Muscovite Samples Research Articles

Mineralogic and stable isotope studies of cassiterite greisen mineralization in the Uljin area, Korea

Vein-type, greisen-related cassiterite deposits occur at the Uljin, Yuchang, and Dongseog mines in eastern Korea within a Precambrian pegmatite dike swarm, and locally, within granite gneiss and metasedimentary rocks. Paragenetic stages of mineralization and alteration are as follows: greisen I, albitization, K feldspathization, and greisen II. A late-stage of quartz-fluorite vug filling is present locally. K-Ar age dating of muscovite from the greisen I stage mineralization indicates a crystallization age of 158 to 179 + or - 6 Ma, in close agreement with previously determined ages of 151 to 179 Ma (Chon et al., 1993). Two samples of muscovite from the pegmatites give ages of 696 + or - 15 and 778 + or - 14 Ma. Greisen-related tin mineralization occurred during the Middle Jurassic to Early Cretaceous and is much younger than either the pegmatite (Late Proterozoic) or the granite gneiss (Early Proterozoic based on Rb/Sr studies of Hong, 1985, and Lee, 1988).Temperatures of greisen I stage mineralization, determined from fluid inclusion homogenization studies, arsenopyrite composition, and quartz-muscovite delta 18 O values, range from 450 degrees to 600 degrees C. The coexistence of sulfide and oxide minerals suggest that during ore deposition f (sub S 2 ) increased and f (sub O 2 ) was constant or decreased slightly. Fluid inclusion analyses indicate that the ore fluid was of low to moderate salinity (2.89-8.55 wt % NaCl equiv), with variable CO 2 content. Oxygen and hydrogen isotope values of quartz and muscovite decrease along a distance of 1,500 m from the northeast (Uljin mine) to the southwest (Dongseog mine) and suggest that fluid delta 18 O and delta D values decreased from approximately 11 to 9 permil, and -55 to -61 per mil, respectively. A similar decrease in fluid delta 18 O and delta D values is recorded temporally with the paragenetic stage at the Uljin mine. Sulfur isotope values of arsenopyrite and molybdenite range from -1.2 to 1.2 per mil.A genetic model of fluid derivation from an underlying Mesozoic granitic pluton, accompanied with the involvement of meteoric water in later stages, is proposed. Isotopic data are consistent with temporal and spatial variations in fluid delta D and delta 18 O values caused either by tapping of a magmatic fluid during various stages of chemical and isotopic evolution, or by reaction and isotopic exchange with high 18 O sedimentary rocks along a fluid flow path. Variations in delta 18 O values of carbonate country rocks from 19.3 to 12.3 per mil are suggestive of selective fluid transport through particularly permeable units in the limestone. Low delta 18 O values of vug-filling quartz suggest the involvement of low-temperature meteoric water in the latest hydrothermal stages of mineralization.

Trace Elements in Muscovite as a Guide to Gem Tourmaline Bearing Pegmatites in Nepal

