Zeolite Group Minerals Research Articles

Zeolitized fossil woods from alkaline volcaniclastic rocks: Unravelling an uncommon mineralization process

Mineralization of fossil woods with unusual mineral phases remains an underconstrained process despite its relatively common occurrences. Aside from common mineralization agents such as silica or carbonates, there are also atypical mineralization associations, such as zeolite-group phases, but the zeolitization process has not yet been investigated in detail. We studied zeolitized woods collected from two localities in the Cenozoic alkaline České Středohoří Volcanic Complex (Ohře Rift, Czech Republic), where fossil woods of diverse paleobotanical classification were deposited in volcaniclastic rocks of the same origin (lahar) and stratigraphic formation (Upper Oligocene). The identical geological setting allowed the investigation of potential variables influencing this type of mineralization by combining paleobotanical classification, detailed mineralogy, mineral chemistry, geochemistry, Sr isotope analysis and KAr chronology.The new results demonstrate the significant potential of fossil woods mineralized with zeolite-group minerals to be used to reconstruct the formation and deposition conditions of the lahars in which these woods are contained. The composition of zeolites is strongly dependent on thermal conditions and material exchange between wood and host rocks. Dominant mineral phases are phillipsite and chabazite in variable proportions. The phillipsite/chabazite ratio correlates well with the magnitude of the Eu anomaly, suggesting crystallization of phillipsite at a higher temperature under hot-lahar conditions of deposition. Chabazite lacking an Eu anomaly represents the later, colder mineralization stage. The 87Sr/86Sr ratios ranging 0.7042–0.7047 provide an additional line of evidence of fluid derivation from volcaniclastic deposits of the Upper Oligocene Děčín Fm.

Mineral Composition and Structural Characterization of the Clinoptilolite Powders Obtained from Zeolite-Rich Tuffs

Clinoptilolite is a precious zeolite mineral that has the most comprehensive physicochemical properties among all the zeolite group minerals. Due to these unique properties, clinoptilolite has a wide range of applications in many different industries. In Poland, the clinoptilolite occurs only as an accompanying mineral in the sedimentary rocks nearby Rzeszów. In Europe, the abundant clinoptilolite-bearing deposits are located in Slovakia and Ukraine, where clinoptilolite mineralization occurs in the volcanic tuffs. Due to clinoptilolite’s rare performance, it is extremely crucial to manage its deposits in a complementary manner. In this paper, the mineralogical and structural characterization of the clinoptilolite powders obtained by mineral processing of the clinoptilolite-rich tuffs from Slovakia and Ukraine deposits were discussed. The scope of research covered determination of the mineral composition of the tuffs, structural analysis of the clinoptilolite crystals, as well as textural and physical properties of the powders obtained by mineral processing of the tuffs. In addition, this paper includes the comparative study of the most significant zeolite deposits in the world and investigated clinoptilolite-rich tuffs. A wide spectrum of methods was used: X-ray powder diffraction (XRD), thermal analysis (DSC, TG), X-ray fluorescence (XRF), optical microscopy, Scanning Electron Microscopy (SEM-EDS), the laser diffraction technique, and low-temperature nitrogen adsorption/desorption. The test results indicated that the major component of the tuffs is clinoptilolite, which crystallized in the form of very fine-crystalline thin plates. The clinoptilolite mineralization in the Ukrainian and Slovakian tuffs exhibited a strong resemblance to the clinoptilolite crystals in Yemeni and Turkish tuffs. With respect to the mineral composition, the investigated tuffs showed excellent conformity with the Miocene white tuffs from Romania. The Ukrainian and Slovakian tuffs do not reveal the presence of the clay minerals, which is quite common for naturally occurring zeolite-rich rocks in various deposits in the world. The textural features together with mineral composition of the investigated samples incline that they are potentially suitable raw materials for the sorbent of petroleum compounds. Moreover, the obtained results can be useful indicators with respect to the crushing and compaction susceptibility of the Ukrainian and Slovakian clinoptilolite-rich tuffs.

