Clay Science 8, 319-327 (1992)

KAOLIN DEPOSITS OF CENTRAL EUROPE*

MILOS KUZVART Department of Mineral Deposits, Charles University, 128 43 Prague Czechoslovakia

(Accepted September 5, 1992)

INTRODUCTION - HISTORY OF KAOLIN UTILIZATION IN CENTRAL

EUROPE

Kaolin deposits in Central Europe are the basis of oldest porcelain production outside of the Far East - Meissen 1710, Karlsbad (Grun) 1792 a.o. So, it is exactly 200 years that Karlsbad kaolin is being used for production of porcelain and almost 100 years that the fundamental questions of kaolin genesis were discussed. Namely, all sections of Karlsbad deposits studied up to now in detail demonstrate that kaolin could not have been formed as the lower zone of laterites (there are no traces of ferruginous sediments in the rocks covering kaolin deposits), that it has no relation to younger coal seams and that the base of kaolinization lies above the erosion base of Paleogene surface, closely related to the pattern of drainage net, thus generally with no relation to juvenile thermal waters known from nearby Karlsbad spa . The same Karlsbad kaolin was the source of Zettlitz Standard kaolin between the two world wars. Namely, the Czechoslovak Ceramic Society proposed at the International Congress of the Union for Theoretical and Applied Chemistry held in Copenhagen in 1924, to declare the Zettlitz (Sedlec) kaolin from Karlsbad (Karlovy Vary) area as an international Standard. With this Standard all other kaolins could have been compared as far as mineralogical composition and technological properties were concerned . Nowadays, after depletion of the Sedlec deposit in 1961, the Standard Ia kaolin is produced by blending of raw material from deposits Hajek, Bozicany and Jimlikov . The composition and properties of washed kaolin produced in 1924 as compared with those of contemporary production (in brackets) are as follows: SiO2 46.27% (47.35%), Al2O3 39.36% (37.00% ), Fe2O3 0.74% (0.83%), TiO2 (0.20%), CaO 0.14% (0.65% ), MgO traces (0 .24%), alkalies 0.20% (1.11%), loss on ignition 13.31% (12.60%), clay substance 98 .5% (98.0%), quartz

1.2% (1%), feldspar 0.3% (1%), refractoriness 1770-1790•‹C (1790•‹C) , firing shrinkage at 1410•‹C 13% (13.2%), residue on sieve 0.06 mm 0.01% (0.01%), particle size 0 .0048 mm in average (0-0.001 mm 57%, 0.001 to 0.002 mm 16%, 0.002-0.003 mm 12% ) . The most valuable ceramic properties of the Karlsbad kaolin are its high strength. after drying and excellent moulding ability together with its white burning colour and good transparency of porcelain. The Karlovy Vary kaolin is also used in the production of sanitary ceramics , electrical insulators, and as a filler for rubber, paper, cosmetics, etc.

* Special lecture presented at 1992 annual meeting of the Clay Science Society of Japan 320 M. Kuivart

Nowadays kaolin deposits in Central Europe are the basis of local ceramic and paper industries and source of washed kaolin exported mostly to the western part of

(about 500 000 tons per year) . Central European kaolin deposits are interesting not only from the point of view of history of utilization and economic significance, but their genetic, paleoclimatological and tectonic aspects are also important for the study of kaolin deposits in general.

