Fig. 7
Microstructures of the GBF. a Unmineralised, clast-supported breccia with angular clasts of mylonite in a matrix of finely milled rock (GR17). b Prominent dark clast of sulphide-stained microcrystalline-quartz-cemented microbreccia (first generation) rebrecciated in light grey matrix (second generation) and subsequently discreetly fractured (third generation) and incompletely mineralised with zoned quartz (GR22). c Breccia supported by clasts of grey-black, microcrystalline-quartz-cemented cataclasite (1), with comb quartz (2) partially occluding interclast porosity and late, brownish geopetal cherty infills (3), (GR22). d Small, unmineralised fracture within the mineralised zone, 34Â m from the master fault, in strongly foliated gneiss of the Grimsel Zone (SD-14-11) e Fine grained chert infill with upwards-fining geopetal cap (see arrow), overgrown by comb quartz, evenly around the pore (GR35). f Geopetal banding of quartz and chert in a pore with at least eight discernible quartz bands (GR35)