Depth to Basement Mapping

Synopsis

The Gawler Ranges, in the central Gawler Craton, remain an underexplored region of South Australia due to poor constraints on the thickness of the Mesoproterozoic Gawler Range Volcanics which creates a risk for mineral explorers. This volcanic sequence covers Paleoproterozoic and Archaean basement rocks which have potential to host iron ore-copper-gold (IOCG), intrusion-related gold (Au), shear-hosted copper-gold (Cu-Au), sediment-hosted lead-zinc (Pb-Zn) and iron ore mineralisation.

The region also has potential to host covered epithermal gold-silver (Au-Ag) and Pb-Zn-Ag±Au mineral deposits near the contact between the Gawler Range Volcanics and underlying basement, similar in style to Menninnie Dam, Paris and Parkinson Dam, where this contact is exposed along the southern margin of the Gawler Ranges.

The thickness of sedimentary cover sequences overlying crystalline basement are typically determined by seismic surveys or modelling of gravity and magnetics data, due to marked contrasts in density and magnetic susceptibility between cover and basement. However, the Gawler Range Volcanics share similar physical properties to the underlying basement, making the identification of the depth to basement challenging.

Background/Aims

The Department of State Development commissioned Archimedes Consulting Pty Ltd to carry out a pilot study to test whether processing of magnetic data can be used to determine the depth to the basement beneath the Gawler Range Volcanics. The pilot study covers the southern Gawler Ranges, including the PORT AUGUSTA and YARDEA 1:250k Map Sheets, extending over an area of 16,500 km².

Archimedes will utilise ACM (Automatic Curve Matching) and HMT (Horizon Mapping Technique) methods to determine the depth to the base of the Gawler Range Volcanics and interpret major fault structures within the volcanics and underlying basement.

Key outcomes

The following datasets will be produced over the project area:

• Filtered magnetics and gravity grids
• Depth to base of volcanics map
• Depth to top of basement map
• Interpretation of magnetic lineaments (faults, dykes and plutons) from the surface to a depth of 10 km
• ACM maps from the surface to a depth of 35 km

The depth to basement of volcanics and top of basement datasets can be tested by mineral explorers in the Gawler Ranges exploring mineralisation under cover of the Gawler Range Volcanics.

Schedule for information and product delivery