棉花坑铀矿床花岗质脉岩地球化学特征及其与铀成矿的关系

粤北棉花坑铀矿床矿体产于一组陡倾的、近南北向展布的构造蚀变带中,在矿体附近多见有细粒花岗质岩脉穿插,通过对该类脉岩的研究表明,其锆石 U Pb 年龄为138．6±1．3 Ma （MSWD＝0.81）,属于晚燕山期岩浆活动的产物.脉岩的硅含量高,镁、铁、钙和钛含量低, ACNK 值均＞1.1, CaO/Na2 O值＜0.3,刚玉分子数C＞1.8％,属于典型的 S型花岗岩类；脉岩中富集大离子元素K、Rb、Th而亏损Ba、Sr、Ti和P,稀土总量低,配分模式明显呈海鸥型,且表现出一定程度的“四分组效应”, Eu亏损明显.细粒花岗质脉岩的侵入作用使围岩中的铀活化、预富集,因此铀矿化与其有成因联系.

Geochemical Characteristic and Ore forming Geological Significance of Fine Crystalline Granite in Mianhuakeng Uranium Deposit,Northern Guangdong

The uranium ore of Mianhuakeng deposit is produced in a steeply dipping SN trending structre alteration zone in Zhuguang pluton,and fine grain granite veins are found to emplace the wall rocks near the ore.Research on the veins shows that the U Pb ages of zircon in the fine grain granite of the deposit is 138.6±1.3 Ma （MSWD=0.81）,the formation period is Late Yanshanian.The granite has a high level of SiO2 ,but a low level of MgO,Fe2 O3 ,CaO and TiO2 ,With the character of ACNK〉1.1 ,CaO/Na2 O〈0.3 ,C〉1.8%,the granite fall into S type.Trace elements in the granite was rich in K,Rb and Th,but poor in Ba,Sr and P.∑REE in the granite is at a low level,but the REE show a Vshaped distribution in chart and has a lower level of Eu.Activation and preconcentration make changes in the wall rocks due to the fine crystalline granite magmatism,so it is closely related to the uranium mineralization.