Mineral and fluid inclusion study of emeralds from the Lake Manyara and Sumbawanga deposits, Tanzania

✍ Scribed by I. Moroz; Y. Vapnik; I. Eliezri; M. Roth

• Book ID: 104354052
• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 797 KB
• Volume: 33
• Category: Article
• ISSN: 1464-343X
• DOI: 10.1016/s0899-5362(01)80070-1

✦ Synopsis

Mineral and fluid inclusions were investigated in Tanzanian emeralds sampled in the Lake Manyara and Sumbawanga deposits. Microthermometry and Raman microprobe analyses were applied for this study. Primary and pseudosecondary H20-CO 2 inclusions, with numerous daughter solid phases, are common in the emeralds from the Lake Manyara deposit. Magnesite, Mg-calcite, aragonite, dolomite, calcite, nahcolite, quartz and chrysoberyl were identified as trapped solids in fluid inclusions. Similar mineral inclusions were also found in the emeralds themselves. The composition of the trapped fluid present at emerald growth is estimated to be a carbonic-rich solution with chloride content of about 6 wt% NaCI equiv. The P-T conditions of emerald growth are as follows: T=370-470°C and P= 3.0-7.0 kbar. Mineral inclusions of phenakite, euclase, bertrandite and helvite are common in the emeralds of the Sumbawanga deposit. CO2-rich inclusions with an aqueous phase (usually below the detection limit), and CaCIsich inclusions with salinity of up to 17 wt% NaCI equiv, are related to emerald growth. The trapping of fluid inclusions postdates the growth of mineral inclusions. The P-T conditions of emerald growth are as follows: T= 220-300°C and P= 0.7-3.0 kbar.