YANG Yu-hong1,2,3, HUANG Yi1,2*, LIU Shen3, ZHANG Xi-gui4, YANG Chao-gui5, YAN Jun6, YE Chun1, GONG Xing-xiang1,3
(1. Bureau of Land and Mineral Resources Reserve of Guizhou, Guiyang 550000, China;
2. Technology Innovation Center of Mineral Resources Explorations in Bedrock Zones, MNR, Guiyang 550000, China;
3. State Key Laboratory of Continental Dynamics, Northwest University, Xi'an 710069, China;
4. 101 Geological Party, Guizhou Bureau of Geology and Mineral Exploration ＆Development，Kaili 556000, China;
5. Institute of Geology and Mineral Resource Exploration, Guizhou Nonferrous Metal and Nuclear Industry Geological Exploration Bureau, Guiyang 550000, China; 6. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China)
Abstract: The lamproites in the Southeastern Guizhou have been widely concerned due to the discovery of China’s first original diamond-bearing lamproite body in the Maping area, Southeastern Guizhou. Based on analyzing the geochemical characteristics of major and trace elements of lamproites found recently in the Daping area of Shibing County, Maping area of Zhenyuan County, and Shibanzhai area of Majiang County in the southeastern Guizhou, the characteristics of mantle source, tectonic evolution, and crustal dynamics in the southeastern Guizhou have been discussed in this paper. The characteristics of major elements (SiO2, Al2O3, CaO, Na2O, K2O and P2O5) of our samples show that they all belong to typical lamproite. The geochemical characteristics of trace elements show that our samples are strongly emriched of HFSE (Th, Nb, Ta, and U), but depleted in LILEs (Rb, K, Sr) and Ti. The REE geochemical characteristics show that samples have relatively high contents of total REE (ΣREE=797×10-6－1488×10-6), with obvious characteristics of enriched LREE but depleted HREE ((La/Yb)N=112~254). The elemental pair ratios of trace elements and REE indicated that the lamproites in the Southeastern Guizhou could be formed by the fractional crystallization of parent magma, which was derived from garnet buchnerite mantle lower than 100km in depth, with no noticeable crustal contamination in the uplift process of magma. Geodynamic analysis shows that the lamproites in the Southeastern Guizhou occurred in a non-orogenic continental dynamic setting of stable craton which were jointly influenced by the intercontinental orogeny between the Yangtze and Cathay plates from the Late Ordovician to Silurian, the Dongwu orogeny from the Middle to Late Permian, the Yanshanian Jiangnan intraplate orogeny, and the geotectonic evolution of Tethys tectonic domain. The favorable conditions for the diamond-bearing lamproites in the area are given below. 1) There are stable tectonic units (the Yangtze and Cathay blocks) for a long time; 2) The lamproite magma was formed at depth deep enough for the diamond stabilization; 3) There is deep fracture cutting through the lithospheric mantle as the magma uplifting channel. However, the beneficial part of lamproites for prospecting diamond might be eroded by the weathering. The targeting areas, which should be kept eyes on for prspecting diamond in the future, are those of the less eroded footwall of the deep fracture and the ancient un-uplifted Caledonian plane.
Keywords: lamproites; geochemistry; source characteristics; Southeastern Guizhou
ACTA MINERALOGICA SINICA Vol. 41, No.3, 2021, page 258-270
