Geochemical Modeling Results Research Articles

How does the coupled action of freeze - Thaw and acidification affect the release of toxic elements from indigenous Zn smelting slags?

Under complicated field conditions, such as the coupled effects of freeze - thaw cycles (FTs) and acidification, the leaching behavior of potentially toxic element (PTEs) from indigenous Zn smelting slags (ZSS) was intricately connected to the mineralogy (e.g., the composition, assemblage, microstructure of mineral particles). In this study, FTs tests were carried out to explore the interactions between PTEs release and ZSS mineralogy. Subsequently, advanced characterization techniques were adopted to quantify the mineralogy and microstructure of ZSS. The results indicated that ZSS were mainly composed of silicate minerals (e.g., quartz, biotite and chlorite) and secondary Fe (III) oxyhydroxides (e.g., magnetite and limonite), accounting for 67.48% and 24.23%, respectively. The occurrence mode analysis revealed that 81.95% of As, 21.31% of Pb and 7.77% of Zn were hosted in limonite. About 37.89%, 59.34% and 34.50% of Cd, Pb and Zn were associated with carbonate bound fractions. Under FTs interacting with different pH conditions, the leaching concentrations of As, Cd, Cu, Pb and Zn did not significantly increase with the increase in FTs and pH. The microstructure damage of mineral particles in ZSS with the higher porosity was caused by both FTs and proton corrosion. More importantly, the geochemical modeling results suggested that the precipitation of hematite and magnetite might have little impacts on PTEs release under FTs and FTs with acidification. This work would provide a deeper understanding of PTEs release from smelting waste slags under complex physicochemical interactions.

Unveiling the release mechanism of potentially toxic elements from Pb/Zn smelter contaminated soils under the coupled effects of freeze–thaw and acidification: Insights from mineralogical analysis

Most Pb/Zn smelter contaminated sites in China are often encountered natural phenomenon known as freeze–thaw (F–T) cycles and acid rain. However, the coupled effects of F–T cycles and acidification on the release behavior of potentially toxic elements (PTEs) from soils remains unclear. A mechanistic study on PTEs release from soils was conducted by revealing the physicochemical weathering characteristics of minerals under F–T cycles combined with acidification. The results from F–T test indicated that among F–T parameters, F–T frequency were the more important factors influencing PTEs release, with the corresponding contribution ranges of 21.20–94.40 %. As pH decreased, the leaching concentrations of As, Cd, Cu, Mn, Pb and Zn did not increase under the same F–T frequency. As F–T frequency increased, the leaching concentrations of these studied PTEs also did not increase under the same pH condition. Microstructure characteristics revealed that the soils were a complex system with multi–mineral aggregates, which had experienced complex physicochemical weathering after F–T combined with acidification treatment. Combined with geochemical modeling results, PTEs release was found to be mainly influenced by the microstructure damage and proton corrosion of minerals, while little affected by their precipitation and dissolution. The mutual coupling relationships of mineral weathering and PTEs release were conducive to the better understanding of the migration behavior of PTEs in contaminated sites under complex environment scenarios. The present study results would provide theoretical instruction and technical support for the longevity evaluation of multi–metal stabilization remediation.

Hydrogeochemical analysis of processes affecting HCH removal using ZVI-based treatment technology

In the 1960s, ca. 3000–5000 tons of HCH residue were disposed of in an overburden dump at the Hájek kaolin/uranium mine site (Czech Republic). The dump leachate, which has a 136 μg/l average total content of hexachlorocyclohexane (HCH) isomers, discharges into a local creek and contaminates the ecosystem. A full-scale prototype for the treatment of dump leachate comprised three sequential stages: 1) permeable reactive modules filled with macro-zerovalent iron (mZVI), 2) a biosorption module and 3) an aerobic wetland module. After commissioning, HCH removal efficiency reached 95%, but decreased to 70% over the following 230 days, primarily due to the efficiency of the mZVI modules dropping from 76% to 39%. Hydrogeochemical analysis and geochemical modelling revealed that the reduction in efficiency was mainly caused by passivation of mZVI surfaces and clogging of mZVI pore spaces through precipitation of goethite, calcite and rhodochrosite, or siderite and magnetite instead of goethite where boundary conditions for O2 differed. XRD analysis of the solid phase from the mZVI modules confirmed the geochemical modelling results. The major part of the precipitated products (46–66 wt%) comprised a ferric hydroxide amorphous phase, especially in the initial mZVI module inlet, with goethite the second most abundant precipitate (10–40 wt%). Siderite and calcite also mainly precipitated in the initial module inlet. In conclusion, mZVI appears to be a suitable reductant for HCH; however, the longevity of the ZVI-based treatment system was negatively affected by precipitates in the presence of high concentrations of iron, manganese and carbonate species.

