Title

Genesis of hydrothermal silver-antimony-sulfide veins of the Bräunsdorf sector as part of the classic Freiberg silver mining district, Germany.

Authors

Burisch, Mathias; Hartmann, Anthea; Bach, Wolfgang; Krolop, Patrick; Krause, Joachim; Gutzmer, Jens

Abstract

The peripheral regions of the Freiberg vein-type silver mining district comprise several sub-districts of which Bräunsdorf was among the richest in terms of Ag grade. Historically, 114 t (about 3.9 million ounces) of Ag were produced from the Neue Hoffnung Gottes mine near Bräunsdorf. The Neuer Segen Gottes Stehender is a sigmoidally shaped NNE-SSW trending vein, which varies significantly in thickness (0.05 to 3 m) and extends over about 2.6 km strike length at the surface. The vein infill is marked by a Pb-Zn-Cu-Fe-sulfide-quartz (stage 1) and an abundant Ag-Sb-sulfide/sulfosalt-quartz ± carbonate assemblage (stage 2). To develop a sound genetic understanding of the polymetallic mineralisation in the Bräunsdorf sub-district, we conducted detailed textural analyses of ore and gangue minerals, fluid inclusion analyses, electron microprobe analyses and thermodynamic computations in order to characterise the ore fluids and ore-forming processes. The early-stage Pb-Zn-Cu-Fe-sulfide mineralisation (stage 1) is related to fluids with low salinities (0.5-4% eq. w(NaCl)) and formed at temperatures ≥ 300 °C. Microthermometric data related to the Ag-Sb-sulfide/sulfosalt assemblage (stage 2) show similar salinites compared to ore stage 1, but have significantly lower homogenisation temperatures in the range of 180-280 °C. Based on fluid inclusion data, cooling can be regarded as the major ore-forming process. Reaction path model calculations for cooling of fluids with different initial pH values (4, 5.5 and 7) reproduce the observed mineral assemblages very well and predict spatial zonation of the Ag-Sb- and Sb-sulfide minerals that are in excellent agreement with field observations. We conclude that Ag-rich zones may well occur below Sb-rich zones in hydrothermal vein-type systems similar to those of the Freiberg district. This relationship may be of potential use for exploration targeting.

Subjects

VEINS (Geology); SILVER; ANTIMONY; SULFIDES; HYDROTHERMAL deposits; MINERALIZATION; STIBNITE; FLUID inclusions

Publication

Mineralium Deposita, 2019, Vol 54, Issue 2, p263

ISSN

0026-4598

Publication type

Academic Journal

DOI

10.1007/s00126-018-0842-0