我国一些含金刚石的古沉积层特征

一、我国含金刚石古沉积层位 (一)第三系 1.山东某盆地北侧,下第三系官庄组砂砾岩和大汶口组石灰质砾岩、角砾岩中,含铬镁榴石,经对比与北侧产金刚石金伯利岩中的矿物特征一致。山东另一盆地以南地段,普遍发现含有金刚石的砾岩或砂砾岩块,充填于不同标高(80—540米)的寒武系、奥陶系石灰岩的裂隙、溶洞、溶沟中。含金刚石砾岩有90％以上见于中、上寒武统的岩溶负地形中,金

The characteristics of diamond-bearing sediments in China

Diamond-bearing old sediments have so far been found at 24 localities distributed in 8 provinces or autonomous regions in China. They occur in 14 strata pertaining respectively to Tertiary, Cretaceous, Jurassic, Devonian, Cambrian, Precambrian, etc. Genetically, they might be grouped into four types: alluvial (fluvial), littoral, drift and karst sediments. The diamonds seem to have been derived from different sources: l) Diamonds in the Mesozoic-Cenozoic Sediments might have come directly from kimberlite nearby; 2) Diamonds formed during Precambrian period are widely distributed in sediments of various ages, i.e., from old strata to present rive bed deposits. As regards material resources, this type of diamonds can be traced to old primary deposits or might be attributed to repeated accumulation of this mineral from old to new strata. Isotope dating of kimberlite from various parts of the world indicate that a single intrusive or region is likely to have several groups of ages, suggesting the repetition and. long duration of magmatic activities of kimberlite. ln China, isotopic age values might likewise fall into nine groups: 70-135 m.y., 230-56 370 m.y., 400-530 m.y., 700 or 800-l000 m.y., 1010-1400 m.y., 1500 m.y., 1800- 2000 m.y. and >2000 m.y., denoting the existence of primary kimberlite deposits of various ages which provided material for diamond-bearing sediments in diverse strata. The emplacement of kimberlite in China, which took place mostly between Ordovician and Sinian, is called "apparent emplacement"; the emplacement reconstructed through an integrated study of the magmatic activity of kimberlite and the strata it intruded is called "actual emplacement"; and a unity linking these two emplacements by means of isotopic ages is termed "holoemplacement". These three emplacements are corrsepondent in time to "time of apparent emplacement:", "time of actual emplacement" and "time of holoemplacement" respectively to imply the long duration and repetition of the magmaitc activity of kimberlite. The diamond-bearing sediments are mostly scattered in strata of Mesozoic- Cenozoic Eras and Cambrian-Sinian Periods, in accord with "actual emplacement" and "apparent emplacement ,suggesting that diamonds came from kimberlite of two major periods.