gems, beryl, emerald, Brazil, inclusions

A detailed mineralogical, geological and economic study of the Santa Terezinha de Goiás emerald deposits, situated about 23 km northeast of the town of Santa Terezinha. Geological mapping identifies emerald mineralization within low-grade metamorphic rocks of the Santa Terezinha Sequence, particularly quartz-carbonate-talc schists and biotite/phlogopite schists, with both lithological and structural controls on ore distribution. The emeralds are characterized by intense green color, refractive indices of approximately 1.580–1.599 and an average specific gravity of about 2.71. Electron-microprobe analyses show significant Cr and Fe, both correlated with increasing color intensity. Mineral inclusions include chromite, carbonates, talc, phlogopite, pyrite, patronite, quartz, barite, beryl and ferropargasite. Mendes discusses several possible sources for the beryllium and concludes that the chromophoric elements were derived from associated meta-ultramafic rocks. The work also examines the organization and economic importance of emerald mining at Santa Terezinha.