TRACE ELEMENTS IN THE GROUNDWATER OF THE NEMYRIV DEPOSIT (UKRAINE)

The data obtained and published to date by experts in various fields indicate that there are no absolutely harmful or absolutely beneficial trace elements, the only question is their concentration and form in natural waters (including groundwater). The forms of occurrence in natural waters are particularly important for elements that may have different degrees of oxidation (e.g., arsenic, manganese) or a high ability to form complexes with water anions (e.g., nickel). In addition, the possible positive and negative effects of biological exposure to drinking water that meets the quality criteria but has slightly elevated levels of trace elements (the so-called “chronic” effect) are currently being actively discussed. The aim of this study is to determine the speciation of biologically active trace elements in the waters of the Nemyriv drinking water deposit in the Southern Bug River basin by geochemical modelling. The modelling was performed using the PHREEQC software. Trace elements found in water in concentrations measured by analytical methods are considered in this paper. The data on the content of 7 elements (As, Mn, Sr, Ni, P, Si and F) in the water of 6 wells in the Skifska area (3 wells in the ravine and 3 wells along the Ustia River) were analysed. The concentrations of Sr, Ni, P and F in the water of the wells considered in the Nemyriv drinking water deposit do not exceed the MPC. The concentration of As exceeds the MPC. Mn concentrations in the wells located in the ravine do not exceed the MPC, but significant excesses are observed in the wells located along the Ustia River. Based on the mineral composition of the rocks, the results of geochemical modelling, and the different supply mechanisms of the wells located in the ravine and along the river, it can be concluded that the manganese is of anthropogenic origin. None of the water in the Skifska area under consideration meet the water quality requirements in terms of the total specific content of pollutants of the first and second hazard classes. The main reason for this discrepancy is the increased concentration of arsenic in the water. However, this is in the relatively safe form of As(V). Phosphorus and arsenic concentrations are largely determined by co-precipitation with iron minerals. Fluorine behaves like a classical halogen in the well water of the Skifska area and is in oxidation state-1, and the main source of fluorine is biotite and fluorite. Strontium and manganese in the well waters of the Skifska area of the Nemyriv deposit are in oxidation degree +2, mainly in the form of Me2+ cations. The manganese occurrence in such a oxidation degree indicates its potential bioavailability, so it is necessary to carry out additional analytical studies to determine the concentrations of Mn and organic compounds, perform repeated geochemical modelling, assess the hazard of these waters to humans and develop additional water treatment measures.

Laboratory Experiments and Geochemical Modeling of Gas–Water–Rock Interactions for a CO2 Storage Pilot Project in a Carbonate Reservoir in the Czech Republic

The aim of this study was to characterize the influence of CO2 in geological structures on mineralogical changes in rocks and assess the sequestration capacity in mineral form and solution of a potential pilot storage site in the Czech Republic. Rock samples from a dolomite reservoir and the overburden level, as well as the corresponding pore water, were used. The most important chemical process occurring in the reservoir rock is the dissolution of carbonate minerals and feldspars during the injection of CO2 into the structure, which increases the porosity of the structure by approximately 0.25 percentage points and affects the sequestration capacity of the reservoir rock. According to the results of geochemical modeling, the secondary carbonate minerals (dolomite, siderite, and ephemeral dawsonite) were present only during the first 50 years of storage, and the porosity at this stage decreased by 1.20 pp. In the caprocks, the decomposition of K-feldspar and calcite resulted in an increase in porosity by 0.15 percentage points at the injection stage only, while no changes in porosity were noted during storage. This suggests that their insulation efficiency can be maintained during the injection and post-injection periods. However, further experimental research is needed to support this observation. The results of this study indicate that the analyzed formation has a low potential for CO2 sequestration in mineral form and solution over 10,000 years of storage, amounting to 5.50 kg CO2/m3 for reservoir rocks (4.37 kg CO2/m3 in mineral form and 1.13 kg CO2/m3 in dissolved form) and 3.22 kg CO2/m3 for caprock rocks (3.01 kg CO2/m3 in mineral form and 0.21 kg CO2/m3 in dissolved form). These values are lower than in the case of the depleted Brodské oil field, which is a porous reservoir located in the Moravian part of the Vienna Basin.

