Continuing exploration undertaken by Electrolytic Zinc Co. (E-Z), looking for possible economic primary stratabound lead-zinc sulphide deposits in the Heysen Range area, was focused on evaluating a newly discovered occurrence of willemite-chalcocite-malachite mineralisation situated about 5 miles north of Brachina Creek, on the western flank of the range and within the Oraparinna National Park. Known as the Toondana prospect, this occurrence within the Lower Cambrian Wilkawillina Limestone was mapped in detail at 1:4800 scale and tested in the subsurface by shallow diamond drilling with portable lightweight equipment (completing 3 inclined holes for 57 feet of total penetration) to try to preserve the environment and avoid constructing a drill rig access road onto the side of the range. The extent of mineralisation was found to thin markedly, from ~ 20 feet thick at the surface to only 2 feet thick at a depth of 14 feet. Based on this observation, it was concluded by E-Z that this willemite occurrence was superficial, and possibly related to local minor faulting. Base metal - anomalous drainage stream sediment samples that had previously been recovered by E-Z from nearby in their former SML 302 were subjected to heavy media separation and electron microprobe analysis of the resulting concentrates, to try to identify the often obscure zinc and lead-bearing minerals present. Apart from obvious willemite, significant other zinc values were found to be associated with manganese in the form of zincian wad, to exist in solid solution in calcite, and to be present in discrete concentrations of chalcophanite. One sample of the rare Pb/Zn silicate mineral calci-larsenite was also identified.