Polymetallic nanoparticles in pyrite from massive and stockwork ores of VMS deposits of the Iberian Pyrite Belt

• Pyrites from VMS deposits of the Iberian belt host NPs. Colloform pyrite contains mainly As–Fe–Pb–Cu Euhedral stockwork hosts Au Transport and precipitation metallic NPs by polymetallic melts. This paper reports first-ever study on nanoscale mineralogy in volcanogenic massive sulfide (VMS) Pyrite Belt, southwestern Peninsula. It targeted colloform-textured grains formed at low temperature distal part a (Pb-Zn) lens hosted felsic volcanoclastic rocks Masa Valverde deposit, euhedral-textured (re)-deposited higher fluids Co-Au rich black shales Filón Norte orebody Tharsis deposit. The results acquired combination techniques for mineral microanalysis characterization (i.e., reflected light, FE-SEM, EPMA, LA-ICP-MS, HRTEM-STEM TEM-EDS) show that trace amounts metals (Au, Ag, As, Pb, Sb, Cu, Co) are incorporated as both lattice-bound into nanoparticles (NPs). mode occurrence is strongly related with evolutionary history mineralization. In colloform collected lens, rhythmic banding/oscillatory zonation up to 3 wt% 5,000 ppm 1,070 Sb 750 Cu defined coexistence several nano-sized layers (5 100 nm) (<100 containing all these metals. include galena [PbS], tetrahedrite [(Cu,Fe) 12 4 S 13 )] arsenopyrite [FeAsS] exhibit euhedral less frequently anhedral droplet-like) morphologies being randomly preferentially oriented respect As-rich bands they usually associated with. These features suggest formation via direct deposition hydrothermal fluid(s) or low-temperature melts entrained them well exsolution elements originally dissolved structure. Additionally, some connected late fractures disrupting chemical zoning documenting third genetic type infiltration post-dating formation. contrast, form well-developed homogeneous discrete porous areas relatively depleted Fe (45.20 wt%), As (8,800 ppm) but enriched Co (5,900 ppm). At nanoscale, Co-enriched domains patchy irregular distribution Co– 200–500 nm thickness. nanometer often disrupted micron-to-nano-sized polycrystalline Au-Ag-Hg particles fill voids areas. Contact morphology anatomy between Co-rich inclusions suggests negative crystals occupying spaces originated coupled dissolution-reprecipitation reaction. Likewise, HRTEM observations along such pyrite-inclusion contacts existence matrices inclusions, former consisting arsenian and/or As-free made multiple crystal including nano-crystallites 0 /Ag electrum. Recognition crystalline nanodomains raises possibility nanomelts already present fluid catalyzed heterogeneous crystals.