Precipitation Of Secondary Minerals Research Articles

Legacy copper/nickel mine tailings potentially harbor novel iron/sulfur cycling microorganisms within highly variable communities.

The oxidation of sulfide-bearing mine tailings catalyzed by acidophilic iron and sulfur-oxidizing bacteria releases toxic metals and other contaminants into soil and groundwater as acid mine drainage. Understanding the environmental variables that control the community structure and metabolic activity of microbes indigenous to tailings (especially the abiotic stressors of low pH and high dissolved metal content) is crucial to developing sustainable bioremediation strategies. We determined the microbial community composition along two continuous vertical gradients of Cu/Ni mine tailings at each of two tailings impoundments near Sudbury, Ontario. 16S rRNA amplicon data showed high variability in community diversity and composition between locations, as well as at different depths within each location. A temporal comparison for one tailings location showed low fluctuation in microbial communities across 2 years. Differences in community composition correlated most strongly with pore-water pH, Eh, alkalinity, salinity, and the concentration of several dissolved metals (including iron, but not copper or nickel). The relative abundances of individual genera differed in their degrees of correlation with geochemical factors. Several abundant lineages present at these locations have not previously been associated with mine tailings environments, including novel species predicted to be involved in iron and sulfur cycling.IMPORTANCEMine tailings represent a significant threat to North American freshwater, with legacy tailings areas generating acid mine drainage (AMD) that contaminates rivers, lakes, and aquifers. Microbial activity accelerates AMD formation through oxidative metabolic processes but may also ameliorate acidic tailings by promoting secondary mineral precipitation and immobilizing dissolved metals. Tailings exhibit high geochemical variation within and between mine sites and may harbor many novel extremophiles adapted to high concentrations of toxic metals. Characterizing the unique microbiomes associated with tailing environments is key to identifying consortia that may be used as the foundation for innovative mine-waste bioremediation strategies. We provide an in-depth analysis of microbial diversity at four copper/nickel mine tailings impoundments, describe how communities (and individual lineages) differ based on geochemical gradients, predict organisms involved in AMD transformations, and identify taxonomically novel groups present that have not previously been observed in mine tailings.

Quantitative analysis of the Permian sediments of Karoo Basin of South Africa using combined petrophysical and X-ray analytical techniques

This study quantifies the petrophysical parameters and determines the impact of mineralogy on the petrophysical parameters of the Permian sediments of the main Karoo Basin, South Africa. Conventional well logs from KDD-01 well, thirty-two and forty-two samples are investigated for mineral and composition analyses using X-ray diffraction and fluorescent techniques, respectively. Three intervals of Abrahamskraal Formation (500–513m), dolerite sill that intruded the Abrahamskraal Formation (513–530m), and Waterford Formation (1014–1048m) are investigated. The results show that the average porosity of the Abrahamskraal Formation is 2.9%, the dolerite interval has an average value of 1.8%, whereas the Waterford Formation has an average value of 2.1%. The average permeability for the Abrahmaskraal Formation is 0.05mD, dolerite 0.04mD, and the Waterford Formation is 0.08mD, respectively. No hydrocarbon was detected. The low values of petrophysical properties may be associated with the pore network, which is poorly connected, intense precipitation of secondary minerals, and pore infilling during burial diagenesis. Quartz mineral dominates in the Abrahamskraal Formation, with an average value of 47% and 61% in the Waterford Formation.In comparison, plagioclase is the main mineral constituent in the dolerite, with an average of 44%. Based on the combined petrophysical and geochemistry classification scheme, the formations evaluated belong to the type III pore structure. The type III pore structure is a poor and ineffective reservoir, with rock porosity usually less than 6% and a permeability of less than 0.15mD. However, regarding the mineral elemental ratio, the Abrahamskraal and the Waterford Formations meet the type II pore structure criteria, while the dolerite is type III. This paper has produced a helpful rock classification scheme based in the Karoo Basin, South Africa, using petrophysical and geochemical data for the first time.

