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

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 δ13C values can vary from 0 to 750 ppm and 0 to −20% 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 μm) for analysis by IR spectroscopy. δ13C 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 δ13C and N concentrations during the period of diamond growth, but the factors controlling N content during diamond growth did not control δ13C.

[1]  B. Harte,et al.  SIMS stable isotope measurement: counting statistics and analytical precision , 2000, Mineralogical Magazine.

[2]  J. Harris,et al.  Carbon isotope ratios and nitrogen abundances in relation to cathodoluminescence characteristics for some diamonds from the Kaapvaal Province, S. Africa , 1999, Mineralogical Magazine.

[3]  P. Cartigny,et al.  Nitrogen isotopes in peridotitic diamonds from Fuxian, China: the mantle signature , 1997 .

[4]  P. Deines,et al.  Carbon isotope ratios, nitrogen content and aggregation state, and inclusion chemistry of diamonds from Jwaneng, Botswana , 1997 .

[5]  H. Judith Milledge,et al.  Kinetics of Ib to IaA nitrogen aggregation in diamond , 1996 .

[6]  Martin L. Smith,et al.  The boron isotopic composition of tourmaline as a guide to fluid processes in the southwestern England orefield: An ion microprobe study , 1996 .

[7]  P. Deines,et al.  The carbon isotopic composition of harzburgitic, lherzolitic, websteritic and eclogitic paragenesis diamonds from Southern Africa; a comparison of genetic models , 1995 .

[8]  J. Gurney,et al.  Geotectonic controls of primary diamond deposits" implications for area selection , 1995 .

[9]  G. Bulanova.  The formation of diamond , 1995 .

[10]  C. Pillinger,et al.  A preliminary study of 15N14N in octahedral growth form diamonds , 1994 .

[11]  F. Pineau,et al.  Modelling the growth of natural diamonds , 1994 .

[12]  H. Kanda,et al.  Inhomogeneous distribution of nitrogen impurities in {111} growth sectors of high pressure synthetic diamond☆ , 1993 .

[13]  B. Harte,et al.  Carbon isotope measurements on diamonds , 1992 .

[14]  P. Deines,et al.  The carbon isotopic composition and nitrogen content of lithospheric and asthenospheric diamonds from the Jagersfontein and Koffiefontein kimberlite, South Africa , 1991 .

[15]  J. Valley,et al.  Ion microprobe analysis of oxygen isotope ratios in granulite facies magnetites: diffusive exchange as a guide to cooling history , 1991 .

[16]  Ė. Galimov.  Isotope fractionation related to kimberlite magmatism and diamond formation , 1991 .

[17]  P. Hoffman.  Geological constraints on the origin of the mantle root beneath the Canadian shield , 1990, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[18]  E. Anders,et al.  Interstellar SiC in the Murchison and Murray meteorites - Isotopic composition of Ne, Xe, Si, C, and N , 1989 .

[19]  C. Pillinger,et al.  Fractionation of nitrogen isotopes in a synthetic diamond of mixed crystal habit , 1988, Nature.

[20]  C. Pillinger,et al.  Multiple growth events during diamond genesis: an integrated study of carbon and nitrogen isotopes and nitrogen aggregation state in coated stones , 1987 .

[21]  P. Deines,et al.  Carbon isotopic composition, nitrogen content and inclusion composition of diamonds from the Roberts Victor kimberlite, South Africa: Evidence for 13C depletion in the mantle , 1987 .

[22]  D. DePaolo,et al.  Proterozoic crustal history of the western United States as determined by neodymium isotopic mapping , 1987 .

[23]  P. Bertrand,et al.  The mutual solubility of coexisting ortho- and clinopyroxene: toward an absolute geothermometer for the natural system? , 1985 .

[24]  K. Nickel,et al.  Empirical geothermobarometry for garnet peridotites and implications for the nature of the lithosphere, kimberlites and diamonds , 1985 .

[25]  R. S. Houston,et al.  The Cheyenne Belt: analysis of a Proterozoic suture in southern Wyoming , 1984 .

[26]  P. Deines,et al.  Associated chemical and carbon isotopic composition variations in diamonds from Finsch and Premier kimberlite, South Africa , 1984 .

[27]  C. Pillinger,et al.  Carbon isotopic variation within individual diamonds , 1983, Nature.

[28]  P. Deines.  The carbon isotopic composition of diamonds: relationship to diamond shape, color, occurrence and vapor composition , 1980 .

[29]  D. Green,et al.  An experimental study of the effect of Ca upon garnet-clinopyroxene Fe-Mg exchange equilibria , 1979 .

[30]  A. R. Lang.  On the growth-sectorial dependence of defects in natural diamonds , 1974, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[31]  G. Davies.  Aggregation of Nitrogen in Diamond , 1970, Nature.

[32]  I. Chinn.  A study of unusual diamonds from the George Creek K1 Kimberlite dyke, Colorado , 1995 .

[33]  J. Eiler,et al.  Ion microprobe evidence for the mechanisms of stable isotope retrogression in high-grade metamorphic rocks , 1995 .

[34]  C. Pillinger,et al.  C and N isotopic composition and the infrared absorption spectra of coated diamonds: evidence for the regional uniformity of CO2H2O rich fluids in lithospheric mantle , 1992 .

[35]  M. Otter,et al.  The application of C isotope measurements to the identification of the sources of C in diamonds: a review , 1991 .

[36]  R. A. Washington,et al.  A broader view. , 1991, Imprint.

[37]  J. Gross,et al.  The Ion Microprobe , 1973 .