
%0 Journal Article
%A Fullagar, Peter K. 
%A Woods, Dennis 
%T Fast 3D Inversion of “Total Field” Resistive Limit TEM Data
%J ASEG Extended Abstracts
%D 2016/08/24
%V 2016
%N 1
%P 1-8
%K 
%R https://doi.org/10.1071/ASEG2016AB185
%U https://www.publish.csiro.au/paper/ASEG2016AB185 
%X Rapid interpretation of transient electromagnetic (TEM) data sets is highly desirable for timely decision-making in exploration. However, full solution 3D inversion of TEM data sets is often impractically slow. Therefore, a fast approximate 3D TEM inversion scheme has been developed for time-integrated (resistive limit) data. The resistive limits are amenable to linear 3D magnetic inversion, which is up to 100 times faster than &#x201c;rigorous&#x201d; 3D TEM inversion. The resistive limit inversion scheme is suitable for airborne, ground, and downhole TEM, both dB/dt and B-field. Its efficacy is illustrated here via application to a heli-borne sub-audio magnetic (HeliSAM) data set recorded over the Lalor Zn-Cu-Au VMS deposit in Manitoba, Canada. The response from the deposit is clear in the &#x201c;total field&#x201d; EM (TFEM) data even though the mineralisation is very deep, extending from depth 575m to over 1100m. A three-stage inversion of resistive limits derived from the TFEM rapidly defined a 3D conductor below the uppermost pyrite-sphalerite lenses, enclosing a volume containing mainly pyrrhotite-chalcopyrite stringer sulphides. Total inversion time was less than one minute on a notebook PC. 