Sulfate-reducing bacteria (SRB) mediated carbonate dissolution and arsenic release: Behavior and mechanisms

Carbonate bound arsenic act as an important reservoir for arsenic (As) in nature aquifers. Sulfate-reducing bacteria (SRB), one of the dominant bacterial species in reductive groundwater, profoundly affects the biogeochemical cycling of As. However, whether and how SRB act on the migration and transformation of carbonate bound arsenic remains to be elucidated. Batch culture experiment was employed using filed collected arsenic bearing calcite to investigate the release and species transformation of As by SRB. We found that arsenic in the carbonate samples mostly exist as inorganic As(V) (93.92 %) and As(III). The present of SRB significantly facilitated arsenic release from carbonates with a maximum of 22.3 μg/L. The main release mechanisms of As by SRB include 1) calcite dissolution and the liberate of arsenic in calcite lattices, and 2) the break of H-bonds frees arsenic absorbed on carbonate surface. A redistribution of arsenic during culture incubation took place which may due to the precipitation of As2Sx or secondary FeAl minerals. To our best knowledge, it is the first experimental study focusing on the release of carbonate bound arsenic by SRB. This study provides new insights into the fate and transport of arsenic mediated by microorganism within high arsenic groundwater-sediment system.

Hydrochemical properties and heavy metal concentrations (ecological and human risk) of lake Rukwa

This study examined lake Rukwa's hydrochemical characteristics and heavy metal levels (ecological and health hazards). Results showed that the pH ranged from 8.83 to8.95, EC ranged from 1470 to 1572.22 µS/cm, and TDS ranged from 1053.04 to 1262.63 Mg/l. The findings revealed that lake Rukwa is characterized by Na-K-HCO3 water chemical type. Gibb's diagram revealed that rock weathering and evaporation regulate water's chemical composition. The calcite and sepiolite precipitation enriches the water with Na-CO3-SO4-Cl. The study suggests silicate mineral weathering, rock-water interactions, direct ion exchange, and secondary mineral precipitation govern the geochemical evolution of lake Rukwa. The results also revealed that 30% of samples had moderate ecological risk (30 < RI < 60), whereas 70% had severe risk (60 < RI < 120). The oral hazard quotient (HQ) values for lead (Pb) in children were significantly higher (HQ > 1) at all locations, indicating a potential health risk. However, the dermal HQ values were found to be within acceptable levels. Most sites had acceptable Hazard Index (HI) values, except for Pb in children and adults. In Monte Carlo simulations, heavy metal HQ values were below standard limits, except for oral Pb exposure, which exceeded 1 for adults (7.29E-04) and children (2.79E-03). The average CR values for oral and dermal Pb in adults (7.29E-04, 3.47E-04) and children (2.79E-03, 1.02E-03) exceeded 1.0E-04, suggesting carcinogenic potential. These findings highlight significant oral and dermal carcinogenic hazards from Pb exposure to lake Rukwa and the necessity for effective comprehensive measures to mitigate these risks.

Vertical distribution and contamination assessment of heavy metals in the vadose zone of a 50-year-old smelter dumpsite, San Antonio Bay, Argentina

This research aimed to assess the contamination levels and mineralogical association of heavy metals in the vadose zone beneath smelter residues that were freely deposited over natural sediments from the 1960 s to the 1980 s. The results revealed elevated concentrations of heavy metals, particularly Fe, Pb, Zn, Cu, and Cd. The highest concentrations were found within the superficial layer, corresponding to the smelter slag (203,703 – 219,998 mg kg−1 Fe; 73,708 – 136,390 mg kg−1 Pb; 18,922 – 29,484 mg kg−1 Zn; 6473 – 7887 mg kg−1 Cu; 20 – 48 mg kg−1 Cd). This residue is an acidic material mainly constituted by secondary sulfates and oxyhydroxides. Although concentrations decreased with depth, the levels of these metals remained higher than the background even at depths of 300 cm. Precipitation of secondary minerals (plumbojarosite, anglesite, Zn-sulfates, and Fe oxydroxides) from the percolating leachates was detected in the vadose zone based on SEM and EDS analysis. According to their vertical distribution, Cd and Zn showed a higher mobility than Cu, Fe and Pb, which were primarily concentrated at the surface layer. The geo-accumulation index (Igeo) was Pb > Cu > Zn > Cd > Ni. The vadose zone is severely polluted and represents a very high risk to the environment based on the ecological risk factor (Eri) and risk index (RI). The metals that contribute most to this condition are Pb > Cd ≈ Cu > Zn. Given the severity of the situation, remediation of the study area is recommended.

