Mantle-derived gaseous components in ore-forming fluids of the Xiangshan uranium

	Mantle-derived gaseous components in ore-forming fluids of the Xiangshan uranium
	Rui-Zhong Hu; P.G. Burnard; Xian-Wu Bi; Mei-Fu Zhou; Jian-Tang Peng; Wen-Chao Su; Jun-Hong Zhao
	2009
发表期刊	Chemical Geology
期号	266 页码:86-95
合作性质	国际
摘要	The Xiangshan U deposit, the largest hydrothermal U deposit in China, is hosted in late Jurassic felsic volcanic rocks although the U mineralization post dates the volcanics by at least 20 Ma. The mineralization coincides with intrusion of local mantle-derived mafic dykes formed during Cretaceous crustal extension in South China. Ore-forming fluids are rich in CO2, and U in the fluid is thought to have been dissolved in the form of UO2 (CO3)22− and UO2 (CO3) 34− complexes. This paper provides He and Ar isotope data of fluid inclusions in pyrites and C isotope data of calcites associated with U mineralization (pitchblende) in the Xiangshan U deposit. He isotopic compositions range between 0.1 and 2.0Ra (where Ra is the 3He/4He ratio of air=1.39×10−6) and correlates with 40Ar/36Ar; although there is potential for significant 3He production via 6Li(n,α)3H(β)3He reactions in a U deposit (due to abundant neutrons), nucleogenic production cannot account for either the 3He concentration in these fluids, nor the correlations between He and Ar isotopic compositions. It is more likely that the high 3He/4He ratios represent trapped mantle-derived gases. A mantle origin for the volatiles of Xiangshan is consistent with the δ13C values of calcites, which vary from −3.5‰ to −7.7‰, overlapping the range of mantle CO2. The He, Ar and CO2 characteristics of the ore-forming fluids responsible for the deposit are consistent with mixing between 3He- and CO2-rich mantle-derived fluids and CO2-poor meteoric fluids. These fluids were likely produced during Cretaceous extension and dyke intrusion which permitted mantle-derived CO2 to migrate upward and remobilize U from the acid volcanic source rocks, resulting in the formation of the U deposit. Subsequent decay of U within the fluid inclusions has reduced the 3He/4He ratio, and variations in U/3He result in the range in 3He/4He observed with U/3He ratios in the range 5–17×103 likely corresponding to U concentrations in the fluids b0.2 ppm.
关键词	The Xiangshan u Deposit
学科领域	中国典型特殊区带大规模成矿作用及其动力学
收录类别	SCI
语种	英语
文献类型	期刊论文
条目标识符	http://ir.gyig.ac.cn/handle/352002/606
专题	矿床地球化学国家重点实验室_矿床地球化学国家重点实验室_期刊论文矿床地球化学国家重点实验室
推荐引用方式 GB/T 7714	Rui-Zhong Hu,P.G. Burnard,Xian-Wu Bi,et al. Mantle-derived gaseous components in ore-forming fluids of the Xiangshan uranium[J]. Chemical Geology,2009(266):86-95.
APA	Rui-Zhong Hu.,P.G. Burnard.,Xian-Wu Bi.,Mei-Fu Zhou.,Jian-Tang Peng.,...&Jun-Hong Zhao.(2009).Mantle-derived gaseous components in ore-forming fluids of the Xiangshan uranium.Chemical Geology(266),86-95.
MLA	Rui-Zhong Hu,et al."Mantle-derived gaseous components in ore-forming fluids of the Xiangshan uranium".Chemical Geology .266(2009):86-95.

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