In situ maturation of sediments within the weathering profiles: An evidence from REE behaviour during weathering of Delhi quartzites

Orthoquartzites of Delhi Supergroup in Delhi region have low abundance of R EE. There is a two-fold enrichment of REE in moderately weathered zones on the quartzites accompanied by increase in the amount of kaolinite. The REE patterns however are nearly identical to those of the unweathered core quar tzite, In the strongly weathered outer zones both kaolinite and REE abundan ce decrease somewhat relative to the lower weak to moderately weathered zon es. The weathering processes here involved are the formation of kaolinite p ossibly by the breakdown of a few grains of mica and the oxidation of pyrit es present in the quartzite. During this process, the REE have been mobiliz ed quantitatively by sulfate-bearing solutions without any fractionation, i n the process the outermost zones have been made friable with lowered REE a bundance. It is possible, that REE and Al depleted top friable zones may ha ve been physically eroded away. Thus, although the REE are mobile in upper zones during weathering processes, they could be quantitatively retained in the lower weathering zones due to clay forming processes resulting in the production of silica-rich, REE depleted mature quartzite by stripping off t he uppermost friable sediments of the rinds.