Investigation of chemical changes in bone material from South African fossil hominid deposits

The bone fragments of the Australopithecus Africanus from the dolomitic cave in the Cradle of Humankind in South Africa have been studied by the use of several spectral techniques. The aim was to establish their degree of preservation and possibilities of inferring the life conditions from them. X-ray diffraction studies revealed the transformation of the mineral components partially into fluoroapatite form with addition of goethite, birnessite and quartz phases and with surprisingly well preserved collagen remains. Several important chemical elements were detected by using the electron (EPMA) and synchrotron-based X-ray fluorescence (XRF) microprobes. Among them, Sr and Zn were distributed in a way following the distribution of Ca, the main element of the bones. We suspect the immanent crystallographic substitution of Ca in this case in native bone. Iron followed the distribution of Sr but while Sr is distributed in a continuous way in more rigid locations, iron occurs mainly in the edge zones of the bones and in spot-like inclusions inside. Some part of the spots located in a very edge of bone is also filled with Mn and Cu. It suggests that the porosity and fracture of bones plays a more significant role in the localization of Fe, Mn and Cu. They also form a rigid thin layer (100–250 μm) avoiding further penetration. As (as AsO₄³⁻?) distribution pattern is unique and seems to occur in those locations where the concentrations of Sr are small. The conditions for bone penetration as determined from Eh-pH diagrams suggest that is rather impossible to preserve the organic matter in locations of Mn and also that Mn and Fe hardly can meet in the same spots.