The Maping kimberlites and its xenocrysts as indicators of diamond minerogenetic condition in Zhenyuan area, Guizhou Province

Zhenyuan area of Guizhou Province is one of the key areas for diamond primary ore prospecting in China. In the Maping D1 rock mass of Zhenyuan area, the kimberlite occurrence with containing primary diamonds was discovered for the first time in 1965. The rocks have structural and componential characteristics of typical kimberlites, the U-Pb geochronology and Hf isotope analyses of zircon xenocrysts entrained in the Maping D1 diamondiferous kimberlites indicate the existence of unexposed Archean basement remnants beneath the study area. Based on the regularity of crust-mantle coupling, with corresponding to the old lithospheric mantle, this nature of ancient craton is a favorable factor for diamond formation. On the other hand, the Maping kimberlites commonly contain associated minerals of Cr-pyrope with high CaO content, most of which belong to the G9 (lherzolite) type rather than the global diamond-rich harzburgite protolith type (G10), suggesting that the state of lithosphere had been partly modified at that time and may not be conducive to the formation of high-quality diamonds. Note that in the processes of diamond prospecting, it should be based on the detailed field work and comparative petrological study, and rely on the investigation of diverse xenoliths/xenocrysts carried by kimberlites and the other associated magma activities, in combination with inversing the characteristics of mantle source by the composition of magmas. Therefore, it is possible to comprehensively reveal the ancient subcontinental lithosphere about the formation age and evolution history, material composition and fine structure, as well as the thickness, thermal state, oxygen fugacity, fluid activity and some other aspects of the subcontinental lithospheric root, thus providing important evidence for diamond prospecting.