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Geochemical Journal
Geochemical Journal An open access journal for geochemistry
Published for geochemistry community from Geochemical Society of Japan.

High 3He/4He ratios in the Wangu gold deposit, Hunan province, China: Implications for mantle fluids along the Tanlu deep fault zone

Jingwen Mao, Robert Kerrich, Hongyan Li, Yanhe Li
Geochemical Journal, Vol. 36, No. 3, P. 197-208, 2002


The Wangu shear zone hosting gold deposit is located on splay faults of the regional scale Tanlu deep fault zone that extends to the MOHO and likely through the lithosphere. Fluid inclusions in pyrite from gold bearing veins have 3He/4He (R/Ra) values of 3.5 to 9.8. Fluid inclusions in pyrite from barren vein have R/Ra values of 0.8, and 0.9. The projections of the analyses in 3He/4He vs. 40Ar/36Ar diagram can be separated obviously as two groups and display the variable degrees of mixing between mantle and crustal fluids. Fluid inclusion in quartz from auriferous veins are characterized by a higher temperature (Th = 207 to 310°C), dilute, aqueous carbonic fluids, with δD and δ18O values overlapping the magmatic fluids, whereas barren veins have low temperature (Th = 138, 145°C), more saline, aqueous fluid with relatively low, light δD and δ18O values, consistent with evolved meteoric water. Lithosphere extension accompanied with displacement of the Tanlu sinistral fault, with development of gas and oil-bearing sedimentary basins proximal to the fault. The CO2-bearing fluids have high He contents of up to 0.1% He, 3He/4He = (3∼7.2)R/Ra, 40Ar/36Ar = 573∼7744, and δ13CCO2 = −3.4 to −16.9‰ (Xu et al., 1995; Tao et al., 1996). During the lithosphere extension and decompressional melting of asthenosphere, noble gases and CO2 exsolved from basalt melts, advected up to the Tanlu fault zone into splay faults where gold mineralization developed, and through sedimentary basin. There was mixing with isotopically and compositionally evolved meteoric water.

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