The pegmatites of Hyakule, and to a lesser extent, of Phakuwa area. Sankhuwa Sabha district. Eastern Nepal, have been a source for gem quality tourmaline since about 60 years. Only 4 pegmatite bodies, 2 each in Hyakule and Phakuwa, out of about 40 dikes altogether, yielded this precious stones despite at least 5 larger openings and probably some smaller ones in other dikes.
 The Phakuwa and Hyakule area occupies the eastern limb of the Arun anticline and consists of high grade metamorphic rocks of possibly Precambrian age belonging to the basal part of the Higher Himalayan crystalline. These rocks thrust south­ ward along the Main Central Thrust over the rocks of the Nawakot complex belonging to the Lesser Himalaya.
 The metamorphic sequence, about 2500 m thick, consists mainly of gneisses, garnet-kyanite and game-staurolite mica schist, quartzites and marbles with intercalated minor calc-silicate rocks. Pegmatites occur in the mica schist and interbedded calc-silicate schist sequence (approximately 1000 m thick) as scattered lenses or possibly dikes of a few min thickness, which cut discordantly through the host rocks. Internal zoning has developed generally into an upper blocky feldspar zone, a central quartz core with tourmaline and beryl (partly as aquamarine) and a lower fine grained, garnet bearing muscovite-quartz­ feldspar zone. Schorl is quite frequent as is biotite, the latter is often more abundant than muscovite. Uraninite and Ta-Nb minerals (tantalite, wodginile, pyrochlore) as well as cassiterite have been found in heavy mineral concentrates of a few investigated pegmatite samples.
 The current paper deals with several questions: what is the type of these pegmatites in terms of a classification? Do all pegmatites belong to the same generation and/or stage of evolution? Why are gem quality tourmalines known only from a few dikes? Is there an exploration method to distinguish between barren and gem tourmaline pegmatites in these areas? Could this method possibly be applied to other pegmatite areas in Nepal?
 We used trace and some major element characteristics of 24 coarse grained muscovite samples from 19 pegmatite dikes in Phakuwa and Hyakule and from localities nearby to answer these questions. Additional 4 muscovite samples from gem tourmaline bearing and barren pegmatites in the Ilam district have been included for comparison. The trace element characteristics, some main elements and some element ratios of coarse grained muscovites in Hyakule and Phakuwa distinguish clearly between a group of gem producing and barren pegmatites. The most powerful distinguishing geochemical features are the concentration ranges of Rb, Ba, MnO and MgO and the element ratios K/Rb and Li/Mg. Less useful are the concentrations of Cs, Sn and Ta because of a somewhat irregular behaviour. Surprisingly, Li is rather low in all samples and does not discriminate very distinctly between the two pegmatite groups. The results of this study can probably be used as a rapid exploration tool in sorting out barren pegmatites from pegmatites with a potential for gem quality tourmaline.

40 Ar- 39 Ar and U-Pb age constraints on the timing of gold mineralization in the Kalgoorlie gold field, Western Australia

The 40 Ar- 39 Ar ages of three hydrothermal muscovite samples associated with auriferous gold stockwork systems at the Mount Charlotte deposit in the Kalgoorlie gold field have a weighted mean of 2602 + or - 8 Ma ( 40 Ar- 39 Ar age errors are 2Sigma ). At the nearby Golden Mile deposit 40 Ar- 39 Ar ages from two muscovite samples associated with shear-hosted lode gold mineralization have a weighted mean of 2629 + or - 9 Ma. On the balance of available evidence these ages are interpreted to represent the timing of gold mineralization in the two deposits.These data indicate that formation of auriferous gold stockwork systems at Mount Charlotte occurred at least 10 million years after formation of the gigantic Golden Mile lode system. This is consistent with geologic relations between the two different styles of mineralization and suggests that separate hydrothermal episodes were responsible for stockwork and shear-hosted gold mineralization.A weighted mean 207 Pb/ 206 Pb zircon age for a postregional metamorphism biotite porphyry intrusion of 2674 + or - 6 Ma (95% confidence limits) provides a minimum estimate for the timing of regional metamorphism of the surrounding greenstone sequence and associated compressive deformation. Hypotheses for the formation of Archcan gold deposits which invoke fluids that are derived from regional metamorphic devolatilization of upper-middle crustal greenstone sequences or from intrusion of spatially related porphyries cannot account for the gold mineralization in the Kalgoorlie gold field. These data indicate that the events occurred 30 to 40 and 60 to 70 million years prior to mineralization at the Golden Mile and Mount Charlotte, respectively.Formation of the Golden Mile appears to have been part of a widespread gold mineralizing event at ca. 2630 to 2640 Ma, supporting models in which crustal-scale hydrothermal circulation at this time is used to explain Archcan gold mineralization within the Yilgarn block. However, such models must now contain the caveat that discrete younger episodes of mineralization, such as that responsible for Mount Charlotte, may also produce significant gold deposits with features similar to typical Archcan gold deposits.

