Pattern of REE distribution in various types of magnesite ore occurring wit
hin the Late Cretaceous ultramafics in Orhaneli Region (Western Anatolia) w
ere studied to interpret their genetic significance. The samples were class
ified into three different groups viz. massive, lentiform and pignolite or
stockwork. Individual groups exhibit distinctly different REE distribution
pattern with variable Eu, Ce and Yb anomalies. Three types of REE distribut
ion patterns are recognizable with the following characteristics: (1) high
LREE/HREE ratios without having Cc and Eu anomalies, (2) similar LREE and H
REE abundance with uncertain positive and negative Eu and Ce anomalies, and
(3) low REE abundance with markedly positive Eu, negative Ce and slightly
negative Yb anomalies. It is postulated that the redox conditions in the pr
imary mineral formation system was subjected to change and as a result, sub
sequent mobilization followed by recrystallization took place in the format
ion of primary magnesite minerals. Although a low temperature environment i
s indicated for magnesite formation, it is possible that REE-poor solutions
derived from the fluid-rock interaction had caused mobilization and later
recrystallization of magnesite ore.