Slab failure‐related magmatism in the Pinheiro Machado Complex, southern Dom Feliciano Belt, Brazil

In the Dom Feliciano Belt, Brazil, the Pinheiro Machado Complex (PMC) includes diorites, tonalites, granodiorites, syenogranites and granites, whose evolution is related to several magmatic pulses and complex petrogenetic processes. Two magmatic stages were identified (early and late), resulting in different rock subgroups. The geochemical data showed that the early magmatism was chemically affected by partial melting. Geochemical modelling results suggest that fractional crystallization processes with assimilation of around 40% from the crustal basement and the decoupling of assimilated magma are crucial for the PMC rocks' genesis. Geochemical data also show that during the early magmatism, the subsequent process of early diorite anatexis developed by heating and continuous activity of the underlying magma chamber possibly occurred at a melting rate of 5%–10%. The hybrid rocks have contributions from the mixing process related to early terms, showing geochemical correlations in the major element curves, for the early diorite and syenogranitic melt members, at 60%–50% and 50%–40%, respectively. Slab failure tectonic context is related to the multi‐intrusive events dynamics recorded in the studied rocks. Recharge and melting events of the recently formed crust due to the constant heating of new pulses of deep slab melting would explain the magmatic interactions observed in the Complex. The results demonstrate that the studied rocks crystallized in an open system, including mixing processes to form hybrid rocks, physical disaggregation and assimilation of early intrusions, truncation, dragging and erosion of early mushes by younger pulses.

Arsenic in the groundwater aquifers of the Venetian Plain: geochemical modelling and occurrence of As-sulfides minerals, a review of data from the medio Brenta domain (Italy)

The Venetian Plain is known for areas with high concentrations of arsenic (As) in groundwater (up to more than 400 μg/L; exceptionally 647 μg/L, in selected areas). A study area was chosen, north of Padua, which exhibits typical residential, industrial, and agricultural characteristics similar to most Western countries and lacks hydrothermal, volcanic, or anthropogenic sources of arsenic. The pilot area was the focus of several studies which are reviewed in this note. The objectives of the studies were to verify the distribution of As concentrations in groundwater and sediments (mineralogical and geochemical analysis of groundwater sediments and of filtered and unfiltered groundwater) and to model the mobility of arsenic arising from water-rock interaction. The grain size of aquifer reservoirs includes gravel, sand, silt, and clay. The amount of organic matter in the aquifer sediments of the study area seems peculiar (higher) compared to other plains in the world; it influences the redox potential and the relative concentration of As in groundwater. Arsenic contamination in groundwater and redox conditions varied greatly in the area. Groundwater under oxidizing and highly reducing conditions had much lower arsenic concentrations compared to groundwater under intermediate reducing conditions. Arsenic minerals (such as realgar-pararealgar) occur in aquifer sediments and they were documented in the studied materials by different analytical techniques for the first time in the context of the Italian plains. Since these minerals are rare throughout the world in plain sediments not affected by volcanic or hydrothermal activity, their occurrence is a distinctive feature of the Venetian Plain aquifer. These arsenic minerals were found in peat sediments of the study area, consistent with geochemical modeling results, which require highly reducing conditions for their precipitation from groundwater. Modeling suggests that under oxidizing and up to slightly reducing conditions (from 200 mV to -50 mV), arsenic is adsorbed on solid phases, but a further decrease in redox potential leads arsenic desorption from solids and consequent groundwater contamination (from -50 mV to -250 mV). If the redox potential becomes even more negative (below -250 mV), geochemical conditions are favorable to the formation of arsenic sulfides. The precipitation of the realgar-pararealgar phases, predicted by the geochemical model, proceeds by extracting arsenic from the groundwater and quantitatively accounts for the lower arsenic concentration measured in the highly reducing groundwater of the study area.

Study on inverse geochemical modeling of hydrochemical characteristics and genesis of groundwater system in coal mine area - a case study of Longwanggou Coal Mine in Ordos Basin.

