18O/16O and V/Cr ratios in gem tsavorites from the Neoproterozoic Mozambique metamorphic belt: a clue towards their origins?
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The combination of oxygen isotope composition with V–Cr–Mn trace element concentrations of V-bearing garnets (tsavorites) originating from the main deposits of the Neoproterozoic Mozambique Metamorphic Belt is reported for the first time. The database enables the identification of the geological and geographical sources of the main productive areas from northern and southern Tanzania, Kenya, and Madagascar. Three consistent sets of δ18O values between 9.5‰ and 11.0‰, 11.6‰ and 14.5‰, and 15.5‰ and 21.1‰ have been recognized for primary deposits hosted in graphitic gneisses related to the Neoproterozic metasedimentary series. The δ18O value of tsavorite is a good tracer of the environment of its formation; the δ18O of the fluid in equilibrium with tsavorite was buffered by the host rock during metamorphism and fluid-rock interaction. This study is a first step in characterizing the geochemistry of gem tsavorite from most of the deposits and occurrences worldwide.
KeywordsMozambique Metamorphic Belt Tsavorite Oxygen isotopes V/Cr ratio Mn Geographic and geologic origins
We thank Dr. Khan T., University of Bahria, Islamabad, Pakistan, Dr. Uher P., Comenius University, Bratislava, Slovakia, Dr. Themelis T., gemologist in Thailand, and Prof. Shiraishi K., National Institute of Polar Research, Tokyo, Japan for providing samples from respectively Jambil, Pezinok, Mogok and Sør Rondane Mountains. The authors thank very much Prof. Dr. Chris Harris, University of Cape Town, Rondebosch, RSA, for reviewing, Dr. Hartwig Frimmel for handling the manuscript, and Dr. Bernd Lehmann, Editor-in-Chief of Mineralium Deposita.
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