Unconformity Uranium Deposits

The unconformity-type deposits are the world’s main source of uranium. These deposits form at or near the contact between an overlying sandstone and underlying metamorphic rocks, often metamorphosed shales. The orebodies have lens – or pod – like shapes, and most often occur along fractures in sandstone or in basement rocks. The host rocks often have disseminated uranium minerals and show hydrothermal alterations, which may indicate that the deposits formed after the rocks. The mineralized bodies may carry minor amounts of sulphide minerals like pyrite, arsenopyrite, galena and sphalerite, as wall as nickel-cobalt arsenides.

Because this type of deposit is a relatively recent discovery – the first uranium deposits in Saskatchewan and northern Australia were found in the late 1960s and early 1970s – geologists are still trading theories about their origin. A model that has gained favor in recent years suggests that fluids with dissolved uranium and other metals, moving through the sandstone, encountered the basement rocks, where chemical conditions were ideal to cause the metals to precipitate from solution.