白沙冲岩体和北炮台岩体均位于个旧矿田的东区北段.白沙冲岩体岩性主要为黑云母花岗岩,而北炮台岩体岩性主要为似斑状黑云母花岗岩.本文通过对白沙冲岩体、北炮台岩体进行岩石学、地球化学、Nd、Sr同位素研究,厘定白沙冲岩体属过铝质的高钾钙碱性花岗质岩石,北炮台岩体属准铝质的钾玄岩系列花岗岩.两岩体均表现出亏损Ba、Sr、Nb、P、Ti,富集Rb、Pb、U的特点.白沙冲岩体稀土总量较低,轻重稀土分馏不明显,具强烈的铕负异常,且具有类似于M型的四组分效应；相对于白沙冲岩体,北炮台岩体稀土总量较高,轻重稀土分馏较明显,具中等程度的铕负异常.Nd同位素结果显示,两岩体均来源于大陆地壳.地球化学特征表明,两岩体在岩浆演化过程中均经历了结晶分异,且白沙冲岩体的分异演化程度较高.区域内同时代花岗岩的相关资料表明,滇东南—桂西一带在晚白垩世存在大规模的岩浆活动—成岩事件,可能为晚中生代华南岩石圈伸展背景下的产物.%The Baishachong and Beipaotai granites are both located in the eastern part of the Gejiu orefield, Yunnan province. In lithology, the Baishachong granite is mainly equigranular biotite granite, whereas the Beipaotai granite is mainly porphyritic biotite granite. In this paper, a systematic petrological, geochemical, and Nd, Sr isotopic study is carried out. On the basis of previous zircon SHRIMP dating, combing the new data obtained in this study, the characteristics, evolution and petrogenesis of the two granitic stocks are documented. The results show that the Baishachong granite is a high-K calc-alkaline peraluminous granite while the Beipaotai granite belongs to shoshonitic metaluminous granite. Both of the Baishachong and the Beipaotai granitiods are enriched in Rb, Pb and U; and depleted in Ba, Sr, Nb, P and Ti. The Baishachong granite shows a lower 2REE, but stronger negative 8Eu anomaly than the Beipaotai granite. What' s more, the Baishachong granite reflects a tetrad-like effect with a shape of " M". Nd isotopic compositions suggest that the source of both the Baishachong and the Beipaotai granites are mainly derived in the crustal. Geochemical characteristics imply that both the Baishachong and the Beipaotai granites experienced a crystal fractionation process, while compared with the Beipaotai granite, the Baishachong granite experienced much stronger fractionated evolution process. The data of the Cretaceous granites around the Youjiang depression area located in southeastern Yunnan and western Guangxi Provinces, western South China, indicate that the granitic magmatism might be related to the lithospheric extension of the South China Block in late Mesozoic.
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