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This paper summarizes historical knowledge of pegmatite occurrences in the vicinity of the Skalsko near Jílové u Prahy (central Bohemia, Czech Republic) and presents the results of a new field and laboratory research. The granite pegmatites near Skalsko were subject of intensive mining of feldspar for ceramic industry especially during the 19th century. The pegmatites are spatially and genetically bound to western part of Hercynian intrusion of biotitic granodiorite of the Požáry type (I - type granite), which forms a part of Central Bohemian Plutonic Complex. Pegmatites, similary as aplites and aplitic granites, usually form subhorizontal embedded bodies with zonal structure with a predominance of granitic and blocky units. A part of pegmatite veins is characterized by anomalous accumulations of molybdenite (average content of about 0.19 wt. % Mo) and thus represents a unique type of Mo ores in the Bohemian Massif, although having a limited extent. Pegmatites have relatively simple mineral composition: K-feldspar, albite, quartz, molybdenite, biotite, occasionally muscovite, apatite and rarely tourmaline. The presence of coarse- and fine-grained aggregates of molybdenite and thinly columnar aggregates of apatite is characteristic. The dominant older K-feldspar (with content up to 3.97 wt. % BaO) is intensive replaced by younger much Ba-richer (4.43 - 9.81 wt. % BaO) K-feldspar. Ba-rich K-feldspar also contains very tiny barite grains. The occurrence of abundant monazite-(Ce) and xenotime-(Y) grains (up to 100 µm in size) is characteristic for aggregates of fluorapatite (with various REE contents). The rare zonal garnet corresponds to Mn-rich almadine with higher content of spessartite component (42 - 43 mol. %) in marginal parts of its aggregates. Biotite (annite) contains higher concentration of Ba (about 0.4 wt. % BaO) and low F (about 0.5 wt. %). The flat to dome embedded pegmatite bodies are formed by predominant older granitic and younger block units, sometimes in asymmetrically repeated positions. The structure of pegmatite bodies indicates their origin in flat fissures with an extense character; sometimes with fuzzy transition between magmatic and hydrothermal stages. Older authors mostly assumed the molybdenite origin in younger hydrothermal stage (and only spatial relation of molybdenite and pegmatites); the results of this new study confirmed that molybdenite is an integral part of pegmatites. Pegmatites from the vicinity of Skalsko has some features of NYF pegmatites (low P in feldspars, elevated Y in garnet) with specified molybdenite enrichment. [ABSTRACT FROM AUTHOR]

Abstract: The Cameros Basin (Iberian Chain, NE Spain) formed during the latest Jurassic–Early Cretaceous rifting stage in an extensional regime characterized by high subsidence rates. Its sedimentary infill (thicker than 6000m) has been subdivided into eight depositional sequences (DS) mainly composed of continental sediments. DS 1 and DS 2 represent the first rifting stage (Tera Group, Tithonian), mainly formed by fluvial and lacustrine sediments. Sandstone petrofacies evolved from quartz-sedimentolithic in DS 1 to quartz-feldspathic in DS 2 due to the rifting process. In DS 2, three different types of detrital feldspars (K-feldspars, albites and polysynthetic plagioclases) with similar sodium-rich compositions (mean: Ab94.0 An4.5 Or1.5) can be recognized. Chemically pure nonluminescent albites (Ab>99%) are common. In DS 2, diagenetic albitization of both plagioclases and K-feldspars is inferred from conventional microscopy observations, cathodoluminescence and electron microprobe analyses. DS 1 contains few plagioclase grains, which show no evidence of transformation into albite. Although the albitization is characterized as diagenetic it seems to be provenance-controlled since it affects the units showing higher original plagioclase/K-feldspar ratio (DS 2), due to the greater influence of plutonic and metamorphic source areas in DS 2. Possible Na sources are: (1) the percolation of moderate to high salinity residual brines from related alkaline lakes developed at top of DS 2 in the eastern sector of the basin, (2) clay mineral reactions (sodium smectite to illite and chlorite) indicated by mudstone composition in the interlayered mudstones, and (3) the replacement of detrital sodium plagioclases by carbonate. These three sources can be complementary. [Copyright &y& Elsevier]

Abstract: An atypical potassium feldspar deposit of real economic potential has been found at Arcu de su Bentu, Southern Sardinia, Italy. The massive mineralization occurs in the Middle Ordovician Porphyroids'' metavolcanic complex, which consists of dominant metarhyolite and minor metarhyodacite lavas and/or ignimbritic flows, erupted in a sub-aerial environment. During Variscan orogenesis, the mineralized area was affected by low-grade (anchizone to greenschist facies) metamorphism. The deposit generally shows uniform macroscopic textural features over the entire outcrop, the significant presence of K-feldspar (sanidine) and quartz megacrystals, the latter being generally smaller than the former. Mafic minerals do not occur in significant proportions although minor amounts of biotite and muscovite occur locally. Besides the uncommon lithological type, the typical feature of this deposit is the unusual coarseness (10 to 20cm in diameter) of the potassium feldspar crystals. The favourable geomorphological conditions of the area, high K2O contents (6 to 8wt.%), high proportion of K-feldspar in the mineralized rock (35 to 51vol.%), and large reserves (estimated at 4,368,000t in just one restricted part of the deposit), are all favourable conditions for future economic exploitation. In spite of this, mineralogical and chemical impurities may adversely affect the possible use of K-feldspar from Arcu de su Bentu in some conventional applications (e.g., manufacture of high-quality products such as ceramics). To assess the real future economic development of the deposit, market-specific beneficiation is required, although it is important to note that the bulk raw materials, even if they have a lower market value, could be still be targeted to specific industrial sectors (e.g., red grès). [Copyright &y& Elsevier]

Abstract: IRSL single-aliquot dating of three feldspar fractions from a Howieson''s Poort (SA) industry site has been investigated. In the case of the plagioclase fraction (ρ >2.62gcm−3) equivalent dose is similar to that of the other fractions (i.e. ρ <2.58gcm−3, high-K-feldspar; and 2.58< ρ <2.62gcm−3; low-K-feldspar). However, the g values measured for this fraction is such that the fading-corrected age is overestimated. The K content of each fraction was estimated by SEM. The DRC-corrected ages for the two lighter feldspar fractions are consistent with the archaeological interpretation. This study shows that reliable single-aliquot luminescence ages can be obtained using K-feldspar and Na-plagioclase. [Copyright &y& Elsevier]

Abstract: Glacial till and inter-till deposits exposed in the Lithuanian coastal region are evidence for multiple glacial advances during the Pleistocene. Stratigraphically, tills are the most important, prominent and well preserved deposits. However, despite the importance of these deposits, there is limited chronological control and it is widely debated whether they belong to one or another Pleistocene glaciation. The aim of the present study was to find features of the glacigenic tills, which allow us to temporally constrain these deposits, which are usually deemed to be undateable by luminescence methods. To achieve the goal, 15 samples from five different till beds and 12 samples from underlying sandy inter-till deposits from the same area were taken for analysis by feldspar-based IR-OSL technique. This paper presents the results, which suggest that the studied deposits, including glacial tills, are mostly of late Pleistocene age (MIS 5 and 4). We discuss analytical data obtained for these materials and implications for stratigraphic subdivision of the till-bearing deposits in the Lithuanian Maritime Region. [Copyright &y& Elsevier]