The exploitation of coal resources has disturbed the equilibrium of the original groundwater system, resulting in a perturbation of the deep groundwater dynamic conditions and hydrochemical properties. Exploring the formation of mine water chemistry under the conditions of deep coal seam mining in the Ordos Basin provides a theoretical basis for the identification of sources of mine water intrusion and the development and utilization of water resources. This paper takes Longwanggou Coal Mine as the research area, collects a total of 106 groups of water samples from the main water-filled aquifers, comprehensively uses Piper trilinear diagram, Gibbs diagram, ion correlation, ion ratio coefficient and mineral saturation index analysis, and carries out inverse geochemical modeling with PHREEQC software, so as to analyze the hydrochemical characteristics and causes of the main water-filled aquifers in deep-buried coal seams in the research area. The results show that the main hydrochemical processes in the study area are leaching and cation exchange, and the groundwater is affected by carbonate (calcite, dolomite), silicate (gypsum) and evaporite. Calculations of mineral saturation indices and PHREEQC simulations have led to the conclusion that the dissolution of rock salt and gypsum in groundwater accounts for most of the ionic action. Na+, Cl- and SO42- are mainly derived from the dissolution of rock salt and gypsum minerals, while Ca2+ and Mg2+ are mostly derived from the dissolution of dolomite and calcite. The results of the inverse geochemical modeling are consistent with the theoretical analysis.

Geochemical modeling of basic pegmatites from Foz do Iguaçu in the Itaipu region, western Paraná, Brazil

In the westernmost portion of the state of Paraná, in the city of Foz do Iguaçu, basic pegmatites occur within inflated pahoehoe basaltic flows of the Paraná Igneous Province. Both rock groups are composed of similar mineral assemblages which include labradorite, augite, ilmenite and titano-magnetite, but pegmatites are medium to coarse grained, whereas basalts are fine grained. Host rocks are geochemically classified as basalts (s.s.), while pegmatitic segregations are basaltic andesite and basaltic trachy-andesite, according to the TAS [(Na2O + K2O) x SiO2] diagram. Based on the AFM [(Na2O + K2O) – (FeOtot) – (MgO)] diagram, all rocks are included in the tholeiitic series, classified as high-Fe tholeiite basalts in the cation plot [Al x (Fetot + Ti) x Mg]. Variation diagrams indicate enrichment of SiO2, TiO2, FeO, Na2O, K2O e P2O5 coupled with depletion of Al2O3, MgO e CaO from basalts to pegmatites. La/LuN ratios range between 5.4 to 6.5 for basalts and 6.3 to 7.9 for pegmatites reflecting a greater degree of fractionation in the pegmatitic segregations and, therefore, their more evolved character. Plagioclase crystals in pegmatites have higher sodic contents when compared to those found in host basalts, while CaO content in basaltic pyroxenes is higher than those from pegmatitic segregations. Trace element geochemical modeling results show that it is possible to generate basic pegmatites from basalts comprised of 55 wt.% plagioclase, 35 wt.% clinopyroxene and 10 wt.% titanium and iron oxides. The process occurs as fractional crystallization with 50% residual melt.

Paleo-Pacific Plate rollback triggered Early Cretaceous intermediate-felsic magmatism in the northern North China Craton

Extensively developed Early Cretaceous intermediate-felsic rocks in the northern North China Craton (NCC), offer an opportunity to unravel the nature of Paleo-Pacific subduction and associated geodynamic processes by investigating their spatio-temporal characteristics and petrogenesis. Here we present geochemical and geochronological results of Early Cretaceous (118–115 Ma) trachyandesites and rhyolites from the eastern Hebei, northern NCC. The trachyandesites show low MgO (0.74–2.65 wt%) and Mg# (17–38), as well as enriched whole-rock Nd-Hf isotopic compositions (εNd(t) = -17.1 to -13.3, εHf(t) = -12.9 to -10.8), suggesting a probable origin of the enriched mafic lower crust. They also exhibit relative enrichment in LREE and flat in HREE. Trace element geochemical modeling results indicate that the trachyandesites likely formed through partial melting of the mafic lower crust at 790–820 °C and ca. 10 kbar (30–33 km). The rhyolites, characterized by higher SiO2 contents and similar εNd(t) (-17.4 to -15.5) and zircon εHf(t) values (-14.4 to -7.6) compared to the trachyandesites, probably represent the magmatic derivates of the trachyandesites. MELTS modeling results suggest that the rhyolites likely formed through fractional crystallization of the trachyandesitic magmas at ∼ 775 °C and 1–3 kbar. Integrating with previous studies, our study confirms that the Early Cretaceous intermediate-felsic magmatism across the northern NCC became younger from northwest to southeast. We propose that the change of the migration direction of these Early Cretaceous intermediate-felsic rocks is primarily attributed to slab rollback of the subducting Paleo-Pacific Plate.

