Composition and Structural Characteristics of Alluvial Diamond from Hunan Province, China

At present, there are few systematic summary reports on the researches about alluvial diamond from Hunan Province, which is one of the important diamond producing region in China. In this paper, the composition and structural characteristics of alluvial diamond from Hunan Province were summarized. The researches show that alluvial diamonds from Hunan Province are mainly ⅠaAB type with the notably higher proportion of Ⅰb and Ⅱa types, and the distribution of nitrogen content and the degree of nitrogen aggregation exhibit significant unevenness. The surface patterns and colours of diamond crystals from Hunan Province are rich, significant variations in morphology; most of them being curved crystal surfaces, which indicate the complex environment in the process of rising to the crust.

The growth structures of alluvial diamonds are different, including simple growth structure or complex mottled and "agate-like" structure. The carbon isotope composition of diamonds from Hunan Province exhibit a broad distribution range, which is more closely to that of eclogite-type diamonds. It may be relatively enriched in light carbon isotopes, and has different carbon sources and formation mechanisms of diamond from North China Craton. The inclusion types include peridotite and eclogite series, and the origin of inclusions from deep mantle is worthy of further exploration. In summary, diamonds from Hunan Province possess multiple sources, multiple stages and complexity. Due to the unique source characteristics of the diamond, it is unfeasible to determine the whole origin of diamonds from Hunan Province simply by individual diamond characteristics. It is necessary to continuously explore the information carried in the existing diamonds to improve the its producing region in Hunan Province.