Geochemical characteristics of gases from the Wudalianchi volcanic area, northeastern China

The origins of gases in springs, pools and wells from the Wudalianchi (WDLC ) volcanic area are discussed based upon molecular and isotope compositions of the gases. Nine gas and water samples were collected from bubbles and w ater of the springs and pools in the WDLC volcanic area, Northeastern China , in August 1997. The molecular components were measured with a MAT-271 mas s spectrometer (MS), helium isotope ratios with a VG-5400 MS, and delta(13) C with a MAT-251 MS in the Lanzhou institute of Geology. The gases are enri ched in CO2, and most of the CO2 concentrations are over 80% (V). The heliu m and methane concentrations have relatively wide ranges of 0.7 to 380 X 10 (-6) and 4 to 180 X 10(-6), respectively. The He-3/He ratios are between 1. 05 Ra and 3.1 Ra (Ra = 1.4 X 10(-6)); the He-4/Ne-20 values are between 0.4 5 and 1011, larger than the atmospheric value (0.32). The delta(13)C (PDB) values of carbon dioxide range from -9.6 to -4.2 parts per thousand. These geochemical data demonstrate that the spring water is from aquifers at diff erent depths, and that helium and carbon dioxide are derived from the mantl e, and are contaminated by crust gases during deep fluid migration. Also, t here are larger fluxes of deep-earth matter and energy in the WDLC volcanic area.