宜章县长城岭浅成花岗质岩浆隐爆机制及找矿意义探讨

The cryptoexplosive mechanism of the hypabyssal granitic magma in Changchengling area,Yizhang County,Hunan Province,and its implications for mineral prospecting

在长城岭铅锌多金属矿区,常见沿花岗斑岩脉与北东向断裂交汇处发育与成矿关系密切的角砾岩。这类角砾岩的空间就位、物质组成、岩石组构及蚀变特征等表明其为隐爆成因,可划分为爆破角砾岩、震碎角砾岩和混杂角砾岩。按照隐爆机制的不同,其又可分为岩浆隐爆角砾岩和热液隐爆角砾岩。区内花岗斑岩的地质地球化学特征表明,燕山早期晚阶段侵入的富含挥发分、流体-溶体相互作用强烈的浅成花岗斑岩具备有利的隐爆条件和明显的隐爆特征。隐爆作用不仅为铅锌多金属矿化富集提供物源及流体源,还为成矿流体汇聚及卸载沉淀提供了重要场所。长城岭地区与铅锌多金属成矿关系密切的隐爆角砾岩的发现对其矿区深部、湘南钨锡多金属矿化集中区乃至南岭中段有色金属找矿研究具有重要意义。

Numerous breccias were identified as the host rocks of the Pb-Zn polymetallic deposit in Changchengling area, Hunan Province. These breccias are restricted to the intersections between the granite porphyry dykes and the NEstriking faults. Their distribution patterns, compositions, textures, and alteration characteristics suggest that they might have resulted from cryptoexplosion. The cryptoexplosive breccias can be divided into explosive breccias, shatter breccias and mixed breccias on the basis of the features of the cryptoexplosive breccias. These breccias can also be divided into igneous cryptoexplosive breccias and hydrothermal cryptoexplosive breccias according to their genesis. The geological and geochemical features of the granite porphyries indicate that the early Yanshanian hapabyssal granite porphyries were rich in volatiles and experienced strong fluidmelt, thus probably belonging to the cryptoexplosion type. The cryptoexplosion provided not only oreforming elements and fluids for the Pb-Zn polymetallic mineralization but also convergent and precipitable space for oreforming fluids. The discovery of cryptoexplosive breccias connected with Pb-Zn polymetallic mineralization in the Changchengling orefield is significant in the search for deepseated mineralization in this orefield as well as in the southern Hunan W-Sn polymetallic concentration area and even in the whole central segment of Nanling region.