KAOLIN DEPOSITS IN CENTRAL EUROPE

Central European deposits are mostly situated on the crystalline rocks of the Bohemian Massif on the territory of Bohemia, Moravia, Austria, Germany and Poland. The kaolinic crust of weathering on Variscan granites in the environs of Karlovy Vary represents only a relic of the originally far more extensive Cretaceous to Paleogene crust, which has been preserved on the downthrown granite blocks on an area of approximately 85 square kilometres. It is covered by Tertiary sediments and volcanic rocks. Proved depth of kaolinization is more than 50 meters, but only 20 to 30 meters thick kaolin top zone (I) with all feldspar weathered is used. Zone II is distinguished by preserved cores of orthoclase phenocrysts in clayey matrix and zone III by unweathered cores of orthoclase and plagioclase also in the groundmass. High grade chinaware kaolin includes frequent blocks of low grade raw material, such as green kaolin high in chlorite and illite, rusty coloured oxidized surficial zones, zones with frequent quartz and quartzine veinlets. On the other hand; dykes of extremely pure kaolin high in clay substances may appear (e.g. abandoned deposit Bohemia), originated by weathering of differentiates of parent granite rich in feldspar. Where kaolin is covered by red weathered tuffs and tuffites, it is contaminated by red iron compounds. The main minerals of Karlovy Vary kaolin are: in the clay fraction kaolinite (close to pM type-maximum 6-7 ƒÊm, mostly less than 1ƒÊm large) and illite (5-10% in clay substance, 50% in fraction below 0.03 ƒÊm, di-octahedral illite is the carrier of trivalent Fe), and quartz, muscovite, accessory tourmaline, zircon, rutile, fluorspar, hematite, magnetite and pyrite in the coarse fraction (mostly 0.032-0.063 mm). Trivalent iron in kaolin is also bound in a not exactly specified form of iron oxide or hydroxide. These two minerals have different influence on the burning colour of kaolin than illite; therefore, materials with the same content of iron may have different colours when burned. Bivalent iron content is much lower than of trivalent, it is bound principally on pyrite and concentrates in the size fractions between 2 and 63 microns. Titanium is fixed in the structures of rutile and anatase. More than 95% of grain size below 2 microns in kaolin from Sedlec is formed by kaolinite. The rest is formed by micaceous mineral and quartz. Kaolin refined on industrial scale in the Karlovy Vary area have practically all the grains smaller than 20 microns, with only a negligible quantity of grains between 20 and 60 microns. The fraction close to 20 microns still contains over 80% of kaolinite besides 9% of mica and 10% of quartz in kaolin from Sedlec. The amount of kaolinite in the industrially refined kaolins oscillates around 90% . Kaolin Standard contains only 0.03% of grains over 0.06 mm. Kaolin deposits of Central Europe 321

Practical output in the dressing plants varies mostly from 20 to 30% of washed kaolin

(below 20 microns) with less than 10% humidity. Raw kaolins that contain unweathered black biotite (so-called black kaolins) from Sedlec district, after dressing offer suitable refined kaolin. In the same North Bohemian Tertiary Graben with downward fault throw of the bottom 800 m as the Karlsbad kaolin deposits to the Northeast kaolins on Precambrian biotite gneisses were exploited. To the SW of Karlsbad in the same graben in the Mitterteich Basin (Germany) there are kaolin deposits on Fichtergebirge granit near Tirschenreuth and Wiese with thicknesses to about 30 m. A remarkable circumstance is that only the

plagioclases are completely kaolinized, whereas the orthoclases have essentially remained unaffacted. In separate grabens kaolinized Carboniferous arkoses in the Pilsen Basin and near Podbofany are being exploited. The parent rocks of kaolin deposits in Plzen basin are arkoses, arkosic sandstones and conglomerates of Carboniferous age (Westphalian D-Stephanian). They are composed of

quartz, feldspar (up to 1-2 cm in diameter), muscovite, biotite and gravels of quartz, lydites, quartzites, porphyries and other rocks of Paleozoic and Proterozoic age. The kaolin deposits of flat lenticular form with dip of less than 20•‹ are conserved in a system of downthrown blocks. Intraformational Carboniferous kaolinization, contemporaneous with sedimentation, is proved by the occurrence of kaolinized arkoses in depths up to 200 meters, and intercalations of sandy clay in kaolinized arkose. The workable thickness of kaolin in the Plzen basin is only 20-30 m (southern part of the basin), or 60 m (northern

