ABSTRACT
The carbon isotopic composition of more than 230 diamond grains from three main diamond mines of kimberlite and lamproite and a placer deposits in China were Investigated. The δ13C values range from –26.06% to +1,5‰ with variation of about 28.00‰. The obtained data indicates mat no definite relationship occurred between the crystallization habit of diamond and their carbon isotopic composition but the colour and crystal type of diamond are certainly related to. The δ13C of diamonds from different mines or different localities has their own feature. The data also show that the large difference in δ13C valus is not attributed to the heterogeneity of the mantle while the definite effect are from the Archaean-Proterozoic subduction and recycling of the crustal carbon joining into the upper mantle. This paper proposes a “two suites and three stages” evolutionary model for explaining reasonably the large difference in δ13C in diamonds. No carbon isotope differentiation occurred in the C-O-H closed system after the formation of kimberlite or lamproite magma. This new idea is of important significance not only to searching and prospecting of diamond but also universal to the Inverstigation of the thickening mechanism of the south rim of Yangtze Craton and other areas in China.
