Geochemical evolution of the Variscan granitoid magmatism as related to the metallogeny of the Bohemian Massif

The Bohemian Massif in Central Europe is known as an extraordinary metallog enic province dominated by the Variscan granitoid magmatism. Its ore potent ial comprises tungsten-tin, uranium, gold, and silver-base metal mineraliza tions. It was, however, unclear why the highly productive W-Sn mineralizati on is associated in the Bohemian Massif only with the Erzgebirge intrusive system. The geochemical analysis reveals that the Variscan igneous rocks of this province, including early intrusions of durbachites as derivatives of the potassic alkaline basaltic magmas, were initially enriched in incompat ible granitophile rare elements. According to recent data, the prolonged, c ollision-related formation of the different Variscan intrusive systems last ed for 15 to 30-40 Ma. The hybrid tonalites and granodiorites, whose format ion was accompanied by a host rock assimilation. are depleted in granitophi le elements as compared to the initial durbachites. The subsequent differen tiation of the palingenetic hybrid magmas resulted in the formation of larg e masses of adamellites and granites with concentrations of granitophile el ements (rare-metal potential), being slightly higher than in durbachites. C onsequently, the ore productivity of adamellites and granites with respect to W-Sn mineralization was low, and these reeks are accompanied only by non commercial mineralization, The postcollisional stage (or tectonomagmatic re activation) was developed only in the Erzgebirge intrusive system. It laste d for 15 Ma, when the late leucogranite complex was emplaced, which is extr emely enriched in rare granitophile elements and accompanied by a highly pr oductive W-Sn mineralization. An abrupt increase in rare metal potential in leucogranites, coupled with their vast volume comparable with that of the preceding collisional granites, indicates that the ore component accumulati on could not be caused by selective melting or magma differentiation. An ex tremely high ore potential of the complex, together with high rare element contents in early durbachites, requires an influx of volatile (F, B), rare, and ore (W, Sn, and U) elements to the deep basaltic and associated crusta l magma chambers. The scale of this influx is proportional to the duration of the intrusive system activity. Unlike the W-Sn mineralization of the gre isenization stage mutually related to the late leucogranite differentiates of the intrusive systems, the postmagmatic hydrothermal mineralization (gol d, silver-base metal, and uranium) accompanied both the early and late stag es of the Variscan magmatism. The intensity of hydrothermal mineralization correlates with a rare metal potential of initial durbachites.