The Hämmerlein skarn-hosted polymetallic deposit and the Eibenstock granite associated greisen, western Erzgebirge, Germany: two phases of mineralization—two Sn sources

The Hammerlein polymetallic deposit is hosted in skarn, schists, and gneisses that reached their metamorphic peak at ~ 340 Ma during the Variscan orogeny. The deposit is spatially closely associated with one of the most voluminous granites of the Erzgebirge, the Eibenstock granite which intruded the metamorphic units at ~ 320 Ma, and locally also developed greisen mineralization. Cassiterite is the main ore mineral in the Hammerlein skarn and in greisen mineralizations associated with the Eibenstock granite. The age of skarn formation is bracketed by multi-mineral Rb-Sr isochron ages of the gneisses (~ 340 Ma) and the end of ductile deformation (> 330 Ma). The dated calc-silicate minerals of the skarn have elevated Sn contents, which implies that some Sn was present in the system during regional metamorphism, i.e., well before the emplacement of the Eibenstock granite. Tin in the > 330 Ma old skarn silicates possibly was mobilized from the metamorphic wall rocks. Retrogression of the skarn mineral assemblage may have released some Sn that formed cassiterite in an assemblage with chlorite and fluorite. The Sr isotope signatures of fluorite indicate that this late assemblage is not related to cooling of the metamorphic rocks, but to the emplacement of the Eibenstock granite, which introduced additional Sn into the skarn. Thus, mineralization in the Hammerlein deposit includes Sn that was introduced during two different events from different sources.