Kimberlites Near Orroroo, South Australia

Abstract A suite of Jurassic dykes occur near Orroroo, South Australia. The petrography, mineralogy and geochemistry of fresh core from one of the dykes is similar to other kimberlites, particularly from the type area near Kimberley, South Africa. This dyke is classified as a hypabyssal, calcite, phlogopite kimberlite. Typical kimberlite indicator minerals have been recovered from concentrates but ultramafic xenoliths are rare. The dykes can be geographically sub-divided into three groups which correlate with variations in abundance and chemistry of the heavy minerals and in diamond content. Diamonds have been recovered and examined. Enstatite and magnesio-wustite occur as syngenetic inclusions in the diamonds. The results suggest that many of the indicator minerals are xenocrystic and that the different groups of dykes have had a different mantle petrogenesis and pre-intrusion history.