Characterizing basalt-atmosphere interactions on Venus: A review of thermodynamic and experimental results

Abstract The surface of Venus is in contact with a hot (~470 °C), high pressure (92 bars), and caustic (CO2 with S, but little H2O) atmosphere, which should cause progressive alteration of the crust in the form of sulfate and iron-oxide coatings; however, the exact rate of alteration and mineral species are not well constrained. Different experimental approaches, each with its own limitations, are currently being used to constrain mineralogy and alteration rates. One note is that no experimental approach has been able to fully replicate the necessary conditions and sustain them for a significant length of time. Furthermore, geochemical modeling studies can also constrain surface alteration mineralogy, again with different assumptions and limitations. Here, we review recent geochemical modeling and experimental studies to constrain the state of the art for alteration mineralogy, rate of alteration, open questions about the surface mineralogy of Venus, and what can be constrained before the fleet of missions arrives later this decade. Combining the new results confirms that basalt on the surface of Venus should react quickly and form coatings of sulfates and iron-oxides; however, the mineralogy and rate of alteration are dependent on physical properties of the protolith (including bulk composition, mineralogy, and crystallinity), as well as atmospheric composition, and surface temperature. Importantly, the geochemical modeling results show that the mineralogy is largely controlled by atmospheric oxygen fugacity, which is not well constrained for the near-surface environment on Venus. Therefore, alteration experiments run over a range of oxygen and sulfur fugacities are needed across a wide range of Venus analog materials with varying mineralogy and crystallinity.

Dissolution behaviors of PuO2(cr) in natural waters

PuO2(cr) dissolution in natural water was investigated at 25°C and 60°C under atmospheric conditions. The concentration of Pu in solutions [Pu], was monitored for 1 year of reaction time. PuO2(cr) dissolution in natural water reached a steady state within 2 months at 25°C. The [Pu] in groundwater and seawater at pH 8 were in the range of [Pu] = 0.9–34 and 3.4–27 nM, respectively. The [Pu] in concrete porewater (rainwater equilibrated with concrete) at pH 8.1–10.9 was in the range of 0.1–3.2 nM. The [Pu] and pH values of groundwater were similar to those of seawater samples having a high ionic strength. The measured [Pu] at equilibrium in all samples was higher than the calculated solubility curves for PuO2(am, hyd). Experimental evidence is insufficient to confirm the oxidation state of Pu in solution and solid phases. However, the results of geochemical modeling indicate that PuO2(am, hyd) and aqueous Pu(IV) species are dominant in natural water samples of this work. The dissolution behavior of PuO2(cr) in natural waters is comparable to the oxidative dissolution of PuO2(am, hyd) in the presence of PuO2(coll, hyd). The dissolution of PuO2 in groundwater decreased at higher temperatures, whereas the influence of temperature in seawater and porewater was not significant under these experimental conditions.

Earth's Earliest Phaneritic Ultramafic Rocks: Mantle Slices or Crustal Cumulates?

AbstractWhen plate tectonics initiated remains uncertain, partly because many signals interpreted as diagnostic of plate tectonics can be alternatively explained via hot stagnant‐lid tectonics. One such signal involves the petrogenesis of early Archean phaneritic ultramafic rocks. In the Eoarchean Isua supracrustal belt (Greenland), some phaneritic ultramafic rocks have been dominantly interpreted as subduction‐related, tectonically‐exhumed mantle slices or cumulates. Here, we compared Eoarchean phaneritic ultramafic rocks from the Isua supracrustal belt with mantle peridotites, cumulates, and phaneritic ultramafic samples from the Paleoarchean East Pilbara Terrane (Australia), which is widely interpreted to have formed in non‐plate tectonic settings. Our findings show that Pilbara samples have cumulate and polygonal textures, melt‐enriched trace element patterns, relative enrichment of Os, Ir, and Ru versus Pt and Pd, and chromite‐spinel with variable TiO2 and Mg#, and relatively consistent Cr#. Both, new and existing data show that cumulates and mantle rocks potentially have similar whole‐rock geochemical characteristics, deformation fabrics, and alteration features. Geochemical modeling results indicate that Isua and Pilbara ultramafic rocks have interacted with low‐Pt and Pd melts generated by sequestration of Pd and Pt into sulphide and/or alloy during magmatism. Such melts cannot have interacted with a mantle wedge. Correspondingly, geochemical compositions and rock textures suggest that Isua and Pilbara ultramafic rocks are not tectonically‐exhumed mantle peridotites, but are cumulates that experienced metasomatism by fluids and co‐genetic melts. Because such rocks could have formed in either plate or non‐plate tectonic settings, they cannot be used to differentiate early Earth tectonic settings.

