鲁西大井头地区金刚石找矿指示矿物特征及其研究意义

Characteristics and research significance of diamond prospecting indicator minerals in the Dajingtou area,western Shandong Province

鲁西大井头地区自然重砂中的金刚石及其找矿指示矿物发现已久,然而找矿工作尚未能取得实质性突破。本文从金刚石找矿指示矿物角度入手,在研究该地区指示矿物晶体形貌特征和化学成分特征的基础上,通过对比大井头地区自然重砂与大井头岩体中的指示矿物特征、大井头地区与其它地区金伯利岩、钾镁煌斑岩中的指示矿物特征后得出:大井头地区既存在金刚石指示矿物,又含有金刚石母岩指示矿物,是鲁西金刚石找矿的有利地区;第四系自然重砂中的指示矿物类型和所占比重与大井头岩体较为一致,认为第四系中的指示矿物由大井头岩体供源;大井头岩体含有较大比重的榴辉岩相指示矿物,如G4组镁铝-铁铝榴石和绿辉石,且其中金刚石多为Ib型,表现出与蒙阴地区金刚石原生矿不同的特征,认为大井头岩体为穿越金刚石生成区边部、并携带了其中特征性矿物成分的钾镁煌斑岩。结合大井头周边地区发现的三处重砂矿物异常和多个可疑岩体,依据钾镁煌斑岩集群分布的特点,认为大井头及周边地区是新区、新类型金刚石找矿的优质靶区,建议今后找矿方向和工作重点向钾镁煌斑岩型金刚石原生矿转移。

Though the occurrence of diamonds and their prospecting indicator minerals in the Dajingtou area of western Shandong Province has long been known, no substantial breakthrough has been made in the exploration of the diamond primary ore. Based on the study of crystal morphology and chemical composition of the indicator minerals, this paper compares the characteristics of indicator minerals in natural heavy sand and in the Dajingtou volcanic rock to reach the following conclusions. Firstly, the Dajingtou area has both diamond indicator minerals and diamond-bearing rock indicator minerals and is a favorable area for diamond mineralization in the western Shandong region. Secondly, the type and proportion of indicator minerals in the Quaternary are consistent with that in the Dajingtou volcanic rock. We propose that the indicator minerals are supplied by the Dajingtou volcanic rock, which contains a large proportion of indicator minerals of the eclogite, such as G4-pyropes, omphacite. Thus, it can be concluded that that the Dajingtou volcanic rock is lamproite that passed through the edge of diamond producing area and carried the characteristic minerals. According to the characteristics of the lamproite’s cluster distribution, the Dajingtou area and its surroundings are potentially high-quality target areas for the new type of diamond prospecting. Future prospecting efforts should be focussed on the primary diamond ore of the lamproite type.