Investigator Group Expedition 2006: Cainozoic Sediments on Flinders Island, South Australia: Description, Age and their Implication for Diamond Exploration

Diamond exploration techniques including geophysics, remote sensing, sampling, geochemistry, mapping, drilling, and exploration expertise were applied to Flinders Island, considered highly prospective for diamonds. Kimberlite indicator grains, predominantly chromites, were recovered from both drill core and sludge samples. Over 900 surface heavy mineral samples were collected to the end of 2007 and a wide range of kimberlite indicator minerals have been recovered, including chromite, pyrope, diopside, picroilmenite, diamond, phlogopite, forsterite and orthopyroxene, with the highest concentration around Gem Pan. The age of the sediments and depositional environments were assigned on palynological evidence. For the first time a detailed geological description of Cainozoic sediments is provided for Flinders Island, including a new stratigraphic unit which has been formally named Flinders Island Sand. Five anomalous indicator mineral zones have been identified and the analysis of mineral grains appears to favour a kimberlitic origin. Mineralogical examination of the indicator minerals show that the grains are relatively fresh and have not been transported far from the source. The kimberlitic source still remains undiscovered, but indicator minerals recovered from analysed samples indicate an age of Miocene or older.