Parental media for diamonds and primary inclusions by evidence of physicochemical experiment

Abstract

The mantle-carbonatite conception of genesis of diamond (Litvin, 2007, 2009) is briefly outlined. A generalized of compositions of the multi-component heterogeneous parental medium for diamond and primary inclusions therein is first developed. Boundary compositions of the parental medium are represented by mineral components of the peridotitic and eclogitic parageneses, mantle carbonatites and C-O-H-fluids, phases of accessory type both soluble in the carbonate-silicate melts (chlorides, phosphates, etc.) and insoluble in them (sulfides), as well as carbon. Phase relations of the multi-component eclogite-carbonatite-sulfide-diamond are studied at 7 GPa. Syngenesis diagram for diamond, paragenetic and xenogenetic minerals (including the solubility curves of diamond in carbonate-silicate and sulfide melts) is constructed. Physicochemical mechanism of formation of diamond and paragenetic minerals is revealed. Genetic classification of primary inclusions in natural diamonds is worked out. Analysis of physicochemical history of diamond formation in the mantle chamber of carbonatite magma is accomplished. Introduction .The mantle-carbonatite conception of genesis of diamond of kimberlite deposits (Litvin, 2007 a, b , 2009) is justified by the complex of mineralogical, experimental and theoretical data. Completely miscible carbonate-silicate growth melts with dissolved elemental carbon (carbon source for diamond) form a basis for the parental media for the dominating mass of natural diamonds and paragenetic minerals. The parental carbonate-silicate-carbon melts are multi-component heterogeneous media with strongly changeable compositions. So, silicate constituents are presented by minerals and components both peridotite and eclogite parageneses (Sobolev, 1974). It is established in the high- pressure high-temperature experiments that both peridotite-carbonatite-carbon and eclogite-carbonatite- carbon melts are represented as highly efficient diamond-forming media. An example of diamond crystallization in melt oversaturated in dissolved carbon of the eclogite-carbonatite system is demonstrated in the fig. 1. Composition of parental medium for diamond and primary inclusions. A generalized of compositions of the multi-component heterogeneous parental medium for diamond and primary inclusions therein is developed (Fig. 2).The major composition tetrahedron of the system peridotite-eclogite-carbonatite-soluble admixture componens is its basic element. Belonging of the mineral assemblage of syngenetic inclusions in natural diamonds to two major parageneses, - peridotitic and eclogitic, - is took into consideration. The boundary compositions of the parental medium are determined with mineral components of the auxiliary tetrahedrons - peridotitic (Ol-Opx-Cpx-Grt), eclogitic (Cpx-Grt-Crn-Coes), mantle carbonatite (Mg, Fe, Ca, K, Na, etc. carbonates), phases and components of admixtured accessory sort - soluble in carbonate-silicate melts (chlorides, phosphates, etc.) including the components of C-O-H-volatile compounds, and carbon too. All the components of the boundary tetrahedrons mentioned above are responsible for formation of paragenetic mineral phases together with diamond and, correspondingly, for capture of the paragenetic inclusions by natural diamonds. At the same time due to physicochemical experiment it turned out that xenogenetic mineral phases are presented within the assemblage of so called syngenetic inclusions. Sulfide minerals which are not soluble in diamond-forming carbonate-silicate melts as well as sulfide melts which are completely immiscible with these are among the xenogenetic phases. In the fig. 2, the auxiliary boundary tetrahedron for sulfide components is positioned out of the major tetrahedron and is