Authigenic mineralization in Surtsey basaltic tuff deposits at 50 years after eruption

Alteration of basaltic glass and in situ mineral growth are fundamental processes that influence the chemical and material properties of Earth’s oceanic crust. These processes have evolved at the basaltic island of Surtsey (SW Iceland) since eruptions terminated in 1967. Here, subaerial and submarine lapilli tuff samples from a 192 m-deep borehole drilled in 2017 (SE-02b) are characterized through petrographic studies, X-ray powder diffraction analyses, and SEM–EDS imaging and chemical analyses. The integrated results reveal (i) multi-stage palagonitization processes in basaltic glass and precipitation of secondary minerals from matrix pore fluids, (ii) multi-stage crystallization of secondary phillipsite, analcime and Al-tobermorite in the vesicles of basaltic pyroclasts and (iii) variations in palagonitization processes as a function of thermal and hydrological domains. Although temperature appears to be an important factor in controlling rates of secondary mineralization, the chemistry of original basaltic components and interstitial fluids also influences reaction pathways in the young pyroclastic deposits. The integration of systematic mineralogical analyses of the 50-year-old tuff from one of the most carefully monitored volcanic sites on Earth, together with temperature monitoring in boreholes since 1980, provide a reference framework for evaluating mineralogical evolution in other Surtseyan-type volcanoes worldwide.

Redox-controlled differential weathering of andesitic pumice: Possible catalytic effects of ferrous/ferric iron on rapid halloysite accumulation in a Holocene tephra layer

Differential weathering process of Holocene andesitic tephra in Atsuma, Hokkaido, northern Japan, were investigated with a specific focus on the flame-like occurrence of halloysite bands and their formation mechanism. The parent material was coarse-grained pumice (Ta-d2) deposited 9 ka to form a highly permeable metre-thick layer atop fine-grained impervious periglacial loam, which is covered by humic soil–tephra sequences. The shallower part of the Ta-d2 layer was weathered to a reddish or yellowish brown colour, which is characterized by intensive leaching of Si and Al, with abundant precipitation of iron (hydr)oxide and amorphous secondary minerals in an oxidizing environment. A reductive grey colour was observed only at the Ta-d2 bottom below the halloysite band, where pumice grains survived significant elemental leaching and contained ferrous iron in the solid phase with abundant dissolved Fe in the liquid phase. Between these oxidized and preserved zones, an irregularly shaped, fine-grained, white iron-rich halloysite layer with a decimetre-scale thickness developed. In this clay band, the molar ratio of Si to (Al + Fe) was nearly 1:1, with a small amount of remnant Ca. Mössbauer analysis revealed that Fe2+ was initially incorporated into the aluminosilicate sheet via Al3+ substitution and transformed into Fe3+ within the structure. The halloysite band was formed at depths in the tephra layer corresponding to the redox front. The abundance of Si and Al in pore water in any zone of the tephra layer meets the stability requirements of halloysite, indicating that the redox condition controls the rapid local accumulation of halloysite through the isomorphous substitution followed by valence change of iron. We propose a new hypothesis stating that iron catalyses halloysite nucleation via a stepwise function, including layer charging to absorb hydrated cations and subsequent charge loss resulting in cation desorption and passive intercalation of water molecules within the 1:1 layer.

Incomplete sulfide oxidation under sub-oxic conditions: Rates and aqueous sulfur speciation

The oxidative dissolution of sulfide minerals consumes oxygen and can generate redox gradients in mine wastes that affect the mobility of redox-sensitive solutes. However, the controls of oxygen depletion on sulfide reactivity and sulfur mobilization remain poorly constrained, complicating the long-term assessment of drainage quality dynamics. We investigated pyrite and Fe-rich sphalerite weathering using aqueous S speciation and quantitative mineralogical analyses under controlled, ambient versus sub-oxic, conditions at 6 < pH < 9. Titration assays revealed that oxidation rates for pyrite (up to 10−10 mol m−2 s−1) were higher than for sphalerite (up to 10−11 mol m−2 s−1) and, for both minerals, decreased by two orders-of-magnitude under sub-oxic (<50 ppm O2) conditions. Precipitation of secondary S-bearing minerals was restricted to elemental S, with no sulfate- or thiosulfate-salts detectable >0.01 wt%. Sulfate was the dominant aqueous S species produced in all experiments, but significant amounts of thiosulfate, tetrathionate, and sulfite were also found. These dissolved intermediate S species were abundant under both sub-oxic and oxic conditions, and broadly in line with known sulfide oxidation mechanisms, even though the weathering of pyrite produced several factors less incompletely oxidized S than that of sphalerite, under otherwise comparable conditions. This work shows that a range of intermediate S species may be produced even in low-reactivity conditions and may help optimize the management of such mine waste materials.

