论文部分内容阅读
日本本州岛中部的远野砂岩型铀矿区地层由中新统下部的湖相沉积岩(18～22Ma)和上部的海相(15～16Ma)沉积岩组成。方解石和黄铁矿是该地层中的主要成岩蚀变产物。湖相和海相的方解石和黄铁矿的特征差别很大。湖相沉积物中方解石的δ~(13)C值低(-19‰～-6‰PDB),而海相地层中的δ~(13)C值高(-11‰～+3‰)。这意味着海相碳酸盐在上部海相沉积岩中所起的作用较大,下部湖相地层中方解石的碳既来源于有机质的氧化作用,又来源于溶解在海水中的无机碳。上部海相地层中草莓状黄铁矿的低δ~(34)S值(-14‰～-8‰CDT),表明有少量海水硫酸盐细菌还原作用,而下部含褐煤长石砂岩中自形-半自形黄铁矿的高δ~(34)S值(+10‰～+43‰),意味着大量封闭体系的海水硫酸盐细菌还原作用。在湖相地层成岩期间,由于海水硫酸盐大量的细菌还原与伴随的有机质的氧化作用和有机质的水解反应,产生CH_4和CO_2促进形成了大量自形-半自形的黄铁矿。在此阶段,由U~(6+)还原为U~(4+)形成了铀矿物(铀石和晶质铀矿)。湖相沉积物中成岩蚀变和铀矿化环境的特点是Eh值低,在低Eh环境下,CH_4和HCO_3~-的浓度几乎相等,还原硫的形式(H_2S,HS~-)在水溶硫形式中占优势,而海相地层中的成岩蚀变的特点是SO_4~(2-)在溶解硫形式中占优势。湖相地层中的现代地下
The formation of the far-field sandstone-type uranium deposits in central Honshu Island in Japan consists of lacustrine sedimentary rocks (18-22 Ma) and upper marine (15-16 Ma) sedimentary rocks in the lower Miocene. Calcite and pyrite are the major diagenetic alteration products in this formation. The characteristics of calcite and pyrite in the lacustrine and marine facies are very different. The δ ~ (13) C values of calcite in lacustrine sediments are low (-19 ‰ ~ -6 ‰ PDB), while the δ ~ (13) C values in marine formations are high (-11 ‰ ~ + 3 ‰). This means that marine carbonates play a greater role in the upper marine sedimentary rocks. The calcite carbon in the lower lacustrine strata originates both from oxidation of organic matter and from inorganic carbon dissolved in seawater. The low δ ~ (34) S values (-14 ‰ ~ -8 ‰ CDT) of strawberry-like pyrite in the upper marine strata indicate that there is a small amount of seawater sulfate reduction, while the lower part of the intrusive - The high δ ~ (34) S value (+ 10 ‰ ~ + 43 ‰) of semi-autosynthetic pyrite means the sulfate reduction of seawater by a large number of closed systems. During the diagenesis of the lacustrine strata, a large amount of self-forming and semi-self pyrite was formed due to the massive bacterial reduction of seawater sulfate and the accompanying oxidation of organic matter and the hydrolysis of organic matter, resulting in the formation of CH 4 and CO 2. At this stage, uranium minerals (uraninite and crystalline uranium ore) are formed by the reduction of U ~ (6+) to U ~ (4+). The characteristics of diagenetic alteration and uranium mineralization in lacustrine sediments are characterized by low Eh values and almost equal concentrations of CH_4 and HCO_3 ~ under low Eh conditions. The reduction of sulfur forms (H_2S, HS ~ -) Form, while the diagenetic alteration in the marine strata is characterized by the predominance of SO 4 2- in the dissolved sulfur form. Modern underground in the lacustrine formation