Secondary Silicate Research Articles

Importance of early diagenesis of deep-sea sediments to the REY enrichment and oceanic element budget

Deep-sea sediments have become an important new type of rare-earth element (REY) resources that have high potential to meet the increasing demand. However, the enrichment mechanisms of such deposits remain unclear. In this paper, we made a detailed discussion in bulk-sample geochemistry along the core profile of GC26 collected at the western Pacific Ocean. Elements are classified into lithophile-, phosphate-, and metal oxide elements, which have affinities to silicate, phosphate, and Fe–Mn (oxyhydr)oxide phases in sediments, respectively. Biophosphate is the major host of REY in deep-sea sediments. Its accumulation has a substantial effect on bulk-sample strontium isotopes, but a weak effect on bulk neodymium isotopes. Although the bulk neodymium isotopes imply there was a slight change in sedimentary provenances, it cannot explain the different behaviors of the three elemental groups simultaneously. Water-rock interactions at high temperature enlighten us that water–sediment interactions at low temperature, also known as early diagenesis, may be the answer of behaviors of the three element groups. Silicate dissolution during early diagenesis releases elements from the silicate lattice. When biophosphate accumulation occurs, the released phosphate elements (including REY) are preferentially incorporated into biophosphate rather than being released into seawater, which is the key to REY enrichment in deep-sea sediments. This is also the case for metal oxide elements (e.g., Mn, Co, and Ni) when oxygen fugacity is high enough to cause Fe–Mn (oxyhydr)oxide deposition as coatings or micro-nodules. Considerable amounts of silicate elements (e.g., Al, Ti, Fe, Cr, and V) are released into seawater to participate into global oceanic element cycle if they are less compatible in newly formed secondary silicate components (e.g., phillipsite). Our results provide new insights into the importance of early diagenesis of deep-sea sediments to REY enrichment and the global oceanic elemental budget.

Nickel isotope fractionation during intense weathering of basalt: Implications for Ni output from continental weathering

Nickel isotope fractionation during continental weathering is not well constrained due to the limited research on Ni isotopes during weathering of mafic rocks such as basalt. This study investigated two weathering profiles (strongly and extremely weathered) derived on basalts in tropical China. The strongly weathered profile was dominated by kaolinite and divided into three layers with depth (soil, saprolite and rock). The extremely weathered profile was mainly composed of Fe- and Al-(oxyhydr)oxides and kaolinite, and included a special ferricrust layer, iron-rich duricrust with ferruginous nodules, between the soil and saprolite. We analysed the Ni speciation (e.g. Fe-oxide phases and residual phase) and isotopic composition of soil, ferricrust, saprolite, rock and water samples in the weathering profiles. Pore water and groundwater were collected underlying the extremely weathered profile, and the size-distribution of particulate Ni (1 kDa–450 nm) in water samples was analysed.Nickel in both profiles was mainly hosted in the residual phase (>71% of total Ni) which included primarily secondary silicates and Al-(oxyhydr)oxides. Weathering intensity controlled the mineral compositions and physico-chemical properties of the weathering profiles as well as Ni isotopic variations. Nickel redistribution (∼30%) and isotope fractionation (Δ60Niregolith-rock = −0.08‰ to 0.07‰) were slight in the strongly weathered profile due to the dominance of secondary silicates in Ni speciation. For the extremely weathered profile, significant Ni depletion (∼67%) and isotope fractionation (Δ60Niregolith-rock = −0.25‰ to 0.32‰) were related to the transformation of secondary silicates into Fe- and Al-(oxyhydr)oxides during lateritic weathering. The positive correlation of δ60Ni and Ni concentrations indicated that Ni isotope fractionation was controlled by Ni adsorption and incorporation of secondary minerals. In the lower saprolite, the calculated isotope fractionation between Ni remaining in the profile and leaching to the solution (Δ60Nisolid-solution = −0.47‰) indicated that Ni isotope fractionation was mainly controlled by the preferential adsorption of isotopically light Ni on Fe- and Al-(oxyhydr)oxides. However, in the soil and ferricrust, acidic pH (∼5.0) might reduce Δ60Nisolid-solution to −0.28‰ by releasing the isotopically light adsorbed Ni, leading to the predominance of incorporated Ni in Fe- and Al-(oxyhydr)oxides. Specifically, the highest δ60Ni value (0.27 ± 0.05‰) and Ni concentration in the upper saprolite indicated that the isotopically heavy Ni leached from the soil and ferricrust was scavenged by precipitating secondary silicates. Finally, the estimated isotopic composition of Ni leached from the extremely weathered profile (δ60Nioutput = 0.02 ± 0.15‰) was close to that of pore water (0.06 ± 0.01‰) where Ni was mainly present in the particulate phase. Compared with groundwater (δ60Ni = 0.33 ± 0.04‰) dominated by dissolved Ni, Ni output from the profile likely consisted of isotopically heavy dissolved Ni and light particulate Ni. Overall, this study provides a comprehensive understanding of Ni redistribution and speciation in basalt weathering profiles, highlighting the significance of weathering intensity in controlling Ni isotope fractionation and its implications for Ni outputs from continental weathering.

