Résumé
Some meteorites were discovered in the Sahara, at southwest of Algeria, close to the region of Tindouf. These are several types from achondrites to ordinary chondrites. We develop in this work a study of some HED achondrites (Howardite-Eucrite-Diogenite) presumably originated from 4Vesta asteroid. Among these HED, were described: (i) a polymict eucrite NWA2268 finely brecciated constituted by clasts of basaltic rocks and minerals (plagioclase, pyroxene, spinel, silica and iron metal); (ii) a monomict eucrite NWA4269 finely brecciated with millimetrics metal grains. This meteorite presents two distinct zones, a coarse-grained with relict ophitic texture formed by plagioclase and exolved pigeonite. The second zone is fine-grained with granoblastic texture constituted by plagioclase, pigeonite, augite, orthopyroxene, silica (quartz a), iron metal (Ni%<0.1), troilite, spinel and phosphates; (iii) a howardite NWA2251 constituted by a brecciated matrix containing basaltic clasts and diogenitic clasts; this latter represent more than 30% of the whole rock; (iv) a diogenite NWA4255, constituted predominantly by centimetric crystals of orthopyroxene. This is an orthopyroxenite that contains in minor phase, spinel and troilite. These four types of meteorites have mineralogical and geochemical affinities, but also similar oxygen isotopic compositions. These meteorites are interpreted as belonging to the HED group attributed to the 4Vesta asteroid. The monomict eucrite NWA4269 does exception by its different oxygen isotopic-ratio. This difference can be explained either by an other origin than 4VESTA or by a heterogenous isotopic composition of this asteroid.