The deepest yet completed, diamond-cored base metal exploration hole in South Australia (DDH MM14 : total depth 5312 feet = 1619.1 m) was drilled on a moderately dipping trajectory at the historic Mutooroo mines, as part of copper exploration being conducted by Mines Exploration Pty Ltd on its SML 105 tenement located in the Willyama Complex of the Olary Province. Country rocks as intersected by this hole in progress of its drilling during 1966-1967 consist predominantly of gneissic amphibolite, pyroxene-bearing granulite, and numerous varieties of quartz + feldspar + mica gneiss. These include augen gneiss and sillimanite + kyanite gneiss. The gneissosity was developed at about 1700 Ma. All lithologies are microscopically folded, and have been retrogressed during a later schistosity-forming folding phase. Where this new schistosity is subparallel or parallel to the original gneissosity, sericitisation is extensive. Chalcopyrite occurs either as disseminations in gneissic amphibolite, or with pyrite and pyrrhotite as aggregates in pegmatitic, leucocratic segregations developed in or near gneissic amphibolite. Multi-element geochemical analysis of twenty drill core samples produced only a single weakly anomalous result in lanthanum (700 ppm La), for chloritic mylonite in a retrograde shear zone on the lower margin of a 380 m thick gneissic amphibolite, at the expected position for lode mineralisation.