The Harris Greenstone Belt in the central Gawler Craton of South Australia has potential for Archaean Ni-Cu-PGE sulphide and Archaean-Proterozoic lode-Au mineralising systems. This map is a preliminary interpretation of the Precambrian basement geology based on aeromagnetics, gravity, and diamond drilling. It highlights the extensive distribution of poorly exposed Archaean komatiites and associated rocks (green) that have a strike extent of at least 300 km. The regional pattern of linear komatiitic sequences associated with ovoid granitic plutons and province-wide shear systems, is very similar to the economically important Eastern Goldfields Province in the Yilgarn Craton, Western Australia.
The ca. 2520 Ga Lake Harris Komatiite in the central Gawler Craton of South Australia is the first documented komatiite outside the West Australian Craton and the easternmost occurrence of such primitive ultramafic rocks in Australia. The steeply dipping ultramafic sequence consists of komatiite cumulates, high- to low-Mg komatiite, komatiitic and tholeiitic basalt, and pyroxenite cumulates. The komatiitic rocks display a range of quenched and cumulus textures defined by the different habits of olivine and its alteration products. Trace sulphides form very small (0.01-0.2 mm) single-phase disseminated grains and coarser disaggregated grains.
Thick ponded lava lake and distal composite sheet flow facies have been identified in the magmatic environment. Systematic whole rock and mineral chemical trends indicate that despite the effects of recrystallisation and re-equilibration during amphibolite-facies metamorphism, the original magmatic geochemical profiles are largely preserved. The whole-rock data for the Lake Harris Komatiite does not show any obvious Ni depletion during fractionation but indicate a strong olivine control in dominantly S-undersaturated environments. The Lake Harris Komatiite has chemical and initial Nd isotope characteristics similar to typical Al-depleted Archean komatiites.
