TIMS, these factors should be taken into account. Our findings emphasize the need for detailed studies of chemical composition of the SPM (time-integrated) in medium-sized rivers and point out the significance of evaluating sampling representativeness during different hydrological conditions.

Stable Isotopes Clearly Track Mangrove Inputs and Food Web Changes Along a Reforestation Gradient

Despite worldwide efforts to restore degraded mangrove forests in the past decades, defining and tracking restoration success remains a major challenge. In this study, we used a multi-isotope approach to trace ecosystem responses to forest clearing and replanting in a tropical mangrove forest reserve at Matang, Malaysia. We measured δ2H or δD deuterium, δ13C and δ15N (HCN isotopes) in common macroinvertebrate consumers (barnacles, prawns, gastropods, and crabs) across a 70-year chronosequence of mangroves. Functional food web recovery was indicated by a decrease in δ13C and δ15N and increase in δD for gastropod and crab consumers in older forests. Timing of this shift in food web isotopic signals took place between 5 and 15 years post-clearing of mangroves. These changes in food web function paralleled changes in crab community composition, but also reflected changes in physicochemical conditions within the forest, such as increased tree cover and shading, which resulted in a shift of the food web base from microalgal-derived to mangrove-derived organic matter. Prawns and barnacles from tidal waters adjacent to the mangrove forests were estimated to derive 17 to 25% of their nutrition from mangroves, primarily from a microbial loop that was processing localised dissolved and particulate organic matter exported from mangrove marshes. The top-down mixing model approach using combined HCN isotope measurements clearly separated inputs from mangroves versus microalgae for the first time in estuarine food web studies, and tracked ecological mangrove ecosystem recovery. This combination of tracers is recommended for future studies of mangrove conservation and restoration.

Activity-based cell sorting reveals responses of uncultured archaea and bacteria to substrate amendment

Metagenomic studies have revolutionized our understanding of the metabolic potential of uncultured microorganisms in various ecosystems. However, many of these genomic predictions have yet to be experimentally tested, and the functional expression of genomic potential often remains unaddressed. In order to obtain a more thorough understanding of cell physiology, novel techniques capable of testing microbial metabolism under close to in situ conditions must be developed. Here, we provide a benchmark study to demonstrate that bioorthogonal non-canonical amino acid tagging (BONCAT) in combination with fluorescence-activated cell sorting (FACS) and 16S rRNA gene sequencing can be used to identify anabolically active members of a microbial community incubated in the presence of various growth substrates or under changing physicochemical conditions. We applied this approach to a hot spring sediment microbiome from Yellowstone National Park (Wyoming, USA) and identified several microbes that changed their activity levels in response to substrate addition, including uncultured members of the phyla Thaumarchaeota, Acidobacteria, and Fervidibacteria. Because shifts in activity in response to substrate amendment or headspace changes are indicative of microbial preferences for particular growth conditions, results from this and future BONCAT-FACS studies could inform the development of cultivation media to specifically enrich uncultured microbes. Most importantly, BONCAT-FACS is capable of providing information on the physiology of uncultured organisms at as close to in situ conditions as experimentally possible.

Textures and compositions of clinopyroxene in an Fe skarn with implications for ore-fluid evolution and mineral-fluid REE partitioning

