Granitic rocks found in the Bayan Obo can be divided into three groups: medium-coarse biotite granite (Gr1), medium-coarse hornblende biotite granite (Gr2) and finegrained biotite granite (GrII). These granites may be attributed to the Hercynian period, whereas Gr1 and Gr2 have been intruded by the younger GrII. The REE content in these rocks varies in range from 224 ppm to 357 ppm and decreases with the ages of rocks. Moreover, the relationship between the total REE content and the major chemical composition of rocks can be traced.The granites are all similar in the distribution pattern of REE, but different in the country rocks, so that the degree of fractionation of REE is somewhat various. It can be explained by the various rock-forming minerals.As the Gr1 and Gr2 are occurred, the feldspar was extensively crystallized, hence Eu would be first of all incorporated into the feldspars. As a result Eu is relatively depleted in younger Grn and the Eu negative anomaly of limited extent may be emerged.From the foregoing statement it can be suggested that the three groups of granite are originated from a identical source.
. 1980, 白云鄂博花岗岩稀土配分型式的初步研究. 地质科学, 15(1): 83-86.
. A PRELIMINARY STUDY OF THE DISTRIBUTION PATTERN OF RARE EARTH ELEMENTS IN GRANITES OF BAYAN OBO, INNER MONGOLIA AUTONOMOUS REGION[J]. Chinese Journal of Geology, 1980, 15(1): 83-86.