Abstract: We present the results of K-feldspar IRSL dating of the four lower terraces (T3–T6) of the Portuguese Tejo River, in the Arripiado-Chamusca area. Terrace correlation was based upon: a) analysis of aerial photographs, geomorphological mapping and field topographic survey; b) sedimentology of the deposits; and c) luminescence dating. Sediment sampled for luminescence dating gave unusually high dose rates, of between 3.4 and 6.2Gy/ka and, as a result, quartz OSL was often found to be in saturation. We therefore used the IRSL signal from K-feldspar as the principal luminescence technique. The K-feldspar age results support sometimes complex geomorphic correlations, as fluvial terraces have been vertically displaced by faults (known from previous studies). Integration of these new ages with those obtained previously in the more upstream reaches of the Tejo River in Portugal indicates that the corrected K-feldspar IRSL ages are stratigraphically and geomorphologically consistent over a distance of 120km along the Tejo valley. However, we are sceptical of the accuracy of the K-feldspar ages of samples from the T3 and T4 terraces (with uncorrected D e values >500Gy). In these cases the Dose Rate Correction (DRC) model puts the natural signals close to luminescence saturation, giving a minimum corrected D e of about 1000Gy, and thus minimum terrace ages; this may even be true for those doses >200Gy. Luminescence dating results suggest that: T3 is older than 300ka, probably ca. 420–360ka (∼Marine Isotope Stage [MIS]11); T4 is ca. 340–150ka (∼MIS9-6); T5 is 136–75ka (∼MIS5); T6 is 60–30ka (MIS3); an aeolian sand unit that blankets T6 and some of the older terraces is 30–≥12ka. Collectively, the luminescence ages seem to indicate that regional river downcutting events may be coincident with periods of low sea level (associated, respectively, with the MIS10, MIS6, MIS4 and MIS2). [Copyright &y& Elsevier]

Abstract: We present Pb isotope and microstructural studies of deformed K-feldspar megacrystic granodiorites in the westernmost part of the Karelian Craton near the Archean–Proterozoic boundary zone in east-central Finland. Our studies place constraints on the timing and the temperature and strain rate conditions of the deformation. The Pb isotope evidence indicates that U was decoupled from Th approximately at the time of crystallization, which generated high whole-rock Th/U ratios. With time, high 208Pb/204Pb ratios were developed at high Th/U domains of the rock. Observed correlation between 208Pb/204Pb ratios and deformation microstructures of K-feldspar megacrysts suggests a later deformation-induced Pb isotope redistribution between K-feldspars and whole rock. The coupled 238U–206Pb and 235U–207Pb systematics show that this Pb isotope exchange occurred at ca. 1.9 Ga concurrently with the peak of the Svecofennian orogeny. Our Th–Pb and U–Pb model age calculations for K-feldspar–whole rock pairs indicate different degrees of incomplete equilibration that correlates with the degree of deformation. The microstructures of K-feldspars indicate low- to medium-T conditions (400–500 °C) and variable strain rates for deformation. We conclude that Pb isotope compositions and microstructures of K-feldspars provide valuable constraints on assessing Proterozoic imprints in Archean rocks. [Copyright &y& Elsevier]

Abstract: We recently proposed a model that reconstructs the natural dose response curve for K-rich feldspars, using laboratory fading measurements and dose response as input parameters. The model is based on the relationship between recombination centre density and trap lifetime. In this study we test the working of the model by comparing modelled feldspar ages with known quartz OSL ages of the same samples and with anomalous fading-corrected feldspar ages. The modelled feldspar ages are in good agreement with quartz OSL ages and corrected feldspar ages, opening possibilities for future use of the model on samples without independent age constraints. Furthermore, we investigate the effects of trap competition on the build-up of IRSL signal using two new variations of the model. Results show that incorporating trap competition into the model reduces the agreement between feldspar IRSL ages and quartz OSL ages. [Copyright &y& Elsevier]

Abstract: Thomsen, K.J., Murray, A.S., Jain, M., Bøtter-Jensen, L. [2008. Laboratory fading rates of various luminescence signals from feldspar-rich sediment extracts. Radiat. Meas. 43, 1474–1486] have identified a number of feldspar signals which show significantly less anomalous fading than the conventional IRSL signal stimulated at 50 °C and detected in the blue–violet region of the spectrum. One of these was the post-IR IR signal in which first an IR bleach is carried out at a low temperature (e.g. 100 s at 50 °C) and a remaining IRSL signal is measured at an elevated temperature (100 s at 225 °C; detection in the blue–violet region). It is the latter signal that is of interest in this paper. We test such a post-IR IR dating protocol on K-feldspar extracts from a variety of locations and depositional environments and compare the results with those from the conventional IR at 50 °C protocol. Based on laboratory tests (recycling ratio, recuperation, dose recovery) we show that our SAR protocol is suitable for these samples. The observed post-IR IR fading rates (mean g 2days = 1.62 ± 0.06%/decade, n = 24; assuming logarithmic fading) are significantly lower than those measured at 50 °C (mean g 2days = 3.23 ± 0.13%/decade, n = 24). The signal is bleachable in nature although residual doses of the order of a few Gy are to be expected. After fading correction the ages are indistinguishable from those measured by IR at 50 °C over an age range from a few ka to >260 ka. However, the correction factor for anomalous fading is only ∼39% of that of the conventional IR at 50 °C signal. This smaller correction factor makes the new post-IR IR ages much less dependent on the inherent assumptions included in the fading correction model. [Copyright &y& Elsevier]

[Display omitted] • A hydrothermal alkaline combined with ammonium hydrogen sulfate solution leaching process was developed to utilize comprehensively K-feldspar. • The transformation of K-feldspar in hydrothermal process is as follow: Microcline → kaliophilite (as metastable materials) → kalsilite. • The K-feldspar is completely decomposed at 280 ℃ for 120 min. • Potassium and aluminum in kalsilite are easily leached by ammonium hydrogen sulfate solution. A novel hydrothermal alkaline process combined with ammonium hydrogen sulfate solution leaching process for improving the comprehensive utilization value of the mineral K-feldspar was developed. In this technology, K-feldspar was first decomposed by the alkaline hydrothermal method, forming kalsilite in the resultant products, where potassium and aluminum were easily leached by ammonium hydrogen sulfate solution. The effects of hydrothermal temperature, concentration, and excess rate of potassium hydroxide on the leaching rate of alumina were investigated. The products obtained under various conditions were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray fluorescence (XRF) and Fourier transform infrared spectroscopy (FTIR). The results show that the hydrothermal temperature has a predominant influence on the hydrothermal decomposition of K-feldspar. With the hydrothermal time of 30 min, the leaching rate of alumina at 280 °C is 62.5 % higher than that at 220 °C. The K-feldspar is completely decomposed at 280 °C for 120 min. The concentration of potassium hydroxide has little effect on the decomposition of K-feldspar. The transformation of K-feldspar in the proposed hydrothermal process is as follows: Microcline → kaliophilite (as metastable materials) → kalsilite. [ABSTRACT FROM AUTHOR]

Feldspars, a type of important and prevalent primary mineral in soils, play a significant role in the migration of radioactive strontium in the environment. Nevertheless, there are rare studies on strontium adsorption on feldspars. This work presents a study on the interaction between strontium and K-feldspar at the solid-water interface. The effects of environmental factors were evaluated using batch experiments with 90Sr tracer. Surface complexation contributed to the chemical adsorption of strontium in the slightly acidic condition. • Strontium adsorption on K-feldspar under environmental factors was studied. • Fitting results of kinetics and isotherms confirmed chemical adsorption. • Adsorption promoted by sulfate and humic acid was mainly in the acidic conditions. • Surface complexation started to contribute adsorption in faintly acidic conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • The ∼1070 m and 1060–1050 m a.s.l. shorelines formed <∼136 ka and 49–22 ka, respectively. • The changes of lake level are sensitive to climatic change in the Jilantai area. • The development of lakeshore of MIS 3a–LGM was likely a geomorphic response. High lake levels were developed in wide areas of western China during the late Quaternary as revealed by an increasing number of studies on dating shorelines; however, whether the high lake level of these lakes occurred simultaneously and what drove them are unresolved problems. In this study, in the Jilantai sub-depression within the Jilantai–Hetao Basin, dating results of the single-aliquot quartz and potassium-enriched feldspar (K-feldspar) single grains from the sediments at the western bank of the present Jilantai Salt Lake indicate that the ∼1070 m and 1060–1050 m shorelines formed after ∼136 ka and 49–22 ka, respectively, supporting the hypothesis that higher lake levels developed at intervals of marine isotope stage (MIS) 5e and MIS 3a–Last Glacial Maximum (LGM) in the Jilantai sub-depression. Considering the previous assumption that the lake at an altitude of 1080–1050 m was fed mainly by water from the Yellow River, the changes in the lakeshore landform features are sensitive to climate change in the Jilantai area, among which the development of lakeshore during MIS 3a–LGM was likely a geomorphic response to the development of dry climatic conditions rather than a representative of the humid climate in arid regions. [ABSTRACT FROM AUTHOR]