part). This higher degree of kaolinization near the recent surface is by some authors ascribed to the influence of younger (Upper Mesozoic to Lower Miocene) weathering of arkoses kaolinized slightly during the Carboniferous. Kaolin near Podbofany originated through weathering of the Permo-Carboniferous arkosic sandstones of fluviatile or lacustrinedeltaic origin. The kaolin deposits follow a narrow depression elongated roughly in the SW-NE direction. According to the degree of decomposition of feldspars, the kaolinized beds can be divided into the upper kaolinized zone containing more than 15 per cent of the kaolin substance (and attaining up to 30 m in thickness), and the lower kaolinized zone containing less than 15 per cent of the kaolin component (and exceeding 100 m in .thickness at Krasny Dvur). Karlsbad, Kadan, Pilsen and Podbofany are situated in grabens close to the centre of the Bohemian Massif. The kaolin deposits on the periphery of the Bohemian Massif are situated on the SE rim of the Massif. In the vicinity of Znojmo (Czechoslovakia) and Mallersbach (Austria) the orthog- neisses of Bites (deposits Plenkovice, Mallersbach), biotite granite (deposits Unanov, Niederfladnitz), and phyllites are kaolinized. Due to intense tectonic influences on the parent rocks the depth of weathering in these deposits is up to 80 m. Let us have a closer lock. on the Austrian deposits. The raw kaolin from Mallersbach consists of approximately 50% kaolinite and mixed-layer (•`1-3%), 42% quartz and feldspar (mainly orthoclase; plagioclase to orthoclase ratio 1:6), muscovite and heavy minerals. The X-ray investigation of the raw kaolin shows besides the characteristic kaolinite lines individual interferences from illite or hydromuscovite. The fine fraction <2ƒÊm 322 M. Kuivart

clearly contained not only kaolinite but also quartz, illite and hydromuscovite. The DTA-analysis of a mud fraction (<2 ƒÊm) indicated the presence of halloysite and small amount of decomposed mica (illite, hydromuscovite) . The electron-microscope pictures confirmed the presence of halloysite and the formation of the micaceous components or transformed micas. A green stratification of a very plastic material was observed which also occurred in combination with fissures. It was determined to be an iron rich montmorillonite. Niederfladnitz Deposit. The kaolinization achieves a maximum depth of about 40 m. The parent rock, outcropping along the edges of the flat basin, belongs to the "Pulkauer Mass" or the "Brno Intrusive Massif'. It is a pre-Devonic granite with large quantities of quartz, microcline, perthite, albite-oligoclase, and transformed biotite. Intercalations of phyllite-like often very tectonically deformed rocks and intercalations of amphibolites can be observed. Besides kaolin in situ, washed-over kaolin clays also occur. X-ray and DTA analyses of kaolin have shown the following mineral content:

kaolinite 40%

quartz 37% feldspar (microcline) 10-18% calcite 3% muscovite incl. clay-mica minerals

(illite, hydromuscovite) 1% limonite 0.5%

The accompanying clays, yellow, green and blue colored, contain 20-30% Al2O3 and have Seger cone refractoriness of 26-33. In connection with the genesis it should be noted that the kaolinization occurred only in part from above and is combined with faults. The deposits of Weinzierl and Kriechbaum (Austria) are situated on downthrown blocks, displaced along NW- and NE-running faults. The deposit Kriechbaum has an elongated lenticular shape with a WNW-strike, whereas the deposit Weinzierl is of rather irregular shape. The depth of kaolinization is around 40 m, of wich 12-13 are mineable. The content of kaolinite is 34% , illite 1-3% , quartz 44% , the rest is feldspar, muscovite and heavy minerals. Furthermore, there are some minor kaolin deposits, such as those in the vicinity of Passau (FRG) and the deposit Grametten near Litschau (Austria). On the NE rim of the Bohemian Massif, in Sudetes, kaolinized biotite granite near Vidnava was used for the manufacture of refractories. Farther North Polish deposits on the granite massif Strzegom - Sobotka are situated. Most of the Polish deposits in Lower Silesia to the North from Vidnava are situated in the granite massifs of Strzegom-Sobotka (deposits Zarow, Gola, Smialowice, Boleslawice, Viry, Dzierkow, Rortoka), on Strzelin-2ulova massif (deposits Wyszonowice, Kuropatnik, Gebczyce) and on gneisses (deposit Kamien). The most important polish kaolin mine is situated in the North-Sudeten Depression.

