陕西省丹凤地区花岗伟晶岩型铀矿特征及找矿方向

Characteristics and Prospecting Direction of Granitic Pegmatite-Type Uranium in Danfeng Area, Shaanxi Province

陕西省丹凤地区花岗伟晶岩型U矿呈脉状产于加里东期花岗岩株内外接触带的富U黑云母花岗伟晶岩脉中,矿石以中粗粒花岗结构、块状构造为主,副矿物组合为磷灰石-锆石,铀矿物主要是晶质铀矿。矿石矿物为富团块状黑云母、棕红色更长石,富Si、富K、铝过饱和,Eu亏损,轻稀土元素富集,富Mo、Zr、F元素特点。该类型铀矿是加里东期壳幔混源含U、含F、低氧逸度的岩浆-热液过渡性流体体系,在拉伸大陆动力学背景下随富U黑云母花岗伟晶岩成岩结晶分异形成。流体体系中U以F的铀酰络合物方式迁移,岩浆结晶分异成岩过程中U形成晶质铀矿物富集于黑云母花岗伟晶岩局部形成了铀矿(化)体,F形成团块状黑云母矿物。岩体东南部花岗岩株内外接触带300m是铀矿体分布范围及找矿方向。

Distributed in vein form, the granitic pegmatite-type uranium in Danfeng Area, Shaanxi Province originates from uranium-rich biotite granitic pegmatite dyke, in the inside and outside contact belts of granitic stock in Caledonian Period. The ore is basically consisted of coarse granitic block and the accessory ore assemblage is apatite-zireon. Containing mass biotite and brownish-red oligoclase, the uranium ore is mainly uraninite, with characteristics like Si- rich, K-rich, Al-oversaturated, Eu-loss, LREE-rich, Mo-rich, Zr-rich, F-rich etc. This kind of Uranium belongs to crust-mantle mixing, magmatic-hydrothermal transitional fluid system with Ur, F elements and low-oxygen fugacity. Under the background of tensile continental dynamics, the uranium deposit is formed along with the differentiation and crystallization of Ur-rich biotite granitic pegmatite. In the fluid system, Ur is transported in F uranyl complex. In diagenetic process of magmatic crystallization differentiation, Ur formed uraninite and enriched in biotite granitic pegmatite, part of it developed into Uranium deposit body, and F developed into mass biotite mineral. It is also concluded that 300 m inside and outside contact belt of granitic stock southeast to the rock mass is the distribution range and prospecting direction of Uranium ore body.