Geological features and resource potential of deep-sea mud highly enriched in rare-earth elements in the Central Pacific Basin and the Penrhyn Basin

Deep-sea mud enriched in rare-earth elements and yttrium (REY-rich mud) has been recognized as a new resource for REY and scandium (Sc). Recently, highly REY-rich mud with more than 2,000 ppm of REY was found in the western North Pacific Ocean. The high REY content was attributed to enhanced deposition of fish debris, which acts as a host for REY, resulting from fish proliferation caused by topographically induced upwelling of nutrients. To investigate the spatial extent of the highly REY-rich mud, we conducted mineralogical and chemical analyses on selected sediment cores collected near topographic highs in the Central Pacific Ocean. The maximum REY content of the study cores was 4,489 ppm. The correlation between REY contents and abundance of fish debris indicated that the presence of large amounts of fish debris was responsible for the REY enrichment. The results of the mineralogical analysis suggested that there are three layers of REY-rich mud on the basis of the presence/absence of zeolite group minerals in the study cores. The first layer with phillipsite formed as a result of fish proliferation due to interactions between water currents and topography in the latest Eocene to early Oligocene. The layers with clinoptilolite probably formed as the result of an increased depositional flux of fish debris in the equatorial high-surface-productivity area in the middle Eocene. The layer without zeolite group minerals likely formed in relation to increased fish debris production caused by increased biological activity and high ecosystem efficiency together with slow sedimentation of other components in the South Pacific Gyre. Calculation of the resource amount in a 1-km2 area around the study sites, based on mining to the depth where the average grade is maximum when mined from the surface, revealed that the highly REY-rich mud could provide 1.4% of the global annual mine production of REY and 0.8–1.3 times the global annual supply of Sc. This finding suggests that REY-rich mud in the Central Pacific Ocean is a prospective REE resource.

Влияние цеолитизации на миграцию пластовых флюидов на примере юрских и неокомских отложений (Ямальский нефтегазоносный район)

To assess the influence of zeolite group minerals on the migration of reservoir fluids in terrigenous deposits, complex (X-ray and gas-geochemical) studies of core material in the Yamal oil and gas region field were conducted. 54 core samples from the Pyakyakhinsky and Yuzhno-Messoyakhsky deposits were studied including 43 zeolitized and 11 non-zeolitized samples. The core samples were studied by gas chromatography to determine the content of hydrocarbons adsorbed in the pore space of the core, as well as by X-ray diffractometry to determine the mineral composition of the samples under study. The regularities of hydrocarbons distribution in the studied samples depending on the degree of their zeolization are established. The differences in the distribution of hydrocarbons in zeolitized and non-zeolitized siltstones have their own explanation. Having an ordered crystal structure and a certain size of the entrance windows zeolites are able to sorb.

Interaction between mafic dike rocks and salt deposits in the Rhine Graben, southwest Germany

ABSTRACT Dikes of primitive olivine melilitites and monchiquites intruded into an Oligocene (Rupelian) potash salt deposit near Buggingen (SW Germany). Ocelli and amygdules reveal distinct mineral assemblages depending on whether the dike rocks are in direct contact with the potash layer or with bituminous shales (Fish Shale). Samples in contact with the potash salt layer show roundish textures that contain smectite ± talc ± chlorite, calcite, and in cases anhydrite and halite, while those close to the bituminous shale mainly comprise smectite, calcite, zeolite group minerals, and analcime. No textural or mineralogical evidence for high-temperature (magmatic) interaction between the dike rocks and the evaporites was observed. This is presumably related to (1) a very low magmatic water activity in the magma, which prevented exsolution of aqueous fluids and appreciable dissolution of the salt, and (2) fast cooling of the magmas, inhibiting melting of the salt deposits and potential liquid mingling and/or assimilation processes. Halite formation in the dike rocks is, rather, related to later, post-magmatic hydrothermal fluids that previously interacted with the salt-rich host rocks. Alteration of the initially glassy groundmass to smectites and zeolites caused an enrichment of Na in the residual fluid, but halite saturation was not attained, as indicated by the absence of groundmass halite. Only fluid–rock interaction in millimeter-sized vugs caused halite precipitation via desiccation by swelling of previously formed clay minerals. Locally, the boron silicate datolite formed in pseudomorphs after olivine. Its precipitation was controlled by the Si and B supply provided by the breakdown of serpentine and smectite.