It contains Upper Cretaceous kaolinitic Oligocene-Miocene or Pleistocene covering (the deposit Boleslawice). The main minerals of kaolin, i.e. kaolinite, quartz and micas occur in all kaolins but in Kaolin deposits of Central Europe 323

variable proportions what depends on the origin of the deposit. Beside of the above minerals

there are many subordinate ones in the Lower Silesian kaolins. Those are feldspars, secondary micas, chlorites, smectites, iron carbonated and iron sulphides, iron oxides and titanium oxides and sometimes also unaltered accessory minerals of parent rocks such as zircon, titanite, apatite, epidote etc. Geochemical investigations of the primary and secondary kaolins from the Lower Silesian deposits yielded the unusually high contents of Pb, Sr and Ba as compared with the other trace elements. Concentrations of Pb, Sr and Ba sometimes reach values over 1000 g/t. Maximum contents of those elements in the secondary kaolin from the deposit Maria III were found in the grain class <2 ƒÊm, whereas in the primary kaolins developed both from the Strzegom and Strzelin granitoids often two different grain classes of each sample of kaolin bear high concentrations of Pb, Sr and Ba. Analysis of the chemical composition and characteristic morphological features of the studied grains proved that in the fine grain classes of kaolin commonly there occur minerals from the groups goyazite SrAl3 [(PO4)2(OH)5)]•H2O and plumbogummite PbAl3

[(PO4)2(OH)4]•H2O. The phosphate molecule contains La, Ce, Ba and Ca. In the Nowa Ruda Coal Basin (Poland) a lateritic weathering crust with overlying bauxites and various refractory clays was found under the Carboniferous layers. The weathering process took place in the Namurian (the bauxites are discordantly overlain by Westphalian material). The kaolin deposit Horna Prievrana near Poltar in Central Slovakia was derived by kaolinization of sericite phyllites, porphyroids and arkoses (Paleozoic) at least partially by action of CO2-changed waters connected with final basalt volcanism (Pliocene). Even recently in close vicinity of the deposit mineral springs with 1300-2750 mg/l of CO2 occur.

The kaolinization involved also the debris of the above mentioned rocks . The resulting material is locally described as kaolinic sands. The kaolinization reaches to 10-35 m (up to 64 m). The deposit is covered by kaolinized debris of the parent rocks (1 to 2 m) and kaolinitic clays and sand (Upper Pliocene , 6-25 m). It was discovered in 1966. The granodiorite kaolins of the Lusatian Massif on the northern rim of the Bohemian Massif show distinct zoning. The three-layer silicate zone is characterized by degraded greenish biotite, smectite, kaolinite and K-(Na-) feldspar. In the kaolinite zone also biotite and K-feldspar are weathered to kaolinite . The iron is fixed in the siderite or in the intergrowths of Fe-minerals and kaolinite (biotite pseudomorphoses) . Hematite and goethite occur only in minor amounts. By hydrocyclone separation most of the iron is removed. The whiteness of the kaolins is greatest in the fine-grained fractions . The refined kaolins contain 80-90% kaolinite, 10-20% mica/illite and very small amounts of quartz, siderite, organic matter and heavy minerals. Some kaolins have a red coloration (e.g. at Wiesa), with the iron fixed mainly in finely divided hematite. Characteristic of the granodiorite kaolin are the epitactic intergrowths of kaolinite and mica . The refined kaolins from Caminau have found wide-spread application as paper coating and filling agents. The whiteness of these kaolin amounts to 80% and can be further enhanced by bleaching. In the Meissen Massif and in the Meissen Eruptive Zone kaolins are being mined at

