Poorly described Lower Carpentarian basement ?basic igneous rocks, occurring over an area of approximately 65 square miles situated 3 to 8 miles east and north-east of Iron Knob, were investigated by BHP to establish their exact nature and to assess the possibility of associated copper-nickel mineralisation. The work herein reported has comprised field geological mapping of the outcrops, and rock chip sampling for petrographic and mineralogical/ geochemical determinations. This study has led to the conclusion that the rocks, now best classified as plagioclase ortho-amphibolites, have undergone substantial regional metamorphism from originally intrusive and extrusive igneous lithotypes of a predominantly intermediate, and only partly basic, whole rock chemistry, corresponding to a source gabbroic magma tending towards a dioritic, even syenitic, composition. An attempt has been made to spatially subdivide the intrusions based on textural differences, with the intent of revealing their internal geometry relative to likely 'feeder' pipes, that could lead to pinpointing sites of possible metallogenic magmatic differentiation arising through fractional crystallization during slow cooling. The study results show that, rather than being the products of differentiation within a single intrusive body, the rock types appear to be representing various separate, probably successive, melt intrusions and outflows. There is definitely nowhere any petrogenetic trend towards an ultramafic composition, and thus no concentration of nickel, nor is any source of sulphur available in the vicinity, which means that even the potential for hydrothermally altered, metamorphosed and disseminated sulphides would be minimal.