A comprehensive and consistent mineral dissolution rate database: Part II: Secondary silicate minerals

This paper describes the creation of a consistent database of the far-from-equilibrium dissolution rates of secondary silicate minerals including clays, zeolites, serpentines, chlorites, prehnite, wollastonite, epidotes, garnets, kyanite, staurolite, cordierite, tourmaline, and feldspathoids. This work, based on the regression of available dissolution rate data normalized to their BET surface area as a function of pH and temperature, was performed using equations described in Heřmanská et al. (2022a) using a least-squares algorithm. The average difference between calculated and measured rates ranged from 0.18 to 0.66 log units depending on the mineral. Where relevant data were lacking, rate parameters are proposed based upon the rate behaviors of minerals with similar structures. All obtained rate equations and parameters have been incorporated into the KINEC.v1.dat database for direct use in geochemical fluid reactive transport software.The far-from-equilibrium dissolution rates of most naturally forming silicate minerals are notably similar to one another at neutral conditions. More than 65% of the silicate minerals considered in this study and that of Heřmanská et al. (2022a) range in value from 10-11.8 to 10-12.5 mol m-2 s-2 at 25 oC and pH 7; this range is within the uncertainties associated with these rates. This similarity in rates is attributed to the likelyhood that breaking Si-O bonds is the rate limiting step of the dissolution of each of these minerals. Faster rates are observed for minerals that can be dissolved without breaking Si-O bonds. Retrieved apparent activation energies for the silicate minerals are found to be similar over all pH conditions and average ∼55 kJ mol-1. This apparent activation energy suggests that rates at 100, 200 and 300 °C will be approximately 86, 3,600 and 42,000 times higher, respectively, than corresponding rates at 25 oC.

The effects of iron-rich ultramafic pegmatite on the composition and mineralogy of the UG2 chromitite: a case study in the western Bushveld Complex, South Africa

Discordant iron-rich ultramafic pegmatites (IRUPs) intersect the UG2 chromitite at many places in the Bushveld Complex. The effects of IRUP interactions on the UG2 ore mineralogy and PGE grade are assessed at the Thaba mine, north-west Bushveld, based on a borehole profile through the UG2 layer and detailed analysis of mineral textures and compositional variations across the UG2-IRUP contacts using micro-XRF element mapping. The UG2-IRUP interaction operated at different scales and probably by different mechanisms. At the local scale (< 10 cm), a thin layer of Fe–Ti–Cr spinel and ilmenite formed on the IRUP side of the contact with UG2, whereas the UG2 chromitite developed grain coarsening, loss of interstitial silicates, and chemical gradients in Cr, Al, Fe, and Ti that extend a few centimeters from the contact into the seam. These local effects are attributed to the intrusion of IRUP melt into the solidified UG2 layer, followed by re-equilibration of the oxide minerals across the contact during cooling. On a larger scale, changes in the ore and gangue mineral assemblages in UG2 took place throughout the entire meter-thick main seam. Compared with regional UG2 compositions, chromite has higher TiO2 and lower Mg#, and there is an anomalously low abundance of interstitial plagioclase. The IRUP-affected UG2 shows relatively abundant secondary hydrous silicates, replacement of PGE sulfides by PGE alloys and PGE-As–Sb–Bi–Te–Pb phases, and formation of secondary Ni–Cu–Fe sulfides after pentlandite and chalcopyrite. These large-scale effects are attributed to hydrothermal fluids derived from IRUP melts. The IRUP bodies at the Thaba mine caused redistribution of PGE within the UG2 layer but did not significantly reduce the overall grade. However, significant changes in the ore mineral assemblage and an increased abundance of secondary silicates can reduce the efficiency of PGE recovery.

Mineral surface area in deep weathering profiles reveals the interrelationship of iron oxidation and silicate weathering

Abstract. Mineral specific surface area (SSA) increases as primary minerals weather and restructure into secondary phyllosilicate, oxide, and oxyhydroxide minerals. SSA is a measurable property that captures cumulative effects of many physical and chemical weathering processes in a single measurement and has meaningful implications for many soil processes, including water-holding capacity and nutrient availability. Here we report our measurements of SSA and mineralogy of two 21 m deep SSA profiles at two landscape positions, in which the emergence of a very small mass percent (&lt;0.1 %) of secondary oxide generated 36 %–81 % of the total SSA in both drill cores. The SSA transition occurred near 3 m at both locations and did not coincide with the boundary of soil to weathered rock. The 3 m boundary in each weathering profile coincides with the depth extent of secondary iron oxide minerals and secondary phyllosilicates. Although elemental depletions in both profiles extend to 7 and 10 m depth, the mineralogical changes did not result in SSA increase until 3 m depth. The emergence of secondary oxide minerals at 3 m suggests that this boundary may be the depth extent of oxidation weathering reactions. Our results suggest that oxidation weathering reactions may be the primary limitation in the coevolution of both secondary silicate and secondary oxide minerals. We value element depletion profiles to understand weathering, but our finding of nested weathering fronts driven by different chemical processes (e.g., oxidation to 3 m and acid dissolution to 10 m) warrants the recognition that element depletion profiles are not able to identify the full set of processes that occur in weathering profiles.

