花岗岩浆－热液过渡阶段的稀土元素分异──来自岩背锡矿区蚀变岩的依据

ON REE EVOLUTION OF TRANSITIONAL PROCESS BETWEEN MAGMATISM AND HYDROTHERMALISM:EVIDENCE FROM YANBEI TOPAZ-BEARING GRANITE AND ITS ALTERED WALL-ROCKS

以江西岩背含黄玉花岗岩的围岩钾长流纹斑岩及其蚀变产物为研究对象，根据蚀变岩和其原岩之间化学成分及稀土元素含量差异，以及包裹体和Ｏ，Ｓ同位素资料，认为蚀变热液是来自含黄玉花岗岩浆的富含Ｆ，Ｃｌ和金属元素Ｓｎ，Ｃｕ，Ｆｅ，Ａｌ，Ｃａ，并含有ＲＥＥ的流体．蚀变岩中Ｅｕ的相对富集系数最大，反映了Ｅｕ相对其它ＲＥＥ更易进入流体，岩浆结晶后期释放的这种富氟流体可能是导致岩背花岗岩强烈Ｅｕ亏损的主要因素之一。

Yanbei tin deposit is located in Huichang,Jiangxi.The plutonic rock related to metallization is topaz-bearing granite,wall-rock of which is K-feldspar rhyolitic porphyry. The main alteration and metallization took place in K-feldspar rhyolitic porphyry. Contrasts between the compositions and REE patterns of altered rocks and unaltered host rocks(K-feldspar rhyolitic porphyry)show that the ore-forming fluid evolved from topaz-bearing granite is rich in F,Cl,Sn,Cu,Fe,Al,Ca and REE, The REE ratios(K values) of altered samples normalized against their unaltered host rock are all more than 1. K Eu is the largest among the K values of all rare earth elements which suggests that Eu is separated from magma into fluid easier than other rare earth elements in melt/ fluid interaction of late stage magmatism,The separation of Eu from magma into fluid might be one of the main factors that resulted in intensive Eu depletion of Yanbei topaz-bearing granite.