Seilitz (parent rock:pitchstone, Dobritz quartz porphyry, felsite) , at Schletta (pitchstone, 324 M. Kievan felsite), at Ockrilla (biotite, granite) and at Radeburg (syenodiorite). Typical of the pitchstone kaolins is the high content of illite-montmorillonite mixed-layer mineral derived from the volcanic glass. The main constituent of the quartz porphyry kaolins is kaolinite, whereas the bio- tite granite kaolins from Ockrilla contain, in addition to kaolinite, mica, smectite and unweathered feldspars. During the Lusatian overfolding the biotite granite was thrust into the Triassic arcoses. The kaolinization affected both rocks, therefore the kaolinization is definitely younger than the overfolding (Subhercynian stage). The syenodiorite kaolins consist of kaolinite, nontronite, dioctahedral mica, K-(Na-) feldspar, quartz and siderite. The uppermost parts of the profiles were leached with concomitant degradation of the nontronite and precipitation of the iron at ground-water level. The most important FRG deposits of ceramic kaolins are situated in the Kemmlitz area. These deposits are troughshaped, separated from each other by eminences of unaltered parent rock, and have thicknesses of up to 50 m. The main parent rocks are Kemmlitz and Rochlitz porphyries. The Kemmlitz prophyry kaolins (lava type) are rich in kaolinite and poor in mixed- layer mineral. The mineral distribution in the porphyric kaolin profile is largely the same in all deposits. In the Rochlitz porphyry (ignimbrite) kaolins however the distribution varies; usually they contain more mixed-layer mineral and less kaolinite than the lava type. A good deal of the quartz is very fine-grained (matrix quartz) and thus it makes up about 20% of the washed kaolins. Since all Kemmlitz kaolins contain the same minerals, though in varying amounts, they can be blended to produce various grades (Oka, BZ, Meka, Eka-S, Wolfka), each meeting specific standards. At present, the kaolin mined from the Fuchsberg-Sud deposit, one of the numerous kaolin deposits in the Halle area, is used for producing refined kaolins. The crude kaolin, derived from the Lobejun porphyry, consists of about 50% kaolinite, 5-10% mixed-layer mineral, about 40% quartz and up to 5% organic matter. By means of grading a refined kaolin is produced which is rich in kaolinite and contains <10% quartz and 10-20% mixed-layer mineral. The relatively high content of organic matter improves the flow properties. The kaolins of Spergau and Roblingen have formed from the arkoses of the middle Bunter sandstone. They consist a fine-grained kaolinite, illite-montmorillonite mixed layer mineral, muscovite and quartz. With decreasing grain size of the parent rocks the content of three-layer silicates and mineral impurities (Fe2O3, TiO2) increases. The parent rock of the kaolin mined in Spergau is sandstone in which thin clay lenses are embedded. If the sandstone has only few clay lenses, the kaolinite-rich refined kaolin contains only small amounts of mica and other mineral impurities. But with growing number and size of the clay lenses the content of mica and impurities increases. In the deposit at ROblingen, the kaolin profile consists of interbedded kaolinized sandstone, siltstone and clay with varying thicknesses. The refined kaolin is a blend of the three kaolinized rocks and its mineral composition and impurity content is determined by the varying proportions of the three types of crude kaolin. The greywacke kaolin of Espenhain, Cunnersdorf and Schwepnitz are characterized by a rather high content of illite/muscovite (>25%), kaolinite (35-40%) and quartz The content of mineral impurities is also high (Fe2O3 = 1.9-6.7%; TiO2 =1%). Kaolin deposits of Central Europe 325

Of the granitic kaolins have a limited occurrence in the FRG only those of Oberrengers-

dorf and Aue have been dealt with. The kaolinite zone at Oberrengersdorf contains

35-50%. kaolinite and halloysite, <10% three-layer silicates and 40-55% quartz . The

mineral impurities occur in local concentrations (brown and red patches) . In the three-layer silicate zone there is a definite increase in the content of illite montmorillonite mixed-

layer mineral and feldspar. The main clay minerals of the Aue kaolin (altered pegmatitic

granite), which may be of hydrothermal origin, are kaolinite (= 90%) and. illite In the SW neighbourhood of the Bohemian Massif kaolin deposits in the region of

Hirschau- () were derived by weathering of Lower Triassic

arkoses, probably by weathering contemporary with sedimentation or after sedimentation , by the action of underground waters.