Abstract: At the International Energy Agency Greenhouse Gas (IEA GHG) Weyburn-Midale Project in Saskatchewan, Canada, CO2 storage research takes place alongside CO2 enhanced oil recovery (EOR) in the Weyburn oil field. Over four years of production well monitoring at Weyburn, measured changes in chemical and isotopic data for produced aqueous fluids and gases (i.e. an increase in Ca2+, Mg2+, K+, SO42-, HCO3-, and CO2 concentration and a decrease in δ13CHCO3- and δ13CCO2 values), confirm the integrity of CO2 storage, trace CO2 migration and dissolution in the reservoir fluids, and record a range of water-rock- CO2 reactions including carbonate mineral dissolution and alteration of K-feldspar. K-feldspar alteration buffers the pH decrease resulting from CO2 injection, enhances aqueous CO2 storage as HCO3- (ionic trapping) and can lead to mineral storage of CO2 as CaCO3. Geochemical reaction path simulations of the water-mineral- CO2 system reproduce the changes in measured data observed over the first few years, confirming proposed reaction pathways and rates. Extension of these history matched reaction path simulations over 100s of years shows that alteration of K-feldspar and other silicate minerals present in the Weyburn reservoir will lead to further storage of injected CO2 in the aqueous phase and as carbonate minerals. [Copyright &y& Elsevier]

Sediment delivery and supply are explicitly controlled by variations in broad-scale processes such as climate, tectonics and eustasy. These in turn influence fluvial processes and hinterland evolution. A bespoke multi-proxy approach (integrating apatite and zircon U-Pb geochronology, trace elements in apatite, and Pb-in-K-feldspar provenance tools) coupled with outcrop investigation is used to constrain the temporal trends in sediment delivery to channel sandstones of the fluvio-estuarine mid-Viséan Mullaghmore Sandstone Formation, Ireland. Provenance data indicate unique detrital signatures for all sampled horizons, indicating the fluctuating nature of sediment supply to this medium-sized basin. Tectonism and/or abrupt relative sea-level fall likely caused fluvial rejuvenation, resulting in local basement sourcing of the initial fill. Older and more distal sources, such as the Nagssugtoqidian Belt of East Greenland, become more prominent in stratigraphically younger channel sandstones suggesting catchment expansion. Paleoproterozoic to Mesoproterozoic sources are most dominant, yet the detrital grain cargo varies in each channel sandstone. Proximal sources such as the Donegal Batholith and Dalradian Supergroup are variable and appear to switch on and off. These signal shifts are likely the result of channel migration and paleoclimatic fluctuation. A monsoonal climate and large-scale wildfire events (evidenced by fusain) likely contributed to modify plant cover, intensify erosion, and increase run-off and sediment delivery rates from specific areas of the hinterland. [ABSTRACT FROM AUTHOR]

Pb isotope compositions of detrital K-feldspars and U-Pb ages of detrital zircons are used as indicators for determining the sources of Peoria Loess deposited during the last glacial period (late Wisconsin, ca. 25-14 ka) in Nebraska and western Iowa. Our new data indicate that only loess adjacent to the Platte River has Pb isotopic characteristics suggesting derivation from this river. Most Peoria Loess in central Nebraska (up to 20 m thick) is non-glaciogenic, on the basis of Pb isotope ratios in K-feldspars and the presence of 34-Ma detrital zircons. These isotopic characteristics suggest derivation primarily from the Oligocene White River Group in southern South Dakota, western Nebraska, southeastern Wyoming, and northeastern Colorado. The occurrence of 10-25 Ma detrital zircons suggests additional minor contributions of silt from the Oligocene-Miocene Arikaree Group and Miocene Ogallala Group. Isotopic data from detrital K-feldspar and zircon grains from Peoria Loess deposits in eastern Nebraska and western Iowa suggest that the immediate source of this loess was alluvium of the Missouri River. We conclude that this silt probably is of glaciogenic origin, primarily derived from outwash from the western margin of the Laurentide Ice Sheet. Identification of the White River Group as the main provenance of Peoria Loess of central Nebraska and the Missouri River valley as the immediate source of western Iowa Peoria Loess indicates that paleowind directions during the late Wisconsin were primarily from the northwest and west, in agreement with earlier studies of particle size and loess thickness variation. In addition, the results are in agreement with recent simulations of non-glaciogenic dust sources from linked climate-vegetation modeling, suggesting dry, windy, and minimally vegetated areas in parts of the Great Plains during the last glacial period. [ABSTRACT FROM AUTHOR]

Abstract: The mineral composition of altered volcanic ash beds, bentonites, deposited in marine environments is typically characterized by smectite or illite–smectite type clay minerals. Silurian bentonites from an unmetamorphosed normal marine sedimentary sequence in the eastern Baltic Palaeobasin, however, show a complex and varied mineral composition with illite–smectite, K-feldspar and kaolinite as the dominant authigenic phases. The whole-rock XRD study of 52 bentonite beds from two drill-cores — Ruhnu and Ohesaare, southwestern Estonia, reveals a range of compositions varying between different beds as well as laterally within a single bed. The observed variations are found to reflect the bentonite development and diversification during initial stages of volcanic ash transformation and diagenesis that was probably overprinted by a later K-metasomatic event. [Copyright &y& Elsevier]

Abstract: This study investigated the sorption characteristics and recovery of selected heavy metal Cd(II) from K-feldspar and sepiolite, representative soil components, using rhamnolipid biosurfactant. Although the proposed technique was classified as a soil bioremediation process, it can also be applied to treatment of waste waters containing Cd(II) ions with minor modifications. The effect of initial Cd(II) concentration on sorption capacity was characterized by determining the sorption isotherms. Of the four models examined, the Freundlich model showed the best fit for the sorption of Cd(II) on K-feldspar, whereas the Langmuir-model was used succesfully to characterize the sorption of Cd(II) on sepiolite. Although a high Cd(II) uptake of 7.49mmol/kg by K-feldspar was obtained, sepiolite was a superior Cd(II) accumulater, with a maximum Cd(II) uptake of 24.66mmol Cd(II)/kg. The presence of Cd(II) in the sepiolite or K-feldspar prior to addition of the rhamnolipid generally resulted in less rhamnolipid sorption to sepiolite or K-feldspar. The maximum Cd(II) desorption efficiency by rhamnolipid from K-feldspar was substantially higher than that of sepiolite and determined to be 96% of the sorbed Cd(II), whereas only 10.1% of the sorbed Cd(II) from sepiolite was recovered by rhamnolipid solution. [Copyright &y& Elsevier]

