The geochemistry, petrogenesis and age of an unusual alkaline intrusion in the western Pilbara craton, Western Australia

Abstract

The recently discovered Yanyare dykes are located approximately 80 km southwest of Karratha in the north-western Pilbara craton, Western Australia. The dykes intrude intercalated sedimentary and volcanic units of the PalaeoProterozoic Fortescue Group. The Yanyare-02 dyke has an inequigranular texture and is comprised of intensely altered olivine macrocrysts set in a matrix of phlogopite (55%), sanidine (20%) and apatite (5%). Replacement of phlogopite by rutile and chlorite is common. Sanidine occurs as euhedral grains and poikilitic plates enclosing apatite and is variably altered to muscovite and calcite. Aside from fluorapatite, no accessory minerals thought to characterise lamproites wer..