Primary Aluminosilicate Research Articles

Diagenetic and Paleoenvironmental Controls on Late Cretaceous Clay Minerals in the Songliao Basin, Northeast China

AbstractSedimentary and diagenetic processes control the distribution of clay minerals in sedimentary basins, although these processes have seldom been studied continuously in continental sedimentary basins. The Songliao Basin, northeast China, is a large continental, petroleum-bearing basin, and provides a unique study site to understand the sedimentary and diagenetic processes that influence clay assemblages. In this paper, the clay mineralogy of a 2500 m-thick Late Cretaceous (late Turonian to Maastrichtian) terrestrial sedimentary succession (SK-1s and SK-1n cores), retrieved by the International Continental Scientific Drilling Program in the Songliao Basin, was examined. The objective was to determine the diagenetic and paleoenvironmental variations that controlled the formation of clay mineral assemblages, and to determine the thermal and paleoenvironmental evolution of the basin. The results from both cores show that illite is ubiquitous through the succession, smectite is frequently encountered in the upper strata, and ordered mixed-layer illite-smectite (I-S), chlorite, and kaolinite are abundant in the lower strata. Burial diagenesis is the primary control on the observed decrease of smectite and increasing illite, I-S, and chlorite with depth. Observations of clay-mineral diagenesis are used to reconstruct the paleotemperatures and maximum burial depths to which the sediments were subjected. The lowermost sediments could have reached a maximum burial of ~1000 m deeper than today and temperatures ~50°C higher than today in the latest Cretaceous. The transition of smectite to I-S in the SK-1 cores and the inferred paleotemperatures provide new constraints for basin modeling of oil maturation at elevated temperatures in the Songliao Basin. Authigenic kaolinite and smectite are enriched in sandstones with respect to the coeval mudstones from the SK-1n core, as a result of early diagenesis with the participation of primary aluminosilicates and pore fluids. In the upper part of both SK-1 cores, variations in smectite and illite were controlled primarily by paleoenvironmental changes. Increases in smectite and decreases in illite from the late Campanian to Maastrichtian are interpreted as resulting from increasing humidity, a conclusion consistent with previous paleoenvironmental interpretations.

Brines in the western part of the Tunguska artesian basin

Geochemistry of brines in the Tunguska artesian basin indicates that these brines were in equilibrium with carbonate, sulfate, and secondary aluminosilicate minerals but not with primary aluminosilicates. Salinity of brines saturated with halite is greater than 360 g/dm{sn3}. Analysis of the Ca/Cl, Sr/Cl, and Br/Cl ratios of the brines testifies that an increase in the salinity of the brines and variations in their composition result from metamorphism in the water–rock system. The principal Ca and Sr sources of the brines are sulfates (anhydrite, gypsum, and celestine), which are dissolved because of reduction of the sulfate ion and its removal from the system: CaSO4 + 2Corg + MgCl2 + 2H2O = MgCa(CO3)2 + H2S + 2HCl. Another process forming the chemical composition of the brines is interaction with primary (Ca, Mg) aluminosilicates according to the reaction: CaAl2Si2O8 + 3H2O + 2CO2 = Al2Si2O5(OH)4 + Ca{sn2+} + 2HCO−3.The principal source of Br for the brines is seawater.

Influence of Hyper-Alkaline pH Leachate on Mineral and Porosity Evolution in the Chemically Disturbed Zone Developed in the Near-Field Host Rock for a Nuclear Waste Repository

This paper evaluates the effect of hyper-alkaline (NaOH/KOH) leachate on the mineralogy and porosity of a generic quartzo-feldspathic host rock for intermediate- and low-level nuclear waste disposal following permeation of the cementitious repository barrier by groundwater. The analysis is made with reference to expected fluid compositions that may develop by contact of groundwater with the cementitious barrier to form a chemically disturbed zone (CDZ) in the adjacent host rock, as informed by relevant natural analogue sites. Theoretical analysis and numerical modelling is used to explore the influence of different host rock mineral assemblages on changes in pore fluid chemistry, multiple mineral dissolution and precipitation reactions and matrix porosity within the CDZ under these conditions. The numerical modelling accounts for kinetic and surface area effects on the mineral transformation and porosity development for periods of up to 10,000 years travel time from the repository and ambient temperature of \(20\,^{\circ }\hbox {C}\). The analysis shows that dissolution of quartz, feldspar and muscovite in the host rock, by the hyper-alkaline waste leachate, will create relatively high concentrations of dissolved Si and Al in the pore fluid, which migrates as chemical fronts within the CDZ. Precipitation of secondary mineral phases is predicted to occur under these conditions. The increase in matrix porosity that arises from dissolution of primary aluminosilicate minerals is compensated by a reduction in porosity due to precipitation of the secondary phases, but with a net overall increase in matrix porosity. These coupled physical and geochemical processes are most important for contaminant transport in the near-field zone of the CDZ and are eventually buffered by the host rock within 70 m of the repository for the 10,000 year travel time scenario. The predicted changes in matrix porosity may contribute to increased transport of radionuclides in the host rock, in the absence of attenuation by other mechanisms in the CDZ.

