粤东北柏埔地区燕山期小岩体地球化学特征与铀成矿探讨

Geochemical characteristics and uranium mineralization of Yanshanian small pluton in Bopu area of northeastern Guangdong

燕山期花岗岩小岩体的岩性为中粒黑云母二长花岗岩,出露于柏埔岩体北部黄田铀矿床南部约3km的范围内。针对中粒黑云母二长花岗岩进行了主量元素、微量元素和稀土元素的分析。结果表明:该岩体表现为SiO2质量分数高(73.07%~74.20%,平均为73.71%),富碱(Na2O+K2O=8.20%~8.78%,平均为8.57%),且钾大于钠,铝过饱和(A/CNK值0.99~1.06,平均为1.03)的特点,属钾玄岩系列。微量元素中,富集Rb、Th、U、Sm,明显亏损Sr、Ce和Ti。稀土元素特征中,重稀土分馏较弱,轻稀土分馏较强,配分曲线呈右倾型,Eu负异常(δEu=0.18~0.26)明显等特征。推测其形成于岩石圈伸展减薄的环境下,源区主要由泥质岩组成。Th/U比平均2.09,小于3,可为区内铀矿化的形成提供丰富的铀源。

Occurred in the north Bopu pluton about 3 km south of Huangtian uranium deposit,the lithology of the Yanshanian granitoid is biotite monzogranite.In this paper,the major elements,trace elements and rare earth elements of biotite monzogranite were analyzed.The results showed that the pluton is characterized by high SiO2 content(73.07%to 74.20%,average 73.71%),rich alkaline(Na2O+K2O=8.20%to 8.78%,average 8.57%)and potassium greater than sodium;and supersaturated aluminum(A/CNK value 0.99 to 1.06,average 1.03),which falls into potassium basalt series.Trace elements is rich in Rb,Th,U,Sm and obviously depleted in Sr,Ce and Ti.The REE showed week fraction in HREE and strong fraction in LREE,and distribution pattern is rightleaning and the strong Eu depletion(δEu=0.18 to 0.26).It is suggested that the monzogranite was formed in the lithospheric extension and thinning environment,and the source area was mainly composed of argillaceous rock.The Th/U ratio is 2.09 which may provide abundant uranium source for the formation of uranium mineralization in the area.