Some studies of rare-earth element (REE) pattems of altered basalts have suggested that REE may be mobile during alteration. When possible effects of total rock mass balance are considered, most published data suggest that (l) only La is required to have been mobile, (2) if other REE have been mobile, changes are within analytical error and do not correlate with mineralogical or major-element changes during alteration, and (3) at !east some other 'immobile' elements, such as Ti, Y, and Zr, may have been mobile in the rocks considered here. REE, excluding La, may be among the most reliable geochemical indicators of the compositional affinities of altered basalts
