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The late-collisional Erzgebirge granites (~325–318 Ma) were INTRODUCTION emplaced at shallow crustal levels in the Variscan metamorphic The Erzgebirge is a NE–SW trending antiformal structure basement shortly after large-scale extension caused by orogenic exposing Variscan crystalline basement rocks at the northcollapse. These granites comprise mildly peraluminous transitional ern margin of the Bohemian Massif. The region is famous I–S-types and strongly peraluminous S-type rocks, which can be among economic geologists for its extensive and highly subdivided into three major groups: low-F biotite granites; low-F variable metallic ore deposits, which have been mined two-mica granites; and high-F, high-P2O5 Li-mica granites. The since the Middle Ages (e.g. Stemprok & Seltmann, 1994; highest degree of differentiation is reached in the Li-mica granites, Tischendorf & Forster, 1994), and for the classic studies which exhibit strongly elevated concentrations of P, F, Li, Rb, Cs, in the fields of economic geology, mining and metallurgy, Ta, Sn, W and U; but very low Ti, Mg, Co, Ni, Sr, Ba, Y, Zr, chemistry and mineralogy (e.g. Werner, 1791; Breithaupt, Hf, Th and rare earth elements. Crystal–melt fractionation is the 1849; Agricola, 1974). dominant process controlling the bulk composition of all groups of As in many of the other Variscan provinces in central granites. However, metasomatic processes involving late-stage residual Europe, granitic rocks make up a large proportion of the melts and high-T orthomagmatic fluids became increasingly more exposed rocks in the Erzgebirge, and a great variety of important in highly evolved units and have modified the abundances compositional and textural types occur (Fig. 1). Knowof mobile elements (P, F, Li, Rb, Cs, Ba, Sr) in the Li-mica ledge of the processes involved in the generation and granites particularly. Isotopic and geochemical characteristics suggest evolution of these silicic magmas is essential for underthat the three granite groups cannot be derived from a common standing heat and mass transport during the Variscan precursor magma. Their discrete compositions are source related, orogeny, and also for the formation of metallic ore and are attributed to melting of quartzo-feldspathic and pelitic deposits. Several lines of evidence indicate that early, crustal lithologies in different proportions. Granites are common in high-temperature Sn–W deposits are associated with the the central European Variscides, but the Erzgebirge is unusual for emplacement of highly evolved, volatile-rich granitic the predominance of evolved Li-mica granites associated with melts (Tischendorf, 1986; Forster & Tischendorf, 1992; economically important Sn, W and U deposits. The abundance of Stemprok, 1993). The role of the granites in formation of Li-mica granites is attributed to a combination of favourable factors: later Permian (U, Pb–Zn) and younger ore mineralization (1) low degrees of anatectic melting of crustal protoliths; (2) wide (F–Ba) is controversial, but good evidence exists that the distribution of fertile lithologies rich in large-ion lithophile elements vein-type U deposits owe their uranium to leaching from and ore elements; (3) extended magmatic differentiation by crystal– the uraninite-rich granites (e.g. Tischendorf & Forster, melt fractionation and subsequent autometasomatism. 1994). |
