Abstract

Diamonds from George Creek, Colorado, preserve complex intergrowth textures between two major growth generations: homogeneous diamond with yellow-buff cathodoluminescence (CL); and diamond with blue-green CL and local growth zonation. Secondary-ion mass spectrometry (SIMS) has revealed large variations in N concentration and C isotope composition within these diamonds. Even within single stones, N contents and delta 13 C values can vary from 0 to 750 ppm and 0 to -20 per mil respectively. These variations are similar to those recorded elsewhere for entire diamond suites. The CL characteristics correlate directly with N: diamond with yellow-buff CL has uniform N contents, whereas the zoned diamond has bright blue CL bands with high N (50-750 ppm) and dark blue or green CL bands with low N (0-20 ppm). These bands are too narrow (10-5 mu m) for analysis by IR spectroscopy. delta 13 C also varies between the two growth generations in any one diamond plate, and to a lesser extent within these generations, but shows no consistent correlations with either CL or N. The George Creek stones preserve evidence of extreme temporal and/or spatial variations in both delta 13 C and N concentrations during the period of diamond growth, but the factors controlling N content during diamond growth did not control delta 13 C.

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