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The Longido region (Tanzania) hosts a distinct corundum–zoisite paragenesis, renowned for its ornamental value and geological significance as a tracer of Pan-African tectonothermal events. Through integrated analyses—including electron probe microanalysis (EMPA), LA-ICP-MS, XRF mapping, and SEM-EDS on five representative samples—we posit that the genetic model for the zoisite–corundum is that pargasite and early-stage corundum were the protolith, which experienced zoisitization prior to hydrothermal fluid influx. This fluid event induced the replacement of zoisite and mechanical compression by newly crystallized corundum. Key findings include textural–chemical concordance: rubies exhibit Al2O3 >98 wt.% with Si anomalies (>5000 ppm) in transitional zones, indicative of fluid-mediated replacement of precursor zoisite. Combined mineralogy, this study explored the debated genesis of Longido red corundum–zoisite assemblages, and a rough model was obtained.
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1 School of Gemology, China University of Geosciences, Beijing 100083, China; [email protected] (L.Y.); [email protected] (H.Z.);, National Mineral Rock and Fossil Specimens Resource Center, China University of Geosciences, Beijing 100083, China
2 School of Gemology, China University of Geosciences, Beijing 100083, China; [email protected] (L.Y.); [email protected] (H.Z.);
3 School of Gemology, China University of Geosciences, Beijing 100083, China; [email protected] (L.Y.); [email protected] (H.Z.);, Beijing Key Labroratory of Mineral Environmental Function, School of Earth and Space Sciences, Peking University, Beijing 100871, China