201和361矿床的地质特征和富铀矿床形成条件的初步分析

GEOLOGICAL FEATURES OF DEPOSITS NO.201 AND NO.361 AND ANALYSES OF FORMATION CONDITIONS OF URANIUM-RICH ORE DEPOSITS

区分出3种基本类型富矿:富矿类型、富矿床和富矿体。赋存于花岗岩中的201和361矿床均属于富铀矿床。它们形成于非带有利的条件,如丰富的来自花岗岩和可能部分来自深部的铀源;深断裂;良好的半封闭储矿构造;稳定的构造和热液对流系统以及充分的氧化还原。业已查明,持续保持■矿物沉淀而伴生的脉石矿物不沉淀或少沉淀是形成富铀矿的基本机制。实验表明,二氧化碳从UO_2^(2+)-CO_2-H_2S—SiO_4^(4-)体系中逸出,有利于沥青铀矿与SiO_2分开沉淀.其原理是二氧化碳从体系中逸出引起pH的增高,从而提高了SiO_2的溶解度,阻止其沉淀。

Three kinds of uranium-rich ore have been recognized. They are uranium-rich ore type, ore deposit and orebody. Both deposits No. 201 and No. 361 hosted in grant es are attributed to uranium-rich ore deposit. They formed in very favourable conditions such as abundant uranium source derived from granites and probably partly from depth, deep-seated faults, good semi-closed ore traps, stable regime of structure and hydrothermal convection systems and sufficient redox. It has been found that the principal mechanism of formation of uranium-rich ore lies in keeping on precipilating uranium minerals with little or small quantity of gangue minerals simultaneously settled down from ore-forming solutions. Experiments show that CO_2 escaping from the UO_2^(2+)-CO_2-H_2S-SiO_4^(4-)system is favourable for pitchblende to deposit separately from SiO_2. It may be explained that CO_2 escaping from the system causes increase of pH, which in turn raises the solubility of SiO_2 and prevents it from further deposition.