Abstract: The origin of dolomite is a key problem in Cambrian-Ordovician exploration in Tadong area of Tarim basin. In view of the above problem, the rare earth element (REE) characteristics of 30 dolomite samples from Well Milan 1 were analyzed based on the observation of cores and thin sections. The results show that the NASC normalized REE distribution patterns of all samples can be classified into five types: the type of δCe negative anomaly, the type of δEu negative anomaly, the type of δEu strong positive anomaly, the type of δEu positive anomaly, the type of “V” shape. Further study found that the δCe of most samples is negative abnormal, indicating that most dolomites have been affected by evaporation pump dolomitization, and many samples also show diverse δEu anomalies and distribution characteristics, indicating that many dolomites were transformed by buried fluids or (and) multiphase hydrothermal fluids in the late stage. Among them, dolomite with fine grains is mainly formed by an evaporation pump, and dolomite with large grains may be formed in a buried or hydrothermal environment, while siliceous dolomite is mostly subjected to a hydrothermal reaction.

Key words: Tarim basin, Tadong area, Well Milan 1, Cambrian, dolomite, rare earth element, geochemistry