Investigates the remains of 40 skeletons from the necropoles of Iwelen and Adrar Bous, in southern Sahara (Niger), to determine their mineral content, carbon isotope ratio, and ¹⁴C activity. Analytical data show that the initial ¹³C/¹²C isotopic ratio of the carbonate hydroxylapatite, albeit accompanied by a change in the crystallinity index, has been preserved. Given local conditions, the increase in the crystallinity index cannot be linked to exchanges with the environment but clearly reflects the decrease of CO₃ radicals in the bone material. The authors suggest a correlation between the crystallinity index and the residual content of organic matter. The ¹⁴C dates obtained for the carbonate hydroxylapatite are identical to those of the material of comparison (leather, charcoal, and associated collagen samples). The potential carbon isotopic exchanges between the carbonate hydroxylapatite and the total dissolved inorganic carbon (TDIC) are too insignificant to be detectable by analysis. These results can be explained by two favorable factors: the waterproof nature of the graves and the arid climate.