Unmixing of hyperspectral data for mineral detection using a hybrid method, Sar Chah-e Shur, Iran

This study aims to detect indicative minerals by spectral unmixing of the Hyperion and HyMap datasets in the Sar Chah-e Shur area. The mineral endmembers and their abundances were therefore determined using a series of hyperspectral processing algorithms. The virtual dimensionality methods including principal component analysis (PCA), minimum noise fraction (MNF), singular valued decomposition (SVD), Harsanyi-Farrand-Chang (HFC)/ (NWHFC), and Hyperspectral signal subspace identification by minimum error (HySime) were applied to estimate the number of endmembers. Five pure pixel-based methods including pixel purity index (PPI), sequential maximum angle convex cone (SMACC), simplex growing algorithm (SGA), N-FINDR, and vertex component analysis (VCA) were then applied for extracting the spectra of endmembers. Clay, serpentine, mica, and zeolite group minerals were identified which are consistent with the geological investigations in the region. The detected minerals were then mapped by the fully constrained least square (FCLS) method. The functionality of the methods and their performances on HyMap and Hyperion data were surveyed by several criteria including the number of recognized endmembers, the matching score of extracted endmembers with the reference spectrum, the agreement of the estimated abundances maps with the relevant lithological units on the geological map, and the average reconstruction error (ARE). Two hybrid maps were generated by combining individual methods that were found highly consistent with the geological map. The XRD analysis of three chips rock samples of two indicative lithological units was used to additionally check the efficiency of the applied methods.

Zeolite-group minerals in phonolite-hosted deposits of the Kaiserstuhl Volcanic Complex, Germany

Zeolite-group minerals in phonolite-hosted deposits of the Kaiserstuhl Volcanic Complex, Germany

Effect of zeolitite addition on soil properties and plant establishment during forest restoration

Zeolitites, rocks with a content of zeolite group minerals greater than 50%, can serve as support for plant nutrients uptake, by enabling the slow release of macro- and micronutrients over time. Zeolitites equally improve soil cation exchange and water holding capacity. We analyzed the effect of zeolitite addition to the soil in forest restoration. We hypothesized that zeolitite ameliorated soil quality and consequently improved sward restoration and seedling establishment.Soil treatments were applied in 2014 and consist of: ploughed and ripped soil (non-amended) and ploughed, ripped and amended with zeolitite soil (amended).After application of the soil treatments, a herbaceous mixture was hand sown. Oak (Quercus robur L.), hawthorn (Crataegus monogyna Jacq.) and elm (Ulmus minor Mill.) seedlings were planted twice in the area, in autumn 2014 and autumn 2015. We monitored soil, sward and seedlings from 2015 to 2017. Seedling survival, which was generally above 50%, was never affected by zeolitite addition. The effect on seedling growth was significant only for hawthorn planted in 2015 that was approximately 5 cm taller in the amended soil. Herbaceous vegetation was also slightly affected by zeolitite addition. The zeolitite increased nitrogen (N) and phosphorus (P) Olsen in 2015, and exchangeable potassium (K) during the whole study period. Other parameters, such as year and growing season had significant effects on soil, sward and seedling dynamics. Time since restoration, plant-plant interactions, mechanical site preparation and meteorological conditions all together influenced the restoration dynamics more than zeolitite application.

