The mantle-derivation theorists of diamonds hold that diamonds are formed at the bottom of the lithosphere and the top of the rheosphere,and the kimberlites or lamproites only serve as carriers for bringing diamonds out to form deposits.The gravity isostatic anomalies reflect not oly the tectonic activities at the depth of the earth crust but also the short term character of these activities.Hence special importance should be attached to the prospecting for young diamond-bearing rock bodies in Yuanjiang river area.