Calcium isotopic geochemistry of geothermal systems in the tectonically active southeastern Tibetan Plateau

The global Calcium (Ca) cycle is closely coupled to the carbon cycle, and Ca isotopes have potential in tracing it. Even though groundwater is one of the main reservoirs of Ca at the Earth's surface, few data are available for groundwater, and the behavior of Ca and its isotopes in geothermal systems remains unknown. Here we analysed the stable Ca and radiogenic Sr isotope compositions of thermal waters distributed along the Jinsha and Yalong river valleys in the southeastern Tibetan Plateau. The Ca isotopic composition of the thermal water ranges from 0.45 to 2.16 ‰ (δ44/40Ca values relative to SRM 915a). The thermal waters collected from carbonate aquifers have higher δ44/40Ca values than bedrocks, which was attributed to secondary carbonate precipitation accompanied by CO2 degassing. In contrast, δ44/40Ca values in thermal waters collected from clastic and igneous rocks are similar to bedrock. Despite some thermal waters undergoing secondary silicates formation and CaNa ion exchange, such processes maybe not play a significant role in governing the Ca isotopic composition of these thermal waters. This suggests that Ca isotopes can be used to trace secondary carbonate precipitation driven by CO2 degassing (e.g. travertine) in geothermal systems located in tectonically active areas.

Ornithogenesis and soil-landscape interplays at northern Harmony Point, Nelson Island, Maritime Antarctica.

Understanding the influence of soil-forming factors and processes in ornithogenic soils is important to predict impacts of climate change on Antarctic ecosystems. Herein, we analyzed the soil-landscape interplays and development of ornithogenic soils at Harmony Point (HP), Nelson Island. We collected, described, and classified 24 soil profiles, combined with vegetation and landforms descriptions. Geoprocessing techniques were employed for mapping. Soil physical, chemical, geochemical, and mineralogical analyses were applied. Patterned ground, "Ornithogenic"/Typic Gelorthent, and moss carpets were the dominant landform, soil and vegetation classes, respectively. Soils from rocky outcrops were more structured, acidic, with higher organic carbon, organometallic complexes, and secondary phosphate minerals, due to former bird influence. Soils from cryoplanated platforms presented higher water pH, base saturation, clay content, and secondary silicate minerals. Soils from marine terraces presented high exchangeable bases, phosphorous, and amorphous phosphate minerals. Soil chemical weathering is enhanced by ornithogenesis and widespread in HP. Besides ornithogenesis, organic matter accumulation, cryoturbation, and cryoclastic processes are also important to pedogenesis of ornithogenic soils. The soils of the cryoplanated platforms exhibited a gradient of pedogenetic development corresponding to increasing biota influence and distance from glacier. In contrast, soils of rocky outcrops were more developed even close to the glacier, due to ornithogenesis.

Ash characterisation formed under different oxy-fuel circulating fluidized bed conditions

The CO2-intensive oil shale power industry accounts for more than 70% of the Estonian energy sector, producing large amounts of ash that are mainly landfilled. Adopting oxy-fuel technology in the Estonian energy sector, in conjunction with CO2 storage, can be a critical tool for reducing carbon footprint. Nevertheless, several differences in ash formation under oxy-fuel conditions can be expected, which can lead to additional ash handling/utilization and related environmental concerns. In this context, the composition of oil shale ash was obtained from a series of combustion experiments in a 60 kWth circulating fluidized bed (CFB) test unit under both air and oxy-fuel combustion regimes studied by means of physical, chemical analysis as quantitative X-ray diffraction and element analysis for ashes from different separation ports. During the experimental work, special attention was given to understanding the impacts of the boiler temperature, recycled flue gas (RFG), and elevated oxygen concentration. As a result, the primary goal of this research is to characterise the ash produced by oxy-fuel combustion of oil shale in order to gain a better understanding of its chemical and mineral compositions, including Ca-Mg silicates and clay minerals, as well as to investigate the behaviour of the formation of free lime and anhydrite, which are the major compounds influencing potential ash utilisation routes. The results show that although the decomposition of calcium carbonates was limited during oxy-fuel combustion because of the high CO2 partial pressure, the contents of secondary silicates and anhydrite were slightly higher. The increased particle temperature and the higher SO2 partial pressure (with RFG) can explain this. The particle size distributions (PSDs) were wider under oxy combustion, and the specific surface area (SSA) in Filter ashes were much higher under elevated inlet O2% atmosphere. Oxy-fuel combustion had no significant impact on the concentration of elements in the ash. Overall, the mineralogy of the ashes formed in air and oxy-fuel combustion environments is similar, yet slight differences exist in the formation of clay minerals in the case of increased oxygen concentrations and with the application of RFG as a result of the increased residence time of the particles.