Study of four K-feldspar megacrystic granitic plutons and related dikes in the Sierra Nevada composite batholith indicates that the megacrysts are phenocrysts that grew in contact with granitic melt. Growth to megacrystic sizes was due to repeated replenishment of the magma bodies by fresh granitic melt that maintained temperatures above the solidus for extended time periods and that provided components necessary for K-feldspar growth. These intrusions cooled 89-83 Ma, are the youngest in the range, and represent the culminating magmatic phase of the Sierra Nevada batholith. They are the granodiorite of Topaz Lake, the Cathedral Peak Granodiorite, the Mono Creek Granite, the Whitney Granodiorite, the Johnson Granite Porphyry, and the Golden Bear Dike. Megacrysts in these igneous bodies attain 4-10 cm in length. All have sawtooth oscillatory zoning marked by varying concentration of BaO ranging generally from 3.5 to 0.5 wt%. Some of the more pronounced zones begin with resorption and channeling of the underlying zone. Layers of mineral inclusions, principally plagioclase, but also biotite, quartz, hornblende, titanite, and accessory minerals, are parallel to the BaO-delineated zones, are sorted by size along the boundaries, and have their long axes preferentially aligned parallel to the boundaries. These features indicate that the K-feldspar megacrysts grew while surrounded by melt, allowing the inclusion minerals to periodically attach themselves to the faces of the growing crystals. The temperature of growth of titanite included within the K-feldspar megacrysts is estimated by use of a Zr-in-titanite geothermometer. Megacryst-hosted titanite grains all yield temperatures typical of felsic magmas, mainly 735-760 °C. Titanite grains in the granodiorite hosts marginal to the megacrysts range to lower growth temperatures, in some instances into the subsolidus. The limited range and igneous values of growth temperatures for megacryst-hosted titanite grains support the interpretation that the megacrysts formed as igneous sanidine phenocrysts, that intrusion temperatures varied by only small amounts while the megacrysts grew, and that megacryst growth ceased before the intrusions cooled below the solidus. Individual Ba-enriched zones were apparently formed by repeated surges of new, hotter granitic melt that replenished these large magma chambers. Each recharge of hot magma offset cooling, maintained the partially molten or mushy character of the chamber, stirred up crystals, and induced convective currents that lofted, settling megacrysts back up into the chamber. Because of repeated reheating of the magma chamber and prolonged maintenance of the melt, this process apparently continued long enough to provide the ideal environment for the growth of these extraordinarily large K-feldspar phenocrysts. [ABSTRACT FROM AUTHOR]

Abstract: Some published studies present evidence that quartz OSL dating of low dose rate material may underestimate the true age of a deposit by at or for values of . It is well known that feldspar IRSL grows to much higher doses than quartz and thus has the potential of performing better in this age range. In this paper we report on our continuing testing of the accuracy of K-feldspar IRSL dating with anomalous fading correction on known-age Eemian material from northern Russia. Using a SAR IRSL protocol the luminescence characteristics of our samples are first documented and values and fading rates (g values) measured. A single site-averaged fading rate of is obtained and this value used to correct the optical ages. We compare the fading corrected IRSL ages with the known age of the deposits and with the results from a similar study on known-age Eemian material in Denmark. Finally, we discuss which dosimeter (K-feldspar or quartz) is preferred for this type of material. [Copyright &y& Elsevier]

Abstract: A strain of thermophilic fungus Aspergillus fumigatus was cultured with K-bearing minerals to determine if microbe–mineral interactions enhance the release of mineralic potassium. Experiments were carried out in two settings, one with the mineral grains and the fungal cells in direct contact, and the other employing a membrane (pore size 0.22μm) to separate the two. Measurements over a period of 30 days showed that, irrespective of the experimental setup, the concentration of free K in the culture was drastically higher than those in any of the control experiments where no living organism was present. Moreover, the occurrence of mineral–cell physical contact enhanced potassium release by an additional factor of 3 to 4 in comparison to the separation experiments. For contact experiments, Electron Probe Microanalysis revealed the formation of mycelium–mineral aggregates, and Atomic Force Microscopy imaging further indicated the possible ingestion of mineral particles by the fungus cells. Contrasting to what was observed and expected in control experiments, the potassium solubilization rate showed a positive dependence upon pH when fungi and minerals were mixed directly, and exhibited no correlations with solution acidity if cell–rock contact was restrained. These results appear to suggest that A. fumigatus promoted potassium release by means of at least three likely routes, one through the complexation of soluble organic ligands, another appealing to the immobile biopolymers such as the insoluble components of secretion, and the third related to the mechanical forces in association with the direct physical contact between cells and mineral particles. [Copyright &y& Elsevier]

This study investigates lacustrine and fluvial sediments on the Sala Us River in the Mu Us Desert in central north China. Significant changes in environmental dose rate in part of the section could be shown to have occurred from measurements of the present day radioactivity and by the age reversal for some samples that had been dated by optically stimulated luminescence (OSL) measurements on quartz. These changes in dose rate can be attributed to recent uptake of radioactive elements found in the sediments; this resulted in significant underestimation of the OSL ages. In this study, the new isochron method using K-feldspar grains has been applied to overcome the effects of changes in dose rate. Calculations are used to show that changes in the environmental dose rate factors, i.e. K, U, Th, water content and cosmic ray flux, and disequilibrium in the U and Th decay chains, e.g. radon escape, have a negligible effect on the isochron age. After applying the new isochron method, the effects of changes in dose rate caused by recent uptake of radioactive elements and changes in past water content were effectively overcome and true ages are obtained; this was verified by repeating the luminescence isochron measurements on samples of overlying and underlying sediments. [ABSTRACT FROM AUTHOR]

Pb isotopes in detrital K-feldspar grains provide a powerful provenance tracer for feldspathic sandstones. Common Pb isotopic compositions show broad (hundred-kilometer scale) regional variation, and this signature can survive weathering, transport, and diagenesis. The feldspar Pb signature can be measured rapidly using laser ablation-multicollector-inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS), and careful targeting can avoid inclusions and altered regions within grains. Here, we combine a new Pb domain map for the circum-North Atlantic with detrital K-feldspar Pb isotopic data from Triassic and Jurassic sandstones from basins on the Irish Atlantic margin. The Pb isotopic compositions reveal otherwise cryptic feldspar populations that constrain the evolving drainage pattern. Triassic sandstones originated from distant Archean and Paleoproterozoic rocks, probably in Greenland, Labrador, and the Rockall Bank to the NW, implying long (>500 km) transport across a nascent rift system. Later, Jurassic sandstones had a composite Paleo- and Mesoproterozoic source in more proximal sources to the north (<150 km away). No recognizable feldspar was recycled from Triassic into Jurassic sandstones, and the change in provenance is consistent with distributed, low-relief Triassic extension in a wide rift, followed by narrower Jurassic rifting with more localized fault-controlled sediment sources and sinks. [ABSTRACT FROM AUTHOR]

Abstract: Conductive potassium feldspar/polyaniline (K-feldspar/PAn) composites were prepared by the chemical polymerization of aniline in the presence of K-feldspar particles using potassium dichromate in an acidic aqueous medium. The effects of K-feldspar particle size, aniline concentration and temperature upon the PAn amount in the composite and the electrical surface resistance of the composites were examined. Electrical conductivity was higher in the composites prepared by the smaller K-feldspar particles in which the PAn yield is low. The microhardness values of K-feldspar/PAn composites increased to a certain PAn content and then decreased. The microhardness of the composites containing PAn in the range of 1–6%, which were prepared by K-feldspar having particle size smaller than 0.125–0.250nm, was higher that of pure K-feldspar and PAn (0.843kPa). Scanning electron microscopy (SEM) showed that PAn covered the surface of K-feldspar particles with an unsmooth PAn layer. The characterization of composites was also made by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). [Copyright &y& Elsevier]

Abstract: Ultraviolet light emission at a wavelength of of a natural K-rich feldspar crystal from Cáceres (Spain) has been studied using high sensitivity thermoluminescence (3D-TL) spectrometry. The spectral emission band has a Gaussian profile and could be linked with radiative electron–hole recombination in radiation-induced defect complexes. The glow curve shows a characteristic shape along the temperature axis, with an exponential rise and a power-law decay (scaling exponent at 2.5°C/s heating rate). This characteristic profile is interpreted as a diffusion-activated luminescence phenomenon in which the trapping-detrapping-transition dynamics is controlled by local cooperative phenomena inside these complexes. The processes involved in the radiative recombinations could represent the reverse sequence of events occurring during defect formation by irradiation. The crystal lattice of this phosphor exhibits the capability of energy storage by luminescent centre formation because of its potential to self-structuring locally into well-organized structural complexes under irradiation. This structural capability must be considered as a systemic property. [Copyright &y& Elsevier]

