Gold and silver deportment in sulphide ores - a case study of the Freiberg epithermal Ag-Pb-Zn district, Germany

Deportment data is essential for the planning of mining and minerals processing operations. This need is particularly tangible for deposits of noble metals, such as gold and silver. Therefore, the current paucity of published gold and silver deportment data for individual ore deposits and districts – and the concomitant lack of understanding how this relates to salient geological and mineralogical features of these deposits – is surprising. In the present study, we apply a combination of bulk geochemistry, laser ablation-inductively coupled plasma-mass spectrometry, electron microprobe analysis, and mineral liberation analysis to gold- and silver-rich samples from the epithermal Freiberg Ag-Pb-Zn district, to investigate variability in gold and silver deportments, as well as the corresponding geological/mineralogical controls. The results show that the main carriers of gold are electrum and arsenopyrite, whereas silver is mostly hosted by Ag-sulfosalts (pyrargyrite, miargyrite, polybasite) and fahlore (freibergite). Deportments vary greatly between samples. These variations can be related to the relative abundances of different minerals within the samples, which in turn reflect their spatio-temporal position within the district. Comparisons with other epithermal Ag-Pb-Zn districts similar to Freiberg indicate that the results presented here are of general significance.