卢惠华 李修平 郝河

摘 要：有学者认为，密怀地区四合堂群层状地质体（表壳岩和铁矿）因受韧性剪切带的剪切作用，变成了一个夹构造残留体的巨大岩浆杂岩体。铁矿体因被剪断、位移、丢失，以至造成矿产的巨大损失，从而影响矿床的工业评价。以铁矿、杂岩体、地层、混合岩化、块状无序的变质岩等为研究重点，多数单位认为，该区可划分出两块面型分布的表壳岩。铁矿勘探，全区获得了十亿吨储量，成果丰硕。四合堂群的铁矿虽然厚度不大，但没有发生被剪切带剪断而丢失的情况，大多数铁矿都稳定的向下延伸了几百米。以事实为据，勘探队认为，对该争议地质体的认识，称岩浆杂岩体不合适，它仍应保留原来的提法，即：四合堂群层状地质体。

关键词：韧性剪切带;岩浆杂岩体;四合堂群;层状地质体;铁矿;密怀隆起

Abstract： Some scholars believe that due to the shear action of ductile shear zone， the layered geological body （surface crust rock and iron ore） of the Sihetang Group in Mihuai area has become a huge magmatic complex intercalated with structural residual body （or structural barrier body）. As a result， the iron ore body is displaced and lost due to shearing， resulting in huge loss of mineral reserves， thus affecting the industrial evaluation of the deposit. This paper carries out a comprehensive geological research， focusing on iron ore， complex， stratum， migmatitization and massive disordered metamorphic rocks. The results show that the majority belief is that this area can be divided into two large surface-type distributed surface crust rocks. Iron ore exploration in the whole region has uncovered 1 billion tons of reserves. Although the ore body in the Sihetang Group is not thick， most of the iron ores extends steadily downward for hundreds of meters without much loss due to shear actions. Based on the facts， it is considered that the magmatic complex is not suitable to call this controversial geological body magmatic complex. It should still retain the original name， i.e.， the layered geological body of the Sihetang Group.

Keywords： ductile shear zone; magmatic complex; Sihetang Group; layered geological body; iron ore; Mihuai Uplift

北京出露有一塊古老的变质岩，分布在密云、怀柔地区，面积约1500 km2。地质学者称其为密怀隆起。那里有丰富的矿产，特别是铁、金和银等金属矿产。20世纪20年代，我国老地质专家孙建初、王曰伦等首次将其划归为太古宇，称桑干系。20世纪50—60年代（1958—1960年），北京地质学院和北京市地质局合作，组成区测联合大队，在该区正式开展1∶50 000填图。索书田和叶盛基等认定它们属于早前寒武系的火山-沉积变质岩，分为2个群7个组，2个群是密云群和张家坟群。这套成果，在生产和教学中发挥了重要作用，但是，也存在不少问题，受到多方面的挑战。改革开放，为赶超先进，改变落后局面，地质矿产部决定要 “把当代地质科学领域中的新理论、新观点、新技术、新方法运用到区域地质调查中，改革传统的区域填图方法，进一步提高我国区域地质研究程度，赶上或达到世界先进水平”。……