湖南桃源理公港地区含金刚石沉凝灰岩的发现及其找矿意义

Discovery of diamond-bearing sedimentary tuff and its prospecting significance in Ligonggang area of Taoyuan County, Hunan Province

湖南桃源理公港地区白垩纪红盆内的灰绿色和紫红色沉积夹层曾选获过金刚石。以灰绿色岩石为研究对象,通过薄片鉴定和电子探针分析来确定岩石名称和岩石中石榴石和云母的属性。显微镜下,灰绿色岩石呈凝灰结构,由约45%的晶屑、35%的岩屑和20%的玻屑组成,为较典型的沉凝灰岩,并非前人所述的金伯利岩。沉凝灰岩中的石榴石和云母分别为G10型镁铝榴石和金云母,镁铝榴石和金云母的成分与辽宁、山东及南非典型岩管含金刚石金伯利岩中的镁铝榴石及金云母的成分基本一致,暗示其来源于含金刚石的金伯利岩。沉凝灰岩的特征表明,其来源地不会太远,这为在附近找寻火山机构奠定了基础;金伯利质岩屑、G10型镁铝榴石和金云母的发现,为在周边寻找原生金伯利岩提供了重要信息。

Diamonds have been picked out from the gray-green and purple-red sedimentary interlayer of the Cretaceous sedimentary red basin in Ligonggang area of Taoyuan County,Hunan Province.Taking the gray-green rock as the research object,the authors determined the rock name and the property of garnet and mica in rock through thin section identification and electron probe analysis.Under the microscope,the gray-green rock has a tuffaceous structure,and it is composed of 45%crystal fragments,35%rock cuttings and 20%vitric fragments,which is the typical sedimentary tuff rather than the kimberlite identified by predecessors.The garnet and mica in sedimentary tuff are respectively G10 pyrope and phlogopite.The chemical composition characteristics of G10 pyrope and phlogopite are similar to the diamond-bearing kimberlite of typical rock tubes from Liaoning,Shandong and South Africa,which indicates that pyrope and phlogopite are from the diamond-bearing kimberlite.The characteristics of the sedimentary tuff indicate that the tuffaceous substance source is not too far,which lays a foundation for finding volcanic edifice in the neighborhood.The discovery of kimberly rock cuttings,G10 pyrope and phlogopite provides valuable information for searching the primary kimberlite in the surrounding areas.