oa Examples of the use of seismic reflection to re-invigorate a mature field: Tennant Creek

Recently seismic reflection has been gaining prominence as a tool for the minerals industry for orebody delineation and exploration in known mineralised terrains particularly where mineralisation extends to depths beyond a few hundred metres. We believe it can also play an important role in establishing the structural architecture of an area due to its unrivalled ability to map the orientation of structures at depth. In this paper we present recent results from an exploration program in the Tennant Creek Mineral Field (TCMF) in the Northern Territory of Australia for both of these objectives.

The program included the completion of 2 x 4km seismic lines close to the Gecko mine and a 60km N-S seismic line centred on Tennant Creek together with borehole full waveform sonic and vertical seismic profile data.

The borehole measurements confirm that the ironstone bodies and associated alteration that host the mineralisation provide a strong acoustic impedance contrast within the Warramunga sediments that otherwise show relatively little acoustic impedance variation.

The 4km seismic lines have generated two targets both at approximately 1km depth. Shallow imaging was hampered by strong surface wave noise but it is the targets that are not detectable by gravity and magnetics that motivated the use of seismic at Gecko and Chariot.

The regional survey was acquired to improve the understanding of the mineralising systems and underlying structural architecture around Tennant Creek. The survey mapped major structures that control mineralisation, such as the Southern Shear Zone, Mary Lane Fault and Gecko Fault. The seismic survey also showed that these structures were north verging and identified similar structural positions that lack surface expression but show many of the characteristics of the mineralised structures.