The dating of the volcanic rocks encountered in EL 600 mineral exploration diamond drillhole DP1 as Archaean (and by definition, also Mulgathing Complex) substantially changes the view of Archaean rocks in South Australia. Elsewhere, Archaean to Early Proterozoic Mulgathing Complex and Sleaford Complex are characterised by strong deformation and high metamorphic grade imposed by the Sleafordian Orogeny at 2500-2300 Ma. Surprisingly, the volcanics in DP1 have been little affected by both the Sleafordian Orogeny and the Kimban Orogeny (1820-1580 Ma), of which the latter event caused rocks to reach granulite grade in the Mount Woods Inlier, only 80 km to the north-west. It follows that the basement block intersected by DP1 must have experienced a different tectonic history from adjoining basement areas, and have constantly resided at a relatively shallow level in the crust while the remainder of the Mulgathing Complex and the Mount Woods Inlier experienced episodes of deep burial and granulite-grade metamorphism. Because of this, it is probable that this basement block is fault-bounded to the northwest against the Mount Woods Inlier, to the southwest against basement in the Kingoonya area, and to the east against basement around Olympic Dam. Its limits away from DP1 are unknown, but may extend a considerable distance towards these faulted boundaries. Several broad magnetic features, possibly representing uplifted basement equivalent to that likely to underlie the volcanics in DP1, are present near Mt Eba, Bon Bon and north and south of Parakylia. Of these, all have interpreted depths to magnetic basement less than the 2000 m suggested for the DP1 area, while the anomaly south of Parakylia also has an associated regional gravity anomaly. The relationship of the volcanics to the rest of the Mulgathing Complex and to the Sleaford Complex is uncertain. The Sleafordian Orogeny, which has affected both complexes, has been dated at 2500-2300 Ma (Rb-Sr; Webb et al., 1986). A syntectonic-intrusive, hypersthene gneiss at Cape Carnot on the southern tip of Eyre Peninsula has been dated at 263721 Ma (U-Pb; Fanning et al., 1986), but no U-Pb geochronology has been undertaken on the Mulgathing Complex, which is much closer to DP1. It may be inferred that the depositional age of the metasediments now forming the Sleaford (and Mulgathing?) Complex is greater that 2640 Ma (Fanning et al., 1986). The volcanics in DP1 may then be a completely separate, younger (~2558 Ma) Archaean sequence, possibly resting at depth on low-grade equivalents of the Mulgathing Complex, which could be the source of the aeromagnetic anomaly seen at the drillsite. No apparent equivalents of the ~2558 Ma volcanics in DP1 are obvious within the Archaean Yilgarn and Pilbara Blocks in Western Australia. In these areas, cratonisation was essentially complete by 2600 Ma, with felsic plutonism continuing sporadically until ca 2500 Ma in the Yilgarn Block. Although direct comparisons cannot be made with the volcanics in DP1, there may be potential in these latter rocks for base metal sulphide mineralisation analogous to the volcanogenic FeCuZn±Pb sulphide accumulations in the Yilgarn Block, which are hosted by acid to basic volcanics and volcaniclastic and pelitic sediments. Notable examples of these are Golden Grove - Scuddles and Teutonic Bore deposits. The volcanics in DP1, although essentially unmineralised, do show pervasive chlorite and sericite alteration, suggesting that economic mineralisation may occur elsewhere in areas subjected to more intense hydrothermal activity, or adjacent to major structures.