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 Germany (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.