The essence of time – fertile skarn formation in the Variscan Orogenic Belt

Extending from Northern America to Central China the Variscan belt is a Paleozoic Orogen exceptionally well endowed in magmatic-hydrothermal ore deposits, including skarn deposits. Yet, the genesis of fertile skarns and their distinction from barren equivalents in orogenic zones is only poorly constrained. Here, we present innovative U-Pb laser-ablation inductively-coupled-plasma mass-spectrometry geochronology of garnet from different skarns in the Erzgebirge, a classic metallogenic province in central Europe. Garnet ages obtained not only constrain the timing of fertile skarn formation and associated Sn, W, Fe, Zn, Cu and In mineralization, but also clearly distinguish these from barren skarn bodies. We show that barren skarns formed during times of peak regional metamorphism at ∼340 Ma whereas mineralized skarns are temporally associated with late-orogenic magmatism at ∼325-313 Ma as well as post-orogenic magmatism at ∼308-295 Ma. The recognition of discrete mineralization events associated with the largest and economically most important skarn deposits provides valuable insight into the punctuated evolution of magmatic-hydrothermal systems in ancient collisional orogens on a regional scale; this has important implications to direct future mineral exploration.