Original paper

Are the granites of the Aue-Schwarzenberg Zone (Erzgebirge, Germany) a major source for metalliferous ore deposits? A geochemical, Sr-Nd-Pb isotopic, and geochronological study

Förster, H.-J; Romer, R.L.; Gottesmann, B.; Tischendorf, G.; Rhede, D.

Abstract

The Aue-Schwarzenberg Granite Zone (ASGZ), in the western Erzgebirge of Germany, is composed of small, late-Variscan F-poor biotite and two-mica granites. The biotite granites (Aue granite suite, Beierfeld, Bernsbach) are weakly to mildly peraluminous (A/CNK = 1.07-1.14; 70-76 wt% SiO2), display similar 87Sr/86Sr initial ratios (0.7065-0.7077; t = 325 Ma), and exhibit a narrow range in εNd325 (-2.6 to -3.5). They are closely affiliated compositionally with the biotite granites in the distant, more voluminous Nejdek massif (Czech Republic). The two-mica granites (Schwarzenberg granite suite, Lauter) are Si-rich (74-77 wt% SiO2) and mildly to strongly peraluminous (A/CNK = 1.17-1.26). The granites from Schwarzenberg are distinctly higher in their Sri ratios (0.709-0.713; t = 325 Ma) and possess lower values of εNd325 (-4.9 to -5.2) relative to the biotite granites. The Lauter granites have a Nd-isotopic composition between -3.6 and -4.0 (t = 325 Ma). Mean Th-U-total Pb uraninite ages (Ma ± 2σ) obtained for the granites from the Aue suite (324.3 ± 3.1), Beierfeld (323.7 ± 3.1), Bernsbach (320.7 ± 2.9), Schwarzenberg (323.3 ± 2.4), and the Kirchberg granite at Burkersdorf (322.7 ± 3.5) indicate that magmatism in the ASGZ commenced in the Namurian and took place early within the major episode of granite formation in the Erzgebirge-Vogtland zone (327-318 Ma). Geochemical and mineralogical patterns of variably altered samples imply that the ASGZ granites are unlikely to have significantly contributed to the formation of spatially associated metalliferous ore deposits (Sn, W, Mo, Pb, Zn, Bi, Co, Ni), except for uranium. In particular the Aue granite suite should have served as major source for U accumulated in the economically important post-granitic deposits of Schneeberg and Schlema-Alberoda.

Keywords

granitessr-nd-pb isotopic compositionu-th-pb agesuraninitealterationu mineralizationvariscan orogenyerzgebirge