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Zeolite-bearing trachyandesite from Dobranka, Ceske stredohori Mts.: petrography, geochemistry and amygdale mineralogy.

1. INTRODUCTION

Mineralogical, petrological and geochemical investigations were carried out on an only poorly known lava flow of zeolite-bearing trachyandesite exposed in a deep valley of the Dobrnsky potok Creek (NE of Decin-Bfeziny). Dobranka is the traditional name of this valley established in the older literature, e.g., Hibsch (1915). The first mineralogical and petro-graphic description of the locality was presented as early as by Hibsch (1915). Short mineralogical notes on natrolite, thomsonite, phillipsite, gismondine and analcime assemblages were presented by Muhlstein and Fengl (1977), gmelinite by Barta and Rychly (1979) and Rychly et al. (1980), phillipsite by Rychly and Barta (1981) and epitaxial intergrowths and overgrowths of natrolite and thomsonite by Ulrych and Rychly (1986). Among similar localities in the vicinity, the zeolite locality of Pusty vrch (Schie-chenberg) near Folknafe is characterized by the presence of thomsonite, chabazite, phillipsite and gismondine occurring in amygdales of a lava flow of "leucite" tephrite composition (Tucek 1962). Other famous mineralogical locality of zeolites (natrolite, analcime, phillipsite, mesolite, thomsonite) together with apophyllite, calcite and chlorite was described by Bouska and Malec (1971) in amygdales of a basanite intrusion near Soutesky.

The present paper was stimulated by the revision of older mineral specimens and newly collected samples provided by the Municipal Museum of the Town of Usti nad Labem within the grant project of the Ministry of Culture of the CR, and a revision of samples kept by mineral collector Josef Barta from Decin. The absence of a modern petrological study of the host rock of zeolites also motivated the origin of the herein presented study on petrography, rock-forming minerals and geochemistry of the host rock of anomalous feldspathoidal trachyandesite composition in the Ceske stfedohofi Mts.

The studied mineralogical material is deposited in the Municipal Museum of the Town of Usti nad Labem (Muzeum Mesta Usti nad Labem) and the Institute of Geochemistry, Mineralogy and Mineral Resources, Charles University, Prague (Ustav geochemie, mineralogie a nerostnych zdroju PfF UK Praha).

2. GEOLOGICAL SETTING

The Dobranka zeolite locality lies in the NE part of the Ceske stredohori Mts., SE of town Decin and within the Dobrnsky potok Valley. Conditions favouring zeolitization occurred in a terrestrial lava flow of amygdaloidal trachyandesite, which belongs among volcanic products of the Ceske stfedohofi Mts. Using volcanological and geochemical criteria, feldspatho-idal trachyandesite lava flow is ranked within the Decin Formation (Cajz, 2000; Ulrych et al., 2001). It poses an erosional relict of a trachybasaltic (Cajz et al., 1999) composite volcano (stratovolcano), which formerly covered a much larger area, overlying the Cretaceous sediments and older volcanic rocks. A high proportion of the volcaniclastics occurring together with thin lava flows suggests high explosive activity of the volcanic events during the deposition of the Decin Fm. (30.8-24.7 Ma). Volcaniclastic rocks containing particles of volcanic glass, also known in redeposited form, prevail in volume over lava flows and sheets, forming favourable hydrogeological environment for pore fluids. The Dobranka trachyandesite flow occurs in the lower sequence of the Decin Formation. Hibsch (1915) recognized at least two petro-graphically different sets of lavas in the Dobranka area: (i) the lower set of nepheline to sodalite "teph-rites" with a tendency towards feldspathoidal trachyandesite (e.g., Dobranka locality), and (ii) the upper set of "leucite" tephrites (pseudoleucite). The rock association of the lower set (i) also includes the tephrite sill from the Bechlejovice borehole, dated by Bellon et al. (1998) at 26.3 Ma, and the augitite dyke exposed in the northern slope of Hlidka Hill (Hibsch 1915). Occurrences of lava flows on Hlidka Hill (440 m a.s.l.) and the northern slope above the Dobranka locality are composed of (pseudo)leucite tephrite pertaining to the upper set (ii). Thomsonite crystals were described by Hibsch (1915) from a strongly vesicular facies of the highest lava flow at the base of Pusty vrch Hill (490 m a.s.l., NW of Dobranka).

The studied feldspathoidal trachyandesite lava flow was exposed by erosion in the valley of the Dobrnsky potok Creek, particularly in its right bank, NE of Bfeziny (altitude of 270-280 m a.s.l.). Newly studied zeolite specimens come from two places, both lying immediately below the road Bfeziny-Dobrna: (1) the upper locality is represented by exposures in the upper part of the incised lava flow (vesicular and amygdaloidal facies) and (2) the lower locality near the building at an abandoned dam (both vesicular and massive varieties) represents the lower part of the same lava flow, however, subjected to landsliding. The upper part of the lava flow became vesicular and scoriaceous due to lava degassing, and strongly affected by postmagmatic zeolitization evidencing volatile-phase activity after the eruption. Larger empty amygdales (cylindrical, up to 10 cm by 2 cm in size) are elongated subhorizontally due to flow movement.

2.1. SMALL-SCALE TECTONICS

Small-scale brittle tectonic structures in the trachyandesite flow are fewer than in other exposed bodies in the Ceske stfedohofi Mts. Moreover, the cliffs on the southern bank of the Dobrnsky potok Creek are incorporated into a large gravitationally displaced block. Prominent contraction planes dipping W to NW at very low angles are combined with pseudo-columnar jointing on the southern bank of the Dobrnsky potok Creek (Fig. 1). It is interesting that the outcrops on the southern bank are dominated by NW-SE-stri-king subvertical joints passing into cylindrical planes, whose axes dip NW at low angles. These joints are combined with a set of NE-SW-striking planes filled with carbonate mineral to form a paired system. Joints dipping SE to ESE at medium angles and bearing fine subhorizontal striae are less frequent. These structures may be compatible with the ENE-WSW compression identified at Marianska hora Hill in Usti nad Labem (Ulrych et al., 2000).

3. METHODS OF INVESTIGATION

Textural development of crystal aggregates, crystal habit and succession were studied mostly under binocular microscope. Textural details of amygdale aggregates were shown more clearly using secondary electron image. Twenty-five key samples with amygdale minerals were subjected to detailed investigations of successive relations (choice from more than 150 selected samples for the genetic investigation). The identification of individual crystals or aggregates separated from amygdales was carried out by the X-ray diffraction using DRON-2 instrument with a CuK[alpha] source at the Faculty of Science, Charles University, Prague, and by electron microprobe. Chemical composition of amygdales as well as rock-forming minerals determined in polished sections was performed using JEOL XM-50A electron microprobe equipped with EDX PV 9400 at the Institute of Geology of the Academy of Sciences, Prague. Operating conditions were 15 kV accelerating voltage, 20 nA beam current, 60 s account timing, and ZAF matrix correction program. Combined natural and synthetic minerals were used as appropriate standards. The reliability of all zeolite analyses was expressed by the "balance error" E (%) varying in the range of [+ or -] 10 % using the Passaglia's (1970) equation.

Two samples of trachyandesite representing two principal facies: DO-1-1 (fresh material without amygdales) and DO-1-2 (zeolitized sample with numerous amygdules), were taken for petrographic and geochemical studies. Major and trace elements were analysed by XRF in the Gematest Laboratory, Cernosice (analyst M. Strublova). The REE abundances were measured by INAA method at the Nuclear Physics Institute, Rez near Prague (analyst J. Frana).

[FIGURE 1 OMITTED]

4. PETROGRAPHY

Both the studied rock samples are porphyritic, with a small amount of phenocrysts formed by ferrifassaite passing to sodic ferrifassaite with kaersutite rims, oligoclase-andesine, and minor zeolitized feldspathoid. Andesine to oligoclase ([An.sub.27-30]) predominate over sodic sanidine and scarce clinopyroxene and titanomagnetite in the matrix of fresh trachyandesite facies. Megacrysts and/or mafic xenoliths are usually absent but clustering of clinopyroxene microphenocrysts is relatively frequent. The facies of zeolitized trachyandesite shows predominance of pseudomorphosed minerals over primary relict minerals.

The well-preserved igneous texture of fresh trachyandesite is trachytic as shown by fluidally aligned plagioclase laths up to 0.7 mm long. Vesicles in this rock facies are rare. A small amount of pseudomorphs after feldspathoid (sodalite?) is also present. The succession during magmatic crystallization was as follows: microphenocrysts of salite to fassaite, feldspathoid and matrix assemblage of oligoclase-andesine mantled by Na-sanidine and titanomagnetite. Owing to the activity of postmagmatic hydrothermal fluids, a complete conversion of feldspathoid (nepheline, sodalite?) preceded secondary thomsonite-gonnardite crystallization.

