诸广-下庄铀矿集区成矿过程中水-岩作用的地质地球化学特征

诸广-下庄铀矿集区是我国最大的花岗岩型铀成矿区,本文从岩石蚀变、不同介质中稀土元素的四分组效应、方解石中碳、氧和锶同位素组成等方面系统讨论了诸广-下庄铀矿集区内与铀成矿有关的各种水-岩相互作用的地质地球化学特征,得到以下主要认识: (1)铀矿田范围内成矿的花岗岩大多发生了强烈的蚀变,是水-岩作用的直接表现,晶质铀矿表面发生的溶蚀作用是铀活化的直接证据,裂变径迹特征揭示面型分布的绿泥石化是花岗岩中以类质同像形式存在的铀从花岗岩中活化出来的主要反映; (2)与铀成矿有关的花岗岩具有 M型四分组效应,而沥青铀矿、黄铁矿、方解石、绿泥石和伊利石等矿石矿物和脉石矿物则具有 W型或 W-M混合型四分组效应,这种共轭存在的 M型和 W型四分组效应表明了流体-花岗岩作用是本区铀成矿作用的关键,沥青铀矿主要是从流体中沉淀成矿的; (3)矿田范围内方解石的δ 13C、 87Sr/86Sr及δ 18O组成特征,及 87Sr/86Sr与δ 18O之间明显的负相关关系,揭示出本区铀成矿过程中的碳、水和铀来源不同--碳是幔源,铀是壳源,流体中的水至少有一部分是大气降水.

Geological and geochemical characteristics of water-rock interaction in the processes of uranium mineralization in Zhuguang-Xiazhuang uranium ore-concentrated district

Zhuguang-Xiazhuang area is the biggest granitic-type uranium ore - concentrated district in China. Alteration of granites, tetrad effects of rare e arth element (REE) in granite and minerals, carbon, oxygen and strontium isotope s in calcite are employed to evaluate the characteristics of water-rock interac tion (WRI) in the processes of uranium mineralization. The results show that int ensive alteration developed in the granites is the direct exhibition of WRI. Cor rosions exhibited on the surface of uraninite reveal the activation of the urani um in the granite. Fission-track results show that chloritization is one of the important reactions to reactive the uranium in the granite occurred in the form of isomorphism. Conjugated M-and W-types of tetrad effects of REE simultaneou sly observed in the granite and minerals show that the fluid-granite interactio n is the key uranium ore-forming process in the Zhuguang-Xiazhuang uranium ore -concentrated district; the mineralization hosted granite rocks and the tourmal inite in granite shown M-type tetrad effects, while pitchblende, chlorite, illi te, calcite and pyrite shown W-type or W-M mixed type tetrad effects. It might infer that pitchblende was deposited from the fluid. Carbon, oxygen and stronti um isotopic values in calcite, especially the negative correlation between oxyge n and strontium isotope, might infer the mantle derived carbon, part of the prec ipitation origin of water and epidermis uranium.