Timing and origin of skarn-, greisen-, and vein-hosted tin mineralization at Geyer, Erzgebirge (Germany)

This contribution presents new insights into the origin and age relationships of the Geyer tin deposit in the Erzgebirge, Germany. Tin mineralization occurs in skarns, greisen, and in cassiterite-bearing fluorite-quartz veins. Skarn alteration replaces marble layers of the Cambrian Jachymov Group and occurs in two clearly distinct stages. The first skarn stage forms skarnoid textured assemblages of clinopyroxene, garnet, and wollastonite with no tin phases recognized. Garnet U-Pb ages of this skarn stage (similar to 322 Ma) relate the earlier skarn stage to the emplacement of the Ehrenfriedersdorf granite (similar to 324 to 317 Ma). The second stage of skarn alteration is marked by the occurrence of malayaite and cassiterite associated with garnet recording ages of 307 to 301 Ma. Greisen- and skarn-hosted cassiterite-bearing veins provide U-Pb ages in the range of 308 to 305 Ma, relating greisenization and vein formation to the same magmatic-hydrothermal event as the second skarn stage. This suggests that tin mineralization at Geyer is related to a distinctly younger magmatic-hydrothermal event, clearly postdating the Ehrenfriedersdorf granite, which was previously assumed as the source of the tin-rich fluids. Fluid inclusions show salinities in the range of 1.0 to 31.5 % eq. w(NaCl +/- CaCl2) and homogenization temperatures between 255 and 340 degrees C. Cassiterite-associated fluid inclusions show indications for heterogeneous entrapment and dilution of hydrothermal with meteoric fluids. Dilution of high-salinity fluids with low-salinity fluids and cooling of the system was probably a decisive process in the precipitation of cassiterite in the Geyer Sn system.

Automated summary

This contribution provides new insights into the origin and age relationships of the Geyer tin deposit in Germany. Tin mineralization is found in skarns, greisen, and cassiterite-bearing fluorite-quartz veins. The ages of different stages of skarn alteration and cassiterite vein formation suggest that the tin mineralization is related to a younger magmatic-hydrothermal event. Fluid inclusions analysis indicates that dilution of high-salinity fluids with low-salinity fluids and cooling of the system played an important role in the precipitation of cassiterite in the Geyer Sn system.