Geochemical and structural evolution of micas in the Rožná and Dobrá Voda pegmatites, Czech Republic

The chemistry, structural parameters, polytypism, optical properties and Rb-Sr isotopes were examined in 11 to 60 samples of biotite, muscovite and lepidolite from the pegmatites at Rožna (the type locality of lepidolite; 323 ± 4Ma) and Dobra Voda (306 ± 9Ma) in western Moravia. At both localities, early endocontact biotite is followed inwards by muscovite and lepidolite, which is concentrated in and around the core. At Rožna, a 1M lepidolite follows after 2M1 muscovite but all later generations of lepidolite are 2M2, close to Tri50 Ply50 and in part associated with muscovite 2M1. At Dobra Voda, all lepidolite types are 1M and free of muscovite, and the late varieties approximate Tri30 Ply70. At both localities, a trend of increasing μHF is indicated during the progress of mica crystallization, culminating in precipitation of topaz. Polytypism of lepidolite is not correlatable with any compositional or growth feature, or their combination. Throughout the mica crystallization, Rb/Cs decreases but K/Rb becomes reversed after an initial decrease. Boron is partitioned preferentially into muscovite (up to 1.10 wt.% B2O3) but Be, Zn, Mn and Sc are enhanced in lepidolite. A slight increase in Fe, Ba and Cl in the last generation of lepidolite might be possibly due to mixing of residual pegmatite fluids with metamorphic pore solutions.

Rb-Sr isotope systematics of muscovite from Pan-African granitic pegmatites of Western and Northeastern Africa

Rb-Sr investigations have been carried out on early-formed muscovite from three pegmatite fields of the late Proterozoic to early Phanerozoic Pan-African Belt. The individual mineral ages obtained are highly discordant for each pegmatite field. Using Best Isochron Diagrams, isochron construction of selected muscovite samples yielded geologically realistic ages of pegmatite formation: around 670 Ma for the Bayuda Desert pegmatites of northern Sudan, around 550 Ma for the Wamba pegmatites of central Nigeria, and around 465 Ma for the Majayahan pegmatites of northeastern Somalia. Initial Sr ratios obtained from isochron calculations have unrealistic values and cannot be used for petrogenetic interpretations. The geologically unrealistic young model ages of some of the muscovite samples are most probably attributed to open-system behaviour and post-crystallization loss of87Sr* from the respective minerals. The amounts of87Sr* losses have been approximated from the discrepancies between isotopically measured and theoretically calculated (from decay of Rb)87Sr* concentrations. The loss of87Sr* from the micas is variable in each pegmatite field. In none of the three cases can this unsystematic, post-emplacement, open-system behaviour be directly related to a particular, temporally confined, geologic event.

Determination of acoustic phonon dispersion curves in layer silicates by inelastic neutron scattering and computer simulation techniques

Inelastic neutron scattering and computer modelling techniques have been used to study acoustic phonons in several layer silicate minerals. Experimental measurements have been made on four layer silicate minerals; namely samples of muscovite, Fe-bearing muscovite, margarite and chlorite. The longitudinal acoustic modes propagating along the [0, 0, ξ] direction of muscovite and Fe-bearing muscovite were found to be the same, within experimental error. The longitudinal and transverse acoustic modes propagating along [0, 0, ξ] of muscovite have been calculated using computer simulation techniques based on lattice dynamics. The experimental and calculated longitudinal modes of muscovite are in excellent agreement, thereby demonstrating the complementary nature of both techniques. The shape of both experimental and calculated dispersion curves was found to be approximately sinusoidal, indicating that interatomic forces act principally between nearest-neighbour atoms.

Laboratory study of the rates and products of the phototransformations of naphthalene adsorbed on samples of titanium dioxide, ferric oxide, muscovite, and fly ash

The photodegradation of naphthalene (NPH), chosen as a model of polynuclear aromatic pollutants, has been studied in the presence of a layer of four water-insoluble inorganic solids which can be found in the troposphere (TiO2, Fe2O3, muscovite, and a fly ash sample). Direct photolysis of NPH is negligible at λ>340 nm. Dark adsorption of NPH on TiO2 (mainly anatase, nonporous, 50 m2 g−1) at 293 K corresponds to a surface coverage ofca. 50% at equilibrium. Under these conditions (saturated surface), the stationary-state photocatalytic degradation reaches 0.4 molecule nm−2 h−1 (λ>340 nm, radiant fluxca. 22 mW cm−2). Dioxygen is required and its partial pressure in air is such that the degradation is zero order in O2. Water vapor markedly increases the rate. The other particulates have also an effect, less important than that of TiO2, however quite noticeable with respect to surface area unit for the fly ash sample which contains 3.2% Fe2O3. Apart from 1,4-naphthoquinone, which is the main intermediate product in all cases, 2-naphthol, phthalide, phthaldialdehyde, phthalic acid, acetophenone, benzaldehyde, benzoic acid are also formed on dry TiO2. Depending on their volatility, these compounds are transferred to the gas phase or remain principally adsorbed on the solid particles where they are further transformed. For instance, phthalic acid (or anhydride) and benzoic acid are generated from 1,4-naphthoquinone. Degradation mechanisms are briefly discussed.

