浙西北晚侏罗世火山期后交代蚀变作用及铀的活化转移

POSTVOLCANIC ALTERATION AND MOBILIZATION OF URANIUM IN THE LATE JURASSIC VOLCANIC ROCKS IN NORTHWEST OF ZHEJIANG PROVINCE

浙西北晚侏罗世火山岩历经四次火山喷发旋回,经受了多次热事件。岩石遭受的火山期后热液交代蚀变,在酸性岩区主要发育钠长石化和绢云母化。这种面型分布的交代蚀变使火山岩中以多种形式赋存的铀发生成岩后的初始活化。尔后,成矿期热液在运移中又将已经活化了的铀从围岩中浸取出来,以补充热液中的铀,并在沿断裂发育的蚀变环境中沉淀成矿。

Calc-alkaline volcanic rocks of Jiande formation in the northwest of Zhejiang province wereformed by four cycles of volcanic activities and underwent many times of thermal events. There aretwo types of hydrothermal metasomatic alterations of the rocks in volcanic terrain, one develops inpostvolcanic period and another in mineralization period. In the terrain of acid rocks, postvolcanic hy-drotermal metasomatic alteration is mainly characterized by albitization and sericitization. It is thispost-diagenetic plane type of metasomatic alteration that brings about the mobilization of uraniumwhich originally exsists in volcanic rocks in varied forms. Afterwards, the activated uranium was ex-tracted from rocks by flowing hydrothermal solution, and therefore, the uranium concentration in thehydrothermal solution was increasing. In the alteration enviroment along the rift, the uranium was de-posited from the hydrothermal solution.