Mineralogical and Geochemical Constraints on Magma Evolution and Late-Stage Crystallization History of the Breivikbotn Silicocarbonatite, Seiland Igneous Province in Northern Norway: Prerequisites for Zeolite Deposits in Carbonatite Complexes

The present work reports on new mineralogical and whole-rock geochemical data from the Breivikbotn silicocarbonatite (Seiland igneous province, North Norway), allowing conclusions to be drawn concerning its origin and the role of late fluid alteration. The rock shows a rare mineral association: calcite + pyroxene + amphibole + zeolite group minerals + garnet + titanite, with apatite, allanite, magnetite and zircon as minor and accessory minerals, and it is classified as silicocarbonatite. Calcite, titanite and pyroxene (Di36–46 Acm22–37 Hd14–21) are primarily magmatic minerals. Amphibole of mainly hastingsitic composition has formed after pyroxene at a late-magmatic stage. Zeolite group minerals (natrolite, gonnardite, Sr-rich thomsonite-(Ca)) were formed during hydrothermal alteration of primary nepheline by fluids/solutions with high Si-Al-Ca activities. Poikilitic garnet (Ti-bearing andradite) has inclusions of all primary minerals, amphibole and zeolites, and presumably crystallized metasomatically during a late metamorphic event (Caledonian orogeny). Whole-rock chemical compositions of the silicocarbonatite differs from the global average of calciocarbonatites by elevated silica, aluminium, sodium and iron, but show comparable contents of trace elements (REE, Sr, Ba). Trace element distributions and abundances indicate within-plate tectonic setting of the carbonatite. The spatial proximity of carbonatite and alkaline ultramafic rock (melteigite), the presence of “primary nepheline” in carbonatite together with the trace element distributions indicate that the carbonatite was derived by crystal fractionation of a parental carbonated foidite magma. The main prerequisites for the extensive formation of zeolite group minerals in silicocarbonatite are revealed.

Phase relations of lawsonite-blueschists and their role as a water-budget monitor: a case study from the Hakoishi sub-unit of the Kurosegawa belt, SW Japan

This study investigated progressive changes in the mineral assemblage of a Palaeozoic lawsonite-blueschist (LBS) unit of the Kurosegawa belt, Kyushu, Japan. The LBS unit is mainly composed of intercalated metachert and metabasaltic rocks surrounded by serpentinite. Based on the spatial distribution of mineral assemblages in the metabasaltic rocks, three mineral zones can be identified in a ~10 km-long east–west oriented unit: (1) a pumpellyite (Pmp) + Na amphibole (Namp) assemblage dominated area (Zone 1); (2) an intermixed area of lawsonite (Lws) + Na/Ca-Na pyroxenes +(Napx) + Pmp and Lws + Namp + Pmp assemblages (transition zone); and (3) an area dominated by Lws + Namp + Napx assemblages (Zone 2); all contain excess chlorite (Chl), albite (Ab), quartz (Qz), titanite (Ttn), and goethite. Napx varies in composition from jadeite(Jd) 20 -diopside(Di) 25 of Zone 1 to Jd 35 Di 15 in Zone 2, with a similar range of aegirine (Aeg) content from 40 to 55 mol%. The Al/(Al + Fe 3+ ) ratio of Na amphibole (= Y Amp ) associated with Lws and Pmp increases from Y Amp = 0.2 in Zone 1 to Y Amp = 0.8 in Zone 2. The Jd contents and the lack of epidote and zeolite-group minerals suggest that the pressure ( P ) conditions of the BS increase from Zone 1 (0.50 GPa) to Zone 2 (0.75 GPa) between 200 and 300 °C, suggesting a low geothermal gradient (~5 to 10 °C/km). Schreinemakers’ analyses in a NaCaMgFe 3+ AlSiH (NCMF3ASH) system, using mean mineral compositions of representative samples and excess Chl, Ab, Qz and H 2 O, suggest that, (1) observed variation in mineral assemblages can be explained by the hydration reaction Pmp + Napx + Chl + H 2 O = Lws + Namp, which was driven by a P increase from Zone 1 to Zone 2, and represents the transition from the Pmp-BS to the Lws-BS sub-facies; (2) the total H 2 O content stored in hydrous minerals increases from 3.6 wt% in the Pmp-Namp assemblage of Zone 1 to 5.0–6.4 wt% in the Lws + Namp + Napx assemblages in Zone 2; and (3) the Napx + Chl assemblage can retain a significant amount of H 2 O, along with the Lws-Namp and Pmp-Namp assemblages, and its stability field can expand to higher P conditions by decrease of the Di and increase of the Jd and Aeg contents in Napx.