Platinum‐group mineral and silicate inclusions in the low‐Al chromitites of the Manipur ophiolite, northeast India: Implications on Cr‐PGE mineralization in nascent subduction zone settings

Low‐Al chromitites from the Manipur ophiolite contain a wide range of mineral inclusions, including hydrous and anhydrous silicates, sulphides, and platinum group minerals (PGM). The common inclusions are primary silicates, such as clinopyroxene, orthopyroxene and secondary silicate inclusions, such as chlorite, serpentine, and garnet. These inclusions are small (&lt;30 μm in PGM, &lt;100 μm in silicates) and randomly distributed throughout their host chromite grains. The shape and texture indicate some inclusions (clinopyroxene, orthopyroxene, PGMs) trapped during the magmatic stage and most inclusions (chlorite, serpentine, and uvarovite) trapped during recrystallization of chromite. Clinopyroxene was discrete inside the chromite, with Cr2O3 content ranging from 0.62 to 1.77 wt.%, and Al2O3 varying between 0.96 to 1.63 wt.%. Orthopyroxene is enstatite (En93Wo2Fs4), Cr2O3 varies from 0.58 to 1.8 wt.% and the minor amount of CaO (0.41–0.81 wt.%), and Al2O3 (0.58–0.83 wt.%). Uvarovite is present in two forms: discrete crystal inclusions (anhydrous) in chromites and fractures (hydrous) as fillings. The chlorite occurs as lath shaped, and patchy phase is Cr‐rich variety ‐ kammererite (clinochlore) and penninite with variable Cr2O3 (0.22–7.25 wt.%) and FeO (2.5–3.9 wt.%). The PGM in the studied chromite are laurite (Ru, Os, Ir)S2. The parental melts of chromitites had low TiO2 (0.16–0.48 wt.%) and Al2O3 (10.18–14.58 wt.%) contents, and primary mineral inclusions, suggesting an arc‐like geochemical affinity, and the estimated melt composition is comparable with that of boninitic magma.

Mineral carbonation of New Caledonian ultramafic mine slag: Effect of glass and secondary silicates on the carbonation yield

New Caledonian nickel (Ni) mines produces ∼12 million metric tons of mine slag every year, that are considered undesired and uneconomic waste materials. However, due to the high content of Mg2+ and Fe2+, these slags exhibit a potential of carbon dioxide (CO2) storage by ex-situ aqueous mineral carbonation. We conducted laboratory batch experiments at 200 °C/ 150 bar, 250 °C/ 300 bar, 300 °C/ 300 bar, in CO2-saturated water to better understand the slag dissolution, secondary mineral formation at the fluid-mineral interface, and the effect of the secondary silicates on the carbonation yield. The slag contains olivine (45 wt%) and glass (55 wt%). Olivine in the slag dissolves faster than glass, contributing to carbonate precipitation (Fe-rich magnesite) at 200 °C/150 bar. At 250 °C/ 300 bar, olivine is almost completely dissolved while glass dissolves only partially, both contributing to the highest recorded carbonation yields of the slag of 44 wt%. Although both olivine and glass are completely dissolved at 300 °C/ 300 bar, the carbonate yield drops at a value half of that at 250 °C/ 300 bar. This is due to formation of large quantity of Mg-bearing phyllosilicates that reduces the amount of Mg2+ available for carbonation. These results emphasize that increasing temperature above 250 °C would not increase the carbonate yield of New Caledonian mine slags. However, as glass only partially reacts at T < 250 °C, mobilizing Mg2+ in glass could potentially increase the carbonation yield, for example by adding suitable organic ligands. Mg-bearing phyllosilicates and amorphous silica that are formed in these experiments do not exhibit passivation properties, and therefore do not affect the carbonation rate.

Geochemistry of Accessory Apatite from the Cu–Ni–Sulfide-Bearing Ultramafic–Mafic Rocks of the Khudolaz Complex (South Urals) as a Monitor of Magmatic and Metasomatic Processes

Abstract —We present results of mineralogical and geochemical studies (optical and electron microscopy, probe microanalysis, and LA-ICP-MS) of accessory apatite from the rocks of four ore-bearing massifs of the Khudolaz Complex: Vostochnyi Buskun, Severnyi Buskun, Malyutka, and Tashly-Tau. Two groups of apatite are recognized by morphology and chemical composition: (1) “magmatic” unaltered apatite (Ap-1) in unaltered and slightly altered rocks and (2) “metasomatized” apatite (Ap-2) surrounded by secondary silicates that replaced primary minerals. Ap-1 is represented by euhedral and subhedral hexagonal crystals with a high content of chlorine (0.7–1.2 wt.% Cl) and an extremely low content of sulfur (&amp;lt;0.05 wt.% SO3). It is enriched in REE (ΣREE = 2.2–3.0 wt.%), shows a pronounced negative Eu anomaly (Eu/Eu* = 0.36–0.58), and is depleted in Co, Ni, and chalcophile trace elements (Zn, Pb, and Bi). The distribution of major and trace elements in Ap-1 made it possible to identify its two generations, early and late, in the Khudolaz Complex. The early generation, characterized by a low content of Ca (Т ≥ 1000 °C, CaO &amp;lt; 54 wt.%), crystallized almost simultaneously with Ca-plagioclase (An81–61). The late generation, characterized by a high content of Ca (Т ≥ 700 °C, CaO &amp;gt; 55 wt.%), is associated with Na-plagioclase (An28–8), amphibole, and phlogopite. Ap-2 is represented by highly cracked grains and is characterized by a low content of chlorine (0.0n–0.5 wt.% Cl) and a high content of sulfur (0.06–0.93 wt.% SO3). The content of fluorine in both groups of apatite varies in the same range (0.6–1.7 wt.% F), which determines its relative inertness during metasomatic processes. Ap-2 is less enriched in REE (ΣREE = 1.1–2.1 wt.%) and shows a less pronounced Eu anomaly (Eu/Eu* = 0.61–0.77) but has high contents of Co, Ni, and chalcophile trace elements. The Ap-1 and Ap-2 show different variations in contents of major elements (Fe, Mg, Na, etc.), which is due to the impact of hydrothermal fluid on the mineral at the postmagmatic stage. It is shown that the low content of sulfur in apatite from unaltered rocks does not indicate a low sulfide ore potential of the Khudolaz Complex. The Cu–Ni sulfide signature of the complex is more clearly evidenced by the composition of metasomatized apatite enriched in S, Co, Ni, and chalcophile elements as a result of their hydrothermal removal from primary sulfide minerals. The high Eu/Eu* value indicates an increase in oxygen fugacity at the postmagmatic stage.

