Acid magmatism and related metallogenesis in the Erzgebirge

Abstract

AbstractIn the Erzgebirge two post‐collisional Hercynian granitoid complexes are developed: an older one, monzogranitic, moderately specialized, Sri = 0·7064–68, εTNd = ‐1·8 to ‐6·2, 1g fO2 < −13 ± 1, 1g fHF/fH2O = ‐3·9 ± 0·2, S‐type, 340–325 Ma in age, and a younger one, monzo‐ to albitegranitic, highly specialized in Li, Rb, Cs, Sn, and W, Sri disturbed by strong autometasomatic influences, εTNd = −3·8 to −6·0, 1g fO2 < −17 ± 1, 1g fHF/fH2O = ‐3 ± 0·3, I‐type, 310–295 Ma. Postplutonic volcanics (rhyolite, rhyodacite, latite, kersantite–minette) in each case complete the magmatic sequences.Muscovite–wolframite–molybdenite–pyrite–quartz association is locally related to the older complex, but numerous centres of cassiterite–wolframite–zinnwaldite (or muscovite) deposits are related to the younger one. Both mineralizations are of orthomagmatic origin and underwent strong physicochemical control. Thus, the granites genetically related to the tin‐free older association are conditioned by medium fO2 but low fHF/fH2O, the tin‐bearing younger association, in contrast, is controlled by low fO2 coupled with high fHF/fH2O.Vertical compositional zonation in magma chambers caused enrichment of compatible elements such as Zn, Pb, Mg, Ca, Ba, Sr, in deeper parts of the chamber and their transition into residual solutions which then may form base metal mineralization as cross‐cutting veins. Mineralization events last up to the Triassic. Probably elements in the later stages were derived either from deep‐originated residual solutions or, increasingly, by leaching of specialized magmatites.