Preparation of muscovite with ultrahigh specific surface area by chemical cleavage

The specific surface area of a muscovite sample increases drastically after exposure to a LiNO3 solution, e.g., from 3.4 m2/g, corresponding to platelets of ca. 200 silicate layers, to 295 m2/g (platelets of ca. 2–3 silicate layers) after treatment at 180°C under atmospheric pressure for 46 h. The efficiency of the cleavage process decreases with decreasing temperature (down to 50°C). The LiNO3/H2O weight ratio is also very important: at 130°C and a reaction time of 46 h, for instance, a value in the range of 1.7–1.8 leads to the highest specific surfaces. The cleaved products have the form of strong papers that disperse readily in water. During the cleaving procedure, not only the particle thickness, but also the diameter decreases. There is no evidence of damage or partial dissolution of the silicate structure after cleavage, by IR spectroscopy and yield. The use of LiCl also leads to an increase in specific surface area, but the effect is weaker than in the case of LiNO3. Treatment with some other alkaline and alkaline earth nitrates and chlorides did not increase the specific surface area of muscovite significantly.

Volume self-diffusion of oxygen in biotite, muscovite, and phlogopite micas

The kinetics of oxygen self-diffusion have been measured in natural samples of biotite, muscovite, and phlogopite micas under hydrothermal conditions using both bulk exchange and profiling analyses. All experiments were run at 1000 bars (100 MPa) water pressure except those designed to measure water pressure dependence, which ranged from 200 to 2000 bars. The Arrhenius relations obtained for layer-parallel diffusive transport in the three micas by bulk exchange experiments, fit to an infinite cylinder model, are Mineral biotite muscovite phlogopite Q (kcal mol) 34 ±2 39 ± 5 42 +- 3 D 0 (cm 2 s) 9.1 × 10 −6 7.7 × 10 −5 1.4 × 10 −4 T(°C) 500–800 512–700 600–900. The results of ion microprobe (SIMS) depth profiling perpendicular to the layers (parallel to c-axis) yield diffusion coefficients 3 to 4 orders of magnitude lower than for transport parallel to the layers. A single layer-parallel step profiling experiment yields a diffusion coefficient identical, within uncertainty, to those obtained from bulk exchange experiments. A slight dependence of diffusion rate on water pressure may obtain in phlogopite; however, the difference is approximately within the uncertainty of the measurement. Diffusion rates are similar, within about a half an order of magnitude, for a range of biotite composition from annite 4 to annite 63, as well as for muscovite. Comparison of oxygen diffusion rates in biotite from this study with Ar, K, and Rb diffusion from published data supports the idea that water is the oxygen-bearing species in hydrothermal diffusion experiments. The implication of these results for natural systems is that the micas, especially biotite, will continue to exchange oxygen isotopes via volume diffusion down to temperatures as low as 300 °C. The rapid diffusion kinetics may explain biotite oxygen isotope disequilibrium, which is commonly observed even in rocks where other mineral phases preserve equilibrium compositions.