Abstract: A monzogranite, here referred to as the Montieri pluton, was encountered along two depth profiles from ca. 2 to 4 km depth in wells of the Larderello–Travale geothermal system, Italy. We obtained high-resolution petrographic and microchemical data on seven fresh samples of the Montieri pluton. These data are required to correctly interpret the combined isotope data for the Rb–Sr and K–Ar systems. Biotite and K-feldspar from all samples were analyzed by Rb–Sr and 39Ar–40Ar. Rb–Sr analyses gave extremely variable two-point Rb–Sr apparent ages and Sr initials, indicating that biotite did not equilibrate with feldspar. Bulk dissolution of K-feldspars does not define a Rb–Sr alignment that could have proved a common origin of all K-feldspar samples from a single magma batch. The leachable fractions of K-feldspar separates have much more homogeneous 87Sr/86Sr ratios around 0.712, which may reflect the isotopic composition of a late-stage circulating fluid. Because of the anatectic origin of the granites from the Larderello–Travale geothermal system, it is likely that every K-feldspar separate contains at least three isotopically distinct feldspar generations: relics of the Hercynian gneiss basement, Pliocene magmatic minerals, and hydrothermal retrogression products. Such heterogeneity can be confirmed and quantified by petrographical observations and electron microprobe analyses. The 39Ar–40Ar age spectra of the biotite samples show some internal discordance. Because of deviations from stoichiometry, biotite discordance can be attributed both to chlorite intergrowths, as predicted from the active fluid circulation, and to the presence of multiple biotite generations, such as have already been documented from other micas from the Larderello–Travale geothermal system and as indeed confirmed by high-resolution petrography. Total K–Ar biotite ages on cluster around 3 Ma and broadly agree with a Rb–Sr age obtained by regressing only the biotite analyses. This suggests that the Montieri pluton, whose known volume is at least 25 km3, was emplaced at that time. The K-feldspar spectra are strongly discordant; no step age approaches the zero-age which would be predicted by Ar diffusivity modelling. The extraneous Ar in the feldspars is not excess Ar, but inherited Ar instead. Ar inheritance in the feldspar separates correlates with inheritance of Sr. Arrhenius trajectories of the apparent Ar diffusivities for all seven feldspars are astonishingly identical, despite the heterochemism amongst samples. However, the apparent diffusivity calculated from the step-heating experiments led to irreproducible models for the thermal history along the depth profile, as well as time-scales shorter than the historical record. This indicates that Ar diffusivities calculated from laboratory experiments must not be extrapolated to geological conditions. [Copyright &y& Elsevier]

The kinetics of batch dry grinding of ceramic raw materials, which are quartz, kaolin and K-feldspar, from the feeds of sieve sizes -3·350+2·360, -2·360+1·400, -1·400+0·850, -0·850+0·600, -0·500+0·425 and -0·300+0·212 mm have been determined using a Bond mill with a mixture of five ball sizes. The mill used was a size of 30·5 cm diameter, 30·5 cm length, providing a total mill volume of 22 272 cm3 with a total mass of 22 648 g steel ball mixtures of 38·10, 31·75, 25·40, 19·05 and 12·70 mm diameters, occupying 22% of mill volume and with a speed of rotation of 70 rpm. The specific rates of breakage (Si) and primary breakage distribution (Bi,j) values, called grinding breakage parameters, were determined for those feed size fractions to predict the product size distributions by simulation for comparison to the experimentally obtained data. As the feed sizes increase, the Si values also increase, that is, faster breakage values from higher to lower values were in the order of quartz, K-feldspar and kaolin by comparison with their α values. The Bi,j values obtained for these minerals were different in terms of characteristic fineness factor, γ. Thus, kaolin produced more fines, while K-feldspar and quartz produced less fines in the mill. In other words, the simulations of product size distributions for these minerals were in good agreement with the experimental data using a ball mill simulation program, called PSUSIM. However, the slowing down effect in the mill started earlier than expected for the minerals studied, unlike the laboratory size ball mill used extensively in our studies. Nevertheless, there exist linear relationships between the simulated time (θ) and experimental time (t) for these minerals. [ABSTRACT FROM AUTHOR]

Abstract: The kinetics of batch dry grinding of binary mixtures of ceramic raw materials, namely quartz–kaolin, quartz–potassium feldspar and kaolin–potassium feldspar, from the feed sizes of −3.350+2.360, −2.000+1.400, −0.850+0.600, −0.500+0.355 and −0.300+0.212mm have been determined using a Bond mill with a mixture of ball sizes of 38.10, 31.75, 25.40, 19.05 and 12.70mm diameter and total mass of 22.648kg. The Bond mill used was a size of 30.5cm diameter, 30.5cm length, with a total volume of 22,272cm3. The fractional ball filling was 22% of mill volume and the mill speed was 70rpm. The breakage parameters were obtained for those mineral mixtures to predict the product size distributions. As the feed sized given above, which were ground in the mill, increase, the specific rate of breakage (S i ) values also increase, which means faster breakage with higher S i value occurs in the order of quartz–kaolin, quartz–potassium feldspar and kaolin–potassium feldspar mixtures when comparing the characteristic α values (slope of S i versus size relationship with higher α value). The cumulative breakage distribution function (B i,j ) values obtained for these mineral mixtures were slightly different in terms of the fineness factor, γ. This means that quartz–potassium feldspar mixture produced less fines with higher γ value, while kaolin–potassium feldspar gave more fines with lower γ value. The simulations of the product size distribution for these mixing were very close to the experimental data. Finally, slowing down effect, treated with false time concept, started earlier than the expected for these binary mixtures. There were some correlations found between the simulated time (θ) and experimental time (t). [Copyright &y& Elsevier]

Abstract: 87Sr/ 86Sr isotope variation was studied in subareas of K-feldspar megacrysts from Late-Palaeozoic granodiorite, diorite and syenite of the Bavarian Forest. Most samples were collected close to the Bavarian Pfahl shear zone and feldspars from these sites reveal remarkably constant initial 87Sr/ 86Sr isotope ratios. These ratios are similar to those of the bulk groundmass or feldspar crystals from the groundmass. Individual feldspar grains however, define isochron ages that are considerably younger (by ∼15 to ∼30 Ma) than the crystallisation age of the host rocks as defined by U–Pb and Pb–Pb zircon geochronology. The Rb–Sr feldspar data probably reflect diffusion controlled isotopic homogenisation under hydrous conditions between 290–310 Ma. A pink feldspar crystal from a hydrothermally altered syenite reveals comparatively large degree of isotopic variation, indicating local disturbance of the Rb–Sr system caused by hydrothermal alteration during Permian–Triassic Pfahl quartz precipitation. A diorite from the Fürstenstein pluton displays some isotopic scatter and slight differences in the initial 87Sr/ 86Sr ratios between the more radiogenic feldspar–megacryst and the less radiogenic bulk groundmass. This rock type was subsequently intruded by the Saldenburg granite and the more radiogenic 87Sr/ 86Sr isotope signature of the feldspar relative to the groundmass is interpreted as being consistent with the feldspar having exchanged with the fluids derived from the granite. This study shows that K-feldspar crystals from slowly cooled plutonic rocks do not necessarily preserve their original Sr isotope composition. However, Sr isotope traverses through single crystals can give robust records of the mm-scale isotope system behaviour also in older plutonic rocks relevant for solving petrological or geochronological problems. [Copyright &y& Elsevier]

