Deep kimberlite prospecting and thrust-nappe structure: Analysis of diamond metallogenic belt in Wafangdian, China

Abstract

ABSTRACT Wafangdian, China, is widely known for its rich primary kimberlite diamond. Kimberlite pipes (veins) are well-developed in Wafangdian, but only exist in shallow areas. The reason for the pinching out or disappearance remains unclear. Some studies have suggested that a possible reason is the thrust fault at the pipe bottom, but no substantial evidence of such geological movement exists. In this study, structural analysis and drilling were integrated based on a detailed field geological survey. We found a new thrust-nappe structure in the Wafangdian diamond metallogenic belt, which comprised a hanging wall allochthonous terrane, footwall autochthon, and thrust fault belt. Statistics of the striation lineation and fold hinge showed that the main direction of thrust nappe is SEE–NWW with a low angle. The calculated horizontal displacement of the major thrust nappe was approximately 3.2 km, and the movement distance of the secondary thrust fault at the bottom of Pipe No. 50 was approximately 1.5 ± 0.5 km. The formation age of the thrust-nappe structure might be the middle to late Jurassic, and the driving force was mainly related to the subduction of the Paleo-Pacific Plate. The discovery of the thrust-nappe structure provides a direction and scientific basis for deep diamond prospecting in Wafangdian, and the SEE areas of Pipe No. 50 and surrounding mines are potential focus areas for future deep exploration. Additionally, a 10-m thick diamond-containing kimberlite was obtained by drilling, providing a leap from theory to practice and serving as a case of deep structural analysis prospecting.