Thi
s study aim
s to determine the
source
s of rare earth element
s (REE
s) in the geothermal and cold water
s of the Ayder and İkizdere (Rize) geothermal fifield
s (NE Turkey). The difffferentiation
stage
s of REE
s in water–rock interaction
s a
s well a
s the migration proce
sse
s of aqueou
s complexe
s of rare earth element
s (REE
s) in the water
s were evaluated. Ba
sed on re
sult
s for major ion
s, the İkizdere geothermal water with a temperature of 61 °C can be cla
ssifified a
s Na-Ca-HCO3
type water, wherea
s the Ayder geothermal water with a temperature of 54 °C can be cla
ssifified a
s Na-Ca-CO3−SO4
type water. ∑REE concentration
s 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. A
s well a
s lower pH value
s, the water
s in the İkizdere geothermal fifield were found to have higher REE concentration
s than tho
se of the Ayder geothermal fifield. Geochemical characteri
stic
s of REE
s from the ho
st rock
s and water
sample
s indicate that the REE
s are derived from
granite and granodiorite ho
st rock
s. Normalized REE plot
s for the ho
st rock
s and water
s showed
similar pattern
s, and in particular, the water
s interacting with granitic rock
s di
splay a pronounced po
sitive Eu anomaly and a le
ss clear Ce anomaly. The po
sitive Eu anomaly in the altered
surrounding rock
s i
s a
ssociated with argillization of feld
spar
s in the granitic ho
st rock
s that the water
s have pa
ssed through. Application of a
speciation model
showed that amorphou
s iron oxy-hydroxide complexe
s of REE
s were
signifificant for a pH value of nearly 9 in the Ayder geothermal water
s wherea
s flfluoride complexe
s are dominant in
the İkizdere geothermal waters whose pH is just below 7.