PHENOCRYSTS

Clinopyroxene phenocrysts (0.2 to 2.1 mm) show a wide range of textures and oscillatory zoning from ferrifassaite yellow-green cores to darker green sodium ferrifassaite rims studded with fine opaque inclusions. A tendency towards glomerophyric clustering, sometimes with kaersutite, was often observed. Opacitized rims around larger clinopyroxene pheno-crysts are much thinner than those around the kaer-sutite ones. Titanomagnetite also forms thin veinlets in fractured grains. Apatite needles (0.1 to 0.15 mm long) occur as inclusions. Larger kaersutite pheno-crysts, reddish brown in colour, tend to be anhedral as well as skeletal or lobate in their habit when replacing fractured clinopyroxene. They are unzoned, up to 2 mm long, with wide opaque rims. They occur in the same quantity as clinopyroxene.

Plagioclase phenocrysts form euhedral laths with a tendency to indistinct zoning. Chemistry of these plagioclases corresponds to oligoclase ([An.sub.22-28]), varying, however, on a broader range ([An.sub.28] [Ab.sub.70] [Or.sub.0.9] in the core and [An.sub.05] [Ab.sub.92] [Or.sub.2] in rims). Albite twinning and slight fracturing of laths due to magma movement were observed.

Automorphous microphenocrysts resembling so-dalite are completely zeolitized (to thomsonite and gonnardite). There is some doubt as to whether the zoned pseudomorphs after the sodalite group mineral do represent converted primary nepheline micropheno-crysts (due to selective reaction with late magmatic fluids) or not. Similar position of the sodalite pheno-crysts has been reported from zeolitized phonolite of the Marianska hora Hill (Ulrych et al., 2000). Back-scattered electron and secondary electron images of altered feldspathoids confirmed zones with different ratios of intimately intergrown thomsonite and gonnardite resembling primary feldspathoid zoning and shaping. Blue-coloured sodalite rarely occurs in negligible amounts. Average size of pseudomorphs after feldspathoid varies from 0.2 mm to 0.6 mm.

MATRIX

Matrix formed by continuous cooling of interstitial melt is fluidally arranged around (micro)pheno-crysts. The mineral assemblage is composed of ande-sine to oligoclase and Na-sanidine laths, small amount of ferromagnesian minerals (predominantly clinopy-roxene and kaersutite), and zeolite pseudomorphs after feldspathoid(s). The size difference between mineral components of matrix, i.e., microphenocrysts (0.03-0.20 mm) and common matrix grains (0.03-0.05 mm), is not expressive. Strongly opacitized salite to sodic fassaite grains of matrix, rounded in shape and pale green in colour distinctly differ in their composition from clinopyroxene phenocrysts. The microphenocrysts of totally zeolitized feldspathoid are clouded, reminding primary sodalite crystals only in their sub-rounded morphology (see Plate I, 3). Brown kaersutite, titanomagnetite, titanian ferrifassaite, apatite, and relicts of unaltered sodalite occur in accessory amounts.

TRACHYANDESITE FACIES TRACHY ANDESITE

Primary magmatic mineralogy of this rock facies was overprinted by pervasive low-temperature autohydrothermal alteration. However, the microtextures observed in altered rocks are mostly consistent with those known from previously described primary rock facies. Alteration generally resulted in complete zeoli-tization of the rock, filling of vesicles and their transformation into amygdales accompanied by general bleaching of the rock. Some of the vesicles were probably coated by volcanic glass or remained hollow. The unusual abundance of larger vesicles and amygdales in this rock facies is not very common (prevailing in intrusive tephrites) in the Ceske stfedohofi Mts. rock suites. Fluxes of autohydrothermal late magmatic fluids and heated meteoric waters caused instability of primary volcanic glass particles and some minerals in the rock. Such process led to leaching of the country rock, especially to increased mobility of alkali and alkali-earth elements.

Primary minerals, such as fassaitic clinopyroxe-ne and kaersutite, are partly broken. Titanomagnetite forming rims of the above mentioned minerals is often replaced by secondary martite? and goethite. Pseudo-morphs after feldspathoid and vitric shards in marginal parts of vesicles are partly or totally dissolved, forming secondary voids, or filled with analcime with mosaic texture. Volcanic glass particles in the neighbourhood of the vesicles commonly contain a marginal film of ferruginous smectite, russet in colour. Volcanic glass is exceptionally developed on the surface of vesicles, passing into a crust of analcime, 0.05-0.1 mm thick. Fibrous zeolites forming a younger generation in some larger vesicles are very thin and their optical identification is problematic. Groundmass plagioclase and Na-sanidine crystals are completely replaced by illitic clay mineral mostly pigmented with goethite.

5. CHEMISTRY OF PRINCIPAL ROCK-FORMING MINERALS

The major phases (Ca-rich clinopyroxene, brown amphibole, plagioclase, Na-sanidine, and titano-magnetite) in both samples were analysed by electron microprobe. Representative analyses with their structural formulae are listed in Tables 1-5.

CLINOPYROXENES

Phenocrysts show compositional zoning from ferrifassaite cores ([Wo.sub.56.1][En.sub.38.5][Fs.sub.3.9][Jd.sub.1.5]) to sodian ferrifassaite rims ([Wo.sub.56.9][En.sub.34.7][Fs.sub.1.9][Jd.sub.3.5]). They have relatively elevated Al contents allowing partition of total Al between tetrahedral and octahedral sites. They are also enriched in tschermakitic compounds, while jadeitic compound varies between 0.57-1.4 mol. % in the core and 2.6-5.7 mol. % in rims. Recalculation of [Fe.sub.2][O.sub.3] from the microprobe analyses yields variable and higher [Fe.sub.2][O.sub.3]/FeO ratio, likely due to secondary oxidation. It may partly reflect the Na[Fe.sup.3+]--CaMg (acmite) substitution in the clinopyroxene rims. [Cr.sub.2][O.sub.3] content is high (0.13-0.31 wt. %) and Mg/(Mg+[Fe.sub.tot]) ratio ranges between 0.53-0.67. The Ti/Al ratio (0.19-0.20) corresponds to that for the clinopyroxene from the tephrite-phonolite lineage (Le Roex et al. 1990) viz E-MAIL.

Some of the late-crystallized ferrifassaite microphenocrysts are poorer in Cr contents (up to 0.16 wt. % [Cr.sub.2][O.sub.3]) and characterized by variable Ti/Al ratios (in the range of 0.19-0.43). Exceptionally, a minor Al deficiency (-0.02 to -0.07 atoms per formula unit, a.f.u.) to complete tetrahedral site occupancy of 2.00 a.f.u. is evident from Table 1 (No. 3c, 3r). Therefore, insufficient Si + Al content is supplemented by ferric iron to complete the expected T-site configuration.

AMPHIBOLE

The brown amphibole rather belongs to the hastingsite-kaersutite than to pargasite-kaersutite series with Si value between 5.75-6.25 atoms per formula unit (a.f.u.) and more than 0.50 Ti a.f.u. used as a lower limit to define kaersutite (Leake et al. 1997). The higher [Fe.sup.3+]/[Fe.sup.2+] ratio characteristic of hastingsite may be suggested from coexisting ferrifassaite or titanomagnetite and according to the charge calculated. There is a moderate amount of [Al.sub.2][O.sub.3] (13.3-13.5 wt. %), mainly occupying tetrahedral site to 8.00 a.f.u. (higher [8 -Si]/[Al.sub.tot] ratio). The A-site occupancy is above 0.50 a.f.u. (Na+K = 0.97-1.08 a.f.u.) at variable K/Na ratio (0.34-0.58), while all Ca is restricted to M4 position only.

Reaction rims around ferrifassaite phenocrysts show moderate enrichment in Cr (0.11-0.35 wt. % [Cr.sub.2][O.sub.3]) and refer to subsilicic kaersutite characterized by a negligible Si deficiency. In contrast, larger free phenocrysts are typical kaersutites, somewhat richer in Mg (Mg/Mg + [Fe.sub.tot] = 0.68). No apparent zoning was determined but most of the grains are surrounded by opaque margins of titanomagnetite, [Fe.sup.3+]/[Fe.sup.2+] ratios thus being uncertain.

FELDSPARS

Phenocrystic plagioclase cores range between [An.sub.43] and [An.sub.10], rarely [An.sub.50]. A mineralogical indicator of increasing differentiation of melt is the common enrichment in orthoclase and celsian components towards rims of the crystals ([Or.sub.4.5] - [Or.sub.7.6], [Cn.sub.0.3-1.2]). The presence of albite admixtures ([An.sub.06]) is exceptional.