Atmospheric particulate matter in proximity to mountaintop coal mines: sources and potential environmental and human health impacts.

Mountaintop removal mining (MTM) is a widely used approach to surface coal mining in the US Appalachian region whereby large volumes of coal overburden are excavated using explosives, removed, and transferred to nearby drainages below MTM operations. To investigate the air quality impact of MTM, the geochemical characteristics of atmospheric particulate matter (PM) from five surface mining sites in south central West Virginia, USA, and five in-state study control sites having only underground coal mining or no coal mining whatsoever were determined and compared. Epidemiologic studies show increased rates of cancer, respiratory disease, cardiovascular disease, and overall mortality in Appalachian surface mining areas compared to Appalachian non-mining areas. In the present study, 24-h coarse (>2.5µm) and fine (≤2.5µm) PM samples were collected from two surface mining sites in June 2011 showed pronounced enrichment in elements having a crustal affinity (Ga, Al, Ge, Rb, La, Ce) contributed by local sources, relative to controls. Follow-up sampling in August 2011 lacked this enrichment, suggesting that PM input from local sources is intermittent. Using passive samplers, dry deposition total PM elemental fluxes calculated for three surface mining sites over multi-day intervals between May and August 2012 were 5.8±1.5 times higher for crustal elements than at controls. Scanning microscopy of 2,249 particles showed that primary aluminosilicate PM was prevalent at surface mining sites compared to secondary PM at controls. Additional testing is needed to establish any link between input of lithogenic PM and disease rates in the study area.

Long-term variations of CO 2 trapped in different mechanisms in deep saline formations: A case study of the Songliao Basin, China

The geological storage of CO 2 in deep saline formations is increasing seen as a viable strategy to reduce the release of greenhouse gases to the atmosphere. There are numerous sedimentary basins in China, in which a number of suitable CO 2 geologic reservoirs are potentially available. To identify the multi-phase processes, geochemical changes and mineral alteration, and CO 2 trapping mechanisms after CO 2 injection, reactive geochemical transport simulations using a simple 2D model were performed. Mineralogical composition and water chemistry from a deep saline formation of Songliao Basin were used. Results indicate that different storage forms of CO 2 vary with time. In the CO 2 injection period, a large amount of CO 2 remains as a free supercritical phase (gas trapping), and the amount dissolved in the formation water (solubility trapping) gradually increases. Later, gas trapping decrease, solubility trapping increases significantly due to the migration and diffusion of CO 2 plume and the convective mixing between CO 2-saturated water and unsaturated water, and the amount trapped by carbonate minerals increases gradually with time. The residual CO 2 gas keeps dissolving into groundwater and precipitating carbonate minerals. For the Songliao Basin sandstone, variations in the reaction rate and abundance of chlorite, and plagioclase composition affect significantly the estimates of mineral alteration and CO 2 storage in different trapping mechanisms. The effect of vertical permeability and residual gas saturation on the overall storage is smaller compared to the geochemical factors. However, they can affect the spatial distribution of the injected CO 2 in the formations. The CO 2 mineral trapping capacity could be in the order of 10 kg/m 3 medium for the Songliao Basin sandstone, and may be higher depending on the composition of primary aluminosilicate minerals especially the content of Ca, Mg, and Fe.

Mineral weathering rates in glacial drift soils (SW Michigan, USA): New constraints from seasonal sampling of waters and gases at soil monoliths

