Carbon isotope ratios and chemical impurities in diamonds from Southern Africa Abiel Kidane 1,2, Monika Koch-Müller 2, Michael Wiedenbeck 2 and Maarten De Wit 1 1 AEON, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa 2 Helmholtz Zentrum Potsdam, Deutsches GeoForschungsZentrum, Potsdam, Germany References: Clifford, T.N., Tectono-metallogenic provinces. Earth and Planetary Science Letters, 1, pp.421–434. Chinn. lL., A study of unusual diamonds from the George Creek K1 kimberlite dyke, Colorado. Unpubl. PhD. Thesis, University of Cape Town, South Africa. Introduction Diamond samples from four kimberlites are investigated for their chemical impurities and carbon isotopic ratios. These samples include:  17 macro-size diamond from Cretaceous Swartruggens Kimberlites.  13 macro-sizes and 8 micro-sized diamonds from Cretaceous Klipspringer kimberlites  16 diamonds from Pretorozoic Premier kimberlites  15 macro-sizes diamonds from early Paleozoic to Neoproterozoic River Ranch. Some of the diamonds contains visible mineral inclusions and some does not.. Methodology Figure 12: Carbon isotopic analysis by SIMS HR at GFZ, Potsdam. Germany. Figure 11: FTIR spectroscopy used for analyses of chemical impurities in amonds at GFZ. Aim  Characterizing diamonds for their physical and chemical impurities.  Constrain the sources of carbon and nitrogen in the mantle.  Testing diamond fingerprinting using chemistry and magnetic properties of diamonds Diamond Geology  Diamond ooccurs in association with the continental crust older than 2.5 Ga (Clifford’s low)  A stability of diamond requires a temperature ranges of °C and pressure of 3-6 GPa.  Diamonds are hosted in kimberlites and lamproites igneous rocks.  Emplacement of kimberlite is controlled by deep seated basement structures such as the fractures, faults and linear grabens..  The main pulses of kimberlites emplacement occur between 200 to 45 Ma and this is thought to be structurally controlled by the breakup of Gondwana. Azanian Craton Figure 1: Geological (left) and tomography (right) map of Africa and the craton (After de Wit 2010) Results Physical properties 1) Diamond from Swartruggens  Extremely resorbed, and corroded crystal features.  Complex internal growth 2) Diamond from River Ranch Figure 6: Physical properties of the diamonds from River Ranch: (A) Colour; (B) crystal intactness (based on Chinn 1995); (C) crystal shape. 3) Diamond from Klipspringer  Dominated by fragment with very few whole crystal structure. Figure 8: Physical properties of the diamonds from Klipspringer: (A) Colour; (B) crystal intactness (based on Chinn 95); (C) crystal shape. Figure 9: CL images of the diamonds from Klipspringer illustrating: (A) open oscillatory zones with zones characterized by non-luminescence zones (Type II) and zones with different brightnesses; (B) a blocky growth structure 4) Diamond from Premier Figure 10: Physical properties of the diamonds from Premier: (A) Colour; (B) crystal intactness (based on Chinn 95); (C) crystal shape Figure 5: Physical properties of the diamonds from Swartruggens: (A) Colour; (B) the classification of crystal intactness (based on Chinn 1995); (C) crystal shape Figure 7: Cathodoluminescence (CL) images of the diamonds from River Ranch showing: (A) a radial structures at which the triangular growth zones are radiating outwards; (B) core- rim development with ‘closed’ highly resorbed oscillatory zones. Discussion and Conclusion  The CL images and the carbon isotopic composition of all the diamonds suggest that diamonds grew in multi-episodic events.  Diamonds from River Ranch exhibit thin oscillatory and resorbed growth zones that may suggest that the diamond grew following spiral (layer by layer) growth mechanism.  Klipspringer diamonds are characterized by the ‘open’ oscillatory growth zones and presence of non-luminescence growth zones (Type II).  Diamonds from Swartruggens show complex internal structure with some sectorial and diamond seed structure.  Time averaged mantle storage temperatures for Type IaAB diamonds are inferred as 1064 °C for Swartruggens, 1191 °C for River Ranch, 1096 °C and 1165 °C for Klipspringer and 1205 °C for Premier.  The carbon isotopic analyses of the diamonds from the four kimberlites yield an average δ 13 C value of: -4.5 ‰ for Swartruggens, -4.7 ‰ for River Ranch, -4.5 ‰ for Klipspringer and -3 ‰ for Premier. With the exception of the diamond from Premier, the average δ 13 C value of the diamonds are near the average δ 13 C value of the mantle (-5 ‰).  The physical, chemical and carbon isotopic ratio reveals that diamond assemblages from Swartruggens and klipspringer can be discriminated from the other kimberlite pipes, but the diamonds from Premier and River Ranch kimberlite pipes cannot be discriminated from each other.  However, an individual or a mixed diamonds from these kimberlites would be difficult to identify their sources.  Initial magnetic experiments on these samples suggested that the magnetic study requires a diamond size >1 mm with visible mineral inclusion.  Although the physical and chemical composition of a diamonds can give insight into diamond sources, but they cannot uniquely fingerprint a single or mixed diamonds. However, with the addition of magnetic studies, fingerprinting of diamond might be possible. Results nitrogen content Figure 2: INitrogen contents quantified from the IR spectra for all the diamonds used during this study. Figure 3: Isotherms plots of all diamond samples at mantle storage time of 3.2 Ga Figure 4: Locality map of the four kimberlite pipes used during this study. Result Carbon isotopic ratios Figure 13: The carbon isotopic composition of the diamonds from all the four kimberlites Figure 14: Carbon isotopic variation along different growth zones (sample from Klipspringer