Occurrence, composition and paragenesis of the zeolites and associated minerals in the alkaline basalt of a maar-type volcano at Haláp Hill, Balaton Highland, Hungary

AbstractHaláp Hill is an eroded remnant of young (∼3 Ma) alkaline basalt in the western part of the Bakony–Balaton Highland Volcanic Field, Tapolca, Hungary. Cavities in the basalt contain miarolitic minerals (augite, apatite, magnetite, plagioclase and sanidine), zeolites (analcime, chabazite-Ca, chabazite-Na, garronite, gismondine, gmelinite-Ca, gmelinite-Na, gobbinsite, gonnardite-Na, natrolite, mesolite, phillipsite-Ca, phillipsite-K, phillipsite-Na and scolecite) and other secondary minerals (calcite, smectite-group minerals, goethite and Mn-oxides). Chabazite-Na, gmelinite-Ca, gonnardite-Na, phillipsite-Na and phillipsite-K are reported from Haláp Hill for the first time. The Ca-rich and Na-rich zeolites and abundant calcite were produced by hydrothermal alteration. Mineral assemblages were characterized by X-ray diffraction, differential thermal analysis, energy-dispersive spectrometry and wavelength-dispersive spectrometry. The secondary mineral assemblages were probably formed as a result of low-temperature hydrothermal activity at 50—100°C. Miarolitic minerals crystallized first in cavities in the basalt; they were followed by zeolite-group minerals and calcite. Analcime and phillipsite with or without chabazite/gmelinite/garronite or gobbinsite were the first zeolite-group minerals to crystallize; gonnardite-Na and natrolite crystallized later from Na-rich fluids. Calcite and smectite-group minerals crystallized continually. This paragenetic sequence is similar to others which have been reported in basalt from other localities in the Balaton Highland, Iceland and Northern Ireland.

The Magmatic to Hydrothermal Evolution of the Intrusive Mont Saint-Hilaire Complex: Insights into the Late-stage Evolution of Peralkaline Rocks

The Cretaceous Mont Saint-Hilaire complex (Quebec, Canada) comprises three major rock units that were emplaced in the following sequence: (I) gabbros; (II) diorites; (III) diverse partly agpaitic foid syenites. The major element compositions of the rock-forming minerals, age-corrected Nd and oxygen isotope data for mineral separates and trace element data of Fe-Mg silicates from the various lithologies imply a common source for all units. The distribution of the rare earth elements in clinopyroxene from the gabbros indicates an ocean island basalt type composition for the parental magma. Gabbros record temperatures of 1200 to 800 degrees C, variable silica activities between 0 center dot 7 and 0 center dot 3, and f(O2) values between -0 center dot 5 and +0 center dot 7 (log delta FMQ, where FMQ is fayalite-magnetite-quartz). The diorites crystallized under uniform a(SiO2) (a(SiO2) = 0 center dot 4-0 center dot 5) and more reduced f(O2) conditions (log delta FMQ similar to-1) between similar to 1100 and similar to 800 degrees C. Phase equilibria in various foid syenites indicate that silica activities decrease from 0 center dot 6-0 center dot 3 at similar to 1000 degrees C to < 0 center dot 3 at similar to 550 degrees C. Release of an aqueous fluid during the transition to the hydrothermal stage caused a(SiO2) to drop to very low values, which results from reduced SiO(2) solubilities in aqueous fluids compared with silicate melts. During the hydrothermal stage, high water activities stabilized zeolite-group minerals. Fluid inclusions record a complex post-magmatic history, which includes trapping of an aqueous fluid that unmixed from the restitic foid syenitic magma. Cogenetic aqueous and carbonic fluid inclusions reflect heterogeneous trapping of coexisting immiscible external fluids in the latest evolutionary stage. The O and C isotope characteristics of fluid-inclusion hosted CO(2) and late-stage carbonates imply that the surrounding limestones were the source of the external fluids. The mineral-rich syenitic rocks at Mont Saint-Hilaire evolved as follows: first, alkalis, high field strength and large ion lithophile elements were pre-enriched in the (late) magmatic and subsequent hydrothermal stages; second, percolation of external fluids in equilibrium with the carbonate host-rocks and mixing processes with internal fluids as well as fluid-rock interaction governed dissolution of pre-existing minerals, element transport and precipitation of mineral assemblages determined by locally variable parameters. It is this hydrothermal interplay between internal and external fluids that is responsible for the mineral wealth found at Mont Saint-Hilaire.

