Geochemical Atlas – Erzgebirge and Vogtland

Thorium (Th) shows a nearly log normal distribution with an arithmetic average of 6.2 mg/kg and a median of 5.3 mg/kg. The absolute maximum is 184 mg/kg and the lowest recorded value is 0.2 mg/kg. The element is partially affine to acidic igneous rocks whereas the intrusions of the study area show important mutual differences in Th concentration. Especially, in the western Erzgebirge, a 5 km NE-SW extending area stands out at the central Kirchberg granite, presenting maximum Th levels of Th > 25 mg/kg. In the eastern Erzgebirge the Schellerhau granite and SE adjacent Teplice rhyolites covering the Zinnwald-Cinnovec Sn-Li-greisen deposit coincide with an 8 km NW-SE extending area of Th > 16 mg/kg. Furthermore, the western part of the Eibenstock granite is related to a west-convex, arc-like area of Th > 6 mg/kg, with a southward increase and a sharp westward decrease at the contact of the granite with Cambro-Ordovician phyllites. An area of nearly similar concentration, only slightly above the arithmetic average, characterises the Markersbach granite and the N-extension of the Altenberg-Teplice Caldera in the eastern Erzgebirge. Also, parts of the Westerzgebirge Complex deposit and an arc of Ordovician metasediments surrounding the Devonian rock units near Oelsnitz in the Vogtland show slightly elevated Th levels. Additionally, Cambro-Ordovician metapelites of the northern study area NW of the Augustusburg deposit coincide with Th levels > 6 mg/kg. Minimum concentrations of Th < 1.6 mg/kg are related to the Fichtelgebirge pluton in the upper Vogtland and to several spots within Proterozoic gneisses of the eastern Erzgebirge such as the area between Freiberg and Dippoldiswalde.