Hydraulic fracturing as unconventional production potential for the organic-rich carbonate reservoir rocks in the Abu El Gharadig Field, north western Desert (Egypt): Evidence from combined organic geochemical, petrophysical and bulk kinetics modeling results

This paper systematically analyzes the organic geochemical, petrophysical, and petrographical properties combined with bulk kinetics modeling of the Abu Roash (F) organic-rich carbonate rocks in the Abu El Gharadig Field. The Abu Roash (F) carbonate-rich samples exhibit high organic content with total organic matter (TOC) values up to 3.04 wt%, and mainly Type II kerogen, with a slight gradient to Type II/III and III kerogens, reaching good to very good oil generation potential. This finding of hydrogen-rich kerogen and oil generation potential was also demonstrated by the abundance of fluorescent alginite, amorphous organic matter (AOM), and bituminite organic matter (OM) as established via ultra violet (UV) light microscopy. The maturity indicators demonstrate that most of the examined Abu Roash (F) carbonate-rich samples from the studied wells, with a deep burial depth of more than 3000 m, are thermally mature, thus defining an early mature to moderate-mature stage. The kinetic models suggest that the Abu Roash (F) carbonate-rich rocks in the deepest burial depth, with calculated vitrinite reflectance (%VRo) values in the range of 0.72–0.83 %, have reached kerogen transformation ratio (TR) in the range of 10–55 %, indicating a high probability of oil production. This finding is confirmed by the presence of the oil crossover in these rocks with an oil saturation index (OSI) of more than 100 mg HC/ g rock. The Abu Roash (F) organic-rich carbonates are intractable rocks as implied by low porosities (up to 2.33 %) and poor permeability in the range of 0.0017–0.0039 mD. The pores in these rocks have a wide range in size, including interparticle, fracture, and organic matter (OM) pores, as recognized in the thin section and scanning electron microscopy (SEM). The development of these pore types and their quality is mainly controlled by high mineralogical brittleness (i.e., carbonates) together with the high OM inputs. Based on the above characteristics, the Abu Roash (F) carbonate-rich rocks in the Abu El Gharadig Field are a candidate for unconventional tight oil reservoir potential, which typically require a form of hydraulic fracturing for possible oil production at deeper burial depths.

Petrogenesis of Eocene high-silica granites in the Maliaoshan area, northern Tibet: Implications for the Eocene magmatic flare-up in the Northern Qiangtang Block

The Eocene magmatic flare-up in the Northern Qiangtiang Block is a key event that was genetically related to the uplift of the Tibetan Plateau. This uplift has been considered to have an important impact on the global cooling and oceanic isotopic compositions. Here, we report zircon ages and bulk rock elemental and isotopic compositions for high-silica porphyritic granites in the Maliaoshan area of the Northern Qiangtang Block. Zircon U–Pb dating shows that the porphyritic granites were generated at ca. 41.02 Ma. The porphyritic granites are characterized by uniformly high SiO2 contents (74.3–75.0 wt%), high contents of total alkalis, metaluminous compositions, and low contents of TiO2, Fe2O3T, MgO, CaO, and P2O5. Moreover, the Maliaoshan porphyritic granites have Nd–Hf isotopic compositions similar to those of coeval metaluminous magmatic rocks in the Northern Qiangtang Block. These data together with geochemical modeling results suggest that the Maliaoshan porphyritic granites were formed by the fractional crystallization of 43.06% major minerals and 0.76% accessory minerals from the assumed starting composition (average Eocene metaluminous igneous rock). Based on our new data and Eocene magmatic flare-up event in the Northern Qiangtiang Block, we propose a new geodynamic model to explain such a magmatic flare-up event. The stress produced by the collision of India and Eurasia gradually transferred northward, prompting the Songpan–Garzê Block to subduct southward beneath the Northern Qiangtang Block at ca. 55 Ma, accompanied by minor magmatic activity. Subsequently, the break-off of the Songpan–Garzê Block at ca. 46 Ma resulted in the Eocene magmatic flare-up.

