Regional setting and correlation of exploration results for the Naarst uranium deposit Dornogobi Province, southeast Mongolia

Abstract

The Naarst uranium deposit lies within an extensive zone of uranium anomalies extending for many kilometres within the Sainshand Basin graben in the southeastern Gobi region in Mongolia. The sedimentary units of the graben filling, Late Cretaceous age, Sainshand-Binshiren (Cenomanian to Santonian) packages seem to be the predominant host for the uranium. Locally, roll front enrichment has occurred, and some resources are hosted and enriched along fault zones where oxidized groundwater has circulated during ongoing intra-basinal fault movement along fault lines cutting the graben basin. This area was extensively explored from the late 1970s to the early 1980s by Soviet-Russian expeditions. During the period of 2007 to 2010, field mapping, carborne radiometric surveying and diamond drilling were carried out over much of the Naarst occurrence to determine the potential of the area for economic uranium mineralization. The best result from the 2008 exploration was from drill hole OR02 at an intersection depth of 175 to 180 m, which consists of sandstone alternations of fine- to coarse-grained sandstone with thin layers of clay stone, grey and occasionally pink, also with clay–mudstone layers, rich in organic material (plant trash) and pyrite disseminations. Soviet exploration results at Naarst were broadly confirmed in terms of the presence of anomalism and uranium mineralization distribution and the occurrence of uranium within particular rock types. There was not, however, the same confirmation of the depth and uranium grade of the mineralized intersections, along those drill sections chosen to test historic and recent results.