Figure 37. Gawler Craton mineralisation and exploration targeting. Seismic Tomography -300 Km depth.
This section looks at exploration targeting in the Gawler Craton, South Australia. Are the controls similar to those in the other Australian cratons? For more detail in a webinar visit https://www.youtube.com/watch?v=6BbsFImSHBM https://www.youtube.com/watch?v=6BbsFImSHB and https://www.youtube.com/watch?v=bFurQYhWjyk
The Gawler craton is a big producer of copper-gold-silver-uranium-REE (Olympic Dam), lead zinc (Broken Hill) and has large deposits of gold and iron. It is Proterozoic (~1.6 Ga) in age. What structures control the deposition of theses deposits?
Exploration targeting using seismic tomography at 300 km depth.
Figure 37. Gawler Craton mineralisation and targeting. Seismic Tomography -300 Km depth.
This plan is of the Gawler Craton mineralisation overlaid onto the seismic tomography at 300 km depth.
The exploration targeting regime which has been used for the last 30 years is to target the edges of the big changes in rock character within the craton. Then the intersection of these areas with the strongest linears was the more localised target area. The Gawler craton has WNW, ENE, NS, and NNE linears. These may be the main fluid pathways?
Exploration targeting (orange shapes) are on the high P/T boundary between the red, slow seismic wave rocks and the fast seismic wave, cooler rocks which are probably the less altered remnants of the original craton. This plan updates and refines that old technique (it was usually used with gravity plans).
Using EagleEye enhancement, one can follow these intra-cratonic boundaries from the surface to the Outer Core. I have picked the 300 km depth because the boundaries seem clearer at this depth.
This boundary should be the highest P/T change area and would be the preferred site for mineral deposition. They are the areas within the orange shapes. EagleEye can define these areas much more clearly than current systems.
The lighter point areas within each colour regime are higher heat flow (P/T change) areas. So, one can target high heat flow areas within the brown or grey rock.
It was noticed that most of the big mines occurred on, or near, these light areas suggesting a connection.
There is a greater difference between high and low heat in the Gawler craton than anywhere else I have researched. Maybe this is a signature of the IOGC Olympic Dam type deposit.
Olympic Dam sits in the middle of the remaining grey area of the craton, a very similar situation to Mount Isa and Kalgoorlie. Broken Hill sits within the red zone but on the craton edge like Gruyere, Tropicana, and Nova deposits in the Yilgarn craton. What this means I’m not sure?
The orange circles are the targets based on the intersection of rings and the linears with the high P/T areas especially the whiter, point, high P/T spots.
These targets will only be proved up by further dedicated targeting and on the ground exploration!