Sr-Na-bearing åkermanite and nepheline in nephelinite from Nagahama, Hamada, Shimane Prefecture, Southwest Japan

Akermanite and nepheline found within melilite-olivine nephelinite in Nagahama Plateau, Hamada city, Shimane Prefecture, Southwest Japan, were investigated to characterize their occurrence and chemical compositions. Samples of massive and dense blue-gray melilite-olivine nephelinite were collected from a Naka-Uchida tunnel construction site. Their bulk composition is characterized by an extremely low SiO2 content of 35.75 wt% and high Sr and Ba contents, reaching 2091 ppm and 958 ppm, respectively. Forsterite, akermanite, augite, ulvospinel and apatite occur as microphenocrysts. Nepheline occurs as an interstitial mineral between these microphenocrysts. Euhedral nepheline, zeolite-group minerals, diopside and calcite occur in druses. Akermanite occurs as prismatic to anhedral microphenocrysts. The rims of the akermanite microphenocrysts are dissolved and overgrown by augite. Akermanite has an average composition of (K0.011Na0.390Ba0.004Sr0.031Ca1.566)Σ2.002(Mn0.007Fe2+0.088Mg0.457Ni0.001Fe3+0.134Cr3+0.001Ti0.003Al0.295)Σ0.986(Al0.074Si1.926)Σ2.000O7, and contains up to 4.62 wt% Na2O, 1.68 wt% SrO, and 0.64 wt% BaO. Calculated Fe2O3 and FeO based on charge balance are 5.36 wt% and 3.11 wt%, respectively. Fe2+/(Fe2+ + Fe3+) ratios estimated from the FeLβ/FeLα intensity ratios range from 0.47 to 0.79, indicating that a considerable amount of Fe3+ is contained within akermanite. The chemical composition of nepheline in the groundmass is (Na0.655K0.304)Σ0.959(Fe3+0.025Al0.978)Σ1.003(Al0.012Si0.988)Σ1.000O4 on average. No excess SiO2 nor anorthite components were detected. The bulk composition of the Hamada melilite-olivine nephelinite and the compositions of akermanite and nepheline are similar to those of equivalents from the carbonatite-nephelinite-phonolite Oldoinyo Lengai volcano in Tanzania. This similarity may support the proposed genetic model that the Hamada nephelinite magma was derived from a source material formed by carbonate metasomatism of a lherzolite upper mantle.

RECONSTRUCTION OF MAGMATIC TO SUBSOLIDUS PROCESSES IN AN AGPAITIC SYSTEM USING EUDIALYTE TEXTURES AND COMPOSITION: A CASE STUDY FROM TAMAZEGHT, MOROCCO

The Eocene Tamazeght (or Tamazert) complex, situated in the High Atlas Mountains of Morocco, comprises a suite of ultramafic to syenitic alkaline to peralkaline units cross-cut by carbonatite diatremes, and dyke rocks of both carbonatite and silicate lithology. In spatially restricted areas, the most evolved silicate unit of the complex (malignites) contains eudialyte-group minerals (EGM) as index phases for agpaitic systems. The chemical composition of EGM is closely related to their textural position; the EGM are stable over a wide range of temperature and chemical composition and readapt their composition to changing subsolidus conditions, including infiltration of external fluids. Therefore, EGM are a powerful petrogenetic indicator in agpaitic systems. Petrography and compositions of EGM record all stages of the (late-) magmatic to subsolidus history including (1) effects of an autometasomatic fluid, (2) infiltration of a fluid derived from associated carbonatites, and (3) opening of the system to meteoric fluids. During the late-magmatic stage 1, the crystallization of interstitial EGM is accompanied by intensive albitization of surrounding feldspars. The replacement of nepheline by sodalite occurs at the postmagmatic stage 2, when primary sector-zoned EGM are cross-cut by irregular bright zones in BSE image that are enriched in Sr, Mn, rare-earth elements (REE) and high field-strength elements (HFSE). Enrichment of these elements in distinct schlieren-like zones in EGM combined with the formation of Ca- and CO2-rich minerals of the cancrinite group points to the associated carbonatites as the potential source of fluid. The latest modifications (3) include the formation of zeolite-group minerals and calcite, which are believed to be a result of the interaction of the rocks with low-temperature meteoric fluids, probably in equilibrium with the surrounding country-rocks.