Time‐Dependent Weakening of Granite at Hydrothermal Conditions

AbstractThe evolution of a fault's frictional strength during the interseismic period is a critical component of the earthquake cycle, yet there have been relatively few studies that examine the time‐dependent evolution of strength at conditions representative of seismogenic depths. Using a simulated fault in Westerly granite, we examined how frictional strength evolves under hydrothermal conditions up to 250°C during slide‐hold‐slide experiments. At temperatures ≤100°C, frictional strength generally increases with hold duration but, at 200 and 250°C, an initial increase in strength transitions to rapid time‐dependent weakening for holds longer than 14 hr. Forward modeling of long hold periods at 250°C using the rate and state friction constitutive equations requires a second, strongly negative, state variable with a long evolution distance. This implies that significant hydrothermal alteration is occurring at 250°C, consistent with microstructural observations of dissolution and secondary mineral precipitation.

Geochemical behavior of heavy metals and radionuclides in a pit lake affected by acid mine drainage (AMD) in the Muskau Arch (Poland)

Pit lakes in the ‘anthropogenic lake district’ in the Muskau Arch (western Poland; central Europe) are strongly affected by acid mine drainage (AMD). The studied acidic pit lake, ŁK-61 (pH <3), is also exposed to floods due to its location in the flood hazard area, which may significantly influence the geochemical behavior of elements. The elemental compositions of water and lake sediment samples were measured with ICP–OES and ICP–MS. The sediment profile was also examined for 137Cs and 210Po activity concentrations using gamma and alpha spectrometry, respectively. Grain size distribution, mineralogical composition, diatoms, and organic matter content in the collected core were also determined. The key factors responsible for the distribution of selected heavy metals (e.g., Cu, Ni, Pb, Zn) and radioisotopes (137Cs and 210Po) in the bottom sediments of Lake ŁK-61 are their coprecipitation/precipitation with Fe and Al secondary minerals and their sorption onto authigenic and allogenic phases. These processes are likely driven by the lake tributary, which is an important source of dissolved elements. The data also showed that the physiochemical parameters of Lake ŁK-61 water changed during an episodic depositional event, i.e., the flood of the Nysa Łużycka River in the summer of 2010. The flood caused an increase in the water pH, as interpreted from the subfossil diatom studies. The down-core profiles of the studied heavy metal and radionuclide (HMRs) contents were probably affected by this depositional event, which prevented a detailed age determination of the collected lake sediments with 137Cs and 210Pb dating methods. Geochemical modeling indicates that the flood-related shift in the physicochemical parameters of the lake water could have caused the scavenging of dissolved elements by the precipitation of fresh secondary minerals. Moreover, particles contaminated with HMRs have also possibly been delivered by the river, along with the nutrients (e.g., phosphorus and nitrogen).

Reactive Transport Modelling of carbon mineralization – a machine learning-based approach

