Abstract

The compositions of fluid inclusions hosted in emerald and quartz (the Maria deposit, Mozambique) were studied using microthermometric and Raman microprobe techniques. The fluid inclusions in the emerald contain fluids within the Na-Ca-Mg-(HCO3)-(CO3)2−-Cl-H2O system saturated in carbonic acid brines. Nahcolite is a main daughter solid phase within the fluid inclusions. The mean nahcolite and NaCl contents are 25 and 5 wt.%, respectively. Mg-calcite, magnesite, calcite and aragonite are also identified as daughter phases in the fluid inclusions. Many fluid inclusions show necked-down appearance. Groups of nahcolite crystals often make up ~50 vol.% of necked-down inclusions. It seems that zones of fluid inclusions with numerous birefringent solid phases are distinctive of the Maria emerald deposit. The likely conditions of emerald growth are 400 < T < 500°C and 3 < P < 4 kbar.

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