Tectonics and sedimentology of accretionary and collisional orogens

The Eocene magmatic flare-up in the Northern Qiangtiang Block is a key event that was genetically related to the uplift of the Tibetan Plateau. This uplift has been considered to have an important impact on the global cooling and oceanic isotopic compositions. Here, we report zircon ages and bulk rock elemental and isotopic compositions for high-silica porphyritic granites in the Maliaoshan area of the Northern Qiangtang Block. Zircon U–Pb dating shows that the porphyritic granites were generated at ca. 41.02 Ma. The porphyritic granites are characterized by uniformly high SiO2 contents (74.3–75.0 wt%), high contents of total alkalis, metaluminous compositions, and low contents of TiO2, Fe2O3T, MgO, CaO, and P2O5. Moreover, the Maliaoshan porphyritic granites have Nd–Hf isotopic compositions similar to those of coeval metaluminous magmatic rocks in the Northern Qiangtang Block. These data together with geochemical modeling results suggest that the Maliaoshan porphyritic granites were formed by the fractional crystallization of 43.06% major minerals and 0.76% accessory minerals from the assumed starting composition (average Eocene metaluminous igneous rock). Based on our new data and Eocene magmatic flare-up event in the Northern Qiangtiang Block, we propose a new geodynamic model to explain such a magmatic flare-up event. The stress produced by the collision of India and Eurasia gradually transferred northward, prompting the Songpan–Garzê Block to subduct southward beneath the Northern Qiangtang Block at ca. 55 Ma, accompanied by minor magmatic activity. Subsequently, the break-off of the Songpan–Garzê Block at ca. 46 Ma resulted in the Eocene magmatic flare-up.

Insight into the effect of SO42− on the precipitation and solubility of ferric arsenate in acidic solutions: Implication for arsenic mobility and fate

The effect of sulfate (SO42−) on the precipitation of As(V) and Fe(III) and the stability of the generated solid phase as well as its underlying mechanisms, which strongly influences the transportation and fate of As in acidic waters (such as acid mine drainage), is still not well known. This work systematically investigated the precipitation, decomposition, and settling properties of the ferric arsenate phase in the presence of different amount of SO42− at pH 1.2 and 1.8. The results showed that on the one side, the presence of SO42− delayed the removal of As and Fe from the aqueous phase and enhanced the solubility of solid ferric arsenate. The geochemical modelling results showed that the coexisting SO42− induced the formation of aqueous SO42−-Fe(III) complexes, inducing the decomposition of produced ferric arsenate solid phase. On the other side, the addition of SO42− promoted the growth rate of generated ferric arsenate and accelerated the settling of solids. The particle size distribution and transmission electron micorscopy analyses elucidated that the presence of SO42− significantly enlarged the ferric arsenate aggregate size. The infrared spectroscopy and S K-edge X-ray absorption near edge structure results proved that SO42− is incorporated into the structure of ferric arsenate by forming ferric arsenate sulfate solid solution, with each SO42− tetrahedron coordinating with approximately two FeO6 octahedra. The S K-edge extended X-ray absorption fine structrure result gave an averaged S-Fe interatomic distance of 3.21 Å. These results demonstrated that the presence of SO42− enlarged the aggregate size of ferric arsenate dominantly via the S-O-Fe bridging, and then accelerated the settling of SO4-ferric arsenate. The contrasting role of SO42− in influencing As obtained in this study is significant for understanding the mobilization and fate of As and the formation mechanisms of ferric arsenate minerals in acidic systems.

Geochemical Assessment of Gypsum Scale Formation in the Hydrated Lime Neutralization Facility of the Daedeok Mine, South Korea

Scale is widely observed in the hydrated lime mine drainage treatment plant of the Daedeok Mine in South Korea. In order to understand the environment in terms of the formation of scale minerals, scale and water were collected from the AMD treatment facility and analyzed. In addition, the saturation index was calculated based on geochemical modeling to predict the minerals that could be produced in the AMD treatment facility, and the results were then compared with an analysis of onsite scale minerals. Furthermore, the onsite mine drainage was neutralized from pH 3 to pH 9 in the laboratory, and the precipitates produced were identified. The changes in the Ca2+ and SO42− concentrations were also identified over time for each pH. The results of geochemical modeling predicted the possible precipitation of gypsum, anhydrite, and bassanite after AMD neutralization. Scanning electron microscope/energy dispersive X-ray spectroscopy (SEM/EDS) analysis results showed that the main mineral in scale formed at the AMD treatment facility was gypsum, produced by the reaction of SO42− and Ca2+ from lime during AMD. The laboratory neutralization experiment showed that gypsum was produced in all neutralization ranges from pH 3 to pH 9, and the higher the neutralization pH, the greater the amount of gypsum produced. It was demonstrated that simulated amounts of 2 g/L and 7 g/L gypsum at pH 5 and 9 were well matched with the experimental results. Iron (Fe), a major pollutant in the mine drainage system, was rapidly precipitated in the form of iron hydroxides after neutralization. As gypsum is produced slowly and continuously for a long period of time, it results in the growth of scale throughout the flow path. As a method of minimizing gypsum production in the AMD treatment facility using hydrated lime, it is recommended that the facility should be operated at the lowest pH possible, which will also enable the removal of major pollutants, such as iron and aluminum.