Carbon mineralisation is currently one of the most promising Carbon Capture and Storage (CSS) options for permanent gas sequestration since it ensures a rapid conversion of carbon from the gas phase to a carbonate mineral. Mafic and ultramafic rocks are the best geological options for mineral carbonation due to the relatively fast dissolution rates of the mineral components that can release carbonatable divalent cations such as Mg2+, Sr2+, Ba2+, Mn2+, Ca2+ and Fe2+. Once in solution, these cations react with dissolved carbonate ions to form, under convenient pH and temperature conditions, carbonate minerals like calcite, magnesite, siderite, rhodochrosite, or dolomite.&#x0D; The viability of carbon mineralization with injection of freshwater has been proven in the CarbFix project [1]. The main feature of the CarbFix method is that CO2 (and other minor gases) is not injected under its gaseous form but already dissolved in an aqueous fluid, which greatly enhances the mineralisation rates. The methodology, however, requires vast amounts of water that can be a limited resource in many regions. Seawater may be the most viable water source for underground carbonation in many areas, but its use raises questions on the efficiency of the carbonation process. The high ionic strength of seawater makes the geochemical interactions between CO2-rock and seawater more complex and, so far, more unpredictable. Reactive transport modelling (RTM) based on experimental thermodynamic and kinetic data of seawater-basalt interaction [2, 3] can shed some light on the expected mineralisation progress in sites with different mineralogy and variable temperature conditions. Figure 1 shows the results obtained with a reactive transport model that simulates the injection of CO2-charged seawater in basaltic rock.&#x0D; geochemical reaction calculations in particular might be considerably slow and are sometimes redundant as they might be based on a very similar set of input values. These challenges are usually faced by introducing a number of simplifications in the models to meet the objectives of the simulation studies. Thus, alternative ways to solving the full system are a priori a potential way to reduce the computational burden of numerical models.&#x0D; One of such alternatives is Machine Learning (ML) and, more specifically, Artificial Neural Networks (ANN), which are inspired on biological neural networks as the ones found in the human brain. They contain several computational “neurons” arranged in different layers. Each of these neurons can be activated based on the response of the other connected neurons. The training process consists of feeding data into the ANN and fitting the connection weights between the neurons to reproduce and learn the hidden relationships of the data. Recently, the authors have coupled ANNs of a geochemical system into a reactive transport simulator [5]. In this approach, Supervised Machine Learning with ANNs is used to accurately predict the geochemical evolution in a reactive transport framework without the need of actually performing the (expensive) chemical equilibrium calculations in the reactive transport model.&#x0D; The goal of this work is to apply and further develop the technology based on Supervised Machine Learning algorithms to drastically boost the efficiency of reactive transport models of carbon mineralization in the Carbfix system [6]. Firstly, a set of geochemical models of CCS are developed in batch systems (0D) as well as reactive transport models in 1D axisymmetric, 2D, and 3D RTM modelling with different degrees of complexity. Modelling focuses on the injection of CO2-charged seawater into basaltic rocks. In this system, CO2 is consumed via a two-step reaction: (1) Dissolution of Basaltic Glass and release of cations (Ca and Mg), and (2) precipitation of Ca-Mg carbonates and other secondary minerals. The RTM models consider a 1 km domain and a characteristic mineralization of 3-4 years. As a first step, these models are solved with the convential (non ML-based) reactive transport simulator iCP [7]. Then, ANNs are trained and validated with the latest developments in setting up neural networks and used to solve these RTM systems with a Comsol-ML library. The resulting ANNs present good accuracies with coefficients of determination (R2) above 0.95 for all outputs, and a batch calculation speedup of 30 as compared to traditional chemical equilibration with PhreeqC. Preliminary results of RTM using ML to predict the chemical step indicate a speedup of on order of magnitude and reasonable accuracy as compared to conventional RTM. Our results demonstrate that it is conceivable to replace a geochemical solver in a RTM environment with significantly faster surrogate-based models powered by a machine learning algorithm

Pressure leach of β-spodumene with carbonic acid: Weak acid process for extraction of lithium

This contribution develops a process for recovering lithium from β-spodumene by sequential pressure leach with solutions of carbonic acid, as a replacement for digestion of β-spodumene with concentrated sulfuric acid. Six sequential steps, each operated at 200 °C and 100 bar for 1 h, retrieve 75 % of lithium from the initial feed material. This compares with a 12.6 % Li recovery from a single-stage (batch) operation. We develop both the thermodynamic and mass-transfer models of the leach process and argue that the lithium extraction is mass-transfer controlled. The underlying mechanism involves: (i) near-instantaneous ion exchange between H+ for Li+ at the onset of the digestion; (ii) direct formation of amorphous Li-depleted rinds; (iii) precipitation of secondary minerals, boehmite (AlO(OH)) and skin-forming amorphous silica (SiO2), the latter only in the batch operation; (iv) counter-current diffusion of H+ and Li+ through the surface layer (surface layer = depleted sublayer + precipitation sublayer); (v) dissolution of the surface layer at the solid-solution interface, through the reactions with water. The evidence comes from the near-proportionality between the lithium recovery and mass of dissolved β-spodumene, no detection of keatite-HAlSi2O6, particle morphology, precipitation of amorphous skins of SiO2 decorated with boehmite specks observed by electron microscopy and predicted from thermodynamic modelling as well as from a mass-transfer analysis of the Li-recovery rates. Direct observations confirm the existence of a three-phase reacting system, as predicted from thermodynamic calculations, with the absence of a supercritical fluid phase. Lithium recoveries, of at least 28 % in a single step, are attainable, but only for long contact time of 48 h. Digestion lasting hundreds of hours is needed for the batch process to reach Li extraction corresponding to that of the sequential leach. The challenges for industrial implementation of the process comprise recycling of large amounts of water, avoiding the precipitation of silica that forms rinds, accelerating the hydrolysis of Li-depleted sublayer, concentrating the dilute solutions of Li+ and overcoming hesitance of industry to consider high-pressure treatment.

