ИСТИНА

GEMOLOGICAL PROPERTIES OF DIAMONDS FROM THE M.V. LOMONOSOV DEPOSIT TATIANA POSUKHOVA (1), GALINA KRIULINA (1), VICTOR GARANIN (2) (1) Department of Mineralogy, Moscow State University, Moscow, 119234, Russia, tposukova@mail.ru, (2) A.E. Fersman Mineralogical museum of the Russian Academia of science, Moscow, Russia M.V. Lomonosov deposit is located within the Zolotitskoe field of the Arkhangelsk diamondiferous province. It consists of six pipes. The industrial production is carried out at two sites: Arkhangelskaya pipe and Karpinskaya-1 pipe. We investigated the collection (more than 500 crystals) of diamonds from these pipes. Comparative studies were carried out on the following properties: habit, a mineralogical groups of diamond (according to classification of Y.L. Orlov, 1984); the relief of surface of the crystals; degree of safety; the degree of etching; presence of negative triangular pyramids; the degree of distortion; the nature of the distortion; intensity of color; color distribution; transparency; the existence, nature, distribution and mineral composition of the inclusions in different zones; cracks; the presence of plastic deformation; color, intensity, and distribution of luminescence. In addition we investigate the content of nitrogen and hydrogen centers and mineral inclusions with different mineralogical method: IR- and Raman spectroscopy, X-ray computed tomography and microprobe analyses. It was established that diamonds in studied pipes have similar gemological characteristics: - Diamonds with different shades (brown, yellow, green, pink, gray) dominated in both cases (40%). - Diamonds with a high degree of transparency dominated (50%) in both pipes. The proportion of non-transparent crystals is low (less than 5%). - Crystals in the form of curve-faced dodecahedra prevail in both pipes. - Crystals of the 1-st varieties according to Yu.L. Orlov’s classification (1984) predominate in the studied collections. - The inclusions of graphite, garnet and fluid detected in diamonds of the both pipes. It was revealed that the diamonds in studied pipes have significant features of the difference: - The pipes are substantially different in content of colored diamonds: in the Karpinskaya-1 pipe the content of such diamonds more larger (20%). - Pipes vary in content of diamonds with different forms of crystals: more than 20% octahedra detected in the pipe Arkhangelskaya and in the pipe Karpinskaya-1- less than 5%. - Crystals of the 3-d and 5-th varieties according to Ju.L. Orlov’s classification (1984) identified in Karpinskaya -1 pipe and in the pipe Arkhangelskaya - no. The differences of gemological and spectroscopic properties of the diamond from studied pipes related to their genetic features. Diamonds with a different color have a different type of spectral characteristics and it means that the color is correlated with nitrogen impurities. Diamonds with high and low content of hydrogen defects are present in each of the transparency group. Spectra of translucent and transparent diamonds vary significantly, either in relation to lattice absorption or in intensity of nitrogen and hydrogen defects. Crystals with high and low concentrations of hydrogen defects were established in each groups of habit. The maximum concentration of points for both pipes corresponds with dodecahedral crystals in which the content of nitrogen varies from 500 to 1500, and the content of CH-defects from 0 to 10. Pipes differ according to the type of the habit of crystals belonging to the area of maximum concentration of the analytical points: in Arkhangelskaya pipe - it is a dodecahedra and in the pipe Karpinskaya-1 - it is a tetra-hexahedra. The bulk of the diamond crystals in the two pipes has a high concentration of hydrogen and nitrogen defects. Content of non-aggregated nitrogen in form A varies from 600 to 1000, and the content of aggregate-nitrogen in the form B - from 0 to 500. Special group of high-hydrogen crystals with high concentration of aggregated nitrogen and low concentration of non-aggregated nitrogen were found in the pipe Arkhangelskaya. Comparison with Yakutian kimberlites showed that the content of total nitrogen and content of hydrogen much higher in our samples, and a range of nitrogen in the B-form in our samples are much wider. The degree of aggregation of nitrogen in Yakutian kimberlites is higher. The indicated differences we associate with different conditions of diamond’s growth in the mantle. Diamonds in studied pipes of the Lomonosov deposit crystallized at lower temperatures. References 1. Bogatikov, O.A. (Ed.) (2000) Arkhangelsk diamondiferous Province (geology, petrology, geochemistry and mineralogy). Moscow: MSU publishers, 524 p. (in Russian). 2. Orlov Yu. L. 1984. Mineralogy of diamonds. Nauka. Moscow. (in Russian ) 3. Possoukhova, T.V., Kudryavtseva, G.P. & Garanin, V.K. (1999) Diamonds and accompanying minerals from the Arkhangelsk kimberlite, Russia. In: In”Mineral Deposits: Processes to Processing”, Balkema, Rotterdam, v. 1. pp. 667-670