Oscar Weiss
Oscar Weiss arrived in South Africa in 1934. In the same year he published a paper on the limitations of geophysical prospecting and was appointed on contract to the Geological Survey to develop a geophysical activity. At the same time D J Simpson and G L Paver were appointed on the permanent staff.
Oscar Weiss’s contribution to the exploration of gold on the Witwatersrand was largely due to his association with the consulting geologist of Union Corporation, Alfred Frost. The latter was born in England and studied at the University of London. His early years at Union Corporation were spent on the East Rand and later in the Orange Free State. Much in line with the approach of Carleton Jones, he also believed in multidisciplinary exploration which led to the establishment of a
Mines Geological Department. Frost was of the opinion that the normal succession of Witwatersrand and Ventersdorp rocks could occur at places in the Orange Free State at shallow depth accessible to mining.
After some trial measurements in the Klerksdorp area in 1935 Weiss suggested that in such situations the lighter quartzites would cause a detectable gravity low while the presence of the heavy Lower Witwatersrand shales would be indicated by a gravity high with associated magnetic anomalies and the Ventersdorp lavas by a gravity high with no magnetic anomalies.
Weiss thus recommended magnetic surveys, as Krahmann before him, to map the outer margin of the Witwatersrand Basin but combined with gravity investigations using an Eötvös torsion balance to outline areas where the lavas overlying the quartzites were thinnest.
In 1937 Western Holdings in which Union Corporation had a large stake, decided to drill a borehole based on Weiss’s work on the farm St Helena. The borehole struck auriferous reef which eventually led to the establishment of the St Helena Gold Mine. Gravity observations using a torsion balance remained painfully slow despite the efforts of Eötvös, to adapt the instrument for fieldwork. It still required every station to be cleared, a tent erected, the instrument to be set up
which included levelling and orientation and the waiting for at least an hour before a reading could be taken. Moreover, readings had to be taken in three directions for each balance station and after every rotation another hour had to elapse before observing. It is interesting to note that at this time the gravimeter was being developed and by 1939 had all but completely replaced the use of the torsion balance.
