The Chang'e 4 team published a paper in Nature today describing the discovery of olivine and low calcium pyroxene-rich rocks consistent with them being derived from the lunar mantle. Such rocks have been long predicted from Aiken Basin and were the prime reason for sending the mission there. Mantle rocks are not represented in the Luna or Apollo samples, or in any lunar meteorites.
Is there a geological/planetary reason that those rocks were not found on the near side of the Moon?
The reason for the South Pole-Aiken Basin being associated with olivine and other mantle related minerals is because it is the largest (2,500 km) and currently deepest (13 km) impact basin. Its transient depth may have been as much as 200 km. Thus it is thought to have excavated deep into the mantle. The SPAB has been infilled over the Aeons, so the best place to look for mantle rocks is along the walls, and of course in the ejecta.
Some smaller near side impacts may have done also, because of the lesser crustal thickness. Kaguya mission data shows that Mare Crisium in particular has olivine rich, and thus possibly mantle derived, material along its rim. But because of its depth of excavation the SPAB has always been the preferred site for investigations.A preference the Chang'e 4 team appear to have vindicated.