Alteration history of Séítah formation rocks inferred by PIXL x-ray fluorescence, x-ray diffraction, and multispectral imaging on Mars.

Collocated crystal sizes and mineral identities are critical for interpreting textural relationships in rocks and testing geological hypotheses, but it has been previously impossible to unambiguously constrain these properties using in situ instruments on Mars rovers. Here, we demonstrate that diffracted and fluoresced x-rays detected by the PIXL instrument (an x-ray fluorescence microscope on the Perseverance rover) provide information about the presence or absence of coherent crystalline domains in various minerals. X-ray analysis and multispectral imaging of rocks from the Séítah formation on the floor of Jezero crater shows that they were emplaced as coarsely crystalline igneous phases. Olivine grains were then partially dissolved and filled by finely crystalline or amorphous secondary silicate, carbonate, sulfate, and chloride/oxychlorine minerals. These results support the hypothesis that Séítah formation rocks represent olivine cumulates altered by fluids far from chemical equilibrium at low water-rock ratios.

Mineralogical Factors Affecting the Dense Medium Separation of Nickel Sulfide Ores

Dense medium separation (DMS) is often used to reject a large portion of gangue material upfront to create cost and energy savings during processing. As lower-grade ores with complex mineralogy are being increasingly exploited, the properties of the gangue minerals begin to play a more important role in the upgrading of the ore. It is therefore important to understand these mineralogical factors to be able to select suitable processing routes for specific ore types. Two nickel sulfide deposits in southern Africa were chosen as case studies to understand differences in DMS efficiency when applied to different ores: Ore A and Ore B. Both ores showed nickel upgrades using DMS and the products were then characterized using QEMSCAN, with the aid of X-ray diffraction and electron probe microanalysis. Overall, particle density remains the main control on the separation, followed by sulfide texture, with massive and net-textured sulfides having larger grain sizes and therefore better liberation than disseminated sulfides. In addition to the concentration of sulfides, primary and secondary silicate minerals are separated by their density differences, which can affect the recovery of finely disseminated sulfides associated with them. Particle size is also important in DMS, with material near the cut-point density separating on size rather than density. The understanding of the mineralogical properties affecting DMS can aid in the prediction of the suitability of DMS for different ore types.

Boron in the strata and waters of the Eocene Green River and Uinta Formations, Uinta Basin, Utah

