Mineralogy of diamonds from the Juina Kimberlite Province, SW Amazon Craton, Brazil: cathodoluminescence, infrared spectroscopy, nitrogen content, and carbon and nitrogen isotopes

The mineralogy of 234 primary and alluvial diamonds from the Juina kimberlite Province has been investigated. The majority of diamonds exhibit low CL intensity and typical blue-sky color. Internal features are rare. The spectra classification of diamonds yields 82% of Type II stones (N-free and a minor amount of highly aggregated Type I diamonds. δ13C in Type II diamonds varies from - 3 to - 26.3% and in Type I from -3.4% - 13.8%. δ15 N in Type I diamonds ranges from +2.2 to - 14.0% and the N content, from 3.85 to 613.74 at.ppm. C and N isotopic compositions are compared to worldwide occurrences and to deep diamond assemblages. The incorporation of N by deep diamonds and the contribution of subducted terrains of the SW border of the Amazon Craton on the formation of the light 13 C diamonds are briefly discussed. (author)