Groundmass plagioclases show generally higher proportion of Ab component than the phenocrystic ones, indicating a fractionation trend. Besides oligo-clase ([An.sub.18.5][Ab.sub.36][An.sub.44][Or.sub.0.3]), albite admixture frequently occurs in outer parts ([An.sub.03][Ab.sub.89][Or.sub.08]). Crystals are also mantled by Nasanidine.

SANIDINE

A high Na content is one of the prominent chemical characteristics of interstitial sanidine. Maxima of the Ab, An, and Cn contents in optically unzoned sanidine are 45.5 %, 5.3 %, and 1.0 %, respectively. Albite overgrowths are a common feature. The contents of Fe are moderately elevated, expressing isomorphous substitution of [Fe.sup.3+] for A1.

OPAQUE OXIDES

The composition of larger lobate grains shows their pertinence to titaniferous magnetite with a higher content of ulvospinel molecule ([Fe.sub.2]Ti[O.sub.4]) and low contents of Mn, Mg, Al, thus forming very low proportions of jacobsite, magnesioferrite, and hercynite, respectively, and sometimes V. The calculated [Fe.sup.3+]/[summation]Fe ratio varies within the range of 0.43-0.46.

6. GEOCHEMISTRY

Two new bulk chemical analyses of feldspathoidal trachyandesite from Dobranka are presented in Table 6 (fresh sample DO-1-1 and zeolitized sample DO-1-2) including trace element analyses (Table 7). Other chemical analyses of tephritic rocks from the Dobranka area (Hibsch, 1915) are shown in Table 6 for comparison. In the TAS classification diagram (Le Maitre ed., 2002), see Fig. 2, both samples from Dobranka plot into the trachyandesite field inside the elongated field of the whole Decin Fm. (Cajz et al., 1999; Ulrych et al., 2001).

The trachyandesitic composition of extrusive volcanic rocks in the Ceske Stredohori Mts. is rather exceptional, representing a more fractionated product. Mg# (36.7-36.8) of the Dobranka lava flow exhibits an evolved product of the fractionation process and falls inside a broader field of the Decin Fm. (Mg# 41-58).

[FIGURE 2 OMITTED]

The C.I.P.W. norms imply silica-undersaturated character of the rock (see Table 6). Wilkinson (1986) favours the name high-Al mildly alkaline andesite for such rock type, due to the lower presence of normative nepheline (Ne [less than or equal to] 10), [Al.sub.2][O.sub.3] contents >16 wt.%, 30>An [less than or equal to] 50 (normative andesine) and the lack of Qz. The [Na.sub.2]O/[K.sub.2]O ratio (in wt.%) lying in the range of 0.47-0.66 indicates a moderately potassic volcanic rock

(Coombs and Wilkinson, 1969). Differentiation index D.I. (67-70) confirms evolved character if compared to other volcanic members of the Decin Fm. (Cajz et al., 1999).

The feldspathoidal trachyandesite is characterized by lower contents of compatible elements (in ppm), such as Ni (5-6), Cr (8.9-9.2), Co (9.9-10.1), and Sc (3.9) and higher contents of incompatible elements, such as Sr (1195-2004), Ba (1421-1651), Zr (487-495), U (4.5-5.0), Th (16.5-17.0), Nb (5355), Ta (2.7) etc. As a possible result of leaching, the content of Rb is relatively low (50-64), causing high K/Rb ratios (467-553). The input of additional K to the rock system follows from higher K/Rb ratio of the zeolitized rock together with a selective loss of Rb. Rb/Sr ratios are relatively very low (0.025-0.054) and indicate also secondary chemical changes in association with zeolitization of the rock, with a more primitive value for the altered rock sample. The ratio of 0.054 is in agreement with average data (0.059) for the Decin Fm. (Cajz et al., 1999). Th/U ratios (3.3-3.8) are somewhat lower if compared to average Decin Fm. value (4.2). Ratios such as Nb/Ta (46.6-49.8) and Zr/Nb (3.6-3.8) mostly correspond to characteristic data for the Decin Fm.

The sum of REE in the feldspathoidal trachy-andesite (381-389 ppm) is lower than that in other rocks of the Decin Fm. (521 ppm). It is generally known that zeolites do not concentrate REE. The La/Lu ratios are relatively high (37.541.1). The Eu/[Eu.sup.*] ratios (0.94) show only a minor negative Eu anomaly reflecting limited plagioclase fractionation in the trachybasaltic member of the Decin Fm. The distribution of chondrite-normalized REE pattern (Fig. 3) is similar to that for phonolitic rocks of the Ceske stredohori Mts. (cf. Ulrych et al., 2000), indicating an enrichment in LREE, strong depletion in MREE and a slight enrichment in HREE. Lowered MREE contents expressed as Gd/[Gd.sup.*] ratio (0.200.21) may be accounted for fractionation of titanite and/or kaersutite (cf. phonolite of Marianska skala Hill-Ulrych et al., l.c.). The chondrite-normalized REE pattern (Fig. 3a) implies pertinence of the Dobranka feldspathoidal trachyandesite to the more primitive group II (Mukarov, Chvojno, Kukla, Velka Javorska, Valkerice, etc.; Ulrych et al., 2001) of rocks forming the Decin Fm. The general incompatible trace element characteristics are illustrated in primitive mantle-normalized multielement variation diagram (Fig. 3b). It shows a characteristic distribution of elements also similar to that of group II sensu Ulrych et al. (2001). The presence of a negative potassium spike in the diagram corresponds to the relict phlogopite in the mantle source. Positive spikes of La, Ce and Nd can be associated with apatite crystallization. The Zr peak probably corresponds to zirconium admixture in clinopyroxenes but no pure Zrminerals were recognized. The minor positive peak of Ba corresponds to plagioclase (sodalite?) crystallization.

[FIGURE 3a OMITTED]

[FIGURE 3b OMITTED]

7. AMYGDALE MINERALOGY

The zeolites, such as analcime, gismondine, natrolite, thomsonite, and barium-bearing phillipsite-Ca were observed in irregular vugs and larger amyg-daloidal cavities within the zeolitized trachyandesite facies. In addition, isolated cavities bear monomineral gmelinite-Ca crusts, sometimes associated with older generation of analcime or with opal in their outer parts. Small quantities of illite (and probably sapo-nite), opal, "wad", and calcite were also encountered.

This mineral association frequently shows simple accretionary features, such as crustifications (e.g., analcime I, Ba-bearing phillipsite-Ca, gismondine, rarely gmeliniteCa) and development of well-defined crystals or fibrous aggregates of natrolite and phillip-site-Ca growing from the walls into open space. Zeolite species probably crystallized from autohydrother-mal solutions representing late stage of volcanic activity. Mineralogical investigation of 150 collected samples provided a somewhat more detailed description of zeolite assemblages in samples with two or more mineral generations. The remaining assemblages are presented only briefly using reference from the literature. The crystallization succession was based on optical study under a magnifying glass or low-power binocular microscope. Five principal types of low-temperature mineral assemblages were recognized:

* illite)--analcime I--analcime II,

* (illite)--analcime I--calcite I--(thomsonite)--natrolite (calcite II),

* (analcime I)--gismondine--thomsonite -phillipsite-Ca analcime II and rare clay minerals,

* analcime I--gmelinite-Ca--analcime II--hyalite

The succession gismondine--clay mineral (probably saponite pseudomorphism) was detected together with Ba-bearing phillipsite-Ca and clay mineral overgrowths. Clay minerals occur either as zeolite precursors or their decomposition products. A certain problem is the presence of gmelinite-Ca forming crystalline crusts in independent amygdales. Some rare zeolites were reported from the locality only episodically. Older mineralogical reports should be therefore revised.

8. MINERALOGICAL CHARACTERISTICS OF STUDIED ZEOLITES

Analcime is present in two generations (Table 8). The first generation belongs to the earliest amyg-dale minerals showing a tendency to grow immediately on the amygdale walls and/or to replace thin illite coatings of vesicles. A fine crystalline crust of analci-me I (particles 0.00X mm in size) on illite, visible at high magnification only, has been considered quart-zose matter or silicified natrolite by Muhlstein and Fengl (1977). It coarsens towards the amygdale centre; freely growing individual crystals of analcime I reach about 1 mm in size (Plate I, 2). Analcime often forms monomineral coatings of vesicles, composed of smaller crystals, reflecting silica-supersaturated solutions and higher temperature at the beginning of crystallization. These coatings are white, as opposed to illite-analcime mixtures which are grey to pink in colour. Morphology of analcime crystals is deltoid dodecahedral with dominant {211} faces.