Boron is a naturally occurring element that can be found in the strata and water of the Eocene Green River and Uinta Formations of the Uinta Basin of Utah. Whereas boron is suspected to be a necessary trace nutrient for proper plant and animal growth and development, higher concentrations of boron can be detrimental to living things, but the element is not known to be carcinogenic. Utah has no limit on boron content in drinking water; however, for irrigation purposes a limit of 750 μg B/L (0.75 mg/L) has been established. The Green River Formation (GRF), deposited in ancient lakes in Wyoming, Colorado, and Utah, is well known for its oil shale and saline mineral deposits, particularly the thick, economic trona beds in Wyoming. Such evaporitic mineral deposits are characteristic of a saline lake environment that existed at the end stages of Eocene lacustrine deposition. In Utah they are found in the upper GRF, and to a minor extent in the lower Uinta Formation, where elevated boron is evident. Boron-bearing minerals are present in the Parachute Creek Member of the GRF in Utah, and they occur as secondary silicate minerals in at least 12 wells across Utah’s Uinta Basin. These minerals were first reported by the U.S. Geological Survey in the 1950s. This study determined that the boron mineral occurrences correlate stratigraphically and coincide with the areas delineated for the hypersaline events in the Parachute Creek Member of the GRF. This argues that boron was concentrated with other saline constituents in Lake Uinta and is an indicator of hypersaline conditions. Water quality analyses reporting boron content from surface and subsurface samples were compiled from public databases from the Utah Department of Environmental Quality, the U.S. Geological Survey, and the Utah Geological Survey. This new database consists of 155 samples from 38 sites from the upper part (Parachute Creek Member) of the GRF, and 58 samples from 26 sites from the lower part (Douglas Creek Member) of the GRF. The boron concentration was found to be different for the two GRF parts. The average boron content of the 58 lower GRF aquifer water analyses is 6338 μg/L, while the mean boron content for the 26 individual sites varies from 15 to 205,000 μg/L. The upper GRF aquifer contains at least twice the boron content of the lower GRF, and the average boron content of the 155 analyses of upper GRF groundwater is 18,172 μg/L. The mean boron content for the 38 individual sites varies 40 to 480,000 μg/L. Areas of highboron concentration in groundwater of the GRF tend to coincide with the location of GRF hypersaline paleodepocenters. Groundwater boron content in the Uinta Formation comes from 40 analyses from 36 sites. The average of the 40 Uinta Formation analyses is 3251 μg B/L, while the mean boron content for the 36 individual sites varies from 40 to 24,000 μg/L. For each interval studied, less boron tends to be found in analyses from sites near the outcrop and boron content tends to increase in the studied formations as they are more deeply buried. Additionally, boron content was compiled for surface waters and springs for 3955 analyses from 374 sites in the Uinta Basin. When the mean boron content of these surface water sites was examined by hydrologic drainage unit subareas, it was found that the tributaries in the northern Uinta Basin, north of the Duchesne and White Rivers, contain the lowest mean boron contents, whereas higher mean boron contents are common for the tributaries in southern part of the basin. The boron content of surface water from the southern Uinta Basin drainages also tends to increase northward toward the demarking water courses. The tributaries in the southern part of the Uinta Basin have higher boron contents due to their waters having contact with the boron-bearing, shallow-inclined strata of the upper GRF or member B of the Uinta Formation. The tributaries in northern part of the basin have lower boron contents because they are not in contact with the GRF, have less contact with the member B of the Uinta Formation, and are diluted by greater snow-melt runoff from the Uinta Mountains which bound the basin to the north.

Quantitative assessment of the relative roles of sulfide liquid collection, magmatic degassing and fluid-mediated concentration of PGE in low-sulfide ores of the Norilsk intrusions

Low-sulfide ores in the upper marginal series of the Norilsk intrusions are distinct from the main massive and disseminated sulfide orebodies in a high platinum-group element (PGE) tenor up to 1,300–1,700 ppm PGE + Au in 100 % sulfide, lower Cu/Pd of ∼100–300 and increased Pt/Pd of ∼0.2–2. These features have previously been considered either as a result of collection by sulfide liquid at extremely high R-factor (silicate to sulfide melt mass ratio) or postmagmatic sulfide removal, although the decoupling between PGE grade and PGE tenor may suggest an additional process of PGE concentration in addition to partitioning into immiscible sulfide liquid. In this study, the distribution of diverse platinum-group minerals (PGM) and their spatial associations with sulfide-silicate assemblages were investigated by automated mineralogy techniques to recognize the mechanism of the PGE concentration. Mineral assemblages were studied from 2D surfaces of polished sections and mineral separate blocks using the Mineral Liberation Analysis and TESCAN Integrated Mineral Analysis in combination with X-ray microtomography and lab- and synchrotron-based microbeam X-ray fluorescence mapping collected over slabs and thick sections, representative of the 3D sub-surficial layer.Palladium minerals (mostly stibnides, bismuthides, tellurides and arsenides) prevail over Pt minerals in all three intrusions (Norilsk 1, Talnakh and Kharaelakh) based on ∼6,600 identified PGM grain statistics from both thin sections and heavy mineral separates. Among Pt minerals, sperrylite and Pt-Fe alloys occur in an equal proportion in Norilsk 1 whereas the alloys are exceptionally rare in Talnakh-Kharaelakh low-sulfide ores. The PGM grains are predominantly locked within secondary silicates with a percentage of their mutual boundaries of ∼50 rel. % in consistency with a high abundance (35–90 area %) of secondary silicates in mineralized rocks. No correlation between the proportions of secondary silicates and PGMs as well as with the degree of their spatial affinity was found. The preferred confinement of PGM grains to the disseminated chromite schlieren is observed in the studied samples, although, among PGMs, only Pt sulfides demonstrate significant spatial affinity (15–34 rel. % mutual boundary) intergrowing with chromite. The spatial association between PGM and base-metal sulfides (∼20 rel. %) is notably higher than the proportion of sulfides in rocks (1.8–2.8 area %) that is interpreted as a quantitative proof of the cogenetic link between PGM and sulfides. However, the significant mm-scale detachment of the PGM grains from the sulfide blebs is persistent throughout the mineralized sections.Element mapping techniques reveal widespread textures of early magmatic degassing (such as amygdules, segregation vesicles, fluid caps and halos), the common tight intergrowths of PGM with volatile-rich minerals and the presence of PGM grains nucleating on the former gas bubble walls. These features are all distinct from the textures of postmagmatic hydrothermal-metasomatic alteration. We propose that an initial composition of sulfide liquid was modified due to S partitioning into a fluid phase during early magmatic degassing. Therefore, the high PGE tenor is not solely a result of sulfide-silicate exchange but was likely enhanced by early magmatic S loss during degassing and PGE fluid transport.