Abstract: Four K-feldspar samples from the Yidun Arc, eastern Tibetan Plateau, were analysed by the 40Ar/39Ar method with the aim of recovering information on their thermal history using multiple diffusion domain (MDD) theory. Arrhenius plots for each of the samples reveal low retentivity early in the heating experiments, a property that is attributed to their recrystallised nature. This low argon retentivity appears to violate the MDD assumption that volume diffusion is the only mechanism for argon transport within the crystals, thus the thermal histories derived from these analyses are considered suspect. Nevertheless, the age spectra themselves suggest that the majority of samples had cooled below ∼200°C prior to the Eocene collision of India with Asia. Thermal history modelling from apatite fission track analyses from the same and nearby samples shows slow cooling through the apatite fission track partial annealing zone during the Cenozoic in samples from the high elevation, low relief areas of the Yidun Arc, while samples from the major Jinsha River valley show rapid cooling through the partial annealing zone beginning in the Miocene. These results suggest that significant Cenozoic denudation has been localised and that most parts of the Yidun Arc have experienced very little denudation during the Cenozoic. [Copyright &y& Elsevier]

Abstract: High spatial resolution UV laser Ar/Ar analyses were performed in situ on K-feldspar overgrowths from sandstone hosted Pb–Zn bodies from central Sweden. Two different populations of ages were detected—Precambrian–Cambrian (528±10 to 567±8 Ma) and late Silurian (403±6 to 453±8 Ma). These were both detected in single pore spaces, with the older population adjacent to the detrital feldspar whilst the younger population was always distal to the detrital grain. This younging of authigenic K-feldspar ages with distance from the detrital grain margin is discussed in terms of disturbance to the argon system within an authigenic overgrowth that is of a single age: (a) the overgrowths are Precambrian–Cambrian in age and the late Silurian population might be an artefact of argon-loss due to partial resetting, (b) the overgrowths are late Silurian and the Precambrian–Cambrian population might have resulted from excess argon uptake, and (c) the overgrowths are late Silurian but the Precambrian–Cambrian population is an experimental artefact arising from the analysis of overlapping detrital/authigenic feldspars. Diffusion modelling shows that the partial resetting scenario is a very unlikely cause for the observed age variation because it requires a very particular arrangement of sub-grain sizes. Excess argon was not detected in either the K-feldspar or quartz. The data are best interpreted as the ages of two discrete diagenetic events—an early burial diagenesis and a later tectonically induced fluid flow event relating to the collapse of the Caledonian orogen. Further, the use of 38ArCl/39ArK as a proxy for Cl/K ratio highlights the physical boundaries between feldspar populations, where all other petrographic, SEM and CL analyses have failed to do so. This study shows that high spatial resolution UV laserprobe Ar/Ar analysis is a powerful tool for extracting age information from complex hydrothermal minerals as a means to investigating fluid flow events. [Copyright &y& Elsevier]

Abstract: Mesoporous aluminosilicate molecular sieves have been synthesized using K-feldspar, a natural ore rich in silicon and aluminum sources, as starting material. In this method, the mixture of K-feldspar and K2CO3 with mass ratio of 2:3 was first calcined at 880°C for 1.2h. The calcined materials were then dissolved in water together with cetyltrimethylammonium bromide as structure-directing agent, resulting in mesoporous molecular sieves after heating the solution at 130°C for 60h. Scanning electron microscopy and transmission electron microscopy observations indicated that the resulting materials were spherical particles with size of about 100nm. The mesoporous structure of the as-synthesized materials was confirmed by low angle X-ray diffraction and nitrogen sorption analysis. The BET surface area of the as-prepared material after calcined at 550°C was 507m2 g−1 and the pore volume was 0.854cm3 g−1. 27Al MAS NMR analysis showed that nearly all of aluminium is incorporated into the framework of the mesoporous material with 4-coordinated state. The acidity of the product was analyzed by FTIR spectroscopy of pyridine-adsorbed product. The product was treated in water at 100°C for 360h, and its mesoporous structure was still intact, suggesting its high hydrothermal stability. [Copyright &y& Elsevier]

Authigenic K-feldspar was investigated in two Albian to Turonian sections in Israel using K-Ar and Ar-Ar dating, X-ray diffraction, scanning electron microscopy and chemical analysis. Both sections comprise a similar succession of shallow-marine limestones, dolomites and marls, with some sandstone and shale beds of continental origin. The HCl-insoluble residue fraction of the studied samples consists of clays, quartz, feldspars, goethite and trace amounts of heavy minerals. Most of the insoluble residues have a relatively high K-feldspar content that has an adularia habit and is concentrated in the 4–7 µm size fraction. The authigenic origin of the K-feldspar in the fine silt fraction is indicated by its high content relative to quartz, the uniform and idiomorphic shape of the crystals and its limited size range. Of the fine silt (4–7 or 4–10 µm) separates, 40% have ages that are similar to stratigraphic ages within the analytical and biostratigraphic errors. Ar-Ar dating of a fine silt fraction with 94% K-feldspar (4–10 µm, sample GYP 7) yields a plateau age identical to the total gas age and similar to the stratigraphic age. These results indicate that the K-Ar age is not a mixture between detrital and late diagenetic K-feldspar ages, but is rather an age of formation within a few million years after deposition. It is suggested that the early formation of the K-feldspar was associated with dolomitization and was induced by residual brines as part of a reflux process. [ABSTRACT FROM AUTHOR]

The solubility of the high grade pelite assemblage albite+K-feldspar+andalusite+quartz at 650 °C and 2 kbar was determined in aqueous solutions over a total chloride range of 0.01–3 mCltot using rapid-quench hydrothermal technique. The concentration of Na, K, Si, and Al was determined in the fluid phase after quench. The K/Na ratio was determined by approaching the equilibrium from below and above. It is 0.34 at low chloride concentrations and decreases slightly to 0.31 with increasing total chloride. Silica and aluminum concentrations were determined only from undersaturation. The silica solubility is found to be independent of chloride concentration and is ∼0.13 molal. Aluminum is nearly independent of chloride concentration decreasing only slightly from ∼0.0015 to ∼0.0007 molal. Comparison of the experimental data with thermodynamic model calculations demonstrates that the silica concentrations are well predicted, while significant differences exist between individual databases for Al speciation and its total concentration. Al concentrations are underestimated by up to 10 to 15 orders of magnitude using the SUPCRT92 database. Predicted K/Na ratios are underestimated by up to 30%. The best predictions achieved for this simplified high-grade pelite assemblage are those using the SUPCRT92 database with revised thermodynamic data for feldspars and K- and Na-species (J. Phys. Chem. Ref. Data 24 (1995) 1401) and additional Al-species (Am. J. Sci. 295 (1995) 1255; Geochim. Cosmochim. Acta 61 (1997) 2175). The use of ideal mixing for neutral complexes in combination with the extended Debye–Hu¨ckel activity model for the charged species yields the most compatible speciation model. [Copyright &y& Elsevier]

In intermediate-acid magmatic rocks, alkaline magmatic rocks, gneisses and migmatitic rocks K-feldspar is a rock-forming rock in which the contents of Pb are highest, just 2 - 10 times those of the whole rock, 3 - 16 times those of mica minerals and 6 - 32 times those of quartz. The lowest contents of K-feldspar are recognized in Early Proterozoic and Achaean rocks, with Pb in the K-feldspar accounting for less than 10% of that in the whole rock; in post-Middle Proterozoic alkaline magmatic rocks, K-feldspar-rich granites and metamorphic rocks the contents of K-feldspar tend to increase, with the proportion of Pb over that in the whole rock being obviously increased. In the alkaline rocks in which K-feldspar accounts for 50% - 70% of the total in the whole rock, the contents of Pb in K-feldspar account approximately for 70% - 95% of the total lead in the whole rock. Being accessible to hydrothermal alteration in the late periods, K-feldspar was conversed to sericite, calcite, quartz, etc. In the process of such conversion the lead would be leached out and then find its way into fluid phase. This kind of transformation can provide sufficient ore-forming material for later Pb metallogenesis. [ABSTRACT FROM AUTHOR]

