Magnetic susceptibility registration in ICDP boreholes - test of a new logging tool

点击翻译按钮获取中文摘要

Magnetic susceptibility is one of the most commonly measured rock physical property. The logging of this parameter on drillcores or in boreholes supports the construction of lithological profiles and correlation between drilling holes. Instruments, recording the magnetic susceptibility are commonly constructed using a fixed field amplitude for the applied ac magnetic field. However, as has been shown in recent work, the susceptibility of important ferrimagnetic minerals as pyrrhotite and titanomagnetite strongly depends on the ac-field amplitude. This has important implications for the interpretation and correlation of susceptibility logs. The newly developed slim-hole sonde MS2H of GFZ-OSG is the first susceptibility logging tool that considers the effect of field dependency. In the framework of this project we plan to test the application of the new sonde in ICDP drillholes. Preliminary case studies have shown that field dependent susceptibility measurements can provide information concering variations in the composition of lava flows and may enable magnetite and pyrrhotite-bearing rocks to be distinguised. The results of such tests are considered to be critical for the effective interpretation of susceptibility logs.