Groundwater isotope survey in the Southern Gobi Region, Mongolia

Abstract:

The strategically biggest mineral deposits are located in South Gobi Region, Mongolia and the Mongolian government has been adhering the policy to operate them in near short terms. Groundwater is one of the important resources since rainfall and surface water availability are limited. This survey was made for the purpose to determination to principle of originating groundwater potentials. For the purpose, groundwater age was investigated with the stable isotope, radiocarbon and tritium method. They were analyzed in the laboratory of CIO of Rijksuniversiteit Groningen (The Centre of Isotope Research), Institute of Groundwater Ecology from the Helmholtz Zentrum and the German Research Center for Environmental Health (GmbH) in Munich, Germany.

Deep groundwater has radiocarbon ages from 13,000 to 45,000 years before present (0.4-18.4% modern C) and δ13C values from -10.0 to -4.6‰, for which it is difficult to assign absolute ages, although these values probably represent the Late Glacial period and late Pleistocene age. Shallow groundwater had tritium values of <1 to 20.8 TU, from which only 2 locations can be referred as recently infiltrated (since 1953) – or recent mixed with fossil groundwater. Groundwater aquifers were mainly found in Cretaceous sediments that have filled-up large basins in the Gobi and there is a good possibility that aquifers are interconnected via these basin sediments, although sedimentary facies changes and geological faults may form barriers to groundwater flow.