Extreme chemical variation in complex diamonds from George Creek, Colorado: a SIMS study of carbon isotope composition and nitrogen abundance

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 variati ons in N concentration and C isotope composition within these diamonds. Eve n within single stones, N contents and delta(13)C values can vary from 0 to 750 ppm and 0 to -20 parts per thousand respectively. These Variations are similar to those recorded elsewhere for entire diamond suites. The CL char acteristics correlate directly with N: diamond with yellow-buff CL has unif orm N contents, whereas the zoned diamond has bright blue CL bands with hig h N (50-750 ppm) and dark blue or green CL bands with low N (0-20 ppm). The se 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 plat e, and to a lesser extent within these generations, but shows no consistent correlations with either CL or N. The George Creek stones preserve evidenc e of extreme temporal and/or spatial variations in both delta(13)C and N co ncentrations during the period of diamond growth, but the factors controlli ng N content during diamond growth did not control delta(13)C.