Origin of Palaeoproterozoic, sub-seafloor Zn-Pb-Ag skarn deposits, Sala area, Bergslagen, Sweden

Abstract Unravelling the genesis of metamorphosed mineral deposits can be complicated due to difficulties in separating between primary features and that formed during metamorphic overprint. Such uncertainty exists for stratabound dolomite- skarn-hosted Zn-Pb-Ag sulfide 1.89 Ga rocks Bergslagen lithotectonic unit (BLU) Sweden, where a metasomatic vs. regional origin skarns has long been discussed. By integrating geological mapping with new lithogeochemical, mineralogical, stable isotope data (C, O, S), we show complexly zoned garnet clinopyroxene Sala area central BLU predate mineralization. Sphalerite-galena mineralization after deposition younger, more Mn-rich ferroan diopside andradite-grossular garnet, is associated phlogopite, tremolite-actinolite, chlorite, serpentine, calcite. Mineralization conjunction transition from high-T metasomatism hydrolytic alteration inferred. An average δ 34 S V-CDT 1.6 ± 1.9‰ sulfides consistent primordial sulfur source. Trends defined by negative shifts 18 O V-SMOW 13 C V-PDB dolomite calcite are fluid infiltration at 300–500 °C. The system sharply truncated unaltered, c. calc-alkaline granite porphyritic intrusions, which along F 1 folding zones suggest metamorphism. interpreted as Zn skarn emplacement intrusions into penecontemporaneous marine volcanic dolomitized limestone strata. unusually Mg-rich mineralogy relation worldwide most likely reflects dolomitic precursor.