Experimental alteration of allanite at 200°C: the role of pH and aqueous ligands

Abstract Allanite is a major host of rare earth elements (REEs) in the continental crust. In this study, reaction mechanisms behind allanite alteration are investigated through batch experiment runs on natural allanite grains in carbonate-bearing hydrothermal fluids at 200°C, with initial acidic (pH = 4) or alkaline (pH = 8) conditions and with different aqueous ligands (120 mmol kg −1 of F, Cl, P or S). Time-series experiment runs in F-doped systems at different durations between 15 and 180 days reached a steady state at 120 days. The pH efficiently controls the allanite alteration process, with initial high pH, alkaline conditions being more reactive (75% alteration compared with 25% under acidic conditions). The ligand also significantly influences the alteration process under initial acidic conditions with the P-doped system (70%) almost non-reactive for the Cl- and S-doped systems (&lt;5%). In the alteration rim, REEs are mainly redistributed in REE-bearing phases either as carbonates (F-doped) or phosphates (P-doped). The relatively flat REE-normalized patterns of the recovered experimental fluids suggest a fractionation of light rare earth elements (LREEs) over heavy rare earth elements (HREEs) during the course of the alteration reactions. It is proposed that secondary REE mineral precipitation at the reaction front creates a local disequilibrium in the solution and a steep chemical gradient promoting allanite dissolution and thus its alterability.

Mapping the mineralogy in the Oxia Planum and Mawrth Vallis ExoMars landing sites – implications for aqueous alteration and paleoenvironmental evolution

Mineralogical studies constitute one of the main tools to investigate geological processes on Mars. Here, the mineralogy of the ExoMars landing sites Oxia Planum and Mawrth Vallis is analyzed based on multispectral datasets of the CRISM Compact Reconnaissance Imaging Spectrometer for Mars of Mars Reconnaissance Orbiter, TES Thermal Emission Spectrometer of Mars Global Surveyor and OMEGA Visible and Infrared Mineralogical Mapping Spectrometer of Mars Express are integrated and interpreted. Primary and secondary minerals of carbonates, oxides, silicates and sulphates mineral groups are characterized, with most minerals produced by aqueous alteration, with 35 mineral species identified, amongst which phyllosilicates are the dominant group. Coexisting mineral types point to distinct hydrothermal and alteration stages. Our investigation supports that water must have been present on early Mars on superficial and endogenous processes, causing direct precipitation and transformations of secondary minerals, with some not usually formed simultaneously. Hence, it is likely that species may have arisen at different times, due to changes of Martian climate. Some minerals may have formed in the subsurface. The Martian palaeoenvironments might include subaerial, underwater, and shallow subsurface hydrothermal systems, cold springs, alkaline lakes, sabkhas, and playas. Our results contribute to our understanding of the planned landing sites to prepare for what the ExoMars rover mission may encounter, highlighting the impact that water may have had on the mineral genesis, alteration processes and their astrobiological potential.

Magmatic rare earth element mineralization and secondary fluid-assisted redistribution in the Kamthai carbonatite complex, NW India

Calcite carbonatites from the Kamthai alkaline complex in western India are highly enriched in Sr and the rare earth elements (REE) owing to their formation from highly differentiated carbonatitic magma. Pegmatitic calcite carbonatites preserve rare magmatic intergrowth of rod/pod-like carbocernaite [(Ca, Na)(Sr, REE, Ba)(CO3)2] and REE + Sr-rich calcite. This intergrowth is interpreted to be the result of rapid simultaneous crystallization of the phases from a brine-rich carbonatitic magma. Primary carbocernaite, calcite, and britholite [(LREE, Ca)5(SiO4, PO4)3(OH, F)] sequestered Sr and REE from the brine-rich melt and constitute the major sources of these elements during hydrothermal redistribution. Replacement textures suggest fluid-assisted, post-magmatic hydrothermal REE redistribution through dissolution-reprecipitation process that concentrated the REE into secondary REE-(fluor/hydroxyl)carbonates, cerianite (ideally Ce4+O2), ancylite [(Sr, Ca)LREE(CO3)2(OH)∙(H2O)], and monazite. Hydrothermal alteration of magmatic calcite leached out the LREE, whereas in case of carbocernaite and britholite, an increase in their REE contents is noticed, followed by pseudomorphic replacement by REE-(fluor/hydroxyl)carbonate minerals.The carbonatite-derived hydrothermal fluids initially transported the REE as sulfate and later as hydroxyl‑carbonate complexes. The ligand transition was a consequence of the precipitation of baryte, celestine, and pyrite, which led to a reduction in fluid sulfur content and increase in its pH due to interaction with carbonates. Precipitation of secondary REE minerals was triggered by decrease in ore fluid temperature due to interaction with relatively cooler, oxidized fluid and interaction with carbonates. Carbocernaite, ancylite, cerianite, and Ce-bearing REE-(fluor)carbonates constitute early precipitated secondary REE minerals along with baryte, celestine, and pyrite as by-product phases, whereas both Ce- and La-rich, hydroxyl-dominated members of bastnäsite, parisite, and synchysite, along with monazite were the dominant REE minerals which precipitated during the advanced hydrothermal stage, with siderite as a by-product.

