We use newly developed spectroscopic methods for determining FeO and TiO2 abundances to study the huge (2500 km diameter) South Pole-Aitken basin. The floor of this basin shows iron and titanium values which are weakly correlated and largely range from 7 to 14 wt % FeO and from 0.5 to 1.5 wt% TiO2. This composition is consistent with an approximate 1:1 mixture of lower crustal material like that found elsewhere on the Moon and mantle rock containing 10--16 wt% FeO and <0.1 wt% TiO2. Although mantle rock appears to compose about 50% of the floor deposits, models of the formation of large impact basins predict that virtually all the floor materials ought to be derived from the mantle. ¿ 1998 American Geophysical Union