This st
udy aims to determine the so
urces of rare earth elements (REEs) in the geothermal and cold waters of the Ayder and İkizdere (Rize) geothermal fifields (NE T
urkey). The difffferentiation stages of REEs in water–rock interactions as well as the migration processes of aq
ueo
us complexes of rare earth elements (REEs) in the waters were eval
uated. Based on res
ults for major ions, the İkizdere geothermal water with a temperat
ure of 61 °C can be classifified as Na-Ca-HCO3 type water, whereas the Ayder geothermal water with a temperat
ure of 54 °C can be classifified as Na-Ca-CO3−SO4 type water. ∑REE concentrations were between 0.64–2.13 μg/L in the İkizdere geothermal fifield and between 0.01–0.32 μg/L in the Ayder geothermal fifield. As well as lower pH val
ues, the waters in the İkizdere geothermal fifield were fo
und to have higher REE concentrations than those of the Ayder geothermal fifield. Geochemical characteristics of REEs from the host rocks and water samples indicate that the REEs are derived from granite and granodiorite host rocks. Normalized REE plots for the host rocks and waters showed similar patterns, and in partic
ular, the waters interacting with granitic rocks display a prono
unced positive E
u anomaly and a less clear Ce anomaly. The positive E
u anomaly in the altered s
urro
unding rocks is associated with argillization of feldspars in the granitic host rocks that the waters have passed thro
ugh. Application of a speciation model showed that amorpho
us iron oxy-hydroxide complexes of REEs were signifificant for a pH val
ue of nearly 9 in the Ayder geothermal waters whereas flfl
uoride complexes are dominant in
the İkizdere geothermal waters whose pH is just below 7.