南岭花岗岩重力场特征与找矿意义

南岭地区是我国重要的有色、稀有金属矿产资源产地,是世界上研究燕山期花岗岩成岩成矿理论最典型的地区之一。该地区多金属矿床与花岗岩侵入关系密切,因此,研究花岗岩的空间分布特征对于成矿规律以及成矿远景预测有重要意义。南岭花岗岩密度较围岩低,呈明显重力负异常特征,本文首先建立直立柱体花岗岩的重力正演模型,通过改变模型参数来分析南岭花岗岩局部重力异常的特征;然后对南岭地区实测布格重力异常采用滑动平均法分离出局部重力异常和区域重力场,并对其特征进行了分析;最后选择过骑田岭、香花岭等地区典型剖面,通过二度半人机交互反演方法得出花岗岩体的形态与侵位特征,得知大型花岗岩体下底延深不超过25km,其侵位机制大多受深大断裂控制,说明南岭花岗岩侵入体属浅源型。

Characteristics of Nanling Granite Gravity Field and Significance of Prospecting

Nanling region is the most important area of producing nonferrous and rare min- eral resources in China, and it is one of the most typical regions for studying Yanshanian granite metallogenic theory in the world. Because of the close relationship between poly- metallic deposit and granite intrusion in this area. to study the features of granite distribu- tion is meaningful to the mineralizing rules and its prospect. In Nanling, the density of granite is lower than surrounding rock and, therefore, it causes obviously negative gravity anomalies. In this paper, initially, we build a granite gravity forward model of vertical cyl- inder and analyze the characteristics of local gravity anomalies of Nanling granite by chan- ging its parameters. Subsequently, local and regional gravity anomalies are separated from measured Bouguer gravity anomalies by using sliding average method and we also analyze their characteristics. Finally, using 2.5D man--machine interactive inversion method for four typical profiles crossing through the rock masses of Qitianling and Xianghualing, it is revealed that bottom depth of large granite body arrives no more than 25 kilometers, and the granite body intrusions are mostly controlled by deep faults. These characteristics dem onstrate that the granite belongs to shallow--source--type, which provides a reason for forecasting metallogenic prospective zone in Nanling region.