It's not my area of expertise. You should ask my colleague Israel Razo Soto. Cheers.

Dear Dr. Omonona,

as far as the so-called stream sediments are concerned the variaton of HREE and LREE elements are mainly controlled by two distinct heavy mineral groups. HREE are enriched in xenotime and some of its decomposition products such as churchite and LREE are enriched by another phosphate monazite and two of its decomposition products florencite (pH < 7) and rhabdophane (pH>7). Apart from these minerals also allanite may be made accountable for elevated LREE contents. This is especially true for arenaceous siliciclastic sediments.  In lateritic sediments and argillaceous ones REE are also concentrated. Laterites mainly contain minerals of the florencite s.s.s. (LREE) but also in minor quantities bastnaesite, hydroxyl-bastnaesite-(Nd), goyazite-(Nd), monazite-(Nd), synchysite, rabdophane-(Nd, Sm, Ce). In some bonebeds LREE are concentrated in apatite s.s.s. In the weathering mantle on granites in Japan and China ion-adsorption processes lead to LREE and locally HREE enrichments. In coal a similar process takes place but less sensitive to one or the other part of the REE spectrum.

Best regards

H.G.Dill

Dear Dr. Omonona

In sediments, REE are mainly controlled by heavy minerals presence. A very important variable is the grain size of the sediment you are measuring. The coarser the more REE enriched.

Ph is also an important variable.

I have attached 2 papers you could find useful.

Regards,

LB.