Clinopyroxene is a common phase in a variety of hydrothermal ore deposits, notably in skarn deposits where it typically occurs as a major constituent. It commonly displays variations in texture and composition due to changing physicochemical conditions and contains relatively high concentrations of rare earth elements (REEs), making it an important petrogenetic indicator. In this study, we integrate textural and geochemical investigations of clinopyroxene from the Baijian Fe skarn deposit (eastern China) to constrain the evolution of ore-forming fluids and provide significant new insights into partitioning of REEs between the clinopyroxene and hydrothermal fluids.In the Baijian Fe skarn, endoskarn clinopyroxene is typically zoned with homogeneous Fe-poor cores and oscillatory zoned Fe-rich rims. The rims are also enriched in Na, Co, Ni, and V and contain primary fluid inclusions with high salinities of 57.7–61.2 wt.% NaCl equiv. The compositional differences between the cores and rims reflect a transition from dilute, Fe-poor fluids to saline, Fe-rich components, likely a result of fluid boiling. In the exoskarn, early formed Fe-poor clinopyroxene is commonly replaced with Fe-rich clinopyroxene through fluid-assisted, coupled dissolution-reprecipitation processes. Overall, the textural features and compositional variations of clinopyroxene reflect a transition from early diffusive metasomatism by low-salinity fluids under low water/rock ratios to later advective metasomatism by high-salinity fluids under high water/rock ratios.When normalized to the modeled composition of the melt-equilibrated fluid, the log light REE and middle REE abundances in the clinopyroxene fit a linear function of the radius parameter (expressed as r0/2 × (ri − r0)2 + 1/3×(ri − r0)3) of the lattice strain model, indicating that crystal lattice strain has exerted a major control on REE clinopyroxene-fluid partitioning. Cores of zoned endoskarn clinopyroxenes show an upward increase in heavy REE (HREE) from Ho to Lu, likely caused by incorporation of those elements both into the eightfold M2 site and the sixfold M1 site of clinopyroxene. The increasing HREE compatibility coincides with elevated Mn contents in the cores of the clinopyroxene grains, implying that Mn has a significant effect on the accommodation of HREE into the sixfold M1 site of clinopyroxene, presumably due to the similar ionic radius between Mn2+ in sixfold coordination (Mn2+ = 0.83 Å) and the HREE (e.g., Lu3+ = 0.861 Å).

Gold-telluride-sulfide association in the Jinqu Au deposit, Xiaoqinling region, central China: Implications for ore-forming conditions and processes

The Jinqu Au deposit, located in central Xiaoqinling gold field along the North China Craton’s southern margin, has total reserve of 21 t of Au with 4.23 g/t Au on average. It consists cccmainly of ore-bearing auriferous quartz veins in amphibolite facies metamorphic rocks of the Archean Taihua Group. The deposit’s mineral paragenesis and ore-forming processes have never been studied. This paper reports its mineral paragenesis, which includes sulfides (pyrite, galena, chalcopyrite, pyrrhotite, sphalerite, molybdenite and bornite), oxides (rutile, scheelite, hematite, magnetite), tellurides (sylvanite [(Au, Ag)2Te4], hessite [Ag2Te], petzite [Ag3AuTe2], krennerite [Au3AgTe8], calaverite [AuTe2], stützite [Ag5−xTe3], empressite [AgTe], rucklidgeite [(Pb, Bi)3Te4], altaite [PbTe], volynskite [AgBiTe2], tetradymite [Bi2Te2S], lingbaoite (AgTe3) and melonite [NiTe2]) and native elements (tellurium and gold). Based on our data, the associated ore-forming processes can be deduced as: iron oxides → (CO2(g) and H2S(g) loss, ƒTe2/ƒS2 ratio increase) sulfides, Au-Ag-tellurides → (condensation of H2Te vapor) Pb-Bi-tellurides → (mixing with meteoric water) carbonate. It has been indicated by thermodynamic modelling that formation of Au-Ag-Te-bearing minerals occurred under physico-chemical conditions of logƒTe2 values from −7.28 to −3.21, logƒO2 values from −26.67 to −26.44, logƒH2S values from −1.34 to 0.34, logƒS2 values from −9.53 to −5.64, logαAu+(aq)/αAg+(aq) values from −4.72 to −4.55 and pH values from 3.33 to 4.20 at 365 ℃ and logƒTe2 values from −10.53 to −6.62, logƒO2 values from −31.99 to −30.98, logƒH2S values from −0.65 to −0.36, logƒS2 values from −13.62 to −7.20, logαAu+(aq)/αAg+(aq) values from −6.42 to −6.21 at 335 ℃. The changes in physico-chemical conditions and in precipitation of Au-Ag-Te-bearing minerals were due to boiling or to condensation of Te-rich magmatic gas into ore-forming fluids. These reflect evolution from an early oxidizing to a later relatively reducing mineralization environment. Therefore, compared with the Dahu Au-Mo deposit and with the Yangzhaiyu Au deposit, which exist in the southern and northern parts of the Xiaoqinling region, respectively, the ore paragenesis and ore-forming physico-chemical conditions of the Jinqu Au deposit were different such that its characteristics are similar to low-sulfidation Au deposits.

