2015-01-20_REVISION - P2009025 (6)

Home Browse Search

GROUNDWATER AND SOIL CONDITIONS AT THE SOUTH T -BAR RANCH Prepared by Adrian Brown, P.E, Geohydrologist, Denver, Colorado History The South T -Bar Ranch occupies a unique and historic location in Colorado. Part of the Ranch contains a number of uranium orebodies, of which the largest is the Hansen Uranium deposit. The locations of the principal deposits in the area are shown on the attached map. As a result of the uranium mineralization present in the area, there has been historic uranium prospecting and some modest uranium production from small mines in the area. In the late 1970s a major development of the Hansen deposit was proposed, and the land parcel which included what today comprises the South T -Bar Ranch was assembled to allow this development to proceed. However the uranium deposits in the area, while large, are of low grade, and are generally buried at great depth below ground surface (typically 600 feet or more). For these reasons, it is not economic to develop these deposits for the extraction of uranium under current or reasonably foreseeable market conditions. As a result, the mine proposal was abandoned, and the parcels of land that make up the South T -Bar Ranch have become available for ranching and residential use. The presence of the uranium deposits beneath some of the areas on the South T -Bar Ranch raises some issues for future use of this land, relating to impact on surface use and on water. These issues have been evaluated by technical experts retained by Land Properties Inc., and the results are presented below. Orebody Formation The uranium in the orebodies beneath the Ranch comes from volcanic eruptions that occurred more than 100 million years ago. The volcanic materials produced in those eruptions covered the entire area around the Ranch, and filled the existing valleys with volcanic rock to considerable depths. These volcanic materials were gradually decomposed and eroded by natural weathering, and small amounts of uranium that were contained within the volcanic material were leached into the ancient groundwater system. This groundwater moved downward from the ground surface, and in the Ranch area flowed through the organic -rich valley fill materials that had been buried by the volcanic eruptions. Conditions in the valley fill material caused the uranium to precipitate out of the groundwater, concentrating the uranium and creating the orebody. Since then sedimentary materials have been deposited in the area, and have consolidated; thus the orebody is now covered with about 600 feet of rock. Relatively recently, a mantle of soil has formed on the surface by sedimentary deposition and weathering of the upper rock materials. Surface Use Because of the way that the orebody developed, and its great depth, the current soil and near- surface rocks in the South T -Bar Ranch area have not been affected by uranium mineralization, and were not the source of the uranium in the orebody. In general the soil is free of uranium,