Feeding experiments were conducted quantitatively to examine the breakdown of mineral grains by earthworm, Eisenia feida, and larva of beetle, Protaetia lugubris insperata. Crushed and sieved test minerals of K-feldspar and/or quartz were mixed with artificial humus that contained no mineral grains. The mixture was fed to the soil animals in the plastic containers. After 1-, 4- and 7-day experimental durations, the ingested mineral grains were collected from the casts excreted by the soil animals in each container. Even 1 day after feeding of mineral grains, the casts of soil animals contained finer, rounded mineral grains that were not included in the initial prepared mineral samples. [Copyright &y& Elsevier]

K-feldspar–plagioclase–quartz mineral textures as well as biotite and hornblende compositions are compared for suites of metamorphosed mafic rocks from two widely separated traverses. A portion of either traverse has experienced a high-grade dehydration event transforming it from an H2O-rich, hornblende-bearing zone to an H2O-poor, hornblende-free, orthopyroxene-bearing, ‘granulite facies’ zone at 700–800°C and 7–8 kbar. In the Kigluaik Mountains, Seward Peninsula, Alaska, dehydration took place over an 85 cm thick layer of metatonalite in contact with a marble during regional metamorphism and involved a CO2-rich fluid, whereas for the Val Strona di Omegna traverse, Ivrea–Verbano Zone, northern Italy, dehydration took place over a 3–4 km thick sequence of metabasites interlayered with metapelites in a contact metamorphic event involving basaltic magmas intruded at the base of the sequence. Orthopyroxene-bearing samples from both dehydration zones show micro-veins of K-feldspar along quartz and plagioclase grain boundaries as well as replacement antiperthite in plagioclase. K came primarily from the breakdown of hornblende + quartz to orthopyroxene ± clinopyroxene, feldspar and fluid. Biotite either was stabilized or formed in the dehydration zones and is enriched in Ti, Mg, F and Cl relative to biotite in the amphibolite facies zone. [ABSTRACT FROM PUBLISHER]

Many points of evidence, especially igneous microstructures and structures resulting from solid-state deformation, indicate that K-feldspar megacrysts in deformed granites of the Papoose Flat pluton are residual phenocrysts, not porphyroblasts. Evidence of an igneous origin includes features such as crystal shapes, simple twinning, zonally arranged euhedral plagioclase inclusions, oscillatory compositional zoning, and local occurrence in microgranitoid enclaves. Evidence of solid-state deformation of the megacrysts (which is consistent with their existence prior to the mylonitic deformation) includes marginal recrystallization and neocrystallization, microcline twinning, marginal replacement by myrmekite, and recrystallized/neocrystallized “tails”. Evidence of porphyroblastic growth, such as overgrown inclusion trails, is absent. This appears to be the situation in most felsic augen gneisses and mylonites. [ABSTRACT FROM AUTHOR]

The fractional glow technique (FGT) applied to the investigation of optically bleached samples of K-felds pars extracted from sediments reveals the coexistence of various groups of traps which are active in the same temperature region over 300 °C. Significant differences between the trap parameters seem to explain the diversity of TL bleaching efficiency for different trap groups. [ABSTRACT FROM AUTHOR]

The fractional glow technique was applied to the investigation of trap occupation in optically bleached K-feldspars separated from sediments. Various bleaching times and two spectra ranges of sunlight simulator were used. Three trap groups exhibit different sensitivities to bleaching. The influence of the spectrum range of the stimulation light on the bleaching efficiency is presented. Results of the fractional glow technique measurements simulations are presented for the case of second order kinetics. [ABSTRACT FROM AUTHOR]

Crushed rocks and mine tailings containing biotite, K-feldspar and nepheline as K-bearing minerals were applied as K fertilizers in a series of 15 grassland field trials. A treatment with KCl as K-source outyielded treatments with rock based fertilizers in the first and the second experimental year. In the third and last year of the study when no K fertilizers were supplied, previously added carbonatite and biotite concentrate supported grass growth as much as previously added KCl did. Although it is concluded that a substantial part of the K bound in biotite and/or nepheline in crushed carbonatites, biotite concentrate and epidote schists is plant available, these rock/mineral products weathered too slowly to replenish the native pool of plant available K within a three year period with five harvests. The K bound in K-feldspar seemed to be nearly unavailable for the grass plants. [ABSTRACT FROM AUTHOR]

Potassium, which is included in certain contents in the structure of K-feldspar minerals, has a very important function in the growth of plants. Turkey hosts the largest feldspar reserves in the world and is by far the leader in feldspar mining. The production of potassium salts from local natural sources can provide great contributions both socially and economically in the agriculture industry along with glass production, cleaning materials, paint, bleaching powders, and general laboratory purposes. In this study, potassium extraction from K-feldspar ore with an 8.42% K2O content was studied using chloridizing (CaCl2) roasting followed by water leaching. Initially, to produce wollastonite and calcite concentrates, froth flotation tests were conducted on wollastonite-calcite ore after comminution. Thus, wollastonite and calcite concentrates with purities of 99.4% and 91.96% were successfully produced. Then, a calcite concentrate was combined with hydrochloric acid (HCl) under optimal conditions of a 1 mol/L HCl acid concentration, a 60 °C leaching temperature, and a 10 min leaching time to produce CaCl2. To bring out the importance of roasting before the dissolution process, different parameters such as roasting temperature, duration, and feldspar—CaCl2 ratios were tested. Under optimal conditions (a 900 °C roasting temperature, a 60 min duration, and a 1:1.5 feldspar—CaCl2 ratio), 98.6% of the potassium was successfully extracted by the water leaching process described in this article. [ABSTRACT FROM AUTHOR]

In an attempt to clarify the significance of Pb model ages in Pb-Zn sedimentary deposits, we report high-precision Pb isotopic compositions for 64 galenas and 52 K-feldspars, the former from ores and the latter separated from granites. All samples are from Spain and the French Pyrenees. Lead from galena ores is of unequivocal continental origin. With few exceptions, Pb model ages systematically exceed emplacement ages by up to 400 Ma, a gap which is well outside the uncertainties of ~ 30 Ma assigned to the model. The histogram of the new high-precision Pb isotope data shows prominent peaks of galena Pb model ages at 94 ± 38 Ma and 392 ± 39 Ma. When the data are consolidated with literature data and examined in 3-dimensional Pb isotope space, cluster analysis identifies five groups. The model ages of the peaks occur, in order of decreasing peak intensity, at 395 ± 40 (Middle Devonian), 90 ± 34 Ma (Middle Cretaceous), and 613 ± 42 Ma (Neoproterozoic), with two minor peaks at 185 + 26 Ma (Jurassic) and 313 ± 41 (Upper Carboniferous). To a large extent, the model ages centered around these peaks correspond to distinct localities. The ages of the peaks do not coincide with any of the Betic, Variscan, or Pan-African tectonic events, which are the main tectonic episodes that shaped Iberian geology, but instead match well-known global oceanic anoxic events. It is argued that surges of metals weathered from continental surfaces scorched during anoxic events accumulated and combined in anoxic water masses with unoxidized marine sulfide released by submarine hydrothermal activity to precipitate the primary Pb-Zn stock. Frozen Pb isotope compositions require that galenas from black shales are the source of the final ores. The sulfides were later remobilized by large-scale convective circulation of basinal and hydrothermal fluids. The peaks of K-feldspar Pb model ages are distinct from those of galenas and do not correlate with magmatic emplacement ages. It is suggested that they instead reflect local circulation in Paleozoic sediments surrounding individual plutons. While Pb isotopes can be used as a regional provenance tool, such an approach requires that the data are considered in a fully 3-dimensional space. • The Pb isotopic composition of 64 galenas and 52 K-feldspars from Spain and the French Pyrenees was analyzed by MC-ICP-MS. • Pb model ages of galenas exceed the emplacement ages of Pb-Zn sedimentary deposits by 10s to 100 s Ma. • Galena Pb model ages date the accumulation of primary Pb-Zn stocks during oceanic anoxic events. • The isotopic composition of frozen Pb indicates that galena from black shales constitutes the source of Pb-Zn deposits. • Pb model ages of K-feldspars from granitic plutons reflect local circulation of sediments rather than magmatic emplacement. [ABSTRACT FROM AUTHOR]