Картографическое обеспечение идентификации природных и техногенных источников растворенного вещества в бассейне озера Байкал

A method of GIS mapping was developed to identify and assess the contributions of sources of matter to the composition of surface waters. The basis for the creation of the GIS database was the results of the study of the spatial diversity of the chemical composition of surface waters. Geoinformation analysis included the creation of a digital framework for mapping, vectorization of mapping sources and Earth remote sensing materials, creation of a single database combining cartographic, statistical information and field observation materials, morphometric relief analysis based on a digital relief model, creating a landscape basis for base maps, creating thematic maps, analyzing changes in the components of geosystems, creating electronic cartographic layers allowing to identify participation of solute sources in formation of water composition. The analysis of component changes was based on the results of different-time studies of the composition of water and bottom sediments. Based on the comparison of the chemical composition of the waters of the Baikal tributaries with the chemical and mineralogical composition of rocks, an approach was developed to identify sources of solute and assess their contributions to the formation of macro- and microelement compositions of surface waters. To solve the problems of the study, methods of statistical analysis of data, multicomponent mixing using systems of linear equations, field methods of data collection were used. Three main categories of solute sources (silicate, sulfide-containing silicate, carbonate rocks) were identified and their contributions to the chemical composition of water were calculated. On the basis of microelement tracers, the contributions of silicate rocks were divided into contributions of primary and secondary silicate rocks, ore-containing silicate rocks without sulfides were isolated. By comparing the ratios of concentrations of trace elements in the waters of uncontaminated territories and wastewater of enterprises, tracers were identified that made it possible to identify sources of surface water pollution. Maps of territories that determine a certain chemical composition of surface waters were compiled, which was first classified on the basis of the ratio of the contributions of drained rocks.

Origin of Fe–Ni–Cu (Co) sulfide and Fe–Ti oxide minerals in the c. 1.77 Ga dolerite dyke, Singhbhum Craton (eastern India)

Abstract Dolerite dyke swarms are widespread within the Singhbhum Craton (eastern India) that emplaced from the Neoarchean to Paleoproterozoic era just after the stabilization of crust before c. 3 Ga. These dyke swarms are oriented in NE–SW to NNE–SSW, NW–SE to WNW–ESE, east–west and north–south directions. The WNW–ESE-trending c. 1.77 Ga Pipilia dyke swarm is sampled from the Satkosia area of Orissa state. The dyke shows a noticeable disparity in terms of the modal proportion and grain size of pyroxenes, plagioclase, Fe–Ti oxide minerals and texture across the trend. In places the primary silicates are altered to secondary hydrated mineral assemblages of amphibole, chlorite and sericite. The primary silicates are clinopyroxene (augite – Mg# = 65.7–82.6; En 37–48 Fs 11–17 Wo 36–41 ), orthopyroxene (clinoenstatite – Mg# = 68.5–78; En 63–70 Fs 20–29 Wo 4–5 ) and plagioclase (An 11–39 Ab 44–82 Or 1–7 ) and the Fe–Ti oxides are titanomagnetite (FeO, 34.38–39.50 wt%; Fe 2 O 3 , 48.26–56.21 wt%; TiO 2 , 5.05–9.60 wt%) and ilmenite (FeO, 40.75–43.79 wt%; Fe 2 O 3 , 3.54–10.03 wt%; TiO 2 , 47.82–50.87 wt%). Application of two-pyroxene thermometry yields an equilibration temperature range of 1065–978°C, and coexisting titanomagnetite–ilmenite pairs reveal 731.39–573.37°C under the oxygen fugacity ( f O 2 ) condition NNO + 0.3 to FMQ − 1.03. The dyke contains disseminated sulfides at the interstices of Fe–Ti oxides and silicates. Major sulfide minerals are pyrite, chalcopyrite and vaesite; pyrite–vaesite assemblages occur in association with secondary silicate minerals. Pyrite grains contain variable concentrations of Co (0.01–5.70 wt%) and Ni (0.02–1.95 wt%). Coexisting vaesite contains Co (2.42–10.44 wt%), Ni (26.40–47.88 wt%) and Fe (7.32–26.55 wt%). Texture, sulfide–silicate assemblage and the presence of low metal/S sulfides such as the pyrite–vaesite assemblage indicate that primary Fe–Ni sulfides (pyrrhotite–pentlandite) that segregated from immiscible sulfide liquid at high temperature are modified by late magmatic/hydrothermal fluid activities. Numerous sulfide-bearing deposits hosted in ultramafic–mafic intrusions of Paleoproterozoic age have been recorded globally and the occurrence of Fe–Ni sulfides in the c. 1.77 Ga Pipilia dyke swarm in the Singhbhum Craton enhances the exploration potential of this craton in eastern India.

