Concepts and working relationships

One of the most important moves the Company has made is to commence diamond exploration on the Gawler Craton. The craton covers a huge area as shown on Figure 1 and is over 1000 km long by 600 km wide extending from York Peninsula in the South to Marla in the north. Considerable previous exploration has been carried out over the craton, particularly by De Beers and Rio Tinto in the 1970s, 80s and 90s. This previous work has located 28 diamonds and 11 non-diamondiferous kimberlites as shown on Figure 1. Clearly there must be some undiscovered diamondiferous kimberlites just waiting to be found.

The reason that Cratons are thought to be good places to look for diamonds on is illustrated in Figure 2. Here, under the thicker continental crust of the Gawler Craton the lithospheric mantle has deeper roots and provides a better repository for diamonds to be picked up by ascending kimberlitic magmas. On the Gawler Craton, the known kimberlites have a geological age of 180 million years or older. This means that they were likely to have been at the old land surface and being eroded during the deposition of the basal Mesozoic sediments about 150 million years ago (Figure 3). Over much of the craton these kimberlites would have been covered up by Jurassic and Cretaceous sediments. Flinders Mines intends to fly detailed helimag surveys over possible kimberlitic anomalies.

Depending on the actual depth of the kimberlite, further exploration and evaluation of its diamond content would be carried out by deep trenching or wide diameter drilling. It is anticipated that any kimberlites would tend to occur in clusters, and if one kimberlite was found in an area, then a larger area of detailed helimag would be flown to locate other pipes. In this exploration strategy, the primary target is kimberlite pipes and not kimberlite dykes or fissures which are difficult to evaluate under moderate depths of cover.

Flinders Mines is working with Primary Industries and Resources South Australia and the University of Adelaide on an Australian Research Council linkage research project which is studying diamonds, kimberlites, crustal structure and geological evolution in the Flinders Ranges. A Post doctorial research fellow has carried out a significant amount of work on diamonds and diamond indicator minerals from the Flinders Ranges. Initial observations are that indicator minerals are being derived from a greater depth in the Mantle as one approaches the Gawler Craton. This means that diamond Prospectivity should also be increasing in that direction. In addition work on inclusions in some of the Flinders Ranges diamonds is showing they have been derived from great depth in the Mantle, possibly as deep as 600 km. Further work is expected on dating of kimberlites. The project is a good example of university-industry co-operation and is providing benefits for both sides.