Topography-driven hydrothermal breccia mineralization of Pliocene age at Grimsel Pass, Aar massif, Central Swiss Alps

摘要: Fault-bound hydrothermally mineralized breccias with a multistage deformation history occur in crystalline rocks of the Aar massif at Grimsel Pass, Central Swiss Alps. The crop out over 4.5 km E‐W along strike and 900 m vertical extent between Trubtensee Gletsch, are up to 2 wide. A characterization these “Grimsel Breccias” was carried elucidate their formation respect alpine uplift fluid circulation history, search for possible evidence past microbial activity. Breccias vary widely grain size range from matrix-rich clast-supported high porosity youngest equivalents. Centimeter-sized voids typically contain stratified geopetal infills fine-grained hydrothermal minerals. mineral assemblage is dominated by quartz (including chalcedony), adularia, illite, celadonitic clay minerals, pyrite (As-rich), marcasite, Mo-sulfide. Analyses bulk (kg) small subsamples (grams) show significant enrichments Mo, As, Sb, Au, Cs, Hg, Tl some samples U. Subthermal thermal springs currently discharging breccia zone Gletsch (18‐19 °C) into gas pipeline tunnel intersecting (up 28 °C), indicating ongoing deep fracture system related Breccia. Microbial biomass Fe‐Mn precipitates enriched Pb, Mn, W, demonstrating that several elements also transported and/or redistributed active water system. 39Ar/40Ar dating late-stage adularia yielded middle Pliocene age (3.30±0.06 Ma), 0.3 1.2 below sea level, if current rates assumed. estimated depth ~3 palaeosurface. Oxygen isotopes combined inclusion data, indicate temperature ranging 160 down approximately 100 °C latest stage. Fluids were low-salinity dominant meteoric component 18O close ‐10‰ SMOW. D values illite-rich consistent water. Pyrite 34S shows limited scatter slightly negative average ‐1.8‰ CDT, an origin sulfide thermochemical reduction Triassic sulfate 220‐260 greater depth. signatures activity during revealed presence extremely uraninite potential microbiological origin, ill-preserved filamentous structures laminated fabrics potentially biofilms, but no indisputable biological involvement. mineralization area demonstrates waters penetrated caused mineralizations geochemically similar epithermal ores associated volcanism. probably derived combination sources (Au, Tl) near-surface oxidized fluids (Mo, U), element precipitation may be result mixing cooling.