160 ANALOGUE MODELLING TECHNIQUES

ANALYSIS OF TURAM MODEL TEST DATA

J.P. WILLIAMS

Bureau of Mineral Resources, Canberra, A.C. T. (Australia)

(Received February 9, 197 1)

A program of Turam model tests was conducted by the Bureau of Mineral Resources from 1967 to 1969. “Thin” rectangular sheets were used to study geometric variations such as dip, depth, distance from the primary field source and changes in thickness and

conductivity for simple conducting bodies. The results showed that dip estimates even for simple bodies are unreliable, but that

the depth to the top of the body and the conductivity/thickness ratio (X) can be deter- mined directly from the Amplitude Ratio and Phase Difference values as accurately as from the Real and Imaginary Components. Moreover the phase difference between ortho- gonal receiving coils (one vertical) over the top of the body is directly relatable to X.

Some complex models were studied. Two parallel sheets responded approximately as one until the spacing between them exceeded a distance governed by the depth and the coil spacing. Then the estimates were too low for good conductors and too high for poor conductors. Depth estimates were too large, but this may be an advantage.

The response of models of simple folds was similar to that of horizontal bodies, with no obvious indication of the type of folds. Estimates of h and depths were too large.

Other models studied were designed to represent shielded bodies, an insulator in a conducting medium and a fence.

For all the models the surrounding medium was air. The extension of the results to the case of typical orebody surrounded by weakly conducting country rock is considered a major problem and is discussed objectively.