Soil solutions and gases were sampled along 200 cm deep soil profiles from four instrumented soil monoliths in southwest Michigan, established on coarse-grained glacial drift deposits. Seasonal sampling enabled evaluation of thermodynamic versus kinetic controls on carbonate- and silicate-mineral weathering rates, allowing better integration with past field hydrogeochemical studies of Michigan soil and surface water systems. Silicate-weathering products dominate water chemistry in the upper soil zones. Carbonate minerals, comprised of subequal amounts of calcite and dolomite, are only present at depths below 150 cm. When present, carbonate dissolution is rapid and soil water Ca 2+ and Mg 2+ concentrations increase dramatically as observed in other natural soil study sites in southern Michigan. Soil water saturation states are near equilibrium with respect to calcite and slightly less saturated with respect to dolomite. The divalent cations of soil waters and soil CO 2 both show a seasonal trend, with concentration maxima occurring in September and minima in April, suggesting that soil water Ca 2+ and Mg 2+ concentrations are under equilibrium control with carbonate solubility limited by temperature-dependent pCO 2 rather than by direct effects of temperatures. Importantly, monolith soil water Mg 2+/Ca 2+ and calcite and dolomite saturation states are lower than those of streams in the same watershed and also lower than those of soil waters in other Michigan watersheds. Because carbonate weight percentages and chemical compositions in these sites are similar, this difference likely reflects the short exposure path (thus short residence time) of soil waters to carbonate-rich horizons in the monoliths. The dissolution reactions of primary aluminosilicate minerals are incongruent with respect to Al and Si due to kaolinite formation. However, major cations (Ca 2+, Mg 2+, K + and Na +) are stoichiometrically released from silicate dissolution. Na ⁎ (soil water Na + after correction for atmospheric input and derived primarily from plagioclase weathering) exhibits much less seasonality than divalent cations, with only slight elevations observed in the summer months. Soil water H 4SiO 4 0 concentrations show seasonal variations similar to the divalent cations, but are determined by the balance between production (silicate-mineral dissolution) and consumption (kaolinite precipitation). Plagioclase and amphibole are below saturation, and these dissolution reactions must be kinetically controlled. Through a conservative tracer study, about 15% to 45% of applied Br passed out of the monolith profiles in 40–160 days and this long mineral–water contact time is especially important for slow reactions such as silicate dissolution. Based on water chemistry and discharge, bulk reaction rates of calcite, dolomite (Ca 0.5Mg 0.5CO 3), K-feldspar and plagioclase are calculated to be at 3400, 3100, 220, and 320 mol ha − 1 yr − 1 , respectively. Based on mass balance of soil composition, long-term plagioclase-weathering rates (over the past 12,500 years) are calculated at about 2400 mol ha − 1 yr − 1 , much higher than the current rates. This agrees with previous conclusions that weathering rates decrease with time, due to loss of reactive mineral surfaces. Furthermore, both long-term and short-term plagioclase dissolution rates in Michigan are relatively high compared to those in other watersheds with similar age, possibly due to fresh surfaces produced by glaciation, in combination with the high discharge and high plagioclase abundances.

CHARACTERIZATION OF ALUMINUM-RICH PHASES IN HEAP-LEACH PADS AT THE LANDUSKY GOLD MINE, MONTANA, USA

Hydrothermal alteration, pre-mining weathering, mining, metal extraction by heap leaching with cyanide, and post-mining alteration of rock at the Landusky gold mine, in Montana, have resulted in repeated transformations of Al-bearing minerals and their eventual dissolution to form Al-rich aqueous solutions. The primary aluminosilicate minerals in the Landusky syenite are K-feldspar and sodic plagioclase. Detailed studies of clay mineralogy and geochemistry have shown that these feldspars were partially altered to illite during hydrothermal alteration of the syenite, probably coincidental with the gold-mineralization event. Kaolinite was formed by weathering of illite and feldspars. Then alkaline conditions (pH >10) during cyanide leaching (1979–1996) caused the hydrothermal illite to become laced with a smectite (the K-dominant analogue of beidellite), which is stable under alkaline conditions. After the mine closed, oxidation of pyrite decreased the pH, and the smectite became unstable, forming kaolinite. Over time, further increases in acidity resulted in the dissolution of kaolinite, thereby generating elevated concentrations of Al in the drainage water (up to 100 mg/L). Precipitation of amorphous aluminum hydroxides and oxyhydroxides from this water resulted in the blockage of drainage pipes, and a reduced efficiency of a treatment plant installed to remove cyanide, selenium and nitrate.