Brewsterite–Ba and Harmotome from the Wicklow Lead Mines, Co. Wicklow, Ireland

The zeolite group minerals brewsterite–Ba and harmotome occur as minor latestage primary phases in the low-temperature Pb–Zn veins at Glendalough and Glendasan, Co. Wicklow. Brewsterite–Ba was identified on a single specimen from the Old Luganure Mine. Harmotome occurs at the Glendalough Mine, the Foxrock Mine and the Old Luganure Mine. Quantitative analyses of crystals of brewsterite–Ba reveal the most barium-rich composition yet reported: (Ba1.88, Sr0.02, K0.01, Na0.01) [Al4.03Si12.02O32]·nH2O. This is close to the hypothetical barium end member. The harmotome is also barium-rich. It contains lesser amounts of sodium and potassium, but no calcium. This is the first record of brewsterite–Ba from Ireland.

Brewsterite-Ba and Harmotome from the Wicklow Lead Mines, Co. Wicklow, Ireland

The zeolite group minerals brewsterite-Ba and harmotome occur as minor latestage primary phases in the low-temperature Pb-Zn veins at Glendalough and Glendasan, Co. Wicklow. Brewsterite-Ba was identified on a single specimen from the Old Luganure Mine. Harmotome occurs at the Glendalough Mine, the Foxrock Mine and the Old Luganure Mine. Quantitative analyses of crystals of brewsterite-Ba reveal the most barium-rich composition yet reported: ($Ba_{1.88},Sr_{0.02},K_{0.01},Na_{0.01}$) [$Al_{4.03}Si_{12.02}O_{32}$]-$nH_{2}O$. This is close to the hypothetical barium end member. The harmotome is also barium-rich. It contains lesser amounts of sodium and potassium, but no calcium. This is the first record of brewsterite-Ba from Ireland.

Classification of zeolite group minerals based on the new definition and some problems

Classification of zeolite group minerals based on the new definition and some problems