The second generation of analcime forms separate colourless crystals (Plate I, 4), up to 2 mm in size, perfectly shaped with prevailing faces {211}. In some cases, analcime II also forms compact, finely crystalline crusts, white in colour.

Natrolite, along with analcime and thomsonite, is prominent and very conspicuous amygdale mineral. Needle-like crystals, up to 10 mm long, with a strong tendency to develop combination of the dominant prismatic {110} and subordinate dipyramidal {111} faces, are grouped into radiating semi-spherulitic aggregates. They are white, yellowish or pink in colour depending on the admixture of [Fe.sub.2][O.sub.3]. Fibrous coatings commonly cover the walls of cavities in about 100 [cm.sup.2]-sized patches. Single crystals and chaotically arranged felty aggregates are present only scarcely. Epitaxial overgrowths of natrolite on thomsonite (or those of thomsonite on natrolite) were found at places where thomsonite crystallized from solutions partly simultaneously with natrolite, as described by Ulrych and Rychly (1986). Natrolite composition appears to be quite uniform; no zoning was determined (see Table 8). The presence of gonnardite in amygdules is problematic, however, a limited substitution of Ca for Na in natrolite was registered.

Thomsonite frequently forms radial aggregates composed of fibrous to prismatic crystals accompanied by younger generation of natrolite II. Epitaxial intergrowths of both minerals sometimes occur in this assemblage. Thickly tabular to columnar crystals of thomsonite, up to 10 mm long, growing on older gis-mondine crystals correspond to a different morphological type. These larger, colourless or white crystal aggregates are arranged pseudoparallel to plane {001}. For chemical composition see Table 8.

Gismondine-Ca is relatively abundant mineral forming crystalline crusts, white or yellowish in colour. If showing subparalel intergrowths, gismondine is usually perfectly bounded, multifaceted and distinctly twinned (pseudotetragonal twinning--Plate II, 3, 4). Crystal size reaches about 2 mm on average, exceptionally 5 mm. Gismondine is sporadically overgrown by a younger thomsonite generation or inter-grown in a complex multiple gismondine cruciform interpenetration. Perimorphs of phillipsite-Ca after gi-smondine or clay mineral (saponite?) encrusting gismodine are rare. Amygdales with gismondine crystals are rather restricted to the southern margin of the zeolitized trachyandesite lava flow (Muhlstein and Fengl, 1977). For chemical composition see Table 9.

Barium-bearing phillipsite-Ca (Fig. 4) usually forms fine crystalline crusts, either white, yellow, or orange to brick red in colour. Rather than single crystals, the most common are multiple twins and penetration twins forming obscure octahedral morphology smaller than 4 mm in size (Plate II, 1). Pseudorhombic dodecahedron-resembling complexes with striated crystal faces are exceptional (Plate II, 2). Incrustation of phillipsite-Ca and smectite on gismondine results from possible chemical interaction between gismon-dine, phillipsite and residual solution. The analysed phillipsite-Ca crystals are largely inhomogenous, richer in Ba and very close to barium-bearing phillipsite-Ca, formerly reported as wellsite (see Table 9). Older classification used the name wellsite for a mineral with an intermediate chemical composition between phillipsite and harmotome.

Gmelinite-Ca (Fig. 4) is a rare zeolite species occurring in smaller amygdales as a sole mineral. Tabular crystals of common and complex rhombohedral twinnings, typically about 2 mm thick, form crystalline crusts on the walls of amygdales. Gmelinite-Ca crystals are pink, orange or yellowish-orange in colour. The SEM study confirmed a complicated cruciform interpenetration (see Plate I, 1), hollows in crystals, and analcime II overgrowths. Hollow crystals of gmelinite-Ca could have probably formed by mutual intergrowth with chabazite (described by Tschernich, 1992) and its later dissolution. Higher values (see Table 9) of the "balance error" E (%) may indicate possible relics of chabazite intergrowth. As usual, gmelinite-Ca forms the outer shell of such gmelinite-chabazite intergrowth (Tschernich, 1992).

Clay mineral of illite composition, forming the older generation, covers vesicle walls and documents chemical changes induced by the hydrothermal alteration of the host trachyandesite with autohydro-thermal fluids. The composition of illite crusts is as follows (in wt.%): Si[O.sub.2] (43.37-45.62), Ti[O.sub.2] (0.86-0.90), [Al.sub.2][O.sub.3] (27.53-30.10), FeO (4.88-5.39), MnO (0.13-0.22), MgO (1.17-1.62), CaO (1.39-1.90), [Na.sub.2]O (0.00-0.24), [K.sub.2]O (4.19-4.44). Transitions were found between the pure clay mineral and pink illite-analcime mixture. Younger generation of the clay mineral reveals a similar chemical composition as the older one. Other clay minerals, e.g. saponite and smectite, could have formed due to possible decomposition reactions of phillipsite-Ca and gismondine with late fluids or due to independent crystallization from a solution. Pseudomorphs and perimorphs of clay minerals after gismondine were also reported from basa-nites of Groft Teichelberg, Bavaria, by Pollmann and Keck (1990).Two generations of "clay minerals" (a post-phillipsite phase crystallizing instead of chabazi-te) were mentioned also by Tschernich (1992) in an assemblage with a general succession of zeolite crystallization controlled by a decrease in Si content (Si/Al ratio).

[FIGURE 4 OMITTED]

[ILLUSTRATION OMITTED]

[ILLUSTRATION OMITTED]

Opal (hyalite) is white, grey, greyish blue or brown in colour, covering inner vesicle walls and older mineral assemblages. Variability of its morphology is expressed by the following forms: individual spheroids, papillate to lobate coatings and finger-like types.

"Wad" forms infrequent fringes on older mineral species, spherulites, and small skeletal crystals. It is rich in manganese and contains iron admixture (on the order of 0.X wt. %).

Calcite occurs in two generations, but no chemical differences were found. Calcite I is somewhat older than thomsonite, forming semi-spherulitic aggregates of radiating texture, pale brown in colour, up to 10 mm in size. However, its position in the succession of other amygdule minerals is uncertain. On the other hand, calcite II represents one of the youngest minerals. Its colourless to pale yellow crystals, approximately 6 mm in size, cover older cavity mineral constituents. Some of the crystals have elongated rhombohedral appearance. Both calcite generations can be considered relatively pure calcium carbonate, with negligible amount of admixtures.

9. CONDITIONS OF ZEOLITE FORMATION

Larger vesicles and amygdales developed during lava degassing, movement and cooling creating the space for crystallization of (a) dominant analcime I generation at higher temperature and (b) Na-Ca zeolite species by influx of slightly alkaline (bicarbonate-bearing) groundwater at reduced temperature. Zeolite crystallization was controlled by favourable composition of autohydrothermal solutions (e.g., due to high alkali and silica contents), their neutral to slightly alkaline reaction, the optimum temperature range, and long-term groundwater circulation in geothermal field (Hall 1998).

As expected from thermodynamic modelling of zeolite equilibria (Chipera and Bish, 1999), analcime stability increases with rising temperature, aqueous sodium concentration, and relatively high silica activity a(Si[O.sub.2]). Thermodynamic calculations performed in the range of 1200 bars showed only negligible effects of low pressure and pH on the calculated equilibria. It is clear that the pH of the autohydrothermal fluids controls on whether or not initial zeolitization takes place., and may be later important in determining the formation of zeolite species at the expense of other potentially stable minerals. The zeolitization process has not been found in volcanic areas where streams flowing off the volcano were acidic ([H.sub.2]S[O.sub.4]- and [H.sub.2]C[O.sub.3]-rich) due to effect of acidic gases on surface water. When the aqueuos silica activity and temperature were reduced, e.g., at log a (Si[O.sub.2]) = -4.3 and temperature of 150[degrees]C, the stability field was created for a new suite of the Na-Ca zeolite species such as gismondine, thomsonite, natrolite, phillipsite-Ca, and gmelinite-Ca. Some changes in their composition may be considered due to exchangeable cation substitution and varying water content. The presence of barium-bearing phillipsite-Ca is also indicative of elevated potassium and barium concentrations in hydrothermal solutions.

A repeated sequential crystallization of analcime, clay mineral and calcite (two generations) suggests renewed thermal event(s) associated with thermal water activity (reheating). Thermal recurrent pulses may have formed, e.g., as a consequence of ongoing volcanic activity and fluid influx.

