Stream sediment sampling, conducted by Kennecott as follow-up to a 1966 regional surface geochemical reconnaissance programme looking for stratabound Mississippi Valley - type base metal deposits in the central Flinders Ranges, has located a small high grade outcrop of zinc mineralisation in the Third Plain area, which lies north of the Oraparinna Diapir near Wirrealpa Homestead. Detailed geological mapping and outcrop sampling has since provided information on the surface grades and areal extent of this mineralisation. The results indicate a broad, 800 foot x 300 foot area of Lower Cambrian limestone containing anomalous zinc values, but few that are >1% Zn. Four very small zones of better-than-average grade (up to 55% Zn) were found, the ore consisting mainly of willemite. However, the overall scale of the discovery was considered insufficient to warrant further investigations. During 1968, after a holding mineral claim had been taken out over the zinc orebodies by Kennecott, and then later acting in response to news of the major zinc deposit discovery by EZ Industries near Beltana on the western side of the Flinders Ranges, the Third Plain deposit was shallowly percussion drilled (23 holes, total 993 feet), which demonstrated that the willemite mineralisation extends to at least 36 feet vertical depth. The ore potential revealed thereby is of the order of 350 tons of 28% Zn per vertical foot, such that the total ore reserves estimate based on the drill intersections is 13,400 tons. This reserves figure is an order of magnitude smaller than the one calculated for the Beltana zinc deposit.