下庄铀矿田337矿床成矿机理及动力学背景

Mineralization mechanism and geodynamic setting of No.337 deposit in Xiazhuang uranium orefield

长期以来人们一直认为337铀矿床是下庄铀矿田成矿年龄最早、成矿温度相对较高、矿岩时差小的岩浆热液型铀矿床的代表。据作者及其他研究者近年来对该矿田及矿床开展的岩体成岩年龄、岩体蚀变年龄、岩体的主量和微量元素组成及同位素等的综合研究揭示：与337铀矿床成矿关系最为密切的帽峰岩体单颗粒锆石测试的成岩年龄为206～238．2Ma，而岩体中次生白云母的^40Ar／^39Ar法坪年龄变化于131～136Ma之间，后者与该矿床主要铀矿化年龄130．3～138Ma相近；在贵东花岗质杂岩体中，Al2O3／TiO2含量比值表明帽峰岩体可能是源区熔融温度最低的岩体，帽峰岩体还是稀土总量最低且是唯一显示较典型“四分组效应”的岩体，同时还具有变化的δ^18O值和最低的（^87Sr／^86Sr）i值。上述研究结果说明337铀矿床的形成过程和动力学背景可能是：印支主碰撞晚期或后碰撞阶段本区富铀地层发生部分熔融作用形成了富铀的强过铝质花岗岩帽峰岩体，燕山晚期（140Ma以后）大陆拉张背景下多期次基性脉岩侵入，带来高热和矿化剂CO2，并驱动大规模流体运动，活化和萃取了富铀花岗岩中的铀，在不同部位（裂隙发育地段或在基性脉岩与花岗岩的接触部位）沉淀形成铀矿体（床），337铀矿床是本区第1期铀成矿作用的典型代表。

Uranium deposit No, 337 in Xiazhuang uranium orefield has been regarclen as a representative of the earliest forming, relatively high temperature and short time gap between the formation of pluton and the mineralization. But the latest study revealed that the formation age of the Maofeng pluton, which is the most important uranium host granite in Xiazbuang uranium orefield, is 206 - 238.2 Ma by LAICP-MS zircon dating, while the secondary origin muscovite in Maofeng pluton has the age of 131-136 Ma by ^40Ar/^39Ar Ar dating which correspond to the main mineralization age of 130.3 - 138 Ma in uranium deposit No. 337. In Guidong granitic complex, Maofeng pluton shown some unique characteristics. It has the Al2O3/TiO2 ratio that infers the lowest forming temperature, the lowest ∑ REE and it is the only pluton which presents typical tetrad effects of REE, it is also shown a varying δ^18O values and the lowest （^87Sr/^86Sr）i values. According to the above findings, a concept model of uranium mineralization and geodynamie setting for No. 337 uranium deposit might be presented： in late or post-collision stage of Indosinian orogeny, strongly peraluminous granite of Maofeng pluton formed from partial melting of uranium rich formations. Intrusion of maficdyke in late Yanshanian Period （ 〈 140 Ma ）, caused large fluid movement. Uranium was reactivated and extracted from the altered granite, and precipitated in some favorite places to form uranium ore bodies. Uranium deposit No. 337 is the typical representative of the first stage uranium mineralization in Xiazhuang uranium orefield.