Wang Yan-xin

Radioactive contamination of the environment as a result of uranium production: a case study at the abandoned Lincang uranium mine, Yunnan Province, China

The distribution of radioactive pollutants, such as222Rn, U, Th and226Ra in the air, surface waters, soils and crops around the Lincang uranium mine, Yunnan Province, China, is studied. The mechanical, geochemical and biogeochemical processes responsible for the transport and fate of the radioactive elements are discussed based on the monitoring data. The pollutants concentrations of effluents from the mine tunnels were dependent on pH and which were controlled by biochemical oxidation of sulfide in the ore/host rocks. Radon anomalies in air reached 4 km from the tailings pile depending on radon release from the site, topography and climate.238U and226Ra abnormities in stream sediments and soil were 40—90 cm deep and 790—800 m away downstream. Anomalies of radioactive contaminants of surface watercourses extended 7.5—13 km from the discharge of effluents of the site mainly depending on mechanical and chemical processes. There were about 2.86 ha rice fields and 1.59 km stream sediments contaminated. Erosion of tailings and mining debris with little or no containment or control accelerated the contamination processes.

Paleoclimate record and paleohydrogeological analysis of travertine from the Niangziguan Karst Springs, northern China

Travertine deposited around the Niangziguan karst springs was used as a new type of paleoclimate record in this study. Five stages of climate change in northern China from 200± ka to 36± ka before the present (B. P.) were reconstructed using the18O and13C isotope record of the travertine. Tendency of the change was towards a more arid climate. Coupling the temporal-spatial evolution of the springs with climate change, the hydrogeological evolution could be divided into four major periods since middle Pleistocene: (1) No spring period; (2) The initial period of spring outcropping as the predominant way of discharge; (3) The culmination period of spring development; and (4) The spring discharge attenuation period. The attenuation is partly related to the decrease of recharge as a result of the dry climate after 90±kaBP.Travertine deposited around the Niangziguan karst springs was used as a new type of paleoclimate record in this study. Five stages of climate change in northern China from 200± ka to 36± ka before the present (B. P.) were reconstructed using the18O and13C isotope record of the travertine. Tendency of the change was towards a more arid climate. Coupling the temporal-spatial evolution of the springs with climate change, the hydrogeological evolution could be divided into four major periods since middle Pleistocene: (1) No spring period; (2) The initial period of spring outcropping as the predominant way of discharge; (3) The culmination period of spring development; and (4) The spring discharge attenuation period. The attenuation is partly related to the decrease of recharge as a result of the dry climate after 90±kaBP.

Strontium hydrogeochemistry of thermal groundwaters from Baikal and Xinzhou

This paper reports our work on the strontium hydrogeochemistry of thermal groundwaters in the Baikal Rift System (BRS) in Russia and Mongolia and the Xinzhou basin of the Shanxi Rift System (SRS) in northern China. Though similar in geological background, groundwaters from the BRS and the Xinzhou basin have different strontium isotope compositions. Both the strontium contents and the87Sr/86Sr ratios of thermal water samples from Xinzhou are higher than those of most samples from Baikal. The major reason is the difference in hostrock geochemistry. The hostrocks of the Xinzhou waters are Archaean metamorphic rocks, while those of the Baikal waters except the Kejielikov spring are Proterozoic or younger rocks. In the study areas, cold groundwaters usually show lower87Sr/86Sr ratio due to shorter water-rock interaction history and lower equilibration degree. Strontium hydrogeochemistry often provides important information about mixing processes. Ca/Sr ratio can be used as an important hydrogeochemical parameter. Case studies at Xinzhou show that thermal waters with lowest Ca/Sr ratios are most weakly affected by mixing with shallow groundwaters, as supported by our hydrochemical and sulfur isotope studies.This paper reports our work on the strontium hydrogeochemistry of thermal groundwaters in the Baikal Rift System (BRS) in Russia and Mongolia and the Xinzhou basin of the Shanxi Rift System (SRS) in northern China. Though similar in geological background, groundwaters from the BRS and the Xinzhou basin have different strontium isotope compositions. Both the strontium contents and the87Sr/86Sr ratios of thermal water samples from Xinzhou are higher than those of most samples from Baikal. The major reason is the difference in hostrock geochemistry. The hostrocks of the Xinzhou waters are Archaean metamorphic rocks, while those of the Baikal waters except the Kejielikov spring are Proterozoic or younger rocks. In the study areas, cold groundwaters usually show lower87Sr/86Sr ratio due to shorter water-rock interaction history and lower equilibration degree. Strontium hydrogeochemistry often provides important information about mixing processes. Ca/Sr ratio can be used as an important hydrogeochemical parameter. Case studies at Xinzhou show that thermal waters with lowest Ca/Sr ratios are most weakly affected by mixing with shallow groundwaters, as supported by our hydrochemical and sulfur isotope studies.