赣南五里亭岩体晶质铀矿中铀离子价态及岩浆氧逸度计算
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摘要
晶质铀矿是花岗岩中广泛产出的副矿物,其铀离子价态的变化及比例关系,对于岩浆氧逸度具有一定的指示意义。笔者利用硅酸盐熔浆中U~(6+)-U~(4+)的平衡关系,推导出花岗岩副矿物——晶质铀矿的氧逸度计热力学计算方程,以及氧逸度(f O2)、温度(T)和不同价态铀离子比值(U~(6+)/U~(4+))的对数关系。以赣南五里亭花岗岩体为例,借助X射线光电子能谱分析,获得U~(6+)与U~(4+)的比例关系(U~(6+)/U~(4+)=0.30～0.46);利用晶质铀矿氧逸度计热力学方程,计算出该岩体形成时的平均氧逸度(为FMQ+0.58)。在温度(T)与氧逸度(lg f O2)协变图中,该结果靠近矿物反应缓冲线(FMQ),显示岩浆为弱还原性。因此,晶质铀矿U~(6+)/U~(4+)氧逸度计算结果能够代表岩浆源区的氧逸度特征,可作为常规氧逸度计算方法的一种有效补充。
Uraninite is widely spread in granite and occurs mainly as accessory mineral. The valence state and content of uranium have an important significance for magmatic oxygen fagucity. This paper derivesthe thermodynamic equation of oxygen fagucity by the equilibrium relationship between U~(6+)and U4+. Ithas a logarithmic relationship between oxygen fagucity( fO2), temperature(T), and the ratio of U~(6+)andU4+(U~(6+)/U~(4+)). Taking the Wuliting granite in south Jiangxi Province for example, we gained the ratio ofU~(6+)/U~(4+)by analyzing X-ray photoelectron spectroscopy. The oxygen fugacity was estimated based on theratio( 0.30 ～0.46) and the value was about FMQ +0.58, which is close to FMQ redox buffer, andpresent weak reducibility. Though the method construction and comparision, we think the estimation ofoxygen fugacity by the U~(6+)/U~(4+)of uraninite can represent the oxygen fugacity characteristics of magma source, and is a supplement to the regular methods of oxygen fugacity estimation.
Uraninite is widely spread in granite and occurs mainly as accessory mineral. The valence state and content of uranium have an important significance for magmatic oxygen fagucity. This paper derivesthe thermodynamic equation of oxygen fagucity by the equilibrium relationship between U~(6+)and U4+. Ithas a logarithmic relationship between oxygen fagucity( fO2), temperature(T), and the ratio of U~(6+)andU4+(U~(6+)/U~(4+)). Taking the Wuliting granite in south Jiangxi Province for example, we gained the ratio ofU~(6+)/U~(4+)by analyzing X-ray photoelectron spectroscopy. The oxygen fugacity was estimated based on theratio( 0.30 ～0.46) and the value was about FMQ +0.58, which is close to FMQ redox buffer, andpresent weak reducibility. Though the method construction and comparision, we think the estimation ofoxygen fugacity by the U~(6+)/U~(4+)of uraninite can represent the oxygen fugacity characteristics of magma source, and is a supplement to the regular methods of oxygen fugacity estimation.
引文
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[8]Haynes WM. CRC handbook of chemistry and physics[M]. CRC press, 2014.
[9]蒋国豪,胡瑞忠,谢桂青,等.大吉山花岗岩体黑云母地球化学特征及其成岩成矿意义[J].矿物岩石, 2005, 25(1):58-61.
[10]Frost BR. Introduction to oxygen fugacity and its petrologic importance[J]. Reviews in Mineralogy and Geochemistry, 1991, 25(1):1-9.
[11]章邦桐.花岗岩物理化学及铀成矿作用[M].北京:原子能出版社, 1992.
[2]邱检生,徐夕生.赣南大吉山五里亭岩体的锆石ELA-ICP-MS定年及其与钨成矿关系的新认识[J].地质论评, 2004, 50(2):125-133.
[3]Strehle M. X-ray photoelectron spectroscopy(XPS)study of single crystal UO2and U3O8on rplane sapphire and yttrium stabilized zirconium(YSZ)substrates[M]. Citeseer, 2011.
[4]Sunder S, Boyer G, Miller N. XPS studies of UO2oxidation by alpha radiolysis of water at100℃[J]. Journal of nuclear materials, 1990,175(3):163-169.
[5]蔡根庆,黄志章.我国天然铀氧化物的结构和化学特征[J].矿物学报, 1988, 8(1):72-80.
[6]Idriss H. Surface reactions of uranium oxide powder, thin films and single crystals[J].Surface Science Reports, 2010, 65(3):67-109.
[7]凌洪飞.论花岗岩型铀矿床热液来源-来自氧逸度条件的制约[J].地质论评, 2011, 57(2):192-206.
[8]Haynes WM. CRC handbook of chemistry and physics[M]. CRC press, 2014.
[9]蒋国豪,胡瑞忠,谢桂青,等.大吉山花岗岩体黑云母地球化学特征及其成岩成矿意义[J].矿物岩石, 2005, 25(1):58-61.
[10]Frost BR. Introduction to oxygen fugacity and its petrologic importance[J]. Reviews in Mineralogy and Geochemistry, 1991, 25(1):1-9.
[11]章邦桐.花岗岩物理化学及铀成矿作用[M].北京:原子能出版社, 1992.