Paragenetic relations of diamond with silicate and carbonate minerals

in the system carbonatite-diamond (experiment at 8.5 GPa)

Spivak A.V., Litvin J.A.

Institute of Experimental Mineralogy of RAS, 142432 Chernogolovka, the Moscow region

Experimental researches of melting phase relations of diamond and syngenetic minerals in multicomponent system natural carbonatite - diamond were carried out at pressure 8.5 GPa and temperatures 1300 - 1800^оС (PT-conditions of thermodynamic stability of diamond). Natural carbonatite of the Chagatai complex (Uzbekistan) gets a mineralization of high-Ca eclogite – grospydites under these conditions. Melting phase diagram of the system was studied and “syngenesis diagram” constructed. The curve of solubility of diamond in completely miscible carbonate-silicate melts (values of solubility - within 15 - 18 wt. % carbon) is of great importance in the syngenesis diagram. The curve of diamond solubility divides the phase diagram into two fields: (1) phase relations with participation nonsaturated to diamond melts-solutions of carbon, liquidus phase is garnet (area of diamond dissolution) and (2) phase relations with participation of saturated to diamond melts-solutions, liquidus phase is diamond (area of diamond crystallization). Diamond bearing phase associations diamond + garnet + melt, diamond + garnet + clinopyroxene + melts, diamond + garnet + clinopyroxene + carbonate + melts and as a result subsolidus association diamond + garnet + clinopyroxene + carbonate are formed from carbonate-silicate melts at temperature lowering in the field of diamond crystallization.

The experimental data testifies the paragenetic nature of silicate and carbonate minerals, crystallized with diamond. Physico-chemical mechanism of diamond formation in carbonate-silicate melts is demonstrated. Analysis of physical and chemical behavior of natural diamond-forming magma chamber is given on the basis of the syngenesis phase diagram.

This study was financially supported by RFBR grant 08-05-00110, 10-05-00110 and grants of the president RF МК-4754.2009.5, МК-4735.2009.5.