Feedbacks between the formation of secondary minerals and the infiltration of fluids into the regolith of granitic rocks in different climatic zones (Chilean Coastal Cordillera)

Abstract. Subsurface fluid pathways and the climate-dependent infiltration of fluids into the subsurface jointly control the intensity and depth of mineral weathering reactions. The products of these weathering reactions (secondary minerals), such as Fe(III) oxyhydroxides and clay minerals, in turn exert a control on the subsurface fluid flow and hence on the development of weathering profiles. We explored the dependence of mineral transformations on climate during the weathering of granitic rocks in two 6 m deep weathering profiles in Mediterranean and humid climate zones along the Chilean Coastal Cordillera. We used geochemical and mineralogical methods such as (micro-) X-ray fluorescence (μ-XRF and XRF), oxalate and dithionite extractions, X-ray diffraction (XRD), and electron microprobe (EMP) mapping to elucidate the transformations involved during weathering. In the profile of the Mediterranean climate zone, we found a low weathering intensity affecting the profile down to 6 m depth. In the profile of the humid climate zone, we found a high weathering intensity. Based on our results, we propose mechanisms that can intensify the progression of weathering to depth. The most important is weathering-induced fracturing (WIF) by Fe(II) oxidation in biotite and precipitation of Fe(III) oxyhydroxides and by the swelling of interstratified smectitic clay minerals that promotes the formation of fluid pathways. We also propose mechanisms that mitigate the development of a deep weathering zone, like the precipitation of secondary minerals (e.g., clay minerals) and amorphous phases that can impede the subsurface fluid flow. We conclude that the depth and intensity of primary mineral weathering in the profile of the Mediterranean climate zone is significantly controlled by WIF. It generates a surface–subsurface connectivity that allows fluid infiltration to great depth and hence promotes a deep weathering zone. Moreover, the water supply to the subsurface is limited in the Mediterranean climate, and thus, most of the weathering profile is generally characterized by a low weathering intensity. The depth and intensity of weathering processes in the profile of the humid climate zone, on the other hand, are controlled by an intense formation of secondary minerals in the upper section of the weathering profile. This intense formation arises from pronounced dissolution of primary minerals due to the high water infiltration (high precipitation rate) into the subsurface. The secondary minerals, in turn, impede the infiltration of fluids to great depth and thus mitigate the intensity of primary mineral weathering at depth. These two settings illustrate that the depth and intensity of primary mineral weathering in the upper regolith are controlled by positive and negative feedbacks between the formation of secondary minerals and the infiltration of fluids.

Hydrogeochemistry of trace and rare earth elements in the Caviahue-Copahue Volcanic Complex

The Caviahue-Copahue Volcanic Complex is one of the most studied active volcanic systems in the South American Andean range, and yet little research has focused on trace and rare-earth elements of waters, especially during an eruptive cycle. In this study, we sampled and investigated natural waters from 23 sites (involving the crater lake, hot springs, streams, rivers, and bubbling pools) in two campaigns in 2017 and 2018, using physicochemical parameters, major, trace and rare-earth elements concentrations. With this novel dataset, it was possible to identify, characterize and compare three groups of waters with distinctive hydrofacies. Indeed, the normalization of water compositions against host rock concentrations showed a particular trace element pattern for each group of waters. Although the absolute concentrations of the elements in each sampling site changed from 2017 to 2018, the normalized patterns did not. Boron, As, Cd, Tl, Se, and Te, commonly recognized as volatile, are the main trace elements that magmatic gases supply to the system headwaters, whereas elements such as Ca, K, and Ba are affected by precipitation of secondary minerals (gypsum, anhydrite, barite, jarosite, and alunite). Furthermore, the main river draining the summit volcano shows a steep decrease in As, Cr, and V concentrations correlated to the precipitation of Fe and Al hydroxysulfates (schwertmannite and basaluminite, respectively). Moreover, it is the first time that a comparison between the different water groups is made using the patterns of the rare-earth elements, allowing us to identify and separate depletion patterns due to dilution processes from those due to precipitation processes.