10. DISCUSSION AND CONCLUSION

Favourable chemistry of the host rock and a specific proportion of glassy particles in analcimized trachyandesite facies show relatively good tendency towards alkali leaching under hydrous alteration conditions. The combined effect of increased temperature, neutral to alkaline reaction of autohydrothermal solution and hydrogeological quality of aquifer is responsible for zeolitization and origin of zeolite species. Nevetheless, the question of why some volcanic bodies are zeolitized while others are not requires a more complex approach, with respect to diagenetic zeoli-tization within prevailing tuffs and lacustrine sediment intercalations governed by different mechanisms (Hall, 1998). Alteration of tuffitic strata exposed in a cliff above the village of Jedlka (SE of Decin) led to the origin of diagenetic analcime, phillipsite-Ca, and chabazite (Novak and Cilek, 2001).

Zeolites, the origin of which was accompanied by low-temperature auto-hydrothermal alteration of feldspathoidal trachyandesite lava flow, are mainly developed in amygdales. The general succession is as follows: (illite) analcime I--gismondine--barium-bearing phillipsite-Ca (calcite I)--thomsonite--natrolite--opal--wad--analcime II calcite II. However, this simplified succession requires some additional explanation due to local exceptions, e.g., various forms of epitaxial growths, the presence of "hollow" gmelinite-Ca crystals, etc.

Simultaneous parallel growth and overgrowth of thomsonite on natrolite studied by Ulrych and Rychly (1986) at this locality only simulate a chemical composition of gonnardite, a transitional member between natrolite and thomsonite. The presence of gonnardite is therefore questionable, because gonnardite was proved by no other independent diagnostic method. Perimorphs and pseudomorphs of clay minerals after gis-mondine, phillipsite-Ca and natrolite have been often reported (cf. Pollmann and Keck, 1993).

The "hollow crystals" of gmelinite-Ca were probably formed by the dissolution of intergrown cha-bazite. This fact, causing a higher "balance error" E(%), can be explained by the presence of K and Ba in fluids favouring chabazite structure. As potassium-bearing zeolite (phillipsite) is present, the origin of pure gmelinite is improbable. Gmelinite-Ca is restricted to a very specific chemical composition within a narrow Si/Al range, while chabazite crystallizes within a wide range of Si/Al ratios and at the presence of various cations such as Ca, K, Na, Mg, Ba, Sr, etc. (Passaglia et al., 1978). Barium-bearing phillipsite-Ca, commonly occurring at the Dobranka locality, implies a higher concentration of Ba in postmagmatic fluids. Phillipsite-K (with dominant potassium) was identified recently in zeolite assemblages of basanite diatre-mes from Jezova and Jeleni hora near Bela pod Bezdezem, northern Bohemia.

ACKNOWLEDGMENTS

The study was supported by the project financed by the Ministry of Culture of the Czech Republic, identification Code RK 99PO3ON035 granted to T. Wiesner, Municipal Museum of the Town of Usti nad Labem. The investigation in the Institute of Geology of the Academy of Sciences of the Czech Republic was performed within Research Programme CEZ: Z3-013-912. We wish to thank J. Rajlichova for her assistance with the drawings.

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Ulrych, J., Cajz, V., Balogh, K. and Erban, V.: 2001, Geochemistry of the stratified volcanosedimentary complex in the central part of the Ceske stredohori Mts., North Bohemia, Krystalinikum, 27, 27-49.

Jiri K. NOVAK (1), Jaromir ULRYCH (1), Marek CHVATAL (2), Anna LANGROVA (1), Vladimir CAJZ (1), Jiri ADAMOVIC (1), Rudolf RYCHLY (3) and Tomas WIESNER (4)

(1) Institute of Geology, Academy of Sciences of the Czech Republic, Rozvojova 135, 165 02 Praha 6, Czech Republic, e-mail: novak@gli.cas.cz, phone +420233087241, fax: +420220922670

(2) Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University, Albertov 6, 128 43 Praha 2, e-mail: mchvatal@mail.natur.cuni.czphone +420221951483

(3) Pod zameckem 404, 500 06 Hradec Kralove 6, phone +420495273648

(4) Municipal Museum of the Town of Usti nad Labem, Masarykova 5, Usti nad Labem, e-mail: museum.usti@ecu.cz, phone/fax +420475211260
Table 1 Representative microprobe analyses
of pyroxene phenocrysts

Sample No.                DO-1, Na-ferrifassaite

Position                1cV     1rV     2cV     2rV

Si[O.sub.2] (wt.%)    47.00    43.94   43.88   45.91
Ti[O.sub.2]            2.08     2.74    2.56    2.01
[Al.sub.2][O.sub.3]    6.76     8.99    8.45    6.69
[Cr.sub.2][O.sub.3]    0.13     0.31    0.26    0.13
FeO                    9.48    10.74   10.96    9.14
MnO                    0.39     0.53    0.53    0.56
MgO                   10.75     9.20    9.30   10.98
CaO                   22.25    21.79   22.30   22.28
[Na.sub.2]O            1.26     1.50    1.64    1.30
[K.sup.2]O               --      --      --      --
[SIGMA]              100.10    99.74   99.88   99.00

Number of ions on the basis of 4 cations

Si                    1.754    1.654   1.648   1.728
Al                    0.246    0.346   0.352   0.272
T=                    2.000    2.000   2.000   2.000
Al                    0.051    0.053   0.022   0.024
Ti                    0.058    0.077   0.072   0.057
Cr                    0.004    0.009   0.008   0.004
[Fe.sup.2+]           0.130    0.100   0.046   0.062
[Fe.sup.3+]           0.166    0.237   0.298   0.225
Mn                    0.012    0.017   0.017   0.018
Mg                    0.598    0.516   0.521   0.616
Ca                    0.889    0.879   0.897   0.898
Na                    0.091    0.109   0.119   0.095
K                        --      --      --      --
M1, M2                1.999    1.997   2.000   1.999
En                    35.85    33.34   35.04   38.47
Fs                     7.78     6.48    3.12    3.90
Wo                    53.32    56.74   60.38   56.10
Jd                     3.05     3.43    1.45    1.52

Sample No.            DO-2, Na-ferrifassaite

Position                3r1     3r2      3c     3r3

Si[O.sub.2] (wt.%)    46.39    44.16   44.23   45.13
Ti[O.sub.2]            1.93    2.87    2.68    2.65
[Al.sub.2][O.sub.3]    7.24    8.93    9.00    8.19
[Cr.sub.2][O.sub.3]    0.26    0.19    0.41    0.25
FeO                    9.49    10.02   10.34   10.40
MnO                    0.44    0.39    0.41    0.46
MgO                   10.69    9.70    9.49    9.55
CaO                   21.81    22.16   21.67   22.50
[Na.sub.2]O            1.61    1.43    1.61    0.75
[K.sup.2]O             0.11    0.09    0.12    0.09
[SIGMA]               99.97   99.94   99.96   99.97

Number of ions on the basis of 4 cations

Si                    1.727    1.654   1.656   1.703
Al                    0.273    0.346   0.344   0.297
T=                    2.000    2.000   2.000   2.000
Al                    0.044    0.048   0.054   0.068
Ti                    0.054    0.081   0.075   0.075
Cr                    0.007    0.006   0.012   0.007
[Fe.sup.2+]           0.061    0.075   0.075   0.199
[Fe.sup.3+]           0.234    0.238   0.249   0.130
Mn                    0.014    0.012   0.013   0.015
Mg                    0.593    0.541   0.530   0.537
Ca                    0.870    0.889   0.869   0.910
Na                    0.116    0.103   0.117   0.055
K                     0.007    0.004   0.005   0.004
M1, M2                2.000    1.997   1.999   2.000
En                    37.81    34.84   34.68   31.59
Fs                     3.91     4.85    4.89   11.67
Wo                    55.44    57.20   56.90   53.49
Jd                     2.83     3.10    3.51    3.23

c-core, r-rim

Table 2 Representative microprobe analyses of pyroxene
and kaersutite

Sample No.                       DO-2, groundmass

Position                   1c        2c        3c        3r

Si[O.sub.2] (wt.%)      47.12     44.48     42.58     46.29
Ti[O.sub.2]              2.40      2.60      4.71      2.65
[Al.sub.2][O.sub.3]      5.63      8.41      7.00      5.36
[Cr.sub.2][O.sub.3]        --      0.16        --        --
FeO                     10.59     10.48     13.92     11.49
MnO                      0.40      0.48      0.68      0.49
MgO                     10.44      9.43      9.28     10.87
CaO                     22.73     22.61     19.78     21.13
[Na.sub.2]O              0.58      1.21      1.86      1.55
[K.sub.2]O               0.01      0.02      0.02      0.02
[H.sub.2]O+(calc.)         --        --        --        --
Cl                         --        --        --        --
[SIGMA]                 99.90     99.88     99.83     99.85

Number of ions on the basis of 4 cations (pyroxene)
and 23 (O) (kaersutite)

