Sharpe, M. R., Brits, R., Engelbrecht, J. P. (1983). Rare Earth and Trace Element Evidence Pertaining to the Petrogenesis of 2.3 GA Old Continental Andesite and Other Volcanic Rocks from the Transvaal Sequence, South Africa, 63 p., Inst. Geol. Res. Bushveld Complex: Pretoria, South Africa, Res. Rept. 40