The kaolinized arkoses are composed of quartz, potassium feldspar (mostly perthitic

microcline), kaolinite, small portions of micas and heavy minerals. The quartz is coarse-

grained size. In general the feldspar is fine-grained than the quartz and dispersed over the sand and silt fractions. The clay fractions are almost free of quartz and feldspar. The

kaolinite of -Schnaittenbach is a well-ordered one, showing sharp reflections in

X-ray diffraction patterns. Electron micrographs of the kaolinite show regular-shaped

pseudo-hexagonal particles. Pseudo-hexagonal books of kaolinite are even found in dressed kaolins. Small quantities of muscovite and occasionally biotite are found in the arkoses . Dioctahedral illite occurs only in the clay fraction <2ƒÊm. Accessory minerals in the fine sand and silt fractions are: ilmenite, leukoxene, anatase, rutile, haematite, tourmaline, monazite, xenotime, zircone, rarely sillimanite, andalusite, staurolite , magnetite, sphene. The parent rocks of the arkoses are the Moldanubian granites and gneisses , which is proved by these accessory minerals being present in the arkoses. The quartz in the arkoses is originated from the granites and gneisses, but the potassium feldspar from the granites only. The gneisses are almost free of potassium feldspar . The original composition of the arkoses is calculated at 55% of quartz and 45% of potassium feldspar at the basis of the rare elements Pb, Cu, Cr and P in the potassium feldspar and the kaolin.

Most important Central European kaolin deposits of hydrothermal origin are situated in the North of Hungary (Mad). The zone adjacent to the supply channel of hydrotherms consists of dickite + kaolinite, quartz, pyrite, illite. Next follow the illite-kaolinite zone , vermiculite-halloysite zone, and chlorite-montmorillonite zone.

AGE OF KAOLINIZATION IN CENTRAL EUROPE

The age of exogenous kaolinization can be determined with great accuracy, if there is a minor time-span between the origin of the parent rocks and the deposition of the overlying sediments (e.g. in the Berzdorf Basin, Lusatia, where volcanic rocks, formed in the Upper Oligocene-Lower Miocene, are kaolinized and covered by sediments of the Miocene age). This period however is usually of considerable length and given the necessary conditions a weathering crust could develop on the continent at any time within this period. Therefore, if the age of kaolinization at a certain locality is to be determined with reasonable accuracy, it is necessary to compare the results od studies of extensive areas. In Central Europe we distinguish two main periods of kaolinization, when the 326 M. Kuzvart palaeoequator crossed Central Europe: Upper Carboniferous and Upper Mesozoic to Miocene.

TECTONIC PREDISPOSITION OF KAOLINIZATION

Jointing, cataclasis, mylonitization and phyllonitization involving the rocks before kaolinization open the parent rocks for the agents of kaolinization to greater depth. Therefore, kaolin of greater thickness originates along tectonically affected zones. More- over, sericite of dynamometamorphic origin is more liable to kaolinization due to its greater surface than feldspar. Kaolin, once existing, is not eroded, but preserved in tectonic depressions (e.g. grabens), especially in the central part of the Bohemian Massif. In the Karlovy Vary area, the elongation of the deposit near Podlesi was caused by NW-SE jointing of granite. The elongation of the Vidnava deposit follows the strike of Sudetic faults (NW-SE). The mylonitization of the parent rocks causes an exceptional depth of kaolinization in the Laianky deposits (113 m) and Plenkovice (more than 80 m). Post-kaolinization faulting has preserved the kaolin deposits in Lusatia, NW-Saxony, Karlovy Vary area, Kadan area, Plzen Basin, near Podbofany and Znojmo in tectonic depressions.

CONCLUSION

What are the differences and common features of kaolins in Central Europe and Japan? Unlike in Japan, in Central Europe very few hydrothermal kaolins are exploited, inspite of the fact that small occurrences of such kaolins are known, e.g. close of Karlsbad and in the Carpathians. Nevertheless, the study of kaolins in Central Europe and Japan is carried out in cooperation for more than two decades. The 1st Kaolin symposium during the 23rd IGC in Prague in 1968 was carried out under somewhat dramatic circumstances. Other kaolin symposia attended by scientists from the whole world followed in Spain, France, England, Mexico, East Germany, Australia. The 7th symposium was organized in Japan 1976. We from Central Europe have heard interesting lectures, seen important deposits and accepted new impulses for research.

REFERENCES

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Proceedings of the 10th Kaolin Symposium (IGCP Project No.23), Acta Miner. - Petrogr. 24, Supplementum, 101-110, Budapest. WIEDEN, P. (1978) Kaolin in Austria. - Guide to excursion of the 9th Kaolin Symposium (IGCP Project No.23), 1-16, Wien.