The Cavendish Test Site: A UTEM Survey Plus a Compilation of Other Ground Geophysical Data

Abstract

This report presents data from three recent University of Toronto surveys at the Cavendish geophysical test site, namely UTEM, horizontal loop (HLEM) and ground magnetic surveys. Interpretation of the UTEM survey has clearly defined the presence of a short strike-length pod of high conductance within the regional zone A conductor, present on line C. The pod is interpreted to have a conductance in excess of 400 Siemens, compared to about 10 Siemens for the regional zone A conductor extending across the grid. HLEM data interpretation strongly confirm this conclusion. Zone B is interpreted to have the top of its main conductivity at some depth. This conclusion, if true would indicate that the crosscutting westerly dip for zone B postulated by Williams et al. (on the basis of one drill hole that did not intersect sulphides) may no longer be necessary to explain the drill data. The detailed magnetic field data collected, when contoured, show a very different picture to that of earlier data. On the basis of UTEM late-time limit interpretation it was possible here to determine the nature of the source of the near surface static magnetic anomalies i.e. whether induced or remnant magnetization is predominant. The second part of the report presents a compilation of ground geophysical data at Cavendish obtained from a variety of sources. This data set is by no means complete, and due to the constraints of the original surveys, no valid inter-system comparisons can be made. A reference list of other, easily available, data on the Cavendish test site is also included. In an appendix the vector diffusion process of EM induction is illustrated in the UTEM E field case for the Cavendish test site.