A geological and mineralogical review of clay mineral deposits and phyllosilicate ore guides in Central Europe – A function of geodynamics and climate change

Abstract

The Central European Variscides and their epicontinental basins and grabens (Mesoeurope sensu Stille) subsided into the uplifted basement as well as the Alpidic Orogens, encompassing the Alpine Mts. Range, the Dinarides, the Northern Carpathians and the depressions in between (Neoeurope) are rife with a great variety of clay mineral assemblages. In many places the clay mineral deposits reach economic grade and several phyllosilicates can be used as an ore guide to non-clay mineral deposits. Time, climate and the geodynamic setting are the decisive parameters for the clay mineral accumulation. Time constitutes the x-axis for the plots illustrating the global climate change and the regional geodynamic crustal variation. It is also some kind of a yardstick to measure the preservation potential and the stability of phyllosilicates. The geological time scale is equivalent to a depth of a drill hole which penetrates different geological units characterized by various zones of post-depositional alteration. As such the geological age of formation is synonymous with an increase of the P-T regime where important boundaries concerning the micaceous phyllosilicates, kaolinite-, smectite-group minerals and the composition of glauconite are observed.The Mg-bearing phyllosilicates are marker for the Permo-Carboniferous to early Triassic and for the Middle to Late Jurassic extensional regimes in Central Europe. They indicate an ensialic geodynamic regime in Mesoeurope and an ensimatic regime in Neoeurope. This is also true for the presence and absence of Li-bearing phyllosilicates and Li-bearing tourmaline and spodumene which are a mirror image of the Permo-Carboniferous compressive regime in the Variscides and the extensional regimes in the Alpides and indicative of an ensialic and ensimatic regime, respectively. In the ensimatic geodynamic setting of the Neo- and Paratethys during the Miocene and Pliocene a felsic volcanic activity in an interarc-to back arc environment brought about an Fe-poor clay mineral assemblage in an ensimatic setting. In the ensialic Variscides only small-sized kaolinite deposits can be taken as an equivalent. Some ferroan saponite and chlorite represent the basic branch of the bimodal rift magmatic activity. Bentonitic clays and bentonites in the Alpine and Carpathian Foredeeps are marker beds for rift-related explosive volcanic activity sourced particularly in the North Atlantic Province and important mineral deposits.Fe-bearing phyllosilicates, e.g. chamosite, in the Early Ordovician and Jurassic ironstones were emplaced in a marginal and epicontinental basins, locally with restricted circulation. The Alpine extensional regimes saw the formation of celadonite in a calcareous depositional environment open to ocean. They act as facies indicators.Some phyllosilicates act as a natural multifunction display. Corrensite and mixed-layer chlorite-corrensite are not only in altered basic magmatic rocks marker for basement rocks but also affected by extraterrestrial impacts. The glauconite-kaolinite-illite-smectite-chlorite assemblages are efficient tools for the depositional environment and the post-depositional alteration, all in one. There exists an antagonism par excellence in terms of the sedimentary environment of formation between glauconite and kaolinite The clay mineral catena together with palygorskite and sudoite can be used as a proximity indicator from land to sea from the various subenvironments, e.g., from a coastal sabkha to the alluvial fan. Chromium muscovite, Cr smectite, and Cr chlorite formed at the brink from hypogene to supergene alteration and pave the way from the geodynamic/ lithofacial - to the climate-induced clay mineralization. They are the most recent clay mineral assemblages in Central Europe proved by radiometric age dating (Mio-Pliocene).The humid-tropical paleoclimate zone occurred from the Late Triassic to the Late Cretaceous, the Late Cretaceous to the Eocene, and during the Miocene. In Central Europe these paleoclimates and the resultant weathering conditions were most effective in the formation of residual clay deposits dominated by kaolin and Ni-Co laterites (garnierites) enriched in Al-, Fe- and Mn-duricrusts of economic grade. The climax of formation was reached around the Paleocene-Eocene Temperature Maximum (PETM).The tropical wet and dry paleoclimate zone in Central Europe was widespread during the Jurassic and Cretaceous leading to similar residual clay deposits impoverished in duricrusts. Residual clays in the tropical arid and semi-arid paleoclimate zones have palygorskite, corrensite and sudoite as typical phyllosilicates which denote the widespread occurrence of evaporates with the precipitation level reaching the K salt and even bittern stages. These clay minerals appeared episodically from the Late Permian through the Late Triassic. It is a paleoclimatic zone still under-explored as to Al-rich Li-Mg-bearing phyllosilicates.The high economic potential of clay minerals in Central Europe may be discovered among construction and non-construction raw materials from cement-making materials to structural clay products. Second to none are clay minerals in the construction sector used for all kinds of bricks and tiles. The majority of clay deposits is allocated to the Cenozoic, mainly Paleogene, followed by Mesozoic, Paleozoic and Precambrian rocks which is a manifesto for the expression “Clay & Time”.