Characteristics of geochemical evolution of trace elements and REE in Gejiu granites,Yunnan Province

The evolution characteristics of Gejiu granites, Yunnan Province are described in terms of their petrology, especially their trace elements and REE geochemistry. The three major types of Gejiu granites: porphyritic biotite monzonitic granite (stage I), medium-coarse-grained biotite-K-feldspar granite (stage II) and two-mica alkali-feldspar granite (stage III) are thought to have been formed successively from the same granite magma source through fractional crystallization (Rayliegh fractionation), because linear correlations are found between log(Rb/Sr)-log Sn, log(Rb/Ba)-log Sn, log(Rb/Ba)-log(Rb/Sr), log La-log Sr, log Ce-log Sr, log Eu-log Sr, etc. In addition, the characteristics of REE distribution patterns in these three major types of granites also reflect the magmatic differentiation features of Gejiu granites. Of the three major types, the two-mica alkali-feldspar granite of stage III underwent the strongest differentiation, and thus has the closest genetic relationship with the Gejiu tin-polymetallic ore deposit. Such tin-polymetal mineralized granites are characterized by high Rb/Sr and Rb/Ba ratios, low K/Rb and ΣCe/ΣY ratios and remarkable Eu depletion.