Episodic rapid uplift in the Himalaya revealed by 40Ar/39Ar analysis of detrital K-feldspar and muscovite, Bengal fan

Detrital K-feldspar and muscovite samples from Ocean Drilling Program Leg 116 cores have been dated by the {sup 40}Ar/{sup 39}Ar technique and have depositional ages from 0 to 18 Ma. From 4 to 13 individual K-feldspars and 1 to 12 individual muscovites have been dated from 7 stratigraphic levels. In every level at least one K-feldspar and one muscovite yielded a minimum age identical, within uncertainty, to the age of deposition. These results indicate that a significant portion of the material in the Bengal fan is first-cycle detritus derived from the Himalaya. Therefore, the substantial amount of sediment deposited in the distal fan in early to middle Miocene time can be ascribed to a significant pulse of uplift and erosion in the collision zone at this time. Moreover, these data indicate that throughout the Neogene, some part of the Himalayan orogen was undergoing rapid erosion (1 to 10 mm/yr); this erosion must have been less than or equal to uplift relative to sea level. The lack of granulite facies rocks in the eastern Himalaya and Tibetan plateau suggests to us that very rapid uplift must have been distributed in brief pulses over different parts of the mountain belt. These datamore » are incompatible with tectonic models in which the Himalaya and Tibetan plateau are uplifted either uniformly over the past 40 m.y. or mostly within the past 2 to 5 m.y.« less

Thermochronology of economic mineral deposits; dating the stages of mineralization at Panasqueira, Portugal, by high-precision 40 / 39 Ar age spectrum techniques on muscovite

40 Ar/ 39 Ar age spectrum dates for 13 muscovites have been used to reconstruct the thermal history (thermochronology) of the Panasqueira, Portugal, tin-tungsten deposit, a deposit spatially associated with a belt of Hercynian plutons. Muscovite samples with an age difference as small as 2.2 m.y. (0.7% of the age) are statistically distinct. Statistics are even better for comparison of multiple samples from separate events; that is, a difference of 0.9 m.y. (0.3%) can be resolved in this approximately 300-m.y.-old deposit. The major tin and tungsten ore-forming stages, which are the oxide-silicate stage, the main sulfide stage, and greisenization, occurred between 296.3 + or - 0.8 (1 Sigma ) and 291.6 + or - 0.8 m.y. (1 Sigma ). The first substage of the oxide-silicate stage was a short-lived thermal pulse at 296.3 + or - 0.6 m.y.; the fluids responsible may have emanated from the known granite cupola. The main sulfide stage was active at 294.5 + or - 0.9 m.y. as a slightly longer lived pulse with oldest evidence for this stage (295.8 + or - 0.6 m.y.) coming from areas farthest away from the known cupola and youngest evidence (293.5 + or - 0.8 m.y.) closest to the cupola. A second substage of the oxide-silicate stage occurred as a short-lived thermal pulse at 292.9 + or - 0.7 m.y., synchronous with greisenization of the cupola and alteration of the silica cap at 292.1 + or - 0.4 m.y. The duration of activity of the oxide-silicate stage, the main sulfide stage, greisenization, and alteration of the silica cap based on the ages of all 13 muscovites was greater than 4.2 + or - 0.5 m.y. (1 Sigma ). Minor argon loss from all dated muscovites occurred during later reheating, probably during the longer lived pyrrhotite alteration stage. A single center, the known cupola, had a prolonged role and was the source for main sulfide stage, oxide-silicate stage II, greisenization, and alteration of the silica cap and possibly oxide-silicate stage I and the pyrrhotite alteration stage; however, a separate source for these latter two stages cannot be ruled out.This study is an example of a new and powerful application of 40 Ar/ 39 Ar age spectrum dating of muscovite. Because of the high precision demonstrated in this study, it is now possible to establish time constraints necessary for solving some of the long-standing problems in economic geology. Beyond this, the unique geologic situation of Panasqueira has allowed us to quantify the thermal characteristics of muscovite. Published fluid inclusion data have been used to estimate a muscovite argon closure temperature of approximately 325 degrees C during rapid cooling or short reheating and a temperature of approximately 270 degrees C during slow cooling or extended reheating. Argon-loss patterns displayed by all dated muscovites resulted from reheating after original closure; the mechanism for this argon loss appears to have been argon transport by volume diffusion. Thus, 40 Ar/ 39 Ar age spectrum dating of muscovite can be used to evaluate thermal conditions controlling argon diffusion as well as age, duration, and number of episodes of mineralization.

