The first field work for the purpose of determining the radioactivity of Pennsylvania black shales in Oklahoma was done in October, 1944, in the vicinity of Tulsa. Small phosphatic nodules were found to have relatively high radioactivity, particularly those in the black shale overlying the Checkerboard limestone. In May and June, 1945, more work was done in order to determine with more assurance, the abundance and radioactivity of the nodules. The later work covered all known black shale horizons in the Pennsylvanian system that could be found. The work extended as far north as Kansas City.
A number of coals of Pennsylvanian age were tested. They are all much too low in radioactivity to be of further interest.
The black shale over the Checkerboard limestone is the best horizon from the standpoint of abundance and radioactivity of nodules. One sample of nodules from this shale contains 0.186 percent equivalent uranium, 0.095 percent uranium. However, the distribution and radioactivity of the nodules are widely variable. The average nodule content of the black shale is about two percent over a thickness of about 2.5 feet. The average equivalent uranium content of the nodules is about 0.035 percent and the average uranium content 0.015 to 0.020 percent. With a product of this grade in view, the large mining operation necessary to produce a relatively small amount of nodules does not seem justified.
Two black shale beds, each about two feet thick and neither of which contains any nodules, contain 0.024 and 0.017 percent equivalent uranium and 0.013 and 0.010 percent uranium respectively. Too little work was done to permit calculations of tonnage, but material of this grade does not merit more detailed work at this time.