Mineralisation of atmospheric CO2 in hydromagnesite in ultramafic mine tailings – Insights from Mg isotopes

In this study we present the first Mg isotope data that record the fate of Mg during mineralisation of atmospheric CO2 in ultramafic mine tailings. At the Woodsreef Asbestos Mine, New South Wales, Australia, weathering of ultramafic mine waste sequesters significant amounts of CO2 in hydromagnesite [Mg5(CO3)4(OH)2·4H2O]. Mineralisation of CO2 in above-ground, sub-aerially stored tailings is driven by the infiltration of rainwater dissolving Mg from bedrock minerals present in the tailings. Hydromagnesite, forming on the surface of the tailings, has lower δ26Mg (δ26MgHmgs = −1.48 ± 0.02‰) than the serpentinised harzburgite bedrock (δ26MgSerpentinite = −0.10 ± 0.06‰), the bulk tailings (δ26MgBulk tailings = −0.29 ± 0.03‰) and weathered tailings containing authigenic clay minerals (δ26MgWeathered tailings = +0.28 ± 0.06‰). Dripwater (δ26MgDripwater = −1.79 ± 0.02‰) and co-existing hydromagnesite (δ26MgHmgs = −2.01 ± 0.09‰), forming in a tunnel within the tailings, and nodular bedrock magnesite [MgCO3] (δ26MgMgs = −3.26 ± 0.10‰) have lower δ26Mg than surficial fluid (δ26Mg = −0.36‰) and hydromagnesite.Complete dissolution of source minerals, or formation of Mg-poor products during weathering, is expected to transfer Mg into solution without significant alteration of the Mg isotopic composition. Aqueous geochemical data and modelling of saturation indices, along with Rayleigh distillation and mixing calculations, indicate that the 26Mg-depletion in the drip water, relative to surficial water, is the result of brucite dissolution and/or precipitation of secondary Mg-bearing silicates and cannot be assigned to bedrock magnesite dissolution. Our results show that the main mineral sources of Mg in the tailings (silicate, oxide/hydroxide and carbonate minerals) are isotopically distinct and that the Mg isotopic composition of fluids and thus of the precipitating hydromagnesite reflects both isotopic composition of source minerals and precipitation of Mg-rich secondary phases. The consistent enrichment and depletion of 26Mg in secondary silicates and carbonates, respectively, underpins the use of the presented hydromagnesite and fluid Mg isotopic compositions as a tracer of Mg sources and pathways during CO2 mineralisation in ultramafic rocks.

The pH dependence of the isotopic composition of boron adsorbed on amorphous silica

The use of the boron content and isotopic composition of secondary silicate minerals and siliceous organisms to trace weathering reactions and past ocean pH requires characterizing the fundamental reactions that govern the incorporation and subsequent isotope fractionation of this element in these materials. Toward this goal we have investigated boron adsorption on the surface of amorphous silica (SiO2·0.32H2O) and quantified its isotopic fractionation. Boron adsorption envelopes and corresponding isotope fractionation factors were measured in dilute aqueous solutions (0.01 M) of NaCl and CaCl2. B maximum adsorbed fraction was found to be about 2 times higher in CaCl2 solutions than in NaCl. The modelling of chemical and isotopic data in NaCl solutions allowed to identify the formation of two main B surface species at the SiO2(am)/water interface: a neutral trigonal (B3) inner-sphere complex, >SiOB(OH)20, characterized by a fractionation factor of ~−16‰ relative to aqueous boric acid, and a negatively charged tetrahedral (B4) inner-sphere complex, >SiOB(OH)3–, with fractionation factors of −5‰ with respect to aqueous borate. In CaCl2 solutions the data modelling indicates the presence of B4 inner-sphere complexes with a fractionation factor of −6.5‰ relative to aqueous borate, but excludes the presence of trigonal surface species and suggests instead the formation of a Ca-B(OH)4– complex that could partly account for the observed increase of boron adsorption in these solutions. These observations indicate that changes in the surface charge density and interfacial water structure due to different background electrolytes can induce changes in concentration and both chemical and isotopic composition of B adsorbed on silica surfaces.Although this study suggests that the B adsorption reaction on SiO2(am) plays a minor role in the B incorporation and isotopic signature of clay minerals and siliceous cements forming during weathering reactions, the acquired data should allow for an improved knowledge of the biomineralization reactions. The observed B isotopic fractionations between adsorbed and aqueous B species should help determining the relative contribution of various processes, such as cellular transport, biological mediation and silicification reactions, on the amount of B incorporated in siliceous microorganisms and its isotopic signatures. In addition, the presence in NaCl solutions of both trigonal and tetrahedral boron complexes at the silica surface could explain the observed weak pH dependence of the boron isotopic composition of marine diatoms.

Thermodynamic and experimental approach of the effect of Si on the sintering of Y3NbO7

The effect of silicon on the natural sintering of Y3NbO7 powders is studied. Characterizations shows that Si increases densification rate and grain growth but it also leads to the apparition of a secondary silicate phase. The silicate precipitation results from the segregation of silicon favored by matter transport through a liquid phase. The distribution of the secondary phase have been studied by electronic microscopy and mapped by micro-luminescence. Thermodynamic calculations of Gibbs energy of the different phase as well as binary and ternary phase diagrams have been conducted to support interpretation of the sintering experimental results.