Uranium-rich xenotime in bitumen, Moonta mines, South Australia

Bitumen from the Moonta copper mines is known to exhibit anomalous radioactivity. The bitumen contains abundant metalliferous inclusions, many of which are copper and iron sulphide minerals. Electron microscope studies reported show that the radioactive mineral is an yttrium phosphate phase, resembling xenotime which exhibits significant substitution by uranium, calcium and silicon. An average of 20 analyses yields the formula (Y0.66 U0.23 Ca0.12)1.01(P0.80 Si0.20)O4. A deficiency in the measured element total suggests that the formula may include up to 6 or 7 water molecules. It is assumed that the carbon in the bitumen was derived from younger sedimentary rocks which formerly overlay the ore deposit. 14 refs., 1 tab., 1 fig