三维井地磁测联合约束反演

3D joint constrained inversion of borehole and ground magnetic data

井中磁测在铁矿等磁性金属矿床勘查中具有举足轻重的作用.针对磁性金属矿床深部资源勘查中存在的有效信号弱、矿体形态复杂等技术难题,本文利用井中三分量磁测资料和地面磁测资料直接反演地下空间磁化率的分布情况,充分发挥纵、横向分辨率高的优势,通过磁化率的变化来确定矿(化)体的范围.分析了磁化率和磁场Hax、Hay、Za、ΔT各参量之间的关系,导出了磁化率反演方程;将钻孔编录、磁化率测井等结果作为约束条件构建了目标函数.以组合倾斜板状体模型为例,验证了方法的有效性,并在青海野马泉铁多金属矿区开展应用试验,试验结果与已有地质资料基本一致.该方法有效抑制了因反演数据源单一、缺乏约束条件而造成反演结果的多解性,实现了磁测资料的精细反演解释,为查明地下矿体空间位置、形态及规模,提高找矿效果,提供了一种新的解决方案.

Borehole magnetic survey plays an important role in exploration of metal deposits.This work attempts to resolve a difficulty in the ground magnetic exploration for deep source bodies,i.e.the observed magnetic anomaly is weak while the source body is complex.The approach suggested is to invert both the ground and borehole magnetic data for magnetization distribution.This method can fully utilize high resolutions in horizontal and vertical directions to determine the scope of ore bodies from susceptibility variation.The basic inversion equation is derived by analyzing the relationship between the magnetic susceptibility and magnetic components(i.e.H a x,H a y,Z a,andΔT).We construct a new objective function using borehole geological logging and magnetic susceptibility logging data.We first test the proposed method based on a multi-inclined-prism model,and then apply it to real magnetic data from the Yemaquan polymetallic ore deposit in Qinghai Province.The inverted magnetization is consistent with the geological data.As a fine inversion,the proposed method can reduce the multiple solution from the inversion of single data and lacking constraints,which could provide a new tool for delineating the position,shape,and scale of ore bodies in the subsurface and enhancing ore-search efficiency.