| Popis: |
Fluid inclusions hosted within various lithologic units of the >40 million metric ton (Mt) Matagami district, Abitibi greenstone belt, preserve samples of Archean volcanogenic massive sulfide (VMS) and postvolcanogenic massive sulfide hydrothermal fluid. Microthermometric measurements on ore-hosted primary two-phase liquid-vapor inclusions from Matagami’s south limb deposits indicate that the VMS hydrothermal fluid was highly saline (16.2 ± 4.7 wt % NaCl-CaCl2 equiv, 1σ, n = 230) and of moderate temperature (trapping temperature, Tt = 208° ± 32°C, 1σ, n = 230). A fluid with these characteristics is capable of transporting ~5 × 10−4 m (30 ppm) Zn as ZnCl3 − and ZnCl4 2− chloride complexes. However, the low temperature of this fluid precluded efficient Cu transport (≤ 3 ppm), which may in part explain the relatively Cu poor nature of the Matagami deposits. Calculated densities of this ore fluid as high as 1.10 g/cm3 are consistent with a bottom-hugging brine model. However, a subset of the data indicate a fluid less dense than ambient seawater, suggesting that buoyant hydrothermal plumes were also present. A microthermometrically determined high CaCl2 content (XNaCl |
