湘西北海相磷块岩中气水溶液铀多金属成矿作用

湘西北地区位于扬子陆块东南缘,在其寒武系纽芬兰统海相磷块岩的微孔隙中发现nm~μm级晶质铀矿。文章通过扫描电镜对铀矿的空间占位进行微区解剖,确定铀以超显微状态(1~4μm)的晶质铀矿形式存在于方硫镍矿中。认为超显微晶质铀矿和辉砷镍矿是同沉积鲕粒状磷块岩在较高的温压条件下,通过海底喷流气水溶液强溶蚀改造并发生结晶时,以超显微包体的形式存在于方硫镍矿中;随着温度、压力的下降,包体中富铀溶液出现过饱和,晶质铀矿从富铀溶液中结晶析出,以独立矿物晶质铀矿的形式呈超显微状态存在于方硫镍矿中。晶质铀矿在中高温热液成矿作用中以超显微状态呈立方体、八面体、立方体与八面体的聚形以及块状体产出,对认识天然条件下晶质铀矿生成的物理化学条件具有重要意义。同时,晶质铀矿呈超显微状态存在的实例对该类型铀矿存在形式的发现和研究具有重要启迪,为揭示扬子陆块东南缘的陆缘裂陷中海底喷流成矿示踪提供了依据。

Uranium polymetallic ore-forming process of gas solution in marine phosphorite of northwestern Hunan

Nanoscale uraninite was found in micropores in Cambrian Terreneuvian marine phosphorite of northwestern Hunan which lies in the Southeast Yangtze plate. Uraninite occurs as ultramicroscopic dispersion in microcracks and micropores in vaesite, as revealed by scanning electron microscopy. It is shown that ultramicroscopic uraninite and gersdorffite exist as ultramicroscopic inclusions formed by the syndepositional oolitic phosphorite crystallization under the conditions of the high temperature and pressure through the submarine exhalation gas solution. With the growth of supersaturated enriched uranium solution with the falling of the temperature and pressure, uraninite was produced from the enriched uranium solution in vaesite in the form of ultramicroscopic independent mineral uraninite. Uraninite existed in the ultramicroscopic state of cubic, octahedral, combinational cubic-octahedral and massive forms in high temperature hydrothermal mineralization. It is of great significance to understand the physical and chemical conditions of uraninite generation. The instance that the uraninite in the form of ultramicroscopic state is an important enlightenment in the search for this type of uranium, and the results achieved by the authors also provide evidence of submarine exhalation in the marginal faulted depression of the Southeast Yangtze plate.