The Thomas Township Test Target: An Example of EM Interpretation Using Simple Models

Abstract

The Thomas conductor, located near to Timmins, Ontario, is a short, wide, graphitic zone located under about 90m of poorly conducting, glacially deposited overburden. Due both to its ease of access and the large quantity of data that has already been collected over it, it has the potential to become a standard geophysical test site. Joint interpretation of moving and fixed transmitter EM data, together with previous limited drilling have accurately defined the geometrical and electrical structure of the conductive zone. The interpretation study showed how simple models such as a thin plate or sphere were able to accurately fit the observed secondary EM fields, but that a good fit did not necessarily imply that a good interpretation had been made. In particular, for fixed transmitter systems, interpreted plate conductors dipping perpendicular to the primary field may have significant thickness.