U-PB DATING OF CARBONATES FROM THE BASAL CEDAR MOUNTAIN FORMATION

We are studying carbonates from the Lower Cedar Mountain Formation to understand how uranium is distributed in this section and the potential for U-Pb dating of these carbonates. Four samples from the Don's Ridge section southwest of Green River, Utah were selected for phosphor image screening that are fairly evenly spaced from near the base to the caprock unit that marks the top of the lower portion of the basal Yellow Cat Member of the Cedar Mountain Formation. Based on phosphor imaging, the two samples from the base of this section do not appear promising, that is, they have little uranium. The two samples from the top of the section have favorable uranium concentrations, on the order of 10's of ppm. The caprock unit has by far the most uranium. This unit is possibly correlative to the caprock unit sampled from the Ruby Ranch Road, which was precisely dated by U-Pb carbonate methods at 115.94 ± 0.6 Ma (Gulbranson et al., 2006). Gulbranson's sample was collected off of I-70 about 15 miles east of Green River, Utah, some 20-30 miles from Kirkland's site at Crystal Geyser and Don's Ridge. U-Pb analyses are underway to determine if the Don's Ridge samples can provide ages of the formation. These data will be presented at the meeting.