GEOLOGY AND MINERALOGY OF THE LITTLE NAHANNI RARE-ELEMENT GRANITIC PEGMATITES, NORTHWEST TERRITORIES

The Little Nahanni rare-element granitic pegmatite group (LNPG; ca. 82 Ma) in the western part of the Northwest Territories, occurs as subparallel dike swarms over an area of ~11 × 5 km in the walls of a series of cirques dominated by schists of the Upper Proterozoic Hyland Group. These pegmatite bodies, up to a few meter wide, are divisible into spodumene-bearing and spodumene-free varieties that occur close together; some dikes split into these two variants. The two types are mineralogically similar. Both contain K-feldspar, plagioclase, quartz, mica (muscovite to lepidolite), columbite-group minerals, cassiterite, tourmaline, beryl, lithiophilite and garnet; they differ in the abundance of mica and accessory phases. The spodumene-free pegmatites have more mica, particularly lepidolite, than the spodumene-bearing variety. Apatite and montebrasite occur primarily in the former, whereas most lithiophilite is present in the latter. Sparse galena, titanian rutile, fluorite and helvite are also found in both variants. Subsolidus phases are zeolite-group minerals, microlite, and secondary phosphate minerals such as triploidite. Internal zoning in both pegmatites varies from complex to symmetrical. Where well developed, the zoning is typical from border through wall and intermediate to core zone. Quartz and the feldspars occur throughout the dikes. Micas and columbite-group minerals initially increase from the border to the wall zone and subsequently decrease toward the core, whereas tourmaline becomes less abundant toward the core. Spodumene and cassiterite first appear in the wall zone and become more abundant toward the core zone, whereas the reverse is true for beryl. Phosphate minerals exist mainly in the intermediate zone of the lepidolite pegmatites, and lithiophilite in the spodumene pegmatites. Garnet remains a trace mineral in all zones, with the exception of the core zone. where it is absent. Sporadic small cavities containing quartz, K-feldspar, apatite, Mg-rich beryl, elbaite and calcite are present in some dikes. The composition of the rock-forming minerals in both types of pegmatite is similar. An example of the chemical evolution of the minerals is shown by tourmaline, which becomes richer in Al and Li, but poorer in Mg, and shows decreasing Na/(Na + vacancy) and increasing Al/(Al + Fe) values from the schist to the inner (wall + intermediate) zone of the pegmatite. These trends, together with the changes in the abundances and paragenetic sequence of the major minerals, are interpreted to reflect an increase in the Rb, Cs, Li, F, P, Be, and Ta contents, and a decrease in the contents of Mg, Fe, and B contents, in the felsic liquids during crystallization.

Kaolin Occurrences in the Erenler Dagi Volcanics, Southwest Konya Province, Turkey

Mainly calc-alkaline, andesitic, and dacitic volcanics from different late Miocene-Pliocene eruption centers crop out WSW of Konya, and locally are interbedded with lacustrine sediments. Hydrothermal alteration within these rocks is widespread. In addition to kaolinite, other major alteration products include halloysite, alunite, cristobalite, quartz, illite, montmorillonite, and zeolitegroup minerals. Based on the cristobalite-quartz relationship, the kaolinization temperature is estimated as ∼100°C. The samples were mineralogically and chemically examined using XRD, SEM-EDS, IR, DTA-TG, and XRF. The crystallinity of the kaolinite is moderate, and shows structural disorder. Both the kaolinite and halloysite are almost stoichometric. Kaolinization generally led to Al2O3 increases and release of alkalies, alkaline earths, most of the Fe2O3, and SiO2. SiO2 and Al2O3 contents are low, and LOI is very high for halloysite deposits relative to kaolin occurrences. The kaolinite-alunite assemblages indicate that pH of the altering solutions initially was ∼4. SEM investigation demonstrates that kaolinite has booklet texture, whereas halloysite is acicular to needleshaped. The chemical, mineralogic, and firing properties of the kaolin deposits are appropriate for use as refractory raw material. The Erenler Dagi kaolin deposits are excellent examples of the acid-sulfate type of hydrothermal alteration. The findings of the study may be useful in exploration for similar hydrothermal mineral occurrences worldwide.

エネルギー分散型電子線マイクロアナライザーによる沸石族の定量分析

This paper reports a technique of quantitative micro-analysis of zeolite group minerals by electron-probe microanalyzer with an energy-dispersive spectrometer system. Natural analcite, laumontite, heulandite and stilbite were used as reference samples. To avoid radiation damages of zeolites, beam diameters of quantitative analysis for each zeolite are set as follows; analcite and laumontite can be analyzed by defocused beam with ca. 5 microns in diameter, our laboratory routine analytical conditions, heulandite and stilbite have to be analyzed by scanning beam with 12.5 microns square or more.Heulandite and stilbite have the same anhydrous formula of CaAl2Si7O18; A water content of heulandite with ideal formula is 15.74 wt.% and that of stilbite with ideal formula is 17.89 wt.%. In analyzing these zeolites, total weight percent of anhydrous oxides sometimes falls between the values expected for two zeolites with ideal formula. As precision of analysis of the crystalline water for two zeolites, which were estimated by the difference between 100 and total weight percent of anhydrous oxides determined, is less than 2 wt.%, the varying anhydrous total is considered real. Thus, the zeolites which have intermediate composition between heulandite and stilbite can not be identified by the present procedure.