Fluid inclusions in emerald from the Jos complex (Central Nigeria)

Fluid inclusions in emerald from the Jos complex, Central Nigeria, were investigated by microthermometric and Raman techniques. The emerald was sampled in a miarolitic cavity of alkaline granite affected by autometasomatic albitization. Primary fluid inclusions are randomly distributed within the central part of the emerald and arranged along the growth faces of crystals in the middle and outer parts of the emerald. Pseudosecondary inclusions are present in every emerald growth stages. There are two types of fluid inclusions: (1) multiphase inclusions which are composed of a Na-Ca-Cl solution with a bulk salinity up to 45 wt%, low-density volatile phase (CO₂ ± CH₄ ± H₂S), halite and calcite ± Mg-calcite ± aragonite; (2) volatile-rich, water-free and water-bearing CO₂ fluid inclusions with a CO₂ phase of very low density (< 0.13 g/cm³). Both types of inclusions are distributed within the middle and outer parts of the emerald and related to the emerald growth. Fluid inclusion data indicate emerald crystallization conditions of the early and intermediate growth stages at 400 to 450 °C and 0.2 to 0.3 kbar.