Investigation on Mineral Characteristic of Diamond and Geochemical Characteristic of Its Host in Langan Area,Anhui Province

The diamond ore occurring in the alkali-basic rocks in Langan area，Anhui Province，which is located in the west side of Tanlu（Tancheng-Lujiang）fault zone.Special care is taken to prevent cross contamination of synthetic diamonds used in the normal drill bits by using a special alloy drill bit.Diamonds are yellow-brownish or yellow colour，transparent，with adamantine luster.These diamonds mainly showed combined growth habit of cube and dodecahedron，a few of cube and octahedron，and a few of octahedron and dodecahedron.The size distribution is 0.5-0.6mm.Laser Raman spectroscopy showed the typical diamond peak at 1 332cm-¹.The host rocks（dolerite）of these diamonds were formed in a tectonic setting of intraplate，with the characteristics of enrichment in LILE（K，Rb，Sr，Th and Ba），and depletion in HFSE（Nb，Ta，Zr and Hf）.The REE features demonstrated the rocks coming from the deep mantle，and undergoing low-degree partial melting of peridotite before emplacement.The obvious Eu negative anomaly indicated the magma was clearly fractionated by crystallization of plagioclases.Based on these geochemical observations，we believe that these alkali-basic rocks in the Langan area may have the possibility of the diamond ore formation.