Energetics of hydroxylbastnäsite solid solutions, La1−xNdxCO3OH

Bastnäsites (LnCO3(F,OH)) are a group of common rare earth elements (REE)-bearing minerals and are one of the primary global sources of REE. Due to the chemical similarities among REE, bastnӓsites tend to occur as solid solutions instead of end members in REE containing ores. To better understand the processes and the mechanisms of formation of such deposits, it is essential to determine the thermodynamic properties of bastnӓsites, including hydroxylbastnӓsite (LnCO3OH) solid solutions. In this work, we performed detailed structural and calorimetric investigations on synthetic hexagonal La–Nd hydroxylbastnӓsite (La1–xNdxCO3OH, x = 0, 0.25, 0.5, 0.75, 1) solid solutions. X-ray diffraction confirms the crystal structure of the solid solution series in the P6¯ space group, and pair distribution function (PDF) analysis reveals local bonding environments characterized by three different types of 9-coordinated metal-oxygen polyhedra. Unit cell parameters of La1–xNdxCO3OH exhibit a nearly linear relation with the Nd content x, suggesting a random distribution of La and Nd in the structure. Their standard enthalpies of formation (ΔH°f) were determined by high temperature oxide melt drop solution calorimetry, from which the enthalpies of mixing (ΔHmix) were derived. The ΔHmix can be fitted by a regular solution model with an interaction parameter of 12.58 ± 0.16 kJ/mol, suggesting enthalpic metastability of La1–xNdxCO3OH relative to the two endmembers. Combining entropy and enthalpy, we further estimated the Gibbs free energies of mixing (ΔGmix) at relevant temperatures, revealing favorable temperatures under which the intermediate La1–xNdxCO3OH phases can be stabilized. Such entropy-driven stabilization, as is consistent with our geochemical modeling results, may explain the enhancement of thermal stability of the solid solutions in nature. Additionally, the temperature range constrained from this study may be used to estimate the thermal history of REE bastnӓsite deposit.

Geo-Accumulation Index of Manganese in Soils Due to Flooding in Boac and Mogpog Rivers, Marinduque, Philippines with Mining Disaster Exposure

This paper presents the effects of flooding on the accumulation of manganese (Mn) in soils within proximity of the Boac and Mogpog rivers in Marinduque of The Philippines. Marinduque, an island province in the Philippines, experienced two catastrophic tailings storage facility (TSF) failures in the 1990s that released sulfide-rich tailings into the two major rivers. The Philippines experiences 21–23 typhoons every year, 11 of which pass thru Marinduque that causing inundation of floodplain areas in the province. A flood hazard map developed using LiDAR DEM was utilized for the Boac and Mogpog rivers for an accurate representation of flooding events. A portable X-ray fluorescence spectrometer (pXRF) and a Hannah multi-parameter device were used for the on-site analyses of Mn concentration and water physico-chemical properties, respectively. Spatial grid mapping with zonal statistics was employed for a comprehensive analysis of all the data collected and processed. Correlation analysis was carried out on Mn concentrations in soil and surface water, electrical conductivity (EC), total dissolved solids (TDS), pH, temperature, curve number (CN), and flood heights. The curve number indicates the runoff response characteristic of the Mogpog-Boac River basin. The results show that 40% of the total floodplain area of Boac and Mogpog were subjected to high hazards with flood heights above 1.5 m. The Mn content of soils had a statistically significant moderate positive correlation with flood height (r = 0.458) and a moderate negative correlation with pH (r = −0.438). This condition suggested that more extensive flooding promotes Mn contamination of floodplain soils in the two rivers, the source of which includes the mobilization of Mn-bearing silt, sediments, and mine drainage from the abandoned mine pits and TSFs. There is also a strong negative correlation between pH and Mn concentrations in surface water, a relationship attributed to the solubilization of Mn-bearing precipitates based on geochemical modeling results. Using Muller’s geo-accumulation index, 77.5% of the total floodplain of the two rivers was identified as “moderately contaminated” with an average Mn soil content of 3.4% by weight (34,000 mg/kg). The Mn contamination map of floodplain soils in the Mogpog and Boac rivers described in this study could guide relevant regional, national, and local government agencies in planning appropriate intervention, mitigation, remediation, and rehabilitation strategies to limit human exposure to highly contaminated areas.