ABSTRACT

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 δ¹³C_CO2 = −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.