Case Study: Dighem Survey for Non-magnetic Dyke Detection; Dorstfontein Colliery, Total Coal RSA

A Dighem airborne geophysical survey (simultaneous acquisition of airborne magnetic and electromagnetic data) was carried out for Total Coal South Africa from September 14 to October 23, 2007. Three blocks in the Secunda area were flown, namely: Dorstfontein, Boschmanskop-Tumelo and Forzando West. This paper deals with the Dorstfontein colliery survey only. The Dorstfontein mining area is located immediately east of the town of Kriel in Mpumalanga, South Africa. The purpose of the survey was to detect both magnetic and non-magnetic dykes. The data quality from the Dighem survey is very good and much improved on previous similar surveys in the 1990s and in 2000. This is due to improvements in technology, especially electronics. The Dighem survey successfully delineated known magnetic and non-magnetic dykes in the Dorstfontein area, as well as probable and possible dykes. Some 60% of the known and probable and possible dykes were detected by the magnetic method and 40% of the probable and possible detected dykes were non-magnetic. Using two flight directions at right angles to each other proved to be important, since if only one flight direction was used, some of the dykes may not have been detected.