Variation of the surface energy characteristics of mica (muscovite) upon grinding

Inverse gas chromatography (IGC), at zero surface coverage, has been used to follow the variation of the surface free energy characteristics of muscovite samples after grinding either in water or in organic media. For initial mica, the value of γ S D measured through IGC, is in agreement with the values given by other methods (30 mJ/m 2 After grinding, γ S D increases and reaches a value of 90 mJ/m 2 when the operation is performed in methanol. At the same time, the acid/base surface properties change as qualitatively indicated by IGC. The variation in surface characteristics, upon grinding, may have significant consequences for the utilization of mica as a filler for composite materials.

Genesis and evolution of water in a two-mica pluton: A hydrogen isotope study

Measurements were made of the hydrogen isotope composition of 74 samples of muscovite, biotite, vein quartz and whole rocks from the Papoose Flat pluton, eastern California, U.S.A., and adjacent metamorphic and sedimentary rocks in order to elucidate the genesis and evolution of water and hydrous minerals in a two-mica granodiorite. Electron microprobe analyses were made of all micas so that the Suzuoki-Epstein equation could be used in evaluating the data. Based on experimental, theoretical and textural evidence of mica paragenesis, a model of hydrogen isotope fractionation between an aqueous vapor and a magma during crystallization has been constructed. This model accounts for the observed hydrogen isotope relations and implies that primary hydrogen isotope compositions have been preserved in a large portion of the pluton. The δ D-values of biotites vary widely over the range −103 to −66% with most values lying between −90 and −70‰ Muscovites, on the other hand, are isotopically more uniform and have δ D-values of −61 to −41‰ with most values lying between −50 and −46‰ These data are consistent with the interpretation that biotite formed over a long period of crystallization whereas muscovite formed in a narrow interval, presumably during the final stages of crystallization when alumina and water contents were at their highest. Only 8 of the 21 muscovite-biotite pairs analyzed are in hydrogen isotope equilibrium as calculated from the Suzuoki-Epstein equation. Biotites in the western half of the pluton have relatively low δ D-values of around −85‰, whereas those in the eastern half have higher values of up to −66‰ This pattern is a consequence of a loss of permeability associated with the syn-intrusive deformation of the western margin of the pluton. This loss of permeability enhanced the preservation of primary hydrogen isotope relations there by diverting water evolved from the magma out through the eastern half of the pluton where some deuteric exchange is documented. A much larger metamorphic aureole with extensive retrograde textures around the eastern end of the pluton attests to the passage of this water.

Rubidium as a Controlling Factor in Potassium Release from Micaceous Minerals

AbstractRubidium is ubiquitons in soils and minerals, occurring with K+. Ease of replacement of interlayer K+ for several samples of biotite, muscovite, vermiculite and vermiculite enriched in K+ and Rb+ was compared with Rb+ content to establish Rb+ as a controlling factor in K+ release. Release rates were determined by continuously leaching mineral samples with 0.01 mol/L CaCl2 at 298 K. Replaceability of interlayer K+ decreased as Rb+ content increased to 1% of the exchange sites. Data for K+ and Rb+ treated vermiculite fit the release trends for untreated mica samples. Rubidium is an important factor in the control of K+ replaceability of micaceous minerals.

40Ar/39Ar dating of terrestrial minerals with a continuous laser

A new method of fusing samples for 40Ar/39Ar dating using a continuous argon‐ion laser is presented. Samples of hornblende, biotite, muscovite and slate were fused with a continuous laser and the results obtained agree with acres determined using our radio‐frequency (RF) fusion system. By varying the laser beam power level, it was possible to perform a step‐heating laser fusion of the slate which closely matched two RF step‐heating runs on the same material. Thus, not only does the continuous laser give an age‐microprobe capability, but it can routinely perform multi‐step heating experiments which are crucial to 40Ar/39Ar age interpretation.