Geochemical and mineralogical investigation of cemented crusts in the tailings cover at Long Lake Gold Mine, Sudbury, Canada

In mine tailings, precipitation of secondary minerals may cement the tailings material and form cemented crusts or hardpans. Hardpans typically form beneath the surface of reactive tailings. However, at the former Long Lake Gold Mine near Sudbury, Ontario, cemented crusts formed in a clean sand cover above the tailings. We applied mineralogical and geochemical techniques to investigate the formation of these cemented crusts. Representative samples were collected from the sand cover and vertical cores from the underlying tailings. Elevated concentrations of arsenic (As), iron (Fe), and sulfur (S) in the sand cover indicate the upward transport of sulfide-mineral oxidation products. The shallow porewater of the tailings is acidic (pH 4 – 6) and contains elevated concentrations of As (up to 346 mg/L), Fe (up to 1844 mg/L), and SO4 (up to 12,000 mg/L). Mineralogical observations indicate that primary sulfide minerals in the near-surface tailings display moderate to strong oxidation, and secondary Fe-arsenate and jarosite minerals are formed both in the near-surface tailings and the sand cover. Upward migration of sulfide-mineral oxidation products leads to the formation of cemented crusts, which with continuing erosion, represent a long-term source of pollution to the surrounding environment.

Increased primary mineral dissolution control on a terrestrial silicate lithium isotope record during the middle Miocene Climate Optimum

Lithium isotopes have great potential to fractionate at subaerial environment, so they are promising proxies for tracing chemical weathering history. However, it remains uncertain how to relate lithium isotopic compositions (δ7Li) in sediments to silicate weathering and past climate in terrestrial setting. To tackle this question, we choose the warm and wet middle Miocene climate optimum (MMCO, 17–14 Ma) with large climate variation amplitude and the following cold and dry middle Miocene climate cooling period (MMCC, 14–11 Ma) with damped climatic variation amplitude, as two climate contrasting intervals to study lithium isotopes and content ([Li]) variations of terrestrial mudrocks. Our study site is located at the eastern Qaidam Basin of the northeastern Tibetan Plateau and the precipitation pattern of this part of the basin is similar to the Chinese Loess Plateau over the two studied intervals. The study site is suitable for clarifying link between climate and δ7Li variations because previous studies have demonstrated no provenance shift over the studied interval and short transport distance from source to the study site suggests little chemical weathering over the transportation process. Both δ7Li and [Li] values show larger amplitude over the MMCO (spanning from −1.2 to 3.2 ‰ and from 32.8 to 93.9 ug/g, respectively) than the MMCC interval (−1.8 to 1.2 ‰ and 41.7–80.8 ug/g, respectively), consistent with general feature of global and Chinese Loess Plateau climate. However, δ7Li data are higher over the MMCO in comparison with the MMCC, contrary to expectation of more lithium isotope fractionation at warm interval. We interpret the more positive δ7Li values over the MMCO using increased ratio of primary mineral dissolution over secondary mineral precipitation. Qaidam mudrock and benthic Li records show complementary changes, suggesting their possible link. Furthermore, past research reveals lack of focused uplift of the northeastern Tibetan Plateau over the studied 18–11 Ma. So we conclude that global climate, rather than Tibetan uplift, played an important role in modulating inland Qaidam Basin climate variations over the middle Miocene and that increased chemical weathering over warm climate can lead to a small magnitude of lithium isotope fractionation. Therefore, interpreting chemical weathering history, and hence climate, using lithium isotope data in terrestrial setting requires considering relative importance of primary mineral dissolution versus secondary mineral precipitation.

The use of copper isotopes for understanding metal transfer mechanisms within the continuum mine-river-dam (Huelva Region, Spain).

Mining areas and in particular those containing massive sulfides have left a heavy environmental legacy with soils and hydrographic networks highly contaminated with metals and metalloids as for example in the Iberian Pyrite Belt (Huelva, Spain). Here, we present new data on copper (Cu) isotopic composition of waters and solids collected along a continuum Mine (Tharsis)-River (Meca)-Lake (Sancho) in the Iberian Pyrite Belt. Our results show that the isotopic signature of pit lakes is spatially variable, but remains stable over the seasons; this signature seems to be controlled by water-rock interaction processes. The data obtained on the Meca River imply a number of attenuation processes such as decrease in the metal concentration by precipitation of secondary minerals. This is accompanied by preferential retention of the heavy isotope (65Cu) with a possibility of living organisms (e.g., algae) participation. The terminal Sancho lake demonstrated constant isotopic signature over the entire depth of the water column despite sizable variations in Cu concentrations, which can be tentatively explained by a superposition of counter-interacting biotic and abiotic processes of Cu fractionation. Overall, the understanding of the isotopic variations along the hydrological continuum is useful for a better understanding of metal element transfer within mining environments and surrounding surface waters.