Gravity and magnetic observations in the Red Hill area, Southern Tasmania

The results of reconnaissance gravity and magnetic traverses in the Red Hill area of Tasmania confirm the structure postulated as most likely on geological evidence. The granophyre which occurs in the higher parts of the Red Hill Dyke has arisen by differentiation of dolerite in situ, but the gravity work shows that it is unlikely that the dyke continues to a depth sufficient for all the granophyre to have been produced solely by differentiation of the vertical column of dolerite, so that some migration of acid residuum from the underlying dolerite sheet into the dyke has probably taken place.
The measurements illustrate how geophysical methods can be helpful in structural problems where dolerite has intruded less dense sediments, but show that caution is necessary when interpreting the results of magnetic surveys.