Influence of Mineralogy and Geological Setting on Trace Metal Concentration within Subtropical Weathered Profiles, Bells Creek Catchment, Queensland, Australia

The effects of mineralogy and geological setting on trace metal concentration and distribution within six weathered profiles developed sandstone and mudstone was assessed. Primary minerals occurring in the weathered profiles are quartz, plagioclase, and K-feldspar. Kaolinite is the most dominant secondary mineral followed by mixed layers of smectite-illite, illite, hematite, siderite, and occasional calcite. Metal concentrations within fresh and weathered samples were investigated by two methods of digestions: HF-based digestion and aqua regia. Results revealed that V and Cr are largely present in the primary aluminosilicate matrix and are not easily available to the environment; however, Cu, Zn, and Pb are present in extractable forms and readily leached. Iron occurs in both primary minerals and insoluble secondary minerals such as hematite. The mineralogical study also showed that drill hole material with more clay minerals tends to contain higher metal concentrations, demonstrating that mineral composition is the major control over trace metal content. Spearman's rank correlation matrix also confirmed the role of mineralogy on trace metal concentration (e.g., V and Cr correlated with kaolinite and Pb correlated well with mixed layers of illite-smectite). Effect of geological setting on trace metal concentration was assessed by examining the geomorphological location of drill holes with respect to paleochannels, surface topography, and water table position. Results revealed that depth of burial of the weathered profile does not have an important effect on weathering and trace metal composition of samples. However, samples located on flat terrain and with shallow water table are more prone to leach metals. Factors controlling degree of chemical weathering and subsequent trace metal distribution are summarized in order of importance: mineralogy > geological setting (topography and parent rock type) > water table depth > depth of profile burial.

Overview of trace element partitioning in flames and furnaces of utility coal-fired boilers

Some coal constituents are potentially toxic, trace metals/metal compounds bound with the coal's mineral and organic matter components. These trace species are released during the combustion process and may pose an environmental and human health risk depending on their abundances, physicochemical forms, toxicity, partitioning behavior in the combustion and environmental control systems, and their ultimate disposal/deposition in the local and regional ecosystems associated with the coal combustion system. This paper provides an overview of recent research efforts to characterize the combustion process in large, utility-scale boilers as it affects the release, transformation and partitioning of coal's trace inorganic components in both the combustion zone and the heat transfer sections of the boiler. Trace element partitioning is initiated at the burner front and continues in the high-temperature radiant section of the furnace as the coal particles are pyrolized and burned. The various trace elements are interdispersed among the fly ash, bottom ash, and combustion flue gas; this depends upon the degree of volatilization of their particular geochemical modes of occurrence within the coal and the extent to which they may be physically or chemically bound to the carbon matrix or the primary aluminosilicate minerals. Those elements (major and trace) that are not volatized during combustion will comprise the matrix of both fly ash and the bottom ash in the form of a homogeneous “melt” as well as crystalline phases; the split between bottom ash and fly ash is determined primarily by the type of furnace design and to a lesser extent by operating conditions and coal rank. Once combustion gases are carried downstream of the combustion zone of a coal-fired boiler, the key factors which influence the final trace constituent transformation/partitioning behavior are the conversion of vaporized components into various solid forms and their collection along with the fly ash. The former is determined, basically, by three complex and interrelated processes — adsorption, condensation, and chemical transformation. While these simultaneous processes compete along the entire boiler gas pathway, conversion will be complete for all but the most volatile species before the combustion gases reach the particulate and desulfurization control systems. Collection of the particulate-based trace species in flue gas cleanup devices, such as ESPs and fabric filters, will depend to a large degree on the size fractionation of the particulate and, therefore, on the original transformation of the major mineral components of the coal into fly ash. Collection of vapor-phase components will ultimately depend upon the flue gas temperature and contact with various scrubber types and sorbents. Recent combustion tests with different coals indicates that both the composition and distribution of mineral matter in the coal matrix, not coal rank, are the most important criteria for predicting volatilization behavior and fume formation. It is theorized that the extent of volatilization, and subsequent condensation, of particular elemental components of the fume depend on their mode of occurrence and their extent of dispersion, as associated with the organic matter or a nonorganic extraneous component. Modes of occurrence help establish high-temperature thermodynamic properties, including volatility. Trace element distribution and the extent to which they are bound (or encapsulated) in the coal matrix influence the probability of volatilization.

