安徽庐江砖桥科学深钻内的铀钍赋存状态研究

Modes of occurrence and composition of uranium and thorium minerals in deep drilling program in Zhuanqiao of Lujiang,Anhui Province

2012年深部探测项目SinoProbe-03-06在安徽省庐江县砖桥地区实施了2012 m科学深钻,在钻孔深部正长岩中发现铀钍异常,局部已达工业边界品位。系统的岩芯观测、显微镜下研究以及电子探针分析揭示,铀钍的赋存状态主要有2种:一种呈铀钍的独立矿物如铀钛矿、铀钍石、晶质铀矿形式存在;另一种以类质同象形式赋存于锆石、磷灰石、金红石等副矿物中。独立铀钍矿物主要呈2种形式产出:一种呈自形赋存于钠长石中,常与锆石在空间上伴生;另一种主要呈微细颗粒散布于金红石、磷灰石、硬石膏等热液蚀变矿物中。与铀钍矿化相关的蚀变主要有钠长石化、电气石化、硬石膏化等高温热液蚀变。砖桥深钻距庐枞盆地南缘铀矿床(点)不远,且均与正长岩有关,虽然两者的铀钍矿化、铀钍比值、赋存状态、蚀变矿化等一系列特征均存在差异,但两者之间可能存在成因联系,科学深钻所揭示出的铀钍矿化可能代表了铀钍在盆地深部岩体中的高温成矿样式。

Deep drilling program named SinoProbe-03-06 was conducted in Zhuanqiao area of Lujiang in Anhui Province. Thorium and uranium anomalies were found in the syenite from the deep drilling, which had reached marginal grade in some places. The authors investigated the thorium and thorium-bearing minerals and summa- rized the relationship between rock-forming minerals and accessory minerals by using microscope and electron mi- croprobe techniques. The results indicate that thorium and uranium have two modes of occurrence in the deposit, i.e., independent thorium minerals, and isomorphic form existing in uranium minerals or micro-isomorphic form lying in accessory minerals. Independent uranium and thorium minerals assume two forms, i.e., euhedral crystal wrapped in albite, often associated with zircon in space; fine particles dispersed in futile, apatite, anhy- drite and other hydrothermal alteration minerals. Alterations associated with uranium and thorium mineralization are albitization, tourmalinization, anhydritization and other high-temperature hydrothermal alterations. A series of features, such as uranium and thorium mineralization, uranium and thorium ratio, mode of occurrence and al-teration in deep drilling, are quite different from those of uranium deposits （ore spots） nearby. That difference might indicate a genetic link which suggests that uranium and thorium mineralization in deep drilling might re- veal high temperature type uranium deposits in the rock bodies in the depth of the basin.