Si                      1.781     1.674     1.618     1.739
Al                      0.219     0.326     0.314     0.237
[Fe.sup.3+]                --        --     0.068     0.024
T=                      2.000     2.000     2.000     2.000
Al                      0.032     0.046        --        --
Ti                      0.068     0.073     0.135     0.075
Cr                         --     0.004        --        --
[Fe.sup.3+]             0.241     0.113     0.123     0.111
[Fe.sup.2+]             0.093     0.217     0.250     0.225
Mn                      0.013     0.015     0.022     0.015
Mg                      0.588     0.529     0.526     0.609
Ca                      0.920     0.911     0.805     0.850
M1,M2 ([SIGMA]A)        1.997     1.997     1.999     1.999
mg=                      0.63      0.60      0.53      0.62

Sample No.                  Kaersutite phenocrysts and
                                 rims around cpx

Position                   4c        4r        5c        5r

Si[O.sub.2] (wt.%)      37.25     37.56     37.10     37.31
Ti[O.sub.2]              4.89      4.70      5.03      4.94
[Al.sub.2][O.sub.3]     13.30     13.35     13.54     13.60
[Cr.sub.2][O.sub.3]      0.34      0.35      0.21      0.11
FeO                     15.88     16.02     15.25     14.65
MnO                      0.45      0.51      0.47      0.35
MgO                      9.90     10.03      9.64      9.82
CaO                     11.44     11.53     11.47     11.44
[Na.sub.2]O              2.83      2.58      2.64      3.06
[K.sub.2]O               1.52      1.44      1.64      1.64
[H.sub.2]O+(calc.)       1.92      1.94      1.93      1.93
Cl                         --        --        --        --
[SIGMA]                 99.72    100.01     98.92     98.85

Number of ions on the basis of 4 cations (pyroxene)
and 23 (O) (kaersutite)

Si                      5.706     5.730     5.713     5.733
Al                      2.294     2.270     2.287     2.267
[Fe.sup.3+]                --        --        --        --
T=                      8.000     8.000     8.000     8.000
Al                      0.107     0.131     0.170     0.196
Ti                      0.563     0.539     0.582     0.571
Cr                      0.041     0.042     0.026     0.013
[Fe.sup.3+]                --        --        --        --
[Fe.sup.2+]           2.029 *   2.007 *   1.964 *   1.883 *
Mn                         --        --     0.045     0.046
Mg                      2.261     2.281     2.213     2.249
Ca                         --        --        --     0.042
M1,M2 ([SIGMA]A)        1.079     1.031     1.019     1.074
mg=                      0.52      0.53      0.53      0.54

Sample No.             Kaersutite phenocrysts
                        and rims around cpx

Position                   6c        6r

Si[O.sub.2] (wt.%)      39.80     39.50
Ti[O.sub.2]              5.02      5.33
[Al.sub.2][O.sub.3]     13.28     13.50
[Cr.sub.2][O.sub.3]        --        --
FeO                     10.83     10.56
MnO                      0.22      0.39
MgO                     13.12     12.75
CaO                     11.25     10.86
[Na.sub.2]O              2.95      3.03
[K.sub.2]O               1.67      1.88
[H.sub.2]O+(calc.)       2.11      2.11
Cl                       0.11      0.13
[SIGMA]                100.36    100.04

Number of ions on the basis of 4 cations
(pyroxene) and 23 (O) (kaersutite)

Si                      5.890     5.868
Al                      2.110     2.132
[Fe.subp.3+]                --        --
T=                      8.000     8.000
Al                      0.207     0.232
Ti                      0.559     0.595
Cr                         --        --
[Fe.sup.3+]                --        --
[Fe.sup.2+]           1.340 *   1.312 *
Mn                         --     0.037
Mg                      2.895     2.824
Ca                         --        --
M1,M2 ([SIGMA]A)        0.974     0.969
mg=                      0.68      0.68

Table 3 Representative microprobe analyses
of feldspars in the groundmass

Sample No.                     DO-2, plagioclase

Position                1c       1r       2c       2r

Si[O.sub.2] (wt.%)   57.08    57.67    56.04    57.54
Ti[O.sub.2]           0.21     0.27       --       --
[Al.sub.2]
  [O.sub.3]          26.55    26.61    26.17    26.23
FeO                   0.69     0.64     0.59     0.87
MnO                   0.01     0.12     0.08     0.02
MgO                   0.07     0.08     0.06     0.07
BaO                   0.06     0.04     0.06     0.07
CaO                   9.48     7.34     9.51     9.32
[Na.sub.2]O           5.10     5.99     4.98     5.20
[K.sub.2]O            0.79     1.34     0.90     0.73
[P.sub.2][O.sub.5]    0.43     0.47     0.34     0.29
E                   100.47   100.57    99.73   100.34

Number of ions on the basis of 32 (O)

Si                  10.225   10.305   10.293   10.319
Al                   5.605    5.604    5.566    5.544
Ti                   0.028    0.036       --       --
P                    0.065    0.071    0.052    0.044
T=                  15.923   16.016   15.911   15.907
Fe                   0.103    0.096    0.089    0.130
Mn                   0.002    0.018    0.012    0.003
Mg                   0.019    0.021    0.016    0.019
Ba                   0.004    0.003    0.004    0.005
Ca                   1.819    1.405    1.839    1.791
Na                   1.771    2.075    1.742    1.808
K                    0.181    0.305    0.207    0.167
O=                   3.899    3.924    3.910    3.923
An                   48.19    37.09    48.48    47.49
Ab                   46.92    54.77    45.94    47.95
Or                    4.78     8.06     5.46     4.43
Cn                    0.11     0.07     0.11     0.13

Sample No.                    DO-2, Na-sanidine

Position                3c       3r       4c       5c

Si[O.sub.2] (wt.%)   62.70    63.68    63.59    62.36
Ti[O.sub.2]             --     0.37     0.38     0.07
[Al.sub.2]
  [O.sub.3]          21.86    20.56    20.20    21.28
FeO                   0.71     0.55     0.56     0.86
MnO                     --       --       --       --
MgO                   0.05     0.07     0.05     0.04
BaO                   0.06     0.03     0.21     0.16
CaO                   1.03     0.65     1.33     3.99
[Na.sub.2]O           5.10     4.37     5.01     3.67
[K.sub.2]O            8.34     9.67     8.57     7.67
[P.sub.2][O.sub.5]      --       --       --       --
E                    99.85    99.95    99.90   100.10

Number of ions on the basis of 32 (O)

Si                  11.393   11.582   11.573   11.337
Al                   4.682    4.407    4.333    4.560
Ti                      --    0.051    0.052    0.010
P                       --       --       --       --
T=                  16.075   16.040   15.957   15.907
Fe                   0.108    0.084    0.085    0.131
Mn                      --       --       --       --
Mg                   0.014    0.019    0.014    0.011
Ba                   0.004    0.002    0.015    0.011
Ca                   0.201    0.127    0.259    0.777
Na                   1.797    1.541    1.768    1.294
K                    1.933    2.244    1.990    1.779
O=                   4.056    4.016    4.131    4.003
An                    5.10     3.24     6.43    20.13
Ab                   45.66    39.38    43.85    33.50
Or                   49.13    57.33    49.35    46.07
Cn                    0.11     0.05     0.37     0.29

c-core, r-rim

Table 4 Representative microprobe analyses
of the microphenocrystic phases

Sample No.                DO-1, plagioclase

Position               1c       1r       2c

Si[O.sub.2] (wt.%)    57.04   57.54    57.74
Ti[O.sub.2]            --       --       --
[Al.sub.2][O.sub.3]   26.17   26.23    26.23
[Fe.sub.2][O.sub.3]    --       --       --
FeO                   0.59     0.87     0.67
MnO                   0.08     0.02     0.11
MgO                   0.06     0.07     0.07
BaO                   0.06     0.07     0.07
CaO                   9.51     9.32     9.32
[NA.sub.2]O           4.82     5.50     5.10
[K.sub.2]O            0.90     0.73     0.73
[P.sub.2][O.sub.5]    0.34     0.29     0.29
[H.sub.2]O             --       --       --
[SIGMA]               99.57   100.64   100.33

Number of ions on the
basis of 32 (O)               80 (O)   40 (O)

Si                    10.302  10.302   10.343
Al                    5.571   5.535    5.537
Ti                      --       --       --
P                     0.052   0.044    0.044
[Fe.sup.3+]             --       --       --
T=                    15.925  15.881   15.924
[Fe.sub.2+]           0.089   0.130    0.100
Mn                    0.012   0.003    0.017
Mg                    0.016   0.019    0.019
Ba                    0.004   0.005    0.005
Ca                    1.840   1.788    1.789
Na                    1.688   1.909    1.771
K                     0.207   0.167    0.167
O=                    3.857   4.021    3.867
OH                      --       --       --
E %                     --       --       --