K–Ar and 40Ar/39Ar geochronology of granitoid rocks from southern Nova Scotia: Its bearing on the geological evolution of the Meguma Zone of the Appalachians

K–Ar and (or) 40Ar/39Ar apparent ages are reported for 28 samples of biotite and muscovite from Nova Scotia's South Mountain batholith and associated northern satellite stocks. In addition, 14 mica samples from the southern satellite stocks were dated. Previous workers, using primarily K–Ar and Rb/Sr techniques, have reported a spread of apparent ages ranging from ~240–420 Ma for these intrusive rocks. The present data set is internally consistent and has been calibrated against accepted interlaboratory standards. A mean age of 367 Ma was obtained for the South Mountain batholith and the northern stocks, a value consistent with results recently obtained in an Rb/Sr study by Clarke and Halliday. No differences in apparent age among the various phases or clear geographic age distribution patterns were evident. Satellite stocks in the southern part of the province have, in general, younger apparent ages clustered in the range ~300–320 Ma. We suggest that in southern areas mica–argon systems record the effects of a Late Carboniferous intrusive and (or) thermotectonic event. This conclusion may have important metallogenic implications.

Elution behaviour of alpha-recoil atoms into etchant and ovservation of their tracks on the mica surface

Muscovite samples, which were irradiated with alpha-recoil atoms emitted from a thinly electrodeposited 232U-source in a vacuum chamber of about 10 −2 Torr, were subjected to a chemical etching treatment with a hydrofluoric acid solution to develop alpha-recoil tracks. The transferred alpha-activities of 224Ra and 212Po, supported by 212Pb, on the mica surface were repeatedly measured after every etching treatment. The results showed that the 224Ra could be rapidly eluted out at earlier etching stages, in contrast to appreciably delayed elution of 212Po. These findings, along with annealing experiments on mica, imply that the recoil range of 224Ra, originated from the parent 228Th by a single decay process, is shorter than the total recoil range of 212Po, which can penetrate partially into inner mica layers through its preceding multiple alpha-decay processes after injection of its precursors into the mica. Scanning electron and phase-contrast microscopic observation of the etched mica surfaces indicated an apparent dependence of the recoil-track etch pit size on the number of succesive alpha-decays.

Oxygen isotopic fractionation between oxygen of different sites in hydroxyl-bearing silicate minerals

A method has been developed for extraction of hydroxyl oxygen from hydroxyl-bearing silicate minerals for oxygen isotopic analysis. The δO 18 of oxygen of the OH groups is significantly different from that in the rest of the mineral structure. The isotopic fractionation between the two types of sites has the potential to be a sensitive geothermometer. Several δO 18 values were obtained for oxygen of the OH attached to different silicate structures as well as for two muscovite samples with quantitatively estimated different temperatures of formation. The 1000 ln α (mineral-OH) values ranged from 5.2%. for muscovite to about 12.6%. for kaolinite and chlorite.

Determination of the water content in muscovites containing large amounts of fluorine by karl fischer titration after fusion with silicon dioxide

Complete release of water (or of hydrogen in the lattice which is finally released as water) from muscovite containing a large amount of fluorine, requires heating above 1500°C or addition of an appropriate flux. Experimental data from differential thermal analysis, x-ray diffraction patterns and dehydration curves showed that silicon dioxide is a useful flux. Samples are mixed with a 3 : 1 (weight) ratio of silicon dioxide in a platinum crucible and heated inductively in a nitrogen stream at 1200°C. The water released is absorbed in anhydrous (1 + 1) methanol—1, 2-ethanediol and titrated by the Karl Fischer method. For a representative muscovite sample, the water contents were 4.26 ± 0.03% at 1300—1400°C and 4.35 ± 0.08% above 1500°C in the absence of silicon dioxide. When silicon dioxide was added as described, the mean result was 4.33 ± 0.01% at 1200°C (95% confidence level) with a standard deviation of 0.015 and a coefficient of variation of 0.35%.

Infrared spectra of muscovites as affected by chemical composition, heating and particle size

AbstractNine muscovite samples from different localities were analysed for all major chemical elements and examined by infrared spectroscopy in the range of 4000–250 cm−1. Iron in the octahedral positions was found to cause an intensity decrease and shifting of some absorption bands. Other structural cations were found not to be effective in producing intensity and frequency changes due to the narrow variations in their amounts. Heating studies indicated that at about 800°C muscovite transforms into a dehydroxylated phase which is stable at least up to 1000°C. Particle size studies showed that 5 µm is the upper size limit for a representative spectrum.