DURIPANS OF THE OWYHEE PLATEAU REGION OF IDAHO

Mineralogical and micromorphic techniques were used to investigate secondary minerals that occur in duripans (Durargids and Durixeralfs) on the Owyhee Plateau region of southwestern Idaho. Opaline silica and sepiolite were the principal secondary minerals found. Opaline silica exhibited three morphogenetic forms. Clearopal, consisting of opal-A with included calcite and unknown crystallites, occurred throughout the duripan, principally as pseudomorphic replacements after calcite pendants. Dirty-opal, a gray, semitran-sparent and nearly x-ray amorphous material, was found in highly altered cores of complex pedogenic concretions. Some opaline silica occurred in a web-like arrangement intimately mixed with calcite and was located in the matrix among loess agglomerates, in the laminar cap and in loess pedotubules. The opal in this microgranular calcite-silica was opal-A with included quartz and appeared to form, in part, by silica supplied in situ from alteration of primary aluminosilicate minerals. Transmission electron microscopic examination of colloidal silica revealed the presence of two types of coatings. Gray-gel was visually homogeneous and semielectron opaque whereas mottled-gel was -less electron opaque and contained many, minute, more electron opaque spheroids. The reorganization of these gels seems to control the formation of opaline silica spheres. In addition, most opaline silica spheres exhibited bubble-like substructures heretofore unrecognized. The presence of poorly crystalline sepiolite was indicated by x-ray diffraction. Imaged with the transmission electron microscope, the sepiolite exhibited a hierarchical structure. At the highest scale of magnification, laths with a crosssectional area of 13 by 23 nm were evident. The laths were organized in bundles. The most visually distinctive bundles were 950 by 1200 nm in length and lacked gel-like coatings. Other bundles were less distinct, more curvilinear, and exhibited less parallel orientation or mesh-like arrangements. These laths and fibers were from 250 to 375 nm in length, coated wtih structurally amorphous material resembling the grey-gel, and surficially sprinkled with opaline silica spheres and spherical units of mottled-gel. In the duripans studied, sepiolite was largely limited to pedogenic concretions in which it occurred as acicular crystals that radiated outward from concretionary laminae of opaline silica. This finding and the association of opal spheres with sepiolite laths suggest that some sepiolite forms via the addition of Mg to opal.

Geochemical evolution of inactive pyritic tailings in the Elliot Lake uranium district

Geochemical data obtained between 1979 and 1983 from a network of piezometer nests and cores from three inactive uranium tailings impoundments in the Elliot Lake district indicate that oxidation of pyrite taking place in the shallow part of the zone above the water table is causing the chemistry of the pore water above and below the water table to change. A two-layer hydrochemical zonation has developed in which infiltration water from rain and snow has resulted in an upper zone of low-pH water with high concentrations of SO4, Fe, and heavy metals. This zone is gradually expanding downward at rates generally between 0.2 and 2 m/year, causing displacement of the original mill process water, which has neutral pH and low concentrations of heavy metals. High concentrations of Fe(III) at shallow depth in the zone above the water table indicate that ferric iron is an important oxidizer of pyrite in the presence of free oxygen.The pe of the groundwaters is controlled by the ferric–ferrous redox couple, and trends in the data indicate iron solubility control by siderite at high pH, by ferric hydroxide at moderate to slightly acid pH values, and possibly by jarosite at low pH. Aluminum solubility controls are complex, and precipitation of amorphous aluminum hydroxide, allophane, and basic aluminum sulfates may occur over different pH ranges. Transport of low-pH conditions is retarded relative to the rate of groundwater flow in the tailings, because of the buffering effect of small amounts of carbonate minerals added during tailings neutralization; primary aluminosilicates such as sericite; and secondary aluminum hydroxides.Field data show that the flux of dissolved iron from the vadose zone to the groundwater zone in the Nordic Main tailings has been decreasing in recent years. However, mass-balance calculations indicate a potential for the generation of high-Fe groundwater for several decades to several hundred years. A long-term potential for acid and iron production is also shown by data from two tailings impoundments that have been inactive 8–10 years longer than the Nordic Main area. Presently only a small portion of the Nordic Main and West Arm tailings areas has become acidic through the entire tailings thickness; however, under existing infiltration conditions more extensive acidification will occur in future decades.

Reversible control of aqueous aluminum and silica during the irreversible evolution of natural waters

Primary aluminosilicates are transformed at low temperature into a sequence of metastable and thermodynamically stable secondary minerals by an irreversible process. The aqueous concentrations in the associated solution may continuously change during the process or they may be maintained constant through hydrodynamic or chemical steady-state mechanisms or through chemical equilibrium with a reversible metastable solid. Disequilibrium indices calculated for 152 natural waters and experimental solutions show that the solutions are unsaturated with amorphous aluminum hydroxide, microcrystalline gibbsite, amorphous silica and amorphous aluminosilicate, and they are supersaturated with gibbsite and kaolinite. The disequilibrium index for halloysite varies widely from unsaturation to supersaturation. Only the index for the reversible metastable cryptocrystalline aluminosilicate whose composition is pH dependent is very close to zero indicating saturation. The index varies in a narrow range. This, supported by electron micrographs and the results of X-ray fluorescence spectroscopy presented by other authors, suggests that this metastable solid, and not the secondary aluminosilicate minerals, controls the concentrations of alumina and silica in natural waters.