An                    49.21   46.21    47.93
Ab                    45.13   49.35    47.46
Or                    5.54     4.31     4.47
Cn                    0.11     0.13     0.13

Sample No.            DO-1, zeolites after felspathoid

Position               4c       5        6        7

Si[O.sub.2] (wt.%)    38.55   37.29    42.17    41.13
Ti[O.sub.2]            --       --       --       --
[Al.sub.2][O.sub.3]   29.26   31.78    28.35    28.30
[Fe.sub.2][O.sub.3]    --      0.17     0.84     0.41
FeO                    --       --       --       --
MnO                    --      0.11      --       --
MgO                    --       --       --       --
BaO                    --       --       --       --
CaO                   10.80   13.10     9.83     8.42
[NA.sub.2]O           7.54     3.73     5.92     8.16
[K.sub.2]O            0.17     0.13     0.12     0.13
[P.sub.2][O.sub.5]     --       --       --       --
[H.sub.2]O            13.68   13.69    12.77    13.45
[SIGMA]               100.00  99.98    100.00   100.00

Number of ions on the basis of 32 (O)  80 (O)   40 (O)

Si                    20.86   20.05    11.12    10.99
Al                    18.64   20.14     8.80     8.90
Ti                      --       --       --       --
P                       --       --       --       --
[Fe.sup.3+]             --     0.07     0.17     0.08
T=                      --       --       --       --
[Fe.sub.2+]             --       --       --       --
Mn                      --     0.05       --       --
Mg                      --       --       --       --
Ba                      --       --       --       --
Ca                    6.26     7.55     2.77     2.41
Na                    7.91     3.89     3.02     4.22
K                     0.06     0.09     0.04     0.04
O=                      --       --       --       --
OH                   24.695  24.55    11.223   11.978
E %                   +9.03   +5.95    +4.06    -1.06

An                    thomsonite and gonnardite zones
Ab
Or
Cn

c-core, r-rim

Table 5 Microprobe chemical analyses
of opaque minerals

Sample No.          DO-1, zeolitized      DO-2
                     trachyandesite

Position         1cV      1rV       2c       1c

Si[O.sub.2]
  (wt.%)        0.06     0.04     0.06     0.10
Ti[O.sub.2]    14.74    15.85    16.54    16.69
[Al.sub.2]
  [O.sub.3]     2.76     1.48     1.51     0.80
[Fe.sub.2]
  [O.sub.3]    38.65    36.43    35.48    36.40
FeO            39.37    44.21    43.43    42.97
[V.sub.2]
  [O.sub.5]      tr.      tr.      tr.      tr.
MnO             2.80     1.80     2.37     2.90
MgO             2.12       --     0.61     0.26
CaO               --       --       --     0.64
[SIGMA]       100.50    99.82   100.01   100.77

                      Number of ions on the
                      basis of 24 cations

Si             0.018    0.012    0.018    0.030
Ti             3.247    3.593    3.721    3.744
Al             0.953    0.526    0.532    0.281
[Fe.sup.3+]    8.519    8.265    7.989    8.171
[Fe.sup.2+]    9.644   11.145   10.867   10.721
V                 --       --       --       --
Mn             0.695    0.460    0.601    0.733
Mg             0.926       --    0.272    0.116
Ca                --       --       --    0.205
[SIGMA]       24.000   24.000   24.000   24.000
  cations

Table 6 Chemical analyses and C.I.P.W. norms of the rocks

Sample No.             DO-1-1       DO-1-2           DO-2

Locality,                Feldspathoidal        Feldspathoidal
rock type                trachyandesite,      trachyandesite,
                            Dobranka,                Dobranka
                          new analyses

Si[O.sub.2] (wt.%)      51.84        52.65              52.34
Ti[O.sub.2]              1.31         1.25               0.14
[Al.sub.2][O.sub.3]     20.46        20.28              19.90
[Fe.sub.2][O.sub.3]      3.78         3.83               6.57
FeO                      1.96         1.60               0.55
MnO                      0.20         0.21               n.a.
MgO                      1.48         1.40               2.26
CaO                      5.68         4.62               6.35
BaO                      n.a.         n.a.               n.a.
[Na.sub.2]O              5.39         5.58               5.66
[K.sub.2]O               3.60         3.33               2.68
[P.sub.2][O.sub.5]       0.51         0.48               0.09
C[O.sup.2]               n.a.         n.a.               n.a.
[H.sub.2]O+              3.44         4.59               3.65
[H.sub.2]O-              n.a.        n. a.               0.41
S                          --           --                 --
S[O.sub.3]               0.02         0.02               0.02
F                        n.a.        n. a.              n. a.
Total                   99.67        99.84             100.62
Qz                         --           --                 --
Ne                       6.83         3.20               6.81
Or                      21.80        20.35              16.14
Ab                      38.22        46.48              40.45
An                      21.53        20.46              21.38
Di                       3.15           --               8.10
Hy                         --           --                 --
Ol                       2.20         3.25               1.73
Mt                       3.32         3.14               5.00
Ilm                      1.87         1.80               0.20
Ap                       1.09         1.04               0.19
AN                       36.0         30.5               34.6
[K.sub.2]O/
  [Na.sub.2]O            0.66         0.60               0.47
Mg#                      25.7         34.7               30.4
D.I.                    66.84        70.03              63.39

Sample No.               DO-3         DO-4

Locality,            Tephrite,   Zeolitized
rock type            Dobranka    tephrite,
                                    Ovesna

Si[O.sub.2] (wt.%)      44.85        46.88
Ti[O.sub.2]              1.78         3.01
[Al.sub.2][O.sub.3]     18.08        15.99
[Fe.sub.2][O.sub.3]      7.71         5.67
FeO                      3.23         4.84
MnO                      n.a.         0.19
MgO                      4.16         3.76
CaO                      9.97         9.23
BaO                      n.a.         0.07
[Na.sub.2]O              3.02         3.38
[K.sub.2]O               3.19         3.09
P2O5                     1.55         0.56
C[O.sup.2]               n.a.         0.05
[H.sub.2][O.sup.+]       2.56         2.68
[H.sub.2][O.sup.-]       0.46         0.58
S                          --         0.02
S[O.sub.3]               n.a.           --
F                        n.a.         0.10
Total                  100.56       100.10
Qz                         --           --
Ne                       5.20         4.55
Or                      19.54        19.16
Ab                      19.45        24.26
An                      27.34        20.29
Di                      10.75        18.87
Hy                         --           --
Ol                       4.90         1.33
Mt                       6.88         5.86
Ilm                      2.57         4.40
Ap                       3.37         1.23
AN                       58.4         45.5
[K.sub.2]O/
  [Na.sub.2]O            1.05         0.88
Mg#                      33.5         32.1
D.I.                    44.19        47.96

* DO-1-1: fresh trachyandesite, DO-1-2: zeolitized
trachyandesite, DO-2: trachyandesite ("hauyne tephrite")
and DO-3 nepheline tephrite (Hibsch 1915), all from the
Dobranka locality, DO-4: zeolitized tephrite, Ovesna.

Table 7 Trace element abundances of the rocks

Sample No.       DO-1-1          DO-1-2          DO-2

Locality,    Feldspathoidal                 Feldspathoidal
rock type    trachyandesite,                trachyandesite,
                Dobranka,                      Dobranka
                   new
                analyses

Rb (ppm)           64              50             --
Cs                1.88            1.23            --
Sr                1,195          2,004            --
Ba                1,421          1,651            --
Sc                3.93            3.92            --
Y                  21              19             --
Cr                9.22            8.67            --
Ni                  5              6              --
Co                9.94            10.1            --
V                  66              68             --
Zn                120.2          128.3            --
Pb                 <10            <10             --
Cu                 --              --             --
Zr                 495            487             --
Nb                 137            129             --
Ta                2.75            2.77            --
Hf                8.92            9.62            --
Th                16.5           17.08            --
U                 5.01            4.52            --
La                134.2          136.6            --
Ce                174.4          177.3            --
Nd                52.7            54.6            --
Sm                 7.2            7.25            --
Eu                 2.1            2.16            --
Gd                6.19            6.56            --
Tb                0.69            0.70            --
Ho                0.69            0.80            --
Yb                2.34            2.61            --
Lu                0.38            0.42            --
Mg#               36.7            36.8
K/Rb              466.9          552.8
Rb/Sr             0.054          0.025
Th/U              3.29            3.78
Zr/Hf             55.5            50.6
Nb/Ta             49.8            46.6
Z REE            380.89          389.00
Eu/Eu *           0.94            0.94
Gd/Gd *           0.20            0.21

