中国原生金刚石形成条件及找矿思考

Formation conditions of primary diamonds and thoughts on their prospecting in China

本文基于中国最主要的含原生金刚石母岩(金伯利岩和钾镁煌斑岩)的喷发时代及所产出时的构造背景,结合华北和华南大陆深部岩石圈的性质及其演化过程,探讨了中国原生金刚石的有利形成和保存条件,如相对古老的、冷的、厚的岩石圈根,且金刚石有足够的地幔存留时间等。同时,通过对金刚石母岩岩浆所经历的深部地幔与浅部侵位过程等联系的综合分析,建立了一个可能的"多期叠加的蘑菇生长方式"的岩浆侵位模型,为加强深部找矿和发现隐伏岩体提供了思路,以期取得中国原生金刚石找矿突破。我们推测,晚期的基性—超基性岩浆活动也有可能会碰巧捕获了隐伏的(或夭折的)早期含金刚石的金伯利岩,或者岩浆在上升过程中恰好经过赋存金刚石的沉积地层。这样的偶然事件导致了一种非常规的现象,即"非金伯利岩"岩体也偶见金刚石。

On the basis of the eruption time and tectonic setting of primary diamond-bearing parental rocks(e.g., kimberlites and lamproites) in China, combined with the nature and evolution of the deep continental lithosphere of North and South China, this study discusses the favorable formation and preservation conditions of primary diamonds in China, such as the relatively old, cold, thick lithospheric keel, and long enough residence time of diamonds in the mantle. In addition, based on relationship between deep mantle and shallow intrusion processes with respect to magmatism of diamond host rocks, it establishes a possible "multi-stage mushroom growth style" model for the emplacement of diamond-bearing parental magmas. This model provides some ideas for enhancing deep prospecting and discovery of blind rock bodies, to potentially enable a breakthrough in the prospecting of primary diamonds. We speculate that the late stage mafic-ultramafic magmas are likely to have fortuitously captured concealed(or abortive) diamondiferous kimberlites that formed in the early stage, or to have luckily passed diamond-bearing sedimentary strata during ascent. These accidental events result in an unconventional phenomenon that "non-kimberlites" rock bodies contain diamonds.