Hydrothermal calcite-fluid REE partitioning experiments at 200 °C and saturated water vapor pressure

Calcite is a common vein mineral associated to ore deposits and alteration zones geothermal systems. The concentration of rare earth elements (REE) in calcite can potentially be used to fingerprint the changing physicochemical conditions during mineralization from hydrothermal fluids. Previous calcite-fluid partitioning experiments have been carried out at ambient temperature but models aiming at predicting the behavior of REE at elevated temperature have not yet been developed. This study aims at determining the controls on REE incorporation into calcite mineralized from hydrothermal aqueous fluids above 100 °C. Here, we present a series of hydrothermal batch-type REE partitioning experiments at 200 °C and saturated water vapor pressure (15.5 bar). The experiments were designed to synthesize REE-doped calcite from fluid mixing with varying initial REE concentrations (250 ppb to 1000 ppb) and permit in situ sampling of the aqueous fluids. Calcite-fluid partition coefficients (KD) were observed to depend on the ionic radius of the REE and vary as a function of initial REE concentrations: logKD of 0.86–1.67 at 250 ppb REE; logKD of 1.05–1.70 at 500 ppb REE; logKD of 0.47–1.07 at 1000 ppb REE. These data fit a parabola according to the lattice strain model from which calculated Young’s modulus (ES) values range between 21.6 and 63.2 GPa. The fits indicate that the partitioning of the light REE is controlled by the strain-induced Ca2+ substitution in the calcite structure, whereas the heavy REE deviate from these trends. The development of a binary REE(OH)3 - CaCO3 solid solution model based on the dual-thermodynamic (DualTh) approach suggests that the REE partitioning is controlled by the following possible coupled substitutions at pH of 6:Eu3++3OH-⇔Ca2++CO32-Eu3++O2-+OH-⇔Ca2++CO32-The lattice strain fits are useful to interpret deviations of the experimental data from the solid solution model and possible non-ideal mixing behavior. Application of this model to natural systems yields some limitations because of the variability of experimental mineral-fluid KD values with REE concentrations in the aqueous fluids. The DualTh approach considers the aqueous speciation and activity-concentration relationships of the aqueous fluids, and therefore, provides an efficient method to evaluate the partitioning of REE between mineral and aqueous fluids. This research is a first step in building an experimental database of calcite-fluid partitioning data at hydrothermal conditions and aims at developing more accurate models for predicting the behavior of the REE in natural mineral-fluid systems.

Genesis of the Yujiadian F-Pb-Zn-Ag deposit, Inner Mongolia, NE China: Constraints from geochemistry, fluid inclusion, zircon geochronology and stable isotopes

The Yujiadian F-Pb-Zn-Ag deposit in the South Great Xing’an Range (SGXR) consists of vein-type fluorite and F-Pb-Zn-Ag mineralization associated with granitoid. The orebodies occur in NS-trending extensional faults. Wallrock alterations are characterized by a series of medium-low temperature hydrothermal alteration, including silification, kaolinization, chloritization, sericitization, pyritic and carbonate alteration. Four stages of primary paragenetic sequences are recognized: polymetallic sulfide stage (stage I), sulfide fluorite sub-stage (stage II-1), silver-fluorite sub-stage (stage II-2), pure fluorite stage (stage III) and late carbonate stage (stage IV). Silver mineralization primarily belongs to the stage II. The 139–135 Ma quartz syenite porphyry is metaluminous and peralkalic, and is classified as A-type granite that formed in a post-orogenic extensional setting. The δ34S (1.8‰) of hydrothermal fluid calculated from coeval minerals (barite and galena) is comparable with the majority of adjacent magmatic hydrothermal deposits in the SGXR, implying a magmatic source. Microthermometric measurements show that ore minerals were deposited at intermediate temperatures (109.7–320.1 °C) and had low salinities (0.18–5.62 wt% NaCl equive). Ore-forming fluid originated from post-magmatic hydrothermal fluid and mixed with heated meteoric water. Successive precipitation of base metals occurred with changing physicochemical conditions and boiling of ore fluid. The main precipitation mechanism for fluorite in the late stage is related to fluid-rock reaction. We propose that the A-type granite related to the fracture-controlled hydrothermal vein-type Yujiadian F-Pb-Zn-Ag deposit forms part of the magmatic response to Paleo-Pacific subduction and associated lithospheric thinning, extension and delamination processes. Furthermore, the deposit represents the terminal and distal member of the regional Mesozoic large-scale mineralization events.