Sample No.        DO-3            DO-4

Locality,       Tephrite,      Zeolitized
rock type       Dobranka       tephrite,
                                 Ovesna

Rb (ppm)           --              42
Cs                 --             1.25
Sr                 --            1,026
Ba                 --             626
Sc                 --             28.3
Y                  --              27
Cr                 --              <7
Ni                 --              8
Co                 --             39.9
V                  --              --
Zn                 --              82
Pb                 --              <7
Cu                 --              23
Zr                 --             444
Nb                 --             100
Ta                 --             4.03
Hf                 --             10.2
Th                 --             9.25
U                  --              <3
La                 --             60.4
Ce                 --             119
Nd                 --              --
Sm                 --             8.93
Eu                 --             2.6
Gd                 --              --
Tb                 --              <1
Ho                 --              --
Yb                 --             1.64
Lu                 --             0.4
Mg#                               44.2
K/Rb                             610.6
Rb/Sr                            0.041
Th/U                               --
Zr/Hf                             43.5
Nb/Ta                              --
Z REE                            192.97
Eu/Eu *                            --
Gd/Gd *                            --

Table 8 Representative microprobe analyses
of the amygdale zeolites

                               analcime                thomsonite

Wt.%                    an1       an2       an3       th1       th2

Si[O.sub.2]           54.09     51.79     52.82     37.96     38.62
[Al.sub.2][O.sub.3]   22.47     22.37     23.24     31.47     29.57
[Fe.sub.2][O.sub.3]    0.51      0.44      0.17      0.09      0.14
MnO                    0.19      0.12      0.27      0.08      0.16
MgO                    0.65      0.54      0.46      0.70      0.81
CaO                    0.17      0.51      0.15     12.31     10.91
BaO                    0.50      0.39      0.13      0.28      0.31
[Na.sub.2]O           11.30     12.19     14.51      4.48      5.43
[K.sub.2]O             0.19      0.17      0.15      0.16      0.11
total                 90.07     88.52     91.90     87.53     86.06

                           formula per 96 (O)     formula per 80 (O)

Si                    32.240   31.637    31.262    20.177    20.853
Al                    15.784   16.104    16.210    19.713    18.816
[Fe.sup.3+]           0.230     0.203     0.076     0.036     0.058
Mn                    0.096     0.062     0.135     0.036     0.073
Mg                    0.578     0.492     0.406     0.555     0.652
Ca                    0.109     0.334     0.095     7.010     6.311
Ba                    0.117     0.093     0.030     0.058     0.066
Na                    13.058   14.436    16.649     4.617     5.684
K                     0.144     0.132     0.113     0.108     0.076
Z                    48.254    47.944    47.532    39.926    39.727
M                    13.202    14.568    16.762     4.725     5.760
D                     0.900     0.981     0.666     7.659     7.102
R                     0.671     0.663     0.658     0.506     0.526
E(%)                  6.761    -1.354    -9.998    -1.465    -5.453

                      thomsonite        natrolite

Wt.%                        th3       na1       na2

Si[O.sub.2]               38.76     45.26     45.48
[Al.sub.2][O.sub.3]       29.16     26.38     26.84
[Fe.sub.2][O.sub.3]        0.13      0.17      0.13
MnO                        0.07      0.26      0.13
MgO                        0.77      0.51      0.66
CaO                       10.57      0.23      0.27
BaO                        0.37      0.27      0.36
[Na.sub.2]O                5.45     16.36     16.38
[K.sub.2]O                 0.16      0.09      0.09
total                     85.44     89.56     90.36

                              formula per 80 (O)

Si                       21.055    23.421    23.320
Al                       18.668    16.088    16.219
[Fe.sup.3+]               0.051     0.067     0.052
Mn                        0.032     0.114     0.056
Mg                        0.624     0.393     0.505
Ca                        6.151     0.128     0.148
Ba                        0.079     0.055     0.072
Na                        5.740    16.413    16.283
K                         0.111     0.059     0.059
Z                        39.774    39.576    39.591
M                         5.851    16.472    16.342
D                         6.886     0.690     0.781
R                         0.530     0.593     0.590
E(%)                     -4.602    -9.507    -9.126

an1 analcime I, orange, compact

an2 analcime I, pink crystal

an3 analcime II, colourless crystal

th1 thomsonite, colourless crystal
th2, th3 thomsonite, white fibrous
aggregate

na1 white natrolite, rim of crystal
na2 the same crystal, core

Z = Si + Al + [Fe.sup.3+]; M = Na + K; D = Mn + Mg + Ca +
Ba; R = Si / (Si + Al): E (%) = 100 (Al + [Fe.sup.3+]) - [Al.sub.th])/
[Al.sub.th]; AW = M + 2D (after Passaglia 1970)

Table 9 Representative microprobe analyses
of the amygdale zeolites

              gismondine                 phillipsite-Ca

Wt.%      gi1      gi2      gi3      ph1      ph2      ph3

SiO2    34.47    35.55    37.60    43.11    42.57    46.81
Al2O3   28.29    29.06    29.21    21.97     22.1    21.66
Fe2O3    0.21     0.00     0.16     0.16     0.13     0.14
MnO      0.19     0.05     0.14     0.26     0.16     0.11
MgO      0.59     0.68     0.82     0.69     0.50     0.64
CaO     15.13    14.79     14.9     6.14     6.16     7.26
BaO      0.23     0.29     0.41     8.74     7.78     2.88
Na2O     0.68     0.78     1.01     0.69     0.67     0.61
K2O      0.10     0.17     0.18     2.81     3.65     3.78
total   79.89    81.37    84.43    84.57    83.72    83.89

           formula per 32 (O)         formula per 32 (O)

Si      8.037    8.105    8.265    9.928    9.881   10.329
Al      7.773    7.808    7.567    5.963    6.045    5.632
Fe3+    0.036    0.000    0.027    0.028    0.024    0.024
Mn      0.038    0.010    0.026    0.051    0.031    0.021
Mg      0.205    0.231    0.269    0.237    0.173    0.211
Ca      3.779    3.613    3.509    1.515    1.532    1.716
Ba      0.021    0.026    0.035    0.789    0.708    0.249
Na      0.307    0.345    0.430    0.308    0.301    0.261
K       0.030    0.049    0.050    0.825    1.081    1.064
Z       15.846   15.913   15.859   15.919   15.950   15.985
M       0.337    0.394    0.480    1.133    1.382    1.325
D       4.043    3.880    3.839    2.228    2.444    2.197
R       0.508    0.509    0.522    0.625    0.620    0.647
E(%)    -7.280   -4.226   -6.926   -3.206   -5.146   -1.068

             gmelinite-Ca

Wt.%      gm1      gm2      gm3

SiO2    46.87    46.16    47.14
Al2O3   19.12    18.74    19.16
Fe2O3    0.31     0.00     0.16
MnO      0.12     0.00     0.00
MgO      0.00     0.00     0.00
CaO      4.88     4.93     4.58
BaO      6.22     6.58     6.29
Na2O     0.64     0.87     0.73
K2O      2.99     2.85     2.84
total   81.15    80.13    80.90

        formula per 48 (O)

Si      16.281   16.295   16.370
Al      7.828    7.797    7.842
Fe3+    0.081    0.000    0.042
Mn      0.035    0.000    0.000
Mg      0.000    0.000    0.000
Ca      1.816    1.865    1.704
Ba      0.847    0.910    0.856
Na      0.431    0.595    0.492
K       1.325    1.284    1.258
Z       24.189   24.092   24.254
M       1.756    1.879    1.750
D       2.698    2.775    2.560
R       0.675    0.676    0.676
4       10.576   4.957    14.761

gi1, gi2, gi3 gismondine, white
crystals

ph1 pale orange phillipsite-Ca

ph2 orange phillipsite-Ca

ph3 pale yellow phillipsite-Ca

gm1, gm2, gm3 gmelinite-Ca, pale
orange crystals

Z = Si + Al + [Fe.sup.3+]; M = Na + K; D = Mn +
Mg + Ca + Ba; R = Si / (Si + Al):
E (%) = 100 (Al + [Fe.sup.3+])--[Al.sub.th])/
[Al.sub.th]; AW = M + 2D (after Passaglia 1970)
COPYRIGHT 2003 Akademie Ved Ceske Republiky, Ustav Struktury a Mechaniky Hornin
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Author:Novak, Jiri K.; Ulrych, Jaromir; Chvatal, Marek; Langrova, Anna; Cajz, Vladimir; Adamovic, Jiri; Ryc
Publication:Acta Montana. Serie A: Geodynamics
Article Type:Report
Date:Jan 1, 2003
Words:11245
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