The question of function of hearths in prehistorical caves is fundamental to characterize the nature of human occupation. The hearths could be used for lightning, cooking or heating. Their spatial repartition, as their paleotemperature, should allow to identify their function. The localization can be visual by the presence of ash and charcoal or by identication of rubefaction. The accumulation of ash and charcoal can also correspond to the emptying of hearths and the rubefaction can be chemical than thermal. The accumulation of ash and charcoal can correspond to the emptying of hearths and the rubefaction can be chemical instead of thermal. The thermoremanent magnetization and the neoformation of magnetic minerals, together induced by heating, produce an importante deformation of the local magnetic field. Thus, the local variations of the magnetic field may allow to localize and to count the hearths without mistake even if the hearths are masked by a draping of clayed deposit. The walls caves morphology are also sources of local deformations of the magnetic field. For this reason it is important to have a 3D information on the deformation of the magnetic field. Moreover, the geolocalisation is difficult in the caves. To resolve these different problems for such kind of prospect, the 3D mapping was realized by tracking the sensor position with a laser tacheometer during the deplacement of the sensor in the space.The protocol was developed in the cave of “les Fraux” (Saint-Martin-de-Fressengeas, Dordogne, France), accidentally discovered in 1989 (Carozza et al., 2009). This cave is a rare example of a Bronze Age site (1300 BC) with archaeological vestiges (ceramics, bones, hearths) and rock art (incision, engraving, finger plot). The conservation of this site is exceptional as the cave entrance just collapsed after the last occupation by man, 3300 years ago. The experimental contraint in this recent prehistorical cave are low compare to the older ones. This allows us to develop a new approach to estimate the paléotemperatures of hearths (Brodard et al., 2010).