Mineralogy and mineral chemistry of detrital platinum-group minerals and gold particles from the Elbe, Germany

• Published in: European journal of mineralogy (Stuttgart) 2023-07, Vol.35 (4), p.439-459
• Main Authors: Junge, Malte, Goldmann, Simon, Wotruba, Hermann
• Format: Article
• Language: English
• Subjects: Alloys; Cassiterite; Dikes; Drainage; Drainage area; Electron probe microanalysis; Electron probes; Ferrous alloys; Geology; Gold; In situ leaching; Iridium; Leaching; Light microscopy; Metamorphic rocks; Microscopy; Mineralization; Mineralogical research; Mineralogy; Minerals; Monazite; Optical microscopy; Osmium; Platinum; Rims; Rivers; Ruthenium; Sand & gravel; Scanning electron microscopy; Sediments; Silver; Transportation; Zircon
• ISSN: 1617-4011; 0935-1221; 1617-4011
• DOI: 10.5194/ejm-35-439-2023

In heavy mineral concentrates of the Elbe, gold and platinum-group minerals (PGMs) are observed. Two fractions (> 63 and  80 atom %), (2) ferroan Pt (20 atom % to 50 atom % Fe), (3) isoferroplatinum (2.64 to 3.04 apfu of sum PGE, platinum-group element), (4) tetraferroplatinum group with Ni + Cu + Fe ≈ 50 atom %, and (5) γ(Pt,Fe) with sum PGE > 3.04 apfu. The Os–Ir–Ru–(Pt) alloys show large compositional variations. Platinum and Fe enrichment is typically observed for Ir-rich Os–Ir–Ru alloys. Gold particles often show compositional zoning of Ag-rich cores and Ag-poor rims due to selective leaching of Ag. Similarly, Hg-rich rims of gold particles are analyzed. These are interpreted as the results of in situ amalgamation due to mobilization of Hg from the associated cinnabar particles. The size and shape of the gold particles generally argue for short transportation distances. Similarly, almost euhedral sperrylite and Pt–Fe alloys suggest a source region close to the sampling site. However, roundish Os–Ir–Ru–(Pt) alloys presumably have experienced longer transportation in the river. Gabbroic dikes of the Lusatia block contain sperrylite and gold particles, which can be the source for these particles found in the concentrate. The composition of the Os–Ir–Ru–(Pt) alloys is similar to previous studies on the Vestřev placer in Czech Republic. Both locations are within the drainage area of the Elbe and can therefore be the source of the PGM and gold particles in the concentrate.