It is popular in geochemical models to assume that chemical differentiation occurs by crystal fractionation from high-melt-fraction magma reservoirs. However, a "crystal mush" reservoir characterized by low-melt-fraction has been gradually accepted in the past decade. Magma differentiation in this scenario remains poorly understand. Located in the East Kunlun orogenic belt, northern Tibet Plateau, the Baishiya granodiorite is an ideal example to investigate magma reservoir processes. Although major elements of the Baishiya granodiorite are relatively homogeneous, there is a distinct variation of magmatic texture, trace elements concentrations, and isotopic ratios from top to bottom. The textural and geochemical signatures above cannot be explained by assimilation-fractionation crystallization, magma mixing or convective self-mixing alone. Within the concept model of crystal mush, we propose a multistage formation process of the studied granodiorite. First, a rhyolitic mushy reservoir once existed. It was replenished by episodic basaltic melts from below, resulting in the textural coarsening of K-feldspar. When the heat and/or melts injection was high enough, the crystal mush could be gradually rejuvenated and subsequently stirred. Some K-feldspar antecrysts would be partly recycled to form mantled plagioclase through convective self-mixing. Thus, the evolved and buoyancy melts exhibited an equilibrated geochemical signature with plagioclase, and ultimately formed the porphyry phase on the top. Moreover, recycling of K-feldspar antecrysts contributed to a depletion of heavy rare earth elements and Y contents, as well as an elevation of Cr concentrations and Eu/Eu* ratios in the residual crystal mush, and finally formed the porphyritic granodiorite. Due to a continuous injection and convective self-mixing, the overall magma reservoir became more mafic gradually until it reached a granodioritic composition. Within a waning intensity of magma flux, the magma reservoir would be locked again. The injected melts would go through a rapid crystallization, and subsequently form microlites, such as the dioritic enclaves and the ground mass of the studied granodiorite. Consequently, traditional mechanisms that are based on low-crystallinity magmas may be a specific part of the protracted history rather than the whole story of the magma reservoir. Geochemical index of granitoid rocks should be used with caution due to this inherited affinity. It should be prerequisite to investigate crystal genesis carefully before utilizing geochemical diagrams. [Display omitted] • The convective self-mixing is responsible for the formation of rapakivi texture. • Geochemical index can be influenced by recycled K-feldspar antecrysts. • Traditional mechanism may be a specific part in a "crystal mush" reservoir. [ABSTRACT FROM AUTHOR]

The Bunu area in Southwestern Nigeria lies within the Basement Complex that forms part of the Pan-African platform of the crystalline rocks. The complex lies within the vast Trans-Saharan Pan African mobile of Neoproterozoic. The belt is characterized by voluminous post-collision granitoid plutons that are well exposed around the study area. The Bunu area consist of two major lithologic suites namely: (i) the gneiss-schist suite which comprised of Migmatized-gniess/ Migmatized Schist and quartz/mica schist with interbedded amphibolites (ii) intrusive suite that include fine-medium grained granite, medium-coarsed grained granodiorite and porphyritic granite and the minor intrusions like pegmatite, aplite, dolerite and quartz veins. Pegmatite outcrops in the Bunu area of the Kabba-Lokoja-Igarra Schist belt belong to the rare-element type and are mined for columbite-tantalite and gem tourmaline. Pegmatitic textures are well developed, these include large K-feldspar (comb textures), layering and graphic intergrowth of K-feldspar + albite + quartz + schorl and linearly arranged garnet crystals that may be developed at deeper levels of the dyke. Ductile and brittle structural features mapped in the area from remotely sensed and field data are generally consistent with the N-S and NE-SW regional orientation associated with Pan-African event and with minor axes of NNW-SSE and E-W planar structures. Trace elements geochemistry of the pegmatite (bulk rock and mineral extracts of K-feldspars and Mica) revealed that Rb, Sr, Ba, Li and Cs are enhanced in the Otafun and Okutose pegmatites indicating higher fractionation levels. Also, the rare-metals Nb, Ta and Sn were also enriched in the most evolved Otafun and Okutose pegmatites. Trace-element variations in mica from the pegmatites indicate that they are per-aluminous LCT (lithium, cesium, and tantalum) family and bery-columbite subtype. The origin of the gradual composition variation trend observed from the host granite bodies to the pegmatites reflects the increasingly fractionated melt composition and systematic enrichment of the incompatible trace elements Li, Rb, Cs, Be, Na, Ta and Sn. The Zr-SiO 2 and Sr-Rb plots of the pegmatite bulk rock samples suggest that they are genetically magmatic and poorly differentiated with little or no post-magmatic metasomatism. Ta vs Cs and Ta vs Ga plots for the chemistry of K-feldspar and muscovite mineral extracts from the pegmatites in Bunu area show potential for tantalum and niobium (>75 ppm) mineralization, thus implying that the mineralization in these pegmatites is probable, therefore investors should use caution. • Bunu pegmatite of the Kabba-Lokoja-Igarra Schist belt is a rare-element type. • High Nb, Ta and Sn recorded in Otafun and Okutose pegmatites. • Magmatic and poorly differentiated [ABSTRACT FROM AUTHOR]

Quartz and feldspar are the two most abundant minerals in the continental crust. The rheology of quartz and feldspar has been used to approximate the rheology of the upper and the lower crust, respectively. However, compared with quartz and plagioclase, the rheology of K-feldspar (Kfs) is much less characterized. We present here systematic axial compression deformation experiments on a relatively dry (22 ± 2 wt ppm) synthetic Kfs aggregates (Or 81 Ab 19) at strain rates of 10−4–10−5 s−1, temperatures of 950–1100 °C and a pressure of 1.5 GPa, using a 5 GPa modified Griggs-type deformation apparatus. The rheology of Kfs aggregates can be best described by the constitutive equation of ε ̇ = 102.4±3.1 σ 3.0±0.6 exp ( − 368 ± 70 RT). EBSD mapping and TEM analyses reveal clear intracrystalline deformation and pronounced crystallographic preferred orientations resulted from activation of dislocation slip along the [100](010) and [100](001) slip systems at elevated temperatures. Extrapolation of the Kfs flow law to a natural strain rate of 10−14 s−1 suggests a weaker strength than that of anorthite of similar water concentrations deformed in the dislocation creep regime. The higher creep strength of relatively dry Kfs and anorthite aggregates comparing to wet quartzite provides an explanation for feldspar forming porphyroclasts in crustal rocks. However, Kfs may also exhibit ductile deformation at high temperatures under lower crustal and deep continental subduction conditions. • We report here first flow law of dry synthetic K-feldspar (Or 81 Ab 19) aggregates. • Kfs can deform by dislocation creep and produce fabrics at elevated temperatures. • Dry Kfs has a flow strength between those of dry anorthite and wet plagioclase. [ABSTRACT FROM AUTHOR]

[Display omitted] • The topographies of micro-sized water droplets on local homogeneous areas are obtained. • More consistent contact angle data are yielded by the present method compared with traditional optical method. • The influences of heterogeneity and roughness on the wettability of K-feldspar surface were reduced. Wettability is a key property of a reservoir rock, which can significantly affect the distribution and transportation of fluids (gas, oil, water, etc.) in reservoir pores which are constructed with various minerals. As for sandstone reservoirs, quartz and feldspar are the common minerals of the framework. However, the study on the wettability of feldspar is much less than that of quartz probably due to the strong heterogeneity and complex composition of natural feldspar minerals. In this study, a method for measuring the contact angle of water droplet on a natural mineral surface is proposed by combining argon ion polishing technique with atomic force microscopy scanning (Ar+-AFM method). Compared with the traditional optical goniometer measurement, this method can apparently reduce the influence of heterogeneity on the wettability of K-feldspar surface and yield more consistent contact angle data. [ABSTRACT FROM AUTHOR]