Diamond Exploration and Regional Prospectivity of the Northern Territory of Australia

The North Australian Craton occupies a large part of Australia’s Northern Territory. However, while much of the Territory is prospective for diamonds, its large size has meant that it is under-explored. Historical exploration methods have been reviewed and critically assessed. Combined with data on mantle lithosphere thickness and structure, and the ages of primary diamond deposits compared to regional rocks, results have been used to rank and model regional diamond prospectivity. The ranking scheme has been supplemented with qualitative modifications and it is concluded that the Territory’s western and eastern flanks are the most prospective. The Territory’s three known diamondiferous kimberlite fields were all discovered using indicator minerals as the principal exploration technique. However, due to intense Cenozoic weathering, traditional indicators are unusually small or absent. Surveys using coarse-spaced sampling or that ignored fine sand particles (<0.25 mm) may therefore have returned false negatives. Indicators are often outnumbered in exploration samples by microdiamonds, considered as unreliable as regional prospecting vectors due to wind transport and their ubiquity in the east. Alteration resulting in elevated Ti relative to Mg in ilmenite and Zn overprints on chromites, and relatively high G9-garnet abundances in diamondiferous pipes place many diamond indicator compositions outside preferred discriminatory fields. The effects of intense weathering on traditional indicator mineral compositions are expected to promote the use of more durable indicator minerals in future exploration, and place a heavier reliance on remote sensing. Given the large areas involved, future diamond exploration will most effectively be conducted as parallel programs to established exploration for other commodities.